Experimental and theoretical insights into 4-(1-piperazinyl)pyridine as an efficient corrosion inhibitor for mild steel in 1.0 M HCl

• A.F. Mahmood¹, H.H. Al-Doori², A.A. Al-Amiery^3,4, M.J. Suriani⁵, W.B. Wan Nik^5,6, A. Pradityana⁶, J. Haque⁷, W. Daoudi⁸, E. Berdimurodov^9,10,11 and A. Saxena¹²

¹ Oil and Gas Engineering Department, University of Technology, P.O. Box: 10001, Baghdad, Iraq
² Al-Karkh University of Science, P.O. Box: 10001, Baghdad, Iraq
³ Energy and Renewable Energies Technology Center, University of Technology, Baghdad, P.O. Box: 10001, Iraq
⁴ Biomedical Engineering Department, College of Engineering, Al-Ayen University (AUIQ), Nile St, Nasiriyah P.O. Box 64001, Dhi Qar, Iraq
⁵ Faculty of Ocean Engineering Technology, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
⁶ Dept. of Mechanical Industrial Engineering, Vocational Faculty, Institut Teknologi Sepuluh Nopember Surabaya, 60111, East Java, Indonesia
⁷ Interdisciplinary Research Center for Refining & Advanced Chemicals, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
⁸ Laboratory of Education, Sciences and Techniques, Higher School of Education and Training of Berrechid, Hassan First University, Morocco
⁹ Faculty of Chemistry, National University of Uzbekistan, Tashkent, 100034, Uzbekistan
¹⁰ University of Tashkent for Applied Sciences, Str. Gavhar 1, Tashkent, 100149, Uzbekistan
¹¹ School of Medicine, Central Asian University, Tashkent, 111221, Uzbekistan
¹² Department of Chemistry, Chandigarh University Gharuan Mohali, Ludhiana-Chandigarh National Highway NH-05, 140413, Mohali, India

Abstract: The corrosion inhibition performance of 4-(1-piperazinyl)pyridine for mild steel in 1.0 M HCl was systematically investigated using gravimetric measurements, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface morphology analysis (SEM), and density functional theory (DFT) calculations. Weight loss results revealed a strong concentration- and time-dependent inhibition behavior, with inhibition efficiency (IE%) increasing from 57.69% at 0.001 M after 1 h to 95.76% at 0.005 M after 24 h. The inhibitor remained highly effective at elevated temperatures, achieving IE% values up to 95.51% at 333 K, indicating thermally enhanced performance. Adsorption followed the Langmuir isotherm with high correlation coefficients (R² > 0.99) and spontaneous adsorption free energies (ΔG⁰_ads = −18.11 to −22.82 kJ/mol), suggesting mixed physisorption–chemisorption behavior. EIS measurements showed a dramatic increase in charge-transfer resistance from 20.4 Ω·cm2 (blank) to 463.7 Ω·cm² at 0.005 M, accompanied by a decrease in double-layer capacitance from 215.3 to 34.1 μF/cm². PDP results revealed a reduction in corrosion current density from 0.708 to 0.007 mA/cm² with a maximum IE of 99.0% and minor shifts in corrosion potential (ΔEcorr ~ 40 mV), confirming mixed-type inhibition. SEM images demonstrated a smooth and compact surface in the inhibited medium. DFT calculations (ΔE = 9.594 eV; ΔN = 0.309) highlighted strong electron-donating ability of nitrogen-rich sites and favorable charge transfer toward iron. The combined experimental and theoretical results confirm that 4-(1-piperazinyl)pyridine is a highly efficient inhibitor for mild steel in acidic environments, with strong potential for industrial acid pickling and descaling applications.

Keywords: 4-(1-piperazinyl)pyridine, mild steel, inhibitor, corrosion, DFT

Int. J. Corros. Scale Inhib., 2026, 15, no. 2, 420-450
doi: 10.17675/2305-6894-2026-15-2-23

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