Nanostructured Materials: Industrial Applications

Abstract

Nanoscience and nanotechnology are transforming materials science in a broad way, in a manner similar to polymer chemistry’s transformation of materials science over the preceding century. The continuous development of novel nanostructured materials and the extensive study of physicochemical phenomena at the nanoscale are creating new approaches to innovative technologies that are constantly resulting in products with a wide range of applications [1–5].

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Introduction

Nanoscience and nanotechnology are transforming materials science in a broad way, in a manner similar to polymer chemistry’s transformation of materials science over the preceding century. The continuous development of novel nanostructured materials and the extensive study of physicochemical phenomena at the nanoscale are creating new approaches to innovative technologies that are constantly resulting in products with a wide range of applications [1–5].

Nanoscience is generally defined as the study of phenomena and manipulation of materials at slightly above atomic or molecular scale, where properties of matter differ significantly from those at the macro scale. The term nanotechnology generally refers to techniques capable of designing and synthesizing nanomaterials that offer advanced material properties for novel applications. The US National Nanotechnology Initiative (NNI) defines a technology as nanotechnology only if it involves all of the following [6]:

• Research and technology development involving structures with at least one dimension in approximately the 1–100 nm range, frequently with atomic/molecular precision.

• Creating and using structures, devices, and systems that have novel properties and functions because of their nanometer scale dimensions.

• Ability to control or manipulate on the atomic scale.

History of Nanomaterials

It should be pointed out that nanomaterials are not entirely new. Carbon black, a material discovered in the early 1900s, is a nanomaterial that is used to increase the life of car tires and to provide the black color. Fumed silica, a component of silicone rubber, adhesives, coatings, and sealants, is a nanomaterial that has been in the market since the 1940s. Several chemicals and chemical processes possess nanoscale features—for example, large polymer molecules made up of tiny nanoscalar subunits. The first nanotechnologists were the Roman glass workers who invented dichroic glass. Other early nanotechnologists were the medieval glass workers who were responsible for providing the nanomaterials that gave stained glass and glazes their bright and vibrant colors. Similarly, nanotechnology has been used to create the tiny features on computer chips for the past several years. Over the last 20 years, the understanding of some preparations of metals, oxides, and other substances as nanomaterials has emerged through a vast body of research and development efforts. Additionally, with the development of more advanced analytical techniques, new nanomaterials are being developed in a systematic manner and with a greater understanding.

The origin of modern nanotechnology is mainly attributed to Professor Richard Feynman’s speech “There’s Plenty of Room at the Bottom,” which was delivered in 1959 at the annual meeting of the American Physical Society at Caltech [7]. At the time, Professor Feynman’s predictions were based on theoretical speculation that the principles of physics should allow the possibility of manipulating things atom by atom. He described such atomic scale fabrication as a bottom-up approach, as opposed to the top-down approach that is generally employed in manufacturing. However, developments such as the invention of the Scanning Tunneling Microscope in 1981 have since made nanoscale science a reality. Nanotechnology is now a rapidly growing field of research and development that is cutting across many traditional scientific boundaries.

Nanomaterials: What and Why

In typical nanomaterials, a large fraction of the atoms are located on the surface of the particles, whereas in conventional materials, they are located in the bulk. As a result, many of the intrinsic properties of nanomaterials are different from conventional materials, since many of the atoms are in a different environment. Two key factors cause the properties of nanomaterials to differ significantly from other materials: increased surface area and quantum effects. Nanomaterials have much greater surface area per unit mass compared to conventional materials. As chemical reactions occur at surfaces, this means that a given mass of nanomaterials will be more accessible than the same mass of material made up of larger particles. In addition, higher surface energies and the presence of many corners, edges, and surface defects cause additional intrinsic reactivity. Quantum effects also begin to dictate the properties of matter as size is reduced to the nanoscale, which in turn affects the optical, electrical, and magnetic behavior of materials.

Since industrial sectors such as aerospace, biotech, energy, healthcare, and transportation depend on materials and devices made of atoms and molecules, they can all be improved by application of nanomaterials. Indeed, this rapidly advancing field of science has afforded a variety of commercially available products including catalysts, cosmetics, electronics, paints, self-cleaning windows, suntan lotions, and stain-resistant clothing [8]. Of all the materials, the most commonly mentioned materials are carbon based on fullerenes and nanotubes, followed by silver, silica, titanium dioxide, zinc oxide, and cerium oxide. Iron nanoparticles appear to have potential for environmental applications, particularly for groundwater remediation [9, 10]. Nanoparticles of titanium dioxide and zinc oxide are included in personal care products such as toothpaste, beauty products, sunscreens, and textiles [11, 12]. Silver nanoparticles are used as antimicrobials in textiles such as socks and underwear and are recommended for use in food packaging and in detergents [8]. Areas producing the greatest revenue for nanoparticles reportedly are chemical–mechanical polishing, magnetic recording tapes, sunscreens, automotive catalyst supports, biolabeling, electroconductive coatings, and optical fibers. The number of consumer products on the market containing nanomaterials (as particles or fibers) now exceeds 1,000 and is growing quickly. This count includes nanomaterials containing carbon, cerium oxide, silver, silica, titanium dioxide, magnesium oxide, and zinc oxide. The remarkable advances in current nanotechnology are mirrored in our capability to design and control the chemical composition, size, shape, and assembly structure for various applications.

The advantages of nanotechnology are spreading to numerous industries and applications. The ability of nanoparticles to make products lighter, stronger, and less expensive will infiltrate nearly every part of our lives from transportation to what we wear to treatments of the human body. Products using nanotechnology are already on the market and include stronger tennis racquets and golf clubs, cleaning products with powerful bactericidal and odor removing capabilities, and fabrics treated with nanoparticles to provide odor, stain, or liquid-resistant clothing. Cosmetic companies are also finding nanomaterials to be increasingly effective in anti-wrinkle creams and sunscreens, along with many other applications that will be discussed later in the chapter.

Governments and global corporations are investing billions of dollars to grow nanotech research and development for many other applications that will be greener and more sustainable than current technologies. This investment will fuel the $1.6 trillion of nanomaterials that are expected to be incorporated into manufactured goods in 2013 [13].

Quite recently, the President’s Council of Advisors on Science and Technology (PCAST) released their review of the US NNI. Among the major recommendations is enhanced support of commercialization efforts including nanomanufacturing along with continued support of science and engineering, better coordination between US agencies, and increased efforts in nanoscience education and in clearly understanding the societal impacts of nanotechnology. Most importantly, a forward-looking view of environmental health and safety for nanomaterials is promoted [14].

Worldwide Initiatives on Nanoscience and Nanotechnology

As mentioned earlier, the existence of nanosized materials has been known for centuries, but only recently has characterization and manipulation of nanoscale systems opened a new era of nanoscience. Worldwide initiatives in nanoscience have gained great momentum from public and private investors due to economic benefits. In the present global market, a market dominated by tough competition, and a taste for superior products and services, experts believe nanotechnology advancements promise a stronger economy, greater return on investments, and soaring job creation. Countries have realized the importance of nanotechnology for future economic development and its potential impact on various industries. Nanotechnology is expected to revolutionize the existing major industries to create new, enhanced products and processes. Energy, medicine, military, communication, electronics, transportation, and material sciences are just a few segments that would be improved by nanotechnology. Experts believe that all areas will be impacted by nanotechnology, which could lead to exponential economic growth and possibly be the next great accelerant for growth similar to the information technology boom. According to Lux Research, public and private investments totaled 18.2 billion USD globally in 2008. For the first time in 2007, private funding for nanotechnology worldwide surpassed public funding, indicating that basic research has led to commercialization and return on investments. The sales of nanotechnology related products grew 41% from 2007 to 2009, to a total of 224 billion USD [14].

Initiative and investment by governments in developed and emergent countries in this technology are an unambiguous indication of the relevance of nanotechnology. A market research firm, Cientifica, reports that in 2004, 85% of worldwide R&D spending was dominated by the European Union (27 EU member states), Japan, and the United States. In 2009, this dropped to 58% reflecting the emergence of additional countries contributing to nanotechnology [15]. Although the EU, Japan, and the US have increased their investments through 2009, other developing countries are catching up. Countries have varied approaches towards nanotechnology advancements. Some countries establish specific agencies to monitor progress, fund research, and transfer research to commercialization, while others utilize existing science technology for their advancements. According to an Organisation for Economic Co-Operation and Development (OECD) report, 17 of the 24 countries surveyed had specific governmental agencies focused on nanoscience, while six of the 24 countries invested in nanotechnology through the existing science and technology (S&T) agencies [16]. As countries continue the race to exploit nanotechnology for socioeconomic benefits, the scale of nanotechnology advancements can be measured by the number of nanotechnology centers and initiatives, public and private funding, number of active companies, number of scientific publications, patents, and number of Ph.D. graduates. The United States invests the most in the field of nanotechnology, but is losing ground against other foreign competitors (Fig. 9.1). Progress in basic and advanced research can be gauged by grouping the number of nanotechnology publications by country in the science citation index. Figure 9.2 illustrates publications reported in various geographical areas. The EU, which acts as the policy maker and funding agency, as well as one voice for Europe, has the most nanotechnology publications. China (including Taiwan) surpassed the US in 2007 for the number of nanotechnology publications [14].

Fig. 9.1

Nanotechnology funding from 2000 to 2008 (includes public and private investments)

Fig. 9.2

Nanotechnology publications in science citation index by year. Source: Chen HC, Dang M, Roco MC. “Updated nanotechnology indicators, January 2010.” Addendum to Chen H, Roco MC (eds). Mapping nanotechnology innovations and knowledge: global, longitudinal patent and literature analysis. New York: Springer, 2008

Figure 9.3 shows China’s dominance in patents compared to other countries. Currently, China has a larger number of patent applications than patents issued; nonetheless, China’s progression in nanotechnology is impressive.

Fig. 9.3

Nanotechnology related patent applications. Source: Kisliuk B, USTPO, unpublished on comparative patent filings, January 2010

The US produces the majority of Ph.D. students in the field of science and engineering, but most of these students are foreign nationals. More than one third of these students leave the US, resulting in technology drain [14].

Governmental involvement in promoting nanoscience is the major driver for the current progress in the area of nanoscience. In the next section, various governmental initiatives introduced to promote nanotechnology growth are discussed. We will focus on key players in regions that have played a major role to date. These regions include North and South America, Europe, Eurasia (Russia), Asia, and Australia.

North and South America

United States of America

The US government, in hopes of maintaining its leadership in the field of nanotechnology, has founded the NNI to promote nanoscale science, engineering, technology research, and development programs. The NNI is a sub-branch of the National Science and Technology Council (NSTC), the cabinet level council by which the President coordinates science, space, and technology policies across the Federal Government. The program was established in 2001, and to date the cumulative investment is 12 billion USD. The proposed NNI budget for fiscal year 2010 is 1.64 billion USD, with a growth of 8.5% over fiscal year 2009. Currently, the NNI involves 25 federal agencies, 13 of which had budgets for nanotechnology R&D in 2010. Table 9.1 displays NNI budgets (2008–2010) for the 13 budgeted federal agencies.

Table 9.1 National nanotechnology initiative (NNI) budget 2008–2010 (millions in USD)

Of the total investment in the 2010 NNI proposed budget, 96% of the total is focused on five federal agencies, which are the National Science Foundation (NSF), the Department of Defense (DOD), the Department of Energy (DOE), the National Institutes of Health (NIH), and the National Institute of Standard and Technology (NIST). The NSF focuses on research across all disciplines of science and engineering; the DOD focuses on science and engineering research advancing defense; the DOE focuses on new and improved energy technologies; the NIH focuses on biomedical research at the intersection of life science and physical science; and the NIST focuses on fundamental research and development of measurement and fabrication tools, analytical methodologies, and metrology for nanotechnology [17].

Canada

Canada contributed 4.5% of the total global investment in 2008. The nanotechnology initiative by the Canadian government includes nine institutes of the National Research Council (NRC) distributed in several provinces. These provinces have spearheaded technological advancements in Canadian nanotechnology. Alberta, British Colombia, Ontario, and Quebec are some of the provinces central to innovation and competiveness in Canada. Currently, there are approximately 50–200 Canadian companies involved in the field of nanotechnology [18].

Brazil

Brazil, the leader of nanotechnology advancements in South America, commenced its governmental initiative in 2001. The National Council of Scientific and Technological Development (CNPq), the agency under the Ministry of Science and Technology (MCT), is dedicated to the promotion of scientific and technological research, human resources, and funding and is involved in the nanotechnological advancement in the country. In Brazil, funds for nanotechnology projects are distributed across various regions for the accepted proposals in hopes of stimulating the regional economy. In 2008, the responsible agency awarded 50% of its budget to the South-East, 15% to the South, and 35% of the budget to the North, North-East, and Center-West regions [19–21].

Europe

United Kingdom

Nanotechnology efforts in the United Kingdom were first initiated in 1986 by the National Initiative on Nanotechnology, led by the National Physical Laboratory. The initiative was jump-started with the Taylor report published in 2002, which highlighted the significance of nanotechnology. Currently, the Technology Strategy Board (TSB) is a governmental agency with a vision to be the global leader for innovation and attract inventive business. The Biotechnology and Biological Science Research Council (BBSRC), Engineering and Physical Science Research Council (EPSRC), and Natural Environment and Research Council (NERC) are the three research councils that drive nanotechnology advancement in the UK [22, 23].

Germany

The Federal Ministry of Education and Research (BMBF) has been funding nanotechnology activities since the late 1980s. The German government initiated a strategy to integrate seven ministries for the advancement of Nanotechnology in its “Nano Initiative-Action Plan 2010.” The goal of the strategy can be summarized in five action priorities:

• Developing future fields and introducing new industries.

• Creating favorable framework conditions for science and economy.

• Recognizing risks and providing guidelines for responsible handling.

• Informing and integrating the public.

• Identifying research demands of tomorrow.

The seven federal ministries include the Federal Ministries for Labor and Social Affairs (BMAS), Environment, Nature Conservation and Nuclear Safety (BMU), Food, Agriculture and Consumer Protection (BMELV), Defense (BMVg), Health (BMG), Commerce and Technology (BMWi), and BMBF [24, 25].

Eurasia

Russia

The Russian government nanotechnology initiative includes the Russian Corporation of Nanotechnology (RUSNANO) with a five billon USD budget, specialized federal R&D program financing (2008–2011) for four billion USD, and Nanoindustry Infrastructure Development in the Russian Federation for a period of 2008–2010 for one billion USD. The primary corporation, RUSNANO, was established in 2007 to advance the field of nanotechnology financed projects which include manufacturing projects to expand nanotechnological products; infrastructure projects to advance innovation, technology centers, technoparks, and information databases; and educational programs to train and educate the workforce for nano industries. The mission of RUSNANO is to make Russia the leading player in nanotechnology [26, 27].

