Graphitic carbon nitride (g-C3N4/Fe3O4/BiOI)-carbon composite electrode as a highly sensitive and selective citric acid sensor: Three-component nanocomposite as a definitive factor for selectivity in catalysis

Graphitic carbon nitride/Fe3O4/BiOI (g-C3N4/Fe3O4/BiOI)-carbon composite is introduced as a new electrode for the electrocatalytic oxidation of citric acid (CA). The electrode showed catalytic activity for the electrooxidation of CA, leading to a distinct decrease in anodic overpotential (100 mV) and a substantial increase in anodic peak (about 10 times), compared to the blank electrode. Various electrodes, modified with Fe3O4, BiOI, g-C3N4/Fe3O4 and g-C3N4/BiOI were prepared and their responses to CA in the absence and presence of some interfering agents were compared with the response of g-C3N4/Fe3O4/BiOI at the same experimental conditions. The selectivity results indicated that three-component nanoomposite (g-C3N4/Fe3O4/BiOI) is the most efficient material among the BiOI, Fe2O3, g-C3N4/BiOI, g-C3N4/Fe2O3 to achieve the highest selectivity for CA determination. Utilizing electrochemical impedance spectroscopy, it was demonstrated that three-component nanonocomposite electrode reduces the charge transfer resistance of CA at the electrode surface. Using the nanocomposite electrode it became possible to determine CA in the concentration range of 0.05-1.0 mM with detection limit of 0.01 mM. The electrode showed very high sensitivity of 54.1 mu A.mM(-1) cm(-2). Thanks to high sensitivity and good selectivity of the electrode, it was applied to measure CA in different fruit juice samples. The satisfactory results obtained, confirmed the applicability of this sensor in the practical analysis.