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An approach for the preparation of noble metal nanoparticles supported on nanostructured metal oxides is described herein. The approach is based on the sequential generation of the noble metal nanoparticles and of a metal oxide phase inside a cross-linked polymer colloid (microgel). By tuning the properties of the employed microgel, the nature and amount of both the noble metal nanoparticles and the metal oxide phase can be independently varied. The resulting composite colloids are colloidally stable and, upon isolation by precipitation and subsequent calcination, produce noble metal nanoparticles dispersed on a crystalline, nanostructured oxide phase. Preliminary catalytic tests provide information on the accessibility of the noble metal nanoparticles and, particularly in the case of gold, result in promising catalytic performances in the aerobic oxidation of alcohols.

In the synthesis of CuInS2 quantum dots (QDs), the halide ions present in the copper salts influence the QD growth and optical properties. X-ray absorption spectroscopy allowed rationalizing the halide incorporation in the lattice and the dependence of electronic properties of the material on the ion's polarizability and interaction with hydrophobic moieties.

In this work we study the surface enhanced Raman scattering (SERS) produced by hierarchical nanostructures obtained by coupling different anisotropic nanomaterial of two SERS active metals, namely Ag nanostars (AgNSs) and Au nanowires (AuNWs). Ag nanostars (AgNSs) are prepared, by a two-step one-pot synthesis by reduction of AgNO3 with hydroxylamine, trisodium citrate and NaOH. AuNWs are obtained by electroless templated synthesis in track-etched polycarbonate membranes with following etching of the template. The two precursors are bound together by bridging with the bifunctional cysteamine molecule, obtaining AgNS@AuNW hierarchical structures. Benzenethiol (BT) is adsorbed on the nanostructured material and used as SERS probe to study the amplification of Raman signals. Experimental results indicate significantly larger Raman enhancement when BT is adsorbed onto the AgNS@AuNW in comparison to AuNWs alone or decorated with quasi-spherical silver nanoparticles obtaining AgNP@AuNW. Digital simulations performed by the boundary element method agree with the experimental findings, showing higher number of hot spots and significantly higher SERS enhancements for AgNS@AuNW versus AuNWs or AgNSs or AgNP@AuNW.

The focus of this work is on the relationship between the quantitative structural characterization of bimetallic Au-Pd nanoparticles dispersed in an amorphous polymer matrix and their catalytic activity in the direct synthesis of hydrogen peroxide (DS reaction). Resonant X-ray powder diffraction with synchrotron radiation was employed to probe selectively and to reveal fine details of the structure of bimetallic nanoparticles embedded in the support. The semi-quantitative analysis of the resonant X-ray powdered diffraction data, made on a large number of metal nanoparticles, shows that in one of the polymer-supported Au-Pd catalyst for the DS reaction (P75) featured by an overall molar Pd/Au of about 5.54, the smallest metal nanoparticles (MNPs), which account for more than 99.9% of the total MNPs number and for more than 95% of the metal surface, are formed by practically pure palladium. The relative number of bimetallic alloyed nanoparticles is very small (less than 4 &times, 102 ppm) and they contribute to only about 2% of the total metal surface. In a second gold-enriched catalyst (P50) with an overall molar Pd/Au of 1.84, the proportion of the bimetallic alloyed nanoparticles increased to about 97% and they account for about 99% of the metal surface. As a result of the metal intermixing, the catalytic productivity for the DS reaction increased from 97 to 109 mmolH2O2/molH2, owing to the gold-promotion of palladium.

The development of new safe inorganic UV filters to effectively protect the skin from ultraviolet (UV) radiation effects is an emerging issue. Bismuth titanate-based UV filters embedded into mesoporous silica nanoparticles (MSN) represent a new class of inorganic sunscreens, with excellent UVA and UVB shielding properties. In addition, the presence of bismuth ions promotes a self-sealing process, allowing (i) the entrapment of the active phases in the deepest core of the system and (ii) the formation of an external glassy silica layer with a consequent suppression of the photocatalytic activity. In this work, aimed at studying in detail the self-sealing mechanism and accessing the role of bismuth ions in the formation of the system, a series of samples impregnated with a different amount of bismuth were investigated. The self-sealing process already occurs at the lowest content of bismuth and the mechanism is demonstrated to be triggered by the ability of Bi to work as a low-melting point agent for silica. Finally, a sunscreen formulation containing the new UV filter was prepared and the Sun Protection Factor (SPF), the pH and the viscosity were measured, demonstrating the potential of the proposed material for large-scale applications.

