Assembly of Oriented Zeolite Monolayers and Thin Films on Polymeric

Sep 12, 2008 - poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and ... The exerted pressure and rubbing time in the manual assembly d...
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Langmuir 2008, 24, 11942-11946

Assembly of Oriented Zeolite Monolayers and Thin Films on Polymeric Surfaces via Hydrogen Bonding Ming Zhou, Xiufeng Liu,* Baoquan Zhang,* and Huiming Zhu School of Chemical Engineering and Technology, Tianjin UniVersity, Tianjin 300072, China ReceiVed June 15, 2008. ReVised Manuscript ReceiVed July 30, 2008 The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique.

I. Introduction Zeolite thin films could be widely applied as separation and/or catalysis membranes,1,2 low-k films,3 light energy harvesting devices,4 microlaser systems,5 and electrode modifiers.6 For controlled synthesis of zeolite films and membranes, the uniformly oriented and closely packed monolayer of zeolite crystals on a solid substrate could be used as a seed layer, on which the outward growth of zeolite membranes was directed.1,7,8 Besides, the highquality composite films fabricated by the layer-by-layer method largely relied on the availability of oriented and closely packed monolayers of constituent particles.9 Until now, oriented zeolite monolayers or arrays on various nonporous substrates have been mainly fabricated by using the postsynthetic assembly of crystal grains on the substrate surface via covalent, ionic, and intermolecular bondings.10,11 The reflux and stirring method was first used to promote the reaction between functional groups tethered to zeolite crystals and the substrate surface. Due to the long reaction time required for 100% coverage (typically 24 h), as well as complicated procedures, the ultrasound-aided agitation was thus invented to intensify the reaction, leading to the significantly reduced assembly time and much stronger linkage between individual crystals and the substrate surface.10 Recently, Lee et al. reported * To whom correspondence should be addressed. Tel.: +86 22 27405165. Fax: +86 22 87898959. E-mail: [email protected] (X.L.); [email protected] (B.Z.). (1) Lai, Z. P.; Bonilla, G.; Diaz, I.; Nery, J. G.; Sujaoti, K.; Amat, M. A.; Kokkoli, E.; Terasaki, O.; Thompson, R. W.; Tsapatsis, M.; Vlachos, D. G. Science 2003, 300, 456–460. (2) Wang, X. D.; Zhang, B. Q.; Liu, X. F.; Lin, J. Y. S. AdV. Mater. 2006, 18, 3261–3265. (3) Li, Z.; Johnson, M. C.; Sun, M.; Ryan, E. T.; Earl, D. J.; Maichen, W.; Martin, J. I.; Li, S.; Lew, C. M.; Wang, J.; Deem, M. W.; Davis, M. E.; Yan, Y. Angew. Chem., Int. Ed. 2006, 45, 6329–6332. (4) Ruiz, A. Z.; Li, H.; Calzaferri, G. Angew. Chem., Int. Ed. 2006, 45, 5282– 5287. (5) Xu, R.; Zhu, G.; Yin, X.; Wan, X.; Qiu, S. J. Mater. Chem. 2006, 16, 2200–2204. (6) Kornic, S.; Baker, M. Chem. Commun. 2002, 1700–1701. (7) Choi, J.; Ghosh, S.; Lai, Z. P.; Tsapatsis, M. Angew. Chem., Int. Ed. 2006, 45, 1154–1158. (8) Snyder, M. A.; Tsapatsis, M. Angew. Chem., Int. Ed. 2007, 46, 7560–7573. (9) Choi, J.; Lai, Z. P.; Ghosh, S.; Beving, D. E.; Yan, Y. S.; Tsapatsis, M. Ind. Eng. Chem. Res. 2007, 46, 7096–7106. (10) Yoon, K. B. Acc. Chem. Res. 2007, 40, 29–40. (11) Zhou, M.; Zhang, B. Q.; Liu, X. F. Chin. Sci. Bull. 2008, 53, 801–816.

