Studies On The Photocatalysis Of Transitional Metal Modified Titanium Dioxide

Photocatalytic hydrogen generation and organic pollutants degradation have attracted more and more attention due to their environmental friendliness and sustainability. Among various photocatalysts, Titanium Dioxide (TiO2) is widely studied because of its stability, non-toxicity and low price. Photocatalytic activity enhancement of TiO2is a critical and hot issue in the recent research and development of TiO2photocatalyst. This work focuses on the synthesis and photocatalysis of transition metals modified TiO2photocatalysts. The functions of transition metals (Fe and Cu) in photocatalytic processes have been inveratigated in details.Using tetra-butyl orthotitanate as the catalyst precursor, nano TiO2was synthesized by typical sol-gel method. TiO2samples were characterized by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and optical diffuse-reflection spectrum (DRS), to understand the changes in structure and morphology in heat treatment process, and optimize the calcination temperature of TiO2. The synthesized TiO2in form of anatase with particle size between10and20nrn exhibits excellent photocatalytic activity, identified by methylene blue (MB) degradation and hydrogen generation, better than commercial TiO2.Bulk and surface Fe3+doped TiO2were synthesized by co-gel method and calcination, respectively. Their photocatalytic activities were evaluated by MB degradation and hydrogen production, respectively. It is found that bulk doping is detrimental to both processes (MB degradation and hydrogen production) but surface doping demonstrates a photocatalytic activity enhancement in MB degradation, revealing that doping position in TiO2plays a very important role in photocatalystic process. Doped Quantum-sized TiO2was synthesized by sol rotatory evaporation method to ensure that TiO2was treated by surface doping. The effect of surface doping disappeared after heat treatment of doped Quantum-sized TiO2, to have an effect of bulk doping. The difference in photocatalytic activity confirms that the surface doping and bulk doping demonstrates different effect in photocatalytic process. Fe3+decomposes MB while irradiated by UV. The adsorbed Fe3+species on surfaces of TiO2enhance MB degradation due to the photocatalytic synergy between Fe^and TiO2. A possible mechanism is suggested.Compared with Fe3+adsorption, Cu2+adsorption has different effects on photocatalytic activity. With increasing of Cu2+doping amount, photocatalytic reaction rates of both processes (MB degradation and hydrogen generation) increase firstly and then decrease. By characterizing the used catalysts through XRD, SEM and X-ray photoelectron spectroscopy (XPS) analysis, it is found that Cu2+is reduced into metallic Cu during hydrogen generation, behaving like Pt loaded TiO2·However, the Cu redox couple functions as a catalytic center in MB degradation process, which enhances the MB degradation. Excess Cu may form recombination centers, inhibiting the MB degradation process. Fe3+and Cu2+doping behave differently regarding to different redox reaction mechanisms, resulting different photocatalytic reaction processes to produce different adsorption effects on photocatalytic activity. A mechanism discussion has been made in this thesis.