Study On Synthesis And Photocatalytic Activity Of Bismuth Oxysalts

Bismuth oxysalt is one kind of inorganic salt which is made up of metal Bi3+ and oxyacid root(most belonging to homopolymolybdate radical), and its composition, phase and morphological structure are changable. Bismuth oxysalt is widely applied in the field of photocatalyst based on its special semiconductor characteristics and good optical response performance due to its unique electron configuration and layered crystal structure. The composition, structure and morphology of bismuth oxysalt and its related photocatalytic properties are greatly influenced by the preparation methods and reaction conditions. Therefore, it is important to study the controllable preparation and morphology regulation of bismuth oxysalt. In this thesis, a series of different bismuth oxysalt compounds with controllable morphology have been prepared by controlling reaction conditions in liquid phase with the aid of soft template according to the structure-activity relationship of bismuth oxysalt. The photocatalysis and degradation property of these compounds have also been evaluated for different organic compound-containing solution. The main research content is as follows:1. A series of γ-Bi2 Mo O6 micro-crystals were synthesized by using surfactant assistance via hydrothermal route. The change of phase and composition of asprepared products impacted by the varied solution p H values and different surfactants was investigated. The visible light catalytic activities of the γ-Bi2 Mo O6 powders were evaluated by means of the catalytic degradation of Rhodamine B aqueous solution, and the degradation effects under different reaction conditions were determined in detail. The results show that when the reactant mole ratio of Bi to Mo is set at 2:1 and the p H value of reaction solution is kept in the range from 3 to 9, the resulting products should be pure orthorhombic γ-Bi2 Mo O6 whether the surfactants are added or not. With the p H value set at 9, the as-obtained γ-Bi2 Mo O6 samples exhibit higher catalytic activity than that in other conditions, leading to 79.62% degradation rate within 3h through visible-light irradiation. The sample obtained with assistance of SDS shows best photocatalytic activity which gives highest Rhodamine B degradation rate of 98.81%. Through the range analysis for the experimental results, the primary and secondary relationship for the related factors and their optimization configuration have been judged and proposed.2. Different kinds of Bi OBr crystal micropowders with different morphological structure have been synthesized via an ethylene glycol solvothermal and hydrothermal route using the methylimidazole bromide reaction type ionic liquid [Cnmim]Br and CTAB as bromo source and soft template. The characterization results with x-ray diffraction(XRD), scanning electron microscopy(SEM) and Brunauer-Emmett-Teller(BET) measurement show that the as-prepared Bi OBr products all belong to tetragonal phase and have high purity. The Bi OBr crystals along(110) lattice plane preferentially grow with the increase of carbon atom number of substituent group in ionic liquid cation. The micro sized Bi OBr particles cluster together to form nanosized petal-like flakes via self-assembly, which shows the radial pattern from spherical center. With the increase of Cn number, the particle size and surface pores all decrease, but the specific surface area increases. The three Bi OBr powders possess different catalytic activity for the visible photocatalytic degradation of aniline solution. The degradation ratios of the aniline solution are 54.13%, 78.67% and 95.06% in 280 minutes, respectively, which are higher that of Bi OBr powders prepared by CTAB assistance. The photogenerated holes should be the main active species in the photodegradation process, but the hydroxyl radical just play a smaller role.3. Bi2WO6 uniform hierarchical nest-like structures have been synthesized through an ionic liquid-assisted hydrothermal method in the presence of 1-butyl-3-methyl imidazolium dicyanamide([Bmim]N(CN)2). The phase and morphology was adjusted by changing the amount of ionic liquid. The results show that Bi2WO6 crystals along(200) lattice plane preferentially grow with the ionic liquid. With the increase of ionic liquid [Bmim]N(CN)2, the particle size decreases first, then increases, and the degradation rate of methyl orange increases first, then decreases. Among them, the Bi2WO6 powders prepared by 10% ionic liquid [Bmim]N(CN)2 show excellent photocatalytic degradation characteristics, and the degradation rate of methyl orange can reach to 97.44%.In conclusion, the morphology and phase constitution of the bismuth oxysalts have great influence on the photocatalytic activity under visible light irradiation. The morphology and phase constitution of the products can be easily adjusted through changing reaction conditions, and can improve its degradation ability for pollutants in liquid system. By using different bromine sources and different methods, the bismuth oxysalt photocatalysts with different composition, morphology and phase constitution, show great degradation ability for the organic pollutants in solution system. The research results further enrich the foundation of the relevant theoratical area, and provide a scientific basis for the application of bismuth oxysalt photocatalyst in the fields of wastewater treatment and environmental protection.