Synthesis,modification And Photocatalytic Performance Of BiOX Photocatalysts

As a kind of newly exploited photocatalysts,BiOX?X=Cl,Br,I?single crystals have great potentials in the photocatalytic degradation of organic substance.However,the low quantum-efficiency and poor interfacial reactions of BiOX still limit their practical applications.To improve their photocatalytic performance,the BiOX single crystals are carefully investigated via the combination strategy of crystal-facet engineering and selective cocatalyst deposition,and the investigations mainly focused on?1?the effect of selective-deposition site of Ag nanoparticles on the photocatalytic performance of BiOCl single-crystalline photocatalytic materials,?2?the synthesis and photocatalytic performance of high-efficiency and stable Pt-Au/BiOBr/CoPi photocatalyst.The main results could be summarized and shown as follows:First,BiOCl single-crystalline nanosheets were employed as an excellent substrate to investigate the controllable site-selective deposition of Ag-electron cocatalyst by different loading methods and the effect of selective-deposition site of Ag nanoparticles on the photocatalytic performance of BiOCl single-crystalline photocatalytic materials.In this study,BiOCl single-crystalline nanosheets were synthesized via a facile hydrothermal route,and then the Ag nanoparticles?as an electron cocatalyst?were selectively deposited on the different surface regions of BiOCl nanosheets via the following three methods:?1?photocatalytic-induced deposition progress,?2?photosensitization-induced deposition route,and?3?direct reduction method.Based on the above strategies,Ag nanoparticles were selectively deposited on the dominant exposed surface?{001}facet?,lateral surfaces?{010}and{110}facets?,and all exposed facets of BiOCl single-crystalline nanosheets,which can be referred as Ag/BiOCl?UV?,Ag/BiOCl?Dye?,and Ag/BiOCl?NaBH₄?,respectively.Photocatalytic results demonstrated that the resultant Ag/BiOCl?UV?exhibited the highest photocatalytic performance(k=0.044 min^-1),which is higher than that of pure BiOCl by a factor of ca.2.6;while Ag/BiOCl?Dye?displayed the lowest efficiency(k=0.007 min^-1),even lower than that of unmodified BiOCl nanosheets.Based on the above experimental results,a possible mechanism was proposed to account for the improved photocatalytic performance of Ag/BiOCl?UV?photocatalyst,namely,the synergistic effect of orientation transfer of photogenerated charges in the BiOCl single-crystalline nanosheets and their rapid interfacial catalytic reactions on the Ag-cocatalyst active sites by the well-coupling strategy of crystal-facet engineering and selective cocatalyst modification.Second,the BiOBr single-crystalline nanosheets were synthesized via a facile hydrothermal route,and the Pt-Au/BiOBr photocatalyst was synthesized by a two-step photodepositing progress,including the Au-nanoparticle deposition on BiOBr nanosheets and selective Pt deposition on the Au surface.It was found that the Pt-Au/BiOBr photocatalyst exhibited the best degradation performance for phenol(k=0.123 min^-1),which is higher than that of pure BiOBr by a factor of ca.15.2.However,the resulting Pt-Au/BiOBr photocatalyst exhibited a decreased activity during repeating tests for the phenol decomposition.To further improve the stability of Pt-Au/BiOBr photocatalyst,CoPi hole-cocatalyst was further loaded on its surface.It was found that the CoPi deposition could dramatically enhance the photocatalytic activity and stability of Pt-Au/BiOBr.On the basis of experimental results,a synergistic effect mechanism of Pt-Au and CoPi cocatalysts was proposed to account for its improved photocatalytic activity and stability of BiOBr single-crystalline nanosheets,namely,the Au nanoparticle functions as an effective electron-transfer mediator and Pt nanoparticle serves as the interfacial catalytic active site,while CoPi rapidly captures photogenerated holes and promote the oxidation reaction of organic substance.