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Corrosion of metals and its alloys destroys our properties, our environment, and our lives. Thus, corrosion control includes a range of developed treatments that take into account material properties, environmental characteristics, and process cost. Typical corrosion inhibitors are known for their excellent efficiency and show great promise. However, they become less used because they cause serious toxicity issues on the environment and affect human and animal health. In recent years, research has intensified on the development of green chemistry technologies, which offer new methods of synthesis and extraction of various non-toxic materials (plant extracts, oils, amino acids, rare earths, etc.), which are highly effective, environmentally acceptable, economical and easily available inhibitors. This chapter deals with a description of corrosion inhibitors with a particular emphasis given to the discussion on the different characteristic features of the green corrosion inhibitors reported in the literature as a comparative view of toxic inhibitors.
Laboratory of Organic Chemistry, Catalysis and Environment, Chemistry Department, Faculty of Sciences, Ibn Tofail University, Kenitra, Morocco
*Address all correspondence to: rehioui.malak0@gmail.com
1. Introduction
Corrosion is an unavoidable natural phenomenon. It is the destruction or deterioration over time of metals and alloys and the alteration of their composition and their physical properties caused by a reaction with the surrounding environment [1]. The tendency of metals to corrode depends on several factors; involving the reactivity of the metal, the presence of impurities, the presence of air, moisture, gases such as sulfur dioxide and carbon dioxide, and the presence of corrosive electrolytes [1, 2]. In addition, corrosion process is defined as the spontaneous tendency of the material to revert back to its original state as found in nature which is more thermodynamically stable form. For this reason, corrosion is also called the reverse of extractive metallurgy [3]. Corrosion processes are a constant and continuous problem that develop rapidly and cause significant damage to society as they deteriorate structural innovations and engineering materials, etc. Corrosion is expensive due to the loss of materials or their properties [4, 5]. Meanwhile, the environmental consequences of corrosion are both severe and complex. They generally extend far beyond the immediate issue of resource depletion. In some cases may be toxic and cause injury [5]. Therefore, corrosion is a subject of great importance due to its economic and safety concerns. This is why metals and alloys require protection in various process industries. Nevertheless, by implementation of corrosion prevention strategies in an appropriate manner, the metal degradation cost can be reduced. At the present time, corrosion control comprises an array of available treatments and approaches that have been developed, such as the isolation of the structure from aggressive media using coatings or the compensation for the loss of electrons from the corroded structure (e.g. cathodic protection by impressed current or by using active sacrificial anodes), or the use of corrosion inhibitors, etc. [6]. Among them, corrosion inhibitors have proved themselves effective in protecting metals against corrosion with obvious advantages regarding availability, strong adaptability, economic efficiency, and high protection efficiency. A corrosion inhibitor is defined as a chemical substance that is added in small concentration to the corrosion medium, which leads to a decrease in the corrosion rate of the metal. It fights against corrosion without directly treating the metal, but intervenes through the medium. Its effectiveness depends on its ability to react with the surface of the metal to form a protective film, thereby reducing or providing protection against corrosion [7, 8, 9].
However, the choice of corrosion inhibitors must also be consistent with non-toxicity criteria, since most traditional corrosion inhibitors have been considered highly toxic to living systems and have negative environmental impacts [9, 10]. Hazards arising from the toxicity of regular inhibitors have created the need to develop and explore highly effective and non-toxic inhibitors called “green inhibitors.” It is based on natural products or plant extracts, oral medicines, food spices, rare earths, etc. The concept of green corrosion inhibitors has gained popularity as environmental awareness has increased dramatically. In this respect, this chapter is intended to present at first regular corrosion inhibitors and show a detailed description of their toxicity. Then, it provides an in-depth view at the contemporary studies on non-toxic natural product inhibitors with their sources, as well as a brief description of their mechanisms for preventing corrosion.
Corrosion inhibitors form a defensive barrier of one or several molecular layers against corrosive agent attack. The frequently used inhibitors can be divided into two main types, inorganic substances, and organic substances.
Indeed, inorganic inhibitors are those in which the active substance is an inorganic compound [10]. Their metallic atoms are enclosed in the film to improve corrosion resistance [11]. Many inorganic inhibitors are known for their excellent efficacy. In particular, chromium (Cr6+) or chromium compounds and chromium salts are among the passivating inhibitors par excellence, but they are environmentally unacceptable and their severe toxicity greatly reduces their use. As has been indicated, strontium chromate, zinc chromate, chrome phosphate, etc., are heavy-metal-based and highly carcinogenic. Small amounts of chromic acid or potassium dichromate can cause kidney failure, liver damage, DNA damage, and blood cell disorders. Chromate mists entering the lungs may eventually lead to lung cancer [12, 13]. Other inhibiting molecules in the form of salts have made it possible to obtain very good yields in terms of metal protection and thus corrosion prevention, such as sodium tungstate (Na2WO4), vandates (NaVO3), nitrites (NaNO2), and silicates (Na2Si2O5). However, these compounds today are highly toxic, leading to serious consequences for the environment and human beings. They can cause temporary or permanent damage to the nervous system, and disrupt the biochemical process and the enzymatic system of our organism [9]. Molybdates (MoO3−) and phosphates (H2PO3−) also provide passivation protection to metallic surfaces by incorporating them into the oxide layer. Borates and arsenates are also known for their promising inhibitory activity against metal corrosion in various aggressive aqueous media. Apart from that, they have also proven to be intolerant because of the threat they pose to nature and social health in the long run [14, 15]. Pyrrole and derivatives exhibit good protection against metals corrosion, especially in acidic media. These inhibitors are also useful application in the formulation of primers and anticorrosive coatings, but the major disadvantage associated with them is their toxicity and as such their use has come under severe criticism [15].
