Modification And Performance Of Layered Nano Materials （Zn Al-LDH、BiOBr、g-C₃N₄） Photocatalysts

Recently, photocatalytic technology has become the research upsurge because of its ability to convert the solar energy into chemical energy. This might provide a good solution for handling the urgent environmental pollution and energy crisis issues on the earth. However, several key issues still need to be solved in the field of photocatalysis. First, taking TiO2 as an example, its visible light response and utilization rate of solar light were relatively low. Second, the rapid recombination of photoinduced electrons and holes leads to the decrease of quantum yield. Third, semiconductor photocatalytic materials are always in the form of powder, they always sink or suspend into the solution. Therefore, it is difficult for us to recycle these power materials. These problems have hindered the large-scale application of photocatalytic technology in industry. Because of their unique layered structure, controllable and special characteristics of electron transport, layered materials have widely used in the fields of electromagnetic and catalysis. In this dissertation, we adopted and modified three kinds of layer materials（ZnAl-LDH, BiOBr and g-C₃N₄） to solve the above problems. The specific work is as follows:Firstly, ZnAl-LDH coated BiVO4 hollow microsphere composite photocatalysts were synthesized by a simple coprecipitation method. X-ray diffraction, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the components and morphologies of the as-prepared samples. With the increase of the content of BiVO4, a slightly red-shift for absorption band was happened. However, the photocatalytic activity was first increased and then decreased. The results show that ZB12 composite, which was prepared when the Zn2+/Bi3+ molar ratio is 1/2, possessed the highest photocatalytic activity for the degradation of malachite green（MG）. The enhanced photocatalytic activity of the composite was mainly attributed to the formation of heterostructure between ZnAl-LDH and BiVO4, which will reduce recombination rate of photoinduced electrons and holes during the degradation process. Hydroxyl radical and holes were the major active species. Besides, the high stability and reusability indicate that ZB12 is a kind of promising material for water purification.Secondly, the floatable composites of expanded perlite（EP） and bromine bismuth oxide（BiOBr） were synthesized by a facile solvothermal method and characterized. BiOBr flower-like microspheres were immobilized on the surface of the EP. When the amount of initial bismuth nitrate material is 3 mmol, perlite granule reach its maximum loading capacity. After 8 days floating test, the amount of still floating materials is 42 wt% for EP-BiOBr-3. The photocatalytic activity of the obtained materials were determined using a model reaction of the degradation of 4-NP and RhB. The ability of the obtained photocatalysts to float, combined with their ability to absorb solar light and recycle stability, make it particularly well suited for the purification of shallow water reservoirs and industrial waste stabilization ponds.Thirdly, floating metal-free photocatalysts based on g-C₃N₄ grafted expanded perlite（EP） were prepared by pyrolysis melamine in the presence of expanded perlite granules at different temperatures（450-580 °C）, and characterized. The XRD, SEM and FT-IR analyses showed that g-C₃N₄/EP composites were successfully prepared and the polymerization degree of g-C₃N₄ for the prepared samples increases with pyrolysis temperature to a maximum at 520 °C, and then decreases, which was further confirmed by the XPS characterization. According to the results of PL spectra and photocatalytic performance, g-C₃N₄ prepared at 520 °C possessed an optimal defect concentration. Moreover, a higher surface area, good absorption in the visible light region and the highest photocatalytic activity were obtained for g-C₃N₄/EP calcined at 520 °C. This indicates that the material can be a promising photocatalyst for the remediation of contaminated waters using solar irradiation.