1,720,994 research outputs found
The immobilization of titania nanoparticles on hyaluronan films and their photocatalytic properties
No full textWe have developed a method to bind titania nanoparticles onto hyaluronic films (HA) photoimmobilized on silanized glass. Titania nanoparticles were deposited on the HA films from commercially available dispersions by casting and dip-coating methods at various pHvalues. XPS was used to monitor the deposition of titania and to estimate the surface coverage of the nanoparticles. The topography of the titania-modified HA films was investigated by means of AFM. XPS results indicate that the titania surface coverage depends on the preparation method and the pH of the dispersion. We found that the maximum titania nanoparticle surface coverage was obtained by the casting method with the formation of aggregates and multilayers of particles. The titania surface coverage for the surfaces prepared
by the dip-coating method is pH-dependent. The surfaces prepared at pH 2 show a surface coverage of 65% and a rather uniform distribution of particles. We found that titania nanoparticles are anchored in a stable way to the HA substrate in a phosphate buffer solution (PBS) and that the interaction between the HA and the titania is through the carbonyl group of
carboxylates and amidic groups of the polymer. AFM images clearly show that titania nanoparticles are uniformly distributed over the HA films. By measuring the average diameter
and the average height of the nanoparticles deposited on HA films it appears that the particles are partially embedded in the polysaccharide films. The results of the study on the photobleaching of methylene blue indicate that the characteristic photocatalytic activity of titania is maintained when the nanoparticles are anchored to the HA substrate
Adsorption of oxygen on Pt3Sn(110) studied by STM and LEED
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Interactions at the CMC/magnetite interface:Implications for the stability of aqueous dispersions and the magnetic properties of magnetite nanoparticles
No full textMagnetite NPs modified with CMC, a polysaccharide containing carboxylic groups derived from cellulose, were prepared. Two different methods were used: addition of CMC to a dispersion of magnetite NPs previously synthesized (ex situ preparation) and addition of NaOH to an aqueous solution of Fe(II) and Fe(III) in the presence of CMC (in situ preparation). The aim of this study was to characterize in detail the interactions between magnetite NPs and CMC and to elucidate the effect of the polymer on the magnetite NP agglomeration. FTIR spectroscopy was used to shed light onto the nature of the interactions between CMC and Fe3O4 NPs. The morphological characterization of the NPs was carried out by FESEM. The size and the ζ-potential of the NPs in various aqueous media were determined by DLS. XRD measurements indicate that the presence of CMC does not modify, within the uncertainty of the measurement, the size of the primary particle (ca. 10 nm). FTIR spectra suggest that CMC chains are anchored to magnetite NPs via carboxylate groups interacting with iron ions at the surface. The FESEM images show that magnetite NPs prepared by the in situ method form aggregates which are significantly smaller than those prepared by the ex situ procedure. The FESEM images reveal a different morphology of the polymeric matrix between the CMC/magnetite NPs prepared following the two procedures. The hydrodynamic diameter of the CMC/magnetite NPs in water at neutral pH prepared in the presence of CMC is 280 nm. The ζ-potential (ca. −80 mV) measured for the dispersions in water at neutral pH of CMC/magnetite NPs prepared according to the two methods explains their long-term stability. The magnetic behaviour of the CMC/magnetite NPs can be explained considering the different size of the aggregates in the two kinds of sample
ToF-SIMS characterization of proteinaceous binders in the wall painting “Madonna and Child enthroned with Saints” by Ambrogio Lorenzetti in the St. Augustine Church (Siena, Italy)
No full textIn this paper, we report the results of investigations, by means of ToF-SIMS and HPLC, of samples taken from the wall painting "Madonna and Child Enthroned with Saints" (1335-1338) by Ambrogio Lorenzetti. The aim of this study was to test the capability of ToF-SIMS to identify the nature of the protein-based binders used in the wall painting. The peaks characteristic of egg components were observed in the ToF-SIMS mass spectra of the a secco-applied layers. On the contrary, the ToF-SIMS spectra of the a fresco-applied layers did not show the markers of egg. The PCA results of the protein peaks are consistent with the presence of a rabbit glue-egg mixture. The PCA of protein peaks in the ToF-SIMS spectra was carried out for artificially aged and non-aged reference samples of rabbit glue, casein, egg and their mixtures in order to estimate the effect of ageing on protein-based binding media. Both ToF-SIMS and HPLC data showed that animal glue was present in the a secco- and a fresco-applied layers. On the basis of these results, we can conclude that animal glue was not used as binding medium but was probably applied to the wall painting in prior restorations
An integrated approach to the study of a reworked painting “Madonna with child” attributed to Pietro Lorenzetti
No full textThe painting "Madonna with Child", attributed to Pietro Lorenzetti (14th century) and reworked around the middle of the 16th century, was studied by several techniques in order to characterize the materials used in the original and in the repainted areas. FORS, light microscopy, ESEM-EDX, ToF-SIMS and GC-MS were used. Red ochre and raw sienna earth were identified by FORS in the original parts of the painting. On the repainted parts of the panel, cinnabar, ultramarine blue and lead white were found. By means of GC-MS and ToF-SIMS measurements it was possible to identify the organic binding media used in the preparatory and painted layers. © 2013 Elsevier Masson SAS
Epitaxial growth of TiO2 films with the rutile(110) structure on Ag(100)
