Papers - IKEDA Shigeru
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Oxidation of hydrophobic alcohols using aqueous hydrogen peroxide over amphiphilic silica particles loaded with titanium(IV) oxide as a liquid-liquid phase-boundary catalyst Reviewed
KM Choi, S Ikeda, S Ishino, K Ikeue, M Matsumura, B Ohtani
APPLIED CATALYSIS A-GENERAL 278 ( 2 ) 269 - 274 2005.1
Joint Work
Authorship:Lead author Publisher:ELSEVIER SCIENCE BV
Phase-boundary catalysis (PBC), a new concept of a heterogeneous catalytic system for oxidation of various hydrophobic alcohols with aqueous hydrogen peroxide (H2O2), has been investigated. A part the external surface of silica (SiO2) particles loaded with titanium(IV) oxides was modified with hydrophobic alkyl groups to obtain amphiphilic particles, having both hydrophobic and hydrophilic surfaces on each particle. The amphiphilic particles were spontaneously assembled at interfaces between dual phase mixtures of aqueous solutions and water-immiscible organic compounds. Upon addition to a dual phase mixture of aqueous H2O2 and toluene-containing hydrophobic alcohols, these particles acted as an efficient catalyst for the reaction, to produce corresponding aldehydes and ketones selectively. Notable features of the PBC system are that the oxidation proceeds even without agitation and that only a few percent of titanium species was detected as dissolved species. Productions of aldehydes and ketones were also observed when titanium loaded SiO2 without modification with alkyl groups was employed for the reaction. However, a large amount of titanium loaded on the material was leached during the reaction. These results indicate that surface-covered alkyl groups not only bring about effective contact with hydrophobic alcohols in the organic phase but also give stability against leaching, leading to heterogeneous catalytic functions. (C) 2004 Elsevier B.V. All rights reserved.
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Photocatalytic preparation of encapsulated gold nanoparticles by jingle-bell-shaped cadmium sulfide-silica nanoparticles Reviewed
B. Pal, T. Torimoto, S. Ikeda, T. Shibayama, K. Sugawara, H. Takahashi, B. Ohtani
Top. Cat. 35 ( 3-4 ) 321-325 2005
Gold (Au) nanoparticles were deposited inside silica: (SiO2) shells containing cadmium sulfide (CdS) nanoparticles through photocatalytic reduction of potassium dicyanogold(I) by CdS. Photocatalytic Au deposition occurred only when core-shell nanoparticles having a void space between the core and shell, i.e., a jingle-bell-shaped structure, were used. These core-shell nanoparticles were prepared by size-selective photoetching of SiO2 -covered CdS nanoparticles. The size of Au nanoparticles could be controlled by adjustment of the void space in SiO2-covered CdS. Dissolution of CdS by acid treatment from the Au-deposited jingle-bell nanoparticles did not have any effect on the surface-plasmon absorption by Au. These facts indicate that Au nanoparticles of adjustable size can be prepared in an SiO2 shell that prevents mutual coalescence of Au nanoparticles but allows permeation of molecules and ions.
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Overall water splitting on tungsten-based photocatalysts with defect pyrochlore structure Reviewed
S Ikeda, T Itani, K Nango, M Matsumura
CATALYSIS LETTERS 98 ( 4 ) 229 - 233 2004.12
Joint Work
Authorship:Lead author Publisher:KLUWER ACADEMIC/PLENUM PUBL
Defect pyrochlore-type oxides, AMWO(6) (A = Rb, Cs; M = Nb, Ta), loaded with nickel oxide showed photocatalytic activity for overall water splitting under ultraviolet-light irradiation. The conduction bands of the materials are thought to be composed of the W5d orbital hybridized with the Nb5d or Ta4d orbital.
