Corrosion Inhibition of Catharanthus Roseus Extract on Q235 Carbon Steel in Acidic Solution

The work aims to develop a new green corrosion inhibitor and find its corrosion inhibition effect on Q235 carbon steel in acidic solution. Catharanthus roseus extract (CR-E) was obtained by reflux extraction with 70% ethanol aqueous solution. The corrosion inhibition performance and mechanism of CR-E on Q235 carbon steel in 0.5 mol/L H2SO4 solution were assessed by classical weight loss experiment, electrochemical comprehensive experiment, flame atomic absorption spectrometry (FAAS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The weight loss experiment showed that CR-E had a good corrosion inhibition effect on Q235 carbon steel in 0.5 mol/L H2SO4 solution. The corrosion inhibition efficiency increased with CR-E concentration to attain 89.84% at 1 000 mg/L at 298 K. After CR-E was added, it could quickly retard corrosion and continue to exert a corrosion inhibition effect. The corrosion rate of Q235 carbon steel containing CR-E was 21.56% of that in the blank one after 3 h exposure and 8.57% after 24 h exposure. The corrosion inhibition efficiency could still reach 89.99% after soaking for 48 h in 0.5 mol/L H2SO4 solution. Adsorption of CR-E on the surface of Q235 carbon steel followed Langmuir adsorption isotherm and was spontaneous. The strong physisorption and weak chemisorption were involved according to the standard Gibbs adsorption free energy (ΔGads0 = –25.81 kJ/mol). According to the findings of the polarization curves, the CR-E performed as an effective mixed-type inhibitor. The parallel cathodic branch revealed that the mechanism of the hydrogen evolution was not affected by the addition of CR-E in H2SO4 solution. The inhibition efficiency calculated by the corrosion current density and polarization resistance increased and went up to 95.54% and 94.22% at 500 mg/L CR-E concentration respectively. A single capacitive loop and only one time constant were observed from electrochemical impedance spectroscopy (EIS), which indicated that the mechanism of the charge transfer process of metal dissolution was unchanged by the presence of CR-E. The enhanced charge transfer resistance of corrosion reaction with increasing CR-E concentration was revealed, and the inhibition efficiency was 89.52% at 500 mg/L CR-E concentration by the EIS parameters from the equivalent circuit analysis. The concentration of Fe was only 7.24% of that in the blank solution by the FAAS analysis, which confirmed that the dissolution of anode iron was inhibited. The similar adsorption peaks of FTIR spectra of CR-E and the CR-E adsorbed layer on Q235 carbon steel surface confirmed that CR-E molecules with N and O groups could be effectively adsorbed on the surface of Q235 carbon steel. SEM microscopy analysis of Q235 carbon steel samples reveals that the degradation rate of carbon steel is significantly lowered and CR-E provides effective protection. The inhibition mechanism of CR-E is mainly attributed to the adsorption of protonated CR-E molecules by electrostatic attraction or coordinate bonds blocking the active site of the corrosion. CR-E has significant corrosion inhibition properties by the adsorption of functional groups on carbon steel in 0.5 mol/L H2SO4 solution, and can be used as a green corrosion inhibitor candidate in the industry. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.