Doping Composite Modification Of CdS Catalyst And Its Photocatalytic Properties

The environmental problems caused by the exploitation and combustion of fossil energy are becoming more and more serious.The emergence of hydrogen energy can just solve the problem of exploitation and combustion of fossil energy.Hydrogen production using semiconductor materials as photocatalysts is one of the ideal ways to convert solar energy into hydrogen energy.The band gap of semiconductor material cadmium sulfide is 2.4e V and it has good light response characteristics in the visible wavelength range.Its energy band structure matches with water decomposition.It is a potential catalyst material for photolysis of water to produce hydrogen.However,the specific surface area of cadmium sulfide material is small,and the generated photogenerated electrons and holes are easy to combine in cadmium sulfide,which greatly affects the photocatalytic hydrogen production efficiency of cadmium sulfide and limits its application in the field of photocatalysis.In order to solve these problems of cadmium sulfide catalyst,this paper designed and prepared cadmium sulfide doping and composite catalyst materials,which not only increased the specific surface area of photocatalyst and promoted the rapid separation of photogenerated electrons and holes in space,but also increased the number of photogenerated electrons and holes in photocatalyst,so as to improve the rate of photolysis of aquatic hydrogen.The specific research contents and conclusions are as follows:（1）A series of bismuth doped Cd S catalysts were prepared by solvothermal method and grinding method.After calculation,the doping amount of bismuth was controlled by adjusting the addition quality of different raw materials.Through the comparison of photocatalytic hydrogen production experiments,it was found that when the molar doping amount of bismuth was 33%,the hydrogen production rate of doped catalyst(Cd₂Bi S_3.5)could reach 544.025μmol/g/h,which was 2.2 times that of Cd S catalyst.The morphology,composition,phase and photoelectric energy of the doped catalyst were characterized by SEM,DRS and XRD.The results showed that the bismuth doped catalyst was successfully prepared,and the chemical composition was consistent with the theoretical calculation.The band gap of these catalysts was characterized and calculated.It was found that the doping of bismuth gradually reduced the band gap of the catalyst from 2.7e V to 1.2 e V,and the band gap of the catalyst with the best bismuth doping amount(Cd₂Bi S_3.5)was 2.1e V,which was a narrow-band gap semiconductor catalyst material.The stability test of the catalyst with the best bismuth doping amount(Cd₂Bi S_3.5)was carried out.The catalyst could still maintain a stable hydrogen production rate after 5 cycles of test.In addition,the mechanism of photocatalytic reaction with increased hydrogen production rate was proposed according to the experimental results.（2）A series of lead doped Cd S catalysts were synthesized by solvothermal method and grinding method.The doping amount of lead was controlled by different quality raw materials.When the molar doping amount of lead was 50%,the hydrogen production rate of doped catalyst（Cd Pb S₂）was the best,which could reach729.341μmol/g/h,which was 2.9 times that of Cd S catalyst.The morphology,composition,phase and photoelectric energy of the doped catalyst were characterized by SEM,DRS and XRD.The results showed that the lead doped catalyst was successfully prepared,and its chemical composition was consistent with the theoretical calculation.The band gap of this series of catalysts was characterized and calculated.It was found that the doping of lead gradually reduced the band gap of the catalyst from 2.7e V to 0.7e V,and the band gap of lead doped catalyst（Cd Pb S₂）with the best hydrogen production performance was 1.2e V.The stability test of the catalyst with the best lead doping amount（Cd Pb S₂）was carried out.It was found that the catalyst could still maintain a stable hydrogen production rate without reduction after5 cycles of test,indicating that the structure and performance of the catalyst were relatively stable.（3）The composite catalyst was synthesized.In the first step,a series of nickel doped cadmium sulfide catalysts were prepared by solvothermal method and grinding method.The photolysis experiment of aquatic hydrogen was carried out on these catalysts.It was found that when the molar doping amount of nickel was 40%,the hydrogen production rate was the highest,which could reach 1110.627μmol/g/h.The hydrogen production rate of Cd_0.6Ni_0.4S catalyst was 4.5 times that of Cd S catalyst,and Cd_0.6Ni_0.4S catalyst was the best catalyst for hydrogen production in these three doped series.The second step was to select the catalyst Cd_0.6Ni_0.4S with the best hydrogen production performance in these three series,let it be compounded with g-C₃N₄to synthesize the doped composite catalyst.Through the photolysis of aquatic hydrogen experiment,it was found that the hydrogen production rate of the doped composite catalyst after compounding was further improved.When the composite mass ratio of g-C₃N₄and Cd_0.6Ni_0.4S was 3:2,the hydrogen production rate reached the highest,reaching 2690.193μmol/g/h,which was 10.8 times higher than that of Cd S catalyst.The morphology,composition,phase and photoelectric energy of the doped composite catalyst were characterized by BET,SEM,DRS and XRD.The results showed the specific surface area of the catalyst after formed g-C₃N₄and Cd_0.6Ni_0.4S（mass ratio of 3:2）becomed 45.4m²/g,which was 2.9 times that of Cd S catalyst.The increased specific surface area made it easier to separate the photogenerated electrons and holes produced by the catalyst in space,while the doping of elements made the catalyst produce more photogenerated electrons and holes.All the composite catalysts improved the hydrogen production rate from two aspects.Finally,according to the experimental results,the mechanism of photocatalytic reaction with increased hydrogen production rate was proposed.