Faculty Profiles - NAKANISHI Kazuki

Papers - NAKANISHI Kazuki

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Spontaneous preparation of hierarchically porous silica monoliths with uniform spherical mesopores confined in a well-defined macroporous framework Reviewed

Xingzhong Guo, Rui Wang, Huan Yu, Yang Zhu, Kazuki Nakanishi, Kazuyoshi Kanamori, Hui Yang

DALTON TRANSACTIONS Vol. 44 ( 30 ) page： 13592 - 13601 2015

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

Hierarchically porous silica monoliths with well-defined interconnected macropores and uniform spherical mesopores were spontaneously prepared by combining polymerization-induced phase separation with an epoxide-mediated sol-gel route without any complicated aging and drying and high-temperature heat treatment. The precise control of pore structures can be realized by using propylene oxide (PO) as the gelation mediation agent, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P123) as the phase-separation inducer as well as the structure-directing agent and 1,3,5-trimethyl-benzene (TMB) as the micelle-swelling agent. The as-prepared silica monolith possesses an interesting hierarchically porous structure constructed by 10 nm uniform spherical mesopores confined in a macroporous framework of well-defined 1 mu m macropores, and exhibits a BET surface area as high as 848 m(2) g(-1). Heat treatment at 400-800 degrees C gradually decreases the BET surface area to 195 m(2) g(-1), while most of the uniform mesoporous structure remains intact.

DOI： 10.1039/c5dt01672j

Sol-gel synthesis of nanocrystal-constructed hierarchically porous TiO2 based composites for lithium ion batteries Reviewed

Wenjun Zhu, Hui Yang, Kazuki Nakanishi, Kazuyoshi Kanamori, Xingzhong Guo

RSC ADVANCES Vol. 5 ( 31 ) page： 24803 - 24813 2015

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

Hierarchically porous TiO2 based composites (pure TiO2 and TiO2/carbon (TiO2/C) composite) were synthesized by a facile sol-gel process followed by post- calcination. Poly(vinylpyrrolidone) (PVP) acts as a phase separation inducer as well as a carbon source. The as-prepared TiO2 based composites possess an interesting hierarchically porous structure constructed of cocontinuous macropores and mesoporous skeletons consisting of interconnected nanocrystals and in situ distributed carbon. The hierarchically porous TiO2/C composite shows excellent electrochemical performance with fast lithium ion diffusion and electronic transport, resulting from the hierarchically porous structure and conductive carbon material. The TiO2/C composite calcined at 500 degrees C exhibits the highest BET surface area of 170 m(2) g(-1), superior cycling stability (delivers a remarkable discharge capacity of 132 mA h g(-1) at 1 C after 100 cycles) and excellent rate capability (over 96 mA h g(-1) at 30 C rate). The results indicate that these hierarchically porous TiO2 based composites could be promising anode materials for high performance lithium ion batteries.

DOI： 10.1039/c5ra03491d

Other Link： http://orcid.org/0000-0002-8069-4780

Impact of Electrolyte on Pseudocapacitance and Stability of Porous Titanium Nitride (TiN) Monolithic Electrode Reviewed

George Hasegawa, Atsushi Kitada, Shota Kawasaki, Kazuyoshi Kanamori, Kazuki Nakanishi, Yoji Kobayashi, Hiroshi Kageyama, Takeshi Abe

JOURNAL OF THE ELECTROCHEMICAL SOCIETY Vol. 162 ( 1 ) page： A77 - A85 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：ELECTROCHEMICAL SOC INC

We report the fabrication of porous titanium nitride (TiN) monoliths through the ammonolysis of porous TiO2 monoliths prepared via the sol-gel process accompanied by phase separation. The obtained TiN monoliths possess good mechanical strength as well as excellent electric conductivity with a superconducting transition at T-c similar to 5.0 K. We have investigated the electrochemical properties of the porous TiN monoliths as an electrode using various electrolytes. The results reveal that the pseudocapacitance of TiN increases in the order of K+ < Na+ < Li+ contrary to the case of EDL capacitance in neutral aqueous electrolytes. It is also found that acidic and strongly basic electrolytes are not suitable due to high corrosivity, while there is no significant deterioration when neutral aqueous electrolytes and organic electrolytes are used. (C) 2014 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0491501jes

