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zeolites
Zeolites have been a challenging class of materials to look at in the TEM primarily due to fast structure disintegration by “knock-on” damage mechanism at high keV electron beam and “radiolysis” at low keV electron beam. We study the physics of electron beam interaction with these materials to minimize damage during characterization. Research in our lab is broadly focused on understanding : (i) the effect of atomic structure on crystal morphology, (ii) the early stages of zeolite growth, and (iii) the structure-property correlation of dopants in zeolite structures like MFI and MWW.
Figure: Growth stages of MFI nanosheets from seed. (a) Bright-field TEM (BF-TEM) images representing different stages of growth of MFI nanosheets starting from seeds approximately 30 nm in diameter. (b) Schematic showing the preferential growth of a seed along the b axis. (c) The corresponding TEM image of the seed in (b); the HR-TEM images overlaid with the crystal structure model along the [100], [010] and [001] zone axes (middle panels) confirming the MFI-type zeolite structure; and diffraction pattern of the seed taken along the [001] zone axis (right panels) confirming elongation of the seed along the b axis. (d) Schematic of a nanosheet growing out of the seed. (e) High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images with different magnifications for the seed in (d) (left and middle panels); and image intensity linescan along the red dotted line (‘Position’ indicates the distance from the left edge of the red dotted line) in the second HAADF-STEM image (right panel), showing a thickness step in the nanosheet that corresponds to a ratio of 5 pentasil chains to 3 pentasil chains from left to right. (f) Schematic showing partial wrap of a b-axis-oriented nanosheet around an a-axisoriented seed. (g) BF-TEM image (left panel) and corresponding [100] zone axis diffraction patterns (right panels) from the seed (red ring) and [010] zone axis diffraction pattern from the sheet (yellow ring). Scale bars from left to right in (a) are 20 nm, 20 nm, 50 nm, 100 nm, 100 nm and 500 nm; in (c) are 20 nm and 1 nm−1 ; in (e) are 50 nm and 20 nm; and in (g) are 100 nm, 1 nm−1 and 1 nm−1. Figure from Ref. 1.
Recommended Reading
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"Ultra-selective high-flux membranes from directly synthesized zeolite nanosheets"
M. Y. Jeon, D. Kim, P. Kumar, P. S. Lee, N. Rangnekar, P. Bai, M. Shete, B. Elyassi, H. S. Lee, K. Narasimharao, S. N. Basahel, S. Al-Thabaiti, W. Xu, H. J. Cho, E. O. Fetisov, R. Thyagarajan, R. F. DeJaco, W. Fan, K. A. Mkhoyan, J. I. Siepmann, M. Tsapatsis
- Nature 543, 690 (2017)
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"Open-Pore Two-Dimensional MFI Zeolite Nanosheets for the Fabrication of Hydrocarbon-Isomer-Selective Memberanes on Porous Polymer Supports"
H. Zhang, Q. Xiao, X. Guo, Najun Li, P. Kumar, N. Rangnekar, M. Jeon, S. Al-Thabaiti, K. Narasimharao, S. N. Basahel, B. Topuz, F. J. Onorato, C. W. Macosko, K. A. Mkhoyan, M. Tsapatsis
- Angew. Chem. Int. Ed. 55, 7184 (2016)
Highlighted on Angewandte Cover.
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"Self-Pillared, Single-Unit-Cell Sn-MFI Zeolite Nanosheets and Their Use for Glucose and Lactose Isomerization"
L. Ren, Q. Guo1, P. Kumar, M. Orazov, D. Xu, S. M. Alhassan,K. A. Mkhoyan, M. E. Davis, M. Tsapatsis
- Angew. Chem. Int. Ed. 54, 10848 (2015)
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"Quantification of thickness and wrinkling of exfoliated two-dimensional zeolite nanosheets"
P. Kumar, K. V. Agrawal, M. Tsapatsis, K. A. Mkhoyan
- Nature Commun. 6, 7128 (2015).
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"2D Zeolite Coatings: Langmuir–Schaefer Deposition of 3 nm Thick MFI Zeolite Nanosheets"
N. Rangnekar, M. Shete, K. V. Agrawal, B. Topuz, P. Kumar, Q. Guo, I. Ismail, A. Alyoubi, S. Basahel, K. Narasimharao, C. W. Macosko, K. A. Mkhoyan, S. Al-Thabaiti, B. Stottrup, M. Tsapatsis
- Angew. Chem. Int. Ed. 54, 6571 (2015).
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