Research On Preparation And Photocatalytic Activity Of Semiconductor Nanocomposite Based On G-C₃N₄

Recently, graphic carbon nitride ?g-C₃N₄?, a metal-free semiconductor material has been widely used as a low-cost, stable and visible-light-active photocatalyst in the sustainable utilization of solar energy owing to its excellent chemical inertness and unique electronic band structure. However, pure g-CsN4 is still far from satisfaction due to its small specific surface area, high recombination rate of photogenerated electron-holes and low quantum yield, which limits its extensive application in the energy and environmental relative fields. To deal with these problems, it may be a feasible approach to construct heterogeneous structure by coupling two different semiconductor materials with matched band structure and band positions to promote the effective separation of the photoinduced electron-hole pairs, and thus enhance the photocatalytic activity. In this thesis, we focus on the preparation and photocatalytic activity of semiconductor nanocomposites based on g-CsN4. The main contents and conclusions are described as follows:?1? The TiO₂/g-C₃N₄ semiconductor nanocomposite had been prepared by an acetic acid assisted sol-gel method combined with thermal polymerization process. The component, microstructure and morphology of various samples were characterized by means of several analysis methods, such as TG, XRD, SEM, TEM, FT-IR, XPS and UV-vis DRS. The results showed the aggregation degree of TiO₂ nanoparticles could be effectively alleviated due to the introduction of g-C₃N₄, and the optical absorption edge of TiO₂/g-C₃N₄ composites had an obvious red shift to the longer wavelength in comparison with pure TiO₂. The performance test showed that TiO₂/g-C₃N₄ composite had more excellent photocatalytic activity in comparison with pure TiO₂ or pure g-C₃N₄. Especially under visible light irradiation, the degradation rate of optimal TiO₂/g-C₃N₄-74.4 nanocomposite on methyl orange ?MO? was 2.80 times as great as that on pure g-C₃N₄. The enhanced photocatalytic activity mainly benefited from the effective separation of photoinduced electron-hole pairs and the extended optical absorption range, both owing to the heterojunction built-in between TiO₂ and g-C₃N₄.?2? The In₂S₃/g-C₃N₄ semiconductor nanocomposite had been fabricated by coupling hydrothermal method with thermal polymerization process. The results showed that the morphology of the obtained In₂S₃ was converted from mainly aggregated nanoparticles into two dimensional interlaced nanosheets due to the introduction of g-C₃N₄, and the optical absorption edge of In₂S₃/g-C₃N₄ composites had an obvious red shift to the longer wavelength in comparison with pure g-C₃N₄. Under visible light irradiation, all obtained In₂S₃/g-C₃N₄ composite samples had more excellent photodegradation activity than pure g-C₃N₄ or pure In₂S₃, and the degradation rate of optimal 0.6In₂S₃/0.4g-C₃N₄ nanocomposite on MO was 5.20 times as great as that of pure In₂S₃ or 16.25 times as great as that of pure g-C₃N₄. The enhanced photocatalytic activity was closely related to the heterojunction structure. Besides, the significant change of morphology which caused an obvious increase in surface area and absorption ability also played a vital role in improving the photocatalytic activity.?3? The SnO₂/g-C₃N₄ semiconductor nanocomposite had also been synthesized by combining hydrothermal method and thermal polymerization process. The results showed that the aggregation degree of SnO₂ nanoparticles could be effectively alleviated due to the introduction of g-C₃N₄, and the UV-vis DRS further displayed that the optical absorption edge of SnO₂/g-C₃N₄ composite had an obvious red shift to the longer wavelength in comparison with pure SnO₂. Under the same condition of the ultraviolet visible light or visible light irradiation, compared with pure SnO₂ or pure g-C₃N₄, the photocatalytic degradation properties of SnO₂/g-C₃N₄ nano-composite on Rhodamine B?RhB? could be remarkably improved. Especially under the condition of visible light irradiation, the degradation rate of the optimal 0.5SnO₂/0.5g-C₃N₄ nanocomposite could reach 13.32×10^-3 min^-1, which was 2.90 times as great as that of pure g-C₃N₄ (4.56×10^-3 min^-1). The enhanced photocatalytic activity could be mostly ascribed to the heteroj unction structure, which promoted the effective separation of photogenerated electron-hole pairs.