The use of nanostructured metal oxides as active electrode components of electrochemical energy storage devices provide benefits both from capacitive effects and from the short path lengths for faradaic processes, both of which becoming increasingly important at nanoscale dimensions. In this work, we analyze the capacitive and faradaic contributions to energy storage for Fe3O4 at two different nanoscale sizes in neutral aqueous media. The understanding of the contributions of each one of the effects at different sizes for different materials may provide clues for the design of devices with both high power and high energy density.

TiO2 anatase nanocrystals were surface modified by deposition of V(V) species. The starting amorphous TiO2 nanoparticles were prepared by hydrolytic processing of TiCl4-derived solutions. A V-containing solution, prepared from methanolysis of VCl4, was added to the TiO2 suspension before a solvothermal crystallization step in oleic acid. The resulting materials were characterized by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared, Raman, and magic angle spinning solid-state V-51 nuclear magnetic resonance spectroscopy (MAS NMR). It was shown that in the as-prepared nanocrystals V was deposited onto the surface, forming Ti-O-V bonds. After heat treatment at 400 degrees C, TEM/electron energy loss spectroscopy and MAS NMR showed that V was partially inserted in the anatase lattice, while the surface was covered with a denser V-O-V network. After heating at 500 degrees C, V2O5 phase separation occurred, further evidenced by thermal analyses. The 400 degrees C nanocrystals had a mean size of about 5 nm, proving the successful synthesis of the colloidal counterpart of the well-known TiO2-V2O5 catalytic system. Hence, and also due to the complete elimination of organic residuals, this sample was used for processing chemoresistive devices. Ethanol was used as a test gas, and the results showed the beneficial effect of the V surface modification of anatase, with a response improvement up to almost 2 orders of magnitude with respect to pure TiO2. Moreover, simple comparison of the temperature dependence of the response clearly evidenced the catalytic effect of V addition.

Metal ferrite (MFe2O4, with M = Fe, Mn, Co Ni Cu, Zn) nanoparticles were synthesized by processing metal oxide sols in a coordinating environment The sols were prepared by forced hydrolysis of the starting metal nitrates, in the presence of acetylacetone for avoiding precipitation Two different processing routes were investigated In the first, the sol was injected into a hot (160 degrees C) solution of dodecylamine in tetradecene In the second route the Injection environment was constituted by pure dodec ylamine heated at the same temperature The precipitate from the first route was heat-treated in air at various temperatures, from 200 to 500 degrees C The redispersible nanoparticles from the second route were annealed in oleylamine at temperatures up to 220 degrees C In the first case, crystallization was obtained only after heat-treatment at 500 degrees C, while 220 degrees C was sufficient for crystallizing 1 he nanoparticles dispersed in oleylamine The samples from the two routes were investigated by X-ray diffraction and transmission electron microscopy/electron energy loss spectroscopy in the case system of NiFe2O4 The product from the first route, after heating at 200 degrees C, was a disordered material, with a broad size distribution of aggregates and Ni depletion regions The product from the second route was constituted by discrete nanoparticles with the correct cation stoichiometry The interpretation of the results allowed concluding that obtaining simple structural reorganization in nanosized volumes is a key factor for crystallization under mild conditions.

TiO2 and TiO2-V-2 O-5 nanocrystals were prepared by coupling sol-gel and solvothermal methods, followed by heat treatment at 400 degrees C, after which the nanocrystal mean size was still about 5 nm. The materials were used to process chemoresistive sensors, which were tested to ethanol and acetone, with concentrations ranging from 100 to 500 ppm and from 25 to 100 ppm, respectively. The sensing data evidenced that the surface deposition of V2O5 onto the anatase TiO2 nanocrystals enhanced the sensor response up to almost two orders of magnitude for both gases. Moreover, the sensors behavior was completely inverted: with TiO2-V2O5, the highest responses were obtained at the lowest operating temperatures, contrarily to pure TiO2, which required very high operating temperatures. The comparison of the sensing data allowed concluding that the V2O5 deposition effect could be interpreted as a catalytic contribution, in terms of lowered activation energies of the involved reactions and more favored gas adsorption at lower operating temperatures with respect to pure TiO2. (C) 2014 Elsevier B.V. All rights reserved.

