Design Synthesis And Properties Of Mn_0.5Cd_0.5S-Based Composite Photocatalytic Materials

The energy crisis is a global crisis of resources.Currently,the energy resources（coal,oil,natural gas）widely used by human beings have limited reserves and are all non-renewable energy sources.After long-term mining and use,they can no longer meet the growing production and living needs of mankind.Besides,the burning of fossil fuels has caused a series of environmental problems,water pollution,air pollution,global warming and so on.The development of new clean energy is a big challenge that human beings must face.Hydrogen energy is recognized as the cleanest energy source in nature.Hydrogen exhibits gaseous state at normal temperature and liquid state at ultra-low temperature and high pressure,which can be used in various environments due to its adaptable storage and transportation.Hydrogen energy also has the advantages of ideal heating value,smaller ineffective loss,higher safety,etc,which is the ideal new energy for human beings.Currently,Countries around the world are studying how to produce hydrogen in large quantities and cheaply.Photocatalytic hydrogen production technology can stimulate the photochemical reactions by photocatalysts under sunlight irradiaion,and converts abundant water resources into hydrogen.This technology is clean,green and efficient,and has become a hot spot in hydrogen production research.However,the high recombination of photo-generated electrons and holes,low quantum efficiency,and low catalyst stability have severely restricted the practical industrial application of photocatalytic hydrogen production technology.In order to solve the above problems,it is necessary to develop and design new photocatalytic systems with high energy efficiency and high stability.In this paper,three different types of semiconductor photocatalysts(MoO₂/Au/Mn_0.5Cd_0.5S、Mn_0.5Cd_0.5S/MoO₂/Cu₂O、Mn_0.5Cd_0.5S/CuInS₂/WS₂)have been prepared by hydrothermal method.The structure,morphology and performance of semiconductor photocatalysts have been systematically characterize by XRD,SEM,TEM,XPS,UV-vis DRS,BET,electrochemical and other characterization methods.Based on the results,the mechanism and essence of the improvement of hydrogen production performance have bee revealed,which can provide theoretical basis and technical support for the preparation of other high-performance heterojunction semiconductor photocatalysts.The main research contents are as follows:（1）Using MoO₂,Cd（CH₃COO）₂·2H₂O,Mn（CH₃COO）₂·2H₂O and HAu Cl₄ as raw materials,the MoO₂/Au/Mn_0.5Cd_0.5S composite photocatalyst was synthesized by one-step hydrothermal method along with deposition method.The effects of loading amounts of MoO₂ and Au nanoparticles on the performance of the ternary MoO₂/Au/Mn_0.5Cd_0.5S photocatalyst were investigated.It was found that the highest photocatalytic performance of the binary MoO₂/Mn_0.5Cd_0.5S can be obtained when the content of the MoO₂co-catalyst was 2 wt%,which was 2.76 times higher than that of pure Mn_0.5Cd_0.5S.The addition of Au nanoparticles could form a plasmon resonance effect with the semiconductor catalyst.When the content of MoO₂ and Au nanoparticles are 2 wt%and 3wt%,respectively,the hydrogen production of the ternary MoO₂/Au/Mn_0.5Cd_0.5S composite is 3.73 times higher than that of pure Mn_0.5Cd_0.5S.（2）Using MoO₂,Cd（CH₃COO）₂·2H₂O and Mn（CH₃COO）₂·2H₂O as raw materials,the binary Mn_0.5Cd_0.5S/Cu₂O photocatalyst was synthesized by aging deposition route,and then MoO₂ was introduced by ultrasound method to form the ternary Mn_0.5Cd_0.5S/Cu₂O/MoO₂ composite photocatalyst.The effects of loading content of MoO₂ and Cu₂O on the performance of the ternary Mn_0.5Cd_0.5S/Cu₂O/MoO₂ photocatalyst were investigated.It was found that the highest photocatalytic performance of the binary Mn_0.5Cd_0.5S/Cu₂O can be obtained when the content of the Cu₂O was 1 wt%,which was 3.31 times highter than that of pure Mn_0.5Cd_0.5S.When the content of MoO₂ and Cu₂O are 2 wt%and 1 wt%,respectively,the photocatalytic efficiency is the highest,the hydrogen production of the ternary Mn_0.5Cd_0.5S/Cu₂O/MoO₂ composite is 4.30 times higher than that of pure Mn_0.5Cd_0.5S.The formation of a p-n heterojunction interface between Cu₂O and Mn_0.5Cd_0.5S improves the charge separation efficiency.In addition,the MoO₂ cocatalyst can improve the charge separation and the H₂-evolution kinetics,which consequently boost the H₂-poduction efficiency over the terary Mn_0.5Cd_0.5S/Cu₂O/MoO₂photocatalyst.（3）Using CuInS₂、WS₂、Cd（CH₃COO）₂·2H₂O and Mn（CH₃COO）₂·2H₂O as raw materials.The ternary Mn_0.5Cd_0.5S/CuInS₂/WS₂ composite photocatalysts was synthesized by a one-step hydrothermal method alone with Ultrasonic method.The effects of loading content of CuInS₂ and WS₂ on the performance of the ternary Mn_0.5Cd_0.5S/CuInS₂/WS₂ photocatalyst were investigated.It was found that the highest photocatalytic performance of the binary Mn_0.5Cd_0.5S/CuInS₂ can be obtained when the content of the CuInS₂ was 1 wt%,which was 2.14 times highter than that of pure Mn_0.5Cd_0.5S.When the content of CuInS₂ and WS₂ are 1 wt%and 6 wt%,respectively,the photocatalytic efficiency is the highest,and the hydrogen production of the ternary Mn_0.5Cd_0.5S/CuInS₂/WS₂ composite is 3.98 times higher than that of pure Mn_0.5Cd_0.5S.CuInS₂ and Mn_0.5Cd_0.5S can form a p-n heterojunction,which improves the separation efficiency of electrons and holes.WS₂ acting as a co-catalyst can accelerate the electron transfer,thereby improving the efficiency of photocatalytic water splitting.