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Electrochemical anodization of low-concentration (0.02-0.2 at% Au) TiAu alloys in a fluoride electrolyte leads to self-organized TiO2 nanotubes that show a controllable, regular in situ decoration with elemental Au nanoclusters of ≈5 nm in diameter. The degree of self-decoration can be adjusted by the Au concentration in the alloy and the anodization time. Such Au particle decorated tubes show a high activity for photocatalytic H2 production from ethanol solutions.

Peas in a pod: A highly aligned Au(np)@TiO2 photocatalyst was formed by self-organizing anodization of a Ti substrate followed by dewetting of a gold thin film. This leads to exactly one Au nanoparticle (np) per TiO2 nanocavity. Such arrays are highly efficient photocatalysts for hydrogen generation from ethanol.

Aiming at producing TiO2-based photocatalytic materials with reduced charge carriers recombination, WO3–TiO2 mixed oxides were synthesized by a sol–gel method employing either an inorganic salt, Na2WO4, or an organic alkoxide, W(OC2H5)6, as tungsten precursor, with different W/Ti ratios. The so-obtained materials were characterized by XRPD, BET, UV–vis reflectance, XPS and EDX analyses and their photoactivity was tested under UV–visible irradiation in both the mineralization of formic acid in aqueous suspension and the gas phase oxidation of acetaldehyde. Both photoactivity results and photocurrent measurements point to a superior performance of photocatalysts obtained from the organic precursor with an optimal tungsten content (3%). The formation of an intimately mixed oxide, as revealed by XRPD analysis, results in photoactivity higher than that of pure TiO2, and also of benchmark P25 TiO2, consequent to a better charge separation due to the migration of photoproduced holes from WO3 domains to TiO2 and of photopromoted electrons in the opposite direction. The persistence of pure anatase phase in W-containing photocatalysts also after calcination at 700 °C and their higher surface area with respect to pure TiO2 also contribute in increasing the photocatalytic activity of the WO3–TiO2 mixed oxides.

TiO2 powders modified through the deposition of surfactant-stabilized preformed metal (Pt, Pd, Au and Ag) nanoparticles (NPs) were tested as photocatalysts for batch ammonia photo-oxidation in aqueous suspension, under UVA irradiation. NH3 conversion and the selectivity toward mildly oxidized N2 and highly oxidized nitrite and nitrate anions were monitored during the runs, in order to study the effects of noble metal NPs deposition on the reaction mechanism. This involves parallel and consecutive paths, also depending on the type of metal deposited on TiO2, as also highlighted by the nitrite photo-oxidation tests performed in the present study. Metal NPs acted as electron traps ensuring better separation of the photoproduced charge couples and consequently higher rates of hole-mediated oxidation reactions. Apart from Au/TiO2, the metal-modified powders exhibited higher photoactivity with respect to that of naked titania, with Ag/TiO2 being the best performing photocatalyst in terms of ammonia conversion. On the other hand, Pd NPs on TiO2 ensured a considerable increase of the selectivity toward N2 and may thus be considered the best co-catalysts of TiO2 for environmentally friendly photocatalytic NH3 abatement.

Semiconductors crystal facet engineering has become an important strategy for properly tuning and optimizing both the physicochemical properties and the reactivity of photocatalysts. In this review, a concise survey of recent results obtained in the field of specific surface-oriented anatase TiO2 crystals preparation is presented. The attention is mainly focused on the fluorine-mediated hydrothermal and/or solvothermal processes employed for the synthesis and the assembly of anatase micro/nanostructures with dominant {001} facets. Their peculiar photocatalytic properties and potential applications are also presented, with a particular focus on photocatalysis-based environmental clean up and solar energy conversion applications. Finally, the most promising results obtained in the engineering of TiO2 anatase crystal facets obtained by employing alternative, possibly more environmentally friendly methods are critically compared.

The effect of TiO 2 surface fluorination in the photocatalytic degradation of the azo dye Acid Red 1 (AR1) was investigated employing a series of TiO 2 photocatalysts including P25, a rutile and high surface area anatase samples. The effects of (i) pH lowering to 3.7 and (ii) TiO 2 surface fluorination at this pH on the reaction rate under 254 nm or polychromatic, mainly visible light, irradiation and on AR1 adsorption on the photocatalyst surface were taken into account separately. In the case of P25 and rutile TiO 2 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.

