Two new 8-hydroxyquinoline derivatives as an efficient corrosion inhibitors for mild steel in hydrochloric acid: Synthesis, electrochemical, surface morphological, UV–visible and theoretical studies

The novel heterocyclic compounds, mainly based on the 8-hydroxyquinoline moiety, namely (8-hydroxyquinolin-5-yl) methyl-4-chlorobenzoate Q1 and (8-hydroxyquinolin-5-yl) methyl-4-nitrobenzoate Q2 have been synthesized and identified through different spectroscopic methods (FTIR, ¹H, ¹³C NMR, and Elemental analysis (EA)). Q₁ and Q₂ were estimated as corrosion inhibitors of mild steel (MS) in the aggressive environment (1 M HCl) utilizing a weight technique (weight loss measurements) and the non-weight techniques (electrochemical techniques), Density Functional Theory (DFT) and Monte Carlo Simulations (MC). However, to better gather information on bonding mechanism of MS surface/inhibitors/1 M HCl medium, the corrosion protection was once also investigated with the aid of ultraviolet-visible spectrophotometry (UV–Vis). Surface studies (SEM) revealed that the HCl medium protected by Q₁ and Q₂ could prevent the surface damage and decrease the roughness. The results clearly exhibit that the inhibition performance (η %) will increase with an increase in the concentration of Q₁ and Q₂ achieves maximum value of 96% (Q₁) and 92% (Q₁) at optimal concentration (10⁻³ M). Withal, potentiodynamic polarization test results exhibited the influence of Q₁ and Q₂ on both anodic and cathodic reactions suppression. Inhibitors formed protective layers on metal surface through adsorption as per Langmuir model. The metal dissolution and inhibitor adsorption phenomena have been studied through the estimation of thermodynamic parameters. DFT calculations and MC simulations were exploited to describe the electronic and adsorption properties of Q₁ and Q₂. The records of both techniques supported the experimental findings.