Corrosion of mild steel in acidic media is still a problem in industry, especially in pickling, cleaning, and acidizing processes, where rapid dissolution of the metal can lead to serious economic and safety problems. In this paper, a new Schiff base derivative was designed and synthesized by the condensation of amoxicillin with 4-hydroxybenzaldehyde and tested as a corrosion inhibitor for mild steel in 1.0 M HCl solution. The innovation of this work derives from transforming amoxicillin, a biologically active pharmaceutical compound, into a Schiff base structure with better electronic properties and adsorption capacity; thus, a new eco-friendly inhibitor candidate is introduced with improved corrosion protection performance. The compound obtained was characterized by FTIR spectroscopy, which revealed the formation of the azomethine (C=N) bond. The corrosion inhibition performance was evaluated by weight loss measurements, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). The inhibitor exhibited very good performance as it reduced the corrosion rate from 1.3403 mg·cm⁻2·h⁻1 for the blank solution to 0.0190 mg·cm⁻2·h⁻1 at 1 × 10⁻2 M, with maximum inhibition efficiency of 94.47%. PDP measurements showed a marked reduction in corrosion current density while EIS results indicated a high charge transfer resistance, thereby confirming the formation of a protective adsorbed layer on the mild steel surface. The calculated standard free energy of adsorption (ΔG°ads = − 29.84 kJ·mol⁻1) pointed to spontaneous adsorption process involving mixed physisorption and chemisorption. From the FESEM and EDX results, it was further confirmed that the inhibitor was adsorbed on the surface, providing better surface protection compared to the uninhibited sample. It also employed density functional theory (DFT) calculations to shed light on the electronic behavior of the parent drug and its Schiff base derivative and to establish a relationship between molecular reactivity and inhibition performance. The results from the experiments and theories prove that the amoxicillin-derived Schiff base synthesized is a very good, cheap, and environmentally friendly inhibitor for the corrosion of mild steel in acid solutions. However, the current research work is limited to the evaluation of corrosion performance under fixed immersion conditions at one temperature. Therefore, another study is recommended for the effect of temperature and long-term stability on the corrosion performance of the inhibitor. Graphical Abstract

Amoxicillin-Derived Schiff Base as an Efficient Corrosion Inhibitor for Mild Steel in 1.0 M HCl: Experimental, Electrochemical, Surface and DFT Studies

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发表日期：

2026年7月29日

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Reyam H. Marah

摘要

Corrosion of mild steel in acidic media is still a problem in industry, especially in pickling, cleaning, and acidizing processes, where rapid dissolution of the metal can lead to serious economic and safety problems. In this paper, a new Schiff base derivative was designed and synthesized by the condensation of amoxicillin with 4-hydroxybenzaldehyde and tested as a corrosion inhibitor for mild steel in 1.0 M HCl solution. The innovation of this work derives from transforming amoxicillin, a biologically active pharmaceutical compound, into a Schiff base structure with better electronic properties and adsorption capacity; thus, a new eco-friendly inhibitor candidate is introduced with improved corrosion protection performance. The compound obtained was characterized by FTIR spectroscopy, which revealed the formation of the azomethine (C=N) bond. The corrosion inhibition performance was evaluated by weight loss measurements, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). The inhibitor exhibited very good performance as it reduced the corrosion rate from 1.3403 mg·cm⁻²·h⁻¹ for the blank solution to 0.0190 mg·cm⁻²·h⁻¹ at 1 × 10⁻² M, with maximum inhibition efficiency of 94.47%. PDP measurements showed a marked reduction in corrosion current density while EIS results indicated a high charge transfer resistance, thereby confirming the formation of a protective adsorbed layer on the mild steel surface. The calculated standard free energy of adsorption (ΔG°ads = − 29.84 kJ·mol⁻¹) pointed to spontaneous adsorption process involving mixed physisorption and chemisorption. From the FESEM and EDX results, it was further confirmed that the inhibitor was adsorbed on the surface, providing better surface protection compared to the uninhibited sample. It also employed density functional theory (DFT) calculations to shed light on the electronic behavior of the parent drug and its Schiff base derivative and to establish a relationship between molecular reactivity and inhibition performance. The results from the experiments and theories prove that the amoxicillin-derived Schiff base synthesized is a very good, cheap, and environmentally friendly inhibitor for the corrosion of mild steel in acid solutions. However, the current research work is limited to the evaluation of corrosion performance under fixed immersion conditions at one temperature. Therefore, another study is recommended for the effect of temperature and long-term stability on the corrosion performance of the inhibitor.

Graphical Abstract