On the other hand, the frequently synthetic organic molecules used as corrosion inhibitors in industrial environments include aliphatic or aromatic thioureas, amines, amides, pyrazoles, pyrimidines, acetylenic alcohols, aldehydes, benzylidenes, carbazones, azoles, Schiff’s base, benzonitriles, dimeric and trimeric acids, etc. Indeed, most of these inhibitors are containing heteroatoms such as nitrogen, sulfur, and oxygen with lone pair of electrons and should have aromatic systems. These compounds can act on the metal surface by means of adsorption and there detracting of the active metallic surface area, leaving inactive sites on the surface exposed to corrosive media. The inhibition efficiency of these compounds is also related to its functional groups, steric effects, and π-orbital character of donating electrons [15]. Even though these organic compounds exhibit high inhibition efficiencies against the corrosion of many types of metals, they are toxic and non-environmentally friendly and their use causes toxic harm to humans, animals, and nature. In addition, the time of exposure is also a factor that can have a strong influence on the toxicity and which can increase the harmful effect of these molecules [13].
So, the environmental and health risks associated with the use of these inhibitors have prompted us to find or use non-toxic or green corrosion inhibitors that would offer maximum protection to metal structures but have minimal impact on human and nature. Because the choice of an effective corrosion inhibitor must not only be cost-effective, stable, compatible with the corrosive medium, and produce the desired effect at small concentrations; but it must also be compatible with the current standards for non-toxicity, biodegradability, bioaccumulation, and environmental protection.
The toxicity of inhibitors and the increase in environmental pollution have led to the enactment of strict international laws for the use of ecological inhibitors and to the demand for a green and ecological approach that deals with the principles of “green chemistry”. These principles refer to efforts toward establishing a comprehensive approach to chemical risk management. This concept is based on the ideas of sustainability, reducing environmental consequences, and preserving natural resources for the following centuries [16]. The requirements for a chemical to be approved as a green corrosion inhibitor have been explicitly set out by legislative bodies essentially the Paris Commission (PARCOM) and the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH), which are non-bio-accumulative, bio-degradable, and zero or very minimal marine toxicity level [17]. Figure 1 illustrates the principles by which green corrosion inhibitors work.
Figure 1.
The principles of green chemistry on which green corrosion inhibitors act.
The major categories of these kinds of inhibitors include plant extracts, oils, rare earths, and amino acids have been discussed briefly below. Other green inhibitors such as ionic liquids, organic polymers, and surfactants [18, 19, 20] are not emphasized in this chapter.
Green corrosion inhibitors are drawing extraordinary interest in the corrosion field and can be used in many industrial applications [11] to promote green chemistry and sustainability. In this perspective, one of the areas in which green chemistry is associated with green inhibitors, through the reduction of ecological impact and wastes, is related to safeguarding metals. Figure 2 shows the importance of green corrosion inhibitors in large industrial applications.
Figure 2.
Application of green corrosion inhibitors in various industrial sectors.
3.1 Rare earth metal compounds
The use of rare earth metal compounds as corrosion inhibitors traced back to 1984 when Hinton et al. [21] published the first paper on the use of cerium chloride salts as corrosion inhibitors, after that a lot of research papers were published and showed that rare earth metal compounds can be used as good alternatives of non-toxic corrosion inhibitors. In 1992, Hinton et al. [22] published a review paper highlighting the use of some rare earth salts as green corrosion inhibitors for a wide range of metals. Rare earth compounds act by producing an oxide film at the cathodic sites of metal substrates that avoid the supply of oxygen or electrons to the reduction reaction, thus minimizing the rate of corrosion. The majority of rare earths metals have zero toxicity [10]. Thus, recent research turns around utilizing rare earth metals as green alternative for toxic inhibitors, especially chromium species.
For instance, Somers AE et al. [23] evaluated four rare earth 3-(4-methylbenzoyl)propanoate (mbp) compounds (RE = La, Ce, Nd, and Y) as corrosion inhibitors for mild steel in 0.01 M NaCl. Results showed that all the compounds can reduce corrosion after 30 min immersion. Surface analysis showed the presence of a film containing inhibitor components.
In another investigation of Manh TD et al. [24] the rare-earth organic compound Gadolinium 4-hydroxycinnamate (Gd(4OHCin)3) was shown to be an effective corrosion inhibitor for mild steel in naturally-aerated 0.1 M chloride solution, not only of general corrosion but also of pitting corrosion. The inhibition efficiency is more important when the concentration of inhibitor increases, reaching values up to 94% at a concentration of 0.93 mM. The results also demonstrated that Gd(4OHCin)3 behaves as good mixed corrosion inhibitor with predominant anodic activity.
Peng Y et al. [25] studied two novel rare-earth (RE) 3-(4-methylbenzoyl)-propanoate (mbp) complexes (RE(mbp)3; RE = La, Y) as corrosion inhibitors for AS1020 mild steel in 0.01 M NaCl solutions. Results disclosed a high corrosion inhibition performance of Y(mbp)3 which is attributed to the build-up of a protective surface film with a high level of corrosion resistance, particularly after 24 hours.
Zhao D et al. [26] focused on the use of the salt of rare earth cerium as corrosion inhibitor of aluminum. Results, revealed that the good corrosion resistance of cerium-based passive coating was obtained when the compositions were as follows: CeCl3·7H2O, 0.05 mol/L; H2O2, 30 mL/L; current density, 1.1 mA/cm2; temperature, 40°C; time, 9 min. Surface analysis showed that the cerium conversion coatings formed on the surface of aluminum alloy were related to cerium hydroxide/hydrated oxide depositions.
Porcayo-Calderon J et al. [27] evaluated the corrosion inhibition effect of rare earth chlorides on API X70 steel in a 3.5% NaCl solution by electrochemical techniques. The results showed that it is a mixed-style inhibitor with an inhibition efficiency greater than 90%, at a concentration of 0.001 M. Its protective action is due to the reduction of the oxygen reduction rate because of the blocking effect of the cathodic sites and to the reduction of the metallic dissolution rate due to the formation of a protective layer on metal surface.
3.2 Plant extracts and oils
The use of natural products to inhibit corrosion may date back to the 1960s when tannins and their derivatives were employed to protect steel, iron tools, and pipelines [28, 29]. Now there are many studies, articles, reviews and books focused on the development of metal corrosion inhibitors, that guarantee high efficiency up to 99%, based on plant extracts and oils rich in active molecules, obtained from different parts of plant-like leaves, fruits, bark, peels, flowers, roots, seeds, stems, and even whole plant extracts. Plants are eco-friendly climate as they prepare their food through the photosynthesis cycle by taking carbon dioxide and releasing oxygen. In addition, the plant extract is also environmentally friendly when used as an inhibitor as these are likewise biodegradable.
