@article{73544027bb634e4495b851b0d5b16d0d,
title = "Green surfactants for corrosion control: Design, performance and applications",
abstract = "Surfactants enjoy an augmented share of hydrophilicity and hydrophobicity and are well-known for their anticorrosive potential. The use of non-toxic surfactants is gaining growing interest because of the scaling demands of green chemistry. Green surfactants have successfully replaced traditional toxic surfactant-based corrosion inhibitors. Recently, many reports described the corrosion inhibition potential of green surfactants. The present article aims to describe the recent advancements in using green surfactants in corrosion mitigation. They create a charge transfer barrier through their adsorption at the interface of the metal and the environment. Their adsorption is well explained by the Langmuir adsorption isotherm. In the adsorbed layer, their hydrophilic polar heads orient toward the metal side and their hydrophobic tails orient toward the solution side. They block the active sites and retard the anodic and cathodic and act as mixed-type inhibitors. Their adsorption and bonding nature are fruitfully supported by surface analyses. They can form mono- or multilayers depending upon the nature of the metal, electrolyte and experimental conditions. The challenges and opportunities of using green surfactants as corrosion inhibitors have also been described.",
keywords = "Biosurfactants, Green corrosion inhibition, Green surfactants, Interface-type and mixed-type inhibition, Sustainability",
author = "Chandrabhan Verma and Hussain, {Chaudhery Mustansar} and Quraishi, {M. A.} and Akram Alfantazi",
note = "Funding Information: Sliem et al. [55] studied the inhibition potential of an eco-friendly surfactant, namely fatty alcohol polyoxyethylene ether-7 (AEO7) surfactant for carbon steel corrosion in 0.5 M HCl solution. The inhibition potential was measured using weight loss, electrochemical, surface and computational investigations. A weight loss study suggests that %IE of AEO7 rises on increasing its concentration and a maximum %IE of 93.2% was derived at 40 ppm concentration for 30-min immersion. The authors did weight loss experiments at different immersion times and observed that there was no significant change in the inhibition performance of AEO7 on increasing the immersion time from 30 min to 180 min. Electrochemical impedance spectroscope (EIS) study indicates the Nyquist curves with and without AEO7 gave a single semicircle validating the single charge transfer mechanism of C-steel (carbon-steel) corrosion in 0.5 M HCl (Fig. 3). The increase in the diameter of Nyquist curves in the presence of AEO7 is attributed to the formation of a charge transfer barrier. This also implies that AEO7 can adsorb at the interface of metal and solution thereby it acts as an interface-type inhibitor. A potentiodynamic polarization study suggests that the presence of AEO7 decreases the anodic and cathodic current densities and overall corrosion rate without affecting the mechanism of corrosion as the shape of Tafel curves with and without AEO7 were similar for C-steel corrosion in 0.5 M HCl (Fig. 4). The decrease in the current density in the presence of AEO7 is attributed to the blocking of the active sites present over the surface. The Adsorption mode of corrosion mitigation was also supported by SEM and atomic force microscope (AFM) analyses in which a significant improvement in the surface morphology of the protected metal surface was derived in the presence of AEO7.Khalaf et al. [56] synthesized two green Gemini surfactants (GSUs) differing in the length of hydrocarbon chain from waste cooking oil and tested them as green inhibitors for the N80 steel/ 1 M H2SO4 system using numerous methods. Potentiodynamic polarization studies suggest that GSUs behave as mixed-type corrosion inhibitors as they affect both anodic and cathodic reactions without affecting the Ecorr (corrosion potential), significantly (Fig. 5). The decrease in the values of icorr (current density), indicates the anticorrosive effect of GSUs. This also suggests that GSUs adsorb effectively and block the active sites responsible for the corrosion. The inhibition mechanism was also supported by EIS analyses where GSUs increase the values of charge transfer resistance up to a great extent. An increase in the diameter of the Nyquist curves also supports this observation (Fig. 5). Their %IE followed the order: 96.48% (GSU-16) & 97.86% (GSU-18) at 1 × 10−3 M. The adsorption mode of inhibition was also supported by a scanning electron microscope (SEM) and FTIR spectral analyses showed that GSUs effectively adsorb on the metal surface and effectively inhibit metallic corrosion. Schematically, the authors proposed that GSUs can interact electrostatically with the metallic surface using their hydrophobic tails and hydrophilic heads. They can form a monolayer or multilayer depending upon the situation. Lastly, density functional theory (DFT)-based quantum chemical calculations were performed to demonstrate their interactions with the metal surface and support the experimental findings and good agreement was derived.A similar observation was recently reported by Liu and coworkers [63] who reported the relative corrosion inhibition potential of three green surfactants namely, betaine, 3-(N, N-dimethyldodecylammonio) propanesulfonate (SB3–12) and 2-(DodecyldiMethylaMMonio) acetate (BS-12) for Q235 steel in 1 M HCl. The inhibition potential was measured using chemical, electrochemical and surface investigations. The outcomes of these investigations suggest that studied green surfactants behaved as mixed- and interface-type inhibitors for the Q235 steel/ 1 M HCl system. Their inhibition efficiencies were greatly dependent upon their concentrations and operating temperature. The inhibition effect of the tested species followed the sequence: betaine < SB3–12 < BS-12. Both SB3–12 and BS-12 are structurally similar as they both contain identical hydrocarbon chain lengths but they contain different functional groups. It was obtained that SB3–13 bearing sulfonic acid group was less effective than BS-12 having carboxylic acid functional moiety. Schematically, the authors proposed that the sulfonic acid moieties of SB3–12 and a carboxylic acid moiety of BS-12 greatly participated in charge sharing i.e. donating and acceptance (Fig. 8i). Using the DFT method, the authors showed that SB3–12 has higher ΔEgap (ELUMO-EHOMO; ELUMO: Energy of lowest unoccupied molecular orbital & EHOMO: Energy of highest occupied molecular orbital) as compared to the BS-12 which indicates that SB3–12 is less potent to transfer its electron and less reactive than BS-12 (Fig. 8ii). This also answers why SB3–12 is relatively less effective. Lastly, the authors demonstrate that BS-12 from a more stable and effective inhibitive film than SB3–12. The adsorption energies were − 175.822 and − 147.998 kcal mol−1 for the adsorption of BS-12 and SB3–12, respectively (Figure 8iii). The adsorption mode of corrosion mitigation was greatly supported by AFM, XPS, SEM and EDX studies. Publisher Copyright: {\textcopyright} 2022",
year = "2023",
month = jan,
doi = "10.1016/j.cis.2022.102822",
language = "British English",
volume = "311",
journal = "Advances in Colloid and Interface Science",
issn = "0001-8686",
publisher = "Elsevier B.V.",
}