Zeolites and zeolite-like materials― crystalline solids containing a large number of uniformly sized pores with diameters of <2 nm―can discriminate between molecules that can enter the pore space and those that cannot on the ba- sis of their size and shape. On page 456 of this issue, Lai et al. (1) demonstrate an impressive example of such selectivity: Their new zeolite membranes discriminate between isomers of the same molecule that differ by less than 0.1 nm in size. Zeolites have historically been used as catalysts, ion exchangers, and adsorbents (2). Emerging areas of application―for example, as magnetic resonance imaging contrast agents and low-k dielectrics for use as electrical insulators―show great promise (3). Supported zeolite membranes are also of interest for future applications. They could function as true molecular recognition and separation barriers and allow for efficient separation of nitrogen from methane and carbon dioxide from air. Such membranes may also provide for the high-temperature separation of molecules, even in environments containing corrosive chemicals. This discrimination between molecules could be coupled to catalytic conversion and/or adsorption, yielding highly specific catalytic reactors and chemical sensors. These and other new technologies will require the preparation of highly selective and permeable molecular sieve films.
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