Belén Cordero, Daphne S.

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    Synthesis, characterization and detemplation of thermally unstable 3-D Metal-Substituted Aluminophosphates.
    (2009) Belén Cordero, Daphne S.; Hernández Maldonado, Arturo J.; College of Engineering; Cardona Martínez, Nelson; Martínez Iñesta, María; Suleiman Rosado, David; Department of Chemical Engineering; Rivera Montalvo, Luis
    The extent of the detemplation process in Me-SBE (Me = Co2+, Mg2+ and Mn2+) aluminophosphates was investigated. Hydrothermal synthesis conditions were optimized to obtain materials with minimal phase impurities. SEM analysis of the Mg- and Mn-SBE assynthesized samples revealed square-plates with truncated corners morphology, grown in aggregated fashion, and contrasting with the hexagonal-plate like morphology of Co-SBE. Treatment in an oxidative atmosphere and vacuum, respectively, was used to study the removal of the structure-directing agent (SDA; 1,9-diaminononane). Calcination in air or nitrogen results in a “non-porous” framework as evidenced by low sorption capacity. Cautious detemplation in vacuum using an evacuation rate of 10 mm Hg/s and a temperature of 648 K resulted in surface areas of ca. 700, 500 and 130 m2/g for Mg-, Co- and Mn-SBE, respectively. TGA and in situ high temperature XRD analyses indicate the frameworks for all the SBE variants experienced collapsing upon treatment in helium at temperatures above 700 K and subsequently formed an aluminophosphate dense phase (i.e., trydimite). In situ XRD-DSC 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 treatments was verified by FT-IR spectroscopy. XPS spectra revealed that most of the Co atoms in vacuum treated samples are in a tetrahedral coordination while the Mn atoms exhibited diverse coordination states and plausible formation of extra-framework species as corroborated by UV-vis, EPR, and MAS-NMR spectroscopy. 27Al MAS-NMR spectra for vacuum detemplated Mg-SBE samples prior to and after dehydration confirmed the reversible formation of aluminum octahedral sites. However, this 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. Detemplation of SBE materials using alternative methods such as ion exchange, solvent extraction, and UV-O3 treatments were also explored but not accomplished. Attempted carbon nanotubes (CNTs) synthesis by pyrolysis of the organic template within the channels of SBE framework was performed. The process itself appears to be very dependent on the exact experimental conditions and requires further investigation.