Investigations of Triphenyl Phosphate and Bis-(2-ethylhexyl) Phosphate Self-Assembled Films on Iron Surface Using Electrochemical Methods, Fourier Transform Infrared Spectroscopy, and Molecular Simulations

Abstract

The protection behaviors of two new phosphate self-assembled films, triphenyl phosphate (TPP) and bis-(2-ethylhexyl) phosphate (BEP), against the corrosion of iron in 0.5 M H2SO4 were investigated using the electrochemical impedance spectroscopy (EIS), polarization curves, Fourier transform infrared (FT−IR) spectroscopy, and molecular simulations. The polarization curves showed a decrease in corrosion current density for the electrode covered with phosphates. Impedance spectra demonstrated that the charge-transfer resistance (Rct) of the electrode covered with phosphate was greater than that of the naked iron electrode. Results show that TPP molecules can adsorb on the iron surface quickly in a short time and that the coverage (θ) of the film will get to the maximum in 4 h. Subsequently, the amount of TPP molecules on the iron surface remains constant, while θ of BEP on the iron surface increases with the immersion time in 24 h. FT−IR spectroscopy was applied for the surface analysis and confirmed the adsorption of phosphates on the iron surface by monitoring the functional group peaks of the compounds. Molecular simulations were performed to illustrate the adsorption process at a molecule level and to provide some theoretical information for our experiment.