Surface Modification Of Zn_（1-x）Cd_xS And Its Study On Photocatalytic Water Splitting To Produce Hydrogen

The technology of photocatalytic water splitting to produce hydrogen,which can convert solar energy into chemical energy,exhibits broad application prospects in alleviating global energy shortage and environmental crisis.Among many semiconductor photocatalysts,Zn_（1-x）Cd_xS has been widely used in the field of photocatalysis due to its suitable conduction band position,good photocatalytic activity and stability.In this work,Zn_（1-x）Cd_xS and its composites were prepared and used in the reaction of photocatalytic water splitting to produce hydrogen.The structure-activity relationship and mechanism of photocatalytic water splitting to produce hydrogen over Zn_（1-x）Cd_xS-based photocatalyst were studied through activity test,catalyst characterization and photoelectrochemical test.The specific research contents and conclusions are as follows:Firstly,Zn_（1-x）Cd_xS nanospheres with different Zn/Cd molar ratios were prepared by a solvothermal method,and the effect of Zn/Cd molar ratio on Zn_（1-x）Cd_xS surface defect,and the effect of surface defect on the efficiency of photocatalytic water splitting to produce hydrogen were studied.It was found that under visible light irradiation(λ≥400 nm,optical power density of 196m W cm^-2),Zn_0.8Cd_0.2S exhibited the highest efficiency of photocatalytic hydrogen production,and the hydrogen production rate reached 7.71 mmol h^-1g^-1,which was 455 times and 1436 times that of Zn S and Cd S,respectively.It was found that the abundant defect sites in Zn_0.8Cd_0.2S can not only served as the electron traps to improve the separation of the photogenerated electrons and holes,but also act as the active sites for photocatalytic water splitting reaction,which greatly enhanced the efficiency of photocatalytic water splitting to produce hydrogen.Secondly,Ni（OH）₂/Zn_0.8Cd_0.2S composite photocatalyst was prepared by in situ growth of Ni（OH）₂nanosheet on the surface of Zn_0.8Cd_0.2S by a coprecipitation method.It was found that when the mass fraction of Ni（OH）₂was 9%,Ni（OH）₂/Zn_0.8Cd_0.2S composite photocatalyst exhibited the highest hydrogen production rate of 12.88 mmol h^-1g^-1under visible light irradiation(λ≥400 nm,optical power density of 103 m W cm^-2),which was 9.9 times that of Zn_0.8Cd_0.2S.It was found that the tight contact interface between the Zn_0.8Cd_0.2S and Ni（OH）₂could effectively promote the transfer of photogenerated electrons from Zn_0.8Cd_0.2S to Ni（OH）₂,which promoted the separation and transfer of photogenerated electrons and holes,thus enhanced the efficiency of photocatalytic water splitting to produce hydrogen.Finally,Ni₂P/P-Zn_0.8Cd_0.2S composite photocatalyst was prepared by growing Ni₂P on the surface of Zn_0.8Cd_0.2S.It was found that when growing Ni₂P,a small amount of P entered the lattice of Zn_0.8Cd_0.2S to obtain the Ni₂P-loaded P-doped Zn_0.8Cd_0.2S composite materials.When the mass fraction of Ni was 0.5%,the Ni₂P/P-ZCS composite photocatalyst exhibited the highest photocatalytic performance.After the reaction of photocatalytic water splitting to produce hydrogen reached a stable stage,and the hydrogen production rate reached 7.32 mmol h^-1g^-1under visible light irradiation(λ≥400 nm,optical power density of 72 m W cm^-2),which was 13.1 times that of Zn_0.8Cd_0.2S.It was found that the tight contact interface between Ni₂P and P-Zn_0.8Cd_0.2S could effectively promote the transfer of photogenerated electrons from P-Zn_0.8Cd_0.2S to Ni₂P,which promoted the separation of photogenerated electrons and holes.At the same time,Ni₂P can be used as the active site for hydrogen production,thus improving the efficiency of photocatalytic water splitting to produce hydrogen.