Unraveling the Synergistic Mechanism of Two Bioderived Imidazole Derivatives and Zinc Ion Combined Corrosion Inhibitors for Carbon Steel in CO ₂ -Saturated Formation Water

In the development of green corrosion inhibitors, amino acids are highly favored by researchers due to their biological molecular properties. However, most amino acids exhibit an unsatisfactory corrosion inhibition property on metal in CO₂-saturated formation water. Herein, two bioderived imidazole derivatives (2-(1<i>H</i>-imidazol-1-yl)-3-mercaptopropanoic acid (IL-1) and 3-(benzylthio)-2-(1<i>H</i>-imidazol-1-yl)propanoic acid (IL-2)) were first synthesized and then combined with zinc ion (Zn²⁺). The inhibitive effect of the combined corrosion inhibitors was assessed by electrochemistry experiments and surface techniques. The findings show that bioderived imidazole derivatives combined with Zn²⁺ could synergistically boost the inhibitive effect of individual bioderived imidazole derivatives and Zn²⁺ (inhibition efficiency of 99.2% for 0.6 mM IL-1 + 0.6 mM Zn²⁺ and 99.5% for 0.6 mM IL-2 + 0.6 mM Zn²⁺). Scanning electron microscopy (SEM) and contact angle measurement results demonstrate that the carbon steel surface after inhibitor adsorption has the least corrosion products and the highest hydrophobicity (contact angle = 71.6°). X-ray photoelectron spectroscopy (XPS) analysis confirmed that the inhibitor molecules can be absorbed on the carbon steel surface. In addition, the synergistic mechanisms were explored by theoretical calculations. It is found that these two bioderived imidazole derivatives have strong adsorption ability, which can adsorb at the steel/solution interface by forming Fe-N and Fe-O bonds. This work develops an environmentally friendly and efficient combined corrosion inhibitor. The adsorption mechanism is conducted by theoretical calculations, which offer valuable scientific insights for the research, development, and practical application of green corrosion inhibitors.