Corrosion inhibition of mild steel in hydrochloric acid using 5-(3-methoxyphenyl)-4-((3-pyridinylmethylene)amino)-4H-1,2,4-triazole-3-thiol: Weight loss studies and DFT analysis

• W.H. Alsaedi¹, N. Betti², S.J. Shoja³, A. Kadhim⁴, A.M. Mustafa⁵, F.F. Sayyid⁵, A.H. Kadhum⁶ and A.A. Alamiery^7,8

¹ Department of Chemistry, Faculty of Science, Taibah University, P.O. Box 30002, Al-Madinah Al-Munawarah, Saudi Arabia
² Materials Engineering Department, University of Technology, P.O. Box 10001, Baghdad, Iraq
³ Institute of Medical Technology, Radiology Department, Middle Technical University, P.O. Box 10001, Baghdad, Iraq
⁴ Department of Laser and Optoelectronics, University of Technology, P.O. Box 10001, Baghdad, Iraq
⁵ Department of Production Engineering and Metallurgy, University of Technology, P.O. Box 10001, Baghdad, Iraq
⁶ Al-Ameed University, P.O. Box 56001, Karbala, Iraq
⁷ AUIQ National Center for Research and Innovation, Al-Ayen Iraqi University, AUIQ, P.O. Box 64001, Thi-Qar, Iraq
⁸ Energy and Renewable Energies Technology Centre, University of Technology, P.O. Box 10001, Baghdad, Iraq

Abstract: The corrosion of mild steel in acidic environments poses significant challenges across various industries. This study investigates the efficacy of 5-(3-methoxyphenyl)-4-((3-pyridinyl¬methylene)amino)-4H-1,2,4-triazole-3-thiol (MPTAT) as a corrosion inhibitor for mild steel in 1 M hydrochloric acid (HCl). Weight loss experiments were conducted at MPTAT concentrations of 0.1 to 1 mM and immersion times ranging from 1 to 48 hours. The inhibitor demonstrated an efficiency of 94.8% at 1 mM after 5 hours of immersion at 303 K. Temperature effects were studied at 303, 313, 323, and 333 K with a 0.5 mM inhibitor concentration over 5 hours, revealing increased inhibition efficiency with rising temperatures. Adsorption of MPTAT on the mild steel surface followed the Langmuir isotherm, indicating both physical and chemical adsorption mechanisms. Density Functional Theory (DFT) calculations provided insights into the electronic properties of MPTAT, supporting its role as an effective corrosion inhibitor. Density Functional Theory (DFT) calculations were performed on both the neutral (gas-phase) and protonated forms of the inhibitor. The calculations provided critical parameters that govern the molecule’s interaction with the mild steel surface in an acidic environment. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were computed to analyze the electron-donating and electron-accepting abilities of MPTAT. The HOMO-LUMO energy gap (Δ𝐸) was determined, reflecting the chemical reactivity and stability of the inhibitor. A moderate energy gap suggests that MPTAT maintains a balance between stability and reactivity, allowing for strong adsorption while remaining resistant to degradation.

Keywords: corrosion, mild steel, HCl, triazoles, DFT

Int. J. Corros. Scale Inhib., 2025, 14, no. 3, 1499-1521
doi: 10.17675/2305-6894-2025-14-3-25

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