Fabrication,modification Of Zn_0.8Cd_0.2S Solid Solution And Its Photocatalytic Performance For Hydrogen Evolution Under Visible Light

In this paper,Zn_0.8Cd_0.2S solid solutions were prepared by precipitation-heat treatment method,characterized by SEM,HRTEM,XRD,UV-vis DRS and room temperature photoluminescence to investigate the effect of the structure and mechanical properties of samples,and the significant influence of heat treatment conditions on visible light absorption,photogenerated electron-hole separation efficiency,hydrophilicity and the photocatalytic performance of Zn_0.8Cd_0.2S solid solutions were also studied.The results show that Zn_0.8Cd_0.2S solid solution prepared by hydrothermal treatment at 200°C exhibits the highest photocatalytic hydrogen evolution rate under visible light irradiation when compared with untreated Zn_0.8Cd_0.2S solid solution nanoparticles.The characterization results indicate that the enhancement of photocatalytic activity is mainly due to the improvement of photogenerated electron-hole separation efficiency and the hydrophilicity of Zn_0.8Cd_0.2S solid solution prepared by hydrothermal treatment at 200°C.In contrast,sample calcined at 200°C displays the lowest photocatalytic activity because of the highest recombination rate of photogenerated carriers.It can be seen that the heat treatment conditions have a great influence on the visible light absorption,the separation efficiency of photogenerated carriers,hydrophilicity and photocatalytic performance of the solid solution.MoS₂ and WS₂ were successfully loaded on the surface of Zn_0.8Cd_0.2S nanoparticles by photocatalytic deposition method.The results show that the introduction of sulfide can improve the photosensitivity of Zn_0.8Cd_0.2S nanoparticles,increase the separation efficiency of photogenerated electrons and holes,and enhance the photocatalytic activity of Zn_0.8Cd_0.2S nanoparticles.The photocatalytic activity of the photocatalytic material was increased first and then decreased with further increasing the loading of MoS₂ or WS₂,and the sample with the loading of 2wt.%MoS₂ or 1.5wt%WS₂ showed the highest photocatalytic activity of 4800?mol·h^-1g^-1and 5500?mol h^-1 g^-1,respectively,which were 1.8 times and 2.1 times of that of the un-deposited sample.The increase in photocatalytic activity of Zn_0.8Cd_0.2S nanoparticles after the deposition of MoS₂ or WS₂ is ascribed to the formation of heterojunction structure between MoS₂?or WS₂?and Zn_0.8Cd_0.2S solid solution,thus improving the separation efficiency of photogenerated electrons and holes.Zn_0.8Cd_0.2S-En hybrid nanosheets with different thickness and size were successfully synthesized by changing the atomic ratio of S/?Zn+Cd?in the hydrothermal reaction.The results show that the content of thiourea in solvent has an important effect on the composition and structure,photoelectric property and hydrophilic property of the prepared solid solution.With the increase of the content of thiourea in the reaction system,the nanosheets of the solid solution were gradually formed and the hydrophilic property decreased gradually.Fluorescence emission spectra?photoluminescence spectra?and photocatalytic activity tests show that the proper S/?Zn+Cd?atomic ratio can improve the separation efficiency of photogenerated electrons and holes,resulting into the superior photocatalytic activity.The maximum yield of Zn_0.8Cd_0.2S-En under visible light irradiation was obtained when the S/?Zn+Cd?was 4.75,reaching 12100?mol h^-11 g^-1.The improvement of photocatalytic activity is maily related to the less surface defects,suitable morphology,good hydrophilicity and formation of new surface states.