We have synthesized and fully characterized some novel allyl palladium complexes stabilized by mixed spectator ligands, namely the water soluble sodium 3,3′,3″-phosphinetriyltribenzenesulfonate, (TPPTS) and three carbenes derived from differently alkylated natural xanthines. In order to explore their potential applications we have tested their catalytic activity in the Suzuki-Miyaura coupling of para-bromoacetophenone with phenyl boronic acid, chosen as standard reaction. Only one of the complexes under study displays a remarkable stability in water and catalytic activity. We have therefore undertaken a catalytic investigation. These results are reported in the present paper together with the solid state structural characterization of a silver precursor of the palladium allyl complexes.

We report a facile, inexpensive, and green method for the preparation of Pd nanoparticles in aqueous medium stabilized by anionic sulfonated surfactants sodium 1-dodecanesulfonate 1a, sodium dodecylbenzenesulfonate 1b, dioctyl sulfosuccinate sodium salt 1c, and poly(ethylene glycol) 4-nonylphenyl-3-sulfopropyl ether potassium salt 1d simply obtained by stirring aqueous solutions of Pd(OAc)2 with the commercial anionic surfactants further treated under hydrogen atmosphere for variable amounts of time. The aqueous Pd nanoparticle solutions were tested in the selective hydrogenation reactions of aryl-alcohols, -aldehydes, and -ketones, leading to complete conversion to the deoxygenated products even in the absence of strong Bronsted acids in the reduction of aromatic aldehydes and ketones, in the controlled semihydrogenation of alkynes leading to alkenes, and in the efficient hydrodechlorination of aromatic substrates. In all cases, the micellar media were crucial for stabilizing the metal nanoparticles, dis...

Eu3+ doped CaF2 and SrF2 nanoparticles were synthesized through a facile hydrothermal technique, using citrate ions as capping agents and Na+ or K+ as charge compensator ions. A proper tuning of the reaction time can modulate the nanoparticle size, from few to several tens of nanometers. Analysis of EXAFS spectra indicate that the Eu3+ ions enter into the fluorite CaF2 and SrF2 structure as substitutional defects on the metal site. Laser site selective spectroscopy demonstrates that the Eu3+ ions are mainly accommodated in two sites with different symmetries. The relative site distribution for lanthanide ions depends on the nanoparticle size, and higher symmetry Eu3+ sites are prevalent for bigger nanoparticles. Eu3+ ions in high symmetry sites present lifetimes of the 5D0 level around 27 ms, among the longest lifetimes found in the literature for Eu3+ activated materials. As a proof of concept of possible use of the Eu3+ activated alkaline-earth fluoride nanoparticles in nanomedicine, the red luminescenc...

Strontium fluoride nanoparticles activated with Nd 3+ ions were studied as nanosized optical thermometers in the first (800–950 nm) and second (1000–1300 nm) biological windows, by monitoring the Nd 3+ emission as a function of the temperature. The variations of the Nd 3+ emissions were correlated with the temperature changes and the thermometric properties of SrF 2 nanoparticles were evaluated using a ratiometric method. The best thermal sensitivity was found to be 0.60% K −1 , a value which is the highest found for water dispersible colloidal nanothermometers based on the near-infrared luminescence of Nd 3+ ions only in single phase materials. The excellent thermometric performance is also demonstrated by a thermal sensitivity of 1.2 °C, that can be achieved in temperature evaluation of real systems. Temperature measurements using a phantom tissue confirmed that the samples serve as efficient ratiometric nanothermometers that can work in two biological windows.

