Ultra-large-pore ordered mesoporous organosilicas and related hollow nanoparticles
Item
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Title
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Ultra-large-pore ordered mesoporous organosilicas and related hollow nanoparticles
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Identifier
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d_2009_2013:0985211ef1c7:10628
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identifier
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10843
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Creator
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Mandal, Manik,
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Contributor
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Michal Kruk
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Date
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2010
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Language
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English
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Publisher
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City University of New York.
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Subject
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Polymer chemistry | Organic chemistry
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Abstract
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My dissertation describes the synthesis of ultra-large-pore ordered mesoporous organosilicas and related hollow nanoparticles. In the first part, we developed a versatile approach through which a series of periodic mesoporous organosilicas (PMOs) with 2-dimensional hexagonal structure and different bridging groups can be synthesized. The bridging groups are methylene (-CH2-), ethylene (-CH2CH2-), ethenylene (-CH=CH-), and phenylene (-C6H4-). For this purpose, a combination of a commercially available triblock copolymer Pluronic P123 (EO20PO70EO 20) with judiciously chosen micelle swelling agent (cyclohexane, or 1,3,5-triisopropylbenzene) was used as a miceller template, and the initial step of the synthesis was performed at temperature between 10 and 18°C, followed by hydrothermal treatment at 100-150°C. The PMOs were characterized using small-angle X-ray scattering (SAXS), nitrogen adsorption, transmission electron microscopy, and solid-state 29Si NMR. For all PMO compositions, the formation of 2-D hexagonal structures with (100) interplanar spacing, d100, up to 21-26 nm was achieved, which is at least seven nanometers larger than d100 reported earlier for any PMO with 2-D hexagonal structure. The nominal (BJH) pore diameters up to 20-27 nm were achieved for the considered compositions of PMOs with with 2-D hexagonal ordering, while even larger pore sizes were sometimes attained for disordered or weakly ordered structures. The mesopores exhibited constrictions or narrow entrances that were widened by increasing the hydrothermal treatment temperature. The pore diameter tended to increase as an initial synthesis temperature decreased, allowing for the pore size adjustment, but the useful temperature range depended on the bridging groups. The present work suggests that the low-temperature micelle-templated synthesis with judicious selected swelling agents is a general pathway to ultra-large-pore 2-D hexagonal PMOs with both aliphatic and aromatic bridging groups.;In the second part, we have demonstrated the synthesis of large-pore ethylene-bridged periodic mesoporous organosilica with face-centered-cubic structure. This was achieved by the use of judiciously chosen swelling agents and Pluronic F127 block copolymers at sub-ambient temperature (∼ 15°C). While our work confirmed that 1,3,5-trimethylbenzene (TMB) which was already employed by other researchers, is a facile swelling agent for Pluronic F127-templated ethylene-bridged PMOs with cubic Fm3m structure and our optimization of the synthesis afforded hitherto unreported unit-cell size and pore size for this PMO, it was also demonstrated that swelling agent predicted to have a higher extent of solubilization in Pluronics than TMB provide vast new opportunities. In particular, xylene was found to afford highly ordered materials with large unit-cell size and pore diameter, and a wide range of moderately or weakly ordered materials with very large unit-cell parameters (up to ∼ 50 nm) and some with very large pore diameters (up to ∼ 20 nm). In this case, the pore size and unit-cell size was tunable by adjusting the amount of inorganic salt (KCl) in the synthesis mixture. The use toluene allowed for the increase in the primary mesopore volume and also afforded large-pore PMOs in the absence of an inorganic salt. The use of the latter was also not required when benzene was used as a swelling agent. The identification of new swelling agents for ethylene-bridged PMO with spherical mesopores is likely to be extendable on PMOs of other framework compositions and for other related materials.;In the third part, based on understanding of the condition for the formation of ordered mesoporous organosilicas, we were able to synthesize hollow nanoparticles with different organic bridging groups. Different organic bridging groups such as methylene, ethylene, ethenylene, and phenylene were incorporated in the organosilica walls of the hollow nanoparticles. Further, we were able to synthesize hollow nanotubules comprising of these bridging groups in the walls.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Chemistry
