Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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DOI： 1246/cl.2011.1411

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DOI： 10.1039/c1cp20814d

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DOI： 10.1016/j.jphotochem.2011.02.029

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DOI： 10.1016/j.jphotochem.2011.03.013

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DOI： 10.1021/am101281n

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DOI： 10.1039/C0JM00454E

Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Sputter deposition of silver (Ag) onto an ionic liquid (IL) produced Ag nanoparticles whose size was varied greatly dependent on the sputtering conditions. Change in discharge current from 10 to 40 mA increased Ag particle size from 5.7 to 11 nm, though prolongation of sputtering time simply caused a higher concentration of Ag nanoparticles in IL without change in their size. Sputter deposition of Ag onto IL solutions containing HAuCl4 resulted in the appearance of a single surface plasmon resonance peak in the absorption spectra of the resulting solution, and their peak position was red-shifted with an increase in the concentration of HAuCl4. The obtained results clearly indicated that Ag metal species sputter-deposited in IL can reduce HAuCl4 to give AuAg alloy nanoparticles and that their chemical composition varies depending on the initial concentration of HAuCl4.

Language：English   Publishing type：Research paper (scientific journal)  

Platinum (Pt) nanoparticles were synthesized with room-temperature ionic liquid (RTIL)−sputtering method under
dry N2 or Ar atmosphere. The resulting Pt nanoparticles were well-dispersed in trimethyl-n-propylammonium
bis((trifluoromethyl)sulfonyl)amide RTIL without any additive like dispersant. Electrocatalytic activity of the Pt nanoparticles embedded on a glassy carbon electrode (GCE) toward oxygen reduction reaction was examined. It
was then found that the catalytic activity increases with increment of heat temperature for embedding the Pt
nanoparticles onto GCE if the nanoparticles are synthesized under Ar atmosphere.

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Au-framed Ag nanocubes were prepared by site-selective electrochemical deposition of Au onto the edges and vertices of Ag nanocubes modified with a self-assembled monolayer (SAM) of 1-octanethiol, and further chemical etching of the Ag cubes used as a template produced Au nanoframes.

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Inorganic multilayer films were prepared by layer-by-layer accumulation of positively charged layered double hydroxide (LDH) nanosheets and negatively charged CdS nanoparticles of different sizes. Nanoparticles were densely immobilized on LDH sheets to form a monolayer
without coalescence into larger particles. The absorbance and photoluminescence intensity of immobilized CdS particles were enlarged with an increase in the accumulation number of the film. Hybrid films produced by accumulation of both monolayers of CdS particles (diameter: 5 nm) and those of smaller CdS particles (2.1 nm) exhibited characteristic photoluminescence spectra
indicating the efficient energy transfer of photogenerated excitons from nanoparticle layers of smaller CdS particles to those of larger ones. LDH/CdS multilayers deposited on an F-doped SnO2 (FTO) electrode behaved as an n-type semiconductor photoelectrode in an acetonitrile
solution regardless of the size of the CdS particles immobilized, but their efficiency for photocurrent generation was greatly dependent on the stacked structure of the films. Accumulation of CdS particles of 2.1 nm in diameter on pre-coated LDH/CdS layers of 5 nm-sized CdS particles on FTO remarkably enhanced the photocurrent intensity in comparison to that in the case of accumulation of these two kinds of CdS particles in the opposite sequence. These observations can be explained by photoinduced electron transfer and energy transfer along
with the band gap gradient in the films.

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Gold nanoparticles sputter-deposited in ionic liquids were
densely immobilized on the surface of highly ordered pyrolytic graphite (HOPG) by spreading the ionic liquid containing Au nanoparticles on HOPG and then heating. The density of immobilized Au particles was greatly dependent on the kind of ionic liquid used, and their size was controlled by the heating temperature. The resulting nanoparticle films were stable and electrochemically
active for oxygen reduction.

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Language：English   Publishing type：Research paper (scientific journal)  

It was recently discovered that the sputter deposition of metal onto the surface of an ionic liquid generates nanoparticles in the liquid with no additional stabilizing agents. We performed small-angle X-ray scattering (SAXS) experiments to investigate the structure of Au nanoparticles synthesized by this method and to reveal the properties of the ionic liquid that affect the formation process. For a systematic study of these properties, we selected imidazolium-based ionic liquids with different alkyl chain lengths fixing the anion BF4-. The Au concentration dependence for the formation of the nanoparticles was also studied. The SAXS results revealed
that Au nanoparticles with 0.75-3.5 nm diameter were generated under the experimental conditions and that the particle size was relatively uniform for a fixed condition. The results demonstrated that the particle size
depends on the type of ionic liquid and on the concentration if the ionic liquid is fixed. Integrating the
experimental results, it was concluded that the surface tension and viscosity of the ionic liquid played important
roles in conjunction with the Au concentration. It was interpreted that the surface tension influences the initial formation process of nanoparticles on the surface of an ionic liquid, and the viscosity affects the aggregation process during the dispersion of the Au particles from the surface into the liquid.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

UV-light induced redox reactions between cationic porphyrins (H2TMPyP) and methyl viologen (MV2+) separately incorporated in titania nanosheets (TNS) and cubic-mesoporous silica (MPS) integrated films, respectively, were investigated. In this system, the following two modified hybrids, i.e., the normally stacked (MV2+–TNS)/(H2TMPyP–MPS) on a FTO electrode and the inversely stacked
(H2TMPyP–MPS)/(TNS) films on a FTO electrode were examined. In accordance with the expected electron flowfromH2TMPyP to MV2+, cathodic photocurrentswere observed for the normally stacked film in acetonitrile (CH3CN) under a negative bias voltage of −0.4 V. However, under the influence of a positive bias voltage of +0.3 V, anodic photocurrents were observed even in CH3CN. On the other hand, anodic photocurrents were also observed in water for the normally stacked films at both bias voltages of +0.3 and −0.4V due to photoreduction followed by proton abstraction of the H2TMPyP molecules from H2O within the MPS nano-cavities. In addition, ca. 0.98 mC of the photocurrents were determined in water for the inversely stacked (H2TMPyP–MPS)/(TNS) films without MV2+, of which ca. 50% resulted in the oxidative consumption of H2TMPyP in the MPS cavities.

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The surface of cadmium sulfide nanorods was modified by 3-mercaptopropyltrimethoxysilane, followed by the hydrolysis of trimethoxysilyl groups to form a silica shell structure (SiO2/CdS[rod]). Size-selective photoetching was applied to SiO2/CdS[rod] to modify the size of the CdS rod core.
The absorption spectra were blue-shifted by irradiation of monochromatic light, and finally absorption onset agreed with the wavelength of irradiation light. These facts indicated that CdS rod particles were photoetched to smaller ones until the irradiated photons were no longer absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdS rod core prevented coalescence between photoetched particles. Changes in the wavelength of irradiation light from 488 to 436 nm caused a decrease in rod width from 3.5 to 2.3 nm along with remarkable decrease in the length of rod from 14 to 4.2 nm, suggesting that the photoetching rate was dependent on the kind of crystal faces and that the photocorrosion reactions at the tips of the CdS rod, that is, on (001)
and/or (00¯1) faces, were faster than those on other faces that appeared on the sides of the rod. This technique enabled control of CdS rod shape by selecting the wavelength of irradiation light.

