The impact of naphthalimide derivative on the mitigation of mild steel corrosion in sulfamic acid medium: experimental and theoretical insights

The deterioration of iron-based alloys, especially mild steel (MS) is one amongst the most challenging problems faced in various chemical industries. The present work focuses on the potential activity of a naphthalimide derivative namely 2-(2-hydroxyethyl)benzo[de]isoquinoline-1,3-dione (HBIQ) as corrosion inhibitor for MS in sulfamic acid (SA) medium in the temperature range from 303 to 323 K. Potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) were employed in the experimental measurement and HBIQ exhibited 89% inhibition at its optimum concentration. HBIQ demonstrated electrostatic interactions with MS surface and behaved as a mixed type of inhibitor by obeying Langmuir's isotherm model. Surface characterization of uninhibited and inhibited MS specimens combined with elemental analysis data provided clear evidences for the formation of a protective adsorption layer of HBIQ on MS surface. Spectral analysis such as Ultraviolet visible and Fourier Transform Infra-red spectral analyses were carried out in order to confirm the adsorption of HBIQ on to the metal surface. The density functional theory calculations supported the experimental results and indicated the contribution of delocalized pi-electrons in the naphthalimide unit and the lone-pair electrons of oxygen in the carbonyl and hydroxyl group for improved adsorption of HBIQ onto MS surface, thereby reducing the corrosion of the alloy in SA environment.