Lignin (G/S type) as a sustainable biopolymer corrosion inhibitor for Cu-Zn alloy in sodium chloride: Extraction, characterization, electrochemical analysis, ab initio calculations, and molecular dynamics simulations.

This work aims to evaluate the potential of the aqueous extract of Ammi visnaga (L.) Lam (AE-AV) as a corrosion inhibitor for Cu-Zn alloy in a 3 % NaCl solution, using both experimental and computational approaches The chemical composition of AE-AV was examined using UV-visible and FTIR spectroscopy, revealing a significant concentration of lignin (G/S type) in this extract. The corrosion inhibition efficacy of AE-AV was evaluated using electrochemical methods such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). According to the PDP study, AE-AV acts as a mixed-type inhibitor with a dominant cathodic action. The EIS results showed that greater AE-AV concentrations and longer immersion time enhanced inhibitory effectiveness, with a maximum of around 91.67 % at 1000 ppm AE-AV after 48 h of immersion. Moreover, surface morphology analysis using SEM and EDX demonstrated that AE-AV compounds form a protective barrier layer on the alloy surface. Quantum mechanics chemistry, using the Dmol3/PBE/DNP+ level of theory, provided vital information on the electronic characteristics of the lignin (G/S type) biopolymer, particularly its capacity to supply and take electrons, allowing for effective adsorption onto the Cu-Zn surface. Furthermore, molecular dynamics (MD) simulations were utilized to investigate the interactions of lignin fragments with various Cu-Zn surfaces. The findings demonstrated the effectiveness of lignin (G/S type) as a corrosion inhibitor, with longer lignin chains having more interactions with Cu-Zn surfaces. This study offers novel insights into the molecular profile of an aqueous extract from Moroccan Ammi visnaga (L.) Lam and reveals the inhibitory effect of lignin (G/S type).