Dependence of photocatalytic activity on particle size of a shape-controlled anatase titanium(IV) oxide nanocrystal

Decahedral anatase titanium(IV) oxide (TiO2) with {1 0 1} and {0 0 1} exposed crystal faces was prepared by hydrothermal treatment of peroxo titanic acid (PTA) solution with polyvinyl alcohol (PVA) as a shape-control reagent. pH of the PTA solution and amounts of PVA and amorphous titania included in the PTA solution had a large influence on size and shape of the prepared particles, and particle width of the decahedral anatase TiO2 was controllable between 25 and 60 nm. Photocatalytic activity of the decahedral anatase TiO2 was examined in terms of the relationship between particle size and photocatalytic activity. Decahedral anatase TiO2 with particle width of ca. 40 nm showed excellent activity because of the optimized balance between efficient separation of redox sites and large specific surface area

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

Solution-processed amorphous niobium oxide as a novel electron collection layer for inverted polymer solar cells

Amorphous niobium oxide (NbOx) as an electron collection layer in inverted polymer solar cells was prepared by a solution process. The power conversion efficiency of inverted polymer solar cells based on a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester was improved to 2.22% by inserting an NbOx layer between the active layer and indium tin oxide electrode. An energy level diagram of component materials in the inverted polymer solar cell indicated that the NbOx layer works as both an electron collection layer and hole blocking layer in polymer solar cells

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

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

Development of a visible-light-responsive titania nanotube photocatalyst by site-selective modification with hetero metal ions

A titania nanotube (TNT), which was obtained by calcinations of a titanate nanotube, was modified with two kinds of transition metal ions, iron(III) (Fe3+) and zinc(II) (Zn2+) ions. TNT with site-selective modification with metal ions showed higher photocatalytic activity than that of bare TNT, presumably due to separation of redox sites, and oxidation on the outside surface and reduction on the inside surface were the preferable separated redox sites on the tubular structure for decomposition of acetaldehyde. Modification of TNT with Fe3+ ions induced improvement of photocatalytic activity under visible-light irradiation as well as ultraviolet (UV) irradiation. On the other hand, TNT modified with Zn2+ ions showed the largest enhancement of photocatalytic activity under UV irradiation, though increase in visible-light activity was hardly observed. Double-beam photoacoustic spectroscopic analyses indicated that Zn2+ ion works efficiently as an electron acceptor, while Fe3+ ion is an effective sensitizer for visible light

Development of highly efficient sulfur-doped TiO2 photocatalysts hybridized with graphitic carbon nitride

Graphitic carbon nitride (g-C3N4) has attracted much attention as a metal-free semiconductor having visible-light absorption and relatively high chemical stability. In the present study, we hybridized g-C3N4 with sulfur-doped TiO2, which is a visible light-responsive photocatalyst with high oxidation ability, in order to improve photocatalytic activity under visible-light irradiation. Hybrid photocatalysts were prepared by three methods: agate mortar, sonication, and planetary mill. Activities of the hybrid photocatalysts depended on the mixing method. The sample prepared by a planetary mill showed the highest photocatalytic activity, 4-times higher than that of sulfur-doped TiO2. We concluded that the high activity of the hybridized sample under visible-light irradiation is induced by charge transfer between the two photocatalysts mimicking the Z-scheme in photosynthesis

Photocatalytic partial oxidation of methylpyridine isomers on TiO2 particles under an anaerobic condition

Photocatalytic oxidation of methylpyridine isomers (2-methylpyridine, 3-methylpyridine, and 4-methylpyridine) was investigated in a mixed solution of acetonitrile and water or acetonitrile using various kinds of TiO2 powders as photocatalysts. The main products from methylpyridine isomers were pyridinecarboxaldehyde isomers (2-pyridinecarboxaldehyde, 3-pyridinecarboxaldehyde, and 4-pyridinecarboxaldehyde). Rutile large TiO2 particles showed the highest level of activity for oxidation of 2-methylpyridine probably because band bending was necessary for the oxidation of 2-methylpyridine. On the other hand, a fine particle having an anatase or rutile phase showed a higher level of activity than large TiO2 particles for oxidation of 3-methylpyridine. A rutile fine particle showed the highest level of activity for the reaction. It was found that pure rutile or pure anatase particles were inactive for oxidation of 4-mathylpyridine. If the particles are not extremely small, pure rutile and pure anatase powders show fairly high levels of activity, and those containing both anatase and rutile phases show the highest level of activity. The activity of pure rutile particles was also enhanced by physically mixing them with a small amount of small anatase particles, which were inactive for this reaction. These results can be explained by the synergism between rutile and anatase particles. All of these reactions effectively proceeded even under anaerobic conditions. Photocatalytic reduction of methylpyridine isomers concomitantly proceeded on TiO2 particles under the conditions used. These results suggest that the activities of TiO2 photocatalysts for oxidation of methylpyridine isomers are dominated by the oxidation potential of alkylpiridine and band bending of TiO2 particles

Selective Oxidation of Benzaldehyde Derivatives on TiO2 Photocatalysts Modified with Fluorocarbon Group

Fluorocarbon groups were introduced onto surfaces of SiO2-covered TiO2 particles (SiO2–TiO2). Oxidation of pentafuluorobenzaldehyde on the surface modified TiO2 powders proceeded much efficiently than that on SiO2-covered TiO2 particles without surface modification. In addition, no enhancement of activity level of surface-modified SiO2–TiO2 for oxidation of benzaldehyde was observed. The enhancement of the surface-modified SiO2–TiO2 is due to the interaction of F atoms between the substrate and fluorocarbon groups introduced on SiO2–TiO2

Oxidation of Aldehydes on TiO2 Photocatalysts Modified with Alkylsilyl Group

Surfaces of SiO2-covered TiO2 photocatalysts were modified with alkylsilyl groups. Oxidation of hexanal on surface-modified TiO2 proceeded more efficiently than that on photocatalysts without surface modification. The improvement of the photocatalytic activities of surface-modified TiO2 photocatalysts is due to the hydrophobic interaction between hexanal and alkylsilyl groups modified on TiO2 photocatalysts