Zeolite Thin Films: From Computer Chips to Space Stations

Abstract

Zeolites are a class of crystalline oxides that have uniform and molecular-sized pores (3-12 A in diameter). Although natural zeolites were first discovered in 1756, significant commercial development did not begin until the 1950s when synthetic zeolites with high purity and controlled chemical composition became available. Since then, major commercial applications of zeolites have been limited to catalysis, adsorption, and ion exchange, all using zeolites in powder form. Although researchers have widely investigated zeolite thin films within the last 15 years, most of these studies were motivated by the potential application of these materials as separation membranes and membrane reactors. In the last decade, we have recognized and demonstrated that zeolite thin films can have new, diverse, and economically significant applications that others had not previously considered. In this Account, we highlight our work on the development of zeolite thin films as low-dielectric constant (low-k) insulators for future generation computer chips, environmentally benign corrosion-resistant coatings for aerospace alloys, and hydrophilic and microbiocidal coatings for gravity-independent water separation in space stations. Although these three applications might not seem directly related, they all rely on the ability to fine-tune important macroscopic properties of zeolites by changing their ratio of silicon to aluminum. For example, pure-silica zeolites (PSZs, Si/Al = infinity) are hydrophobic, acid stable, and have no ion exchange capacity, while low-silica zeolites (LSZs, Si/Al < 2) are hydrophilic, acid soluble, and have a high ion exchange capacity. These new thin films also take advantage of some unique properties of zeolites that have not been exploited before, such as a higher elastic modulus, hardness, and heat conductivity than those of amorphous porous silicas, and microbiocidal capabilities derived from their ion exchange capacities. Finally, we briefly discuss our more recent work on polycrystalline zeolite thin films as promising biocompatible coatings and environmentally benign wear-resistant and antifouling coatings. When zeolites are incorporated into polymer thin films in the form of nanocrystals, we also show that the resultant composite membranes can significantly improve the performance of reverse osmosis membranes for sea water desalination and proton exchange membrane fuel cells. These diverse applications of zeolites have the potential to initiate new industries while revolutionizing existing ones with a potential economic impact that could extend into the hundreds of billions of dollars. We have licensed several of these inventions to companies with millions of dollars invested in their commercial development. We expect that other related technologies will be licensed in the near future.

Computational Molecular Modeling of Transport Processes in Nanoporous Membranes

“…Zeolites are aluminosilicate crystals with ordered pore sizes ranging from 0.3 nm to >1.0 nm depending on the framework type. Zeolites with higher Si/Al ratios are electrically insulating and are also extremely stable in both acidic and basic conditions due to their inert chemical nature [28][29][30]. Previously, thin zeolite membranes have been observed to enable water/ion separation via the size-exclusion mechanism [8,31,32].…”

Evanescent Field Based Photoacoustics: Optical Property Evaluation at Surfaces

“…Advancements in the understanding of optical materials 1,3,4,6,7,10,[13][14][15][16] have provided new insights into the creation of thin film materials for a host of optical devices, including antireflection coatings on lenses, high extinction ratio optical filters, and highly absorbing slab waveguides 17 . These advancements would not be possible without the use of many characterization techniques, such as ellipsometry 4,6,18 , contact angle measurement, atomic force microscopy 7,11,19 , and scanning/transmission electron microscopy, which assist in the iterative improvement of these technologies by providing direct measures or indirect estimates of fundamental optical material properties.…”

“…With such a small optical penetration depth, the evanescent field is able to interact with the environment very close to the interface of the two materials, and well below the optical and acoustic diffraction limits. The optical properties of materials or particles within this range may perturb the field or otherwise alter its generation, which interaction can be detected by a variety of methods 3,5,6,10,15,17,18,21,23,[25][26][27][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][84][85][86][87][88][89][90][91][92][93][94][95] .…”

Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

“…Zeolites are also considered for a wide range of other applications such as chemical separation, sensing, catalysis or cooling [7][8][9][10]. For example, zeolites can be used for the development of sorption-based heat exchangers for heat recovery and cooling applications [11][12][13][14][15].…”