The inhibition efficiency of these green inhibitors is due to the presence of phytochemicals [30]. Most phytochemicals contain polar functional groups such as amide (–CONH2), hydroxyl (–OH), ester (–COOC2H5), carboxylic acid (–COOH), and amino (–NH2) which aid in their absorption on metal surface [31]. Phytochemical type and content vary based on the choice of plant components for extraction. Some of the most common phytochemicals that have a corrosion-inhibiting effect are flavonoids, glycosides, alkaloids, saponins, phytosterols, tannins, anthraquinones, phenolic compounds, triterpenes, and fluoptanins. Among them, we quote some published works:
The flavonoid extract from Erigeron floribundus was studied as green inhibitor for mild steel corrosion in 2 M HCl solution using gasometric method. The study revealed that the inhibition efficiency increased with increase in concentration of the inhibitor. The adsorption mechanism was spontaneous and occurred according to Langmuir adsorption isotherms with also physical adsorption [32].
Fouda AS et al. [33] have studied the extracts of henna (Lawsonia Inermis) for corrosion inhibition of carbon steel in 1 M HCl solution applying weight loss and electrochemical measurements. Results showed that the inhibition efficiency increases with increasing inhibitor concentration and reached 83.1% at 300 ppm, however, it decreases with increasing temperature. Surface analysis has been carried out using energy-dispersive X-ray and scanning electron microscopy.
Rehioui et al. [34] explored the anticorrosion behavior of the Opuntia dillenii seed oil incorporated in a formulation labeled FOD as an ecofriendly corrosion inhibitor to protect iron in acid rain. Corrosion inhibition effect of FOD was studied by gravimetric methods, electrochemical measurements, and scanning electron microscopy coupled with elemental analysis (SEM/EDX). Obtained results revealed that FOD acted as a good mixed corrosion inhibitor with predominant anodic activity. Inhibition efficiency was found to vary with concentration and period of immersion, reaching values up to 99% at the concentration of about 1000 ppm. The adsorption study showed that it followed Langmuir adsorption isotherm with both chemisorption and physisorption mechanism.
Torres-Acosta AA [35] has investigated Opuntia-Ficus-Indica (Nopal) mucilage as a steel corrosion inhibitor in alkaline media. Results showed good corrosion-inhibiting effect of Opuntia-Ficus-Indica (Nopal) mucilage. The addition of Nopal led to the formation of a denser and more packed oxide/hydroxide surface layer on the steel surface that decreased corrosion activity. This oxide/hydroxide layer growth was confirmed from microscopic evaluation of the metal surface.
The performances of the extract obtained from Rosmarinus officinalis (RO) on the corrosion inhibition of XC48 steel in 1 M HCl at different temperatures were carried out through mass loss, electrochemical measurements, surface analysis, and quantum chemical calculations. Results showed that RO extract is a mixed-type inhibitor. The inhibition efficiency increased at greater concentration of the inhibitor and decreases with the rise of the temperature. The adsorption mechanism is physisorption that is adequately described by the Langmuir equilibrium model. The retrieved outcomes are confirmed by surface observations, which reveal that the adsorbed inhibitor molecules completely hinder the HCl attacks at the steel grain boundaries [36].
Chellouli et al. [37] determined the inhibitive effect of a green formulation based on the seed oil of Nigella Sativa L. against iron corrosion in acid rain solution by applying gravimetric methods, electrochemical measurements, and surface analysis. Results demonstrated that the formulation acts as a good mixed-type inhibitor. The metal dissolution rate decreased with increasing inhibitor concentration and immersion time. A maximum inhibition efficiency of around 99% is achieved for a concentration of 2500 ppm. The surface analysis confirmed a good protective action of the inhibitor by the formation of a film on the surface of the iron in an environment simulated with acid rain.
The performance of other recently developed plant extracts and oils as green corrosion inhibitors of different metals and alloys in various aggressive media is listed in Table 1.
Inhibitor (concentration)
Metal/alloy
Test condition
Test techniques
Maximum efficiency (%)
Reference
Viscum Album extract (300 ppm)
Carbon steel
1 M HCl
Weight loss Electrochemical measurements Atomic force microscopy Attenuated total reflection infrared X-ray spectroscopy
Electrochemical measurements Scanning electron microscope Atomic force microscopy X-ray diffractometer Density functional theory Fourier transform infrared spectroscopy
Some plant extracts as corrosion inhibitors of different metals and alloys.
3.3 Amino acids
Amino acids are considered as green corrosion inhibitors because they are non-toxic, biodegradable, inexpensive, soluble in aqueous media, and easy to produce purities higher than 99%. Amino acids are organic compounds that contain at least one carboxyl group (–COOH) and one amino group (–NH2) bonded to the same carbon atom (α- or 2-carbon) [60]. The presence of heteroatoms and conjugated π-electrons system have made amino acids a significant class of green corrosion inhibitors thanks to their environmental aspect. It has been demonstrated by various authors that certain amino acids have been shown to be good and reliable corrosion inhibitors for many metals in various aggressive environments, which has led to a growing interest in these compounds as alternatives to conventional corrosion inhibitors, which are often toxic, as mentioned in the previous section. However, from then, the number of studies dealing with amino acids as corrosion inhibitors increased rapidly. In other respects, amino acids are used in food and feed technology and as intermediates for the chemical industry (e.g. for pharmaceutical and cosmetic applications) [61].
Among the amino acids, El-Sayed NH [62] signaled the corrosion inhibition of carbon steel in stagnant naturally aerated chloride solutions by certain amino acids including glycine, valine, leucine, cysteine, methionine, histidine, threonine, phenylalanine, lysine, proline, aspartic acid, arginine, and glutamic acid using electrochemical techniques. Results showed that all of the amino acids acted as mixed-style inhibitors while cysteine, phenylalanine, arginine, and histidine showed remarkably high corrosion inhibition efficiency at a concentration of 10 mM/dm3.
Amin AM et al. [63] studied corrosion inhibition of copper in O2-saturated 0.5 M H2SO4 solutions by four selected amino acids glycine, alanine, valine, and tyrosine, using electrochemical measurements at 30°C. The inhibition efficiencies of almost 98 and 91% were obtained with 50 mM tyrosine and glycine, respectively. On the other hand, alanine and valine reached only about 75%.
