Co-reporter:Carl-Hugo PélissonTakahiro Nakanishi, Yang Zhu, Kei Morisato, Toshiyuki Kamei, Ayaka Maeno, Hironori Kaji, Shunki Muroyama, Masamoto Tafu, Kazuyoshi Kanamori, Toyoshi ShimadaKazuki Nakanishi
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 1) pp:
Publication Date(Web):December 14, 2016
DOI:10.1021/acsami.6b12653
Polymethylhydrosiloxane has been grafted on the surface of a hierarchically porous silica monolith using a facile catalytic reaction between Si–H and silanol to anchor the polymer. This easy methodology leads to the functionalization of the surface of a silica monolith, where a large amount of free Si–H bonds remain available for reducing metal ions in solution. Palladium nanoparticles of 15 nm have been synthesized homogeneously inside the mesopores of the monolith without any stabilizers, using a flow of a solution containing Pd2+. This monolith was used as column-type fixed bed catalyst for continuous flow hydrogenation of styrene and selective hydrogenation of 3-hexyn-1-ol, in each case without a significant decrease of the catalytic activity after several hours or days. Conversion, selectivity, and stereoselectivity of the alkyne hydrogenation can be tuned by flow rates of hydrogen and the substrate solution, leading to high productivity (1.57 mol g(Pd)−1 h–1) of the corresponding cis-alkene.Keywords: catalysis; hydrosilylation; mesoporous materials; palladium nanoparticle; polymer; selective hydrogenation; silica monolith;
Co-reporter:Yang Zhu, Koji Yoneda, Kazuyoshi Kanamori, Kazuyuki Takeda, Tsutomu Kiyomura, Hiroki Kurata and Kazuki Nakanishi
New Journal of Chemistry 2016 vol. 40(Issue 5) pp:4153-4159
Publication Date(Web):30 Nov 2015
DOI:10.1039/C5NJ02820E
Hierarchically porous titanium phosphate monoliths combining well-defined co-continuous macropores and accessible large mesopores have been synthesized for the first time via a sol–gel process accompanied by phase separation using titanium oxysulfate and phosphoric acid as precursors. The macropore size was tunable over a broad range from 0.6 μm to 10 μm by changing the starting composition, while the mesopore size and the specific surface area of the as-synthesized amorphous monoliths are 21 nm and 320 m2 g−1, respectively. Crystallization of the gel network can be induced in two different ways. Calcination at elevated temperature (800 °C) leads to the formation of TiP2O7 and the collapse of both the macro- and meso-structures, while the solvothermal treatment of the as-synthesized gel in ethylene glycol leads to the formation of platy crystals of titanium phosphate with a layered structure at relatively low temperature. The titanium phosphate monoliths with a hierarchically porous structure are expected to be useful in various applications such as continuous-flow catalysis, water remediation and ion batteries.
Co-reporter:Yang Zhu, Kazuyoshi Kanamori, Nirmalya Moitra, Kohei Kadono, Shugo Ohi, Norimasa Shimobayashi, Kazuki Nakanishi
Microporous and Mesoporous Materials 2016 Volume 225() pp:122-127
Publication Date(Web):1 May 2016
DOI:10.1016/j.micromeso.2015.12.002
•Macroporous metal zirconium phosphate monoliths are synthesized.•Glycerol ensures homogeneous distribution of metal salt in the gel skeleton.•Polycrystalline monolith with hierarchically porous structure was obtained.•Ultralow thermal expansion was observed due to the presence of nanoscale porosity.A versatile synthetic method has been developed for the fabrication of metal zirconium phosphate (MZP) macroporous monoliths via a sol–gel process accompanied by phase separation. More than 30 kinds of MZP monolithic polycrystalline monoliths with co-continuous macroporous structure have been synthesized by simply adding the target metal salt in the starting solution with optimized compositions. Glycerol, due to its high boiling point, plays the key role as the solvent to prevent metal salt from recrystallization, allowing a homogeneous distribution of metal salts over the polymerizing zirconium phosphate network. Hierarchically porous polycrystalline strontium zirconium phosphate (SrZrP) monolith has been obtained when the dried gel was calcined at 1000 °C. Very low thermal expansion (coefficient of thermal expansion (CTE) as 1.4 × 10−6 K−1) over a wide temperature range (38 °C–1000 °C) together with good mechanical properties (flexural modulus as 8.0 GPa from 3 point bending test and Young's modulus as 1.9 GPa from uniaxial compression test) has been demonstrated, while high porosity (43%) due to the presence of macropores reduces bulk density. As compared with dense ceramics of the same composition, the CTE value is lower and can be attributed to the presence of nanometer-sized small pores, which absorbs the anisotropic thermal expansion of each crystallite in the macropore skeletons at elevated temperatures.