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Hadi Nur, Shigeru Ikeda, Bunsho Ohtani
Journal of the Brazilian Chemical Society 15 ( 5 ) 719 - 724 2004.9
Joint Work
Publisher:Sociedade Brasileira de Quimica
The catalytic potential of phase-boundary catalyst for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalyst was prepared by impregnation of niobic acid on the external surface of NaY and followed by a partial modification of the external surface of NaY with alkylsilyl groups. When the particles were added to a mixture of water and 1,2-epoxyoctane, they were feasibly located just at the liquid-liquid phase boundary and efficiently catalyzed hydration of the epoxide even without stirring. In order to investigate the effect of the location of the active sites, alkylsilylated HZSM-5 and sulfonic acid functionalized NaY in which the active sites are located dominantly on the internal surface of zeolites were prepared. In that case, mechanical stirring was needed to increase the reaction rate. It was suggested that alkylsilylation on the external surface of zeolite, when the active site is mainly inside the pore, could not change the mode of the catalytic action
it is still necessary to stir the reaction mixture to drive the mass transfer of substrates and reagents. -
Light intensity dependence of the action spectra of photocatalytic reactions with anatase titanium(IV) oxide Reviewed
T Torimoto, Y Aburakawa, Y Kawahara, S Ikeda, B Ohtani
CHEMICAL PHYSICS LETTERS 392 ( 43103 ) 220 - 224 2004.7
Joint Work
Publisher:ELSEVIER SCIENCE BV
Light intensity dependence of action spectra of photocatalytic reactions was investigated using anatase single-phase titanium(IV) oxide powders as photocatalysts. The action spectra normalized at 350 nm were not changed in methanol dehydrogenation with the range of intensities of ca. 0.1-10 mW cm(-2), while those for acetic acid decomposition were red-shifted with increase in light intensity. The apparent quantum yield of the former was almost independent of the irradiation intensity, but that of the latter was declined with increase in light intensity, the degree being considerably enhanced with the irradiation at shorter wavelength when the light intensity was higher than 2 mW cm-2. These can be explained by the difference in the utilization efficiency of photogenerated charge carriers. (C) 2004 Elsevier B.V. All rights reserved.
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Amphiphilic NaY zeolite particles loaded with niobic acid: Materials with applications for catalysis in immiscible liquid-liquid system Reviewed
H Nur, S Ikeda, B Ohtani
REACTION KINETICS AND CATALYSIS LETTERS 82 ( 2 ) 255 - 261 2004.7
Joint Work
Publisher:AKADEMIAI KIADO
The catalytic potential of catalysts for acid-catalyzed reactions has been demonstrated by NaY zeolite loaded with alkylsilane-covered niobic acid in the liquid phase hydration of 1,2-epoxyoctane with water. The catalytic activity of the catalysts was correlated to the amphiphilic character of the solid catalyst particles.
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Asymmetrically modified titanium(IV) oxide particles having both hydrophobic and hydrophilic parts of their surfaces for liquid-liquid dual-phase photocatalytic reactions Reviewed
S Ikeda, Y Kowata, K Ikeue, M Matsumura, B Ohtani
APPLIED CATALYSIS A-GENERAL 265 ( 1 ) 69 - 74 2004.6
Joint Work
Authorship:Lead author Publisher:ELSEVIER SCIENCE BV
Titanium(IV) oxide (TiO2)-based photocatalyst particles assembled at the phase boundary of a liquid-liquid dual-phase mixture were prepared by partial modification of the external surface of each particle with alkylsilyl groups. The average surface coverage of alkylsilyl groups was estimated by elemental analyses of carbon and ash components of the samples and floatability on aqueous ethanol solutions. Results revealed that the hydrophobicity-hydrophilicity of asymmetrically modified samples was comparable to that of samples fully covered with alkylsilyl groups. TiO2 particles asymmetrically or fully modified with alkylsilyl groups showed photocatalytic activity for benzene oxidation to produce phenol from an aerated benzene-water dual-phase mixture even without agitation, while bare TiO2 required mechanical agitation to induce the photocatalytic reaction. However, prolonged irradiation precipitated some of the surface-modified particles in the aqueous layer due to photocatalytic decomposition of surface alkylsilyl groups. The photostability was improved by employment of TiO2 particles coated with porous silica (SiO2) as a starting material. Compared with the SiO2-coated TiO2 particles fully modified with alkylsilyl groups (o-Si/Ti), the asymmetrically modified SiO2-TiO2 particles (w/o-Si/Ti) showed slightly higher photocatalytic activity for benzene oxidation. On the other hand, a notable difference between the two types of particles was observed in photocatalytic hydrogen evolution in the presence of sacrificial donors from a benzene-water mixture and from an aqueous solution under deaerated conditions; w/o-Si/Ti showed the activity more than two-fold greater than that of o-Ti/Si, presumably because of efficient contact of w/o-Si/Ti with both aqueous and organic phases compared with o-Si/Ti, which was rather difficult to contact with the aqueous phase. (C) 2004 Elsevier B.V. All rights reserved.
