DOI: https://doi.org/10.55373/mjchem.v26i5.10

Keywords: Thiosemicarbazone; HCl; weight loss; DFT; Langmuir isotherm

Abstract

Corrosion has been discovered to degrade metal surfaces in acidic media. In-situ synthesis of indole-3-carbaldehyde 4-methyl-3-thiosemicarbazone [ICar4MTSC] as a corrosion inhibitor was carried out. The predicted structure of ICar4MTSC was supported by elemental analysis, melting point, FT-IR, UV-Vis, and NMR analysis. To assess the efficacy of ICar4MTSC, weight loss was conducted in an acidic environment (1M HCl). The results revealed that as its concentration increases, so does the corrosion inhibition's performance. The R2 = 1 value of the Langmuir adsorption isotherm pointed out that the ICar4MTSC designed a monolayer on the mild steel surface and interacted with the adsorbed inhibitors. The Gibbs free energy value: ΔGads = -21.9873 kJ mol-1 implies that the ICar4MTSC displayed both forms of adsorption types (chemisorption and physisorption). The surface morphology of mild steel at its highest concentration (0.5 μM) that had been soaked in 1M HCl for 24 hours was imaged using SEM-EDX and mapping. The results deduced that a protective layer of ICar4MTSC (0.5 μM) was created, resulting in a smoother surface. Whereas the rough and pitting surface on the mild steel denotes the absence of ICar4MTSC (blank). The DFT (intrinsic molecular characteristics and MEP) analysis showed that the ICar4MTSC contains promising adsorption sites (C=S, N atoms of the thiosemicarbazide moiety, and the benzene of the indole ring) which could potentially adsorb the mild steel surface by chemisorption and physisorption.