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) ionic liquid. It was found that the BMI-PF6 supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF6-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS -functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF6. The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF6 aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the M PS -functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.

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Multilayer films of layered double hydroxide (LDH) nano-sheets and semiconductor nanoparticles of ZnS-AgInS2 solid solution (ZAIS) or CdS were prepared by a layer-by-layer deposition technique. The photoluminescence properties were remarkably dependent on the stacked structure of the films owing to the energy transfer from CdS to ZAIS nanoparticles.

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The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered.

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Based on our previous discovery that ionic liquid (IL) can be observed by a scanning electron microscope (SEM) without charging the liquid, we have developed several novel techniques for SEM observation. Coating of insulating sample with IL is useful for providing electronic conductivity to the samples like metal or carbon coating by vacuum vapor deposition. In this case, dilution of the IL with appropriate volatile solvent like alcohol is effective for coating thin layer of IL on the sample. As a biological sample, seaweed including IL was attempted to be observed by SEM. A seaweed leaf swollen by water was put in an IL bath and the bath was put in an outgassed desiccator to replace water in the seaweed leaf with IL. The resulting sample gave a SEM image of the swollen seaweed whose thickness was several times larger than dried one. Furthermore, the introduction of the IL in vacuum chamber allowed us to develop the in situ electrochemical SEM observation system. Using this system, we observed changes in polypyrrole film thickness caused by the redox reaction of the film and the electrochemical deposition of silver and its oxidative dissolution. It was also found that the energy dispersive X-ray fluorescence (EDX) analysis was available even for the electrode polarized in IL.

Language：English   Publishing type：Research paper (scientific journal)  

We report that ionic liquids (ILs) can be observed by electron microscopy without any charging of the liquid. Based on this, we present an in situ electrochemical scanning electron microscopy (in situ ECSEM) system. The key technology that enables in situ ECSEM is that charges can be removed from an IL by grounding it with a Pt wire, even if the IL is in an insulating gloss cell. As a first demonstration, we describe the redox reaction of a polypyrrole (PPy) film accompanied by changes in its thickness when it is polarized by the film-deposited Pt electrode in the IL. Further more, energy-dispersive X-ray fluorescence (EDX) analysis can be employed for the electrode polarized in the IL. The component analysis by EDX of PPy in an IL containing K+ as a marker, reveals doping of electrolyte cations into the PPy film upon the latter's reduction and dedoping of cations from the film upon oxidation.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Nanoparticles of ZnS-AgInS2 solid solution (ZAIS) were synthesized by the thermal decomposition of (AgIn)(x) Zn2(1-x)(S2CN(C2H5)(2)) 4 precursors in a hot oleylamine solution. X-ray powder diffraction analyses revealed that the resulting nanoparticle powders were not a mixture of ZnS and AgInS2 but a ZnS-AgInS2 Solid solution in which the fraction of ZnS was enlarged with a decrease in the value of x, that is, an increase in the content of Zn2+ in the precursors used. The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution. Intense emission was observed at room temperature, regardless of the kind of the particles, the peak wavelength of PL being blue-shifted from 720 to 540 nm with a decrease in the value of x. The highest quantum yield of ca. 24% was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I-III-VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS-CuInS2 solid solution.

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A core-shell composite of TiO2 particles encapsulated in a hollow silica was fabricated, and the core-shell composite showed size-selective photocatalytic activity for decomposition of organics without reducing the intrinsic activity of the naked TiO2 core.

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Photoirradiation (l=5-436 nm) of a deaerated 2-propanol
aqueous solution containing nitrobenzene and rhodium-loaded
silica-coated cadmium sulfide nanoparticles produced azoxybenzene with relatively high selectivity (68%), the photocatalytic activity being enhanced with a decrease in the size of the semiconductor particle core.

Language：English   Publishing type：Research paper (scientific journal)  

A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO2) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO2 with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO2, but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The uniquesize-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO2 particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable. oatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.

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Size-quantized cadmium chalcogenide nanoparticles were
effectively deposited on a porous zinc oxide particulate film electrode by a one-step hydrothermal method in which an increase in the concentration of 3-mercaptopropionic acid reduced the size of deposited nanoparticles. The photoelectrochemical properties of the resulting electrodes varied depending on the kind of metal chalcogenide nanoparticles deposited and their
size.

Language：English   Publishing type：Research paper (scientific journal)  

For the first time, we report highly stable CdS quantum dots sensitized TiO2 sandwich type photoelectrochemical solar cells. A unique combination of a sensitized electrode and a polysulfide electrolyte has provided the most stable solar cell with the highest IPCE of approximately 70%.

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A nonionic surfactant, n-dodecyl glyceryl itaconate (DGI), self-assembles into bilayer membranes in water having a spacing distance of submicrometer in the presence of small amounts of ionic surfactants, and shows beautiful iridescent color. Ionic surfactants have strong effects on this iridescent system. We have interestingly found that the iridescent color changes with time after mixing DGI and ionic surfactants and the color in equilibrium state changes greatly with concentration of the ionic surfactants. The time-dependent color change results from the transformation of DGI aggregate structure after being mixed with ionic surfactant. It is first found that the iridescent color of this nonionic system can be changed
from red to deep blue by altering the concentration of ionic surfactants added even though the total concentration of surfactant is almost constant. Such large blue shift of the iridescent color in equilibrium state cannot be fully explained by the ordinary undulation theory applied so far for this phenomenon. The flat lamellar sheets tend to curve by increasing the concentration of ionic surfactants to form separated onion-like and/or myelin-like structures. These separated structures of lamellar system result in the decrease of spacing distance between bilayer membranes because
some vacant spaces necessarily appear among these structures.

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In situ photoabsorption properties of titanium(IV) oxide (TiO2) powders under continuous ultraviolet irradiation
were investigated by double-beam photoacoustic (PA) spectroscopy. This PA measurement enabled observation
of two kinds of ultraviolet-light-induced intermediate species appearing on various kinds of TiO2 powder samples. Most of the samples (type 1) exhibited photoabsorption due to the production of trivalent titanium (Ti3+) species, while transient absorption assigned to trapped holes or surface peroxy species was also observed for anatase samples with a relatively large specific surface area (type 2). Time-resolved measurements and analyses of the kinetics of photoinduced Ti3+ species suggest that electrons accumulated in type-2 samples have high reactivity toward molecular oxygen compared to type-1 samples. Saturation limits of intensity of the PA signal attributed to Ti3+ species under deaerated conditions in the presence of surface-adsorbed methanol were estimated for both types of samples, and their linear relation with density of Ti3+ species estimated by a conventional photochemical technique was observed. This suggests that the present double-beam PA technique is an alternative feasible method for estimation of density of Ti3+ species, which is a potential measure of density of crystalline defects.