Asia

Japan

Japan, one of the earliest players in the field of nanotechnology, leads the governmental effort through the agency MEXT (Ministry of Education, Culture, Sports, Science and Technology). MEXT is responsible for basic research and spearheads the nanotechnology advancement. The Ministry of Economy, Trade, and Industry (METI) leads the industrial development and commercialization efforts [28].

China

In 2001, an aggressive plan titled “Compendium of National Nanotechnology Development (2001–2010)” was issued to jump-start the Chinese initiative in Nanotechnology. The Chinese government spent 600 million USD in 2007 to promote nanotechnology with approximately 70 institutions engaging in nanotechnology research. The government backed funding agencies include the Chinese Academy of Science (CAS), National Science Foundation of China (NSFC), Ministry of Education (MOE), and Ministry of Science and Technology (MOST) [29, 30].

South Korea

South Korea’s aggressive plan to become one of the top three in the world by 2015 in nanotechnology competitiveness has led to the allocation of 16 billion USD for the period 2001–2010. The purpose of the Science and Technology framework law of 2001, launched by MOST, is to advance the nanotechnology effort in South Korea. MOST focuses on basic research and funds the knowledge base. The Ministry of Commerce, Industry, and Energy (MOCIE) and the Ministry of Information and Communication (MOIC) also promote nanotechnology growth in South Korea. The MOCIE focuses on commercialization efforts, whereas the MOIC funds projects that connect information technology with nanotechnology [31].

India

In 2001, India joined the race by launching the Nano Science and Technology Initiative (NSTI) under the Department of Science and Technology (DST), with a 20 million USD budget that financed infrastructure and 100 projects over 5 years. NSTI was superseded by the aggressive program Nano Mission within the DST with a budget of 254 million USD for 5 years. The objective of the Mission includes: Basic Research Promotion, Infrastructure Development for Nano Science & Technology Research, Nano Application and Technology Development Programs, Human Resource Development and International Collaborations. Other agencies involved in nanotechnology development include the Council of Scientific and Industrial Research (CSIR), the Department of Biotechnology (DBT), agencies under the Ministry of Information and Communication Technology, the Ministry of Family and Health and Welfare, the Ministry of Defense, and the Ministry of New and Renewable Energy [32–34].

Australia

Australia has made nanotechnology a national priority since 2004. A study conducted in 2004 by Australia Research Council (ARC) highlighted the shortcomings of Australia’s position in the global race. Numerous initiatives by the government were introduced to improve Australia’s status on the world stage. According to the Nanotechnology Australian Capability report, 75 nanotechnology research organizations, along with 80 nanotechnology companies, lead the nanotechnology effort. The government channels funding for nanotechnology through main agencies like the ARC, the Commonwealth Scientific and Industrial Research Organization (CSIRO), and the National Health and Medical Research Council (NHMRC). According to the Australian Office of Nanotechnology (AON), 21 of Australia’s 41 universities participate in nanotechnology advancements. For the period of 2008–2009, 107.7 million USD were allocated to nanotechnological advancement by participating governmental agencies [35, 36].

Nanotechnology Companies

Companies focusing primarily on nanotechnology products, as well as established companies with a nanotechnology sub-branch, are on the rise. The drivers for private entities include return on profit, superior product/services, and monopoly. According to Nanovip International Nanotechnology Business Directory, in November 2008 there were 1,608 companies with nanotechnology products and services; however, this is only an estimate due to various standards as qualifiers in different countries. Currently, the US dominates the race for the number of companies compared to other nations [37].

Nanostructured Materials as Destructive Adsorbents

Nanostructured materials based on diatomaceous earth, carbon, zeolites, lime, and clays have been in use as adsorbents for many years to physically remove contaminants from surfaces [38]. Many of these materials were not initially recognized as being “nanostructured.” Nanostructured materials can exist as atomic, molecular, or crystallite clusters. They may form different shapes including, but not limited to, cages, sheets, tubes, spheres, and rods. In the process of forming these unique shapes, voids and defects are also formed which increase the nanostructured materials’ surface area and porosity through pits, holes, tunnels, and edges. These defects allow the nanostructured material to absorb liquids and trap gaseous molecules. The contaminants in the area are then removed by containment within the nanostructured materials’ overall structure.

Destructive adsorbents based on high surface area inorganic metal oxides act upon contacted contaminants in two ways: they contain the contaminant by trapping the liquid or gas into their structure, and they alter the original structure (destructive adsorption) such that the contaminants are immobilized. Typically immobilization is done through interaction with reactive sites on the adsorbent. The nanostructures’ inherent molecular structure discontinuity gives additional reactive sites such as terminal hydroxyls or coordination sites for anions and cations. Bonding of the adsorbate to the adsorbent through van der Waals forces usually begins the destructive process and instigates the reaction with the surface structures of the adsorbent.

Materials that combine these characteristics can be used in several ways, with the primary usages focused on air purification and destruction and immobilization of bulk quantities of hazardous chemicals [39]. Specifically, the high surface areas, increased porosity, large concentrations of surface defects, and unusual stabilized exposed planes are credited for these useful applications [40–42]. Several mechanisms can be facilitated by these surface structures including oxidation, hydrolysis, and elimination of appropriate functional groups from the adsorbed contaminant (Fig. 9.4).

Fig. 9.4

Reaction schemes depicting destructive adsorption of GD and HD on nanocrystalline metal oxide surfaces

Nanomaterials Based on Metal Oxides

Some of the materials that have garnered the most attention are based on metal oxides and zeolites. Each of these materials can be further modified with doping agents and functional groups to tailor the material to its intended use. Literature evidence for proving destructive adsorption is heavily directed towards high surface area metal oxides; therefore, metal oxides are the focus of this section. High temperature desorption by thermo gravimetric analysis (TGA) in combination with Fourier transform infrared (FTIR) or GC-MS show what heat releasable by-products are observable or key changes are seen in the reacted sorbent’s NMR peaks or FTIR spectral bands. Most available analyses rely on observed reduction in the challenge agent either through sorbent extraction or measurement of a gas stream before and after entry into the sorbent bed (flowthrough or breakthrough). In general, the best characteristics for a destructive adsorbent to have are high surface area, pore size, and volume in a mesoporous range for increased contact of adsorbate and a high number of surface hydroxyls to allow for a variety of species to interact with the surface groups [43].

Nanocrystalline high surface area titanium oxide (TiO₂) has been extensively studied by several groups for its reaction with dimethyl methylphosphonate (DMMP), a common chemical warfare agent simulant for VX and G agents. Trubitsyn and Vorontsov examined ambient reactions of the anatase form by FTIR, comparing successive and simultaneous reaction processes of reactive adsorption, hydrolysis, and photocatalysis at both high and low DMMP concentrations, with and without humidity [44]. The rate of exposure to DMMP and relative humidity play a role in product formation and the degree of product binding to the surface of TiO₂ during adsorption and hydrolysis. The photocatalytic process is also affected by deactivation of sites by non-volatile products. Humidity aids in both hydrolysis and the release of converted volatiles. Interestingly, when all processes occur simultaneously, the destruction of DMMP is complete within 30 min.

Panayotov and Morris observed two paths that DMMP takes toward decomposition: molecular adsorption through hydrogen bonding at the hydroxyl groups and reactive adsorption through the Lewis acid active oxygen sites [45, 46]. They found that at low temperatures (295–400 K), nucleophilic attack from the neighboring surface hydroxyls form the Ti–CH₃ and P–O _x surface groups, while at higher temperatures (400–600 K) the lattice oxygens oxidize the Ti–CH₃. However, as the lattice oxygens are slowly poisoned and the non-volatiles accumulate, the isolated hydroxyls can be regenerated through thermal treatment in oxygen. Similar results were found during a molecular dynamics computer generated simulation performed by Quenneville et al. with varied surface hydroxylation of amorphous silica (SiO₂) and DMMP [47].

Li et al. have thoroughly investigated adsorption and decomposition of organophosphorus compounds with magnesium oxide (MgO) using an in situ pulse reactor GC-MS technique [39]. Comparison of two different MgO sorbent beds of varied surface areas (130 and 390 m²/g), after exposure to various gaseous organophosphorus compounds, revealed several important facts related to decomposition temperature, product distribution, and capacity for destructive adsorption. Overall, MgO reduces the decomposition temperatures for these compounds via dealkylation reactions, proton abstractions, and nucleophilic displacements; the capacity for the reaction is dependent on surface area; and presence or absence of water affects product distribution.

Photocatalytic studies with high surface area TiO₂ and SiO₂-TiO₂ using the HD simulant, 2-chloroethyl ethyl sulfide (2-CEES), by FTIR show both partial and full oxidation products in addition to aldehydic, carboxylate, and carbonate products that are surface bound [48, 49]. Multiple reactive sites are used by TiO₂, while Si–OH sites hydrogen bond to 2-CEES through the sulfur and chlorine moieties. Similar studies with diethyl sulfide (DES) found other specific roles for the chlorine.

Studies with nano MgO and 2-CEES also found that liquid phase reactions are greatly affected by the solvent used. The most rapid results were observed from use of inert organic solvents with some addition of water to enhance the surface hydroxyl group numbers [50]. Nanomaterials that are prepared such that they are intimately intermingled with two or more nanomaterials can show synergistic performance compared to those prepared singularly. Studies with 2-CEES and mixed metal oxides found that the surface hydroxyls and the Lewis acid sites were responsible for conversion to the surface bound alkoxy species and vinyl products and swift reaction time [51, 52].

Carnes et al. explored the destructive adsorption reaction with an aluminum oxide (Al₂O₃) and MgO mixture for performance against diethyl 4-nitrophenyl phosphate (paraoxon) [53]. UV–vis and FTIR studies showed that very little paraoxon is released back to the environment after washing with solvent. Similarly, nano zinc oxide (ZnO), copper oxide (CuO), and nickel oxide (NiO) have been found to have increased reactivity and capacity towards paraoxon over commercially available forms [54, 55].

In a series of studies, Wagner et al. have explored the room temperature reaction of nanocrystalline MgO, calcium oxide (CaO), Al₂O₃, and nanotubular TiO₂ with real agents (VX, GD, and HD) by ¹H, ³¹P, ²⁷Al, and ¹³C NMR [42, 56–58]. All of these nanomaterials hydrolyze VX and GD to surface bound non-toxic compounds. With HD, both hydrolysis and elimination were observed by destructive adsorption modes. The many layers of nanotubular TiO₂ and the surfaces and pores of MgO, CaO, and Al₂O₃ trap water allowing for rapid hydrolysis, whereas the presence of water on CaO with HD creates a CaCl₂ coated surface, catalyzing fast elimination of HCl after an initial induction period. Rates of some of these reactions were found to approach the speed of liquid decontamination solutions.

Koper et al. have also studied the destruction of various chlorinated hydrocarbons over high surface area CaO (conventionally prepared—CP and aerogel prepared—AP) and compared to commercially available non-nano or micro material (CM) in a bed at different temperatures with and without water [59, 60]. Comparison of these materials of differing surface areas (CM ~10 m²/g; CP ~100 m²/g; AP ~120 m²/g) led to several key conclusions. The material preparation method is critical, as it affects the surface area. Higher surface area generally results in faster reaction time, lower reaction temperature, and higher reaction capacity; however, this is highly compound dependent. While CP performs better with certain compounds, the reactions are slower with a higher capacity when compared to their AP prepared counterparts. Temperatures must be fine tuned for high efficiency and no graphite poisoning of the bed. Nanocrystalline zinc oxide (ZnO), copper oxide (CuO), and nickel oxide (NiO) have also been found to have increased reactivity and capacity towards carbon tetrachloride (CCl₄) over the corresponding non-nano metal oxides [54, 55].

High surface area MgO and TiO₂ reactions with the halocarbons CF₂Cl₂ and CFCl₃ were found to have increased efficiency at lower reaction temperatures compared to their non-nano commercial forms. Interestingly carbon coating of these high surface area metal oxides also appear to improve the reactivity of the nano forms [61]. Addition of Fe₂O₃ or other transition metal oxides to high surface area nanocrystalline CaO was found to improve destructive adsorption activity against CCl₄ and C₂Cl₄ to near stoichiometric quantities at elevated temperatures [62]. Several polar organic compounds are also destructively adsorbed by nanocrystalline MgO with transition metal oxide shells such as vanadium oxide; however, powder forms perform better than pelletized forms [63].

Decker et al. and Khaleel et al. explored this application with Al₂O₃/MgO and other coated formulations against SO₂ (an acid industrial gas) [62, 63]. This intermingling of metal oxides shows that acid gas adsorption is also improved over its singularly prepared individual components. Vacuum desorption and FTIR studies show well bound monodentate SO₂ species on the surface of the powder. Similarly, nano ZnO, CuO, and NiO were found to have increased reactivity and capacity towards SO₂ over the corresponding non-nano forms [54, 55].

Room temperature FTIR studies of nanocrystalline MgO, CaO, and Al₂O₃ with volatile organics, such as aldehydes, ketones, amines, and alcohols, found high capacity adsorption of these materials through a multi-layer dissociative process at functional groups [64]. Similarly, acetaldehyde is adsorbed by nano TiO₂ and as temperature is slowly raised surface intermediates are observed by aldol condensation [65].

Reactions of H₂S with sol- or aero-gel prepared CaO, ZnO, Al₂O₃, strontium oxide (SrO₂), and MgO proceed with increased capacity over their non-nano formulations due to their higher surface areas as well as higher inherent reactivities. Nano ZnO and CaO work with high efficiency and the observed efficacy is attributed to nanocrystallites and unique morphology of the materials allowing for deeper reaction into the material [66]. High surface area SrO₂ was found to be a unique material which had greatly enhanced efficiency (stoichiometric) at RT, while at elevated temperatures exhibited reduced efficiency due to temperature induced crystal growth [67].

Studies of nanocrystalline MgO, CaO, Al₂O₃, TiO₂, and cerium oxide (CeO₂) with and without halogen (Cl₂, Br₂, and I₂) or interhalogen (ICl, IBr, and ICl₃) treatment have been carried out against Escherichia coli, Bacillus cereus, Bacillus globibii, aflatoxins, and MS2 bacteriophage [68, 69]. Vegetative cell studies found appreciable reduction of E. coli and B. cereus with halogenated MgO and CaO within minutes. Spore studies show some reduction of B. cereus by both halogenated and non-halogenated nano MgO and CaO within several hours. Colorimetric studies with aflatoxin show a neutralizing effect and MS2 studies found no plaque forming units after 5 min with some halogenated formulations. Atomic force microscopy (AFM) and TEM imagery illustrate significant changes in the cells or spores [70]. These biocidal properties are thought to be promoted by the abrasiveness, basic character, electrostatic attraction, and oxidation power of the wet slurries or dry powders of nanomaterials [71]. Other known antimicrobial materials may be incorporated into these metal oxides to provide additional biocidal properties. Photocatalytic and biological testing of nanostructured novel Ag–C–S–TiO₂ formulations shows both photodegradation of acetaldehyde and inactivation of E. coli and Bacillus subtilis spores without light activation compared to P25–TiO₂ [72].

