A copper(ii)-based metal–organic framework: electrochemical sensing of Cd(ii) and Pb(ii) and adsorption of organic dyes†

A new inorganic–organic hybrid complex, namely [Cu₃L₂(DMF)₂]·H₂O (Cu-L), has been synthesized using a sulfur-rich ligand, 3,3′,3′′-(1,3,5-triazine-2,4,6-triyltrisulfanediyl)tripropanoic acid (H₃L) and metal cations under hydrothermal conditions. The metal atoms are interconnected to form a paddle-wheel-like structure, which is ultimately linked to the ligands to create a three-dimensional architecture. Cu-L, employed to fabricate an electrochemical sensor denoted as Cu-L@GCE (glassy carbon electrode), is capable of simultaneously detecting Cd²⁺ and Pb²⁺ at approximately −0.82 V and −0.58 V (vs. Ag/AgCl reference), exhibiting high sensitivity and selectivity. Cu-L@GCE demonstrates broad linear detection ranges of 8–28 μM for Cd²⁺ and 2–14 μM for Pb²⁺, along with low limit of detection (LOD) values of 0.01363 μM and 0.00212 μM, respectively. Furthermore, Cu-L@GCE achieves LOD values of 0.00209 μM and 0.000034 μM when detecting both ions simultaneously. The constructed sensor successfully detects Cd²⁺ and Pb²⁺ in mineral water, tap water, and river water with satisfactory recoveries. Additionally, the adsorption performance for organic dyes has been studied in detail using Cu-L as an adsorbent. The results indicate good adsorption selectivity for methylene blue (MB) and neutral red (NR) compared to methyl orange (MO) and rhodamine B (RhB) molecules.