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In the present work, two H 2 evolution photocatalysts were prepared by employing two different oxides, TiO 2 and zirconium titanate (ZrTiO 4 ), as the support of various copper phases. For both the supports the same Cu loading (0.5% w/w) was adopted, but two different impregnation procedures have been followed, leading to different forms of Cu in the final composite material that are: (i) Cu(II) species dispersed on the oxide surface and (ii) Cu 2 O particles dispersed on the oxide surface. The present paper based on the parallel use of photocatalytic test and spectroscopic analysis performed in catalytic conditions illustrates the evolution of photocatalytic systems occurring during the H 2 evolution reaction tests, pointing out that the as-prepared materials represent a pre-catalyst and they are modified during irradiation leading to the real working systems different from the starting ones. The herein presented spectroscopic analysis aims to contribute to the living debate on the oxidation state of copper in mixed Cu/oxide materials and on its role in hydrogen evolution under photocatalytic conditions.

The accumulation of nitrogen compounds represents a pivotal problem in the management of fish culture. Several methods were investigated in the last decades for treatment of waste waters, and the use of photocatalytic materials has received increasing attention. The photocatalytic degradation (PCD) process with titanium dioxide (TiO 2 ) represents the most promising single-step method to promote the removal of nitrogen compounds from water. The present study compares for the first time the effects on fish culture of a classical mechanical, biological, and ultraviolet purification system to a TiO 2 -PCD one, with particular emphasis on water chemistry and on physiological responses in zebrafish. Fish were exposed for 14 days to the two different purification systems and samplings were performed 7 and 14 days after the experiment beginning. The photocatalytic system showed excellent efficiency in removing nitrogen compounds from water with no significant adverse effects on fish. Physiological analysis on fish samples included histological analysis of gills and gut, TUNEL assay of the gills, and real-time polymerase chain reaction (liver) of genes involved in stress response and growth. No significant biological alterations were detectable on the cultured fish.

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.

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.

We introduce the use of pure molten ortho-phosphoric acid (o-H3PO4) as an electrolyte for self-organizing 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.

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 photocatalytic H2 production increase. An innovative criterion is introduced for the design of plasmonic composites with increased efficiency under visible light.

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., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A little dopey: Ta-doped titania (TiO2) nanotube (NT) arrays can be grown by electrochemical anodization onto low-Ta-concentration (0.03-0.4 at % Ta) Ti-Ta alloys. Under optimized conditions (0.1 at % Ta, annealing at 650 °C and 7 μm thickness), Ta-doped TiO2 NT arrays show a significantly enhanced activity in photoelectrochemical water splitting under simulated sunlight conditions (see figure)., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

The importance of the choice of a suitable substrate as supporting material for photoactive TiO(2), 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(®) TiO(2) P25 by Evonik Degussa Corporation) and the support, directly involved in the photocatalytic activity in the NO(x) 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 TiO(2) under investigation., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Two series of doped titanium dioxide samples (S-TiO(2) and F-TiO(2)) were prepared by the sol-gel method in the presence of different amounts of dopant source (thiourea and NH(4)F, respectively), followed by calcination at 500, 600 or 700 °C, and characterised by BET, UV-vis absorption, XPS, HRTEM, XRD and EPR analyses. Reference undoped materials were prepared by the same synthetic procedure. Their photocatalytic activity under visible light was investigated employing the photocatalytic degradation of formic acid in aqueous suspension as test reaction. S-doped TiO(2) showed a photocatalytic activity quite similar to that of undoped materials. In this regard, the insertion of S, characterised by a relatively large ionic radius, into the TiO(2) crystalline structure appears rather difficult, as confirmed by XPS analysis. On the contrary, moderate F doping was beneficial in increasing the rate of formic acid photocatalytic degradation, especially for photocatalysts calcined at high temperature, consisting of highly crystalline pure anatase, in which the rate of detrimental charge carrier recombination was reduced. For both series of doped materials, high doping levels appear to limit the semiconductor photoactivity, probably due to the formation of a progressively increasing number of charge recombination centres. The EPR characterisation of the investigated doped TiO(2) samples evidenced the presence of nitrogen containing species (nitric oxide radical encapsulated in micro-void, with no photoactivity, and N(b)˙ species, active in visible light sensitisation) and of titanium reduced centres Ti(3+), due to charge imbalance consequent to dopant introduction in the TiO(2) lattice either in anionic (F(-)) or in cationic form (S(6+))., (© The Royal Society of Chemistry and Owner Societies 2011)

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 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 degradation of methyl tert-butyl ether (MTBE) in water was kinetically investigated in a O(2)/Ar 80:20 atmosphere employing either sonolysis at 20 kHz, or photocatalysis on TiO(2) (with 315 nm< lambda(irr) <400 nm), or simultaneous sonolysis and photocatalysis (i.e. sonophotocatalysis), as degradation techniques. In all investigated conditions, MTBE concentration decreased according to a first order rate law; under ultrasound the degradation rate was stirring-dependent. The time profile of the reaction intermediates gave information on the reaction paths prevailing under the different experimental conditions. The energy consumption of the employed degradation techniques was also evaluated, which might be decisive for their practical application.

The time-resolved laser-induced fluorescence of a series of polycyclic aromatic compounds (PAHs) and mixtures of these latter in aqueous solution was measured by means of an apparatus equipped with optical fibers, which allows their real time in situ monitoring. The potential of such spectroscopic technique, yielding 4-way fluorescence data arrays, together with the application of multi-way models to the matricized data, was tested for the resolution of complex aqueous mixtures containing low concentrations of PAHs, as typical fluorescent pollutants in aquatic systems. PARAllel FACtors analysis was employed for the qualitative resolution of PAHs mixtures and for calculating the fluorescence lifetimes of single PAHs; n-way partial least squares analysis was applied for evaluating the concentration of the single PAHs in the aqueous mixtures.