Indolin-2-one derivatives as corrosion inhibitors: Structural insights and evaluation through experimental and computational techniques

Effective corrosion management is a pivotal challenge facing various industries and holds crucial importance in aligning industrial processes with sustainability goals. This study focused on the synthesis and evaluation of two indolin-2-one derivatives: (E)-1-allyl-3-(2-(5-oxo-4,4-diphenyl-4,5-dihydro-1H-imidazol-2-yl)hydrazono)indolin2-one (AIHI) and (E)-3-(2-(5-oxo-4,4-diphenyl-4,5-dihydro-1H-imidazol-2-yl)hydrazono)-1-(prop-2-yn-1-yl) indolin-2-one (PIHI), as sustainable corrosion inhibitors for N80 carbon steel (N80CS) in a 15 wt. % HCl medium. Chemical, electrochemical, and surface characterization techniques were utilized to evaluate the corrosion inhibition mechanism and the performance of the compounds under investigation. The weight loss method highlighted that tested compounds exhibited promising inhibition efficiencies: 91.54 % for AIHI and 81.97 % for PIHI, respectively, at 303 K, with an outstanding performance of 87.17 % at 363 K for AIHI. The simultaneous addition of AIHI and PIHI in HCl led to a substantial increase in the polarization resistance (RP) and a remarkable decrease in the corrosion current density (icorr). The potentiodynamic polarization (PDP) technique validated that both indolin-2-one compounds function as anodic/cathodic corrosion inhibitors with remarkable anodic effect. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that inhibitors altered steel surface morphology, forming a protective layer, and significantly reduced surface roughness. Atomistic simulations (DFT and SCC-DFTB methods) pointed out that the inhibitors AIHI and PIHI acted by physicochemical adsorption through donor-acceptor interactions between AIHI or PIHI molecules (s and p orbitals) and the 3d orbitals of Fe(110). The insights obtained serve as a foundation for future advancements in greener corrosion management strategies for sustainable industrial applications, thus reinforcing our commitment to biocircular economies and sustainable chemistry.