Quantum-size effects in the titanosilicate molecular sieve

Borello, E.; Lamberti, Carlo; Bordiga, Silvia; Zecchina, Adriano; Areán, C. Otero

doi:10.1063/1.120060

Cited by 102 publications

(127 citation statements)

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“…The spectrum of this sample ( Fig. 7(a)) shows a sharply defined absorption edge at about 4.0 eV, in good agreement with the calculated band gap [28] and previously reported spectra [27,28]. Also shown is the spectrum of a commercially prepared sample of ETS-10 supplied by Engelhard Corporation.…”

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confidence: 80%

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Nanosize effects in titania based photocatalyst materials

Hanley

Krisnandi

Eldewik

et al. 2001

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Abstract.A review is given of recent work in the authors' laboratory on the characterization of different forms of nanostructured titania. It is shown that nanocrystalline anatase powders and nanocrystalline anatase thin films differ significantly in their optical properties, due primarily to differences in sintering behaviour on drying. It is argued that the electronic properties of these systems are determined by surface phenomena rather than quantum size effects. The novel titanosilicate zeolite ETS-IO which contains one dimensional "quantum wires" of titania provides an alternative system for studying quantum size effects which has considerable potential for photocatalysis.

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confidence: 80%

“…Attention has been drawn recently to the unusual optical properties shown by a novel titanosilicate zeolite structure ETS-10 (Na2TiSi~O13) in which one dimensional chains of TiO6 octahedra imbedded in a microporous siliceous network exhibit quantum size effects [27,28]. The structure of ETS-10 is represented in Fig.…”

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confidence: 99%

Nanosize effects in titania based photocatalyst materials

Hanley

Krisnandi

Eldewik

et al. 2001

Ionics

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“…The m z value may be much smaller if the l value of the TiO 3 2À molecular wire in E-0.3 is longer than 50 nm, which is also possible. If the l value for E-0.3 is assumed to be as small as 25 nm, as estimated by others, [16][17][18] the m z value from the fit is 0.0027 m e , which is still much smaller than the smallest values yet reported (for InSb, m z = 0.014 m e , [29] for carbon nanotubes, m z = 0.019 m e ; [30] Table SI-6). …”

mentioning

confidence: 94%

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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“…The combination of a wide band-gap semiconducting oxide [37][38][39][40] with a three-dimensional 12-membered ring microporous framework offers many potential advantages in photocatalysis, such as excellent diffusion of reactant molecules, trapping and, in particular, shape selectivity. As a high selectivity toward the photodegradation of large aromatic molecules has been observed, it has been concluded that molecules entering the pore system were protected from photodegradation, which occurred on the external surface on specific defects.…”

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Selective Catalysis and Nanoscience: An Inseparable Pair

Zecchina

Groppo

Bordiga

2007

Chemistry A European J

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Selective catalysts can be considered as nanomachines designed to perform the synthesis of molecules with high reaction activity and high selectivity. These properties arise from a precise control of the structure of the active sites, of the three-dimensional environment and of their relationship. In both homogeneous and heterogeneous catalysts the active site three-dimensional environment ensemble is always a complex structure resembling the tuneable structure of enzymes, which are the most efficient catalysts optimized by nature over billions of years. To illustrate this concept the structure of a few homogeneous and heterogeneous catalysts for alkenes hydrogenation and for olefin polymerization are chosen and discussed as examples.

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Quantum-size effects in the titanosilicate molecular sieve

Cited by 102 publications

References 25 publications

Nanosize effects in titania based photocatalyst materials

Nanosize effects in titania based photocatalyst materials

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

Selective Catalysis and Nanoscience: An Inseparable Pair

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Quantum-size effects in the titanosilicate molecular sieve

Cited by 102 publications

References 25 publications

Nanosize effects in titania based photocatalyst materials

Nanosize effects in titania based photocatalyst materials

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

Selective Catalysis and Nanoscience: An Inseparable Pair

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