The effect of noble metal (Pt and Au) nanoparticle photodeposition on a series of NH4F-doped TiO2 photocatalysts calcined at 700 °C was investigated both in a thermodynamically down-hill reaction, i.e. the degradation of formic acid in aqueous suspension, and in an up-hill reaction, i.e. hydrogen production from methanol-water vapour mixtures. All photocatalysts were characterized by BET, XRD, UV-vis absorption and HRTEM analysis. Intriguing synergistic effects of simultaneous bulk and surface TiO2 modification were evidenced in both photocatalytic reactions, which can be interpreted in relation to the structural features of the materials. On one hand NH4F doping guarantees that the most active TiO2 anatase phase is stabilised up to high calcination temperature, ensuring high crystallinity and good photoinduced charge carriers production, on the other hand noble metal nanoparticles contribute in increasing the separation of photoproduced charge carriers, resulting in enhanced photocatalytic performances of the surface- and bulk-modified photocatalyst systems.

A 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.

TiO2 and Ti-W mixed oxide photocatalysts, with W/Ti molar ratios in the 0–5% range, were prepared through a simple sol-gel method, followed by annealing at 500 or 700 °C, and their photoactivity was tested in the photo-oxidation of formic acid in the aqueous phase under ambient aerobic conditions. XRPD analysis evidenced that in the presence of tungsten the anatase phase was stable even after calcination at 700 °C, with a progressively larger surface area and smaller particle dimensions with increasing tungsten content. Tungsten can both enter the titania lattice, as demonstrated by HAADF-STEM analysis, and also segregate as amorphous WO3 on the photocatalysts surface, as suggested by XPS analysis. The best performing Ti/W oxide photocatalyst is that containing 1.0 mol% W/Ti, mainly due to the tungsten-induced stabilization effect of the anatase phase, whereas electron transfer from TiO2 to WO3, though compatible with the here performed EPR measurements, appears to have no beneficial effect in the investigated reaction, likely due to the low energy level of the conduction band of WO3, from which electrons cannot efficiently transfer to adsorbed dioxygen.

A series of Pt/Cu/TiO2 photocatalysts, showing very high performance in photocatalytic hydrogen production from methanol/water vapour mixtures, were prepared under mild conditions by Cu(II) grafting on commercial P25 TiO2, with nominal Cu/TiO2 ratios ranging from 0.05 to 0.5 wt.%, followed by 0.5 wt.% Pt nanoparticles deposition by the deposition-precipitation method in the presence of urea. The structural features of the so obtained materials were fully characterized by X-ray absorption spectroscopy, which provided information on the oxidation state of the two metals and on the metal-metal and metalTiO(2) interactions, and by EPR analysis, which evidenced electron transfer phenomena involving copper under irradiation. The photocatalysts showed a volcano-shaped photoactivity trend in hydrogen production with increasing nominal Cu content, the maximum rate of H2 evolution (27.2 mmol h-1 gcat-1) being attained with the photocatalyst containing 0.1 wt.% of copper. In this sample CuO nanoclusters appear to be intimately coordinated with surface Ti atoms in a surface structure that partially stabilizes pre grafted copper in metallic form, possibly acting as an electron-transfer bridge at the interface between CuO nanoclusters and TiO2. Synergistic effects in H-2 photocatalytic production are clearly induced by the co-presence of grafted Cu nanoclusters and Pt nanoparticles on the TiO2 surface, with the copper oxidation state switching under UV-vis irradiation, facilitating electron transfer to adsorbed protons. (C) 2017 Elsevier B.V. All rights reserved.

The effect of Cu or Cu-Pt nanoparticles in TiO2 photocatalysts prepared by flame spray pyrolysis in one step was investigated in hydrogen production from methanol photo-steam reforming. Two series of titanium dioxide photocatalysts were prepared, containing either (i) Cu nanoparticles (0.05–0.5 wt%) or (ii) both Cu (0 to 0.5 wt%) and Pt (0.5 wt%) nanoparticles. In addition, three photocatalysts obtained either by grafting copper and/or by depositing platinum by wet methods on flame-made TiO2 were also investigated. High hydrogen production rates were attained with copper-containing photocatalysts, though their photoactivity decreased with increasing Cu loading, whereas the photocatalysts containing both Cu and Pt nanoparticles exhibit a bell-shaped photoactivity trend with increasing copper content, the highest hydrogen production rate being attained with the photocatalyst containing 0.05 wt% Cu.

Due to its ∼2.4 eV band gap, BiVO4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO3/BiVO4 heterojunction films, the electrons photoexcited in BiVO4 are injected into WO3, overcoming the lower charge carriers’ diffusion properties limiting the PEC performance of BiVO4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO4 excitation, a favorable electron transfer from photoexcited BiVO4 to WO3 occurs immediately after excitation and leads to an increase of the trapped holes’ lifetime in BiVO4. However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO4. PEC measurements reveal the implication of these wavelength-depen...