[RhCl(COD)] 2 in combination with a water soluble sulphonated pyridyl-triazolyl N,N -bidentate ligand efficiently catalyzes styrene and 1-hexene hydroformylation in water/organic solvent biphasic systems. The catalyst displays a good activity affording mixtures of linear and branched aldehydes with complete chemoselectivity. The aqueous catalytic phase may be recycled four times giving complete substrate conversion by 18 h. Mercury-poisoning experiments and transmission electron microscopy indicate that, after the first catalytic run, rhodium is present in the aqueous phase in nanoparticle form.

Here, we present a thorough study of pegylated silica nanoparticle (SNP) interaction with different biological environments. The SNPs have a mean diameter of about 40 nm and are coated with polyethylene glycol (PEG) of different molecular weights. The physicochemical characterization of SNPs allowed the confirmation of the binding of PEG chains to the silica surface, the reproducibility of the synthesis and the narrow size-dispersion. In view of clarifying the SNP interaction with biological environments, we first assessed the SNP reactivity after the incubation with two cell lines (macrophages RAW 264.7 and primary human fibroblasts), observing a reduced toxicity of pegylated SNPs compared to the bare ones. Then, we investigated the effect of the protein adsorption on the SNP surface using the model serum protein, bovine serum albumin (BSA). We found that the protein adsorption takes place more heavily on poorly pegylated SNPs, promoting the uptake of the latter by macrophages and leading to an increased mortality of these cells. To better understand this mechanism by means of flow cytometry, the dye Ru(bpy)3Cl2 was incorporated in the SNPs. The overall results highlight the SNP potentialities as a drug delivery system, thanks to the low interactions with the macrophages.

CaF 2 nanoparticles activated with Nd 3+ ions have been investigated as potential optical nanothermometers in the biological windows. The variation of the Nd 3+ emission around 850 and 1060 nm as a function of the temperature has been measured. A ratiometric approach, based on the relative changes in the intensities of different emission bands of the Nd 3+ has been considered to investigate the thermometric properties of the NPs. The evaluated thermal sensitivity is around 0.12% K −1 , a value that is similar to those found for other water dispersible nanothermometers based on the near-infrared luminescence of the Nd 3+ lanthanide ion. The temperature uncertainty is around 1.8 °C, small enough to monitor the local temperature during a photothermal treatment.

Gold nanoparticles supported onto a nanoporous semicrystalline polymorphic polymer matrix consisting of syndiotactic polystyrene- cis -1,4-polybutadiene multiblock copolymer (AuNPs-sPSB) were investigated as catalyst in the reduction of nitroarenes into anilines using sodium borohydride as reductant. The crystalline phase and the morphology of the polymeric support were varied to assess their influence on the selectivity of the reaction pathway. The β and γ crystalline forms, which are not permeable to small molecules, led to a partial reduction of nitrobenzene into both azoxybenzene and diazobenzene whereas the porous δ and e crystalline forms efficiently catalyze the complete reduction into aniline through the condensation route of the reaction mechanism proposed by Haber, achieving the highest activities reported so far for this reaction.

Different metal precursors and reducing agents were applied in the preparation of 1 wt % Pd catalysts supported on commercial ion-exchange resin (Lewatit K2621) and used in the direct synthesis of ...

TiO2–SiO2 composites containing 10 wt%, 20 wt%, 30% and 40 wt% of TiO2, obtained by using preformed mesoporous silica nanoparticles (MSNs) and titanium isopropoxide as titanium source, have been investigated in detail using a variety of techniques. All the samples were characterized by N2-physisorption, X-ray powder diffraction (XRPD), diffusive reflective UV-vis spectroscopy (DRUV-vis), X-ray photoelectron spectroscopy (XPS) and imaged using transmission electron microscopy (TEM). The TiO2–MSN composites, that exhibited a spherical morphology, high specific surface areas and titania in the anatase phase, owing to their specific chemical–physical properties were studied as catalysts in the photocatalytic degradation of methylene blue, methyl orange and paracetamol, as examples of polluted wastewaters. The well-defined porous structures of MSNs may offer a special environment for titania nanoparticles, increasing the specific surface area and the thermal stability of the composite, thus modifying the photocatalytic behavior of the materials. The TiO2 loading, the particle size and the surface characteristics were related to the degree of UV absorption and the measured energy band gap of the nanocomposites. A cooperative effect between the two components (TiO2 and SiO2) could be the key factor at the basis of the good photocatalytic performances: nanostructured TiO2 in intimate contact with MSN provides the sites for generation of OH˙ radicals by oxidation of water and the SiO2 skeleton is able to adsorb the molecules of cationic dyes and prevent poisoning of the TiO2 surface.