Srivastava V et al. [64] studied the effect of three novel amino acids 2-(3-(carboxymethyl)-1H-imidazol-3-ium-1-yl)acetate (AIZ-1), 2-(3-(1-carboxyethyl)-1H-imidazol-3-ium-1-yl)propanoate (AIZ-2), and 2-(3-(1-carboxy-2-phenylethyl)-1H-imidazol-3-ium-1-yl)-3-phenylpropanoate (AIZ-3) on the corrosion of mild steel by electrochemical methods, surface analysis, and theoretical investigations. Among the studied inhibitors, AIZ-3 showed the maximum inhibition efficiency (IE) of 96.08% at a concentration of 0.55 mM (200 ppm).
Zeino et al. [65] investigated polyaspartic acid (PASP) for corrosion inhibitory effect on mild steel in a 3% NaCl solution. PASP alone showed a moderate inhibition efficiency of 61% at 2 g/L, but when zinc ion was added to PASP, the inhibition efficiency rise to 97% at a reduced PASP concentration of 0.5 g/L.
Amin MA et al. [66] have used glycine derivative to prevent corrosion of mild steel corrosion in 4 M H2SO4 solutions at different temperatures (278–338 K) [37] using electrochemical methods. The inhibition efficiency increased with an increase in inhibitor concentration and decreased with temperature, suggesting the occurrence of physical adsorption.
Zhang DQ et al. [67] investigated the corrosion inhibition of three amino acid compounds namely serine, threonine, and glutamic acid on copper in aerated 0.5 M HCl by electrochemical method, reflected FT-infrared spectroscopy, and quantum chemical calculations.
Some other recently reported amino acid-based as green corrosion inhibitors of variety of metals and alloys are depicted in Table 2.
Gravimetric and electrochemical measurements Scanning electron microscopy Energy dispersive analysis of X-rays Fourier transform infrared spectroscopy Atomic force microscopy
Weight loss Electrochemical measurements Fourier transform infrared spectroscopy UV-visible Scanning electron microscopy Energy dispersive analysis of X-rays
4. Mechanism of action of green corrosion inhibitors
During corrosion, metal ions migrate into the solution in the active regions (anodic site) and transfer electrons from the metal to the acceptor at less active regions (the cathode); the cathodic process requires the presence of an electron acceptor functioning as oxygen, oxidizing agents or hydrogen ions. Green corrosion inhibitors have adsorbing properties and are known as site blocking elements [85]. They can minimize the corrosion rate through adsorption of active species onto the metal/alloy surface when added to many industrial systems by:
The change of the rate of anodic and/or cathodic reactions;
The influence of the diffusion rate of aggressive ions in interaction with metal structures;
The increase of the electrical resistance of the metal surface by forming a film on it.
In fact, many researchers have postulated several theories to explain the mode of action of green corrosion inhibitors. For example, the active constituent derived from natural inhibitors varies from one plant species to another. The best sources of green inhibitors are natural products because they contain polar compounds with multiple “heteroatoms” similar to organic inhibitors. These heteroatoms present in the plant extracts act as an active center and adsorb on metallic surface by creating a film that denies access to corrosive agent. Non-polar compounds with aromatic rings, aliphatic chains, heterocyclic rings, and functional moieties are abundant in plant extracts. These compounds can be effectively adsorbed on the mineral surface and thus protect it from corrosion without harming the environment like inorganic compounds [86].
There are several methods to identify the inhibitory mechanism of green corrosion inhibitors. Electrochemical techniques such as electrochemical impedance spectroscopy and potentiodynamic polarization analysis have been successfully implemented and provide valuable information on the corrosion rate and the mechanism of corrosion protection. These methods are briefly described in this section.
Potentiodynamic polarization is an electrochemical method used to determine green corrosion inhibitors performance, instantaneous corrosion rates and to elucidate the corrosion prevention mechanism. This method relies on changing the current or potential across a sample under study and recording the corresponding potential or current change. This can be facilitated using either a direct current source or an alternating current source. In most studies, a conventional three-electrode cell is used for the measurement, consisting of a counter electrode (Pt or graphite), a reference electrode (calomel or Ag/AgCl), and a working elecrode (metal substrate) immersed in the test solution [87]. The reference electrode measures and controls the system’s voltage (V) and the counter electrode measures and controls current (I). The open circuit potential (Eocp) of a metal changes when electrochemical reactions occur. Once equilibrium is reached, a steady value is measured, and then the potentiodynamic polarization curve is performed by providing ranges of potential values. The plots are then used to calculate the corrosion potential (Ecorr) and the corrosion current density (icorr). Additionally, different concentrations of green inhibitors and experimental temperatures can be used to examine their different effects on corrosion prevention performance [88].
Electrochemical impedance spectroscopy is one of the best and powerful analytical tools for following in situ electrochemical progression with insight into the physical phenomena acting at the metal-electrolyte interface, providing valuable information on the surface properties and electrode kinetics via impedance diagrams. In this technique, an AC voltage (in the case of potentiostatic EIS) or current (in the case of galvanostatic EIS) is applied to the system under study to receive a response in the form of AC current (voltage) or voltage (current) as a function of the frequency. This technique can be implemented in a three-electrode cell, similar to Potentiodynamic polarization. Electrochemical impedance spectroscopy is usually used to determine resistance and current flow values, both when green corrosion inhibitor is present in the solution and when it is not. The reported result is usually a Nyquist diagram, with the real part of the impedance (Z′) on the X-axis and the imaginary part (Z″) on the Y-axis [89].
