Morphology and pore structure of zirconia particles prepared by the thermal treatment of zirconium tetra-<i>n</i>-propoxide in glycols

Zirconia particles were prepared by thermal treatment of zirconium(IV) tetra-n-propoxide (ZNP) in C2–C6 glycols (Glycothermal method) at 300 °C and morphology and pore structures of the products were examined. X-ray diffraction results revealed that nanocrystals of tetragonal zirconia phase were mainly obtained in all cases. However, the morphology and pore structures of the products were quite different depending on the glycols used. The products prepared in 1,4-butanediol (1,4-BG) were spherical particles with ca. 5 µm size while aggregations of fine particles were observed for other glycols. The samples obtained in 1,4-BG had large surface areas and showed narrow pore-size distributions in the mesopore region. To investigate the formation process of the products having such a unique morphology and pore system, the mixtures of ZNP and glycols were heated at lower temperatures. It was found that the thermal reaction of ZNP in 1,4-BG at 200 °C afforded intermediates with layered structures, which subsequently changed into nanocrystalline ZrO2 at elevated temperatures. These stepwise crystallization processes attribute to the unique morphology and pore system of the products obtained by the thermal treatment of ZNP in 1,4-BG.