Synthesis, Characterization And Visible Light Photocatalytic Activity Of Bi₂MoO₆-Based Photocatalysts

Environmental and energy issues are vital for the sustainable development of human beings. The photocatalytic technique is one of the most promising solutions to pollution treatment and energy problem, which can effectively degrade organic pollutants in the most wastewaters and exhaust gases into inorganic small molecules, such as CO2, H2 O and so on. Additionally, the technique can produce hydrogen through water-splitting. It works by semiconductor photocatalysts directly harvesting and using solar energy and possesses a series of advantages such as high efficiency, energy saving, cleanliness, non-toxicity, simplicity in operation and so on. Among various semiconductors, TiO2 is the most widely studied photocatalyst in the past decades. However, wide band gap and the poor quantum yield in TiO2 materials seriously inhibit their practical applications in visible light photocatalysis. Therefore, in recent years, photocatalysts with visible light response have greatly attracted researchers, and studies in this field are also frequently reported. Two approaches have been employed to enhance materials’ visible light photocatalytic activity. One is to regulate the morphologies of semiconductor photocatalysts; the other starts from the composition point of view, including fabrication of traditional photocatalysts, design of novel photocatalytic materials responsive to visible light and so on. In this dissertation, to improve the photocatalytic performance of Bi2MoO6, several modifications were carried on. The synthesis, characterization and visible light catalytic performance of the hierarchical Bi2MoO6 microspheres and the AgI/Bi2MoO6 heterostructured photocatalysts were studied.The details of this thesis are summarized briefly as follows:(1) Bi2MoO6 hierarchical flower-like microspheres were successfully synthesized through phase transformation from BiOI hierarchical flower-like microspheres under hydrothermal condition. The crystal structure, composition and morphology of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller(BET) surface area analysis. The visible light catalytic activity was evaluated by the degradation of model dye rhodamine B(RhB) and phenol. The influences that the amount of sodium citrate, reaction time and different Bi-source on the morphology of the Bi2MoO6 products were systematically investigated. In addition, the enhancement reasons of photocatalytic activity were also discussed.(2) Bi2MoO6 microspheres were modified by loading AgI nanoparticles on the surface through a facile deposition-precipitation method at room temperature and atmosphere pressure. The crystal structure, composition, morphology and optical properties of the as-prepared samples were characterized by several techniques(XRD, SEM, TEM, BET and DRS). The influence of the mass ratio of AgI in the composite and different preparation method on the photocatalytic performance was investigated. Finally, the photocatalytic mechanism of AgI/Bi2MoO6 heterostructure was proposed.Experiment results above reveal that the photocatalytic activity of semiconductor photocatalysts can be enhanced by regulating the morphology of materials and forming the heterojunction with another semiconductor, which is due to not only the improvement in light-harvesting property of semiconductors and surface area but also the effective inhibition to recombination of photogenerated charge carriers. The as-prepared photocatalysts in this thesis are promising for the practical purification in wastewater. The prepared strategies of hierarchical Bi2MoO6 and AgI/Bi2MoO6 heterostructure photocatalysts are expected to be extended to synthesize hierarchical 3D structure of nanomaterials and construct heterostructure photocatalysts.