Water-stable metal-organic frameworks for aqueous removal of heavy metals and radionuclides: A review

Abstract

Heavy metals and radionuclides in water are a global environmental issue, which has been receiving considerable attention worldwide. Water-stable MOFs are green and recyclable materials to eliminate the environmental impacts caused by the hazardous heavy metal ions and radionuclides in water. This paper presents a systematical review on the current status of water-stable MOFs that capture and convert a wide range of heavy metal ions (e.g., As(III)/As(V), Pb(II), Hg(II), Cd(II), and Cr(III)/Cr(VI)) and radionuclides (e.g., U(VI), Se(IV)/Se(VI) and Cs(I)) in aqueous solution. Water-stable MOFs and MOF-based composites exhibit the superior adsorption capability for these metal species in water. Significantly, MOFs show high selectivity in capturing target metal ions even in the presence of multiple water constituents. Mechanisms involved in capturing metal ions are described. MOFs also have excellent catalytic performance (photocatalysis and catalytic reduction by formic acid) for Cr(VI) conversion to Cr(III). Future research is suggested to provide insightful guidance to enhance the performance of the MOFs in capturing target pollutants in aquatic environment.

Keywords: Adsorption; Heavy metals; Metal-organic frameworks; Photocatalytic reduction; Pollution remediation; Radionuclides.