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The effect of trimesic acid (TA) on the surface of γ-Al2O3 for CoMoP catalysts has been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The γ-Al2O3 support was modified by surface impregnation of a solution of TA to afford TA/Co molar ratios (0.5, 1.0 and 2.0) in the final composition. The CoMoP material with atomic ratio of TA/Co = 1.0 displayed the highest HDS activity. FT-IR results suggest that the carboxylic acid moieties (AA) of the TA deposited on the γ-Al2O3 interact with the Mo and Co species. The DRS UV vis revealed the presence of Co species in distorted octahedral symmetry. The MoOh/MoTh ratio varied depending on the amount of the organic additive. TGA results indicated that the TA on the catalyst with TA/Co ratio = 1.0 often decomposes at lower temperature in comparison with the other samples. Thus, a lower temperature decomposition favors the surface concentration of metals species for the sulfurization degree. The interaction of the TA induces moderate metal-support interaction. Raman spectroscopy showed that the presence of TA influenced significantly on the ratio Mo O/(Mo O + Mo O Mo + Mo O) on the catalyst surface. Raman results also evidenced the highest ratio Mo O/(Mo O + Mo O Mo + Mo O) for the CoMoP (1.0) sample. Apparently, the augment of the Mo O species is related to a major availability of Mo species for the formation of MoS2 for HDS reaction. The XPS and HRTEM results showed higher formation and more dispersed MoS2 and CoMoS species for the catalysts modified by TA compared to that of the reference sample. The CoMoP (1.0) showed higher Moe/Mot ratio in comparison with CoMoP (0.0), which resulted in a higher gas oil HDS activity.

Washing with xylene (X), 2,6 bis 1 hydroxy 1,1 diphenyl methyl pyridine (A) and in situ reactivation with molybdenum acetylacetonate (AceMo) on the NiMoP/Al2O3 spent surface catalyst has been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The spent catalyst was washed and dried at 120 °C before in situ reactivation. The sulfided catalysts were characterized by temperature programmed reduction (TPR), nuclear magnetic resonance (NMR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The HDS reactions were carried out at 5.5 MPa of H2 and the reaction temperatures at 340 °C, 360 °C and 380 °C. The CatAXAceMo displayed the highest HDS activity. The TPR results advice that CatAX presented more “rigid” MoS2 edges than CatRef catalyst. NMR results suggest that CatAXAceMo showed lower aromatic or polyaromatic hydrocarbons surface concentration deposited after HDS reaction than CatAceMo and CatRef. Raman spectroscopy revealed the formation of coke crystallites with shorter size for CatAXAceMo than others catalysts. XPS spectroscopy results exhibited that CatAXAceMo presented smaller superficial carbon and a larger concentration of MoS2 active phase. A relation between the coke crystallites size and MoS2 superficial concentration was found. A lower aromatic concentration favors the shorter coke crystallites sizes and a major availability of Mo species for the formation of MoS2 to HDS reaction.

Background: Metal nanoparticles have been widely investigated due to their unique optical, mechanical, and chemical properties compared with those of the same bulk material. These properties can be tuned by controlling their size or shape, in this sense, several nanomaterials have been obtained by means of both chemical and physical methods. For instance, silver nanoparticles have been obtained in liquid media by using laser ablation or chemical reduction techniques. Another way to obtain a colloidal silver nanoparticles is through the well-known pulsed laser irradiation method which can produce a stable colloidal solution in a few minutes of irradiation and without stabilizing molecules or ligands. Methods: Silver nanopowder suspended in ethanol was irradiated with a pulsed laser at 532 nm via optical fiber. Previously, the fiber was prepared by cleaving and removing its coating and then placed in the middle of a cell. The pulse width was 15 ns and the pulse repetition frequency was 10 kHz. Scanning and transmission electron microscopes were used to observe the silver nanoparticles before and after laser irradiation, respectively. The samples were analyzed by means of UV-Vis spectrophotometer to observe the absorption spectra. Results: The absorption spectra show that particle size distribution increases according to the irradiation time. The colloidal solution showed a color change (from gray to yellow) after having irradiated it for 5 minutes. From TEM images, it can be observed that silver nanopowder was transformed to semispherical particles with diameters smaller than 1μm, however, due to the wide particle size distribution the colloidal solution was centrifuged for 30 min to separate the nanoparticles. Conclusion: The pulsed laser irradiation method via optical fiber was successfully used to obtain a stable yellow colloidal solution. Photomelting, photofusion, and photofragmentation are the responsible phenomena for the change in morphology and size of the silver nanopowder.

