Preparation Of ZnCdS-based Composites And Its Photocatalytic Properties

With the development of industrialization,global environmental pollution and energy crisis are becoming more and more serious.Organic pollutants pose a serious threat to the health of humans and other living organisms.Removing organic pollutants from the environment and developing new green and efficient energy sources has become a global challenge.Photocatalytic technology has the characteristics of simple process,high efficiency,complete degradation and no secondary pollution,and has been widely used in the degradation of organic pollutants.However,the single photocatalyst represented by Ti O₂has the disadvantages of low photoutilization rate and high photogenerated carrier recombination.Zn Cd S is a ternary metal compound,which has the advantages of suitable bandgap energy,good stability,good oxidation reduction capacity and low cost.It has broad application prospects in the fields of photocatalytic degradation of pollutants and photocatalytic hydrogen production by water splitting.However,it still has some defects,such as poor light absorption and rapid recombination of photogenerated electron-hole pairs.In this paper,two modification methods were studied to improve the activity of photocatalytic degradation and photocatalytic hydrogen production of Zn Cd S.The specific work of this paper is as follows:The MgTi₂O₅/ZnCdS composite photocatalysts were prepared by hydrothermal and room temperature co-precipitation methods using magnesium acetate,tetrabutyl titanate,zinc acetate,cadmium acetate,sodium sulfide,etc.as raw materials.Using methyl orange as the target pollutant,the photocatalysts were evaluated for photocatalytic degradation activity.The results show that the photocatalytic degradation activity of Mg Ti₂O₅/Zn Cd S composite is significantly higher than that of pure Zn Cd S.When the content of Mg Ti₂O₅in the Mg Ti₂O₅/Zn Cd S composite is 15%,the sample has the highest photocatalytic degradation efficiency,and the degradation rate in 90 min can reach as high as 93%,which is 1.55 times to that of pure Zn Cd S.However,pure Mg Ti₂O₅almost has no any photocatalytic activity under visible light.Further,through a series of test methods,the morphology,structure and electrochemical properties of the samples were characterized and analyzed,and the reaction mechanism of Mg Ti₂O₅/Zn Cd S composite photocatalyst for degradation of methyl orange was preliminatively identified.Mainly due to a Z-scheme structure formed between the close contact surface of Mg Ti₂O₅and Zn Cd S,and the separation efficiency and migration of electrons and holes on the heterojunction surface significantly improved,and so the synthesized Mg Ti₂O₅/Zn Cd S composite materials showed high oxidation capacity for methyl orange.Using adenine and phosphomolybdic acid as raw materials,Mo₂C was prepared by hydrothermal method and high-temperature solid phase reaction.Zn Cd S and Mo₂C/Zn Cd S photocatalytic materials were prepared by hydrothermal method.Photocatalytic water splitting and hydrogen evolution experiments show that the photocatalytic hydrogen production efficiency of Zn Cd S modified by Mo₂C is significantly improved.When the amount of Mo₂C is 5%,the photocatalytic hydrogen production rate of Mo₂C/Zn Cd S reaches 5.26 mmol·g^-1·h^-1,which is 4.35 times higher than that of pure Zn Cd S.Through the characterization tests of the morphology,structure,electrochemical properties,and work function of the prepared samples,the mechanism of Zn Cd S photocatalytic activity improvement was preliminarily clarified.On the one hand,because Mo₂C has similar metal characteristics and has a large power function,when it comes into contact with Zn Cd S,due to the existence of power function difference,a built-in electric field will generate,and the electron in Zn Cd S will flow to Mo₂C.In the presence of this electric field,the photogenerated electrons and holes in Zn Cd S can be effectively separated and migrate to Mo₂C.On the other hand,due to the metalloid-like nature and high conductivity of Mo₂C,electrons transported to the interface can move quickly to the active site and participate in the reaction.At the same time,because Mo₂C has a low hydrogen evolution overpotential,surface electrons can easily react with H⁺absorbed on the activity site,and realizing the efficient photocatalytic hydrogen evolution.