A bilayer WO3 photoelectrode was obtained by radio frequency (RF) plasma sputtering in a reactive 40% O-2/Ar atmosphere by depositing two successive WO3 coatings on a tungsten foil at two different total gas pressures (3 Pa and 1.7 Pa, respectively), followed by calcination at 600 degrees C. Two monolayer samples deposited at each of the two pressures and a bilayer sample deposited at inverted pressures were also prepared. Their photoelectrocatalytic (PEC) activity was evaluated by both Incident Photon-to-Current Efficiency (IPCE) measurements and separate evolution of H-2 and O-2 by water splitting in a two-compartment PEC cell. SEM analysis revealed that the photoanodes have a nanostructured porous double layer surmounting a columnar basement (Staffa-like morphology, after the name of the Scottish island). Mott-Schottky analysis showed that the single layer deposited at 3 Pa has a conduction flat band potential 0.1 V more positive than that deposited at 1.7 Pa. The equivalent n-n heterojunction at the interface of the double-layer creates a built-in electric field that facilitates the photopromoted electron transfer toward the lower lying conduction band material, while the columnar innermost layer introduces percolation paths for efficient electron transport toward the conductive tungsten foil. Both phenomena contribute to decrease the interfacial charge transfer resistance (R-ct) and lead up to a ca. 30% increase in the PEC performance compared to the monolayer and the inverted bilayer coatings and to a 93% faradaic efficiency, which is among the highest reported so far for WO3 photoanodes. Upon methanol addition an outstanding 4-fold photocurrent density increase up to 6.3 mA cm(-2) was attained over the bilayer WO3 photoanode, much larger than the usually observed current doubling effect.

Evolution of pure hydrogen and oxygen by photocatalytic water splitting was attained from the opposite sides of a composite Pt/Ti/TiO2 photoelectrode. The TiO2 films were prepared by radio frequency (RF)-Magnetron Sputtering at different deposition time ranging from 1 up to 8 h and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible-near infrared (UV-vis-NIR) diffuse reflectance spectroscopy. The photocatalytic activity was evaluated by incident photon to current efficiency (IPCE) measurements and by photocatalytic water splitting measurements in a two-compartment cell. The highest H2 production rate was attained with the photoelectrode prepared by 6 h-long TiO2 deposition thanks to its high content in the rutile polymorph, which is active under visible light. By contrast, the photoactivity dropped for longer deposition time, because of the increased probability of electron-hole recombination due to the longer electron transfer path.

Crystal 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.

The photocatalytic abatement of aqueous ammonia, the major nitrogen-containing compound in livestock manure, was investigated employing (i) a batch reactor equipped with an immersion UVA lamp, containing aqueous suspensions of different commercial TiO 2 powders and (ii) a 40 L prototype plug flow photo-reactor, suitable for the photocatalytic treatment of real swine and bovine manure, consisting of 9 vertical elements connected in series, internally coated with a TiO 2 film, each one centrally housing a UVA lamp. A preliminary systematic investigation performed with the first photo-reactor evidenced that ammonia conversion and the selectivity toward the main oxidation products (N 2 , NO 2 − and NO 3 − ) depend on the amount of dissolved O 2 , on pH and on the photocatalyst's amount and structural features. Extremely promising results, in terms of both ammonia conversion (up to the 88%) and selectivity to nitrogen gaseous species (99%), were achieved when the prototype photo-reactor was fed with suitably pre-treated manure. The TiO 2 -based photocatalytic treatment can thus be considered an effective remediation technology for the abatement of nitrogen-containing pollutants in surface and groundwater, originating from large-scale animal husbandries.

The importance of the choice of a suitable substrate as supporting material for photoactive TiO2, either in the form of powders or thin films or in photoactive paints, is frequently disregarded. In this paper four different supports (stainless steel, sand-blasted stainless steel, Teflon and glass) are object of investigation. The final aim is to verify the presence of interactions between the photocatalyst (AEROXIDE® TiO2 P25 by Evonik Degussa Corporation) and the support, directly involved in the photocatalytic activity in the NOx abatement. The characterization results have been correlated with the photoactivity of the different samples. In particular, a coating of about 6–9 μm seems to allow a photocatalytic result free from any positive or negative interference with the supporting material, therefore giving reliable results about the photoactivity of the TiO2 under investigation.

Commercial TiO(2) samples with different phase composition and surface area were tested as photocatalysts in the photoinduced reduction of Cr(VI) in aqueous suspensions at pH 3.7 under UV-visible light irradiation. This reaction was also coupled with the simultaneous photocatalytic oxidation of the pollutant azo dye Acid Orange 8 (AO8) and of formic acid, acting as hole scavengers. The co-presence of oxidizable and reducible species ensured better separation of photogenerated charge carriers, resulting in a higher rate of both organics' oxidation and Cr(VI) reduction, especially in the case of high surface area anatase TiO(2), having the strongest affinity for Cr(VI) and AO8, as demonstrated by competitive adsorption tests. The effects on Cr(VI) photocatalytic reduction of gold nanoparticles photodeposited on TiO(2) and of the Au loading were also investigated, aiming at ascertaining if this noble metal plays a role in the electron transfer processes involved in Cr(VI) reduction.

