Nao Tsunoji

Remarkable Charge Separation and Photocatalytic Efficiency Enhancement through Interconnection of TiO2 Nanoparticles by Hydrothermal Treatment.

Although tremendous effort has been directed to synthesizing advanced TiO2 , it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2 , which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2 , inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

Synthesis of high-silica AEI zeolites with enhanced thermal stability by hydrothermal conversion of FAU zeolites, and their activity in the selective catalytic reduction of NOx with NH3

High-silica AEI zeolites with Si/Al ratios of 13–20 were synthesized by FAU interzeolite conversion, in which tetraethylphosphonium (TEP) cations as a structure-directing agent (SDA) and NaF or NH4F as a fluoride source were added to the starting gels. During the thermal treatment of the AEI zeolites, TEP cations in the zeolitic pores decomposed to yield the P-modified AEI zeolites with various P/Al ratios. The thermal stability of the P-modified AEI zeolite was higher than that of the non-modified AEI zeolite synthesized using the N,N-diethyl-2,6-dimethylpiperidinium cation as an SDA. The framework structure of the P-modified AEI zeolite was maintained after calcination at 1000 °C for 1 h, indicating an enhanced thermal stability by phosphorus modification. The catalytic performance of Cu-loaded AEI zeolites with different P/Al ratios in the selective catalytic reduction (SCR) of NOx with NH3 was also investigated. The NO conversion was found to increase with decreasing P/Al ratio. No decrease in the NO conversion was observed after hydrothermal treatment at 900 °C for 4 h, indicating the high potential of the P-modified AEI zeolite for NH3-SCR of NOx.

Synthesis and characteristics of novel layered silicates HUS-2 and HUS-3 derived from a SiO2–choline hydroxide–NaOH–H2O system

Three kinds of layered silicates, HUS-2, HUS-3, and HUS-4, were synthesized using amorphous silica, sodium hydroxide, and choline hydroxide as a structure-directing agent (SDA). Structural analyses by powder X-ray diffractometry and solid-state magic-angle-spinning (MAS) NMR spectroscopy revealed that HUS-2 had a layered structure, which was composed of four-, five-, and six-membered rings. Its framework topology was partially similar to that of a HEU-type zeolite including bre (10T)-type composite building units. Structural refinement by the Rietveld method showed that the choline cations that were used as an SDA were incorporated into the interlayers. Double silicate layers were included in each unit cell. The interlayer distance was estimated to be ca. 0.36 nm. The presence of hydrogen bonding between adjacent terminal O atoms was clearly revealed by 1H MAS NMR spectroscopy and through the electron-density distribution obtained by the maximum entropy method. Although the crystal structure of the layered silicate HUS-3 could not be analysed, the HUS-3 was transformed into a CDO-type zeolite by calcination, indicating that the structure of HUS-3 was partially similar to that of a CDO-type zeolite precursor. The crystal structure of HUS-4 was similar to that of PLS-1 synthesized using tetramethylammonium hydroxide. We also demonstrated that the layered silicates HUS-2 and HUS-3 exhibited high catalytic activities as base catalysts in a Knoevenagel condensation reaction.

Design of layered silicate by grafting with metal acetylacetonate for high activity and chemoselectivity in photooxidation of cyclohexane.

We succeeded in the immobilization of Ti(IV) acetylacetonate onto interlayer surfaces of a layered silicate HUS-2 (Hiroshima University Silicate-2, Si20O40(OH)4·4[C5H14NO]) and investigated the photocatalytic acitivity of Ti-incorporated HUS-2 toward the partial oxidation of cyclohexane to cyclohexanol and cyclohexanone under solar light irradiation. XRD, SEM/EDX, (13)C CP and (29)Si MAS NMR and UV-vis measurements of Ti-incorporated HUS-2 confirmed that the isolated tetrahedral Ti species were homogeneously immobilized onto silicate sheets via Si-O-Ti covalent bond and acetylacetonate ligands were removed after calcination. Ti-incorporated HUS-2 showed ca. 100% selectivity for partial cyclohexane oxidation and considerably higher yields (cyclohexanol and cyclohexanone) than TS-1, a typical Ti-containing zeolite. Higher yields were obtained when the calcined Ti-incorporated HUS-2 with a larger amount of the grafted Ti were used.

Molecular recognitive adsorption of aqueous tetramethylammonium on the organic derivative of Hiroshima University Silicate-1 with a silane coupling reagent

Hiroshima University Silicate-1 (HUS-1), composed of silicate sheets with a halved sodalite cage and the interlayer tetramethylammonium (TMA) cation in the cage, was modified with dimethyldichlorosilane to form the organic derivative in which a dimethyl group was grafted onto the interlayer surface and a part of the TMA was removed, and the silylated HUS-1 effectively and selectively adsorbed TMA from water even in the presence of aqueous phenol.

A BODIPY sensor for water based on a photo-induced electron transfer method with fluorescence enhancement and attenuation systems

It was found that BODIPY MH-1 can act as a dual function-based fluorescent sensor for trace amounts of water possessing fluorescence intensity and fluorescence quantum yield as a function of water detection based on the PET (photo-induced electron transfer) method with fluorescence enhancement and attenuation systems.