High-porosity nanostructured amorphous tungsten OXIDE (a-WO3) films were synthesized by a Hot Filament Chemical Vapor Deposition technique (HFCVD) and then transformed into a crystalline WO3 by simple thermal annealing. The a-WO3 films were annealed at 100, 300, and 500 &deg, C for 10 min in an air environment. The films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and UV&ndash, vis spectroscopy. Results revealed that the a-WO3 films were highly porous, composed of cauliflower-like structures made of nanoparticles with average sizes of 12 nm. It was shown that the effect of annealing on the morphology of the a-WO3 films leads to a sintering process. However, the morphology is conserved. It was found that at annealing temperatures of 100 &deg, C, the a-WO3 films are of an amorphous nature, while at 300 &deg, C, the films crystallize in the monoclinic phase of WO3. The calculated bandgap for the a-WO3 was 3.09 eV, and 2.53 eV for the film annealed at 500 &deg, C. Finally, the results show that porous WO3 films preserve the morphology and maintain the porosity, even after the annealing at 500 &deg, C.

The effect of 2,6-bis-(1-hydroxy-1,1-diphenyl-methyl) pyridine (BDPHP) in the preparation of NiMoP/γ-Al2O3 catalysts have been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The γ-Al2O3 support was modified by surface impregnation of a solution of BDPHP to afford BDPHP/Ni molar ratios (0.5 and 1.0) in the final composition. The highest activity for NiMoP materials was found when the molar ratio of BDPHP/Ni was of 0.5. X-ray diffraction (XRD) results revealed that NiMoP (0.5) showed better dispersion of MoO3 than the NiMoP (1.0). Fourier transform infrared spectroscopy (FT-IR) results indicated that the organic additive interacts with the γ-Al2O3 surface and therefore discards the presence of Mo or Ni complexes. Raman spectroscopy suggested a high Raman ratio for the NiMoP (0.5) sample. The increment of the Mo=O species is related to a major availability of Mo species in the formation of MoS2. The temperature programmed reduction (TPR) results showed that the NiMoP (0.5) displayed moderate metal–support interaction. Likewise, X-ray photoelectron spectroscopy (XPS) exhibited higher sulfurization degree for NiMoP (0.5) compared with NiMoP (1.0). The increment of the MoO3 dispersion, the moderate metal–support interaction, the increase of sulfurization degree and the increment of Mo=O species provoked by the BDPHP incorporation resulted in a higher gas oil HDS activity.

Indium oxide (In 2 O 3 ) microstructures were synthesized through carbothermal reaction by the close-spaced vapor transport (CSVT) technique at low temperatures and without the use of catalysts. Morphological characterization by scanning electron microscopy (SEM) showed that the CSVT technique provides high-efficiency for the mass transport at low temperatures, as low as 650 °C, considering that in the synthesis indium oxide powders were used as a source. In addition, it is observed that the microstructures are formed mainly of microcubes with microspheres attached on their faces. Measurements of X-ray (XRD), Raman, and Energy-dispersive X-ray spectroscopy (EDS) showed that the microcubes tend to the stoichiometry of In 2 O 3 and the microspheres have an excess of indium. Based on the above results, the microstructures were converted to In 2 O 3 nanobelts by a simple post thermal annealing for 16 h in a nitrogen environment, according to additional morphological and structural characterizations. The results revealed that the In 2 O 3 nanobelts have several micrometers in length with rectangular cross sections in the range from 50 to 250 nm and correspond to body-centered cubic (bcc) In 2 O 3 single crystal. The growth mechanisms of the microstructures and nanobelts are discussed in detail. Finally, Photoluminescence spectrum showed a broad emission around 600 nm. Refined studies showed three peaks at 420, 592, and 673 nm, which were attributed to oxygen vacancies.

In this work, we show a simple way to functionalize tungsten oxide nanowires (WO3-NWs) using a saturated palladium chloride (PdCl2) solution deposited by a drop-casting method. WO3-NWs were synthesized by close-spaced chemical vapor deposition (CSVT). The morphological and structural characterizations showed that the diameters of WO3-NWs are in the range from 50 to 200 nm with lengths above 10 μm, and correspond to the orthorhombic phase of WO3, respectively. The sensor was fabricated using the WO3-NWs and tested with hydrogen and volatile organic compounds (VCO's). A comparative study was done on the sensing performance, before and after the Palladium functionalization of the WO3-NWs, considering a wide range of gas concentrations and moderate operating temperatures (100–400 °C). The results show that this simple functionalization process significantly increases the sensor sensitivity and reduces the time constants. In addition, it has been shown that at 300 °C the decorated sensor becomes more selective to hydrogen and xylene for all concentrations considered in this research. Finally, the mechanisms involved in improving the gas sensing properties of WO3-NWs functionalized with Palladium are discussed.

