Zeolite-Y nanocrystals

High-quality molecular sieve nanocrystals can be prepared by hydrothermal crystallization in the initial reaction gel system. The key point is the strict control of the reaction conditions. In 2003, Yan and colleagues[126] investigated the influence of [TMA+] concentration and anion [Br ] and [OH-] concentrations on the formation and yield of zeolite Y nanocrystals in the 1.00 A1203 4.35 Si02 2.4 (TMA)20(2 OH-) (1 1.2) (TMA)20(2 Br ) 0.048, a20 249.0 H20 system at 100°C. When TMABr was added to the reaction system as a second SDA, the nanocrystal size decreased (generally stable under 40 nm), and a yield improvement of zeolite Y could be observed due to the increase of nucleation rate. Furthermore, the effect of the TMABr/TMAOH ratio in the reaction system on the nanocrystal sizes and yield of as-made product was also studied, and, based on this, zeolite Y nanocrystals with controllable particle sizes of 32 120 nm were synthesized. 

B. A. Holmberg, H. Wang, J.M. Norbeck, and Y. Yan, Controlling Size and Yield of Zeolite Y Nanocrystals Using Tetramethylammonium Bromide. Microporous Mesoporous Mater, 2003, 59, 13-28. 

Jiang, Y.-X., Si, D., Chen, S.-P., and Sun. S.-G. 2006. Self-assembly film of zeolite y nanocrystals loading palladium on an au electrode for electrochemical applications. Electroanalysis 18, 1173-1178. 

Tricoli and Nanetti [17] prepared a novel zeolite-Naflon composite manbrane by embedding zeolite fillers in Nafion. The zeolites used in this study were chabazite and clinoptilolite. The presence of zeolites in the membranes caused notable changes in conductivity, methanol permeability, and selectivity with respect to pure Nafion. In another interesting study, Holmberg et al. synthesized and characterized zeolite-Y nanocrystals for Nafion-zeolite-Y composite proton exchange membranes. The composite membranes were found to be more hydrophilic and proton conductive than the base-unmodified membranes at high temperatures [18]. 

B. Holmberg, H. Wang, J. Norbeck and Y. Yan, Synthesis and characterization of Zeolite Y Nanocrystals for Nafion Zeolite Y composite proton exchange membranes, AIChE, Spring National Meeting, New Orleans, Los Angeles, USA, March 10-14 (2002). 

Figure 24. Photolytic charge separation with nanocrystalline zeolite (a) correlation of percentage crystallinity of nanocrystals (shown in parentheses) with PVS" production (b) comparison of the rate of PVS " radical generation for nanocrystalline zeolite X and micronsized zeolite Y.

Just as some metal complexes can be incorporated during synthesis, functional organic molecules can also be entrained in this way. In one such example, Mintova et al. incorporated the photosensitive 2-(2 -hydroxyphenol)ben-zothiazole in nanocrystals of zeolite Y. Such approaches aim toward the development of nanoscale devices for sensing, LTV filtering and molecular switching. 

Fig. 5.2 (a) Typical absorption spectrum of CdSe nanocrystal QDs (Data from Jorge et al. 2007. Published by MDPI. Open access.), (b) Photoluminescence spectra of ZnS nanoparticles and ZnS nanoclusters in zeolite Y (X =280 nm) (Reprinted with permission from Chen et al. 1997, Copyright 1997 American Institute of Physics)... 

The zeolite nanocrystals have attracted the considerable attention of many researchers [1-5]. The syntheses of several types of zeolites with different nanometer sizes, such as silicalite-1, ZSM-5, A-type and Y-type, have been reported. Recently, micellar solutions or surfactant-containing solutions have been used for the preparation of zeolite nanoerystals [4,5], We have also successMIy prepared silicalite nanoerystals via hydrothermal synthesis using surfactants. In this study, we demonstrate a method for preparing mono-dispersed silicalite nanoerystals in a solution consisting of surfiictants, organic solvents and water. 

Wang, H., Holmberg, B.A., and Yan, Y. (2002) Homogeneous polymer-zeolite nanocomposite membranes by incorporating dispersible template-removed zeolite nanocrystals. /. Mater. Chem.,... 

H. Wang, B.A. Holmberg, and Y. Yan, Synthesis of Template-free Zeolite Nanocrystals by Using In Situ Thermoreversible Polymer Hydrogels. J. Am. Chem. Soc., 2003, 125, 9928-9929. 

L. Huang, Z. Wang, H. Wang, J. Sun, Q. Li, D. Zhao, and Y. Yan, Hierarchical Zeolite Structures with Designed Shape by Gel-casting of Colloidal Nanocrystal Suspensions. Chem. Commun., 2001, 1364—1365. 

Wang, Y.J. Tang, Y. Wang, X.D. Dong, A.G. Shan, W. Gao, Z. Fabrication of hierarchically structured zeolites through layer-by-layer assembly of zeolite nanocrystals on diatom templates. Chem. Lett. 2001, 11, 1118-1119. 

Wang, H. Huang, L. Wang, Z. Mitra, A. Yan, Y. Hierarchical zeolite structures with designed shapes by gelcasting of colloidal nanocrystal suspensions. Chem. Comm. 2001, 1364-1365. 

Huang L, Wang Z, Wang H, Sun J, Li Q, Zhao D, Yan Y. Hierarchical porous structures by using zeolite nanocrystals as building blocks. Micropor Mesopor Mater 2001 48(1-3) 73-78. 

Via confined space synthesis with porous carbon as inert support material, synthesis of nanosized zeohte crystals of several topologies is possible and their recovery via controlled pyrolysis of the carbon becomes feasible [155]. In the 45-nm carbon black pores nanocrystals of ZSM-5 (MFI) of about the same size were obtained. The method is of general utiUty, as it seems possible to make nanosized zeohtes of Beta zeolite X and Y and L (LTL), which can be easily washed, ion exchanged and finally isolated via calcination [156]. 

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