Zeolites nanocrystal

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. 

In order to prepare ZSM-5 zeolite nanocrystals, an A1 source of aluminium isopropoxide was added into solution A, and hydrothermal synthesis of the solution A containing Si and A1 sources was carried out in an 0-15/cyclohexane solution at 120 degree C for 50 h. Figures 4 show ac-NHj-TPD spectra and a SEM photograph of the ZSM-5 zeolite nanocrystals. Nanocrystals with a diameter of approximately 150 nm were observed, and the NH3-TPD spectrum showed desorption of NHj above 600 K, indicating that the nanocrystals possessed strong acid sites. 

Mono-dispersed silicalite and ZSM-5 type zeolite nanocrystals with a diameter of 80-120 nm were successfully prepared in a surfactant-oil-water solution. The ionicity of the surfactants used in the preparation affected the crystallinity and structure of the silicalite crystals, and silicalite nanocrystals could he obtained when using a nonionic sur ctant. By adding an A1 source into the synthetic solution, ZSM-5 type zeolite nanocrystals with strong acid sites could be obtained. 

A novel zeolite material possessing an inherent hierarchical structure with good mechanical and chemical strength has been prepared by the LbL assembly of zeolite nanocrystals and PDDA on the diatomite substrates [129]. The diatomite used has a disk-like morphology (Figure 7.12A) and exhibits abundant and uniform macropores (about 300-500 nm) in the diatomite plates (Figure 7.12B). The zeolite-diatomite (ZD)... 

Fig. 7.12 SEM images ofthe diatomite substrate through sequential assembly of positively-at low (A) and high (B) magnification. The di- charged PDDA and negatively-charged zeolite atomite has a disk-like shape about 1.2 pm in nanocrystals (C). The inset in (C) shows an thickness and 20-40 pm in diameterwith a nearly enlarged view of the nanoparticle-modified sur-regular array of submicrometer-sized pores face. (Reprinted from [129] with permission of (about 300-500 nm). SEM images of diatomite Wiley-VCH.) coated with three layers of zeolite ( nanocrystals...

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

For a better understanding of the consequences of this relation, it is useful to discuss an example more explicitly. We choose the ion-exchange equilibrium [Fq. (3)]. The total concentration of dye molecules inside an ensemble of zeolite nanocrystals dispersed in a solvent [Dzltou expressed with respect to the total volume under consideration, is... 

However, in the post-treatment approach, the sur ce area decreases quickly with the formation of zeolite phase. The mesoporous material eventually becomes an aggregate of zeolite nanocrystals. The zeolite seed hydrothermal amroach, on the other han produces materials with only indirect hints of zeolitic nature. Neither the FTIR nor Ae XRD spectrum showed strong evidence for the formation of zeolite structure. 

Finally, zeolite nanoparticles have been used as building blocks to construct hierarchical self-standing porous stmctures. For example, multilayers of colloidal zeolite crystals have been coated on polystyrene beads with a size of less than 10 p,m [271,272]. Also, silicalite-1 membranes with a thickness ranging from 20 to several millimeters and controlled mesoporosity [273] have been synthesized by the self-assembly of zeolite nanocrystals followed by high-pressure compression and controlled secondary crystal growth via microwave heating. These structures could be useful for separation and catalysis applications. 

LBL self-assembly of zeolite nanocrystals on the surface of polystyrene beads. 

Patterned zeolite films have been investigated for possible optical, magnetic, and electronic applications. Zeolite nanocrystals have been used as building blocks for patterned films.[140] Silicalite-1 nanocrystals were synthesized hydrothermally and the resulting crystals, after redispersion in ethanol, were deposited onto a smooth surface, such as a silicon wafer. A polydimethylsilane (PDMS) stamp was applied with adequate... 

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 Porous Structures by Using Zeolite Nanocrystals as Building Blocks. Microporous Mesoporous Mater, 2001, 48, 73-78. 

Zeolite nanocrystals have been demonstrated to be versatile building blocks for constructing hierarchical porous structures. " The use of nanoparticles as building blocks allows mild processing conditions... 

Fig. 9 Zeolite structures constructed by using zeolite nanocrystals as building blocks.. (From Refs. " " l)...

Another interesting application is microreactors. Zeolite adsorbents and catalysts have been an important part for the conventional reaction-separation system. As the efforts to miniaturize the reactors evolve, using zeolite nanocrystals as building blocks could be an ideal way to introduce zeolites into these microreactor systems. 

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. 

Siliceous MEL-type (silicalite-2) zeolite nanocrystals with average particle size of less than 100 nm have been investigated by and Si MAS NMR. ... 

FIGURE 4.10 Schematics of the assembly of mercapto-trimethoxysilanes and zeolite nanocrystals on gold electrodes. 

Zeolites are widely used as acid catalysts, especially in the petrochemical industry. Zeolites have several attractive properties such as high surface area, adjustable pore size, hydrophilicity, acidity, and high thermal and chemical stability. In order to fully benefit from the unique sorption and shape-selectivity effects in zeolite micropores in absence of diffusion limitation, the diffusion path length inside the zeolite particle should be very short, such as, e.g., in zeolite nanocrystals. An advantageous pore architecture for catalytic conversion consists of short micropores connected by meso- or macropore network [1]. Reported mesoporous materials obtained from zeolite precursor units as building blocks present a better thermal and hydrothermal stability but also a higher acidity when compared with amorphous mesoporous analogues [2-6]. Alternative approaches to introduce microporosity in walls of mesoporous materials are zeolitization of the walls under hydrothermal conditions and zeolite synthesis in the presence of carbon nanoparticles as templates to create mesopores inside the zeolite bodies [7,8]. 

A new approach for the synthesis of mesostructured zeolitic materials (namely UL-TS-1 and UL-ZSM-5) is reported. The materials were obtained in the solid state by heating TPAOH-impregnated mesoporous materials for several days. Various techniques including XRD, N2 adsorption, UV-visible, FTIR, TEM and Si MAS NMR were used to monitor the physicochemical properties of these materials as a function of crystallization time. The increase in the percentage of crystallinity is correlated with the corresponding variations in micropore and mesopore volumes, BET and BJH surface areas. The results indicate that the mesopore walls consist of zeolite nanocrystals. Depending on crystallization time, a range of materials from totally amorphous up to 80% crystalline is observed, while some of mesopores are preserved. 

Macroporous zeolite Beta structures were prepared by a self-assembly of monodisperse polystyrene spheres and zeolite nanocrystals followed by a hydrothermal treatment. The characteristic features of the self-assembled and hydrothermally treated macroporous structures were studied by XRD, FTIR, SEM, TG/DTA and nitrogen adsorption measurements. The hydrothermal treatment of the self-assembled composites led to intergrowth and closing of the mesopores between the nanocrystals building the walls of macropores. The mechanical properties of the macroporous zeolite structures were substantially improved by the secondary growth of the zeolite crystals. 

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