Synthesis, experimental and theoretical analysis of 5-aminoindazole derivatives for corrosion prevention of mild steel in sulfuric acid across different temperatures

Abstract

Corrosion inhibition investigations were undertaken to assess the efficacy of 5-aminoindazole (IND) and its derivatives in preventing corrosion of mild steel within 0.5 M H₂SO₄ solutions. The derivatives underwent synthesis, purification, and characterization through Nuclear Magnetic Resonance (NMR) spectroscopy, which revealed the anticipated carbon and proton signals. Subsequent to synthesis, gravimetric analysis was conducted, revealing that 2-(((1H-indazol-6-yl)amino)methyl)-4-chloro-6-methoxyphenol (IND–10), achieving an efficiency of 86.97 %, demonstrated superior inhibition efficiency at 323 K compared to 5-aminoindazole (IND) (33.68 %) and 2-(((1H-indazol-6-yl)amino)methyl)-4,6-dinitrophenol (IND–01) (51.97 %). Adsorption isotherm and thermodynamic evaluations indicated that IND–10 adhered to a chemisorption mechanism, whereas IND and IND–01 displayed mixed inhibition (chemisorption-physisorption) at reduced temperatures according to the Langmuir isotherm. Notably, IND did not conform well to the Langmuir model but corresponded more closely with the Frumkin isotherm, implying a predominant physisorption mechanism. Analysis of the Frumkin data showed that Gibbs free energy decreased with higher temperatures, while lateral interactions increased. The inhibitor increased activation energy, forming a protective metal layer as its concentration lessened. This was confirmed by Scanning Electron Microscope images displaying inhibitor adherence to the metal surface, offering corrosion protection. Quantum chemical analysis corroborated these findings through energy gap (ΔE) calculations, which demonstrated greater stability for IND–10 with ΔE = 2.95 eV, compared to IND (3.05 eV) and IND–01 (3.03 eV). This analysis suggested that IND–10 served as a more efficacious inhibitor relative to both IND and IND–01.