Search

This paper presents the influence of the presence of a modified organoclay, Cloisite® 20A (MMTA) on the structural and drug release properties of ureasil organic–inorganic hybrid. Sol–gel process was used to prepare the hybrid nanocomposites containing sodium diclofenac (DCF) at 5% wt. The effect of the amount of MMTA incorporated into the ureasil hybrid matrix was evaluated and characterized in depth by different techniques such as X-ray diffraction (XRD), small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and swelling properties. The influence of MMTA on ureasil nanocomposites release profile was evaluated by in situ UV–vis. The diffraction patterns of the UPEO–MMTA nanocomposites showed a synergistic contribution effect that led to an intensity increase and narrowed the diffraction peaks, evidencing a crystallite PEO growth as a function of the modified nanoclay content. The interactions between polyether chains and the hydrogenated tallow of MMTA led to an easy intercalation process, as observed in UPEO–MMTA nanocomposites containing low (1% wt) or high (20% wt) nanoclay content. The waterway (channels) created in UPEO–MMTA nanocomposites contributed to a free volume increase in the swollen network compared to UPEO without MMTA. The hypothesis of the channels created after intercalation of the PEO phase in the interlayer of MMTA containing organoammonium ions corroborates with the XRD results, swelling studies by SAXS, and release assays. Furthermore, when these clay particles were dispersed in the polymeric matrix by an intercalation process, water uptake improvement was observed, with an increased amount of DCF release. The design of ureasil-MMTA nanocomposites containing modified nanoclay endows them with tunable properties; for example, swelling degree followed by amount of controlled drug release, opening the way for more versatile biomedical applications. [ABSTRACT FROM AUTHOR]

Operando time‐resolved X‐ray absorption spectroscopy (XAS) was used to determine nickel species supported on porous MgO during the ethanol steam reforming reaction. The Principal Component Analysis (PCA) of the nickel K‐edge XAS spectra revealed Ni(OH)2, NiMgO, and metallic Ni during the activation and reaction of the catalysts. The Multivariate Curve Resolution‐Alternating Least Squares (MCR‐ALS) method for the time‐resolved XAS spectra data permitted to calculate the concentration of species during the activation and reaction steps and to determine the formation of NiMgO and nickel reduction degree. The samples prepared with surfactants, Ni10MgO‐F127 and Ni10MgO‐P123, showed less nickel reduction (less than 30 %) but were more active and stable than the reference Ni10MgO catalyst, which reduced 52 %. It happened due to the smaller particle size and a larger specific area of the porous supports. The samples synthesized without Pluronic deactivated, and ethanol dehydrogenation became predominant instead of the ethanol steam reforming. [ABSTRACT FROM AUTHOR]

Nanotechnology in building materials has still not been widely explored, despite its great potential in developing a new generation of smart and eco-efficient cementitious materials based on the addition of nanoparticles. In this context, layered double hydroxides (LDH) are a family of anionic clays that can regenerate their nanostructure after thermal decomposition to the corresponding mixed oxides (MO). This memory effect involves the reversible recrystallization of the LDH nanoparticles from nanocrystalline MO in contact with water or anionic solutions. It has shown promise in the immobilization of different anions, such as chloride and carbonate, that could compromise the durability of reinforced concrete. This study proposes the incorporation of nanocrystalline MO in the cementitious matrix to control the rheological properties of the paste and reduce the porosity of the cement because the regeneration of the lamellar nanostructure occurs by the dissolution and reprecipitation of LDH nanoparticles inside the pores formed during the consolidation of the paste. Time-resolved wide-angle X-ray scattering (WAXS) was used to study the mechanism of regeneration of the LDH structure following contact of the MO with the cement pore solution. The results showed that the regeneration of the LDH, which occurs by an aggregative growth of anisotropic nanoparticles, changed the rheological behavior by increasing the elastic modulus (G′) and consequently contributing to the consolidation of the paste, demonstrating the potential of these materials for application in three-dimensional (3D) printing. Regarding the pore structure of the hydrated cement, a porosity reduction of up to 20% was observed with the addition of 2.0 wt % of MO. Furthermore, after 28 days of hydration, the specific surface area of the cement was reduced from 60 to 36 m2 g–1 with the incorporation of 1.0 wt % of MO. The use of LDH nanoparticles as a cement smart nanofiller proved to be advantageous in the kinetic control of cement curing and improvement of the porous structure of the hydrated cement. [ABSTRACT FROM AUTHOR]

