Adsorption and inhibition effect of two aminopyrimidine derivatives on steel surface in H2SO4 solution

The adsorption and inhibition effect of two aminopyrimidine derivatives of 2-aminopyrimidine (AP) and 2,4-diaminopyrimdine (DAP) on steel surface in 0.5 M H2SO4 solution were studied by weight loss, open circuit potential (OCP), potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) methods. Quantum chemical calculation of density function theory (DFT) and molecular dynamics (MD) simulations were applied to theoretically determine the relationship between molecular structure and inhibition efficiency. The results show that two aminopyrimidine derivatives act as good inhibitors, and inhibition efficiency follows the order: DAP > AP. The adsorption of each inhibitor on steel surface obeys Langmuir adsorption isotherm. Both AP and DAP are arranged as mixed-type inhibitors. EIS diagram appears a large capacitive loop at high frequencies (HF) followed by a small inductive loop at low frequencies (LF), and the addition of aminopyrimidine inhibitor increases the impedance of electrode. The electron densities of both HOMO and LUMO are localized principally on the pyrimidine ring, which could be both the acceptor of the electron and the donor of the electron. The donating electrons to metal follows the order: DAP > AP, which is in completely accordance with that of inhibitive performance. MD simulations reveal both aminopyrimidine molecules adsorb on the Fe(0 0 1) surface in the nearly flat manner, and the sequence of either adsorption energy (Eads) or binding energy (Ebin) agrees well with that of inhibition efficiency.