Johan Martens

Martens group
Celestijnenlaan 200f - box 2461
3001 Leuven
Belgium

tel:
+32 16 32 16 37
contact

Home

About People Research Spin-offs

About Johan Martens

Johan Martens received his PhD (1985) and his habilitation (1988) in applied biological sciences at the KU Leuven. He started his academic career in 1982 at the Research Foundation Flanders; from 1988 on he was lecturer, later senior lecturer at KU Leuven. In 1997 he became a professor at this university, being the Head of the Department of Microbial and Molecular Systems (2005 - 2010) and also the Head of Centre of Excellence in Catalytic Science (2005 - 2009).  

Professor Martens’ core expertise is in synthesis and application of functionalized nanoporous materials in catalysis, adsorption, molecular separation and controlled release. He contributed substantially to the understanding of molecular mechanisms of formation of structured nanoparticles, zeolites, ordered mesoporous materials and porous materials in general. He performed experiments under microgravity in the International Space Station, and combined advanced physico-chemical techniques to reveal the supramolecular assembly mechanisms of inorganic structures on organic sacrificial templates.

Professor Martens has never been constrained to a single area of research and has always been attracted by real-world problems, seeking collaboration with colleagues from other disciplines and especially physics and pharmaceutical and biomedical sciences to tackle scientific challenges of high societal relevance. Quite unique is that he has contributed to very fundamental studies as well as to the implementation of fundamental knowledge into practical solutions. In this sense he is a pioneer of translational research. 45 patent families were granted to Professor Martens. Several of these basic research inventions are being implemented in commercial applications or commercialized in spin-off companies founded by him. Johan Martens received several awards: the biannual Exxon Chemical European Science and Engineering Award in 1995, the ESA Certificate of Merit in 2002, the “Enterprize 2005” – a contest for innovation and entrepreneurship in Belgium. In 2008 he received the Methusalem funding – the highest level of structural funding in Flanders granted in regard to proven excellence. The funding was renewed in 2014. Since 2012 he is an active member of the Royal Flemish Academy of Belgium for Science and the Arts.

 

Honors and Awards

  • Exxon Chemical European Science and Engineering Award (1995)
  • ESA Certificate of Merit (2002)
  • Enterprize innovation and entrepreneurship contest (2005)
  • Recipient of prestigious long-term Methusalem funding (2008, 2014)
  • Best Idea for a CO2-lean Society by 2050, 4th Strategic Energy Forum (2009)
  • Member of the Royal Flemish Academy of Belgium for Science and the Arts (since 2012)
  • Francqui Chair holder (2013)
  • Materials Innovation Prize of the Federation of European Materials Societies (2013)

 

Teaching

Johan Martens teaches multiple courses on Catalytic Science, Physical Chemistry, Inorganic Chemistry and Highly Divided Solids. An overview is given here.

 

Publications

A selection of recent publications is shown below. For a complete overview, follow this link.

