Safflower plant extract as a sustainable corrosion inhibitor for carbon steel in acidic media: a combined electrochemical and computational study

Abstract

This study investigates the corrosion inhibition efficiency of safflower plant (SP) extract on carbon steel in hydrochloric acid (HCl) solutions. The SP extract, obtained through Soxhlet extraction, was tested for its ability to reduce corrosion using electrochemical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM). The study revealed that the SP extract functions as an effective mixed-type inhibitor, significantly reducing the corrosion current density and enhancing inhibition efficiency at concentrations up to 2.5 g L^-1. It achieved an inhibition efficiency of 89.56% at 2.5 g L^-1. The adsorption mechanism is described in terms of both physical and chemical adsorption processes, with the Langmuir isotherm fitting the adsorption data. Computational modeling using density functional theory (DFT) further supported the experimental findings, identifying key active compounds in SP extract that contribute to its inhibitory performance. The study demonstrates the potential of SP extract as a sustainable and eco-friendly corrosion inhibitor for industrial applications.

Fig. 1. Leaves of safflower flowers and the chemical structure of some important molecules present in it.

Fig. 2. OCP vs. time curves for steel in 0.5 N HCl solution without and with different concentrations of SP at 25 °C.

Fig. 3. Potetiodynamic polarization curves for steel in 0.5 N HCl solution without and with different concentrations of SP at 25 °C.

Fig. 4. Electrochemical frequency modulation curves for steel in 0.5 N HCl solution without and with different concentrations of SP at 25 °C.

Fig. 5. Nyquist plots (a), Bode, phase angle plots (b), Nyquist plots at different immersion time (c) for steel in 0.5 N HCl solution without and with different concentrations of SP at 25 °C.

Fig. 6. Potentiodynamic polarization curves for carbon steel in a 0.5 N HCl acidic solution and an SP extract inhibitor at different temperatures.

Fig. 7. The relationship between the absolute solution temperature (K), the corrosive current density (A), and corrosion efficiency in the corrosion medium (B).

Fig. 8. The Arrhenius plot for carbon steel deterioration in the absence and presence of SP extract.

Fig. 9. Langmuir adsorption models for SP on the steel surface in 0.5 N HCl.

Fig. 10. SEM images of (A): polished steel, (B): steel/0.5 N HCl and (C): SP/steel/0.5 N HCl.

Fig. 11. ATR-FTIR spectrum of SP inhibitor on the carbon steel surface after immersion for 24 h in 0.5 N HCl with the optimum concentration of 2.5 g L⁻¹ of SP inhibitor.

Fig. 12. UV-visible spectra of SP before and after immersion in carbon steel.

Fig. 13. Optimized structures of compounds 1–5.

Fig. 14. Frontier molecular orbitals and energy gap of compounds 1–5.

Fig. 15. Density of states of compounds 1–5.

Fig. 16. MEP maps of compounds 1–5.