Claudia L. Bianchi

Effect of Nature and Location of Defects on Bandgap Narrowing in Black TiO2 Nanoparticles

The increasing need for new materials capable of solar fuel generation is central in the development of a green energy economy. In this contribution, we demonstrate that black TiO(2) nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption. The electronic structure of black TiO(2) nanoparticles is determined by the unique crystalline and defective core/disordered shell morphology. We introduce new insights that will be useful for the design of nanostructured photocatalysts for energy applications.

Selective liquid phase oxidation using gold catalysts

Au/C and Au/oxide (Al2O3, TiO2) have been compared in the liquid phase oxidation of glycols and a different trend in reactivity revealed. On the oxides the activity of supported gold increases by decreasing particle size, whereas on carbon maximum activity is achieved with gold particle mean diameter around 7–8 nm. XPS revealed that in the latter case activity depends not only on the size of the gold particle but also on its surface concentration.

Magnesium salts and oxide: an XPS overview

Abstract XPS measurements have been performed on a series of Mg II salts (NO 3 − , CO 3 2− , SO 4 2− , Cl − , CH 3 COO − ), hydroxides and oxides, these latter compounds are both commercial and prepared in laboratory. The binding energy (BE) of the anionic partner in Mg II salts compares well in any case with literature data for the same anions in other alkaline and alkaline earth compounds. The BE of Mg II appears to be affected by the electroattractive nature of the parent anion. The Mg II spectra, in the case of MgO samples, are not influenced either by the nature of the oxide precursor salt or by the temperature of the oxide preparation (873 K, 1073 K, 1253 K). The BE of Mg 2p ranges between 49.9 eV and 50.2 eV. Oxygen spectra are regular and show the presence of the surface chemisorbed -OH component even at heating temperatures of 1473 K. The choice, as internal reference, of the hydrocarbon contaminant carbon peak is discussed, specifically, in the case of MgO samples with reference to specific lattice and surface properties of the oxide itself.

Cu/Cu-oxide nanoparticles as catalyst in the “click” azide–alkyne cycloaddition

Mixed Cu/Cu-oxide nanoparticles are an effective catalyst for the “click” 1,3-dipolar cycloaddition between azides and terminal alkynes, featuring short reaction times, soft reaction conditions and full regioselectivity.

Mn3O4 and γ-MnOOH powders, preparation, phase composition and XPS characterisation

Abstract The paper reports data relative to the preparation of Mn 3 O 4 and γ-MnOOH powders by following hydrothermal procedures. The mixed valence spinel was prepared starting either from manganous sulphate or chloride and oxidising in suspension (by either air or oxygen) the alkaline precipitate. Manganite was obtained by oxidising manganous sulphate solutions with H 2 O 2 , subsequent alkalisation and refluxing. The samples were characterised for phase composition by X-ray diffraction. Pure phase oxides were obtained in the case of both Mn 3 O 4 and γ-MnOOH when Mn(II) sulphate was used as the precursor. The pure phase samples were submitted to X-ray photoelectron spectroscopy (XPS) investigation, in the case of manganese, for both 2p and 3s spectral regions. The binding energies of the un-fitted experimental Mn peaks compare well with the relative values reported in the literature for the compounds. With the aim of assessing the actual Mn speciation, in the external layers, the fitting procedure of the experimental XPS peaks has been performed by modulating the relative intensities of the spectral components on the grounds of distinct hypotheses consistent with the oxide formulas. The possibility of extending the outcome of this elaboration to the bulk composition of the samples is also discussed.

Graphene oxide based Pt-TiO2 photocatalyst: ultrasound assisted synthesis, characterization and catalytic efficiency.

An ultrasound-assisted method was used for synthesizing nanosized Pt-graphene oxide (GO)-TiO2 photocatalyst. The Pt-GO-TiO2 nanoparticles were characterized by diffused reflectance spectroscopy, X-ray diffraction, N2 BET adsorption-desorption measurements, atomic force microscopy and transmission electron microscopy. The photocatalytic and sonophotocatalytic degradation of a commonly used anionic surfactant, dodecylbenzenesulfonate (DBS), in aqueous solution was carried out using Pt-GO-TiO2 nanoparticles in order to evaluate the photocatalytic efficiency. For comparison purpose, sonolytic degradation of DBS was carried out. The Pt-GO-TiO2 catalyst degraded DBS at a higher rate than P-25 (TiO2), prepared TiO2 or GO-TiO2 photocatalysts. The mineralization of DBS was enhanced by a factor of 3 using Pt-GO-TiO2 compared to the P-25 (TiO2). In the presence of GO, an enhanced rate of DBS oxidation was observed and, when doped with platinum, mineralization of DBS was further enhanced. The Pt-GO-TiO2 catalyst also showed a considerable amount of degradation of DBS under visible light irradiation. The initial solution pH had an effect on the rate of photocatalytic oxidation of DBS, whereas no such effect of initial pH was observed in the sonochemical or sonophotocatalytic oxidation of DBS. The intermediate products formed during the degradation of DBS were monitored using electrospray mass spectrometry. The ability of GO to serve as a solid support to anchor platinum particles on GO-TiO2 is useful in developing new photocatalysts.

Sono-photocatalytic degradation of 2-chlorophenol in water: kinetic and energetic comparison with other techniques

The degradation of 2-chlorophenol in water was kinetically investigated using the following different techniques, employed either separately or simultaneously, always with the same experimental set-up: light irradiation (315-400 nm), sonication, photocatalysis with different types of TiO2, photocatalysis with sonication. The influence of the reaction volume and of different gas mixtures, containing Ar and O2, as well as O2/O3, was also investigated. Finally, an energetic comparison among these different techniques was performed, focused on an industrial application of some of them.

Surface enamel remineralization: biomimetic apatite nanocrystals and fluoride ions different effects

A new method for altered enamel surface remineralization has been proposed. To this aim carbonate-hydroxyapatite nanocrystals which mimic for composition, structure, nanodimensions, and morphology dentine apatite crystals and resemble closely natural apatite chemical-physical properties have been used The results underline the differences induced by the use of fluoride ions and hydroxyapatite nanocrystals in contrasting the mechanical abrasions and acid attacks to which tooth enamel is exposed. Fluoride ions generate a surface modification of the natural enamel apatite crystals increasing their crystallinity degree and relative mechanical and acid resistance. On the other hand, the remineralization produced by carbonate-hydroxyapatite consists in a deposition of a new apatitic mineral into the eroded enamel surface scratches. A new biomimetic mineral coating, which progressively fills and shadows surface scratches, covers and safeguards the enamel structure by contrasting the acid and bacteria attacks.

XPS analysis of gallium oxides

Abstract Samples of Ga 2 O, synthesized by reacting Ga 2 O 3 and metallic gallium, are analyzed by XPS measurements. These samples reveal the presence of a new photoelectron signal, assigned to Ga(I), with 3d binding energy of 19.0 eV, which is lower than the measured Ga III (3d) binding energy (20.6 eV) and higher than the measured Ga 0 (3d) binding energy (18.5 eV). A comparison between available XPS data on the Ga 2 O 3 /HZSM-5 catalytic system and the gallium binding energies measured in this work is proposed.

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO2Prepared by Ultrasound

Nanocrystalline TiO2samples were prepared by promoting the growth of a sol–gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NOxin air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p3/2region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energyper volume (Etot/V) and not the acoustic intensity or the pulsed/continuous mode.