Research On Methods And Mechanism Of Modification Improving Photo-induced Charges Separation Of TiO₂

TiO₂ photocatalysis has two bottleneck factors, including low quantum efficiency and low efficiency for utilizing solar light. This paper has discussed and explored the method of improving the separation rate of photo-induced carriers and utilization of visible light using of modification by phosphoric acid, surfactant and silver bromide for two bottlenecks of nanosized TiO₂. The dynamics processes of photoinduced charges separation and transformation of TiO₂ photocatalysis have been mainly investigated by means of the surface photovoltage, photoelectrochemical test and transient absorption spectra technologies. The results are as follows:Phosphoric acid modification nanosized TiO₂ has been prepared by a sample impregnation method. The results showed that phosphoric acid modification with proper amount increased in the SPS responses and the lifetime of photoholes of TiO₂ nanocrystalline in oxygen gas. It demonstrated that phosphate modification was useful for photoelectrons to be captured by the adsorbed oxygen molecular, leading to the enhancement of the separation rate of photoinduced charges, which revealed the essential reason of the improvement of photocatalytic activity of TiO₂ nanocrystalline. Moreover, photoinduced charge carriers of the phosphate modified TiO₂ had longer lifetime than those of the unmodified one, indicating that charge separation situation was improved. These dynamic differences were attributed to the surface-carried negative charges of nanocrystalline TiO₂ due to the phosphate modification. The results were favorable to reveal the reason of the enhancement of photoelectrochemical current density of TiO₂ film electrode.The nanocrystalline anatase TiO₂, which was synthesized by a sol-hydrothermal process in advance, has successfully modified with cetyltrimethylammonium bromide （CTAB） in the acidic condition. The results showed that the TiO₂ nanocrystalline were successfully transferred from the water phase to the organic phase, and the modification mechanism is closely related to Br-. The CTAB modification could improve the separation of photoinduced charge carriers and the adsorption ability of pollutants, which were mainly responsible for the enhanced photocatalytic activity. The enhanced photocatalytic activity of modified TiO₂ is attributed to the role that the Br- can easily capture photoinduced holes and then form active Br. Moreover, TiO₂ film with super-hydrophilic property under non-UV light was prepared by the surfactant modification, which was related with the combination between TiO₂ and PEG to improve of TiO₂ film surface structure. The prepared method improved the photocatalytic activity as well as the hydrophilic property of TiO₂ nanocrystalline.AgBr-TiO₂ nanocomposite were prepared in similar microemulsion system, on the base of the previous studies that TiO₂ nanocystalline could be modified by CTAB surface modification in the acidic condition. The results showed that AgBr were more effectively combined with TiO₂ nanoparticles in similar microemulsion system than in water phase system. It was favorable to the enhancement of the separation rate of photoinduced charge of AgBr-TiO₂ nanocomposite, inducing to the improvement of the photocatalytic activity of TiO₂ nanoparticles under visible light.This study has provided some reference methods and ideas for designing and synthesizing high performance TiO₂ based photocatalysts and provided some important experimental basis for enrich the theory of TiO₂ photocatalytic technology.