Intercalation and grafting of hydrogen phosphates and phosphonates into synthetic hydrotalcites and a.c.-conductivity of the compounds thereby obtained

Abstract

A well crystallized Zn–Al–CO 3 hydrotalcite-like compound was obtained by co-precipitation of Zn(II) and Al(III) hydroxycarbonates from `homogenous solution'. The carbonate was converted into the chloride form via a gas–solid reaction. The chloride ions of the hydrotalcite obtained, Zn 0.65Al 0.35(OH) 2Cl 0.350.4H 2O, were then fully exchanged with H 2PO 4 −, HPO 4 2− and C 6H 5PO 3H − anions and the materials produced were characterized for their composition, X-ray diffraction patterns and thermal behaviour. The a.c. conductivity was determined at 100°C, in the 50–90% relative humidity (R.H.) range and in the 30–100°C range at 50% relative humidity. At 100°C and 50% R.H., the a.c. conductivity was found to decrease with the increasing base strength of the intercalated anion, being ∼10 −5 and ∼10 −6 S cm −1 for the H 2PO 4 − and HPO 4 2− grafted hydrotalcites. A similar trend was observed for the a.c. conductivity of hydrotalcite exchanged with CO 3 2−, SO 4 2−, Cl −, HCOO − and C 6H 5COO − anions.