Suzuko Yamazaki

Kinetic studies of oxidation of ethylene over a TiO2 photocatalyst

Abstract The photo-assisted catalytic degradation of ethylene was studied in the tubular photoreactor packed with TiO2 pellets prepared by sol–gel method. The dependence of the reaction rate on the light intensity, feed composition (ethylene, oxygen and water vapor) and temperature were investigated. More than 95% ethylene was always completely mineralized irrespective of the reaction conditions. The reaction rate for ethylene conversion was greatly suppressed when the water vapor mole fraction was increased in the reactant gas stream. The rate determining step is the oxidation of C2H4OH radicals with oxygen on the catalyst surface. The rate law is expressed as follows to account for the results obtained: − d [ C 2 H 4 ] d t = k 9 K 8 I a φK C 2 H 4 P C 2 H 4 K O 2 P O 2 k OH (1+K C 2 H 4 P C 2 H 4 +K H 2 O P H 2 O )(1+K O 2 P O 2 )

Photocatalytic degradation of trichloroethylene in water using TiO2 pellets

A recirculating system of aqueous trichloroethylene (TCE) solutions through the packed bed reactor with TiO2 pellets has been developed in order to mineralize TCE without difficulties for filtration and recovery of catalyst. The TiO2 pellets prepared by sol gel method have photocatalytic activity similar to commercially available PC-101 and PC-102 in the powder form and to ST-B11 pellets. In batch experiments with TiO2 powders, Degussa P-25 is the most active photocatalyst, which indicates that specific surface area is not an important factor controlling the photocatalytic activity in aqueous solutions. The degradation rates of TCE in the recirculating system with TiO2 pellets decreased in the presence of H2O2, while were remarkably accelerated by adding S2O8(2-). The presence of S2O8(2-) ions more than 0.01 mol dm(-3) completely suppressed hole-electron recombination and mineralized 50 ppm TCE with the 2 h irradiation. In a reactor without TiO2 photocatalysts, TCE was photodegraded by SO4- radicals which produced by photodissociation of S2O8(2-). The degradation rates increased with increase of the initial S2O8(2-) concentration. However, TCE was not mineralized but converted to intermediates which were slowly degraded to Cl- by continuing the irradiation.

Environmentally benign oxidation using a palladium catalyst system

A clean and environmentally benign process to convert benzylic and allylic alcohols into the corresponding carbonyl compounds using a catalytic amount of palladium on activated charcoal under an ethylene atmosphere is developed. The combination of Pd(OAc)2 and vinyl acetate is an excellent system. The efficient conversion is based on hydrogen transfer between allylic and benzylic alcohols and simple olefins such as ethylene and vinyl acetate. In the oxidation of D-glucal to the corresponding enone (1,5-anhydrohex-1-en-3-ulose), the palladium catalyst is proven to be reused without a decrease of catalytic activity. This extremely simple process is not only economically advantageous but it is also environmentally friendly in comparison to conventional methods using chromium or manganese salts.

Photocatalytic degradation of gaseous tetrachloroethylene on porous TiO2 pellets

The photo-assisted catalytic degradation of tetrachloroethylene (PCE) was studied in a tubular photoreactor packed with TiO2 pellets prepared by sol–gel method. The experiments were performed in a noncirculating mode. Dichloroacetate on the catalyst surface together with phosgene and CCl4 in the gas phase were detected. The effects of operating conditions on the observed rate of reaction were investigated. Water vapor competed with PCE for the same adsorption sites on the TiO2 surface. Therefore, reaction rates decreased when the mole fraction of H2O was 50–60 times higher than that of PCE. Reaction temperature and space time play key roles in the degradation of PCE to CO2. Under the best of our experimental conditions, 80% of the initial PCE could be completely mineralized.

Controllable Adsorption and Ideal H-Aggregation Behaviors of Phenothiazine Dyes on the Tungsten Oxide Nanocolloid Surface

The monomer-aggregate equilibrium of four phenothiazine (PN) dyes, containing thionine (TH), methylene blue (MB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMB), in the tungsten(VI) oxide (WO(3)) nanocolloid solution has been investigated by means of UV-vis spectroscopy. Addition of PN dye into the WO(3) nanocolloid solution brought about significant changes in the absorption spectrum, suggesting the formation of H-type (face-to-face fashion) trimer on the WO(3) nanocolloid surface. The adsorptivity of PN dyes onto the WO(3) nanocolloid surface was diminished by the raising the ionic strength, indicating the evidence of the electrostatic interaction between cationic PN dye and negatively charged WO(3) nanocolloids. The detail analysis of each spectral data provided insight into the effect of molecular structure of PN dyes on the adsorption and aggregation behaviors on the WO(3) nanocolloid surface. Moreover, in situ measurement of PN dye aggregation using the centrifugal liquid membrane (CLM) technique revealed that the aggregation of PN dyes on the WO(3) nanocolloid surface proceeded in a two-step three-stage (monomer --> dimer --> trimer) formation. The aggregation mechanism of PN dyes on the WO(3) nanocolloid surface was discussed on the basis of Kashas exciton theory.

