Molecular Structure Impact of Two Bisphenol-Containing Nitro and Bromo on Carbon Steel Corrosion Inhibition in 1 M HCl Medium: Electrochemical, Spectroscopic, and Theoretical Investigations

Two newly developed bisphenols, 2,2′-((1E,1′E)-(((methylazanediyl)bis(propane-3,1-diyl))bis(azaneylylidene))bis(methaneylylidene)) bis(4-nitrophenol) (BS-NO₂) and 2,2′-((1E,1′E)-(((methylazanediyl)bis(propane-3,1-diyl))bis(azaneylylidene))bis(ethan-1-yl-1-ylidene))bis(4-bromophenol) (BS-Br) were investigated for carbon steel (C_S) anti-corrosion in 1 M HCl medium using electrochemical means, surface state, and UV–visible analyses coupled with theoretical approaches. The potentiodynamic polarization assessment revealed that the substituted bisphenols react as mixed-nature inhibitors. It is found that their anti-corrosion performance improves with inhibitor concentrations, attaining a maximum of 91% and 89% at 0.001 M BS-Br and BS-NO₂, respectively. So, the presence of the resonance-donating group (-Br) at the para-position on the phenol circle is thought to account for BS-Br′s greatest inhibition efficiency, whereas the existence of the attractor assembly by the mesomeric influence (-NO₂) at the para-position on the phenol circle is accountable for the lowermost inhibition efficiency of BS-NO₂. In addition, these compounds adsorb chemically on the C_S area according to the Langmuir adsorption isotherm. These findings were explained and established by the surface examination and the UV–visible analysis with the establishment of a thick defensive film on the area and the molecule inhibitor-iron complex in the electrolyte, respectively. Finally, the theoretical investigations explained and confirmed the action mode of the two substituents (-Br and -NO₂) on the C_S inhibition corrosion.