The photocatalytic reforming of methanol was investigated kinetically under steady conditions as a function of the methanol-to-water partial pressure ratio in the gas mixture fed to the photoreactor. Similar results were obtained with two TiO2-based photocatalysts, one containing platinum nanoparticles and prepared by flame spray pyrolysis and the other prepared by the deposition of preformed Au nanoparticles on P25 TiO2. Methanol oxidation proceeds on the photocatalyst surface up to CO2 through the formation of formaldehyde and formic acid as intermediate species. The steady-state formaldehyde, formic acid, and carbon dioxide production rates, plotted vs. the methanol molar fraction in the aqueous solution generating the gaseous reaction mixture, were successfully fitted on the basis of a reaction scheme, in which each elementary oxidation step occurs through either an indirect ·OH radical-mediated path, or a hole-mediated direct path, or a water-assisted path, when oxidation occurs on titania surface sites far from noble metal nanoparticles. H2O/D2O isotopic-exchange experiments allow a clear distinction between the direct and the indirect oxidation paths and fully support the proposed reaction scheme.

The effect of the crystalline phase of TiO 2 (anatase, rutile and brookite) on its photocatalytic activity in hydrogen production from methanol-water vapours has been investigated by testing a series of both home-made and commercial TiO 2 photocatalysts, either bare or surface-modified by deposition of a fixed amount, i.e. 1 wt%, of platinum as co-catalyst. For all of the TiO 2 samples the rate of hydrogen production increased by one order of magnitude upon Pt deposition, because of the ability of Pt to enhance the separation of photoproduced electron-hole pairs. Under irradiation in the 350-450 nm wavelength range, brookite and anatase showed similar photoactivities, both superior to that of rutile. By contrast, rutile, possessing a narrower band gap, was active also under visible light (λ > 400 nm), whereas no hydrogen evolution was observed with anatase and brookite under such conditions. Surface area proved to be a key parameter, strongly influencing photoactivity. However, as the particle size became ultra-small, the semiconductor absorption edge was blue-shifted because of size quantisation effects, with a consequent decrease in hydrogen production rate due to the smaller portion of incident photons absorbed by the photocatalyst. © The Royal Society of Chemistry and Owner Societies 2011.

The photocatalytic production of hydrogen from aqueous systems is reviewed, stressing the very promising features of the process as an environmentally friendly, perfectly renewable way to produce hydrogen, the ideal fuel for the future. Starting with a brief historical background, the most recent achievements in the field on the basis of both relevant patents and published literature, are discussed here, with particular emphasis on the development of innovative materials able to capture a larger portion of the solar spectrum with respect to traditional photocatalytic materials, and on the different setups and devices which have been developed and tested.

The photocatalytic production of hydrogen by methanol steam reforming was studied over a series of pristine or noble metal (Ag, Au, Au–Ag alloy and Pt) – modified TiO2 photocatalysts, synthesised by flame spray pyrolysis or by the deposition of preformed noble metal nanoparticles on TiO2. A closed recirculation apparatus was employed, with the photocatalyst bed continuously fed with methanol/water vapours. Methanol underwent oxidation up to CO2 through the formation of formaldehyde and formic acid. Carbon monoxide, methane, methyl formate, acetaldehyde and dimethyl ether were identified as side products. Hydrogen evolved at constant rate, which significantly increased upon noble metal addition, Pt being the most effective co-catalyst, followed by gold and silver, according to their work function values. A systematic investigation into the effects of the inlet gas composition gave valuable information on the prevailing reaction paths and on the conditions of process optimisation, also in terms of distribution of CH3OH oxidation products.

Anatase–rutile and anatase–brookite–rutile composite nanocrystals were synthesized by a controlled sol–gel reaction followed by hydrothermal growth and by mechanically mixing pure crystalline phase precursors, respectively. Their physicochemical and photocatalytic properties were investigated in comparison with those of several home-made and commercial pure anatase, rutile and mixed phase TiO 2 samples. In particular, the phase composition and the crystallite size were determined by X-ray diffraction measurements. The photocatalytic degradation of the azo dye Acid Red 1 (AR1) and of formic acid (FA) in aqueous suspension were employed as test reactions. Hydrogen peroxide evolution, the main reductive process occurring in parallel, was also monitored during the runs. The investigated photocatalysts exhibit different photoactivity scales towards the two organic substrates, depending on the prevailing photodegradation path. High surface area anatase samples were particularly active in FA degradation, principally occurring through direct interaction with photoproduced valence band holes, whereas rutile samples, even possessing high surface areas, but exhibiting poor wettability, were scarcely active. A good linear correlation was found between H 2 O 2 evolution and the rate of AR1 photodegradation on the investigated series of photocatalysts, whereas no H 2 O 2 was detected during FA mineralization, apart in the case of a low surface area anatase sample, whose peculiar photocatalytic properties were ascribed to the presence of Ti 3+ ions in its structure.