Co-reporter:Kazuki Nakanishi
Journal of Sol-Gel Science and Technology 2016 Volume 79( Issue 2) pp:241
Publication Date(Web):2016 August
DOI:10.1007/s10971-016-4124-y
Co-reporter:Yang Zhu, Taiyo Shimizu, Takara Kitajima, Kei Morisato, Nirmalya Moitra, Nicolas Brun, Tsutomu Kiyomura, Kazuyoshi Kanamori, Kazuyuki Takeda, Hiroki Kurata, Masamoto Tafu and Kazuki Nakanishi
New Journal of Chemistry 2015 vol. 39(Issue 4) pp:2444-2450
Publication Date(Web):20 Nov 2014
DOI:10.1039/C4NJ01749H
Hierarchically porous monolithic materials are advantageous as adsorbents, catalysts and catalyst supports due to the better accessibility of reactants to the active sites and the ease of recycle and reuse. Traditional synthetic routes, however, have limitations in designing hierarchical porosity as well as the mechanically stable monolithic shape in inorganic phosphate materials, which are useful as adsorbents and catalysts. We present a low-temperature, one-step liquid phase synthesis of hierarchically porous zirconium phosphate (ZrP) monoliths with tunable compositions (from Zr(HPO4)2 (Zr:P = 1:2) to NaSICON (Na super ionic conductor)-type ZrP (Zr:P = 1:1.5)) as well as macropore size (from 0.5 to 5 μm). The as-synthesized ZrP monolith with a high reactive surface area (600 m2 g−1) and relatively high mechanical strength (Young's modulus 320 MPa) was applied to ion adsorption. A simple syringe device inserted tightly with the ZrP monolith as a continuous flow setup was demonstrated to remove various toxic metal ions in aqueous solutions, which shows promising results for water purification.
Co-reporter:Shotaro Fukumoto, Kazuki Nakanishi and Kazuyoshi Kanamori
New Journal of Chemistry 2015 vol. 39(Issue 9) pp:6771-6777
Publication Date(Web):04 Jun 2015
DOI:10.1039/C5NJ00479A
Copper hydroxide-based monolithic xerogels with controlled hierarchical pores have been prepared directly by a sol–gel process from an ionic precursor, CuCl2·2H2O. Propylene oxide acts as a gelation inducer by increasing pH homogeneously in a reaction solution. Poly(acrylamide) is utilized not only to control macroscopic phase separation but also to support the network physically. Glycerol contributes to the formation of monolithic gels by suppressing the growth of copper hydroxide crystals. An appropriate starting composition leads to co-continuous gel skeletons and macropores. Although the as-dried gels were amorphous, post-treatments (calcination and solvothermal treatment) formed metallic copper and copper oxides (CuO and Cu2O) without the collapse of the monolithic form and macrostructure.
Co-reporter:Yang Zhu;Kei Morisato;George Hasegawa;Nirmalya Moitra;Tsutomu Kiyomura;Hiroki Kurata;Kazuyoshi Kanamori
Journal of Separation Science 2015 Volume 38( Issue 16) pp:2841-2847
Publication Date(Web):
DOI:10.1002/jssc.201500444
The optimization of a porous structure to ensure good separation performances is always a significant issue in high-performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high-performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high-performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high-performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36 000 m−1. Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans-stilbene with separation factor as 7 and theoretical plate number as 76 000 m−1 for cis-stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long- established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.
Co-reporter:Nirmalya Moitra ; Shun Ichii ; Toshiyuki Kamei ; Kazuyoshi Kanamori ; Yang Zhu ; Kazuyuki Takeda ; Kazuki Nakanishi ;Toyoshi Shimada
Journal of the American Chemical Society 2014 Volume 136(Issue 33) pp:11570-11573
Publication Date(Web):August 6, 2014
DOI:10.1021/ja504115d
Inspired by homogeneous borane catalysts that promote Si–H bond activation, we herein describe an innovative method for surface modification of silica using hydrosilanes as the modification precursor and tris(pentafluorophenyl)borane (B(C6F5)3) as the catalyst. Since the surface modification reaction between surface silanol and hydrosilane is dehydrogenative, progress and termination of the reaction can easily be confirmed by the naked eye. This new metal-free process can be performed at room temperature and requires less than 5 min to complete. Hydrosilanes bearing a range of functional groups, including alcohols and carboxylic acids, have been immobilized by this method. An excellent preservation of delicate functional groups, which are otherwise decomposed in other methods, makes this methodology appealing for versatile applications.
