Preparation And Visible Light Photocatalytic Activities Of Pt-TiO₂and Pt-N-TiO₂

TiO₂has been considered as a superperformance photocatalyst in the heterogeneous photocatalyticreactions. But TiO₂wide band gap （3.0³.2eV） can absorb only the ultraviolet （UV） light which accountsfor less than5%of solar light energy. Therefore, it is a hotspot to improve the optical response of TiO₂toutilize visible light. Doping TiO₂with various elements can effectively expand the optical response of TiO₂by narrowing its band gap. However, the role of doped elements is still disputable. In order to learn aboutthe factors influencing visible light photoactivity, Pt-doped TiO₂and Pt, N codoped TiO₂were prepared bydifferent methods using nanotubular titanic acid （NTA） as the precursor with its high specific surface in thisdissertation. Specific contents are as follows:①Pt-doped TiO₂was prepared by a hydrothermal method with NTA as the precursor. Thephotocatalytic activity was evaluated by monitoring the oxidation of propylene under visible lightirradiation （λ≥420nm）. The results indicated that Pt-doped TiO₂all showed visible light photocatalyticactivity, especially the sample prepared at160℃with the highest activity. Oxygen vacancy is suggestedto be a basic reason for the visible light responsible. In addition, the chemical composition of platinum, thesize and crystal structure of photocatalysts all effect the photocatalytic activity. During the hydrothermalreaction, the hydroxyl group on the surface of NTA could neutralize the chloroplatinic acid, which resultedin a pH value increase. According to crystal transformation process of NTA, the mechanism of platinumdoping into TiO₂was discussed.②NTA was suspended in chloroplatinic acid solution at low temperature. Pt-doped TiO₂sampleswere prepared by calcinating the resultant mixture in flowing argon. The XPS results declared thatPt-doped TiO₂samples existed different platinum chemical composition by the calcination of thechloroplatinic acid precursor at different temperature. The nanotublar samples were modified by PtClxat300℃. Then Pt2+was doped into TiO₂crystal lattice interstitial site with the rise of calcinationtemperature. Pt was loaded on the samples in the presence of metal Pt0when the calcination temperaturereached600℃. The photocatalytic activity was evaluated by monitoring the oxidation of propylene under visible light irradiation. The results indicated that the Pt-doped TiO₂prepared at500℃showed thehighest activity, but the photocatalytic activity was decreased with the calcination temperature T≥600℃.Combined with morphology, crystal structure and paramagnetism analysis, the photocatalytic activities aredetermined by oxygen vacancy, crystal structure, photocatalysts size, chemical composition and the size ofplatinum.③TiO₂codoped with Pt and N was synthesized from NTA precursor, in association with urea solid orammonia gas as nitrogen source respectively. The photocatalytic activity was evaluated by monitoring theoxidation of propylene under visible light irradiation. The results indicated Pt and N codoped TiO₂showedgood photocatalytic activity when the nanotubular structure of NTA was destroyed into TiO₂nanoparticles,whatever urea or ammonia as nitrogen source. The samples in presence of urea prepared at700℃showed the highest activity. The samples in presence of ammonia prepared at400℃showed the highestactivity. Pt nanoparticles loaded on TiO₂in the presence of N had good dispersion and very small size,which could improve the separation of carriers and the activity of photocatalyst. Compared with the visiblelight photocatalytic activity of single Pt doped TiO₂samples, the results showed that the activity of Pt andN codoped TiO₂had higher activity. This conclusion indicated that TiO₂codoped with metallic andnonmetallic element could observably improve TiO₂visible light photocatalyst activity. In addition,considering the physical and chemical characteristics of samples, this paper analysised the factorsinfluencing the photocatalyst activity of Pt and N codoped TiO₂samples, and discussed a synergistic effectamong oxygen vacancies and dopants nitrogen plus platinum.