In situ techniques were used to investigate the hierarchical porous structure of alumina monoliths formed by the combined processes of sol–gel transition and spinodal phase separation. The addition of low molecular weight poly(ethylene oxide) (PEO) in the sol–gel reaction of aluminum chloride induced phase separation between aluminate gel and PEO solvent. In situ time-resolved small-angle X-ray scattering (SAXS) measurements revealed that structural evolution during gelation of a sample without PEO was dominated by Ostwald ripening. With PEO addition, this coarsening mechanism, occurring during a short intermediate stage (6 min), was followed by the aggregative coalescence of phase separating domains during the late stage of spinodal decomposition. The effect of PEO in the gelation mechanism also influenced the porous structure formed by calcination of the alumina monoliths. During calcination for PEO removal and conversion from xerogel to ceramic, in situ SAXS monitoring evidenced that the formation of mesopores followed the spinodal decomposition mechanism proposed by Cahn's theory. Alumina with well-defined meso- and macropore families, high specific pore volume (2.0 cm3 g−1), and high surface area (252 m2 g−1) was obtained as a result of spinodal decomposition during the sol–gel transition followed by heat treatment. Highlights: Elucidation of the structure formation process of hierarchical porous alumina with high pore volume. In situ SAXS used to probe the gelation mechanism and coarsening of phase-separated domains. Mesoporosity evolution during heat treatment followed Cahn's model for spinodal decomposition. [ABSTRACT FROM AUTHOR]

The effect of sol-gel alumina characteristics on the supported Co catalyst properties was investigated at the different steps of catalyst preparation. Porous alumina with variable surface reactivity were prepared from the sol-gel transition and the spinodal decomposition induced by polymers. The hydrophobicity of polymer or the calcination temperature controls the amount of the hydroxyl groups. The dried catalysts are composed of cobalt alumina hydrotalcite-like compounds up to 64 %. After calcination, higher proportions of CoAl2O4 are observed in the alumina presenting a greater content of hydroxyl and hydrotalcite. The Co speciation during activation investigated by Quick X-ray absorption spectroscopy evidences that both Co3O4 and CoAl2O4 are first fully reduced to CoO and then partially transformed into point-like Co0 nucleus. The catalysts were highly active in the ethanol steam reforming reaction; however, coke deposition leads to deactivation. This deleterious effect was minimized for catalysts operating with a CoO/Co0 ratio close to 1:3. [ABSTRACT FROM AUTHOR]

Structural and surface features of highly dispersed copper catalysts supported on hierarchical porous alumina were evaluated for the ethanol dehydrogenation reaction. The catalysts were prepared by incipient wetness impregnation of alumina obtained by a dual template sol-gel procedure. Structural characterizations provided evidence that the copper was highly dispersed on the alumina in the form of monomeric octahedral Cu2+ species adsorbed into an incomplete layer. A two-step reduction was observed for the catalysts in a temperature range of 50-250 °C under H2/He flow. The temperature for onset of reduction and the percentage of Cu+ species formed upon activation were dependent on the Cu loading. At lower Cu loadings, the amount of Cu+ increased, leading to a slower and less complete reduction. Based on the apparent activation energy and turnover frequency, it could be concluded that Cu+ containing a mixture of Cu+/Cu0 results in a more efficient catalyst than Cu0 for the ethanol dehydrogenation reaction. [ABSTRACT FROM AUTHOR]

This work deals with a red phosphor, Y3BO6:Eu3+, and its corresponding poly(N-vinylpyrrolidone) (PVP)/Y3BO6:Eu3+ luminescent composite film suitable for applications in the next generation of Hg-free lamps based on near ultraviolet (UV) light emitting diodes (LEDs). Well crystallized samples of Y3BO6 powders with the Eu3+ content up to 20 mol% were prepared by the Pechini method. After structural, morphological and optical characterization, the best doping rate of Eu3+ in the matrix was determined to be 15 mol%. This optimal powder, which is highly friable, was easily ground into fine particles and homogeneously dispersed into a PVP polymer solution to give rise to a polymer phosphor composite. Structural and optical features of the composite film have been studied and compared to those of a pristine PVP film and Y3BO6:Eu3+ powder. All the characterization (XRD, SAXS, luminescence…) proved that the red phosphor particles are well incorporated into the polymer composite film which exhibited the characteristic red emission of Eu3+ under UV light excitation. Furthermore, photostability of the polymer/phosphor composite film under UV-LED irradiation was evaluated from exposure to accelerated artificial photoageing at wavelengths above 300 nm. [ABSTRACT FROM AUTHOR]

This work focuses on the study of BaMgAl10O17:Eu2+ (BAM:Eu) nanophosphors prepared by a microwaveassisted combustion procedure and more especially on the polymer/BAM:Eu nanocomposite film suitable for optical devices such as solid-state-lighting. Powder presented a specific nanomorphology, highly friable and thus easily ground into fine particles. They were then homogeneously dispersed into a polymer solution (poly(N-vinylpyrrolidone) or PVP) to elaborate a polymer phosphor nanocomposite. The structural, morphological and optical features of the nanocomposite film have been studied and compared to those of a pristine PVP film and BAM:Eu powder. All the characterizations (XRD, SEM, SAXS, etc.) proved that the blue phosphor nanoparticles are well incorporated into the polymer nanocomposite film which exhibited the characteristic blue emission of Eu2+ under UV light excitation. Furthermore, the photostability of the polymer/phosphor nanocomposite film has been studied after exposure to accelerated artificial photoageing at wavelengths above 300 nm. [ABSTRACT FROM AUTHOR]

