Theoretical analysis of Curcuma longa polyphenols as eco-friendly corrosion inhibitors for copper in acidic medium

Protecting copper against corrosion in harsh acidic conditions continues to be a significant challenge in materials research. This study examined three natural curcuminoids from Curcuma longa: curcumin (CUR), demethoxycurcumin (DEM), and bisdemethoxycurcumin (BIS), as environmentally benign corrosion inhibitors. Density functional theory (DFT) studies indicated that CUR possesses the shortest HOMO-LUMO energy gap (3.606 eV), the highest global softness, and the highest electrophilicity index, signifying increased chemical reactivity and robust donor-acceptor interactions. DEM exhibited a notable capacity to receive back-donated electrons. Adsorption studies indicated that all molecules assume a planar form on the copper surface, promoting π-surface interactions. Among the examined compounds, CUR had the greatest binding affinity with the lowest adsorption energy (-41.494 kJ.mol⁻¹). These findings underscore that C. longa constituents are viable, sustainable, and eco-friendly alternatives to synthetic corrosion inhibitors for copper in acidic environments.

ORCA and Quantum ESPRESSO were employed to conduct all calculations within the context of density functional theory (DFT). Geometry optimizations and electronic structure calculations were conducted under strict self-consistent field (SCF) convergence criteria using the B3LYP functional, def2-SVP basis set, and def2/J auxiliary basis set. Periodic DFT calculations were conducted in Quantum ESPRESSO to investigate the adsorption properties. The wave functions were subjected to plane-wave cutoff energies of 30 Ry, while the charge density was subjected to 240 Ry.