The photocatalytic activity of thin, nanostructured films of titanium dioxide, synthesized by supersonic cluster beam deposition (SCBD) from the gas phase, has been investigated employing the photodegradation of salicylic acid as test reaction. Because of the low deposition energy, the so-deposited highly porous TiO2 films are composed of nanoparticles maintaining their original properties in the film, which can be fully controlled by tuning the deposition and post-deposition treatment conditions. A systematic investigation on the evolution of light absorption properties and photoactivity of the films in relation to their morphology, determined by AFM analysis, and phase composition, determined by Raman spectroscopy, has been performed. The absorption and photocatalytic activity of the nanostructured films in the visible region could be enhanced either through post-deposition annealing treatment in ammonia containing atmosphere or employing mild oxidation conditions, followed by annealing in N2 at 600 °C.

TiO2 and 1% Au/TiO2 powders, synthesised by flame spray pyrolysis and possessing high specific surface area (106 m2 g−1) and anatase content (ca. 90%), were tested as photocatalysts in hydrogen production from methanol photoreforming, employing a closed recirculation apparatus. The irradiated photoreactor consisted either in a quartz vessel containing an aqueous suspension of the photocatalyst, or in a newly set-up Plexiglas cell, containing the same amount of catalyst immobilised on quartz grains, which was continuously fed with methanol/water vapours. The gas-phase composition during irradiation was analysed by gas chromatography and quadrupolar mass spectrometry, which allowed the identification of formaldehyde as the only intermediate species. The photocatalytic activity of the flame-made materials was higher than that of commercial Degussa P25 TiO2 and of 1% Au/P25 obtained via deposition of preformed gold nanoparticles on P25. In particular, a 30 times higher photocatalytic hydrogen production was obtained upon gold addition to TiO2. Furthermore, a 30% higher reaction rate was attained with the vapour phase reactor, i.e. in the absence of liquid-phase mass transfer rate limitations, ensuring the production of up to 10.2 mmol of H 2 h - 1 g cat - 1 , with an apparent photon efficiency of 6.3%.

A set of titanium dioxide and gold-modified titanium dioxide samples were prepared by flame spray pyrolysis (FP) and characterized by BET, XRD, HRTEM and UV–vis reflectance analysis. Their photocatalytic activity in hydrogen production in water suspension, either from water photosplitting or from methanol photoreforming, was tested in an expressly set up, closed recirculation laboratory scale photoreactor and compared to those of commercial TiO2 samples, including Degussa P25, pure rutile and pure anatase. The rate of hydrogen evolution ( r H 2 ) increased with increasing the anatase content, pure anatase being the most active photocatalyst. Surface area and crystallinity, both key properties of photocatalysts, can be tuned up by properly setting FP operation parameters, including the selection of the organic solvent/fuel. In particular, FP-made TiO2 prepared from a xylene solution showed more active than P25. Finally, r H 2 increased by one order of magnitude in water photosplitting and by ca. 30 times in methanol photoreforming upon 1% gold addition on TiO2.

The rate of 1,4-dichlorobenzene (1,4-DCB) degradation and mineralization in the aqueous phase was investigated either under direct photolysis or photocatalysis in the presence of commercial or sol-gel synthesized TiO2, or under sonolysis at 20 kHz with different power inputs. Two lamps, both emitting in the 340-400 nm wavelength range with different energy, were employed as irradiation sources. Photocatalysis ensured faster removal of 1,4-DCB with respect to sonolysis and direct photolysis. The highest degradation and mineralization rate was attained with the combined use of photocatalysis and sonolysis, i.e. under sonophotocatalytic conditions. The efficiency of the employed advanced oxidation techniques in 1,4-DCB degradation is discussed also in relation to their energy consumption, which might be decisive for their practical application.

The effects of TiO

We introduce the use of pure molten ortho-phosphoric acid (o-H3PO4) as an electrolyte for selforganizing electrochemistry. This electrolyte allows for the formation of self-organized oxide architectures (one-dimensional nanotubes, nanochannels, nanopores) on metals such as tungsten that up to now were regarded as very difficult to grow self-ordered anodic oxide structures. In this work, we show particularly the fabrication of thick, vertically aligned tungsten oxide nanochannel layers, with pore diameter of ca. 10 nm, and illustrate their potential use in some typical applications.

