Francesca Spadavecchia

Time effects on the stability of the induced defects in TiO2 nanoparticles doped by different nitrogen sources

N-doped TiO2 samples are claimed to be the most promising among the so-called second-generation photocatalysts, but their success in photocatalysis is still under debate. In this study, N-doped TiO2 nanocrystals are obtained by a simple, quick, and effortless procedure, starting from titanium alkoxide as the precursor for the sol–gel route, with the N source being either inorganic (NH3) or organic (triethylamine, urea). Structural, morphological, and optical characterizations are compared with electron paramagnetic resonance (EPR) data to give an integrated picture of such materials. No literature data on the “aging” features in the dry state of the fresh calcined samples on the EPR and diffuse reflectance spectra (DRS) measurements are reported. Our N-doped TiO2 powders show different stabilities of paramagnetic and optical signals. The photocatalytic activity is tested, toward the degradation of ethanol in aqueous media, under both visible and UV irradiation, in this latter case resembling the same trend of the paramagnetic species decay.

Investigation and optimization of photocurrent transient measurements on nano-TiO2

Chronoamperometry with chopped light has been applied to commercial and homemade TiO2 nanopowders, both doped and undoped, to gain information on the charge recombination processes which take place in the oxide and affect its photocatalytic performance. The photocurrent transients can be attributed to photoinduced electron–hole separation, trapping, recombination, and scavenging. In order to evaluate what mainly affects the shape of the transients and the transient time constants (τ) which can be derived, the type and concentration of the electrolyte, the irradiation source (UV or visible light), and the presence of a hole acceptor (oxalate) were varied. The reproducibility of quantitative measurements was best when an inert electrolyte (NaClO4) has been employed under an N2-saturated atmosphere. Under these conditions, both Pr-TiO2 and N-TiO2 samples show a definitely higher τ than the undoped oxide, which indicates a slower recombination kinetics, both under UV and visible irradiation. Therefore, these are promising as photocatalysts.

Effect of the Preparation Procedure on the Morphology of Thin TiO2 Films and Their Device Performance in Small-Molecule Bilayer Hybrid Solar Cells

Flat titanium dioxide films, to be used as the acceptor layer in bilayer hybrid solar cell devices, were prepared by spray-pyrolysis and by spin-casting. Both preparation methods resulted in anatase titania films with similar optical and electronic properties but considerably different film morphologies. Spray pyrolysis resulted in dense TiO₂ films grown onto and affected by the surface roughness of the underlying conducting glass substrates. The spin-casting preparation procedure resulted in nanoporous titania films. Hybrid solar cell devices with varying layer thickness of the small-molecule semiconducting dye TDCV-TPA were investigated. Devices built with spray-pyrolyzed titania substrates yielded conversion efficiencies up to 0.47%. Spin-cast titania substrates exhibited short circuits for thin dye layer thickness. For thicker dye layers the performance of these devices was up to 0.6% due to the higher interfacial area for charge separation of these nanoporous TiO₂ substrates.

Mesoporous titania nanocrystals by hydrothermal template growth

Mesoporous TiO2 nanocrystals have been synthetized by a classical sol-gel route integrated by an hydrothermal growth step using monomeric (dodecylpyridinium chloride, DPC) or dimeric gemini-like (GS3) surfactants as template directing agents. Adsorption isotherms at the solid/liquid interface of the two surfactants have been obtained on aqueous dispersion of titania; the nature of the oxide/adsorbate interactions and the molecules orientation/coarea are discussed. The effects produced by the presence of the two surfactants on the different morphological (surface area, porosity, and shape) and structural (phase composition and aggregate size) features of the final TiO2 samples, calcined at 600°C, are discussed.

Use of Screen-Printed Electrodes in the Determination of Some Environmental Carcinogens

The use of commercially available Screen Printed Electrodes (SPEs) in Pulsed Voltammetric techniques for the determination of carcinogenic compounds, (namely furan, benzidines and chromium (VI)), is presented. The advantages related to the SPEs disposability and to the electrodes protection with Nafion® membrane for fouling prevention is shown.