Type-A zeolites with hydroxyapatite surface layers formed by an ion exchange reaction

To enhance adsorption of harmful ions on type-A zeolites (LTA), hydroxyapatite (HAp) thin layers were synthesized on the LTA surface by an ion exchange reaction of Ca2+ for NH4+ under hydrothermal treatment. The temperatures and durations in the reactions were varied ranging from 25 to 200 °C and from 1 to 168 h. The samples synthesized were characterized by X-ray diffraction method (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmet-Teller method (BET). The structure of LTA was not destroyed by the hydrothermal treatments at 25 to 160 °C for 8 h and also at 120 °C for 1 to 72 h. The yield of HAp grown on the LTA surface, synthesized at 120 °C for 8 h, showed a maximum value of 0.82. The morphologies of HAp were dependent mainly on the temperatures. The specific surface area remained unchanged in the treatments at 25 to 40 °C for 8 h, as compared to the specific surface area of Ca-LTA, however up to 80 °C, the value decreased with an increase of exchange temperature.