Protective behaviour of naphthylamine derivatives for steel reinforcement in the simulated concrete pore solutions: Detailed experimental and computational explorations

Two novel naphthalimide derivatives, namely [ N -(2-(2,3-dihydroxybenzylideneamino)ethyl)]-1,8-naphthalimide(DHN) and [ N -(2-(2,3,4-trihydroxybenzylideneamino)ethyl)]-1,8-naphthalimide (THN), were synthesized and evaluated as corrosion inhibitors for steel reinforcement in simulated concrete pore solution by polarization curves(PC) tests, electrochemical impedance spectroscopy(EIS) tests, scanning electron microscope(SEM) and energy spectrometer(EDS) tests. The EIS results showed that DHN and THN formed protective layers on the steel reinforcement, the PC results indicated that both were mixed-type inhibitors, the efficiency increased with increasing concentration and decreased with increasing temperature. According to the Langmuir adsorption isotherm, DHN and THN are in the physical adsorption mode. Foremost, the inhibition mechanism of DHN and THN was investigated using quantum mechanical calculations (DFT) and correlated with the experimental results that THN showed a better performance due to the phenolic hydroxyl group. Overall, this study provides an idea for the synthesis of new corrosion inhibitors.