Synthesis and Electrocatalytic Mechanism of SrO/Monolayer C3N4 Composite for Vanillin Detection

Abstract

Synthesis at low temperature and interface characteristics in electrocatalysis for nanocomposites are alternative challenge up to date. A SrO nanoparticles (NPs)/g-C₃N₄ nanosheets (SrO/ng-C₃N₄) composite was prepared by a feasible one-pot synthesis at 80 °C without post-sintering, where SrO NPs (with diameters of 20 ∼ 50 nm) were loaded onto ng-C₃N₄ nanosheets to form an efficient electrocatalyst. By the aid of XPS and FT-IR analysis, it confirms that SrO NPs were anchored in proximity to the s-triazine units of ng-C₃N₄ via SrN bonds. Based on the surface charge characteristics, the electrostatic adsorption between SrO/ng-C₃N₄ and vanillin as a catalysant was verified. C₇H₅O₂⁻ anions after the hydrolyzation and ionization of vanillin in PBS solution were adsorbed on the surface of positively charged SrO/ng-C₃N₄ before electro-oxidation. The electrocatalytically active centers, i.e., oxygen vacancies on the surface of SrO NPs, facilitate in the oxidation of vanillin, and further the overpotential of the electrocatalyst by SrO/ng-C₃N₄ toward vanillin is reduced. A detail eletro-oxidation process of vanillin was identified by UV–vis spectra and differential pulse voltammetry analysis. Based on the Laviron equation, two electrons transfer from vanillin during the oxidation reaction, and speculates the reaction mechanism. Under optimal conditions, vanillin oxidation current is linear to its concentration in the range of 2.0 × 10⁻⁸ to 1.4 × 10⁻⁵M, with a detection limit of 6.7 nM (S/N = 3). The limit value complies with the requirements of the World Health Organization and the Chinese Health Standard. As-prepared sensor applied for the quantification of vanillin in milk samples is long-term stable, selective, and feasible.