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Jhung, Sung ,Hwa,Jin, Taihuan,Hwang, Young ,Kyu,Chang, Jong-San WILEY-VCH Verlag 2007 Chemistry Vol.13 No.16
<P>Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW–MW, MW–CE, CE–MW, and CE–CE (in the order of nucleation-crystal growth). In the case of synthesis by MW–CE or CE–MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW–MW<MW–CE≈CE–MW<CE–CE synthesis. The fast crystal growth and small crystal size observed in the synthesis from microwave-nucleated precursor can be explained in terms of the fact that the microwave-nucleated samples have higher population of nuclei with smaller size than the samples nucleated by conventional heating.</P> <B>Graphic Abstract</B> <P>Microwave synthesis: Microporous materials can be synthesized under microwave irradiation very efficiently. This work demonstrates that the effect of microwave irradiation appears to be much more significant on the nucleation step compared to crystal growth even though the microwave method accelerates both steps of the syntheses (see figure: MW: microwave irradiation, CE: conventional electric heating). <img src='wiley_img/09476539-2007-13-16-CHEM200700098-content.gif' alt='wiley_img/09476539-2007-13-16-CHEM200700098-content'> </P>
Microwave synthesis of metallosilicate zeolites with fibrous morphology.
Hwang, Young Kyu,Jin, Taihuan,Kim, Ji Man,Kwon, Young-Uk,Park, Sang-Eon,Chang, Jong-San American Scientific Publishers 2006 Journal of Nanoscience and Nanotechnology Vol.6 No.6
<P>In this paper, we report syntheses of silicalite (Si-MFI) zeolite crystals with tetravalent metal ions incorporated to synthesize metallosilicalite (M-MFI; M = Sn, Zr, Sn/Zr, Ti/Zr) zeolite crystals by using microwave irradiation reactions. Beta-Diketonate (acetylacetone) was used as a chelating ligand of the metal precursors, in order to reduce their hydrolysis rates and, therefore, to enhance framework incorporation of each metal in the syntheses of M-MFI zeolites. The zeolite crystals formed show puck-like morphology, and these crystals are stacked to form fibers with the degree of self-assembly varied depending on the nature of the tetravalent metal ion used. Importantly, the self-assembly of the zeolite crystals and the resultant fibrous morphology are observed only when the substituting metal ions are present. Powder X-ray diffraction, infrared and ultraviolet diffuse reflectance spectroscopic data all indicate that Sn and Ti atoms are well substituted for Si, but Zr is not well incorporated in the resulting MFI crystals. These results are discussed in terms of the ionic sizes and bulk dielectric constants of the corresponding metal oxides of the substituting metal ions.</P>
Phase transformations and phase-selective syntheses of aluminophosphate molecular sieves.
Jhung, Sung Hwa,Jin, Taihuan,Hwang, Jin-Soo,Chang, Jong-San American Scientific Publishers 2007 Journal of Nanoscience and Nanotechnology Vol.7 No.8
<P>A few aluminophosphate (AlPO) molecular sieves are synthesized hydrothermally under microwave irradiation and conventional electric heating. Less stable AlPO molecular sieves especially with large pore can be obtained preferentially in a short crystallization time because the inter-conversion of less stable phase into a more stable one is prohibited in short reaction time. The VFI transforms into AFI, and finally into APC, with the increase of reaction time since the relative stability is VFI < AFI < APC under the chosen reaction conditions. The relative stability can be explained with the pore size or by the framework density of each structure. Due to the rapid crystallization involved in the microwave method and instability of porous materials with large pore, these porous materials can be selectively synthesized by microwave irradiation. The synthesis of extra-large-pore VPI-5 using triethylamine is also reported for the first time, and the synthesized VPI-5 is very stable that can be dried at 100 degrees C at atmospheric pressure without the phase-transformation into AIPO-8.</P>