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

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, E-o' = 0.550 V vs Ag/AgCl with a peak-to-peak potential difference, Delta E-p similar to 0 V. A specific interaction between the pi-electrons of the aromatic compound and sp(2) 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.