Preparation And Photocatalytic Activities Of Novel Visible-light-responsive Composite Catalysts

With the development of socio-economic level, environment pollution and energy shortage have become a core issue. In recent years, the advanced oxidation technology based on semiconductor photocatalysis has wide applications in solving environmental problems and energy conversion. Highly toxic organic and inorganic pollutants can be effectively degraded into non-toxic or low toxic substances by this method, thereby reduce environmental pollution; besides, it can convert solar energy into storable hydrogen, to solve the energy shortage. However, the photocatalytic technologies still face with many problems in practical applications. For example, although TiO2 as a typical conventional photocatalytic material has gained wide interest because of non-toxic, inexpensive and stable, it is still limited by a wide band gap, narrow light response range(only responsence to UV light), easy recombination of photogenerated electron-hole and poor recyclability for the pollutant degradation or hydrogen production, which is restricted greatly in practical application. Therefore, the development of visible-light- or solar-responsive, efficient, recyclable and stable photocatalysts have become the core task in the research field of photocatalytic technology. Based on the above issue, this dissertation mainly focuses on the controlled synthesis and photocatalytic performance of novel visible-light-responsive composite catalysts. The main contents are discussed as follows:1. Metal-organic frameworks(MOFs) is a novel crystal material with multidimensional network structure composed of metal clusters and organic ligands formed through coordination bond, have attracted great interest as fascinating materials for sustainable energy and environmental remediation. In recent years, MOFs as a new representative of the photocatalytic material has been recieved considerable concern in the field of photocatalytic technology. However, highly active MOF-based materials still faced with a problem for practical application, that is, high dispersion leading to inconvenient recovery. Here, we design a multifunctional MOF-based heterostructure composed of one-dimensional MIL-53(Fe) microrods with the magnetic nanospheres decoration(MHMCs), which can be easily fabricated by a one-pot solvothermal process. Moreover, the MHMCs show high efficiency in a H2O2-mediated visible light photocatalysis process. The MHMCs/H2O2 system exhibits enhanced apparent rate constants for the degradation of Rhodamine B(RhB) and p-nitrophenol(PNP), which are significantly higher than those of Fe2O3 and Fe3O4 photocatalysts under visible light irradiation.2. Effective separation of photogenerated charge carriers is an important way to enhance the photocatalytic activity. Based on large specific surface area and good electron transport of graphene, we design and fabricate a series of visible-light-responsive photocatalysts based on one-dimensional iron terephthalate(MIL-53(Fe)) microrods hybridized with grapheme(GR) and experimentally demonstrates their remarkably improved visible-light-induced photocatalytic activity. During the solvothermal process, the reduction of graphene oxide(GO) is accompanied by the MIL-53(Fe) crystallization, which endows them with effective interfacial contact, thus facilitating the transfer of photogenerated charge to lower the recombination rate of photoinduced charge carriers. The GR/MIL-53(Fe)-H2O2 systems exhibit significantly higher photocatalytic activity toward degrading Rhodamine B(RhB) than that of bare MIL-53(Fe)-H2O2 under visible light irradiation. The introduced H2O2 induces photosynergistic generation of more amounts of hydroxyl radicals to contribute to the improved photocatalytic activity.3. We present a successful example on efficient conversion of solar energy by Ag/AgBr coupled photocatalysts that hold unique synergistic dual photoexcitation. A series of Ag/AgBr coupled photocatalysts were controllably synthesized by an easily manipulated mild solvothermal process. The physicochemical properties of the as-prepared Ag/AgBr coupled photocatalysts were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray energy dispersive spectroscopy(EDS) and UV-vis diffuse reflectance spectroscopy(DRS). The results showed the solvothermal reaction time played key role for controlling crystalline structure, morphology, composition, and visible light absorption ability of the resulting photocatalysts. The as-prepared Ag/AgBr coupled photocatalysts exhibited remarkable photocatalytic performance and good reusability for decomposing organic dyes in aqueous solution under the irradiation of commercial 20 W cool daylight fluorescent lamp, owing to the synergistic dual photoexcitation cooperating between plasmonic Ag nanoparticles and narrow-band-gap AgBr.