Synthesis And Photocatalytic Properties Of Bi₂WO₆ Composite Material

Bismuth tungstate(Bi2WO6)as the simplest sample Aurivillius type oxide,its special perovskite lamellar structure,good stability and photocatalytic activity of widespread concern.However,Bi2WO6 still has some flaws:photogenerated electron-hole pairs of high probability of recombination,the degradation of the lower selectivity,and the separation of catalytic systems difficult.In this paper,Bi2WO6 photocatalytic materials were modified on these problems.The major work includes the following aspects:(1)The Bi2WO6 were prepared by a hydrothermal method with bismuth nitrate pentahydrate(Bi(NO3)3·5H20)and sodium tungstate dihydrate(Na2WO4·2H20)were used as the Bi and W sources and water as the reaction media.The effect of the pH of the reaction solution on the activity and structure of Bi2WO6 photocatalyst was studied by a single factor method,and the optimum preparation conditions of Bi2WO6 photocatalyst were determined.The crystalline structures,morphologies and optical properties of the photocatalysts are characterized by XRD,SEM,UV-Vis DRS and so on.The photocatalytic activity of the as-prepared sample was evaluated by degradation of Rhodamine B(4mg/L RhB),Tartrate tylosin solution(10mg/L TYL)under visible light irradiation.The results show that the optimal conditions for preparation Bi2WO6 are as follows:value of pH is 9,reaction time is 20h and reaction temperature is 160 ?.When the reaction time of photocatalysis is 80min,dosage of Bi2WO6 is 0.04g,the degradation rate of RhB and TYL can reach above 90%.(2)In order to solve the problem of low photocatalytic activity of Bi2WO6 photocatalyst.BiOCl/Bi2W06 composite photocatalyst was synthesized by hydrothermal-solvothermal method on the basis of Bi2WO6.The effect of different BiOCl complexes on the photocatalytic activity of BiOCl/Bi2W06 composite photocatalyst was studied.The result shows that the degradation rate reached 98%of RhB after irradiation for 20min when the mass fraction of BiOCl is 15 percent in composite photocatalyst,after the composite photocatalys were used 4 times,the degradation rate of RhB change is not obvious,can still be reached 95%.And the degradation rate reached 99%of TYL after irradiation for 40 min.Compared with the pure Bi2WO6 photocatalyst,the light absorption capacity of 15%BiOCl/Bi2WO6 composite photocatalyst is enhanced,the band gap decreases,the PL emission peak intensity decreases,and the specific surface area is increased by 400%.(3)In order to solve the problem that the photocatalyst is not selective for degradation.The molecule imprinted photocatalysts(MIP-BiOCl/Bi2WO6)are prepared by surface polymerization method with tylosin solution as template molecule,BiOCl/Bi2WO6 as carrier,methacrylic acid as functional monomer,ethylene glycol dimethyl acrylic ester as cross-linking agent,and a series of characterization and catalytic properties of samples are studied.The experimental results show that the degradation rate of MIP-BiOCl/Bi2WO6 photocatalyst to TYL and RhB solution were 90%and 17.2%at 60min in single solution,while BiOCl/Bi2WO6 photocatalyst was in 20min,the degradation rate of RhB and the degradation rate of TYL were 100%at 40min.In the mixed TYL and RhB,the degradation rate of TYL was more than 90%in 60min,but the degradation rate of RhB was only 20.1%in 60min.The BiOCl/Bi2WO6 photocatalyst was in the range of the degradation rate of TYL was more than 92%at 60min,and the degradation rate of RhB was 100%.The experimental results show that the MIP-BiOCl/Bi2WO6 photocatalyst has the ability of preferential degradation of the template molecule tylosin.(4)In order to solve the problem of low photocatalytic activity of Bi2WO6 photocatalyst.In this paper,we also try to improve the photocatalytic activity of Bi2WO6 photocatalyst by using rare earth ion doping.On the basis of Bi2WO6,La/Bi2WO6 photocatalyst was synthesized by hydrothermal method.The experimental results show that the lattice parameter d(hkl)of La3+ modified Bi2WO6 will increase the value of 2?,the band gap of La/Bi2WO6 photocatalyst will increase,the PL emission peak will decrease,the specific surface area increased by 550%.The photocatalytic activity of La/Bi2WO6 photocatalyst with 5%doping content is the best,and the degradation rate of rhodamine B is 98%at 25min.Under the visible light,the degradation rate of RhB and TYL were degraded,and the degradation rate of RhB was still up to 97%after 3 times of recycling.(5)Photocatalysts is still limited mainly due to difficult separation from treated water and the low reused rate.In order to solve the problem,the La/Bi2WO6 and the magnetic y-Fe2O3 can be used to prepare the magnetic y-Fe2O3/La/Bi2WO6 composite photocatalyst,and it can be easily separated from the reaction by external magnetic field.The magnetic photocatalyst particles are separated and recovered easily by using magnetic separation.The saturation magnetization of 5%y-Fe2O3/La/Bi2WO6 is 8.19emu·g-1 by VSM analysis and external magnetic field separation experiment.The composite photocatalyst can be separated from the solution by external magnetic field separation of the purpose of recovery.The photocatalytic activity of 5%?-Fe2O3/La/Bi2WO6 photocatalyst was the best,and the degradation rate of RhB was 98.6%at 70min.Under the visible light,the degradation rate of RhB and antibiotic TYL were degraded,and the degradation rate of RhB was 95.3%after 3 times of recycling.