Zeolite films, oriented

S. Lai, T. Louisa, and K. Yeung, Influence of the Synthesis Conditions and Growth Environment on MFI Zeolite Film Orientation. Microporous Mesoporous Mater., 2002, 54, 63-77. 

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

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]. 

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

Chemical sensors are important for industrial process control and environmental monitoring. They also find critical use in medical and defense applications. Two of the critical performance parameters of a sensor are selectivity and sensitivity. When integrated with an appropriate sensor platform (e.g., quartz crystal microbalance or electrochemical quartz crystal microbalance), a zeolite film can improve the selectivity and sensitivity of the sensor due to its ability to selectively adsorb a component out of a mixture. A large number of publications have appeared in this area, and an in-depth review on zeolite films for chemical sensor applications up to 1996 was provided as a section in a recent review by Bein. " Here, we highlight a recent development of selective chemical sensor based on continuous oriented zeolite films. 

Almost all applications for zeolite films could benefit from a preferred orientation. This is especially critical for zeolites with anisotropic pore systems. One particularly interesting h-oriented MFI film is shown in Fig. 7. It is a continuous monolayer film (0.4-0.5pm thick) by in situ crystallization on metal substrates (SS and... 

A detailed study of the growth process and the structural evolution of silicalite-1 (MFI) films was undertaken with the aid of grazing incidence synchrotron X-ray diffraction. [65] The diffraction data of the adsorbed and grown zeolite films at different incident and exit angles reflect the distribution of the crystal orientation along the film thickness. The films were prepared via assisted adsorption of nanoscale MFI seed crystals, followed by calcination and subsequent hydrothermal synthesis on the seed layers. The adsorbed (multi-) layer of seed crystals consists of randomly oriented crystals. With progressing hydrothermal growth, the film surface becomes smoother and a preferred crystal orientation with the b-axis close to vertical to the substrate develops. 

A striking example of molecular sieving in a stable, continuous b-oriented silicalile-1 film (having pores of about 0.55 nm) on an electrode was recently demonstrated with redox probe molecules of different sizes (Fig. 13).[100] Specifically, the smaller complex Ru(NII3)63+ with a diameter of ca. 0.5 nm was shown to travel through the film, while the larger complex Co(phen)32+ with a diameter of ca. 1.3 nm was completely excluded from the zeolite film and thus from redox processes. 

So far, only few studies have been reported on the use of porous zeolite films for optical applications. While significant efforts have been extended towards the encapsulation of various dye molecules into zeolite crystals or powders (see section 2.2), integration of such systems into thin films has not been pursued by many groups yet. As one of the few examples reported so far, we discuss the inclusion of oriented hemicyanine dyes into thin zeolite films aimed at Second Harmonic Generation (SHG).[106] The zeolite film plays the important role... 

The possibility of growing epitaxial zeolite films on micrometer-sized, structurally different zeolite support crystals was explored with the aim to develop polyfunctional zeolite materials with spatially separated adsorptive and/or catalytic functions. Support crystals of one zeolite type were added to a hydrogel for crystallization of a second zeolite type. Tuning of the crystallization conditions led to the formation of a MAZ-on-EMT overgrowth material consisting of an oriented, continuous film of MAZ crystallites completely covering the surface of the EMT support crystals. The epitaxial relations between the two phases were established using HRTEM and SAED. 

Pham TCT, Kim HS, Yoon KB. Growth of uniformly oriented silica MFI and BEA zeolite films on substrates. Science 2011 334 1533-1538. 

Figure 11.18 Three-level structure of a zeo-lite/sintered metal fiber catalytic bed (a) microstructure of a zeolite film of oriented submicron crystals, (b) mesostructure of...

The template-assisted synthetic strategies outlined above produce micro- or mesoporous stmetures in which amorphous or crystalline polymers can form around the organic template ligands (174). Another approach is the use of restricted spaces (eg, pores of membranes, cavities in zeolites, etc.) which direct the formation of functional nanomaterials within thek cavities, resulting in the production of ultrasmaU particles (or dots) and one-dimensional stmetures (or wkes) (178). For example, in the case of polypyrrole and poly(3-methylthiophene), a solution of monomer is separated from a ferric salt polymerization agent by a Nucleopore membrane (linear cylindrical pores with diameter as small as 30 nm) (179—181). Nascent polymer chains adsorb on the pore walls, yielding a thin polymer film which thickens with time to eventually yield a completely filled pore. De-encapsulation by dissolving the membrane in yields wkes wherein the polymer chains in the narrowest fibrils are preferentially oriented parallel to the cjlinder axes of the fibrils. 

Early work regarding the polymerization of acetylene in zeolites was performed by Tsai et al. They reported that the extent of pol5nnerization on X-zeolites was related to the size of the alkali metal cations present in the cages, and that the cations activate the acetylene molecules. The photopolymerization of diacetylenes (3,5-octadiyne-l,8-diol) on various surfaces, including molecular sieves 5A and 13X, was examined. On polar surfaces, the first molecular layers are absorbed through hydrogen bonds, but due to their relative orientation these molecules do not polymerize. However, additional layers can be photopolymerized to form stable polymer films on the surface. 

Thus Geus et al. studied oriented silicalite-1 crystals in an expoxy matrix on perforated metal with each crystal fully covering one hole of the metal support [12], Geus also investigated [13] monolayers of silicalite-1 crystals on macroporous alumina covered with a thin clay film. Zeolite surface coverages of 75% were achieved (Figure 4). 

Various improvements have broadened the research in the held of zeoUte membranes and films, such as the development of new synthesis procedures, the use of new supports with speciUc characteristics (monoliths, foams, etc.) or the use of modified supports by means of masking or grafting techniques, the appUcation of new analytical techniques (isotopic-transient experiments, permporometry, etc.), the control of the orientation of the crystals (by means of covalent Unkages, synthesis conditions, etc.) and of the thickness of the membranes, and the preparation of new zeolites as membranes or new zeoUte related-materials. In addition, a variety of zeoUtes can now be prepared as coUoidal systems with particle dimensions ranging from tens to a few hundred nanometers. 

Wang Z and Yan Y. Oriented zeolite MFI monolayer films on metal substrates by in situ crystallization. Micropor Mesopor Mater 2001 48 229-238. 

Example 3 Preparation of b-axis-oriented MFI zeolite thin films. 

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