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Elucidation of the local structure of active titanium(IV) sites on silica-based phase-boundary catalysts for alkene epoxidation with aqueous hydrogen peroxide Reviewed
K Ikeue, S Ikeda, A Watanabe, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 6 ( 9 ) 2523 - 2528 2004.5
Joint Work
Authorship:Lead author Publisher:ROYAL SOC CHEMISTRY
Structural and functional aspects of active titanium sites for phase boundary catalytic (PBC) epoxidation of 1-octene with hydrogen peroxide (H2O2) were investigated in detail using X-ray absorption fine structure (XAFS) analysis and ultraviolet and visible-light diffuse reflectance (UV-Vis-DR) spectroscopy. By analysis of the Ti K-edge X-ray absorption near edge fine structure (XANES) spectra of several titanium-loaded silica catalysts, the ratio of the amount of 4-coordinated titanium oxide (T-tet) to that of a 6-coordinated one (T-oct) was determined. Monotonic increments of catalytic activity for epoxide production and efficiency of H2O2 utilization with the ratio T-tet/(T-tet + T-oct) revealed that the highly active catalysts mainly include T-tet but not T-oct. UV-Vis-DR spectra of samples with external surfaces partially covered with alkylsilyl groups indicated that there are at least two kinds of T, sites with different ligands. One site anchors an acidic hydroxyl (T-tet(OH)), giving absorption centered at the wavelength of ca. 230 nm and the other, exhibiting an absorption peak at the wavelength of ca. 210 nm, is directly attached to an alkylsilyl group (T-tet(OSiR)) formed via reaction of an acidic hydroxy of T-tet(OH) with an alkylsilane reagent. Since the catalysts have both an alkylsilyl-grafted hydrophobic surface and a hydroxy-terminated hydrophilic surface, it is postulated that the former is located on both hydrophilic (T-tet(OH,w)) and hydrophobic (T-tet(OH(9)o)) surfaces and the latter, T-tet(OSiR), exists only on the hydrophobic surface. From analyses of catalytic activities of several catalysts with different distributions of these T-tet sites, both T-tet(OH,o) and T-tet(OSiR) sites on the hydrophobic surface were proved to be active, while T-tet(OH,w) on the hydrophilic surface did not work for the present PBC system. Among the sites on the hydrophobic surface, moreover, it was found that a T-tet(OSiR) site acted as a more effective site for selective epoxidation when compared with T-tet(OH,o), which induced ring-opening of epoxide to give a by-product, 1,2-octanediol.
DOI: 10.1039/b316818b
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Photocatalytic organic syntheses: selective cyclization of amino acids in aqueous suspensions Invited Reviewed
Ohtani, B; Pal, B; Ikeda, S
CATALYSIS SURVEYS FROM ASIA 7 ( 43134 ) 165 - 176 2003.9
Joint Work
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Development of a novel photocatalytic reaction system for oxidative decomposition of volatile organic compounds in water with enhanced aeration Reviewed
R Villacres, S Ikeda, T Torimoto, B Ohtani
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 160 ( 43102 ) 121 - 126 2003.8
Joint Work
Authorship:Lead author Publisher:ELSEVIER SCIENCE SA
A novel photocatalytic reaction system, composed of solution and gas spaces that are divided by a thin Teflon film and titanium(IV) oxide (TiO2)-coated mesh or cloth, for the treatment of contaminated aqueous solutions was developed to be operated with enhanced aeration without bubbling of air in the solution. First, the photocatalytic activities of TiO2 particles immobilized on two kinds of support material, stainless steel mesh (SSM) and fiberglass cloth (FGC), were investigated for photocatalytic oxidation of 2-propanol, as a model volatile organic compound, dissolved in aerated aqueous solution. The TiO2 particles immobilized on both support materials exhibited photocatalytic activity to oxidize 2-propanol into acetone and carbon dioxide (CO2), and the activity levels of the TiO2 particles immobilized on the two kinds of support materials were comparable. Presumably due to the presence of a small amount of metal species originating in SSM that might work as reduction catalysts, molecular hydrogen (H-2) was also liberated on the TiO2-immobilized SSM. Results of analysis of weight loss after photoirradiation suggested that the stability of the TiO2-immobilized FGC was better than that of the TiO2-immobilized SSM. On the basis of these results, FGC was employed in construction of a photocatalytic reactor equipped with an oxygen (O-2)-permeable Teflon membrane in order to make oxygen pass from a gas space to a solution space and to keep the surface of the immobilized TiO2 photocatalyst, facing an aqueous solution containing volatile organic compounds, saturated with dissolved O-2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO2 particles could be sufficiently supplied with O-2 from the gas space through the membrane to accelerate the oxidation. (C) 2003 Elsevier Science B.V. All rights reserved.
