Anticorrosion studies of benzaldehyde derivatives on iron in HCl using experimental and theoretical analysis

Abstract

A recent investigation explored the corrosion-fighting potential of five benzaldehyde derivatives: 4-Formylbenzonitrile (BA 1), 4-Nitrobenzaldehyde (BA 2), 2-Hydroxy-5-methoxy-3-nitrobenzaldehyde (BA 3), 3,5-Bis(trifluoromethyl)benzaldehyde (BA 4), and 4-Fluorobenzaldehyde (BA 5). These compounds were tested for their ability to protect mild steel from corrosion in 1 M hydrochloric acid solution using a range of techniques, including potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), adsorption isotherms, and computational methods. Supporting techniques like Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible (UV-Vis) spectroscopy, were also employed to validate the results. Despite sharing a common benzaldehyde ring, the molecules differ in their substituents, allowing for a comprehensive examination of the substituents' impact on corrosion inhibition. After a thorough analysis of the PDP and EIS data, the inhibitors demonstrated outstanding inhibitory efficiency, with the following ranking: BA 2 > BA 1 > BA 3 > BA 4 > BA 5. The Tafel analysis revealed that the inhibitors exhibited mixed-type inhibition behaviour, meaning they interacted with both the anodic and cathodic reactions, influencing the corrosion process. EIS analysis revealed that benzaldehyde derivatives formed a protective passive film on mild steel, exhibiting high corrosion resistance by shielding the alloy from corrosive attacks. The benzaldehyde inhibitors conformed to the Langmuir adsorption isotherm, with high 𝑅² values approaching unity, indicating a monolayer adsorption mechanism. Furthermore, the negative values of ∆𝐺𝐴𝑑𝑠𝑜(less than -20 kJ mol⁻¹) for five inhibitors suggested a physisorption interaction between the inhibitors and the mild steel surface.The computational study produced promising results, with the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) figures indicating that the benzaldehyde ring and substituents are capable of donating and accepting electrons. The calculated parameters indicate that all molecules possess a high affinity for adsorption on the metal surface, confirming their potential as effective corrosion inhibitors. The EHOMO values reveal that these inhibitors possess high electron-donating ability, with BA 3 exhibiting the highest EHOMO value among them. This is likely attributed to the presence of electron-donating methoxy and hydroxy groups. Furthermore, these inhibitors showed lower ELUMO values, indicating their ability to accept electrons, with BA 2 having the lowest value, signifying a high electron-accepting ability. The presence of the nitro group (-NO2) in BA 2 likely enhances its electron-accepting capability, facilitating the acceptance of electrons from the metal surface. FTIR and UV-Vis spectroscopy revealed the molecular interactions between mild steel and the inhibitor molecules, providing insight into the binding mechanism.