Construction And Performance Of Sulphide-Based Photocatalysts Toward Hydrogen Evolution From Water Splitting

With the development of society and the improvement of people's living standards,the demand for energy is increasing in today's society.The problem of energy shortage and environmental pollution is becoming more and more serious.Therefore,it is urgent to seek sustainable development of clean energy to replace traditional fossil fuels.Solar energy is favored by governments and researchers due to its advantages of free availability,local materials availability,and no pollution.The photocatalytic decomposition of water to produce hydrogen by semiconductor has attracted wide attention because of its advantages such as mild reaction conditions,simple operation,low cost and economic application.Sulfide solid solution is considered to be one of the most promising photocatalysts due to its narrow band gap,and the proper position of the conduction band and valence band.This article systematically explored the relationship between the synthesis method,microstructure and apparent morphology of the sulfide solid solution photocatalyst and hydrogen production activity.The main research contents are as follows:1. A novel Co₃O₄/Cd_0.9Zn_0.1S photocatalyst with p-n heterojunction was constructed,which showed high efficiency in photocatalytic water splitting for hydrogen evolution under visible light.When the content of cobalt atom was 2 mol%,the hydrogen production rate of Co₃O₄/Cd_0.9Zn_0.1S was the highest(139.78 mmol·g^-1·h^-1),which was better than that of Co₃O₄/Cd_0.9Zn_0.1S-M(26.24 mmol·g^-1·h^-1)and Pt/Cd_0.9Zn_0.1S(15.69 mmol·g^-1·h^-1).The excellent hydrogen production performance was mainly due to the p-n heterojunction formed between Co₃O₄ and Cd_0.9Zn_0.1S and the enhancement of the visible light absorption ability,which enabled the effective separation and transfer of photogenerated carriers.2. Mn_xCd_1-xS solid solution with different composition and apparent morphology could be obtained by changing the ratio of manganese source and cadmium source via one-step solvothermal method.When the ratio of manganese atom to cadmium atom was 3:7,Mn_0.3Cd_0.7S was nanorod-like structure with the highest hydrogen production rate.Then,with Mn_0.3Cd_0.7S as the main catalyst and Cu?NO₃?₂·3H₂O as the copper source,Cu S/Mn_0.3Cd_0.7S complex was prepared by simple ion exchange method,1 mol%Cu S/Mn_0.3Cd_0.7S has the highest hydrogen production rate(93.03 mmol·g^-1·h^-1),which was significantly better than pure Mn_0.3Cd_0.7S and Cu S/Mn_0.3Cd_0.7S-M.The presence of Cu S promoter accelerated the migration rate of photogenerated carriers,and Cu S/Mn_0.3Cd_0.7S photocatalyst with higher hydrogen production activity could be obtained.3. The Ni S/Mn_0.3Cd_0.7S p-n heterojunction photocatalyst was synthesized by simple one-step hydrothermal method,when the content of Ni S is 1 mol%,Ni S/Mn_0.3Cd_0.7S had the highest hydrogen production rate,reaching 65.81 mmol·g^-1·h^-1,which was higher than Ni S@Mn_0.3Cd_0.7S synthesized by the two-step method(26.01 mmol·g^-1·h^-1).Ni S was in close contact with Mn_0.3Cd_0.7S,forming a large number of p-n junctions,which was conducive to the timely transfer and separation of photogenerated carriers and significantly improved their photocatalytic hydrogen production activity.4. Ni₂P loading and Ni²⁺doping could be achieved simultaneously in Ni₂P/Ni²⁺-Mn_0.3Cd_0.7S composite photocatalyst through one-step solvothermal process.After Ni₂P loading and Ni²⁺doping,the rate of Mn_0.3Cd_0.7S photocatalytic decomposition of water to produce hydrogen significantly increased.Ni₂P/Ni²⁺-Mn_0.3Cd_0.7S-10 had the highest hydrogen production rate,reaching 60.45 mmol·g^-1·h^-1,which was 1474 times that of pure Mn_0.3Cd_0.7S.accelerating the migration rate of photogenerated carriers.Ni²⁺doping introduced impurity level above the Mn_0.3Cd_0.7S valence band,broadening the spectral response range,thus promoting the improvement of photocatalytic decomposition of water to produce hydrogen.5. Using one-step solvothermal method,Mn_0.3Cd_0.7S as the main catalyst,amorphous Fe_xP modified Mn_0.3Cd_0.7S nanocomposites were synthesized.After the loading of Fe_xP,the hydrogen production activity and stability of Mn_0.3Cd_0.7S increased rapidly.The hydrogen production rate of 20 mol%Fe_xP/Mn_0.3Cd_0.7S was as high as 31.42 mmol·g^-1·h^-1,which was766.34 times that of pure Mn_0.3Cd_0.7S.After 24 hours of reaction,the hydrogen production rate hardly dropped.The reason for the improvement of photocatalytic hydrogen production activity and stability was as follows:amorphous Fe_xP as cocatalyst provided hydrogen production active sites,reducing H⁺to H₂.XPS characterization results showed that the Fe-S bond formed between Fe_xP and Mn_0.3Cd_0.7S was conducive to the migration and separation of photogenerated carriers,and promoted the improvement of photocatalytic decomposition of water to produce hydrogen.