Faculty Profiles - NAKANISHI Kazuki

Papers - NAKANISHI Kazuki

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Hierarchically Structured Porous Materials: Application to Separation Sciences Reviewed

Nakanishi, K

HIERARCHICALLY STRUCTURED POROUS MATERIALS: FROM NANOSCIENCE TO CATALYSIS, SEPARATION, OPTICS, ENERGY, AND LIFE SCIENCE page： 517 - 529 2012

Controlled pore formation in organotrialkoxysilane-derived hybrids: from aerogels to hierarchically porous monoliths Reviewed

Kazuyoshi Kanamori, Kazuki Nakanishi

CHEMICAL SOCIETY REVIEWS Vol. 40 ( 2 ) page： 754 - 770 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

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).

DOI： 10.1039/c0cs00068j

Facile Preparation of Hierarchically Porous TiO2 Monoliths Reviewed

George Hasegawa, Kazuyoshi Kanamori, Kazuki Nakanishi, Teiichi Hanada

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 93 ( 10 ) page： 3110 - 3115 2010.10

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Monolithic titania (TiO2) with multiscale porous structures have been successfully prepared via the sol-gel route accompanied by phase separation utilizing a chelating agent and mineral salt. The TiO2 gels obtained possess well-defined macropores derived from spinodal decomposition and mesopores as interstices of anatase TiO2 nanocrystallites. Most of the chelating agent were removed by hydrolysis and subsequent decarbonation through the gradual solvent exchange from ethanol to water. The TiO2 particles comprising TiO2 gel skeletons spontaneously converted from amorphous to anatase through the solvent exchange process in a mild condition at 60 degrees C. The present method of the fabrication of porous TiO2 monoliths is advantageous for widespread applications because the reaction occurs under an almost neutral condition and does not require a hydrothermal process, which was indispensable to strengthen the monolith in the method previously reported.

DOI： 10.1111/j.1551-2916.2010.03831.x

Elastic Aerogels and Xerogels Synthesized From Methyltrimethoxysilane (MTMS) Reviewed

Kanamori Kazuyoshi, Nakanishi Kazuki, Hanada Teiichi

POLYMER-BASED SMART MATERIALS - PROCESSES, PROPERTIES AND APPLICATION Vol. 1134 page： 173 - + 2009

Preparation of Macroporous Poly(divinylbenzene) Gels Via Living Radical Polymerization Reviewed

Hasegawa, J; Kanamori, K; Nakanishi, K; Hanada, T; Yamago, S

POLYMER-BASED SMART MATERIALS - PROCESSES, PROPERTIES AND APPLICATION Vol. 1134 page： 139 - + 2009

Hierarchically porous oxides, hybrids and polymers via sol-gel accompanied by phase separation Reviewed

Kazuki Nakanishi

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 51 - 62 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MATERIALS RESEARCH SOCIETY

In various crosslinking systems containing metal oxides, organo-siloxane polymers and pure hydrocarbons, monolithic materials with hierarchical well-defined macropores and controlled mesopores have been synthesized. Synthetic progress in alkoxy-derived macroporous silica lead to the preparation of long-range ordered mesoporous skeletons in well-defined. macroporous framework. Alkylene-bridged silicon alkoxides can also be prepared into similarly hierarchical porous structures with broadened variations in framework morphology. Macro-mesoporous alkoxy-derived pure titania and zirconia have been prepared using hydrochloric acid - mediated processes. Compared with those prepared from colloidal dispersions, alkoxy-derived macroporous titania exhibited much higher mechanical strength. Titania monolith is a promising candidate as a separation medium to discriminate phosphorylated compounds in a liquid chromatography mode. Pure alumina macroporous monolith has been first synthesized from aluminum salt using propylene glycol as a proton scavenger to thrust the solution pH from acidic into neutral conditions. Alumina-based complex oxides such as garnets and spinels can also be prepared in pure phases. Polymerization and phase separation in organic crosslinker system was also controlled to obtain well-defined co-continuous macro-frameworks instead of those composed of aggregated particles. These examples demonstrate the versatility of using phase-separation in gelling systems to obtain well-defined macroporous structures.

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Phase separation in alkoxy-derived silica system containing polyacrylamide Reviewed

Kousuke Kawamoto, Kazuki Nakanishi, Teiichi Hanada

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 63 - 68 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MATERIALS RESEARCH SOCIETY

By inducing phase separation parallel to the sol-gel transition of alkoxy-derived silica systems, gels having both macroporous and mesoporous structures can be obtained. Using poly(acrylamide) (PAAm) as a phase-separation inducer, macro/mesoporous silica gels were synthesized. After solvent exchange by water, the size distribution of mesopores of wet gels was evaluated by thermoporometry using a differential scanning calorimetry (DSC). Alternatively, gels were evaporation-dried after solvent exchange by ethanol or water/ethanol, followed by heat-treatment to completely remove volatile and organic components. Characterization of the dried or heat-treated samples was carried out using a scanning electron microscope (SEM) and by nitrogen adsorption measurements. Experimental results showed that the interaction between PAAm and silica is not so strong as the case of polymers having poly(oxyethylene) chains. The contribution of the secondary phase separation within the crosslinking silica-rich phase was suggested to be responsible for the mesopore formation in the PAAm-silica system.

