Corrosion inhibition performance of 2-(4H-1,2,4-triazol-4-yl) phenol for mild steel in 1 M HCl: electrochemical, weight loss, SEM, adsorption and DFT investigations

• H.H. Al-Doori¹, A.F. Mahmood², S.A. Yousif³, A. Alamiery^3,4 and A.H. Kadhum⁵

¹ Al-Karkh University of Science, P.O. Box: 10001, Baghdad, Iraq
² Oil and Gas Engineering Department, University of Technology, P.O. Box: 10001, Baghdad, Iraq
³ College of Pharmacy, Al-Ayen Iraqi University, AUIQ, An Nasiriyah, P.O. Box: 64004, Thi Qar, Iraq
⁴ Energy and Renewable Energies Technology Center, University of Technology-Iraq, 10066 Baghdad, Iraq
⁵ Faculty of Medicine, University of Al-Ameed, P.O. Box: 56001, Karbala, Iraq

Abstract: The corrosion inhibition performances of 2-(4H-1,2,4-triazol-4-yl)phenol (TP) on mild steel were evaluated in a 1.0 M HCl solution using potentiodynamic polarization (PDP), gravimetric weight loss measurements, scanning electron microscopy (SEM), density functional theory (DFT), and adsorption isotherm modeling. In addition, PDP study enabled to classify the TP molecules as mixed-type inhibitors that interfered with both cathodic and anodic processes. Also, an increase in TP concentration from 0.10 to 0.50 mM greatly lowered corrosion current densities, with a maximal degree of inhibition of 93.71% occurring at 0.50 mM. Consistent weight loss results in weight loss gravimetry, demonstrating 91.3% of inhibition efficiency against the extension of immersion test, which is excellent documentation for the electrochemical study. SEM micrographs confirmed the formation of a protective absorption film with smoother and less corroded surfaces in the presence of TP. Adsorption isotherms matched the Langmuir model; this, along with the large enthalpy values, affirms a mutual decision to the binding process, and demonstrates the way TP species may be adsorbed to form good protection against corrosion. DFT calculations show that both the high frontier molecular orbital energies and electron-donating properties of TP agree favorably in corroborating the strong adsorption potential of this inhibitor. Thus, the overall outcome of this study demonstrates that TP is a promising, fast-acting and environmentally benign inhibitor for mild steel in acidic media.

Keywords: corrosion inhibition, triazole, Langmuir, DFT, SEM

Int. J. Corros. Scale Inhib., 2026, 15, no. 1, 147-169
doi: 10.17675/2305-6894-2026-15-1-7

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