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The microscopic structures of two nano-structured inorganic films, the one based on titania nanosheets
(TNS) and the other on mesoporous silica (MPS), were investigated. Clear stacking structure of the TNS and MPS films was observed for the XRD, SEM, and TEM analyses. Both porphyrin derivatives and viologens were separately and selectively adsorbed into the MPS nano-cavities and the TNS nano-layers, respectively by means of their absorption and energy-dispersive spectroscopies (EDS).

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Photoluminescence enhancement, photoetching and photostability of CdS nanocrystals were investigated under light irradiation. Strongly photoluminescent nanocrystals were obtained when the nanocrystal was weakly photoexcited in an aqueous solution at pH = 11 in the presence of oxygen. With the support of XPS measurements, the following photoactivation mechanism is proposed: Cd2+ ions are released from the CdS surface owing to slow photocorrosion in the presence of oxygen, and Cd-OH bond formation occurs on the CdS surface under the alkaline conditions, removing the surface trap states. The wavelength of the irradiating light and the pH of the solution were determined as key parameters for nanocrystal surface modification. For the stability measurements the nanocrystals were extracted with an ammonium salt in a non-polar solvent. The photoluminescence quantum yield for the nanocrystals in the non-polar phase reached approximately 30%. The extracted nanocrystals were remarkably stable even under UV light irradiation, and the photoluminescence intensity was maintained for several months.

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Authorship：Lead author   Language：Japanese  

Language：Japanese  

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Light-emission intensity of CdS nanoparticles doped in a PMMAfilm is enhanced by a UV irradiation in air, but the emission intensity is strongly de-enhanced at a low pressure of 10−5 torr. Atmospheric gas as well as UV irradiation is essential for the enhancement, and these enhancement and de-enhancement processes are almost completely reversible. The emission of CdS nanoparticles doped in a PMMA film is also quenched by applying an external electric field, suggesting that the non-radiative
decay rate from the emissive exciton state is accelerated by an external electric field.

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Sputter deposition of gold Au onto ionic liquids ILs resulted in the formation of highly dispersed Au nanoparticles without additional chemical species, such as reducing and/or stabilizing agents. The Au nanoparticles in 1-ethyl-3-methylimidazolium tetrafluoroborate had an average diameter (dav) of 5.5 nm with a standard deviation (s) of 0.86 nm, while sputter deposition onto N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide resulted in the formation of much smaller Au nanoparticles with dav of 1.9 nm and s of 0.46 nm. Prolongation of sputtering time results in a higher concentration of Au nanoparticles in ILs, but did not cause a remarkable change in their size.

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Structural and energetic investigations based on semiempirical PM5 and ab initio HF and MP2 calculations suggested that the selfassembled monolayer of an atropisomeric compound, (R)- or (S)-1,10-binaphthalene-2,20-dithiol (BNSH), on a gold (111) surface selectively
adsorbs one enantiomer of phenylalanine (Phe), resulting in chiral discrimination, through hydrophobic, cation(NHþ3
Þ–p and NH(Phe)–p (BNSH) interactions in a nanometer-sized screw-hole-like pocket composed of three BNSH molecules in the monolayer.

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Electric-field-induced changes in absorption and emission spectra of colloidal CdS nanoparticles ranging in size from 1.0 to 5.0 nm in diameter have been measured by using electric field modulation spectroscopy. The analysis of the electroabsorption spectra indicates that the dipole moment in the first exciton state becomes larger with increasing particle size. The presence of the large dipole moment following photoexcitation into the first exciton band suggests that the CdS nanoparticles have large CT character in the first exciton state. The quantum yields both of the exciton emission and of the trap emission are markedly reduced by application of an electric field. On the basis of the direct measurements of the field-induced change in emission decay profile, it is suggested that the field-induced de-enhancement of these emission yields results from the fieldinduced decreases both in lifetime and in initial population of each emitting state. It is also found that the emission intensity of CdS nanoparticles increases under the UV light irradiation in air and decreases in a vacuum condition and that fluorescence lifetime in the former case is longer than that in the latter. This enhancement and de-enhancement process in emission intensity is almost reversible at least in several cycles.

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Language：English   Publishing type：Research paper (scientific journal)  

Photochemical Electron Transfer (ET) between an organic dye, the porphyrin derivative TMPyP, and an electron acceptor, methyl viologen MV2+, have been investigated at the interface of two different inorganic films, i.e., layered titania nano-sheets (TNS) and a monolayer film of spherical and mono-dispersed mesoporous silica (sMPS) particles (ca. 0.5 mm). TMPyP ions were intercalated within the sMPS nano-cavities to form (TMPyP–sMPS) while MV2+ ions were intercalated into the TNS interlayers to form (MV2+–TNS). The (TMPyP–sMPS) and (MV2+–TNS) films were then stacked on a silica substrate in this order to form a (MV2+–TNS)/(TMPyP–sMPS) film and, upon UV light irradiation, ET could be induced. However, when this
film was stacked inversely, i.e., for the (TMPyP–sMPS)/(MV2+–TNS) films on a silica substrate, no photoinduced ET were observed. Interestingly, however, even for this photo-inactive inversely stacked film, ET could be generated by inserting a gold vapor-deposited layer between the
(MV2+–TNS) and (TMPyP–sMPS) films. The conjugation conditions at the interface of the inversely stacked (TMPyP–sMPS)/(MV2+–TNS) hybrid film were, thus, confirmed to strongly affect the photoinduced electron transfers and their efficiencies.

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The emission spectrum of CdSe/ZnS quantum dots adhering to the surface of a microsphere resonator is measured and
discussed. Only certain peaks are observed, and the order numbers of the modes (l = 5 to 7) of the observed peaks are
different from those previously reported (l = 1 and 2). [Nano Lett. 1 (2001) 399]. A detailed analysis is presented using the cavity mode efficiency , which is a function of surface roughness, the absorption coefficient of the quantum dots, and mode parameters. The difference between the observed order number modes is explained to be due to the ratio of the rate of absorption by the quantum dots to that of the leakage rates of the modes. The surface roughness of a quantum-dot-coated microsphere and the absorption coefficient of the quantum dots on the sphere are estimated in the analysis.

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Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the
luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle
films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/
CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence
image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.

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Photoabsorption properties of titanium(IV) oxide powders were investigated by photoacoustic (PA) spectroscopy. The photoacoustic spectra obtained under steady-state ultraviolet irradiation showed appearance and growth of two kinds of PA signal bands, which were attributable to trivalent titanium species (Ti3+) and trapped holes or surface peroxide species. The saturation limit of the PA signal was estimated by analyzing the time course of Ti3+ signals and compared to the density of Ti3+ determined by a photochemical method. The results suggest that the photoacoustic spectroscopic technique is a feasible alternative method for estimation of Ti3+ as an empirical measure of defect density.

