Zeolite films

The FPI principle can also be used to develop thin-film-coating-based chemical sensors. For example, a thin layer of zeolite film has been coated to a cleaved endface of a single-mode fiber to form a low-finesse FPI sensor for chemical detection. Zeolite presents a group of crystalline aluminosilicate materials with uniform subnanometer or nanometer scale pores. Traditionally, porous zeolite materials have been used as adsorbents, catalysts, and molecular sieves for molecular or ionic separation, electrode modification, and selectivity enhancement for chemical sensors. Recently, it has been revealed that zeolites possess a unique combination of chemical and optical properties. When properly integrated with a photonic device, these unique properties may be fully utilized to develop miniaturized optical chemical sensors with high sensitivity and potentially high selectivity for various in situ monitoring applications. 

Choi, J., Ghosh, S Lai, Z., and Tsapatsis, M. (2006) Uniformly a-oriented MEl zeolite films by secondary growth. Angav. Chem. Int. 

Method for preparing DDR type zeolite film, DDR type zeolite film, and composite DDR type zeolite film, and method for preparation thereof. U S Patent Application 2004/0173094 Al. 

Rebrov et al. [158] synthesized ZSM-5 zeolite in micro channels. The main focus of this work was to assess the performance benefits of zeolitic coatings in micro channels compared with conventional zeolite-based pellets and powders. The coatings were performed in a sandwich of two plates of 1 cm length and width at a thickness of 2 mm. The plates carried seven channels each, which were 1 cm long and had a diameter of500 pm. The plates were positioned at a distance of280 pm from each other in the housing of the reactor. A zeolitic film of one crystal thickness was formed under the optimum synthesis conditions, which were determined as a water/silicon ratio of 130 and a template/aluminum ratio of 2 at a temperature of 130 °C after 35 h on a flat plate. The Si/Al ratio of the zeolite, which also lowers the crystal size when decreased, was optimized to a value of 28. 

Torres, M., Lopez, L., Dominguez, J. M., Mantilla, A., Ferrat, G., Gutierrez, M. and Maubert, M. Olefins catalytic oligomerization on new composites of beta-zeolite films supported on a-Al203 membranes. Chem. Eng. J., 2003, 92, 1-6. 

The ultimate design of an inert membrane reactor would consist of well chosen crack free zeolite film membranes. The difficulties in this case are even more deterrent for industrial scale reactors since only a small number of holes or cracks would ruin the potential advantages of the design. 

Fig. 57. (a) Transmission electron micrograph of a cross-section of an approximately 3-nm-thick zeolite film on Si(l 00), with the inset showing a diffraction pattern. The atomically resolved interface area is shown in (b) the inset displays an image area enhanced by Fourier filtering adapted from (25) with permission from Elsevier. 

Three other methods of electrode preparation include photopolymerization of vinyl-saturated zeolites on a Pt electrode [163], direct synthesis of zeolite films on metal supports [164] (although electrochemical studies on this system have not been reported) and the use of agitated suspensions of zeolite, where zeolite particles contact the electrode at random [165]. 

Masuda T., Sato A., Hara H., Kouno M. and Hashimoto K., Preparation of a dense ZSM-5 zeolite film on the outer surface of an alumina ceramic filter, AppL Catal. A /// 143 (1994). 

Sano T, Kiyozumi Y, Kawamura M., Mizukami F., Takaya H., Mouri T., Inaoka W., Toida Y, Watanabe M. and Toyoda K., Preparation and characterisation of ZSM-5 zeolite film. Zeolites 77 842 (1991). 

Coronas J and Santamaria J. The use of zeolite films in small-scale and micro-scale applications. Chem Eng Sci 2004 ... 

Nair S and Tsapatsis M. Infrared reflectance measurements of zeolite film thickness, refractive index and other characteristics. Micropor Mesopor Mater 2003 58 81-89. 

Vilaseca M, Mateo E, Palacio L, Pradanos P, Hernandez A, Paniagua A, Coronas J, and Santamaria J. AFM characterization of the growth of MFI-type zeolite films on alumina substrates. Micropor Mesopor Mater 2004 71 33-37. 

Vilaseca M, Coronas J, Cirera A, Comet A, Morante JR, and Santamarfa J. Use of zeolite films to improve the selectivity of reactive gas sensors. Catal Today 2003 82(1 ) 179-185. 

Basaldella El, Kikot A, Quincoces CE, and Gonzalez MG. Preparation of supported Cu/ZSM-5 zeolite films for DeNO(x) reaction. Mater Lett 2001 51(4) 289-294. 

Madhusoodana CD, Das RN, Kameshima Y, Yasumori A, and Okada K. Characterization and adsorption behavior of ZSM-5 zeolite film on cordierite honeycombs prepared by a novel in situ crystallization method. J For Mater 2001 8(4) 265-271. 

Mintova S and Bein T. Nanosized zeolite films for vapor-sensing applications. Micropor Mesopor Mater 2001 50(2-3) 159-166. Osada M, Sasaki I, Nishioka M, Sadakata M, and Okubo T. Synthesis of a faujasite thin layer and its application for SO2 sensing at elevated temperatures. Micropor Mesopor Mater 1998 23(5-6) 287-294. 

Single-layer zinc-phosphate zeolite crystals were grown with more than 90% of their (111) faces oriented to a gold-coated silicon surface. Sudi oriented zeolite films might find application as membrane catalysts or as specific chemical sensors [66]. 

So far, essentially three different approaches have been reported for the preparation of zeolitic membranes [119]. Tsikoyiannis and Haag [120] reported the coating of a Teflon slab during a "regular" synthesis of ZSM-5 by a continuous uniform zeolite film. Permeability tests and catals ic experiments were carried out with such membranes after the mechanical separation of the coating from the Teflon surface [121]. Geus et al. [122] used porous, sintered stainless steel discs covered with a thin top layer of metal wool to crystallize continuous polycrystalline layers of ZSM-5. Macroporous ceramic clay-type supports were also applied [123]. 

Lai, R. Kang, B. S. Gavalas, G. R., Parallel synthesis of ZSM-5 zeolite films from clear organic-free solutions, Angew. Chem., Int. Ed. 2001, 40, 408—411... 

Techniques involved in the preparation of zeolitic films on stable supports can be divided into four categories (1) pre-treatment of the supports, in which the most important is chemical treatment (such as the siloxation of surface-to-anchor zeolite crystallites), (2) synthesis of zeolite film precursors, (3) growth of films on the support surfaces, and (4) elimination of small defects, which can be achieved by chemical vapor deposition (CVD) of silica sources (by reaction with silicon alkoxide or other silylation agents) and other techniques. Processes (2) and (3) are crucial in the preparation of films,... 

In the next example (Example 2), a different approach for the preparation of zeolite films will be presented. This method was first proposed by Iler in 1979,11321 and involved the assembly of charged nano-sized particles layer by layer to form multilayer films based on electrostatic interaction, hence called the layer-by-layer (LBL) self-assembly technique. 

Example 2 Applications of LBL self-assembly technique in the preparation of zeolite films.[133]... 

Example 4 Preparation of a-axis-oriented MFI zeolite films. 

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