Bimetallic Ag/Pd nanoparticles were fabricated by laser ablation of a silver target in water and successive addition of palladium nitrate to promote a partial galvanic replacement of silver with palladium. The obtained nanoparticles, as shown by a microscopic investigation coupled with EDX and SAED analysis, exhibit a silver core, able to produce SERS enhancement, and a Pd cloudy shell at the surface that can interact with organic molecules in catalytic reactions. The test was carried out using as a molecular probe an aromatic nitroderivative, which, by adsorption on the metal substrate, undergoes an almost total reduction to azoderivate, as evidenced by the comparison between the SERS spectra recorded on pure Ag and Ag@Pd nanoparticles. © 2013 Elsevier B.V. All rights reserved.

The commercially available ion-exchange resin Amberlite IR120 has been used as the stabilizing agent for the preparation of a size controlled nanostructured hematite phase. The employed synthetic approach, based on the loading of Fe3+ by ion exchange and the subsequent treatment with an aqueous base solution, produces a nanocomposite material with a remarkably high content of oxide nanoparticles (iron content = 18.8% w/w, corresponding to 24.9% w/w of Fe2O3). Scanning electron microscopy and energy dispersive X-ray spectroscopy investigation show that the iron distribution is egg-like and parallels the distribution of the sulfonic groups of the ion-exchanger. Transmission electron microscopy characterization reveals that the size of the ferric oxide nanoparticles in the nanocomposites is narrowly distributed in the 4-6 nm range and that it is the same after the first and the fifth ion-exchange-precipitation cycle. Selected area Electron Diffraction (SAED) analysis of the nanostructured oxide after five ion-exchange-precipitation cycles indicates that it is hematite with a distorted structure.

Catalytic reforming of CH4 with CO2 was investigated on mono and bimetallic Pd(or Pt)-Ni based samples supported on Al2O3 and ZrO2. A simple temperature-programmed procedure was used to study both reforming and coke formation via CH4 or CO decomposition. Catalysts supported on zirconia are more active than alumina-supported samples. The addition of Pt or Pd to Ni/ZrO2, preferably by co-impregnation, prevents coke formation. The co-impregnated Ni-Pd/ZrO2 catalyst looks the most promising for a possible industrial application.

Synthesis of gold nanoclusters inside strongly acidic ion exchangers, in beaded forms, is carried out under different conditions. After metallation with [Au(en) 2 ]Cl 3 and reduction with H 2 in the absence of any added aqueous phase, Au 0 / -SO 3 H nanocomposites are produced that are compared with Au 0 / -SO 3 − Na + ones obtained with NaBH 4 as reductant in aqueous medium. Reduction conditions allow control of both distribution and size of the metal nanoclusters. Metal distribution inside the polymer beads appears to be quite homogeneous under the hydrogen reduction conditions and metal nanoclusters size turns out to be size-controlled in the 3–5 nm range. In the case of the action of NaBH 4 in water, metal distribution inside the polymer beads appears to be quite peripheral and the metal nanoclusters turn out to be size-controlled but definitely larger, 5–7 nm, than those obtained by action of molecular hydrogen.

Nanoporous gold (NPG) layers have been fabricated by silver leaching of Ag–Au alloys with different dealloying processes and working temperatures. Structural, compositional and optical properties of the different samples have been analyzed with several experimental techniques: scanning and transmission electron microscopy (SEM/TEM), electrochemical impedance spectroscopy (EIS), Rutherford back scattering (RBS), spectroscopic ellipsometry. A periodic pattern has been realized on samples surface with focused ion beam (FIB) lithography in order to exploit NPG metallic behavior for surface plasmon polaritons (SPPs) excitation. The plasmonic response of the several NPG gratings has been analyzed and related to structural properties and fabrication conditions.

