<![CDATA[Corrosion is the degradation of metallic materials that can compromise their durability, particularly under acidic conditions. This study aimed to evaluate the effectiveness of Acacia mangium leaf extract as a green corrosion inhibitor for mild steel in 0.75 M H₂SO₄ solution. The inhibition performance was investigated using weight-loss measurements, adsorption isotherm analysis, and evaluation of thermodynamic parameters. Various extract concentrations (0.5, 1.0, 1.5, 2.0, and 2.5 g/L) were evaluated at different temperatures (30, 40, 50, and 60 °C). Surface characterization using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and contact angle measurements was performed to elucidate the interaction between the extract compounds and the steel surface. Then the experimental result were confirmed by quantum chemical calculations using at B3LYP/6-311G (d,p). The results demonstrated that the corrosion rate of mild steel decreased progressively with increasing Acacia mangium leaf extract concentration. The maximum inhibition efficiency of 94.74% was achieved at 30 °C with an extract concentration of 2.5 g/L. The thermodynamic parameters, including ΔGads (-16.8825 kJ mol⁻¹), ΔHads (-45.0793 kJ mol⁻¹), and ΔSads (-93.0588 J mol⁻¹ K⁻¹), indicated that the adsorption process was spontaneous, exothermic, and predominantly governed by a physisorption mechanism. FTIR analysis revealed that functional groups including O–H, C–H, C=C, C=O, and C–O contributed to the adsorption of extract molecules onto the steel surface, while SEM analysis confirmed reduced surface deterioration after inhibitor addition. Furthermore, contact angle measurements demonstrated an increase in surface hydrophobicity, supporting the formation of a protective layer on the mild steel surface. DFT calculations revealed favorable electronic properties of flavonoid and proanthocyanidin for corrosion inhibition.]]>
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