Article
Inhibition behavior of Tragia involucrata L. phenolic compounds against acidic medium corrosion in low carbon steel surface

https://doi.org/10.1016/j.cjche.2018.10.008Get rights and content

Highlights

  • Analysis of TPC-TFC, antioxidant and anticorrosion activity of T. involucrate L.

  • FT-IR and UV–vis spectra showing the inhibitor protective layer on low carbon steel

  • A maximum IE of 88% was achieved using 0.25 g·L−1 of the T. involucrate L. extract.

Abstract

The antioxidant and anticorrosive effect of Tragia involucrate L. (T. involucrate L.) was evaluated to aid in finding new compounds which can be used for various purposes. The total phenolic (TPC) and flavonoid content (TFC), antioxidant activity (DPPH, reducing potential and phosphomolybdenum), and electrochemical measurements, Fourier transform infrared (FT-IR), UV–visible (UV–vis) spectral analysis, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM–EDX) and atomic force microscopy (AFM) were done to analyze the potency and also the inhibition efficiency of T. involucrate L. against 1 mol·L−1 HCl on low carbon steel. The TPC (145.21 mg GAE·g−1), TFC (52.32 mg QCE·g−1) and antioxidant activities were found to be significant. The electrochemical studies performed by AC impedance measurements showed significant changes in impedance spectra without causing any change in Nyquist plots. An increase in charge transfer resistance (Rct) values, a blockage in active sites exhibiting cathodic and anodic inhibition shows the action of inhibitor on low carbon steel. This was later confirmed by FT-IR and UV–vis which showed variation in absorption band at 270 nm and 273 nm (before immersion) and 208 and 281 nm (after immersion). The same was tested again by SEM–EDX through altered strength of iron and oxygen bands and using AFM by analyzing the change in average roughness values of low carbon steel before (61.65 nm) and after (97.87 nm) exposure to blank acid without inhibitor, while it was shifted to 81.58 nm in acid with inhibitor. All these results showed strong evidence adding values to T. involucrate L. plant extract in inhibiting corrosion on low carbon steel and by promoting antioxidant importance of the extract which helps in scavenging free radicals.

Introduction

The low carbon steel is an excellent material used for the construction of automobiles, ships, machines, weapons and buildings. Their high strength to weight ratio, low density, high thermal conductivity and environmental stability make it a crucial material in petroleum production, metal and chemical processing industries, marine applications and in oil refineries. It is made of less than 0.15% carbon which reciprocates it to become vulnerable to corrosion created by hostile media like sulfuric acid and hydrochloric acid (HCl) [1], [2], [3], [4]. The two forms of corrosions, sweet and sour occurring by carbon dioxide and hydrogen sulfide are causing major economical problems in industries. This corrosion is generally inhibited by chemical containing sulfur, hydrophobic hydrocarbons, aromatic resins, oxygen, and nitrogen and by using other organic and inorganic inhibitors which act by forming a protective layer on the surface of low carbon steel. These protective layers are formed either by physical adsorption (electrostatic change) or by chemical adsorption (bonds between shared bonds). The inhibitors are organic or inorganic in nature, some act as cathodic and anodic compound and few even as antioxidants and oxidants in order to reduce or prevent corrosion [5], [6]. The corrosion inhibitors work by controlling the dissolution of metal and its acid consumption. The protective barrier formed by the inhibitors on the surfaces of metal leads to decreased reduction and oxidation reactions occurring during corrosion. These reactions are done by the interaction of functional groups having oxygen, nitrogen and sulfur with lone pair of electrons to interact with metal surface. These two reactions aid in inhibiting the corrosion at great level [7], [8]. Many plant derived components like proteins, amino acids, organic dyes, alkaloids, vitamins, vanillic acid, vanillin and biopolymers are identified to be efficient in inhibiting corrosion. As plant compounds are easy to extract, nontoxic and cost effective, these types of inhibitors are gaining the interest of various researchers [9], [10], [11], [12], [13], [14]. Plants namely Delonix regia, rosemary leaves, Datura stramonium, Coreopsis tinctoria, Cassia occidentalis, Polygonatum odoratum, Poinciana pulcherrima, Papaia, Auforpio turkiale and Calotropis procera were studied for its corrosion inhibition efficiency against hydrochloric acid and sodium chloride solutions. Even natural honey had been investigated for its anticorrosion effect. All these had proven the capacity of plant extracts and other natural agents as significant corrosion inhibitors [15], [16]. An investigation made using Centaurea cyanus aqueous extract had shown 63.95% of inhibition against carbon steel even at 313 K [17]. Another research on carbohydrate biopolymer chitosan had been tested for its inhibition capacity (90%) in combination with 0.005 g·L−1 KI which was 73.8% when used alone at a concentration of 0.2 g·L−1 [18].

