Study On Preparation And Performance Of New Type Tungstate Photocatalyst

In this study,novel tungstate photocatalysts were prepared by sol-gel method.Using quartz microspheres as the carrier,the effects of quartz microspheres addition quantity and calcination temperature on the synthesized composite photocatalytic materials were examined.The experimental conditions for synthesizing ZnWO₄/SiO₂ composites with the optimal photocatalytic activity were established.Low-density composite tungstate photocatalytic materials were prepared using glass bubbles of the S60HS type as carriers,and the effects of different loading amounts of zinc tungstate on the degradation rate of azophloxine were investigated.Ytterbium,a rare earth element,was used as the doping element to investigate the strength of the ytterbium-doped zinc tungstate photocatalysts prepared with different doping concentrations to degrade the dye;meanwhile,the loading modification of ytterbium-doped zinc tungstate was carried out with quartz microspheres as the carrier.The prepared photocatalysts were characterized by XRD,SEM,EDS,FT-IR,BET and BJH to investigate the intrinsic mechanism of catalyst activity enhancement.（1）The loaded photocatalyst ZnWO₄/SiO₂ was prepared by the sol-gel method using quartz microsphere as a carrier.Quartz microspheres were used as a support in the zinc tungstate synthesis route,the crystalline phase of the original crystals was not changed,and the wolframite type of monoclinic crystals was still maintained.SiO₂ could improve the dispersion performance of ZnWO₄ and reduce the grain size of ZnWO4.The specific surface area of the photocatalyst increased after loading,which promoted the photocatalytic activity.When the calcination temperature was 550℃,the 40%ZnWO₄/SiO₂ composite photocatalyst had the optimal photocatalytic activity.After50 min of illumination,the efficiency of 40%ZnWO₄/SiO₂ in degrading azophloxine reached 90.7%.（2）The low density ZnWO₄/S60HS hollow spheres were prepared by loading ZnWO₄ on S60HS glass bubbles using a sol-gel route.After the catalyst was loaded with S60HS glass bubbles,the growth of crystals was inhibited and the cell volume and grain size were reduced.After loading,ZnWO₄ was uniformly dispersed on the surface of S60HS glass bubbles.The N₂ adsorption-desorption isotherms of ZnWO₄/S60HS and ZnWO₄ present the classical type IV isotherm that is subjected to mesoporous material.The degradation experiments of azophloxine showed that the catalyst with low density of 50%ZnWO₄/S60HS was comparable to the photocatalytic activity of ZnWO₄.The composite was well mixed with water under very gentle mixing to take part in the pollution treatment process,and the material floated on the water surface after treatment for the photocatalyst-water separation.（3）Doping modification of ZnWO₄ by elemental ytterbium.The doping does not change the crystalline phase and no impurity phase is generated.The specific surface area and pore volume were increased by doping element ytterbium in the sol.The doping of elemental ytterbium can reduce the complexation of hole-electron pairs and increase the carrier lifetime,which in turn promotes the improvement of photocatalytic activity.The photocatalytic degradation of azophloxine by 2%Yb-ZnWO₄ was 77.4%under 30 min of light;the photocatalytic degradation of the dye by pure ZnWO₄ was 33.8%under the same conditions.（4）Yb-ZnWO₄/SiO₂ composite catalysts were prepared using quartz microspheres as the carrier.The loading of Yb-ZnWO₄ on SiO₂ reduced the crystallite size of Yb-ZnWO₄.The hole-electron recombination efficiency is reduced after supporting the Yb-ZnWO₄ on quartz microspheres The increased production of hydroxyl radicals was related to the enhanced photocatalytic activity of the composites.The maximum activity of the catalysts was achieved when the mass fraction of 2%Yb-ZnWO₄ was 40%.After 40 min of photocatalytic reaction,the degradation rate of azophloxine reached 96.6%.The reaction rate constants for the photocatalytic degradation of azophloxine were 0.0346,0.0669,and 0.0822 min^-1 for the 2%Yb-ZnWO₄,2%Yb-ZnWO₄（20%）/SiO₂,and 2%Yb-ZnWO₄（40%）/SiO₂,respectively.