No full textUltrathin films of TiO2 were grown on Ag(100) by evaporation of titanium in the presence of O2 at a pressure in the 10-4 Pa range and annealing at 770 K. The composition of the deposited films was monitored by XPS and LEIS. The morphology at the nanometric scale of the TiO2 films and their crystallographic structure were investigated by means of STM, LEED and XPD. Above the monolayer coverage (at which the oxide film has a lepidocrocite-like structure), STM images show the formation of multilayer islands with a distribution of heights. XPD results indicate that these oxide islands have the rutile (110) structure and are epitaxially oriented with the sides of the oxide unit cell parallel to those of the substrate unit cell. The results of the DFT calculations justify the 3D growth of rutile (110) on Ag(100). The
calculated strain energy required to match the metal substrate can explain the incommensurate growth of the overlayer in the direction of the long side of the oxide unit cell. The results of
the calculations indicate that a commensurate growth of rutile (110) may be possible along the short side of the oxide unit cell, taking into account the relatively small strain energy to fit the
lattice parameter of the substrate. The DFT calculations predict a considerable increase of the work function upon deposition of titania films on Ag(100), which can be attributed to a charge
transfer from the metal to the 3d Ti empty states
Remediation of acid mine drainage-affected stream waters by means of ecofriendly magnetic hydrogels crosslinked with functionalized magnetite nanoparticles
No full textAcid mine drainage (AMD) is a global environmental challenge that represents a primary source of contamination of heavy metals in both active and abandoned mining areas. The present study explored the suitability of a carboxymethylcellulose (CMC) hydrogel cross-linked with functionalized magnetite (Fe3O4) nanoparticles, (CMC-Fe3O4), for the removal of heavy metals from AMD-affected stream waters and tested its eco-friendly nature. AMD-affected stream waters, collected in a former mining site located in the Metalliferous Hills ore district (Central Italy), were chosen as a suitable benchmark for validating the CMC-Fe3O4 hydrogel applications. The remediation capability of the CMC-Fe3O4 hydrogel was investigated on solutions of Zn(II) in deionized (DI) water and on samples of AMD-affected stream waters. The CMC-Fe3O4 hydrogel was able to adsorb Zn(II) from DI water solutions as well as to reduce significantly the concentration of Zn and other heavy metals such as Cd, Co, Cu, Ni and Pb, in AMD-affected stream waters. CMC-Fe3O4 hydrogel and treated waters (both Zn-solution and AMD-affected stream waters) were tested for their effects on the freshwater green alga R. subcapitata by using 72-h growth inhibition tests. No effects were observed on the R. subcapitata growth upon exposure to CMC-Fe3O4 hydrogel, suggesting its eco-friendly nature. Moreover, CMC-Fe3O4 hydrogel was able to reduce the toxicity of heavy metals to the green alga, both in DI and AMD-affected stream water. Based on our findings, CMC-Fe3O4 hydrogel could be considered as a valuable tool for an environmentally safe treatment of AMD-affected stream waters
Growth mechanism and structure of nickel deposited on Ag(001)
No full textThe initial growth stages of nickel deposited on Ag(0 0 1) have been investigated by LEIS, XPS, STM and XPD. Embedded atom method (EAM) calculations were performed to obtain information about the dynamics of Ni adatoms on the Ag(0 0 1) surface. Amounts of Ni ranging from submonolayers up to 4 monolayers were deposited on the Ag(0 0 1) surface under UHV conditions at room temperature. The LEIS spectra indicate that the Ni islands are almost completely covered by silver. In agreement with previous studies, STM images show that Ni grows on Ag(0 0 1) forming three dimensional islands. A significant fraction of islands with a thickness of 2-3 atomic layers is present even at coverages as low as 0.1 ML. The observation of islands protruding from the surface with heights below that expected for one atomic layer of Ni covered by one atomic layer of Ag suggests that Ni atoms are incorporated in the outermost layer of the substrate. From the EAM calculations the energy barrier for incorporation of a nickel atom into the outermost layer was found to be 0.19 eV, substantially lower than that for bridge site hopping over the substrate (0.61 eV). On the basis of the EAM calculations, a diffusion mechanism for Ni atoms incorporated within the first layer of the surface is proposed to explain the growth of Ni islands. As far as the geometric structure of the Ni film is concerned, the XPD curves indicate that at a coverage of ≈0.3 ML, the structure of the film is distorted with respect to the fcc lattice. The displacement of the forward scattering peaks towards higher polar angles is consistent with the formation of pseudomorphic Ni islands (i.e. with the same in-plane lattice parameter of the substrate). The XPD results lead to the conclusion that pseudomorphic Ni clusters coexist with undistorted fcc Ni islands. Even at the highest coverage studied here, a fraction of the islands maintains a strained fcc structure. © 2005 Elsevier B.V. All rights reserved
ToF-SIMS and XPS study of ancient papers
No full textThe surface composition of 18th century papers was investigated by means of ToF-SIMS and XPS. The aim of the present study was to explore the possibility of using these surface sensitive methods to obtain information which can help to determine the manufacturing process, provenance and state of conservation of ancient papers. The ToF-SIMS results indicate that the analyzed papers were sized by gelatin and that alum was added as hardening agent. The paper sheets produced in near geographical areas but in different paper mills exhibit a similar surface composition and morphology of the fibers as shown by the ToF-SIMS measurements. The ToF-SIMS and the XPS results indicate that a significant fraction of the cellulose fibers is not covered by the gelatin layer. This was observed for the ancient papers and for a modern handmade paper manufactured according to the old recipes. (C) 2010 Elsevier B.V. All rights reserved
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