query=user:U0008614 year:[2012 TO 2024] &institution=lirias&from=1&step=20&sort=scdate
showing 1 to 20 of 436
Items per page 10 |20 |50
Sort newest first |author |title |popularity
  • thesis-dissertation
    Reher, Thomas; 2024. Agrivoltaics: optimizing the synergy of crop production and solar panels.
    LIRIAS4151389
    description
    Sustainable crop production and the continued profitability of agriculture in Europe are increasingly perceived as two opposing goals. The desire to continue traditional farming while reducing chemical inputs and fossil energy consumption brings with it many challenges. Also, the changing climate challenges agriculture in many new ways: jeopardizing harvests, pressuring growers to adopt new management practices or changing cropping systems entirely. To remain relevant and competitive, new ways of crop production will need to be considered. An ever-increasing global population and rise in energy demand stands in stark contrast with the available renewable energy in our electricity mix. Despite sustained efforts, the transition away from fossil fuels progresses at an insufficient pace. Additionally, increased opposition against nuclear energy leads to a re-uptake of gas- and coal-fired power stations, further increasing greenhouse gas emissions. To reach, or even approach our climate goals, solar- and wind energy production must be increased. Agrivoltaic (AV) production systems can serve as a bridge between agricultural sustainability and climate change challenges. By integrating solar panels on agricultural land, provided careful design choices are made, crop production can be maintained while solar energy generation can be expanded. Under AV, plants experience a modified microclimate characterized by reduced solar irradiance, changed temperatures and shifted precipitation inputs. Solar energy generation almost exclusively relies on crystalline silicon solar cells. New approaches such as perovskite-silicon tandem cells or wavelength selective technology show promise for continuing PV efficiency growth. A variety of solar panel types are available for AV. Fuel production directly from solar energy and ambient water has become a reality with the development of hydrogen panels. The use of hydrogen fuel can be a key factor in overcoming the energy density and storage problems associated with electric PV. By capturing water from the air, H2 panels thrive alongside transpiring crops. Where additional light transmission may be required, a range of semitransparent options are available. AV systems can make use of semitransparent modules, since they represent a useful tool for fine-tuning irradiance levels for the crops. One of the biggest challenges of implementing AV as a new sustainable farming system, is knowing the impact on crop productivity ahead of time and dealing with the uncertainty of fluctuating energy prices, both impacting profitability. We first performed an extensive literature search related to all the constraints that determine an AV system. Practical farming constraints, such as the use of heavy machinery, or intensive manual labor leads to a variety of AV system requirements. The variation in shade tolerance among commonly cultivated crops requires tailor-made AV system designs to optimize both energy production and agricultural yield. We distinguish three types of crop responses under AV. Crops such as maize or strawberry tolerate shade only to a limited extent and exhibit a steep decline in productivity with increasing shade. Other crops such as pear, grass or blackcurrant decrease in yield but at a much slower rate. Finally, there are crops that exhibit some level of shade tolerance, such as blueberry or raspberry. Another challenge for AV systems is determining its place in the landscape. Selecting suitable sites for AV systems requires the consideration of many factors and stakeholders' requirements. A GIS multi criteria decision analysis of Flanders revealed 60 % of its agricultural land as suitable for AV. All crops contended with important restrictions due to the proximity of heritage sites or areas of significant natural value. Most of the fruit cropping area reached AV suitability scores exceeding 0.95 out of a max of 1, while arable crops and vegetables scored on average 0.12 points lower. Despite contending with a highly fragmented landuse, agrivoltaic systems can supply up to 200 TWh of electricity per year- 4 times the current yearly electrical consumption of Flanders. Besides assessing the theoretical suitability of crops and determining the geographical selection of ideal farming plots for AV implementation, we also conducted field trials on several different AV systems in Flanders. We evaluated two experimental agrivoltaic pilot sites on arable farmland as well as an AV setup in a mature pear orchard. On the fist arable site, we investigated static and single-axis tracked bifacial modules paired to sugar beet, an important industry crop, at a light reduction of 15-20 %. Beets proved challenging to manage in practice due to weed and fungal pressure, with yields that were reduced by 11-19 % depending on position. Roots were found to be smaller but maintained sugar levels. The other arable AV pilot assessed the potential of wheat under an elevated agrivoltaic system at 22-30 % shading using traditional PV modules and hydrogen panels. Wheat suffered higher losses of 33-46 %. Smaller grains with high protein content were recorded under AV. Collectively, arable crops reached a land equivalent ratio (LER) between 1.00 and 1.22. In a third field experiment, we evaluated pear agrivoltaics under semitransparent PV cover. Fruit production represents a much smaller fraction of the agricultural landscape in Flanders. However, fruits have a much higher economical value per hectare, and are often cultivated in long-term orchards. In a pioneering agrivoltaic pilot installation, three consecutive growing seasons of 'Conference' pears were evaluated under Agrivoltaics, with a yearly average light reduction of 24 %. We examined how the microclimate changes under AV with regard to canopy air temperature, pear yield, and fruit quality. The AV system was found to increase nighttime air temperatures during periods of frost by 0.5°C, and temper higher temperature peaks during a hot summer period. Fruit yield was consistently reduced by 15% over the 3 years of trial, without impacting postharvest quality or storability. However, a discrepancy in fruit shape was observed under AV, leading to an increased percentage (93 % increase on average) in bottle-shaped pears and a caliber that was decreased by 5mm. Despite these changes, the AV system was found to have no effects on flowering and fruit development, and flower and fruit abscission, but it delayed leaf senescent in the fall. It also offered some additional protection against sunburn. In conclusion, innovative crop production systems such as AV, often require initial fine-tuning and engineering to enable implementation to the fullest potential. By selecting an appropriate location, establishing a profitable energy use-case and implementing it for an appropriate shade-tolerant crop with the right light penetration percentage, agrivoltaic systems can contribute to advances in modern farming. This way, it has the potential to provide benefits for the cultivated crops (protection against climate change events), while expanding the amount of sustainable electricity production by means of PV in a local and rural community. Our research and practical experiences suggest that agrivoltaics not only represent a viable solution to the challenges faced by farmers, but also offer a viable pathway towards harmonizing energy production with profitable crop production. With carefully chosen system designs and crop types, agrivoltaics can improve land use efficiency, sustain or enhance crop yields, and contribute to the dual objectives of energy sustainability and food security.

