Horikoshi Satoshi

The photocatalytic decomposition of the cationic rhodamine-B (RhB) dye was examined in aqueous TiO2 dispersions using an integrated microwave/UV-illumination (PD/MW) method. This procedure proved to be superior in the degradation of the dye than the TiO2 photocatalytic degradative method alone. With few exceptions, the integrated PD/MW method also proved superior for other chemical systems. The greater efficacy of the PD/MW technique appears to be the result of the following two considerations: (i) there is enhanced formation of reactive oxygen species ((OH)-O-. radicals), as attested to by DMPO spintrap ESR methods and their attack on the dye; and although speculative at this time, (ii) the activity of bulk water or the TiO2 particle surface is somehow affected by microwave radiation, The greater efficacy of the PD/MW degradation method was also observed at low concentrations of molecular oxygen and at low radiant excitance of the light source. A brief mechanistic description is given on the basis of results obtained on the two model compounds, (i) benzoic acid and (ii) pyronin-B dye.

An infrared study of the adsorption of L-alpha-alanine (L-Ala) on TiO2 powder in aqueous suspension was carried out. When the amino acid is in the zwitterionic form and the TiO2 surface is positively charged, experimental results indicated that L-Ala molecules are adsorbed on titania through the carboxylated group, which gives rise to a bridged structure with the positive centers (protonated hydroxyls) of the TiO2 surface. Adsorbed amino acid was photodegradated in model conditions by exposing the sample to UV light through the quartz walls of the IR cell. The amine function was found to be preferentially removed from the adsorbed L-Ala molecules during the initial period of UV irradiation, and then the complete mineralization of the rest of the molecular structure occurred. This surface process agrees with the results of the analysis of the species that diffuse from the surface of the photocatalyst into the bulk of the liquid medium in the actual photodegradation carried out with TiO2 suspended in aqueous solutions of L-Ala.

The enhancement of photocurrent and photodegradation of organic pollutants was investigated using hybrid TiO2 thin films prepared by a combined paste/sol-gel technique to immobilize the TiO2 Particles onto optically transparent electrodes (OTEs); they were connected in series in a continuous flow, bench-top, two-compartment photoreactor. The benzene sulfonate (BS) of the model substrate surfactant used was photodegraded in aqueous media to test the efficacy of the TiO2/OTE electrode preparation and the construction of the photoreactor. Results indicate that the hybrid TiO2 film/OTE electrodes were more efficient than either the pasted TiO2/OTE electrode or the sol-gel TiO2/OTE electrode for the photo degradation of BS, as evidenced by the evolution of carbon dioxide and the photocurrent generated. The extent of ring opening and generated photocurrent during the photodegradation of BS with the hybrid (HY) electrode was correlated to the pasted TiO2 electrode and to the number of dip-coatings in the sol-gel. High photocurrents were generated in the cylindrical large photoreactor under continuous flow of the aqueous BS solution. Optimization of experimental factors for optimal efficiency of the setup was addressed with regard to the preparation of the HY electrodes, and to their size and location in the photoreactor. (C) 2001 Elsevier Science B.V. All rights reserved.

The photocatalytic degradation of six-membered heteroaromatics (pyridazine, pyrimidine and pyrazine) in aqueous TiO(2) suspension was investigated. The initial mechanistic sequence(s) in the TiO(2)-photocatdyzed oxidation of the constituent heterorings was predicted theoretically by molecular orbital (MO) calculations such as frontier electron densities and point charges on all the atoms. The cleavage of the heterocyclic moiety was examined by UV-VIS spectroscopy. The evolution of N(2) and CO(2) gas was determined by gas chromatography. The formation of NH(4)(+) and NO(3)(-) ions was assessed by ion-HPLC, and that of carboxylic acid intermediates by HPLC. The disappearance of six-membered heteroaromatics and the formation of intermediates were observed by LC-MSD. The heterorings containing an N=N fragment lead to the evolution of Nz gas, and those containing a C-N=C fragment lead to the generation of a large amount of NH(4)(+) ions and a minor amount of NO(3)(-) ions. The photodegradation of these heteroaromatics is closely related to the position of the nitrogen in the heterorings. The mechanism of the photodecomposition of the heterocyclic aromatics was revealed through comparison of experimental data with the analytical simulation. (C) 2001 Elsevier Science B.V. Ail rights reserved.

