Integration of covalent organic frameworks into hydrophilic membrane with hierarchical porous structure for fast adsorption of metal ions

Abstract

Covalent organic frameworks (COFs) including their preparation and application as research focus have attracted attention of researchers. Most of COFs exhibit the powder form, therefore they inevitably suffer many difficulties during use of catalysis, separation and so on. In previous study, our group have fabricated COF-based monoliths through ring-opening polymerization in which the micropores/mesopores of COF were easily blocked by unreacted monomer and solvent resulting in low specific surface area of COF-based monoliths. Herein, we designed and fabricated two kinds of hydrazone-linked COF-integrated chitosan membranes (CM@COF and COF@CM) with hierarchical porous structure using chitosan, poly(ethylene glycol) diglycidyl ether (PEGDE), 1,3,5-triformylphloroglucinol (TP), oxalyldihydrazide (ODH) in the presence of mesitylene and 1,4-dioxane, and acetic acid as catalyst. The resulting CM@COF is monolithic material to overcome disadvantages of COF powder, meanwhile it possessed hierarchical porous structure containing mesoporous and macroporous structure and higher specific surface area (117.4 m2 g-1) than chitosan membrane (0.4 m2 g-1). And the CM@COF was applied to adsorption of heavy metal ion, and its adsorption capacities for Cu(II) and Cr(VI) ions were 144 mg g-1 (pH = 7) and 388 mg g-1 (pH = 6), respectively, indicating that the CM@COF had potential for fast removal of heavy metal ions.