A multiscale experimental study of the structural, compositional, and morphological characteristics of aluminosilicate (LTA) and pure-silica (MFI) zeolite materials surface-modified with MgO xH y nanostructures is presented. These characteristics are correlated with the suitability of such materials in the fabrication of LTA/Matrimid mixed-matrix membranes (MMMs) for CO 2/CH 4 separations. The four functionalization methods studied in this work produce surface nanostructures that may appear superficially similar under SEM observation but in fact differ considerably in shape, size, surface coverage, surface area/roughness, degree of attachment to the zeolite surface, and degree of zeolite pore blocking. The evaluation of these characteristics by a combination of TEM, HRTEM, N 2 physisorption, multiscale compositional analysis (XPS, EDX, and ICP-AES elemental analysis), and diffraction (ED and XRD) allows improved understanding of the origin of disparate gas permeation properties observed in MMMs made with four types of surface-modified zeolite LTA materials, as well as a rational selection of the method expected to result in the best enhancement of the desired properties (in the present case, CO 2/CH 4 selectivity increase without sacrificing permeability). A method based on ion exchange of the LTA with Mg 2+, followed by base-induced precipitation and growth of MgO xH y nanostructures, deemed "ion exchange functionalization" here, offers modified particles with the best overall characteristics resulting in the most effective MMMs. LTA/Matrimid MMMs containing ion exchange functionalized particles had a considerably higher CO 2/CH 4 selectivity (∼40) than could be obtained with the other functionalization techniques (∼30), while maintaining a CO 2 permeability of ∼10 barrers. A parallel study on pure silica MFI surface nanostructures is also presented to compare and contrast with the zeolite LTA case. © 2012 American Chemical Society.
|Original language||English (US)|
|Number of pages||10|
|Journal||The Journal of Physical Chemistry C|
|State||Published - Apr 23 2012|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-I1-011-21
Acknowledgements: This work was supported by King Abdullah University of Science and Technology under Award # KUS-I1-011-21. Microscopy research was supported in part by Oak Ridge National Laboratory’s ShaRE User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy. We acknowledge the following colleagues: (Georgia Tech) Y. Berta for assistance in microscopy, W. Long and P. Bollini for XPS data collection, J. Vaughn, J. Thompson, and W. J. Koros for assistance with gas permeation measurements; (ORNL): S. K. Reeves for assistance in TEM sample preparation, and L. F. Allard Jr. and D. N. Leonard for useful comments.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.