Hydrogen production by steam reforming of methanol and ethanol is studied over a series of Cu/ZnO/Al(2)O(3) catalysts prepared by different coprecipitation procedures and modified with the introduction of Ni and Co. The catalysts are characterized using N(2) physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR) techniques, N(2)O decomposition, high resolution transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). Despite the influence of the preparation method on the texture and structure of Cu/ZnO/Al(2)O(3) catalysts, their catalytic behavior appears not significantly affected. While Cu/ZnO/Al(2)O(3) shows poor H(2) selectivity in the ethanol steam reforming reaction, the presence of a second metal (Ni or Co) significantly improves the reforming reaction. Although coke deposition remains a drawback for these systems, formation of an alloy between Ni and Cu appreciably reduces carbon deposition with respect to the Co/Cu-based system. (C) 2010 Elsevier B.V. All rights reserved.

We report a facile strategy to obtain multiwalled carbon nanotubes (MWCNTs) functionalized with covalently bonded lysozyme. The functionalization procedure has been investigated by means of several techniques, including thermogravimetry, Raman spectroscopy, transmission electron microscopy, and cyclic voltammetry. A functionalization of about 1 lysozyme molecule every 4000 carbon atoms is obtained. The modified lysozyme-CNTs nanocomposite shows a significant increase of the antibacterial activity towards the Gram-positive S. aureus if compared with lysozyme in solution.

Starting from the gel-type, cross-linked copolymer co-poly-{(N,N-dimethethylacrylamide/4-vinylpyridine/N,N′-methylenebisacrylamide} (DV44) we prepared nanoclusters of several noble metals (Ru, Rh, Pd, Pt, Ag, Au) inside its polymer framework through the so-called “template-controlled synthesis” approach. This procedure involves the immobilization of the relevant metal centers inside the polymer framework, followed by their reduction to M0 nanoclusters (in our case, uptake from solutions of suitable precursors and reduction with aqueous solutions of NaBH4, respectively). In this way, a set of monometallic polymer supported nanoclusters (M/DV44, M = Ru, Rh, Pd, Pt, Ag, Au) were obtained. The experimental conditions were set so as to generally obtain a homogeneous radial distribution of the metal throughout the particles of the materials. The latter were characterized by means of transmission electron microscopy for the assessment of the metal nanocluster sizes. The diameter of the nanoclusters generated by reduction inside water-swollen DV44 were compared with the size of the nanopores of the water-swollen polymer framework that had previously been determined by means of inverse steric exclusion chromatography. The diameter of the prevailing pore fractions in water-swollen DV44 was 3.2–4.3 nm and the largest available pores observed had a diameter of 8.1 nm. Nanoclusters with diameters larger than this value were observed in no cases, and in all cases the average diameter of the nanoclusters never exceeded the diameter of the prevailing pore fraction. For Pd/DV44, Ag/DV44 and Au/DV44, the average nanocluster diameter compared very well with the diameter of the prevailing pore fraction.

At 35 °C, in the presence of supercritical carbon dioxide (80–150 bar) as a solvent, α-olefins (RCHCH2, R = C4–C6) undergo highly selective self-metathesis catalyzed by supported Re-oxide (7%). To the best of our knowledge, this is the first procedure for the metathesis of alkenes, in which heterogeneous catalysts are combined with the use of dense CO2. The intrinsic eco-compatibility and the unique physicochemical properties of this medium offer both environmental and synthetic advantages: not only conventional toxic solvents (e.g. n-heptane and toluene) can be replaced, but the reaction is faster. For instance, after 2 h, the average conversion of 1-octene is 67% and 40% in scCO2 and n-heptane, respectively. The product of self-methatesis, 7-tetradecene, can be isolated in yields up to 68%. At 90 bar, the reaction is rather sensitive to the mole fraction of the olefin (in scCO2); though, the enhancement of the pressure (and the density) of the supercritical medium does not induce significant effects on either the rate or the selectivity of the process. The nature of the catalytic support also greatly affects the reaction outcome: Re-oxide shows good activity if dispersed over γ-Al2O3, while silica-based systems are ineffective.

