Synthesis of hierarchically porous silica and metal oxide beads using emulsion-templated polymer scaffolds

Uniform, hierarchically porous inorganic beads (SiO₂, A1 ₂O₃, TiO₂, and ZrO₂) have been produced using emulsion-templated polymer beads as templates. The polymer scaffolds were prepared by oil-in-water-in-oil (O/W/O) sedimentation polymerization (Zhang, H.; Cooper, A. I. Chem. Mater. 2002, 14, 4017). The inorganic beads were prepared by simply immersing the polymer scaffold beads in a range of inorganic precursor solutions, followed by sol-gel condensation in air and subsequent calcination of the polymer phase. The hierarchical structures are composed of mesopores (diameters 2-5 nm), micropores (in the case of silica beads), and large emulsion-templated macropores of around 5-10 μm. All of the pores are highly interconnected. The inorganic beads exhibit high macropore volumes as characterized by mercury intrusion porosimetry. Polymer-silica composite beads with micropores and high macropore volumes were also produced. These large inorganic beads (diameters 1.0-1.5 mm) are easily handled and separated and may be useful in applications such as catalysis and separation, especially for macromolecules or viscous systems where large pores are needed to improve mass transport into the pore structure.