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The main spectroscopic and spectromagnetic methods are applied to investigate the electronic structure of inorganic and coordination compounds

A new solid isomeric form (α) of Cu(NCO)2py2 was obtained as a first reaction product of copper nitrate, potassium cyanate and pyridine. This form can be transformed into the already known β form by recrystallization. Comparison of the spectroscopic and spectromagnetic properties of the two isomers suggests the absence of significant intermolecular interactions in the α form, the β one being characterized by a pseudo-bridging position of the NCO groups. The difference in the relative orientation of the tetragonal axes of the copper centers is responsible for different exchange coupling effects between the metal ions. © 1990.

The electrical properties of dislocations and grain boundaries (GB) in directionally solidified polycrystalline silicon were extensively studied as a function of the carbon, oxygen, and nitrogen content, as well as of the relative grain orientation. As a first result of this study we obtained the experimental evidence that the oxygen and carbon content are not independent variables of the material. Therefore, the density and the electrical activity of dislocations are shown to be strongly dependent on the amount of oxygen-carbon compensation. As a second result, experimental evidence was also achieved which demonstrated that grain boundaries are strongly passivated and that recombination losses at GB do not present any relevant relationship with mutual crystallographic orientations of the grains. It appears, therefore, that a careful choice of the growth and postgrowth conditions yields a material which behaves like crucible grown single-crystal silicon. © 1988, The Electrochemical Society, Inc. All rights reserved.

Borophosphosilicate glasses (BPSG) containing boron and phosphorous in the range 0-12 molar percent were prepared by the sol-gel method, from Si(OCH3)4, B(OCH3)3 and P(OCH3)3 precursors. Infrared, Raman and Electron Paramagnetic Resonance investigations suggested that B and P doping elements substitute Si in the silica network. Thus the low flow temperature (Tf) and the ability to trap Na+ impurities, both properties related to the presence of doping elements, are expected to depend on the stoichiometric composition of glasses.

The reactivity of nanosized Ru(Pd,Pt)-doped SnO2, obtained by sol-gel synthesis, towards NO/Ar was investigated by Electron Paramagnetic Resonance (EPR), Mossbauer and Electrical Resistance measurements. A sensing mechanism was proposed that involves (i) the formation of bielectronic oxygen vacancies V-O, (ii) their single-ionisation to V-O(center dot), which injects electrons to SnO2 conduction band, (iii) the transfer of V-O(center dot) electrons to the transition metal centers reducing them to lower oxidation states. It was suggested that the electronic exchange between oxide and transition metal is responsible for the enhancement of the reactivity in doped SnO2 with respect to the undoped material

N-doped TiO2 nanocrystals with high photoactivity in the visible range, were successfully synthesized by hydrothermal method, followed by thermal annealing at different temperatures (350-600 degrees C), in order to allow differential nitrogen diffusion into the TiO2 lattice. Optical and magnetic properties, studied by diffuse reflectance spectroscopy, electron paramagnetic resonance and X-ray photoelectron spectroscopy analysis, revealed that TiO2 was effectively doped. The thermal treatment induces insertion of nitrogen into TiO2 lattice in the form of nitride anion N-, detected as N-center dot by EPR, whose ionic character varies with the temperature of annealing. The amount of N-center dot increases till 450 degrees C, then it decreases. Similar trend was observed for the photomineralization of phenol under visible light irradiation (lambda > 385 nm): the photoactivity of N-doped samples becomes maximum for N-TiO2 annealed at 450 degrees C. The overall results suggest that the efficacy of the catalyst depends on the ability of N- centers to trap photogenerated holes. This effect lowers the rate of electron-hole recombination and allows the N-center dot (N- + h(+)) center acts as strong oxidizing agent. (C) 2009 Elsevier B.V. All rights reserved.

The sensing behavior of pyramidal (PY), prismatic hexagonal (EP) and hexagonal rod-like (ER) ZnO micro and sub-microparticles, has been compared with that of commercial ZnO (ZnO®) particles having nanometric size and uneven shape. The performances have been firstly related to the predominance of specific crystal surfaces and then, more in depth, to the paramagnetic defects in ZnO ( and ), detected by Electron Spin Resonance (ESR), in order to associate the particles morphology with the defects amount and reactivity and, in turn, with a particular sensing mechanism. The results showed that the sensing behavior of ZnO® containing irregular nanoparticles is essentially related to the alternate formation and filling of oxygen vacancies during the gas pulse (oxygen vacancy mechanism), while that of ER and EP crystals does not seem to directly involve the defects. In particular, the sensing properties of shape controlled ZnO particles are mainly attributed to the ability of (0001) exposed surfaces in favoring a far better chemisorption of negatively charged oxygen species, then available for the reactions with the reducing gas (i.e. ionosorption mechanism). The outcomes and the approach adopted in this study may positively contribute to the debate still existing between the oxygen vacancy and ionosorption models by giving indications on the predominance of a specific sensing mechanism in shape controlled ZnO.