WO3 precursor solutions were prepared by methanolysis of WCl6 in presence of acetylacetone as a stabilizer. Chromium addition was achieved by mixing Cr 2-ethylhexanoate with the pure solutions, with Cr: W atomic concentrations ranging from 2% to 22%. Powders were prepared by drying the solutions and heat-treating the product up to 700 degrees C. After heat-treating at 400 degrees C, crystalline WO3 was obtained, and X-ray diffraction and Transmission Electron Microscopy showed that the powders were constituted by a mixture of the WO3 monoclinic and triclinic crystallographic phases. The Cr-modified samples, with a Cr concentration of at least 5%, presented the additional phase Cr2WO6. Structural investigations suggested that this phase was favored instead of chromium oxides due to the incorporation of Cr in the WO3 lattice in interstitial position. The sensing tests towards ammonia gas, in concentrations ranging from 50 to 500 ppm, showed that, up to 5% concentration, Cr addition is beneficial in lowering the best operating temperatures and/or improving the response with respect to the pure powders. For higher Cr concentrations, the response severely decays. This result was interpreted in terms of the Cr2WO6 grains and of the influence of lowered concentration of interstitial Cr on the oxygen vacancies.

Breathanalysishasapowerfulpotentialfordiseasediagnosticsandmetabolicstatusmonitoring.Asol-gelSnOz­basedmicromachinedsensorarraywasdevelopedandtestedforpotentialapplicationinbreathanalysis.Asuitablebreathsamplingsystemwasusedtosamplethealveolarairvolumefromtheairvolumeofoneexpiration.Breathtestsonalveolarairsampledbysomevolunteers,i.e.smokersandnonsmokersindividuals,werecarried out.PrincipalComponentAnalysisappliedtogassensorresponsesshowedgoodpropertiesofdiscriminationbetweensmokersandnonsmokersindividuals.

Mesoporous phases of ceria (CeO2) and ceria-zirconia solid solutions up to 50% of Zr have been synthesized using hard template method. The structures of the obtained metal oxides replicas correspond to the chosen structures of the KIT-6 and SBA-15 silica. This method allows obtaining materials with a uniform and homogenous porous size distribution as replica of the used nanotemplate. This structure facilitates the interaction with the gas molecules, their diffusivity inside the material and the porous size control. Obtained replicas were analysed using a variety of characterization techniques. TEM results reveal successful formation of the expected structures which were also supported by BET measurements. Replicas obtained applying SBA-15 and KIT-6 nanotemplates present similar behaviour although KIT-6 shows a slightly higher (about 5%) active surface with values in the range of 125 m(2)/g after thermal annealing. XRD and Raman spectra confirm formation of solid solutions with cubic structure up to 20% of zirconium above which, formation of tetragonal phase was observed. Functionally, besides their high active surface, these ceria-zirconia solid solutions show significant improvement in their oxygen storage capacity (OSC). In comparison with pure mesoporous ceria, it has been found that due to the introduction of zirconium even for a few percentage of zirconium (5%) the OSC increases (more than 30 times) which is attributed to the presence of substitutional zirconium in the ceria lattice. (C) 2011 Elsevier B.V. All rights reserved.

WO3 thin films were prepared by spin-coating methanol solutions of a tungsten chloromethoxide, and easily modified with Cr by the addition of Cr 2-ethylhexanoate. The films were heat-treated up to 700 degrees C, and characterized by X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Electron Energy Loss spectroscopy. The film morphology was rough and porous, not depending on Cr presence, while their structure was constituted by packed spheroidal or elongated dense structures, giving rise to the peculiar film surface morphology. Cr was distributed in the film structure without phase separations, up to as high as 5% Cr atomic concentration.

