Novel carbon dots as efficient green corrosion inhibitor for mild steel in HCl solution: Electrochemical, gravimetric and XPS studies

https://doi.org/10.1016/j.jpcs.2021.110341Get rights and content

Highlights

  • Studied carbon dots, CDMU and CDMH act as efficient eco-friendly corrosion inhibitor.

  • CDMU and CDMH act as mixed inhibitors.

  • Adsorption of CDMU and CDMH obeyed Langmuir adsorption isotherms.

  • SEM, AFM and XPS studies suggested adsorption of inhibitor on MS surface.

Abstract

Eco-friendly, good water soluble and inexpensive, carbon dots (CDMU and CDMH) were synthesized, characterized and applied as corrosion inhibitor for mild steel (MS) in 15% HCl solution. The characterization of both inhibitors was carried out by FTIR, UV–vis, photoluminescence, XPS and TEM. The average size of CDMU and CDMH were found as 2.03 and 2.5 nm, respectively. The inhibitive effect of CDMU and CDMH was evaluated by weight loss measurement, electrochemical impedance spectroscopy and potentiodynamic polarization measurement. Both CDMU and CDMH exhibited 97.89 and 90.10% of inhibition efficiency, respectively, at 100 mg/L concentration and 303 K temperature. Adsorption of CDMU and CDMH on MS surface followed Langmuir adsorption isotherm. The surface morphology of uninhibited and inhibited MS specimens was studied by the FESEM, AFM and XPS analysis.

Introduction

Mild steel is frequently used in several industrial sectors due to its numerous physical properties and inexpensiveness [1], but MS corrosion is one of the serious problems encountered by the industries. The corrosion causes, ample expenses for the reestablishment, renewal of various constitutes and equipment, life loss, and environmental problems [2]. Most of the industrial processes such as oil well acidization to increase the production of crude petroleum oil is carried out by pouring 15% HCl solution through steel tubes because it removes deposited salts and scales in flow channels. However, the aggressive nature of 15% HCl solution causes severe corrosion and damage to the steel, degrade its properties and limit the application of steel. Because of all these issues, researchers thought towards the corrosion problem and made plans to increase the functioning life of infrastructure, machines, metallic devices and so on. Degradation of various metals can be suppressed significantly by using various corrosion protection methods such as, improving the materials, applying inhibitors, alloying, using various types of coating, and by modifying the environment. Out of these methods, application of corrosion inhibitors is most simple and cost-effective method for corrosion protection. Corrosion inhibitors protect the materials from corrosion by adsorption on the metal surface and show outstanding anticorrosive activities [3]. The compounds framed with heteroatoms such as N, S, O and π electrons in their structure are reported as good corrosion inhibitor in acidic environment [[4], [5], [6], [7], [8], [9], [10]]. These types of molecules easily adsorbed on the surface of the metal by π and non-bonded electrons present in the moiety, thus decreases the contact area of the metal for interaction with the corrosive medium [[11], [12], [13], [14]]. This results in a suppression of the corrosion by hindering the active sites of the surface. Corrosion inhibitors are widely used in various industries for preventing the corrosion in acidic environments. The major industries using corrosion inhibitors are the oil and gas exploration and production industry, the petroleum refining industry, the chemical industry, the heavy industrial manufacturing industry, the water treatment industry and the additive product industry. Presently, various organic compounds have been reported as corrosion inhibitor [[15], [16], [17], [18], [19]], but most of them are toxic in nature and effective at higher concentration. The increased awareness towards human health and environmental pollution has directed chemists to searching for the anticorrosive compounds having non-toxic, eco-friendly, safe and outstanding inhibition efficiency [20,21].