Mesoporous Cr or Pt-doped WO3 thin films to be employed as ammonia gas sensors were prepared by a fast one-step sol–gel procedure, based on the use of triblock copolymer as templating agent. The obtained films were constituted by aggregates of interconnected WO3 nanocrystals (20–50 nm) separated by mesopores with dimensions ranging between 2 and 15 nm. The doping metals, Pt and Cr, resulted differently hosted in the WO3 mesoporous matrix. Chromium is homogeneously dispersed in the oxide matrix, mainly as Cr(III) and Cr(V) centers, as revealed by EPR spectroscopy; instead platinum segregated as Pt (0) nanoparticles (4 nm) mainly included inside the WO3 nanocrystals. The semiconductor layers containing Pt nanoclusters revealed, upon exposure to NH3, remarkable electrical responses, much higher than Cr-doped and undoped layers, particularly at low ammonia concentration (6.2 ppm). This behavior was attributed to the presence of Pt nanoparticles segregated inside the semiconductor matrix, which act as catalysts of the N–H bond cleavage, decreasing the activation barrier in the ammonia dissociation. The role of the mesoporous structure in influencing the chemisorption and the gas diffusion in the WO3 matrix appeared less decisive than the electronic differences between the two examined doping metals. The overall results suggest that a careful combination between mesoporous architecture and metal doping can really promote the electrical response of WO3 toward ammonia. Keywords Pt and Cr—doped WO3 Mesoporous thin film Gas sensors Morphological, electronic and electrical

TiO 2 –SiO 2 composite materials with photocatalytic properties similar to those of slurry powdered TiO 2 is obtained by a novel sol–gel synthetic strategy involving the hydrolysis/condensation of TMOS assisted by PEG as templating agent and the grafting of preformed titania nanocrystals onto the macropore walls of the silica matrix. In order to anchor TiO 2 particles to the surface of SiO 2 , avoiding their embedding into silica matrix, functionalization with carboxylic acid or amine derivatives was carried out. The functionalization induces the confinement of titania nanocrystals in PEG, during the silica formation, and allows their dispersion on the silica surface. TiO 2 –SiO 2 materials exhibit high thermal and chemical stability and a photocatalytic activity in the phenol mineralization comparable to that of powder TiO 2 in slurry (half degradation time ∼120 min). These results suggest that the immobilization procedure here reported provides high accessibility of the catalyst active sites preserving the functional properties of the photoactive catalyst.

TiO2 dispersed in polyester acrylate membranes was tested as a photocatalyst in the phenol mineralization reaction assisted by molecular oxygen. Kinetics experiments revealed that, although embedded, the oxide maintains significant catalytic activity. This result was first attributed to the homogeneous dispersion inside the polymeric host of TiO2 nanocrystals, which can be easily irradiated and interact with the reactants. Furthermore, the investigation of the photogenerated charge carriers in the photocatalyst demonstrated that electrons are trapped on Ti3+ centers, while holes are trapped on C-centered species of the polymer matrix. In the presence of O-2, the C-centered radicals of the polymer transform into peroxy radicals, reinforcing the charge separation in the polymer-embedded oxide with respect to the powder. The positive interference of the polymer matrix in reinforcing the electron hole separation is responsible for the relevant photoactivity of the embedded TiO2.

Photomineralization of methane in air (10.0–1000 ppm (mass/volume) of C) at100%relative humidity (dioxygen as oxygen donor) was systematically studied at318±3 K in an annular laboratory-scale reactor by photocatalytic membranes immobilizing titanium dioxide as a function of substrate concentration, absorbed power per unit length of membrane, reactor geometry, and concentration of a proprietary vanadium alkoxide as photopromoter. Kinetics of both substrate disappearance, to yield intermediates, and total organic carbon (TOC) disappearance, to yield carbon dioxide, were followed. At a fixed value of irradiance (0.30 W⋅cm-1), the mineralization experiments in gaseous phase were repeated as a function of flow rate (4–400 m3⋅h−1). Moreover, at a standard flow rate of 300 m3⋅h−1, the ratio between the overall reaction volume and the length of the membrane was varied, substantially by varying the volume of reservoir, from and to which circulation of gaseous stream took place. Photomineralization of methane in aqueous solutions was also studied, in the same annular reactor and in the same conditions, but in a concentration range of 0.8–2.0 ppm of C, and by using stoichiometric hydrogen peroxide as an oxygen donor. A kinetic model was employed, from which, by a set of differential equations, four final optimised parameters,k1andK1,k2andK2, were calculated, which is able to fit the whole kinetic profile adequately. The influence of irradiance onk1andk2, as well as of flow rate onK1andK2, is rationalized. The influence of reactor geometry onkvalues is discussed in view of standardization procedures of photocatalytic experiments. Modeling of quantum yields, as a function of substrate concentration and irradiance, as well as of concentration of photopromoter, was carried out very satisfactorily. Kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading to mineralization, were considered, and it is paralleled by a second competition kinetics involving superoxide radical anion.

Tin dioxide and ruthenium(platinum)-doped tin dioxide were synthesized in the form of inverted opals, aiming to investigate the interaction of these materials with CO reducing gas. The results of electron paramagnetic resonance (EPR) investigation allowed us to conclude that CO interaction causes the formation of singly ionized oxygen vacancies located in the subsurface region. These ones transfer their electrons to transition metal centers, Ru or Pt, enhancing the SnO2 surface reactivity toward CO. The reduction of Ru4+ and Pt4+ was assessed both by EPR and Mössbauer spectroscopy. Resistance measurements showed that the materials are well-suitable for use in CO sensor devices because of their reproducible and fast electrical response; this was related to the homogeneous and high dispersion of Ru and Pt centers in the oxide matrix and to the subsurface location of the species active in the electron-transfer processes. © 2005 American Chemical Society.

