Oxygen vacancy-mediated electron transfer in porous hollow-sphere graphitic carbon nitride/NiCo2O4 composite for ultrasensitive lead ion (Ⅱ) detection

Developing highly sensitive sensors for toxic lead ion (Pb 2+ ) is critical for environmental safety. Herein, a porous hollow-sphere graphitic carbon nitride /NiCo 2 O 4 (phg-C 3 N 4 /NCO)composite was synthesized via hydrothermal-calcination to construct an electrochemical sensing platform. The unique hollow structure of phg-C 3 N 4 enhanced Pb 2+ adsorption via unsaturated nitrogen sites and pore confinement, while NCO nanosheets synergistically accelerated electron transfer through oxygen vacancies and redox pairs (Co 2+ /Co 3+ , Ni 2+ /Ni 3+ ). The composite-decorated glassy carbon electrode (GCE) achieved an ultrahigh sensitivity of 10.94 μA·μM −1 and a low detection limit of 0.010 μM (S/N=3) within the Pb 2+ concentration range of 0.1 μM−7.0 μM, surpassing single-component electrodes (NiO (2.33 μA·μM −1 ), Co 3 O 4 (2.52 μA·μM −1 ), NCO (5.11 μA·μM −1 ), or phg-C 3 N 4 (5.34 μA·μM −1 )) by 2.05−4.71 fold. The sensor exhibited exceptional selectivity against common interferents (Cd 2+ , Cu 2+ , Fe 2+ , Ni 2+ , Zn 2+ , Fe 3+ , phenol, humic acids) and reliable applicability in real water samples with 98.02−112.30% recovery. X-ray photoelectron spectroscopy (XPS) analysis confirmed the strong Pb 2+ adsorption and oxygen vacancy-mediated enhancement mechanism. This work provides a novel strategy for designing high-performance heavy metal ion sensors.