    Accepted
  • journal-article
    Reher, Thomas;Lavaert, Cas;Willockx, Brecht;Huyghe, Yasmin;Bisschop, Jolien;Martens, Johan A;Diels, Jan;Cappelle, Jan;Van de Poel, Bram; 2024. Potential of sugar beet (Beta vulgaris) and wheat (Triticum aestivum) production in vertical bifacial, tracked, or elevated agrivoltaic systems in Belgium. Applied Energy; 2024; Vol. 359; iss. 359; pp.
    LIRIAS4140410
    description

    Publisher: Elsevier
    Published online
  • Morais, alysson;Radhakrishnan, Sambhu;Arbiv, Gavriel;Dom, Dirk;Duerinckx, Karel;Chandrasekharan Nair, Vinodchandran;Martens, Johan;Breynaert, Eric; 2024. Noncontact In Situ Multidiagnostic NMR/Dielectric Spectroscopy. Analytical Chemistry; 2024; Vol. 96; iss. 13; pp. 5071 - 5077
    LIRIAS4149190
    description
    Introduction of a dielectric material in a nuclear magnetic resonance (NMR) probe head modifies the frequency response of the probe circuit, a phenomenon revealed by detuning of the probe. For NMR spectroscopy, this detuning is corrected for by tuning and matching the probe head prior to the NMR measurement. The magnitude of the probe detuning, “the dielectric shift”, provides direct access to the dielectric properties of the sample, enabling NMR spectrometers to simultaneously perform both dielectric and NMR spectroscopy. By measuring sample dielectric permittivity as a function of frequency, dielectric permittivity spectroscopy can be performed using the new methodology. As a proof of concept, this was evaluated on methanol, ethanol, 1-propanol, 1-pentanol, and 1-octanol using a commercial cross-polarization magic angle spinning (CPMAS) NMR probe head. The results accurately match the literature data collected by standard dielectric spectroscopy techniques. Subsequently, the method was also applied to investigate the solvent-surface interactions of water confined in the micropores of an MFI-type, hydrophilic zeolite with a Si/Al ratio of 11.5. In the micropores, water adsorbs to Bro̷nsted acid sites and defect sites, resulting in a drastically decreased dielectric permittivity of the nanoconfined water. Theoretical background for the new methodology is provided using an effective electric circuit model of a CPMAS probe head with a solenoid coil, describing the detuning resulting from the insertion of dielectric samples in the probe head.
    Publisher: American Chemical Society
    Published
  • dataset
    MORAIS, Alysson;RADHAKRISHNAN, Sambhu;ARBIV, Gavriel;Dom, Dirk;Duerinckx, Karel;CHANDRASEKHARAN NAIR, Vinodchandran;MARTENS, Johan;BREYNAERT, Eric; Replication Data for: Non-contact in situ multi-diagnostic NMR/dielectric spectroscopy. Publisher: KU Leuven RDR
    LIRIAS4147636
    description
    The dataset contains the data supporting the development of dielectric spectroscopy using Nuclear Magnetic Resonance (NMR) probe heads. It shows how the detuning of the NMR probe head upon insertion of a sample can be be related to the dielectric permittivity of the sample. The dataset contains calibration curves for these measurements using standard commercial probe heads and the dielectric spectra of methanol, ethanol, 1-propanol, 1-pentanol, 1-octanol and water confined in a ZSM5-type (MFI) zeolite acquired using the new technique. Replication data of the paper published in DOI: 10.1021/acs.analchem.3c03007

    Published online
  • journal-article
    Van Steenweghen, Frea;Hollevoet, Lander;Martens, Johan A; 2024. Green ammonia synthesis from stationary NO< /sub>< /i>x< //i>< //sub> emission sources on a catalytic lean NO< /sub>< /i>x< //i>< //sub> trap. Green Chemistry; 2024; Vol. 26; iss. 5; pp.
    LIRIAS4145173
    description

