Adsorption and corrosion of renewable inhibitor of Pomelo peel extract for mild steel in phosphoric acid solution

Pomelo peel extract (PPE) was evaluated as green and renewable corrosion inhibitor for mild steel in 1.0 mol/L H3PO4 solution. The inhibition behaviour was studied using mass loss, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. The chemical structure of PPE was investigated using Fourier transform infrared (FT-IR) and ultraviolet-visible (UV–vis) spectroscopy. The corrosion morphology of mild steel was analysed via scanning electron microscopy (SEM). The adsorption thermodynamics and kinetics was discussed. The results show that PPE confers an acceptable long-term effect (inhibition efficiency of 95.0% and 92.8% for corroding 23 h and 224 h in the presence of 5.0 g/L PPE inhibitor) and functions as a mixed inhibitor. The adsorption of PPE on mild steel simultaneously follows the Langmuir, El-Awady and Temkin isotherms at 35, 45 and 55 °C. PPE is mixed adsorption dominated with physical adsorption at room temperature or with higher PPE concentrations. PPE possesses many polar functional groups such as hydroxyl, carbonyl and hetero-aromatic rings. The inhibition mechanism is closely related to these polar groups, as is the surface coverage of steel.