A method to manage the resistivity of n-type ZnO films is presented. It involves the controlled diffusion of Zn at low temperature in N2 atmosphere into the ZnO/Zn/ZnO structure. The structures were made by DC sputtering technique. The diffusion periods were varied from 5 to 30 min. This process allow us to obtain ZnO films with excess of Zn (ZnO:Zn). The electrical characterization showed that the resistivity of the films can be varied from 0.01 to 100 omega-cm, the electron concentration from 10(19) to 10(17) cm(-3) and the carrier mobility from 10 to 40 cm2N-s. The films are nanocrystalline with preferred (002) orientation and crystal size that varies from 13 to 20 nm depending on the diffusion period. The films have a band gap of 3.18 eV and 70% of transmittance in the visible region, these properties were obtained from the transmittance measurements of low-resistivity films. Films have good structural, optical and electrical properties, and could be used in the manufacture of light emitting diodes.

The growth of tungsten oxide nanowires on silicon substrates without using any catalyst is demonstrated by means of close-spaced vapor transport (CSVT) technique at atmospheric pressure. The source was formerly prepared from a tungsten foil to produce a tungsten oxide film. CSVT array is completed with silicon substrates located at a distance of ~350 m over the tungsten oxide source at moderate temperatures (~750°C). Two distinct kinds of nanostructures were produced; a uniform distribution of free standing tungsten oxide wires of several micrometers in length with diameters less than 150 nm; and wires assembled to form nanowire bundle. The X-ray diffraction characterizations show that the phases of WO2.7 and WO2.9 are present.

Hot Filament Chemical Vapour Deposition (HFCVD) was used to deposit tungsten oxide clusters on a graphite surface using a tungsten filament as source. These clusters were subsequently transported onto quartz and Si substrates where they transformed into WO 3 − X nanowires. The transport of tungsten species from source to substrate was made through the Close Spaced Vapour Transport (CSVT) technique. The synthesized nanostructures were characterized by means of SEM, EDS, XRD techniques as well as by Raman spectroscopy. The results show that the nanowires have a monoclinic structure, a diameter about 100 nm and they were extended many tenths of micrometers.

Nanostructures of gallium phosphide (GaP) were fabricated through the close-spaced vapor transport technique (CSVT). Such nanostructures were grown on crystalline gallium arsenide (GaAs) by using a GaP powder source in the absence of any catalyst. Nanostructured GaP products were structurally and morphologically characterized by means of physicochemical and spectroscopic techniques, such as SEM, EDS, XRD, and NMR. Results showed that GaP structures present a nanoflower-like morphology. Indeed, these nanoflowers are constituted by numerous nanowires. The diameters of the GaP nanowires were in the interval of 80–300 nm, with lengths varying from several to tens of micrometers.

An optical method to obtain a colloidal solution starting from a mixture of silver nanopowder and ethanol is presented. The particles of the silver nanopowder do not exhibit a specific shape, however in the colloidal solution are spherical. This method is carry out when the mixture is irradiated with a pulsed laser at 532 nm via optical fiber. Due to a stronger absorption of the laser light by silver nanoparticles arise both photofragmentation and photomelting processes. The photomelting process starts when the laser energy is 5 mJ/cm 2 , inducing an enlargement of nanoparticles whereas the photofragmentation occurs when the laser energy is 25 mJ/cm 2 causing a reduction on their sizes (the higher energy is, the smaller nanoparticles are). Results show that it is possible to obtain a colloidal silver solution and to control the particle size by adjusting the laser energy. Experiments were performed at 5 and 25 mJ/cm 2 , and the results are presented.

