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RISS 인기검색어
- 검색키워드
- 저자 : Jaroniec, Mietek (검색결과 12 건)
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Gierszal, Kamil P.,Jaroniec, Mietek,Kim, Tae-Wan,Kim, Jeongnam,Ryoo, Ryong Royal Society of Chemistry 2008 New journal of chemistry Vol.32 No.6
<P>The effect of high temperature treatment of ordered mesoporous carbons (OMCs) under neutral atmosphere is studied for OMCs prepared by using different carbon precursors (furfuryl alcohol, sucrose, acenaphthene and mesophase pitch) and different ordered mesoporous silica (OMS) templates (MCM-48 and KIT-6). The OMS-templated carbons were thermally treated at various temperatures ranging from 900 °C to 2400 °C to study changes in their porosity and framework crystallinity. The KIT-6 silica was synthesized at different conditions to control the size of primary mesopores and interconnecting complementary pores. The use of MCM-48 silica as template afforded the carbon replicas, CMK-1, which underwent a structure transition from <I>Ia</I>3̄<I>d</I> to <I>I</I>4<SUB>1</SUB>/<I>a</I>. The use of the KIT-6 silica template, depending on the size of complementary pores, afforded a faithful inverse replica, CMK-8, as well as the CMK-1-type structure that underwent the aforementioned symmetry transition. The XRD patterns for the carbons studied showed that their thermal treatment led to a gradual deterioration of the carbon structure, which was associated with structure shrinking and pore walls fracturing. Particularly significant changes in the structural properties of the carbons studied occurred for those heated (graphitized) at 2400 °C, which manifested itself in a partial or complete loss of the pore volume. It was found that the CMK-1-type graphitized carbons exhibited better thermal stability, which is reflected by the presence of residual mesopores and/or nanostructure ordering. The degree of graphitization for the carbons heated at 2400 °C depended insignificantly on the type of carbon precursor; however, the precursor effect became more pronounced with decreasing temperature of the thermal treatment.</P> <P>Graphic Abstract</P><P>Adsorption and structural properties of ordered mesoporous carbons prepared by templating <I>Ia</I>3<I>d</I> silica mesostructures with different precursors are studied upon high temperature treatment in argon ranging from 900 °C to 2400 °C. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b716735k'> </P>
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Cho, Eun-Bum,Choi, Eunji,Yang, Shu,Jaroniec, Mietek Elsevier 2018 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.528 No.-
<P><B>Abstract</B></P> <P>We present a facile preparation of hollow mesoporous organosilica nanospheres with well-defined, uniform mesopores by controlling the morphology of pentablock copolymer templates under acidic conditions. The CBABC type poly(lactic acid-<I>co</I>-glycolic acid)-<I>b</I>-poly(ethylene oxide)-<I>b</I>-poly(propylene oxide)-<I>b</I>-poly(ethylene oxide)-<I>b</I>-poly(lactic acid-<I>co</I>-glycolic acid) (PLGA-<I>b</I>-PEO-<I>b</I>-PPO-<I>b</I>-PEO-<I>b</I>-PLGA) pentablock copolymers were synthesized via a step-growth and ring-opening polymerization method using Pluronic F68 and F108 as macro-initiators. Two kinds of pentablock copolymers, (LA<SUB>45</SUB>GA<SUB>12</SUB>)EO<SUB>75</SUB>PO<SUB>30</SUB>EO<SUB>75</SUB>(LA<SUB>45</SUB>GA<SUB>12</SUB>) and (LA<SUB>28</SUB>GA<SUB>9</SUB>)EO<SUB>141</SUB>PO<SUB>54</SUB> EO<SUB>141</SUB>(LA<SUB>28</SUB>GA<SUB>9</SUB>), were used as single soft templates to prepare mesoporous ethane-silica and benzene-silica hollow nanospheres by sol-gel chemistry in acidic aqueous solutions. The inner cavity diameter was controlled up to ∼20 nm by varying acidity and the chain length of the hydrophobic PLGA block without using additional swelling agents. The evolution of hollow nanospheres could be explained by single flower-like micelle template mechanism and the variation of morphology of pentablock copolymers upon solution acidity. Moreover, the amine-functionalized hollow benzene-silica nanospheres showed high carbon dioxide adsorption at ambient conditions. The hollow organosilica nanospheres were characterized by small-angle X-ray scattering, nitrogen adsorption-desorption, solid-state <SUP>13</SUP>C- and <SUP>29</SUP>Si nuclear magnetic resonance, and scanning and transmission electron microscopy and so on.