Innovative Characterization of Coffee Waste Extracts and Their Derivatives as Efficient Ecological Corrosion Inhibitors for Copper Alloy in 3% NaCl: Phytochemical Investigations, Electrochemical Explorations, Morphological Assessment and New Computational Methodology

Corrosion inhibitors are critical for safeguarding metal objects, particularly in industrial settings. Traditional synthesis techniques for these inhibitors frequently entail complicated and multi-step processes, which are being challenged by the push for green chemistry. This study investigates the possibility of natural inhibitors obtained from biomass waste as environmentally beneficial alternatives. This study investigates the usage of spent ground coffee waste (SCGW) extracts as eco-friendly corrosion inhibitors for brass in a 3% NaCl solution, using a combination of experimental and computational methodologies. Maceration was used to extract active chemicals from SCGW, resulting in the EX-MAC extract, while Soxhlet extraction produced the EX-SOX extract. EX-MAC and EX-SOX’s chemical composition was analyzed using high-performance liquid chromatography (HPLC). The principal components in both extracts were caffeine (31.2% for EX-MAC and 35.83% for EX-SOX) and caffeic acid (31.2% for EX-MAC and 12.49% for EX-SOX), with EX-MAC characterized by the presence of a third significant molecule, cyanidin-3-glucoside (20.74%). The effectiveness of EX-SOX and EX-MAC as eco-friendly corrosion inhibitors was evaluated through electrochemical experiments, including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). This research demonstrated that both of our extracts investigated operate as cathodic agent type inhibitors. The ɳ_EIS (%) rises with increasing EX-MAC and EX-SOX concentrations, with values of 95.37% for EX-MAC and 85.15% for EX-SOX at 1 g/L inhibitor concentration. Surface characterizations using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) demonstrated the formation of protective layers by EX-MAC and EX-SOX, mitigating brass deterioration in corrosive environments. Furthermore, computational studies employing molecular dynamics (MD) simulations and density functional theory (DFT) methods revealed significant adsorption of EX-MAC and EX-SOX compounds onto various copper surfaces (Cu (111)/Cu₂O (111)). Additionally, the inhibitory and synergistic interactions between the different components in the extracts under study were clarified using MD simulation experiments. Among the mixtures, MAC exhibits the strongest synergistic effect and provides the best protection for the Cu (111) and Cu2O (111) surfaces, surpassing mixture SOX. The binding energies for Cu (111)/mixture MAC and Cu2O (111)/mixture MAC are 520.3101 and 855.2326 kcal/mol, respectively. The integration of theoretical and experimental approaches underscores the potential of SCGW phenolic extracts as sustainable and effective corrosion inhibitors, contributing to our understanding of the corrosion inhibition process.