Spectroscopic monitoring for the formation of mesoporous MCM-41 materials upon microwave irradiation |
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Authors: | Hyung Mi Sung-Suh Dae Sung Kim Yong-Ki Park Sang-Eon Park |
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Institution: | (1) Industrial Catalysis Research Laboratory, Korea Research Institute of Chemical Technology (KRICT), Taejon, 305-606, South Korea |
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Abstract: | The mesoporous MCM-41 materials were prepared in very short crystallization time (∼40 min) upon microwave irradiation in comparison
with conventional hydrothermal heating method. With both microwave irradiation and hydrothermal heating, the MCM-41 formation
via supramolecular templating method has been monitored by fluorescence and electron spin resonance (ESR) spectroscopy. Pyrene
as a fluorescence probe and 4-(N,N-dimethyl-N-hexadecyl)ammonium-2,2,6,6-tetramethyl piperidinyloxy iodide (CAT16) as a spin probe were respectively dissolved into the micelle solutions to form
the MCM-41 precursor gels. These probes allow the monitoring of the supramolecular interaction between the anionic silicate
species and the cationic surfactant molecules during the MCM-41 formation. Analyses of fluorescence and ESR spectra indicate
that the fast increase of hydrophobicity and microviscosity at the solubilzation sites of the probes results from the accelerated
condensation of silicates onto the micelle surface upon microwave irradiation. The fluorescence change from the silicate L-center
in the MCM-41 precursor gel also probes the fast silicate condensation upon microwave irradiation. It seems that the fast
formation of MCM-41 upon microwave irradiation is ascribed to the microwave-susceptible head groups of surfactant molecules
in addition to fast dissolution of the precursor gel. |
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