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A monoparticulate layer assembly of silica (SiO2)-coated cadmium sulfide (CdS) nanoparticles (SiO2/CdS) was prepared at an air-water interface and accumulated as thin films on solid substrates by the Langmuir-Blodgett technique. Size-selective photoetching of the CdS core by irradiation of monochromatic light induced a blue shift of diffuse reflectance spectra of the nanoparticulate films, indicating the formation of jingle-bell-shaped CdS core-SiO2 shell nanoparticles in the film. Photoluminescence of thus-photoetched SiO2/CdS nanoparticulate films was quenched by the addition of trialkylamines, the degree being dependent on their molecular size, while little change in the emission intensity was observed in the original films, regardless of the size of trialkylamines added. These facts were attributable to the molecular-size-selective penetration of quencher molecules from the bulk solution to the void space through the pores of the SiO2 shell of the jingle-bell-shaped nanoparticles.

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It has been discovered that ionic liquid can be observed by a scanning electron microscope without accumulation of electron charges, allowing SEM observation of insulating specimens wetted with ionic liquid.

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A facile one-step method to modify the surface of luminescent US nanocrystals by alkylamines, without their luminescence intensity loss, was established. The interfacial modification inducing spontaneous transfer of the US from an aqueous to a non-polar organic phase was found to be controlled simply by choosing the alkyl group of the amine. Analysis of the absorption and emission spectra revealed the phase transfer yield of ca. 100%.

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Photocatalytic deposition of gold (Au) and silver (Ag) nanoparticles was investigated using jingle-bell-shaped silica (SiO2)-coated cadmium sulfide (CdS) nanoparticles (SiO2/CdS), which each had a void space between the CdS core and SiO2 shell, as a photocatalyst. A size-selective photoetching technique was used to prepare the jingle bell nanostructure of SiO2/CdS. Nanoparticles of Au and Ag were deposited by irradiation of the photoetched SiO2/CdS in the presence of the corresponding metal complexes under deaerated conditions. Chemical etching of Au-deposited particles enabled the selective removal of CdS without any influence on the surface-plasmon absorption of Au. TEM analyses of the resulting particles suggested that some particles were encapsulated in hollow SiO2 particles, while other Au particles were deposited on the outer surface of the SiO2 shell. Emission spectra of the photoetched SiO2/CdS showed that the metal deposition developed a broad emission with a peak around 650 nm originating from surface defect sites, the degree being dependent on the kind of metal nanoparticles and their amount of deposition. This fact can be explained by the formation of metal-CdS binary nanoparticles having defect sites at the interface between metal and CdS.

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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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Silica-coated cadmium sulfide nanoparticles (SiO2/CdS) having a jingle-bell structure were prepared via size-selective photoetching and were used as photocatalysts for dehydrogenation of methanol. Irradiation Of SiO2/ CdS suspended in an aqueous solution containing methanol induced the liberation of hydrogen (1-12), the amount of which increased linearly with increase in the time of irradiation. The observed stable photocatalytic activity was attributed to the prevention of coalescence between CdS core particles by the surrounding SiO2 shells during the photocatalytic reaction. The rate of H, liberation increased with decrease in the wavelength of irradiation light for the size-selective photoetching, that is, the smaller the size of the CdS core, the higher the rate of H-2 liberation, probably because of increased reduction and oxidation abilities of CdS as a result of decrease in their particle size, that is, size quantization effect. Rhodium photodeposited on SiO2/CdS worked as a cocatalyst for the enhancement of dehydrogenation. The photocatalytic activity was reduced by increase in shell thickness because of a decrease in the rate of penetration of chemical species or the transfer of electrons and holes through the SiO2 layer. Also, the close contact between the core and shell retarded the photocatalytic reaction, indicating that the surface of the CdS core for methanol dehydrogenation was covered with a SiO2 shell layer. The results indicate that the jingle-bell-shaped SiO2/CdS nanoparticles can be an efficient and stable photocatalyst with a flexibly tunable structure, in contrast to s urface- modified CdS particles prepared by a conventional technique.

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Isolated CdS nanocrystals exhibiting intense luminescence can be prepared in aqueous solution, and combination of this new method with the previously developed size-selective photoetching method produces fluorescent markers emitting desired wavelengths.

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Treatment of surface silanol groups with hydrophilic compounds enabled silica-coated cadmium sulfide (SiO2/CdS) nanoparticles of core-shell morphologies to be dissolved in a water/methanol mixture. Size-selective photoetching of the particles was performed by irradiation with monochromatic light at 458 nm, resulting in a blue shift of its absorption onset because of the decreasing size of the CdS. TEM analyses revealed that the SiO2 shell structure was not shrunken by photoetching and that a void space (ca. 2.3 nm) was formed between the US core and the SiO2 shell to give a jingle-bell structure. The emission spectra of photoetched particles showed the development of band-gap emission when cadmium ion (Cd2+) was added and the pH was adjusted to 10, whereas the same treatment of original particles gave no peaks assigned to band-gap emission, indicating that the SiO2 shell was sufficiently porous for small ionic species such as Cd2+ to penetrate through the shell and that the photoetched US core incorporated in the SiO2 shell had a bare surface to be covered with a cadmium hydroxide layer. With increasing shell thickness, the rate of CdS photoetching was reduced as a result of decrease in the rate of scavenging of the photogenerated electrons in US by electron acceptors such as O-2 and methyl viologen (MV2+) in solution. The structure of the SiO2 layer was varied by surface modification of the US with both 3-mercaptopropionic acid (MPA) and 3-mercaptopropyltrimethoxysilane (MPTS) followed by hydrolysis of its trimethoxysilyl group. FT-IR spectra showed that MPA molecules, but not MPTS molecules, attached to the US core surface were eliminated by photoetching of the particles, resulting in the formation of windows in the SiO2 shell. The behavior of US emission quenching suggested that MV2+ is transported through the windows to the void space inside the SiO2 shell to reach the US core.

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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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The size-selective photoetching technique was used to control the size of a CdS nanoparticle inside a silica shell. With monochromatic light irradiation, the diffuse reflectance spectra of silica-coated CdS nanoparticles were blue-shifted, and the size of the resulting CdS nanoparticles incorporated in the silica shells was adjustable by varying the wavelength of irradiated light. TEM observation revealed that the original CdS nanoparticle seemed to be in close contact with the amorphous silica shell to leave almost no clearance, while the monochromatic light irradiation caused the decrease in the size of CdS particles, resulting in the formation of a void space between the photoetched CdS core particle and the silica shell. The average void spaces available in the shells were calculated to be ca. 1.4 and 2.4 nm with the irradiation at 514 and 458 nm, respectively. These results indicated that the size-selective photoetching technique enables the regulation of void space formed in the core-shell structure by choosing the wavelength of irradiation light.

