Construction Of Hollow Tubular Composites And Their Photocatalytic Properties

With the development of modern society and industry,problems such as energy shortage and environmental pollution caused by rapid consumption of fossil resources have become serious in recent years,increasingly.In view of these challenges,developing sustainable green energy to replace fossil fuels has become an inevitable measure for human to achieve sustainable development.As a kind of clean and renewable energy,the conversion and utilization of solar energy is of great significance.The research of converting solar energy into hydrogen energy by photocatalytic decomposition of water has shown a broad application prospect.In order to obtain the ideal photocatalytic efficiency,the reasonable design and preparation of photocatalyst is the key.Recently,semiconductor materials with hollow structure have become one of the hot materials in the study of photocatalysis due to their unique structural advantages,such as the enhanced reflection and scattering of incident light,the shortened movement distance of photogenerated charges from the bulk phase to the surface,and their surface area is large and specific.At the same time,considering the strong visible light response ability of transition metal sulfide（TMS）semiconductor and suitable hydrogen evolution conduction band potential,the design of hollow structure based on TMS semiconductor is expected to develop high performance photocatalyst.However,the photocatalytic activity of TMS is decreased due to the high charge recombination rate and photocorrosion.It has been shown that the electric field built in the semiconductor heterojunction can drive the photogenerated electrons and holes to move in opposite directions to the interface,thus significantly inhibiting the recombination process of carriers.In addition,vacancy defects in semiconductors can be used as effective capture sites for photogenerated electrons or holes,thus further improving the efficiency of charge separation.Based on the above reasons,this paper synthesizes structured TMS semiconductor nanotubes using template method,and effectively improves the photocatalytic performance of H₂ evolution capability by constructing heterojunction and S-vacancy defect engineering.The main research contents and conclusions are summarized as follows:（1）Briefly,by constructing the nanosheet-based nanotubes with Cd-doping and S vacancies,a highly improved visible-light-driven H₂ production for Zn In₂S₄ is achieved.Unlike nanoflowers aggregated with nanosheets,the nanosheet-assembled hierarchical nanotubes allow multiple scattering and reflection of incident light within the interior space,leading to an enhanced light-harvesting efficiency.Together with the benefits from Cd-doping and S-vacancy engineering,including narrowed bandgap,efficient transmission and separation of charge carriers,abundant catalytically active sites,heightened photo-stability and photo-electron reduction capacity,as well as a strong electrostatic attraction to protons,the synthesized S-deficient Cd_xZn_1-xIn₂S₄ hierarchical nanotubes exhibit an extraordinary photocatalytic H₂ evolution capability under visible-light irradiation,delivering an outstanding H₂-generation activity of 28.99 mmol`g<sup>-1</sup>`h^-1（corresponding to an apparent quantum yield of 37.1%at 400 nm）,which is much superior to that of Cd_xZn_1-xIn₂S₄ nanoflowers,Pt-loaded Zn In₂S₄ nanotubes,and most ever reported Zn In₂S₄-based photocatalysts.Our study could inspire the development of low-cost and high-performance photocatalysts via rational structural design and optimization.（2）Firstly,CoS₂-MoS₂ nanosheet based multistage nanotubes were prepared by calcination and vulcanization with MoO₃@ZIF-67 as the precursor,and then the unique multistage nanotubes were obtained by growing CdS nanocrystals with S-vacancy.In visible light（λ>400 nm）,CoS₂-MoS₂/CdS multilevel nanotube exhibited excellent hydrophotolystic activity,with the highest hydrogen yield rate of 33.05 mmol`g<sup>-1</sup>`h^-1,and the apparent quantum yield of hydrogen production at 400 nm reached 40.4%.The hydrogen production property of CoS₂-MoS₂/CdS composites is significantly higher than that of Pt-supported CdS and most reported CdS-based photocatalysts.In addition,CoS₂-MoS₂/CdS showed good cyclic and long-term photocatalytic hydrogen production stability.The excellent photocatalytic performance of CoS₂-MoS₂/CdS can be attributed to the following aspects:excellent visible light trapping ability;efficient charge separation process endowed by tightly coupled heterojunction;rich S₂^2-hydrogen producing active sites provided by MoS₂ cocatalyst.The self-sacrificial template method provides a new strategy for the design and synthesis of one-dimensional layered tubular,multi-component and efficient nanocatalysts.