Fabrication of hierarchically porous monolithic layered double hydroxide composites with tunable microcages for effective oxyanion adsorption Reviewed

Naoki Tarutani, Yasuaki Tokudome, Megu Fukui, Kazuki Nakanishi, Masahide Takahashi

RSC ADVANCES Vol. 5 ( 70 ) page： 57187 - 57192 2015

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

Removal of toxic substances from industrial wastes is an urgent issue for realizing a sustainable society. Layered double hydroxides ( LDHs) are expected to be an effective adsorbent for toxic anions, especially oxyanions, because of their high anion adsorption capacity and reusability. Monolithic LDH materials with rational meso- and macropores are expected to show high adsorption capacity/rate towards targeted toxic substances owing to their large specific surface area and liquid transport property. Besides fabricating hierarchical pores, size control of microcages in LDH crystals is required to achieve selective removal of oxyanions. Herein, we prepared hierarchically porous monolithic LDH composites with tunable microcages by changing the combination of cationic species in the LDH crystal. Monolithic Mg-, Mn-, Fe-, Co- and Ni-Al type LDH composites with hierarchical pores were successfully prepared via an epoxide-mediated sol-gel reaction accompanied with phase separation. The monolithic Co-Al type LDH composite with hierarchical pores exhibited the highest CrO42- adsorption capacity because its microcage size easily fits the CrO42- size. Also Co-Al type LDH composites adsorbed different oxyanions, depending on their affinity with the LDH, in a SO42-, CrO42-, MoO42- and HVO42- co-existing solution. The pore size controllability in discrete length-scales of micrometers, nanometers, and picometers offers LDHs with tailored surface chemistries and physical properties desirable for effective and selective oxyanion adsorption.

DOI： 10.1039/c5ra05942a

Synthesis of robust hierarchically porous zirconium phosphate monolith for efficient ion adsorption Reviewed

Yang Zhu, Taiyo Shimizu, Takara Kitajima, Kei Morisato, Nirmalya Moitra, Nicolas Brun, Tsutomu Kiyomura, Kazuyoshi Kanamori, Kazuyuki Takeda, Hiroki Kurata, Masamoto Tafu, Kazuki Nakanishi

NEW JOURNAL OF CHEMISTRY Vol. 39 ( 4 ) page： 2444 - 2450 2015

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

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 mu m). The as-synthesized ZrP monolith with a high reactive surface area (600 m(2) 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.

DOI： 10.1039/c4nj01749h

Facile synthesis of monolithic mayenite with well-defined macropores via an epoxide-mediated sol-gel process accompanied by phase separation Reviewed

Xingzhong Guo, Xiaobo Cai, Jie Song, Yang Zhu, Kazuki Nakanishi, Kazuyoshi Kanamori, Hui Yang

NEW JOURNAL OF CHEMISTRY Vol. 38 ( 12 ) page： 5832 - 5839 2014.12

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

Monolithic mayenite with well-defined macropores has been successfully synthesized from ionic precursors via a sol-gel process accompanied by phase separation. The addition of propylene oxide (PO) to the starting solution leads to homogenous gelation and modifies the gel skeleton, whereas the addition of poly(ethylene oxide) (PEO) induces phase separation. Glycol acts as a chelating agent to suppress the precipitation of Ca2+ ions, and formamide works as a drying control chemical additive to enhance the drying behavior. Appropriate amounts of solvents, PEO, and PO allow the formation of calcium aluminate gets with co-continuous macroporous structure. The reaction mechanism of the sol-gel process of the Ca-Al-O system is also investigated by TG-DSC, FT-IR and NMR. The dried gels are amorphous and the crystalline phase Ca12Al14O32Cl2 forms after heat-treatment at 1000 degrees C in air, while the macroporous structure is preserved. The resultant monoliths before and after heat-treatment possess both high porosity and smooth and dense skeletons.

