In-Situ Electrochemical Reduction of Nitrobenzene and Surface-Confinement of Nitrosobenzene-Intermediate on Graphene Oxide for Efficient Electrocatalytic Ascorbic Acid Oxidation

Nitrobenzene (NB; Ø–NO 2 ) is an important organic compound involved in the synthesis of various drug molecules, azo dyes, explosives, flavoring agents, and pesticides. In this work, the electrochemical reduction of NB on a graphene oxide (GO) modified glassy carbon electrode (GCE/GO) was investigated at pH 7 phosphate buffer solution using a cyclic voltammetric technique. A specific electrochemical reduction peak (C 1 ) for NB was observed at −0.8 V vs Ag/AgCl. Subsequently, a highly redox-active organic molecule with a standard electrode potential, E 0 = −0.1 V versus Ag/AgCl, was selectively entrapped on the GCE/GO surface. This molecule exhibited a reversible redox couple (A 2 /C 2 ) with a negligible peak-to-peak potential separation (Δ E p ) of ∼10 mV at a scan rate of 10 mV/s and a surface-excess value of 2.51 × 10 –8 mol/cm 2 . The modified electrode was characterized using Raman, IR, TEM, in-situ electrochemical quartz crystal microbalance (EQCM), and LC-MS techniques. Results indicated that the electrochemical reduction of NB led to the formation of phenylhydroxylamine (Ø–NHOH), which subsequently reacted with nitrosobenzene (Ø–NO) to form a reversible redox couple. This couple was trapped on the GO surface through π–π and multiple hydrogen bond interactions. The GCE/GO@Ø–NO electrode demonstrated excellent electrocatalytic oxidation of ascorbic acid (AA), a crucial biochemical and biofuel cell component, in physiological solution. Cyclic voltammetry and rotating disk electrode techniques were employed to study the kinetics and mechanism of the oxidation reaction. Using the Savéant-Andrieux kinetic approach, a heterogeneous electron-transfer rate constant of 1.5 × 10 4 dm 3 mol –1 s –1 was calculated. As a practical application, the electrochemical oxidative sensing of AA was performed using amperometric i – t technique. The modified electrode exhibited good selectivity demonstrating negligible interference from common electroactive biochemical species.