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Photochemical hydrogen evolution from aqueous triethanolamine solutions sensitized by binaphthol-modified titanium(IV) oxide under visible-light irradiation Reviewed
S Ikeda, C Abe, T Torimoto, B Ohtani
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 160 ( 43102 ) 61 - 67 2003.8
Joint Work
Authorship:Lead author Publisher:ELSEVIER SCIENCE SA
Surface modification of titanium(IV) oxide (TiO2) powders with 1, 1-binaphthalene-2,2'-diol (bn(OH)(2)), having two phenolic hydroxyls and atropisomeric chirality, in refluxed ethanol led to the formation of a deep yellow-colored surface complex, giving visible-light absorption at a wavelength below ca. 550-600 nm. Quantitative analyses of the surface complex revealed that absorption intensity at 450 nm in diffuse reflection (DR) measurement was almost proportional to its amount and that its amount depended strongly on the amount of surface hydroxyl groups of TiO2 but not on the crystal structure of TiO2, anatase, and rutile. The bn(OH)(2) complexation was also applied to platinized TiO2 to drive photocatalytic molecular hydrogen (H-2) evolution from deaerated triethanolamine solutions under visible-light irradiation at a wavelength even longer than 540 nm. The photonic efficiency of the photocatalytic reaction at 450 nm was estimated to be 0.02% for bn(OH)(2)-modified TiO2 (JRC-TIO-3) loaded with 0.1 wt.% of platinum. On the basis of these experimental results, the reaction mechanism, which involves visible-light excitation of the surface complex, injection of electrons from the complex to TiO2, and migration of the electrons to platinum deposits, where reduction of H+ takes place to give H-2, was elucidated. (C) 2003 Elsevier Science B.V. All rights reserved.
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Photocatalytic redox-combined synthesis of L-pipecolinic acid from L-lysine by suspended titania particles: effect of noble metal loading on the selectivity and optical purity of the product Reviewed
B Pal, S Ikeda, H Kominami, Y Kera, B Ohtani
JOURNAL OF CATALYSIS 217 ( 1 ) 152 - 159 2003.7
Joint Work
Publisher:ACADEMIC PRESS INC ELSEVIER SCIENCE
Photocatalytic (> 300 nm) conversion of L-(S)-lysine (L-Lys), in its neutralized aqueous solution, into L-pipecolinic acid (L-PCA) under deaerated conditions at 298 K was investigated in detail using suspended TiO2 powders (Degussa P-25, Ishihara ST-01, and HyCOM TiO2) loaded with platinum (Pt), rhodium (Rh), or palladium (Pd). A common feature of the results of experiments using a wide variety of metalloaded TiO2 photocatalysts is that the rate of PCA formation (r(PCA)) was greatly reduced when higher optical purity of PCA (OPPCA), i.e., enantio excess of the L-isomer of PCA, was obtained; higher rPCA was achieved by the use of Pt-loaded TiO2 powders, while these powders gave relatively low OPPCA. Selectivity of PCA yield (S-PCA), i.e., amount of PCA production based on L-Lys consumption, also tended to increase with decrease in OPPCA, giving a master curve in the plots of OPPCA versus S-PCA. Among the TiO2 powders used in this study, HyCOM TiO2 showed relatively high OPPCA and S-PCA but not optimum S-PCA and OPPCA simultaneously. In order to interpret such relations, the mechanism of stereoselective synthesis of the L-isomer of PCA (L-PCA) was investigated using isotope-labeled alpha-N-15-L-lysine with quantitative analysis of incorporation of N-15 in PCA and ammonia (NH3), a by-product. It was observed for several photocatalysts that the N-15 proportion (P-15) in PCA was almost equal to OPPCA, suggesting that oxidative cleavage by photogenerated positive holes of the epsilon-amino moiety of L-Lys gave optically pure L-PCA through retention of chirality at the alpha-carbon in the presumed intermediate, a cyclic Schiff base (alpha-CSB), which undergoes reduction by photoexcited electrons into PCA. From P-15 in NH3 and PCA, the selectivity of oxidation between alpha and epsilon-amino groups in L-Lys by photoexcited positive holes (h(+)) and the efficiency of reduction of alpha-CSB (produced via epsilon-amino group oxidation to give optically pure PCA) and epsilon-CSB (produced via alpha-amino group oxidation to give racemic