Porous Materials: Functional Macroporous Oxides and Composites with Enhanced Toxic Metal Capture and Exchange Efficiency
Importance
One approach to the fabrication of macroporous scaffolds is via templating using close-packed spherical arrays that are analogous in structure to the gemstone opal (Stein, 2001; Velikov et al., 2002). Naturally occurring gemstone opals have microstructures composed of close packed silica spheres from which light diffracts giving rise to iridescence. Inverse opals (inverse replicas of opals) consist of regular arrangements of spherical void spaces surrounded by solid walls. Such three-dimensionally ordered macroporous (3DOM) ceramic networks have been synthesized to take advantage of their porosity, low-density, 3D order and large effective surface area. To date, 3DOM research has focused on photonics applications, but more recently the potential of such materials as ecomaterials has been recognized. The benefits of adopting macroporous architectures are:
- Excellent mass transport for contacting pollutants with functional materials;
- Improved rheological handling of nanocrystalline material;
- Large surface area for selective adsorption or ion exchange;
- Mechanical robustness as reactive scaffolds; and
- Controlled fabrication of nanocomposites.
A particular difficulty has been the creation of specific functionality in the macropore walls, as carefully controlled soft chemical methods are required. For this reason, most reports are of walls of amorphous silica or crystalline alumina, zircona or titania. However, such simple oxides are of limited use from a pollution control viewpoint. In the past six months, CARE has made substantial advances in the fabrication of more chemically complex materials including:
