Inhibition Effect of Bamboo Leaf Extract on the Corrosion of Aluminum in HCl Solution

A bamboo leaf inhibitor (designated PSLE) was extracted from Phyllostachys sulphurea (Corr. Riviere) leaves using a series of C2H5OH-water solutions (20%-80% (volume fraction)). The solutions were characterized by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-Vis) spectrophotometry. The total flavonoid content of the PSLE was determined. The inhibition effect of PSLE toward the corrosion of aluminum in HCl solution was studied by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Density functional theory (DFT) quantum chemical calculations including solvent effects were used to investigate the adsorption of light by the two major components vientin and isovientin. The results show that PSLE is a good inhibitor and the adsorption of PSLE on the aluminum surface obeys the Langmuir adsorption isotherm. The inhibition efficiency increases with PSLE concentration while it decreases with temperature and HCl concentration. A good correlation exists between the total flavonoid content and the inhibition performance. This implies that the flavonoids are the major contributor to inhibition activity. PSLE behaves as a cathodic inhibitor. The EIS spectra are characterized by one large capacitive loop at high frequencies followed by a large inductive loop at low frequency values. The impedance value increases with increasing inhibitor concentration. SEM results confirm that the corrosion of aluminum is retarded remarkably by PSLE. The quantum calculation results indicate that the adsorption center of either vientin or isovientin is mainly a flavonoid backbone structure (FBS).