In this paper we report on optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, Fe2O3) as a function of temperature in the range 25500 °C, in order to study the optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in concentrated solar power (CSP).

TiO2 nanocrystals were prepared by solvothermal treatment in oleic acid at 250 degrees C of amorphous TiO2 nanoparticles. The latter were prepared by sol-gel processing in dodecylamine at 100 degrees C of starting solutions synthesized from TiCl4. For preparing Pt/TiO2 nanocomposites, with Pt/Ti nominal atomic ratio of 0.05, the required amount of Pt precursor was added to the amorphous TiO2 nanoparticles before heating at 250 degrees C. Control synthesis experiments, evaluated by X-ray diffraction and X-ray photoelectron spectroscopy showed Pt(acac)(2) as the best Pt precursor, and 250 degrees C as the optimum temperature for simultaneous TiO2 crystallization and efficient Pt nucleation. Transmission electron microscopy observations evidenced Pt nanocrystals dispersed in the surrounding TiO2 host, with a mean size of 4 nm. The TiO2 host was constituted of rod-shaped anatase nanocrystals. Comparison with pure TiO2 showed that the rod shape was favored by the presence of Pt species. As an example of application, the nanocomposites were used for preparing ethanol-sensing devices. The Pt addition remarkably improved the response with respect to pure TiO2 sensors, and electrical characterization of the sensors helped in establishing that the effect of Pt was due to spillover rather than electronic sensitization.

Ta2O5 thin films were prepared by spin-coating methanol solutions of Ta chloromethoxide. It was prepared by reacting TaCl5 with methanol, followed by water addition (H2O: Ta molar ratio was 16). Thin films were deposited by spin-coating onto SiO2/Si substrates, followed by drying at 90 degrees C and heat-treatment up to 700 degrees C. The films were characterized by X-ray diffraction, transmission electron microscopy and field emission scanning electron microscopy. Crystallization was obtained only after heating at 700 degrees C, in the Ta2O5 orthorhombic phase. The resulting films had a thickness of 100 nm. Their structure was constituted by porous crystals with size up to 50 nm, while the pores had a size of about 10 nm. The results demonstrated that TaCl5 is very convenient precursor for the wet chemical synthesis of Ta2O5 thin films. (C) 2013 Elsevier B.V. All rights reserved.

We report for the first time the synthesis of monoclinic WO3 quantum dots. A solvothermal processing at 250 degrees C in oleic acid of W chloroalkoxide solutions was employed. It was shown that the bulk monoclinic crystallographic phase is the stable one even for the nanosized regime (mean size 4 nm). The nanocrystals were characterized by X-ray diffraction, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis, Fourier transform infrared and Raman spectroscopy. It was concluded that they were constituted by a core of monoclinic WO3, surface covered by unstable W(V) species, slowly oxidized upon standing in room conditions. The WO3 nanocrystals could be easily processed to prepare gas-sensing devices, without any phase transition up to at least 500 degrees C. The devices displayed remarkable response to both oxidizing (nitrogen dioxide) and reducing (ethanol) gases in concentrations ranging from 1 to 5 ppm and from 100 to 500 ppm, at low operating temperatures of 100 and 200 degrees C, respectively. The analysis of the electrical data showed that the nanocrystals were characterized by reduced surfaces, which enhanced both nitrogen dioxide adsorption and oxygen ionosorption, the latter resulting in enhanced ethanol decomposition kinetics.

