Authors: Marietta E MarcanoGonzález José N PrimeraPedrozo Zulmarie JiménezLaureano Riqiang Fu Arturo J HernándezMaldonado
Publish Date: 2012/11/09
Volume: 48, Issue: 5, Pages: 2053-2066
Abstract
UPRM5 is a flexible titanium silicate first prepared using tetraethylammonium TEA+ and that exhibited improved structural and adsorption properties when compared to other titanium silicates In order to further tailor these properties we have employed tetrapropylammonium TPA+ and tetrabutylammonium TBA+ as structure directing agents SDAs respectively Analysis of the localrange structure using 29Si magic angle spinning nuclear magnetic resonance spectroscopy suggested silicon environments corresponding to Si2Si 2Tiocta and Si3Si 1Tisemiocta as expected for a flexible titanium silicate A quantitative analysis however revealed that the amount of semioctahedral titanium centers was greater in the variant prepared with TPA+ suggesting that the nature of the NR4 + cation plays an important role in the formation of framework faulting Both UPRM5 variants were detemplated and modified to include extraframework Sr2+ and produce materials for carbon dioxide adsorption Their thermal stability and pore contraction were first investigated by means of in situ hightemperature Xray powder diffraction and nitrogen porosimetry Materials prepared with TBA+ showcased better thermal stability when compared to variants prepared with TPA+ and even TEA+ probably due to the relative low level of structural faulting All variants however displayed a pore contraction process associated with the release of tenacious water Carbon dioxide uptakes varied considerably depending on the choice of SDA employed and the isosteric heat of adsorption profiles correlated with a heterogeneous surface The results suggest that Sr2+–UPRM5 TPA materials could be tailored for purification applications whereas Sr2+–UPRM5 TBA materials could be tailored for bulklevel separation applicationsThis publication is based upon work supported by the National Aeronautics and Space Administration under Grant No NNX09AV05A Partial support was also provided by the National Science Foundation NSF under Grant No HRD 0833112 CREST Program We also wish to acknowledge support from the PRLSAMP Bridge to the Doctorate Program and the Puerto Rico Institute for Functional Nanomaterials The NMR measurements were performed at the National High Magnetic Field Laboratory NHMFL supported by NSF Cooperative Agreement No DMR0654118 the State of Florida and the US Department of Energy
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