An Investigation of Molecular Templating in Amorphous Silicas by Cross-Polarization NMR Spectroscopy

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The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium (TPA), a structure-directing agent for zeolite ZSM-5, into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. Silicon and carbon NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix ... continued below

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12 p.

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Assink, R.A.; Brinker, C.J.; Click, C.A. & Naik, S.J. July 12, 1999.

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This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided by UNT Libraries Government Documents Department to Digital Library, a digital repository hosted by the UNT Libraries. It has been viewed 25 times . More information about this article can be viewed below.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM, and Livermore, CA (United States)
    Place of Publication: Albuquerque, New Mexico

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Description

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium (TPA), a structure-directing agent for zeolite ZSM-5, into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. Silicon and carbon NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment involving the {sup 1}H nuclei of TPA and the {sup 29}Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Bulk xerogels, prepared by gelation and slow drying of the corresponding sols, exhibited only weak interactions between the two sets of nuclei. Thin film xerogels, where drying stresses are greater, exhibited significantly increased interactions. Intramolecular cross-polarization experiments between the {sup 1}H and {sup 13}C nuclei of the template molecule demonstrated that much of the increased efficiency was a result of reduced rotational mobility of the TPA molecule.

Physical Description

12 p.

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OSTI as DE00009019

Medium: P; Size: 12 pages

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  • Journal Name: Journal of Physcial Chemistry; Other Information: Submitted to Journal of Physical Chemistry

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  • Report No.: SAND99-1753J
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 9019
  • Archival Resource Key: ark:/67531/metadc792441

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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Creation Date

  • July 12, 1999

Added to The UNT Digital Library

  • Dec. 19, 2015, 7:14 p.m.

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  • April 6, 2017, 8:21 p.m.

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Assink, R.A.; Brinker, C.J.; Click, C.A. & Naik, S.J. An Investigation of Molecular Templating in Amorphous Silicas by Cross-Polarization NMR Spectroscopy, article, July 12, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc792441/: accessed May 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.