Carbon dots (CDs) have gained so much attention due to their excellent properties such as low toxicity, high-water solubility, unique photoluminescence (PL) and biocompatibility [22,23]. In general, carbon dots have applications in sensing, optoelectronic devices, cell imaging, biomedicine, catalysis and corrosion inhibition [4,24]. Ye.et al. prepared three types of N-CDs by hydrothermal process, first type N-CDs was prepared by taking citric acid, N-carboxysuccinimide and (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride as raw material, second type N-CDs was prepared by using ammonium citrate as raw material and third type N-CDs was synthesized by taking methacrylic acid and n-butylamine as starting material and reported that these eco-friendly N-CDs displayed corrosion inhibition efficiency of 93.4, 84 and 94%, respectively, at 200 mg/L concentration and 303 K temperature for MS in 1 M HCl solution [4,25,26]. Yang et al. synthesized citric acid based functionalized ionic liquid CDs and studied its inhibitive nature on carbon steel in HCl and NaCl solution, got 92.6 and 83.45% efficiency, respectively, at 200 mg/L concentration [27]. Cen et al. prepared CDs by aminosalicylic acid and thiourea as initial material and reported 93% efficiency on carbon steel in NaCl solution at 50 mg/L concentration [28]. Cui et al. prepared CDs by 4- aminosalicylic acid as starting material and found its inhibition efficiency as 87.2% on steel in HCl at 100 mg/L concentration [29]. Wang et al. prepared N-doped CDs and calculated its inhibition effect on copper in H2SO4 solution, got 89.2% efficiency at 50 mg/L concentration [30]. Ye et al. synthesized functionalized carbon dots by taking l-histidine and citric acid as precursor and found 90% efficiency at 100 mg/L of concentration for Q235 steel in .1 M HCl solution [31]. Cui et al. synthesized N-doped CDs from p-phenylenediamine and o-phenylenediamine and examined its inhibitive nature on carbon steel in HCl, got 83.1 and 81.9% efficiency at 200 mg/L of concentration [32]. Cui et al. synthesized N-doped CDs from p-phenylenediamine and o-phenylenediamine and examined its inhibitive nature on carbon steel in HCl, got 83.1 and 81.9% efficiency at 200 mg/L concentration [33]. Li et al. prepared N-doped CDs by urotropine, EDTA and sulfamic acid as initial material and utilized as corrosion inhibitor for carbon steel in NaCl solution, found 83.7% efficiency at 600 mg/L concentration at 70 °C temperature [34]. We have already studied in our laboratory the inhibition efficiency of N, S-CDs and N-CDs for mild steel in hydrochloric solution and reported 96.4 and 90.0% inhibition efficiency, respectively, at 100 mg/L concentration and 303 K temperature [35]. Keeping in mind the good corrosion inhibition efficiency, eco-friendly nature and water solubility of carbon dots reported by other investigators as well as by us, we have planned to synthesize and characterize some new carbon dots having sufficient number of active sites and to study their corrosion inhibition efficiency for mild steel in 15% hydrochloric acid solution.

Therefore, two novel carbon dots, CDMU and CDMH, were synthesized using malononitrile, urea and 5-hydroxyisopthalic acid as starting material and used as corrosion inhibitor for MS in 15% HCl solution. Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), photoluminescence (PL), X-Ray photoelectronic spectroscopy (XPS) and transmission electron microscopy (TEM) were used to know the structure and composition of prepared inhibitors. Weight loss measurement (WL), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurement (PPM) were used to study the inhibitive effect of both carbon dots. The surface morphology of MS specimens was performed by using FESEM, AFM and XPS analysis.

Section snippets

Synthesis

The synthesis of CDMU and CDMH was accomplished by hydrothermal technique (Scheme 1). For CDMU equimolar mixture of malononitrile (0.198g, 3 mmol) and urea (0.18g, 3 mmol) were dissolved in 10 mL of water with sonication. Then, the dissolved mixture was transferred to autoclave and heated at 180 °C for 8 h. After completion of 8 h, mixture was cooled at room temperature. Then, the mixture was filtered and got desirable product. In case of CDMH whole procedure was same, but 5-hydroxyisopthalic

HRTEM analysis

TEM analysis was carried out to examine the morphology of CDMU and CDMH as shown in Fig. 1. The morphology of CDMU and CDMH was unevenly spherical. The average size of CDMU and CDMH was found as 2.03 and 2.5 nm respectively. The success rate of the green synthesis hydrothermal approach in producing carbon dots was confirmed by HRTEM images, which were as displayed in Fig. 1.

UV & PL study

We have synthesized CDMU and CDMH by hydrothermal technique. Both CDMU and CDMH showed blue colour emissive carbon dots.

FESEM analysis

To get the detailed information about the changes occurred on MS surface during corrosion process with and without inhibitors, FESEM micrographs were taken (Fig. 28).

Fig. 28 (a) displayed the polished MS surface without any pits and cracks except some polished abrading scratches. Fig. 28 (b) displays the MS surface after dipping in aggressive solution without inhibitor shows highly corroded surface and presence of many cracks and pits because of severe corrosion; Hence MS surface is badly

Corrosion inhibition mechanism

The inhibitor CDMU and CDMH get adsorbed on the surface of MS through heteratoms (nitrogen and oxygen) by donor-acceptor bonds (chemisorptions) and charge on CDMU and CDMH in acid solution also has a significant influence on the adsorption through electrostatic force of attraction (physisorption). The synthetized carbon dots possess several functional groups, such as hydroxyl, amino, cynide and carbonyl groups as confirmed by FTIR (Fig. 22) also supports the adsorption of inhibitor molecules on

Conclusions

CDMU and CDMH were found as very good water-soluble corrosion inhibitor for MS in 15% HCl solution. The studied carbon dots were synthesized by hydrothermal method and characterized by using Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, photoluminescence, X-Ray photoelectronic spectroscopy and Transmission electron microscopy. The average size of CDMU and CDMH were found 2.03 and 2.5 nm, respectively. The inhibition efficiency of CDMU and CDMH at 100 mg/L of

Data availability

The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

Author statement

Vandana Saraswat: Methodology, Data curation, Writing - Original Draft Software, Validation, Mahendra Yadav: Supervision, Writing - Review & Editing.

Credit author statement

Vandana Saraswat: Methodology, Data curation, Writing - Original Draft Software, Validation, Mahendra Yadav: Supervision, Writing - Review & Editing.

Declaration of competing interest

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.

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