Synergistic mixture of Camellia Oleifera shell extract and KI as an eco-friendly and highly efficient composite inhibitor for steel corrosion in H2SO4 media

Abstract

To address the severe corrosion problems faced by steel, a natural corrosion inhibitor derived from Camellia Oleifera shell extract (COSE) was developed. The effectiveness of COSE as well as its synergistic mixture of COSE/KI in inhibiting the corrosion of steel in H2SO4 was investigated using weightlessness and electrochemical techniques. The results show that the maximum inhibition efficiency of individual COSE is 77.28 % at 20 °C, and is increased to 93.08 % for the mixture of COSE/KI. The adsorption of COSE, KI and COSE/KI on steel surface conform to Langmuir adsorption isotherm. COSE/KI has a stronger adsorption than either COSE or KI. Electrochemical analysis indicates that COSE/KI is a hybrid inhibitor primarily focusing on the cathodic inhibition. Mixing COSE with KI shows considerably larger charge transfer resistance and smaller double-layer capacitance than individual COSE and KI. Characterization tests such as metallurgical microscopy, SEM, AFM and contact angle confirm that the addition of COSE/KI could reduce the roughness of steel surface, while increase the hydrophobicity, then effectively alleviate the corrosion on the steel surface. XPS analyses demonstrated that the corrosion inhibition layer on the steel surface was induced by the adsorption of the polar groups in COSE. The components responsible for COSE’s effectiveness were thoroughly examined using FTIR and liquid chromatography-mass spectrometry (LC-MS), which identified the presence of compounds such as flavonoids and phenylpropanoids. The synergistic effect of the active ingredients (rutin, quercetin, tea saponin, tea polyphenols, et al.) with KI was also confirmed. Finally, theoretical calculations were conducted to analyze properties of rutin, quercetin and tea polyphenols on the iron layer. The results show all these molecules exhibit efficient inhibition, with quercetin showing better inhibitive ability by parallel adsorption.