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

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

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

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

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

Simultaneous Measurements of Photoabsorption and Photoelectrochemical Performance for Thickness Optimization of a Semiconductor Photoelectrode

We established a system for simultaneous measurements of photoelectrochemical (PEC) reaction and photoabsorption in a semiconductor photoelectrode. This system uses a photoacoustic technique and photoelectrodes with a film-thickness gradient that was prepared by electrophoretic deposition of tungsten(VI) oxide particles while pulling up a substrate. The system enabled high-throughput determination of optimum film thickness, and the results showed that irradiation direction has a significant influence on PEC performance for a photoelectrode with a thick film. Furthermore, the mechanism of enhancement of PEC performance by postnecking treatment was discussed