a manual assembly method for production of oriented zeolite monolayers by way of ionic and hydrogen bondings.12 In comparison with either the reflux and stirring or the ultrasoundaided assembly, the manual assembly method is incredibly simple. The solvent and the reactor for assembly of molecular linkers and zeolite crystals are not required anymore. Although the manual assembly of zeolite monolayers was much faster, high-quality monolayers of silicalite-1 crystals sized from 0.5 to 12 µm could be manually assembled onto bare glass plates with satisfactory degrees of coverage (DOC) and close packing (DCP). However, the manual assembly method was only effective with clean and smooth surfaces. Usually, the binding strength between silicalite-1 crystals and the substrate surface was weak when glass plates and porous solids were employed as substrates.13 In this contribution, we will focus on the manual assembly of oriented zeolite monolayers on glass plates using poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) as intermediate linkers via hydrogen bonds that were formed between silicon-bound hydroxyl groups on zeolite crystals or the glass plate and ether, hydroxyl, amino, or carbonyl groups on polymeric surfaces. The use of polymeric linkers can greatly increase the binding strength between zeolite crystals and the substrate surface.13 In addition, the method established above is applied to fabricate zeolite monolayers on commercially available polymeric substrates and multilayered zeolite films using the layer-by-layer technique. In the past decade, the synthesis and applications of zeolite-polymer composite materials have attracted much attention worldwide. According to literature reports, selfassembled PEO monolayers were used as a template to direct the nucleation and the subsequent oriented growth of TS-1 thin films.14 Hybrid polymer-inorganic nanocomposite materials that contain both PEO and zeolite components revealed new chemical and physical properties.15 PVA-zeolite composite materials were (12) Lee, J. S.; Kim, J. H.; Lee, Y. J.; Jeong, N. C.; Yoon, K. B. Angew. Chem., Int. Ed. 2007, 46, 3087–3090. (13) Zhang, B. Q.; Zhou, M.; Liu, X. F. AdV. Mater. 2008, 20, 2183–2189. (14) Lee, Y.; Ryu, W.; Kim, S. S.; Shul, Y.; Je, J. H.; Cho, G. Langmuir 2005, 21, 5651–5654. (15) Kennedy, C. A.; Zhan, B. Z.; White, M. A. J. Compos. Mater. 2005, 39, 193–198.

10.1021/la801879x CCC: $40.75  2008 American Chemical Society Published on Web 09/12/2008

Assembly of Oriented Zeolite on Polymeric Surfaces

used as catalysts in hydrogenation16 and as organic-inorganic composite membranes in ethanol dehydration.17 Similar to zeolites, chitosan could be used as low-cost adsorbents for heavy metals18 and new hemostatic agents for battlefield hemorrhage control.19 The chitosan-based composite films with homogeneously dispersed zeolite crystals throughout the chitosan matrix demonstrated improved separation performance and tensile strength.20 The zeolite membrane covered with a chitosan toplayer offered better resistance to acid attack and higher selectivity for water over alcohols.21 Recently, Hu et al. prepared the zeolitefilled PMMA membranes which clearly showed a higher gas permeability coefficient for O2 and N2, and the oxygen sorption was significantly enhanced compared with pure PMMA membrane.22 Evidently, the organization of zeolite crystals into uniformly oriented monolayers with high DOC and DCP on the surface of PEO, PVA, chitosan, and PMMA thin films ought to be of great interest to scientists and engineers for various reasons, which could trigger extended applications in innovative materials, microreactors, microelectronic devices, supramolecular lightharvesting systems, and nonlinear optical films.11,23

