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

Kinetic parameters for three anion exchange reactions - Zn-LDH-NO 3 → Zn-LDH-Cl, Zn-LDH-NO 3 → Zn-LDH-SO 4 and Zn-LDH-NO 3 → Zn-LDH-VO x - 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 NO 3 − → Cl − host anions are completely released, while in the case of NO 3 − → SO 4 2− the reaction ends without complete release of nitrate anions. The exchange of Zn-LDH-NO 3 → Zn-LDH-VO x 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 V 4 O 12 4− and V 2 O 7 4− , nitrate anions were not completely released. The rate of replacing NO 3 − anions by guest ones can be represented as Cl − > SO 4 2− > VO x y − . The first kinetic study of the anion exchange reactions on LDH conversion layers, with corrosion relevant species.