Determination of the mechanism(s) for the inclusion of arsenate, vanadate, or molybdate anions into hydrotalcites with variable cationic ratio.

Hydrotalcites with cationic ratios of 2:1, 3:1, and 4:1 were synthesised using the co-precipitation method. The mechanism of inclusion of arsenate, vanadate, and molybdate into these structures is investigated using the combination of X-ray diffraction, Raman spectroscopy, and thermal analysis. Results show that hydrotalcites with cationic ratios of 3:1 are thermally more stable then the 2:1 and 4:1 structures. The increase in thermal stability of the 3:1 hydrotalcite structures is understood to be due to the intercalation of arsenate, vanadate, or molybdate, by an increase in hydrogen bonds associated with the intercalated anion. The 3:1 vanadate hydrotalcite is the most thermally stable hydrotalcite investigated. It is observed that the predominant mechanism for inclusion of the three anionic species is adsorption for 2:1 and 4:1 hydrotalcites, and intercalation for the 3:1 hydrotalcite structures. The intercalation of arsenate, vanadate, and molybdate into the hydrotalcite structure increased the interlayer distance of the hydrotalcite by 0.14, 0.13, and 0.26 A, respectively.