Ce-doped borosilicate (BSG), phosphosilicate (PSG), and borophosphosilicate (BPSG) glasses (B:P:Si molar ratios 8:0:92, 0:8:92, and 8:8:84; Ce:Si molar ratio 1 x 10(-)(4) to 1 x 10(-)(2)) were prepared by the sol-gel method. High-resolution transmission electron microscopy (HRTEM), (31)P, (29)Si, and (11)B magic angle spinning nuclear magnetic resonance (MAS NMR), electron paramagnetic resonance (EPR), and UV-vis absorption investigations demonstrated that, in PSG and BPSG, Ce(3+) ions interact with phosphoryl, [O=PO(3/2)], metaphosphate, [O=PO(2/ 2)O](-), and pyrophosphate, [O=PO(1/2)O(2)](2)(-), groups, linked to a silica network. This inhibits both CeO(2) segregation and oxidation of isolated Ce(3+) ions to Ce(4+), up to Ce:Si = 5 x 10(-)(3). In BSG, neither trigonal [BO(3/2)] nor tetrahedral [BO(4/2)](-) boron units coordinate cerium; thus, Ce(3+) oxidation occurs even at Ce:Si = 1 x 10(-)(4), as in pure silica glass (SG). The homogeneous rare-earth dispersion in the host matrix and the stabilization of the Ce(3+) oxidation state enhanced the intensity of the photoluminescence emission in PSG and BPSG with respect to BSG and SG. The energy of the Ce(3+) emission band in PSG and BPSG matrixes agrees with the phosphate environment of the rare earth.

In the present paper, the performance of a pilot plant for domestic use was investigated, able to operate continuously, and in which tap water was fed ( inorganic carbon IC: 81.6 +/- 0.5 ppm; total organic carbon TOC content: 1.52 +/- 0.02 ppm). This plant produced 130 L/d of purified water. The tap water was first subjected to a prefiltration by a membrane microfiltration unit, followed by filtration through a membrane immobilising activated carbon, then through a reverse osmosis membrane, at a transmembrane pressure of 4 bar, and finally through a photocatalytic membrane unit, constituted by a metallic membrane, onto which the semiconductor and its photopromoters were present as a 3 - 4 mu m thick surface layer, directly produced on the nanotechnologically treated surface of this membrane, irradiated at a power of 9.6W in the range of optical absorption by semiconductor. Efficiency of these operations was compared by carrying out parallel experiments, using two other commercial plants ( I and II), in which the photocatalytic treatment was not provided for. All the three plants were able to soften the tap water down to 6 - 8 ppm IC, but, as regards TOC, ( I) yielded a purified water still containing 1.12 +/- 0.05 ppm of organic carbon, and ( II) 0.908 +/- 0.009 ppm, while the TOC content of water purified in the pilot plant of present work was lowered down to 0.06 +/- 0.02 ppm. In order to compare further efficiency of these plants, a simulated feed solution was treated, containing 3.05 ppm of humic acids, or 2.16 ppm of atrazine, or 4.23 ppm of symazine. Reverse osmosis, which was present in all the three kind of plants examined, even if coupled with active carbon adsorption, was not able to remove entirely contamination due to organic micropollutants. This goal, on the contrary, was successfully achieved by the plant fitted with the photocatalytic membrane unit, particularly by considering that this plant showed substantially the same abatement efficiencies of plants ( I) and ( II), if the photocatalytic unit was switched off.

Monolithic borophosphosilicate glasses (BPSG) were prepared by the sol-gel route through xerogel densification. Tetramethoxysilane (Si(OCH3)4), trimethylborate (B(OCH3)3), and trimethylphosphite (P(OCH3)3) were used as source compounds for Si, B, and P, respectively. After gel drying, samples underwent thermal treatment up to 700 °C, resulting in transparent and crack-free monolithic glasses. In this work, x-ray photoelectron spectra of a representative glass specimen are presented and discussed. Beside the wide scan spectrum, a detailed analysis of Si 2p, O ls, P 2p, B 1s + P 2s is performed. Moreover, a quantification procedure aimed at resolving problems arising from the overlap between B 1s and P 2s photopeaks in oxide-based systems is proposed.

Silica–natural rubber nanocomposites were obtained through a novel non-aqueous in situ sol–gel synthesis, producing the amount of water necessary to induce the hydrolysis and condensation of a tetraethoxysilane precursor by esterification of formic acid with ethanol. The method allows the synthesis of low hydrophilic silica nanoparticles with ethoxy groups linked to the silica surface which enable the filler to be more dispersible in the hydrophobic rubber. Thus, high loaded silica composites (75 phr, parts per hundred rubber) were obtained without using any coupling agent. Transmission Electron Microscopy (TEM) showed that the silica nanoparticles are surrounded by rubber layers, which lower the direct interparticle contact in the filler–filler interaction. At the lowest silica loading (up to 30 phr) silica particles are isolated in rubber and only at a large amount of filler (>60 phr) the interparticle distances decrease and a continuous percolative network, connected by thin polymer films, forms throughout the matrix. The dynamic-mechanical properties confirm that the strong reinforcement of the rubber composites is related to the network formation at high loading. Both the improvement of the particle dispersion and the enhancement of the silica loading are peculiar to the non-aqueous synthesis approach, making the method potentially interesting for the production of high-loaded silica–polymer nanocomposites.

