Preparation and characterization of $TiO_2$-base mixed oxide photocatalysts

Abstract

This study was focused on the photocatalytic wastewater treatment technology, especially on the heterogeneous photocatalyst systems which use $TiO_2-based$ mixed oxides as a photocatalyst. The enhancement of the photocatalytic activity of $TiO_2$ was investigated as a function of added amount of other oxides to promote desired redox reaction. This thesis included the preparation and characterization of $TiO_2$ base mixed oxide photocatalysts. By introducing a metal-ion, modified redox energy level in the energy band gap can play a role to retard recombination rate by trapping some of charge carrier and to enhance interfacial charge transfer. The mixed oxides of $Nb_2O_5$ or $Li_2O$ with $TiO_2$ prepared by a sol-gel process. While the $Nb_2O_5$/$TiO_2$ had a deleterious effect on the oxidation rate of DCA, the excess electrons due to the doping of $Nb_2O_5$ into $TiO_2$ promoted the reduction process for $Cr^{6+}$. $Li_2O$ (1wt%) with $TiO_2$ was found the most efficient photocatalyst for the DCA oxidation, resulting in photocatalytic activity of 50%. Preparation and characterization of a nano-sized Mo/Ti and Fe/Ti mixed oxide photocatalysts were performed. Nano-sized molybdenum-doped $TiO_2$ (Mo/Ti) mixed oxide photocatalyst was prepared with the $Mo{5+}$ content varying from 0 up to 2.5 mol. TEM-electron diffraction and X-ray diffraction patterns showed that particles were in the form of anatase with the diameter of ca. 4 nm. The appreciable red shift in the UV/VIS absorption spectra was monitored at each preparation stage-aging and dialyzing. The red-shift varied with addition of Mo, in the case of 2.5% Mo/Ti the UV/VIS absorption started at around 0.22 eV less than in nano-sized pure $TiO_2$ (about 3.42 eV). EDAX verified that the amount of Mo in the prepared mixed oxides was as required, and XPS analysis revealed that Mo(V) existed in the $TiO_2$ lattice. The measured photonic efficiency increased to 0.28 with DCA at 0.5 mol% Mo, and then decreased as...