Synthesis,Characterization And Photocatalytic Performances Of Covalent Triazine Framework Photocatalysts

Covalent triazine frameworks(CTFs)as a new class of covalent organic frameworks(COFs)which are composed of triazine units have recently attracted considerable attention for their unique chemical functionalities and structural properties.Recently,they have been explored as catalysts for organic synthesis and sorbents for gas storage.However,the reports about their applications in photocatalysis are still less and the applications are still limited by critical preparation conditions and poor photocatalytic activity.Therefore,if the covalent triazine frameworks can be prepared under an optimized condition and their electronic band structures can be optimized by the nonmetal doping,the photocatalytic activity may be improved effectively.In the present thesis,a kind of CTFs has been synthesized by the terephthalonitrile trimerization reactions at room temperature.And then,the as-prepared CTF was further modified by the sulfur or phosphorus doping through a simple solid reaction method.The main results and conclusions obtained from the present research are as follows:(1)The CTF has been successfully prepared at room temperature and explored as a photocatalyst for water splitting into H2 under visible light irradiation for the first time.The characterizations show that the as-prepared CTF as a kind of organic porous materials has a layered crystalline structure and a band gap of 2.94 eV.The photocatalytic tests show that CTF exhibits excellent photocatalytic activity and stability for H2 evolution under visible light irradiation.The apparent quantum efficiency of the H2-evolving half-reaction is about 2.4%at 420 nm.(2)The sulfur-doped CTFs(CTFSx)have been successfully prepared by a solid reaction method using CTF and sublimed sulfur as precursors.The CTFSx photocatalysts show much higher photocatalytic hydrogen evolution activity than the pristine CTF.Notably,the highest photocatalytic activity obtained at CTFS10 is about 5 times higher than that of pristine CTF sample.The rate of hydrogen evolution reaches 10.2 ?mol h-1.(3)The phosphorus-doped CTFs(CTFPx)have been successfully prepared by a solid reaction method using CTF and red phosphorus as precursors.The CTFPx photocatalysts show much higher photocatalytic hydrogen evolution activity than the pristine CTF.Notably,the highest photocatalytic activity obtained at CTFP10 is about 5 times higher than that of pristine CTF sample.The rate of hydrogen evolution reaches 9.9 ?mol h-1.The original results of this study are as follows:(1)Aiming at the critical conditions of the preparation of covalent triazine frameworks,we developed a mild liquid polymerization method at room temperature for the covalent triazine frameworks which could avoid the contamination of metallic residue.And the as-prepared CTF has been explored as a visible-light-driven photocatalyst for H2 evolution reation for the first time.This approach could also be used to prepare other CTFs from different monomers.(2)The electronic band structure of the as-prepared CTF has been modified by the nonmetal doping for the first time,which can not only widen the photoresponse scope of the CTF but also improve the production and separation efficiency of photoinduced electron-hole pairs,thus enhance their photocatalytic activity effectively.