The two main adsorption mechanisms are physisorption and chemisorption. It has been recommended that physisorbed molecules attach to the surface at the cathodes and basically retard metal dissolution by the cathodic reaction, whiles chemisorbed molecules shield anodic areas and reduce the inherent reactivity at the sites where they are attached. It is acknowledged that the values of the standard free energy of adsorption ΔGoads in aqueous solution are −20 kJ.mol−1 or lower establishes the physisorption process. While, those around −40 kJ.mol−1 or more negative include charge sharing or transfer of electrons from inhibitory molecules to the metal surface, point toward coordinate or covalent bond. It is important to signal that both mechanisms can take place together on the same metal surface. Isotherm equations were used to validate the adsorption mechanism, and to ascertain the closest equation that relates the dosage of inhibitors to the adsorbed concentration at saturation. Empirical equations functioning as hyperbolic, exponential, logarithmic, and power are complicated to relate to the given adsorption mechanisms. There are many mathematical equations called adsorption models that estimate the adsorbate amount in the absorbent at constant temperature. Most of the time, green inhibitors obey the Langmuir isotherm model, but some also adhere to the Freundlich and Frumkin isotherms [7].
However, the study of the precise mechanism of the adsorption process is complex because most of the constituents moderate the corrosion reactions in many ways, which makes it difficult to assign the credit for corrosion mitigation to a particular constituent. Moreover, the nature of the adsorption of an inhibitor onto a metal surface is largely governed by characteristics such as chemical and electronic properties of the inhibitor, temperature, type of electrolyte, steric effects, and the nature and charge of the surface of the metals [90]. The negative surface charge will enhance the adsorption of the cation while the adsorption of the anion with the positive surface charge is preferred.
Simulation and computational modeling backed by wet experimental results would help to better understand the mechanism of inhibitor action, their adsorption patterns, and the inhibitor metal surface interface and aid the development of designer inhibitors with an understanding of the time required for the release of self-healing inhibitors. This is achieved by density functional theory (DFT) which is based on quantum chemical calculations that have emerged as potential tools for studying metal-inhibitor interactions between inhibitors and metallic surfaces [91]. Monte Carlo simulation is also well known as a traditional and powerful method if computational complexity and time are not limiting [92].
5. General extraction methods and challenges faced for sustainability
The most crucial step is the field of green inhibitors is the extraction of active substances. In general, extraction is a separation process, in which the active ingredients are isolated from the plant. Proper extraction processes are needed to extract the required active ingredients from the plants. The suitability of the extraction method depends on the polar or non-polar nature of the target compound, the size of the sample particles, and the presence of interfering materials. In addition, the selection of the solvent for extraction has to be rigorous and guarded as it should be based on the type of plant, part to be extracted, the availability of solvent, and the nature of the bioactive compounds [7]. Generally, extraction of polar compounds involves polar solvents, while nonpolar solvents are applied in extraction of nonpolar compounds. Several commonly used techniques [7, 91] can be applied to separate and extract the required extract from the plants among them:
Supercritical fluid extraction
Microwave-assisted extraction
Ultrasound-assisted extraction
Soxhlet extraction
Enzyme assisted extraction
Hydro-distillation extraction
Steam-distillation extraction
Ultra-high pressure extraction
Accelerated solvent extraction, etc.
Each extraction method has its own characteristics. The type of extraction process can greatly affect the final natural products obtained. It should be chosen with caution according to the objective of the study. It has an effect on purity, price and yield and depends on the compound of interest and the required degree of purity. However, the choice of extraction and purification methods is another important fact. Some process is tedious, cumbersome, energy-consuming, time-consuming, and expensive. For example, plant extracts comprise only tiny portion of active constituents, therefore, a large amount of plants is mandatory to achieve satisfactory inhibition ability which results in a high cost. High temperature could lead to the deterioration of the sensitive active constituents and thus reduce the relative inhibition efficiency. In addition, the extraction process is too complex to be appropriate for large-scale applications in industries. Extraction requires relatively the use of high-level organic solvents that emit greenhouse gases that threatened humans, agriculture, and microorganisms. Moreover, excessive use of solvents leads to enormous waste of by-products. Unlike these dangerous techniques, further research is needed to introduce efficient and environmentally friendly processes such as “green processing,” “green solvents,” and “green products.”
This chapter collects a variety of discussed and summarized studies advocating the use of plant extracts, oils, rare earths, and amino acids as corrosion inhibitors of metals and alloys. These inhibitors also present certain challenges, but they offer many advantages, and they remain the most ideal and promising alternative as they are generally synthesized from natural and non-toxic products, which increases their availability and effectiveness in terms of environmental and human safety.