II. Experimental Section II.1. Materials. PEO (Mw ) 100 000, Aldrich), PVA (polymerization degree ) 1750 ( 50, Tianjin Kewei Chemical Co., Ltd.), chitosan (medium molecular weight, Aldrich), PMMA (Mw ) 100 000, Tianjin Le Tai Chemical Co., Ltd.), tetraethyl orthosilicate (TEOS, 98%, Aldrich), tetrapropyl ammonium (TPAOH, 20%, Aldrich), and acetic acid (99.5%, Tianjin Chemical Reagent Co., Ltd.) were used as supplied. The silicalite-1 crystals sized ca. 1.6 µm × 1.2 µm × 0.6 µm and 0.8 µm × 0.5 µm × 0.2 µm were synthesized using the ingredients of 1TEOS/0.167TPAOH/76.7H2O and 1TEOS/0.2TPAOH/100H2O. At first, TEOS was hydrolyzed in the TPAOH solution. The clear gel was stirred at room temperature for 12 h and transferred to an autoclave, followed with stirring at 180 or 130 °C for 15 h. The obtained silicalite-1 crystals were thoroughly washed with a copious amount of deionized distilled water (DI water) and dried at 120 °C overnight. II.2. Bonding Mechanism with Polymeric Intermediate Linkers As shown in Figure 1a, each PEO unit has one ether linkage that can associate with a hydroxyl group to form a hydrogen bond on the surface of zeolite crystals or on the glass plate, whereas in each unit of PVA, the carbon-bound hydroxyl group can associate with the silicon-bound surface hydroxyl group of zeolite crystals or the glass plate to form a hydrogen bond, just as indicated in Figure 1b. Similarly, in chitosan units there are hydroxyl and amino groups and ether linkages which can associate with zeolite crystals or the glass plate to form hydrogen bonds as demonstrated in Figure 1c. However, in each unit of PMMA, there is an ester bond that can form a hydrogen bond with the hydroxyl group on the surface of zeolite crystals or on the glass plate as illustrated in Figure 1d. Therefore, the use of PEO, PVA, chitosan, and PMMA as intermediate linkers can make sure of the formation of hydrogen bonds between zeolite crystals and the glass plate supported polymeric thin film in the manual assembly (Figure 1e), which will be essential to gain uniformly (16) Liu, L.; Xia, D.; Zhang, Q.; Huang, M. Y.; Jiang, Y. Y. Polym. AdV. Technol. 1999, 10, 103–107. (17) Huang, Z.; Guan, H. M.; Tan, W. L.; Qiao, X. Y.; Kulprathipanja, S. J. Membr. Sci. 2006, 276, 260–271. (18) Bailey, S. E.; Olin, T. J.; Bricka, R. M.; Adrian, D. D. Water Res. 1999, 33, 2469–2479. (19) Whang, H. S.; Kirsch, W.; Zhu, Y. H.; Yang, C. Z.; Hudson, S. M. J. Macromol. Sci., Polym. ReV. 2005, 45, 309–323. (20) Rhim, J. W.; Hong, S. I.; Park, H. M.; Ng, P. K. W. J. Agric. Food Chem. 2006, 54, 5814–5822. (21) Budd, P. M.; Ricardo, N. M. P. S.; Jafar, J. J.; Stephenson, B.; Hughes, R. Ind. Eng. Chem. Res. 2004, 43, 1863–1867.

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Figure 1. Structure of hydrogen bonding between zeolite crystals or the glass plate with PEO (a), PVA (b), chitosan (c), and PMMA (d). The binding mechanism between zeolite crystals and the glass plate helped with a polymer film (e). The symbol Z/G represents zeolite or glass plate.

oriented and closely packed monolayers of zeolite crystals with satisfactory binding strength. II.3. Preparation of Glass-Supported Polymeric Thin Films. The glass plate supported PEO, PVA, chitosan, and PMMA thin films were prepared according to literature reports.13,24-26 PEO was first dissolved in DI water to get 1% (wt %) aqueous PEO solution. Due to that the melting point of PEO is ca. 65 °C, the water evaporation from the PEO film was performed at ca. 45 °C under clean air for 24 h. To prepare 1% (wt %) aqueous PVA solution, PVA was dissolved in DI water. The water in the PVA film was evaporated at ca. 120 °C for 30 min. Chitosan was dissolved in 5% acetic acid solution to form 1% (wt %) aqueous chitosan solution. The evaporation of water and acetic acid from the chitosan film was carried out at ca. 120 °C for 30 min. The 0.05% (wt %) PMMA solution was prepared by dissolving it in toluene. As the melting point of PMMA is ca. 100 °C, the solvent evaporation was performed at ca. 80 °C in clean air for 24 h. Glass plates (19 mm × 25 mm) were first dipped into an acid bath consisting of 5 g of potassium dichromate, 10 g of H2O, and 100 mL of concentrated sulfuric acid for 12 h to remove possible organic residues. Then, the treated glass plates were washed with a copious amount of DI water, followed by drying at 120 °C for 3 h. As shown in Figure 2a, the thin PEO, PVA, chitosan, and PMMA films on glass plates were prepared using a spin-coater (KW-4A, Microelectronic Institute of Chinese Academy of Sciences). The film deposition was carried out for ca. 120 s with spinning rates of 1000 rpm for PEO and PVA and 2000 rpm for chitosan and PMMA. II.4. Manual Assembly of Zeolite Monolayers. The glass plate supported polymeric thin film was placed on a clean white manifold paper. Subsequently, zeolite crystals (ca. 10 mg) were placed on top of the thin film, followed by rubbing the powder on the whole film surface using a finger. To avoid the contamination of the substrate surface and crystal grains with moisture or other pollutants from the finger, a clean soft latex glove was employed. The typical rubbing time required was 30 s for the glass plate sized 19 mm × 25 mm as shown in Figure 2b. In order to fabricate the high-quality zeolite monolayer, the manual assembly was generally carried out in two steps. At first, zeolite crystals were pressed with force by the finger, followed by rubbing on the polymeric thin film. This would give zeolite crystals enough (22) Hu, C. C.; Liu, T. C.; Lee, K. R.; Ruaan, R. C.; Lai, J. Y. Desalination 2006, 193, 14–24. (23) Kim, H. S.; Pham, T. T.; Yoon, K. B. J. Am. Chem. Soc. 2008, 130, 2134–2135. (24) Sardone, L.; Marletta, G.; Cacialli, F.; Samori, P. Synth. Met. 2004, 147, 123–125. (25) Murray, C. A.; Dutcher, J. R. Biomacromolecules 2006, 7, 3460–3465. (26) Liu, X.; Bai, Y.; Chen, L.; Wei, F. X.; Zhang, X. B.; Jiang, X. Y.; Zhang, Z. L. Microelectron. J. 2007, 38, 919–922.

