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A Silicon, Carbon and Deuterium NMR Investigation of Molecular Templating in Amorphous Silicas

Published online by Cambridge University Press:  10 February 2011

R. A. Assink ,
C. A. Click ,
T. M. Alam ,
C. J. Brinker  and
S. J. Naik
R. A. Assink
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185–1407
C. A. Click
Affiliation:
University of Missouri, Rolla, MO 65401
T. M. Alam
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185–1407
C. J. Brinker
Affiliation:
Sandia National Laboratories, Albuquerque, NM 87185–1407 University of New Mexico, Albuquerque, NM 87131.
S. J. Naik
Affiliation:
University of New Mexico, Albuquerque, NM 87131.
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Abstract

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. 29Si and 2H NMR experiments were performed to evaluate the efficacy of our templating approach. The 29Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment between the 1H nuclei of TPA and the 29Si 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 xeorgels, where drying stresses are greater, resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The 2H NMR wideline spectra consisted of a partially narrowed resonance, corresponding to template molecules which were undergoing restricted rotational motion, and an isotropically narrowed resonance, corresponding to molecules which were undergoing rapid rotational motion. The number of isotropically rotating template molecules decreased for the thin film specimens, consistent with improved templating of amorphous silica by TPA.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 576: Symposium DD – Organic/Inorganic Hybrid Materials II , 1999 , 83
Copyright
Copyright © Materials Research Society 1999

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References

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