Co-reporter:Nirmalya Moitra, Kazuyoshi Kanamori, Yumi H. Ikuhara, Xiang Gao, Yang Zhu, George Hasegawa, Kazuyuki Takeda, Toyoshi Shimada and Kazuki Nakanishi
Journal of Materials Chemistry A 2014 vol. 2(Issue 31) pp:12535-12544
Publication Date(Web):04 Jun 2014
DOI:10.1039/C4TA01767F
Supported metal alloy nanoparticles demonstrate high potential in designing heterogeneous catalysts for organic syntheses, pollution control and fuel cells. However, requirements of high temperature and multistep processes remain standing problems in traditional synthetic strategies. We herein present a low-temperature, single-step, liquid-phase methodology for designing monolith-supported metal alloy nanoparticles with high physicochemical stability and accessibility. Metal ions in aqueous solutions are reduced to form their corresponding metal alloy nanoparticles within hierarchically porous hydrogen silsesquioxane (HSQ, HSiO1.5) monoliths bearing well-defined macro- and mesopores and exhibiting high surface redox activity due to the presence of abundant Si–H groups. Supported bi-, tri- and tetrametallic nanoparticles have been synthesized with controlled compositions and loadings, and characterized in detail by microscopy and spectroscopy techniques. Examination of these supported metal alloy nanoparticles in catalytic reduction of 4-nitrophenol shows high catalytic activities depending on their compositions. Their recyclability and potential application in continuous flow reactors are also demonstrated.
Co-reporter:Nirmalya Moitra;Kazuyoshi Kanamori;Toyoshi Shimada;Kazuyuki Takeda;Yumi H. Ikuhara;Xiang Gao
Advanced Functional Materials 2013 Volume 23( Issue 21) pp:2714-2722
Publication Date(Web):
DOI:10.1002/adfm.201202558
Abstract
A facile synthesis of a new class of reactive porous materials is reported: hierarchically porous hydrogen silsesquioxane (HSiO1.5, HSQ) monoliths with well-defined macropores and mesopores. The HSQ monoliths are prepared via sol-gel accompanied by phase separation in a mild condition, and contain micrometer-sized co-continuous macropores and high specific surface area reaching up to 800 m2 g−1 because of the small mesopores. A total preservation of Si–H, which is always an issue of HSQ materials, is confirmed by 29Si solid-state NMR. The HSQ monolith has then been subjected to reduction of noble metal ions to their corresponding metal nanoparticles in simple aqueous solutions under an ambient condition. The nanoparticles produced in this manner are immobilized on the HSQ monolith and are characterized by X-ray diffraction (XRD) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Both the bare HSQ and nanoparticles-embedded HSQ are promising as heterogeneous catalysts, exhibiting reusability and recyclability.
