Covalent Organic Frame/CdS Composites And Their Photocatalytic Properties

In recent years,photocatalytic water splitting to produce hydrogen has become one of the effective ways to utilize solar energy,and people are actively exploring and developing efficient photocatalysts.As we all know,covalent organic frameworks is a type of semiconductor with visible light absorption ability.It has excellent crystal form,chemical stability,high specific surface area and uniform and ordered pores.It can be used as a attractive carrier for active nanoparticles.This article will consider the three issues of light absorption,photo-generated hole-electron separation and transfer,and surface reaction to prepare an excellent photocatalyst:firstly,a covalent organic framework is used as the carrier material to disperse and stabilize the semiconductor nanometer with visible light response.The purpose of preparing binary composite materials from particles is to optimize the favorable and efficient separation and transfer of photo-generated holes and electrons.Secondly,the introduction of precious metal Pt nanoparticles as co-catalysts to prepare ternary composite materials can quickly capture photo-generated electrons and provide effective proton reduction.Active sites reduce the reaction potential to promote the occurrence of the reaction,and improve the photocatalytic water splitting hydrogen production performance of the composite material.In this paper,CdS nanoparticles are used to modify covalent organic frameworks to prepare binary composites COF/CdS.On the basis of binary composites,precious metal Pt nanoparticles are used as co-catalysts to prepare ternary composites COF/CdS/Pt.The photohole-electron transport mechanism and hydrogen production activity of these two kinds of composites were studied under visible light irradiation.1.TpPa-COF was synthesized by solvothermal method with 1,3,5-trialdehyde resorcinol（Tp）and p-phenylenediamine-benzophenone（Pa）as raw materials.The composite TpPa-COF/CdS was prepared by modification of CdS nanoparticles.The hydrogen production test of photocatalyst performance was carried out in water-ascorbic acid system.The photocatalytic hydrogen production performance of TpPa-COF/CdS composites is closely related to the loading capacity of CdS materials.The hydrogen production rate of TpPa-COF/CdS-7.9%water decomposition is 424 μmol·g^-1·h^-1,which is superior to that of TpPa-COF and CdS materials.When the precious metal Pt nanoparticles are used as co-catalyst to prepare TpPa-COF/CdS composite,the hydrogen production performance of TpPa-COF/CdS composites is significantly higher than that of TpPa-COF/CdS composite.The hydrogen production rate of TpPa-COF/CdS-7.9%/Pt was as high as 5565 μmol·g^-1·h^-1.The increase in hydrogen production performance may be due to the fact that the composite material formed by TpPa-COF and CdS has a matching HOMO/LUMO energy band,which provides a feasible path for photo-generated hole-electron transfer.In addition,the precious metal Pt nanoparticles have excellent electron trapping ability as a co-catalyst,provide more active sites,and promote the reduction of protons H+in water to produce hydrogen.2.TpBD-COF was synthesized by solvothermal method with 1,3,5-trialdehyde resorcinol（Tp）and biphenylenediamine（BND）as raw materials.The composite TpBD-COF/CdS was prepared by dispersing and stabilizing CdS nanoparticles.The hydrogen production performance of TpBD-COF/CdS was tested in the water-ascorbic acid system.The hydrogen production performance of TpBD-COF/CdS^-10.1%composite is affected by different CdS nanoparticles loads.The hydrogen production rate of TpBD-COF/CdS^-10.1%composite is 515μmol·g^-1·h^-1,which is better than that of TpBD-COF material.When precious metal Pt nanoparticles were used as co-catalyst to prepare TpBD-COF/CdS/Pt composites,the hydrogen production rate of TpBD-COF/CdS^-10.1%/Pt was as high as 4144μmol·g^-1·h^-1.The possible reason for the improvement of hydrogen production performance is that the spatial structure of the TpBD-COF material provides loading sites for CdS and Pt nanoparticles.On the one hand,the band structure matched by TpBD-COF and CdS provides a feasible path for the transfer of electrons.On the other hand,Pt nanoparticles with metallic properties are used as co-catalysts and have excellent electron capture capabilities,which can further promote electron transfer and participate in surface reactions,thereby improving hydrogen production performance.