DOI： 10.1039/c4nj00898g

Other Link： http://orcid.org/0000-0002-8069-4780

Facile preparation of silver nanoparticles homogeneously immobilized in hierarchically monolithic silica using ethylene glycol as reductant Reviewed

Huan Yu, Yang Zhu, Hui Yang, Kazuki Nakanishi, Kazuyoshi Kanamori, Xingzhong Guo

DALTON TRANSACTIONS Vol. 43 ( 33 ) page： 12648 - 12656 2014.9

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

A facile and "green" method was proposed to introduce Ag nanoparticles (Ag NPs) into the hierarchically monolithic silica uniformly in the presence of (3-aminopropyl)-triethoxysilane (APTES) and ethylene glycol. APTES is used to modify the monolith by incorporating amino groups onto the surface of meso-macroporous skeletons, while ethylene glycol is employed as the productive reductant. Ag NPs are homogeneously immobilized in hierarchically monolithic silica after reduction and drying at 40 degrees C for different duration times, and the embedded amount of Ag NPs can reach 15.44 wt% when treated once. The embedment of Ag NPs increases with the repeat treatment and the APTES amount, without uncontrollable crystalline growth. The surface areas of Ag NPs embedded in silica monoliths after heat treatment at 300 and 400 degrees C are higher than those before heat treatment. The modification via APTES and the embedment of Ag NPs does not spoil the morphology of monolithic silica, while changing the pore structures of the monolith. A tentative formation process and a reduction mechanism are proposed for the modification, reduction and embedment. Ag NPs embedded in monolithic silica is promising for wide applications such as catalysis and separation.

DOI： 10.1039/C4DT00655K

Experimental and numerical validation of the effective medium theory for the B-term band broadening in 1st and 2nd generation monolithic silica columns Reviewed

Sander Deridder, Alison Vanmessen, Kazuki Nakanishi, Gert Desmet, Deirdre Cabooter

JOURNAL OF CHROMATOGRAPHY A Vol. 1351 page： 46 - 55 2014.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Effective medium theory (EMT) expressions for the B-term band broadening in monolithic silica columns are presented at the whole-column as well as at the mesoporous skeleton level. Given the bi-continuous nature of the monolithic medium, regular as well as inverse formulations of the EMT-expressions have been established. The established expressions were validated by applying them to a set of experimental effective diffusion (D-eff)-data obtained via peak parking on a number of 1st and 2nd generation monolithic silica columns, as well as to a set of numerical diffusion simulations in a simplified monolithic column representation (tetrahedral skeleton model) with different external porosities and internal diffusion coefficients. The numerically simulated diffusion data can be very closely represented over a very broad range of zone retention factors (up to k '' = 80) using the established EMT-expressions, especially when using the inverse variant. The expressions also allow representing the experimentally measured effective diffusion data very closely. The measured D-eff/D-mol-values were found to decrease significantly with increasing retention factor, in general going from about D-eff/D-mol = 0.55 to 0.65 at low k '' (k '' congruent to 1.5-3.8) to D-eff/D-mol = 0.25 at very high k '' (k '' congruent to 40-80). These values are significantly larger than observed in fully-porous and core-shell particles. The intra-skeleton diffusion coefficient (D-pz) was typically found to be of the order of D-pz/D-mol = 0.4, compared to D-pz/D-mol = 0.2-0.35 observed in most particle-based columns. These higher D-pz/D-mol values are the cause of the higher D-eff/D-mol values observed. In addition, it also appears that the higher internal diffusion is linked to the higher porosity of the mesoporous skeleton that has a relatively open structure with relatively wide pores. The observed (weak) relation between D-pz/D-mol and the zone retention factor appears to be in good agreement with that predicted when applying the regular variant of the EMT-expression directly to the mesoporous skeleton level. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2014.04.099

Other Link： http://orcid.org/0000-0002-8069-4780

Polymethylsilsesquioxane-Cellulose Nanofiber Biocomposite Aerogels with High Thermal Insulation, Bendability, and Superhydrophobicity Reviewed

Gen Hayase, Kazuyoshi Kanamori, Kentaro Abe, Hiroyuki Yano, Ayaka Maeno, Hironori Kaji, Kazuki Nakanishi

ACS APPLIED MATERIALS & INTERFACES Vol. 6 ( 12 ) page： 9466 - 9471 2014.6

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

Polymethylsilsesquioxane-cellulose nanofiber (PMSQ:CNF) composite aerogels have been prepared through sol-gel in a solvent containing a small amount of CNFs as suspension. Since these composite aerogels do not show excessive aggregation of PMSQand CNF, the original PMSQnetworks are not disturbed. Composite aerogels with low density (0.020 g cm(-3) at lowest), low thermal conductivity (15 mW rn(-1) K-1), visible light translucency, bending flexibility, and superhydrophobicity thus have been successfully obtained. In particular, the lowest density and bending flexibility have been achieved with the aid of the physical supporting effect of CNFs, and the lowest thermal conductivity is comparable with the original PMSQ aerogels and standard silica aerogels. The PMSQ: CNF composite aerogels would be a candidate to practical high-performance thermal insulating materials.

