Oxygen vacancy-engineered NiCo2O4 nanorods/coconut shell biochar hybrids for highly sensitive and selective Pb2 + electrochemical detection

Driven by the urgent demand for ultrasensitive detection of trace lead (Ⅱ) ions (Pb 2+ ), we developed a novel electrochemical sensor based on oxygen vacancy-engineered NiCo 2 O 4 (NCO) nanorods anchored on coconut shell-derived porous biochar (BC). The BC/NCO composite was prepared via a synergistic NaHCO 3 -assisted one-step carbonization activation and hydrothermal metal oxide doping strategy, which simultaneously introduced abundant oxygen vacancies and optimized the heterostructure interface. The unique rod-like morphology of NCO, coupled with abundant oxygen-containing functional groups on BC, creates synergistic adsorption-catalytic sites for Pb 2+ . The BC/NCO-modified glassy carbon electrodes (GCE) demonstrate exceptional sensitivity (24.90 µA·µM −1 ), outperforming bare GCE (0.60 µA·µM −1 ), BC-modified GCE (7.92 µA·µM −1 ), and NCO-modified GCE (4.90 µA·µM −1 ) by 42.03-fold, 3.14-fold, and 5.08-fold, respectively. This performance is attributed to oxygen vacancy-mediated electron transfer acceleration, redox pair interactions (Co 2+ /Co 3+ , Ni 2+ /Ni 3+ ), and enhanced Pb 2+ adsorption via complexation and pore confinement. The sensor achieves an ultralow detection limit of 0.004 µM (S/N = 3) and maintains robust anti-interference performance against common coexisting interferences (Cd 2+ , Cu 2+ , Fe 2+ , Ni 2+ , Zn 2+ , Fe 3+ , Hg 2+ , As 3+ , Cr 6+ , catechol, hydroquinone, resorcinol), with 98.3 −106.5 % recovery in real water samples. This work not only advances the design of eco-friendly sensing platforms through defect engineering and biomass valorization but also demonstrates high practicality for on-site heavy metal monitoring.