The Study On Photocatalytic Activities Of Au/TiO₂ Nanocomposites

TiO₂ has received broad attentions due to its potential application for environmental and energy fields. However, TiO₂ is far from being a perfect photocatalyst, one reason is its wide bandgap which limits its photo-absorption to only the UV region（about 5% of solar light）, another reason is its low quantum yield owing to high electron-hole recombination rate. Therefore, we focus on regulating the micro-structure and energy band structure of TiO₂ in this thesis. Through a modification, three different TiO₂ nanostructures were synthesized. Furthermore, based on these nanostructures, we tried to extend their light response range and to improve the photocatalytic activity by depositing Au NPs on these nanostructures respectively, which will make a contribution to designing and realization of high efficient Au/TiO₂ photocatalysis.A simple deposition-precipitation method was used to deposit Au NPs on nanoporous anatase TiO₂ Mesocrystal（denoted as Au/MesoTiO₂） which synthesized through a solvothermal method using tetrabutyl titanate as the titanium source and acetic acid as the solvent. FESEM, XPS and DRS confirmed the Au NPs were successfully deposited on MesoTiO₂. The photocatalytic activity of Au/MesoTiO₂ samples were evaluated by the degradation capability of methylene blue. It was found that Au/MesoTi O2 showed superior photocatalytic activity compared with P25 and Au/P25. The photocatalytic activity of Au/MesoTiO₂ increased with Au loading content increasing, however, further increasing Au content, decreased catalytic activity. The highest activity has been noticed for 3.0% Au/MesoTiO₂, which shows a 3.80 fold photocatalytic activity improvement over Meso TiO₂. The MB photodegradation efficiency changed relatively little after 5 cycles of experiment under identical condition, indicating that the photocatalyst has superior photocatalytic stability. Finally, through trapping experiments of reactive species, we investigated the Au/MesoTiO₂ catalytic mechanism under ultraviolet-visible and visible light irradiation.Based on tetrabutyl titanate-acetic acid system, square-flake TiO₂ with exposed active（001） facets have been successfully prepared through a solvothermal method with suitable content of hydrofluoric acid and ethylene glycol. In the preparation process, ethylene glycol and hydrofluoric acid have a major impact on the morphology of TiO₂. The different ratio of the exposed（101） and（001） facets of TiO₂ were synthesized by controlling the amount of adding hydrofluoric acid. Interesting observations were that whether the ethylene glycol was added or not, the TiO₂, synthesized by adding 0.24 mL of hydrofluoric acid, showed the highest photocatalytic activity. It was found that the Au/TiO₂-EG（2 mL）-HF（0.18 m L） with suitable gold content could significantly enhance the photocatalytic activity.Ti³⁺ self-doped TiO₂ were synthesized through a solvothermal method using tetrabutyl titanate and titanium trichloride as the titanium source and acetic acid as the solvent. XPS confirmed the presence of Ti3+ in TiO₂. The morphology of TiO₂ was directly related to the volume ratio of different titanium source, and TiO₂（3:2） with capsule-like structure showed the highest photocatalytic activity. Ti3+ self-doped TiO₂ coupled with Au NPs to form Au/TiO₂ composites will be benefit to improve the photocatalytic acticity.