DOI： 10.1021/am501822y

Other Link： http://orcid.org/0000-0002-8069-4780

Preparation of macroporous cordierite monoliths via the sol-gel process accompanied by phase separation Reviewed

Xingzhong Guo, Kazuki Nakanishi, Kazuyoshi Kanamori, Yang Zhu, Hui Yang

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY Vol. 34 ( 3 ) page： 817 - 823 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Monolithic cordierite with a cocontinuous macroporous structure has been successfully prepared by the sol-gel process accompanied by phase separation in the presence of poly(acrylamide) (PAAm). Propylene oxide (PO) acts as an acid scavenger to mediate the gelation of MgO-Al2O3-SiO2 ternary system, while PAAm works as a phase-separation inducer as well as a network former. The dried gel and that heat-treated at 800 degrees C are amorphous, and the sapphirine begins to precipitate at 900 degrees C, then transforming to orthorhombic beta-cordierite at 1100 degrees C. After heat-treated at and above 1200 degrees C, the resultant beta-cordierite further transforms to stable hexagonal alpha-cordierite. Heat-treatment changes the macroporous structure of cordierite monoliths such as macropore size and its distribution. The macroporous cordierite monolith after heat-treated at 1200 degrees C is found to possess a total porosity of 54%, interconnected macropores and dense solid skeletons. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jeurceramsoc.2013.08.016

Fabrication of nitrogen-doped TiO2 monolith with well-defined macroporous and bicrystalline framework and its photocatalytic performance under visible light Reviewed

Olim Ruzimuradov, Suvankul Nurmanov, Mirabbos Hojamberdiev, Ravi Mohan Prasad, Aleksander Gurlo, Joachim Broetz, Kazuki Nakanishi, Ralf Riedel

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY Vol. 34 ( 3 ) page： 809 - 816 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

In this study, hierarchically porous bicrystalline nitrogen-doped titania (N-doped TiO2) monolithic material was fabricated by a simple two-step approach: (i) preparation of TiO2 porous monolith by a sol-gel process of titanium alkoxide in a mild condition utilizing a chelating agent and mineral salt and (ii) annealing of TiO2 porous monolith obtained under a modest flow of ammonia gas at 700 degrees C for 2 h. The phase composition, crystal structure, morphology, pore structure, and porous properties of the final product were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen physisorption measurement, respectively. The resultant N-doped TiO2 porous monolith possesses a bicrystalline (anatase and rutile) framework with a well-defined macroporosity. The results from X-ray photoelectron spectroscopy (XPS) confirm the formation of O-Ti-N bonds in the N-doped TiO2 porous monolith. The photocatalytic activity of N-doped TiO2 porous monolith was evaluated by the photodegradation of Rhodamine B over the samples under visible light. Nearly 50% of Rhodamine B in aqueous solution was efficiently degraded by N-doped TiO2 porous monolith with the mixed-phase of anatase and ruffle under visible light within 120 mm. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jeurceramsoc.2013.10.009

Controlled polymerization of protic ionic liquid monomer by ARGET-ATRP and TERP Reviewed

Nakamura Y., Nakanishi K., Yamago S., Tsujii Y., Takahashi K., Morinaga T., Sato T.

Macromolecular Rapid Communications Vol. 35 ( 6 ) page： 642 - 648 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Macromolecular Rapid Communications