1.Zehra S, Mobin M, Aslam J. An overview of the corrosion chemistry. Environmentally Sustainable Corrosion Inhibitors. 2022:3-23
2.Chigondo M, Chigondo F. Recent natural corrosion inhibitors for mild steel: An overview. Journal of Chemistry. 2016;2016:1-7
3.Birat J-P. Chapter 5 Corrosion and oxidation of materials. Sustainable Materials Science—Environmental Metallurgy. 2020;1:229-246
4.Koch G. Cost of corrosion. Trends in Oil and Gas Corrosion Research and Technologies. 2017:3-30
5.Hansson CM. The impact of corrosion on society. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. 2011;42:2952-2962
6.Zehra S, Mobin M, Aslam R. Chapter 2—Corrosion prevention and protection methods. Eco-Friendly Corrosion Inhibitors. 2022:13-26
7.Kumari P, Lavanya M. Plant extracts as corrosion inhibitors for aluminium alloy in NaCl environment—Recent review. Journal of the Chilean Chemical Society. 2022:67
8.Abbout S. Green inhibitors to reduce the corrosion damage. In: Singh A, editor. Corrosion. London: IntechOpen; 2020
9.Abo El-Enin SA, Amin A. Review of corrosion inhibitors for industrial applications. International Journal of Engineering Research and Reviews. 2015;3:127-145
11.Shehata OS, Korshed LA, Attia A. Green Corrosion Inhibitors, Past, Present, and Future. IntechOpen: Corrosion Inhibitors; 2018
12.Shahid M. Corrosion protection with eco-friendly inhibitors. Advances in Natural Sciences: Nanoscience and Nanotechnology. 2010;2:1-6
13.Singh WP, Bockris JOM. Toxicity issues of organic corrosion inhibitors: Applications of QSAR model. Nace Corrosion. 1996
14.Obot IB, Obi-Egbedi NO, Umoren SA, Ebenso EE. Synergistic and antagonistic effects of anions and ipomoea invulcrata as green corrosion inhibitor for aluminium dissolution in acidic medium. International Journal of Electrochemical Science. 2010;5:994-1107
15.Amitha Rani BE, Basu BBJ. Green inhibitors for corrosion protection of metals and alloys: An overview. International Journal of Corrosion. 2012;2012:1-15
16.Boxall ABA. Global climate change and environmental toxicology. In: Wexler P, editor. Encyclopedia of Toxicology. 3rd ed. Elsevier Science; 2014. pp. 736-740
17.Umoren SA, Solomon MM, Obot IB, Suleiman RK. A critical review on the recent studies on plant biomaterials as corrosion inhibitors for industrial metals. Journal of Industrial and Engineering Chemistry. 2019;76:91-115
18.Sabirneeza AAF, Geethanjali R, Subhashini S. Polymeric corrosion inhibitors for iron and its alloys: A review. Chemical Engineering Communications. 2015;202:232-244
19.Kobzar YL, Fatyeyeva K. Ionic liquids as green and sustainable steel corrosion inhibitors: Recent developments. Chemical Engineering Journal. 2021;425:131480
20.Sliem MH, Afifi M, Bahgat Radwan A, Fayyad EM, Shibl MF, Heakal FE-T, et al. AEO7 surfactant as an eco-friendly corrosion inhibitor for carbon steel in HCl solution. Scientific Reports. 2019;9:2319
21.Hinton BRW, Arnott DR, Ryan NE. Inhibition of aluminum alloy corrosion by cerous cations. Metals Forum. 1984;7:211-217
22.Hinton BRW. Corrosion inhibition with rare earth metal salts. Journal of Alloys and Compounds. 1992;180:15-25
23.Somers AE, Hinton BRW, de Bruin-Dickason C, Deacon GB, Junk PC, Forsyth M. New, environmentally friendly, rare earth carboxylate corrosion inhibitors for mild steel. Corrosion Science. 2018;139:430-437
24.Manh TD, Hien PV, Nguyen QB, Quyen TN, Hinton BRW, Nam ND. Corrosion inhibition of steel in naturally-aerated chloride solution by rare-earth 4-hydroxycinnamate compound. Journal of the Taiwan Institute of Chemical Engineers. 2019;104:177-189
25.Peng Y, Hughes AE, Deacon GB, Junk PC, Hinton BRW, Forsyth M, et al. A study of rare-earth 3-(4-methylbenzoyl)-propanoate compounds as corrosion inhibitors for AS1020 mild steel in NaCl solutions. Corrosion Science. 2018;145:199-211
26.Zhao D, Sun J, Zhang L, Tan Y, Li J. Corrosion behavior of rare earth cerium based conversion coating on aluminum alloy. Journal of Rare Earths. 2010;28:371-374
27.Porcayo-Calderon J, Ramos-Hernandez JJ, Porcayo-Palafox E, de la Escalera LMM, Canto J, Gonzalez-Rodriguez JG, et al. Sustainable development of corrosion inhibitors from electronic scrap: Synthesis and electrochemical performance. Advances in Materials Science and Engineering. 2019;2019:1-14
28.Bregman JI. Corrosion Inhibitors. New York: Macmillan; 1963
29.Evans UR. The Corrosion and Oxidation of Metals. London: Edward Arnold; 1960. pp. 170-178
30.Kaur J, Daksh N, Saxena A. Corrosion inhibition applications of natural and eco-friendly corrosion inhibitors on steel in the acidic environment: An overview. Arabian Journal for Science and Engineering. 2022;47:57-74
31.Wei G, Deng S, Li X. Eupatorium Adenophora (Spreng.) leaves extract as a highly efficient eco-friendly inhibitor for steel corrosion in trichloroacetic acid solution. International Journal of Electrochemical Science. 2022;17:1-20
32.Abeng FE, Idim VD. Green corrosion inhibitor for mild steel in 2 M HCl solution: Flavonoid extract of Erigeron floribundus. World Scientific News. 2018;98:89-99
33.Fouda AS, Hegazi MM, El-Azaly A. Henna extract as green corrosion inhibitor for carbon steel in hydrochloric acid solution. International Journal of Electrochemical Science. 2019;14:4668-4682
34.Rehioui M, Abbout S, Benzidia B, Hammouch H, Erramli H, Ait Daoud N, et al. Corrosion inhibiting effect of a green formulation based on Opuntia Dillenii seed oil for iron in acid rain solution. Heliyon. 2021;7:e06674
35.Torres-Acosta AA. Opuntia-Ficus-Indica (Nopal) mucilage as a steel corrosion inhibitor in alkaline media. Journal of Applied Electrochemistry. 2007;37:835-841
36.Belakhdar A, Ferkous H, Djellali S, Sahraoui R, Lahbib H, Ben Amor Y, et al. Computational and experimental studies on the efficiency of Rosmarinus officinalis polyphenols as green corrosion inhibitors for XC48 steel in acidic medium. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2020;606:125458
