Growth kinetics of vanadium pentoxide nanostructures under hydrothermal conditions

The work reported here involved a study of the growth kinetics of V2O5nH2O nanostructures under hydrothermal conditions. The coarsening process of V2O5nH2O nanoribbons was followed by subjecting the as-prepared suspensions to hydrothermal treatments at 80 °C for periods ranging from 0 to 7200 min. X-ray diffraction (XRD) confirms that the hydrothermal treatments at 80 °C caused no significant modification of the long-range order structure of samples subjected to different periods of hydrothermal treatment. Field emission scanning transmission electron microscope (FE-STEM) was used to analyze the morphology and width distribution of the nanostructures. The results indicated that the crystal growth mechanism in the [1 0 0] direction of vanadium pentoxide 1D nanostructure under hydrothermal conditions is well described by the oriented attachment (OA) mechanism. This evidence was supported by HRTEM images showing the existence of defects at the interface between nanostructures, which is characteristic of the oriented attachment (OA) mechanism.FAPESPCNPqLNL

An efficient synthesis route of 'Na IND.2''V IND.6''O IND.16.n''H IND.2'O nanowires in hydrothermal conditions

Na2V6O16·nH2O nanowires were synthesized using an environmentally friendly and one-step low-temperature hydrothermal route. The synthesis involved the hydrothermal reaction between V2O5, H2O2 and NaOH, without the addition of any organic surfactants or inorganic ions. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and thermal gravimetric analysis (TGA) techniques were used to characterize the structure, morphology, chemical composition and thermal stability of the nanostructured samples. High purity hydrated Na2V6O16·nH2O nanowires of diameters around 20–30 nm can be more efficiently obtained when subject to hydrothermal treatment at 140 °C for 24 h. The variation in the electronic and local atomic structure was analyzed using X-ray absorption spectroscopy (XAS). Based on the results obtained from the present study, a mechanism for the formation of Na2V6O16·nH2O nanowires in hydrothermal conditions was proposed.FAPESPCNP

Local structure study of vanadium pentoxide 1D-nanostructures

Vanadium pentoxide (V2O5·nH2O) 1D-nanostructures as nanowires and nanorods have been obtained by decomposition of vanadium peroxide in hydrothermal conditions. Electron microscopy, Raman spectroscopy, and X-ray absorption spectroscopy (XAS) were employed to characterize the morphology and the local structure of as-obtained samples. Scanning transmission electron microscopy (STEM) revealed that the diameter of the nanowires and nanorods were found to be 10–20 and 30–40 nm, respectively. The results demonstrated that a combination of Raman and XAS techniques allowed the accurate characterization of the local structure of V2O5 1D-nanostructures which are related to different morphologies. Analyses of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra reveals that the local structure of V in the as-obtained samples is similar to the bulk V2O5 (in orthorhombic phase), except for a higher degree of local symmetry within the structure of the VO5 square pyramid. Additionally, the nanostructures prepared by this technique present a single crystalline nature and could emit visible light at room temperature which is related to the local order of V atoms of the studied samples.FAPESPCAPESCNP

Now you see me, now you don't : a case study of the effect of the sampling method on the perceived struture of Ichthyological communities

Fauna and Flora of the Atlantic Islands : Proceedings of the 3rd Symposium, Ponta Delgada, 21-25-September 1998.The fish community of a small rocky area near Ponta Delgada, Azores, was assessed using two methods: visual census and rotenone collections. The results obtained with each method are analysed and compared. A total of 46 species was recorded for this site. The visual census recorded more species than did the rotenone collections, but each method detected species that escaped the other. The total fish diversity was found to be similar to that reported in other localized studies of littoral rocky areas of the eastern Atlantic and the Mediterranean. Each method used revealed a different spatial structure and different trophic relationships of the ichthyological community. The visual census put in evidence the pelagic/demersal component, while the rotenone collections emphasized the benthic one. Both methods agree on the importance of the benthic primary production in the trophic food web. Visual census data further suggest that the relevance of the direct consumption of algal material by omnivores and herbivores is greater than could be guessed by the species diversity in this group. Strategies are discussed for combining visual and destructive sampling methods in order to achieve a more accurate representation of a given fish community