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Figure 2. Manual assembly procedure of oriented zeolite monolayer on glass-supported polymer film.

power to form hydrogen bonds with the polymeric thin film and simultaneously break parasitic crystals from the corresponding mother crystals, while the forced surface migration of zeolite crystals during rubbing contributed to the close packing of adjacent crystals by contact of their side faces. The assembled entity of zeolite crystals on the glass plate supported polymeric surface generally demonstrated a randomly packed second layer on the closely packed first layer as shown in Figure 2b. In the second step, the assembled zeolite multilayer was gently rubbed by a clean finger to remove physically adsorbed crystals on the hydrogen-bonded layer of silicalite-1 crystals (Figure 2c). II.5. Detection of Binding Strength between Zeolite Crystals and Glass Plate Supported Polymeric Thin Films. With the use of an ultrasonic bath equipped with two ultrasound generators (40 kHz, 100 W each), the silicalite-1 monolayer on either the bare glass plate or the glass plate supported polymeric thin film was sonicated in DI water for 1, 5, 10, 20, and 30 min to test the survival ability for zeolite crystals to be detached from the substrate surface. The binding strength between zeolite crystals and the substrate surface could be qualitatively obtained by observing the detachment percentage of zeolite crystals from the substrate surface after sonication. II.6. Instrumentation. Scanning electron microscopy (SEM) images were recorded on a Philips XL30ESEM at an acceleration voltage of 20 kV. X-ray diffraction (XRD) measurements were performed on a Rigaku D/max 2500v/pc diffractometer using Cu KR radiation. Digital camera images were taken with a Samsung S600 camera under fluorescent lamp.

III. Results and Discussion The SEM images of silicalite-1 monolayers on the glass plate supported PEO films are given in Figure 3. As shown in Figure 3a, there were some physically adsorbed crystals on top of the chemically bonded monolayer of silicalite-1 crystals after the first step of manual assembly. The second step of manual assembly by a clean finger was essential for removal of the physically adhered crystals on top of the monolayer for silicalite-1 crystals of different sizes shown in Figure 3, parts b and c. According to available results, when the reflux and stirring or ultrasound-aided assembly was adopted, the parasitic crystals were commonly kept on their cross-shaped mother crystals after the b-oriented silicalite-1 monolayer was formed.10-13 However, almost all the parasitic crystals were dislodged from their mother crystals when the silicalite-1 monolayer on the glass plate was fabricated via the manual assembly.12 As shown in the upper insets in Figure 3b, the removal of parasitic crystals from crossshaped mother crystals was also observed for the manual assembly of silicalite-1 crystals on polymeric thin films. Similarly, parasitic crystals could be broken from their mother crystals and were further assembled onto the polymeric thin film during rubbing (the upper insets, Figure 3c).