The cross-linked polyurea support EnCat 30, its related macromolecular complex Pd(II)/EnCat 30 and its related Pd(0)/EnCat 30NP nanocomposite are thoroughly investigated with SEM, TEM, ISEC and ESR in the solid state (SEM and TEM) and swollen state in THF (ISEC and ESR). Pd(II)/EnCat 30 and its related Pd(0)/EnCat 30NP are obtained by microencapsulation of palladium acetate in a polyurea framework, which is formed upon hydrolysis/condensation of mixtures of multi-functional oligo-arylisocyanates in dichloroethane. Most remarkably, both Pd(II)/EnCat and Pd(0)/EnCat 30NP turn out to be far more (nano)porous and swellable materials than the blank polyurea matrix (EnCat 30). It is proposed that there is a strong nanostructural effect exerted by Pd(II) species due to its interaction with functional groups (amines stemming from the hydrolysis of the isocyanato groups or ureido groups belonging to the polymer chains) during the growth of the cross-linked polymer framework. As a consequence, the catalytic species in both Pd(II)/EnCat 30 and Pd(0)/EnCat 30NP are much more accessible to molecules diffusing from liquid phases in contact with the materials and, hence, are better catalysts than expected from the morphology of blank polyurea EnCat 30.

The relationship between the catalytic activity and Pd particle size in Pd/ultradispersed diamond catalysts is established in the hydrodechlorination of 1,3,5-trichlorobenzene under multiphase conditions.

We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.

Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control deals with the synthesis of metal nanoclusters along all known methodologies. Physical and chemical properties of metal nanoclusters relevant to their applications in chemical processing and materials science are covered thoroughly. Special attention is given to the role of metal nanoclusters size and shape in catalytic processes and catalytic applications relevant to industrial chemical processing. An excellent text for expanding the knowledge on the chemistry and physics of metal nanoclusters. Divided in two parts; Part I deals with general aspects of the matter and Part II has to be considered a useful handbook dealing with the production of metal nanoclusters, especially from their size-control point of view.

Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the preparation parameters, namely, temperature and electric field intensity across the samples. This technique, which allowed to dope the glass matrix with high metal concentration values, can be used as the first step in combined methodologies for the preparation of nanostructured glass composites. The shape of the measured Co diffusion profiles indicates that the migration process depends not only on the experimental parameters but also on the behavior of alkali ions within the glass. Chemical phenomena occurring at the metal/glass interface also play a significant role in the penetration of the Co ions. The possibility of doping the glass with two different metal species was also investigated, with the aim to create the condition for the formation of core-shell or alloy nanoclusters. In particular, preliminary results on Co+Au field-assisted co-diffusion are presented. (c) 2005 Elsevier B.V. All rights reserved.

Silica films containing metal particles in the nanometer size range exhibit optical properties that make them useful in several applications. In this work, copper-containing silica films were synthesized by a radiofrequency magnetron sputtering co-deposition technique, and then thermally-treated (in some cases sequentially) in different annealing atmospheres, i.e. either oxidizing or reducing (700–900 °C of temperature range, 2–5 h of time range, 400 °C/h of heating rate and 250 °C/h of cooling rate). Depending on the thermal treatment, the crystallite average surface-weighted dimension ranges between 5 and 9 nm for metal copper, and is larger than 25 nm for CuO. The preparation protocols to obtain these characteristics were determined in order to control cluster formation and growth. Characterization of the samples following the various preparation steps was performed by Rutherford backscattering spectrometry, optical absorption spectroscopy, and X-ray diffraction. Our experimental observations showed that the composite formation was a function of the annealing conditions.

The liquid phase oxidation of glycerol with oxygen has been studied using a series of monometallic and bimetallic catalysts based on Au, Pd and Pt metals supported on carbon, in order to study the effect of the metal on the distribution of the products. It was found that by using bimetallic catalysts (Au-Pd, Au-Pt) the distribution of the products could be controlled. Moreover, bimetallic catalysts were by far more active than monometallic catalysts. Selectivity could be tuned by using different preparation method. © 2005 Elsevier B.V. All rights reserved.

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.