    Publisher: Royal Society of Chemistry
    Published online
  • thesis-dissertation
    Vanderschaeghe, Hannah; 2024. Deliquescent salts, hydrogels and thermo-responsive polymers for atmospheric water harvesting applications.
    LIRIAS4139878
    description
    Tackling the global water scarcity crisis requires innovative solutions, and capturing water from the atmosphere is emerging as a promising and viable technology. This research explores various strategies, including established methods such as active air cooling and sorption-desorption cycles with desiccants, alongside emerging technologies like deliquescent salt reverse osmosis (DESARO) and thermo-responsive hydrophilicity switching polymers. These recently proposed technologies, characterized by a single-phase transition, offer an energetic advantage. The selection of hygroscopic materials to be applied in the aforementioned processes plays a crucial role in the effectiveness of water vapor harvesting technologies. In this study, thermodynamic equilibria and kinetics of the water vapor uptake of salts, hydrogels, and thermo-responsive polymers are investigated to build a comprehensive database currently lacking in the literature. Such a database is indispensable in an efficient material selection process for the different atmospheric water production applications. Salt are attractive materials for both standard desiccation and the new DESARO process. Although water vapor uptake by salts has been known for ages, literature provides reliable data only for a limited number of salts. This work provides the water uptake data for a large collection of 35 different salts with organic and inorganic ions. The examination of the behavior of a large number of deliquescent salts reveals systematics that have not been emphasized in the literature. This research reveals that, after deliquescence, the water uptake of salt solutions expressed in mol water per mole salt ion is consistent for all salts and correlates uniquely with the environmental relative humidity. The deliquescence point which was found to be inversely proportional to the solubility emerges as a critical parameter for salt selection, along with the chemical nature and cost. Hydrogels for water vapor absorption are an attractive alternative to deliquescent salts. Favorable absorption-desorption cycles on these materials invite for application in atmospheric water production. The compressibility and the release of liquid water upon compression are attractive features for a DESARO-inspired process. Liquid water expulsion from a sodium polyacrylate hydrogel by centrifugal forces is demonstrated. Suitable hydrogels take up water vapor mainly in the mid to high relative humidity range. The degree of crosslinking of hydrogels proves irrelevant to the water vapor uptake. The ion content emerges as the key determinant in the water vapor uptake of ionic hydrogels. Interestingly, hydrogels can also be handled as a host material for deliquescent salts, to suppress water leaching. Thermo-responsive polymers alter their behavior from hydrophilic to hydrophobic with moderate temperature changes at high energy efficiency. A minimum hydration degree is needed to obtain the hydrophilicity switch. This critical absorbed water content enabling thermally driven water expulsion of thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) is determined to be 0.6 g/g. The polymer readily absorbs liquid water in sufficient quantity, but absorption of water vapor is limited. The water uptake of this polymer at 90 % relative humidity is only 0.24 g/g at 25 °C, which is insufficient to trigger liquid water expulsion by thermo-response. In literature, an interpenetrating polymer network of thermo-responsive PNIPAM and conducting polypyrrole chloride is proposed as a super moisture-absorbent gel (SMAG) able to capture sufficient water vapor to enable the thermo-response. Despite extensive efforts, the reported results of SMAG could not be confirmed experimentally. Extensive characterization of the synthesized materials and comparison with literature leads to a hypothesis on the required properties. A combination of capillary condensation and osmotic forces is proposed to be needed, a combination coined "osmocapillary". Alternative strategies are explored to enhance the water uptake such as interpenetrating polymer networks and combinations with deliquescent salts as well as the creation of mesopores suited for capillary condensation.