</P> <P><B>Graphical abstract</B></P> <P>Hollow mesoporous organosilica nanospheres with uniform and large inner pore cavity were prepared with PLGA-PEO-PPO-PEO-PLGA pentablock copolymers as a single template in acidic aqueous solutions.</P> <P>[DISPLAY OMISSION]</P>
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Choi, Eunji,Cho, Eun-Bum,Jaroniec, Mietek The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.40
<P>Periodic mesoporous organosilicas were prepared using 1,2-bis(triethoxysilyl)ethane (BTEE) in the presence of a poly(ethylene oxide)-<I>b</I>-poly(d,l-lactic acid-<I>co</I>-glycolic acid)-<I>b</I>-poly(ethylene oxide) triblock copolymer (LGE538) template under strongly and weakly acidic conditions. White solid powders were obtained even under weakly acidic conditions using iron chloride hexahydrate. Small angle X-ray scattering (SAXS) and nitrogen adsorption isotherms showed a highly ordered hexagonal (<I>p</I>6<I>mm</I>) mesostructure and a high specific surface area of around 1000 m<SUP>2</SUP>g<SUP>−1</SUP>. The hydrothermal stability of these materials was also investigated because it is a crucial factor in their usage in the chemical industry. The powders were placed in sealed vials inside a convection oven at 373 K for 4 weeks. The hydrothermally treated samples were analyzed every week over the 4 weeks using SAXS and nitrogen adsorption. Solid-state<SUP>29</SUP>Si CP-MAS NMR analysis was also performed to observe the stability of siloxane bonds over the 4 weeks of hydrothermal treatment. The results indicate that the ethane-silica samples show quite good stability, which makes them attractive as catalysts or supporting materials for up to one month.</P>
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Cho, Eun-Bum,Park, Jeonghyun,Jaroniec, Mietek American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.41
<P>Periodic mesoporous thiophene-silicas with hexagonal (<I>p</I>6<I>mm</I>) symmetry were synthesized using a 2,5-bis(triethoxysilyl)thiophene (BTET) precursor in the presence of Pluronic P123 (EO<SUB>20</SUB>PO<SUB>70</SUB>EO<SUB>20</SUB>) and PLGE (EO<SUB>17</SUB>(L<SUB>28</SUB>G<SUB>7</SUB>)EO<SUB>17</SUB>) triblock copolymers at different acidic conditions. P123-templated mesoporous thiophene-silicas with <I>p</I>6<I>mm</I> ordered structure were prepared in the presence of hydrochloric acid and iron(III) chloride hexahydrate used as acid catalysts. However, it was found that a relatively large fraction of the Si–C bonds in thiophene-bridging groups were decomposed during the synthesis process. On the other hand, thiophene-silicas synthesized at lower acidic conditions were disordered and nonporous structures. In contrast, PLGE-templated thiophene-silicas with <I>p</I>6<I>mm</I> ordered mesostructure were prepared using copper(II) perchlorate hexahydrate and boric acid as well as hydrochloric acid. Importantly, up to 97.3% of the Si–C bonds in mesoporous thiophene-silica prepared in the presence of boric acid were retained. Solid state <SUP>29</SUP>Si MAS NMR clearly showed that the structural stability of the Si–C bond is dependent on the acidity and time of the initial self-assembly stage. Also, the thermal stability of the thiophene-bridging groups was shown to be dependent on the acidity of the synthesis gel.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-41/jp408385t/production/images/medium/jp-2013-08385t_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp408385t'>ACS Electronic Supporting Info</A></P>
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Pal, Nabanita,Cho, Eun-Bum,Kim, Dukjoon,Jaroniec, Mietek American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.29
