Study On Preparation And Photocatalytic Performance Of Bi₂WO₆ Based Composite Materials

Bismuth tungstate（Bi₂WO₆）,as a new semiconductor material with narrow band gap,excellent stability and photocatalytic activity,has broad application prospects in the fields of antibacterial,environmental management and new energy.However,Bi₂WO₆ also has shortcomings such as narrow photoresponse range and easy recombination of photogenerated charges,which greatly limits its photocatalytic activity.Therefore,in order to improve the photocatalytic efficiency of Bi₂WO₆,Bi₂WO₆,Ag/Bi₂WO₆and TiO₂/Bi₂WO₆ composite materials were prepared in this paper by morphology control,surface precious metal deposition and semiconductor compounding methods.The effects of different reaction conditions on the material structure,morphology,optical properties and catalytic performance were studied.The main research contents are as follows:1.Bi₂WO₆ photocatalytic materials were prepared by hydrothermal synthesis method with Bi（NO₃）₃·5H₂O and Na₂WO₄·2H₂O as raw materials without any surfactant.The effects of different mineralizers and reaction temperatures on the structure,morphology,optical properties and photocatalytic properties of the materials were studied,and the growth mechanism and photocatalytic degradation mechanism of Bi₂WO₆ were analyzed.The experimental results show that nanoparticles,nanosheet and flower-shaped microspheres Bi₂WO₆ can be obtained by changing the types of mineralizers.Among them,the flower-like microspheres Bi₂WO₆ obtained by using water as a mineralizer showed good photocatalytic activity.The degradation rate of Rh B solution reached 89.9%after being irradiated with visible light for 120 min.And after five cycles of experiments,the degradation rate can still reach more than 70%,and its phase structure has no obvious change,indicating that the material has high cycle stability.By changing the reaction temperature,it is found that the photocatalytic performance of Bi₂WO₆ increases first and then decreases with the increase of temperature,Bi₂WO₆ prepared at 180℃has better performance.In the free radical capture experiment,it was found that holes（h⁺）and superoxide radicals（·O₂^-）were the main active groups in the photocatalytic reaction,and the photocatalytic mechanism of Bi₂WO₆ degradation of organic pollutants was analyzed.2.Ag/Bi₂WO₆ composites were prepared by photoreduction method,the effects of changing the mass ratio of Ag NO₃/Bi₂WO₆ on the structure,morphology and photocatalytic performance were studied.The photocatalytic mechanism was also analyzed.The results show that the presence of Ag improves the light absorption capacity of the photocatalyst and inhibits the recombination of photogenerated electrons and holes.Therefore,Ag/Bi₂WO₆ composites prepared with different Ag NO₃/Bi₂WO₆ mass ratios exhibit better photocatalytic performance than Bi₂WO₆.Among them,when the mass ratio of Ag NO₃/Bi₂WO₆ is 4%,Ag/Bi₂WO₆ has high photocatalytic activity,the degradation rate of Rh B can reach 99.2%after 120 min of visible light irradiation.And after five cycles of experiments,the degradation rate of Rh B can still reach more than 90%.3.TiO₂/Bi₂WO₆ composites were prepared by in-situ hydrothermal synthesis,furthermore,TiO₂/Bi₂WO₆/ACF composite was prepared by using PDA as adhesive and ACF as carrier.The effects of different TiO₂ content on the structure,morphology and properties of TiO₂/Bi₂WO₆ were studied.Meanwhile,the degradation effect of TiO₂/Bi₂WO₆/ACF on gaseous benzene series was investigated.The results show that when the content of TiO₂ is 1 mmol,the TiO₂/Bi₂WO₆ composite shows better photocatalytic performance,and the degradation rate of Rh B can reach 98.4%under120 min visible light irradiation.It was found that the degradation efficiency of benzene series by TiO₂/Bi₂WO₆/ACF composites increased firstly and then decreased with the increase of TiO₂/Bi₂WO₆content.The better degradation performance of benzene series was obtained when the content of TiO₂/Bi₂WO₆ is 0.2 g,the degradation rates of toluene,ethylbenzene and xylene reached 35.1%,51%and 47.5%after 6 h of visible light irradiation,respectively.