1,720,952 research outputs found
Activation, Reactivity and Dynamics of Manganese Pincer Complexes in Hydrogenation Catalysis
No full textThe growing demands for sustainable chemical technologies have prompted a wave of searching new catalysts based on earth-abundant metals. In the field of (de)hydrogenation catalysis, however, the huge performance gap is commonly seen between the 3d-metal-based catalysts and their noble metal counterparts, which largely hampers their practical applications. In particular, while the Mn-catalyzed (de)hydrogenation has witnessed significant progress since the pioneering work by Beller and co-workers in 2016, most of the reported systems still require relatively high catalyst loadings. Apart from developing new synthetic methodologies based on the hydrogen transfer reactivity of Mn, searching highly active catalysts for (de)hydrogenation reactions therefore remains one of the central topics in Mn chemistry. The current approach to catalyst development is mainly based on the screening of the ligand backbones that proved to be effective for noble metal-based catalysts. However, the screening assessments with the reaction yields as the sole performance metrics do not probe the intrinsic reactivities of the catalysts and can easily result in the overlook of the potential ones due to suboptimal condition choice. In this thesis, we demonstrate in this thesis that the catalyst performance is defined by a complex reaction network comprised of multiple stages of catalyst operation, that is catalyst activation, deactivation, and catalytic turnover. The reactivity of the catalyst itself and the reaction environment of each process determine synergistically the catalytic performance. As a result, the catalytic transformation should be viewed from the system perspective with the performance being a dynamic and highly condition-dependent characteristic.ChemE/Inorganic Systems Engineerin
Color-Based Optical Detection of Glass Transitions on Microsecond Timescales Enabled by Exciplex Dynamics
No full textEvery measurement technique operates on a given timescale and measurements using emissive small molecule sensors are no exception. A family of luminescent sensors providing first optical characterization of dynamic phenomena in polymers at a timescale of several microseconds is described. This performance originates from the dynamics manifested in the excited state of the sensor molecules where diffusioncontrolled events select the emission color while radiative phenomena define the global operation timescale. Since the mechanism responsible for signal generation is confined to the short lived excited state of emissive probe, it is possible observe an unprecedented link between the timescale of sensory action and that of photoluminescence. An application of this new methodology is demonstrated by performing general, short timescale detection of glass transitions in a temperature ranges precluding the informative range of conventional techniques by tens of degrees.ChemE/Catalysis EngineeringChemE/Inorganic Systems Engineerin
Environmentally Sensitive Luminescence Reveals Spatial Confinement, Dynamics, and Their Molecular Weight Dependence in a Polymer Glass
No full textPolymer glasses have an irregular structure. Among the causes for such complexity are the chemically distinct chain end groups that are the most abundant irregularities in any linear polymer. In this work, we demonstrate that chain end induced defects allow polymer glasses to create confined environments capable of hosting small emissive molecules. Using environmentally sensitive luminescent complexes, we show that the size of these confinements depends on molecular weight and can dramatically affect the photoluminescence of free or covalently bound emissive complexes. We confirm the impact of chain end confinement on the bulk glass transition in poly(methyl acrylate) (pMA) and show that commonly observed Tg changes induced by the chain ends should have a structural origin. Finally, we demonstrate that the size and placement of luminescent molecular probes in pMA can dramatically affect the probe luminescence and its temperature dependence, suggesting that polymer glass is a highly irregular and complex environment, marking its difference with conventional small molecule solvents. Considering the ubiquity of luminescent glassy materials, our work lays down a blueprint for designing them with structural considerations in mind, ones where packing density and chain end size are key factors.ChemE/Advanced Soft MatterChemE/Inorganic Systems Engineerin
Exploring the mechanics of DNA origami nanopores via DNA PAINT imaging
No full textNanopores are narrow channels in cell membranes that control the passage of small molecules. In recent years, they have been repurposed for diverse applications, including single molecule sensing and drug delivery. Due to the small diameters of conventional protein-based, current research efforts are directed to designing nanopores from other materials to achieve larger diameters. DNA origami has emerged as a promising method for the precise fabrication of nanoscale structures. Using advances in structurally-adaptable DNA origami nanotechnology, here we investigate DNA-based nanoactuators with size-adjustable diameters, which can potentially reach diameters of up to 100 nm, that could be used for macromolecules translocation. The focus of this thesis is the study of the mechanical states of these nanoactuators, which can be triggered to change shape in response to a specific molecular trigger. Given the nanoscopic dimensions of our actuators, we select DNA PAINT for imaging, which is a type of super resolution technique, that can achieve a resolution of 10 nm, beating the optical diffraction limit (~200 nm) of conventional light microscopy. DNA PAINT