Electrochemical, surface and computational studies on the inhibition performance of some newly synthesized 8-hydroxyquinoline derivatives containing benzimidazole moiety against the corrosion of carbon steel in phosphoric acid environment

Four new 8-hydroxyquinoline derivatives, namely 5-((1H-benzimidazol-2-yl)methyl)quinolin-8-ol (BIMQ), 5-((5-methyl-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (MBMQ), 5-((5-chloro-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (CBMQ) and 5-((5,6-dichloro-1H-benzimidazol-2-yl)methyl)quinolin-8-ol (DCBMQ) were prepared in moderate to good yields through the condensation of 5-(carboxymethyl)-8-hydroxyquinoline and substituted o-phenylenediamine. 1H, 13C NMR and elemental analysis confirm the formation of the desired compounds. The anti-corrosive potential of these heterocyclic compounds has been studied on carbon steel in 2M phosphoric acid (H3PO4) electrolyte by means of electrochemical measurements. The inhibition efficiency of these heterocyclic compounds was strongly linked to the concentration and the structure of the molecules; reached a maximum of 94.7% for DCBMQ at 10−3M. Data generated from potentiodynamic revealed that the investigated 8-hydroxyquinoline derivatives are mixed type inhibitors. The influence of temperature on the corrosion behaviour was assessed. The four quinoline derivatives adsorbed according to the Langmuir's adsorption isotherm. Surface analysis (SEM and XPS) confirmed the formation of a protective layer adsorbed on the steel surface. DFT calculations suggested that 8-hydroxyquinoline derivatives adsorb on the metal via the 8-hydroxyquinoline ring and their corrosion inhibition potential have some linear correlation with the degree of co-planarity of the benzimidazole and hydroxyquinoline rings. Monte Carlo simulations showed that the molecules adsorbed on Fe(110) surface through the 8-hydroxyquinoline in a near-flat mode and the adsorption energies both in the absence and presence of aqueous phosphate ions agree with the observed trends of inhibition efficiencies.