Co-reporter:Yang Zhu, Kei Morisato, Wenyan Li, Kazuyoshi Kanamori, and Kazuki Nakanishi
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 6) pp:2118
Publication Date(Web):February 26, 2013
DOI:10.1021/am303163s
Silver nanoparticles (Ag NPs) have been homogeneously introduced into hierarchically porous monolithic silica columns with well-defined macropores and SBA-15-type hexagonally ordered mesopores by using ethanol as the mild reductant. Within the cylindrical silica mesopores treated with aminopropyl groups as the host, monocrystalline Ag NPs and nanorods are obtained after being treated in silver nitrate/ethanol solution at room temperature for different durations of reducing time. The loading of Ag NPs in the monolith can be increased to 33 wt % by the repetitive treatment, which also led to the formation of polycrystalline Ag nanorods in the mesopores. Although the bare silica column cannot separate aromatic hydrocarbons, good separation of those molecules by noncharged Ag NPs confined in the porous structure of the monolith has been for the first time demonstrated with the Ag NP-embedded silica column. The NP-embedded monolithic silica would be a powerful separation tool for hydrocarbons with different number, position, and configuration of unsaturated bonds.Keywords: aromatic hydrocarbons; hierarchical pores; separation media; silica monolith; silver nanoparticles;
Co-reporter:Yasuki Kido, Kazuki Nakanishi, Nao Okumura, Kazuyoshi Kanamori
Microporous and Mesoporous Materials 2013 Volume 176() pp:64-70
Publication Date(Web):August 2013
DOI:10.1016/j.micromeso.2013.03.042
Highlights•Sol–gel synthesis of hierarchically porous Ni/C composite monolith is studied.•Poly(acrylic acid) induces the phase separation and also acts as the network former.•Effects of starting compositions on the morphologies are investigated.•Carbothermal reduction by the heat-treatment in Ar produces Ni/C composite.•The Ni/C material possesses hierarchical pores and high specific surface areas.Utilizing a facile sol–gel reaction accompanied by phase separation, rigid monolithic nickel hydroxide-based xerogels and nickel/carbon composites with hierarchical porosity have been successfully fabricated. In the synthetic route starting from nickel chloride as a nickel precursor, trimethylene oxide acts as a gelation initiator to increase pH in a reaction solution. In addition, poly(acrylic acid) plays a double role as a phase separation inducer and as a co-constituent with nickel hydroxide to comprise continuous gel skeletons in the micrometer range. As a result, obtained xerogels possess well-defined macropores evidenced by microscopy observation and mercury porosimetry. Subsequent heat-treatment in air led to the crystallization of NiO at 300 °C, while calcination under argon flow brought about the formation of nickel/carbon (Ni/C) composites with hierarchical pores and large specific surface area at temperatures higher than 300 °C. This is the first report on the preparation of rigid monolithic xerogels and metal/carbon composite with well-defined macropores based on a metal salt precursor containing “divalent” cation.Graphical abstract
Co-reporter:Yasuki Kido, Kazuki Nakanishi and Kazuyoshi Kanamori
RSC Advances 2013 vol. 3(Issue 11) pp:3661-3666
Publication Date(Web):10 Jan 2013
DOI:10.1039/C3RA22481C
Starting from an aqueous solution, porous zinc ferrite-based xerogel monoliths have been prepared via a sol–gel route accompanied by phase separation mediated by propylene oxide in the presence of poly(acrylamide). The xerogels possess well-defined macropores, and the macroporous morphologies could be easily controlled (macropore size ranges from 0.55 to 1.29 μm) by simply changing the starting composition. As-dried xerogel samples were amorphous under X-ray diffraction, while heat-treatment in air brought about the formation of spinel type ferrite phase, ZnFe2O4. Calcination under Ar atmosphere allowed the crystallization of various iron-based phases/carbon composites (Fe3O4, Fe1-δO, Fe3N, Fe4N, Fe3C, and Fe). Samples heated under Ar flow exhibited hierarchical pore structures, including continuous macropores, in addition to mesopores and micropores embedded in the carbon-containing composite matrices.
Co-reporter:Xingzhong Guo;Huan Yu;Hui Yang;Kazuyoshi Kanamori
Journal of Porous Materials 2013 Volume 20( Issue 6) pp:1477-1483
Publication Date(Web):2013 December
DOI:10.1007/s10934-013-9733-z
Macroporous methylsilsesquioxane (MSQ) monoliths have been prepared by in situ two-step processing using an initial acid catalysis step accompanied by an epoxide-mediated condensation step in the presence of ammonium chloride (NH4Cl). We investigate the effects of duration time of acidic step, heat-treatment and hydrothermal treatment on the macroporous morphology and pore structures of MSQ monoliths. The duration time of acidic step gives an important effect on the macroporous morphology and pore structures of MSQ monoliths, resulting from the polymerization of MSQ. Heat-treatment and hydrothermal treatment basically do not spoil the macroporous morphology of MSQ monoliths, while obviously varies the mesopore/micropore structures including pore size, pore volume, and pore size distribution. The macroporous MSQ materials with thick skeleton and intrinsic hydrophobicity are promising for wide applications such as ultra performance liquid chromatography (UPLC), superhydrophobic materials and so on.
Co-reporter:Kazuki Nakanishi
Journal of Sol-Gel Science and Technology 2013 Volume 65( Issue 1) pp:2-3
Publication Date(Web):2013 January
DOI:10.1007/s10971-012-2790-y
Co-reporter:Nirmalya Moitra, Toshiyuki Kamei, Kazuyoshi Kanamori, Kazuki Nakanishi, Kazuyuki Takeda, and Toyoshi Shimada
Langmuir 2013 Volume 29(Issue 39) pp:12243-12253
Publication Date(Web):2017-2-22
DOI:10.1021/la402205j
Synthesis of class II hybrid silica materials requires the formation of covalent linkage between organic moieties and inorganic frameworks. The requirement that organosilylating agents be present to provide the organic part limits the synthesis of functional inorganic oxides, however, due to the water sensitivity and challenges concerning purification of the silylating agents. Synthesis of hybrid materials with stable molecules such as simple alcohols, rather than with these difficult silylating agents, may therefore provide a path to unprecedented functionality. Herein, we report the novel functionalization of silica with organic alcohols for the first time. Instead of using hydrolyzable organosilylating agents, we used stable organic alcohols with a Zn(II) catalyst to modify the surface of a recently discovered highly reactive macro-mesoporous hydrogen silsesquioxane (HSQ, HSiO1.5) monolith, which was then treated with water with the catalyst to form surface-functionalized silica. These materials were comprehensively characterized with FT-IR, Raman, solid-state NMR, fluorescence spectroscopy, thermal analysis, elemental analysis, scanning electron microscopy, and nitrogen adsorption–desorption measurements. The results obtained from these measurements reveal facile immobilization of organic moieties by dehydrogenative addition onto surface silane (Si–H) at room temperature with high loading and good tolerance of functional groups. The organic moieties can also be retrieved from the monoliths for recycling and reuse, which enables cost-effective and ecological use of the introduced catalytic/reactive surface functionality. Preservation of the reactivity of as-immobilized organic alcohols has been confirmed, moreover, by successfully performing copper-catalyzed azide–alkyne cycloaddition (CuAAC) “click” reactions on the immobilized silica surfaces.
Co-reporter:Yasuki Kido, Kazuki Nakanishi, Akira Miyasaka, and Kazuyoshi Kanamori
Chemistry of Materials 2012 Volume 24(Issue 11) pp:2071
Publication Date(Web):May 8, 2012
DOI:10.1021/cm300495j
Various iron-based polycrystalline monoliths, Fe3O4, iron, and Fe3C, with hierarchically distributed pores have been synthesized from ionic precursors using a sol–gel process accompanied by phase separation. Propylene oxide acts as a proton scavenger to increase pH moderately and uniformly in a reaction solution, which leads to homogeneous gelation. On the other hand, poly(acrylamide) works as a phase separation inducer as well as a precipitation inhibitor. Appropriate choice of iron precursor, solvent, polymer, and epoxide allowed the formation of iron(III)-based xerogels with cocontinuous macroporous structures. The dried gels were amorphous, whereas heating in air above 300 °C led to the formation of α-Fe2O3. Calcination under an inert condition above 400 °C formed Fe3O4, iron, and Fe3C without collapse of macrostructures. Examination has been carried out using SEM, TG-DTA, FT-IR, Hg intrusion, pH measurement, X-ray diffraction, and N2 adsorption–desorption.Keywords: hierarchically porous; iron carbide; iron hydroxide; iron oxide; monoliths; phase separation; propylene oxide; sol−gel; xerogel;
Co-reporter:Kazuyoshi Kanamori and Kazuki Nakanishi
Chemical Society Reviews 2011 vol. 40(Issue 2) pp:754-770
Publication Date(Web):17 Nov 2010
DOI:10.1039/C0CS00068J
Porous polysilsesquioxane gels derived from sol–gel systems based on trifunctional silanes are reviewed. Although it is well known that trifunctional silanes possess inherent difficulties in forming homogeneous gels, increasing attention is being paid on these precursors and resultant porous polysilsesquioxanes because of hydrophobicity, functionality, and versatile mechanical properties. Much effort has been made to overcome the difficulties for homogeneous gelation, and a number of excellent porous materials with various pore properties have been explored. In this critical review, we put special emphasis on the formation of a well-defined macroporous structure by making use of phase separation, which in turn is a serious problem in obtaining homogeneous gels though. Porous polysilsesquioxane monoliths with the hierarchical structure and transparent aerogels with high mechanical durability are particularly highlighted (169 references).
Co-reporter:Yasuaki Tokudome;Akira Miyasaka
Journal of Sol-Gel Science and Technology 2011 Volume 57( Issue 3) pp:269-278
Publication Date(Web):2011 March
DOI:10.1007/s10971-010-2184-y
Starting from calcium chloride dihydrate (CaCl2·2H2O), phosphoric acid (H3PO4), and poly(acrylic acid) (PAA) dissolved in a mixture of water and methanol (MeOH), dicalcium phosphate anhydrous (DCPA, CaHPO4) monoliths with co-continuous macropores and mesopores have been synthesized by the addition of propylene oxide. Macropores are formed as a result of phase separation, while mesopores as interstices between primary particles with the size of ca. 30 nm. Propylene oxide acts as a proton scavenger and leads to moderate pH increase in a reaction solution, which brings about gelation in several minutes. On the other hand, PAA acts as a crystal growth inhibitor as well as a phase separation inducer. The extensive crystal growth of DCPA is hindered by the addition of PAA which allows morphological control of the structure in micrometer range. Fourier transform infrared spectroscopy indicates that PAA and DCPA form composite via interaction between the carboxyl groups and the surface of crystals, and together form gel phase. The solvent phase, which is converted to macropores after evaporative drying, is mainly comprised of solvent. The degree of supersaturation in a reaction solution considerably influence on the crystallization process, and thereby, influences on the porous structure in nano- and micrometer ranges.
Co-reporter:Yasuaki Tokudome, Kazuki Nakanishi, Sho Kosaka, Ayuta Kariya, Hironori Kaji, Teiichi Hanada
Microporous and Mesoporous Materials 2010 Volume 132(Issue 3) pp:538-542
Publication Date(Web):August 2010
DOI:10.1016/j.micromeso.2010.04.005
Using macroporous alumina as an aluminum source as well as structural support, high- and low-silica zeolites with trimodal pores have been fabricated in a monolithic form. Trimodally porous zeolites are obtained by the hydrothermal treatment of a monolithic alumina support impregnated with a mixture of AEROSIL 200, H2O, and sodium hydroxide or tetrapropylammonium hydroxide. The results of XRD measurement and 27Al NMR analysis reveal the formation of zeolites and the incorporation of Al into zeolite frameworks in tetrahedrally-coordinated environment. Low-silica zeolites, such as PHI- and ANA-type zeolites are formed when sodium hydroxide is utilized as a base and a structure directing agent (SDA). On the other hand, MFI-type zeolites are crystallized from highly supersaturated solutions with the use of tetrapropylammonium hydroxide. High alkaline resistance of alumina support enables the choice of wide range of OH−/SiO2 ratio, and moreover, the choice of desirable degree of supersaturation. As a result, the homogeneous crystallization of zeolites onto the alumina support has been successfully achieved.
Co-reporter:Yasuaki Tokudome, Kazuki Nakanishi, Kazuyoshi Kanamori, Koji Fujita, Hirofumi Akamatsu, Teiichi Hanada
Journal of Colloid and Interface Science 2009 Volume 338(Issue 2) pp:506-513
Publication Date(Web):15 October 2009
DOI:10.1016/j.jcis.2009.06.042
Detailed nanostructures have been investigated for hierarchically porous alumina aerogels and xerogels prepared from ionic precursors via sol–gel reaction. Starting from AlCl3·6H2O and poly(ethylene oxide) (PEO) dissolved in a H2O/EtOH mixed solvent, monolithic wet gels were synthesized using propylene oxide (PO) as a gelation initiator. Hierarchically porous alumina xerogels and aerogels were obtained after evaporative drying and supercritical drying, respectively. Macroporous structures are formed as a result of phase separation, while interstices between the secondary particles in the micrometer-sized gel skeletons work as mesoporous structures. Alumina xerogels exhibit considerable shrinkage during the evaporative drying process, resulting in relatively small mesopores (from 5.4 to 6.2 nm) regardless of the starting composition. For shrinkage-free alumina aerogels, on the other hand, the median mesopore size changes from 13.9 to 33.1 nm depending on the starting composition; the increases in PEO content and H2O/EtOH volume ratio both contribute to producing smaller mesopores. Small-angle X-ray scattering (SAXS) analysis reveals that variation of median mesopore size can be ascribed to the change in agglomeration state of primary particles. As PEO content and H2O/EtOH ratio increase, secondary particles become small, which results in relatively small mesopores. The results indicate that the agglomeration state of alumina primary particles is influenced by the presence of weakly interacting phase separation inducers such as PEO.Hierarchically porous alumina aerogel showing compositional dependences of structure both in micrometer and nanometer ranges.