<P>A series of Mn-doped ordered mesoporous ceria–silica composites was synthesized by using hexadecyltrimethylammonium bromide as a soft template under ammonia basic conditions. After template removal, Mn-doped mesoporous ceria–silica composites were thoroughly characterized by small-angle X-ray scattering, which revealed highly ordered 2D-hexagonal (<I>p</I>6<I>m</I>) framework. Other techniques such as wide-angle X-ray diffraction, N<SUB>2</SUB> adsorption, scanning and transmission electron microscopic analysis with energy-dispersive spectrometry mapping, inductive coupled plasma atomic emission spectrophotometry, ultraviolet–visible spectrometry, and <SUP>29</SUP>Si cross-polarization magic-angle spinning NMR were used to show the effect of Mn incorporation into the ceria–silica composites. The electronic states of the surface Mn and Ce species were also investigated by X-ray photoelectron spectroscopy. These Mn-doped mesoporous ceria–silica composites were successfully reduced under a flowing H<SUB>2</SUB>/N<SUB>2</SUB> gas mixture at an elevated temperature without noticeable changes in their hexagonally ordered mesostructures. These materials were applied as heterogeneous and reusable catalysts for transesterification of different esters, such as methyl benzoate and ethyl cyanoacetate, in the presence of various alcohols, such as <I>n</I>-octanol and <I>n</I>-butanol, to produce biodiesels under solventless mild conditions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-29/jp504801h/production/images/medium/jp-2014-04801h_0016.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp504801h'>ACS Electronic Supporting Info</A></P>
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Cho, Eun-Bum,Kim, Dukjoon,Mandal, Manik,Gunathilake, Chamila A.,Jaroniec, Mietek American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.30
<P>Highly ordered mesoporous benzene–silicas with 2D hexagonal (<I>p</I>6<I>mm</I>) and 3D cubic (<I>Im</I>3<I>m</I>) symmetry were prepared using weaker acids than hydrochloric acid in the presence of Pluronic P123 and F127 triblock copolymer templates. The resulting ordered mesostructures of 1,4-bis(triethoxysilyl)benzene (BTEB) were well-organized when iron(III) chloride hexahydrate (weak Brönsted acid with <I>K</I><SUB>a</SUB> = 6.3 × 10<SUP>–3</SUP>) was employed; 2D hexagonal structure was obtained at the concentration exceeding 0.064 M (pH ≤1.76) and 3D cubic structure was obtained at the concentration about 0.112 M (pH ≤1.63). The specific surface areas and pore diameters of the hexagonal benzene–silicas studied were in the range from 707 to 966 m<SUP>2</SUP> g<SUP>–1</SUP> and from 7.5 to 8.2 nm, respectively; the corresponding values for cubic benzene–silicas were 514–604 m<SUP>2</SUP> g<SUP>–1</SUP> and 8.5–9.0 nm, respectively. Also, type IV nitrogen adsorption–desorption isotherms and very narrow pore size distributions were obtained for these materials, which are similar to those for mesoporous benzene–silica prepared in the presence of strong hydrochloric acid.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-30/jp302718r/production/images/medium/jp-2012-02718r_0007.gif'></P>
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Cho, Eun-Bum,Han, Oc Hee,Kim, Sunha,Kim, Dukjoon,Jaroniec, Mietek Royal Society of Chemistry 2010 Chemical communications Vol.46 No.25
<P>Imine-containing bridging groups were formed during self-assembly of periodic mesoporous organosilicas by <I>in situ</I> dynamic covalent chemistry of aldehyde and amine groups in the presence of poly(ethylene oxide)–poly(<SMALL>DL</SMALL>-lactic acid-<I>co</I>-glycolic acid)–poly(ethylene oxide) block copolymer in acidic aqueous solutions.</P> <P>Graphic Abstract</P><P>Imine-containing bridging groups were formed during self-assembly of PMOs by <I>in situ</I> dynamic covalent chemistry of aldehyde and amine groups in acidic aqueous solutions. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cc00704h'> </P>
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