The photocatalytic degradation of formic acid (FA) and benzoic acid (BA), chosen as model organic molecules with acidic properties, was investigated in TiO2 and ZnO water suspensions under different experimental conditions. Hydrogen peroxide evolution, formed through a reductive pathway started by conduction band electrons, was also simultaneously monitored during the degradation runs. The effect of different initial amounts of substrates and the dependence of the reaction rate on the initial pH of the TiO2 suspensions was interpreted under the light of a pseudo-steady state Langmuir–Hinshelwood rate form and of the electrostatic interactions occurring at the water–semiconductor interface. ZnO appeared a more effective photocatalyst than TiO2 for BA, but not for FA degradation. A much higher amount of hydrogen peroxide was detected in ZnO irradiated suspensions, both in the presence and in the absence of the substrates, mainly because of its lower photocatalytic decomposition rate on such oxide. The rate of hydrogen peroxide evolution during the photocatalytic oxidation of BA on TiO2 could be related to the rate of the oxidation process, while H2O2 could not be detected during the photocatalytic degradation of FA on this oxide, mainly because of the reduced shielding ability of this substrate.

The mechanism of atrazine degradation in aqueous phase was investigated under sonolysis at 20 kHz, ozonation, photolysis at 254 nm and photocatalysis in the presence of TiO2, employed either separately or in combination. Ozonation and photocatalysis induced atrazine de-alkylation, followed by slower de-chlorination, while direct photolysis at 254 nm produced very efficient de-chlorination. Simultaneous sonolysis had beneficial effects on ozonation and photocatalysis, especially by increasing the rate of photocatalytic de-alkylation, and no effect on the unimolecular photolytic de-chlorination of atrazine. Although complete atrazine mineralization could not be attained, because of the stability of the s-triazine ring toward oxidation, atrazine degradation and overall detoxification, as related to the disappearance of chlorinated by-products, proceeded at the highest rate when photolysis at 254 nm was combined with ozonation.

The effect of TiO2 surface fluorination on the hydrogen peroxide evolution occurring in photocatalytic runs was investigated employing the azo dye Acid Red 1 (AR1) and two model organic molecules with acidic properties, i.e. formic acid (FA) and benzoic acid (BA), as substrates of oxidative degradation. While AR1 and BA photocatalytic degradation on fluorinated titanium dioxide (F–TiO2) was markedly faster than on unmodified TiO2, because of enhanced hydroxyl radical formation, H2O2 concentration during the photodegradation of both substrates on F–TiO2 was lower, possibly because of the reduced rate of interfacial electron transfer. By contrast, FA underwent slower photocatalytic degradation on F–TiO2, but, at the same time, hydrogen peroxide concentration was relatively high, while no H2O2 could be detected during FA photodegradation on unmodified TiO2. Photocatalytic runs in the presence of the nitrate anion, able to react with the CO2˙− species produced from FA oxidation, but not with conduction band electrons, demonstrated that CO2˙− plays a relevant role in H2O2 formation during FA degradation on F–TiO2. In fact, surface fluoride, having a shielding effect at the semiconductor–water interface, not only inhibits the photocatalytic decomposition of H2O2, but also favours CO2˙− desorption and reaction with dissolved O2, generating H2O2. By contrast, CO2˙− mainly gives electron transfer to the conduction band of naked TiO2 and surface reduction of the photocatalytically produced H2O2.

Summary: Surface modification induced on poly(ethylene terephthalate) (PET) fibers by cold SF6 plasma treatment has been investigated systematically as a function of plasma device parameters. The observed wettability modifications of fibers plasma-treated under different operating conditions were correlated to their dyeability modifications and to the changes in surface chemical composition, determined by X-ray Photoelectron Spectroscopy (XPS), and topography, investigated by atomic force microscopy (AFM). Optical emission spectra from the SF6 plasma at different pressures gave information on its content of fluorine atoms. A striking transition was observed between the increased hydrophilicity and high dyeability, imparted by plasma treatment at low pressure (

Photocatalysis on TiO2, with irradiation wavelength λirr=254 nm or 315 nm

FTIR and microcalorimetric analysis of adsorbed pyridine has been employed for the characterisation of a set of Fe-MFI zeolite catalysts with different Si/Al and Si/Fe ratios, used for the gas phase hydroxylation of benzene to phenol by N2O. Catalysts behaviour in terms of activity and deactivaton rate is discussed in relation to the nature, concentration and strength of their surface acid sites. Surface acidity, though not involved directly in the hydroxylation reaction, plays a major role in determining catalyst lifetime. Coke formation, leading to catalyst deactivation, is triggered by further undesired reactions of phenol and is favoured by the strong adsorption of the latter on Lewis acid sites, restraining its diffusion out of the zeolite pores.

