Electrochemical investigation of a tulsi-holy basil-crude plant extract on graphitized mesoporous carbon nanomaterial surface: Selective electrocatalytic activity of surface-confined rosmarinic acid for phenyl hydrazine-pollutant oxidation reaction

Abstract The mystery of > 2000 years of Hindu culture holy basil plant-Tulsi (Ocimum tenuiflorum)’s active ingredient for health benefit has been revealed by performing a blind cyclic voltammetric based electrochemical experiment (without pre-targeted chemicals) with a crude solution of the Tulsi-plant-water extract (TE) using a graphitized mesoporous carbon nanomaterial modified glassy carbon electrode (GCE/GMC) in pH 2 solution. The as-prepared chemically modified electrode was characterized using TEM, FTIR, Raman, UV–Vis, HPTLC, UPLC and with several control samples to identify the active molecular species trapped by GMC. It has been revealed that amongst various phytochemicals-ingredients, the rosmarinic acid (RA) in the TE-extract trapped selectively on the graphitic sites and showed an exceptionally efficient redox behavior at an apparent standard electrode potential, Eo’ = 0.550 V vs Ag/AgCl with a peak-to-peak potential difference, ΔEp ∼ 0 V. A specific interaction between the π-electrons of the aromatic compound and sp2 carbon of GMC is found to be an influencing parameter for the selective electrochemical micro-extraction of the RA from the TE (GMC@TE-RA). This electrochemical methodology helps for qualitative and quantitative analysis of the phytochemical, RA in the TE. The GMC@TE-RA is found to involve selective electrocatalytic oxidation of phenylhydrazine-pollutant in pH 2 KCl-HCl medium. Electrochemical impedance spectroscopic analysis of the modified electrode showed a superior electronic activity over the respective unmodified electrode. A scanning electrochemical microscopy (SECM) has been used to image the active site of the electrocatalytic surface. As a sustainable and green electrochemical approach, a highly selective electrocatalytic oxidation and flow injection analysis-based sensing of phenylhydrazine using the GCE/GMC@TE-RA has been demonstrated without any interference from hydrazine and other common electroactive chemicals and biochemicals.