PCA) by photoexcited electrons (e(-)) were calculated. The former was found to be independent of the kind of photocatalyst, especially the loaded metal, while the latter was influenced markedly only by the loaded metal. It was clarified that OPPCA and S-PCA obtained for various TiO2 powders used in the present study were strongly governed by the reduction stage, i.e., the efficiency of reduction of two types of CSB. When S-PCA was relatively low, photocatalysts, favoring the reduction of alpha-CSB rather than epsilon-CSB, gave higher OPPCA but lower S-PCA, since some epsilon-CSB remained unreduced to give racemic PCA. In contrast, at higher S-PCA, both CSBs were reduced nonselectively and OPPCA was found to be determined mainly by the selectivity in the oxidation stage. The relatively low yield of molecular hydrogen (H-2) when higher S-PCA was achieved is consistent with the mechanism in which H-2 liberation occurs instead of the reduction of CSBs by e(-). Thus, the general tendency of plots between OPPCA and S-PCA could be explained by the above-described redox-combined mechanism of photocatalysis.
(C) 2003 Elsevier Science (USA). All rights reserved -
Photoinduced chemical reactions on natural single crystals and synthesized crystallites of mercury(II) sulfide in aqueous solution containing naturally occurring amino acids Reviewed
B Pal, S Ikeda, B Ohtani
INORGANIC CHEMISTRY 42 ( 5 ) 1518 - 1524 2003.3
Joint Work
Publisher:AMER CHEMICAL SOC
Photoirradiation at >300 nm of aqueous suspensions of several natural crystal specimens and synthesized crystallites of mercury(II) sulfide (HgS) induced deaminocyclization of optically active or racemic lysine into pipecolinic acid (PCA) under deaerated conditions. This is the first example, to the best of our knowledge, of photoinduced chemical reactions of natural biological compounds over natural minerals. It was found that the natural HgS crystals had activity higher than those of synthesized ones but lower than those of other sulfides of transition metals, e.g., CdS and ZnS, belonging to the same II-IV chalcogenides. In almost all of the photoreactions, decompostion of HgS occurred to liberate hydrogen sulfide (H2S) and Hg2+, and the latter seemed to have undergone in-situ reductive deposition on HgS as Hg-0 after a certain induction period (24-70 h) during the photoirradiation, as indicated by the darkened color of the suspensions. The formation of PCA, presumably through combination of oxidation of lysine and reduction of an intermediate, cyclic Schiff base, could also be seen after a certain induction time of the Hg-0 formation. This was supported by the fact that the addition of small amount of Hg2+ (0.5 wt % of HgS) increased the PCA yield by almost 2-fold. We also tried to elucidate certain aspects of the plausible stereochemical reactions in relation to the chiral crystal structure of HgS. Although, in some experiments, slight enantiomeric excess of the product PCA was observed, the excess was below or equal to the experimental error and no other supporting analytical data could not be obtained; we cannot conclude the enantiomeric photoproduction of PCA by the natural chiral HgS specimen.
DOI: 10.1021/ic025916g
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Quantitative analysis of defective sites in titanium(IV) oxide photocatalyst powders Reviewed
S Ikeda, N Sugiyama, S Murakami, H Kominami, Y Kera, H Noguchi, K Uosaki, T Torimoto, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 5 ( 4 ) 778 - 783 2003.2
Joint Work
Authorship:Lead author Publisher:ROYAL SOC CHEMISTRY
The molar amounts of defective sites (M-d) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. Measurements of pH dependence of typical anatase and rutile TiO2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO2 in ranges of 0-0.35 V for anatase and 0-0.25 V for rutile, A linear relation of M-d with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that M-d could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between M-d and the specific surface area suggests that the surface area was not directly reflected on M-d. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and M-d revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.
