(681a) Colloidal Array of Silica Nanospheres As Template for Fabricating Three-Dimensionally Ordered Metal Oxides

We have developed a simple and novel liquid-phase method for preparing uniform-sized silica nanospheres (SNSs) ca. 12 nm in size. The SNSs can be synthesized through hydrolysis and condensation reactions of TEOS in the presence of basic amino acids such as lysine and arginine under weekly basic conditions. Recently, the particle size control of SNSs ranging from 14 to 550 nm was achieved through a process of regrowing the SNSs. These silica spheres easily self-assemble into a cubic closed packed (ccp) colloidal array by solvent evaporation or centrifugation. Very recently, we have found out that the colloidal array of the SNSs can be re-dispersed into polar solvents and the re-dispersed SNSs can be re-assembled without adding any chemicals by simple solvent evaporation or centrifugation. The colloidal array of the SNSs with a morphological reversibility is expected to be suitable for template for ordered nanomaterials.

Here we report the synthesis of the colloidal array of hollow-structured zirconia nanospheres (ZNSs) with a size of less than 100 nm by using the SNSs with a morphological reversibility as a template. The synthetic procedures consist of the five major steps: (1) preparation of colloidal array of the SNSs, (2) re-dispersion of the SNSs into the ethanol - water solution, (3) coating the SNSs with zirconia, (4) self-assembly of the zirconia-coated SNSs spheres, (5) removal of the silica template to obtain the colloidal array of hollow-structured ZNSs. Note that the shell of the hollow structure is composed of nanoparticles ca. 4 nm in size. Therefore, the hollow-structured ZNSs possess high surface area and bimodal pore system arising from the hollow structure and interparticle voids of zirconia nanoparticles. The size of hollow void can be tuned from 50 to 500 nm by changing the particle size of the SNSs. Finally, the crystallization of hollow-structured ZNSs was also demonstrated.