The structure and the thermodegradation behavior of both poly(methyl methacrylate)- co-poly(3-tri(methoxysilyil)propyl methacrylate) polymer modified with silyl groups and of intercalated poly(methyl methacrylate)- co-poly(3-tri(methoxysilyil)propyl methacrylate)/Cloisite 15A™ nanocomposite have been in situ probed. The structural feature were comparatively studied by Fourier transform infrared spectroscopy (FTIR), 13C and 29Si nuclear magnetic resonance (NMR), and small angle X-ray scattering (SAXS) measurements. The intercalation of polymer in the interlayer galleries was evidenced by the increment of the basal distance from 31 to 45 Å. The variation of this interlayer distance as function of temperature was followed by in situ SAXS. Pristine polymer decomposition pathway depends on the atmosphere, presenting two steps under air and three under N2. The nanocomposites are more stable than polymer, and this thermal improvement is proportional to the clay loading. The experimental results indicate that clay nanoparticles play several different roles in polymer stabilization, among them, diffusion barrier, charring, and suppression of degradation steps by chemical reactions between polymer and clay. Charring is atmosphere dependent, occurring more pronounced under air. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO2 films. Two thin film layers of TiO2 (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1 s at 100 and 400 °C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29 nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO2–Co treated at 400 °C, the ESI-MS showed the fragments formed during the methylene blue decomposition. [ABSTRACT FROM AUTHOR]

Acetylacetone has been used as a chemical modifier for the synthesis of undoped and Tb3+-doped Y3Al5O12powders. A systematic investigation concerning its influence on the structural and morphological properties of amorphous and crystallized samples has been carried out. These properties have been comparatively studied by means of X-ray diffraction, infrared spectroscopy, SEM, XAS and SAXS. 27Al NMR and EPR experiments have been performed to complete the study. The combined results have evidenced that acetylacetone promotes organic groups departure during calcination, entailing a better structural organization at lower temperatures compared with unmodified powders. Structuration has been proven to occur at short-scale range until a 600 °C heating treatment before being extended by coalescence at higher temperatures. Finally, the presence of acac ligands on the alkoxides leads to a monomer-cluster aggregation process, and thus to a more open network. [ABSTRACT FROM AUTHOR]

Reports on SnO[sub 2] thin films obtained by the sol-gel method starting from inorganic precursor solutions. Comparison of the undoped and Sb-doped SnO[sub 2] films prepared by dip-coating; Characterization of the porous nanostructure by grazing incidence small-angle X-ray scattering; Use of X-ray reflectivity to determine the density and the thickness of the films.

Reports on the deposition of indium-doped zinc oxide films by the pyrosol process on glass substrates at different temperatures from solutions containing In/Zn molar ratios up to ten percent. Investigation of the nanostructure of the films using grazing-incidence small-angle X-ray scattering; Indication of the presence of elongated nanopores with long axes perpendicular to the film surface.

Examines the structure of weakly bonded silica-polypropyleneglycol (PPG) nanocomposites. Properties of the nanocomposite materials; Shape of small-angle X-ray scattering curves; Components on the structure of the nanocomposites.

Focuses on a small-angle x-ray scattering analysis of the smart thermo-optical behavior of zirconyl aqueous colloids. Details on the changes in the transparency of the colloids during heating; Effects of chloride ion concentration on the structural characteristics of the system; Mechanisms involved in the sol-gel transition.

The Back Cover picture shows the characterization of alumina‐supported copper catalysts using synchrotron radiation (XAS) and the transformation of ethanol from sugarcane in compounds with higher aggregate value, such as hydrogen, acetaldehyde, and ethyl acetate. In their Full Paper, W. H. Cassinelli et al. perform a correlation between structural and surface features of highly dispersed copper supported on hierarchical porous alumina for ethanol dehydrogenation. Evaluation of catalysts showed that the mixture Cu+/Cu0 is more active than Cu0 in the ethanol dehydrogenation reaction. The article highlighted by this cover can be found on p. 1668 ff. of Issue 11, 2015. [ABSTRACT FROM AUTHOR]

Zirconia-based ceramics that retain their metastable tetragonal phase at room temperature are widely studied due to their excellent mechanical and electrical properties. When these materials are prepared from precursor nanopowders with high specific surface areas, this phase is retained in dense ceramic bodies. In this work, we present a morphological study of nanocrystalline ZrO2–2.8 mol% Y2O3 powders synthesized by the gel-combustion method, using different organic fuels – alanine, glycine, lysine and citric acid – and calcined at temperatures ranging from 873 to 1173 K. The nanopore structures were investigated by small-angle X-ray scattering. The experimental results indicate that nanopores in samples prepared with alanine, glycine and lysine have an essentially single-mode volume distribution for calcination temperatures up to 1073 K, while those calcined at 1173 K exhibit a more complex and wider volume distribution. The volume-weighted average of the nanopore radii monotonically increases with increasing calcination temperature. The samples prepared with citric acid exhibit a size distribution much wider than the others. The Brunauer–Emmett–Teller technique was used to determine specific surface area and X-ray diffraction, environmental scanning electron microscopy and transmission electron microscopy were also employed for a complete characterization of the samples. [ABSTRACT FROM AUTHOR]