WO3 and Cr-WO3 powders were prepared by sol-gel process, with Cr:W atomic concentration ranging from 2% to 8.8%. WCl6 was used as W precursor and reacted with methanol in presence of acetyacetone as stabilizer. The required amount of Cr 2-ethylhexanoate was then added to the resulting solution, which was subsequently dried. The resulting powder was heat-treated at temperatures ranging from 200 to 700 degrees C. With increasing the Cr concentration, the samples heat-treated at 500 degrees C contained an increasing amount of the additional phase Cr2WO6, as evidenced by X-ray diffraction and Transmission Electron Microscopy. The sensing tests toward ammonia gas, from 50 to 500 ppm showed that, up to 5% concentration, Cr addition lowered the best operating temperatures and/or enhanced the response with respect to pure WO3, then the response remarkably decayed. DFT modeling showed that Cr(III) incorporation was more favorable in interstitial position while Cr (VI) was more favored in substitutional configuration. In this case, highly acidic Cr sites are present, enhancing the adsorption of ammonia species and reactions not involving NO2 as by-product. Beyond 5% Cr concentration, Cr2WO6 formation extracts Cr from the WO3 structure, so decreasing the ammonia response. Moreover, the appearance of Cr2WO6 seems to deactivate the surface adsorption properties of the material.

TiO2 (anatase) nanocrystals were prepared and their surface was modified by sol-gel deposition of vanadium oxide species. The resulting surface-modified TiO2 combines the good properties of both materials and new, synergistic properties arise, resulting in an increased electrical conductivity, voltage window, specific capacitance, and cycling stability.

TiO2 anatase nanocrystals were prepared by solvothermal processing of Ti chloroalkoxide in oleic acid, in the presence of W chloroalkoxide, with W/Ti nominal atomic concentration (R-w) ranging from 0.16 to 0.64. The as-prepared materials were heat-treated up to 500 degrees C for thermal stabilization and sensing device processing. For R0.16, the as-prepared materials were constituted by an anatase core surface-modified by WOx monolayers. This structure persisted up to 500 degrees C, without any WO3 phase segregation. For Rw up to R0.64, the anatase core was initially wrapped by an amorphous WOx gel. Upon heat treatment, the WOx phase underwent structural reorganization, remaining amorphous up to 400 degrees C and forming tiny WO3 nanocrystals dispersed into the TiO2 host after heating at 500 degrees C, when part of tungsten also migrated into the TiO2 structure, resulting in structural and electrical modification of the anatase host. The ethanol sensing properties of the various materials were tested and compared with pure TiO2 and WO3 analogously prepared. They showed that even the simple surface modification of the TiO2 host resulted in a 3 orders of magnitude response improvement with respect to pure TiO2.

The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.

The decomposition of metal (Ti, Zr, Sn) alkoxides at 250 degrees C in a solution of tetradecene and dodecylamine resulted in the formation of ultra-small (1-2 nm) oxide nanoparticles. The nanoparticles showed unusual structural properties. The high-pressure orthorhombic phase was found for SnO2. The as-synthesized ZrO2 nanoparticles were only partially crystallized. It was possible to observe their in situ crystallization under the TEM beam. The TiO2 nanoparticles appeared amorphous, with only a few nanocrystals dispersed in the sample. The temperature evolution of the samples was investigated in situ by Raman spectroscopy. All SnO2 was converted to stable cassiterite at 350 degrees C. TiO2 and ZrO2 samples displayed phase stability reversal over a broad range of temperatures.

Ceriazirconia solid solution nanocrystals, (1-x)CeO2xZrO2, 0 = x = 1, are prepared by solgel processing in dodecylamine of solutions obtained by forced hydrolysis of inorganic salts. The as-prepared nanoparticles have a ceria cubic structure, up to x = 0.35, or are amorphous. Heat-treatment is carried out at temperatures ranging from 500 to 800 degrees C, the latter temperature begin suitable to obtain solid solutions throughout the composition range. For all the heating temperatures and x values, the fluorite cubic structure of pure CeO2 transforms to a mixture (c') of the cubic c and tetragonal t? phases for x = 0.35, and to tetragonal t phase only for x = 0.8 at 650 degrees C, x = 0.65 at 800 degrees C, and, to a very limited extent, x = 0.5 at 1000 degrees C. No evidence is obtained at low x values of the t phase, which is detrimental to the oxygen storage capacity. Prolonged heating at 1000 degrees C demonstrates that only for x = 0.65 a limited separation of CeO2-rich nanocrystals occurs. The samples undergo the same transition without simultaneous occurrence of different phases, apart for the two mentioned limited cases. This result is attributed to the intimate mixing of the metal cations even in the early stages of processing. In as-prepared samples the Zr distribution becomes inhomogeneous when going from x = 0.2 to x = 0.35, but no early phase separations appear. The oxygen storage capacity is favorably influenced by the persistence of the cubic c' phase.

