Anthraquinone derivatives isolated from Asphodelus microcarpus Salzm. and Viv as efficient corrosion inhibitors for mild steel: experimental and theoretical insights.

The present work investigates the anticorrosive performance of two anthraquinone-based compounds, namely 1,2-dihydroxyanthraquinone (M1) and 2-anthraquinone acid (M2), extracted and isolated from Asphodelus microcarpus Salzm. & Viv collected in Morocco. The isolated molecules were characterized using several spectroscopic and chromatographic techniques, including Infrared Spectroscopy (IR), Proton Nuclear Magnetic Resonance (1H NMR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), and High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS). Their inhibition effect on mild steel corrosion in 1.0 M HCl medium was evaluated through potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. The findings reveal that M1 provides slightly better corrosion protection than M2 under acidic conditions. In addition, the inhibition efficiency was found to increase with higher inhibitor concentrations, while an increase in temperature led to a reduction in performance. Polarization results indicate that both compounds act as mixed-type inhibitors. Moreover, density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level were performed to gain insight into the electronic structure and reactivity of the studied molecules. The calculated theoretical parameters showed strong consistency with the experimental electrochemical data, supporting the enhanced inhibitory effectiveness of M1 compared to M2.