TiO₂Nanostructures, Composites And Their Photocatalytic Properties

Titanium dioxide has attracted broad attentions in fundamental science and technologicalapplications due to their chemical stability, light resistance, non-toxic and low cost,including light harvest, solar energy conversion and photocatalysis et.al. However, TiO2, asa wide band gap semiconductor, can only be excited by UV light and has low quantumyield because of high electron-hole recombination rate. Therefore, much efforts have beenmade to enhance their visible-light absorption and quantum yield. In this thesis, variousTiO2nanostructures were synthesized by low cost solution methods. Furthermore, basedon this nanostructures, microstructure, noble metal, and narrow bandgap semiconductormodification methods were tried to extend their absorption and improve the photocatalyticefficiency. The photocatalytic mechanism were also investigated by EPR and IPCE, whichwill be benefit for the design and realization of high efficient photocatalysis.Using TBOT and TiCl3as titanium precursors, the anatase TiO2nanoparticles weresynthesized by mild solvethermal method. Ti3+self-doped TiO2can be realized bycontrolling titanium sources.The presence of Ti3+in TiO2has emerged as an effectiveapproach to improve photoactivity, which is important for photocatalyst. The bestphotocatalytic properties of the TiO2nanoparticles can be obtained by optimizing theratio of titanium sources. Based on Ti3+self-doped TiO2(TBOT:TiCl3=3:2), TiO2/CdSphotocatalysts have been prepared by hydrothermal method, in which CdS nanoparticles actas an effective sensitizer for the improvement of absorption and photocatalysis. Thephotocatalytic activities of the TiO2/CdS samples were evaluated for the degradation ofmethyl blue (MB) under simulated sunlight irradiation. Results revealed that the TiO2/CdScatalysts exhibited higher photocatalytic degradation activities and rate, which is1.5times of pure TiO2samples.A low-cost solution method was employed to synthesize two-dimensional TiO2ultrathin nanosheets with5-nm-thick. The influence of annealing temperature on crystalcrystallinity and hydrogen production performance of TiO2was systematic studied. Resultsindicated that the crystallinity of TiO2ultrathin nanosheet increased with the increase ofannealing temperature, however, the hydrogen production efficiency dropped significantlybecause less photoinduced Ti3+appeared on the surface of the annealing samples by electron paramagnetic resonance analysis. To utilize the visible light, TiO2nanosheetsweres ensitized by CdSe quntum dots. The TiO2/CdSe nanosturctures exhibited improvedphotocatalytic activities under the sunlight irradiation. The apparent quantum efficiency andelectron paramagnetic resonance analysis indicated that photoexcited electrons from CdSecan be transferred to the TiO2, which reduce Ti4+to form Ti3+and react with the surfaceadsorbed species. Through further analysis of the catalytic mechanism in the process ofhydrogen production, we can infer that surface defect Ti3+is the active site of H.and Pt isthe active site of H2generation.Anatase TiO2nanocrystals with dominant {001} facets were snythesized through anonaqueous seeded growth method in a TiF4and TiCl4mixed solution., The morphology ofTiO2nanocrystals can be controlled by adjusting surfactant types and their ratio. Theclassical nucleation and gowth theory has been employed to synthesize TiO2/M (M=Au, Ag)heterojunction nanostructures, which used the TiO2nanocrystals exposed {001} facets asraw materials. The growth of precious metal on TiO2nanocrystals were controlled viatuning the concentration of precursor, reaction temperature, surface treatment, et al. TheTiO2/M (M=Au, Ag) heterojunctions with dominant {001} facets have great potential inhigh efficient photocatalysis.