Highly active and selective Ti-incorporated porous silica catalysts derived from grafting of titanium(IV)acetylacetonate

Metallosilicate catalysts with tetrahedrally coordinated transition metals covalently linked into silica frameworks are attractive because of their highly selective oxidation activities for a wide variety of hydrocarbons. Here, we report highly active and selective titanosilicate catalysts featuring an active titanium species with a uniform tetrahedral coordination state and homogeneous distribution derived from grafting Ti(IV)acetylacetonate (Ti(acac)4) onto the surfaces of porous silicas, such as mesoporous silicas MCM-41 and SBA-15, and nanoporous silica HUS-6. Ti-grafted porous silicas showed excellent catalytic performances in the epoxidation of cyclohexene with tert-butyl hydroperoxide as an oxidant. The catalytic turnover number was approximately 8 times higher than that of Ti-containing mesoporous silica MCM-41 prepared by conventional one-pot hydrothermal synthesis. The Ti-grafted MCM-41 with a higher Ti content exhibited higher catalytic activity for epoxidation, with a turnover frequency of 346 h−1 and reaction rate of 159 mmol g−1 h−1. We also found that the Ti-grafted porous silicas were effective for the epoxidation of a plant-derived olefin, limonene, using tert-butyl hydroperoxide as an oxidant.

Design of Microporous Material HUS-10 with Tunable Hydrophilicity, Molecular Sieving, and CO2 Adsorption Ability Derived from Interlayer Silylation of Layered Silicate HUS-2.

The attractive properties of zeolites, which make them suitable for numerous applications for the energy and chemical industries and for life sciences, are derived from their crystalline framework structures. Herein, we describe the rational synthesis of a microporous material, HUS-10, utilizing a layered silicate precursor, HUS-2, as a structural building unit. For the ordered micropores to be formed, interlayer pillars that supported the original silicate layer of HUS-2 were immobilized through the interlayer silylation of silanol groups with trichloromethylsilane and a subsequent dehydration-condensation reaction of the hydroxyl groups on the preintroduced tetrahedral units. An actual molecular sieving ability, enabling the adsorption of molecules smaller than ethane, was confirmed in the ordered micropores of HUS-10. The hydrophilic adsorption could also be controlled by changing the number of methyl and hydroxyl groups in the immobilized interlayer pillars. In addition, when the adsorption behaviors of CO2, CH4, and N2 on HUS-10 were compared to those on siliceous MFI and CDO zeolites with approximately the same pore diameter, the CO2 adsorption capacity of HUS-10 was comparable. Conversely, because of the adsorption inhibition of CH4 and N2, HUS-10 exhibited larger CO2/CH4 and CO2/N2 adsorption ratios relative to those of MFI and CDO zeolites. These results reveal that the unique microporous framework structure presented by the rational structural design using the layered silicate precursor HUS-2 has the potential to separate CO2 from gas mixtures.

Synthesis and characteristics of novel layered silicate HUS-7 using benzyltrimethylammonium hydroxide and its unique and selective phenol adsorption behavior

A new layered silicate, HUS-7, was synthesized using amorphous silica, sodium hydroxide, biphenyl, and benzyltrimethylammonium hydroxide as a structure-directing agent (SDA). Structural analyses by powder X-ray diffractometry and solid-state magic-angle-spinning (MAS) NMR spectroscopy revealed that HUS-7 had a layered structure, which was composed of four-, five-, and six-membered rings. Its framework topology was partially similar to that of a HEU-type zeolite including the bre (10T)-type composite building unit. Structural refinement by the Rietveld method showed that the benzyltrimethylammonium cations used as the SDAs were incorporated into the interlayers. The presence of hydrogen bonding between adjacent terminal O atoms was clearly revealed by 1H MAS NMR spectroscopy and the electron-density distribution obtained by the maximum entropy method. HUS-7 selectively and effectively adsorbed phenol from acetonitrile solution containing benzene and phenol. The adsorption of phenol occurred through the exchange of water molecules in the interlayers with phenol.

Fe oxide nanoparticles/Ti-modified mesoporous silica as a photo-catalyst for efficient and selective cyclohexane conversion with O2 and solar light

We report a new, environmentally and economically friendly photocatalytic process with unprecedentedly high activity for partial cyclohexane oxidation. Mesoporous silicas containing isolated tetrahedrally coordinated Ti and Fe oxide nanoparticles immobilized on the pore surface were synthesized by reacting SBA-15 with Ti(IV) acetylacetonate and Fe(III) acetylacetonate successively. A variety of characterizations suggested that the grafted tetrahedrally coordinated Ti species were coupled with Fe oxide nanoparticles via Ti–O–Fe bonds. The SBA-15 photocatalysts showed a high yield (up to sub-mmol) and nearly 100% selectivity for the production of cyclohexanol and cyclohexanone with molecular O2 under solar light. The unprecedentedly high activity could be explained by the lengthened lifetime of the active Ti species by electron delocalization over Ti–O–Fe bonds and the visible light (λ > 420 nm)-induced activity endowed by Fe oxide nanoparticles coupled to the Ti species.