Agri-food wastes extract as sustainable-green inhibitors corrosion of steel in sodium chloride solution: Aclose look at the mechanism of inhibiting action

Abstract

The inhibition performance of agri-food wastes(AFWE) for carbon steel in neutral medium was evaluated by several methods like gravimetric and electrochemical tests, surface analysis. The maximum corrosion inhibition efficiency (about ∼98.0%) was obtained in the presence of 500 ppm AFWE after 48 h immersion. The polarization results also revealed that by the addition of AFWE, the corrosion current density of the mild steel significantly decreased from 20.1 μA/cm2 for the sample without inhibitor to 2.91 μA/cm2 for the sample containing 500 ppm of AFWE). LPR method assesses the time-dependent effect of inhibitors during OCP corrosion. It was demonstrated that the polarization resistance with a higher concentration (500 ppm) enhanced from ∼6 to ∼10 × 10−3 Ohm after 48 h of immersion. In this paper AFWE was tested as a green “pro-inhibitor” for mild steel in sodium chloride solution. This extract contains mostly phenolic acids and flavonoids according to high-performance liquid chromatography analysis (HPLC-DAD-MS). The steel surface is acquired by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The chemistry the formed film/ or compounds on the steel were probed via the Fourier-transform infrared spectroscopy (FT-IR). First-principles calculations proposed that the polymerization products have much more carbon atoms in the skeletal structure, arranged in an aromatic pattern, plus some hydroxyl groups and additional of aromatic groups that enhances the adsorption on the steel surface. Such structures of compounds have a large ability of being strongly bonded to metal surfaces via oxygen heteroatom and π-π interactions. In addition, the obtained adsorption free energy (ΔG˚) of –32.01 kJ/mol indicates that the AFM interaction with the MS surface was a mix of physical and chemical adsorptions.