Publications (17) View all
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Article: Preparation and Photoelectrochemical Properties of p-type Cu5Ta11O30 and Cu3Ta7O19 Semiconducting Polycrystalline Films
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ABSTRACT: New p-type polycrystalline films of semiconducting Cu5Ta11O30 and Cu3Ta7O19 were prepared on fluorine-doped tin oxide (FTO) glass starting from their CuCl-flux synthesis as highly faceted micrometer-sized particles. The particles were annealed on FTO at 400–500 °C, followed by a mild oxidation in air at between 250 and 550 °C. In an aqueous 0.5 M Na2SO4 electrolyte solution (pH = 6.3), the films exhibit strong cathodic photocurrents under irradiation by visible and/or ultraviolet light, which increased with higher annealing and oxidation temperatures owing to increased p-type carrier concentration and better electrical contact between particles. Thermogravimetric analyses show that the oxidation treatments result in an oxygen uptake at concentrations of 3 × 1020 cm–3 at 250 °C, to 4 × 1021 cm–3 at 550 °C, with the higher temperatures leading to the decomposition of the film. The Cu5Ta11O30 and Cu3Ta7O19 bulk powders exhibit band-gap sizes of 2.59 and 2.47 eV, respectively, and show an onset of their cathodic photocurrents at wavelengths of 500–550 nm. Mott–Schottky measurements of their flat-band potentials have been used to determine the valence band positions at approximately +1.06 and +1.19 V versus RHE (pH = 6.3), and thus conduction band positions of about −1.53 and −1.28 V for Cu5Ta11O30 and Cu3Ta7O19, respectively. The band positions are thus suitably located for the photon-driven reduction and oxidation of water. The highest observed incident photon-to-current efficiencies (IPCE %) for hydrogen production were 5% at 350 nm and 1–2% at 500–600 nm. Electronic structure calculations based on density functional theory methods show that the conduction band states are delocalized within layers of TaO7 pentagonal bipyramids, whereas the valence band states originate within layers of linearly coordinated Cu(I) cations. The lowest-energy band-gap transitions involve a metal-to-metal charge transfer between Cu(I) and Ta(V) cations in these two types of layers. Compared to other Cu(I) oxides, these structures possess sufficiently disperse bands for high carrier mobility within these layers, and thus the strong cathodic photocurrents of the films.The Journal of Physical Chemistry C 04/2012; 116(19):10490-10497. · 4.80 Impact Factor -
Article: Photoelectrochemical Investigation and Electronic Structure of a p-Type CuNbO3 Photocathode
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ABSTRACT: A new p-type CuNbO3 photoelectrode was prepared on fluorine-doped tin oxide (FTO) glass and characterized by X-ray diffraction (XRD), UV–vis spectroscopy, and photoelectrochemical techniques. Solid-state syntheses yielded a red-colored CuNbO3 phase (space group: C2/m (No. 12), Z = 8, a = 9.525(1) Å, b = 8.459(2) Å, c = 6.793(1) Å, β = 90.9(2)°) with a measured optical bandgap size of 2.0 eV. Phase-pure samples could be deposited and annealed on FTO slides at 400 °C under vacuum. Photoelectrochemical measurements showed the onset of a photocathodic current driven under visible-light irradiation and reaching incident-photon-to-current efficiencies exceeding 5%. The p-type CuNbO3 film also exhibits a stable photocurrent and notable resistance to photocorrosion, as shown by X-ray diffraction. Electronic structure calculations based on density functional theory reveal the visible-light absorption originates from a nearly direct bandgap transition owing primarily to copper-to-niobium (d10-to-d0) excitations. A promising new p-type semiconductor is thus revealed of potentially broad use in solar-energy conversion.The Journal of Physical Chemistry C 05/2011; 115(27):13534–13539. · 4.80 Impact Factor -
Article: The effect of platinum on the performance of WO3 nanocrystal photocatalysts for the oxidation of methyl orange and iso-propanol
Journal of Chemical Technology & Biotechnology 03/2011; 86(8):1018-1023. · 2.17 Impact Factor -
Article: Room temperature oxidation of methyl orange and methanol over Pt-HCa2Nb3O10 and Pt-WO3 catalysts without light.
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ABSTRACT: The layered semiconductor Pt-HCa(2)Nb(3)O(10) can catalyze room temperature air oxidation of methyl orange. It is also more effective than Pt-WO(3) in catalyzing reaction of methanol with air. Pt-HCa(2)Nb(3)O(10) could find wide application as a mild oxidizing catalyst.Chemical Communications 11/2010; 47(3):881-3. · 6.17 Impact Factor -
Article: Growth of single crystalline barium titanate nanowires from TiO2 seeds deposited on conducting glass.
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ABSTRACT: A new synthetic method is reported for depositing BaTiO(3) nanowire film on conducting glass. First, a TiO(2) particle thin film is prepared by spray coating, and then transformed to single crystalline BaTiO(3) nanowires grown on the conducting glass by hydrothermal treatment using TiO(2) particles as seeds of nanowire growth. The BaTiO(3) nanowires are 50-100 nm in diameter and have a film thickness of 4 µm. The capacitance of the BaTiO(3) one-dimensional (1D) nanowire array film was found to be 4.5 times higher than that of the nanoparticle film by measuring the impedance. The piezoelectric property of an individual BaTiO(3) nanowire was also demonstrated by piezoforce microscopy.Nanotechnology 10/2010; 21(42):425601. · 3.98 Impact Factor
