Unveiling the local structure of 2-mercaptobenzothiazole intercalated in (Zn2Al) layered double hydroxides

Gerard Novell-Leruth,Germán Pérez-Sánchez,Tiago L.P Galvão,Dziyana Boiba,Sergey Poznyak,Jorge Carneiro,João Tedim,José R.B Gomes

doi:10.1016/j.clay.2020.105842

Gerard Novell-Leruth, Germán Pérez-Sánchez + Show 6 more

Open Access

https://doi.org/10.1016/j.clay.2020.105842

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Abstract

The structure and composition of a zinc‑aluminum layered double hydroxide (Zn2Al LDH) with the intercalated 2-mercaptobenzothiazole corrosion inhibitor (a.k.a. benzo[d]thiazole-2-thiol) are interpreted by means of atomistic molecular dynamics (MD) simulations. The results concerning the proportion of intercalated 2-mercaptobenzothiazole and water species in the Zn2Al LDH interlayer were correlated with experimental X-ray diffraction (XRD) and thermogravimetric analysis (TGA) data of samples obtained at pH 8.5, 10 and 11.5. While the sample synthesized at the lowest pH is almost free of contaminants, the sample obtained at the highest pH is contaminated by a small fraction of a material with intercalated OH−. The comparison of the calculated and XRD interlayer distances suggests that the most stable structure has a ratio of ~4.5 water molecules per intercalated organic species, which is higher than the ratio of ~2 typically reported in the literature. The distribution of molecules in the LDH interlayer consists of a layer of water near the hydroxides, a second layer grown over the first layer, with the 2-mercaptobenzothiazole species adopting conformations with the sulfur of the thioamide group facing the hydroxide/water layers and the 6-member ring oriented towards the middle of the interlayer. Different structural analyses were done to explain the equilibria between the different species in the interlayer space, and their molecular interactions with the LDH metal hydroxide layers.

Highlights

Layered double hydroxides (LDH) are biocompatible layered materials incorporating a large number of ions in the interlayer volume that have been thought for different applications in chemistry and biology (Arrabito et al, 2019; Galvão et al, 2020)
Molecular dynamics simulations considering large molecular models were employed to study the intercalation of the 2-mercaptobenzothiazole compound in Zn2Al layered double hydroxides (Zn2Al(OH)6-MBT LDH), for the first time
It was found that the mercaptobenzothiazole species interact with the metal hydroxide layers through the heteroatoms and the terminal sulfur atom, while the benzenic rings are pointing towards the middle of the gallery space

Summary

Introduction

Layered double hydroxides (LDH) are biocompatible layered materials incorporating a large number of ions in the interlayer volume that have been thought for different applications in chemistry and biology (Arrabito et al, 2019; Galvão et al, 2020). LDH prepared by different methods, e.g. co-precipitation or ion-exchange, with a variety of intercalated organic and inorganic species, have been tested for anti-corrosion applications. They were demonstrated to be quite effective when used as dual-action smart coating additives, since they are able to release the intercalated moieties while entrapping the corrosive anions (e.g. chlorides) from the surroundings (Tedim et al, 2012). The cations in the LDH metal hydroxide layers were found to have some effects in corrosion protection. The small but experimentally detected amounts of Zn2+ cations dissolved from the Zn-Al LDH were suggested to have a positive corrosion protective effect (Buchheit et al, 2003; Poznyak et al, 2009; Galvão et al, 2016b)

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