Silica/styrene butadiene rubber (SBR) nanocomposites were prepared by blending method using shape-controlled spherical and rod-like nanoparticles with different aspect ratios as filler for the rubber reinforcement. The differently shaped silica particles were synthesized by sol-gel method using tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTSM) as silica precursors, and cetyltrimethylammonium bromide (CTAB) as structure directing agent. This strategy allowed to study the influence of the particle morphology on the reinforcing effect independently of the silica surface chemistry and considering the aspect ratio as the only geometrical variance. Spherical and anisotropic rod-like particles, dispersed in the nanocomposites, formed a network of particles bridged by thin rubber layers throughout the SBR matrix. Moreover, differently oriented domains of aligned rods are observed when the aspect ratio of particles increases and is >=2. Dynamic-mechanical properties demonstrated that the rod-like particles with the higher aspect ratio provided stronger reinforcement of the rubber. This was related to the self-alignment of the anisotropic particles and to the consequent larger filler/polymer interface, compared to that of spherical ones. © 2014 Elsevier Ltd. All rights reserved.

The reactivity towards CO and air of SnO 2 defects, singly and doubly ionized oxygen vacancies (V o ⋅ V o ⋅⋅ ), bivalent tin centers, was studied in ruthenium-supported tin oxide (Ru/SnO 2 ), and compared with that in pure SnO 2 . Electron paramagnetic resonance and X-ray photoelectron spectroscopy studies demonstrated that CO treatment produces V o ⋅ and V o ⋅⋅ defects in SnO 2 , some V o ⋅ transferring their electrons to Sn 4+ centers; instead in Ru/SnO 2 , some V o ⋅ defects transferred their electrons to Ru n + centers ( n =0,1,2,3) and no one bivalent tin center was observed. When contacted with air, pure SnO 2 transferred a part of the electrons of V o ⋅ and of bivalent tin centers to O 2 , instead Ru/SnO 2 emptied all V o ⋅ defects transferring the electrons from V o ⋅ to ruthenium and to O 2 . The via ruthenium transfer increases the number of electrons exchanged between SnO 2 and the surrounding atmosphere and gave a rationale for the higher sensitivity towards CO displayed by transition metal-doped SnO 2 with respect to pure SnO 2 .

Silica-dispersed copper molybdates having different Cu:Mo and Cu:Si molar ratios were prepared both by a sol-gel route and a conventional impregnation technique. These materials, used as catalysts for the propene oxidation, were studied in order to assess whether the different preparation methods and/or different Cu:Mo and Cu:Si molar ratios affected the copper(II) coordination. Electron paramagnetic resonance spectroscopy showed that oxo/hydroxo-bridged copper(II) dimers were present in xerogel catalyst precursors and on the surface of fresh impregnated precursor materials, their amount increasing with Cu:Si molar ratio and in impregnated samples. The value of the zero field interaction is very low and decreases with increase in temperature. This means that Cu(II) centres in dimers are spaced fairly far apart and lie in a strongly distorted symmetry field which varies because of the flexible host matrix. Thermal treatment of both xerogels and impregnated samples gave silica-dispersed Cu 3 Mo 2 O 9 catalysts from samples with Cu:Mo molar ratio 1:1 and silica-dispersed CuMoO 4 from those with Cu:Mo 1:2. The presence of polynuclear metal compounds in the crystalline phase seems to be connected to the presence of dimeric species in the precursor. The sol-gel method is more efficient than impregnation to produce catalysts with small and homogeneous particle dimensions of the active phase, for a wide range of Cu:Si molar ratios.

Electron paramagnetic resonance (EPR) studies have been carried out on lattice oxygen vacancies produced by the interaction of carbon monoxide with SnO 2 obtained by sol–gel type condensation. Under a 0.5% CO–argon reducing atmosphere the vacancies can transfer electrons to Sn 4+ producing Sn 2+ centres. In air the lattice defects interact with molecular oxygen in a manner which depends on whether the gas reducing treatment was performed under dry or moist conditions. Defects that undergo oxygen interaction at the SnO 2 surface, reduce O 2 to O 2 - or O 2- , depending on the temperature of the reaction with oxygen.

Spectroscopic and spectromagnetic investigations on molybdenum centres in MoO3 . H2O and its polymer-supported form have been carried out. Both were tested as catalysts for cyclohexene epoxidation in a heterogeneous phase; both needed activating pretreatment before the reaction. XPS and EPR data show that the metal is mainly present as Mo-VI. The activation process increases the acidic character of Mo-VI and its efficiency depends both on the oxidizing power of the activating reactant and on the accessibility of the metal to the reactant. The steric hindrance of Mo-VI lowers the catalytic activity owing to the replacement of H2O by carboxylic groups of the functionalized resin.