37.Chellouli M, Chebabe D, Dermaj A, Erramli H, Bettach N, Hajjaji N, et al. Corrosion inhibition of iron in acidic solution by a green formulation derived from Nigella sativa L. Electrochimica Acta. 2016;204:50-59
38.Elgyar OA, Ouf AM, El-Hossiany A, Fouda AE. The inhibition action of Viscum Album extract on the corrosion of carbon steel in hydrochloric acid solution. Biointerface Research in Applied Chemistry. 2021;11:14344-14358
39.Batah A, Anejjar A, Bammou L, Belkhaouda M, Salghi R. Effect of apricot almond oil as green inhibitor for steel corrosion in hydrochloric media. Portugaliae Electrochimica Acta. 2020;2020(38):201-214
40.Zouarhi M, Chellouli M, About S, Hammouch H, Dermaj A, Said Hassane SO, et al. Inhibiting effect of a green corrosion inhibitor containing Jatropha Curcas seeds oil for iron in an acidic medium. Portugaliae Electrochimica Acta. 2018;36:179-195
41.Abbout S, Zouarhi M, Chebabe D, Damej M, Berisha A, Hajjaji N. Galactomannan as a new bio-sourced corrosion inhibitor for iron in acidic media Said. Heliyon. 2020;6:e03574
42.Souza AV, da Rocha JC, Ponciano Gomes JAC, Palermo LCM, Mansur CRE. Development and application of a passion fruit seed oil microemulsion as corrosion inhibitor of P110 carbon steel in CO2-saturated brine. Colloids and Surfaces A. 2020;599:124934-124948
43.Nasr K, Fedel M, Essalah K, Deflorian F, Souissi N. Experimental and theoretical study of Matricaria recutita chamomile extract as corrosion inhibitor for steel in neutral chloride media. Anti-Corrosion Methods and Materials. 2018;65:292-309
44.Sahooa S, Nayaka S, Sahoo D, Mallik M. Corrosion inhibition behavior of dual phase steel in 3.5 wt % NaCl solution by Carica papaya peel extracts. Materials Today: Proceedings. 2019;18:2642-2648
45.Singh A, Ahamad I, Quraish MA. Piper longum extract as green corrosion inhibitor for aluminium in NaOH solution. Arabian Journal of Chemistry. 2016;9:S1584-S1589
46.Ahmed RK, Zhang S. Bee pollen extract as an eco-friendly corrosion inhibitor for pure copper in hydrochloric acid. Journal of Molecular Liquids. 2020;316:113849
47.Abdelaziz S, Benamira M, Messaadia L, Boughoues Y, Lahmar H, Boudjerda A. Green corrosion inhibition of mild steel in HCl medium using leaves extract of Arbutus unedo L. plant: An experimental and computational approach. Collid Surface A. 2021;619:126496
48.Xu C, Tan B, Zhang S, Li W. Corrosion inhibition of copper in sulfuric acid by Leonurus japonicus Houtt. Extract as a green corrosion inhibitor: Combination of experimental and theoretical research. Journal of the Taiwan Institute of Chemical Engineers. Chemical Engineers. 2022;139:104532
49.Shahen S, Abdel-karim AM, Gaber GA. Eco-friendly Roselle (Hibiscus sabdariffa) leaf extract as naturally corrosion inhibitor for Cu-Zn alloy in 1M HNO3. Egyptian Journal of Chemistry. 2022;65:351-361
50.Gonzalez-Rodriguez JG, Gutierrez-Granda DG, Larios-galvez AK, Lopez-sesenes R. Use of thymus vulgaris extract as green corrosion inhibitor for bronze in acid rain. Journal of Bio- and Tribo-Corrosion. 2022;8:77
51.Deyab MA, Al-Qhatani MM. Green corrosion inhibitor: Cymbopogon schoenanthus extract in an acid cleaning solution for aluminum brass. Zeitschrift für Physikalische Chemie. 2021;236:215-226
52.Ansari A, Ou-Ani O, Oucheikh L, Youssefi Y, Chebabe D, Oubair A, et al. Experimental, theoretical modeling and optimization of inhibitive action of Ocimum basilicum essential oil as green corrosion inhibitor for C38 steel in 0.5 M H2SO4 medium. Chemistry Africa. 2022;5:37-55
53.Najem A, Sabiha M, Laourayed M, Belfhaili A, Benhiba F, Boudalia M, et al. New green anti-corrosion inhibitor of citrus peels for mild steel in 1 M HCl: Experimental and theoretical approaches. Chemistry Africa. 2022;5:969-986
54.Zhang X, Jiang W-F, Wang H-L, Hao C. Adsorption and inhibitive properties of Apigenin derivatives as eco-friendly corrosion inhibitors for brass in nitric acid solution. Journal of Adhesion Science and Technology. 2019;33:736-760
55.Sun X, Qiang Y, Hou B, Zhu H, Tian H. Cabbage extract as an eco-friendly corrosion inhibitor for X70 steel in hydrochloric acid medium. Journal of Molecular Liquids. 2022;365:119733
56.Wu Y, Zhang Y, Jiang Y, Qian Y, Guo X, Wang L, et al. Orange peel extracts as biodegradable corrosion inhibitor for magnesium alloy in NaCl solution: Experimental and theoretical studies. Journal of the Taiwan Institute of Chemical Engineers. 2020;115:35-46
57.Onukwuli OD, Anadebe VC, Okafor C. Optimum prediction for inhibition efficiency of Sapium ellipticum leaf extract as corrosion inhibitor of aluminum alloy (AA3003) in hydrochloric acid solution using electrochemical impedance spectroscopy and response surface methodology. Bulletin of the Chemical Society of Ethiopia. 2020;34:175-191
58.Boudalia M, Fernández-Domene RM, Tabyaoui MH, Bellaouchou A, Genbour A, García-AntónJ. Green approach to corrosion inhibition of stainless steel in phosphoric acid of Artemesia herba albamedium using plant extract. Journal of Materials Research and Technology. 2019;8:5763-5773
59.Chraka A, Raissouni I, Seddik NB, Khayar S, Ibn Mansour A, Tazi S, et al. Identification of potential green inhibitors extracted from Thymbra capitata (L.) Cav. For the corrosion of Brass in 3% NaCl solution: Experimental, SEM–EDX analysis, DFT computation and Monte Carlo simulation studies. Journal of Bio- and Tribo-Corroions. 2020;6:80
60.Hamadi L, Mansouri S, Oulmi K, Kareche A. The use of amino acids as corrosion inhibitors for metals: A review. Egyptian Journal of Petroleum. 2018;2018(27):1157-1165
61.Tonouchi N, Ito H. Present global situation of amino acids in industry. Advances in Biochemical Engineering/Biotechnology. 2017;159:3-14
62.El-Sayed NH. Corrosion inhibition of carbon steel in chloride solutions by some amino acids. European Journal of Chemistry. 2016;7:14-18