The mechanism of photo-oxidation of the water-soluble polyvinylpyrrolidone (PVP) having a pendant five-membered lactam ring is complicated by the manner by which the macromolecule adsorbs on the TiO2 particle surface in a heterogeneous dispersion. Experimental results and computer simulation of the initial process(es) infer three major steps for the photodegradation of the PVP structure. The first step is adsorption (or coagulation) of PVP on TiO2 particles as evidenced by the size distribution of TiO2 particles by dynamic light-scattering and by the electric charge on the TiO2 particle surface assayed by zeta -potential measurements. Molecular orbital simulations of initial processes were calculated at the AMI level using the MOPAC system available in the CAChe package. The second step, namely attack of PVP by (OH)-O-. and/or (OOH)-O-. radicals, involves cleavage of the PVP main chain and opening of the lactam ring in the PVP structure probed by temporal UV spectral changes and by a decrease of the molecular weight using gel permeation chromatographic methods. Additional details of the photo-oxidation mode of the lactam ring was examined by a detailed examination of the photo-oxidation of the model compound 2-pyrrolidone to ascertain formation of (OH)-O-. radical adducts, opening of the lactam ring, and identification of intermediates by HPLC, and C-13- and H-1-NMR methods. The fnal major step in the mechanism involves generation and subsequent conversion of the primary amine (methylamine from opening of the lactam ring) to yield ultimately NH4+ and NO3- ions, and conversion of the propanoic acid to acetic and formic acids and then to CO2. The effects of the extent of polymerization and variation in light intensity were examined using PVP samples having different hardness factors (hf) of 15 and 30, and different light intensities (namely, 1, 2, 3 and 4 mW cm(-2)), respectively. (C) 2001 Elsevier Science B.V. All rights reserved.

This study reports on a comparative assessment of the efficiencies of TiO2/SnO2-doped OTE thin film electrodes fabricated by three different deposition methods. Process efficiencies, as measured by the kinetics of degradation, were examined by monitoring the photo-oxidative fate of two test substrates, namely the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the model compound sodium benzenesulfonate (BS). Methods chosen to fabricate the TiO2/OTE electrodes comprised (i) pulsed laser deposition, (ii) deposition of a TiO2 paste on the OTE plate, and (iii) sol-gel deposition. Both DBS and BS are readily photo-oxidized and, under our conditions, were partially mineralized to CO2 with the process being made particularly more efficient when the TiO2/OTE electrodes were anodically biased at +0.3 V, which generated a photocurrent during the photoelectrolysis. The sol-gel {C} and anatase {B1} electrodes proved especially useful under the +0.3 V bias. In the absence of any bias, however, DBS photodegraded faster on the TiO2-pasted electrode. Under otherwise similar conditions, the pulsed laser rutile TiO2/OTE electrode showed very little photoactivity. Some of the characteristics of the TiO2 film, such as the TiO2 crystalline form, film thickness, surface roughness, and film transparency appear to have some effect on the overall photodegradative process efficiency. (C) 2001 Elsevier Science B.V. All rights reserved.

In this study we focus on elucidating the mechanism of the photocatalyzed transformation of the primary, secondary and tertiary amines found in ethanolamine, diethanolamine and triethanolamine when present in illuminated aqueous titania dispersions. Photodecomposition of these ethanolamines leads to the evolution of CO2 through prior formation of various intermediate species. Ammonium (NH4+) and nitrate ions (NO3-) are the ultimate products formed in the photoconversion of the amine nitrogen atoms, with NH4+ cations produced in greater quantity than NO3- anions for all three ethanolamines. Photooxidation of triethanolamine yields various intermediates, including a 3-pyrrolidone derivative, diethanolamine, and then ethanolamine, before complete mineralization occurs. The nature of the initial steps in the photodegradation was predicted by computer-aided molecular orbital (MO) calculations of point charges, and by frontier electron densities of all atoms in the ethanolamine structures.

Sodium benzene sulfonate (BS) was decomposed in aqueous TiO(2) dispersions under highly concentrated solar light illumination to examine the photocatalytic characteristics of a parabolic round concentrator (PRC) reactor to degrade the pollutant without visible light absorption. The effects of such operational parameters as initial concentration, volume of the aqueous BS solution, oxygen purging, and TiO(2) loading on the kinetics of decomposition of BS were investigated. An effective photodegradation necessitates a suitable combination of initial volume and concentration of BS solution. Relative to atmospheric air, oxygen purging significantly accelerates the degradation process at high initial concentrations of BS (0.40 mM or 1.0 mM). Optimal TiO(2) loading was 9 g l(-1), greater than previously reported. Elimination of TOC (total organic carbon) followed pseudo first-order kinetics in the initial stages of the photodegradation process. The relative photonic efficiency for the photodegradation of BS is zeta (rel) = 1.0. (C) 2001 Elsevier Science Ltd. All rights reserved.

