Synthesis And Properties Of TiO₂-Based Nanophotocatalysts

Titanium dioxide(TiO2), as one of the most promising semiconductor photocatalysts, has been extensively applied in environment pollutants and the photoelectrochemical conversion of solar energy due to its apparent merits including relatively high efficiency, excellent chemical stability, and nontoxicity. The major limitations to achieve high photocatalytic efficiency are that TiO2 only can be activated under UV light irradiation due to its lager band-gap of 3.2 eV, the quick recombination of photo-generated charge carries and low quantum efficiency. Therefore, strong efforts have been made in improving the photocatalytic activity of TiO2. By doping, crystal face regulation and semiconductor composite can significantly improve its photocatalytic properties. In this dissertation,we expanded the range of light response of TiO2 by the nitrogen doping and reduced the recombination of photo-generated electron-hole pairs by prepared MoS2/TiO2 nanocomposites.Our works include two aspects. First we reported the synthesis of nanoporous N-doped TiO2 microspheres by a facile one-step hydrothermal route using HNO3 as the nitrogen source and TBOT as the titanium source. Then We prepared the MoS2/TiO2 nanocomposites with a two-step hydrothermal method.The photocatalytic activities of MoS2/Ti O2 composites under visible light are excellent. The prepared TiO2 photocatalysts were characterized by XRD, XPS, SEM, BET, DRS and other means. The photocatalytic performance of the samples was evaluated with RhB as a simulated organic pollutant. The effects of the amount of HNO3 and MoS2 on their structural and photocatalytic properties were investigated respectively and analyzes the mechanism and enhancement reasons of photocatalytic degradation process. The research was mainly composed of two parts:(1) We reported the synthesis of nanoporous N-doped TiO2 microspheres by a facile one-step hydrothermal route using HNO3 as the nitrogen source. The effects of the amounts of HNO3 on their structural and photocatalytic properties were investigated. The amount of HNO3 has a remarkable effect on the photodegradation efficiency of N-doped TiO2. With increasing the amount of HNO3, the morphology of Ti O2 gradually from an irregular shape into microspheres and the photodegradation rate increases and reaches the maximum value at 1.2 mL HNO3. The results showed that we successfully prepared N-doped Ti O2 microspheres. The N-doped TiO2 sample prepared with 1.2 ml HNO3 presented the highest photocatalytic activity in the degradation of RhB under visible-light irradiation. The special nanoporous structure and appropriate N-doping could be responsible for the superior visible-light photocatalytic performance.(2) Then, we successfully prepared anatase titanium dioxide(TiO2) nanosheets with {001} facets. The influences of different amounts of HF were investigated. The results indicated that HF has a great influence on the morphology and size of TiO2,and the fluorine can make {001} facets of TiO2 nanosheets more stable.The photocatalytic activities of the samples were evaluated by Rh B degradation. The results show that TiO2 nanosheets with exposed {001} facets had anatase crystal and showed high photocatalytic activities under ultraviolet light irradiation. With increasing the amount of HF, the photocatalytic activity of TiO2 was increased and then decreased gradually. TiO2 shows the best photocatalytic activities when HF was 2.0 ml. We prepared the MoS2/TiO2 nanocomposites with hydrothermal method. The results show that the structure of Ti O2 nanosheets disappeared. The MoS2/TiO2 with 99.5% TiO2 and 0.5% MoS2 showed the best photocatalytic performance. Compared with pure TiO2, the photocatalytic activities of MoS2/TiO2 nanocomposites was increased.