The direct synthesis of structurally well-defined protic polymeric ionic liquid (PIL) with controlled molecular weight and molecular weight distribution is examined using N,N-diethyl-N-(2-methacryloylethyl) ammonium bis(tri-fluoromethylsulfonyl)imide (DEMH-TFSI) as a monomer. Three polymerization methods, namely, atom transfer radical polymerization (ATRP), activators regenerated by electron transfer (ARGET)-ATRP, and organotellurium-mediated living radical polymerization (TERP) are employed in this study. While the polymerization by ATRP is slow and does not reach high monomer conversion that under ARGET-ATRP and TERP proceeds smoothly and affords structurally well-defined poly(DEMH-TFSI)s. TERP is especially efficient for the control and poly(DEMH-TFSI)s with low to high molecular weights (M̄n = 49 100-392 500) and narrow molecular weight distributions (M̄w/M̄n = 1.17-1.46) are obtained. These results represent the first example of synthesis of a structurally well-defined protic, ammonium PIL by direct polymerization of the protic ionic liquid monomer. The polymerization of N,N-diethyl-N-(2- methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEMM-TFSI), which possesses a quaternary ammonium salt, also proceeds in a highly controlled manner under TERP conditions. A diblock copolymer, polystyrene-block-poly(DEMH-TFSI), is also successfully synthesized by TERP. Structurally well-defined protic polymeric ionic liquid is prepared by the direct polymerization of protic ammonium-salt ionic liquid monomers, N,N-diethyl-N-(2-methacryloylethyl) ammonium bis(tri-fluoromethylsulfonyl)imide (DEMH-TFSI), under ARGET-ATRP and TERP conditions. TERP is especially suitable for the controlled polymerization and afforded poly(DEMH-TFSI) with low to high molecular weight (M̄n = 49 100-392 500) and a narrow molecular weight distribution (M̄w/M̄n = 1.17-1.46). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/marc.201300855

Preparation and characterization of macroporous TiO2-SrTiO3 heterostructured monolithic photocatalyst Reviewed

Ohm Ruzimuradov, Suvankul Nurmanov, Mirabbos Hojamberdiev, Ravi Mohan Prasad, Alexander Gurlo, Joachim Broetz, Kazuki Nakanishi, Ralf Riedel

MATERIALS LETTERS Vol. 116 page： 353 - 355 2014.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Macroporous TiO2 monolith was first prepared by the sol-gel method and then macroporous TiO2-SrTiO3 heterostructured monolith was obtained by the impregnation of the as-prepared macroporous TiO2 monolith in the strontium-containing aqueous solution followed by calcination at different temperatures. The formation of SrTiO3 crystals in the TiO2 network was confirmed by X-ray diffraction and electron microscopy analyses. Macroporous structure of the heterostructured monolith was analyzed by mercury porosimetry. The photocatalytic activity of macroporous TiO2-SrTiO3 heterostructured monolithic photocatalyst was evaluated for the photodegradation of Rhodamine B over the samples under visible light irradiation. The obtained results reveal that the samples show an enhanced photocatalytic activity for the degradation of organic dye molecules. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2013.11.065

Detailed characterization of the kinetic performance of first and second generation silica monolithic columns for reversed-phase chromatography separations Reviewed

Deirdre Cabooter, Ken Broeckhoven, Roman Sterken, Alison Vanmessen, Isabelle Vandendael, Kazuki Nakanishi, Sander Deridder, Gert Desmet

JOURNAL OF CHROMATOGRAPHY A Vol. 1325 page： 72 - 82 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The kinetic performance of commercially available first generation and prototype second generation silica monoliths has been investigated for 2.0 mm and 3.0-3.2 mm inner diameter columns. It is demonstrated that the altered sol-gel process employed for the production of second generation monoliths results in structures with a smaller characteristic size leading to an improved peak shape and higher efficiencies. The permeability of the columns however, decreases significantly due to the smaller throughpore and skeleton sizes. Scanning electron microscopy pictures suggest the first generation monoliths have cylindrical skeleton branches, whereas the second generation monoliths rather have skeleton branches that resemble a single chain of spherical globules. Using recently established correlations for the flow resistance of cylindrical and globule chain type monolithic structures, it is demonstrated that the higher flow resistance of the second generation monoliths can be entirely attributed to their smaller skeleton sizes, which is also evident from the external porosity that is largely the same for both monolith generations (epsilon(e) similar to 0.65). The recorded van Deemter plots show a clear improvement in efficiency for the second generation monoliths (minimal plate heights of 13.6-14.1 mu m for the first and 6.5-8.2 mu m for the second generation, when assessing the plate count using the Foley-Dorsey method). The corresponding kinetic plots, however, indicate that the much reduced permeability of the second generation monoliths results in kinetic performances (time needed to achieve a given efficiency) which are only better than those of the first generation for plate counts up to N similar to 45,000. For more complex samples (N >= 50,000), the first generation monoliths can intrinsically still provide faster analysis due to their high permeability. It is also demonstrated that - despite the improved efficiency of the second generation monoliths in the practical range of separations (N = 10,000-50,000) - these columns can still not compete with state-of-the-art core-shell particle columns when all columns are evaluated at their own maximum operating pressure (200 bar for the monolithic columns, 600 bar for core-shell columns). It is suggested that monolithic columns will only become competitive with these high efficiency particle columns when further improvements to their production process are made and their pressure resistance is raised. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2013.11.047

