Enhanced Protection of Carbon Steel Against Acid Corrosion: Synergistic Effect of s-Triazine-Anilino-Morpholino-Pyrazolyl Hybrids Through Electrochemical and Computational Insights

Corrosion inhibitors extend material lifespan and reduce maintenance costs by forming protective layers on metallic surfaces. Herein, two molecular hybrids: N-(4-chlorophenyl)-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-morpholino-1,3,5-triazin-2-amine (1) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-N-(4-methoxyphenyl)-6-morpholino-1,3,5-triazin-2-amine (2) were prepared and characterized. Corrosion inhibition efficiencies of C-steel in acid were evaluated using weight loss, impedimetric, and potentiometric techniques, complemented by computational calculations. The inhibition efficiency (%IE) was 96.5 % for inhibitor (1) and 99.2 % for (2) at 100 ppm (0.26 mM). The inhibitors functioned as mixed-type corrosion inhibitors, effectively protecting the steel surface, as demonstrated by scanning electron microscopy (SEM). Inhibitors (1) and (2) followed Temkin and Langmuir adsorption model respectively. Moreover, density functional theory (DFT) for the neutral and protonated forms in both gaseous and aqueous phases, revealed that derivative (2), incorporating methoxy group, exhibited greater inhibition efficiency on a metal surface compared to derivative (1) incorporating Cl-(electron-withdrawing group). This is attributed to the electron-donating effect of the methoxy group in (2), in consistence with the experimental results. Additionally, MC simulations indicated a higher value of ΔEads/ΔNi associated with the metal adsorbate interaction for derivative (2), and thus more favorable and stable adsorption on the metal surface. This stronger interaction contributed significantly to its superior corrosion inhibition performance compared to derivative (1).