Commercial Uses

The commercialization of nanotechnology using destructive adsorption has, so far, been limited to studies developed by one company, which has been particularly successful with this technology. NanoScale Corporation, located in Manhattan, KS, has been using nanocrystalline metal oxides for neutralizing toxins since 1995 for customers worldwide. The technology was originally developed at Kansas State University under Dr. Kenneth J. Klabunde. After years of continuous progress, FAST-ACT^® (First Applied Sorbent Against Chemical Threats) was developed for the US Army for chemical warfare decontamination. FAST-ACT can be used on a variety of chemical releases to adsorb and eliminate chemical threats. The same technology was adapted to fit industrial and institutional needs for chemical hazards in the ChemKlenz^® line of products. NanoScale offers products based on destructive adsorption of odors as well [73].

Destructive adsorption provides a superior technology to many alternatives since it does not release or mask contaminants. Guild Associates also uses adsorption technology in their material provided to the US Army [74]. Guild provides chemical and biological decontamination in various products. They have developed several types of mats and blankets, a protective barrier used for transport, wipes, laundry systems, and masks, among others.

Nanostructured Materials in Catalysis

Nanotechnology in the field of catalysis is ahead of other nanotechnology segments and is referred as “the engine that powers the world at the nanometer length scale” [75]. The exceptional morphology of nanostructured materials is responsible for their enhanced catalytic properties [76]. Catalysts, by definition, accelerate chemical reactions by transforming reactants to products without being consumed during the process [77]. In the presence of an ideal catalyst, the preferred reaction can proceed at a faster rate, resulting in desired products and improved yields. The speed of the reaction is guided by catalytic activity, while the preferred reaction is a reflection of catalytic selectivity [78]. Catalysts at the same phase as reactants are known as homogenous and contribute to 10–15% of the catalyst market, whereas catalysts in a different phase are referred to as heterogeneous catalysts. In this topic we will focus on heterogeneous catalysts due to their extensive applications. Approximately 90% of newly developed chemical processes utilize catalysts, and improving catalyst efficiency via nanotechnology would have a significant impact on resources and the environment [79]. More specifically, improved process efficiency through use of enhanced nanocatalysts will allow for greener chemistry. Breakthroughs in energy and environmental applications with nanoscale catalysts have established great commercial success. For example, petroleum processing and the catalytic converter for automobiles utilize catalysts at nanoscale and are considered to be significant contributors [14]. Table 9.2 indicates cost and energy saving in the US per annum from exploiting nanoscale catalysts [80].

Table 9.2 Estimated impact of nanocatalysts [80]

Refinery Industry

The refinery industry has successfully applied nanotechnology to improve the previously inefficient refining process by exploiting catalysis. Naphtha reforming and cracking are examples of unit processes where nanocatalysts have made major contributions [81]. Naphtha is used as a feedstock for the production of high octane gasoline by reforming and restructuring the hydrocarbons of low octane. Currently, bimetallic nanocatalysts based on Pt-Re/Pt-Sn on an acidic alumina substrate are commercially in use in the reforming units. Pt-Re on acidic alumina allows for longer catalytic activity with improved stability and Pt-Sn on acidic alumina has enhanced selectivity at low pressure. Metal moieties are the catalytic sites where dehydrogenation reactions occur, while acidic sites are required for isomerization, cyclization, and hydrocracking reactions [82, 83]. The improvements over the Pt-alumina monometallic catalyst introduced in 1950 have led to higher octane levels and lower usage of the precious metals. Additionally, previously used octane enhancers like lead and benzene are being phased out. Techniques to produce oil at a lower cost by minimizing the amount of catalyst by reducing the particles to nano-size have been widely successful in the petroleum industry. Over the last six decades, advancement in technology has resulted in the particle size decreasing from 100 nm to less than 2 nm. Materials with improved catalysis efficiency are obtained by synthesizing materials with uniform active sites, size, and shapes [84].

In the petroleum refinery, cracking is the largest volume process where crude oil of high molecular weight (high boiling point) is cracked to low molecular weight hydrocarbons like gasoline, diesel, or olefinic gases by the process of fluid catalytic cracking (FCC) [85]. Currently, nano-size catalysts based on zeolites are commonly used for catalytic cracking. Zeolite structures can be manipulated to 1 nm and provide an adjustable cage-like structure that allows specific molecular interactions for enhanced selectivity. AkzoNobel, ChevronTexaco, Engelhard, Exxon Mobil, and CRI International are major producers of zeolite catalysts [84].

Environmental Related

Air Purification

Nanocatalysts play a crucial role in air filtration applications related for odor removal and chemical remediation. Combustion engines, coal burning facilities, and chemical plants are all sources of toxic nitrogen, sulfur, and other volatile organic compounds (VOC) [86]. Nanocatalysts are designed for the specific polluting source for VOC removal. Metal oxides based on heterogeneous photocatalytic oxidation (HPO) in the presence of sunlight have been proven to degrade toxic organic pollutants to less toxic by-products by semiconductor photocatalysts in the presence of an energetic radiation source and an oxidizing agent [87–89]. For example, heterogeneous photocatalysts based on TiO₂ and ZnO are useful for capturing toxic VOCs by UV activation, similar to the water purification described in the next section. The energy of solar electromagnetic radiation should be larger than the band gap of the nanomaterials in order to activate the photocatalytic reaction. One such photocatalyst that can be activated by electromagnetic radiation from the sun is crystalline phase anatase TiO₂ which has a band gap of 3.2 eV at wavelength shorter than 387 nm [90, 91]. However, only 2.7% of the solar energy is at this region. To harvest more of the electromagnetic radiation from the sun, photocatalysts exploiting the visible light region are being explored [92]. Doping with transition metal ions such as V, Mn, Cr, and Fe, or with nonmetals such as N, C, F, and P, semiconductor coupling with WO₃, CdS, or In₂O₃, and dye incorporated photocatalysts are a few methods to utilize a broader range of electromagnetic radiation from the sun [93–97]. For example, Lee et al. [92] reported carbon-doped titania with a pore size of 5–17 nm had a narrow band gap and was able to be activated at a wavelength of less than 550 nm. Similarly, Sathish et al. [98] reported a nano-photocatalyst of N-doped TiO₂ with activity in the visible region of the electromagnetic spectrum. These nanophotocatalysts are incorporated in curtains, blinds, or glass, where natural available UV sources are used to activate and purify air, as well as destroy pathogenic microorganisms [96, 99, 100].

Nanocatalysts in the catalytic converter and exhaust system of a chemical or coal burning facility have a different approach to neutralizing the exhaust air. These exhaust air streams are rich in NO_x, CO, and unburned hydrocarbons (UHC), which are greenhouse gases and are regulated by environmental agencies. A conventional catalytic converter utilizes precious metals such as Pt, Rh, and Pd to purify the exhaust stream. These metals tend to agglomerate into larger clumps upon exposure to hot exhaust gases, reducing the catalytic activity due to decreased surface area and thus requiring more of the expensive metal particles. Mazda Motor Corporation and Nissan Motor Company have successfully utilized metal nanoparticles in their catalytic converter systems for purifying exhaust emissions. Although their techniques are proprietary, the Mazda improved catalytic converter requires 70% less of the precious metal nanoparticles. Their nanosized particles are embedded in the substrate preventing agglomeration and enabling improved oxygen absorption and release rates for enhanced emission cleaning [101].

Chemical Industry

Nanocatalysts in the chemical industry are credited for maximizing synthesis efficiency, minimizing by-product formation, and saving energy by improving selectivity and activity. This is achieved by manipulating and controlling the size, shape, spatial distribution, surface composition, electronic structures, and stability of the catalyst materials. The detailed synthesis and mechanism of various nanocatalysts used in the chemical industry is beyond the scope of this report; however, economic benefits due to the use of nanocatalysts is briefly discussed. According to catalyst experts in Los Alamos National Laboratory, a $4 billion per year cost saving in production cost is possible with nanocatalysts. Table 9.2 depicts savings in production cost and energy savings utilizing catalysts at nanoscale in a common chemical manufacturing process. The data reported in Table 9.3 is based on the REMI model widely used in nonprofit institutions, universities, and US state governments [80].

Table 9.3 Cost analysis of chemical production utilizing nanocatalysts [80]

Catalysts are widely used in all industries; however, the value of improved catalysts such as nanoscale catalyst is in exponential increase as the high energy demand, stringent pollution regulations, high process efficiencies, reduced supply of material, and low carbon footprint requirement are drivers for superior catalysts.

Commercialization

According to Global Industry Analysts, Inc., the global nanocatalyst market is estimated to reach six billion USD by 2015. A large part (about 743 million USD) is contributed to the refinery industry, but the environmental applications will be the fastest growing. Concerns about air pollution and depleted energy sources are drivers for the environmental applications. Other major markets include the food processing industry and the chemical industry, where catalysts at the nano size offer unique and valuable benefits [102].

Green Millennium, Inc., Corona, CA, is using nanotechnology in their photocatalytic air purifying technology. Their TiO₂, when exposed to light and water vapor, produces hydroxyl radicals and a superoxide anion which allow the oxidation of airborne VOCs and toxic organic matter into carbon dioxide and water. This reaction provides deodorization, air and water purification, and sterilization providing a cheap and low energy consumption technology for air purification. With this technology, windows and walls can become self-cleaning and anti-soiling. Green Millennium offers three TiO₂ coatings for use across industries such as transportation, environmental, medical, food, construction, manufacturing, and more [103].

NanoStellar, Inc., Redwood City, CA, develops materials containing precious metals for the power industry. They have created more efficient nano-engineered catalyst materials that reduce exhaust and increase catalyst effectiveness of precious metals by 25–30%. They stress the use of computation materials science, novel synthesis, and chemical engineering for their success in development.

NanoStellar’s answer to the increasingly ambitious goals of countries to reduce emissions and pollutants are three products. NanoStellar promoted Platinum is available for low CO oxidation light-off temperatures and tunable NO oxidation characteristic applications. NanoStellar Pt:Pd 2:1 offers 25–30% better performance over traditional platinum only materials and can be used for light duty diesel vehicles. NanoStellar Gold™ improves hydrocarbon oxidation by 20% over Nanostellar Pt:Pd and is suitable for heavy-duty trucks and high efficiency diesel engines. NanoStellar products offer improved thermal stability, greater resistance to poisoning, and better light-off temperature [104].

Altimate Envirocare, Singapore, has created a PhotoCatatSmart Coating known as EnviroCare TiO₂ Photo-Compound Range. This is a spray coating that binds to many surfaces to provide a protective coating. Their TiO₂ Photo-Compounds, in reaction with light, produces “Super-Oxides” to destroy micro-organic substances through vaporization. This provides buildings, vehicles, textiles, and other surfaces with continuously clean surfaces. EnviroCare TiO₂ can be utilized in medical facilities to destroy infectious diseases like MRSA, E. coli, and others [105].

Nanostructured Materials in Environmental Remediation

Environmental pollution is a global concern. In the United States alone, there are approximately 1,244 US EPA Superfund sites—sites where the soil, air, and/or water are so polluted as to be an imminent health threat to anyone in the vicinity [106]. Environmental pollution may arise from innumerable sources and processes, both natural and anthropogenic. Wildfires and volcanoes pollute the air, as do many forms of transportation and industrial processes. Torrential rainfall washes topsoil and agricultural chemicals into watersheds. Seasonal winds blow pollutants far from their source into forests and grasslands. As pollution does not tend to stay confined to one area because of the natural patterns of air and water movement, pollutants released in one region may have dramatic impacts on another. Research by both the Commonwealth Scientific and Industrial Research Organization Marine and Atmospheric Research in Australia (CMAR) and the National Aeronautics and Space Administration (NASA) in the US has confirmed a link between air pollution and severe drought; a link which became more obvious after wildfires in the western US led to a drought in sub-Saharan Africa [107, 108]. More recently, there has been a great deal of debate about the process of “fracking,” where high pressure fluids are injected into hydrocarbon-containing bedrock in order to liberate stores of oil and natural gas. In April 2010, the Cabot Oil and Gas Corporation was banned from further oil production in the state of Pennsylvania after an investigation showed that its operation in Dimock Township had contaminated the drinking water wells of 14 homes there [109]. April 2010 also saw the BP oil disaster, where 4.9 million barrels of oil were released into the Gulf of Mexico when the Deepwater Horizon drilling rig exploded [110]. Contaminants from such assorted sources as chemical spills, pharmaceuticals, fertilizer and pesticide runoff, abandoned mining and industrial sites, and airborne gaseous and particulate matter from various exhausts pollute the environment we live in and demand our attention for an efficient prevention strategy. Sustaining and enhancing air, soil, and water quality represent some of the most difficult challenges facing the global society in the twenty-first century.

Arsenic contamination of water is found worldwide, with incidents occurring in Thailand, mainland China, Taiwan, Bangladesh, India, Nepal, Argentina, Chile, and many sections of the U.S [111]. Arsenic is a toxic element that occurs naturally in soils, rocks, and groundwater. It enters drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. Long-term drinking water exposure can cause serious health problems such as skin, lung, bladder, and kidney cancer. Many different nanostructured materials have been used to remediate As(III) contamination, including Fe-based materials (particularly nanoscale zero valent iron, or NZVI), high surface area alumina [112], and photocatalytic reactions with nanocrystalline TiO₂ [113].

Because of these diverse sources, causes, and types of pollution, there is a constant need for environmental remediation. Effective remediation strategies can render polluted air breathable, enable polluted water to support aquatic life once more, and restore polluted soils to a more pristine state. Nanostructured materials are expected to play a role in these strategies, and some successes have already been reported in the literature. Because of their high surface area to volume ratio, nanostructured materials can be significantly more chemically reactive than their bulk counterparts. Tunable nanostructured materials designed to target specific pollutants in a specific setting (water, air, or soils) are also a possibility.

Water Remediation

Water pollution is a very common environmental problem. While surface water pollution is more prevalent, groundwater pollution is also widespread. A number of different nanostructured materials, many of them based on Fe(0) nanoparticles, have been shown to be effective against common water pollutants including halogenated organic compounds (HOCs) and heavy metals. Previously, it has been shown that granular iron can degrade many chlorinated compounds, including chlorinated aliphatics, chlorinated aromatics, and polychlorinated biphenyls (PCBs), as well as nitroaromatic compounds. Early studies by Gillham and O’Hannesin examined the utility of zero valent iron [Fe(0)] in the degradation of 14 chlorinated aliphatic hydrocarbons [114]. Fe(0) nanoparticles have been shown to actively degrade PCBs and trichloroethene [115]. Additionally, bimetallic nanoparticles of Pd/Fe, Pd/Ag, Ni/Fe, and Pd/Zn have been shown to destructively dechlorinate hexachlorobenzene [116–118].

