Synergistic Adsorption and Barrier Effects of a Schiff Base Conjugated Oligoelectrolyte/ZnO Composite on Mild Steel in Acidic Media

Abstract Conjugated oligoelectrolytes (COEs) have been identified as potential materials for corrosion protection due to their interfacial and electrochemical properties. In the present study, a COE containing a Schiff base backbone (pHH) derived from hydrazine hydrate and p-hydroxybenzaldehyde was successfully developed and examined by using FTIR, 1H NMR, 13C NMR, and mass spectrometry techniques. The Schiff base-based COE (pHHCOE) was further incorporated with zinc oxide nanoparticles (ZnO) to fabricate a pHHCOE/ZnO composite. The formation and structural features of the pHHCOE/ZnO were confirmed through Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), UV–vis spectrophotometry, cyclic voltammetry, field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) analysis. The anticorrosive effectiveness of the pHHCOE/ZnO on mild steel in 2 M HCl solution was evaluated via the weight loss study, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) at different concentrations and temperatures. The electrochemical results indicated exceptional inhibition efficiencies of 97.04% and 97.15% from the PDP and EIS measurements, respectively. Furthermore, the composite maintained high inhibition efficiency (93.75%) even at elevated temperatures, demonstrating its thermal stability and robust protective behavior. Surface morphology studies using scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed the formation of a smooth and protective adsorbed film on the mild steel exterior. The corrosion inhibition mechanism involves both physisorption and chemisorption processes. The pHHCOE ensures strong interfacial adsorption and surface coverage, while ZnO nanoparticles enhance barrier protection and regulate the electron transfer processes. Overall, the pHHCOE/ZnO composite exhibits outstanding prospects as an efficient corrosion inhibitor agent for mild steel under acidic conditions.