An alternative to zeolite?
10 Feb 2003
Scientists at the University of California, Riverside have synthesised a large family of semiconducting porous materials that have an unprecedented and diverse chemical composition.
The new materials show several different properties such as photoluminescence, ion exchange, and gas sorption. They also have a large surface area and uniform pore sizes. In addition, they have a pore size larger than zeolites. The synthetic approach has the potential to generate new materials with even larger pore sizes.
'This research represents a major advance in the development of crystalline porous materials,' said Pinyung Feng, assistant professor of chemistry.
Currently, the most important porous materials are zeolites. Zeolites are currently used as adsorbents for non-cryogenic air separation and as solid acid catalyst to crack down large hydrocarbon molecules to make small hydrocarbon molecules such as gasoline and other petrochemical products. Porous materials are also called molecular sieves because their unique pore size allows the distinction of molecules based on their size and shape.
'Properties of porous materials are intimately related to their framework topological features and chemical compositions,' explained Feng. 'Therefore, the development of porous materials with new compositions and topologies can lead to new applications or much improved current applications.'
Today's porous materials such as zeolites have various limitations. Their pore size is less than 1nm and, therefore, they have little utility in reactions involving large molecules such as pharmaceutical molecules. In addition, because zeolites are made from aluminium, silicon, and oxygen, they are insulators. Therefore, they have little use in applications that utilize electronic, optical, or electrooptical properties.
The new materials are a new class of porous materials. Like traditional porous materials, e.g., zeolites, they may find applications in areas such as catalysis and separation. More important, because they combine zeolite-type porosity with semiconductivity, they may have unique applications that are not possible with other materials.
The combination of porosity with semiconductivity in the new materials opens up more applications such as electronic and optoelectronic devices, electrocatalysis, electroanalysis and sensors. The materials may be used as high surface area electrodes for electrochemical cells to molecular scale composite materials for microelectronics and sensor technologies.
'More research is needed to realize the application potential of these materials,' said Feng. 'Zeolites have a direct impact in many aspects of people's lives - gasoline production, smog reduction, water softening, cleanup of radioactive wastes, and so on. The materials we have developed are designed to improve and extend the applications of zeolites and, as such, the potential for direct impact on people's life is significant.'