Nanostructured Fe-based materials have also shown some capacity for removing inorganic metal contaminants, such as Cr(VI) [119], As(III) [120], and Pb(II) [121–123], from polluted water. Chromium contamination is a common result of the tanning industry and lead contamination results from activities such as mining and wildfowl hunting, while arsenic contamination is usually natural in origin. As ingestion of these metals may cause both acute and long-term chronic health issues, the ability to remove them from the water supply is sorely needed. Unfortunately, the removal of Cr(VI) proceeds poorly in the presence of bicarbonate, magnesium, or calcium ions. One study showed a 55–77% drop in removal capacity when these ions were present [124]. The removal of As(III) has also been shown to be impacted by the presence of certain ionic species [125, 126]. Figure 9.5 shows the typical appearance of surface waters with heavy metal contamination.

Fig. 9.5

Surface waters with heavy metal contamination. Left: uranium contamination; right: acid mine drainage and lead contamination (Images courtesy of the Center for Hazardous Substance Research, Kansas State University)

Probably the most common cause of water pollution is microbial contamination. A multitude of microorganisms commonly reside in water, both in surface water and in groundwater. While the water supply in developed countries is highly regulated and protected from sources of contamination, this is not the case in developing countries where people commonly obtain water from communal wells or surface bodies of water. In these cases microbial contamination from human and animal waste, as well as soil bacteria, is widespread. Contaminated water can spread cholera, polio, typhus, amoebic dysentery, hookworms, elephantiasis, and many other diseases. Fortunately, nanostructured materials have been shown to have some activity against many common waterborne diseases.

It has been reported that single or mixed metal oxide nanoparticles such as zinc oxide, copper oxide, aluminum oxide, or titanium oxide, incorporated into a filtration media containing a binder matrix, can destroy bacteria [127, 128]. These approaches are believed to offer advantages over the current process of drinking water purification, which relies upon the addition of disinfectants and sanitizers to kill microbes plus flocculants to settle out larger particles. In one study, the metal oxide nanocrystals were included in amounts ranging from approximately 0.1% up to about 10% by weight, based on the entire filtration media. In another series of studies, it was shown that MgO nanoparticles are very effective biocides against Gram-positive and Gram-negative bacteria (Escherichia coli and Bacillus megaterium) and bacterial spores (B. subtilis) [70]. Other studies have shown that Ag-based materials are effective against viruses in drinking water [129].

Soil Remediation

Soil is essentially an agglomeration of mineral and organic matter, with pore spaces containing air, water, and nutrient solutions [130]. Specific soils develop under the influence of five different factors: Parent material, climate, living organisms, topography, and time [131]. The mineral portion may include both clays and mineral crystallites, while the organic portion consists of plant and animal residues and secondary products formed by bacterial action on the organic residues. Soil pollution, like water pollution, is relatively widespread and may be the result of both natural and anthropogenic practices.

Common soil contaminants include heavy metals such as arsenic and mercury; halogenated compounds such as PCBs; anthropogenic compounds such as estrones; and radioactive materials such as thorium [132]. The elemental contaminants, such as the radioactive materials and the heavy metals, may originate either from mining and manufacturing or may occur naturally as the result of weathering or leaching of minerals rich in those materials. For example, the minerals orpiment, lorandite, and smithite are rich in arsenic, and their weathering may release arsenic into the soil and water [133]. Historically, many metal-containing minerals have been valued by humans. Mining these minerals exposes even more of the naturally occurring mineral deposit to weathering and leaching thus accelerating soil contamination. The area of the Almadén del Azoque, Ciudad Real, Spain, where cinnabar has been mined since ancient times, is still heavily contaminated by mercury [134–136].

Non-elemental contaminants originate almost exclusively from human activity. Estrones, steroid hormones which are endocrine disrupting chemicals (EDCs), find their way into the environment as metabolites from birth control pills and fertility medications. They have a strong affinity for humic acid which leads them to bind to dissolved organic matter and be deposited when the matter drops out of solution [137]. PCBs were widely used as coolants and lubricants in capacitors, transformers, and other electrical equipment because of their nonflammable and insulating properties. While PCBs are no longer manufactured in the US, they are still present in old transformers and capacitors and are pollutants in soils and sludge in more than 400 US sites [138].

Many of the same nanostructured materials which are useful for water remediation also have some utility for soil remediation. Free iron and iron-based nanoparticles have been demonstrated to be highly effective at removing heavy metals, chlorinated organic solvents, polyaromatic hydrocarbons, and PCBs; however, they tend to aggregate rapidly and demonstrate poor mobility in porous media [139, 140]. Stabilized Fe(0) nanoparticles, which can be produced by a variety of methods including by surfactant modification or in colloidal solution with activated carbon or colloidal poly(acrylic acid) remain unagglomerated in solution for extended periods of time, which increases their mobility in contaminated soils, and are as reactive as free nanoparticles [141, 142]. There have also been efforts to incorporate these materials into membranes which can be placed in the path of contaminant plumes [143]. One study of removal of As(III) by NZVI found that the reaction resulted in the rapid formation of the minerals magnetite and lepidocrocite, which arose from corrosion products of the NZVI and adsorbed As(III). At pH values ranging from 4 to 10, between 88.6 and 99.9% of the aqueous As(III) was removed from solution. The presence of NO ⁻₃ , SO ⁻₄ , or HCO ⁻₃ negatively affected the ability of the NZVI to adsorb As(III), as did the presence of H₄SiO₄ and H₂PO ²⁻₄ [125, 126].

Pd(0) nanoparticles are also used for soil remediation as both free nanoparticles and as supported nanoparticles, where the supporting substrate may be various solid foams. Free Pd(0) nanoparticles produced by the bacteria Shewanella oneidensis were shown to reductively dechlorinate PCBs in solution, and supported Pd-Fe nanoparticles have been shown to assist in reductively dechlorinating 1,2,4-trichlorobenzene. In one such experiment, PCB 21 (2,3,4-chloro biphenyl) solubilized in M9 microbiological media at a concentration of 1 mg/L was reduced to undetectable levels within 1 h when 500 mg/L of palladized S. oneidensis (bioPd) was added to the mixture and incubated at 28°C. For the most part, Pd(0) nanoparticles appear to resist the agglomeration and oxidation problems which plague Fe (0) nanoparticles [144].

Nanostructured TiO₂ may be used to remove radioactive Th from soils. Experiments conducted in soils in the presence or absence of soil humic acid and fulvic acid demonstrated that both the fulvic and humic acids increased the sorption of Th(IV) to TiO₂ nanoparticles at acidic pH. Bare TiO₂ nanoparticles by themselves were able to form surface complexes with 94% of the available Th(IV); this percentage increased to 97–98% in the presence of fulvic or humic acids and remained stable with increasing pH [145].

Air Purification

Many VOCs, nitrogen oxides (NO_x), and sulfur oxides (SO_x) in air contribute to smog and high ozone levels, which harm human health [146]. Some of these, such as SO_x, may be produced both naturally and anthropogenically, while others are primarily the result of human activity. Nanostructured materials which are being used to purify the air include catalysts, which are currently in use and constantly being improved upon [147, 148], and nanostructured membranes, which are under development [149, 150].

Historically, carbon-based adsorbents or destructive oxidation have been used for air purification and particularly for VOC removal. More recently, nanoparticles of metal oxides (MgO and CaO) and core/shell binary oxides (Fe₂O₃/MgO or V₂O₃/MgO) have been tested against typical air pollutants such as acetaldehyde, propionaldehyde, perfluoropropene, and a number of other polar organic compounds [63]. MgO or CaO having a monolayer coating of Fe₂O₃ show enhanced reactivity for the destruction of chlorocarbons, organophosphates, and acid gases [152]. This destructive adsorption, where toxic gases are broken down into non-toxic or less-toxic products, is more desirable than the simple adsorption capability offered by carbon filters.

TiO₂ is widely used for photocatalysis of pollutants, as it generates hydroxyl radicals under UV radiation and the generated hydroxyl radicals then oxidize pollutants on the catalyst surface to form less harmful products. For example, oxidation of NO_x forms NO ⁻₃ on the catalyst surface [153], meaning that TiO₂ has the potential for removing NO_x from polluted air [154]. In another study, it was found that mesoporous γ-MnO₂ displayed a good performance in the removal of NO_x (72 mg/g) and SO_x (700 mg/g) [155]. Nanocrystalline CaO was shown to react with SO₂ at a relatively low temperature to generate a mixture of calcium sulfite, calcium sulfate, and calcium sulfide [40]. The presence of a small amount of Fe₂O₃ on the surface of CaO enhances the ability of the CaO to act as a destructive adsorbent for SO₂.

Commercial Uses

According to a Bharat Book report, environmental remediation accounted for the largest end-user market, capturing 56% in 2007. The projection, however, is that environmental applications will decline through 2013 [156]. However, some technologies have already entered industry use.

To date, a number of businesses have begun utilizing nanotechnology for environmental remediation. Golder Associates, founded in Toronto, Canada, has been in the remediation industry for almost 30 years. They utilize NZVI to treat organic contaminants. The large surface area and high reactivity provide a cost efficient solution for remediating deeply contaminated sites. By injecting the NZVI into the subsurface, the chlorinated organics can be broken down. Other potential applications include treating sludge from various industries and polluted soils in situ instead of excavating them [157].

NanoH₂O, Inc., Los Angeles, CA, uses nanotechnology to desalinate and reuse water. Its Thin Film Nanocomposite membrane has specific characteristics including the membrane roughness, hydrophilicity, and surface charge. This inhibits the adhesion of bacterial cells leading to less biofilm coverage. The minimization of biofilm formation decreases the energy consumption and chemicals used making the reverse osmosis process more productive [158].

NanoStellar, Inc. is helping automakers bring diesel emissions levels down by using a unique nanotechnology. NanoStellar uses the surface chemistry of nanomaterials to engineer precious metals such as platinum, palladium, and gold on a nano-scale level in order to make more effective catalysts for the chemical reactions in emissions control. It is also a key supplier in the diesel industry and is expecting a growth in business due to the worldwide need for reduced diesel emissions [104].

NanoScale Corporation produces and markets nanomaterial-containing filters for improving indoor air quality in houses affected by contaminated drywall (which emits corrosive hydrogen sulfide and other air pollutants). Use of the filters has been shown to dramatically reduce copper corrosion and odor issues in affected houses. Figure 9.6 shows the copper corrosion in affected houses before, during, and after treatment.

Fig. 9.6

Copper coupon corrosion (unexposed coupon = negative control, day 5 = baseline prior to treatment, day 10 = after first 5-day treatment, day 15 = after second 5-day treatment)

Finally, the Dow Chemical Company offers a water treatment media called ADSORBSIA. This treatment media is used by many municipalities to remove dangerous levels of arsenic from water. It offers a number of advantages over conventional water treatment media including handling and disposal advantages [159].

Environmental Concerns Related to Nanomaterial Usage

While nanomaterials offer a great deal of promise in environmental remediation, their usage also comes with some environmental concerns. The impact of nanomaterials on the microbial populations of bodies of water, including surface water and groundwater, is not well studied. The impact of nanomaterials on the microbial populations of different soils has also not yet been thoroughly explored. Finally, questions have arisen about the potential health effects of nanomaterial exposure on wildlife and plants. Preliminary studies indicate that the microbial populations of aquifers change rapidly in response to nanomaterial exposure, but revert to baseline shortly thereafter [160]. NZVI particles also do not appear to have adverse effects on the germination and survival of certain plant species [161]. However, they do appear to have adverse effects on fish, particularly on the gills and intestines [162]. Their effect on larger animals and environmentally sensitive animals, such as frogs and salamanders, is currently unknown.

In conclusion, the environmental remediation possibilities offered by nanomaterials are extensive. However, as nanomaterials themselves may cause environmental damage in certain situations, it is imperative that the decision to use nanomaterials in the environment be made responsibly and with consideration to potential harmful effects. Companies such as NanoScale Corporation, located in Manhattan KS, have undertaken toxicology testing in response to these conditions; however, many nanomaterial producers have yet to follow suit.

Nanostructured Materials in Textiles

Nanotechnology in textiles is a powerful combination; integrating materials manipulated at atomic to molecular levels results in textiles with superior properties. Previously, the functions of textiles were traditionally limited mainly to clothing, comfort, decoration, and protection from temperature extremes. Advancement in nanotechnology, particularly in the field of textiles, led to novel functions and superiority over former materials. These novel functions include anti-static, water repellency, wrinkle resistance, UV protection, self-cleaning, protection against toxic chemical, biological and other pollutants, impact resistance, and protection against fire [163]. Textiles using nanotechnology have also advanced to provide superior protection against extreme weather and improved comfort in terms of weight, moisture transport and permeability, plus superior tear and puncture resistance [164]. The market for nanotechnology in textiles will reach $115 billion in 2012 [165]. In the following sections, highly specialized applications of nanotechnology in textiles are presented.

Chemical Protection

A chemical and biological (CB) protective suit is a necessary safety requirement for individuals who may come in contact with toxic chemicals and bioactive agents. Farmers, chemical plant employees, firefighters, soldiers, and all individuals who will likely come in contact with toxic chemicals or biological agents require a safety barrier. In the contemporary world, no market driver is as important as human life or safety. Exposure to hazardous chemicals and bioactive agents often leads to grave expenses, fines, and negative public relations. The unfortunate outcome of the 2001 anthrax attack in the US, the 1995 sarin gas attack on the Tokyo subway, the Bhopal disaster in 1984 due to the methyl isocyanate (MIC) gas leak, and 1980s Iran–Iraq chemical warfare are some of the more recent ill-fated events that have cost human life and suffering [166, 167]. Currently, two main categories of CB protective suits are available: impermeable polymer ensemble and permeable sorbent-based gear. Although impermeable polymer provides the most protection against CB threats, they cause a great amount of physiological strain. Productive time for the wearer is limited during strenuous activity due to heat stress [168]. The lack of moisture exchange can be detrimental to health causing various illnesses and in some cases death [169]. In sorbent-based technology, sorbent is sandwiched between the textile layers to create a composite laminate. This shields the wearer from the ill effects of toxic contaminants. Figure 9.7 shows a schematic of the concept behind sorbent-based CB protective clothing.

Fig. 9.7

Schematic of CB protective clothing liner

Activated carbon spheres have been the traditional sorbent incorporated between the textile layers to provide chemical protection. The carbon-based technology predominantly involves physical entrapment of toxins or chemical pollutants [170]. The toxin’s proximity to the wearer, the potential of preferential adsorption of water by carbons, and a change in temperature resulting in off-gassing of adsorbed toxins are the major disadvantages of carbon-based chemical protective clothing (CPC). In sharp contrast, highly reactive nanocrystalline metal oxide sorbents integrated with textile matrices are expected to offer significant improvement in terms of true protection [171]. These high surface area sorbents with neutralizing capability decontaminate the toxic chemicals to non-toxic by-products.

NanoScale Corporation, as a commercial supplier of nanocrystalline metal oxides, markets its products under the NanoActive^® brand name. Their nanocrystalline metal oxides are fine powders, with particles in the 1–10 μm range, similar to ordinary metal oxides, such as talcum powder. However, closer examination shows that they consist of very small crystals (usually 2–10 nm in size) that form large clusters. Figure 9.8 shows a photomicrograph of NanoActive TiO₂.

Fig. 9.8

Photomicrographs of NanoActive TiO₂. High-resolution photo (right) shows amorphous and nanocrystalline regions

NanoActive metal oxides are highly porous, with high surface areas (for example, NanoActive TiO₂ typically has a surface area exceeding 500 m²/g). However, for reactivity, even more important than particle size and surface area is the presence of edges and corners, in which ions have a reduced coordination number, as conceptually illustrated in Fig. 9.9 (blue dots are examples of pentavalent surface ions, yellow dots are tetravalent edge ions, and red dots are trivalent corner ions). Such unusual morphology results in enhanced chemical reactivity and suggests a two-step decomposition mechanism on nanocrystalline metal oxides (the first step being adsorption of toxic agent on the surface by means of physisorption, followed by a second step, chemical decomposition).

Fig. 9.9

Conceptual sketch, showing coordinatively unsaturated sites, as well as a vacancy defect site

The fate of chemical warfare agent simulants 2-CEES and DMMP was studied after permeation testing of nanomaterial incorporated textile swatches by ASTM F739. The performance of prototype reactive liners incorporated with nanocrystalline metal oxides was compared against carbon laminate. After the permeation testing, fabric laminates were extracted with ethyl ether and analyzed by gas chromatography-flame photometric detector (GC-FPD). Table 9.4 shows the outcome of permeation testing of 2-CEES exposed liners. As seen from the data, production of 2-hydroxyethyl ethyl sulfide (HEES) confirms destructive adsorption by nanocrystalline sorbent incorporated reactive liners.

Table 9.4 Gas chromatography-flame photometric detector (GC-FPD) analysis of textile swatches after permeation testing with 2-CEES

Multiple analyses were performed to determine the fate of DMMP from the reactive liners. Solvent extraction of the liners retrieved from the permeation testing yielded unreacted DMMP. As seen from the data in Table 9.5, there was less extractable DMMP from the NanoScale prototype liner compared to the carbon control. The evidence for destructive adsorption of DMMP was acquired by TGA of sorbent material after permeation testing, which confirmed the presence of methyl phosphonic acid (MPA).

Table 9.5 GC-FPD analysis of textile swatches from permeation testing of dimethyl methylphosphonate (DMMP)

Table 9.6 Biological activity of modified nanocrystalline metal oxides^a

Figure 9.10 displays the TGA coupled with a 3D FTIR spectrum for DMMP adsorbed on nanocrystalline metal oxide. The band at 3039–2985 cm⁻¹ due to off-gassing at 483–600°C is assigned to CH₃-P asymmetric stretch, a characteristic band for MPA seen with NanoScale sorbent, but not with carbon-based sorbent (Fig. 9.11). This band was confirmed by analyzing the neat MPA TGA profile (Fig. 9.12). From the comparison of Fig. 9.10 against Fig. 9.12, it is clear that the DMMP challenged nanocrystalline formulation generates MPA.

Fig. 9.10

Thermo gravimetric analysis (TGA) of dimethyl methylphosphonate (DMMP) adsorbed on nanoscale sorbent

Fig. 9.11

TGA analysis of DMMP adsorbed on carbon

Fig. 9.12

TGA analysis of neat methyl phosphonic acid (MPA)

Biological Protection

Nanocrystalline metal oxides have also shown activity against biological agents. Table 9.4 displays the biological activity of modified nanocrystalline metal oxides against B. subtilis spores and vegetative cells of Burkholderia gladiolii. Sporicidal testing was conducted according to ASTM 2414-05 “Standard test method for quantitative sporicidal three-step method (TSM) to determine sporicidal efficacy of liquids, liquids sprays, and vapor or gases on contaminated carrier surfaces.” Biocidal activity was determined as per ASTM E 2149-01 “Standard test method for determining the antimicrobial activity of immobilized antimicrobial agents under dynamic contact conditions” [172].

Textile industries in the field of medicine have made significant progress by incorporating nanotechnology in the area of antibacterial textiles, antimicrobial wound dressing, and anti-adhesive wound dressings [173]. Antibacterial textiles have broad applications in the medical field; patient’s clothing, hospital bedding, facial masks, and hospital furniture are a few examples. Wound dressings exploiting nanotechnology have also become commonplace. Commercial wound dressings with incorporated nanocrystalline silver release ionized silver, facilitating wound healing. They have been clinically tested on burn wounds [174], ulcers, and other wounds [175]. Acticoat^®, marketed by Smith & Nephew, Hull, UK, is an example of this class of wound dressings. Wound dressings based on a silica nanosol derived from long chain alkyltrialkoxysilane function as anti-adhesive bandages with improved moisture permeability. These cover the wound without causing further irritation, unlike the traditional wound dressing, which adheres to the wound. The anti-adhesive dressings accelerate the healing process and provide additional comfort.

Self-Cleaning Fabrics

Self-cleaning fabric, a property made possible by exploiting nanotechnology, is useful for consumers ranging from soldiers in the battlefield to toddlers at home. In the US, approximately two billion kg of surfactant are used annually. The laundry process requires significant energy, water, and detergent, causing greater energy usages and contamination of water streams from the use of detergent [176]. Nanotechnology is expected to make a promising contribution to this area, in the production of self-cleaning fabric via green chemistry. These fabrics are an improvement not only because they have a positive impact on the environment, but also because their usage saves time and effort. Self-cleaning fabrics can be further classified into those which act via photocatalytic activity and those which act via the Lotus effect.

The photoactivity of nanomaterials, in particular metal oxides with high surface area, is useful in decontaminating toxins and neutralizing odors. In the presence of sunlight or UV, electrons jump from their valance band (lower energy state) to their conduction band (higher energy state), leaving a strong oxidizing site in the valance band and creating a reduction site in the conduction band. These sites are reactive to adsorbed species. These reactive metal oxides, in particular TiO₂ coated on fabric, exist as Ti(IV) with an oxygen atom. When charged with UV radiation, the Ti(IV) cation is converted to Ti(III) by electron transfer and simultaneously reacts with the adsorbed species using the oxygen. This electron hole weakens the titania and oxygen bond, resulting in detachment of oxygen containing the adsorbed species. This site is further hydroxylated, and later oxidized back to Ti(IV) in a slow process in the absence of UV radiation. Thus, the fiber coated with TiO₂ acts as a catalyst [177].

The lotus effect is a phenomenon utilized by the Lotus plant (Nelumbo nucifera) to self-clean its leaves by exploiting the property of contact angle and sliding angle. The contact angle of a lotus leaf can reach 160 °, which is classified as a superhydrophobic surface. Lotus leaves have a rough surface due to structures called micropapillae which are 5–9 μm, and nanostructures within the micropapillae. When a water droplet contacts the leaf surfaces, it sits on the nanostructure as the air bubbles occupy the crevices in between nanostructures, thus minimizing drag for the droplet allowing the droplet to roll off the leaf [178]. This droplet removes dirt or particulate matter on the surface during the roll off making the surface clean. Mimicking this natural phenomenon, advancements in the area of superhydrophobic fabrics with high surface roughness have been made by using coatings with nanoparticles [179]. Carbon nanotubes on cotton fabric [180], fluorinated carbon [181], zinc oxide nanorod film [182], titiania [183], and silica [184] on polymeric substrates are a few examples of materials utilized to enhance superhydrophobicity.

Smart Textiles

Sensors using nanoscale systems have gained momentum in recent years. Smart textiles with sensors have become a complex tool monitoring the environment, health of the wearer, and gauging the life of the fabric. The unique characteristics of nanoscale materials are ideal for sensing physical, chemical, and biological signals. Sensors are widely used in present technology, and advanced sensors based on nanostructured metal oxides enable sensing of much lower signals at room temperature [185, 186]. Electrical conductivity, catalytic activity, high crystallinity, and high surface area of these metal oxides are properties required for sensing toxic gases in low levels [187]. Examples of metal oxides include: SnO₂, ZnO, TiO₂, WO₃, In₂O₃, Fe₂O₃, CuO, NiO, Ga₂O₃, and V₂O₅. SnO₂ is sensitive to all gaseous species, which makes it an excellent substrate for surface doping. This functionalized material enhances gas selection and sensitivity. Sensors based on nanostructured metal oxides are thermally activated; however, textile incorporation requires sensors operating at room temperature which limits the selection of metal oxides. SnO₂-based sensors for sensing NO₂, H₂, and CO function at room temperature. Similarly, ZnO-based sensors are reactive to H₂, H₂S, and NH₃ at room temperature [188]. Lim et al. outlines the mechanism of hydrogen gas sensors based on ZnO nanorods [189]. Oxygen molecules adsorb to the surface of ZnO nanorods and withdraw electrons from the conduction band to form the electron rich oxygen species O ⁻₂ , O⁻, and O²⁻, which chemisorb at room temperature. This results in an electron poor space at the ZnO nanorod surface and creates resistance; however, when exposed to hydrogen gas, adsorbed oxygens are reduced to release electrons. This results in an electron rich space at the surface allowing decreased resistance. The sensitivity of this ZnO nanorod sensor can be improved greatly by doping with Pt or Pd metal which enhances the catalytic dissociation of H₂ to atomic hydrogen and eases the reduction of chemisorbed oxygen. These nanostructured metal oxides, when incorporated into textile matrices, are excellent indicators for exposure to toxic gases. Physical sensors based on nanoscale systems integrated into textiles which convert mechanical strain to electricity have multiple functions [190]. For example, CNT-based fabric sensors monitor respiration signals by measuring electrical resistance from the strain caused by respiration movements. Similarly, piezoelectric materials based on CNT-based fabric sensors generate electrical energy by sensing strain caused by movement [191]. Carboxylic acid and lactate oxidase functionalized single carbon nanotube (SCNT) are used to detect pathological disorders by sensing the pH and lactate present in excreted sweat. These biological sensors are excellent diagnostic tools [192]. Although incorporation of these physical, chemical, and biological sensors are at the initial stage of development, these smart textile-based nanoscale sensors are bound to change textile industry in the near future.

Textiles exploiting nanotechnology have long strides to make before their full introduction to the market place; these improvements include the durability to be washed and worn repeatedly without compromising functionality, large scale development needs, cost, and safety concerns. However, many textile products utilizing nanotechnology are commercially available and a few examples are listed below [193].

Commercial Uses

Nano-Tex^®, based in Oakland, CA, uses nanotechnology to transform the molecular structures of fibers to produce fabrics that resist stains, moisture, odors, and static. According to Nano-Tex, more than 80 textile mills worldwide use Nano-Tex treatments in products sold by more than 100 leading apparel and commercial interior brands. Nano-Tex claims their treatment is permanently attached to fibers to improve the function of the garment without limiting the life [194].

NanoHorizons Inc., in Bellefonte, PA, uses technology based on silver nanoparticles less than 15 nm in size, incorporated into fabrics. A patented technology uses the antimicrobial properties of silver and their nanotechnology capabilities to combat microbial growth. NanoHorizons is able to permanently chemically bind molecules to fiber, foam, plastic, or coatings. NanoHorizons markets their technology under the brand SmartSilver^® [195].

Although great advancements are being made in the textile industry, some of the most promising technology is still being developed. There is a substantial benefit to not having smelly, wrinkled clothing, but nanotechnology can do so much more. Sensatex Inc., Bethesda, MD, is developing what they have called the “SmartShirt.”™ The SmartShirt has nanoscale wires interwoven into the fabric to track vital signs and control temperature and can communicate results through a PDA to a base station where they can be monitored [196]. Garments like these can be used on soldiers and law enforcement to promote safe missions and provide immediate notice if care is needed.

Nanostructured Materials in Electronics

When one thinks of nanostructured materials in electronics, several topics come to mind: batteries, devices, and components. In reality these three topics could be broken down to numerous subtopics. We use some form of nanostructured materials everyday in our cars, homes, schools, hospitals, and our personal belongings. However, a closer look reveals that two basic formats exist for preparing these materials, top-down and bottom-up production. Historically, the top-down approach has been used to make smaller, faster, improved devices and components, starting from bulk materials and carving or etching away unwanted material to create nanosystems, devices, and materials [197]. Much electronic circuitry is prepared in this manner. The bottom-up approach is where a desired object is built up from smaller building blocks such as atoms or molecules. Both methods have promise to improve current electronics, but much of the research focused on improving bottom-up methods is more closely related to traditional nanomaterials synthesis.

Nanostructures are of great interest in electronics due to the shape, size, and observed composition properties, as compared to their larger scale counterparts. With these smaller dimensions, electron relaxation rates and interfacial crossing rates of electrons and holes in composite structure become more favorable [198]. Controlling these parameters during growth can be done by template synthesis (colloidal synthesis using various ratios of precursor and capping material) and surface impurities. Similarly, Wei and Zamborini have produced a synthetic vessel which allows real time monitoring of nanostructure growth through AFM [199].

Several materials have found use as lithium-ion batteries. It is thought that these materials can potentially be the answer for high power and energy demands of small mobile electronics and electric cars; however, cost, safety concerns, and various deficiencies must be overcome. Cathode materials from LiNi_xMn_yCo_1–x–y O₂, LiMn₂O₄, and LiFePO₄ are considered the most desirable while the most used anode material is still graphite. The lithium materials are prepared through many methods including solid-state, hydrothermal, and sol–gel processes. The small particles of the base cathode material are a good fit for high power applications due to the large surface area, internal structure, short diffusion length, and faster kinetics. Nanoparticles are also more accommodating to volume changes with less risk of cracking and minimal diffusion path lengths. However, the large surface area allows for side reactions on the electrode, coating the material and reducing the life-cycle of the cell, affecting the capacity retention [200, 201].

Several devices use nanomaterials for their electronic components. These include carbon nanotubes used in flat panel color displays, silicon nanowires for electrical conduits in electric and optical devices (photovoltaics and LEDs), and other materials for chemical and biological sensors [202, 203]. Caminade and Majoral have investigated the implementation of phosphorous-based dendrimer macromolecules as a method of coating and modifying surfaces, imparting nanostructures to various components [204].

Woehrle et al. has found a method to organize gold nanoparticles (1.5 nm) into linear chains through biomolecular nanolithography. These gold chains of DNA templates result in angstrom-level precision for controlled interparticle spacing which is a key requirement for electrical and optical applications [205].

Hannon et al. have continued the search for methods to selectively place and orient carbon nanotubes for use in circuitry by micro contact printing and conventional lithography of alkylphosphonic acids onto metal oxide surfaces. This method could improve large-scale integration of superior performance of the carbon nanotube field-effect transistor over the conventional silicon device [206].