The photocatalytic oxidation of oxalyldihydrazide, N, N'-bis(hydrazocarbonyl)hydrazide, N, N'-bis(ethoxycarbonyl)hydrazide, malonyldihydrazide, N-malonyl-bis[(N'-ethoxycarbonyl)hydrazide] was examined in aqueous TiO2 dispersions under UV illumination. The photomineralization of nitrogen and carbon atoms in the substrates into N-2 gas, NH4+ (and/or NO3-) ions, and CO2 gas was determined by HPLC and GC analysis. The formation of carboxylic acid intermediates also occurred in the photooxidation process. The photocatalytic mechanism is discussed on the basis of the experimental results, and with molecular orbital (MO) simulation of frontier electron density and point charge. Substrate carbonyl groups readily adsorb on the TiO2 surface, and the bonds between carbonyl group carbon atoms and adjacent hydrate group nitrogen atoms are cleaved predominantly in the initial photooxidation process. The hydrate groups were photoconverted mainly into N-2 gas (in mineralization yields above 70%) and partially to NH4+ ions (below 10%). The formation of NO3- ions was scarcely recognized. (C) 2000 Elsevier Science Ltd. All rights reserved.

Visible light-induced photocatalytic oxidation of the dye alizarin red (AR) has been examined in TiO2 aqueous dispersions. The ESR spin-trapping technique was used to detect active oxygen radicals formed during in situ visible irradiation of AR/TiO2 dispersions. Evidence for the production of superoxide (O-2(.-) or HOO.) (formed in the reduction of O-2) and hydroxyl radicals ((OH)-O-.) (formed by a multistep reduction) in the initial photoexcitation stage is presented. Meanwhile, the pathway of the photooxidation of AR is theoretically predicted on the basis of molecular orbital (MO) calculations by frontier electron densities and point charges on all the individual atoms of the dye. The relatively high negative point charges on the sulfonic oxygens lead to a strong adsorption of the dye onto the TiO2 particle surface through the sulfonate function. The position of the dye molecule attacked by the active oxygen species (e.g. O2(.-) or HOO. radicals) and/or O-2 is correlated with frontier electron densities, there is a perfect agreement between MO calculations and the results of experiments. A plausible mechanism of photooxidation under visible irradiation is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

Study was made to determine the photomineralization mechanisms of two nonionic surfactants, N- (2-hydroxyethyl) dodecanoyl amide and N, N-bis (2-hydroxyethyl) dodecanoyl amide based on temporal changes in surface tension, ζ-potential, evolution of CO₂ gas, formation of NH₄⁺ and NO₃^- ions, and formation of carboxylic acids. The adsorption of surfactants on the TiO2 surface was also examined by dynamic light-scattering. The generation of NH₄⁺ ions exceeded that of NO₃^- ions in the photodegradation of either surfactant. Positions on the surfactants attacked by ^·OH radicals were determined by molecular orbital calculations of frontier electron density. Negatively charged positions in the surfactants adsorb on the positive TiO₂ surface and could consequently be easily attacked by ^·OH radicals. A photooxidation mechanism of N- (2-hydroxyethyl) dodecanoyl amide and N, N-bis (2-hydroxyethyl) dodecanoyl amide is proposed on the base of the present experimental data and comparison with calculation results.

The mechanistic sequence(s) in the TiO2-photocatalytic oxidation of constituent pyrimidine and purine bases in nucleic acids is examined theoretically by molecular orbital calculations of frontier electron densities and point charges on all atoms, and experimentally by UV-Vis spectroscopy and gas chromatography to assess how the chemical structure of the bases affects their photocatalyzed mineralization. Rates of formation of NH4+ and NO3- ions in the pyrimidine bases are closely dependent on the existence of the carbonyl and amino groups; for example, formation of NO3- ions is faster than formation of NH4+ ions for uracil (Ura) and thymine (Thy) having the carbonyl function. By contrast, NH4+ ions are produced faster than NO3- ions in the case of cytosine (Cyt) which possesses a primary amine function. In comparison with uric acid, which has no amino group, the photocatalyzed mineralization of the purine bases adenine (Ade) and guanine (Gua) generates a greater quantity of NH4+ ions than NO3- ions, in the initial stages. In nearly all cases examined, formation of NO3- ions takes place only after an induction period and originates mostly from the ring nitrogen atoms of the bases. (C) 1999 Elsevier Science S.A. All rights reserved.

