Unveiled understanding on corrosion inhibition mechanisms of hydrazone derivatives based on naproxen for mild steel in HCl: A joint experimental/theoretical study

Abstract

The current investigation seeks to explore the adsorption mechanism of newly synthesized Naproxen-based hydrazones on mild steel (MS) surface in 1.0 M HCl solution and their corrosion inhibition efficiencies. To this end, two hydrazone derivatives namely, (E)-N′-(1-(4-chlorophenyl)ethylidene)-2-(6-methoxynaphthalen-2-yl)propanehydrazide (PHDCl) and (E)-N′-(1-(4-hydroxyphenyl)ethylidene)-2-(6-methoxynaphthalen-2-yl)propanehydrazide (PHD-OH) were synthesized, characterized and their corrosion inhibition effects were evaluated using a combined electrochemical and theoretical approach. It is evidently clear from the findings presented in this investigation that the two inhibitors exhibited excellent protection efficiency, and the best inhibition performance was shown by PHD-OH inhibitor (96% at 5 × 10−3 M). Weight loss measurements revealed that the optimum concentration of inhibitors is 5 × 10−3 mol/L. The experimental results obtained by electrochemical techniques (potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)) indicated that the presence of PHD-Cl and PHD-OH compounds greatly increased the polarization resistance and affected both anodic and cathodic reactions, i.e. mixed-type inhibitors. Based on electrochemical results, the polarization resistance was greatly increased, from an initial value for the MS (in 1.0 mol/L HCl) of 29 up to 871 Ω cm2 for the inhibited solution (1.0 mol/L HCl with 5 × 10−3 mol/L of PHD-OH). Furthermore, the adsorption isotherm coincides well with the Langmuir isotherm model. The effect of temperature on PHD-OH adsorption was investigated, experimentally using weight loss tests, and theoretically using molecular dynamic simulations (MD). Moreover, the study found that a protective barrier was set up through the adsorption of the studied compounds on MS surface which is confirmed by scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX).Moreover, molecular proprieties of corrosion inhibitor molecules were explored from a theoretical viewpoint using Density Functional Theory (DFT), molecular dynamic (MD) simulation and radial distribution function (RDF) studies. Theoretical results that were in good agreement with experimental findings demonstrated strong interactions between inhibitor molecules and metal surface.