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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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The public concern regarding the sustainability of our planet has seen a significant growth during the last decades. As a result, the global con cept of green and sustainable chemistry was introduced in our society an d entails the search for possibilities to reduce and prevent pollution f rom industrial and domestic processes. The use of solar light energy as a renewable energy source is such an interesting possibility. In this Ph D work, light energy is used to induce reactions in the presence of a so lid catalyst, which is categorized as heterogeneous photocatalysis. This PhD work focuses on two objectives of photocatalysis. The first th ree experimental chapters cover different topics within the environmenta l application, whereas the last experimental chapter uses photocatalysis to postsynthetically modify semiconductors. The aim of the first part was to develop solid materials that are visible light responsive and show photocatalytic activity under visible light illumination. Therefore, we investigated the possibility of using iron(I II) oxide materials since iron(III) oxide shows an inherent visible ligh t absorption. However, due to the high electron/hole recombination rate in the nanosecond time scale in pure iron(III) oxide particles, they can not be used directly. To prevent this recombination, we incorporated ir on(III) oxide based clusters, more specific Fe3-μ3-oxo cluste rs, inside a metal-organic framework. In these small Fe3-µ3-oxo clusters the surface area of the photocatalytic active centers is inc reased resulting in a reasonable chance that the photogenerated electron s and holes reach the surface where they can react with adsorbed molecul es before recombination occurs. A series of MOFs which contain such Fe3-µ3-oxo clusters (MIL-100(Fe), MIL-88B(Fe) and amino-substitut ed MIL-88B(Fe) and MIL-101(Fe)) were investigated for the photocatalytic degradation of rhodamine 6G. Upon visible light illumination, successfu l photocatalytic degradation of rhodamine 6G was observed. Moreover, two amorphous materials containing such Fe3-μ3-oxo clusters (Bas olite F300 and Fe(III)-aminogel) were tested and displayed signific ant photocatalytic activity as well. From this, it was concluded that cr ystallinity over extended length scales is not required to yield an effe ctive photocatalyst, but only a local order around the Fe3-µ3-oxo clusters is sufficient. Furthermore, amino-substitution of the link er has no significant effect on the photocatalytic activity of the Fe(II I)-MOFs. In the next part, further examination of these Fe(III)-MOFs containing Fe3-µ3-oxo clusters was conducted to better understand the photochemical mechanism(s) involved. The photocatalytic properties of the following Fe(III)-MOFs were confirmed through redox reactions: MIL-100(Fe ), Basolite F300, MIL-88B(Fe) and aminosubstituted MIL-88B(Fe) and MIL-1 01(Fe). On the one hand N,N,N’,N’-tetramethyl-p-phenylene-diamine as ele ctron donor and on the other hand methyl viologen dichloride as electron acceptor were added to the MOF suspension and upon illumination the cor responding blue colored radicals were formed. These results suggested th at at least a fraction of the photogenerated holes and electrons in the Fe(III)-MOFs under study was able to escape recombination and both charg e carriers were accessible at the surface of the MOFs. Furthermore, the generation of long-lived species in MIL-88B(Fe) was proven via transient absorption spectroscopy. These experiments indicate that the electron/h ole recombination is actually delayed to the microsecond time scale when iron(III) oxide based clusters are incorporated into the rigid network of a MOF. Besides in liquid environment, photocatalysis can also be used for gaseo us reactions. Therefore, the third part was focused on diminishing the e mission of nitrogen oxides in the atmosphere by reducing them into nitro gen en water via the selective photocatalytic reduction with ammonia (ph oto-NH3-SCR). The commercial TiO2 photocatalyst PC500 showed a significa nt higher photocatalytic efficiency compared to P25 and displayed also a higher photocatalytic activity in comparison with the thermal photocata lyst Cu-ZSM-5 at 150 °C. This indicates that photocatalysis can offer a solution for processes which occur at lower temperatures. The parameters of contact time and water content were also investigated. Furthermore, mesoporous TiO2 was tested and the sample which was calcined at 600 °C d isplayed and even higher efficiency than the highly active PC500. When u sing the photo-NH3-SCR, unreacted ammonia can remain in the outlet gas. This so called NH3-slip is harmful and should be degraded. It was found that ammonia can be oxidized via the selective photocatalytic oxidation (photo-SCO) over three commercial TiO2 samples (P25, PC500 and UV10 0). PC500 displayed again the highest activity at 150 °C under UV illumi nation as nearly complete conversion of NH3 into nitrogen was observed. The superior activity of PC500 was ascribed to its high adsorption affin ity. Furthermore, evidence was provided that the photo-SCO over titanium dioxide proceeds via the internal SCR mechanism. Finally, photocatalysis was utilized for the post-synthetic modification of metal deposition on zinc oxide. Illuminating ZnO crystals with UV li ght resulted in the reduction of silver ions to silver metal. Via optica l and fluorescent microscopy, it was observed that the photocatalytic si lver reduction does not occur homogeneously but more rapidly in certain zones. Further illumination resulted in the remarkable growth of well se perated large dendritic silver nanostructures. Such a dendritic silver s tructure was not one ontinuous metal structure but rather a heterog eneous structure with multiple silver nano-features because it generated luminescence. As a result of these nano-features, these dendritic struc tures could be excellent SERS substrates which was onfirmed through Rama n mapping experiments. The Raman enchancement was reasonably homogeneous throughout the whole structure which is important for sensing applicati ons. In summary, multiple aspects of photocatalysis were examined is thi s work. Firstly, a series of Fe(III)-MOFs were identified for their application in water purification and the investigation to better understand the pho todynamic processes in these materials was started. Secondly, the photoc atalytic degradation of nitrogen oxide and ammonia over different titani um dioxide samples was examined. Finally, photocatalysis was used to dep osit metal particles on zinc oxide resulting in the remarkable growth of dendritic nanostructures which are excellent SERS substrates.