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The XRD pattern of the manually assembled silicalite-1 monolayer as shown in Figure 3d revealed the specific reflections at 2θ ) 8.9°, 17.8°, 26.9°, 36.1°, and 45.6° in the range between 5° and 50° with relative intensities of 55 763, 19 790, 11 526, 4842, and 18 365 that corresponded to (020), (040), (060), (080), and (0100) planes, respectively. This clearly indicated that almost all the silicalite-1 crystals were oriented with their b-axes perpendicular to the polymeric surface. The digital camera photographs of the glass plate and the silicalite-1 monolayer on the glass plate supported PEO film sized 19 mm × 25 mm are given in Figure 3, parts e and f, respectively. The size of the monolayer of zeolite crystals could be easily extended by using the manual assembly, which would be essential for scaling up with the monolayer preparation. It should be noted that the morphology, DOC, and DCP of the resulting silicalite-1 monolayer on the glass plate supported polymeric thin film was almost the same for PEO, PVA, chitosan, and PMMA. The sonication-induced detachment of zeolite crystals from the substrate surface was applied to test the binding strength between silicalite-1 crystals and the substrate surface. According to literature reports, the predominant detachment of zeolite crystals from the substrate surface usually happened within the first 5 min.10,13 The multilayered silicalite-1 film either on the glass plate supported chitosan thin film or on the bare glass plate could be obtained after the first step of manual assembly (Figure 4, parts a and b). By sonication in the ultrasonic bath for 5 min, the multilayered silicalite-1 film on the glass plate supported chitosan thin film turned from opaque white to uniform translucence (Figure 4c), indicating that a b-oriented silicalite-1 monolayer with satisfactory DOC and DCP was kept on the substrate surface (inset, Figure 4c), whereas the multilayered silicalite-1 film on the bare glass plate became unevenly transparent (Figure 4d), showing that most silicalite-1 crystals on the glass plate were detached including the zeolite crystals that had been attached on the surface of the glass plate (inset, Figure 4d). In addition, the binding strength was checked by sonicating the silicalite-1 monolayers in the ultrasonic bath for 1, 5, 10, 20, and 30 min. The experimental results shown in Figure S1 (Supporting Information) indicated that the use of polymeric layers made the binding strength between silicalite-1 crystals and the substrate surface much stronger. After being sonicated for 20 min, the silicalite-1 monolayer on the bare glass plate disappeared, whereas most of the silicalite-1 monolayer was still on the glass plate supported polymeric film. The silicalite-1 monolayers prepared by using different rubbing pressures demonstrated almost the same binding strength (Figure S2, Supporting Information). Similarly, the time of rubbing does not affect the binding strength between silicalite-1 crystals and the substrate surface (data not shown). Therefore, it can be concluded that the introduction of the polymeric thin film between zeolite crystals and the glass plate significantly increases the binding strength. Because the functional groups in polymeric units can react with the silicon-bound hydroxyl group on the surface of zeolite crystals and the glass plate to form hydrogen bonds, the better binding strength can be expected. Inspired by the finding that zeolite monolayers could be manually assembled onto the glass plate supported PEO, PVA, chitosan, and PMMA surfaces, we extended the manual assembly of zeolite crystals to a lens in a pair of spectacles and a compact disc (CD). The lens and the CD were, respectively, made of PMMA and polycarbonate, both of which were commercially available in the market.

Assembly of Oriented Zeolite on Polymeric Surfaces

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Figure 3. (a-c) SEM images of silicalite-1 monolayers on glass plate supported PEO thin films by using the manual assembly. (d) The corresponding X-ray diffraction (XRD) pattern for the silicalite-1 monolayer in (c), where the inset is the XRD pattern of silicalite-1 powders. (e and f) Digital camera photographs of the glass plate supported PEO film sized 19 mm × 25 mm and the silicalite-1 monolayer on the glass plate supported PEO film.

