Zeolite Thin Films: From Computer Chips to Space Stations

摘要

Zeolites are a class of crystalline oxides that have uniformnand molecular-sized pores (3 12 Å in diameter). Althoughnnatural zeolites were first discovered in 1756, significant com-nmercial development did not begin until the 1950s when syn-nthetic zeolites with high purity and controlled chemicalncomposition became available. Since then, major commercialnapplications of zeolites have been limited to catalysis, adsorp-ntion, and ion exchange, all using zeolites in powder form.nAlthough researchers have widely investigated zeolite thin filmsnwithin the last 15 years, most of these studies were motivatednby the potential application of these materials as separationnmembranes and membrane reactors. In the last decade, we havenrecognized and demonstrated that zeolite thin films can havennew, diverse, and economically significant applications that oth-ners had not previously considered. In this Account, we high-nlight our work on the development of zeolite thin films as low-ndielectric constant (low-k) insulators for future generationncomputer chips, environmentally benign corrosion-resistant coatings for aerospace alloys, and hydrophilic and microbiocidal coat-nings for gravity-independent water separation in space stations.nAlthough these three applications might not seem directly related, they all rely on the ability to fine-tune important macro-nscopic properties of zeolites by changing their ratio of silicon to aluminum. For example, pure-silica zeolites (PSZs, Si/Al ∞) arenhydrophobic, acid stable, and have no ion exchange capacity, while low-silica zeolites (LSZs, Si/Al 2) are hydrophilic, acid sol-nuble, and have a high ion exchange capacity. These new thin films also take advantage of some unique properties of zeolites thatnhave not been exploited before, such as a higher elastic modulus, hardness, and heat conductivity than those of amorphous porousnsilicas, and microbiocidal capabilities derived from their ion exchange capacities.nFinally, we briefly discuss our more recent work on polycrystalline zeolite thin films as promising biocompatible coatings andnenvironmentally benign wear-resistant and antifouling coatings. When zeolites are incorporated into polymer thin films in the formnof nanocrystals, we also show that the resultant composite membranes can significantly improve the performance of reverse osmo-nsis membranes for sea water desalination and proton exchange membrane fuel cells.nThese diverse applications of zeolites have the potential to initiate new industries while revolutionizing existing ones with a poten-ntial economic impact that could extend into the hundreds of billions of dollars. We have licensed several of these inventions to compa-nnies with millions of dollars invested in their commercial development. We expect that other related technologies will be licensed in thennear future.