64.Srivastava V, Haque J, Verma C, Singh P, Lgaz H, Salghi R, et al. Amino acid based imidazolium zwitterions as novel and green corrosion inhibitors for mild steel: Experimental, DFT and MD studies. Journal of Molecular Liquids. 2017;244:340-352
65.Zeino A, Abdulazeez I, Khaled M, Jawich MW, Obot IB. Mechanistic study of polyaspartic acid (PASP) as eco-friendly corrosion inhibitor on mild steel in 3% NaCl aerated solution. Journal of Molecular Liquids. 2018;250:50-62
66.Amin MA, Ibrahim M. Corrosion and corrosion control of mild steel in concentrated H2SO4 solutions by a newly synthesized glycine derivative. Corrosion Science. 2011;53:873-885
67.Zhang D-Q , Cai Q-R, Gao L-X, Lee KY. Effect of serine, threonine and glutamic acid on the corrosion of copper in aerated hydrochloric acid solution. Corrosion Science. 2008;50:3615-3621
68.Nady H. Tricine [N-(Tri(hydroxymethyl)methyl)glycine]—A novel green inhibitor for the corrosion inhibition of zinc in neutral aerated sodium chloride solution. Egyptian Journal of Petroleum. 2017;26:905-913
69.Yeganeh M, Khosravi-Bigdeli I, Eskandari M, Alavi Zaree SR. Corrosion inhibition of l-methionine amino acid as a green corrosion inhibitor for stainless steel in the H2SO4 solution. Journal of Materials Engineering and Performance. 2020;29:3983-3994
70.Jano A, Lame A, Kokalari E. Lysine as corrosion inhibitor for low alloy carbon steel in acidic media. Analele Universitatii “Ovidius” Constanta—Seria Chimie. 2014;25:11-14
71.Kowsari E, Arman SY, Shahini MH, Zandi H, Ehsani A, Naderi R, et al. In situ synthesis, electrochemical and quantum chemical analysis of an amino acid-derived ionic liquid inhibitor for corrosion protection of mild steel in 1M HCl solution. Corrosion Science. 2016;16:73-85
72.Gowri S, Sathiyabama J, Rajendran S, Robert Kennedy Z, Agila DS. Corrosion inhibition of carbon steel in sea water by glutamic acid-Zn2+ system. Chemical Science Transactions. 2013;2:275-281
73.Gowri S, Sathiyabama J, Rajendran S. Corrosion inhibition of carbon steel in sea water by L-arginine-Zn2+ system. International Journal of Chemical Engineering. 2014;2014:1-9
74.Wang D, Gao L, Zhang D, Yang D, Wang H, Lin T. Experimental and theoretical investigation on corrosion inhibition of AA5052 aluminium alloy by l-cysteine in alkaline solution. Materials Chemistry and Physics. 2015;169:142-151
75.Fu J-J, Li S-N, Cao L-H, Wang Y, Yan L-H, Lu L-d. L-tryptophan as green corrosion inhibitor for low carbon steel in hydrochloric acid solution. Journal of Materials Science. 2010;45:979-986
76.Prathipa V, Raja AS, Prabha SS. L-aspartic acid: An efficient water soluble inhibitor for corrosion of carbon steel in aqueous media. International Journal of Chemical, Material and Environmental Research. 2016;3:35-41
77.Unnimaya, Shetty P, Kumari P, Kagatlkar S. Glutathione as green corrosion inhibitor for 6061Al-SiC(p) composite in HCl medium: Electrochemical and theoretical investigation. Journal of Solid State Electrochemistry. 2023;27:255-270
78.Sahaya Raja A, Rajendran S, Sathiyabama J, Prathipa V, Karthika IN, Krishnaveni A. Use of L-alanine as nature—Friendly corrosion inhibitor for carbon steel In aqueous medium. International Journal of Nano Corrosion Science and Engineering. 2015;2:26-40
79.Zhang QH, Hou BS, Li YY, Lei Y, Wang X, Liu HF, et al. Two amino acid derivatives as high efficient green inhibitors for the corrosion of carbon steel in CO2-saturated formation water. Corrosion Science. 2021;189:109596
80.Loto RT. Corrosion inhibition effect of non-toxic α-amino acid compound on high carbon steel in low molar concentration of hydrochloric acid. Journal of Materials Research and Technology. 2019;8:484-493
81.Rahiman A, Subhashini S. Corrosion inhibition, adsorption and thermodynamic properties of poly(vinyl alcohol-cysteine) in molar HCl. Arabian Journal of Chemistry. 2017;10:S3358-S3366
82.Raja A, Rajendran S, Satyabama P. Inhibition of corrosion of carbon steel in well water by DL-phenylalanine-Zn2+ system. Journal of Chemistry. 2013;2013:1-8
83.Zunita M, Wahyuningrum D, Wenten I, Boopathy R. Carbon steel corrosion inhibition activity of tofu associated proteins. Bioresource Technology Reports. 2022;17:100973
84.Wang J, Liu C, Qian B. A novel L-histidine based ionic liquid (LHIL) as an efficient corrosion inhibitor for mild steel. Royal Society of Chemistry Advances. 2022;12:2947-2958
85.Singh P, Srivastava V, Quraishi MA. Novel quinoline derivatives as green corrosion inhibitors for mild steel in acidic medium: Electrochemical, SEM, AFM, and XPS studies. Journal of Molecular Liquids. 2016;216:164-173
86.Issaadi S, Douadi T, Zouaoui A, et al. Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media. Corrosion Science. 2011;53:1484-1488
87.Verma C, Quraishi MA. Thermodynamic, electrochemical and surface studies of dendrimers as effective corrosion inhibitors for mild steel in 1 M HCl. Analytical and Bioanalytical Electrochemistry. 2016;8:104-123
88.Popoola LT. Organic green corrosion inhibitors (OGCIs): a critical review. Corrosion Reviews. 2019;37:71-102
89.Al-Amiery AA, Kadhum AAH, Kadihum A, Mohamad AB, How CK, Junaedi S. Inhibition of mild steel corrosion in sulfuric acid solution by new Schiff base. Materials (Basel). 2014;7:787-804
90.Maayta AK, Al-Rawashdeh NAF. Inhibition of acidic corrosion of pure aluminum by some organic compounds. Corrosion Science. 2004;46:1129-1140
91.Verma DK. Density Functional Theory (DFT) as a Powerful Tool for Designing Corrosion Inhibitors in Aqueous Phase. London, UK: Intechopen; 2018
92.Verma CB, Lgaz H, Verma DK, Ebenso EE, Bahadur I, Quraishi MA. Molecular dynamics and Monte Carlo simulations as powerful tools for study of interfacial adsorption behavior of corrosion inhibitors in aqueous phase: A review. Journal of Molecular Liquids. 2018;260:99-120
Written By
Malak Rehioui
Submitted: 13 December 2022Reviewed: 04 January 2023Published: 27 January 2023
Open access peer-reviewed chapter
