Research On Synthesis And Properties Of Novel Semiconductor Photocatalysts

In recent years,the problem of energy shortage and environmental deterioration has become increasingly severe.In order to solve these two issues,solar energy,owing to green,infinite,safe and other favorable characteristics has gradually attracted the attention of researchers.The new photocatalyst can make full use of solar energy and convert light energy into chemical energy.It can be used in the degradation of pollutants,sterilization,CO₂ reduction and hydrogen production.It has the merits of high efficiency,no secondary pollution and high reuse rate.In the early stage of the development of photocatalysis technology,titanium dioxide is the most representative photocatalyst,but its wide band gap determines its narrow range of light response and low absorption efficiency to solar energy.Therefore,researchers are constantly looking for photocatalysts with a wide range of light response,which can respond to visible light.At present,bismuth-based materials and graphite-like carbon nitride have become one of the most promising photocatalysts,which have narrower band gap and can absorb visible light.However,the single photocatalyst still has some shortcomings,such as low light absorption efficiency,easy recombination of photogenerated electrons and holes,small specific surface area and so on,which would have negative effect on its photocatalytic activity.Therefore,bismuth tungstate?Bi₂WO₆?and graphite-like carbon nitride?g-C₃N₄?are selected as the research objects in this paper.In view of their own disadvantages,rare earth elements ions are doped,precious metals are deposited,and heterostructures are constructed to improve photocatalytic activity.The specific contents of this paper are as follows:?1?Bi₂WO₆:Yb³⁺,Er³⁺photocatalysts were prepared by hydrothermal method,and Bi₂WO₆:Yb³⁺,Er³⁺photocatalysts deposited by Ag were prepared by solvothermal method.XRD,SEM,EDS,XPS,UV-vis and PL were used to analyze the morphology,composition,structure,luminescent properties and chemical valence of the samples.The liquid-phase photocatalytic experiments were carried out to degrade methylene blue under visible light.It is concluded that when the deposition ratio of Ag is 1.5 mol%,the degradation efficiency of photocatalyst is the highest and85.2%.The photocatalytic activity of Ag-deposited Bi₂WO₆:Yb³⁺,Er³⁺photocatalysts was also proved by photocatalytic experiments under 980 nm near infrared light.Finally,the mechanism of improving photocatalytic activity was analyzed.The doping of Yb³⁺,Er³⁺rare earth ions could make Bi₂WO₆ have near infrared photocatalytic activity.The reason why the photocatalytic efficiency is enhanced by the modification of Ag deposition is that under the action of Schottky barrier,photogenerated electrons migrate from Bi₂WO₆ surface to Ag,while photogenerated holes remain on Bi₂WO₆ surface.The recombination probability of photogenerated electron-hole pairs is greatly reduced and the photocatalytic activity is improved.?2?Melamine was treated with acetic acid to prepare porous g-C₃N₄.Then Bi₂MoO₆/g-C₃N₄ composite photocatalyst was prepared by hydrothermal method combined with porous g-C₃N₄.By XRD,SEM,EDS,XPS,UV-vis,PL and nitrogen adsorption-desorption tests,the morphology,composition,structure,chemical valence,specific surface area and pore size distribution of the samples were analyzed,and the liquid phase photocatalysis of methylene blue was carried out under visible light.Then it was concluded that when the ratio of Bi₂MoO₆ to porous g-C₃N₄ was17.5wt%,the photocatalyst had the highest degradation efficiency and reached 91.8%at 25 min.Finally,the mechanism of improving photocatalytic activity is analyzed.The porous structure can effectively increase the specific surface area and make the catalyst fully contact with pollutants,thus improving the catalytic efficiency.Heterostructure can migrate photogenerated electrons of g-C₃N₄ to Bi₂MoO₆conduction band,and the hole of Bi₂MoO₆ will migrate to the valence band of g-C₃N₄,so that photogenerated electron-hole pairs can be effectively separated and not easily recombined,and the catalytic activity can be improved.