Study On Interface And Surface Defects Of SnO₂-Based Photocatalysts

The n-type wide-bandgap semiconductor SnO₂（Eg=3.6 eV）is a promising oxide photocatalyst.However,its narrow light absorption range and serious recombination of photogenerated electrons and holes greatly hinder its application in the field of photocatalysis.In this work,SnO₂/SnS₂heterojunction was constructed by in situ method,and another self-doped SnO_2-xphotocatalyst with rich surface oxygen vacancies was prepared under the guide of defect engineering.The improvement mechanism of SnO₂/SnS₂heterojunction and SnO_2-xwith surface oxygen vacancies on SnO₂photocatalytic performance has been investigated.The main contents are as follows:1.Visible-light-driven 0D/2D SnO₂/SnS₂heterojunction photocatalysts with good cycling stability were prepared in situ by a two-step hydrothermal method.When the molar ratio of SnO₂to SnS₂is 1:2,the SnO₂/SnS₂1:2 has the best photocatalytic performance.The degradation efficiency of MO by SnO₂/SnS₂1:2 under visible light irradiation reaches 99.1%in 70 min,and the apparent rate constant is 10.9 times and 5.0times higher than those by SnS₂and physical mixed samples,respectively.The efficiency of reducing Cr（VI）in 40 min is as high as 98.4%,and the apparent rate constant is 66.7times,7.6 times and 4.5 times higher than those by SnO₂,SnS₂and physical mixed samples,respectively.2.Both the experimental and theoretical calculation results have confirmed that the interfacial charge transfer of SnO₂/SnS₂is consistent with the S-scheme heterojunction.Under the action of built-in electric field,energy band bending,and Coulomb attraction,the photogenerated electrons on SnS₂CB and the holes on SnO₂VB with strong redox ability are preserved,which can provide a stronger driving force for photocatalytic degradation of MO and reduction of Cr（VI）.3.An excellent SnO_2-xphotocatalyst integrating adsorption and photocatalytic reaction was successfully constructed by introducing oxygen vacancies into SnO₂by partially oxidizing Sn²⁺to Sn⁴⁺via low-temperature hydrothermal method.Under simulated sunlight,the degradation efficiency of MO by SnO_2-x（90）reached 97.8%after 6min,and the apparent rate constant is 377.2 times and 281.3 times higher than those by SnO₂and H₂O₂-SnO_2-x,respectively.The reduction efficiency of Cr（VI）reached 98.3%after 4 min,and the apparent rate constant is 54.0 times and 148.4 times than those by SnO₂and H₂O₂-SnO_2-x,respectively.4.Oxygen vacancies in single SnO_2-xcan reduce the band gap to 3.16 eV and increase the reducing power of conduction band electrons.Surface oxygen vacancies can trap photogenerated electrons and prolong their lifetimes,and also serve as active sites for the adsorption and photocatalytic reactions of MO and Cr（VI）,facilitating the mass transfer process that occurs at the surface.In addition,the possible relationship between oxygen vacancy content and carrier concentration is also discussed.