Low resistive and good corrosion-resistant noble metal, transition metal, or silicon thin films have been used as contacts and conductors in electronics. Two deposition methods are typically used: vapor-phase or liquid-based growth. Díaz et al. used a different method for thin film deposition, namely, pyrolysis of metallophosphazene in air at 800°C [207]. The resulting thin film’s morphology is dependent on the polymeric or oligomeric nature of the precursor, preparation method used, and the surface to be coated. This could create a cheaper more controlled method for clean array formation with versatile film application compared to currently restrictive gold films through chemical methods.

Commercialization

In 2005, the National Center for Manufacturing Sciences (NCMS) surveyed 600 manufacturing companies to scope the future of nanotechnology. These companies included automotive, semiconductor, aerospace, energy, utility, and information technology sectors. The response? Sixty percent expected to include nanotechnology in their products by 2009, just a few years later [208].

Last year the NNI created a multi-agency collaboration, led by NSF, to promote nanoelectronics. “Nanoelectronics for 2020 and Beyond” pushes NSF, DOD, NIST, DOE, and IC to promote five areas of research and development.

• Exploring new or alternative “state variables” for computing

• Merging nanophotonics with nanoelectronics

• Exploring carbon-based nanoelectronics

• Exploiting nanoscale processes and phenomena for quantum information science

• Creating a National Nanoelectronics Research and Manufacturing Infrastructure Network

The goal of this research is to reduce power consumption and heat production in small electronics through carbon-based solutions, gain significant growth over other nations’ electronic capabilities, create high quality jobs, and lastly, create a foundation to foster other nanoelectronic successes [209].

NanoMarkets predicted the nanoelectronics market to reach $82.5 billion this year. The leading push on this market is expected to come from the demand of high-performance, non-volatile memories. Nanosensors are expected to capture a significant portion of the market in medical, homeland security, and aerospace applications [210].

Nanostructured Materials in Medicine

One of the most exciting potential uses of nanostructured materials is in medicine. Research into the mechanisms underlying different medical pathologies, particularly cancers, has led to a better understanding of the causes, progression, outcomes, and potential treatments for these conditions. Unfortunately, a greater understanding of a medical condition does not necessarily lead to an immediate advance in the therapy for the condition. The human body is an extremely complicated and very intricate structure, with the result that a therapy must be carefully designed to provide the maximum benefit with a minimum of associated side effects or toxicity. Nanostructured materials, with their unique capacity to be directed to specific individual cells, will provide safer and more effective treatments for a large number of medical conditions.

Nanomaterials and Cancer Therapies

One area where nanostructured materials are being investigated is in the diagnosis and treatment of cancer. Cancer is one of the most feared medical diagnoses, even though cancerous conditions are relatively common and most cancers are well understood. According to the CDC, the most common cancers are prostate, breast, lung, colon, uterine, urinary bladder, non-Hodgkin’s lymphoma, melanoma, kidney, and ovarian [211]. Cancer incidence is strongly associated with age, and its incidence increases dramatically after age 40 [212]. In the 6-year period from 1999 to 2005, more than nine million people in the US were diagnosed with cancer, which works out to approximately 1.5 million people in the US who are diagnosed annually, or approximately 1 in 200 [213].

Why is this relatively common and well-understood type of disease so feared? One reason for the anxiety surrounding this disease is the way it is currently treated. Most cancers are treated with a combination of surgery (to remove as much of the tumor as possible), radiation (to destroy any cancerous cells which could not be removed by surgery), and chemotherapy (to destroy any invasive or metastatic cancerous cells). Most cancer patients find the course of radiation and chemotherapy to be extremely unpleasant, which is to be expected when the side effects include fatigue, skin problems, loss of appetite, hair loss, and lowered blood count (from radiation therapy) [214] and nausea, muscle and nerve problems, fatigue, anemia, and difficulty breathing (from chemotherapy) [215]. Worse yet, more than one round of treatment may be required to eliminate all the cancerous cells from the body. Cancers which have evaded detection until they have progressed to advanced stages may be incurable, and the patient may undergo treatment only to prolong life.

Nanostructured materials are expected to provide substantial improvements in the diagnosis and treatment of cancer. Most types of cancer are very treatable in the early stages, with good chances of cure or lasting remission. However, many cancer types are difficult to detect in these early, highly treatable stages. Soft tissue cancers, such as ovarian, esophageal, and pancreatic cancer, are especially difficult to detect. These cancers commonly cause vague, poorly defined symptoms such as fatigue and digestive disturbances. As a consequence, these cancers are often not diagnosed until they are very advanced. The median survival time after a diagnosis of pancreatic cancer is currently—3–6 months, with fewer than 4% of those diagnosed still alive 5 years post-diagnosis [216].

Fortunately, improved diagnostic tools for these cancers are in development. In one experiment, functionalized semiconductor quantum rods were used to optically image pancreatic cancer in mice [217]. Other nanomaterials, including gold nanorods [218] and CdSe quantum dots, [219] offer enhancement of existing imaging techniques by acting as contrast agents. Improved imaging capabilities can mean substantial improvements in patient quality of life and treatment outcomes via improved staging of cancers and improved ability to gauge tumor invasiveness. In situ imaging, which discloses the exact location and size of the tumor, is particularly useful. However, nanomaterial-based assays which demonstrate improved detection sensitivity are also desirable. One such assay, in which a nanoparticle immunoassay measured the degree of protein aggregation of known cancer biomarkers, found that the level of protein aggregation or complexation was a positive indicator of certain cancer types [220]. Another research group designed a detection system capable of detecting as few as 25 target cancer biomarker protein complexes. This system is based on fluorescent-conjugated polymers on Ag/Au nanorods [221].

Many developmental nanomaterials have shown promise as potential treatments for cancer. Iron-based nanoparticles, including iron oxide nanoparticles, are being widely investigated for both their imaging properties and their potential use in anti-tumor therapies. These nanomaterials may be used for drug delivery [222, 223] or may be used for imaging and hyperthermia treatments [224, 225]. Other nanomaterials which show potential as therapies include carbon nanotubes [226–228], copper sulfide nanoparticles [229], and silica-based nanomaterials [230, 231].

Drug Targeting

In addition to providing improved detection and treatment of cancer, nanostructured materials may be designed to enhance existing treatments. The drug Cisplatin is widely used to treat solid malignancies, both alone and in combination with other chemotherapy medications. Unfortunately, the drug also has a wide array of dangerous side effects, including fatigue, nausea, vomiting, diarrhea, nerve damage, immune system suppression, kidney damage, hearing loss, and even the formation of secondary cancers resulting from treatment. The kidney damage resulting from administration of this drug can be severe, so much so that it is often dose-limiting [232].

In an effort to improve the drug by reducing its nephrotoxicity, a team from the Department of Medicine at Brigham and Women’s Hospital in Cambridge, MA, engineered a nanostructured version of this drug. Their nanostructured version consists of a polymer which self-assembles in the presence of the appropriate amount of platinum to produce a nanoparticle. This nanoparticle releases Cisplatin in a pH-dependent manner and is rapidly targeted into the lysosomes of cancer cells, where it releases the drug and kills the cells. Compared to the free Cisplatin, the nanoparticle demonstrated a reduced distribution in the system as a whole, which led to reduced toxicity [233].

A number of medicines have now been prepared by coprecipitating drugs and polymers to produce polymeric nanoparticles, including Cyclosporine A [234], Tamoxifen [235], and Daunorubicin [236]. In general, this approach is reported to result in improved tumor targeting, greater efficacy, and reduced toxicity.

The improved tissue targeting capability of nanoparticulate preparations of drugs is not limited to anti-cancer agents. Other areas of the body, most notably the central nervous system (CNS), are difficult to reach for most medications. In one study, poly(dl-lactic-co-glycolic acid) (PLGA) nanoparticles with modified surfaces (chitosan or Polysorbate 80) were found to be capable of passing the blood–brain barrier [237]. Other therapeutic nanomaterial preparations have been designed to deliver to the eye [238], across the mucosa [239], through the dermis [240], and to bone [241].

In contrast, organs involved in detoxification and excretion, such as the liver and kidneys, are frequent recipients of medications whether or not the medication is supposed to reach them [242]. This leads to toxicity and side effects from the medication, which can limit the dosage or usage. However, medical nanomaterials have been shown to greatly improve the targeting of these drugs to the tissue in need of treatment and away from the liver and kidneys [233]. This improved targeting not only allows the drugs to be more effective therapeutically, but also lessens any toxicity caused by detoxification and excretion.

Treatments for Lifestyle Illnesses

Medical nanomaterials also show promise in the treatment of “lifestyle illnesses” such as obesity, heart disease, and type 2 diabetes. As the population in the industrialized world grows fatter, more and more people will suffer the effects of being overweight. As a result, the demand for improved medical therapies for these conditions is growing. Patients want less invasive therapies for diabetes (no needle sticks for insulin administration or blood glucose analysis), heart disease (no shunts or coronary by-passes), and obesity (no gastric surgery and the ability to eat what they want, when they want). While it is improbable that medicine will advance to the point where patients can “have their cake and eat it too,” any advances in treatment will be welcomed.

Diabetes currently affects 7.8% of the total US population. Of those 60 and older, the prevalence rises to 23.5% [243]. The CDC predicts that by 2050 this incidence will double or triple [244]. Clearly, the need for less invasive treatments will continue to increase for the foreseeable future.

The current method of insulin delivery by injection has disadvantages including the potential for infection and the stress associated with self-injection. Nanoencapsulation of insulin in zirconium phosphate for oral delivery has been explored in vitro and is reported to result in the stable release of insulin from the nanocapsules [245]. Supercritical antisolvent (SAS) micronization of insulin has also been investigated for transdermal insulin delivery [246], and solid lipid nanoparticles have been investigated as carriers of insulin for pulmonary delivery [247]. If one or more of these insulin delivery methods proves to be as safe and effective as insulin injections, daily injections will soon be a thing of the past.

Fewer nanomaterial options are available for the treatment of obesity. Currently, one of the few efforts reported in the literature is the production of nanosized particles of orlistat, a gastrointestinal lipase inhibitor [248]. This allows the drug to be handled and administered more easily, plus the nanosized particles are better absorbed than their conventional counterparts. Another is the development of PEGylated all-trans retinoic acid nanoparticles, which have been shown in vitro to prevent adipocyte development and differentiation [249]. As the incidence of obesity increases, obesity research involving nanomaterials is likely to become more urgent.

The options for treatment of cardiovascular disease are more varied. Approaches currently under study include the use of nanomaterials to produce synthetic High-Density Lipoproteins (HDL) [250], injection of peptide nanofibers to enhance stem cell therapy [251], the use of nanoparticles to prevent atherosclerosis [252], and making nanoformulations of growth factors for therapeutic angiogenesis [253]. These approaches encompass both the prevention of cardiovascular disease via the prevention of atherosclerosis and treatment of diagnosed disease via cell therapy to re-grow the damaged tissues and improve organ function.

Other Medical Nanomaterial Uses

Nanomaterials also have potential usages in gene therapy. The use of nanomaterials has been shown to enhance the transfection of different target cells, including cancer cells [254] and skeletal muscle cells [255]. Transfecting regulatory genes into cancer cells encourages the cells to down-regulate their growth, up-regulate their differentiation, and can cause them to recognize their abnormal condition and trigger their self-destruction pathway. The ability to transfect skeletal muscle cells will, it is hoped, provide a cure for several inherited degenerative muscle diseases which are currently fatal. Nanomaterials also offer a great deal of hope for various opthalmic conditions which are currently difficult to treat or for which there is no treatment, such as retinal degenerative disease [256]. Because of the unique structure, composition, and function of the eye, many conditions are currently difficult or impossible to treat. However, current research in medical nanomaterials may eventually change this.

Finally, nanomaterials may provide an improved way to prevent infection. Some potential uses for nanomaterials in this area include oral biofilm prevention [257], control of airborne indoor bacteria [258], and the production of titanium alloys which discourage infection [259].

Commercial Uses

The impact of nanotechnology on healthcare is likely to be the largest among nanotech applications. North America has the largest market, worth $4.75 billion in 2009 with Europe following at $3.65 billion. The drug delivery market alone is expected to grow to $16 billion by 2014. Other markets such as biocompatible implants and coatings and diagnostics are expected to grow 42 and 21.8%, respectively, from 2009 to 2014 [260].

Elan Drug Technologies, headquartered in Dublin, Ireland, has found a solution to a problem that could lower the dosage of the medicines you take. Their NanoCrystal^® technology reduces the size of drug particles to less than 2,000 nm, exposing a larger surface area. Many drugs exhibit poor solubility and the NanoCrystal technology is a commercially available answer. This technology has produced five products and brought in $1.8+ billion annually in market sales [261].

NanoBio Corporation, Ann Arbor, MI, has technologies in development for topical anti-infective treatments and mucosal vaccines. This technology, NanoStat™, uses emulsions manufactured at the range of 150–400 nm. NanoStat treatments are toxic to microbes but non-irritating to skin and mucous membranes. This technology has shown effectiveness against certain bacteria, viruses, fungi, and spores. Since the mechanism involves a physical and not a chemical process, the potential for the development of drug resistance is substantially lowered. Vaccines for influenza and Hepatitis B are in current development [262].

There are numerous companies working on the delivery of drugs, typically in cancer applications. For example, the nanoscale development of gold-based drug compounds can be used to target tumors, limiting the impact on surrounding organs and tissues. Current issues with drug delivery are in the efficiency of loading and controlling the drug [263]. Future successes in nanotech drug delivery will depend greatly on the ability to scale up the technology, meaning a close scientist–engineer relationship to create an efficient, effective product.

In conclusion, the medical uses for nanomaterials are numerous and varied. Nanomaterials may eventually be used to provide routine treatments for conditions which are currently untreatable, such as muscular dystrophy and retinal degeneration, in addition to providing improved therapies for conditions such as cancer, cardiovascular disease, and diabetes.

Nanostructured Materials in Coatings

Another potential usage of nanomaterials is in coatings technology. There are innumerable different types of coatings, all designed for improving the characteristics of the coated material. A short list of coating types includes fabric coatings for improved stain resistance [264], antimicrobial coatings for infection prevention [265] and product preservation [266], conductive coatings for solar cells and other electronic applications [267], scratch-resistant coatings for optics [268], and antifouling coatings for marine applications [269]. Nanomaterials offer the opportunity for improvements in nearly all coating fields and applications.

Edible Nanomaterial Coatings

A number of different industries are currently using or are expected to use nanomaterial coatings. The food processing industry has been researching nanocellulose-based edible coatings for improved shelf life of fresh fruits, vegetables, and meat products [270, 271]. The medical industry uses nanosilver coatings on catheter surfaces and textiles [272], and marine equipment manufacturers use antifouling nanomaterial coatings [273]. Multiple applications for nanomaterial coatings exist in the electronics industry [274], most notably for applications such as solar cells [275].

