Novel 8-hydroxyquinoline compounds used to inhibit mild steel corrosion in the presence of hydrochloric acid 1.0 M: an experimental and theoretical electrochemical study

The present study examined the corrosion inhibition property of two derivatives of 8-hydroxyquinoline, namely diethyl 1,1-(4-(4-chlorophenyl)-1-((8-hydroxyquinoline-5-yl)methyl)-2, 6-dimethyl-1, 4-dihydropyridine-3,5-diyl) diethanone (P1) and diethyl 1,1-(4-(4-bromophenyl)-1-((8-hydroxyquinoline-5-yl)methyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-diyl)diethanone (P2). against mild steel (MS) degradation in 1.0 M hydrochloric acid (HCL) solution. The study was carried out using electrochemical techniques such as dynamic potential polarisation (DPP) and impedance spectroscopy (EIS) at different temperatures (298–328 K). Inhibition efficiency (IE %) increased with inhibitor concentration, reaching 97.0% for P1 and 91.8% for P2 at 10−3 M (298 K). Impedance measurements indicated that charge transfer resistance (Rct) increased, while double-layer capacitance (Cdl) decreased with increasing concentration of P1 and P2. Analysis of the polarisation curves shows that P1 and P2 act as mixed-type inhibitors. According to the Langmuir isotherm and thermodynamic parameters, P1 and P2 are adsorbed onto the mild steel surface by chemical interactions. The SEM/EDX analysis results revealed the formation of an adsorption film on MS. DFT calculations show that free heteroatom doublets of oxygen (O) and nitrogen (N) promote electron sharing between the molecules studied and the steel surface. Data from theoretical methods (DFT) confirm the experimental results. © 2025 Canadian Institute of Mining, Metallurgy and Petroleum.