35,680 research outputs found
Morphological characterization of shape-controlled TiO2 anatase through XRPD analysis
No full textPreferential growth of anatase crystallites along different directions is known to deeply affect their photocatalytic properties, especially with respect to the exposure of the reactive {001} facets. Its extent can be easily quantified through simple geometric calculations, on the basis of crystal sizes extracted for specific directions by means of X-Ray Diffraction data analysis. Nevertheless, the actual results depend on themethod employed for such a quantification. Here we report on a comparative morphological investigation, performed by employing the Scherrer equation and the line profile from Rietveld refinements, on shapecontrolled anatase photocatalysts produced by employing HF as capping agent. Compared to the Rietveld-based method, the use of the Scherrer equation produces a systematic underestimation of crystallite dimensions, especially concerning the [100] direction, which in turn causes the percentage of exposed {001} crystal facets to be underestimated. Neglecting instrumental-related effects may further reduce the estimate
In-situ spectrofluorimetric identification of natural red dyestuffs in ancient tapestries
No full textThe non-destructive identification of organic dyes in works of art is still a challenging goal for scientists devoted to the diagnostic of cultural heritage. In the present study, a non-destructive and in-situ analytical method was developed to this aim and applied to sets of ancient tapestries (XV–XVI century) compared with reference wool samples dyed in the laboratory. The target analytes are the red organic dyes of natural origin mostly used to dye textiles in ancient times, i.e. madder, kermes, cochineal, brazilwood and lac dye. In order to discriminate among them, the collected data were processed by a multivariate statistical approach, using principal component analysis (PCA) and cluster analysis. To validate the method, chromatographic analyses were performed on selected fragments from the same textiles previously analyzed by spectrofluorimetry. The consistency of the results allowed us to sustain the correctness of the non-invasive approach and to exploit it to analyze details of three tapestries of the precious “Arazzi dei Mesi” cycle (beginning of XVI century), belonging to the collection of the Castello Sforzesco in Milan (Italy)
Effects of gold nanoparticles deposition on the photocatalytic activity of titanium dioxide under visible light
No full textThe effects of gold nanoparticles deposited on titanium dioxide on the photocatalytic oxidative degradation of two organic substrates, i.e. formic acid and the azo dye Acid Red 1, and on
the parallel O2 reduction yielding hydrogen peroxide have been investigated under visible light
irradiation. The method employed to reduce Au(III) to metallic gold in the preparation of Au/TiO2 photocatalysts was found to affect their photoactivity, also by modifying the
properties of TiO2. The presence of gold on TiO2 facilitates both the electron transfer to O2 and
the mineralization of formic acid, which mainly proceeds through direct interaction with photoproduced valence band holes. The so-formed highly reductant CO2 intermediate species
may contribute in maintaining gold in metallic form. The controversial results obtained in the photocatalytic degradation of the dye were rationalised by taking into account that with this substrate, which mainly undergoes oxidation through a hydroxyl radical mediated mechanism, the photogenerated holes may partly oxidise gold nanoparticles, which consequently act as recombination centres of photoproduced charge carriers
A comparative study on the effects of sulphur and fluorine doping on the photocatalytic activity of TiO2 in aqueous suspension
No full textSurface Aspects of Semiconductor Photochemistry
No full textEditorial of the Surfaces Special Issue entitled "Surface Aspects of Semiconductor Photochemistry", devoted to the 7th International Conference on Semiconductor Photochemistry (SP7), which was held on September 11-14, 2019 in Milano, Italy, with the active participation of more than 160 attendants in an intense program, including 12 plenary and keynote lectures, 60 oral presentations, 20 flash presentations by young authors and 2 poster sessions.