experiments are performed in combination with total internal reflection fluorescence (TIRF) microscopy to characterize the behavior of DNA origami nanopores in physiological conditions. By testing various parameters sample related and imaging software ones we identify optimal conditions suggesting 5mM Mg^(2+) ions in buffer solution and 1nM DNA nanopores. Laser power (40mW), exposure time (400ms), waiting time between frames (300ms), and image duration (50s) are optimized, resulting in the expected fluorescent blinking behavior which enables us to perform single-molecule localization. The individual corners of the nanopores were, however, not resolved with this technique due to limitations in the resolution of the imaging system. We recommend that future work could exploit the even better resolution of a modified DNA PAINT approach i.e. Exchange PAINT, which has been proven to achieve Angstrom level resolution for imaging of DNA nanostructures.Materials Science and Engineerin
Performance of homogeneous catalysts viewed in dynamics
No full textEffective assessment of catalytic performance is the foundation for the rational design and development of new catalysts with superior performance. The ubiquitous screening/optimization studies use reaction yields as the sole performance metric in an approach that often neglects the complexity of the catalytic system and intrinsic reactivities of the catalysts. Using an example of hydrogenation catalysis, we examine the transient behavior of catalysts that are often encountered in activation, deactivation and catalytic turnover processes. Each of these processes and the reaction environment in which they take place are gradually shown to determine the real-time catalyst speciation and the resulting kinetics of the overall catalytic reaction. As a result, the catalyst performance becomes a complex and time-dependent metric defined by multiple descriptors apart from the reaction yield. This behaviour is not limited to hydrogenation catalysis and affects various catalytic transformations. In this feature article, we discuss these catalytically relevant descriptors in an attempt to arrive at a comprehensive depiction of catalytic performance. ChemE/Inorganic Systems EngineeringTeam Georgy Filonenk
Combined Self-Healing Method for Lifetime Extension in Asphalt: A Mechanical and Sustainability Assessment
No full textOver the last 15 years or so, research has revealed the great self-healing prospects possessed by asphaltic mixtures. Researchers have proposed novel methods to harness this capability, aiming to prolong the service life of asphalt pavement, particularly in porous asphalt. To date, the most promising of the healing methods is the combined capsule-induction system. This thesis aims to ascertain whether such a system would show positive results in stone mastic asphalt (SMA). Following that, an optimisation of the composition of self-healing SMA was proposed by assessing the mechanical and healing properties via laboratory testing. Finally, an evaluation of sustainability from an environmental perspective was done using Life Cycle Analysis (LCA) methodology. Results of the healing assessment revealed that each combined healing system was able to recover between 58-63\% of its original fracture strength after 8 healing cycles, while the reference mix (without healing) was only able to regain 10\% fracture strength before failure after 2 cycles. Inclusion of the combined healing system slightly reduced the strength, stiffness and water sensitivity of the SMA mixture compared to the reference. However, improved rutting resistance was observed in each self-healing case. Within the self-healing mixtures, increasing capsule content reduced asphalt density, stiffness and strength and resulted in an increase in asphalt void content.The LCA results show that the self-healing system had environmental benefits in some facets such as a 14\% reduction in fossil fuel resource depletion and a 21\% reduction in land use. However, the present total known environmental costs of other impacts are approximately 15\% lower in the reference system based on a cradle to gate, and use phase analysis. Almost half of this total cost was attributed to maintenance activities. It was concluded that a 32\% increase in maintenance efficiency would ensure environmental viability of a self-healing mixture over a reference mixture within the constraints of the analysis conducted.Materials Science and Engineerin
Homogeneous hydrogenation of saturated bicarbonate slurry to formates using multiphase catalysis
No full textFormic acid and formate salts are key intermediates along the pathways for CO2utilization and hydrogen storage. Herein we report a highly efficient multiphase catalytic system utilizing a ruthenium PNP pincer catalyst for converting supersaturated bicarbonate solutions and slurries to aqueous formate solutions up to 12 M in molarity. The biphasic catalytic system delivers turnover frequencies up to 73 000 h−1and remains stable for up to 474 000 turnovers once reaction conditions are optimized.ChemE/Inorganic Systems EngineeringChemE/Algemee
Investigating the role of potassium cations during electrochemical CO<sub>2</sub> reduction
No full textThe specific identity of electrolyte cations has many implications in various electrochemical reactions. However, the exact mechanism by which cations affect electrochemical reactions is not agreed upon in the literature. In this report, we investigate the role of cations during the electrochemical reduction of CO2 by chelating the cations with cryptands, to change the interaction of the cations with the components of the electric double layer. As previously reported we do see the apparent suppression of CO2 reduction in the absence of cations. However, using in situ-SEIRAS we see that CO2 reduction does indeed take place albeit at very reduced scales. We also observe that cations play a role in tuning the absorption strengths of not only CO2 as has been speculated, but also that of reaction products such as CO.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Materials for Energy Conversion and StorageChemE/Inorganic Systems Engineerin