Macroporous WO3 films with inverted opal structure were synthesized by one-step procedure, which involves the self-assembly of the spherical templating agents and the simultaneous sol-gel condensation of the semiconductor alkoxide precursor. Transition metal doping, aimed to enhance the WO3 electrical response, was carried out by including Cr(III) and Pt(IV) centers in the oxide matrix. It turned out that Cr remains as homogeneously dispersed Cr(III) centers inside the WO3 host, while Pt undergoes reduction and aggregation to form nanoclusters located at the oxide surface. Upon interaction with NH3, the electrical conductivity of transition metal doped-WO3 increases, especially in the presence of Pt dopant, resulting in outstanding sensing properties (S = 110 ± 15 at T = 225 °C and [NH3] = 74 ppm). A mechanism was suggested to explain the excellent electrical response of Pt-doped films with respect to the Cr-doped ones. This associates the easy chemisorption of ammonia on the WO 3 nanocrystals, promoted by the inverted opal structure, with the catalytic action exerted by the surface Pt nanoclusters on the N-H bond dissociation. The overall results indicate that in Pt-doped WO3 films the effects of the macroporosity positively combine with the electrical sensitization promoted by the metal nanoclusters, thus providing very lightweight materials which display high functionality even at relatively low temperatures. We expect that this synergistic effect can be exploited to realize other functional hierarchical metal oxide structures to be used as gas sensors or catalysts.(Figure Presented) © 2011 American Chemical Society.

The promising properties of anatase TiO(2) nanocrystals exposing specific surfaces have been investigated in depth both theoretically and experimentally. However, a clear assessment of the role of the crystal faces in photocatalytic processes is still under debate. In order to clarify this issue, we have comprehensively explored the properties of the photogenerated defects and in particular their dependence on the exposed crystal faces in shape-controlled anatase. Nanocrystals were synthesized by solvothermal reaction of titanium butoxide in the presence of oleic acid and oleylamine as morphology-directing agents, and their photocatalytic performances were evaluated in the phenol mineralization in aqueous media, using O(2) as the oxidizing agent. The charge-trapping centers, Ti(3+), O(-), and O(2)(-), formed by UV irradiation of the catalyst were detected by electron spin resonance, and their abundance and reactivity were related to the exposed crystal faces and to the photoefficiency of the nanocrystals. In vacuum conditions, the concentration of trapped holes (O(-) centers) increases with increasing {001} surface area and photoactivity, while the amount of Ti(3+) centers increases with the specific surface area of {101} facets, and the highest value occurs for the sample with the worst photooxidative efficacy. These results suggest that {001} surfaces can be considered essentially as oxidation sites with a key role in the photoxidation, while {101} surfaces provide reductive sites which do not directly assist the oxidative processes. Photoexcitation experiments in O(2) atmosphere led to the formation of Ti(4+)-O(2)(-) oxidant species mainly located on {101} faces, confirming the indirect contribution of these surfaces to the photooxidative processes. Although this work focuses on the properties of TiO(2), we expect that the presented quantitative investigation may provide a new methodological tool for a more effective evaluation of the role of metal oxide crystal faces in photocatalytic processes.

Anthracycline antitumor drugs weakly inhibit protein kinase C (PKC) activity; this effect is enhanced by coordination with transition metal ions. The present study shows that copper(II) by itself inhibits PKC activity; when Cu(II) is present as the anthracycline-Cu(II) complex [Cu(EpiDXR)2], a significant enhancement is observed as compared to the inhibitory effects of either metal or drug alone. Both regulatory and catalytic sites of PKC are involved in this effect. Electron paramagnetic resonance (EPR) studies indicate an interaction between PKC and Cu(II). It is suggested that Cu(II) is responsible for the inhibitory action of Cu(II)-anthracycline complexes on PKC; anthracycline molecules potentiate this effect, possibly by stabilizing Cu(II) and increasing its availability at enzyme target sites.

Photomineralisation of 2,4-dichlorophenol (DCP) in aqueous solutions (10.0–100.0 mg/L of C) was systematically studied at318±3 K, in an annular laboratory-scale reactor, by photocatalytic membranes immobilizing titanium dioxide, as a function of substrate concentration, and absorbed power per unit length of membrane. Kinetics of both substrate disappearance, to yield intermediates, and total organic carbon (TOC) disappearance, to yield carbon dioxide, were followed (first series of experiments). At a fixed value of irradiance (1.50 W⋅cm−1), other series of mineralization experiments were repeated (second series of experiments) by carrying out only analyses of chemical oxygen demand (COD), in order to compare modelling results of the two sets of experiments. In both sets of experiments, stoichiometric hydrogen peroxide was used as oxygen donor. For the first series of experiments, a kinetic model was employed, already validated in previous work, from which, by a set of differential equations, four final optimised parameters,k1andK1,k2andK2, were calculated. By these parameters, the whole kinetic profile could be fitted adequately. The influence of irradiance onk1andk2could be rationalised very well by this four-parameter kinetic model. Modelling of quantum yields, as a function of irradiance, could also be carried out satisfactorily. As has been found previously for other kinds of substrates, modelling of quantum yields for DCP mineralization is consistent with kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading finally to carbon dioxide, paralleled by a second competition kinetics involving superoxide radical anion. For the second series of experiments, on the contrary, the Langmuir-Hinshelwood model was employed. Uncertainties of COD analyses, coupled with discrepancies of this model and with its inability to reproduce kinetics up to complete mineralization, are underlined.

