Amide-based covalent organic frameworks materials for efficient and recyclable removal of heavy metal lead (II)

Abstract

Covalent organic frameworks (COFs) materials with designed skeleton structure and controlled pore size are a new class of adsorbent materials for environment remediation. Here, we synthesize two amide-based COFs materials via a polymerization reaction of acyl chloride and amino groups by mechanical ball milling at room temperature for Pb2+ removal as adsorbents. Two types of diamine monomers are selected to construct COFs with different framework structure and functional groups contents, i.e. COF-TP from aromatic diamine and COF-TE from linear diamine. The as-prepared COFs materials display typical lamellar structure, and the amide groups on COFs skeleton are confirmed to behave as active adsorption sites for Pb2+ capture via multi-coordination. COF-TE exhibits superior Pb2+ adsorption capacity to COF-TP, because that less aromatic skeleton and weak π-π stacking of COF-TE facilitate higher internal diffusion of Pb2+ adsorption. Meanwhile, the higher amide group content on COF-TE leads to its higher saturated adsorption capacity of 185.7 mg/g than COF-TP of 140.0 mg/g. Finally, great recycling stability of Pb2+adsorption allows the amide-based COFs materials to be promising adsorbents for heavy metal Pb2+ removal or recovery.