Other Link： http://orcid.org/0000-0002-8069-4780

The thermal conductivity of polymethylsilsesquioxane aerogels and xerogels with varied pore sizes for practical application as thermal superinsulators Reviewed

G. Hayase, K. Kugimiya, M. Ogawa, Y. Kodera, K. Kanamori, K. Nakanishi

JOURNAL OF MATERIALS CHEMISTRY A Vol. 2 ( 18 ) page： 6525 - 6531 2014

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

High-performance thermal insulating materials are desired especially from the viewpoint of saving energy for a sustainable society. Aerogel is the long-awaited material for extended applications due to its excellent thermal insulating ability. These materials are, however, seriously fragile against even small mechanical stress due to their low density, and their poor mechanical properties inhibit their practical use as superinsulators. In this paper, we report relationships between the thermal conductivity, pore size and mechanical properties of organic-inorganic hybrid polymethylsilsesquioxane (PMSQ) aerogels with improved mechanical properties and controllable pore sizes from similar to 50 nm to 3 mu m. The dependency of thermal conductivity on gas pressure and pore properties can be well explained by the thermal conduction theory of porous materials. These PMSQ aerogels show improved mechanical properties due to their elastic networks, which enable easier handling compared to conventional aerogels and facile production by simple ambient pressure drying. An aerogel-like "xerogel" monolithic panel has been successfully prepared via ambient pressure drying, which shows a low thermal conductivity (0.015 W m(-1) K-1) comparable with those of the corresponding PMSQ aerogel and conventional silica aerogels. These results would open the gate for practical applications of these porous materials.

DOI： 10.1039/c3ta15094a

Layered double hydroxide composite monoliths with three-dimensional hierarchical channels: structural control and adsorption behavior Reviewed

Naoki Tarutani, Yasuaki Tokudome, Kazuki Nakanishi, Masahide Takahashi

RSC ADVANCES Vol. 4 ( 31 ) page： 16075 - 16080 2014

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

Hierarchically porous layered double hydroxide (LDH) materials have potential in anion-exchange, adsorption and catalysis applications, because of their large surface areas and liquid transportation capabilities. The preparation of monolithic LDH-Al(OH)(3) composites with hierarchical mm and nm-scale channels and their adsorption behavior is reported. Monolithic gels were synthesized via sol-gel processing, from metal salt precursor solutions. mu m-scale macrochannels spontaneously formed by inducing phase separation during sol-gel transition. nm-scale mesochannels were accommodated as interstices between primary/secondary particles. In this study, these hierarchical channel sizes were controlled. The macrochannel size was controlled by tuning the degree of phase separation. The mesochannel size was controlled independently, by tuning the crystallite size of LDH under different solvothermal conditions. The relationship between pore characteristics and adsorption behavior of tailored hierarchically porous LDH-Al(OH)(3) monolithic gels were investigated by using dye molecules as adsorbates. Monolithic gels with larger macrochannels and mesochannels exhibit faster adsorption rate and higher affinity, respectively. LDH-Al(OH)(3) monolithic gels with hierarchical channels may have potential in some applications such as biosensing, water purification and catalysis.

DOI： 10.1039/c4ra00873a

Other Link： http://orcid.org/0000-0002-8069-4780

A new hierarchically porous Pd@HSQ monolithic catalyst for Mizoroki-Heck cross-coupling reactions Reviewed

Nirmalya Moitra, Ayumi Matsushima, Toshiyuki Kamei, Kazuyoshi Kanamori, Yumi H. Ikuhara, Xiang Gao, Kazuyuki Takeda, Yang Zhu, Kazuki Nakanishi, Toyoshi Shimada

