In situ kinetics studies of Zn-Al LDH intercalation with corrosion related species

Phys Chem Chem Phys. 2020 Aug 21;22(31):17574-17586. doi: 10.1039/d0cp01765e. Epub 2020 Jul 27.

Abstract

Kinetic parameters for three anion exchange reactions - Zn-LDH-NO3→ Zn-LDH-Cl, Zn-LDH-NO3→ Zn-LDH-SO4 and Zn-LDH-NO3→ Zn-LDH-VOx- were obtained by in situ synchrotron study. The first and the second ones are two-stage reactions; the first stage is characterized by the two-dimensional diffusion-controlled reaction following deceleratory nucleation and the second stage is a one-dimensional diffusion-controlled reaction also with a decelerator nucleation effect. In the case of exchange NO3-→ Cl- host anions are completely released, while in the case of NO3-→ SO42- the reaction ends without complete release of nitrate anions. The exchange of Zn-LDH-NO3→ Zn-LDH-VOx is a one-stage reaction and goes much slower than the previous two cases. The latter is characterized by a one stage two-dimensional reaction with an instantaneous nucleation. As a result, at the end of this process there are two crystalline phases with different polyvanadate species, presumably V4O124- and V2O74-, nitrate anions were not completely released. The rate of replacing NO3- anions by guest ones can be represented as Cl- > SO42- > VOxy-.