Oxygen vacancy mediated step-scheme heterojunction of WO2.9/g-C3N4 for efficient electrochemical sensing of 4-nitrophenol

•An S-scheme heterojunction of Vo-S-WO2.9/g-C3N4 was fabricated.•The formation of S-scheme heterojunction can induce built-in electric field.•The sensor exhibited superior electrochemical performance for detecting 4-NP.•With the introduction of Vo, excitons can be dissociated into free-charge-carriers. Excitonic effects induced via Coulomb interactions and an appropriate interfacial contact of electrode modified materials play crucial roles in transfer/separation of interfacial charge carriers during the electrochemical sensing process. Herein, an oxygen vacancy (Vo) mediated step-scheme (S-scheme) heterojunction of WO2.9/g-C3N4 was fabricated by electrostatic self-assembly of high-purity commercial WO2.9 nanoparticles and ultrathin g-C3N4 nanosheets, where g-C3N4 nanosheets were prepared via polymerization followed ultrasonic-assisted exfoliation. The fabricated Vo-S-scheme WO2.9/g-C3N4 heterojunction-based sensor exhibited superior electrochemical performance for detecting environmental hormone 4-nitrophenol (4-NP). Due to the introduction of Vo, an increased free-charge-carriers, a built-in electric field and a high adsorption energy are generated at the heterojunction interface, which all can significantly improve the sensitivity of this proposed sensor. It also showed good reproducibility, high accuracy, good recovery, and strong feasibility for 4-NP detection in real samples. This work not only conduces significantly to understanding the defective structures and S-scheme heterojunctions, but also provides new insights into designing and constructing novel efficient electrochemical sensors.