Preparation And Photocatalytic Performance Of Sn₃O₄ Based Photocatalytic Materials

As a common chemical raw material,hexavalent chromium（Cr（VI））has a wide range of applications in industrial production.However,the problem of excessive Cr（VI）in industrial wastewater has attracted widespread attention at home and abroad.Since the 21st century,the photocatalytic technology with sunlight as the driving force has been widely studied and used to treat heavy metals such as Cr（VI）in water due to its many advantages such as environmental protection,high efficiency and energy saving.Tin tetroxide（Sn₃O₄）is a new type of photocatalytic material with visible light response,which has attracted wide attention due to its unique physical and chemical properties.However,the quantum efficiency of a single Sn₃O₄ semiconductor photocatalyst is low,and the photocatalytic activity cannot meet the actual demand.In order to improve the catalytic performance of a single Sn₃O₄ photocatalyst,this paper proposes to construct a binary heterojunction,support precious metals and construct heterojunction-doping These three methods of metal ions modify Sn₃O₄ to increase the specific surface area of the catalyst,improve the utilization efficiency of photogenerated carriers,and then improve the performance of Sn₃O₄for photocatalytic reduction of heavy metal Cr（VI）.The main research contents are as follows:1.A series of y wt%Zn O/Sn₃O₄（y=10,15,20,25,30）heterostructure composite photocatalysts were prepared by a two-step hydrothermal method.The effects of composite Zn O with different contents on the physical structure and photocatalytic performance of Sn₃O₄ were investigated.It was found that a heterojunction was formed between the introduced Zn O and Sn₃O₄interface,which not only significantly increased the specific surface area of the catalyst,but also effectively reduced the recombination probability of photogenerated electrons（e^-）and holes（h⁺）,and improved e^-and h⁺Utilization efficiency.When the composite content of Zn O was 20%,the catalyst showed the best performance.The removal rate of Cr（VI）by 20 wt%Zn O/Sn₃O₄ reached94%,which was 36%and 68%higher than that of pure Sn₃O₄ and pure Zn O samples,respectively.2.A series of composite photocatalysts m%Ag-Sn₃O₄ deposited with noble metals were prepared by photodeposition method（m=1,2,3,4,5,m is the mass ratio of Ag to Sn₃O₄）.Depositing Ag nanoparticles could not only effectively increase the specific surface area of the Sn₃O₄ catalyst,but also could be used as a conductive medium to form a close contact interface with Sn₃O₄,which could quickly and effectively transfer the photogenerated electrons generated on the Sn₃O₄ conduction band,and improved the separation efficiency of e^-and h⁺.Therefore,the Ag-Sn₃O₄ photocatalyst exhibitd excellent performance in the reduction of heavy metal Cr（VI）.Among them,the removal rate of Cr（VI）for the 3%Ag-Sn₃O₄ sample was 35.8%higher than that of the pure Sn₃O₄ sample.3.A series of SnO₂/x%Ti-Sn₃O₄（x=0.3,0.5,0.7,0.9,x is the molar ratio of Ti to Sn）photocatalyst was prepared by one-step hydrothermal method.It was found that after the introduction of Ti⁴⁺,a composite photocatalyst of Sn O₂/Ti-Sn₃O₄,a heterojunction-ion doping interaction,would be formed.In this catalyst,Sn O₂ covered the surface of Sn₃O₄ and formed a heterojunction with it,while Ti⁴⁺entered the Sn₃O₄ lattice to form substitute doping.The doping of Ti⁴⁺and the formation of Sn O₂/Ti-Sn₃O₄ heterojunction together could not only increase the specific surface area of the catalyst,but also expand the light absorption range and effectively improve the separation efficiency of e^-and h⁺,thereby increasing the carrier usage efficiency.The Sn O₂/Ti-Sn₃O₄ catalyst not only exhibited excellent photocatalytic activity in the reduction of Cr（VI）,but also exhibited significant photocatalytic activity in the degradation of azo dyes such as methyl orange（MO）and acid orange II（AO-II）.Among them,the removal rate of Cr（VI）for Sn O₂/0.5%Ti-Sn₃O₄ sample was 40%higher than that of pure Sn₃O₄ sample.The above studies indicated that heterostructure building,precious metal deposition and heterostructure building-metal ion doping are effective means to improve the performance of Sn₃O₄ photocatalysts,which can effectively improve the quantum efficiency of Sn₃O₄.