Study On The Modification Of ZnWO₄ Nano-photocatalytic Material And Its Photocatalytic Performance

Zinc tungstate(ZnWO4),a n-type direct semiconductor,composed by[ZnO6]and[WO6]of stratified structures,which belongs to monoclinic wolframite structure.These stratified structures could produce the built-in electric field,which lead to the separation of photo-generates electrons holes pairs.The particular layer structure also cause the excellent photocatalytic activity.In this paper,we use Zn(Ac)2·2H2O and Na2WO4·2H2O as raw material to synthesize pure ZnWO4.The ZnWO4,doped/loaded with Pd and Bi elements,are synthesized by solvothermal method and chemical reduction method.And the heterojunction of BiOI/ZnWO4 is prepared by chemical deposition method.In order to explore the photocatalytic activity of photocatalysts,we use simulated sun light and visible light as illuminant to remove NOx.Main tasks as follows:(1)Semiconductor photocatalyst of Pd0/Pd2+/ZnWO4(Pd/ZPWO)is prepared by hydrothermal method combined with the chemical deposition method.The Pd2+/ZnWO4(ZPWO)is prepared by hydrothermal method.Among the various ion concentrations,0.5 mol%Pd2+ions has the highest activity.The removal rate for NO up to 50.79%after xenon lamp irradiation.Upon the 0.5%mol Pd2+/ZnWO4(ZPWO),the Pd0 nanoparticles with varied concentration had been deposited by chemical reduction method.The sample of Pd/ZWO and Pd/ZPWO is prepared by raw material K2PdCl6.And the Pd/ZWO with 1.5%mol Pd0 nanoparticles shows the best photocatalytic activity.The removal rate of NO up to 52.69%and 55.02%for Pd/ZWO and Pd/ZPWO with suitable proportion.Furthermore,the surface plasmon resonance,caused by Pd0 nanoparticles,lets the composite samples exhibit activities under visible light.Samples show high stability after four cycles.And the composed samples which are modified by Pd2+ions and Pd0 nanoparticles have better stability.(2)Low-cost metal of Bi could also exhibit the SPR effect.Firstly,The sample of Bi3+/ZnWO4(ZBWO)is prepared by hydrothermal method.And then,the Bi0particles are deposited on ZWO and ZBWO to form the Bi/ZnWO4(Bi/ZWO)and the Bi/ZBWO Bi element comes from the Bi(NO3)3 5H2O.The photocatalytic activity of Bi/ZWO and Bi/ZBWO is higher than pure ZnWO4(ZWO).Under simulated sunlight irradiation,the removal rate of NO from Bi/ZBWO up to 55.29%after 30 minutes.Under visible light,all composite samples exhibit photocatalytic activity during 30 minutes.Among them,the Bi/ZBWO shows the best photocatalytic performance,which removal rate of NO up to 11.7%.After five cycles,Bi/ZBWO shows excellent stability,which removal rate of NO still exceed 50%.(3)Pure ZnWO4 combine with BiOI(BOI)by facile chemical bath method to form p-n junction.Various methods are introduced to explore the characters of photocatalysts,such as XRD,SEM,TEM and UV-vis.The results indicate that the ZnWO4 maintains nanorods,and the BOI is nanosheet.Composite samples improve the photocatalytic activity obviously under visible light.Composite samples show the best photocatalytic activity when the concentration of BOI up to 20 mol%,which removal rate of NO up to 48.24%and 32.32%under simulated sunlight and visible light irradiation,respectively.After five cycle experiments,20 mol%BOI/ZnWO4 exhibits a certain inactivation,while the NO removal rate still stay at 40%.