Tinospora cordifolia extract as an environmentally benign green corrosion inhibitor in acid media: electrochemical, surface morphological, quantum chemical, and statistical investigations

Abstract

The inhibiting capacity of Tinospora cordifolia extract (TCE) was evaluated on mild steel in 1 M HCl and 0.5 M H2SO4 by physicochemical and electrochemical techniques and by utilizing statistical tools such as response surface methodology and the Box-Behnken design (BBD). Surface properties were ascertained by scanning electron microscopy and atomic force microscopy to confirm the adsorption performance of the inhibitor molecules on the surface of the metal. Experimental results were found to agree with quantum chemical calculations of the active principle of TCE, Tinosponone. Weight loss measurements exhibited extreme inhibition power of TCE as 94.73% and 82.53% in 1 M HCl and 0.5 M H2SO4, respectively, at 5 v/v% concentration at 303 K. Electrochemical impedance spectroscopy (EIS) studies were agreed with weight loss measurements as EIS showed an inhibition efficiency of 93.51% in 1 M HCl and 88.68% in 0.5 M H2SO4 solutions. Electrochemical studies were evident that TCE can hinder reactions of the cathode and anode of mild steel. Kinetic and thermodynamic studies indicated the mixed-type adsorption behavior of TCE on mild steel by following the Langmuir adsorption isotherm in both acid media. The BBD method was applied to verify the impact of three test factors, temperature, TCE concentration, and acid concentration, on inhibition efficiency of mild steel in HCl medium. Experimental and theoretical results confirmed the anticorrosion potential of the environment-friendly inhibitor TCE.