Preparation Of Hybrid CdS-Based Composite Photocatalyst And Its Hydrogen Production Performance

In recent years,the heavy use of chemical resources has caused very serious environmental pollution and energy crisis.As a new generation of clean and pollution-free energy,hydrogen has high energy density(122 kJ g^-1)and environmental friendliness,and is considered as an attractive alternative energy carrier.Therefore,people have explored various methods to obtain hydrogen,but traditional methods such as thermochemical hydrogen production have some problems such as large energy consumption.Therefore,the use of solar photocatalytic technology to produce hydrogen is a potential method.Among many semiconductors,CdS has a series of excellent characteristics,such as a suitable band gap for visible light absorption,a conduction band potential for reduction,and a rich presence on earth.However,the rapid recombination of photogenerated electron-hole pairs and photocorrosion phenomena have limited their development.Therefore,people have explored various methods to solve these problems,such as constructing heterojunctions,ion doping,and morphology control.In this work,organic-inorganic hybrid material CdS-diethylenetriamine（CdS-DETA）is used as an example to systematically describe how to improve the photocatalytic hydrogen production performance and stability of CdS-DETA.The specific research results are as follows:1.We synthesized the CdS-DETA-based semiconductor composite by hydrothermal method.First,we synthesized the organic-inorganic hybrid material CdS-DETA as a precursor by using sulfur,cadmium chloride,and diethylenetriamine（DETA）.Then the WO₃/CdS-DETA composite of Z-scheme is formed by in-situ growth.The research results show that the introduction of the Z-scheme photocatalytic system formed by WO₃ can effectively promote the spatial separation of photogenerated electron-hole pairs and has a strong redox properties,which improves photocatalytic hydrogen production performance and stability.2.Graphene has a high specific surface area,excellent optical properties and good electrical conductivity and is widely used in the field of photocatalysis.In this study,we first use carbon nanotubes to exfoliate to form porous graphene（PGO）,and then grow CdS-DETA in situ by hydrothermal method to form porous reduced graphene（PRGO）/CdS-DETA composite.Porous graphene modification has better properties than ordinary graphene.The larger specific surface area can provide more active sites.Therefore,photogenerated electron-hole pairs can be separated more quickly,which further improves the photocatalytic hydrogen production performance of PRGO/CdS-DETA composites.3.At present,most photocatalytic systems use noble metals as co-catalysts to accelerate the migration of electrons and efficiently separate electron-hole pairs,thereby improving the photocatalytic performance.In the above study,we used noble metal Pt as the co-catalyst,and the noble metals are expensive,so in subsequent studies we introduce noble-metal-free metal Ni₂P as a co-catalyst to make the electrons on the conduction band of CdS-DETA efficiently migrate to noble-metal-free metal Ni₂P,which reduces the recombination rate of electron-hole pairs in CdS-DETA and improves photocatalytic performance.4.Although we introduced noble-metal-free metal Ni₂P as a co-catalyst,the hydrogen production activity is still not ideal.Based on the above investigation,CdS-DETA is used as the base material,and then 2D/2D step-scheme SnNb₂O₆/CdS-DETA heterojunction is built,the heterojunction enables the electron-hole pairs to be effectively separated and maintains the strong redox properties of each single component.Finally,the noble-metal-free metal Ni₂P was used to modify the SnNb₂O₆/CdS-DETA heterojunction to form a new ternary structure,which further accelerated the electron transfer and further enhanced the catalytic activity.