DOI: 10.1039/b206594k
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Discrimination of the active crystalline phases in anatase-rutile mixed titanium(IV) oxide photocatalysts through action spectrum analyses Reviewed
T Torimoto, N Nakamura, S Ikeda, B Ohtani
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 4 ( 23 ) 5910 - 5914 2002.12
Joint Work
Publisher:ROYAL SOC CHEMISTRY
The active crystalline phases in powdered titanium(IV) oxide (TiO2) photocatalysts of anatase-rutile mixtures were investigated by measuring the action spectra of the photocatalytic reactions of H-2 evolution, Ag deposition and acetic acid decomposition. All of the pure anatase powders used in this study gave action spectra for the three kinds of reaction that were blue-shifted by about 30 nm from those of the pure rutile powders, being consistent with their photoabsorption behavior observed in the diffuse reflectance spectra. On the other hand, the action spectra of the mixed TiO2 powders varied, depending both on the kind of photocatalytic reaction and the content of the crystalline phases. In the case of H-2 evolution, the action spectra were intermediate between those of the pure anatase and rutile phases and were shifted toward that of the rutile phase with a decrease in the content of the anatase phase; i.e., the action spectra are governed mainly by the photoabsorption of each powder. The Ag deposition and acetic acid decomposition reactions gave action spectra of the mixed TiO2 powders that were similar to those of pure rutile and anatase phases, respectively, regardless of the content of the crystalline phases; the active phase in the former was rutile while that in the latter was anatase, even when these active phases were only minor parts of the mixed powder. The results indicate that the active crystalline phase differs with the kind of photocatalytic reaction even if the same mixed TiO2 powders were used as photocatalysts.
DOI: 10.1039/b207448f
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A Di Paola, E Garcia-Lopez, S Ikeda, G Marci, B Ohtani, L Palmisano
CATALYSIS TODAY 75 ( 43104 ) 87 - 93 2002.7
Joint Work
Publisher:ELSEVIER SCIENCE BV
Some probe catalytic photooxidation reactions with aliphatic and aromatic organic compounds having different acid strengths, i.e. methanoic acid, ethanoic acid, benzoic acid and 4-nitrophenol, were carried out in aqueous systems by using polycrystalline TiO(2) powders doped with various transition metal ions (Co, Cr, Cu, Fe, Mo, V and W). The Co-doped powder showed to be more photoactive than the bare TiO(2) for methanoic acid degradation while the behaviour of TiO(2)/Cu and TiO(2)/Fe was similar to that of the support. TiO(2)/W was the most efficient sample for the photodegradation of benzoic acid and 4-nitrophenol, TiO(2) the most active powder for ethanoic acid. A tentative explanation is provided by taking into account: (i) the dissociation constants (K(a)) of the different acids used as substrates; (ii) their aliphatic or aromatic nature; (iii) the points of zero charge (PZC) of the photocatalysts; (iv) their relative rate constants for photoelectron-hole recombination (k(r)) determined by femtosecond pump-probe diffuse reflectance spectroscopy. (C) 2002 Elsevier Science B.V. All rights reserved.
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Visible light-induced hydrogen evolution from aqueous suspensions of titanium(IV) oxide modified with binaphthol Reviewed
S Ikeda, C Abe, T Torimoto, B Ohtani
ELECTROCHEMISTRY 70 ( 6 ) 442 - 445 2002.6
Joint Work
Authorship:Lead author Publisher:ELECTROCHEMICAL SOC JAPAN
The reaction between titanium(IV) oxide (TiO2) powders and 1,1'-binaphthalene-2,2'-diol (bn(OH)(2)), both of which are originally colorless, led to the formation of surface TiO2-bn(OH)(2) complexes giving a broad absorption in the visible-light region below ca. 550 nm. When the surface complex was made on TiO2 loaded with platinum deposits, the powder exhibited photocatalytic activity for H-2 evolution from deaerated triethanolamine solution under visible-light irradiation (>430 nm). On the basis of the experimental results, the reaction mechanism seems to involve visible-light excitation of the surface complexes, electron injection to TiO2, and its migration to platinum deposits, where reduction of H+ takes place.
