Comparative Analysis of Corrosion Inhibition of Carbon Steel by Aqueous Extracts of Guava Leaves in Simulated Acidic Environments

Corrosion of carbon steel infrastructure in acidic environments remains a persistent maintenance challenge in Nigerian industrial facilities, particularly in chemical processing and petroleum sectors across the South South zone. This study investigates the corrosion inhibition efficacy of aqueous Psidium guajava leaf extract against mild steel corrosion in 0.5 M and 1.0 M hydrochloric acid solutions, with potential application in acid cleaning operations at facilities in Warri, Delta State. Guava leaves were collected from orchards in Asaba, shade-dried, and extracted using hot distilled water. Inhibition performance was evaluated using weight loss measurement and electrochemical techniques including potentiodynamic polarisation and electrochemical impedance spectroscopy at inhibitor concentrations of 100 to 1,000 mg/L and temperatures of 25 to 55 degrees Celsius. Inhibition efficiency increased proportionally with extract concentration, reaching 87.4% at 1,000 mg/L in 0.5 M HCl at 25 degrees Celsius. Polarisation curves indicated mixed-type inhibitor behaviour. Langmuir adsorption isotherm analysis confirmed that inhibitor molecules adsorb onto the steel surface as a monolayer with a free energy of adsorption of negative 31.2 kJ/mol, indicative of physisorption. Inhibition efficiency decreased with rising temperature, consistent with the desorption of adsorbed molecules. Phytochemical screening identified quercetin and gallic acid as probable active inhibiting constituents. The study supports guava extract as an eco-friendly corrosion inhibitor for mild steel in acidic media relevant to South South Nigerian industrial contexts. Keywords: corrosion inhibition, guava leaf extract, carbon steel, hydrochloric acid, green inhibitor