Charge transfer reductive doping of nanostructured TiO 2 thin films as a way to improve their photoelectrocatalytic performance

Electrochemistry Communications (Impact Factor: 4.43). 10/2006; 8:1713-1718. DOI: 10.1016/j.elecom.2006.08.006

ABSTRACT Nanostructured TiO 2 films can be reversibly doped by applying a potential of À0.6 V Ag/AgCl in aqueous 0.1 M HClO 4 for several min-utes. This charge transfer reductive doping causes significant changes of the cyclic voltammograms in the dark. Furthermore, an up to 6-fold increase of the efficiency for water photooxidation is observed upon electrochemical reductive doping. Both observations are explained by the build-up of a space charge layer through agglomerates of appropriately sized and shaped nanoparticles.

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    ABSTRACT: A combined photoelectrochemical and IR spectroscopic approach was used to study the photooxidation of oxalic acid on thin films consisting of oriented rutile TiO(2) nanowires (diameter: approximately 2 nm). Anodic spikes appear in the photocurrent transients particularly at low oxalic acid concentrations and point to mass transport limitations due to the presence of narrow pores (< or = 1 nm) in the nanowire films. Accordingly, IR measurements reveal that the photocurrent decrease at low concentrations is accompanied by an adsorbate depletion as tracked by the decrease of IR bands at 1699 cm(-1) (adsorbate species A) and 1720 cm(-1) (adsorbate species B). The relative intensities of the two bands are found to change with illumination time. Based on the comparison of the equilibrium adsorption constants as deduced independently from photocurrent transients and from IR spectra, the photocatalytic oxidation of oxalate seems to proceed on the surface of rutile nanowires mainly via species A, which is also the one with the largest adsorption constant. The strong decrease of the IR band at 1720 cm(-1) is rationalized by a fast replenishment of photooxidized species A by species B. In a more general vein, the challenges and prospects of combining photoelectrochemical and spectroscopic measurements are discussed.
    Physical Chemistry Chemical Physics 09/2010; 12(35):10503-11. · 3.83 Impact Factor
  • Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2010; 157(7).
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    ABSTRACT: Nanoparticle-covered electrodes have altered properties as compared to conventional electrodes with same chemical composition. The changes originate from the large surface area and enhanced conduction. To test the mineralization capacity of such materials, TiO2 nanoparticles were deposited on titanium and gold substrates. The electrochemical properties were investigated using cyclic voltammetry and impedance spectroscopy while the mineralization was tested by immersion in simulated body fluid. Two types of nucleation and growth behaviours were observed. For smooth nanoparticle surfaces, the initial nucleation is fast with the formation of few small nuclei of hydroxyapatite. With time, an amorphous 2D film develops with a Ca/P ratio close to 1.5. For the rougher surfaces, the nucleation is delayed but once it starts, thick layers are formed. Also the electronic properties of the oxides were shown to be important. Both density of states (DOS) in the bandgap of TiO2 and the active area were determined. The maximum in DOS was found to correlate with the donor density (N d ) and the active surface area. The results clearly show that a rough surface with high conductivity is beneficial for formation of thick apatite layers, while the nanoparticle covered electrodes show early nucleation but limited apatite formation.
    International Journal of Dentistry 01/2013; 2013:139615.


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May 26, 2014