Preparation Of Functionalized Two-Dimensional Covalent Organic Framework Materials And Their Preliminary Investigation Of Adsorption Properties And Applications

Benefited from its excellent properties,covalent organic frameworks（COFs）have been widely used in fields such as adsorption,catalysis and so on.However,the direct synthesis of the expected COFs constructed from designed organic molecular units via various methods sometimes does not achieve the expectations very well.In this paper,many COFs were chosen as matrix to introduce different functional groups and active centers via the post-synthesis functionalization method.Meanwhile,the adsorption capacity,catalytic performance and applications of these synthesized functionalized COFs were further studied.And the research contents of this paper are as follows:（1）In order to solve the serious environmental pollution and human health problems caused by the discharge of industrial wastewater containing Ag⁺,adenine groups were grafted into the pore structure of COFs containing alkyne groups by the facile and effective one-pot tandem“click”reaction.And the obtained COFs with adenine groups can be used for the extraction of Ag⁺.Subsequently,the adsorption capacity of COF-Ad for silver ions at different concentrations was investigated.And the results showed that there was interaction between adenine functionalized COF-Ad and Ag⁺,which contributed to its high adsorption capacity of Ag⁺（61.23 mg/g）at low concentration.Meanwhile,the study also found that COF-Ad exhinbited good selective adsorption for Ag⁺under the influence of other interfering ions.After several cycles,it still maintains great adsorption capacity for Ag⁺,so the functionalized COFs can be used to improve the problem of silver ion pollution in wastewater.（2）Post-synthetic modification（PSM）provided effective approaches for the functionalization of imine COFs.To address the rapid decline of sulfur cathodes caused by the shuttle effect of soluble lithium polysulfide in lithium sulfur batteries,the COFs（COF1）connected by imine bond was selected as the initial matrix material,and 1,4-diethynylbenzene was grafted into the channel of COF1 by aza-Diels-Alder cycloaddition reaction to obtain the intermediate products containing alkynyl units.After that,the cationic COFs（COF-PA-AI）was prepared via one-pot tandem“click”reaction.After doping with sulfur,the obtained cationic COF-based composite（COF-PA-AI/S）displays faster electrochemical kinetics,greater tolerance to high current shocks and better rate performance in the electrochemical tests.The discharge capacity of COF-PA-AI/S was kept at 665.3 m A h g^-1 at 0.5 C,which was higher than that of the neutral COF-Ph/S composite,suggesting that it maight be owing to the ordered channel structure of cationic COF composites and the strong interaction between quaternary ammonium cations and polysulfide anions,which can effectively inhibit the shuttle effect of polysulfides and improve the performance of lithium-sulfur batteries.（3）In order to solve the problem of low efficiency caused by slow electron transfer in the electrocatalytic oxygen evolution reaction（OER）,a series of Co/Fe metal-modified COFs composite catalysts were prepared and used for electrocatalytic OER through the coordination between bipyridine groups and metal ions.And the electrocatalytic tests display that the optimized bimetallic modified COFs composites exhibited great performance for electrocatalytic OER activity compared with monometallic metal Co or Fe loaded COFs composites.Furthermore,compared with other Fe and Co bimetallic modified COFs composites,Co0.75Fe0.25@COF-TB displayed lower overpotential（331 m V）,lower charge transfer resistance and better cycle stability,which can be effectively used as a composite catalyst for OER.