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Preparation of polycrystalline TiO(2) photocatalysts impregnated with various transition metal ions: Characterization and photocatalytic activity for the degradation of 4-nitrophenol Reviewed
A Di Paola, G Marci, L Palmisano, M Schiavello, K Uosaki, S Ikeda, B Ohtani
JOURNAL OF PHYSICAL CHEMISTRY B 106 ( 3 ) 637 - 645 2002.1
Joint Work
Publisher:AMER CHEMICAL SOC
A set of polycrystalline TiO(2) photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning, electron microscopy, point of zero charge determination, and femtosecond pump-probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the particles, and a not homogeneous distribution of the metal species onto the surface of catalyst particles. The impregnated samples revealed recombination rates always higher than that of bare TiO(2). The photoactivity of TiO(2) was reduced by the presence of transition metal ions with the exception of W, which instead played a beneficial role. The results of femtosecond pump-probe diffuse reflectance spectroscopy appear quite in accord with the observed photocatalytic activity only for the lowest values of electron-hole recombination rate of the samples.
DOI: 10.1021/jp013074l
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Direct observation of bimodal amphiphilic surface structures of zeolite particles for a novel liquid-liquid phase boundary catalysis Reviewed
S Ikeda, H Nur, T Sawadaishi, K Ijiro, M Shimomura, B Ohtani
LANGMUIR 17 ( 26 ) 7976 - 7979 2001.12
Joint Work
Authorship:Lead author Publisher:AMER CHEMICAL SOC
Amphiphilic NaY zeolite particles were prepared by a partial modification of the external surface of NaY with alkylsilyl groups. When the particles were added to a mixture of aqueous hydrogen peroxide and normal alkene, they were feasibly located just at the liquid-liquid phase boundary and efficiently catalyzed epoxidation of the alkenes even without stirring. Fluorescence microscopic observation of these particles selectively modified with fluorescent dye revealed that each particle has a bimodal amphiphilic surface structure; one side of the external surface is hydrophilic and the other is hydrophobic.
DOI: 10.1021/la011088c
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Phase-boundary catalysis of alkene epoxidation with aqueous hydrogen peroxide using amphiphilic zeolite particles loaded with titanium oxide Reviewed
H Nur, S Ikeda, B Ohtani
JOURNAL OF CATALYSIS 204 ( 2 ) 402 - 408 2001.12
Joint Work
Publisher:ACADEMIC PRESS INC ELSEVIER SCIENCE
A new heterogeneous catalytic system, phase-boundary catalysis, for epoxidation of alkene with aqueous H2O2 is proposed. Amphiphilic titanium-loaded zeolite particles, a part of the external surface of which was covered with hydrophobic alkyl groups and the rest being left hydrophilic, were prepared by deposition of titanium species from titanium(IV) tetra-2-propoxide and attachment of octadecylsilyl groups from n-octadecyltrichlorosilane (ODS) onto an NaY zeolite powder. Due to their amphiphilicity, the catalyst particles lay at the liquid-liquid phase boundary between upper alkene and lower aqueous phases, and they showed catalytic activity for epoxidation of 1-alkenes (e.g., 1-octene) with aqueous hydrogen peroxide. The phase-boundary catalytic system required neither stirring to make an emulsion nor addition of a cosolvent to make a homogeneous solution to drive the epoxidation. The yield of 1,2-epoxyoctane, a sole oxidation product from 1-octene, strongly depended on the apparent interphase area of the aqueous-organic phase boundary. The amphiphilic catalyst exhibited much higher catalytic activity than that of hydrophilic titanium-loaded NaY, without modification by ODS, or of a hydrophobic catalyst with almost full coverage by the alkyl groups. A similar trend in the activities of these catalysts was also observed when the reaction was carried out with vigorous stirring, in the presence of a cosolvent, or in a water-carbontetrachloride (CCl4) Mixture, where the aqueous hydrogen peroxide phase lies above the CCl4 phase. The phase-boundary catalytic system could also be applied to epoxidation of other normal alkenes. Compared with nonporous silica particles, the use of microporous NaY with a relatively large surface area had a beneficial effect, probably due to an increase both in the surface contact between the aqueous and organic layer and in the number of effective active sites of titanium species on its external surface. On the basis of these experimental results, a reaction model is proposed. (C) 2001 Elsevier Science.