This Special Issue well highlights the main aim of the SP7 conference to cover the current developments in the area of semiconductor photochemistry and photo(electro)catalysis, focusing specific attention on either new findings related to “historical” TiO2-based materials or to up-to-date results obtained with emerging and promising semiconductor photo(electro)catalytic materials
Cr(VI) photocatalytic reduction on TiO2: effect of the presence of an azo dye in relation to the photocatalyst structure
No full textEffects of Surface Modification of TiO2 Particles on the Photocatalytic Reaction Paths in Aqueous Suspension
No full textPhotocatalytic activity of TiO2-WO3 mixed oxides in relation to electron transfer efficiency
No full textAiming at producing photocatalysts with minimized photoproduced electron - hole pairs recombination, a series of titanium - tungsten mixed oxides has been prepared, by coupling TiO2 with different amounts of WO3, according to an alkaline-catalyzed sol-gel method followed by an incipient wetting procedure. The photocatalysts were characterized by surface and bulk techniques and tested in both an oxidation and a reduction photocatalytic reaction, i.e. in formic acid (FA) mineralization and in Cr(VI) reduction. Tungsten was mainly present as hexagonal WO3 on the TiO2 surface, though a fraction of W migrates into the TiO2 lattice substituting Ti atoms, as evidenced by XRPD analysis. Different photoactivity scales were found in the two test reactions, both occurring in the same pH range under similar substrate-photocatalyst electrostatic interactions. In fact, photoexcited electrons transferred from the conduction band (CB) of TiO2 to the CB of coupled WO3, being energetically unable to reduce O2 molecules, easily recombine with photoproduced holes, with a consequent photoactivity decrease in FA photo-mineralization with increasing W/Ti ratio. On the contrary, coupling TiO2 with small WO3 amounts (0.2-1.0mol%) is beneficial in the removal of Cr2O72- anions. These species, being characterized by a redox potential more positive than the CB edge of WO3, may efficiently accept the electrons trapped in WO3 domains, converting into less toxic Cr(III) species. Thus, WO3 surface domains effectively promote photoproduced charge separation by efficiently trapping CB electrons; increased photocatalytic efficiency depends on the redox potential of the electron acceptor species directly (or indirectly) involved in the photocatalytic process
Effects of gold nanoparticles deposition on the photocatalytic activity of titanium dioxide under visible light
No full textThe effects of gold nanoparticles deposited on titanium dioxide on the photocatalytic oxidative
degradation of two organic substrates, i.e. formic acid and the azo dye Acid Red 1, and on
the parallel O2 reduction yielding hydrogen peroxide have been investigated under visible light
irradiation. The method employed to reduce Au(III) to metallic gold in the preparation
of Au/TiO2 photocatalysts was found to affect their photoactivity, also by modifying the
properties of TiO2. The presence of gold on TiO2 facilitates both the electron transfer to O2 and
the mineralization of formic acid, which mainly proceeds through direct interaction with
photoproduced valence band holes. The so-formed highly reductant CO2
intermediate species
may contribute in maintaining gold in metallic form. The controversial results obtained in the
photocatalytic degradation of the dye were rationalised by taking into account that with this
substrate, which mainly undergoes oxidation through a hydroxyl radical mediated mechanism, the
photogenerated holes may partly oxidise gold nanoparticles, which consequently act as
recombination centres of photoproduced charge carriers
Unraveling the Multiple Effects Originating the Increased Oxidative Photoactivity of {001}-Facet Enriched Anatase TiO2
No full textCrystal shape control on a series of anatase photocatalysts was achieved by varying the amount of HF employed as a capping agent in their hydrothermal synthesis. A systematic comparison between their physicochemical properties, determined by several complementary surface and bulk techniques before and after thermal treatment at 500 °C, allowed one to discern the influence of the relative amount of exposed {001} crystal facets among a series of effects simultaneously affecting their oxidative photocatalytic activity. The results of both formic acid and terephthalic acid photo-oxidation test reactions point to the primary role played by calcination in making {001} facets effectively photoactive. Annealing not only removes most of the residual fluorine capping agent from the photocatalyst surface, thus favoring substrate adsorption, but also produces morphological modifications to a crystal packing that makes accessible a larger portion of surface {001} facets due to the unpiling of platelike crystals. The photocatalyst bearing the highest amount of exposed {001} facets (60%) shows the highest photoactivity in both the direct and the •OH-radical-mediated photocatalytic test reaction
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