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Phase separation in Al2O3 sol-gel system incorporated with high molecular weight poly(ethylene oxide) Reviewed

Yasuaki Tokudome, Kazuki Nakanishi, Koji Fujita, Kiyotaka Miura, Kazuyuki Hirao

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 69 - 74 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MATERIALS RESEARCH SOCIETY

Pure alumina monoliths with well-defined macropores and mesostructured skeleton have been synthesized via a spontaneous route from the aqueous and ethanolic solution of aluminum salts in the presence of propylene oxide and high molecular weight poly(ethylene oxide)(PEO). The addition of propylene oxide to the starting solution controls the gelation, while the addition of PEO induces the phase separation. Appropriate choice of the starting composition, with which the phase separation and gelation concur, produces large-dimension (10mmx10mmx10mm), bicontinuous macroporous Al2O3 monoliths. The mean size of the continuously connected pores is controlled in the micrometer range, depending on the PEO concentration and polarity of the solution. On the other hand, micropores and mesopores, originated from the interstices among primary particles, exhibit median pore size of about 2.6 mn and the BET surface area as high as 396 m(2)/g after dried temperature at 40 degrees C.

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Preparation of Macroporous Poly(divinylbenzene) Gels Via Living Radical Polymerization Reviewed

Joji Hasegawa, Kazuyoshi Kanamori, Kazuki Nakanishi, Teiichi Hanada, Shigeru Yamago

POLYMER-BASED SMART MATERIALS - PROCESSES, PROPERTIES AND APPLICATION Vol. 1134 page： 139 - 144 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MATERIALS RESEARCH SOC

Macroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotellurium-mediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a non-reactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. The properties of the macropores have been controlled by changing starting composition.

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Elastic aerogels and xerogels synthesized from methyltrimethoxysilane (MTMS) Reviewed

Kanamori K., Nakanishi K., Hanada T.

Materials Research Society Symposium Proceedings Vol. 1134 page： 173 - 178 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Transparent organic-inorganic hybrid aerogels and aerogel-like xerogels have been prepared from methyltrimethoxysilane (MTMS) respectively by supercritical drying (SCD) and ambient pressure drying (APD). The new aerogels and xerogels significantly deform without collapsing on uniaxial compression and almost fully relax when unloaded. This elastic behavior, termed as "spring-back", allows APD without noticeable shrinkage and cracking. The flexible network composed of lower cross-linking density (up to three bonds per every silicon atom) compared to silica gels (up to four bonds) and repulsion between hydrophobic methyl groups bonded to every silicon atom largely contributes to the pronounced deformability and relaxing, respectively. Lower surface silanol group density also plays a crucial role for the "spring-back" behavior. © 2009 Materials Research Society.

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Multiscale templating of siloxane gels via polymerization-induced phase separation Reviewed

Kazuki Nakanishi, Tomohiko Amatani, Seiji Yano, Tetsuya Kodaira

CHEMISTRY OF MATERIALS Vol. 20 ( 3 ) page： 1108 - 1115 2008.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

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.

DOI： 10.1021/cm702486b

Hierarchically porous oxides, hybrids and polymers via sol-gel accompanied by phase separation Reviewed

Nakanishi Kazuki

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 51 - 62 2008

Phase separation in alkoxy-derived silica system containing polyacrylamide Reviewed

Kawamoto, K; Nakanishi, K; Hanada, T

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 63 - 68 2008

Phase separation in Al<sub>2</sub>O<sub>3</sub> sol-gel system incorporated with high molecular weight poly(ethylene oxide) Reviewed

Tokudome, Y; Nakanishi, K; Fujita, K; Miura, K; Hirao, K

ORGANIC/INORGANIC HYBRID MATERIALS - 2007 Vol. 1007 page： 69 - 74 2008

Sol-gel with phase separation. Hierarchically porous materials optimized for high-performance liquid chromatography separations Reviewed

Kazuki Nakanishi, Nobuo Tanaka

ACCOUNTS OF CHEMICAL RESEARCH Vol. 40 ( 9 ) page： 863 - 873 2007.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Sol-gel processes for fabricating oxides or metalloxane polymers with controlled porous structures have been reviewed. Gel materials having controlled macropores are synthesized by polymerization-induced phase separation and concurrent sol-gel transition in a variety of chemical compositions. Several variations of tailoring mesopore structures within the macroporous materials are introduced, which enable one to design hierarchically porous metal oxide and metalloxane polymer materials. Applications of monolithic silica gels having hierarchical macro/mesoporous structure to the separation media of high-performance liquid chromatography, HPLC, are described.

