116 research outputs found
Preparation of uniformly dispersed copper nanocluster doped silica glasses by the sol gel process
No full textThe synthetic mechanism of uniformly dispersed Cu-nanocluster doped (0.05-1.0 wt%) silica glasses (copper ruby glasses) was investigated by UV-VIS and FTIR spectroscopy, DSC, XRD, surface area and density measurements at different stages of drying/densification up to glass formation. The monolithic gels were prepared from Cu(NO3)2, H2N(CH2)2NH(CH2)3Si (OCH3)3 (DAMO) and acid hydrolysed Si(OH2H5)4 (TEOS). DAMO was used to immobilize the Cu2+ ions in the silica matrix. The formation and decomposition of Cu-DAMO complexes in the silica gel monoliths were studied. The doped gels were densified under H2 and He gas atmospheres. A maximum matrix (SiO2) density of 1.70-1.73 g cm-3 (77-79% of the theoretical density) could be achieved in an H2 atmosphere at 900°C. However a density close to silica glass 2.17 g cm-3 (>98.5% of theoretical) was achieved when the gels were densified in H2 up to 800°C followed by He gas at 980°C. The surface area data also confirmed this densification behaviour. Uniformly dispersed Cu metal nanoclusters were formed during the heat-treatment of the gels and as a result a surface plasmon (SP) band of Cu-nanoclusters (563-580 nm) was observed. The increase of heat-treatment temperature caused the growth of nanoclusters and as a consequence the SP band was blue-shifted. XRD data also confirmed this
Efficient Solar Light Photocatalyst Made of Ag3PO4 Coated TiO2-SiO2 Microspheres
No full textSolar light active photocatalyst was prepared as silver phosphate (Ag3PO4) coating on titania–silica (TiO2–SiO2) microspheres. Titania–silica microsphere was obtained by spray drying TiO2–SiO2 colloidal solutions, whereas Ag3PO4 was applied by wet impregnation. XRD on the granules and SEM analysis show that the silver phosphate particles cover the surface of the titania–silica microspheres, and UV-visible diffuse reflectance analysis highlights that Ag3PO4/TiO2–SiO2 composites can absorb the entire visible light spectrum. BET measurements show higher specific surface area of the composite samples compared to bare Ag3PO4. Photocatalytic activity was evaluated by dye degradation tests under solar light irradiation. The prepared catalysts follow a pseudo-first-order rate law for dye degradation tests under solar light irradiation. The composite catalysts with an Ag3PO4/TiO2–SiO2 ratio of 1:1.6 wt% show better catalytic activity towards both rhodamine B and methylene blue degradation and compared with the results with uncoated TiO2–SiO2 microspheres and the benchmark commercial TiO2 (Evonik-P25) as a reference. The composite photocatalyst showed exceptional efficiency compared to its pristine counterparts and reference material. This is explained as having a higher surface area with optimum light absorption capacity
Copper-ruby monoliths by the sol-gel process
No full textPreparation and properties of uniformly dispersed Cu metal nanoclusters embedded in bulk silica are described. Clear gels were prepared from Cu(NO3)2, H2N(CH2)2NH(CH2) 3Si(OCH3)3 (DAMO), and acid hydrolyzed Si(OC2H5)4 (TEOS). The role of DAMO to immobilize Cu2+ in silica network is studied. The appearance of a strong surface plasmon band of Cu colloids at 562 nm was observed after heat treatment of the gels at 900°C in 5%H2-95%N2 gas atmosphere. At this stage very uniform ruby-red color of the sample was established due to the formation of copper nanocrystals of mean diameter 15 nm, as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM)
TiO2 colloidal nanocrystals surface modification by V2O5 species: Investigation by Ti-47,Ti-49 MAS-NMR and H-2, CO and NO2 sensing properties
No full textEvidence of catalytic activation of anatase nanocrystals by vanadium oxide surface layer: Acetone and ethanol sensing properties
No full textAcetone sensors based on TiO2 nanocrystals modified with tungsten oxide species
No full textTiO2 nanocrystals were prepared by solegel/solvothermal processing and modified by the addition of W precursor before the solvothermal step. The W: Ti nominal atomic ratio (R-W) was fixed to 0.16 and 0.64. Surface modification of TiO2 occurred for R-W = 0.16 while for R-W = 0.64 nanocomposites with WO3 nanocrystals were obtained after heat-treatment at 500 degrees C. Pure TiO2 proved to be very poorly performing in acetone sensing in all the operating conditions. Instead, the addition of bothWconcentrations largely enhanced the sensor response. It ranged over two orders of magnitude of conductance variation for all the tested concentrations at as low as 200 degrees C operating temperature. The results showed that it is possible to enhance the performance of an otherwise almost inactive oxide like TiO2 by proper combination with another more active oxide like WO3. (C) 2016 Elsevier B.V. All rights reserved.CSIC/CNR [2010IT0001]; SOLAR project [DM19447]; Generalitat de Catalunya [2014 SGR 1638]; Spanish MICINN project e-ATOM [MAT2014-51480-ERC]; Turkish Ministry of National EducationAuthors acknowledge CSIC/CNR project 2010IT0001 (SYNCA-ON) and the SOLAR project DM19447. We thank Giovanni Battista Pace for the help with the sample preparation, and Nicola Poli for the help with the sensing measurements. A.G. acknowledges the funding from Generalitat de Catalunya 2014 SGR 1638, the Spanish MICINN project e-ATOM (MAT2014-51480-ERC) and the Turkish Ministry of National Education for the PhD scholarship. We also thank Jordi Arbiol for the additional HRTEM characterization
Solvothermal, Chloroalkoxide-based Synthesis of Monoclinic WO3 Quantum Dots and Gas-Sensing Enhancement by Surface Oxygen Vacancies
No full textSurface modification, heterojunctions, and other structures: composing metal oxide nanocrystals for chemical sensors
No full textMAPLE deposition and characterization of SnO2 colloidal nanoparticle thin films
No full textIn this paper we report on the deposition and characterization of tin oxide (SnO2) nanoparticle thin films. The films were deposited by the matrix-assisted pulsed laser evaporation (MAPLE)
technique. SnO2 colloidal nanoparticles with a trioctylphosphine capping layer were diluted in toluene with a concentration of 0.2 wt% and frozen at liquid nitrogen temperature. The frozen
target was irradiated with a KrF (248 nm, τ = 20 ns) excimer laser (6000 pulses at 10 Hz). The nanoparticles were deposited on silica (SiO2) and Si substrates and submitted to
morphological (high resolution scanning electron microscopy (SEM)), structural Fourier transform infrared spectroscopy (FTIR) and optical (UV–Vis transmission) characterizations.
SEM and FTIR analyses showed that trioctylphosphine was the main component in the as-deposited films. The trioctylphosphine was removed after an annealing in vacuum at
400 ◦C, thus allowing to get uniform SnO2 nanoparticle films in which the starting nanoparticle dimensions were preserved. The energy gap value, determined by optical characterizations, was 4.2 eV, higher than the bulk SnO2 energy gap (3.6 eV), due to quantum confinement effects
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