    Published
  • journal-article
    De Ras, Michiel;Hollevoet, Lander;Martens, Johan A;Liu, Tianxi;Nicolai, Bart M;Hertog, Maarten LATM;Hofkens, Johan;Roeffaers, Maarten BJ; 2024. Beyond acceptable limits: intrinsic contamination in commercial < /SUP>15< //SUP>N< /sub>2< //sub> impedes reliable N< /sub>2< //sub> reduction experiments. Green Chemistry; 2024; Vol. 26; iss. 3; pp. 1302 - 1305
    LIRIAS4140909
    description

    Publisher: Royal Society of Chemistry
    Published
  • journal-article
    Jamoul, Jelle;Smet, Sam;Radhakrishnan, Sambhu;Chandran, C;Martens, Johan A;Breynaert, E; 2024. Polysilicate Porous Organic Polymers (PSiPOPs), a Family of Porous, Ordered 3D Reticular Materials with Polysilicate Nodes and Organic Linkers. Chemistry Of Materials; 2024; Vol. 36; iss. 3; pp. 1385 - 1394
    LIRIAS4141609
    description
    Spherosilicate, consisting of a double 4-ring cyclosilicate core (D4R; Si8O20) with every corner functionalized with a dimethylsilyl chloride group (-SiMe2Cl), was used as a node to construct an isoreticular series of porous expanded network materials. Interconnecting the nodes with linear, aliphatic α,ω-alkanediol linker molecules yields PolySilicate Porous Organic Polymers (PSiPOPs), a new type of ordered reticular material related to the well-known metal–organic and covalent organic frameworks (MOFs and COFs). In the synthesis, sacrificial hydrogen-bonded Si8O20 cyclosilicate crystals are first converted into silyl chloride-terminated spherosilicate. In the second step, these nodes are linked by alkanediol units via the intermediate formation of a Si–N bond with catalytic amines such as pyridine and dimethylformamide. Overall, the presented synthesis converts D4R cyclosilicate into an ordered reticular framework with [Si8O20]-[Si(CH3)2-]8 nodes and O-(CH2)n-O linkers. Example materials with ethylene glycol, 1,5-pentanediol, and 1,7-heptanediol as linkers (n = 2, 5, and 7) were produced and characterized. On a macroscopic level, the synthesis yields porous frameworks exhibiting thermal stability up to 400 °C and chemical stability between pH 1 and 12. N2 physisorption revealed a secondary mesopore structure, indicating future options to produce hierarchical materials using soft templates. The molecular-level structure of these reticular PSiPOP materials was elucidated by using an NMR crystallography approach implementing a combination of 1D and 2D 1H and 29Si solid-state MAS NMR spectroscopy experiments. Previously reported reticular COF/POP materials implementing D4R-based nodes used Si8 octakis (phenyl) D4R POSS as a node, connecting it to the linker via a Si–C bond instead of a Si–O–C linkage.
    Publisher: American Chemical Society
    Published online
  • Beckwée, EJ;Houlleberghs, Maarten;Ciocarlan, R;Chandrasekharan Nair, Vinodchandran;Radhakrishnan, Sambhu;Hanssens, Lucas;Cool, P;Martens, Johan A;Breynaert, E;Baron, GV;Denayer, JFM; 2024. Structure I methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading. Applied Energy; 2024; Vol. 353; pp.
    LIRIAS4118112
    description
    Confinement of water and methane in mesopores of hydrophobized SBA-15 is demonstrated to promote methane hydrate formation. In comparison to as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics of methane storage in and delivery from the hydrate. C8 grafting density was determined at 0.5 groups nm−2 based on TGA and quantitative NMR spectroscopy. Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close spatial proximity between the grafted C8 chains and pore-intruded water species. X-ray diffraction demonstrates formation of Structure I hydrate on SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on hydrophobized SBA-15 C8 reaches 96% as compared to only 71% on a pristine SBA-15 sample with comparable pore size, pore volume and surface area. The clathrate loading amounted to 14.8 g/g. 2D correlation NMR spectroscopy (1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of SBA-15 C8 as well as in interparticle volumes. Following the initial crystallization of SBA-15 C8-supported methane hydrate taking several hours, a pressure swing process at 248 K allows to desorb and re-adsorb methane from the structure within minutes and without thawing the frozen water structure. Fast loading and unloading of methane was achieved in 19 subsequent cycles without losses in kinetics. The ability to harvest the gas and regenerate the structure without the need to re-freeze the water represents a 50% energy gain with respect to melting and subsequently recrystallizing the hydrate at 298 K and 248 K, respectively. After methane desorption, a small amount of residual methane hydrate in combination with an amorphous yet locally ordered ice phase is observed using 13C and 2H NMR spectroscopy. This effect offers an explanation for the enhanced hydrate formation kinetics in adsorption-desorption cycles. These findings open new perspectives for clathrate hydrate-based methane storage.
    Publisher: Elsevier
    Published
  • journal-article
    Smet, Sam;Vallaey, Brecht;Sree, Sreeprasanth Pulinthanathu;Martens, Johan; 2023. Cross-Linking Nanometer-Sized Reactive Spherosilicates to Synthesize Tuneable Hydrophobic POSiSil Foams Suitable for Applications as Sensors. ACS Applied Nano Materials; 2023; Vol. 6; iss. 23; pp. 22202 - 22208
    LIRIAS4131769
    description