Co-reporter:Kazuki Nakanishi, Tomohiko Amatani, Seiji Yano and Tetsuya Kodaira
Chemistry of Materials 2008 Volume 20(Issue 3) pp:1108
Publication Date(Web):December 28, 2007
DOI:10.1021/cm702486b
By combining the micellar templating in nanometer-scale with the polymerization-induced phase separation in micrometer-scale, we can synthesize monolithic silica or silsesquioxane gel materials with hierarchical well-defined macropores and shape-controlled mesopores. Depending on the mechanism of enhancing micellar-templating of siloxane oligomers, macroframeworks containing long-range-ordered cylindrical mesopores with different degrees of order have been produced. Alkylene-bridged silicon alkoxides can also be prepared into similarly hierarchical porous structures with broadened variations in framework morphology. These examples demonstrate the versatility of using phase-separation in micellar-templated gelling systems to obtain well-defined macroporous structures.
Co-reporter:Haruko Saito, Kazuyoshi Kanamori, Kazuki Nakanishi, Kazuyuki Hirao, Yukihiro Nishikawa, Hiroshi Jinnai
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2007 Volume 300(1–2) pp:245-252
Publication Date(Web):1 June 2007
DOI:10.1016/j.colsurfa.2006.12.075
Three-dimensional (3D) observation of co-continuous macropore structure was performed using laser scanning confocal microscopy (LSCM). The obtained LSCM images were reconstructed into 3D images, and further subjected to image analysis. The LSCM observation and the following image analysis provided geometrical parameters of the macropore surfaces, which cannot be obtained by classical techniques for macropore characterization, such as scanning electron microscopy (SEM) observation or mercury intrusion method. Based on the obtained structural parameters, influences of viscoelastic properties on the liquid-phase structural formation mechanism were examined.
Co-reporter:Haruko Saito, Kazuki Nakanishi, Kazuyuki Hirao, Hiroshi Jinnai
Journal of Chromatography A 2006 Volume 1119(1–2) pp:95-104
Publication Date(Web):30 June 2006
DOI:10.1016/j.chroma.2006.03.087
The geometrical properties of co-continuous macroporous silica monoliths have been studied by laser scanning confocal microscopy (LSCM) and a comparison has been made with those obtained by conventional mercury intrusion method. Tetrahedral skeleton model (TMS), which mimics the gel skeleton shape of monoliths, was compared with real monoliths in terms of macropore and porosity using the geometrical parameters extracted from the LSCM observations. Liquid flow behavior through the macroporous silica monoliths was examined in comparison with those simulated using TSM, based on the geometrical properties obtained from LSCM observations. Heterogeneity in macropore topology and connectivity in pores and skeletons are suggested to contribute to the improvement of the model structure for macroporous monoliths.
Co-reporter:Yoshitaka Suzumura, Kazuyoshi Kanamori, Kazuki Nakanishi, Kazuyuki Hirao, Junta Yamamichi
Journal of Chromatography A 2006 Volume 1119(1–2) pp:88-94
Publication Date(Web):30 June 2006
DOI:10.1016/j.chroma.2006.02.059
When bicontinuous gels are prepared via sol–gel method in a 2-dimensionally (2D) confined space, the gel skeletons in the vicinity of interface of a mold are elongated perpendicular to the interface. This phenomenon was attributed to the dynamic wetting of polymerizing siloxane phase onto the interface of the mold under gravity. In this paper, we report the successful preparation of monolithic columns with an oriented pillar structure in a variety of 2D confined spaces. Starting from a solution, which consists of methyltrimethoxysilane (MTMS), the macroporous structure is prepared in situ by a completely spontaneous process. In the oriented pillar structure, bicontinuous siloxane skeletons deformed or disappeared and most pillars are oriented along the direction of gravity. Gel morphologies with the pillar structure were examined by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). Geometrical information on gel morphologies was numerically derived from the obtained 3D LSCM images.
