Thermal decomposition of n-alkylamine α-zirconium phosphate intercalates

Abstract

The thermal decomposition of the n-alkylamine α-zirconium phosphate intercalates [Zr(C n H 2n + 1 NH 3PO 4) x (HPO 4) 2−x · nH 2O] is studied. The differential thermogravimetry (DTG) curves show three temperature regions (30–165, 150–400 and 400–800 °C), which can be attributed to the dehydration, desorption of the amine and dehydroxylation, respectively. Dependent on the amine loading, the dehydration and dehydroxylation occur in different steps. With respect to the dehydration, these steps are governed by the existence of two types of hydrophilic sites (POH and PO −+NH 3R). An additional loss of water is observed at about 165 °C if a part of the sample is not intercalated. This non-intercalated part is also the reason for the occurrence of two dehydroxylation peaks. The POH groups present in the non-intercalated part of the sample have a higher thermal stability than the POH groups of the intercalated part. At saturation capacity the zirconium phosphate is completely intercalated and only one type of phosphate group (PO −+NH 3R) remains, corresponding to a one-stage dehydration and dehydroxylation. Except for the low loadings, the amine desorption is also a two-stage process. The assignment of the two steps is based on the existence of two distinct POH groups in the α-zirconium phosphate structure.