Unlocking coordinatively unsaturated Bi sites in mixed-linker Bi-MOFs on laser-induced graphene electrode for on-site monitoring of toxic heavy metals.

Background

To protect public health and ensure food safety, heavy metal ions in environment and food must be identified both quickly and accurately. Electrochemical techniques have become a focus of research interest, largely owing to their potential for simultaneous quantification of multiple heavy metal ions, low cost, ease of miniaturization, and simple operation.

Results

A newly developed electrochemical sensor using a defective bismuth-based metal-organic framework (BiFcFc'-MOF) on laser-induced graphene (LIG) is reported for the simultaneous analysis of Pb2+ and Cd2+ ions. The BiFcFc'-MOF was synthesized using Bi ions coordinated with 1,1'-ferrocene dicarboxylic acid (Fc) and ferrocene carboxylic acid (Fc') as mixed π-conjugated linkers, which creates abundant coordinatively unsaturated Bi sites. The combination of BiFcFc'-MOF and LIG allows for large surface area and rapid electron transfer through the conductive LIG network, resulting in an enhanced sensitivity and a reduction in detection limits (LOD). The sensor demonstrates low LOD values of 0.38 μg/L for Cd2+ and 0.98 μg/L for Pb2+ under optimal conditions, surpassing numerous electrochemical platforms in performance. The practical potential was also confirmed by applying the sensor to lake water, soil, soybean, sorghum, and rice, yielding satisfactory recovery rates. Significance and Novelty: A defective BiFcFc'-MOF with abundant coordinatively unsaturated Bi sites is first fabricated via a mixed ferrocene-based ligand strategy, breaking the activity-conductivity trade-off of conventional MOFs. This study presents a hopeful strategy for on-site monitoring of toxic metal ions in complex samples.