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Bij het uitwerken van mijn stageopdracht is mijn eindwerk opgesplitst in 4 hoofdstukken. In het eerste hoofdstuk wordt een beknopte beschrijving gegeven van Inalfa Metal nv met daarin haar doelstelling en de nood aan certificaten. In het tweede hoofdstuk wordt de pers onder de loep genomen. De werking en de omstelling van de pers worden omschreven. De nodige begrippen worden uitgelegd en de rol van de technische dienst en de gereedschapmakerij worden verduidelijkt. In het derde hoofdstuk gaan we de huidige analyse grondig analyseren. De oorzaak van de intense capaciteitstoename wordt uitgelegd. Alle knelpunten worden blootgelegd en de bottleneck wordt verklaart. We komen tot de belangrijkste probleemstelling, namelijk de te lang durende omstellingen. In het vierde hoofdstuk wordt het probleem aangepakt met six-sigma. We stellen een visgraatdiagram op. De huidige werkwijzen worden geoptimaliseerd en gestandaardiseerd en de voorlopige resultaten worden weergegeven.

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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.

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Microplastic pollution is one of the most critical environmental issues in the world right now. Many studies about human exposure to these micro-and nanoplastics (MNP) and the toxic effects they can cause are being conducted at this moment. Quantification and identification of these MNP lie at the bottom of solving this global problem. The most popular identification methods are Fourier-transform infrared spectroscopy and Raman spectroscopy. These techniques are lacking in non-destructive analysis with high sensitivity and low background noise. This thesis aims to develop an optical spectroscopy method to detect and identify microplastics after staining with Nile Red. The latter is a lipophilic solvatochromic dye. Staining will cause the particle to fluoresce, with its emission spectrum depending on its polarity. More polar plastics will have a more red-shifted emission maximum. Via hyperspectral analysis, the MNP can be identified based on this spectrum. Fluorescence lifetime imaging microscopy is also implemented. The fluorescence lifetime is the time that a fluorophore spends in the excited state, after absorbing a photon, before returning to the ground state. The lifetime depends on the fluorophore's micro-environment and therefore is also different for each MNP type. Differentiation is possible based on this lifetime value, but a graphical, fit-free phasor approach is also used. This allows for the mapping of the lifetime distribution in an image. When two different MNP types are present in one sample, they will each have a separate distribution cloud on the phasor plot, allowing for the graphical distinguishment of MNP. The plastics used are PP, PVC, HDPE, PET, and PS, these samples contain a range of shapes and sizes. A bought suspension of pure PS polymer particles of a fixed shape and size of 0,6 μm was also examined. The spectral data were processed in two ways. By calculating a ‘weighted average’ with the intensity values at each wavelength. This resulted in each MNP being attributed a weighted average value. After recording spectra of different particles, a statistical analysis, ANOVA and t-test, was done. This showed that the weighted averages of PP & HDPE and PS (self-made) & PVC do not differ significantly. The second option is through comparing the spectra themselves, using a relative similarity percentage. Because of the low similarity MNP gave when compared with themselves, only MNP with a significantly large similarity percentage could be distinguished. The same statistical tests were done on lifetime data. Measurements done on different particles of the same plastic showed that only HDPE & PET lifetimes did not differ significantly. Multiple measurements done on the same particle showed slightly different lifetimes. It could be concluded that HDPE & PET and PS (self-made and 0,6 μm) & PET cannot be differentiated. Finally, phasor plot analysis of samples containing two different plastics showed a possibility of recognizing MNP types based on the location of their phasor cloud on a phasor plot. When combining these two techniques, making use of the ’weighted average’ value and lifetime analysis, it could be possible to identify each plastic. The combination with similarly weighted averages, PP & HDPE give significantly different fluorescent lifetimes values and are possible to separate on a phasor plot. Still, both techniques have some flaws and improvement is possible.