The increase in interest on green inhibitors has stroked the interest of many researchers round the globe to search for natural plant based inhibitors. One such plant named Tragia involucrate L. commonly known as kaanchori or Indian stinging nettle in India and in sinhala as wel-kahambiliya was investigated in this study. The plant belonging to Euphorbiaceae is a hispid herb, perennial plant with stinging and scattered hairs. It is found throughout in India, Burma, China and Sri Lanka. The plant is known for its biological properties such as curing skin eruptions, treating gastropathy, vomiting, and inflammation, and antimicrobial, antidiabetic, mosquito repellant, wound healing and antiepileptic activities [19], [20]. In Tamil Nadu, a southern region of India, T. involucrate L. is being used as a traditional medicine by Kani tribals. They along with other plant leaves and roots specifically from Cipadessa baccifera Miq., Aristolochia tagala, Crotalaria pallida aiton and Wrightia tinctoria were used to prepare decoction to cure bites of insect, scorpion, and snake and also to treat skin disease by applying its paste [21]. Apart from this, the plant is known to procure healing effect against parasites, bacteria, epilepsy, subacute and acute inflammations and Culex quinquefasciatus a vector of lymphatic filariasis. The roots, leaves, stems and flowers were identified to possess flavonoids, alkaloids, volatile oils, sterols, glycosides, tannins, lipids, proteins, starch and sugars [22], [23], [24], [25].

This medicinal plant is used not only by Tamil tribes but also by various communities residing in Kerala, Punjab, Meghalaya, lower Himalayas and Assam whose constituents were analyzed in UV–vis and FT-IR to confirm the presence of anhydrides, alkenes, alkyl halides, amides, carboxylic acids and phosphines [26]. In a study, conducted to evaluate the antifungal activity of Asteriscus imbricatus against Botrytis cinerea 50%–70% inhibition was observed in extracts prepared using methanol, ethyl acetate and ether which was conformed through weight loss and electrochemical methods and was found obeying the Langmuir isotherm [27]. Many plants like the Origanum compactum (aerial parts), Ipomoea triloba, W. tinctoria and Clerodendrum phlomidis (leaves) were identified to possess anticorrosive properties against 0.5 M sulfuric acid evaluated using scanning electron microscopy, electrochemical impedance spectroscopy (EIS), electrochemical polarization and weight loss assays [28], [29]. The roots, stems and leaves of Clerodendrum L. are the known sources of numerous antioxidants specifically flavonoids (scutellarein, apigenin, hispidulin and luteolin), phenols (benzoic acid, quercetin, pectolinarigenin, syringic acid, friedelin, betulinic acid and maslinic acid) and terpenes (Luperol, α-amyrin, β-amyrin, clerodendrin A, B and C) [30]. On screening Mentha suaveolens aerial parts, worthy antioxidant and anticorrosion activity was identified by 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), electrochemical techniques (EIS and potentiodynamic polarization curves) and weight loss measurements with the concentrations of 0.25–2 g·L−1 [31]. Many natural low molecular weight antioxidants were already known for its association in reducing free radicals. The vitamin C is a standard antioxidant used for curing wound, metabolic process, osteogenesis, and improving immune system and has many other roles. Various analytical methods like DPPH, phosphomolybdenum, reducing power assay and many other tests are considered eminent in identifying the true potential of given samples. Researches had found a positive correlation between the TPC, TFC and antioxidant assay, as higher number of TPC and TFC leads to significant antioxidant activity measured through a spectrophotometer a more reliable method for identifying antioxidants [32], [33]. As there is an increase in need to find a plant source which has immense use as anticorrosive and antioxidant material every day, in this study, we have introduced a new and effective acid corrosion inhibitor (T. involucrate L. leaf extract). The plant is a known source for many active components like flavonoids, tannins, sterols, alkaloids, and volatile oils. In fact the active components can assist the protection of low carbon steel in acid medium via forming a protective film on metal surface. In addition, the antioxidant property of the plant extract was also studied. The DPPH, reducing potential and phosphomolybdenum assays were used to study the antioxidant property of the methanolic leaf extract. This was followed by electrochemical measurements (polarization and impedance), FT-IR and UV–vis spectral analysis. Subsequently surface examination studies were performed through SEM, EDX and AFM.

Section snippets

Plant extract preparation

The T. involucrate L. leaves were collected from Salem, Tamil Nadu, South India. All the samples were washed in running tap water to remove dust and other deposits on it. These were then kept under sunlight for a week to dry and grained into fine powder. To 100 g of plant material 3 L of methanol was added and mixed well. This was incubated for 72 h at room temperature [(RT) 303 K ± 1 K]. The solvent was changed thrice at 24 h intervals until a clear extract was obtained. The final extract was

TPC and TFC

The TPC was identified as 145.21 mg GAE·g−1 and TFC as 52.32 mg QCE·g−1 as per Fig. 1.

The TPC and TFC of the plant extract were identified by a well-known method which uses Folin–Ciocalteu reagent, a molybdotungstophosphate heteropolyanion compound along with an alkali (carbonate) when reacts with phenolic compound yields blue color which is measured at 760 nm [42]. The same reagent without tungstate is being used to detect the total antioxidant capacity of extract. As both total phenol and

Conclusions

This study concludes the use of T. involucrate L. plant extract as antioxidant and anticorrosive material. The plant inhibitor acts on the low carbon steel surface to inhibit the reduction of hydrogen ions. The analysis by FT-IR and UV–vis spectrophotometer helps in identifying the functional groups present on the metal surface. The electrochemical impedance spectroscopy measurements have a good agreement with polarization data. The SEM and AFM images stand as a solid proof for the action of

Acknowledgments

This paper was supported by the KU Research Professor Program of Konkuk University.

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