Molecular dynamics simulation of inhibition mechanism of 3,5-dibromo salicylaldehyde Schiff’s base

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Highlights

  • The adsorption energy of three inhibitors followed order of E (L2) > E (L1) > E (L3).

  • Chemical adsorption of three inhibitors occurs on the surface of Fe.

  • The diffusion coefficients followed order of D (L3) > D (L1) > D (L2) for the Cl and H3O+.

  • The diffusion coefficients of all films followed order of D (H2O) > D (H3O+) > D (Cl).

  • DFT study confirm the inhibition efficiency follow order of EI (L2) > EI (L1) > EI (L3).

Abstract

Molecular dynamics simulation method was adopted to investigate the absorption behavior, inhibition mechanisms on Fe (1 0 0) surface in aqueous solution and the diffusion behavior of H3O+, Cl and H2O in three of 3,5-dibromo salicylaldehyde Schiff base inhibitor films, including 3,5-dibromo salicylaldehyde-2-pyridinecarboxylic acid hydrazide (L1), 3,5-dibromo salicylaldehyde-2-thiol-phenecarboxylic acid hydrazide (L2), 3,5-dibromo salicylaldehyde-2-aminobenzothiazole (L3). The effects of the interaction energy, radial distribution function and the self-diffusion coefficient were studied accompanying with density functional theory (DFT) study. The results demonstrated that the order of adsorption energy is E (L2) > E (L1) > E (L3), absorption manner is a multi-center chemical adsorption for three inhibitor films; for different inhibitor films, the diffusion coefficients followed the order of D (L3) > D (L1) > D (L2) for the Cl corrosive particles, the diffusion coefficients followed the order of D (L3) > D (L1) > D (L2) for the H3O+ corrosive particles. For the three inhibitor films, the diffusion coefficients of the three corrosive particles all followed the order of D (H2O) > D (H3O+) > D (Cl). The inhibition efficiency order was obtained from the diffusion coefficient which is agreed well with the experimental results as EI (L2) > EI (L1) > EI (L3). Three kinds of inhibitor films have good corrosion inhibition efficiency in aqueous solution.

Graphical abstract

In the initial of adsorbed configuration, the inhibitor molecules are oriented vertically attached on the metal surface as shown in Fig. 2. After the simulation, the result shows that the existence of water molecules have a great influence on Schiff base inhibitor molecules, according to movement of surrounding water molecules, they occur a slight vibrations. When the inhibitor molecules continue move to the bottom of the solvent layer, they interact with water molecules, the inhibitor molecules continue tilt slowly until parallel to metal surface (Fig. 8).

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Introduction

Nowadays, computer technology is renewed by the rapid development of science and technology, accompanying with hot topic of organic inhibitors mechanism study in corrosion science. It is very useful to develop new inhibitors and study their adsorption behaviors and inhibition effects. Molecular dynamics simulations (MD) can be carried out to study the dynamic adsorption process and inhibition mechanism of inhibitor molecules adsorption film on the metal surface effectively [1], [2], [3], [4]. There are some reports focused on corrosion inhibitors by molecular dynamics simulation [5], [6]. Zeng and coworkers studied inhibition effect of inhibitors on iron, such as PASP, HPMA and PESA in aqueous solution, the results show that three kinds of corrosion inhibitors can attach on iron surface with good inhibition effects [7]. Khaled and coworkers studied adsorption mechanism of three kinds of corrosion inhibitors META, PARA and ORTHO on nickel surface [8]. Zhang and coworkers investigated the adsorption mechanism of imidazoline inhibitor on the Fe surface [9]. Khaled studied the adsorption behavior and inhibition mechanism of benzimidazole derivatives on the Fe surface [10]. Formerly, our group studied the adsorption mechanism of dehydroabietylamine Schiff base derivatives on the carbon steel surface in sea water [11].

