Preparation of Hollow Zeolite Spheres and Three‐Dimensionally Ordered Macroporous Zeolite Monoliths with Functionalized Interiors

Dong, Angang; Ren, Nan; Yang, Wuli; Wang, Y.; Zhang, Yahong; Wang, Deren; Hu, Jing; Gao, Zi; Tang, Yongliang

doi:10.1002/adfm.200304405

Cited by 102 publications

(81 citation statements)

References 26 publications

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“…The presented approach provides a thus-far unused method to tailor the fabrication of hollow zeolite crystals, offering clear advantages to other methodologies pursuing hollow zeolite entities. 9,10 Our results are of fundamental interest in materials science and may open auspicious uses of alkaline-treated zoned ZSM-5 zeolites.…”

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confidence: 83%

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

et al. 2005

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Zeolites are crystalline aluminosilicates that possess an exceptional combination of properties such as high thermal stability, Brønsted acidity, and microporosity. Accordingly, these materials are frequently practiced in industrial processes, for example, fluid catalytic cracking (Y), cumene production (mordenite), and toluene disproportionation and xylene isomerization .The presence of regular micropores of molecular dimensions is responsible for the zeolites' unequaled shape selectivity in catalytic conversions and separations, but this feature also poses diffusional limitations due to the restricted transport of molecules to and from the active sites. As a consequence, generation of mesoporosity in microporous crystals is attracting significant research interest. 1,2 The created mesopores facilitate physical transport and should lead to a more effective use of these materials. Desilication, that is, extraction of framework Si, is an efficient methodology to create intracrystalline mesoporosity in MFI-type zeolites. 3,4 The Si extraction and related mesopore formation is controlled by framework Al, and an optimal bulk Si/Al ratio of 25-50 has been identified. 5 A high framework Al concentration prevents Si extraction, while a low Al concentration leads to excessive extraction and formation of large pores. However, how the porosity is distributed throughout the crystals and the effect of crystal size is practically ignored. This information is indispensable to rationally devise potential applications of alkaline-treated zeolites.The occurrence of Al zoning, that is, an Al-rich external surface as compared to the bulk aluminum concentration, is well-known in large ZSM-5 crystals. 6,7 Accordingly, it can be anticipated that this Al gradient will affect the Si extraction throughout the zeolite particle. Dessau et al. 8 have observed the nonuniform dissolution of large ZSM-5 crystals (5-10 µm) upon prolonged treatment at high concentrations of alkaline solution. This was speculatively attributed to the nonuniform concentration of Al in the crystals. However, a systematic study on the impact of Al gradients and the effect of crystal size to tailor the porosity development under optimized treatment conditions has not yet been accomplished.Here we show that by controlled desilication of both large and small ZSM-5 crystals we have been able to address and make use of the impact of Al-zoning on the mesoporosity development. The presented approach provides a thus-far unused method to tailor the fabrication of hollow zeolite crystals, offering clear advantages to other methodologies pursuing hollow zeolite entities. 9,10 Our results are of fundamental interest in materials science and may open auspicious uses of alkaline-treated zoned ZSM-5 zeolites.Two procedures were applied to synthesize ZSM-5 zeolite with small (SZ) and large (LZ) crystals in the optimal bulk Si/Al range of 25-50. The alkaline treatment was performed as described in the Supporting Information. The chemical composition and textural properties of the n...

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confidence: 83%

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

et al. 2005

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“…This material was deposited on a carbon-coated Cu grid and analyzed by TEM. [8] As shown in Figure 3, CdSe nanoparticles are found in the pores of TNPS in a well-dispersed fashion. The yield of encapsulation estimated from the TEM image was 60 %.…”

Section: Npsmentioning

confidence: 97%

Preparation of Functional Nanoporous Silica for Encapsulation of CdSe Nanoparticles

