Post-Functionalization Of Covalent Organic Frameworks Via One-Pot Approach And Their Applications

Covalent organic frameworks（COFs）connected by reversible covalent bonds are a new type of organic porous materials,which possess regular pore structure.In the design and preparation of COFs,choosing reasonable building units and topological structures can achieve accurate control of the pore structure and spatial distribution of COFs.COFs have been widely used in the fields of adsorption and separation of organic compounds,catalysis,optoelectronics and gas and energy storage due to their well crystallinity,low density,high specific surface area,and highly designable.In this work,a series of COFs with high specific surface area were prepared on the basis of imine COFs by adopting a simple and effective economic post functionalization strategy,and were applied to adsorb fluorine-containing pesticides and cathode materials for lithium sulfur batteries.（1）The economical and convenient one-pot approach plays an important role in chemical synthesis and material design.However,there are limited reports on the one-pot synthesis of COFs and their functionalization.In this work,three different functional groups（fluoroalkyl,borate,and alkyl）and three leaving groups（-I,-OTs,-Br）were selected to prove that the multi-component one-pot tandem reaction can be used as an economic strategy for the surface post functionalization of COFs.The results showed that the economic strategy not only greatly shortened the experimental steps,reduced the cost,and improved the economic benefits,but also maintained the good crystalline structure of the prepared COFs materials.Subsequently,we also prepared two kinds of fluorine-containing COF(COF-F_0.5 and COF-F)and butyl-containing COF（COF-bu）through this economic strategy to explore the influence of the COFs nature（porosity and number of functional groups）on the adsorption of fipronil.Compared with COF-F and COF-F_0.5,which both contains contain specific functional groups,the saturated adsorption capacity(194.7 mg g^-1)of COF-F_0.5(1573 m² g^-1)with the largest BET surface area was larger than that of COF-F(149.8 mg g^-1).In addition,compared with butyl grafted COF-bu(122.4 mg g^-1),the adsorption capacity of COF-F(149.8 mg g^-1)with fluoroalkyl chain structure was higher.（2）In this work,the quaternary ammonium salt groups were grafted onto the pores of the COFs to synthesize cationic mesoporous COF（COF-NI）.Then,sulfur was loaded into the porous material COF-NI to obtain COF-NI/S,which was used as the cathode material of lithium-sulfur battery and successfully constructed a lithium-sulfur battery with high capacity and long-term stability.The experimental results show that compared with COF Bu/S(521 m A h g^–1),the discharge capacity of cationic COF-NI/S remains 758 m A h g^–1 after 100 cycles.This reason may be due to the electrostatic interaction between quaternary ammonium salt and polysulfide,which can better capture polysulfide and suppress the shuttle effect,so that the constructed battery has better cycle stability.These results proved that the target COFs can be obtained via reasonable design,thus improving the performance of the lithium-sulfur batteries.