Er:YAB nanoparticles and vitreous thin films by the polymeric precursor method

Abstract The synthesis of Y 0.9 Er 0.1 Al 3 (BO 3 ) 4 crystalline powders and vitreous thin films were studied. Precursor solutions were obtained using a modified polymeric precursor method using D-sorbitol as complexant agent. The chemical reactions were described. Y 0.9 Er 0.1 Al 3 (BO 3 ) 4 composition presents good thermal stability with regard to crystallization. The Y 0.9 Er 0.1 Al 3 (BO 3 ) 4 crystallized phase can be obtained at 1,150°C, in agreement with other authors. Crack-and porosity-free films were obtained with very small grain size and low RMS roughness. The films thickness revealed to be linearly dependent on precursor solution viscosity, being the value of 25 mPa s useful to prepare high-quality amorphous multi-layers (up to * 800 nm) at 740°C during 2 h onto silica substrates by spin coating with a gyrset technology

Structural and optical properties of CaTi'O IND.3' perovskite-based materials obtained by microwave-assisted hydrothermal synthesis: an experimental and theoretical insight

CaTiO3 powders were synthesized using both a polymeric precursor method (CTref) and a microwave-assisted hydrothermal (CTHTMW) method in order to compare the chemical and physical properties of the perovskite-based material as a function of the synthesis method. To this end, X-ray diffraction, Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy and experimental Ti and Ca K-edge X-ray absorption near-edge structure spectroscopy, as well as measurements of photoluminescence (PL) emission, were used to characterize the typical bottom-up process of the CaTiO3 perovskite phase at different times. Detailed Rietveld refinements show a random polycrystalline distortion in the powder structure, which can be associated with the tilting (α angle < O–Ti–O) between adjacent TiO6 octahedra (intermediate range) for CTHTMW samples and an intrinsic TiO6 distortion (short range) in relation to the polymeric precursor CTref sample. These properties were further investigated by first-principles calculations based on the density functional theory at the B3LYP level. The relationship between this tilting on the PL profile is highlighted and discussed. Thus, a structural model derived from both experimental results and theoretical simulations reveals a close relationship between this tilting and the presence of intermediate energy states within the band gap which are mainly responsible for PL emissionsCAPESCNPQFAPESP/CEPID 98/14324-

A high-throughput, solvent free method for dispersing metal atoms directly onto supports

Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated high activity and selectivity in many catalytic reactions. However, dispersing and stabilising individual atoms in support materials in an atom/energy-efficient scalable way still presents a significant challenge. Currently, the synthesis of ADMCs involves many steps and further filtration procedures, creating a substantial hurdle to their production at industrial scale. In this work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free, one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC production of 4.8 mg h1 and generates no chemical waste. Deposition of only 0.5 weight percent of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the charge carrier recombination from the photogenerated electron–hole pairs of Pt/g-C3N4 thereby enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach can produce effective ADMCs with no further synthetic steps required, and that they can be readily used for catalytic reactions

Strong violet-blue ligth photoluminescence emission at room temperature in SrZr'O IND.3'

Ultrafine ordered and disordered SrZrO3 powders were prepared by the polymeric precursor method. The structural evolution from structural disorder to order was monitored by X-ray diffraction and X-ray absorption near-edge spectroscopy. Complex cluster vacancies [ZrO5.VZO and [SrO11.VZO ] (where VZO = VXO, VO' and VO") were proposed for disordered powders. The intense violet–blue light photoluminescence emission measured at room temperature in the disordered powders was attributed to complex cluster vacancies. High-level quantum mechanical calculations within the density functional theory framework were used to interpret the experimental results.FAPESP/CEPIDCNPq/PRONEXCAPE

Hydrothermal microwave: a new route to obtain photoluminescent crystalline BaTi'O IND.3' nanoparticles

Hydrothermal microwave method was used as a new route to synthesize pure BaTiO3 (BT) nanoparticles at 140°C for 10 min under rapid reacting with stoichiometric Ba/Ti ratio. The crystalline products were characterized by X-ray powder diffraction (XRD) and the structure was refined by the Rietveld method from the tetragonal structure, which was supported by the Ti K-edge X-ray absorption near-edge structure (XANES). The pre-edge of Ti in the XANES spectra indicated that titanium ions are localized in a nonregular octahedron. Typical FT-Raman spectra for tetragonal BaTiO3 nanoparticles presented well-defined peaks, indicating a substantial short-range order in the system. However, a scattering peak at 810 cm-1 was attributed to the presence of lattice OH- groups, commonly found in materials obtained by hydrothermal process. Besides, the peak at 716 cm-1 can be related to eventual Ba2+ defects in the BaTiO3 lattice. BaTiO3 (BT) nanoparticles presented spherical morphology with a non-uniform distribution of particle sizes. An intense and broad photoluminescence band was observed around the green color emission at room temperature. By means of an excitation energy of 2.54 eV (488 nm), it was noted that the maximum profile emission (2.2 eV) is smaller than the forbidden band gap energy of BaTiO3, indicating that certain localized levels within the band gap must exist.CAPESCNPqFAPES