Emrick²,

Chang³

2005

Advanced Materials

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Nanoporous silica materials prepared from surfactant templates contain pore structures that are of interest for catalysis, separations, and molecular imprinting and engineering.[1] Suitable methods for effective pore functionalization will provide considerably more diverse application opportunities than are available at present. Two methods have been reported for the preparation of functionalized mesoporous silica: 1) grafting of a functionalized monolayer in the pores; and 2) co-condensation of functional alkoxysilanes (i.e., [R¢(RO) 3 Si]) with the tetraalkoxysilanes used in the conventional preparation of nanoporous silica.[2] While some recent advances are producing favorable results, considerable challenges remain with regard to the controlled introduction of functionality into the pores. In addition, as only a limited number of functionalized organoalkoxysilanes are commercially available, new synthetic methods designed to tailor the functionality of nanoporous silica will open new opportunities in functional-composite materials science.Here we report a new methodology for functionalizing nanoporous silica using an amphiphilic organotrialkoxysilane designed to integrate an affinity for nanoparticles into the nanoporous silica structure. The chosen silane contains a thermally labile urethane moiety, which upon heating dissociates to produce an isocyanate functionality tethered to the silica structure.[3] The organotrialkoxysilane used in this work is amphiphilic, and is thus expected to act as a surfactant in the gelation with tetraethoxysilane, forming a micellar structure where the hydrophobic portion is located inside the micelle. The presence of the isocyanate moieties in the nanoporous structure can be exploited in numerous ways; for example, through nucleophilic chemistry for structural and chemical modification. Described below is a method for producing thiol-functionalized nanoporous silica for encapsulation of cadmium selenide nanoparticles (quantum dots). The impressive optical and electronic properties of CdSe nanoparticles make them attractive for integration into nanoporous polymer thin films [4] and silica-based materials, with potential applications in nanoparticle-based devices such as sensors, active displays, light-emitting diodes, etc.[5]Tetra(ethylene glycol) nonyl ether (TEGNE)-phenol-Si, the key molecule for this study, was prepared as shown in Scheme 1. This amphiphilic molecule consists of a nonyl aliphatic chain, a tetra(ethylene glycol) spacer, and a reactive triethoxysilyl group. In the synthesis, 1-bromononane was first substituted with tetra(ethylene glycol) in tetrahydrofuran (THF) at 75 C to afford TEGNE. TEGNE was tosylated in dichloromethane, then end-capped with hydroquinone in THF to give a chain-end phenol. Finally, TEGNE-phenol was functionalized with 3-(triethoxysilyl)propyl isocyanate in THF in the presence of dibutyltin dilaurate to give the urethane-linked TEGNE-phenol-Si.Nanoporous silica (NPS) materials were fabricated by sol± gel chemistry, by co-condensation of a ...

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“…[10,11] Zeolite L is a crystalline aluminosilicate with hexagonal symmetry. [12,13] Its anionic framework and the positions of the charge-compensating cations are illustrated in Figures 1a-d.…”

Section: Full Papermentioning

confidence: 99%

Energy Collection, Transport, and Trapping by a Supramolecular Organization of Dyes in Hexagonal Zeolite Nanocrystals

Minkowski

Pansu

Takano

et al. 2005

Adv Funct Materials

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The incorporation of guest molecules into the cavities of molecular sieves leads to a large variety of highly interesting materials. Zeolite L—an aluminosilicate with one‐dimensional channels of open diameter 7.1 Å—is a very versatile material for building highly organized host–guest systems. We present materials where organic dye molecules have been incorporated into the channels of zeolite L by means of diffusion, to build artificial photonic antenna systems. The channel entrance can be plugged by adding closure molecules that then connect the guest molecules inside with materials or molecules outside of the zeolite channels, since they can act as extensions of the interior of the zeolite crystal. The photophysical processes taking place in such dye‐loaded zeolite L antennae can be studied either on single‐micrometer‐ or submicrometer‐sized crystals or on crystals dispersed in a solvent or coated as thin layers on a support. The energy‐transfer process occurring is of the Förster‐type, and its transfer rate can be tuned by separating the donor dyes and the acceptor dyes locally by varying amounts of spacer molecules. The distribution of the dye molecules and empty sites within a zeolite crystal has been modeled by means of a Monte Carlo simulation. The Förster energy migration and transfer steps are described as a random walk.

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Preparation of Hollow Zeolite Spheres and Three‐Dimensionally Ordered Macroporous Zeolite Monoliths with Functionalized Interiors

Cited by 102 publications

References 26 publications

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

Creation of Hollow Zeolite Architectures by Controlled Desilication of Al-Zoned ZSM-5 Crystals

Preparation of Functional Nanoporous Silica for Encapsulation of CdSe Nanoparticles

Energy Collection, Transport, and Trapping by a Supramolecular Organization of Dyes in Hexagonal Zeolite Nanocrystals

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