Design And Synthesis Of Triazine-based Covalent Organic Framework (CTF-1) Composites For Photocatalytic Hydrogen Evolution

Photocatalytic decomposition of water for hydrogen production is considered as a clean hydrogen energy preparation technology because of its mild reaction,simple operation and direct utilization of solar energy.At present,there are low efficiency and unstable catalyst problems widely in the developed photocatalytic hydrogen production system,and the reasonable construction of composite materials has the advantages of improving the properties,changing the active sites and improving the stability of materials are effective strategy to solve these problems.Therefore,the design and development of efficient and stable composite photocatalysts is the key to develop photocatalytic decomposition of water hydrogen production technology.Covalent organic frameworks（COFs）are gradually becoming a promising class for high-efficiency photocatalysts due to their unique composition and structural characteristics.Among them,triazine-based COFs are particularly attractive in the design and development of composite photocatalysts because of their excellent visible light absorption and conductivity,as well as the strong electronegativity of triazine structure.However,there are few reports on the design and synthesis of triazine based COFs composites.Consequently,in this paper,the design and synthesis of triazine based COFs composite was explored,and its photocatalytic decomposition of water for hydrogen production was studied in detail.The specific research contents and conclusions are as follows:（1）CdS NPs-decorated covalent triazine-based frameworks（CdS NPs/CTF-1）were controllably synthesized via a facile one-pot solvothermal method.The strong electronegativity of the triazine structure in the composites impels CdS to be highly dispersed on the CTF-1 surface in the form of nanoscale size.Furthermore,the results of photoelectrochemical tests show that the strong interaction between CdS NPs and CTF-1 is not only beneficial to the effective separation of photogenerated electrons and holes,but also overcomes the aggregation of CdS NPs and photocorrosion,which will greatly promote its photocatalytic hydrogen production efficiency in theory.The as-prepared CdS NPs/CTF-1 assembly showed higher photocatalytic activity in hydrogen evolution reaction under visible light irradiations as compared with pure CdS,CTF-1 and their physical mixture.（2）The cyano groups on the surface of the CTF-1 were converted into carboxyl groups under the action of alkali,and the monodisperse Pt nanoparticle-loaded Pt NPs/CTF-COOH complex materials were prepared on its surface by photodeposition.The strong nucleophilic property of COO^-can provide anchor point for Pt deposition,and carry out strong interaction,so that it can obtain highly stable,monodisperse and uniform Pt NPs on CTF-1.COO^-not only as anchor points,but also as a tie of CTF-1 and Pt NPs.It can provide a dynamic channel for the charge transfer between them,which can effectively improve the separation efficiency of photoinduced charge of composite materials.The photocatalytic hydrogen production results show that despite the influence of cyano hydrolysis amount on the catalytic activity,the hydrogen production efficiency of the prepared Pt NPs/CTF-COOH(4853μmol·h^-1·g^-1)is much higher than that of Pt/CTF-1 composites without carboxylation modification(1220μmol·h^-1·g^-1).The innovation of this paper:（1）Coupled with the strong electronegativity of triazine structure and CdS photocatalytic hydrogen production performance,a highly efficient and stable photocatalytic hydrogen production system of CdS NPs/CTF-1composites was constructed.（2）The CTF-1 was modified by alkaline hydrolysis of cyano group,a stable and efficient Pt NPs/CTF-COOH hydrogen production system was constructed.The application scope of CTF-1 was expanded,which provided theoretical guidance for the development of efficient COFs photocatalytic system.