    Publisher: American Chemical Society
    Published
  • journal-article
    Geerts-Claes, Hannelore;Vanbutsele, Gina;Sree, Sreeprasanth Pulinthanathu;Radhakrishnan, Sambhu;Chandrasekharan Nair, Vinodchandran;Breynaert, Eric;Martens, Johan A;Smet, Sam; 2023. RHO Zeolites with High Hydrothermal Stability. Crystal Growth & Design; 2023; Vol. 23; iss. 11; pp. 7829 - 7840
    LIRIAS4120984
    description

    Publisher: American Chemical Society
    Published online
  • thesis-dissertation
    Houlleberghs, Maarten; 2023. Characterization and application of nanoconfined water in cosmetic and pharmaceutical formulations and energy storage.
    LIRIAS4083832
    description
    Confinement of water molecules in nanoporous materials results in an aqueous phase with different properties than bulk water due to several interactions with the pore walls. In this research, the role of nano-confined water structures in cosmetic and pharmaceutical applications, and in energy storage applications, i.e. in the form of clathrate hydrates, is characterized by means of newly developed NMR and XRD methodologies.

    Published
  • thesis-dissertation
    Romolini, Giacomo; 2023. Synthesis and Advanced Characterization of Metal Clusters within Unexplored Microporous Frameworks for Potential Industrial Applications.
    LIRIAS4088602
    description
    The interest for functional (sub-)nanometers systems has grown over the last decades, due to the significant differences in physicochemical properties compared to their bulk counterparts, making sub-nanomaterials very attractive for a wide variety of applied research fields, from biotechnology and environmental sciences to fundamental chemistry and physics. Their properties make them useful as catalyst or for use in opto-electronic devices. However, stability of these types of materials is often hindering its use in reallife applications, as is for the case of luminescent metal cluster. Enhanced stability was obtained by self-assembling these subnanometer particles inside the framework of zeolite materials based upon a ship-in-a bottle confinement. This approach has led to stunning results with materials displaying high photoluminescent efficiencies, even reaching values of almost unity. However, the exact mechanisms to control luminescence properties and enhanced stability are at the moment not yet known. The expansion of the template structures used for confinement to other inorganic frameworks will enhance our knowledge on the synthesis of these samples and their properties. This will enable the establishment of general rational design protocols for the fabrication of new type of LED phosphors which could be used in white LEDs for general lighting purposes and backlight displays, reducing the fabrication cost and environmental impact of these LEDs.

