Engineering a three-dimensional ion–Electron co-transport Interface on MXene for multiplex electrochemical determination of heavy metal ions

One-step MXene/CNTs-COOH/CS/IL sensing interface was constructed. • CNTs-COOH alleviated MXene restacking and promoted electron transport. • CS and ionic liquid enhanced metal-ion enrichment and ionic transport. • The sensor simultaneously determined Cd 2+ , Pb 2+ , Cu 2+ , and Hg 2+ . • Real-water results agreed well with ICP-MS measurements. Rationally coordinating ion accessibility, electron transport, metal-ion enrichment, and film stability within a facile electrode architecture remains challenging for multiplex electrochemical analysis. Herein, an MXene-based multicomponent sensing interface was constructed through the one-step integration of carboxylated carbon nanotubes (CNTs-COOH), chitosan (CS), and an ionic liquid (IL) with Ti 3 C 2 T x nanosheets. CNTs-COOH act as conductive nano-spacers that alleviate MXene restacking and improve electronic connectivity, while CS provides coordination-active amino and hydroxyl groups for metal-ion enrichment and contributes to film stability. The incorporation of IL improves component dispersion and ionic transport and partially mitigates the interfacial transport limitation associated with the CS-containing layer. Structural and electrochemical characterization results collectively support complementary roles of the four components in regulating interfacial accessibility, analyte accumulation, and charge-transfer behavior. Under the optimized conditions, the resulting electrode enabled the simultaneous determination of Cd 2+ , Pb 2+ , Cu 2+ , and Hg 2+ by differential pulse anodic stripping voltammetry over linear ranges of 0.5–22.5, 0.5–60, 0.5–87, and 0.5–62 μM, respectively. The corresponding detection limits were 0.1539, 0.0746, 0.2279, and 0.0931 μM. The sensor also exhibited satisfactory selectivity, reproducibility, and long-term stability, retaining approximately 92–95% of its initial response after 30 days. Recoveries of 92.2–96.0% were obtained in spiked tap-water and river-water samples, and the measured concentrations were consistent with those obtained by ICP-MS. These results demonstrate a functionally coordinated interface-engineering strategy for the simultaneous electrochemical determination of multiple heavy metal ions. Download: Download high-res image (139KB) Download: Download full-size image