Investigation of biological activities of biopolymer based catalysts and applications of artificial photosynthesis

Growing economies, population increases, and changes in the quality of life emphasize the world's economies' dependence on energy and the importance of accessing energy through reliable and economical means. The predominant use of fossil fuels to meet energy demand causes significant harm due to environmental pollution. Finding alternative green and ecological methods to replace traditional energy production methods has become an inevitable necessity for all humanity. The use of renewable energy sources and green energy production techniques instead of fossil fuels is of great importance to reduce the continuously increasing CO2 levels as a result of global warming and environmental pollution. In this thesis, carbon-based and biopolymer-based catalysts were synthesized, and their structural, optical, and morphological characterizations were performed. Applications of artificial photosynthesis and studies on biological activity were conducted with the obtained catalysts. As carbon-based catalysts, CNT/ZnO, rGO/ZnO, and TEGO/ZnO nanocomposite catalysts were synthesized, and photocatalytic hydrogen production studies were carried out. The photocatalytic hydrogen production activities of CNT/ZnO, rGO/ZnO, and TEGO/ZnO nanocomposites were investigated using MoSx and Pt co-catalysts. The improved hydrogen production efficiency of the catalysts, enhanced active surface area, charge separation, formation of unsaturated S atoms, and low exciton formation rates were associated with the co-catalysts applied through the photodeposition method. As biopolymer-based catalysts, commercial SiC and nanofiber catalysts obtained from lanthanide group transition metal oxides such as CeO2 and Yb2O3 (Yb2O3/SiC and CeO2/SiC) were made light-sensitive with EY dye due to their wide bandgap, in the presence of biopolymers such as sodium alginate, cellulose, chitosan, and chitin. Photocatalytic hydrogen production activities were investigated. It is anticipated that the increase in active reaction surface area and conductivity, along with the reduction of electron/hole recombination, will be achieved through the organic/inorganic structured catalysts obtained by forming biopolymer-based structures. Additionally, using different biopolymers such as sodium alginate, cellulose, chitin, and chitosan as support materials in the presence of MoSx or Pt co-catalyst precursors has enhanced the photocatalytic hydrogen production activities carried out with SiC catalysis. All biopolymers aimed to increase the hydrogen production activity of the catalysts by providing active surface area, preventing agglomeration, facilitating electron transfer, and providing binding sites for catalysts and co-catalysts. The use of sodium alginate, chitosan, cellulose, and chitin as biological support materials for semiconductors indicates that the hydrogen production activity has increased due to the synergistic effect between the biopolymer and the inorganic catalyst. Morphological and optical findings in studies using biopolymers as support materials confirm their effective role in photocatalytic hydrogen production reactions. Furthermore, in the antibacterial activity studies conducted as part of this thesis, it was found that the SiC, Yb2O3/SiC, and CeO2/SiC composite materials showed no antibacterial activity against both E. coli and S. aureus bacteria in dark and LED light environments. This thesis highlights the potential of using biological support materials and co-catalyst integration to significantly improve the photocatalytic hydrogen production performance of catalysts, leading to the development of efficient and sustainable energy conversion technologies.