Recent Advances in Azo-Based Corrosion Inhibitors for Steel in Acidic Media: Adsorption Mechanism, Electrochemical Performance, and Theoretical Insights( review article)

Abstract

Azo and azo–Schiff base derivatives have been widely explored as corrosion inhibitors for steel in acidic environments due to their electron-rich heteroatoms and conjugated π-systems. This review critically examines recent experimental and computational studies, with emphasis on adsorption thermodynamics, electrochemical response, and structure–efficiency relationships in 1 M HCl and H₂SO₄ solutions. Reported inhibition efficiencies frequently exceed 90%, although performance varies depending on molecular substitution pattern and medium conditions. Adsorption behavior is commonly described by the Langmuir isotherm, with ΔG°ads values (−28 to −42 kJ mol⁻¹) indicating spontaneous adsorption involving both physical and chemical interactions. Electrochemical impedance spectroscopy and polarization measurements consistently show increased charge transfer resistance and reduced corrosion current density in the presence of azo-based inhibitors. Complementary density functional theory (DFT) calculations further clarify the role of molecular electronic descriptors, such as EHOMO and energy gap (ΔE), in determining adsorption strength and inhibition performance. By integrating thermodynamic analysis with quantum chemical insights, this review outlines key structure–performance trends and highlights strategic considerations for the rational development of high-efficiency azo-derived corrosion inhibitors