DOI： 10.1021/ar600034p

New transparent methylsilsesquioxane aerogels and xerogels with improved mechanical properties Reviewed

Kazuyoshi Kanamori, Mamoru Aizawa, Kazuki Nakanishi, Teiichi Hanada

ADVANCED MATERIALS Vol. 19 ( 12 ) page： 1589 - + 2007.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Transparent organic-inorganic hybrid aerogels and xerogels are prepared by using a sol-gel synthesis from a single trifunctional precursor, methyltrimethoxysilane (see figure). Obtained aerogels show a reversible shrinkage-recovery response against uniaxial compression. Aerogel-like xerogels are successfully obtained by evaporation drying under ambient pressure because the gels recover from the temporal shrinkage caused by the capillary force of a drying solvent. Pore properties and nanotextures are well-preserved in the resultant xerogels.

DOI： 10.1002/adma.200602457

Performance of monolithic silica capillary columns with increased phase ratios and small-sized domains Reviewed

Takeshi Hara, Hiroshi Kobayashi, Tohru Ikegami, Kazuki Nakanishi, Nobuo Tanaka

ANALYTICAL CHEMISTRY Vol. 78 ( 22 ) page： 7632 - 7642 2006.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Monolithic silica capillary columns for HPLC were prepared from tetramethoxysilane to have smaller sized domains and increased phase ratios as compared to previous materials, and their performance was evaluated. The monolithic silica columns possessed an external porosity of 0.65-0.76 and a total porosity of 0.92-0.95 and showed considerably higher performance and greater retention factors in a reversed-phase mode after chemical modification than columns previously reported. An octadecylsilylated monolithic silica column with the smallest domain size (through-pores of similar to 1.3 mu m and silica skeletons of similar to 0.9 mu m) showed a plate height of less than 5 mu m at optimum linear velocities (u) of 2- 3 mm/s in 80% acetonitrile for a solute having retention factors of similar to 1, and similar to 7 mu m at u) 8 mm/s. With a permeability similar to that of a column packed with 5-mu m particles, the monolithic silica columns were able to attain column efficiencies comparable to that of particulate columns packed with 2- 2.5-mu m particles, and showed performance in the "forbidden region" for the previous columns. The performance of the monolithic column can be compared favorably with that of a particle-packed column when 15 00030 000 or more theoretical plates are desired at a pressure drop of 20-40 MPa or lower. The increased homogeneity of the co-continuous structures, in addition to the small-sized domains, contributed to the higher performance as compared to previous monolithic silica columns.

DOI： 10.1021/ac060770e

Living radical polymerization in size-exclusion silica gel column reactors Reviewed

Katsube M., Ouchi M., Ando T., Sawamoto M., Nakanishi K., Ishizuka N.

Polymer Preprints, Japan Vol. 55 ( 1 ) 2006.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

This work was aimed to development of continuous-flow living radical polymerization in a silica-gel column, "Chromolith", focusing its separation function by combination of surface chemical absorption and size-exclusion via uniquely shaped mesopores, Thus, living radical copolymerization of two monomers with different polarities, methyl methacrylate (MMA) and 2(dimethylamino)ethyl methacrylate (DMAEMA) was performed with a catalyst [2; Ru(Ind)Cl(PPh3)2] coupled with an initiator (1). Copolymers were continuously produced, and molecular weight distributions were narrower than that in the corresponding batch process.

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Preparation of novel macroporous polymer monoliths using polymerization-induced phase separation Reviewed

Kanamori K., Nakanishi K.

Polymer Preprints, Japan Vol. 55 ( 1 ) 2006.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Preprints, Japan

Macroporous polymer monoliths with rigid three-dimensional networks have been prepared via living radical polymerization of multi-functional vinyl crosslinkers. By incorporating a polymeric agent to effectively induce phase separation, well-defined macroporous morphology with highly interconnected gel skeletons and macropores has been formed presumably by spinodal decomposition. The pore size and volume are found to be controlled simply by changing starting compositions.

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Rigid macroporous poly(divinylbenzene) monoliths with a well-defined bicontinuous morphology prepared by living radical polymerization Reviewed

Kazuyoshi Kanamori, Kazuki Nakanishi, Teiichi Hanada

ADVANCED MATERIALS Vol. 18 ( 18 ) page： 2407 - + 2006.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Rigid macroporous poly(divinylbenzene) monoliths with good mechanical and thermal stability and possessing a well-defined bicontinuous structure (see figure) are synthesized using living radical polymerization and a polymeric phase separator. The macropore size and volume can be independently tuned by varying the starting compositions of the mixtures. Scale bars represent 20 m, a-d show increasing polydimethylsiloxane concentration

DOI： 10.1002/adma.200601026

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Papers - NAKANISHI Kazuki