Efficient Dihydroxylation of Naphthalene on Photoirradiated Rutile TiO2 Powder in Solution Containing Hydrogen Peroxide

We report on enhanced dihydroxylation of naphthalene on photoirradiated TiO2 particles by addition of H2O2 to the reaction solution. The rate was enhanced by 6–40 times by the addition of H2O2, and the quantum yield reached as high as 76% for rutile TiO2 powders. On the other hand, no such enhancement was observed for anatase TiO2 powders

Stereospecific Epoxidation of 2-Hexene with Molecular Oxygen on Photoirradiated Titanium Dioxide Powder

Photocatalytic oxidation of 2-hexene on TiO2 powder was investigated under a stream of oxygen gas. The main product was 2,3-epoxyhexane with the chemical yield ranging from 65% to 83% depending on the TiO2 powders. When trans-2-hexene was used as the starting material, the epoxide was also trans. On the other hand, cis epoxide was the chief product from cis-2-hexene. From mixed 2-hexene (trans/cis = 1.7), larger amounts of trans epoxide were obtained than cis-epoxide in the initial period of the reaction, indicating that trans-2-hexene is more reactive than the cis isomer on the photocatalyst

Chromosomal integration of blaCTX-M genes in diverse Escherichia coli isolates recovered from river water in Japan

Occurrence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBLEC) in environmental waters is of great concern. However, unlike clinical ESBLEC, their genetic characteristics, in particular the genetic contexts of ESBL genes, are not well understood. In this study, we sequenced and analyzed the genomes of CTX-M-producing E. coli isolates recovered from river water to fully characterize the genetic contexts of blaCTX-M genes. Among the 14 isolates with completed genomes, blaCTX-M genes were detected on the chromosome in nine isolates. All but one chromosomal blaCTX-M genes were associated with ISEcp1 and were carried on different transposition units ranging in size from 2, 855 bp to 11, 093 bp; the exception, blaCTX-M-2, was associated with ISCR1. The remaining five isolates carried blaCTX-M genes on epidemic IncI1 plasmids of different sequence types (STs) (ST3, ST16, ST113, and ST167) (n = 4) or on an IncB/O/K/Z plasmid (n = 1). This study revealed that environmental E. coli carry blaCTX-M genes in diverse genetic contexts. Apparent high prevalence of chromosomal blaCTX-M potentially indicates that some E. coli can stably maintain blaCTX-M genes in environmental waters, though further studies are needed to confirm this

Dihydroxylation of Naphthalene by Molecular Oxygen and Water Using TiO2 Photocatalysts

TiO2-catalyzed photo-reaction of naphthalene was investigated in mixed solutions of acetonitrile and water. The main products were confirmed to be 1,8- and 1,3-dihydroxynaphthalene, without any 1- or 2-naphthol being detected. Both O2 and H2O were essential to yield the products. The quantum efficiency of the 1,8- and 1,3-dihydroxynaphthalene products reached about 10% at 365 nm after irradiated for 1 h

Formation of new crystal faces on TiO2 particles by treatment with aqueous HF solution or hot sulfuric acid

We have demonstrated that new crystal faces are generated on anatase and rutile TiO2 particles by means of chemical etching in aqueous hydrofluoric acid or hot sulfuric acid. In the treatment with aqueous hydrofluoric acid, the {112} face of anatase particles and the {021} face of rutile particles are newly formed. When treated with hot sulfuric acid, anatase particles exposed the {122} face and rutile particles exposed the {001}, {010}, {021} and {121} faces. In both cases, anatase particles are etched at a higher rate than rutile particles. The etched particles are expected to show photocatalytic properties unique to the crystal faces. For example, the {112} face of anatase particles is demonstrated to be active in the oxidation of Pb2+ ions

Photocatalytic Activity of S-doped TiO2 Photocatalyst under Visible Light

In order to effectively utilize visible light in photocatalytic reactions, we have developed S-doped TiO2 particles. They show strong absorption for visible light and high activities for degradation of methylene blue in aqueous solution under irradiation at wavelengths longer than 440 nm. The oxidation state of the S atoms incorporated into the TiO2 particles is determined to be S6+ from the XPS spectra

Crystal faces of rutile and anatase TiO2 particles and their roles in photocatalytic reactions

A titanium dioxide powder consisting of 1 μm size rutile and anatase particles was obtained, on which developed crystal faces were observed by a scanning electron microscope. From electron diffraction analyses, it was found that the rutile particles exposed {011} and {110} crystal faces, and the anatase particles exposed {001} and {011} faces. This powder showed high activity for some photocatalytic reactions, including oxidation of water. After photocatalytic oxidation of water on the powder using hexachloroplatinate(IV) ions as the electron acceptors, Pt deposits were observed mostly on the rutile particles, especially on the {110} face. When 2-propanol was added to the solution, Pt was deposited on both the anatase and rutile particles. Using the thus prepared Pt-deposited TiO2 powder, Pb2+ ions were photocatalytically oxidized into PbO2. After this reaction, PbO2 deposits were seen on the {011} face of the rutile particles. On the anatase particles, PbO2 deposits were observed in a larger amount on the {001} face than on the {011} face. These results indicate that the crystal faces help in the separation of electrons and holes, and that this effect is stronger for the rutile particles than for the anatase particles

TiO2-Photocatalyzed Epoxidation of 1-Decene by H2O2 under Visible Light

1-Decene was converted to 1,2-epoxydecane on UV-irradiated TiO2 powder using molecular oxygen as the oxygen source. Other main products were nonanal and 2-decanone. For anatase-form TiO2 powders, the reaction rate was hardly affected by addition of hydrogen peroxide to the solution. In contrast, for rutile-form TiO2 powders, the rate of epoxide generation was significantly increased by addition of hydrogen peroxide. In this case, the reaction occurred under visible light as well as UV light. The selectivity of the production of 1,2-epoxydecane was higher under visible light than under UV light. The conversion efficiency of an incident photon to 1,2-epoxydecane was about 2% when irradiated with visible light in the range 440–480 nm. UV–visible diffuse reflection spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested the generation of a Ti–η2-peroxide on rutile TiO2 surface after treatment with hydrogen peroxide. The initial step of the reaction under visible light was attributed to a photochemical reaction of this peroxide with 1-decene