ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Corrosion inhibition performance of expired cyclobenzaprine drug in acidic media: weight loss, electrochemical, and DFT studies

Agneesh Verma, Harvinder Singh Sohal, Navneet Kaur, Manvinder Kaur, and Ankush Mehta

Materials and Natural Product Laboratory, Department of Chemistry, Chandigarh University, Gharuan, Mohali, India

E-mail: drharvinder.cu@gmail.com

Received: 25 December 2025  Accepted: 20 February 2026

Abstract:

Corrosion inhibition performance of an expired drug, cyclobenzaprine hydrochloride (CBH) on mild steel (MS) in 1 M H₂SO₄ was examined using gravimetric, electrochemical, surface, spectroscopic, and computational methods. From gravimetric studies, it was discovered that inhibition efficiency (IE) of the drug rose proportionally with its concentration, reaching a maximum of 98.39% at 400 ppm after 6 h, while prolonged immersion periods led to a gradual reduction in IE, decreasing to 80.82% after 48 h at the same concentration of inhibitor. Potentiodynamic polarization results demonstrated a significant reduction in corrosion current density to 1.37 × 10^− 4 A/cm² from 5.92 × 10^− 3 A/cm², with a maximum IE of 98.65% at 400 ppm drug concentration, thereby confirming that CBH functions as a mixed-type inhibitor. Electrochemical impedance spectroscopy demonstrated enhanced charge-transfer resistance and decreased double-layer capacitance with increasing inhibitor concentration, corroborating rapid formation of a protective layer. Adsorption studies showed that CBH followed the Freundlich isotherm, suggesting multilayer adsorption, and XPS, UV-Vis, SEM, AFM, and contact-angle analyses confirmed formation of a compact, adherent inhibitor film, reduced surface roughness, and altered wettability. DFT calculations supported the experimental findings. HOMO-LUMO energy gap showed reduction from 3.1062 eV (free CBH) to 1.3790 eV for Fe³⁺ coordinated complexes, thereby marking an increased charge transfer capability. Collectively, these findings establish expired CBH drug as an immensely effective, economical and eco-friendly corrosion inhibitor for MS in acidic media, exhibiting strong adsorption, durable surface protection, and excellent mixed-type inhibition behavior.

Keywords: Expired drug inhibitor; Corrosion inhibitor; Surface morphology; Adsorption isotherms; Density functional theory; Sustainable corrosion solution

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04757-x

Chemical Papers 80 (6) 6155–6176 (2026)