academic collection --- 541.128 <043> --- 541.14 <043> --- 541.14 <043> Photochemistry--Dissertaties --- Photochemistry--Dissertaties --- 541.128 <043> Catalysis. Acceleration and retardation of reactions by catalysts. Autocatalysis. Spontaneous combustion--Dissertaties --- Catalysis. Acceleration and retardation of reactions by catalysts. Autocatalysis. Spontaneous combustion--Dissertaties --- Theses

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Fotokatalysatoren zoals zinkoxide zijn in staat om milieuverontreinigende stoffen af te breken na absorptie van voldoende energetisch licht. Een belangrijke beperking van dit fotokatalyse proces is de recombinatie van gegenereerde elektronen en gaten, wat resulteert in een verlies van fotokatalytische activiteit. Deze recombinatie wordt in dit onderzoek grotendeels voorkomen door afzetting van zilver nanopartikels op zinkoxide kristallen. De gegenereerde elektronen worden als het ware 'gevangen' in de zilver nanostructuren waardoor een verhoogde fotokatalytische activiteit wordt waargenomen. In een eerste fase worden twee reeds gepubliceerde procedures voor het genereren van ZnO microkristallen onder de loep genomen en verder verfijnd door verschillende parameters aan te passen. Op deze manier zijn drie zinkoxide microkristallen met een geschikte structuur voor dit onderzoek gesynthetiseerd: ZnO microrods [800 nm x 3,6 µm], ZnO microrods [1,5 µm x 2 µm] en ZnO staven [1 µm x 10 µm]. Deze ZnO kristallen verschillen in lengte, diameter en aanwezige kristalvlakken en hun structuur is uitvoerig door de scanning elektronenmicroscoop bestudeerd. Als vervolg worden zilver nanostructuren door middel van fotokatalytische reductie op de ZnO kristallen afgezet. Aan de hand van een fluorogene reactie wordt de fotokatalytische activiteit van de gesynthetiseerde halfgeleiders op bulk niveau bestudeerd. De reactie bestaat uit de fotoreductie van resazurine naar het fluorescente resorufine. Aan de hand van veranderingen in absorptie-eigenschappen en emissie-intensiteit van een resazurine oplossing in aanwezigheid van de katalysator, kan de efficiëntie van de fotokatalyse worden opgevolgd. Na afzetting van zilver nanostructuren op de zinkoxide kristallen wordt een meer efficiënte fotokatalysator verkregen gezien een twee- tot driemaal snellere katalytische omzetting kan worden waargenomen. In een laatste fase wordt de verhoogde fotokatalytische activiteit op 'single molecule' niveau onderzocht. Met een state-of-the-art geïntegreerde licht- en elektronenmicroscoop, worden de fotokatalytische omzettingen gecorreleerd met de oppervlakte-eigenschappen van de ZnO-zilver halfgeleiders. Zowel de 'in situ' zilverafzetting als de katalyse van de fluorogene reactie worden bij de drie gesynthetiseerde ZnO microkristallen geanalyseerd. Op het oppervlak van de ZnO microrods [800 nm x 3,6 µm] en ZnO staven [1 µm x 10 µm] worden dendriet- en plaatvormige zilverstructuren gevormd. Uit de overlap van de fotokatalytische activiteitsmappen met de structurele informatie via SEM blijkt dat de meeste activiteit wel degelijk op deze zilverstructuren is gelokaliseerd.

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In this thesis, an investigation on the influence of iron impurities on the optical properties of zeolites and the luminescence properties of silver-exchanged zeolites was performed. The main source of these impurities originates from the source materials used in the synthesis procedures, therefore, a comparative study on the optical purity between commercial zeolites and self-synthesized zeolites was performed. First, the influence of different synthesis procedures on the topology and crystal morphology of the self-made zeolites was determined. The followed procedures differed in silica source, organic template and overall batch composition. Each procedure contained multiple samples with a different crystallization time. Second, the presence of absorbing species, such as iron and organic components, was determined using DRS and ESR measurements. The DRS analysis gives direct information on the amount of absorbing species and the absorption region of the impurities. The relative concentration of iron in the zeolite was determined by ESR. Some of the self-synthesized samples were also subject to a post-synthesis treatment before the silver-exchange to extract the unavoidable trace amounts of iron impurities. After analyzing the physiochemical characteristics, the zeolites were exchanged with silver ions and a further thermal activation step was used to form the emissive silver clusters. These silver species are typically excited with UV light yielding a visible light emission and the corresponding quantum efficiency of emission (EQE) and the influence of the zeolite purity on it was studied in detail. In order to measure the EQE in a correct fashion, the exact position of the excitation and emission maxima of the silver-exchanged were determined using spectrofluorimeter. Based on the EQE and the 2D excitation-emission spectra obtained for the different samples the effect of several parameters, such as impurities, zeolite topology and counter-balancing ion on the l...