General synthesis of fibrous mesoporous metal oxides in polycarbonate membrane

Mesoporous metal oxide fibers such as silica, alumina, titania, zirconia, niobia, and tantala were fabricated through the penetration of surfactant-containing precursor solutions into the cylindrical confined spaces of polycarbonate (PC) membrane, followed by calcination to remove both the surfactants and the PC membrane completely. The SEM images showed that the average diameters of the mesoporous fibers were ca. 200 nm, being related to that of the confined spaces of the original PC membrane. The cylindrical spaces of the PC membrane are more useful as a hard template for compositional variation than those of porous anodic alumina membranes that have been used for the synthesis of ordered mesoporous silica fibers. The TEM images, the SAXS profiles, and the N2 adsorption-desorption isotherms supported the formation of mesoporous structures inside the fibers. Calcination at a temperature appropriate for each fiber directed to the crystallization of the non-silica-based frameworks with the retention of mesoporous structures. The wide-angle XRD patterns of the non-silica fibers revealed the crystallization to typical Al2O3 (γ-phase), TiO2 (anatase), ZrO2 (tetragonal), and Nb2O5 (pseudo-hexagonal) phases, which was also supported by the corresponding EDS mappings.