Electrochemical determination of gallic acid using a sensitive sensor based on g-C3N4/AuNPs modified carbon paste electrode

Abstract

Introduction: Gallic acid (3,4,5 hydroxybenzoic acid) is an important phenolic acid in industry and exists in plants as free or conjugated form. Gallic acid is used in food, medicine, paper and photography industeries, besides its therapeutic and antioxidant properties [1,2]. Using modified electrodes to identify trace elements and chemical markers is a common method in electrochemistry. Graphitic carbon nitride (g-C3N4), is a graphite-like material with a two-dimensional layered structure that can improve the kinetics of electron transfer reactions occurred on the modified electrode surface. It is a class of polymeric materials mainly composed of carbon and nitrogen covalently bonded by π-conjugation. Application of gold nanoparticles beside g-C3N4 (g-C3N4/AuNPs) in electrochemical sensors is of high importance and innovation [3]. Experimental / Methods: In this study, g-C3N4/AuNPs nanocomposite was synthesized by in situ wet chemical reduction method to modify the carbon paste electrode (g-C3N4/AuNPs/CPE). Analytical methods such as FTIR, XRD, EDX and SEM images were used to characterize g-C3N4/AuNPs structure and morphology. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were used to investigate the electrodes conductivity and electrochemical behavior of gallic acid on the surface of the g-C3N4/AuNPs/CPE. Results and discussion: The EIS results showing that the charge transfer resistance (RCT) of the modified g-C3N4/AuNPs /CPE was greatly reduced compared to the bare CPE (250 vs. 1500 Ω, respectively). The CV voltammogram of g-C3N4/AuNPs/CPE were recorded in phosphate buffer (PBS; 0.1 M, pH 2.0) containing 2.5 µM GA with scan rate of 0.1 Vs-1. In this cyclic voltammogram the anodic and cathodic peaks for GA was observed around potentials 0.5 and 0.45 V, respectively. Also, regards to GA determination through DPV, the linear range of 0.16-4.0 µM and detection limit of 0.25 µM were obtained. Furthermore, due to the presence of GA as a potential marker with plant origin in honey, the proposed g-C3N4/AuNPs/CPE was successfully used to its measurement in thyme honey (0.016 mg/g). Conclusion: Due to the favorable performance of the fabricated g-C3N4/AuNPs/CPE, it can be used to measure gallic acid in food products of vegetable origin, including honey, herbal extracts, etc.