It should be mentioned that corrosion always occurs when the corrosive medium is in contact with the metal in the process of oil production. Hopefully, inhibitor molecules could be adsorbed on the metal surface in order to separate water molecules and metal ions in solution to stop corrosion. When the metal surface is covered by water molecules in solution, the inhibitor molecules can be adsorbed on the metal surface, they need to expel water molecules on the metal surface and show stronger adsorption energy than water molecules. The inhibitor molecules not only obstruct water molecules on the metal surface, but also obstruct water molecules in aqueous solution. It is foreseeable that the adsorption process will be more difficult and longer in solution than in vacuum [12], [13], [14].

Inhibitor adsorption performance is an important factor to evaluate performance of corrosion inhibitors. To be a qualified corrosion inhibitor, it not only has good adsorption performance, but also can form film which can stop the corrosion ions move to metal surface. Because that inhibitor molecules film can effectively prevent corrosion ions migrate to the metal surface, avoid corrosion ions contacting with the metal directly, the best corrosion effect of inhibitors are contributed by the best adsorption performance and the strongest inhibition [15], [16], [17], [18]. Therefore, corrosion inhibitors must have strong ability to inhibit corrosion ions diffusion in oilfield water [19].

In this paper, molecular dynamics simulation method was adopted to investigate the absorption behavior, inhibition mechanisms on Fe (1 0 0) surface in aqueous solution and the diffusion behavior of H3O+, Cl and H2O in three of 3,5-dibromo salicylaldehyde Schiff base inhibitor films, including 3,5-dibromo salicylaldehyde-2-pyridinecarboxylic acid hydrazide (L1), 3,5-dibromo salicylaldehyde-2-thiol-phenecarboxylic acid hydrazide (L2), 3,5-dibromo salicylaldehyde-2-aminobenzothiazole (L3). Three key parameters, including interaction energy, radial distribution function curves and self-diffusion coefficient accompanying with DFT study were selected to analyze the corrosion inhibition mechanism. The inhibitive properties of these three Schiff’s base inhibitors were investigated experimentally, using measurements based on weight loss, Tafel polarization, electrochemical impedance spectroscopy.

Section snippets

Computational methods

The diffusion behaviors of the three corrosive particles in the three corrosion inhibitor films was carried out using a commercial software package called Materials Studio 5.5 developed by Accelrys Inc.

Experimental procedures

Experiments were carried out using mild steel specimens (0.09% P, 0.38% Si, 0.01% Al, 0.05% Mn, 0.21% C, 0.05% S and remainder iron) (5.0 × 1.0 × 0.2 cm) as the electrode material. Steel sheets were mounted in Teflon with surface area of 4.0 × 1.0 cm2. The surface area of 1.0 × 1.0 cm2 was abraded using emery papers and polished with Al2O3 (0.5 μm particle size) carefully, cleaned in distilled water in an ultrasonic bath, and subsequently rinsed with dry ethanol and redistilled water for use. The same

Weight loss study

The corrosion of mild steel specimens in simulative oilfield water, without and with various concentrations of three tested schiff’s base inhibitors was studied by weight loss measurements. Values of corrosion rate and the inhibition efficiency obtained are given in Table 2. It can be seen in Table 2, the corrosion rate values of mild steel decrease when the inhibitor concentration increases. The inhibition efficiency increases with the concentration of L1, L2 and L3 reaching a maximum value

Conclusion

In this study, measurements include weight loss, Tafel polarization, electrochemical impedance spectroscopy were adopted to investigate inhibitive properties of three schiff’s base inhibitors on mild steel. Three key parameters, including interaction energy, radial distribution function curves and self-diffusion coefficient accompanying with DFT study were selected to study adsorption behaviors and corrosion inhibition mechanism of three inhibitors on Fe (1 0 0) surface in aqueous solution and

Acknowledgments

This work was supported by the National Nature Science Foundation of China (Nos. 21266006, 61301038, 61271119) and the Nature Science Foundation of Guangxi Province (No. 2012GXNSFAA053034).

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