Inhibition mechanism and corrosion protection of mild steel in hydrochloric acid using 2-hydroxynaphthaldehyde thiosemicarbazone (2HNT): Experimental and theoretical analysis

This study explores the inhibitory properties of 2-hydroxynaphthaldehyde thiosemicarbazone (2HNT) on mild steel corrosion in 1 M hydrochloric acid.The investigation of adsorption and inhibition mechanisms employed weight loss analysis, scanning electron microscopy (SEM), and density functional theory (DFT) techniques.Adsorption parameters were derived using various theoretical approaches.Optimal inhibitive efficacy, reaching 93.88%, was observed at a concentration of 500.0 ppm for the inhibitor during a 10-hour immersion period at 303 K.The study further examined the impact of immersion durations (5, 10, 24, and 48 hours) and inhibitor concentrations (100-1000 ppm) at 303 K, revealing 10 hours as the optimum immersion time.Inhibition efficiency increased with rising inhibitor concentration and remained steady beyond 10 hours up to 48 hours.Temperature effects were explored for different inhibitor concentrations, with 10 hours identified as the optimal immersion time.The Langmuir adsorption isotherm model was employed to elucidate the adsorption inhibition mechanism.Changes in activation energy values indicated distinct interactions between inhibitor molecules and the mild steel surface.Scanning electron microscopy analyses confi0rmed inhibitor molecule adsorption and the formation of a protective film on the mild steel surface.The mild steel-inhibitor interaction was scrutinized through DFT, revealing a minimal energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).The experimental and theoretical findings demonstrated congruence, affirming