Vanadium chloromethoxide was prepared by the methanolysis Of VCl4. The addition of water with a H2O:vanadium molar ratio ranging between 0 and 16 changed the solution color from green to deep blue at a rate increasing with water concentration. UV-vis, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy investigations showed that VCl4 precursor is initially methanolyzed to (VO)Cl-x(OCH3)(y) (x + y = 4) monomers. Upon water addition, methoxo ligands undergo hydrolysis. The presence of chlorine ligands and of the vanadyl group explains the long-term stability of the solutions. V2O5 thin films and powders were prepared, respectively, by spin-coating onto silicon substrates and drying of the solutions, followed by heat-treatments at temperatures up to 500 degrees C. Films and powder precursors were characterized by X-ray diffraction, FTIR, Raman, UV-vis, and EPR spectroscopy, transmission electron microscopy, and thermal analyses. The structural evolution begins by condensation of the initial monomers to form amorphous structures with poor extension of the three-dimensional network. Heat-treatment at higher temperatures induces further condensation and the elimination of the chlorine ligands, which leave an oxygen-defective structure and cause the initial formation of substoichiometric V3O7 phase. When the samples were annealed at T >= 400 degrees C, only the V2O5 phase was found. V2O5 powders annealed at 500 degrees C were used in chemoresistive gas sensing devices and were able to detect reducing gases such as ammonia and ethanol over a broad range of concentrations by stable and reliable signal.

Nanostructured Pt-doped SnO2 thin films are obtained by a sol-gel route using tetra(tert-butoxy)tin(IV) and bis(acetylacetonato) platinum(II) as precursors. Acetylacetone was added as a chelating agent to control the hydrolysis and condensation of tin alkoxide and, consequently, the gelation rate. This procedure allows obtaining a sol phase viscosity suitable for the spin-coating process. © 2008 Springer Vienna.

Monolithic and transparent Sn-doped SiO2 glasses, where Sn atoms replaced Si centers in the SiO2 network, were prepared by a new sol-gel route by using tetraethoxysilane (TEOS) and dibutyltindiacetate (DBTDA) as precursors. The maximum amount of Sn doping was 1.40 wt % SnO2/(SnO2+SiO2) (corresponding to 0.55 mol %). At higher tin content (≥ 1.60 wt %, corresponding to 0.64 mol %) crystalline nanosized particles of SnO2 (6–10 nm) segregated in silica matrix.

Paramagnetic point defects sensitive to the surrounding atmosphere were observed in ZnO powder. Changes in EPR lines following either thermal-vacuum treatment or contact with molecular O2 led to definite conclusions regarding the nature of the ZnO point defects and the electron-transfer processes active at the ZnO/O2 interface. Two different point defects are identified: A (gA = 1.955), assigned to ionized interstitial zinc centres Zni+, and B (gB = 1.958), assigned to ionized oxygen vacancies vo+. Both are able to reduce molecular oxygen, but only vo+ defects give rise to O2-. ZnO-supported ruthenium was also investigated: dispersed Ru improves the electron transfer from the oxide to the O2 molecules of the surrounding atmosphere.

The cardiotoxic and cytotoxic effects of the Cu(II)-doxorubicin (DXR) complex [Cu(DXR)]n are compared with those of the parent drug. It is shown that 10-4M [Cu(DXR)]n has no depressant effects on isolated rat atria, in contrast with an equimolar concentration of the parent drug. No differences were found between the cytotoxic activities of the Cu(II) complex and free DXR on B16 melanoma and HeLa cells. A reduced penetration of the polymeric [Cu(DXR)]n into the myocardial cells as compared with the free drug was invoked to account for the absence of cardiotoxicity of the DXR complex. On the other hand, the observation that copper-complexation does not affect the cytotoxicity of the drug suggests that extracellular as well as intracellular mechanisms may be involved in the development of its antitumor activity. © 1990 Springer-Verlag.

Kinetics of photocatalytic oxidation of methane, ethane, and n-heptane, to yield intermediates, and photomineralization of intermediates, to yield carbon dioxide and water, was studied in the gaseous phase, at 308±2 K, by a laboratory-scale photoreactor and photocatalytic membranes immobilizing 30±3 wt.% of TiO2, in the presence of aerosolized stoichiometric hydrogen peroxide as oxygen donor, and at a relative humidity close to 100%. The whole volume of irradiated solution was 4.000±0.005 L, the ratio between this volume and the geometrical apparent surface of the irradiated side of the photocatalytic membrane was 3.8±0.1 cm, and the absorbed power was 0.30 W/cm (cylindrical geometry). The pinetic parameters of the present work substantially coincide with those of the same molecules previously studied in aqueous solution, within the limits of experimental uncertainty. Photocatalytic processes thus appear to be controlled by interface phenomena, which are ruled kinetically, and apparently also thermodynamically, by concentration gradients, independently on diffusion and other processes in the aqueous or gaseous bulk, if turbulence in these phases is adequately assured. Copyright © 2006 Ignazio Renato Bellobono et al.

Inverted opal Ce-doped silica glasses (Ce : Si molar ratio 1 . 10(-3)) were prepared by a sol-gel method using opals of latex microspheres as templates. The rare earth is homogeneously dispersed in silica host matrix, as evidenced by the absence of segregated CeO2, instead present in monolithic Ce-doped SG with the same cerium content. This suggests that the nanometric dimensions of bridges and junctions of the host matrix in the inverted opal structures favor the RE distribution avoiding the possible segregation of CeO2. Copyright (C) 2006 R. Scotti et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Nanocrystalline TiO2catalysts based on pure rutile (R100) and a 30% of anatase and 70% of rutile (R70) were synthesized by the sol-gel method, using Pluronic PE 6400 as templating agent. Catalysts were characterized in terms of structural and morphological properties; moreover, the formation of paramagnetic charge carriers under UV irradiation was studied and related to the activity of TiO2in the photoinduced degradation of phenol. With respect to Degussa P25, the two sol-gel catalysts show lower surface area and a wider pore size distribution. The EPR spectra recorded under UV irradiation show enhanced charge separation in the sol-gel samples, with the O−species in higher amount than in Degussa P25. This result is in agreement with the high catalytic activity of R100 sample in the photoinduced degradation of phenol, very similar to that displayed by Degussa P25 and higher than that of R70 sample.

