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

High visible-light active Ir-doped-TiO2 brookite photocatalyst synthesized by hydrothermal microwave-assisted process

Iridium-doped TiO2 having a brookite phase was synthesized as a visible light-active photocatalyst. It was prepared by using a hydrothermal assisted-microwave process as an improved competitive production method over the traditional hydrothermal process. The prepared materials were tested for decomposing acetaldehyde or toluene in gas phase under visible light irradiation (λ 455 nm), and they showed a strong photocatalytic activity response. The activity of the prepared brookite TiO2 material was optimized by adjusting the concentration of iridium ions as a dopant. The photocatalytic efficiencies of all of the prepared Ir-doped-TiO2 photocatalysts were higher than the values obtained from commercially available visible-light responsive photocatalysts under the same experimental conditions

Fabrication of morphology-controlled TiO2 photocatalyst nanoparticles and improvement of photocatalytic activities by modification of Fe compounds

Our previous studies suggested that redox reaction proceeded separately on specific exposed crystal faces of TiO2 nanoparticles. Site-selective deposition of metal or metal oxide on TiO2 specific exposed crystal faces successfully proceeded using the unique reactivity properties on the surface of TiO2 nanoparticles under photoexcitation. A remarkable improvement of photocatalytic activity of shape-controlled brookite and rutile TiO2 nanorods with modification of Fe3+ compounds was observed under visible light. Crystal face-selective metal compound modification on exposed crystal faces of TiO2 nanorods with brookite and rutile phases was successfully prepared. Brookite and rutile TiO2 nanorods prepared by site-selective modification with metal compounds should be ideal visible-light responsive TiO2 photocatalysts because of the remarkable suppression of back electron transfer from TiO2 to oxidized metal compounds on the surface of the TiO2 nanorod with a brookite or rutile phase. In this paper, the development of exposed crystal face-controlled TiO2 nanorods with rutile and brookite phases was described. The obtained rutile and brookite TiO2 nanorod, showing remarkably high activity for degradation of organic compounds compared with the photocatalytic activities of anatase fine particles (ST-01), is one of the most active commercially available photocatalysts for environmental cleanup in Japan. The technology of visible-light responsive treatment for morphology-controlled rutile and brookite TiO2 nanorods by crystal face-selective modification of Fe3+ compounds was also discussed in this paper. The Fe3+ compound-modified rutile and brookite TiO2 nanorods show much higher activity than conventional visible-light responsive N-doped TiO2, which is commercially available in Japan

Fabrication and characterization of a p-type Cu3Nb2O8 photocathode toward photoelectrochemical reduction of carbon dioxide

We report a new p-type Cu3Nb2O8 as a thin film photocathode, which was fabricated through spin-coating by a metal organic decomposition method. The p-type Cu3Nb2O8 photocathode exhibited a strong cathodic photocurrent, and the incident photon-to-current conversion efficiency plot confirmed that the p-type Cu3Nb2O8 photocathode has the ability to utilize the visible light (λ < ca. 480 nm). Furthermore, we demonstrated photoelectrochemical reduction of carbon dioxide with the primary product being carbon monoxide by utilizing the p-type Cu3Nb2O8 photocathode under AM 1.5 G solar light irradiation. From the results of Mott–Schottky analysis, UV–vis measurement and ultraviolet photoemission spectroscopy, the conduction band potential of p-type Cu3Nb2O8 was estimated to be –1.21 V versus a normal hydrogen electrode (NHE) at pH 7 with its conduction band edge located at a more negative potential than the reduction potential of carbon dioxide to carbon monoxide. Although the cathodic photocurrent of the p-type Cu3Nb2O8 photocathode gradually decayed with time, it recovered upon thermal annealing in air. This behavior suggests that the photocurrent response of the p-type Cu3Nb2O8 photocathode is intimately related to variation of the valence state of copper ions. In this paper, the photoelectrochemical properties of the p-type Cu3Nb2O8 photocathode are described in conjunction with optical, electrical and structural properties, and characteristics of the p-type Cu3Nb2O8 photocathode for the photoelectrochemical reduction of carbon dioxide are discussed

Photocatalytic reaction over iron hydroxides: A novel visible-light-responsive photocatalyst

Photocatalytic properties of iron hydroxide (FeOOH) particles prepared by a hydrothermal method were estimated under visible-light irradiation. Hydrothermal treatment in the presence of ethanol induced α-FeOOH (goethite) formation even under an acidic condition, while the presence of chloride ion led to preferential formation of β-FeOOH (akaganeite). α-FeOOH particles with largest specific surface area showed the highest photocatalytic activity among commercial and prepared FeOOH samples and exhibited total decomposition of acetaldehyde even under visible-light irradiation. The progress of photocatalytic reaction may be due to multi-electron reduction of oxygen over FeOOH particles

Photoelectrochemical CO2 reduction by a p-type boron-doped g-C3N4 electrode under visible light

Graphitic carbon nitride (g-C3N4) has attracted much attention as a metal-free semiconductor having visible light absorption and relatively high chemical stability under visible light irradiation. Graphitic carbon nitride (g-C3N4) and boron-doped g-C3N4 (B-doped g-C3N4, BCNx) were prepared by heating melamine and a mixture of dicyanodiamide and BH3NH3, respectively. X-ray diffraction, a Brunauer, Emmett and Teller (BET) apparatus, and UV–vis spectra were used to analyze the physical properties of the prepared samples. Electrodes of these samples were prepared by using the electrophoresis method. X-ray photoelectron spectroscopy analyses confirmed the incorporation of boron atoms in the g-C3N4 framework as well as the amount of boron atoms.Au, Ag or Rh as a co-catalyst was coated on the surface of g-C3N4 and B-doped g-C3N4 by using the magnetron sputtering method. The photocurrent response was observed using a solar simulator as a light source. The photocurrent response of B-doped g-C3N4 was about 5-times larger than that of pure g-C3N4. B-doped g-C3N4 coated with Rh as a co-catalyst showed the highest photocurrent response under solar light irradiation, its photocurrent being about 10-times larger than that of original g-C3N4. Under photoelectrochemical conditions, we also observed the products in gas phase and aqueous phase. C2H5OH was observed as a main product, while small amounts of CO and H2 were observed in gas phase. We also discuss the relationship between co-catalysts and photocurrent responses and the carbon source of C2H5OH as a main product. The source of carbon of C2H5OH obtained by CO2 reduction is discussed on the basis of results of a labeling experiment using 13CO2

Synthesis high specific surface area nanotube g-C3N4 with two-step condensation treatment of melamine to enhance photocatalysis properties

High specific surface area nanotube g-C3N4 was fabricated by a simple two-step condensation method. Photocatalytic activity was evaluated by decomposition of Rhodamine B (Rh B) under visible light. Nanotube g-C3N4 showed 12 times higher photocatalytic activity than bulk g-C3N4. The improvement of photocatalytic activity was mainly due to the higher surface area, the unique morphology and the number of defects

Photolysis of Hydrophobic Vitamin B12 Derivatives Covalently Bound to Lipid in Aqueous Media

An alkyl ligand coordinated to hydrophobic vitamin B12 derivatives covalently bound to N,N-dihexadecyl-Nα-[6-(trimethylammonio)hexanoyl]-L-aspartamide bromide underwent a novel bromination reaction along with its rearrangement in the single-walled vesicle of N,N-dihexadecyl-Nα-[6-(trimethylammonio)hexanoyl]-L-alaninamide bromide under photolysis conditions

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