Food safety is a significant public health concern. The CDC estimates that 48 million Americans are sickened annually by foodborne illnesses [276]. Because many food products are now mass produced, contaminated foodstuffs may easily produce nationwide outbreaks of foodborne illness. Additionally, fresh foodstuffs, such as produce, are highly perishable and have short shelf lives even under ideal conditions. Spoiled food represents a loss to everyone involved in food production and consumption: the consumer, who sees higher prices and lower availability thanks to spoilage; the grocer, who must pay to dispose of the spoiled food; and the producers and distributors, who don’t get paid for producing and transporting the food.

One high-tech solution which has been proposed to lower the incidence of contamination and prevent spoilage is the use of edible coatings. These coatings, which would predominantly be used on fresh or raw foods, could be designed with antioxidant capabilities (to prevent spoilage) as well as antimicrobial capabilities (to prevent contamination). Most commonly, the coatings consist of macro materials such as chitosan [277] or alginate [278]. However, a small number of researchers have reported that nanomaterials such as cellulose nanofibers [279] may be used to enhance the properties of these coatings. While only a few instances of edible nanomaterial coatings are currently known, the use of such coatings can be expected to increase as their safety is established and their organoleptic properties (their taste and smell) are improved.

Medical Nanomaterial Coatings

As was mentioned in depth in the Sect. 8, nanomaterials have a large number of uses in the medical field. However, here we will focus solely on nanomaterial coatings with medical uses.

One use for medical nanomaterial coatings is for infection prevention. The use of catheters and ports leaves patients more vulnerable to infection, as these indwelling medical devices lack the anti-infective properties of natural body orifices and are readily colonized by infectious organisms [280]. The most common antimicrobial nanomaterial coating currently in use is nanosilver, which is commonly encountered on medical instruments [281], in catheters [282], and in wound dressings [272]. The antimicrobial activity of nanosilver, when incorporated into these materials, offers the patient some protection against nosocomial infection and microbial colonization. These products are widely commercially available from a variety of suppliers and are widely used in hospitals and clinics.

Other medical uses of nanomaterial coatings include drug delivery [283, 284] and tissue scaffolding to enhance medical implant integration, particularly into bone [285, 286]. Naturally, prosthetic implants such as dental and joint implants are more successful if the patient’s healing process will integrate the implant into the existing bone, thereby securing it and allowing for more natural functioning. Hydroxyapatite nanoparticles (which can be incorporated by the body into bone structures) are especially useful when combined with the silica-polymerizing enzyme silicatein α (which encourages the process). Hydroxyapaptite nanoparticles are commercially available from suppliers such as Sigma Aldrich for use as a bone injectable substrate and for bone grafting.

Additionally, researchers are working on a nanomaterial coating that can safely eradicate Staphylococcus aureus (MRSA). A coating of this nature would be applied to a variety of surfaces including medical instruments and surgical masks. The research uses a naturally occurring enzyme which kills the target bacteria, attached to a carbon nanotube for increased mobility [287].

Industrial Nanomaterial Coatings

In addition to applications in food processing and medicine, nanomaterial coatings also have a great many industrial uses. Antifouling coatings are highly useful for the shipping industry, as smooth hulls and propellers create much less drag, which makes fuel usage more efficient [288]. Likewise, bioreactors and oil pipelines are expected to benefit from this technology [289], as are heat exchangers involved in food [290] or energy production [291]. The use of anti-adhesive or antifouling coatings on heat exchangers in power plants is expected to dramatically increase efficiency, as a 1 mm thick biofilm accumulation on the wall of a low carbon steel heat exchanger results in a resistance to heat transfer equivalent to an 80 mm increase in tube wall thickness [292]. There are environmental and safety concerns with some of this technology, as biocide-releasing coatings can adversely affect marine organisms or can lead to the presence of biocides in foodstuffs.

Other types of nanomaterial coatings, including self-cleaning coatings [293], are also expected to be extremely useful. Self-cleaning coatings on items such as solar cells could decrease maintenance costs and increase energy output. Currently, solar cell output can be severely affected by the presence of dust, with even tiny amounts such as 1/7th of an ounce per square yard decreasing power conversion by 40% [294]. Since the best locations for solar cells are in areas which receive large amounts of sunshine (and conversely, very little precipitation), dust is a serious problem. Self-cleaning coatings would go a long way towards remedying the effects of dust. Additionally, many optical instruments have parts which are difficult or time-consuming to clean, so self-cleaning coatings would decrease maintenance needs in these cases as well. Other less obvious uses for self-cleaning coatings include exterior coatings for building materials such as wood and stucco, which soil easily and can be colonized by algae and other microorganisms [295].

Scratch-resistant nanomaterial coatings have some obvious uses, such as in abrasion-resistant coatings for automobiles, industrial parts, furniture, and flooring [296]. Less obvious uses include abrasion-resistant coatings for use on teeth and bones [297]. Alumina nanoparticles are most commonly used for these coatings, although silica nanoparticles may also be used [298].

Finally, conductive nanomaterial coatings offer improved performance characteristics over currently used conductive coatings like indium tin oxide. Indium tin oxide coatings, while widely used, are brittle, expensive, and chemically unstable. Nanomaterials such as single-walled carbon nanotubes [299], conductive polyamide fibers [300], and single-walled carbon nanotubes with silver nanowire films [301] all offer advantages such as flexibility and improved chemical stability. Additionally, some of these coatings can be applied to inexpensive substrates to produce inexpensive energy storage devices.

Commercial Uses

Nanomaterial coatings are already a large portion of the commercial nanotechnology industry, as a whole. In 2008, commercial nanomaterial coatings generated revenues exceeding 600 million USD. Targets of these technologies include construction, healthcare, transportation, and defense markets. The commercial nanomaterial coatings market is expected to reach over five billion USD in revenues in 2013, according to a Research and Markets report [302].

Companies like Xurex, Inc., a manufacturer of nanomaterial coatings located in Albuquerque, NM, could make significant contributions to conserving building materials and lowering costs across many fields. Xurex offers coatings to combat the corrosion and degradation of pipes, roads, bridges, ships, etc., which could potentially save millions of dollars [303]. Other applications in technology include self-cleaning surfaces and more durable materials, such as concrete. These energy efficient improvements could reduce the 41% of all energy use that is lost to commercial and residential buildings [304].

There is a real commercial need for alternative coatings in relation to the aerospace and defense industries. Coatings for thermal barrier, anti-ice, and surface protection are a necessity. Funding from governments is pushing these applications as nanocoatings can typically offer additional properties, including heat resistance, as well as offering an environmentally friendly alternative to standard coatings [305].

Environment, Health, Safety Issues Related to Nanostructured Materials

Nanostructured materials have come into play in the consumer market after a relatively short development period. As they are part of such a new science, relatively little is known about them except for those that have been studied as desirable characteristics for developing products with distinct performance advantages. The greatest concern surrounding the use of nanotechnology is the possibility of toxicity or other damaging interactions with living organisms. Naturally, while toxic interactions with pathogens are desirable for some classes of nanomaterials, toxic interactions with organisms in general are not. The situation is further complicated by the fact that chemically identical nanomaterials with different sizes and shapes can and will show different toxicological profiles [306], different tissues and organisms used to assess toxicity will exhibit greater or lesser sensitivities, and approved, standardized methods for evaluating nanomaterial toxicity are scarce. Worse, the use of in vitro assays as a means of assessing toxicity may lead to erroneous conclusions regarding the toxicity of the nanomaterial in whole organisms.

For example, it is known that some mammalian organs and organ systems are more sensitive to nanomaterial toxicity than are others. The lungs, in particular, are known to be highly sensitive to nanomaterials [307]. However, toxicity assays which are conducted on lung tissues in vitro and in vivo can show very different outcomes. A study conducted on the toxicity of both nanoscale and fine zinc oxide particles in rat lungs found several confounding factors, including the failure of commercial samples to match the manufacturer’s specifications and the development of “metal fume fever” in animals exposed to levels of zinc oxide which caused no demonstrable cytotoxicity in vitro [308]. Indeed, at exposure levels which were pathological to the animal, the in vitro assays failed to show evidence of any inflammatory responses including increased chemokine production. And what are we to make of another study, which found that the toxicity of zinc oxide nanoparticles could be lessened by doping them with iron [309], although iron oxide nanoparticles have themselves been found to be toxic? [310].

Some nanoparticles have demonstrated similar toxicity towards plants and bacteria. Phytotoxicity is usually measured by assessing seed germination and root elongation in seeds and seedlings exposed to the test material. One study which measured the effects of multiwalled carbon nanotubes and nanoparticulate forms of metallic copper, metallic silver, zinc oxide, or silicon on zucchini plants found that while exposure to these materials did not reduce germination, root elongation and plant biomass production was negatively affected [311]. Biomass in particular was greatly affected, with exposed plants showing biomass reductions of up to 75% of controls. As has been found in other studies, the negative effects were significantly more pronounced after exposure to nanoparticulate forms as compared to bulk forms. Nanomaterials have also been shown to be toxic to cyanobacteria and microalgae [312] and to microbial soil communities collected from California grassland [313]. In the case of the soil bacteria, nanomaterial exposure reduced the overall biomass of the community and altered the composition and diversity of the community. The effect of these changes on the chemical processes which occur in the soil, and on other denizens of the grassland, is not known.

How are analysts to proceed when confronted by these types of toxicological results? Conducting subsequent experiments to better understand the underlying mechanisms is one obvious answer, but various interested parties must still determine how to reasonably proceed safely in the meantime. The approach to nanomaterial safety currently taken by the US government is to make a coordinated effort to (1) monitor both expected and unexpected consequences of nanotechnology and (2) identify and prioritize nanomaterial health and safety research needs [314]. These actions were taken as part of the NNI, which was established in 2000. The findings from research undertaken by this group will be used to guide public policies at regulatory agencies such as the EPA and FDA. Currently, the EPA can’t ask a chemical producer to provide data regarding the risk assessment of a chemical, unless the EPA already has data showing that the chemical presents an “unreasonable risk” to human health or the environment [315]. Regulatory policies are greatly needed, as nanomaterial production and usage becomes more widespread. As a group of Swiss analysts found, many companies in industrial sectors other than those specifically identified as “nanotechnology” are already using nanomaterials [316].

Another approach, taken by members of the insurance industry, was to perform a relative risk assessment based on the nanomaterial manufacturing process. This risk assessment took into account the normal operations risk, incident risk, and latent contamination risk [317]. At the conclusion of the assessment, the risks of fabricating five different nanomaterial types (single-walled carbon nanotubes, buckyballs, zinc selenide quantum dots, alumoxane nanoparticles, and titanium dioxide nanoparticles) were determined to be comparatively low in relation to other manufacturing processes such as battery production.

There also is a movement towards understanding what safety steps other industrial nanomaterial producers are taking. Surveys of health and safety measures taken by industrial producers have found that most producers have given the issue some thought, with many specifying the use of PPE and engineering exposure controls [318]. Undertaking exposure and hazard assessment procedures are common in industry [319].

Waste management is another area impacted by nanotechnology. The introduction of nanomaterial containing products has instigated use of various assessment tools (i.e., life-cycle assessment, LCA) to establish the impact of products on global warming/climate change, stratospheric ozone depletion, human toxicity, ecotoxicity, and others. Nanocomponents are assessed for aspects that include material selection, manufacturing, application, and disposal/recycle. Physical properties must be well documented and investigated because they influence the toxicological impact through transport and interaction of the materials when released to the environment. Many products are currently using nanocomponents containing titanium, carbon, silver, iron oxide, zinc, gold, and/or silicon/silica. These include appliances, automotives, electronics and computers, food and beverage, children’s goods, health, personal care, sporting goods, and home and garden products. Most products are assessed for toxicity by producers on a cradle-to-gate basis, vs. cradle-to-grave, leaving the onus for safe disposal on the consumer and the public waste facilities [320].

Walser et al. performed a LCA for nanosilver t-shirts and compared the data to both triclosan biocidal t-shirts and non-biocidal t-shirts. The cradle-to-gate study found the flame spray pyrolysis method of producing nanoparticles had a climate footprint of 2.7 kg of CO₂-equivalents; the plasma polymerization with silver co-sputtering had 7.67–166 kg of CO₂-equivalents (depending on maturity). In contrast, regular and triclosan t-shirts had 2.55 kg of CO₂-equivalents. Based on this study, it is clear that the consumers’ wash cycle habits and eventual disposal of garments have minor effects on climate footprint. On the other hand, mining operations for raw materials have a greater effect due to toxic silver emissions [321].

One of the beneficial uses of TiO₂ is as a sunscreen due to its effective UV reflection and adsorption capacities. The nano-TiO₂ has higher transparency and efficiency making it even more desirable. Sunscreens undergo extensive testing in direct exposure to the skin scenarios but not further in its life-cycle. Botta et al. have investigated environmental release of these nano-TiO₂ containing sunscreens to water (fresh and salt) after artificial aging of the solutions. Their results found that in salt water, a major part of the nano-TiO₂ containing residue will aggregate and sediment, further affecting bottom dwelling sea life. In contrast, the fresh water released portion will remain stable and accessible to the entire water column [322].

Another application in use is nanoparticle CeO₂ as a diesel fuel additive. This additive has been designed to increase mileage by performing as a combustion efficiency aid. However, some CeO₂ <100 nm has been found in the expelled particulate matter. This is then released into the environment in relatively low concentrations. Several studies have been performed to determine toxicity of these particles, but no testing has been done on the diesel additive exhaust system emitted particles, or on low concentrations of ceria nanoparticles [323].

Currently, limited studies are available for nanomaterials that enter waste facilities. A newly emerging term, “nanowaste,” is defined as any waste stream(s) that contain nanomaterials or synthetic by-products of nanoscale dimensions, generated either during production, storage, and distribution, or waste stream(s) resulting from the end of lifespan of formerly nanotechnology-enabled materials and products, or items contaminated by nanomaterials such as pipes, PPE, etc. Additionally, BSI British Standards Guide PD 6699-2 defines nanowastes in four forms: pure nanomaterials at point of production, materials and surfaces that have been contaminated with nanomaterials (containers, PPE, etc.), liquid suspensions containing nanomaterials, and solid matrices containing nanomaterials. Concerns that have been raised dealing with these nanowastes include increased uncontrolled releases of nanomaterials to the environment, the technological and legislative challenges nanowastes pose to waste management systems, establishing a nanowaste classification system, and ways to enhance current and ongoing management of nanowastes. The very nanostructures that are prized for their applications are now a concern due to their potential ability to aid faster bonding with pollutants, facilitating faster transfer and greater transport of hazardous materials through air, soil, and water. Traditional wastewater treatment by-products (biosolids from settling tanks) can become too concentrated with pollutants such as Ag to be reused as compost or fertilizer, flocculation methods can be thwarted by surface coatings or other functionalities present on the nanomaterial, or nanomaterials can just simply pass though without any interaction at all [324].

