Green synthesis of a water-stable thiol-decorated Zr-MOF for selective heavy metal removal

Abstract

A green, water-based synthesis of thiol-decorated, Zr-carboxylate metal–organic framework is reported. A mixture of capping and bridging, thiol containing, organic linker approach utilizing mercaptoacetic acid (MA) and mercaptosuccinic acid (MSA) resulted in an open Zr-based MOF with thiol-decorated cages (Zr-MSA-MA MOF). Tailoring the nanospace within the micropores of water-synthesized and water-stable MSA-MOF led to several desirable attributes including: (i) chemical stability in aqueous media due to strong –CO₂–Zr(IV) linkage, (ii) tight pore system leading to optimized electronic interactions with guest ions, and (iii) thiol-functionalized cages that affect selective capture of soft metal ions. The Zr-MSA-MA MOF demonstrated exceptionally high capacity for Cd (370.4 (±35.5) mg g⁻¹, 3.29 mmol g⁻¹) and Pb (500 (±16.8) mg g⁻¹, 2.41 mmol g⁻¹). It also exhibited remarkable stability indicated by its ability to regenerate and reuse the MSA-MOF for 10 consecutive cycles with nearly 95% retention of initial activity towards heavy metal removal. Moreover, the thiol-decorated MOF demonstrated high selectivity for Pb and Cd in the presence of competing Cu, Zn, Ni, Mn, Fe, and Co ions. These findings highlight the potential of Zr-MSA-MA MOF as a highly efficient, selective, and regenerable sorbent for heavy metal remediation.