NEW JOURNAL OF CHEMISTRY Vol. 38 ( 3 ) page： 1144 - 1149 2014

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

Pore architecture of catalyst supports is an important factor facilitating accessibility of reactants to catalytic sites. This holds the key to improving catalytic activities. Amongst various catalytic reactions, supported Pd nanoparticles-catalyzed C-C cross-coupling reactions have been attracting a great deal of attention in the last decade. Although various supports have been examined, applications of hierarchically porous monolithic materials have never been reported, mainly because of difficulties in multistep synthesis of catalysts. We herein report a novel on-site reduction-based methodology using hierarchically porous hydrogen silsesquioxane (HSQ) monoliths for one-step synthesis of Pd nanoparticles-embedded monoliths (Pd@HSQ). Characterization of these monoliths evidences the on-site reduction, i.e. formation of Pd nanoparticles and conversion of Si-H present in the monolith to Si-OB similar to. Fast, quantitative reduction of Pd2+ to Pd(0) to form supported Pd nanoparticles is achieved with preservation of the porous structure of the original monolith, which makes this material attractive as a catalyst for C-C cross-coupling reactions. The obtained Pd@HSQ catalyst has been employed in the Mizoroki-Heck cross-coupling reaction. High accessibility of reactant molecules, undetectable leaching of Pd nanoparticles and easy separation of the monolith from liquid media provide high catalytic activity, reusability and easy handling.

DOI： 10.1039/c3nj01433a

Porous chromium-based ceramic monoliths: oxides (Cr2O3), nitrides (CrN), and carbides (Cr3C2) Reviewed

Yasuki Kido, George Hasegawa, Kazuyoshi Kanamori, Kazuki Nakanishi

JOURNAL OF MATERIALS CHEMISTRY A Vol. 2 ( 3 ) page： 745 - 752 2014

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

In this research, we have successfully prepared hierarchically porous chromium-based non-oxide ceramic monoliths (chromium nitride (CrN) and chromium carbide (Cr3C2)) by facile two-step methods. By utilizing an epoxide-mediated sol-gel reaction accompanied by phase separation, a well-defined macroporous structure is tailored in the chromium (oxy) hydroxide-urea composites in the presence of poly(acrylic acid). Urea works as a nitrogen and/or carbon source through the following heat-treatment, whereas poly(acrylic acid) behaves as a phase separation inducer as well as a network-supporting constituent. The macroporous morphology of xerogels is controllable by changing the starting composition. Heat-treatment for thus obtained xerogels under an air atmosphere provides chromium oxide (Cr2O3), whereas that under a nitrogen atmosphere leads to the crystallization of CrN at 700 degrees C and Cr3C2 at 900 degrees C without any deterioration of the porous morphologies. The heat-treated samples possess a high specific surface area up to 450 m(2) g(-1) as well as high porosity over 80%, preserving good mechanical strength. This facile and novel synthesis strategy has a potential extendability to other macroporous monoliths with high surface area based on various metal nitrides and carbides, which are useful in various applications such as catalysts, semiconductor devices, magnetic materials, and refractory materials.

DOI： 10.1039/c3ta13725b

Synthesis and electrochemical performance of hierarchically porous N-doped TiO2 for Li-ion batteries Reviewed

George Hasegawa, Tatsuya Sato, Kazuyoshi Kanamori, Kazuki Nakanishi, Takeshi Abe

NEW JOURNAL OF CHEMISTRY Vol. 38 ( 4 ) page： 1380 - 1384 2014

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

Hierarchically porous N-doped TiO2 materials have been synthesized from macroporous inorganic-organic hybrid gels composed of titanium bridged with ethylenediamine. Homogeneously dispersed nitrogen in the precursor gel networks leads to TiO2 doped with a large amount of nitrogen, which delivers high discharge capacity and good cycle performance as a negative electrode for Li-ion batteries.

DOI： 10.1039/c3nj01332d

Other Link： http://orcid.org/0000-0002-8069-4780

Reduction on reactive pore surfaces as a versatile approach to synthesize monolith-supported metal alloy nanoparticles and their catalytic applications Reviewed

Nirmalya Moitra, Kazuyoshi Kanamori, Yumi H. Ikuhara, Xiang Gao, Yang Zhu, George Hasegawa, Kazuyuki Takeda, Toyoshi Shimada, Kazuki Nakanishi

JOURNAL OF MATERIALS CHEMISTRY A Vol. 2 ( 31 ) page： 12535 - 12544 2014

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

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.

DOI： 10.1039/c4ta01767f

Other Link： http://orcid.org/0000-0002-8069-4780

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