Prepration And Visible Light Photocatalytic Hydrogen Evolution Of MoS₂/CdS Nanocomposites

In recent years,many researchers focused on hydrogen energy because of its large storage,environment friendly and high colorific value.It is a promising way to produce hydrogen through photocatalytic technology under solar light.As a narrow bandgap?-?semiconductor,CdS has good response to visible light,and the potential of conductive band is more negative than the redox potential of H⁺/H₂.Thus,CdS is considered to be one of the most promising photocatalysts.However,high recombination rates of photogenerated electrons and holes have bad influence on the photocatalytic activities of CdS.In this paper,controlling crystal structure of CdS,synthesis of h-CdS/c-CdS homojunction and construction of MoS₂/h-CdS/c-CdS heterojunction were researched for improving photocatalytic perfermances of photocatalysts.The main results were as follows:?1?The CdS nanostructure was prepared by solvothermal method using the cadmium chloride and sublimed sulfur as precursors,diethylenetriamine?DETA?and deionized water as solvents.The results showed that when the concentration of DETA was 30 vol%,the CdS exhibited improved photocatalytic performance for hydrogen evolution,the total amount of hydrogen evolution was 519.83?mol,which was about 2.9 times when compared with the CdS without DETA,the average rates of CdS for hydrogen evolution was 5.62 mmol h^-1 g^-1,which was about 4.0 times when compared with the CdS without DETA.?2?On the basis of CdS nanostructure,the h-CdS/c-CdS homojunction was synthesized by the solvothermal method.The content of hexagonal and cubic phase in h-CdS/c-CdS homojunction was controlled by varying the molar ratio of Cd and S.The results showed that when the molar ratio of Cd and S was 1:1,the h-CdS/c-CdS homojunction exhibited further enhanced photocatalytic performance for hydrogen evolution,the total amount of hydrogen evolution was 1767.48?mol,which was about3.4 times when compared with the h-CdS/c-CdS homojunction?Cd:S=1:8?,the average rates of CdS for hydrogen evolution was 17.50 mmol h^-1 g^-1,which was about 3.1 times when compared with the h-CdS/c-CdS homojunction?Cd:S=1:8?.?3?On the basis of the h-CdS/c-CdS homojunction,MoS prepared via hydrothermal method was deposited on the surface of h-CdS/c-CdS homojunction by ultrasonic method to form the MoS₂/h-CdS/c-CdS heterojunction.The results showed that when the mass fraction of MoS₂ was 1.5 wt%,the MoS₂/h-CdS/c-CdS heterojunction exhibited excellent photocatalytic performance for hydrogen evolution,the total amount of hydrogen evolution was 3753.12?mol,which was about 2.1 times when compared with the h-CdS/c-CdS homojunction?Cd:S=1:1?,the average rates of CdS for hydrogen evolution was 40.79 mmol h^-1 g^-1,which was about 2.4 times when compared with the h-CdS/c-CdS homojunction?Cd:S=1:1?.?4?The photocatalytic hydrogen evolution mechanism research shows that for the CdS with rich sulfur vacancies,the photocatalytic performance for hydrogen evolution is improved because the presence of sulfur vacancies can introduce impurity levels in the bandgap,and the impurity level act as a conductive band,which reduces the bandgap of CdS.In addition,the sulfur vacancies also act as active sites for hydrogen evolution,which can accelerate the consumption of photogenerated electrons,which further inhibit the recombination of photogenerated electrons and holes.For h-CdS/c-CdS homojunction,the main reason for the improvement of photocatalytic hydrogen evolution is the increasing of the specific surface area,which can effectively promote the photocatalytic hydrogen evolution reaction.For MoS₂/h-CdS/c-CdS nanocomposites,the improvement of the photocatalytic hydrogen evolution is attributed to the introduction of MoS₂,which not only improves the response to visible light,but also provides a lot of active sites for the photocatalytic hydrogen evolution.