First-principles Calculation,preparation And Performance Study Of SnO₂-based Photocatalytic Materials

In recent years,photocatalysis technology has attracted great attention because of its application in the degradation of organic pollutants and the preparation of chemical energy sources such as H₂,CH₄,and so on,which can effectively solve the two major global problems of environmental pollution and energy crisis.The light absorption efficiency and the separation efficiency of photogenerated electrons and holes are the key factors limiting the photocatalytic efficiency.At present,the common method for improving the light absorption efficiency is to adjust the band gap width of the semiconductor material through defect introduction,and the common method for improving the efficiency of the separation of photogenerated electron holes is to construct a semiconductor heterostructure.The modification of these two methods can effectively improve the photocatalytic efficiency of semiconductor materials.This paper takes SnO₂-based photocatalytic materials as the research object,and explores the two methods of doping and constructing heterojunction to improve the photocatalytic efficiency of SnO₂.The contents are as follows:Through the first-principles calculation,the effect of different oxygen vacancies and Zn²⁺ doping concentration on the energy band structure and light absorption properties of SnO₂ semiconductor was investigated.The analysis of the energy band structure shows that the electrons on the 5s and 5p orbits of Sn form the conduction band of the SnO₂ semiconductor,and the electron movements of the 2s and 2p orbits of O constitute the valence band in the semiconductor.In SnO₂ crystals with different concentrations of oxygen vacancies,as the proportion of oxygen vacancies increases,the valence band moves upward,the conduction band position moves downward,the band gap is significantly narrowed,the absorption in the visible light region is enhanced,and the curve is red-shifted.The results of simulating different concentrations of Zn²⁺ doped SnO₂ crystals show that with the increase of Zn²⁺ concentration,the valence band region between-10 e V?0e V moves upward,and the conduction band moves downward.The 6.25% Zn²⁺ doped amount has the best absorption performance.SnO₂/ZIF-8 was constructed by three different methods: hydrothermal,solvothermal,and reflux,and SnO₂/ZIF-8 prepared by solvothermal method was used as a precursor to calcinate SnO₂/ZIF-NC heterostructure,and SnO₂ was studied./ZIF-NC heterostructure photocatalytic performance.In the hydrothermal system,compared with SnO₂/ZIF-8 precursor prepared by adding SnO₂ to ZIF-8 growth system,the morphology of SnO₂ prepared by adding ZIF-8 to SnO₂ growth system is more uniform,but the petal-like structure The thickness can reach 173 nm.In the reflux system,the Sn-EG diffraction peak prepared at 195 ? is sharper.Compared with the combination of Sn C2O4 and ZIF-8 at room temperature or at low temperature,the combination of the two is tight and the distribution is more uniform.In the solvothermal system,the thickness of the prepared SnO₂/ZIF-8 precursor petal-like structure is about 50-60 nm,and EDS shows that it contains Sn,Zn,C,N,O elements.Using SnO₂/ZIF-8 prepared by solvothermal as a precursor,the SnO₂/ZIF-NC heterostructure was calcined in an inert atmosphere.The photocatalytic performance test showed that when the molar ratio of SnO₂ and ZIF-8 was 1:1,the alkali concentration When it is 0.2 M/L,the photocatalytic performance is the best,and the degradation rate of methylene blue can reach 84%.And the photocatalytic performance is affected by the alkali concentration and the ratio of SnO₂ to ZIF-8.The lower the alkali concentration and the ratio of ZIF-8,the higher the photocatalytic efficiency.