The Regulation Of Cocatalyst For Non-metallic Photocatalysts Enhanced Photocatalytic Activity Towards Hydrogen Evolution

In the 21st century,energy shortage and environmental problems are two enormous challenges for human beings.Therefore,the development of energy sources that to replace traditional fossil fuels has become a research focus.Solar energy attracted widespread attention because of its inexhaustible unique advantages.Researchers have devoted great efforts to realize the conversion of industrial applications solar energy into energy that can be used directly.Photocatalytic water splitting has become an important branched field of catalysis due to its clean,non-polluting,low energy consumption and renewable characteristics.At present,most of the catalysts used to photocatalytic water splitting are semiconductors,but many of them have low catalytic activity due to the quick recombination of photo-generated charge carriers and wide-bandgap.Therefore,suppressing the recombination of the electron-holes of the catalyst and reducing the bandgap of the semiconductor are the key factors to improve the photocatalytic activity of the catalyst.The loaded cocatalyst also provides an effective approach to improve the activity of the catalyst.In order to enhance the photocatalytic activity of the catalyst,this thesis regulated the ratio of Pt-based and NiS cocatalysts and modified the semiconductor material for improving the charge separation and transfer capabilities.The main research contents and results are as follows:（1）The platinum–tin alloy and platinum–copper decorated graphene nanohybrid（PtSn/GN and Pt Cu/GN）were prepared by an in situ photoreduction deposition method.The hydrogen evolution activity was remarkably improved for PtSn/GN and Pt Cu/GN by dye sensiting under visible light irradiation.The amounts of H₂ produced of PtSn/GN and Pt Cu/GN were 1136μmol and 1008μmol in 6 h,respectively,which was about 2 times higher than that of the Pt/GN under the same reaction condition.This was attributed to the fact that PtSn and Pt Cu alloy cocalysts could promote the efficient charge separation,transfer and provide more active sites for hydrogen production.（2）The CNx photocatalyst was synthesized by calcining g-C₃N₄ using two-step calcination method.The H₂ evolution performance of CNx was improved under visible light irradiation,resulting from the upshift of conduction band of CNx compared to g-C₃N₄,which can drastically enhance the redox driving force and the subsequent photocatalytic activity toward water reduction.The hydrogen production rate of CNx is 1.394 mmol g^-1 h^-1.To further promote catalyst activity,PtSn cocatalyst was introduced onto CNx with the aim of improving photocatalytic water splitting activity.PtSn alloy cocalyst can promote capable of assisting in electron-hole separation.The hydrogen production rate of PtSn/CNx optimized to2.96 mmol g^-1 h^-1,which was 2.13 times higher than that of CNx,and the highest apparent quantum efficiency（AQE）of CNx-4 reached 41.63%at 430 nm.（3）A series of g-C₃N₄/NiS composite photocatalysts were prepared by a simple in-situ ion-exchange process at room temperature.The activity of g-C₃N₄ can be significantly enhanced after loading NiS as cocatalyst.When the loading amount of NiS was 4%,the sample exhibited the highest properties for photocatalytic hydrogen generation about 500μmol g^-1.It is due to the effective transfer of photoelectron.