1,721,054 research outputs found
Photocatalytic reduction of Cr(VI) in TiO2 water suspensions : synergistic effect of an azo dye
No full textPhotocatalytic Abatement of Aqueous Ammonia on Ru/TiO2: Effects of the Route of Ru Nanoparticles Deposition on TiO2
No full textThe effects of TiO2 surface modification by Ru nanoparticles (NPs) deposition have been investigated in the photocatalytic decomposition of aqueous ammonia. Two main Ru NPs deposition routes were chosen, i.e. (i) the deposition of surfactant-stabilized preformed metal NPs and (ii) a modified version of the well-known deposition-precipitation technique, employing urea as precipitating agent. Other Ru/TiO2 photocatalysts were prepared (iii) by simply grafting Ru(III) metal ions on TiO2, which were tested either as prepared or (iv) after their thermal reduction under H2 atmosphere, in order to obtain Ru NPs in full metallic state. The role played also by the relative nominal metal amount on the so obtained photocatalyst powders was investigated in terms of both ammonia conversion and selectivity towards mildly oxidized N2 or highly oxidized nitrite and nitrate ions. The Ru NPs deposition technique was found to affect the reaction paths especially in terms of products selectivity, with fully reduced Ru NPs on TiO2 being able to promote the environmentally friendly, highly desirable photocatalytic conversion of ammonia into innocuous N2
Effects of phase composition and surface area on the photocatalytic paths on fluorinated titania
No full textThe effect of TiO2 surface fluorination in the photocatalytic degrdn. of the azo dye Acid Red 1 (AR1) was investigated employing a series of TiO2 photocatalysts including P25, a rutile and high surface area anatase samples. The effects of (i) pH lowering to 3.7 and (ii) TiO2 surface fluorination at this pH on the reaction rate under 254 nm or polychromatic, mainly visible light, irradn. and on AR1 adsorption on the photocatalyst surface were taken into account sep. In the case of P25 and rutile TiO2 photocatalysts the reaction rate did not vary upon pH lowering in the absence of fluoride, but almost doubled upon fluorination at pH 3.7, an effect to be attributed exclusively to the surface fluorine-induced modification of the reaction paths. By contrast, in the case of high surface area anatase samples a pH lowering from natural conditions down to 3.7 led to a remarkable increase of the reaction rate, which however was clearly inhibited upon surface fluorination at pH 3.7, with a trend perfectly matching that of AR1 adsorption on anatase. Thus, reaction paths favored by direct interaction of the substrate with the photocatalyst surface appear to prevail for high surface area anatase photocatalysts with respect to those which take advantage of a less reactive (and less adsorptive) fluorinated photocatalyst surface
Effects of the calcination temperature on the photoactivity of B- and F-doped or codoped TiO2 in formic acid degradation
No full textIn the framework of a large systematic investigation on the effects of doping TiO2 with first raw p-block elements of the Period Table, we discuss here the results obtained with a series of TiO2 photocatalysts doped or co-doped with boron and fluorine, prepared by sol-gel synthesis and calcined at 500 °C or at 700 °C. The photocatalytic activity of such materials in the oxidative decomposition of formic acid is related to their surface and structural properties, determined by BET, XRPD and Uv–vis absorption analyses. The photoactivity of singly doped or codoped TiO2 full anatase materials calcined at 500 °C appears to increase with their specific surface area and to be not related to electronic structure modifications due to the presence of the dopants. The photoactivity increase observed upon B-doping TiO2, which leads to B2O3 surface segregation, may thus simply result from their increased surface area, the presence of B2O3 having negligible effects on photoactivity. Highly crystalline F-doped or BF-codoped TiO2 materials calcined at 700 °C exhibit the highest photoactivity, essentially due to the retarded anatase into rutile transformation intrinsic of fluorine-doped materials
Doping TiO2 with p-block elements : effects on photocatalytic activity
No full textA critical overview is presented on the role that first row p-block elements boron, carbon, nitrogen and fluorine, employed as dopants of TiO2, have in improving the capability of this photocatalyst in harvesting solar light for photocatalytic applications. The peculiar physicochemical properties of doped TiO2 materials are described in terms of the results of both theoretical calculations and photocatalytic efficiency tests, in relation to their bulk and surface features. The limitations of doping titania with non metal elements are outlined and a few recent examples of very promising co-doping effects are discussed
Effects of fluorine doping and co-doping and of noble metal nanoparticles deposition on the photoactivity of TiO2
No full textA detailed analysis of the effects produced by fluorine doping or co-doping with nitrogen and boron on the UV-vis photoactivity of TiO2 in both down-hill (decomposition of organics) and up-hill reactions (hydrogen production by methanol photoreforming) reveals that fluorine doping is the sole responsible for the photoactivity increase in the UVA region observed with full anatase, highly crystalline doped TiO2 calcined at high temperature, possibly due to the formation of surface oxygen defects. Noble metal (Au or Pt) nanoparticles on the photocatalyst surface contribute in increasing the separation of photoproduced charge carriers resulting in increased photocatalytic performance of the surface and bulk-modified photocatalyst systems. Almost identical bell-shaped photoactivity trends were obtained for the naked, Au- and Pt- modified titania with increasing the dopant content, demonstrating the crucial role that the electronic structure of the doped materials has in determining the absorption features and the separation and mobility of photoproduced charges within the doped oxide photocatalysts. The main role of the noble metal is limited to an increased efficiency of electron-hole separation by “capturing” conduction band electrons, Pt always being more efficient than Au, in line with their work functions. TiO2 doping with fluorine provides a synergistic positive contribution to the beneficial effect that noble metal nanoparticles have in the reduction paths leading to hydrogen production from methanol photoreforming
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