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Layer-by-layer accumulation of monolayers of silica-coated cadmium sulfide (CdS) was achieved through repeated monolayer deposition–hydrolysis cycles using CdS particles (average diameter: 5 nm) modified with 3-mercaptopropyltrimethoxysilane (MPTS) and glass substrates. Absorption spectroscopic analyses of the resulting yellow films revealed that each layer had almost the same thickness, the estimated density of which corresponded to ca. 66% of that for close hexagonal packing of nanoparticles. Monochromatic light
irradiation at 488, 458, or 436 nm onto the film immersed in oxygen-saturated aqueous methylviologen solution caused a decrease in the size of the CdS core depending on the irradiation wavelength, while atomic force microscopic analyses suggested that the size of the silica
shell of the immobilized nanoparticles was almost unchanged by irradiation, i.e., the immobilized silica-coated CdS nanoparticles had void spaces between the photoetched core and the silica shell, and their sizes could be regulated by choosing the wavelength of irradiation light. This size-selective photoetching was applied to nanoparticulate films that had been heat-treated at 473, 573 or 673K to observe the blue-shift of the absorption edge of CdS to the irradiation wavelength. The amount of CdS remaining in the film after the photoetching process depended on the temperature of heat treatment. The largest amount among as-prepared and heat-treated samples was obtained at 473K and decreased with an increase in temperature. The growth of particles, i.e., the diminution of particle number, and/or the diminution
of number of separated independent shells may account for this dependence.

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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 (H2) 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 (O2)-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 O2. From the results of photocatalytic oxidative decomposition of 2-propanol, it was clarified that the surfaces of TiO2 particles could be sufficiently supplied with O2 from the gas space through the membrane to accelerate the oxidation.

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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 (H2) 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 H2, was elucidated.

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The molar amounts of defective sites (Md) 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
Md with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that Md could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between Md and the specific surface area suggests that the surface area was not directly reflected on Md . A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and Md revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.

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PbS ultrathin films were prepared by sequential underpotential deposition of S and Pb on Au(111) substrates. Observations of the resulting films with high resolution electron microscopy and energy dispersive X-ray spectrometry revealed the deposition of PbS thin films having the cubic rock salt crystal structure, the (200) planes of which were parallel to the Au surface. The scanning tunneling microscope images showed that the surface of the prepared PbS film was flat on an atomic level and no large protrusions were present, while etch pits with the height of the monatomic step of Au(111) were seen through the deposited films irrespective of the number of PbS monolayers. The PbS film-deposited Au electrodes showed anodic photocurrents in an aqueous solution containing triethanolamine as a sacrificial electron donor. The onset wavelength of their action spectra was largely blue-shifted from that of the bulk PbS due to the size quantization effects. The energy gap of the PbS thin films determined from the action spectra of anodic photocurrents decreased with an increase in the film thickness.

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Photoelectrochemical quartz crystal microbalance measurements were used for in situ monitoring of the photoelectrochemical deposition of PbO2 onto a TiO2 nanoparticulate film electrode. It was found that the photodeposition behavior of PbO2 was influenced by pH of solution. At pH 3.8, the mass of the TiO2 film electrode decreased in the initial stage of irradiation due to the desorption of Pb2+ from the TiO2, surface and then linearly increased due to PbO2 deposition with an increase in the charge flowing as a photocurrent, while the initial decrease of the mass was much smaller at pH 1.8.

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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 H2 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 H2 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.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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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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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Ultrasmall CdS nanoparticles were prepared by the size-selective photoetching technique. The smallest size of the CdS nanoparticles was obtained by the irradiation with the monochromatic light having the wavelength of 365 nm, while the absorbance of CdS nanoparticles monotonically decreased, for the whole wavelength, to null if the irradiation was performed using a wavelength less than 365 nm. The surface modification of US nanoparticles with thiophenol caused the red-shift of the absorption spectra due to the electric interaction between the bound thiophenol molecules and the CdS core, the degree being enhanced with a decrease in the particle size. H-1 NMR signals of thiophenol bound on the surface of the smallest US nanoparticles prepared by 365-nm irradiation were shifted upfield compared to those obtained for the larger thiophenol-modified CdS nanoparticles prepared by the longer wavelength irradiation, and the signals appeared in positions similar to those of chemically synthesized CdS cluster molecules. The observation with transmission electron microscopy revealed that the smallest thiophenol-modified CdS nanoparticles had an edged pyramidal shape with a size of about 1.7 nm in contrast to the larger CdS nanoparticles of almost spherical shape. The particle size and chemical compositions of the smallest thiophenol-modified US nanoparticles roughly agreed with those of Cd32S14(SC6H5)(36). 4DMF, which has been reported to be one of the largest chemically synthesized US cluster molecules. The similarity between the emission and excitation properties indicated that the smallest thiophenol-modified CdS nanoparticles had the energy structure almost equal to that of Cd32S14(SC6H5)(36). 4DMF.

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Two-dimensionally organized CdS nanoparticle films were prepared with the use of Langmuir-Blodgett (LB) technique. Propanethiol-modified CdS nanoparticles were spread on water subphase, which contained 1,6-hexanedithiol as a cross-linking agent for binding the surface-modified CdS nanoparticles with each other. Surface pressure-area isotherms of CdS monoparticle layer taken after the cross-linking were largely different from those obtained without addition of 1,6-hexanedithiol in water subphase. After the cross-linking, the CdS monoparticle layer was transferred from the air-water interface to 1,6-hexanedithiol-modified gold substrate using the LB technique to give CdS monoparticulate film electrodes with dense packing of the nanoparticles on the gold substrate. By repeating the same techniques, the monoparticulate him was cumulated with desired amounts. The prepared CdS nanoparticle films showed n-type photosensitivities in proportion to the cumulation number of the monoparticle layers for less than five layers. Beyond that value, a saturation tendency of the photocurrent appeared.

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Superlattice electrodes composed of three molecular layers of CdS and one to three molecular layers of ZnS were prepared on gold (111) film by using electrochemical atomic layer epitaxy. The prepared electrodes exhibited similar behavior to those of n-type semiconductor
electrodes. The energy gap was not changed at all by changing the number of molecular layers of ZnS and by increasing the number of periods in the superlattice structure up to four. The magnitude of the anodic photocurrent was, however, influenced by these variables. It increased with an increase in the number of periods in the superlattice structure and decreased with increasing number of molecular layers of ZnS.

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Utilities of hybrid photocatalyst consisting of TiO2 and an adsorbent such as activated carbon in photoinduced mineralization of organic substances of very dilute present concentrations are demonstrated for the photodecomposition of propionaldehyde in air atmosphere, and propyzamide and bromoform dissolved inwater. The substrates of target were adsorbed on the adsorbent
support, and then a high concentration environments of the substrate was formed around the loaded TiO2, resulting in an increase in the photodestruction rate. Evidences for the diffusion of propionaldeyde adsorbed on the mordenite support to the loaded TiO2 are presented. Merits of the use of the adsorbents as the support for TiO2 loading is discussed.

