Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The rational improvement of solid catalysts requires a thorough understanding of the structure-activity relationship down to the smallest possible length scales. Recently developed approaches that correlate fluorescence microscopy (FM) and scanning electron microscopy (SEM) allow such insights by direct linking of nanoscale catalytic activity maps, as recorded using fluorescence, to the local structural context. The goal of this PhD was to investigate structure-activity relationships at the nanoscale, by developing an integrated light and electron microscope (ILEM) that combines the power of single molecule sensitive FM to resolve reactivity at the nanoscale with a high-end SEM. Initially, the ILEM was applied to visualize silver nanoparticle photodeposition from an aqueous silver(I) solution on individual ZnO crystals, in real time. This was enabled by the ability to simultaneously perform local UV irradiation using the integrated light microscope and SEM imaging at the same region of interest (ROI) while the sample was contained inside a specialized liquid cell. This research revealed that silver nanoparticle formation predominantly occurs at crystal edges. However, the contribution of the electron beam during silver nanoparticle deposition was found to be non-negligible. Follow-up research was performed by applying the ILEM in a correlative fashion; i.e., by performing structural imaging before and after, and not during, UV induced silver photodeposition. As such, the facet dependent photocatalytic reactivity could be explored at the single particle level and, at the sub-particle level, variations were related to crystallographic structural features and defects. The first correlative super-resolution fluorescence and electron microscopic investigation of zeolite catalysts was made possible after resolving several technical challenges encountered during the ZnO research and by further optimizing the fluorescence microscope to enable the detection of individual catalytic fluorogenic conversions. This improved setup made it possible to directly observe the effect of intercrystalline intergrowths on the overall catalytic performance of acid mordenite zeolites. By determining the orientation of the individual reaction products compared to the underlying zeolitic framework, it was found that shape-selectivity was maintained at the defect-rich intergrowth boundary. Hence, the intergrowth was identified as a void space that facilitates mass transport into these pores. Acid leaching did not dramatically change this, as activity increased on previously active regions while the molecular orientation was maintained. A second correlative zeolite structure-activity investigation targeted individual ZSM-22 catalyst particles. The typical needle-shaped morphology of these particles results from a lateral fusion of elementary nanorods and indirect experimentation already suggested that during this lateral fusion, external, catalytically inactive, aluminum is converted into catalytically active internal aluminum. This was confirmed by the visualization of catalyst activity and shape-selectivity at the sub-particle level on the ILEM. In summary, over the course of this PhD, a performant ILEM was developed that combined super-resolution fluorescence microscopy based on the localization of individual fluorescent molecules with high-end field emission SEM. Also the necessary experimental routines and software tools were developed, enabling the determination of the structure-activity relationship of heterogeneous catalysts at the nanoscale. This powerful research tool allows a direct correlation of catalyst structure and activity beyond the single particle level. It is anticipated that the further application and development of this ILEM will ultimately lead to a more rationalized catalyst optimization.

