Preparation,loading And Photocatalytic Activity Of Bi₂O₃-based Photocatalysts

Based on social development situation,it is important to develop a stable,efficient,low-toxicity photocatalytic material.Based on the appropriate structure and photocatalyst properties of?-Bi₂O₃,the pure?-Bi₂O₃,cerium doped?-Bi₂O₃,zirconium doped?-Bi₂O₃ and silver deposited?-Bi₂O₃ were prepared in this paper.By means of XRD,SEM,TEM,UV-vis DRS and PL,the physical and chemical properties of the prepared samples,such as crystal phase composition,particle size,band gap energy and fluorescence intensity,were characterized.The effects of catalyst crystal type,doping type,doping ratio and deposition modification on the properties of Bi₂O₃-based catalysts were investigated.The loaded catalysts were prepared by electrophoretic deposition process and zein bulk foaming method,and the photocatalyst properties were also compared with the unload catalysts.The needle?-Bi₂O₃ particles with a length of about 30?m were prepared by direct precipitation method with sodium hydroxide as precipitator.The nanometer?-Bi₂O₃ particles were synthesized by base flow and precipitation process with ammonia as precipitator.Using?NH₄?₂Ce?NO₃?₆ and ZrO?NO₃?₂ as the source of cerium and zirconium,the doped Ce/?-Bi₂O₃ and Zr/?-Bi₂O₃ photocatalysts with different molar ratios were prepared by precipitation process,and the particles sizes are about 30 nm and the particle agglomeration were well improved.The effects of different crystal types,the type and proportion of ion doping,the amount of catalyst,the concentration of the substrate and the pH of the solution on the photocatalytic efficiency were investigated.The catalysts were recycled for several times to evaluate the stability and repeatability.The mechanism of photocatalytic reaction was also studied by the scavenger contrast experiment.The photocatalytic degradation mechanism of MO is mainly due to the direct oxidation of light induced vacancies,actually the light induced electrons react with oxygen to form hydroxyl radical,which is the necessary complement for oxidation of MO degradation.The adsorption of photocatalyst is the precursor to cross the photocatalytic reaction barrier,which is helpful to the photocatalytic reaction.Noble metal modification is one of the most effective methods to improve the photocatalytic efficiency of Bi₂O₃ semiconductors.In this study,Ag/?-Bi₂O₃ catalysts with deposited silver mass amount of 1.0wt.%,2.0wt.%and 3.0wt.%were preparedby the in-situ reduction process at room temperature in the presence of?-Bi₂O₃ and AgNO₃ as the starting material.The Ag nano particles are evenly wrapped around?-Bi₂O₃ particles,and are not easily fall off or removed from Bi₂O₃ phases.Compared with pure Bi₂O₃ composite,the band gap energy of Ag/?-Bi₂O₃ composite catalysts was decreased and the photocatalytic performance was improved.It is shown that the deposition of noble metals can be used as electron traps,which can prolong the path of electron hole and improve the photocatalytic performance of Ag/?-Bi₂O₃.In this paper,the loaded Bi₂O₃-based photocatalyst was prepared by the electrophoretic deposition process and zein bulk foaming method.The graphite plates as the electrodes,the dispersed catalyst powders can be loaded on the cathode and formed the bismuth oxide film on the graphite electrode by electrophoretic deposition method.Zein can form a porous foam material by heated at 180?,and the?-Bi₂O₃/zein porous bulk were prepared by dispersing bismuth oxide powder into zein alcohol solutions.The loaded?-Bi₂O₃/zein porous bulk can be repeatedly used and easily recoved during use.The Bi₂O₃-based photocatalyst prepared in this experiment not only has the decolorization effect on methyl orange,acid chrome blue K,but also has catalytic activity for the reduction of p-nitrophenol.