    Published
  • journal-article
    Vaneeckhaute, Ewoud;Tyburn, Jean-Max;Kempf, James G;Martens, Johan A;Breynaert, Eric; 2023. Reversible Parahydrogen Induced Hyperpolarization of < /SUP>15< //SUP>N in Unmodified Amino Acids Unraveled at High Magnetic Field. Advanced Science; 2023; Vol. 10; iss. 23; pp.
    LIRIAS4084098
    description
    Amino acids (AAs) and ammonia are metabolic markers essential for nitrogen metabolism and cell regulation in both plants and humans. NMR provides interesting opportunities to investigate these metabolic pathways, yet lacks sensitivity, especially in case of 15 N. In this study, spin order embedded in p-H2 is used to produce on-demand reversible hyperpolarization in 15 N of pristine alanine and ammonia under ambient protic conditions directly in the NMR spectrometer. This is made possible by designing a mixed-ligand Ir-catalyst, selectively ligating the amino group of AA by exploiting ammonia as a strongly competitive co-ligand and preventing deactivation of Ir by bidentate ligation of AA. The stereoisomerism of the catalyst complexes is determined by hydride fingerprinting using 1 H/D scrambling of the associated N-functional groups on the catalyst (i.e., isotopological fingerprinting), and unravelled by 2D-ZQ-NMR. Monitoring the transfer of spin order from p-H2 to 15 N nuclei of ligated and free alanine and ammonia targets using SABRE-INEPT with variable exchange delays pinpoints the monodentate elucidated catalyst complexes to be most SABRE active. Also RF-spin locking (SABRE-SLIC) enables transfer of hyperpolarization to 15 N. The presented high-field approach can be a valuable alternative to SABRE-SHEATH techniques since the obtained catalytic insights (stereochemistry and kinetics) will remain valid at ultra-low magnetic fields.
    Publisher: Wiley
    Published
  • thesis-dissertation
    Lubbe, Foster; 2023. Investigating the potential of air-based freshwater and hydrogen production technologies in the Witzenberg Valley of South Africa.
    LIRIAS4088294
    description
    Self-sufficient fresh water and renewable energy are two pillars of sustainable development. In regions with limited fresh water sources, air capture of water vapor is an alternative solution. The captured water can be made potable and serve uses in agriculture and industrial activity. Hydrogen gas is an emerging energy vector. At remote locations with limited water sources it may be produced by electrolytically splitting the water molecules found in the air. In this work the potential of atmospheric water harvesting technologies to produce water and hydrogen gas at a specific location in South Africa, is analyzed. The research departs from a microclimate study in the Witzenberg valley. Temperature profiles, relative humidity and wind speed and direction were monitored with a weather station over a 3-year period. Three different water capturing technologies were considered, namely, the use of desiccants, the use of deliquescent salts in combination with reverse osmosis (DESARO), and thermoresponsive polymers. A computer model was developed to predict water yields and energy needs of the rival technologies using the microclimate data. The model predictions were verified with water capturing experiments using a device that was designed, built and mounted next to the weather station. The model also enabled an estimation of the possible impact of extracting water from the air on the local air-borne water content. The modelling results showed a potential to produce 16 of fresh water using thermoresponsive polymer during the year 2021 at the Witzenberg valley site, 30 using desiccant, and 7.7 using a DESARO-system. The model furthermore predicts that thermoresponsive polymers will remove 2.6% of the available moisture in the air, when replacement rates based on wind speeds are taken into account. The extraction rate for a DESARO-system was estimated to be 0.6%, while it was estimated to be 8.5% for a desiccant-based system. Energy autonomy based on locally produced hydrogen was the second aspect of the research. Solar hydrogen generators produce hydrogen using sunlight and do not need electricity supply from the grid. Hydrogen panels producing hydrogen gas from water captured from the air is a pioneering example. Hydrogen produced with solar hydrogen generators is intrinsically additional, and contrasting with hydrogen gas produced by electrolysers powered by electricity from a grid. The new category of Golden hydrogen is introduced to emphasize the distinction from other types of hydrogen contributing differently to reaching global sustainability. The outcome of this study at one specific location was used to define a protocol for estimating the potential of water-from-air technologies at different locations. The potential value in the broader context of water and energy supply in SouthAfrica is also discussed.

    Published
  • journal-article
    Beckwée, Emile Jules;Watson, Geert;Houlleberghs, Maarten;Esteban, Daniel Arenas;Bals, Sara;Voort, Pascal Van Der;Breynaert, Eric;Martens, Johan;Baron, Gino V;Denayer, Joeri FM; 2023. Enabling hydrate-based methane storage under mild operating conditions by periodic mesoporous organosilica nanotubes. Heliyon; 2023; Vol. 9; iss. 7; pp.
    LIRIAS4090724
    description
    Biomethane is a renewable natural gas substitute produced from biogas. Storage of this sustainable energy vector in confined clathrate hydrates, encapsulated in the pores of a host material, is a highly promising avenue to improve storage capacity and energy efficiency. Herein, a new type of periodic mesoporous organosilica (PMO) nanotubes, referred to as hollow ring PMO (HR-PMO), capable of promoting methane clathrate hydrate formation under mild working conditions (273 K, 3.5 MPa) and at high water loading (5.1 g water/g HR-PMO) is reported. Gravimetric uptake measurements reveal a steep single-stepped isotherm and a noticeably high methane storage capacity (0.55 g methane/g HR-PMO; 0.11 g methane/g water at 3.5 MPa). The large working capacity throughout consecutive pressure-induced clathrate hydrate formation-dissociation cycles demonstrates the material’s excellent recyclability (97% preservation of capacity). Supported by ex situ cryo-electron tomography and x-ray diffraction, HR-PMO nanotubes are hypothesized to promote clathrate hydrate nucleation and growth by distribution and confinement of water in the mesopores of their outer wall, along the central channels of the nanotubes and on the external nanotube surface. These findings showcase the potential for application of organosilica materials with hierarchical and interconnected pore systems for pressure-based storage of biomethane in confined clathrate hydrates.
    Publisher: Elsevier
    Published online
  • journal-article
    Mirena, Juan I;Constales, Denis;Martens, Johan;Dendooven, Jolien;Yablonsky, Gregory S;Galvita, Vladimir V; 2023. TAP analysis of single and double peak responses during CO oxidation over Pt. Catalysis Today; 2023; Vol. 417; pp.
    LIRIAS4091644
    description