Co-reporter:Kazuki Nakanishi and Kazuyoshi Kanamori
Journal of Materials Chemistry A 2005 vol. 15(Issue 35-36) pp:3776-3786
Publication Date(Web):03 Aug 2005
DOI:10.1039/B508415F
Siloxane-based organic–inorganic hybrid monoliths with well-defined macropores and/or mesopores have been synthesized by a sol–gel process, accompanied by polymerization-induced phase separation. Using aklyltrialkoxysilanes and alkylene-bridged alkoxysilanes, two different categories of organosiloxane networks have been characterized in view of macroporosity (based on phase separation) and mesoporosity (supramolecularly templated by surfactants). While the alkyl-terminated poly(siloxane) networks exhibit substantial surface hydrophobicity accompanied by mechanical flexibility, the alkylene-bridged networks behave much more similarly to those prepared from tetraalkoxysilanes with regard to surface hydrophilicity, mechanical rigidness and mesopore-forming ability. The supramolecular templating of mesopores embedded in the gel skeletons (which comprise well-defined macroporous networks) has proven to give a wide variety of hierarchically-designed macro–mesoporous hybrid materials.
Co-reporter:Yang Zhu, Kazuyoshi Kanamori, Nicolas Brun, Carl-Hugo Pélisson, Nirmalya Moitra, François Fajula, Vasile Hulea, Anne Galarneau, Kazuyuki Takeda, Kazuki Nakanishi
Catalysis Communications (5 December 2016) Volume 87() pp:112-115
Publication Date(Web):5 December 2016
DOI:10.1016/j.catcom.2016.09.014
•A hierarchically porous zirconium phosphate monolith with high surface area is fabricated.•Both Lewis and Brønsted acid sites are found present in the as-synthesized and calcined monoliths.•High catalytic activity over dehydration of xylose into furfural reaction is demonstrated.We report the application of hierarchically porous zirconium phosphate monoliths with high surface area as acidic heterogeneous catalysts for the dehydration of xylose into furfural. Analyses by NH3-temperature programmed desorption and 31P solid state NMR reveal the presence of both Lewis and Brønsted acid sites in the as-synthesized zirconium phosphate monolith and that calcined at 600 °C. High accessibility and availability of the acidic sites and easy separation of the monolith from the liquid medium result in good catalytic activity (initial reaction rate for furfural production as 8.7 mmol gcat− 1 h− 1) with easy handling of the catalyst.Download full-size image
Co-reporter:Kazuyoshi Kanamori and Kazuki Nakanishi
Chemical Society Reviews 2011 - vol. 40(Issue 2) pp:NaN770-770
Publication Date(Web):2010/11/17
DOI:10.1039/C0CS00068J
Porous polysilsesquioxane gels derived from sol–gel systems based on trifunctional silanes are reviewed. Although it is well known that trifunctional silanes possess inherent difficulties in forming homogeneous gels, increasing attention is being paid on these precursors and resultant porous polysilsesquioxanes because of hydrophobicity, functionality, and versatile mechanical properties. Much effort has been made to overcome the difficulties for homogeneous gelation, and a number of excellent porous materials with various pore properties have been explored. In this critical review, we put special emphasis on the formation of a well-defined macroporous structure by making use of phase separation, which in turn is a serious problem in obtaining homogeneous gels though. Porous polysilsesquioxane monoliths with the hierarchical structure and transparent aerogels with high mechanical durability are particularly highlighted (169 references).
Co-reporter:Nirmalya Moitra, Kazuyoshi Kanamori, Yumi H. Ikuhara, Xiang Gao, Yang Zhu, George Hasegawa, Kazuyuki Takeda, Toyoshi Shimada and Kazuki Nakanishi
Journal of Materials Chemistry A 2014 - vol. 2(Issue 31) pp:NaN12544-12544
Publication Date(Web):2014/06/04
DOI:10.1039/C4TA01767F
Supported metal alloy nanoparticles demonstrate high potential in designing heterogeneous catalysts for organic syntheses, pollution control and fuel cells. However, requirements of high temperature and multistep processes remain standing problems in traditional synthetic strategies. We herein present a low-temperature, single-step, liquid-phase methodology for designing monolith-supported metal alloy nanoparticles with high physicochemical stability and accessibility. Metal ions in aqueous solutions are reduced to form their corresponding metal alloy nanoparticles within hierarchically porous hydrogen silsesquioxane (HSQ, HSiO1.5) monoliths bearing well-defined macro- and mesopores and exhibiting high surface redox activity due to the presence of abundant Si–H groups. Supported bi-, tri- and tetrametallic nanoparticles have been synthesized with controlled compositions and loadings, and characterized in detail by microscopy and spectroscopy techniques. Examination of these supported metal alloy nanoparticles in catalytic reduction of 4-nitrophenol shows high catalytic activities depending on their compositions. Their recyclability and potential application in continuous flow reactors are also demonstrated.
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