Preparation And Characterization Of Novel Modified TiO₂ Photocatalyst With Efficient Degradation Of Organic Pollutants

Although TiO2 photocatalytic technology has attracted attention in a wide range of academic disciplines including materials science, chemistry, environmental science and engineering, the large band gap of TiO2 restricts its photocatalytic applications only to the UV range of solar spectrum. A big portion of solar energy consists of energy within wavelength of 400-600nm which is within the visible region, and ultraviolet energy constitutes less than 5% of sunlight. TiO2 photocatalyst has a poor response to visible light, which greatly restricts its application in the processing of environmental pollution. Therefore, in order to overcome the limitations of conventional TiO2 photocatalysts, a series of novel and efficient modified nano-TiO2 photocatalyst were designed and prepared. The modification and photocatalytic mechanism were also be studied in this thesis. The main contents of this thesis are as follows:A series of N co-doped and tri-doped with other metal or non-metal elements TiO2 photocatalysts were prepared in this thesis. All the catalysts were characterized by XRD, UV-DRS, XPS and other techniques to study their structural features and optical properties. Experiments on photodegradation of organic pollutants under UV and visible light irradiation were carried out using the doped catalysts. The conclusions are listed as follows:There are two states of nitrogen doped in TiO2. The photocatalytic activity of N-TiO2 is improved by the nitrogen doped into TiO2 lattice. In contrast, the nitrogen chemically adsorbed on the surface of catalyst reduces the photocatalytic performance of N-TiO2; The N-TiO2 was further modified by surface adsorption of Fe3+, and then reduced by sodium borohydride. The structure of Fe compounds changed from Fe2O3 toγ-FeOOH after the NaBH4 redox treatment, which induced a process ofγ-FeOOH photoreductive dissolution; To the boron and nitrogen co-doped TiO2, the B-N synergistic effect works through the formation of different structures on the surface of catalysts. These structures are responsible for the improved photoactivity of co-doped catalysts under both visible and UV light. According to the results of density functional theory (DFT) calculations, the B-N synergistic effect at the (101) surface can introduce a localized state and largely reduce the band gap of TiO2; Tri-doped TiO2 with iron, boron and nitrogen were successfully synthesized by hydrothermal method. The synergistic effect between metal and non-metal elements leads to the narrowing of TiO2 band gap, resulting in its enhanced visible light photocatalytic activity. It is worth mentioning that there is no synergistic effect between iron and boron.Different facet controlling agents were used to synthesize TiO2 single crystals with exposed high-energy facets. Carbon and lanthanum co-doped TiO2 nano-crystals with exposed{001} facets have been synthesized by a simple one-step hydrothermal method without any addition of fluorides. As the carbon-doping source and a crystal growth directing agent, glucose play an important role in the formation of {001} facets and the excellent photocatalytic performance of the catalyst. The characterization results of TEM, SEM, XPS and other measurements indicate that the glucose not only can be selectively adsorbed on the {001} surface, maximizing the exposure of {001} facets, but also acts as an effective carbon source adsorbing on the catalyst surface to generate a large number of carbonaceous species embedded in the TiO2 matrix, resulting in the formation of new active sites. In addition, HF was used as the directing agent to prepare the TiO2 single crystal with exposed {001} and {110} facets by adjusting the dosage of HF. The DFT calculation results suggested that the distance between the centre of the crystal to any of the four corners in the middle is in the range of 0.43-0.67 J·m-2. This is the first time to theoretically demonstrate that the {110} facet can be induced by adjusting the concentration of HF. In addition, to further improve the activity of exposed facets, nano-sized Au particles were dispersedly loaded on the surface of exposed {001} and {110} facets, which promoted the transfer of photo-excited charges and the photocatalytic activity of TiO2 single crystal.This thesis reports a simple and economic method to modify Degussa P25 and other metal oxides with a vacuum activation procedure, resulting in a high photo-active and photosensitive products, which suggests that the novel vacuum activation method is apply to photocatalysis. Vacuum activation method can also be used to prepare the hydrophobic MCF loaded with F-doped TiO2 photocatalysts. Comparing it with the reported F-doping TiO2 prepared by the traditional method, the catalysts mentioned here possess superior UV light and sunlight photo activities. Most important, for the first time we detected the existence of F-doping impurity level experimentally, and hence verified the doping and photocatalytic mechnism. In addition, vacuum activation method was used to successfully load the TiO2 nanoparticles or nanorod on the surface of graphene. During the vacuum activation processing, graphene oxide and TiO2 were reduced simultaneously. All the reduced catalysts present enhanced UV and visible light photo-activity.A cheap and low toxic inorganic NH4F was used for the first time to prepare the superhydrophobic MCF loaded with TiO2 photocatalysts. The NH4F can be used as a new hydrophobic modifier on the future research of hydrophobic material. The catalysts possessed permanent superhydrophobicity and excellent organics adsorption capacity, which can be used as an "organic extractant". Our supported mesoporous catalyst greatly facilitated the surface fluorination, which enhanced its UV light photo activity. And the surface fluorination together with Ti3+ generation promoted its visible light photo activity. Our research will be significant to the application of hydrophobic materials in the field of photocatalysis, shipbuilding and other industries.A one-step hydrothermal method was used to prepare stable Ti3+ doped TiO2 by using tetrabutyl titanate as the titanium source and NaBH4 as the reducing agent. Through UV-DRS, EPR, XPS and other measurements, we confirmed that the Ti3+generation is the reason for the superior visible light absorption and photocatalytic activity of reduced TiO2. The concentration of Ti3+ is determined by the dosage of NaBH4 during the hydrothermal preparation. Interestingly, the visible light absorption capacity and photocatalytic activity of Ti3+ doped TiO2 was enhanced greatly by the HCl cleaning treatment. Compare to the suppression of UV photo activity of TiO2 caused by the metal doping, Ti3+ doping have no obvious effect on its UV light photocatalytic activity. When the dosage of NaBH4 is 0.13g, the corresponding catalyst contained the highest concentration of Ti3+ and the optimal photocatalytic activity.