| Despite the high quality of life brought by the advanced science and technology since the 21st century, humans are still under undying warnings:the resources and self-healing ability of the earth is limited and increasing survival crisis is coming. Among these major issues, the energy and environmental crisis are the two of the most urgent problems faced by China and the developed countries.Since the first realization of water splitting using TiO2 as the electrode by Fujishima and Honda in 1972, this safe, clean and abundant solar energy has been concerned by researchers and thus the technology of photocatalysis have been sufficiently developed. Based on the photocatalysis process that photocatalyst can not only turn the solar energy into chemical energy,but also form hydroxide radical to realize the degradation of organic pollutants, scientists have proposed various semiconductor photocatalysts to solve the energy and environmental problems in some degree. Amog the semiconductor photocatalysts, TiO2 is one of the most studied materials virtually for its stable physical and chemical properties, nontoxicity, low price and high activity, which have the great potential to apply for the industry. However, because of its intrinsic wide bandgap, high recombination rate of excited electron-hole arid low charge transfer ability, the conventional TiO2 photocatalysts is limited to ultraviolet light. Thus the utilization of solar energy is quite low, resulting poor photocatalytic activity. In order to extend the utilization of solar energy and promote the charge transfer thus enhancing its photocatalytic activity, TiO2-based composited photocatalysts have become a hotspot of current research in this field.In this dissertation, the photocatalysis process and the representative photocatalyt (TiO2 materials) were briefly introduced firsly. And the mechanism of semiconductor photocatalysis and the preparation and analysis methods for TiO2 photocatalyst were also included. The existing modification technologies of TiO2 were summaried and the modification by noble metal and carbon materials were highlighted. In order to broaden the scope of the spectrum and inhibit photo-induced electron-hole pairs' recombination of TiO2, the pristine TiO2 was modified by compositing noble metals and carbon materials. The pristine TiO2 matrixs were prepared through solvothermal and hydrothermal methods. The modification was realized by the in-situ deposition method and the dipping wet chemical method. Four kinds of TiO2-based photocatalyst were successfully designed and prepared in this way, obtaining significantly enhancement of the photocatalytic activity under UV or visible light. By designing of these modification structures, extended light response, promoted separation of photo-generated carriers and improved energy absorption efficiency were realized, all of which contributed to the highly enhanced photocatalytic activity. The main work is presented in the following three aspects:1, The prepared TiO2@C/Au and TiO2@ C/Ag composited photocatalysts exhibit extended light response and enhanced harvest of solar energy contributing to highly improved photocatalytic activity. The effect of interface amorphous carbon layer and the noble metal concentration on the photocatalytic activity was also studied. The pristine TiO2 samples with various surface structures of amorphous carbon layers were synthesized by solvethermal method assisted with heat treatment at different temperatures. The particle size and crystallization of the prepared anatase TiO2 at about 15nm wasn't affected during the annealing process. Then the deposition of noble metal on the TiO2 particles was carried out by the Ti3+ on the TiO2 surface generated under UV light irradiation. The diameters of reduced Au and Ag nano particles arranged between 1.5 nm and 2 nm. By controlling the surface status of TiO2 through amorphous carbon layer adjusting, the concentration of Ti3+ was tunable which could result in tunable concentration of noble metal. This phenomenon verifys the fact that the amorphous carbon layer will great influence the separation and transport of photo induced electron and thus play an important role during the photocatalysis process.The degradation of methyl orange was carried out under visible light and both of TiO2@C/Au and TiO2@ C/Ag samples obtained efficient photocatalytic degradation. Besides, the photocatalytic activity was closely related to the concentrations of noble metal which could generate electron under visible light through surface plasmon resonance. And the final results depicted that the Au and Ag particles around 1.5-2nm would have efficient performance at quiet low concentration, correponding to TiO2-70-Au-10 and TiO2-70-Ag-7, respectively, In this way, we find an efficient method to extend the light response and promote the photocatalytic activity at low concentration with the interface engineering assistance.2, The prepared TNF/Au composites displayed enhanced photocatalytic water splitting performanc. The TiO2 nanowire film (TNF) was firstly fabricated by hydrothermal method and the Au nano particles was loaded on the surface of TNF by wet-impregnation method with tunable concentrations. The results shows that the surface plasmon resonance in this composites could not contribute to the realization of water splitting under visible light because of the high barrier potential at the interface inhibiting the transport of photo induced electron on the Au particles to conducting band of TiO2. The size effect of Au nano particle have a great influence on the photocatalytic water splitting performance for TNF/Au composites that Au particle of 10 nm exhibited the best performance at the same concentration with stable recycling ability compared to the activity of 20 nm and 30 nm.At the same time, the concentration effect of Au particle was also explored and the results revealed that the water splitting performance of the composites would be gradually improved with the concentraion before surface distribution valve value. The results of water splitting performance of the TNF/Au composites under different light sources displayed a new phenomenon that the photocatalytic activity in the ultraviolet light could be affected by irradiation of visible light without the assistance of surface plasmon resonance. While there is no hydrogen generation under white light LED, the performance under both of UV LED and white light LED is much better than pure UV LED revealing the complicated mechanism of photocatalysis for TNF/Au composites.3, The prepared TNF/Cdots with various concentrations of carbon dots by hydrothermal method conbined with wet-impregnation method obtained highly improved photocatalytic water splitting performance. The TiO2 nanotube films with various surface morphologies and structures were firstly fabricated by hydrothermal method at 130 ? for different reaction time. The TNF-15 samples displayed best performance for PEC analysis benefited from the extraordinary surface structure for light harvest and absorption. Secondly, the carbon dots solutions were prepared by solvethermal method at 160 ? using ascorbic acid and ethanol as carbon source and solvent, resepctively. These carbon dots of 5nm exhibited excellent distribution and optical properties.The pure TNF samples and TNF/Cdots composites were used to split water under 300 W xenon lamp. With the increasing content of carbon dots, the photocatlytic water splitting performance of the TNF/Cdots composites could be successfully adjusted. The improved PEC performance of TNF/Cdots composites furtherly testified the contribution of carbon dots to efficient separation and transport of photo induced electron and hole pairs. The TNF decorated by carbon dots of 1000 mg/1 obtained 400% enhancement of hydrogen generation compared to pure TNF samples. |
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