Almond Hulls and Shells Extract Characterized as a High-Performance Eco-Friendly Antioxidant and Corrosion Inhibitor

The focus of this study is to extract secondary metabolites from the lignocellulosic wastes of the Almond industry. The study used the Soxhlet method to obtain methanolic and ethanolic extracts from almond hulls (AH) and almond shells (AS). The extracts were then subjected to phytochemical screening to determine their polyphenol, condensed tannins, and total flavonoid content. To evaluate the extracts' antioxidant activity, Iron Reducing Antioxidant Power (FRAP test) and free radical scavenging capacity (DPPH test) were conducted. The study also investigated the extracts’ corrosion inhibitory power on steel in an acidic medium (HCl 1 M) as a function of their concentration and medium temperature. The study employed potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and mass loss measurement for this purpose. The phytochemical analysis results showed that AH extracts have a more diverse phytochemical composition than AS extracts, This study found that the corrosion inhibition efficiency increases with the concentration of the methanolic extracts. The maximum percentage efficiency was observed at 88.37% for AH and 86.46% for AS (200 ppm) at 25 °C. The performance of the extracts was excellent at the temperature studied, but it decreased with increasing temperature. Furthermore, the AH extracts had a higher antioxidant power than the AS extracts as determined by the FRAP and DPPH methods. Overall, the results demonstrate their potential as natural antioxidants and corrosion inhibitors and suggest that Almond industry waste extracts could be considered as a potential source of natural antioxidants and corrosion inhibitors.