The assembly procedure shown in Figure 2 was used with gentle rubbing. In the manual assembly, due to the adhesion of zeolite crystals onto the substrate surface the transparent Plexiglas plates turned opaque after the first step of assembly. The opaque Plexiglas plates then turned semitransparent after the second step of assembly, on which only closely packed and oriented zeolite monolayer was attached, just as what is demonstrated in Figure 5, parts a and b. The rubbing time required for the monolayer assembly on the CD was increased from 30 s to 1 min owing to the much larger surface area (Figure 5b). The structure of hydrogen bonding between zeolite crystals and the polycarbonate surface is given in Figure 5c, while the structure of hydrogen bonding between zeolite crystals and the PMMA surface was already shown in Figure 1d. Therefore, the hydrogen bonding would be formed between hydroxyl groups on the surface of zeolite crystals and ether linkages or carbonyl groups on the Plexiglas surface in the manual assembly as given in Figure 5d. In addition to the zeolite-filled PMMA membrane,22 the zeolitefilled polycarbonate membrane also possessed higher gas separation performance compared with that of the pure polycarbonate membrane.27 On the other hand, Plexiglas materials have a number of advantages over the conventional glass. The availability of Plexiglas-supported zeolite monolayers with

uniform orientation, high DOC, and close packing will open a new gate for diverse applications of zeolite thin films and membranes. On the basis of the established method above, preferentially oriented zeolite-polymer composite films and membranes can be easily fabricated using the layer-by-layer technique. Take the layered zeolite-chitosan composite film as an example. By repeating the preparation of the chitosan thin film and the manual assembly of silicalite-1 crystals on top of the monolayer of silicalite-1 crystals on the glass plate supported chitosan thin film, the zeolite-chitosan film of silicalite-1/chitosan/silicalite1/chitosan/glass plate was obtained. The XRD data in Figure 6 indicated that silicalite-1 crystals in the zeolite-polymer composite film were uniformly b-oriented and closely packed with each other by contact of side faces (see the inset).

IV. Conclusions We have manually assembled oriented zeolite monolayers on glass plate supported polymeric thin films (including PEO, PVA, chitosan, and PMMA) for the first time. The polymeric thin film serves as the intermediate linker between zeolite crystals and the glass plate, leading to much enhanced binding strength between zeolite crystals and the substrate surface. The zeolite monolayer

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Figure 4. Digital camera images of the zeolite layer on both the glass plate supported chitosan film (a) and the bare glass plate (b) and the zeolite layer left on both the glass plate supported chitosan film (c) and the bare glass plate (d) after sonication for 5 min.

on the glass plate supported polymeric film prepared using different rubbing pressure and time demonstrate almost the same binding strength. On the basis of the finding that oriented zeolite monolayers can be manually assembled onto PEO, PVA, chitosan, and PMMA thin films, we have further applied the manual assembly to manufacturing zeolite monolayers on commercially available Plexiglas surfaces (including a lens of PMMA and a CD of polycarbonate). Both the in situ growth under hydrothermal conditions and the postsynthetic assembly of zeolite crystals helped with sonication or reflux and stirring cannot be applied to fabricate the zeolite monolayer when a Plexiglas material is used as the substrate due to its low melting point and solubility in most organic solvents. However, the manual assembly method established in this study provides a feasible way to manufacture zeolite monolayers on Plexiglas. It should be an effective means for fabrication of zeolite-polymer composite films and membranes by way of the layer-by-layer technique. Acknowledgment. This work is supported by the National Natural Science Foundation of China (Nos. 20476074, 20636030, and 20776100), the National Basic Research Program of China (No. 2003CB615702), and the Program of Introducing Talents of Discipline to Universities, China (No. B06006). Supporting Information Available: The experimental details on binding strength between silicalite-1 crystals and the surface of various substrates including bare glass plate and glass plate supported polymeric

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Figure 5. Digital camera photographs of the PMMA lens and the lens after being manually assembled with zeolite monolayer (a) and the polycarbonate CD and the CD after being manually assembled with zeolite monolayer (b). (c) The structure of hydrogen bonding between zeolite crystals and the polycarbonate surface. (d) The binding mechanism between zeolite crystals and the PMMA or polycarbonate surface.

Figure 6. XRD pattern of the zeolite-chitosan composite membrane (silicalite-1/chitosan/silicalites/chitosan/glass plate), where the inset is the corresponding cross-sectional SEM image at magnification of 10 000×. films. This material is available free of charge via the Internet at http://pubs.acs.org. LA801879X (27) Sen, D.; Kalipcilar, H.; Yilmaz, L. Desalination 2006, 200, 222–224.