Atriplex leucoclada extract: A promising eco-friendly anticorrosive agent for copper in aqueous media
Graphical abstract
Introduction
Copper is an important metal and is used in heat exchangers, electrical and electronic appliances, and in the power and aerospace industries [1], [2], [3] because of its high electrical conductivity [4], high thermal conductivity, ductility, strength, chemical stability [5], and weldability. Although copper is relatively resistant to corrosion by common chemicals and by the atmosphere, it is easily corroded in harsh environments, such as in strongly acidic media. However, the use of corrosion inhibitors can address this problem [6]. To date, many corrosion inhibitors have been developed, including synthetic organic and inorganic compounds. Initially, inorganic inhibitors were widely used because they are highly effective in preventing the corrosion of pure copper. However, the use of these materials has been increasingly restricted because of their high toxicity and environmentally unfriendly nature. Organic corrosion inhibitors are typically unsaturated compounds that contain O, N, S, P, and active functional groups. The functional groups and π-bonds are effective for corrosion inhibition [7], [8], [9], [10], [11], [12] because they form a protective layer on the metal surface, thus serving as a barrier between the corrosive medium and the metal surface [13], [14]. Hence, the corrosion of metal surfaces can be significantly reduced using organic inhibitors. However, these inhibitors have several disadvantages, including exhaustible resources and high costs. Consequently, there is a need to develop effective green corrosion inhibitors that are non-toxic, inexpensive, and can be prepared from renewable resources [15], [16], [17], [18], [19].
Green corrosion inhibitors are environment-friendly because they do not contain heavy metals or harmful chemicals and are biodegradable [20]. Plant materials are herbal in nature, widely available, inexpensive, and contain tannins, phenolics, organic and amino acids, alkaloids, and flavonoids, which are believed to possess corrosion-inhibitory properties [21]. Furthermore, simple procedures can be used to extract these materials from plants at a low cost. With the development of science and technology, considerable importance has been placed on environmental protection. Accordingly, several plant extracts have attracted attention as anticorrosive agents. These natural extracts are promising sources of effective natural active antioxidants, many of which can be considered safe [22], [23], [24], [25], [26], [27], [28], [29], [30]. Natural products, such as Egyptian licorice extract [31], Rosa canina fruit extract [32], aloe plant extract [33], mimosa extract [34], Santolina chamaecyparissus extract [35], Rollinia occidentalis extract [36], watermelon rind extract [37], nettle leaf extract [38], Urtica dioica extract [39], plant-derived cationic dye [40], inulin [41], and Artemisia mesatlantica essential oil [42], have recently been confirmed to be effective in reducing metal corrosion rates in corrosive media. The corrosion-inhibiting activity such extracts is often due to some of their organic constituents (phytochemicals), which have electronic structures similar to those of traditional organic corrosion inhibitors. The existence of complex organic compounds containing nitrogen, oxygen, and sulfur atoms and triple bonds, conjugated double bonds, or aromatic rings, which are the main adsorption centres, in the molecular structures increase the corrosion-inhibition efficiency of these plant extracts.
In this study, we evaluated the anti-corrosive properties of Atriplex leucoclada is a plant that grows well in desert and saline environments. It contains complex compounds, including organic acids, cardenolides and flavonoids, alkaloids [43], polyphenols, tannins, and phosphatidylglycerol [44], [45], [46], [47], which are potential corrosion inhibitors. In fact, some of these compounds have been used in previous studies as corrosion inhibitors. These compounds form a protective layer on the Cu surface; thus, they efficiently separate the corrosive medium from the copper surface [48], [49], [50], [51]. However, to date, A. leucoclada has not been investigated as a source of green corrosion inhibitors. Therefore, in this study, we investigated the ability of A. leucoclada extract (ALE) to prevent the corrosion of copper in an acidic environment (1 M aqueous HCl). We harvested specimens of A. leucoclada during July 2019 from a region of western Iraq that experiences a moderate and dry climate. ALE was prepared, and its components were analysed via gas-chromatography–mass spectrometry (GC–MS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), electrochemical analysis, scanning electron microscopy (SEM), and energy dispersive X-ray analysis to gain insight into the mechanism of the corrosion inhibition of copper in 1 M HCl. The adsorption type and mechanism responsible for protecting the Cu surface from corrosion were also examined through adsorption experiments.
Section snippets
Electrode and corrosion medium formation
For the electrochemical analyses, copper electrodes were sealed in epoxy resin to leave only their square faces (1 × 1 cm) exposed to the corrosive HCl solution. For the AFM and XPS studies, plate-like specimens (1.0 × 0.1 × 0.1 cm) were prepared from high-purity (99.99%) copper. In addition, cubic specimens (2 × 2 × 2 cm) were prepared for the electrochemical experiments and SEM observation (0.5 × 0.5 × 0.5 cm). The specimens were carefully and sequentially abraded with clean emery paper with a fineness from
Gas-chromatography–mass spectrometry results
ALE contains complex components, that may have an inhibitory effect on corrosion. In this study, GC–MS was conducted to determine the constituents of ALE. The most important and most abundant components are listed in Table 1. References to studies that identified these components as green corrosion inhibitors are also provided.
FTIR analysis
Fig. 1 presents the FTIR spectrum of ALE, which was used to determine the functional groups of the ALE constituents adsorbed on the copper surface. The broad band at
Conclusions
In this study, the ability of ALE to act as a green corrosion inhibitor for copper under highly acidic conditions was investigated. The main components of ALE were identified via GCMS, and FTIR spectroscopy revealed the presence of the same functional groups as those identified through the GCMS analysis. These functional groups are appropriate for interaction of ALE components with a copper surface and thus enable the formation of a protective film. Based on the results of Tafel analysis, we
Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Chinese National Foundation for Natural Science [grant numbers 21878029, 21676035, and 21706195] and the Guangdong, China Sail Programme [grant number 2015YT02D025].
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