Bismuth-based conductive MOF/COF hybrids enable efficient electrochemical heavy metal ion quantification

Abstract

The high toxicity of heavy metal ions (HMIs), especially Pb2+ and Cd2+, makes them a serious concern for human health and environmental safety. Therefore, it is crucial to develop sensitive, accurate, and portable methods for HMIs monitoring. Conductive metal-organic frameworks (MOFs) not only possess large surface area and abundant metal active sites but also own high electrical conductivity, greatly expanding their electrochemical applications. Integrating MOFs with covalent organic frameworks (COFs) has been regarded as an effective way to design highly efficient electrocatalyst. In the present work, a hybrid of bismuth-based conductive MOF based on 2,3,6,7,10,11-hexathioltriphenylene (Bi-HHTP) and COF (Bi-HHTP/COF) was produced for the first time in electrochemical quantification of Pb2+ and Cd2+ through differential pulse anodic stripping voltammetry (DPASV). Due to the synergistic effect of Bi-HHTP with excellent electronic conductivity and abundant adsorption sites for Cd2+ and Pb2+ as well as COF with extremely high porosity, good electronic conductivity and high specific surface area, the Bi-HHTP/COF hybrid achieved a boosted electrochemical capability for Cd2+ and Pb2+. In the range of linearity of 2.5–400 μg/L, this sensor can determine Pb2+ and Cd2+, featuring detection limits of 0.67 and 0.18 μg/L, respectively. Environment and food samples including milk, lake water, honey and tap water were employed as real samples for the analysis of Pb2+ and Cd2+, and acceptable results of recovery were gained. Meanwhile, the sensor owned outstanding anti-interference properties, stability and reproducibility. This work not only introduces an effective approach for building bismuth-based conductive MOF/COF hybrids but also proves application potential in electrochemical heavy metal ion determination.