Synthesis of Highly Ordered Three-Dimensional Macroporous Structures of Amorphous or Crystalline Inorganic Oxides, Phosphates a

Chem. Mater. 1999, 11, 795-805

Synthesis of Highly Ordered Three-Dimensional Macroporous Structures of Amorphous or Crystalline Inorganic Oxides, Phosphates and Hybrid Composites

Brian T. Holland, Christopher F. Blanford, Thang Do, Andreas Stein^*

Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, 55455

Abstract

The synthesis of highly ordered macroporous materials has been accomplished in a straightforward, single-step reaction. Inorganic frameworks composed of oxides of Si, Ti, Zr, Al, W, Fe, Sb and a Zr/Y mixture were formed from metal alkoxide precursors templated around polystyrene (latex) spheres. Monodisperse latex spheres were ordered into close-packed arrays by centrifugation. The interstices between latex spheres were permeated by the alkoxide, which hydrolysed and condensed. An inorganic framework was formed upon drying. Removal of the latex spheres was accomplished through either calcination at temperatures between 450 and 1000 deg. C or extraction with a tetrahydrofuran/acetone mixture. The resulting products consisted of periodic, interconnected networks of monodisperse submicron pores extending over hundreds of micrometers. Depending on the technique of template removal, various phases of the inorganic oxide could be formed. For example, in the case of titania, an amorphous phase was formed upon extraction of TiO₂ and anatase by calcination at 450 deg. C. The synthesis has also been expanded to other compositions including aluminophosphates and hybrid organosilicates, as well as silicates with bimodal distributions of meso- and macropores. The materials presented in this paper show the diversity of macroporous materials achievable with this technique. These structures could potentially find applications as chromatographic support materials, solid catalysts, battery materials, thermal insulators, or photonic crystals.