Advanced functional carbon electrode for ultra-sensitive detection of hexavalent chromium in water: Performance, mechanism, and application

Accurate and rapid detection of trace Cr(VI) in water is essential for environmental pollution control and human health protection. In this study, we developed a novel electrochemical sensor co-modified with polyaniline-functionalized Fe 3 O 4 nanoparticles and a Ce-based metal–organic framework (Ce-MOF). The unique interface morphology and outstanding electrocatalytic properties of the modified electrode enabled ultra-sensitive detection of Cr(VI), with excellent linearity in the range of 1 to 1000 μg/L and a limit of detection (LOD) of 0.05 μg/L. Combined with DFT and XPS analysis, the catalytic mechanism of the Ce and Fe bimetals for Cr(VI) detection was deeply investigated. The Cr d-orbitals are hybridized with Fe d-orbitals and O p-orbitals around −5.0 eV, indicating strong electronic coupling between Cr atoms and Fe/O atoms is achieved based on the optimized model structure (Fe 3 O 4 /Ce-MOF/Cr). Additionally, Ce facilitated the valence cycling of Fe, promoting Fe 2+ generation and enhancing electron donation, which in turn improved the reduction of Cr(VI). Significantly, we firstly integrated this composite with laser-induced graphene technology to create flexible integrated electrodes that meet practical requirements, breaking through the previous limitations of poor portability and expanding application scenarios. This study provides new insights for accurate, efficient, and portable on-site detection of Cr(VI) in water environments.