The Al2O3 promotion of ZrO2/SO4 has been shown to influence n-butane isomerization activity. In this paper we report a study of the influence of a small addition of Al2O3 (0.6−10.3 wt %) onto the ZrO2 structure and microstructure. The addition of alumina is related to an increase of the surface area. A detailed X-ray diffraction analysis by the use of the modified Rietveld method allowed us to follow the changes in the crystalline phases and to quantify the amount of amorphous phase. When the Al2O3 content is increased, a decrease of the ZrO2 particle sizes is observed, paralleled by an increase of the amorphous phase. When the Al2O3 content is larger than 3.7 wt %, only amorphous phase can be detected. No crystalline peaks of Al2O3 were ever observed. These data were supported also by TEM and Raman measurements.

Time-resolved X-ray diffraction measurements were performed in situ on a Pd/C catalyst during two successive thermal treatments from 300 to 873 K. Analysis of the diffraction patterns, as a function of thermal treatment, reveals anomalous features in the evolution of Pd particles. An intermediate Pd1-xCx phase (x ∼ 0.1) is observed and dissolved into pure Pd at ∼700 K. Moreover, the size of metal particles, remaining almost constant (∼10 nm) during the annealing, abruptly increases to 30 nm in close connection with the dissolution of the Pd1-xCx phase. These effects clearly point out an interaction between the metal and the support and suggest that the formation of the Pd1-xCx phase would prevent the metal-particle sintering, thus maintaining the catalyst dispersion at a high level. There is no evidence of the formation of a Pd1-xCx phase during the second temperature treatment since only metallic Pd was detected. As for the growth in particle size, a small increase to 32 nm was observed.

We investigated the nucleation and crystallization behavior of multi-phase glass-ceramic materials (in the Li2O–Al2O3–SiO2 system to which low amounts of oxides such as TiO2, ZrO2, P2O5, BaO, Sb2O3 and ZnO were added), with interest in their transparency properties as glazes for industrial tiles with high scratch resistance. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. XRD showed that the nucleating oxides produce, during the nucleation stage (at 953 K for 20 h), an orthorhombic ZrTiO4 phase, which maintains a similar crystallite size (about 4 nm) during the subsequent crystallization processes. We succeeded in determining the concentration of nuclei by using XRD data only. This quantity resulted close enough to the corresponding one, determined using the classical TEM method. The formation of each crystalline phase, developed during the crystallization stage, as a function of the thermal treatment, was quantitatively measured using the Rietveld method. In particular, the isothermal transformations at 1003 and 1023 K of the characteristic main phase, i.e., β-eucryptite s.s., which is richer in silica with respect to the relevant stoichiometric phase, into β-spodumene s.s., also richer in silica, were found to be consecutive solid state reactions. Moreover, this preliminary investigation aims at improving knowledge of the mechanisms leading to the development of transparent/opaque materials during the thermal treatment of Li2O–Al2O3–SiO2 glass-ceramics.

In this work we have determined, on a series of 0.5% Pd/C catalysts, the palladium particle sizes by the following physical techniques: (i) X-ray diffraction (XRD) line broadening (LB) method, associated with the Rietveld method, (ii) small-angle X-ray scattering, and (iii) transmission electron microscopy. The catalysts, suitably aged at different temperatures (673, 773, 873, and 973 K), had significantly different metal dispersions. Since the XRD-LB technique is not able to measure directly very small metal particles or clusters (roughly ≤25 A in size), because they give diffuse X-ray scattering spreading out into the background, we have tackled this problem by means of a suitably tailored Rietveld quantitative analysis. This analysis allowed determination of the Pd fraction “visible” in the Voigtian XRD peaks and its average crystallite size using the LB method. As to the nanoparticle size of the undetectable fraction, an average value of 20 A was assumed, corresponding to the size of a cubooctahedral...

Sol–gel preparation of ZrO2–WO3 is reported. The sol–gel technique allows preparation to be simplified and yields a more reliable and reproducible product. Catalysts were characterized by X-ray, BET and were tested in the isomerization of n-butane and 1-butene. Catalysts prove to be active with respect to analogous samples prepared by traditional methods.