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Size-quantized ZnS thin films were prepared by sequential underpotential deposition of S and Zn on Au{111} substrates. Observations of the high-resolution electron microscope and the energy-dispersive X-ray spectrometer revealed that ZnS films were epitaxially deposited on the Au{111} facet with a stoichiometric composition. The scanning tunneling microscope images showed that the surface of the prepared films was flat in an atomic level and no large protrusion was contained, while etch pits with the height of the monatomic step of Au{111}, which were formed in the UPD of the first S layer on the naked Au surface, were seen through ZnS films with independence of the number of ZnS layers deposited. The ZnS film-deposited Au electrodes showed anodic photocurrents in an aqueous solution containing triethanolamine as a sacrificial electron donor. The energy gap determined from the action spectra decreased with an increase of the film thickness up to ca. 15.5 ZnS layers at which the bulk band gap was obtained.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

It was found that the size-selective photoetching of CdS particles prepared in Nafion films could be achieved only for particles having the particle sizes smaller than about 12 nm in the diameter. The particles greater than this threshold size were photocorroded until complete dissolution was attained.

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Cadmium sulfide nanoparticles (Q-CdS) modified with 2-mercaptoethanesulfonate and 2-amiaoethanethiol in a molar ratio of 2:1 were covalently immobilized onto-an Au surface covered with a self-assembled monolayer of 3,3'-dithiobis(succinimidylpropionate), and the resulting electrodes were further immobilized with Q-CdS using glutaraldehyde as a binding agent. The degree:of anodic photocurrents was greatly influenced by charged conditions of hole scavengers used because of the presence of sulfonate groups on the Q-CdS surfaces; triethylamine having positive charges gave large photocurrents, triethanolamine medium photocurrents, and formate small photocurrents. If Q-CdS having a large emission from their surface trap states was used, anodic photocurrents were depressed with increasing anodic polarization from the onset potentials which were ca. -1.1 V vs SCE for the use of any kinds of hole scavengers, and the greatest depression appeared at -0.25 V, beyond which a steep increase in anodic photocurrents was seen. In contrast, no significant depression in photocurrents was observed and anodic photocurrents were monotonically increased, in the case of using Q-CdS having an intense band-gap emission. When the energetic position at the emission maximum is correlated to the potential at which the greatest photocurrent depression appeared, photocurrent-potential characteristics are discussed in terms of involvements of surface states in the photoelectrode reactions.

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Effects of mordenite as a support material for TiO2 on photodegradation rates of gaseous propionaldehyde, acetone, and propane were investigated using TiO2 (50 wt%)-loaded mordenite as a photocatalyst in reference to unsupported TiO2. The supported photocatalyst allowed adsorption of all the substrates several times greater than the unsupported photocatalyst, resulting in higher photooxidation rates for them. Detailed analysis suggests that the enhancement of the decomposition rate caused by the use of mordenite support is more remarkable for lower amounts of adsorption of the substrates on the support. The concentration of oxygen was found to have little influence on the photodegradation rates, suggesting that the rate of degradation of the organic substrates was not decided by photogenerated electron transfer processes but by the consumption of photogenerated holes by adsorbed organic substrates.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Positively charged CdS nanoparticles having diameter of 3.0 +/- 0.2 nm were prepared by the chemical modification of their surfaces with thiocholine. Chains of size-quantized CdS nanoparticles were prepared by using the electrostatic interaction between positively charged nanoparticle surfaces and the phosphate groups of DNA molecules. The observation by transmission electron microscopy revealed that the CdS nanoparticles were arranged in a quasi one dimension with dense packing. The line width of a nanoparticle array was equal to the diameter of CdS nanoparticles that was ca. 3.0 nm. The average distance between the centers of the adjacent nanoparticles was estimated to be 3.5 nm, which was almost equal to the length of 10 base pairs in DNA double strands.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Several kinds of nearly monodisperse size-quantized CdS particles (Q-CdS) capped with 2-aminoethanethiol were prepared by means of size selective photoetching and were covalently immobilized onto a gold electrode substrate coated previously with a self-assembled monolayer of 2-aminoethanethiol. The potential of the conduction band edge of Q-CdS estimated from the onset potential of photocurrents was negatively shifted with a decrease in the diameter of CdS nanoparticles, the results being in good accord with the theoretical prediction.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Two-dimensionally organized CdS nanoparticle films were prepared with the use of the Langmuir-Blodgett (LB) technique. 2-Aminoethanethiol-modified CdS nanoparticles were spread on a water subphase which contained glutaraldehyde as a cross-linking agent for binding the surface-modified CdS nanoparticles with each other, and the cross-linking reaction was undertaken under several different compressions of the CdS nanoparticle layer spread on the water subphase. Surface pressure-area isotherms of the CdS monoparticulate layer taken after the cross-linking were largely different depending on the area used for the cross-linking. By transfer of the CdS monoparticulate film prepared at the air-water interface to the 2-aminoethanethiol-modified gold substrate using the LB technique, CdS monoparticulate films containing different surface concentrations were prepared on the gold substrate. It was easily done to cumulate the monoparticulate film on the gold substrate using the same transfer technique. The prepared CdS nanoparticles films showed n-type photosensitivities which were enhanced by increasing the number of cumulation of monoparticulate films.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The photodecomposition of propyzamide in the aqueous solution was investigated using TiO2-carbon black composite films. It was found that the photodecomposition rate was largely influenced by the content of carbon black in the photocatalyst film. The decomposition rate increased with increasing the carbon black content up to an optimal value, beyond which the photocatalytic activity showed a decreasing tendency. The increase of the photodecomposition rate seems to result from increase of adsorbability for propyzamide in the TiO2-carbon black composite films. With further increase of carbon black from the optimum value, however, relative occupation of TiO2 to carbon black decreases, and the time needed for adsorbed propyzamide on carbon black to diffuse to TiO2 particles becomes great, resulting in the decrease of the apparent photocatalytic activity of the film. Experiments employing a circulating photoreactor system also showed that the TiO2-carbon black composite films had higher photocatalytic activities than the naked TiO2 film.

Language：English   Publishing type：Research paper (scientific journal)  

Three structurally variant alkyl-substituted porphyrins [zinc(II) 2,3,7,8,12,13,17,18-octa-n-decylporphyrin 2, metal(II) meso-5,10,15,20-tetra-n-undecylporphyrin 3 (metal = cobalt, copper, palladium, and zinc), and zinc(II) meso-5,10,15,20-tetrakis(phenoxy-n-nonyl)porphyrin 4] exist as photoconductive insulators and produce significant short circuit photocurrent and open circuit photopotential when irradiated as solid thin films in an indium-tin oxide sandwich cell. Liquid crystalline phase stability, the identity of the inserted metal, and the nature of its supramolecular packing all influence the observed photoelectrochemical response. Porphyrin 2, which has a stable liquid crystalline phase, produces higher steady-state photocurrents than do the corresponding meso-substituted porphyrins 3 and 4, although liquid crystallinity is not an absolute requirement for observation of a photoresponse. Among porphyrins 3, the zinc complex gave the highest steady-state photocurrent. When a phenyl ring orthogonal to the porphyrinic plane was present (as in 4), the observed photovoltaic response was significantly diminished, probably because of difficulties in achieving effective close packing.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The photocorrosion behavior of CdS nanoparticle colloid containing particles ranging from 4 to 10 nm was investigated using two kinds of monochromatic light, one of which was prepared by passing light from a Xe lamp through interference filters, and the other was obtained by an Ar ion laser. CdS particles were photocorroded to smaller particles until irradiated photons were not absorbed anymore; and the CdS particles obtained after the complete photocorrosion by laser light were much smaller than those resulting from the use of monochromatic light of comparable wavelength. The size selective photocorrosion with the Ar ion laser allowed the preparation of much smaller particles than those in the original colloid. It was found that the rate of photocorrosion decreased when the pH of the colloid was raised, while the fluorescence intensity due to bandgap transition increased. The importance of hole trap sites in the photodissolution of CdS is discussed based on these findings.