Ce3+-doped boro, phospho and borophosphosilicate monolithic glasses (BSG, PSG and BPSG) were prepared by sol-gel method. The inclusion of the glass formers P and B in silica lowered the tendency of rare earth (RE) to segregate as CeO2 with respect to pure SiO2 matrix (SG). In PSG and BPSG, Ce3+ co-ordination to P=O groups was responsible for the inhibition of both CeO2 segregation and oxidation of isolated Ce3+ ions to Ce4+. The better ion dispersion in the host matrix and the stabilization of Ce3+ oxidation state improved PSG and BPSG luminescence properties with respect to BSG and SG.

Kinetics of photocatalytic oxidation of methane, ethane, n- heptane, n- decane, and n- dodecane, to yield intermediates, and photomineralisation of intermediates, to yield carbon dioxide and water, was studied in aqueous solution, by a laboratory- scale photoreactor and photocatalytic membranes immobilizing 30 +/- 3 wt.% of TiO2, in the presence of stoichiometric hydrogen peroxide as oxygen donor. The whole volume of irradiated solution was 4.000 +/- 0.005 L, the ratio between this volume and the geometrical apparent surface of the irradiated side of the photocatalytic membrane was 3.8 +/- 0.1 cm, and the absorbed power 0.30 W/ cm ( cylindrical geometry). A kinetic model was used, by which mineralisation of substrate to CO2 was supposed to occur, by kinetic constants k(1), through one single intermediate, mediating the behaviour of all the numerous real intermediates formed in the path from the substrate to CO2 ( kinetic constants of formation of the latter being k(2)). A competitive Langmuirian adsorption of both substrate and " intermediate" was also supposed to be operative, as expressed by apparent adsorption constants K-1 and K-2, possessing a, partly at least, kinetic significance. By Langmuir- Hinshelwood treatment of initial rate data, starting values of the k and K couples were obtained, from which, by a set of differential equations, the final optimised parameters, k(1) and K-1, k(2) and K-2, were calculated, able fit the whole photomineralisation curve, and not only its initial segment, as the Langmuirian parameters do. The parameters of present work are critically compared with those obtained in two preceding set of studies relative to n- alkanoic acids and to n- alkanols. They are interpreted on the basis of a closer behaviour of hydrocarbons to alkanols, from the photocatalytic point of view, than to carboxylic acids are. Discussion of limiting effective quantum yields, and their comparison with maximum, theoretical values, are also carried out.

Monolithic borophosphosilicate glasses were prepared by the sol-gel route through xerogel densification. Tetramethoxysilane (Si(OCH3) 4), trimethylborate (B(OCH3)3), and trimethyl phosphite (P(OCH3)3) were used as source compounds for Si, B, and P, respectively. After drying, samples underwent thermal treatment up to 700 °C with alternating flowing oxygen and reduced pressure steps, resulting in transparent, monolithic glasses. The sample chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). Densification was investigated by vibrational spectroscopies (FT-IR, micro-Raman). The boron oxygen hole centers (BOHC) and phosphorus oxygen hole centers (POHC) paramagnetic defects generated by X-ray irradiation of glasses were studied by electron paramagnetic resonance (EPR) spectroscopy. The results obtained on borophosphosilicate glasses showed that paramagnetic defects are not created by independent processes, as expected for randomly distributed noninteracting B and P doping elements. Diamagnetic precursors of BOHC and POHC are thus proposed to be spatially close together in the glasses.

The mechanism of NO interaction with nanocrystalline (6-10nm particle size) SnO2 powdered samples, obtained by sol-gel synthesis, was studied by electron paramagnetic resonance and Mössbauer spectroscopy. Resistance measurements on nanostructured (3nm particle size) SnO2 thin films (80-160nm), still obtained by sol-gel route, were coupled to spectral results. Spectroscopic investigations demonstrated that the NO interaction involves electron injection to the oxide, formation of oxygen vacancies, and chemisorption of NO2- and NO3- anions. The amount of oxygen vacancies depends on the annealing atmosphere of SnO2. When it was previously annealed under inert (Ar) atmosphere, the NO interaction causes a great amount of oxygen defects as the lack of chemisorbed oxygen species forces NO to interact with lattice oxide anions; instead when annealed in air, NO also reacts with chemisorbed oxygen species giving NO2- and NO3- anions. Accordingly, the electrical response is higher in the case of predominant NO interaction with lattice oxide anions, because a great amount of NO electrons are transferred to SnO2. © 2003 Elsevier B.V. All rights reserved.