    Publisher: Elsevier
    Published
  • journal-article
    Geerts - Claes, Hannelore;Smet, Sam;Hengst, Christoph;Schuetze, Frank-Walter;Verheyen, Elke;Minjauw, Matthias;Detavernier, Christophe;Sree, Sreeprasanth Pulinthanathu;Martens, Johan; 2023. Molecular Mechanism of Low-Temperature Passive NOx Adsorption (PNA) on Palladium-Loaded FER Zeolite. Journal Of Physical Chemistry C; 2023; Vol. 127; iss. 15; pp. 7119 - 7130
    LIRIAS4082645
    description

    Publisher: American Chemical Society
    Published online
  • thesis-dissertation
    Lejaegere, Charlotte; 2023. Ultra trace analysis of off-flavors in water.
    LIRIAS4069120
    description
    Off-flavor is an overall term for an earthy and musty flavor and taste. 2-Methylisoborneol and geosmin are the most important molecules causing off-flavor. People are very sensitive regarding these taste and odor molecules with ultralow organoleptic limits of approximately 10 parts-per-trillion in water. Microorganisms present in biofilms in water pipes and reservoirs produce 2-methylisoborneol and geosmin as secondary metabolites. The molecular structures are chemically inert and difficult to eliminate from water. Accumulation of the off-flavor compounds results in the typical earthy flavor in the water and the in-water-produced foodstuff. Although there is no health risk for the consumer, off-flavor taints the quality perceived by the consumer and makes the product unmarketable. The parts-per-trillion concentrations require advanced analysis equipment, i.e. solid-phase micro-extraction combined with gas chromatography and mass spectroscopy, unsuited to be applied in production environments. A new methodology for 2-methylisoborneol and geosmin, suitable for a wide range of environments, is introduced. The technique combines selective concentration of both compounds on an adsorbent with simplified gas chromatography analysis. Hydrophobicity of potential adsorbent materials is a prominent parameter. Different mechanisms are at play in aqueous medium versus vapor phase. Currently described hydrophobicity measurements for adsorbent materials do not provide accurate information. This work introduces a new approach to determine the hydrophobic property of materials in aqueous medium. In situ nuclear magnetic resonance spectroscopy was used to study the adsorption behavior of linear alcohols in MFI zeolites. An additional adsorption mechanisms, hydrogen bonding to the siloxane bridges, was identified on the hydrophobic MFI zeolites co-existing with the traditionally accepted alcohol adsorption mechanisms. The insights of the in depth study indicated 1-pentanol as a suitable probe molecule to evaluate hydrophobic properties. A new rank system, the Pentanol Hydrophobicity Index based on the adsorption of 1-pentanol from an aqueous solution was defined. The Pentanol Hydrophobicity Index was evaluated for over forty adsorbent materials. The insight regarding hydrophobic materials was applied to develop a selective adsorption material for 2-methylisoborneol and geosmin. Based on the adsorbent material, a concentration module and protocol were developed to selectively adsorb the 2-methylisoborneol and geosmin present in parts-per-trillion concentrations from a water sample. Concentration factors up to 6000 were achieved with a maximum sample volume of 1 liter. All gained insights led towards the development of a prototype of a relatively simple analytical device, on-line solid phase extraction combined to gas chromatography and flame ionization detection, suitable for application in production environments.

    Published
  • journal-article
    Brito, Larissa;Payan, Francois;Albrieux, Florian;Guillon, Emmanuelle;Martens, Johan A;Pirngruber, Gerhard D; 2023. Hydrocracking of a Long Chain Alkyl-Cycloalkane: Role of Porosity and Metal-Acid Balance. Chemcatchem; 2023; Vol. 15; iss. 5; pp.
    LIRIAS4072702
    description

    Publisher: Wiley
    Published online