The photoelectrical degradation of the amino acids L-aspartic acid (L-Asp), L-glutamic acid (L-Glu), L-leucine (L-Leu), L-alpha-alanine (L-alpha-Ala) and beta-alanine (beta-Ala) was examined on TiO2/OTE electrodes prepared by a pulse laser deposition method. The disappearance of amino acids and their mineralization into CO2 were determined with and without an applied anionic bias of 0.3 V. The generation of photocurrent was also measured during the photoelectrical degradation of substrates on the TiO2/OTE electrode assembly considering it as a possible type of solar cell. The relationship between the photoelectrodegradation rate, the photocurrent and the structure of the amino acids was established.

The photooxidative degradation of a TiO2-blended poly(vinyl chloride) (PVC) film and other PVC specimens was carried out under UV light and under solar exposure to test the feasibility that such polymeric materials can be mineralized. The effects of the degree of polymerization and the presence of a plasticizer (o-dioctyl phthalate; DOP) in the PVC on the photooxidation process were examined by scanning electron microscopy (SEM), by X-ray photoelectron spectroscopy (XPS), by gel permeation chromatography, and by gas chromatography for CO;, evolution. The TiO2-blended PVC thin film is more easily decomposed than PVC particles (or film) alone in a TiO2 particulate dispersion. The collapse phenomena of polymeric films are closely dependent on the photodegradation rate of DOP in the PVC film. Ames mutagenic assays for the photodegraded solution in aqueous TiO2/PVC dispersions showed a slight mutagenic activity in TA98 without S9 mix for products formed during the photodegradative oxidation.

The pathway to the photomineralization of the three amino acids L-serine (L-Ser), L-phenylalanine (L-Phe) and L-a-alanine (L-Ala) is described experimentally on the basis of CO2 evolution and conversion of the amino group to NH4+ and NO3- ions, and theoretically on the basis of molecular orbital calculations to define frontier electron densities and point charges on all the individual atoms. The relatively high negative point charges on the carboxylate oxygens are consistent with adsorption of the amino acids to the TiO2 particle surface through the carboxylate function. Mineralization to carbon dioxide is complete for L-Ser (similar to 98%) and nearly so for L-Ala (similar to 90%), whereas for L-Phe the extent of mineralization is 59% corresponding to the total photooxidation of the phenyl ring carbons; for the amine function the extent of conversion is 87% for L-Ser, 97% for L-Ala and 91% for L-Phe. Relative formation yields of NH4+ and NO3- ions depend on the structural fragment R attached to the a-amino carboxylic acid functions, R-CH(NH2)COOH. Primary attack of the amino acids by the (OH)-O-. radical is correlated with the frontier electron densities. Ammonia is formed through a photoreductive step by electron attachment onto the zwitterionic form of the amino acids, whereas nitrate is produced through a photooxidative step implicating a very tortuous series of events. (C) 1998 Elsevier Science S.A. All rights reserved.

The fate of DNA, RNA and their pyrimidine and purine bases was examined on exposure to WA and UVB radiation in the presence of a physical sunscreen agent (TiO(2), anatase/rutile particles) to assess the potential damage that such an agent may cause on contact with such substrates. DNA and RNA were partially decomposed and the bases were converted to carbon dioxide (nitrogen atoms to ammonia and nitrate ions) in a Pyrex reactor under conditions simulating UVA and UVB sunlight. The physical and chemical damage inflicted on DNA and RNA was also confirmed by scanning electron microscopy and gel permeation chromatography. (C) 1997 Elsevier Science S.A.

Titanium dioxide (TiO2) has been noted (US Federal Register, 43FR38206, 25 August 1978) to be a safe physical sunscreen because it reflects and scatters UVB and UVA in sunlight. However, TiO2 absorbs about 70% of incident UV, and in aqueous environments this leads to the generation of hydroxyl radicals which can initiate oxidations, Using chemical methods, we show that all sunscreen TiO2 samples tested catalyse the photo-oxidation of a representative organic substrate (phenol), We also show that sunlight-illuminated TiO2 catalyses DNA damage both in vitro and in human cells, These results may be relevant to the overall effects of sunscreens. (C) 1997 Federation of European Biochemical Societies.

