Oriented Molecular Sieve Membranes by Heteroepitaxial Growth

Jeong, Hae‐Kwon; Krohn, John; Sujaoti, Khristina; Tsapatsis, Michael

doi:10.1021/ja020947w

Cited by 92 publications

(67 citation statements)

References 28 publications

(78 reference statements)

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“…The high-quality ETS-10 crystals prepared could also be used as membranes for molecular separation. [34] Received: April 16, 2007 Revised: May 13,2007 Published online: July 2, 2007 . Keywords: electronic properties · molecular wires · zeolites …”

Section: Communicationsmentioning

confidence: 99%

Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10

Jeong¹,

Lee²,

Yoon³

2007

Angew Chem Int Ed

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Efforts have been directed at the synthesis and characterization of 1D quantum-confined semiconductor materials, since they have great potential to be widely used as building blocks for nanoscale electronic devices and other novel applications. [1][2][3][4][5][6][7][8][9][10][11] Of the 1D quantum-confined semiconductor materials, molecular wires are the thinnest. [1][2][3][4][5] However, examples of molecular wires are still very rare, and there is no method of synthesizing them in uniform diameters and controlled lengths. Accordingly, the relationship between the wire length (l) and the band-gap energy (E g ) in the quantum confinement region has not yet been determined for molecular wires, despite the fact that this relationship is crucial for the elucidation of the properties of the wires.Zeolites are crystalline inorganic materials having nanometer-sized pores and channels with uniform shapes and sizes. These materials are widely used as catalysts, catalyst supports, adsorbents, ion-exchangers, and molecular sieves. ETS-10 (Na 2 TiSi 5 O 13 ) is a unique titanosilicate zeolite that contains regularly spaced 1D TiO [12-15] Each TiO 3 2À wire is surrounded by nanoporous silica with a pore size of 8 5 2 . In highly crystalline ETS-10, the lengths of the TiO 3 2À molecular wires are greater than 25 nm. [16,17] Hence, it would be difficult to determine the l-E g relationship in the quantum confinement region unless the Bohr radius of the exciton in the molecular wire were to exceed 25 nm, since the quantum confinement effect (E g increases with decreasing l) is observed only in the region in which l is smaller than the exciton Bohr radius.The diameter of the TiO 3 2À molecular wire in ETS-10 is comparable to that of a single-wall carbon nanotube (d = 0.7 nm).[2] However, from the point of view of titanates, an important class of inorganic materials widely used in industry, the TiO 3 2À molecular wire is ultimately the thinnest wire. Furthermore, no other molecular wires or nanorods have been produced in the form of a superlattice embedded in a chemically inert large-band-gap medium. ETS-10 can be produced in large quantities at low cost by hydrothermal synthesis.[12-15] Therefore, ETS-10 provides an unprecedented opportunity to systematically study the l-E g relationship of the titanate molecular wire and to explore the applications of molecular-wire superlattices as advanced materials.Zecchina and co-workers, however, assumed that the band gap of the TiO 3 2À wire in ETS-10 is independent of the length of the wire when the length is greater than 25 nm. [16,17] This assumption has been widely accepted by the community during the last decade. [18,19] The verification of its validity has not been possible owing to the inability to synthesize highquality ETS-10 crystals of different sizes.[20] The standard approach to vary the size of a zeolite crystal is to vary the reaction time and temperature. Unfortunately, this standard approach has not worked for ETS-10. For instance, Southon and Howe demonstrated that, for a...

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Section: Communicationsmentioning

confidence: 99%

Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10

Jeong¹,

Lee²,

Yoon³

2007

Angew Chem Int Ed

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“…Epitaxial growth of zeolite X on zeolite A was observed on large crystals synthesized by a modified Charnell's method. [15] Oriented overgrowth of cancrinite on large sodalite crystals was described by Okubo et al [16] Tsapatsis and co-workers [17] used the heteroepitaxial growth of ETS-10 on ETS-4 to synthesize oriented-molecular-sieve membranes. This type of overgrowth usually takes place on a specific crystal face and cannot be employed for complete overgrowth of the core crystal.…”

Section: Full Papermentioning

confidence: 99%

Core–Shell Zeolite Microcomposites

Bouizi

Dı́az

Rouleau

et al. 2005

Adv Funct Materials

122

105

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Core–shell zeolite composites possessing a core and a shell of different zeolite structure types have been synthesized. A characteristic feature of the obtained composites is the relatively large single‐crystal core and the very thin polycrystalline shell. The incompatibility between the core crystals and the zeolite precursor mixture yielding the shell layer has been circumvented by the adsorption of nanoseeds on the core surface, which induced the crystallization of the shell. The pretreated core crystals are subsequently subjected to a continuous growth in a zeolite precursor mixture. The feasibility of this synthetic approach has been exemplified by the preparation of core–shell β‐zeolite–silicalite‐1 composites. The synthesized composites have been characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, and scanning electron microscopy. The integrity of the shell layer has been tested via N2‐adsorption measurements on materials comprising a calcined core (β‐zeolite) and a non‐calcined tetrapropylammonium (TPA)‐containing shell, the latter being non‐permeable for the N2 molecules. These measurements have shown that 86 % of the β‐zeolite crystals are covered with a defect‐free TPA–silicalite‐1 shell after a single hydrothermal treatment, while after three consecutive crystallization steps this value reaches 99 %. The shell integrity of the calcined composite has been studied by the adsorption of butane, toluene, and 1,3,5‐trimethylbenzene, which confirmed the superior performance of the triple‐shell composites.

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“…These target different applications, such as ion exchange [20][21][22][23][24], adsorption [25][26][27][28], membrane separation [29][30][31][32], pillaring templating [33,34] and oxidation catalysis [35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

et al. 2018

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An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential 'matrices' according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with tert-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts. Abbreviation

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Oriented Molecular Sieve Membranes by Heteroepitaxial Growth

Abstract: Heteroepitaxial growth of titanosilicates (ETS-10 and ETS-4) is reported. Using this heteroepitaxial growth, oriented ETS-10/-4 membranes have been fabricated, demonstrating a novel way to achieve preferred orientation of molecular sieve films.

Cited by 92 publications

References 28 publications

Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10

Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10

Core–Shell Zeolite Microcomposites

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

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Oriented Molecular Sieve Membranes by Heteroepitaxial Growth

Abstract: Heteroepitaxial growth of titanosilicates (ETS-10 and ETS-4) is reported. Using this heteroepitaxial growth, oriented ETS-10/-4 membranes have been fabricated, demonstrating a novel way to achieve preferred orientation of molecular sieve films.

Cited by 92 publications

References 28 publications

Length‐Dependent Band‐Gap Shift of TiO32− Molecular Wires Embedded in Zeolite ETS‐10

Length‐Dependent Band‐Gap Shift of TiO32− Molecular Wires Embedded in Zeolite ETS‐10

Core–Shell Zeolite Microcomposites

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

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Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10

Length‐Dependent Band‐Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS‐10