Design And Preparation Of Two-dimensional CTF Materials And Their Application In The Field Of Photocatalysis

The covalent triazine framework(CTF)is one of the novel organic polymers constructed by various organic monomers via covalent bonds,which can be considered as a kind of"functional g-C₃N₄".The structure and corresponding performance of CTF can be finely tuned at molecular level through selection of appropriate organic building blocks.Therefore,it possesses great potential for some applications.In this work,several photoactive 2D CTF materials were prepared by condensation of aldehydes and amidines monomers and their performances for photocatalytic hydrogen production and photocatalytic oxidation were investigated.Especially,the relationships between structure and photocatalytic property,as well as the photocatalytic mechanism were explored.The main summary is as follows:(1)The stacking manners of two-dimensional CTF materials were finely tuned via introducing methyl groups and the effect of stacking manner on photocatalytic hydrogen production was explored.A series of two-dimensional CTF materials with different stacking manners were prepared by designing tridimensional organic monomers with methyl groups.The characterization results show that the obtained two CTF with different stacking manners possess similar intrinsic properties,such as light absorption properties,charge-carrier lifetime,band structure,but their photocurrent density and interfacial charge transfer impedance properties are quite different.The relevant mechanism analysis shows that the compact stacked CTFs have shorter interlayer distance,which can promote electron tunneling process,and then can improve electron migration rate to active sites,boosting hydrogen production activity.On the contrary,the longer interlayer distance of incompact stacked CTFs suppress the electron tunneling process and ultimately leads to lower photocatalytic activity.(2)Two-dimensional CTF material containing alkynes was prepared for photocatalytic water splitting for hydrogen evolution.The existence of alkynes avoids the space resistance of hydrogen atom on benzene ring and improves the compact stacking degree of two-dimensional CTF.The morphology and optoelectronic properties of the CTF show that the conjugation of alkynyl and benzene ring increased the degree of electron delocalization,so that the electrons can transport more efficiently.This also provides new ideas for improving photocatalytic performance.(3)Electron-deficient two-dimensional CTF material containing benzothiadiazole was prepared for photocatalytic oxidation.Experiment results show that the CTF with benzothiadiazole unit possesses higher photocatalytic oxidation activity than electron-rich two-dimensional CTF material containing alkynyl group,which can be attributed to the inherent appropriate band structure,higher photocurrent density and lower interfacial charge transfer impedance of the CTF containing benzothiadiazole.The results of photocatalytic experiments show that the conversion and selectivity of thioanisole oxidation to sulfoxide were up to 100%and 98%in the presence of oxygen.Besides,it owns good cycle stability,which makes the material outstanding in photocatalytic organic transformation.