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

CONTEXT: 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.

METHODS: 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.