Chelation ability of spironaphthoxazine with metal ions in silica gel

Spironaphthoxazine (SNO) and three metal ions, Mg2+, Zn2+, and Al3+, were dispersed in silica gels by the sol-gel method. The chelation ability of SNO with the metal ions in silica gels was investigated by measuring the fluorescence spectra and was compared to that of 8-hydroxyquinoline (8-HQ) in ethanol and silica gels. A merocyanine-type isomer photoderived from SNO as well as 8-HQ easily formed complexes of the metal ions in the order of Al3+, Zn2+, and Mg2+ because the coordination ability of the metal ions to such ligands depended on their electron affinity. The changes in the fluorescence spectra of the silica gel samples during light irradiation were also investigated. The relative band intensity due to the intermediate species between the original SNO and the merocyanine species decreased and that of the complex increased with the UV irradiation time. The reverse process was observed during visible irradiation. The UV irradiation effects on the chelation of SNO and its photochromic property also depended on the electron affinity of the metal ions.ArticlePHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES. 11(7):1164-1173 (2012)journal articl

Photoinduced electron transfer in rhodamine B-containing amorphous titania gels

Amorphous titania gel films containing the dye rhodamine B (RhB) were prepared by a sol-gel method, without heating. The RhB existed in the films as the RhB cation, which was transformed into the rhodamine 110 (Rh110) cation; its xanthene skeleton then decomposed during irradiation with visible light. This process was induced by electron transfer from the RhB cation to the titania gel matrix, because formation of the RhB radical on loss of an electron caused sequential dissociation of the N-ethyl groups. During irradiation with visible light a photocurrent was observed in electrodes coated with the RhB-containing titania gel and immersed in an I-2-LiI electrolyte. This photocurrent resulted from electron injection from the LUMO level of the dye into conduction band-like states of the titania gel. Because of its effective electron supply the electrolyte inhibited dissociation of the N-ethyl groups of RhB.ArticleRESEARCH ON CHEMICAL INTERMEDIATES. 41(6):3803-3816 (2015)journal articl

Influence of dye dispersion on photoelectric conversion properties of dye-containing titania electrodes

Dye-dispersing titania electrodes were prepared from the dye-containing titanium alkoxide sols by a room temperature sol-gel process and steam treatment at 110 degrees C. The spectroscopic and photoelectric conversion properties of the electrodes were investigated in order to clarify the influences of the dye dispersion and the co-dispersion of the two dyes on the electron transfer process. The fluorescein and eosin Y molecules were dispersed into the titania as their monomers. The shapes of the photocurrent action spectra of the fluorescein and/or eosin Y-dispersing titania electrodes corresponded well to those of their absorption spectra because the excited electrons in the dyes were directly injected into the titania conduction band without any interaction between the dye molecules, such as energy transfer. This result indicated that the dye molecules were separately encapsulated in the pores between the titania nanoparticles and tightly adsorbed or bonded to the titania particle surface. The internal quantum efficiency of the photoelectric conversion was higher than that of the conventional dye-adsorbing titania electrodes in which the dye molecules were easily aggregated and thus deactivated by the energy transfer. The co-dispersion of the two dyes on the titania surface allowed effective extension of the visible light region for the photoelectric conversion.ArticleCATALYSIS SCIENCE & TECHNOLOGY. 3(6):1512-1519 (2013)journal articl

Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein-Dispersing Sol-Gel Titania Films

Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band.ArticlePHOTOCHEMISTRY AND PHOTOBIOLOGY. 90(4):747-759 (2014)journal articl

Influence of gas flow on argon microwave plasma jet at atmospheric pressure

Many kinds of an atmospheric-pressure plasma jet have been developed and used for widespread applications such as a surface treatment and modified. This study focused on the argon atmospheric-pressure m jet generated by discharging of RF power of 2.45 GHz microwave. The plasma jet shows sensitivity to surrounding environment: pressure, temperature and gaseous species. It is therefore absolutely imperative that a nature of atmospheric-pressure plasma jet should be understood from a point of fluid dynamics. This study, therefore, focused on the interrelationship between the plasma jet and the working gas. Motion of the plasma jet and the working gas was evaluated by velocity measurement and fast photography. As a result, the unsteady sinusoidal waving motion in the radial direction of a torch was observed. Advection velocity of the plasma in just downstream region of the torch exit increases with the supplying flow rate, and the velocity ratio is in the range of 0.75-0.87.ArticleSURFACE & COATINGS TECHNOLOGY. 206(6):1449-1453 (2011)journal articl

Photoelectrochemical properties of dye-dispersing allophane-titania composite electrodes

Dye-dispersing allophane-titania composite electrodes were prepared from titanium alkoxide sols containing dye and allophane. The photoelectric conversion properties of the electrodes were investigated by photoelectrochemical measurements. The photocurrent values in the UV range decreased with an increase in the allophane content, whereas those in the visible range were increased by adding 1.0% (Al/Ti ratio) allophane. As a small amount of allophane nanoparticles were highly dispersed in the titania electrodes, the dye molecules were dispersed in the electrodes without decreasing the efficiency of the electron injection from the dye to the titania conduction band. The dye molecules dispersed on the titania nanoparticle surface were capped with allophane nanoparticles which prevented desorption. The dye molecules strongly interacted with the titania nanoparticle surface and efficiently injected the excited electrons into the titania conduction band. (C) 2015 Elsevier B.V. All rights reserved.ArticleAPPLIED CLAY SCIENCE. 107:138-144 (2015)journal articl

Dimerization of xanthene dyes in sol-gel titania films

Dye-dispersing titania gel films were prepared by the sol-gel method using titanium alkoxide solutions containing xanthene dyes, i.e., fluorescein, eosin Y, rhodamine 110, and rhodamine 123. Dimerization of the xanthene dyes in the films, depending on their concentrations, and their photoinduced electron transfer processes to the titania gels were investigated using spectroscopic and photoelectric techniques. The dye having a higher dimerization constant in solution formed a higher amount of the dimer in the titania gel. There was only a slight difference between the photoelectric conversion efficiencies of the monomer and dimer. The titanium species were coordinated to the carboxylate of the dyes. The dimers as well as the monomers were encapsulated in the narrow spaces of the gel films and strongly interacted with the surrounding titania matrix in the dye-dispersing titania gel films. The dye having a more nucleophilic carboxylate oxygen could easily form the coordination complex with the titanium species. The dye-titania interaction played an important role in the electron injection from the dye to the titania conduction band.ArticleCATALYSIS SCIENCE & TECHNOLOGY. 3(10):2786-2792 (2013)journal articl

Interaction between dye and zinc in the dye-dispersing ZnO films prepared by a wet process

Dye-dispersing ZnO precursor gel films were prepared on indium tin oxide electrodes from a zinc acetate solution containing eosin Y by dip-coating, steam treatment, and then heating at a low temperature. The electronic interaction between the dye and zinc in the dye-dispersing gel films were investigated by spectroscopic and electrochemical measurements. A photocurrent was observed in the dye-dispersing gel electrodes before the steam treatment. The photocurrent value increased by the steam treatment and heating due to crystallization of the gel and removal of organic impurities. The dye molecules existed between the interlayers of the layered zinc hydroxide coexisting with the ZnO. The photoexcited electron in the dye should be injected into the ZnO conduction band via the layered zinc hydroxide. The value increased with an increase in the dye content even though the ZnO crystallinity decreased. The dye-zinc interaction, i.e., the complex formation and photoinduced electron injection, played an important role in the electron transport and photoelectric conversion.ArticleRESEARCH ON CHEMICAL INTERMEDIATES. 41(9):6559-6574 (2015)journal articl