Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis The Valorization of Various Wastewater for Hydrogen Production by Photocatalytic Oxidation(01. Izmir Institute of Technology, 2021) Orak, Ceren; Yüksel Özşen, AslıHydrogen is a clean, green and sustainable energy and photocatalysis a better approach for hydrogen production from various wastewaters. It was aimed to evolve new hybrid solar-driven catalysts for photocatalytic hydrogen production from various wastewaters. Firstly, catalysts were synthesized. Their characterization study were performed and PL results show that the most promising catalyst was GLFO. The impacts of pH, catalyst loading and light over hydrogen production from SMS were investigated using all synthesized catalysts. The hybrid catalysts show higher efficiency. FFD was created to elucidate the impacts of reaction parameters and graphene content of catalyst had a major impact. To optimize the reaction parameters for all hybrid catalysts, an experimental matrix was created using BBD. The higher hydrogen amounts were observed using GLFO. The same experimental matrix was used to search the effects of reaction parameters over produced hydrogen amounts from sugar beet wastewater using all hybrid catalysts and the highest hydrogen production was observed using GLFO. The observed reaction followed first order reaction model based on TOC removal. Therefore, the degradation of organic pollutants in wastewater streams and hydrogen evolution could simultaneously be achieved. Same experimental matrix was also used for hydrogen evolution from DBU using all hybrid catalysts. Relatively lower hydrogen amounts were obtained so that it was also treated under subcritical conditions. FFD was created to search the impacts of reaction parameters and NaOH concentration and current density had an impact over DBU removal. Based on GC-MS results, the hazardous intermediates did not form during hydrothermal electrolysis.Doctoral Thesis Development of a Novel Hybrid Process for the Conversion of Cellulose Into High-Value Chemicals by Applying Voltage in Hot Compressed Water(Izmir Institute of Technology, 2017) Akın, Okan; Yüksel Özşen, AslıIn this study, a novel hybrid method of hydrothermal electrolysis implemented for the decomposition of microcrystalline cellulose (MCC) into high value added chemicals such as levulinic acid, 5-hydroxymethylfurfural (5-HMF), and furfural. The hypothesis of the study was that, when direct current (DC) is applied the formation of ionic and radical species can alter the hydrolysis of cellulose. Based on this hypothesis, the purpose of the study was to build an integrated method of hydrothermal electrolysis that can lower energy requirement of cellulose hydrolysis by altering the selectivity. In order to investigate the individual and coupled effect of operating parameters such as reaction temperature (170-200 ℃), time (30-120 min.), electrolyte concentration (1-50 mM H2SO4), constant current (0-2 A), statistical analysis was conducted by a fractional factorial design. Analysis of variance (ANOVA) test was applied to the main hydrolysis products yields of MCC, total organic carbon (TOC) and cellulose conversion. Based on the response surface plots, 1A of current at 200 ºC maximized TOC yield and cellulose conversions to 62% and 81%, respectively. In order to enhance the selectivity, constant voltage (2.5, 4.0 and 8.0 V) was applied at 200℃. Application of 2.5 V increased TOC (54%) and alter the selectivity of 5-HMF (30%) and levulinic acid (21%). The structural changes in solid residues were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and found that MCC particles functionalized by carboxylic acid and sulfonated groups by application of 2.5 V. Therefore, change in the selectivity values were conducted with the functionalization of MCC particles due to applied voltage under sub-critical conditions.