Some selective cold plasma processing modify specific surface properties of textile polymeric materials such as their dyeability, wettability and hydrorepellence. To correlate the sample surface changes with the acquired surface properties allows one to obtain information on the chemical and physical processing involved in plasma treatment. In this work, atomic force microscopy (AFM) has been applied to investigate the morphological and topographical surface modifications induced by RF cold plasma processing of poly(ethyleneterephthalate) (PET) fabrics. Rms surface roughness and surface area of the samples are measured before and after the treatments. The morphology changes have been analysed as a function of the treatment time and air gas pressure. Measurements have been performed also using plasmas produced by different gases such as He, Ar, SF6, and CF4. The PET shows different behaviour with different gas plasmas. In the case of air, He and Ar gases the sample surface modifications seem to be mainly due to etching effects, while the fluorine atoms grafting probably is responsible for surface rearrangement process using SF6 and CF4 gases. As a consequence different surface properties are produced in the plasma treated samples.

Some selective plasma treatments are described, aiming at modifying specific surface properties of textile polymeric materials, such as their hydrorepellence and dyeability. The prevailing plasma–polymer interactions were identified by correlating the physico-chemical modification of treated polymer surfaces to the characteristics of the plasma sources.

The degradation of 2-chlorophenol and of the two azo dyes acid orange 8 and acid red 1 in aqueous solution was investigated kinetically under sonolysis at 20 kHz and under photocatalysis in the presence of titanium dioxide particles, as well as under simultaneous sonolysis and photocatalysis, i.e. sonophotocatalysis. The influence on the degradation and mineralisation rates of the initial substrate concentration and of the photocatalyst amount was systematically investigated to ascertain the origin of the synergistic effect observed between the two degradation techniques. The evolution of hydrogen peroxide during kinetic runs was also monitored. Small amounts of Fe(III) were found to affect both the adsorption equilibria on the semiconductor and the degradation paths. Ultrasound may modify the rate of photocatalytic degradation by promoting the deaggregation of the photocatalyst, by inducing the desorption of organic substrates and degradation intermediates from the photocatalyst surface and, mainly, by favouring the scission of the photocatalytically and sonolytically produced H(2)O(2), with a consequent increase of oxidising species in the aqueous phase.

The surface chemical and physical modifications of poly(ethylene terephthalate) (PET) fibers induced by radiofrequency air plasma treatments were correlated with the characteristics of the discharge parameters and the chemical composition of the plasma itself, to identify the plasma-induced surface processes prevailing under different operating conditions. Treated polymer surfaces were characterized by water droplet absorption time measurements and XPS analysis, as a function of the aging time in different media, and by AFM analysis. They exhibited a remarkable increase in hydrophilicity, accompanied by extensive etching and by the implantation of both oxygen- and nitrogen-containing polar groups. Etching was mainly a consequence of ion bombardment, yielding low molecular weight, water soluble oxidation products, while surface chemical modifications were mainly due to the action of neutral species on the plasma-activated polymer surface. (C) 2003 Elsevier Science B.V. All rights reserved.

Cathodoluminescence spectroscopy is profitably exploited to study energy transfer mechanisms in Au and Pt/black TiO2 heterostructures. While Pt nanoparticles absorb light in the UV region, Au nanoparticles absorb light by surface plasmon resonance and interband transitions, both of them occurring in the visible region. The intra-bandgap states (oxygen vacancies) of black TiO2 play a key role in promoting both hot electron transfer and plasmonic resonant energy transfer from Au nanoparticles to the TiO2 semiconductor with a consequent photo-catalytic H2 production increase. An innovative criterion is introduced for the design of plasmonic composites with increased efficiency under visible light.

Aiming at understanding how plasmonic reactions depend on important parameters such as metal loading and strong metal-support interaction (SMSI), we report the plasmonic photodegradation of formic acid (FA) under green LED irradiation employing three TiO2 supports (stoichiometric TiO2, N-doped TiO2, black TiO2) modified with Au nanoparticles (NPs) 3-6 nm in size. The rate of FA photo-oxidation follows different trends depending on Au loading for stoichiometric and doped Au/TiO2 materials. In the first case, the only contribution of hot electron transfer produces a volcano-shaped curve of photoreaction rates with increasing the Au loading. When TiO2 contains intra-bandgap states the photoactivity increases linearly with the Au NPs amount, thanks to the concomitant enhancement produced by hot electron transfer and plasmonic resonant energy transfer (PRET). The role of PRET is supported by Finite-Difference Time-Domain simulations, which show that the increase of both A u NPs inter-distance and of SMSI enhances the probability of charge carrier generation at the Au/TiO2 interface.

Photocatalysis and sonolysis exhibit synergistic effects in the degradation of organic molecules in aqueous suspension, when low ultrasound frequency (i.e. 20 kHz) is employed. The degradation of the azo dye Acid Orange 8 in aqueous suspensions was systematically evaluated under sonolysis, photocatalysis and sonophotocatalysis as a function of dye concentration, amount and type of photocatalyst (TiO2 or ZnO) and catalase addition, in terms of pseudo-first-order degradation rate constants. The evolution of hydrogen peroxide was also monitored. Synergistic effects of the combination of ultrasound and photocatalysis should mainly involve the aqueous phase and be due to an increased concentration of reactive radicals, consequent to the action of ultrasound on the peroxide species produced by both photocatalysis and sonolysis.

