Combined electrochemical and surface characterization (SEM/AFM) of a benzodiazepine derivative for corrosion protection of mild steel in 15 % HCl

Abstract

The present study evaluates the anticorrosive performance of a novel benzodiazepine derivative, PNO 2 , on mild steel in an aggressive 15% HCl medium at 298 K. A combination of gravimetric measurements, potentiodynamic polarisation, and electrochemical impedance spectroscopy (EIS) was used to quantify the corrosion inhibition efficiency at different concentrations of PNO 2 . Surface characterisation techniques, including Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR), were employed to examine the morphology and chemical interactions on the steel surface after immersion. The results revealed a significant decrease in corrosion rate and current density upon addition of the inhibitor, with maximum inhibition efficiencies reaching 84.8% and 84.4% based on gravimetric and electrochemical data, respectively, at 10 -3 M. The Nyquist plots demonstrated an increased charge transfer resistance and reduced double-layer capacitance, confirming the formation of a protective film. AFM analysis showed a notable reduction in surface roughness, while SEM/EDX spectra confirmed the adsorption of PNO 2 . Furthermore, adsorption studies indicated that PNO 2 follows the Langmuir adsorption isotherm, with ΔG° ads values supporting a spontaneous chemisorption mechanism. Overall, PNO 2 exhibited strong inhibitory action through mixed-type inhibitor, even under highly acidic conditions, making it a promising candidate for corrosion control in industrial environments.