Language：English   Publishing type：Research paper (scientific journal)  

The photocatalytic reduction of carbon dioxide on CdS particles with and without surface modification by several kinds of thiol compounds was investigated in various kinds of solvents. Formate and carbon monoxide were obtained as the major reduction products, and the ratio of the former to the latter was largely influenced by the kind of solvents when naked cadmium sulfide was used as the photocatalyst, and with increase of the dielectric constant of the solvent, the ratio increased. Even if CdS particles were modified by thiol compounds, the effect of the solvent was not eventually altered, but the ratio of formate to carbon monoxide became greater with increase of the surface modification of CdS. The observed effect of the surface modification of CdS is discussed in terms of involvement of Cd2+ sites adjacent to surface vacancies of CdS photocatalysts in adsorption of anion radicals of CO2.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Photocatalytic reduction of CO2 in the presence of nitrate ions in various solvents was studied using TiO2 nanocrystals embedded in SiO2 matrices as photocatalysts. Both formate and carbon monoxide were produced as the reduction products of CO2, ammonia as the reduction product of nitrate, and in addition to these products, urea was formed as a major reduction product of both CO2 and NO3-. The selectivity of these reactions was greatly influenced by the kind of solvents used, and with increasing the dielectric constant of solvents, the amount of formate and carbon monoxide produced decreased, while those of urea and ammonia increased. These results suggest that the reduction reaction of nitrate ions was the rate-determining step of the formation of urea.

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Size-quantized CdS thin films were prepared by sequential underpotential deposition of S and Cd on Au(lll). The prepared films in an aqueous solution containing triethanolamine as a sacrificial electron donor showed n-type photoelectrode behaviors. Action spectra of anodic photocurrents were red-shifted with an increase of the film thickness toward characteristic values of those of bulk materials. The energy gap of the film determined from the action spectra showed a remarkable tendency of decrease with an increase of the film thickness up to 3.5 nm. Beyond 3.5 nm the rate of decrease with increase in the film thickness declined. An energy gap value characteristic of bulk materials was obtained with CdS films greater than 6.8 nm.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Photocatalytic degradation of gaseous propionaldehyde over TiO2-loaded adsorbent films was investigated after adsorption equilibrium was obtained using silica, alumina, activated carbon, and several kinds of zeolites as adsorbents. Irradiation of one-tenth of the TiO2-loaded adsorbent film caused complete mineralization of the adsorbed substrate in the entire film, although the rates obtained in that case were much lower than one-tenth of the rates obtained with the total area irradiation, indicating a considerable contribution of supply of the adsorbed substrate from the nonirradiated part of the film to the irradiated part. The apparent diffusion coefficient D-app of adsorbed substrate was evaluated by applying the time course of CO2 evolution obtained in the area-selective photodecomposition reaction to a one-dimensional diffusion model. The D-app values estimated for various kinds of TiO2-loaded adsorbent supports explain well the differences in the photodecomposition rates obtained at these photocatalysts. On the basis of experimental results, the effect of diffusion of the adsorbed substrate on the photodecomposition kinetics is quantitatively discussed.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

The effect of the amount of TiO2 loading on activated carbon support on the photodecomposition of dichloromethane was studied. The apparent adsorption constant of the TiO2-loaded activated carbon for dichloromethane was found to decrease with increase of the fraction of the loaded TiO2. It was found that the apparent rate constant of CO2 evolution became small with increase of the activated carbon content, suggesting that the adsorbed substrate on the activated carbon support was not easily involved in the photodecomposition reaction. However, the use of mixed suspensions of TiO2 and activated carbon showed lower activities than the TiO2-loaded activated carbon for photodegradation of dichloromethane. The role of the activated carbon support in the photodecomposition of dichloromethane is discussed.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Photocatalytic reduction of CO2 in various kinds of solvents was studied using TiO2 nanocrystals embedded in SiO2 matrices (Q-TiO2/SiO2) as the photocatalyst. It was found that the major reduction products were formate and carbon monoxide, and their total amount increased on increasing the concentration of CO2 dissolved. The ratio of formate to carbon monoxide was greatly influenced by the kind of solvent, and increased on increasing the dielectric constant of the solvent. If bulk TiO2 was used as the photocatalyst, the rate of CO2 reduction was low compared to that obtained with Q-TiO2/SiO2, but the ratio of formate to carbon monoxide obtained was not greatly different from that obtained with the Q-TiO2/SiO2. The effect of solvent on the reduction behavior of CO2 is discussed in terms of stabilization of reaction intermediates.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Irradiation with a very high intensity laser pulse (355 nm) induces blue color in TiO2 powders and films. The blue color, which is assigned to the formation of Ti3+ in the particle, persists in air for several months. With an increase of the concentration of Ti3+ in a given particle, photocatalytic activity is decreased because of a decrease in the thickness of the space-charge layer as deep Ti3+ traps are populated.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Photodecomposition in aqueous solution of 3,5-dichloro-N-(3-methyl-1-butyn-3-yl)benzamide, whose popular name is propyzamide, was investigated using naked TiO2 and TiO2-loaded adsorbent supports as photocatalysts. The adsorbent supports used were zeolite (mordenite), silica, and activated carbon. The use of adsorbent supports was found to enhance the rate of mineralization of propyzamide and to reduce the concentration of solution-phase intermediates. The experimental results suggest that the adsorbent support concentrates a target substrate of low solution-phase concentration on its surface, providing the substrate-rich environment at the adsorbent/TiO2 interface, This concentration effect results in an enhanced rate of propyzamide mineralization. The intermediates are also retained on the adsorbent support and subsequently decomposed, thereby reducing the concentration of possibly toxic intermediates in the bulk solution.

