Preparation of anion-uptake powder compact containing layered double oxide and metakaolinite

A powder compact with anion-uptake ability was prepared prior to the proceeding of the solid-state reaction involving layered double hydroxide (LDH) and kaolinite during calcination. LDH features anion-exchangeable capability, and kaolinite is used as a raw potty material because of the sintering property. In the present study, the solid-state reaction of LDH with kaolinite did not proceed at 750°C, resulting in the formation of a mixture of layered double oxide (LDO) and metakaolinite. Unlike LDO, which typically undergoes anion-uptake accompanied by LDH reconstruction, metakaolinite does not revert to kaolinite without the use of hydrothermal conditions. In addition, the powder compact composed of LDO crumbled, whereas the one containing a mixture of LDO and metakaolinite remained intact. When the powder compact of LDO and metakaolinite mixture was immersed in a methyl orange (MO) aqueous solution, an LDH–MO intercalation compound was generated within the compact. By contrast, no such compound was generated when LDO powder was immersed in an MO aqueous solution. These results indicated that the successful preparation of a powder compact with distinct anion-uptake ability was different from powder, owing to that the solid-state reaction of LDO with metakaolinite did not proceed at 750°C.