Preparation And Performance Of Bismuth Tungstate Based Photocatalyst

Photocatalytic degradation technology has become the main means of wastewater treatment because of its simple process,eco-friendly,economic and high degradation rate.Among many semiconductor photocatalytic materials,Bi₂WO₆ has attracted extensive attention in recent years due to its good visible light response,high stability,strong oxidation ability,non-toxic and harmless and low preparation cost.However,the high efficiency of photogenerated carrier separation and low visible light utilization still can not meet the increasingly demanding needs of wastewater treatment.In this thesis,the hydrothermal process parameters of Bi₂WO₆ material with better photocatalytic performance were obtained by changing different reaction conditions by simple hydrothermal method.On this basis,it was modified by doping solid solution and semiconductor composite.The specific research work is as follows:（1）Study on controllable synthesis process parameters of Bi₂WO₆ microspheres.The effects of hydrothermal time,precursor concentration ratio,solution p H and surfactant on the structure,morphology and photocatalytic activity of the product were investigated.The test results show that Bi₂WO₆ microspheres prepared under the conditions of hydrothermal heating at 180℃for 12h,Bi/W=2:1,p H=0.1 and no active agent have relatively good photocatalytic activity.The degradation rate of 50 ml Rh B aqueous solution with concentration of 20 mg/L in 80 min is 94.6%,which lays a foundation for the modification work in the next two chapters.（2）Mo doping replaces w to form molybdenum tungsten solid solution.The photocatalytic activity of Bi₂WO₆ material is improved by introducing appropriate defect sites and reducing band gap.Bi₂Mo_xW_1-xO₆（x=0,0.05,0.25,0.50,0.75,0.95,1）solid solution was synthesized by one-step hydrothermal method.The experimental results show that with the increase of Mo doping,the photocatalytic efficiency increases first and then decreases,and when x=0.25,the degradation rate of sample material is the highest,and the degradation rate of Rh B aqueous solution can reach about 96.7%in 60 min,which is about 26.3%higher than that of pure Bi₂WO₆.The improvement of photocatalytic activity caused by x=0.25 Mo ion solution can be attributed to two reasons:on the one hand,appropriate defect sites are introduced into the Bi₂WO₆ lattice to effectively separate photocarriers;On the other hand,the band gap is reduced by 0.30 e V and the response range of visible light is broadened.（3）Bi₂WO₆/Bi OCl heterostructure was constructed to further improve the photocatalytic activity by broadening the light response range of the material and improving the separation efficiency of photogenerated carriers.Bi₂WO₆ nanostructures were grown on Bi OCl lamellar structures by a new one-step hydrothermal method.The experimental results show that with the increase of NH₄Cl concentration,the photocatalytic efficiency of the composite first increases and then decreases,and the degradation rate of Bi₂WO₆/Bi OCl-3 composite is the highest.It can nearly completely degrade Rh B aqueous solution in 30 minutes,which is about 116.1%higher than that of pure Bi₂WO₆.The improvement of photocatalytic activity can be attributed to the effective separation of photogenerated carriers in space due to the difference of energy band structure after Bi₂WO₆ and Bi OCl form composites;On the other hand,Bi₂WO₆ has high visible light utilization,and the photogenerated holes of Bi OCl have stronger oxidation ability.The synergistic effect of the two materials promotes the catalytic reaction.