Some concerns with nanoparticulate materials are their capability for dispersion into air and water, then further into the environment. Drugs, personal care products, quantum dots, and environmental remediation projects all have high potential for uncontrolled environmental release and their incidence is expected to dramatically increase. Nanostructure characteristics that are a determining factor include particle size, surface area, chemical nature, and charge, while reactive oxygen species at the surface may have an effect. As human data is rather limited, animal studies have been performed. Major hazards include inhalation of particles <100 nm as they deposit in the pulmonary region causing inflammation of the lungs. Nanoparticulate to ultra fine particles (including PTFE, carbon [general, fullerenes, and nanotubes], and TiO₂) have been found to impair lung function, increase respiratory syncytial virus infection, impair phagocytosis, encourage tissue thickening or fibrosis, increase coughing and sputum production, give rise to higher risk of chronic bronchitis, encourage tumors, and cause lung cancer. Nanoparticles may penetrate lung tissue to enter the blood stream (and on to the heart, liver, and brain). Studies have found that SiO₂, TiO₂, ZnO, and Al₂O₃ can penetrate skin layers. Ingested TiO₂ particles (200 nm) are immunologically active and can further penetrate the intestinal barrier (onto the lymphatic and blood systems) [325].

NIOSH has partnered with several organizations throughout the world in government, academia, and business, creating the Nanotechnology Research Center (NTRC) to assess safe nanotechnology in the workplace. They have been investigating critical topic areas; namely, toxicity and internal dose, measurement methods, exposure assessment, epidemiology and surveillance, risk assessment, engineering controls and PPE, fire and explosion safety, recommendations and guidance, communication and information, and applications. NIOSH NTRC is collaborating with NNI to pursue these mutual goals [326, 327]. The investigations have been instrumental in providing guidance for those who produce and work with nanomaterials and nanomaterial-enhanced products. As work is continuing in each of these critical areas, information has been found to make the nanomaterial workplace a safer one. General guidelines have been determined for working with nanomaterials. These include minimizing worker exposure through engineering controls to reduce aerosol exposure, even up to source enclosure and isolation. Implementation of a risk management program should include: (1) evaluation of hazard posed by nanomaterials based on its available physical and chemical property data, toxicology, or health effects; (2) worker task exposure assessment; (3) good work practice education and training; (4) establishing criteria and procedures for installing and evaluating engineering controls at exposure locations; (5) procedures for determination of need and selection of PPE; and (6) systematic evaluation of exposures to ensure control measures are working properly and workers are being provided appropriate PPE. Filtration studies to date have indicated that high-efficiency particulate air (HEPA) filter applications (exhaust ventilation and vacuum pickup) should effectively remove nanomaterials from the air. When engineering controls are not enough, preliminary data suggests that a NIOSH-certified respirator will be useful; however, no guidelines have been set for airborne engineered nanoparticles [328]. Several tools have been developed for guidance in the form of documents for medical screening and hazard surveillance (DNNH NIOSH Publication No. 2009-116), managing health and safety concerns (DNNH NIOSH Publication No. 2008-112), and a searchable on-line library for nanoparticles, etc. [329].

From these results, it is obvious that more research into the environmental effects and fate of nanomaterials, and their known and potential effects on human health and the environment, is needed. Additionally, it is clear that an improved regulatory framework is also needed, in order to facilitate the collection, interpretation, and dissemination of the experimental findings.

Nanostructured Materials in Other Consumer Products

Nanotechnology has been finding its way into more and more consumer products over the past decade. As the realization of potential applications for nanotechnology grows, the knowledge will continue to spread. The bottom line for nanotechnology in consumer products will be “Is there a demand?” The consumer has the final say. Skeptics and scientists alike will be susceptible to the consumer’s last word, or rather, last dollar. The final say in 2009 was a resounding 1.545 billion USD spent on golf clubs, electronics, skin cream, and a plethora of other products that utilize nanotechnology. The skeptics lose out to the optimistic forecasts of Research & Markets report “The World Market for Nanotechnology and Nanomaterials in Consumer Products, 2010–2015,” which expects that number to triple by 2015. In 2015, 5.335 billion USD will be spent on innovative products that stand out from the rest because of something 100,000 times smaller than a human hair [330].

Tracking Commercial Nanomaterial Products

In April 2005, the Project on Emerging Nanotechnologies (PEN) was initiated. PEN contains the largest online inventory of commercial products with nanotechnology along with other nanotech learning resources. New products are added as often as they are found, which in 2008, was at a rate of 3–4 per week. PEN is a joint effort between the PEW Charitable Trusts and Woodrow Wilson International Center for Scholars. As of August 2009, the list of commercially available products contained over 1,000 products. The list realized a 379% growth since March 2006 [331].

Many groups worldwide, like PEN, are trying to identify the number of products available that use nanotechnology. Challenges exist which prevent a complete list from being formed. Currently, there are no requirements for nanotechnology products that would identify or separate them from their non-nano competition. Some products which claim to contain nanomaterials do not, and some products that do contain nanomaterials do not outwardly claim this. Nanotech products do not have special regulations, as of yet. Debates are raging on this topic and governments are being pressured to look further into the proposed risks. Until a decision is reached and the technology is tracked, nano products may be sold under the label of the manufacturers’ choosing.

Commercial Uses

Amid all of the debates and controversies, innovative and earth friendly products are being developed by companies large and small. What most people do not know is that some of the most widely known products, like the iPhone by Apple^®, are products of nanotechnology. The iPhone features a memory chip which is a result of nanotechnology [332]. Additionally, many everyday products are being improved through the use of nano-sized materials. According to “The Nanotechnology Consumer Products Inventory,” the most common material mentioned in the product description was silver (259 products) [333]. Carbon was the second most referenced (82 products including fullerenes and nanotubes), followed by titanium dioxide (31), zinc oxide (24), silica (15), and cerium oxide (1). Among potential environmental applications of nano materials, remediation of contaminated ground water with nanoscale iron is one of the most important examples [10]. Nanoparticles of titanium dioxide and zinc oxide are included in personal care products such as beauty products, sun screens, toothpaste [334], and textiles [335]. Silver nanoparticles are increasingly used as antimicrobial components in detergents, food packaging, and textiles such as socks and underwear [333]. Other potential uses for silver nanomaterials include portable filters for water purification which could be used in remote or underdeveloped areas lacking water treatment infrastructure [336].

In addition to the use of nanotechnology to improve these classic consumer products, entirely new uses which take advantage of the novel physics of nanomaterials are being developed. Nano-emulsions, a variation on the “oil and water” mixture used for salad dressings and cosmetics, also hold great promise for applications as different as future food technology, pharmaceutical development, disinfection, and pesticide application [337].

Large companies, like Samsung and IBM, are in the midst of nanotechnology use and development and have products on the market. Samsung makes nanopowders and has prototype field emission displays (FED) [338]. IBM has a science department devoted to nanoscale research in carbon nanotubes and nanometer-scale local oxidation [339].

In addition to the large companies making the technology known through their products and research, smaller companies are also working to get their name and products on the market. The odor elimination products marketed as OdorKlenz^® by NanoScale Corporation use destructive adsorption to neutralize odors. This technology stems from NanoScale’s flagship product, FAST-ACT^®. The OdorKlenz product line includes a laundry additive, a surface treatment, a skunk treatment for pets, and a vomit absorbent. OdorKlenz also features an air filtration cartridge available to the disaster restoration market for odors after fires, floods, or other disasters. The OdorKlenz branded products were introduced to the market in 2007 [73].

Regulation

Decisions made in the near future may alter the currently optimistic outlook of nanotechnology. Governments have difficult decisions to make on the risk of nanotechnology in products from skin creams to foods to socks. One author, a member of the European Commission, stated “Further research is needed on the toxicological and ecotoxicological properties of nanoparticles, their uptake in the body, accumulation in the tissues and organs, transport characteristics, exposure and dose–response data, and their distribution and persistence in the environment” [340]. This uncertainty about regulatory issues has a discouraging effect on the commercial development of nanomaterials, as manufacturers are reluctant to develop products without a suitable regulatory framework and guidance on safety requirements. However, at the present time the promise of nanotechnology appears to outweigh any potential risks, and thus R&D efforts continue. There is no doubt that, one way or another; nanotechnology will become an integral part of our daily lives.

Concluding Remarks and Future Outlook

Previous chapter sections have reviewed a large number of different nanotechnology applications in various areas, including medicine, textiles, catalysis, electronics, and others. Nanomaterials are already in commercial use in many of these areas, with new technologies in development, as well. Consequently, nanomaterials are now widely encountered in daily life, although many consumers remain unaware of their presence in the products they use.

Despite the enormous promise offered by nanomaterials, there are still multiple barriers to their development and use. One substantial consideration for those seeking to commercialize a nanotechnology or include it in their commercial product is the regulatory framework which exists for nanotechnology. Consumers demand safe products, so product manufacturers and distributors put a great deal of time and effort (and money) into ensuring that their products comply with the appropriate regulations—and this is the primary hurdle to nanomaterial usage. Presently, many regulatory agencies such as the US EPA have few guidelines on how to regulate nanomaterials [341]. Without a suitable regulatory framework, manufacturers and distributors have difficulty assuring themselves and their buyers of the safety of their product.

How did this situation come about? The same unique qualities that enable nanomaterials to have their capabilities also make them difficult to regulate. Bulk materials, such as carbon, have set physical properties and capabilities. However, carbon nanomaterials have an entirely different set of physical properties and capabilities. Worse (from a regulatory standpoint), these physical properties and capabilities change with the size, shape, and structure of the carbon nanomaterial. Whereas bulk carbon does not conduct electricity very well, carbon nanotubes do [342]. Bulk carbon has few detrimental effects on aquatic life, but carbon nanotubes are known to be toxic [343], and a slightly different form, fullerenes, may accentuate the toxicity of other chemicals [344]. The quantum mechanics which regulate nanomaterials’ interactions with other substances also make their toxicological behavior difficult to predict.

A number of organizations, including federal bureaus such as the EPA and testing standards developers such as ASTM, have begun developing methods to assess nanomaterial properties. ASTM currently has seven standards related to nanotechnology: One defining the standard terminology [345], two defining methods for determining some of the physical characteristics of nanomaterials [346, 347], and four standards relating to health and safety [348–351]. Once sufficient research has been performed, trends in the toxicology of different nanomaterial types should become apparent, and a regulatory framework with standard assay methods can be established.

Previous chapter sections have given multiple estimates on the future size of different nanomaterial markets. If nanomaterials are not found to have serious adverse health or environmental effects, then the optimistic predictions of their worth will likely not fall short of the mark. However, if nanomaterials are found to have serious environmental effects or detrimental effects on human health, their commercial future is considerably less rosy.

In conclusion, much more research is needed into the properties and capabilities of nanomaterials. Nanomaterials offer great improvements in many different areas and may have very positive impacts on human health and the environment, but they may also have negative impacts which are not yet understood. As research and development efforts progress, both the promise of and the problems with nanomaterials will become apparent. Only after both of these aspects are recognized can the full potential of nanomaterial technologies be realized.

Questions

• 1. Why do nanomaterials behave differently from their macro counterparts?

  Answer: Because of the small size of nanomaterials, a large fraction of atoms are located close to the surface of the material instead of in the bulk, which increases their reactivity. Additionally, at such a small scale, quantum effects become increasingly important in governing the behavior of the material.

• 2. What are the advantages and disadvantages of a government guided research initiative like that of Germany as opposed to more independent research other countries use?

  Answer: The main advantage of government guided research is that a more focused approach will be implemented. With more researchers looking into the same set of problems, an outcome could be more likely. The disadvantage would be the limitations that are set on exploring new discoveries.

• 3. Should companies manufacturing nanotechnology containing products be mandated to add this information to their product labels?

  Answer: Yes, companies should be mandated to add the phrase “nanotechnology containing products” to their product labels should safety concerns arise later. All products should be labeled to include this information.—OR—No, the manufacturer should maintain the right to market/label as they see necessary unless risks become known. Restricting labels may inhibit the advancements of the nanotech industry.

• 4. What are some benefits of nanomaterials for use in cancer treatments?

  Answer: The benefits of using nanomaterials in cancer treatments include more accurate dosing, reduced side effects, reduced toxicity, accurate and non-invasive diagnostics.

• 5. Describe the significance of Richard Feynman’s speech and his approach to nanotechnology.

  Answer: Richard Feynman’s speech in 1959 opened discussion of the bottom-up approach as opposed to the top-down approach to nanotechnology and revolutionized the idea of nanotechnology.

• 6. What benefits do nanostructured materials bring to environmental remediation?

  Answer: Increased surface area means increased reactivity and adsorption capacity, therefore nanomaterials are more efficient than their non-nano counterparts in environmental remediation. For example, Fe(0) nanoparticles do not have mobility issues as larger Fe(0) particles.

• 7. Why is there so much regulatory uncertainty surrounding nanomaterials?

  Answer: One of the reasons there is so much regulatory uncertainty surrounding nanomaterials is because the properties of nanomaterials are dramatically different from those of bulk materials. Furthermore, because of quantum effects, the physical configuration (shape, structure) of a given nanomaterial can cause it to behave differently than another chemically identical nanomaterial with a slightly different physical structure. For example, carbon nanotubes will behave differently from carbon nanospheres, even though they may be chemically identical, even to the extent of containing the same number of carbon atoms.

• 8. Describe the two mechanisms of action of nanocrystalline high surface area TiO₂ on the chemical warfare agent simulant DMMP.

  Answer: Nanocrystalline high surface area TiO₂ can adsorb DMMP via hydrogen bonding to exposed hydroxyl groups (molecular adsorption) and via its titanium sites (reactive adsorption).

• 9. Why is the protection offered by textiles containing nanomaterials potentially preferable to that offered by textiles containing activated carbon spheres?

  Answer: Activated carbon spheres entrap chemical pollutants or toxins, but do not destroy them as nanomaterials do. Additionally, activated carbon spheres can off-gas the absorbed chemical during temperature changes and preferentially absorb humidity in the air rather than the toxin or pollutant.

• 10. You are a graduate student supported on an EPA fellowship research grant whose focus is removing Cr(VI) contamination from groundwater in a limestone (calcium carbonate) aquifer. One of your research committee members has suggested Fe-based nanomaterials. Is this approach likely to work?

  Answer: No, using Fe-based nanomaterials for removing Cr(VI) contamination from groundwater in a limestone (calcium carbonate) aquifer is not likely to work. Research has shown that, while Fe-based nanomaterials can remove Cr(VI) from contaminated waters, removal capacity drops to 55–77% in the presence of magnesium, calcium, or carbonate ions. As limestone is composed of calcium carbonate, the groundwater would almost certainly contain calcium and bicarbonate ions.

• 11. Which country has the largest number of nanotechnology companies?

  Answer: The United States of America has the largest number of nanotechnology companies.

• 12. How will self-cleaning and conductive coatings promote greener energy production?

  Answer: Both self-cleaning and conductive coatings are expected to improve the performance of solar cells promoting greener energy production. Self-cleaning surfaces will prevent dust build-up, while conductive coatings can provide both more efficient energy capture and potentially cheaper production of the cells and energy storage devices.