Construction Of Metal Oxide Based S-scheme Heterojunctions And Photocatalytic Performance Research

Recently,with the rapid development of social economy,energy shortage and environmental pollution are becoming increasingly serious,which threaten the sustainable development of human society.Solar energy varies greatly from day to night/seasons,is not evenly distributed and cannot be stored directly.While the chemical energy can be reused and easily stored.Semiconductor photocatalytic technology takes the inexhaustible solar energy as the energy source,and converts it into chemical energy through efficient,stable and economical semiconductor catalysts.It is one of the effective ways to solve above two issues.Metal oxides are widely studied in the field of photocatalysis due to their wide sources,easy preparation and low cost.However,pure/single metal oxides suffer from low utilization of solar energy and rapid recombination of photocarriers,resulting in pretty low photocatalytic efficiency.Therefore,it is an efficient strategy to improve the photocatalytic efficiency by constructing metal oxide-based S-scheme heterojunction photocatalysts through surface modification or semiconductor coupling strategies,which can broaden the light response range and improve the separation efficiency of photogenerated electrons and holes.In this paper,the metal oxide ZnO and In₂O₃were chosen as the research objects.By constructing ZnO and In₂O₃-based S-scheme heterojunction photocatalysts,the photocatalytic H₂O₂production and CO₂reduction activities enhanced significantly.Moreover,the mechanism of S-scheme heterojunction enhancing the photocatalytic performance was analyzed systematically.The main research contents include:（1）Three-dimensional inverse opal（3DIO）structure of porous ZnO was prepared by template method,and then polydopamine（PDA）was coated on the surface of ZnO by in-situ self-polymerization,thus ZnO@PDA composite photocatalyst was successfully prepared.The work function results showed that the Fermi level of PDA was higher than that of ZnO.In this case,the electrons at the interface were transferred when they contacted with each other and a built-in electric field directed from PDA to ZnO can be formed.Under light irradiation,the photoinduced electrons in ZnO CB transferred to PDA as evidenced by in-situ XPS results,forming an S-scheme heterojunction between ZnO and PDA.Meanwhile,the ZnO@PDA S-scheme heterojunction can improve the utilization of visible light.The photocatalytic performance results showed that the S-scheme heterojunction photocatalyst exhibited higher photocatalytic H₂O₂production rate(1011.4μmol·L^-1·h^-1),which was 4.4 and 8.9-flod of the pure ZnO and PDA,respectively.This work may provide a new idea for the design of ZnO-based S-scheme heterojunction photocatalysts.（2）The hollow hexagonal In₂O₃was prepared by calcining the MOF precursor（In-MIL-68）.Then the ZnO precursor was adsorbed on the surface of In₂O₃by the impregnation method.Finally,the In₂O₃/ZnO composite was obtained after calcination.The XPS results indicated that the electrons at the In₂O₃interface transferred to ZnO in dark,thus forming a built-in electric field pointing form In₂O₃to ZnO.Under light irradiation,driven by the internal electric field,the photogenerated electrons in ZnO CB transferred to In₂O₃and recombined with the photoinduced holes in its VB.Thus,an S-scheme heterojunction was formed between In₂O₃and ZnO,which greatly promoted the effective separation of photocarriers.Compared with pure In₂O₃and ZnO,In₂O₃/ZnO S-scheme heterojunction exhibited enhanced CO₂photoreduction performance.Isotope(¹³C)tracer test confirmed that the products were produced from the photocatalytic reduction of the CO₂source instead of any organic contaminants.This work offers an alternative approach to rationally design and synthesize In₂O₃-based photocatalysts toward high-efficiency CO₂photoreduction.