Preparation Of Zn_xCd_1-xSe Solid Solution By Liquid Phase Method And Its Photocatalytic Hydrogen Production Performance

The pollution of air,water and soil caused by fossil fuels has brought severe challenges to human survival.Hydrogen energy has gradually become the hot spot in the field of energy owing to its high energy efficiency,non-toxic,innocuity and sufficient supply.The rapid development of photocatalytic technology promotes the continuous progress of hydrogen energy industry.Inorganic semiconductors with appropriate band gap have been widely studied as photocatalysts.In particular,CdSe has attracted extensive attention because of its excellent visible light response and appropriate conduction band potential.However,the sensitivity of CdSe to photo-corrosion limits its application.In recent years,the construction of multicomponent CdSe based solid solution has been proved to be an effective method.Its controllable energy band structure and effective separation of photogenerated carriers greatly improve the photocatalytic hydrogen production activity.In this paper,Zn_xCd_1-xSe solid solutions with different phases and morphological forms were synthesized through two methods,and the photocatalytic performance was further enhanced by the introduction of cocatalyst Ni₂P.Combined with the characterization and experiment,the energy band arrangement,separation and migration of carriers were analyzed,and the specific mechanism in the photocatalytic reaction was illustrated.The main research contents of this paper are as follows:（1）Zn_xCd_1-xSe（x=0～1）nano photocatalyst with adjustable energy band was successfully synthesized by one pot method.Zn_0.5Cd_0.5Se showed the optimum hydrogen production rate of 320.6μmol g^-1 h^-1 under visible light（λ>420 nm）,which was 12 times higher than that of pure CdSe and 17 times higher than that of pure Zn Se.X-ray diffraction analysis and transmission electron microscope images show that Zn_xCd_1-xSe solid solution has similar phase composition and micro morphology.UV-vis diffuse reflectance spectra and XPS valence band spectra confirmed that the energy band structure of Zn_xCd_1-xSe solid solution changed orderly with the change of Zn/Cd molar ratio,which was helpful to explain the different roles of conduction band and band gap in the reduction process.The band gap width affects the absorption of light,and the conduction band position is related to the reduction ability.The photoelectrochemical property test further clarified the rapid separation and migration of photogenerated carriers in Zn_0.5Cd_0.5Se photocatalyst is due to the balance of conduction band potential and band gap.（2）A series of novel Zn_xCd_1-xSe solid solutions with tunable energy band structure were prepared by simple solvothermal method.It is impressive that the maximum hydrogen production rate of Zn Se is 1056μmol g^-1 h^-1,which is much higher than that of CdSe and Zn_xCd_1-xSe solid solutions.Combined with X-ray diffraction analysis and scanning electron microscope images,it is illustrated that the specific crystal phase composition and band structure enhance the photocatalytic activity.After the Ni₂P/Zn_xCd_1-xSe composite system was constructed by introducing two-dimensional（2D）Ni₂P nanosheets,the hydrogen production performance of the photocatalyst was further improved,and the hydrogen evolution rate of Ni₂P/Zn Se reached 4.1 times that of Zn Se(4336μmol g^-1 h^-1).The cyclic photocatalytic experiment also showed that the sample had superior structure and performance stability.Photoelectrochemical tests,photoluminescence and time-resolved photoluminescence spectra show that Ni₂P/Zn Se has excellent photocatalytic performance due to the effective separation and directional movement of photogenerated electron hole pairs.In addition,2D Ni₂P nanosheets as high-efficiency cocatalysts provide a large number of hydrogen evolution active sites,improve the migration path of photogenerated carriers and reduce the hydrogen evolution overpotential.