Degradation of trichloroethylene using highly adsorptive allophane-TiO(2) nanocomposite

A highly adsorptive allophane-TiO(2) nanocomposite photocatalyst was prepared by dispersing nanopartides of the natural clay mineral allophane into a titanium alkoxide solution by the sol-gel method. During the photocatalytic degradation of trichloroethylene using the allophane-TiO(2) nanocomposite, emission of the intermediate product, phosgene, was drastically inhibited. Trichloroethylene was transformed into the intermediate products, phosgene and dichloroacetyl chloride, on the TiO(2) during the UV irradiation. These compounds are rapidly adsorbed on the allophane. The compounds then gradually degraded after diffusing to the TiO(2).ArticleAPPLIED CATALYSIS B-ENVIRONMENTAL. 102(3-4):470-474 (2011)journal articl

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

Reaction of spironaphthoxazine with acid

The reaction of spironaphthoxazine (SNO) with acid in ethanol was investigated by spectroscopic analyses SNO was protonated and then transformed into a complex in an acidic ethanol solution in the dark. It is presumed that the complex contains a hydrated proton and its structure is similar to that of the metal complex of a merocyanine-type isomer photoderived from SNO based on its UV-vis absorption and fluorescence spectra. The complex dissociated into SNO by adding base. The complex was further changed under acidic conditions after a long time. Highly concentrated acid decomposed SNO to an indoline compound having a carboxyl group and 1-amino-2-naphthol, which was revealed by fluorescence, IR, and GC-MS analyses. These reaction processes were promoted by UV irradiation.ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 252:100-106 (2013)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

Photofuel cells using glucose-doped titania

Glucose-doped titania electrodes were prepared from titanium alkoxide sols containing glucose in order to examine the validity of the fuel material concentrated on the photocatalyst surface. The observed photocurrent and CO(2) and H(2)O productions indicated that the oxidation of the glucose enhanced the generation of electricity during the UV irradiation. Steam treatment of the electrodes improved the glucose oxidation and the photocurrent. However, refluxing of the precursor sol did not improve them. Not only the titania conductivity, but also the contact between the glucose and titania is important in order to obtain a high photofuel electric conversion. The concentration of the fuel material on the photocatalyst surface improved the energy conversion efficiency.ArticleAPPLIED CATALYSIS B-ENVIRONMENTAL. 106(1-2):250-254 (2011)journal articl

Nitrogen doping into titanium dioxide by the sol-gel method using nitric acid

N-doped TiO(2) has been prepared by use of sol-gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and nitrous ions were observed by FT-IR measurement during the sol-gel reaction. The N-doping was confirmed by the observation of N-O peaks in the XPS spectrum of the sample heated at 400 A degrees C. The nitrate ion acted as an oxidizer of the ethanol solvent and titanium species. The TiO(2) became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples. These results indicated that the added nitric acid was reduced during the sol-gel transition and heating process, and the resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was confirmed by the degradation of trichloroethylene.ArticleRESEARCH ON CHEMICAL INTERMEDIATES. 37(8):869-881 (2011)journal articl

Quantitative characterization of acidic groups on acid-treated multi-walled carbon nanotubes using 1-aminopyrene as a fluorescent probe

Acidic functional groups produced on the surface of acid-treated multi-walled carbon nanotubes (MWCNTs) were quantified by fluorescence measurements using 1-aminopyrene (1-AP) as an in situ probe molecule. The 1-AP cation-like bands were observed on the HNO3/H2SO4 mixture-treated MWCNT surfaces because the 1-AP molecule was tightly immobilized by the hydrogen bonding interaction between its amino group and the Bronsted-acidic groups on the MWCNT surface. The fluorescence measurement, allowed us to confirm the Langmuir-type adsorption of 1-AP on the functional groups of the MWCNTs, and estimate their amount of the functional groups and adsorption equilibrium constant. A longer acid treatment caused the chemical modification to generate higher amounts of the Bronsted-acidic functional groups and improve the adsorption ability on the MWCNT surface. About 2% of carbon in the MWCNTs was oxidized by the 24 h acid treatment. This value corresponded to 15-22% of carbon in the surface layer.ArticleCARBON. 66:560-566 (2014)journal articl

Photochromic behavior of spironaphthoxazine in metal ion-containing solutions

The isomerization and metal chelation of spironaphthoxazine (SNO) in ethanol solutions have been investigated by measuring the UV-vis absorption spectra as a function of time. The protonated species of merocyanine (MC), an isomer of SNO, was gradually formed in the solutions containing SNO and aluminum ions in the dark. The proton was provided by the reaction of the aluminum ions with a slight amount of water contained in the ethanol solvent. The protonated species was slowly transformed into the aluminum chelate complex of MC by ligand exchange of the ethanol-solvated aluminum for MC in the dark. UV irradiation promoted the isomerization and chelation without forming the protonated species. The spectroscopic analysis with various compositional ratios of SNO and aluminum ions revealed that one aluminum ion was coordinated to three bidentate MC ligands in the ethanol solution.ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 222(1):236-240 (2011)journal articl

Photo-electric conversion in dye-doped nanocrystalline titania films

Influences of the titania nanostructure and dye dispersion in a dye-doped titania electrode on its photoelectric conversion property were investigated by simple spectroscopic and electric measurements. The dye-doped nanocrystalline titania electrodes were prepared on the glass plates coated with ITO and normal crystalline titania films by the following two procedures: (1) the dye-doped titania gel films were prepared from a titanium alkoxide solution containing the dye and then steam-treated, and (2) the titanium alkoxide sol containing the dye was refluxed and then spread onto the plates. The photocurrent quantum efficiency remarkably increased by the steam treatment and the reflux compared to that of the untreated dye-doped electrode consisting of amorphous titania gel. The efficiency in the former was higher than that in the latter. The growth and crystallization of the titania particles and the decrease in the defect density by these treatments improved the electric conductivity. The steam treatment was the more prominent method because it enhanced the electric conductivity of the titania depending on its nanostructure and the dye-titania interaction depending on the dye dispersion. These factors appear to play important roles in transport in the electron through the electrode.ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 207(2-3):204-208 (2009)journal articl