Indium oxide microstructures were synthesized by close-spaced chemical vapor transport (CSVT) technique at low temperatures and without the use of catalysts. Morphological characterization by scanning electron microscopy (SEM) showed that the CSVT technique provides high mass-transport efficiency at temperatures as low as 650°C, considering that indium oxide powders were used as a source for the synthesis. It is observed that the microstructures are formed mainly of cubes with semi-spheroids attached to their faces. Additional measurements of X-ray (XRD), Raman, and Energy-dispersive X-ray spectroscopy (EDS) showed that the cubes tend to have the stoichiometry of cubic indium oxide while the semi-spheroids have a metallic nature. The microstructures were converted to indium oxide nanobelts by a simple post thermal annealing during 16 hours in a nitrogen environment, according to the morphological and structural characterizations. The results revealed that the indium oxide nanobelts have several micrometers in length with rectangular cross sections in the range from 50 to 250 nanometers and correspond to indium oxide in the cubic and face-centered phases. The growth mechanisms of the micostructures and nanobelts are discussed in detail.

A study of optically induced Zn/ZnO nanoparticles selective deposition using a coherent light source on single-mode fiber optic end is presented. In the numerical studies, Zn/ZnO spherical nanoparticles are considered dissolved in isopropyl alcohol with different diameters under the influence of a Gaussian beam with fundamental mode and linear polarization. The results of this study show that the gradient force is not sufficient to move Zn nanoparticles toward optical fiber end face, but it is sufficient to move ZnO nanoparticles of a certain diameter. In the experimental studies, Zn/ZnO nanoparticles were mixed with isopropyl alcohol and subsequently deposited on the fiber end face using an infrared laser. The results obtained by atomic force and optical microscopy show a good uniform distribution of nanostructures deposited on the core of the fiber end face.

By using the Hot Filament Chemical Vapor Deposition (HFCVD) technique tungsten thin films were deposited on amorphous quartz substrates. To achieve this, a tungsten filament was heated at 1300 °C during 30 minutes maintaining a constant pressure inside the chamber at 460 mTorr and substrate at 700 °C. Transition from tungsten oxide deposits to tungsten thin films, by varying the substrate temperature, were characterized by means of Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM), X-Ray Diffraction and, micro-Raman spectroscopy. The SEM micrographs reveal that the tungsten films have no more than 200 nm in thickness while XRD show evidence of the films crystallize in the a-tungsten modification. On the other hand, AFM shows that the tungsten thin films exhibit a uniform and smooth surface composed with semi-spherical shapes whose diameters are below than 50 nm. Furthermore, to the naked eye, the as-deposited tungsten films exhibit a high mirror-like appearance.

Experimental studies of titania nanotubes (TiO 2 ) and tungsten oxide nanospheres (WO3) as devices of saturable absorption for a fiber laser in ring configuration to optical short-pulse generation are presented. A deposition technique, based on optical pressure radiation generated from a coherent source at 1550 nm is used to deposit the nanostructured materials. Since this nanomaterials can be deposited directly on the optical fiber, this proposal results very interesting for applications of saturable absorbers. Experimental results, by using nanotubes TiO 2 and nanospheres deposited on the fiber as a saturable absorption device, show that the TiO 2 nanotubes exhibit better saturable absorption properties than WO 3 nanospheres, generating pulses with a wavelength of 1550 nm, frequency of 10 MHz, temporally width of 4.5 ps and an output power of 1 mW.

High quality ZnO films were obtained by thermal oxidation of Zn films on the temperature range from 300 to 700 °C. Zn films of 190 nm in thickness were deposited on silicon and glass substrates by the sputtering technique. Thermal oxidation was done at normal environment conditions. The complete oxidation of the Zn films was determined by the ZnO films transparency. The ZnO films resulted dense with mirror-like surface. The film structural characterization was realized by X-ray diffraction measurements. The electrical characteristics were measured by the van der Pauw method at room temperature. The ZnO films resulted n-type with carrier concentration of 1016 to 1017cm−3 and mobility values in the range of 1 to 50 cm2/V-s.

Spherical ZnO microspheres were obtained in a simple system using a short time process, without catalysts, at atmospheric pressure and using water as oxidant agent. Analysis with SEM shows the microstructures have spherical shapes covered with pencil-like structures. XRD spectrum reveals that as-synthesized ZnO products crystallize in the wurtzite phase.

An experimental and theoretical study about selective photodeposition of metallic zinc nanoparticles onto an optical fiber end is presented. It is well known that metallic nanoparticles possess a high absorption coefficient and therefore trapping and manipulation is more challenging than dielectric particles. Here, we demonstrate a novel trapping mechanism that involves laser-induced convection flow (due to heat transfer from the zinc particles) that partially compensates both absorption and scattering forces in the vicinity of the fiber end. The gradient force is too small and plays no role on the deposition process. The interplay of these forces produces selective deposition of particles whose size is directly controlled by the laser power. In addition, a novel trapping mechanism termed convective-optical trapping is demonstrated.