Fe-Doping-Regulated CoMoO ₄ with Synergistically Optimized Co ²⁺ /Co ³⁺ Ratio and Oxygen Vacancies for Highly Sensitive Hg ²⁺ Detection

Mercury ions (Hg 2+ ) are highly toxic heavy-metal pollutants in aquatic environments because of their strong mobility and pronounced bioaccumulation. To achieve highly sensitive and anti-interference electrochemical detection of Hg 2+, In this study, a three-dimensional (3D) nanoflake electrocatalyst (CFMO) was synthesized using a simple one-step method. By optimizing the Fe loading, an optimized CFMO-2 was prepared. The effects of Fe doping on the material structure, surface electronic states, and sensing performance were systematically investigated. The results show that Fe incorporation effectively regulates the Co 2+ /Co 3+ ratio and promotes the formation of oxygen vacancies (OVs) without destroying the main crystal phase of CoMoO 4, thereby reconstructing the surface electronic structure. Benefiting from a more favorable Co 2+ /Co 3+ ratio, abundant OVs, and stronger interfacial electron-transport capability. By optimizing the Fe loading, an optimized CFMO-2 was prepared, with a sensitivity of 26.74 μA μM –1 and a limit of detection (LOD) of 11 nM, together with good anti-interference ability, repeatability, and applicability to real water samples. These results demonstrate that the synergistic optimization of Co valence-state regulation and defect enrichment induced by Fe doping is an effective strategy for improving the electrochemical sensing performance of CoMoO 4 -based materials toward heavy metals.