Carboxyethyltin Modified Tungstophosphate And Tungstate Assisted Synthesis Of G-C₃N₄ Composite Nanomaterials And Their Photocatalytic Production Of Hydrogen Peroxide

As a green oxidant,hydrogen peroxide（H₂O₂）is widely used in fields of organic synthesis,environmental remediation,disinfection and fuel cells.The traditional anthraquinone method for the preparation of H₂O₂ has the problem of high energy consumption.The photocatalytic production of H₂O₂ by reduction of O₂ is a sustainable development route.Therefore,it is of great significance to develop efficient and stable photocatalyst for the photocatalytic production of H₂O₂.Graphite carbon nitride（g-C₃N₄）is a non-metallic semiconductor,which has excellent stability and high selectivity for the two-electron reduction of O₂.However,the intrinsicπ-πconjugated structure of g-C₃N₄ leads to the rapid recombination of photogenerated carriers,and the block structure formed by thermal polymerization usually leads a small specific surface area,which makes the concentration of H₂O₂ formed by g-C₃N₄ photocatalysis is still relatively low.Therefore,modification of g-C₃N₄ is an important topic to further improve the yield of photocatalytic production of H₂O₂.Based on this,this thesis carries out work from the following two aspects:1.A series of g-C₃N₄（CN）based nanocomposites PWSn-CN-x（x=0.03,0.06,0.09,0.18,0.24,0.3）were prepared by one-step thermal polymerization using carboxyethyltin modified tungstophosphate（PW₉-Sn R）and dicyandiamide as precursors.The structure,composition and morphology of the composites were characterized by XRD,FTIR,XPS,SEM and TEM.The results show that the pure CN has the sheet stacked bulk structure,and the composites have the lamellar or rod-like aggregate of nanoparticles,which have the larger specific surface area than CN.The metal oxides derived fro m PW₉-Sn R are uniformly dispersed in the layered CN structure.A series of photoelectrochemical tests,RDE electrochemical tests and free radical capture experiments were carried out to analyze the reasons for the improvement of the photocatalytic performa nce of the composites,and the mechanism of the photocatalytic reduction of O₂ was proved to be a main two-step one-electron reduction process.In addition,the photocatalytic oxidation of cyclohexanol to cyclohexanone of composites was discussed.2.A series of CN nanocomposites Na WO-CN-x（x=0.02,0.04,0.06,0.08,0.1,0.14,0.2）were prepared by one-step thermal polymerization using simple tungstate（Na₂WO₄·2H₂O）and dicyandiamide as precursors.The structure,composition and morphology of the composites were characterized by XRD,FTIR,XPS and SEM.The results show that Na₂WO₄·2H₂O assisted synthesis of CN composite can simultaneously introduce nitrogen defects（?C≡N）and WO_3-X into the CN structure,and the composite has stronger spectral absorption capacity and carrier separation efficiency.Under visible light（λ>420 nm）,Na WO-CN-0.1 has the highest photocatalytic activity for H₂O₂ production.RDE electrochemical tests and free radical capture experiments further proved that the photocatalytic reduction mechanism of Na WO-CN-0.1 was a main one-step two-electron reduction process.