Preparation Of ZnO Nanorod-based Photocatalysts And Their Enhanced Photocatalytic Performance

Photocatalysts can capture solar energy and convert low-density solar energy into valuable chemical energy,which shows a promising application prospect in solving the problem of energy shortage and environmental pollution.Zinc oxide has attracted great interest due to its non-toxic,low-cost,high photocatalytic activity and stability.However,due to its wide band gap(3.2 e V),single ZnO can only use 4%of the solar light,and the high recombination rate of photogenerated electrons and holes has become two key factors restricting its practical application.Therefore,it is necessary to develop ZnO based composite photocatalysts to expand the spectral absorption range and reduce the recombination rate of photogenerated carriers.Based on the position of conduction band and valence band of ZnO,different morphologies of ZnO based photocatalysis systems were designed.(1)ZnO nanorods were planted on the silver nanowires with a diameter of 100nm.The Pb S quantum dots were deposited on the ZnO nanorods through continuous ion layer adsorption and reaction.The loading amount of Pb S was controlled by the number of cyclic reactions.The structures with different cycles were named x Pb S QDs/ZnO NRs/Ag NWs.The crystal structure,elemental composition,optical properties and morphology of the synthesized materials were characterized by XRD,XPS,UV-vis DRS,FESEM and HRTEM.In the photocatalytic experiment,a Xe lamp with a power of 300 W was selected to simulate the degradation of methylene blue under sunlight irradiation to explore the photocatalytic activity of the material.The results of photocatalytic experiment show that the composite structure of 9Pb S QDs/ZnO NRs/Ag NWs has the best photocatalytic activity and can completely degrade methylene blue within 30 minutes.Compared with pure ZnO,the enhanced photocatalytic activity can be attributed to the formation of p-n heterojunction between Pb S and ZnO,which promotes the separation of photogenerated electrons and holes.At the same time,as the core structure,silver nanowires act as electron traps and further improve the separation efficiency of electrons and holes.(2)Under low temperature conditions,a simple method is used to synthesize zinc oxide nanorods with uniform diameter,and then use In Cl₃ and Na₂S reaction to generate In₂S₃ wrapped on the surface of the ZnO NRs to form In₂S₃/ZnO NRs heterojunction.Under conditions,the silver nitrate is reduced with ethylene glycol,and the silver nanoparticles are deposited on the formed In₂S₃/ZnO NRs structure to form a ternary composite structure of Ag/In₂S₃/ZnO NRs.The synthesized materials were characterized by XRD,XPS,UV-vis DRS,FESEM,HRTEM,and ESR.In particular,it should be pointed out that the ESR test shows that active substances of hydroxyl radicals are generated during the photocatalytic reaction,which indicates that the photocatalytic oxidation reaction occurs on the valence band of zinc oxide,because the valence band of In₂S₃ is not enough to convert H₂O or OH^-to hydroxyl radicals,which shows that the formation of In₂S₃ and ZnO is no longer the traditional type-?heterojunction,but the Z-scheme heterojunction with stronger redox ability.In the photocatalytic degradation experiment of 4-nitrophenol,the ternary composite structure showed the best photocatalytic effect,and it could be completely degraded within 50 minutes.The improved photocatalytic activity can be attributed to the formation of a Z-scheme heterojunction between In₂S₃ and ZnO,which effectively separates the photogenerated electrons and holes.In addition,the silver nanoparticles on the surface act as a promoter.The Schottky barrier formed with In₂S₃ and the LSPR effect of silver under light conditions have a significant impact on the improvement of the catalytic effect.