Interlayer intercalation and arrangement of 2-mercaptobenzothiazolate and 1,2,3-benzotriazolate anions in layered double hydroxides: In situ X-ray diffraction study


2-mercaptobenzothiazole (MBT) and 1,2,3-benzotriazole (BTA) are very promising inhibitors for the corrosion protection of aluminum alloys. These inhibitors can be incorporated in protective coatings in the form of anions intercalated into interlayers of layered double hydroxides (LDHs). Capacity and performance of such LDH-nanocontainers depend on the arrangement of the anions in their interlayers. In this work, intercalation of MBT− and BTA− into Mg–Al–NO3 and Zn–Al–NO3 LDHs were studied in detail using X-ray diffraction (XRD) methods including in situ XRD. The nitrate-to-MBT(BTA) anion exchange is much faster than considered previously. Well-formed Mg–Al–MBT, Zn–Al–MBT, Mg–Al–BTA LDHs were obtained after a 20-min exchange reaction at pH 11.5 at room temperature. It was demonstrated that Zn–Al–BTA LDH cannot be obtained under the same conditions due to the reaction between BTA and the Zn–Al hydroxide layers. Substitution of nitrates by organic anions occurs with the participation of hydroxide anions. Although no intermediate LDH phase intercalated with the combination of NO3-NO3- and OH− appears, formation of the LDH–MBT and LDH–BTA phases results also in appearance of an LDH phase intercalated with OH− at the final stage of the anion exchange. In the LDH interlayer, MBT− and BTA− form a double layer in which these species have a tilted orientation against the layer plane (herringbone-like arrangement). Such an arrangement meets the LDH layer–interlayer electroneutrality and matches well with the observed values of the layer–interlayer distance.
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