Experimental and theoretical investigations of porphyrin derivatives as corrosion inhibitors for carbon steel in acidic environments

Abstract

The corrosion inhibition effectiveness of two porphyrin molecules—5,10,15,20-tetrakis(4-phenoxyphenyl)porphyrin (PF-1) and 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (PF-2)—on carbon steel (CS) immersed in 0.5 M H₂SO₄ solutions was investigated. The study utilized various techniques, as well as computational methods like Density Functional Theory (DFT) and Monte Carlo (MC) simulations, to determine the adsorption behavior and corrosion inhibition efficiency of PF-1 and PF-2 on the Fe(110) surface in an acidic environment. The surface morphology of CS was tested using different techniques. The inhibition efficiency (% η) of PF-1 and PF-2 was determined at a concentration of 21 × 10⁻⁶ M, 25 °C, reached 95.9%, 91.4%, respectively. This is depending on the substituent group present in the molecule. Increasing the temperature to 45 °C at the same 21 × 10⁻⁶ M concentration caused the efficiencies to decrease to 88.0% and 77.8%, respectively. Across all concentrations studied, the PF-1 molecule consistently exhibited a higher inhibitory efficacy than PF-2 due the presence of four Oph attached to the molecule, which increase both charge density on the molecule and the surface coverage of CS. The inhibitory action is attributed to the spontaneous physicochemical adsorption of the porphyrin molecules onto the CS surface, a process that conforms to the Langmuir adsorption isotherm. The PFs derivatives are considered mixed-kind inhibitors and proved to be the best inhibitors for CS dissolution in 0.5 M H₂SO₄. Additionally, thermodynamic activation parameters were calculated and analyzed.