Multidentate Schiff bases as new and effective corrosion inhibitors for mild steel in hydrochloric acid solution: an electrochemical and quantum chemical assessment

Three multidentate Schiff base ligands (A = 3-(2-aminobenzylimino)-1-phenylbutan-1-one], Hbzacabza; B = 3-[({o-[(E)-(o-Hydroxyphenyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol, H(2)bzacabzasal; and C = 3-[({o-[(E)-(2-Hydroxy-1-naphthyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol, H(2)bzacabzanapht) were synthesized and their inhibiting effect on the corrosion of mild steel in 1 M hydrochloric acid was examined using potentiodynamic polarization and electrochemical impedance spectroscopy. These compounds are effective corrosion inhibitors with inhibition efficiency A < B < C. The adsorption of inhibitors obeys Langmuir adsorption isotherm and the thermodynamic parameters K (ads), Delta GA(ads)(0), E (a) are extracted. The order of K (ads) and E (a) values conforms to the observed inhibition efficiency of these compounds. The values of Delta GA(ads)(0) are close to -40.00 kJ/mol (in the range of -33.01 to -35.04 kJ/mol) and indicate that the corrosion inhibition effect involves both chemisorption and physisorption followed by the blocking of the active electrochemical sites on steel surface. The effect of A, B and C on mild steel was also studied by quantum chemical calculations.