| Affected by the excessive fossil energy consumption,lack of renewable energy and environmental issues,searching for sustainable energy resources has become a pressing task.Among many new energy sources,H2 is regarded as the most promising green energy in the 21st century because of its advantages such as high heat value of combustion,high energy density,clean and pollution-free.Semiconductor photocatalytic H2 production from water splitting technology is currently regarded as the most ideal H2 development approach,and has attracted great attention from domestic and foreign scholars.At present,the key to promote the development of this technology is to develop economical,efficient and stable photocatalysts.Among many excellent semiconductor photocatalytic materials,Mn,Cd1-xS solid solution has attracted extensive attention due to its adjustable band gap and excellent optical response properties.In this study,the Mn0.2Cd0.8S solid solution with nanowire morphology was used as the matrix.In order to solve the problems of low charge separation efficiency and severe photocorrosion.The p-n Mn0.2Cd0.8S/NiWO4 binary heterojunction was constructed through semiconductor coupling.In addition,through the combining the two strategies of semiconductor coupling and co-catalyst modification,two kinds of co-catalyst modification of Mn0.2Cd0.8S/Co3O4 and Mn0.2Cd0.8S/NiCo2O4 p-n heterojunctions were realized,thereby constructing Mn0.2Cd0.8S/MoS2/Co3O4 and Mn0.2Cd0.8S/Ni2P/NiCo2O4 two ternary heterojunctions,in order to promote the migration and separation of photogenerated charges of Mn0.2Cd0.8S nanowires,and increase the active sites of H2 production reaction,thus improving its photocatalytic H2 production efficiency.In related studies,the crystal structure,microscopic morphology,element composition,specific surface area,light absorption performance and energy band structure of the heterojunction photocatalysts were studied through a variety of characterization methods,and the photocatalytic H2 production activity of the prepared samples was investigated.The charge separation mechanism of heterojunction photocatalysts and the possible photocatalytic H2 production mechanism were discussed.The specific research details are in the following.In part one,a series of Mn0.2Cd0.8S/NiWO4 binary heterojunction were synthesized by hydrothermal method,and their structure characterization and H2 production performance were tested.The results showed that Mn0.2Cd0.8S/NiWO4-30 wt%binary heterojunction exhibited optimal activity of of 17.76 mmol g-1 h-1 and the highest apparent quantum efficiency(AQE)of 17.56%at 420 nm.After four cycle experiments of photocatalytic H2 production,the Mn0.2Cd0.8S/NiWO4-30 wt%binary heterojunction still had good stability.The remarkably improved photocatalytic H2 production performance of Mn0.2Cd0.8S/NiWO4 binary heterojunction could be attributed to the formation of the p-n heterojunction,which not only improved photogenerated charge separation efficiency,but also inhibited the photocorrosion reaction of Mn0.2Cd0.8S,thus improving the photocatalytic H2 production activity of the composite material.In the second part,a series of Mn0.2Cd0.8S/MoS2/Co3O4 ternary heterojunction were prepared by two-step solvothermal method using two strategies of semiconductor coupling and co-catalyst modification,and their structure characterization and H2 production performance were tested.The results showed that the ternary heterojunction loaded with 0.62 wt%MoS2 and 1.51 wt%Co3O4 exhibited the highest photocatalytic H2 production rate of 16.45 mmol g-1 h-1 and the AQE of 16.27%at 420 nm.After six cycle experiments of photocatalytic H2 production,the binary heterojunction still had good stability.The enhanced photocatalytic H2 production activity of ternary heterojunction was attributed to the synergistic effect of semiconductor coupling and co-catalyst modification.On the one hand,the p-n heterojunction was formed between Mn0.2Cd0.8S and Co3O4,which not only improved photogenerated charge separation efficiency,but also inhibited the photocorrosion reaction of Mn0.2Cd0.8S.On the other hand,MoS2 as a co-catalyst could provide sufficient active sites for the system.In the third part,a series of the Mn0.2Cd0.8S/Ni2P/NiCo2O4 ternary heterojunction were prepared by two-step hydrothermal method.In this ternary heterojunction system,the close contact between Mn0.2Cd0.8S and NiCo2O4 formed the p-n heterojunction,and Ni2P as a co-catalyst could provide sufficient active sites,thus achieving efficient H2 production.The results showed that the ternary heterojunction loaded with 2 wt%Ni2P and 5 wt%NiCo2O4 exhibited the highest photocatalytic H2 production rate of 24.47 mmol g-1 h-1 and the AQE of 23.75%at 420 nm.After four cycle experiments of photocatalytic H2 production,the binary heterojunction still had good stability. |