ZnO@SnO2 multilayered network was deposited on fluorine doped tin oxide (FTO) glass and applied as photoanode in dye sensitized solar cells whose functional performances are compared with single oxide-based photoanodes made of SnO2 nanoparticles and ZnO microparticles. Multi-oxide photoanodes provide for enhanced photoconversion efficiency (3.31%) as compared with bare SnO2 nanoparticles (1.06%) and ZnO microparticles (1.04%). Improved functional performances of the ZnO@SnO2 layered network are ascribable to partial inhibition of back electron transfer from SnO2 to the redox electrolyte, guaranteed by the ZnO, which acts as a capping layer for the underlying SnO2.

TiO2 and TiO2-V2O5 nanocrystals were prepared by coupling sol-gel and solvothermal methods, followed by heat-treatment at 400 degrees C, after which the mean nanocrystal size was about 5 nm. The materials were characterized by X-ray diffraction, transmission electron microscopy and solid state nuclear magnetic resonance spectroscopy. It was shown that while the TiO2 phase was always anatase even after heat-treatment at 500 degrees C, the presence of the vanadium oxide species enhanced the surface re-configuration of the Ti ions. Hence the coordination environment of surface Ti atoms was drastically changed, by formation of further bonds and imposition of a given local geometry. The final hypothesis was that in pure titania surface rearrangement occurs, leading to the new NMR signal, but this modification was favored in the TiO2-V2O5 sample, where the Ti surface atoms were forced into the final configurations by the bonding with V atoms through oxygen. The materials heat-treated at 400 degrees C were used to process chemoresistive sensors, which were tested to hydrogen, CO and NO2, as examples of gases with peculiar sensing mechanisms. The results evidenced that the surface deposition of V2O5 onto the anatase TiO2 nanocrystals was effective in modifying the adsorption properties of the anatase nanocrystals. (C) 2015 Elsevier B.V. All rights reserved.

A titanium chloromethoxide solution was prepared by reacting TiCl(4) with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO(2) nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250 A degrees C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO(2) nanocrystals with a mean size of 3.3 nm. The TiO(2) nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors.

Layered multi-oxide concept was applied for fabrication of photoanodes for dye-sensitized solar cells based on ZnO and SnO2, capitalizing on the beneficial properties of each oxide. The effect of different combinations of ZnO@SnO2 layers was investigated, aimed at exploiting the high carrier mobility provided by the ZnO and the higher stability under UV irradiation pledged by SnO2. Bioxide photoanodes performed much better in terms of photoconversion efficiency (PCE) (4.96%) compared to bare SnO2 (1.20%) and ZnO (1.03%). Synergistic cooperation is effective for both open circuit voltage and photocurrent density: enhanced values were indeed recorded for the layered photoanode as compared with bare oxides (V-oc enhanced from 0.39 V in case of bare SnO2 to 0.60 V and J(sc) improved from 2.58 mA/cm(2) pertaining to single ZnO to 14.8 mA/cm(2)). Improved functional performances of the layered network were ascribable to the optimization of both high chemical capacitance (provided by the SnO2) and low recombination resistance (guaranteed by ZnO) and inhibition of back electron transfer from the SnO2 conduction band to the oxidized species of the electrolyte. Compared with previously reported results, this study testifies how a simple electrode design is powerful in enhancing the functional performances of the final device.