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The generation of clean, renewable energy sources has been a hot research topic for the past decades. Photocatalysis is a plausible way to store intermittently available solar energy in chemical bonds. So far, many metal oxides, metal sulfides, metal complexes, and their composites have been investigated for their efficiency as visible-light photocatalysts. It is still of great interest and practical importance to develop a cost-effective visible-light-driven catalyst for artificial photosynthesis.Recently, metal halide perovskites (MHPs) have been actively investigated to exploit their excellent optical properties, such as high visible-light absorption coefficients, long-range balanced electron-hole transport, etc., in combination with the potential of cheap and easy fabrication processes. However, the instability of MHPs in a polar environment limits the potential for their application as photocatalysts. To overcome this instability issue, reactions are usually performed in non-polar or low polarity solvents or in strongly concentrated metal halide solutions, which reverses the decomposition. As a prominent representative, cesium lead halides (CsPbX3, X = Cl, Br, I) have been seen as potential candidates for photocatalysis. Also, composite materials construction strategies have been actively utilized to optimize the activity and stability of MHPs in polar solvents. So far, CsPbBr3-based composites have been generated through the post-synthetic combination of preformed CsPbBr3 with other stabilizing materials. However, the in situ synthesis of composite materials offers enhanced surface contact with potentially improved activity and stability. Therefore, the in situ construction of CsPbBr3-based composites, comprising a type-II heterojunction, has been mainly investigated here.

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De laatste decennia is er een toenemende belangstelling voor fotokatalyse. Eén van de voordelen is de mogelijkheid om zonlicht te gebruiken om bijvoorbeeld CO2 om te zetten in hernieuwbare chemische brandstoffen. TiO2 is een algemeen gebruikte fotokatalysator omdat het een grote band gap-energie, hoge stabiliteit en lage kosten heeft, maar de lichtabsorptie is beperkt tot het UV-gebied. Om de lichtabsorptie in het zichtbare lichtgebied te optimaliseren en de recombinatiesnelheid te verlagen, worden heterojunctie fotokatalysatoren gebruikt. De heterojunctievorming tussen de twee halfgeleiders in de fotokatalysator hangt af van de materiaaleigenschappen (bandgap, kristalstructuur, etc.) van de halfgeleiders. Het Type II- en Z-schema heterojuncties zijn de meest onderzochte typen heterojuncties, elk met zijn eigen voordelen en beperkingen. Het Z-schema vertoont een goed oxidatief en reducerend vermogen en ladingsscheiding, maar dit gaat ten koste van de helft van de ladingsdragers als gevolg van recombinatie aan het grensvlak tussen de twee halfgeleiders. In Type II vindt deze grensvlakrecombinatie niet plaats, waarbij de hoeveelheid beschikbare licht-gegenereerde ladingsdragers wordt gemaximaliseerd, maar ten koste van het oxidatieve en reductieve vermogen van respectievelijk de gaten en elektronen. In dit masterproefproject wordt de ladingsoverdracht in de heterojuncties met verschillende verhoudingen van CsPbBr3 nanokristallen en Bi2MoO6 nanosheets onderzocht. Eerst werd de synthesemethode bestudeerd om de vorming van de heterojunctie te verzekeren. De hot-injectie-methode is een gemakkelijke manier om perovskiet-nanokristallen met een kleine grootteverdeling op de Bi2MoO6-nanosheets te vormen. Om de gesynthetiseerde heterojunctie en de twee materialen in de heterojunctie te onderzoeken, werden de relevante materiaaleigenschappen geanalyseerd: (1) de bandgap van de halfgeleiders in de heterojuncties werd bestudeerd door Diffuse Reflectance Spectroscopie (DRS), (2) de kristalstructuur van de halfgeleiders geanalyseerd met röntgendiffractie (XRD), (3) de kristalgroottes gemeten met scanning elektronenmicroscopie (SEM) en berekend via de verandering in bandgap en de PL maxima en (4) de atomaire samenstelling van de heterojunctie werd bepaald door inductief gekoppelde plasma-optische emissiespectrometrie (ICP-OES). Om de licht-gegenereerde dynamiek van ladingsdragers in de composietmaterialen te analyseren, werden verschillende fotokatalytische tests met de gesynthetiseerde fotokatalysator uitgevoerd. De oxidatie van benzylalcohol tot benzaldehyde en de reductie van CO2 tot CO werden gebruikt voor de fotokatalyse met de heterojunctie. De redoxreacties zullen alleen plaatsvinden als de ladingsoverdracht de Z-schemaroute volgt, vanwege hun overeenkomstige redoxpotentialen. Er werd waargenomen dat de gecombineerde reactie, oxidatie van benzylalcohol en reductie van CO2, plaatsvond via de gewenste Z-schema-route, maar deze leidde tot een lage vorming van BAD en CO. Dit geeft aan dat de ladingsdragerroute veranderde van Z-schema naar Type II tijdens de fotokatalyse.