Ammonia interaction with chromium-doped WO3 nanocrystalline powders was investigated. Chromium centres were characterised by EELS, Raman, XPS, EPR and UV-visible spectroscopy. Essentially, these studies revealed that chromium was well distributed on WO3, forming Cr(III) species and chromyl groups [Cr=O]3+. Test of thick-film gas sensors based on chromium-doped WO3 revealed that chromium addition boosted sensor response to NH3. Besides, it also avoided unsatisfactory dynamic behaviour previously found in gas sensors based on pure WO3. DRIFT spectroscopy and TPD were used to investigate the surface chemistry of ammonia over pure and chromium-doped WO3 nanocrystalline powders. It was concluded that chromium favours the combustion of ammonia into molecular nitrogen and nitrous oxide on chromium centres, which contributes to the improvement in the sensing properties of the material.

Nanocrystalline powders of WO3, pure and with catalytic additives such as copper and vanadium, for ammonia gas detection are analyzed in detail. Material was annealed at two different temperatures (400 and 700degreesC) and catalytic additives were introduced in two different concentrations (0.2 and 2%) in order to study the gas sensor performances of these WO3-based materials. Crystalline structure characterization shows that a mixture of triclinic and monoclinic structure was present in the materials analyzed. Additive characterization reveals that catalytic metals were located as cations in the matrix lattice. Thick-film gas sensors based on pure WO3 show an abnormal sensor response, which is attributed to a complex process originated by the oxidation of ammonia to NO. On the other hand, catalyzed WO3-based gas sensors show a more direct and simple sensor response. Interaction of ammonia with WO3 was studied by diffuse reflectance infrared spectroscopy. Only pure WO3 presented a W=O overtone band decrease and some nitrosil bands. In this case, NH3 would react with the surface oxygen of terminal W=O bonds and would lead to the formation of NO. Catalyzed WO3 avoided this reaction and so the unselective catalytic oxidation of NH3, improving sensor response. Influence of introduced additives on ammonia oxidation and thus on sensor response is discussed. (C) 2003 The Electrochemical Society.

The oxidation of dimeric lignin model compounds (arylglycerol - β - aryl ethers and phenylcoumarans) by molecular oxygen, catalyzed by [N, N′ - bis(salicylidene) -ethane - 1,2-diaminato] cobalt(II), [Co(salen)], was studied in order to find novel processes for the production of chemicals by degradation of polyphenols contained in waste waters from the pulp and paper industry. All the studied compounds reacted at room temperature in chloroform with high conversion already after 30 minutes; after 48 h the reaction was essentially complete and interesting low molecular weight compounds were isolated with good yields. An EPR investigation of the reaction mixtures indicates the presence of a phenoxy cobalt radical, [CoIII(salen)(RO-)(RO•)], as a reactive intermediate for ROH as phenolic substrate. The electron donor properties of the phenolic substrate and the stability of the phenoxy radical control the yields of the oxidation products

The interaction of molecular oxygen with polycrystalline Bi2O3 was investigated by infrared (IR) and thermogravimetric (TGA) analyses, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The results indicate the formation of “end-on” and “bridging” superoxide species, which are trapped in the β-Bi2O3 vacant oxygen sites, Bi(IV) and Bi(V) centres also being produced. O2− interacts with Bi(IV) centres giving two superoxide adducts with temperature-dependent relative amounts, Bi(IV)–O2− and Bi(IV)–O2−–Bi(III), both having a triplet spin state.

Silica glasses with substitutional Sn-doping or with dispersion of SnO2 nanoclusters were prepared by the sol–gel method. The occurrence of SnO2 clustering was investigated by optical absorption, Raman scattering and electron paramagnetic resonance spectroscopies, varying both the tin concentration and the densification temperature of Sn-doped silica xerogels. The 3.7 eV absorption edge of SnO2 and the A1g Raman mode at 630 cm−1 of the SnO2 phonon spectrum were used to assess the presence of SnO2 nanoclusters; the yield of X-ray induced paramagnetic E′ Sn centres was monitored to probe the variation in the amount of substitutional Sn centres. The results indicate that the clustering of SnO2 becomes effective for Sn concentrations ≥ 0.8 mol% and it is competitive with the substitutional doping in xerogels densified at T ≥ 900 °C. No evidence of pre-existent clustering was observed in xerogels densified at lower temperatures in the investigated doping range.

Heterogeneous alkene epoxidation catalysts prepared by immobilization of species derived from MoO2(acac)(2) on two polymers, a polystyrene N-hydroxypropyl aminomethylpyridine resin and a polybenzimidazole resin, are known to behave differently. The two catalyst species have now been characterized extensively in terms of both the molecular structure of the Mo(VI) centers and the resin morphologies, and significant differences have been demonstrated in both aspects. Molecular structural characterization has involved elemental analysis and FTIR, electronic, and X-ray photoelectron spectroscopies, together with EXAFS analysis and associated modeling. Morphological studies have employed high-resolution transmission electron microscopy with Mo mapping, N-2 sorption, and Hg intrusion porosimetry and solvent imbibition measurements. The differences observed account for the observed variation in catalytic behavior, and these structural and morphological differences are discussed in detail. (C) 1999 Academic Press.

SnOi, Ru/SnC2 and Pt/SnO2 were prepared by sol-gel condensation method. Ru/SnOa was also obtained by supporting the metal on SnU2 xerogel. The reactivity of these materials towards CO and ah-, studied by Electron Paramagnetic Resonance spectroscopy (EPR), suggests that the electron transfer processes at the oxide surface are favored by the presence of the metal, in the order Pt Ru ion-exchanged Ru-supported. A rationale was given for the differences and for the choice of a material suitable to high sensitivity gas sensors