Photocatalytic Degradation of Chlorinated Ethanes in the Gas Phase on the Porous TiO2 Pellets: Effect of Surface Acidity

The photocatalytic degradation of chlorinated ethanes was studied in a tubular photoreactor packed with TiO(2) pellets prepared by sol-gel method. The steady-state condition was not obtained, but the deterioration in the photocatalytic activity was observed during the irradiation. Effects of mole fractions of water vapor, O(2), and C(2)H(5)Cl or C(2)H(4)Cl(2) and reaction temperature on the photodegradation of C(2)H(5)Cl or C(2)H(4)Cl(2) were examined, and these data were compared with those obtained by the photodegradation of chlorinated ethylenes. On the basis of the products detected with and without oxygen in the reactants gas stream, we proposed the degradation mechanism. Measurement of diffuse reflectance infrared Fourier transform spectroscopy of pyridine adsorbed on the catalysts showed that decrease in the conversion for the photodegradation of C(2)H(5)Cl was attributable to the formation of Brønsted acid sites. Comparison of the data obtained with the TiO(2) and the sulfated TiO(2) (SO(4)(2-)/TiO(2)) pellets indicated that the photodegradation of C(2)H(5)Cl was suppressed by the presence of the Brønsted sites, but that of trichloroethylene was not affected. Such a difference is attributable to the adsorption process of these reactants on the acid sites on the catalyst surface.

Photochromic Properties of Tungsten Oxide/Methylcellulose Composite Film Containing Dispersing Agents

Tungsten oxide-based photochromic films which changed reversibly in air between colorless- transparent in the dark and dark blue under UV irradiation were prepared by using methylcellulose as a film matrix and polyols such as ethylene glycol (EG), propylene glycol (PG), and glycerin (Gly) as dispersing agents. Influence of the dispersing agents and water in the films on the photochromic behavior was systematically studied. Under UV irradiation, absorption bands around 640 and 980 nm increased and the coloring rate was the following order: Gly > EG > PG. An increase in the amounts of dispersing agents or water accelerated the coloring rate. By increasing the water content of the film, a new absorption peak appeared at ca. 775 nm and the Raman spectra indicated a shift of W-O-W stretching vibration to lower wavenumber which was due to the formation of hydrogen bonding. All absorption spectra were fit by three Lorentz functions, whose bands were ascribed to various packing of WO6 octahedra. After the light was turned off, the formation of W(5+) was stopped and bleaching occurred by the reaction with O2 in air to recover its original transparent state. We anticipate that the biodegradable photochromic films developed in this study can be applied in recyclable display medium and especially in detachable films for glass windows whose light transmission properties are changed by sunlight, i.e., for usage as an alternative of smart windows without applying voltage.

Kinetic characteristics of enhanced photochromism in tungsten oxide nanocolloid adsorbed on cellulose substrates, studied by total internal reflection Raman spectroscopy

The nanostructured tungsten(VI) oxide (WO3)/cellulose derivatives (cellulose (CE) and triacetyl cellulose (TACE)) hybrid films were prepared by a solution-dipping adsorption process, and their structure and optical properties have been investigated. Various techniques, including adsorption isotherm, transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), in situUV-Vis absorption, and in situ total internal reflection Raman spectroscopy, were used for the characterization of the WO3/CE and WO3/TACE hybrid materials. Under UV irradiation, the photochromism (colorless → blue) was confirmed from the WO3/CE hybrid film, although no coloration of the WO3/TACE hybrid film was observed. This distinct difference in the coloration suggested that the interfacial interaction between hydroxyl groups present on the surface of the CE substrate and WO3 nanoparticlesviahydrogen bonding plays a major role in the enhancement of photochromism in the WO3/CE hybrid system. Moreover, the joint evidence in in situUV-Vis absorption and in situ total internal reflection Raman studies clearly revealed that the photogenerated coloration is related to a partial reduction of W6+ cations into W5+ cations in the WO3/CE hybrid film. The findings in this study have great implications for the development of the novel green-functional inorganic/organic hybrid materials in optical devices.

Chirality induction and amplification in methylene blue H-aggregates viaD- and L-phenylalanine pre-adsorbed on the tungsten oxide nanocolloid surface

In the methylene blue (MB)–phenylalanine (Phe)–tungsten(VI) oxide (WO3) colloid ternary aqueous solution, the MB H-aggregates, which could recognize the chirality of D- and L-Phe, were formed and investigated by means of UV-Vis absorption and CD spectroscopy. These results demonstrate a chirality transfer and amplification from only the pre-adsorbed Phe molecules to MB aggregates formed on the WO3 colloid surface via non-covalent interactions.

Density functional study of the primary events on TiO2 photocatalyst

Density functional calculations at the B3LYP/6-311G**//B3LYP/6-311G level of theory were used to study the initial process of ethylene degradation on the TiO2 photocatalyst by adopting the dimeric titanium structure Ti2O6H4 as a model of the catalyst surface. Adsorption energies of water and ethylene were calculated to be 31.9 and 20.4 kcal mol−1. The photogenerated OH radical does not desorb from the catalyst surface and the further reaction with ethylene proceeds since the adsorption energy was estimated to be 39.3 kcal mol−1. Our calculation also indicated that under steady illumination, ethylene directly attacks the OH radical bound to the TiO2 surface even though the surface has vacant sites available for ethylene adsorption.