The photoelectrochemical degradation of amino acids and derivatives such as glutamic acid, glutamine, glutaric acid, lysine, beta-alanine, 8-aminooctanoic acid and phenylalanine has been examined on an irradiated TiO2/OTE particulate film electrode. The photooxidative disappearance of the substrates ultimately transforms the nitrogen into NO3- and NH3 (as ammonium ions under our conditions), whereas the carbonaceous residues are converted into CO2. Variations in photocurrent were observed during the temporal course of the photodegradative process. The rates of conversion and the quantity of degraded products depend on the external applied bias and appear to be closely related to the molecular structure of the substrates. A photoelectrochemical degradative pathway is discussed briefly on the basis of the experimental observations. (C) 1997 Elsevier Science S.A.

The fate of nitrogen in various amino acids was examined following their photooxidative (and/or reductive) transformation catalyzed by UV-A and UV-B illuminated aqueous TiO2 dispersions. The nitrogens in the amino acids are photoconverted predominantly into NH, (analyzed as NH4+) and to a lesser extent into NO3- ions; NH4+/NO3- ratios span the range 3-12 after ca. 8 h irradiation. Extensive evolution of CO2 is also observed; in some cases it is quantitative. Variations in the NH4+/NO3- ratio in the transformation of amino acids are dependent on the substrates molecular structure. Some of the steps in an otherwise complex mechanism of the heterogeneous photocatalyzedmineralization are described. (C) 1997 Elsevier Science S.A.

The photo-oxidative degradation of sodium benzene sulfonate, 2-phenoxyethanol, ethyleneglycol, diethyleneglycol, acetic acid and formic acid, was examined on a TiO2 particulate film immobilized on a transparent conductive oxide (TCO) glass electrode assembly. The photocurrents generated during the photodegradation of these organic compounds were monitored. Formation of intermediate species (acetic acid and formic acid) during the temporal course of the photo-oxidative process(es) appears to have a direct effect on the photocurrents.

The photocatalyzed oxidative decompositions of solid particles of Polyvinylchloride (PVC size about 100 to 200 μm), of the polyvinylidene chloride copolymer (95% PVC/5% PVLC size ∼ 400-600 μm), and a PVC film have been examined in suspensions of titania and zinc oxide illuminated by UV light and/or by natural sunlight. Dechlorination and evolution of carbon dioxide were monitored, the latter occurring by the intermediacy of acetic and formic acids. The photodegradation of polymer specimens was enhanced in TiO2/water media by such added oxidants as hydrogen peroxide and potassium persulfate. Photocorrosion of these particulates was also examined by scanning electron microscopy. © 1996 John Wiley &amp Sons, Inc.

Anionic (DBS), cationic (CTAB, BTDAC, C₁₂-PC), non-ionic (C₁₂E5, N-DHA) and amphoteric (C₁₂-betaine, C₁₂-amidobetaine, C₁₂-HAA) surfactants were photodegraded in TiO₂ semiconductor suspensions under UV irradiation. Dependence of the rate of photodegradation on the chemical structure was investigated based on temporary variation of total organic carbon (TOC) in photodegraded solution. Differences in the photocatalytic effect of other metal-oxide catalysts such as ZnO, W03, TiO₂ (anatase or rutile), TiO₂ (UV-100) and TiO₂ (T-805) were also examined. TiO₂ (anatase) and Zn0 showed superior catalytic activity. TOC decreased with increase in irradiation time, since the surfactants were oxidized with the consequent evolution of CO₂ gas. TOC in solution after sonication without exposure to UV was less than that of the starting solution, indicating that surfactant to be preadsorbed on the TiO₂ surface. The rate of photodegradation of the anionic surfactants was greater than for the nonionic, cationic and amphoteric surfactants. The increase in concentration caused decrease in the photodegradation rate. From the results of laser flash photolysis using colloidal TiO₂ and benzene sulfonate (BS), the surfactant is implicated in the scavenging of the charge carrier, thereby producing either a ground-state BS⁺ cation radicals or ·OH adducts with the benzene ring of BS.

Effects of such n-type semiconductors as TiO₂ (anatase, rutile or surface-modified TiO₂ and Pt-loaded TiO₂), ZnO, WO₃ and MoS₂ on the photodegradation of anionic DBS and cationic BDDAC surfactants, and related model compounds were examined in the present study. The anatase form of TiO₂ showed greater photocatalytic activity than the rutile form. Noble-metal loaded catalysts (e. g., TiO₂/Pt) were less photooxidative than the naked anatase TiO₂ catalyst, possibly due to suppression of electron transfer of O₂ to give O₂, namely photoreduction. The ZnO semiconductor catalyst decomposed DBS more rapidly than anatase Ti0₂. The photocatalytic activity of the other semiconductors examined (WO₃ and MoS₂) was only slight in each case.