Improved corrosion behaviour of A36 carbon steel in 3.5% NaCl solution via bio-inhibitor of mangkok leaf extract (Polyscias Scutellaria)

• Polyscias scutellaria extract used as a green bio-inhibitor for A36 steel in 3.5% NaCl. • Demonstrates effective corrosion inhibition at moderate temperatures. • Adsorption follows Langmuir behavior with monolayer surface coverage. Corrosion is a major issue in the industry, particularly affecting carbon steel structures such as ASTM A36, which is widely used in storage tanks. The application of synthetic corrosion inhibitors frequently has negative environmental impacts, prompting the search for environmentally friendly alternatives. This work aims to evaluate the effectiveness of mangkok leaf extract (Polyscias scutellaria) as a bio-corrosion inhibitor for A36 carbon steel in a 3.5% NaCl solution at various concentrations (0, 100, 300, and 500 mg/L) and temperature variations (30, 40, 50, and 60°C). Characterization was conducted using electrochemical methods, including potentiodynamic polarization, EIS, as well as FTIR, XRD, SEM-EDX, and AFM. The results showed that the PSE (Polyscias scutellaria extract) bio-inhibitor significantly reduced the corrosion rate at an optimal concentration of 300 mg/L, achieving an inhibition efficiency of 84.61% at 30°C. However, the efficiency decreased at a concentration of 500 mg/L due to saturated adsorption and compound degradation at higher temperatures. XRD, SEM-EDX, and AFM confirmed the formation of a protective layer on the steel surface, most effectively at 300 mg/L. It indicates the strong potential of PSE as an effective green corrosion inhibitor in chloride environments.