A study was made of the iron species dislodged from the tetrahedral lattice position by thermal treatments in four Fe silicalite samples with Si/Fe ratios of 25, 50, 90, and 150. The last two samples have a sufficiently low iron concentration to be considered true catalysts (i.e., having Fe dilutions as low as that used in the industrial conversion of benzene to phenol (Si/Fe>80)) in partial oxidation reactions. A systematic spectroscopic study is presented in order to obtain a global picture of a system whose complexity can be understood by assuming the formation of a wide variety of transient coordinatively unsaturated iron species, with different oxidation states, which ultimately lead to grafted or anchored isolated and/or clustered species by interaction with residual tetrahedral Si(OH)Fe, defective SiOH groups, or strained SiOSi bridges of the hosting matrix. The structure characterization was obtained by means of the parallel use of IR, X-ray absorption near-edge spectroscopy, and electron paramagnetic resonance techniques, before, during, and after interaction with CO, N2O, and NO probe molecules. This approach was applied to samples characterized by different iron content, activation temperature, and redox treatments. This allowed us to throw light onto structure, oxidation state, and mutual interconversion of a very complex family of extraframework iron species. Oxidation with O2 or N2O led to the formation of strongly bonded oxygen species. The relation between these species and the so-called α-oxygen species, claimed as the active sites for the hydroxylation of benzene to phenol by N2O, is discussed.

Water molecules retained in native cellulose gels obtained from Acetobacter xylinym (AX) were displaced by poly(ethylene glycol)s (PEG) of different molecular weight. The so obtained native cellulose/PEG material, characterized in film form by differential scanning calorimetry, dynamic mechanical thermal analysis and wide angle X-ray scattering, revealed that strong interactions occur between PEG and cellulose and that the polymer mixture is in the rubbery state at ambient temperature. Moreover, it could be dyed in supercritical carbon dioxide by disperse dyes, thus exhibiting typically lipophilic properties and suitability to be employed as a bio-compatible support for lipophilic active species.

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.

Silk samples, treated in an appositely set-up radio frequency SF6 plasma reactor under different operation conditions, were characterized by XPS, EPR, DSC, XRD, ATR analyses and water contact angle measurements, also as a function of storage time after the treatment. Efficient attachment of fluorine atoms on the polymer surface occurred during the plasma treatment, imparting water repellence to it. Also the percentage of surface oxygen increased after the treatment, partially as a consequence of radical scavenging by molecular oxygen and the formation of peroxides. An increase in silk crystallinity during the treatment seems to contribute to ensuring durable water repellence properties.

This research concerns the development of a SF6 RF discharge at low pressure in a small reactor for industrial applications. The plasma is produced in the pressure range 0.05-1 mbar by a RF supply. The pumping system sustains a flowrate of about 50 cm s-1, with residence time in the discharge of about 0.2 s at a pressure of 0.1 mbar. The discharge parameters were measured at a low operation power. Measurements were performed by means of movable electrostatic probes and a photodiode. Particular care in the analysis of the data proved to be necessary due to the presence of a substantial amount of negative ions. The reactor has been employed for textile treatment in order to modify the surface properties of the fibres. Favourable operating conditions leading to an improved hydrophobicity of the textiles were achieved.

Poly(ethylene terephthalate) (PET) and cotton fibres, treated in an appositely set up RF SF6 plasma reactor under different operating conditions, were characterised by XPS, EPR, DSC, XRD, ATR analyses, water contact angle and water droplet roll-off angle measurements. The ageing of plasma-treated samples was also investigated under different post-treatment conditions. Plasma treatment led to efficient implantation of fluorine atoms on the surface of both polymers; this resulted in water repellence without altering the bulk properties of the polymers. The radical species formed in the plasma-activated polymer surface were involved in its fluorination and in the subsequent uptake of atmospheric oxygen. Surface reorganisation of polymer segments, tending to reduce the interfacial energy between the polymer and the phase in contact with it, induced the surface modifications observed under ageing and in samples plasma-treated several times. An increase in the depth of the fluorinated layer, leading to outstanding stable hydrorepellence, was achieved by repeated SF6 plasma treatments, followed by surface rearrangements favoured by swelling.

Innovative neutralizing and strengthening treatments for aged acidic paper have been developed, based on the use of supercritical carbon dioxide (CO2SCF) as solvent system. After treatment with the non toxic neutralizing agent CaCO3 in CO2SCF, acidic papers exhibited a pH increase of water extracts, the creation of an alkaline reserve and a decrease in the rate of artificial aging, while mechanical tensile properties of aged acidic papers improved after treatment with catechol both simply dissolved in ethanol or in CO2SCF in the presence of ethanol as co-solvent.