Aqueous Route Synthesis of Mesoporous ZrO_2 by Agarose Templation

摘要

Mesoporous zirconia with high surface area has been synthesized using self-assembling agarose gel as a template. Agarose gel was formed in the presence of aqueous zirconyl nitrate solutions followed by precipitation of zirconium (hydr)oxide in the gel framework. A porous zirconia structure is obtained by pyrolysis of agarose. Fourier transform infrared spectroscopy is employed to assess the agarose-zirconia precursor interaction. Changes in the C-O absorption bands indicate zirconium association with the OH groups of the agarose. Solid state ~(13)C NMR studies of the nanocomposite showed a shift in intensity from 70 to 75 ppm indicating conversion of ～7% of C-O-H to C-O-Zr. Scanning electron microscopy reveals that both aga-rose/zirconia nanocomposite and zirconia have similar morphological features as that of pure agarose gel confirming agarose templation. Phase transformation of zirconia from amorphous to tetragonal between 300℃ and 500℃, and gradually into monoclinic phase up to 900℃ is observed using X-ray powder diffraction. Specific surface area and pore size distribution are determined using nitrogen adsorption, employing BET and Barrett-Joyner-Halenda methods, respectively. The specific surface area of porous zirconia after heat treatment at 500℃ was determined to be 86 m~2/g, which reduced with increasing temperature to 13 m~2/g above 900℃. Transmission electron microscopy confirmed the hierarchical structure of porous zirconia.