Intercalation of n-alkyltrimethylammonium ions into layered calcium octyl phosphates thermally treated in vacuo

Abstract

Layered calcium octyl phosphate (CH 3(CH 2) 7OPO 3Ca·1.6H 2O: CaOP), which is composed of a multilayer alternating bilayer of octyl phosphates and a dicalcium phosphate dihydrate (DCPD)-like phase, was thermally treated in vacuo and the intercalation of n-alkyltrimethylammonium ions into the materials was examined. The octyl groups in the layer were eliminated by outgassing above 250 °C to give the amorphous calcium phosphates. Further, the specific surface area was steeply increased and mesopores with a diameter of ca. 2.0 nm were formed. IR results indicated that the surface POH groups were generated by outgassing at 250 °C. When the CaOP outgassed at 250 °C was treated with n-alkyltrimethylammonium ion solutions (carbon number of alkyl group, n=14–18), three XRD peaks reappeared below 2 θ=15° and the d-spacing ratio of these peaks was 1:1/2:1/3. These facts indicate that the n-alkyltrimethylammonium ions were intercalated into the amorphous calcium phosphate phases.