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

In deze masterproef werd aangetoond dat verschillende koolstofsoorten, gaande van zuivere grafietdeeltjes tot roetachtige deeltjes, geoxideerd konden worden in relatief milde reactiecondities door de werking van een chemische stof die actief wordt onder ultraviolet licht. Bovendien werd dit fotokatalytische mechanisme versterkt door een oxiderend gasmengsel bestaande uit reactieve stikstofoxiden, die de atmosfeer sterk vervuilen. Daardoor werden deze schadelijke stikstofoxiden omgezet naar het ongevaarlijke stikstofgas. Zonder de aanwezigheid van de actieve chemische stof, bekend als de fotokatalysator, was de koolstofoxidatie echter niet mogelijk, tenzij in veel hardere reactieomstandigheden. Toepassingen van de foto-oxidatie van roetachtige koolstof zwart deeltjes in de aanwezigheid van stikstofoxiden worden voornamelijk gevonden in systemen voor luchtzuivering. Zowel de kleine, roetachtige fijnstofdeeltjes als de schadelijke stikstofoxiden, die beiden de uitstoot van dieselmotoren zeer vervuilend maken, werden weggereageerd door de wisselwerking tussen de oxidatie- en reductiereactie. Grafietoxidatie wordt heel vaak uitgevoerd omdat grafietoxide, grafeenoxide en grafeen dat gemaakt wordt via de geoxideerde tussenproducten veelbelovend zijn voor tal van nieuwe toepassingen door hun uitzonderlijke fysische en chemische eigenschappen. Enkele actuele toepassingen zijn fietsbanden (door Vittoria), buigbare schermen (door Samsung) en grafeenoxide gebaseerde katalysatoren voor organische reacties. Het oxidatieproces verloopt tegenwoordig nog steeds via een niet-duurzame, gevaarlijke vloeistoffase oxidatiemethode. De fotokatalytische grafietoxidatie uit dit thesisonderzoek bood echter een uitstekend alternatief voor deze klassieke oxidatiemethode. Het bleek een nieuwe oxidatiemethode te zijn die milieuvriendelijker en veel beter te controleren was. Grafiet, dat bestaat uit zuiver koolstof, is chemisch zeer stabiel en dus helemaal niet reactief. Dankzij de ontwikkelde groene oxidatiemethode werd zuurstof gebonden aan de verschillende grafietvlakken, waardoor het product verder benut zou kunnen worden. Het fotokatalytisch geoxideerd grafietproduct werd gekenmerkt door randen die veel sterker geoxideerd waren dan de grote, gladde buitenoppervlakken. Deze plaatsafhankelijke oxidatie werd in verband gebracht met de structuurdefecten van grafiet, die reactiever zijn dan gewoon grafitisch koolstof. De gecontroleerde aard van de foto-oxidatie werd ook weerspiegeld in de relatief hoge structurele orde van de geoxideerde grafietdeeltjes.

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The process of new blood vessel formation out of already existing vasculature called “angiogenesis” is a crucial process in the development of new tissue and organs, wound healing and a broad range of diseases. To the benefit of humankind, it is essential to fully understand angiogenesis. Research has already proven that the glycolysis is the metabolic pathway responsible for most of the ATP production in endothelial cells. For example, diseases like cancer, resulting in an excess of angiogenesis, can be treated by inhibiting this process. Therefore an inhibitor, 3PO, was determined, which inhibits the rate-limiting step of the glycolysis. During this thesis, a special, truly three-dimensional microscopy technique was established for investigating angiogenesis with high temporal resolution. The advantages of light sheet microscopy are: fast dynamic image acquisition, less photo bleaching and photo toxicity resulting in an excellent tool for time lapse microscopy. After gathering the data, algorithms of traction force microscopy were employed in order to determine the displacements of the beads compared to the reference bead position of the last time point. While imaging, Cytochalasin D (CytoD), an inhibitor of the actin cytoskeleton was used with the purpose to achieve a stress free state of the cells. Angiogenic sprouts have subsequently been examined involving cell culture, light sheet microscopy and algorithms of traction force microscopy. Samples were prepared where human umbilical vein endothelial cells were seeded on a collagen containing fluorescent beads. This gel contains a pro-angiogenic factor as well, which induces the formation of sprouts. Those sprouts were then imaged with a light sheet microscope. There is a strong indication that CytoD can be used to induce the relaxed state in light sheet displacement microscopy. Furthermore, the inhibitor 3PO is likely to indeed have an effect on the cells, due to a decrease in the dynamics of the bead displacements. In the next set of experiments, fast filopodia movement of the sprouts was observed using the advantage of a possible high time resolution with light sheet microscopy. A 20 or 25 μm z-stack was imaged every four seconds. Sprout- and filopodia formation were examined in different collagen concentrations. Especially the length of the sprouts seems to be influenced by the collagen concentration. The filopodia formation and attempts during imaging seemed to have a trend, but only 1 significant result was observed due to the limited number of imaged sprouts per sample.