Insight into the anti-corrosion performance of capparis spinoza extract as a green corrosion inhibitor for carbon steel in hydrochloric acid environment

Capparis Spinoza extract (CPS) was evaluated as a green corrosion inhibitor for carbon steel (CS) in 1 M hydrochloric acid (HCl) solution. Weight loss (WL) measurement, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques were employed to assess its efficacy. CPS demonstrated excellent inhibition efficiency (% IE) By increasing both concentration and temperature. % IE reached 90.6% at 25 °C, 300 ppm, but it reached 95.2% at 45 °C and at the same concentration. Adsorption isotherm analysis indicated Temkin-type behavior, suggesting both physical and chemical adsorption mechanisms, with the latter being predominant. Thermodynamic calculations (-ΔG°_ads = -38.1 kJ mol^{- 1} at 25 °C) confirmed the spontaneous adsorption process, the stability of the formed adsorbed layer and shows that the CPS is mixed (physical and chemical) adsorbed on CS surface. PDP data classified CPS as a mixed-type inhibitor. EIS spectra exhibited characteristic inductive and capacitive loops at low and high frequencies, respectively. The formation of a protective CPS film on the CS surface was confirmed by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FT-IR). The corrosion inhibition mechanism was elucidated through a combination of experimental and surface characterization techniques.