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SBE-type metal-substituted aluminophosphates: detemplation and coordination chemistry

Belén-Cordero, Daphne S. and Kim, Chul and Hwang, Son-Jong and Hernández-Maldonado, Arturo J. (2009) SBE-type metal-substituted aluminophosphates: detemplation and coordination chemistry. Journal of Physical Chemistry C, 113 (19). pp. 8035-8049. ISSN 1932-7447.

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The detemplation process in Me-SBE (Me = Co^2+, Mg^2+, and Mn^2+) aluminophosphates was studied to elucidate materials stability and framework characteristics. In addition, the hydrothermal synthesis conditions were optimized to obtain materials with minimal phase impurities. This was accomplished by means of decreasing reaction temperature and increasing aging periods. Scanning electron microscopy analysis of the Mg- and Mn-SBE as-synthesized samples revealed square plates with truncated corner morphologies grown in aggregated fashion and contrasting with the previously reported hexagonal platelike morphology of Co-SBE. Cautious detemplation in vacuum, using an evacuation rate of 10 mmHg/s and a temperature of 648 K, resulted in surface areas of about 700, 500, and 130 m^2/g for Mg-, Co-, and Mn-SBE, respectively. Thermal gravimetric analysis and in situ high-temperature powder X-ray diffraction analyses indicate the frameworks for all of the SBE variants experienced collapse upon treatment with helium at temperatures above 700 K and subsequently formed an aluminophosphate trydimite dense phase. Detemplation in air at all times resulted in framework destruction during detemplation. In situ differential scanning calorimetry−powder X-ray diffraction data showed that the SBE frameworks experience breathing modes related to specific endothermic and exothermic scenarios during air treatment. Decomposition and elimination of the organic template during vacuum treatment was verified by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy revealed that most of the Co atoms in vacuum-treated samples are in tetrahedral coordination, while the Mn atoms exhibit various coordination states. Ultraviolet-visible, electron paramagnetic resonance, and magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy corroborated the latter result in addition to providing evidence for the formation of Mn extra framework species. ^(27)Al MAS NMR spectra for vacuum-detemplated Mg-SBE samples prior to and after dehydration confirmed the reversible formation of aluminum octahedral sites. This, however, did not affect the porous nature of detemplated Mg-SBE samples as these are capable of adsorbing 19 water molecules per super cage at 298 K.

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Hwang, Son-Jong0000-0002-3210-466X
Additional Information:© 2009 American Chemical Society. Received: December 15, 2008; Revised Manuscript Received: March 25, 2009. Funding for this work was provided by National Science Foundation (NSF) Awards CBET-0546370 and CBET-0619349. The NMR facility at California Institute of Technology was supported by NSF Grant 9724240 and partially supported by the Materials Research Science and Engineering Centers (MRSEC) Program, NSF Award DMR-0520565. The authors gratefully acknowledge help from professors Dr. Carlos Rinaldi and Dr. Carlos Velázquez [University of Puerto Rico, Mayagüez (UPR-M) Chemical Engineering] for providing admittance to FT-IR and SEM/EDX analyses, respectively. We wish to specially thank John Bullis and Hiden Analytical Ltd. (Warrington, U.K.) for kindly providing the water adsorption analysis. We also acknowledge support from Dr. Raphael Raptis and Dr. Esteban Fachini [University of Puerto Rico, Río Piedras (UPR-RP), Chemistry] for their collaboration with UV-vis and XPS spectroscopy analyses, respectively
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Issue or Number:19
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14616
Deposited By: Jason Perez
Deposited On:10 Aug 2009 17:27
Last Modified:03 Oct 2019 00:51

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