Language：English   Publishing type：Research paper (scientific journal)  

Size-quantized TiO2 particles immobilized in polyvinylpyrrolidinone (Q-TiO2/PVPD) films, were prepared by electrophoretic deposition of Q-TiO2 colloids in 2-propanol in the presence of PVPD as a stabilizing agent. The Q-TiO2 prepared had the average diameter of 3.3 nm with a standard,deviation of 1.1 nm. Illumination of the Q-TiO2/PVPD film in water-free 2-propanol resulted in the production of acetone as a sole oxidation product and Ti3+ species as the reduction product, and when the Ti3+ species was accumulated, hydrogen evolution began to occur. The same was true for bulk TiO2 particles immobilized in the same matrix, which were prepared by soaking the Q-TiO2/PVPD film in water, but the rate of these photoinduced reactions was much slower than that of the Q-TiO2. The photoformation of Ti3+ in the TiO2 particles was suppressed by introduction of NO3- to 2-propanol, suggesting that the formation of the Ti3+ species is controlled by kinetics of electron transfer to accepters in solution.

Authorship：Lead author   Language：English  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Effects of the use of inert supports for TiO2 loading on photocatalyzed decomposition of propionaldehyde in the gas phase was investigated for mordenite support with various amounts of TiO2 loading and for several kinds of supports such as other zeolites, alumina, silica, and activated carbon. The adsorption constant and the amount of adsorption of propionaldehyde were evaluated for TiO2-loaded supports by obtaining Langmuir adsorption isotherms. By correlating these parameters to the photodecomposition rates of propionaldehyde, the involvement of the support in the photodecomposition reaction is clarified. The photocatalytic activity of TiO2 on mordenite having various amounts of TiO2 loading increases with increase in the amount of loaded TiO2 up to an optimum value (ca. 50 wt %), beyond which a decreasing tendency of the activity appeared. In the region of ascending activity, plenty of adsorbed substrate is available and the activity is controlled by the content of TiO2, while in the region of descending activity, the decrease in the amount of adsorbed substrate due to a decrease in the occupancy of the support by the TiO2 loading is responsible for the activity decrease. The photocatalytic activities are greatly influenced by the kind of inert supports used and show a volcano type dependence on the adsorption constant of the TiO2-loaded supports. In cases where the adsorption constant is low, the decomposition rate is determined by the amount of adsorbed substrate, while if the adsorption constant is very high, plenty of adsorbed substrate is available on the support, but it is not mobile to the loaded TiO2. We conclude that the use of an inert support having a medium adsorption constant is necessary to obtain the highest activity, where a high amount of adsorbed substrate that can be supplied to TiO2 particles is available.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

CdS microcrystals (Q-CdS) covalently bound with 1-decyl-1'-(3-mercapto) propyl-4,4'-bipyridinium were prepared. The surface viologen groups picked up photo-generated electrons in the conduction band of Q-CdS particles, causing a decrease of their emission. Irradiation of these particles resulted in new absorption peaks which are assigned to viologen radical cation monomers and their dimers. The photo-reduced viologen groups can mediate photo-generated electron transfer from Q-CdS to methylene blue in solution.

Language：English   Publishing type：Research paper (scientific journal)  

Zinc sulfide microcrystals fully modified with ethanethiol, butanethiol, and octanethiol of about 4 nm diameter with a narrow size distribution were prepared. The rate of photoinduced electron transfer from the microcrystals to methyl viologen (MV(2+)) in solution showed a linear dependence on the concentration of MV(2+), while at bulk ZnS particles the Langmuir-Hinshelwood type kinetics prevailed. It is concluded from the observed logarithmic dependence of the rate constant on the inverse of the chain length of the modified alkanethiols that the electron tunneling controls the photoinduced reduction of MV(2+).

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Size-quantized CdS microcrystals (Q-CdS) modified with various amounts of electroactive 1-decyl-1'-(3-mercaptopropyl)-4,4'-bipyridinium dibromide (VSH) and electroinactive decanethiol were prepared. The surface-modified VSH was photoreduced by irradiation of Q-CdS to give both dimeric and monomeric radical cations of the viologen, and the formation of the former was enhanced by increasing the amount of the surface-bound VSH. Kinetic analyses revealed that the rate constants for the reduction of the surface-modified VSH and for the reoxidation of the produced radical cations were independent of the amount of the VSH, Q-CdS having the higher amount of VSH showed the higher activity for electron transfer to methylene blue in solution, evidencing that the surface-bound viologen mediated electron transfers from Q-CdS to the electron acceptor in solution.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Two kinds of quantized PbS microcrystals modified with 4-aminothiophenol (4-ATP/Q-PbS) having different surface coverage were prepared by using two different concentration ratios of [Pb2+]/[S2-] in the synthesis of the 4-ATP/Q-PbS particles. The rates of photoinduced reduction of methylviologen on the two kinds of 4-ATP/Q-PbS particles were influenced by the kind of hole scavengers (sodium tartrate or triethanolamine) and the pH of solutions, and the higher reduction rates were obtained under conditions where the higher amount of adsorption of the hole scavenger occurred. High reduction rates of methylviologen were obtained at the photocatalyst having a high coverage of the surface modifier, because high electrostatic attractive interactions between the hole scavenger and the surface are operative when tartrate was used as a hole scavenger and a high amount of adsorption sites due to a high coverage of the surface modifier are available when triethanolamine was used. The validity of such interpretation was supported by kinetic analysis based on rate equations. Furthermore, it was found that inert electrolyte anions such as ClO4- had a retarding action for the photoreduction of methylviologen when tartrate was used as the hole scavenger, as a result that the adsorbed tartrate anions were replaced by the inert electrolyte anions depending on their concentrations. The adsorbability of inert electrolyte anions (Cl-, Br-, and ClO4-) as well as tartrate anions was found to be influenced by the degree of surface modification of the Q-PbS particles with 4-aminothiophenol. As for the case of using electronically neutral triethanolamine as the hole scavenger, the inert electrolyte anions did not influence the photoreduction rate of methylviologen.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Quantized PbS microcrystals capped with 4-hydroxythiophenol (ArSH) were prepared using two different concentration ratios of [Pb2+]/[S2-] = 1.2 and 3.0 with fixed concentration ratio of [ArSH]/[Pb2+] = 4.0. The size distributions of the prepared PbS particles were determined. Two different surface structure models of fully occupied and partially occupied surface sites of PbS microcrystals with the capped ArSH are assumed, and chemical compositions of these particles are evaluated by taking the experimentally determined particle size distributions into account. By examining the fitness of the chemical analyses data of the PbS particles to the evaluated compositions, it is proposed that the PbS particles prepared [Pb2+]/[S2-] = 3.0 had the capped ArSH in all the surface sites, while PbS particles prepared with [Pb2+]/[S2-] = 1.2 had some surface sites free from the modifier. The proposed surface structures of the two kinds of PbS microcrystals were rationalized by experimentally found differences both in agglomeration tendencies of the particles and in the effect of the addition of Pb2+ ions on the rate of photoinduced reduction of methyl viologen on the particles.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Event date： 2022.3

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Venue：大阪 (on-line)   Country：Japan  

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Venue：大阪 (on-line)   Country：Japan  

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Event date： 2021.9

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Event date： 2021.9

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