Boric acid functionalized triazine-based covalent organic frameworks with dual-function for selective adsorption and lithium-sulfur battery cathode

Functional triazine-based covalent organic frameworks (COFs) with boric acid units, COF-Tr-BA, are designed and synthesized via cycloaddition of imine-linked COFs, COF-Tr, with (4-ethynylphenyl) boronic acid. Owing to the chemical interaction between boric acid units and adjacent dihydroxyl groups, COF-Tr-BA is used as the adsorbent for the selective adsorption of genistein isomer 4′6,7-trihydroxyisoflavone, showing an excellent selectivity and great adsorption performance with 5.4 times adsorption capacity (67.5 mg g−1) as high as 4′5,7-trihydroxyisoflavone (12.5 mg g−1). Meanwhile, COF-Tr-BA as the sulfur host for lithium-sulfur (Li-S) battery also exhibits a better electrochemical property, giving an initial discharge capacity up to 1349 mA h g−1 and a substantial capacity of 627 mA h g−1 after 200 cycles at 0.5C. It is attributed to the sulfiphilic interaction between the introduced boric acid groups and polysulfides (PSs), as well as the lithiophilic interaction between N atoms from quinoline and triazine moieties on the backbone of COF-Tr-BA and lithium ions (Li+), thus alleviating the dissolution and reducing the shuttle effect of LiPSs. The boric acid functionalized material COF-Tr-BA with the dual-function for selective adsorption and Li-S battery proposed here lays a significant foundation for multifunctional COFs as a versatile platform in practical application.