Mechanochemistry of Spiropyran under Internal Stresses of a Glassy Polymer
No full textMechanophores are powerful molecular tools used to track bond rupture and characterize mechanical damage in polymers. The majority of mechanophores are known to respond to external stresses, and we report in this study the first precedent of a mechanochemical response to internal, residual stresses that accumulate during polymer vitrification. While internal stress is intrinsic to polymers that can form solids, we demonstrate that it can dramatically affect the mechanochemistry of spiropyran probes and alter their intramolecular isomerization barriers by up to 70 kJ mol-1. This new behavior of spiropyrans (SPs) enables their application for analysis of internal stresses distribution and their mechanochemical characterization on the molecular level. Spectroscopy and imaging based on SP mechanochemistry showed high topological sensitivity and allowed us to discern different levels of internal stress impacting various locations along the polymer chain. The nature of the developed technique allows for wide-field imaging of stress heterogeneities in polymer samples of irregular shapes and dimensions, making it feasible to directly observe molecular-level manifestations of mechanical stresses that accompany the formation of a vast number of solid polymers. BN/BionanoscienceBN/Cees Dekker LabTeam Georgy Filonenk
The lignocellulose binding phenomena and interlaminar fracture toughness of living <i>Ganoderma lucidum</i>
No full textMycelium based composites (MBC) have revolutionised the field of material production, where a living fungus is employed to overgrow and bind lignocellulosic substrate materials together. Their bio-based nature, low embodied energy, and biodegradability, mark their great potential to reduce the increasing pressure conventional materials put on the environment. Unfortunately, the material's applications are limited due to its low mechanical properties, that are equivalent to those of foams or natural fibre boards. Furthermore, where the material is primarily used and studied in its heat-treated non-living form, harnessing the biological power of the fungus shows to give the material self-healing and sensing capabilities. The required hydrolysed state is however shown to further decrease its mechanical properties, and yet hardly evaluated in literature. Especially the mechanics of the mycelium-lignocellulose interface are inadequately studied, and important to evaluate for a broadening of the living composite material's applications.In this study we present the development of a double cantilever beam (DCB) test according to ASTM D5528, setup to quantify the interlaminar fracture toughness (GI) of Ganoderma lucidum (G. lucidum) grown in between wood veneers. The data was evaluated using an analytical approach based on a decrease in the beams' compliance. The specimens were fabricated with the use of additive manufacturing, allowing precise control over the placement of the fungus and its provided nutrients. Its growth behaviour into the substrate was qualitatively assessed through optical microscopy and scanning electron microscopy (SEM), and its digestive ability on the surface by fourier-transform infrared spectroscopy (FTIR).A mycelium-laden ink presented by Gantenbein et al. (2023) was reproduced with a 75% lower agar content to serve a stable source of mycelium on the DCB specimens [1]. A growth period between 3 and 4 weeks from the printed hydrogel was required for substantial mycelium-substrate binding, which stabilised after 4 weeks of growth. Furthermore, the provision of malt extract (ME) was required, but not needed to be higher than 5% of the ink's weight. The GI was in these conditions reported to be 1.83 J/m2 on hornbeam veneers, where a maximum value of 3.46 J/m2 was reached. Variable growth generated substantially different mechanical properties, which resulted in the lower GI of mycelium grown on beech and spruce samples, caused by the use of an older fungal inoculum of a different reference plate. A stronger binding on beech than spruce did suggest a more important role of the substrate chemistry than its density. The mycelium always showed cohesive failure, showing the low GI to not result from poor substrate adhesion, but rather from the mechanics of the hyphae network developed. Microscopy and FTIR evaluations showed the ability of G. lucidum to digest the hornbeam's lignin. The full depths of hornbeam and beech veneer substrates with 5 and 3 mm thickness were colonised, where vessel elements served as the main pathway for the hyphae.This study was, to the best of our knowledge, the first to isolate the binding behaviour of a living mycelium in a mode-I loading condition. It thereby provides valuable new insights in the field of living MBC, and contributes to the further development of this advanced, eco-friendly, and living material. The setup can now be utilised to study the binding behaviour of different fungi on substrates of varying chemistry and porosity. Furthermore, aiming to elucidate the use of additive manufacturing in the composite production, this study opened up pathways into controlling the composite's properties in the future.[1] Silvan Gantenbein et al. “Three-dimensional printing of mycelium hydrogels into living complex materials”. In: Nature Materials 22.1 (2023), pp. 128–134.Materials Science and Engineerin
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