Synthesis of copper schiff base nanocomplex as green inhibitor for 316 L stainless steel corrosion in an aggressive acidic environment

Using inhibitors is a typical way to mitigate metal degradation by forming barriers or altering reactions. Herein, the nanocomplex of copper(II) ion with 1-((E)-(2-mercaptophenylimino) methyl) naphthalen-2-ol (H₂L) Schiff base ligand was successfully synthesized via an environmentally friendly approach using Coriandrum Sativum (CS) extract in ethanol. According to transmission electron microscopy (TEM), the average particle size of the produced nanocomplex was 12.71 nm. Using various electrochemical and physical techniques, namely, open-circuit potential (OCP), impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and SEM/EDX methods, the inhibitory effect of green Cu nanocomplex (Cu₂L₂) on the corrosion of 316 L stainless steel in a harsh mixed acid solution (1 M HCl + 1 M HNO₃) was scrutinized. The findings revealed that the Cu nanocomplex exhibited mixed-type inhibition behavior, with a maximum efficiency of 85.56% achieved at 600 ppm addition. EIS results indicated an increase in the charge transfer resistance and a decrease in the double-layer capacitance by increasing Cu₂L₂ concentration in the ambient aggressive acidic solution. Isotherm fitting analysis suggested that Cu nanocomplex adsorption on the stainless steel surface followed the Langmuir isotherm model. Density functional theory (DFT) calculations further supported the experimentally obtained findings. The molecular dynamics (MD) simulations also endorsed that the Cu₂L₂ inhibitor lay flat on the metal surface, indicating better surface coverage.