Surface Atoms Regulation Of Covalent Triazine Frameworks For Gas Selective Adsorption And Separation

Covalent triazine framework（CTFs）is a kind of organic porous polymer containing triazine group.Among various POPs,covalent-triazine frameworks（CTFs）,which are synthesized from dynamic trimerization reactions of simple,cheap,and abundant aromatic nitriles in ion thermal conditions,are a series of high-performance polymer frameworks with excellent thermal and chemical stability.Taking the advantages of their microporosity,high concentration of nitrogen-doping,and unique band structure,CTFs have shown interesting properties for optoelectronic devices,gas adsorption and separation,catalysts,and energy storage devices.For the demand of selective adsorption and separation of gases such as volatile organic pollutants（VOCs）and carbon capture,in this paper,we report that specially designed CTFs exhibit excellent performance on the selective adsorption.In particular,to investigate the influence of the framework pore structure and surface atoms on the gas adsorption performance of CTFs.We study the VOCs air purification and carbon capture capabilities of CTFs materials under real air conditions and combine with theoretical calculations to study the structure-activity relationship between the structure of CTFs and gas adsorption.It is divided into the following three aspects:1)The pore structure design of covalent triazine framework and the study of VOCs adsorption performance:terephthalonitrile and 1,1’-biphenyl-4,4’-dicarbonitrile were used to synthesize CTF-1-400 and CTF-2-400 with tunable porous structures,respectively.we report that specially designed CTFs exhibit excellent performance on the selective adsorption of xylene isomers and the large capability to specifically capture xylenes from the air.One CTF material（CTF-2-400）that is constructed from biphenyls and triazine motifs can effectively adsorb xylene isomers with the remarkable capacities of 523（p-xylene）mg g^-1,exceeding most of the reported porous adsorbents.Its exceptional xylene adsorption ability is vividly illustrated by the column breakthrough experiment,in which CTF-2-400 exhibits a long-lasting ability of capturing xylenes from the air(>196 h g^-1).The excellent xylene adsorption properties of CTF-2-400 is attributed to the triazine rings in the framework,which enhance the polarization of framework and the negative charge distribution of the pore surface,and thus promote adsorption of xylene molecules through multiple C-H…πinteractions.2)Perchloro covalent triazine-based framework for enhanced adsorption of volatile organic compounds:the effective adsorption capacity of a perchlorinated covalent triazine-based framework（Cl CTF-1-400）materials are all greater than 500 mg g^-1 at 25 ^oC,larger than most reported porous adsorbents.We further infer that the multiple C-Cl…πinteractions and H…Cl interactions between the CTFs framework and aromatic molecules account for the observed excellent BTEX adsorption performance.3)Study on direct fluorination of covalent triazine framework and selective gas adsorption separation:to improve selectivity of the materials to CO₂/N₂,CO₂/CH₄,we use a simple process to directly fluorinate CTF with fluorine gas at different temperatures.The results of IAST calculation show that the material after room temperature fluorination has a selectivity of 60.The breakthrough experiment shows that the fluorinated material can capture CO₂ under relatively mild conditions and is a good capturer of CO₂.