Ordered macroporous materials by emulsion templating

Abstract

Ordered macroporous materials with pore diameters comparable to optical wavelengths are predicted to have unique and highly useful optical properties such as photonic bandgaps1,2,3 and optical stop-bands4. Tight control over the pore size distribution might also lead to improved macroporous materials (those with pores greater than approximately 50 nm) for application as catalytic surfaces and supports5, adsorbents, chromatographic materials, filters6, light-weight structural materials7, and thermal, acoustic8 and electrical insulators9. Although methods exist for producing ordered porous materials with pore diameters less than 10 nm (refs 10, 11), there is no general method for producing such materials with uniform pore sizes at larger length scales. Here we report a new method for producing highly monodisperse macroporous materials with pore sizes ranging from 50 nm to several micrometres. Starting with an emulsion of equally sized droplets (produced through a repeated fractionation procedure12), we form macroporous materials of titania, silica and zirconia by using the emulsion droplets as templates around which material is deposited through a sol–gel process13. Subsequent drying and heat treatment yields solid materials with spherical pores left behind by the emulsion droplets. These pores are highly ordered, reflecting the self-assembly of the original monodisperse emulsion droplets into a nearly crystalline array14. We show that the pore size can be accurately controlled, and that the technique should be applicable to a wide variety of metal oxides and even organic polymer gels.