Preparation And Performance Study On Bismuth Tungstate Semiconductor Photocatalytic Materiats

With the more dramatical excavation of natural resources,severe ecological pressure,environmental pollution,energy crisis have such restriction on the progress of human society that novel solutions with low energy cost to natural resources pressure are urgently demanded.Compared with conventional pyrolysis,catalytic technique and adsorption technology,semiconductor photocatalysis is a green pollution treatment technology which is highly effective and energy saving.Due to its avirulence,low cost and photocatalytic efficiency,monolayer Bi₂WO₆ has received considerable research attention among various photocatalysis.The forbidden band of monolayer Bi₂WO₆ is 2.7e V and since monolayer Bi₂WO₆ has the special sandwich structure,i.e.,[Bi O]+–[WO4]2-–[Bi O]+,when monolayer Bi₂WO₆ receives direct light,its surface will generate cavity and middleware will generate light-generated electron,and thus monolayer Bi₂WO₆ has very high charge separation rate surface and active surface.We in this dissertation propose two approaches to further enhance its photocatalysis performance.First,based on the resonance effect Ag plasma,Ag nanoparticles are attached on the surface of monolayer Bi₂WO₆,resulting in composite monolayer Bi₂WO₆/Ag.Second,on the surface of monolayer Bi₂WO₆,we attempt to attach Ag Br nanoparticles with forbidden band 2.6e V and grain diameter about 10 nm,and thus achieve a new P-N type monolayer Bi₂WO₆/Ag Br composite photocatalyst.These two new materials are capable to accelerate the separation of light-generated electron and cavity,can suppress the composite of photon-generated carriers,and thus significantly improve the photocatalysis performance.In this dissertation,we establish comprehensive study on the composite materials,i.e.,monolayer Bi₂WO₆/Ag and monolayer Bi₂WO₆/Ag Br,including the mechanism of improving photocatalytic performance and potential solutions.First,we use monolayer Bi₂WO₆ nano-materiel as precursor,on which Ag nanoparticles are attached using three different reduction methods.Second,we adopt sedimentation-deposit method to attach Ag Br to monolayer Bi₂WO₆.Once these two nano-materials are composited,we further perform representation analysis,including the study on crystal texture,microscopic appearance and composition,microstructure,spectral absorption properties and photocatalytic properties.The analysis is performed from two perspectives.First,as for the composition of Bi₂WO₆/Ag,we observe that Glycol reduction is superior to the other two approaches,and can guarantee better photocatalytic performance of the composite materials.We also discuss the effects of ultrasonic power,ultrasonic time and Ag content,and observe that the best composite materials Bi₂WO₆/60wt%Ag can be achieved with the configuration 90% ultrasonic power,30 min ultrasonic time and 60% Ag in Bi₂WO₆ measured by mass fraction.We use 500 W xenon lamp to imitate sunlight.With 2h exposure,the best photocatalytic performance can be achieved,in which degradation rate to Rh B is up to 97.4%,and after 6 recurrent performance test its value is further up to 62.2%.Besides,the composite material can be recycled.Second,as for the monolayer Bi₂WO₆/Ag Br,we study the effects of water volume,mixing time,reaction temperature and the content of Ag Br in the Reaction system.Experimental results show that the configuration with water volume 45 m L,reaction temperature 27℃,3h mixing time,30% Ag Br in Bi₂WO₆ can produce the best composite Bi₂WO₆/30wt%Ag Br,whose degradation rate to Rh B is up to 98.7% after 2h exposure using 500 W xenon lamp,and after 5 recurrent performance test is 80.8%.This dissertation comprehensively reveals the key effects to photoelectric conversion performance including the size of the composite photocatalytic material,energy band structure etc,drives the real applications of bismuth tungsten acid semiconductor photocatalyst,and thus provides novel and effective solutions to solve energy and environmental issues.