Enhanced The Photocatalytic Degradation Performance Of Amorphous MoSe_x And Its Heterojunction

MoSe₂has attracted much attention in the field of photocatalysis due to its excellent properties such as large specific surface area and narrow band gap.However,the following two problems still need to be solved when MoSe₂is put into practical application.First,the band gap of MoSe₂is generally narrow,leading to the high carrier compound efficiency and the degradation of photocatalytic performance.Second,due to the small size of nanoscale MoSe₂,it is easy to agglomerate in solution,leading to the reduction of active sites.In order to overcome the above difficulties,the scientists used atom doping,crystal engineering,morphology control and heterojunction recombination to improve the photocatalytic performance.In this work,the non-stoichiometric amorphous MoSe_x（a-MoSe_x）was used as the main research object,and the novel Z-scheme and traditional Type-Ⅱheterojunction were constructed respectively to enhance the photocatalytic performance.The Z-scheme Cd Se/a-MoSe_xheterostructure was synthesized by simple and convenient hydrothermal method and grinding method,and the Type-ⅡAg₂Se/a-MoSe_xheterojunction was constructed by one-step hydrothermal method.The amorphous MoSe_xbased heterojunction prepared has high separation efficiency of photogenerated electrons and holes,and abundant active sites of photocatalytic reaction at the edges.The detailed research contents are as follows:（1）Z-scheme Cd Se/a-MoSe_xheterojunction with excellent photocatalytic performance was successfully prepared by the combination of grinding method and hydrothermal method.The photocatalytic degradation efficiency of Cd Se/a-MoSe_xZ-scheme heterojunction on methylene blue was up to 97.3%under visible light,while the degradation efficiency of pure Cd Se and amorphous MoSe_xsamples after 120 min under visible light was 58.8%and 67.0%,respectively.Different from the traditional crystalline MoSe₂,the presence of unsaturated Se atoms in the amorphous MoSe_xprovides abundant reactive sites for photocatalytic reactions.The unique Z-scheme heterojunction structure not only overcomes the shortcoming of easy recombination of the narrow band gap semiconductor material of MoSe₂,but also has stronger redox activity ability.Finally,the photocatalytic performance of the Z-scheme Cd Se/a-MoSe_xheterojunction has been significantly improved.（2）The Type-ⅡAg₂Se/a-MoSe_xheterojunction with excellent photocatalytic degradation performance was successfully prepared by one-step hydrothermal method.The results of photocatalytic experiments indicated that the Type-ⅡAg₂Se/a-MoSe_xheterojunction showed the highest photocatalytic degradation efficiency.After 120minutes of visible light irradiation,the photocatalytic degradation efficiency of methylene blue was up to 95.7%,while the pure amorphous MoSe_xdegradation efficiency was only 62.4%.The photocatalytic performance was improved because the introduction of Ag₂Se enhanced the light absorption intensity and provided more photogenerated electrons and holes for the photocatalytic reaction.The unsaturated Se atoms in amorphous MoSe_xincrease the number of active sites,and the Ag₂Se/a-MoSe_xheterojunction provides an important channel to promote carrier separation.Therefore,the photocatalytic performance of Ag₂Se/a-MoSe_xheterojunction is further improved.