Showing papers by "Nicola Bazzanella published in 2015"

Comparative gas-sensing performance of 1D and 2D ZnO nanostructures

Abstract: In this work we have grown one-dimensional (1D) and two-dimensional (2D) zinc oxide nanostructures. Changing the deposition parameters we were able to obtain ZnO nanowires with an average diameter of 80–250 nm. Nanosheets grown in different conditions show thickness values in the range 70–360 nm. These kinds of nanostructure have been used to fabricate conductometric gas sensors for liquid petroleum gas (LPG) detection. Different sensing parameters are investigated in both cases as a function of the dimensionality and size of the zinc oxide nanostructures. A first approximation of the “depletion layer sensing mechanism” is used to explain how the geometrical factors of one- and two-dimensional nanostructures affect their sensing parameters. The depletion layer affects two dimensions of nanowires and only one of nanosheets. This greatly improves the sensor response of 1D-nanostructures. On the other side two-dimensional nanostructures have a larger cross-section, which increases the base current, thus lowering the limit of detection. At the same operative conditions, nanowires show a better percentage response when compared to similar thickness nanosheets, but 2D nanosheets demonstrate an improved limit of detection (LoD).

Highly photo-catalytically active hierarchical 3D porous/urchin nanostructured Co3O4 coating synthesized by Pulsed Laser Deposition

Abstract: A porous coating assembled with hierarchical 3D Co3O4 urchin-like particles was synthesized by Pulsed Laser Deposition (PLD) and thermal oxidation. Laser ablation of Co B powder, used as the target material, in oxygen atmosphere formed core–shell particles on the coating surface with mainly a metallic Co core and a mixture of Co, B and O accommodating the shell. The thermal oxidation of these core–shell particles in air at 600 °C induces the morphological transformation to urchin-like particles consisting of nanowires (NWs) (diameter: 30–60 nm and length 1–3 μm) grown radially from the core surface. The extrusion marks on the surface of NWs indicate that the stress induced growth process is caused by difference in the thermal expansion coefficient. XRD, Raman, EXAFS and HRTEM analysis confirmed that the NWs are polycrystalline consisting of pure Co3O4 phase. A wet-chemistry hydrothermal procedure was also employed to synthesize nanostructured urchin-like particles which are hollow and the structure is held together by the radially oriented nanorods (diameter: 40–150 nm). During photocatalysis, urchin-like particles synthesized by PLD displayed significantly higher (∼5 times) degradation rates when compared to chemical urchins for degradation of methylene blue dye via a photo-Fenton reaction in presence of H2O2 and visible light. This is mainly attributed to poor stability of the nanorods in the chemical urchin structure. Features such as high surface area, enhanced stability against agglomeration, polycrystalline nature of the NWs, porous surface and superior adhesion, are responsible for the enhanced photocatalytic activity of Co3O4 urchin-like particles assembled in a porous coating synthesized by PLD and thermal oxidation. Reusability tests also demonstrate the robust nature of the catalyst coating.

Ruthenium nanoparticles supported over carbon thin film catalyst synthesized by pulsed laser deposition for hydrogen production from ammonia borane

Abstract: Ruthenium nanoparticles (NPs) supported over carbon thin films (Ru/C thin films) catalysts were synthesized by pulsed laser deposition and used as catalysts for hydrolysis of ammonia borane (AB). Highly irregular and porous carbon films with high surface area were deposited by varying Ar gas pressures during the deposition. By taking the advantage of phase explosion phenomena, occurring at high laser fluence, the surface of the carbon films were decorated with crystalline Ru NPs with size below ∼10 nm. Ru/C thin film catalyst produced H 2 with 6 times higher H 2 generation rate as compared to unsupported Ru NPs assembled film, and with a high turnover frequency value of 70.5 mol H 2 mol −1 Ru min −1 . A combination of morphological features and high content of sp 2 bonded C atoms provides good dispersion of Ru NPs over a large surface area. Both these features contribute in generating large number of active sites leading to the increase in catalytic efficiency. A possibility of using the present form of catalyst as an ON/OFF switch for H 2 production was also tested. Although the catalytic activity decreased with the number of hydrolysis cycles, Ru/C thin film catalyst was able to generate the expected amount of H 2 gas in each cycle when it was reused several times. The observed low activation energy (∼28 kJ mol −1 ) and high H 2 generation rate (15.5 L H 2 min −1 g −1 of Ru) by hydrolysis of AB suggest that Ru/C thin film catalyst is highly efficient.

CO2 Laser irradiation of GeO2 planar waveguide fabricated by rf-sputtering

Abstract: We present a fabrication protocol combining radio frequency sputtering technique and CO2 laser annealing for GeO2 based planar optical waveguides. The effects of pulsed CO2 laser irradiation on the optical and structural properties of pure GeO2 planar waveguide are evaluated by different techniques as m-line and micro-Raman spectroscopy and AFM measurements. Amorphous GeO2 planar waveguide was fabricated by Radio Frequency magnetron sputtering system on v-SiO2 substrate. An increase of the refractive index of approximately 0.04 at 1.5 μm and a decreasing of the attenuation coefficient from 0.9 to 0.5 dB/cm at 1.5 μm have been observed after pulsed CO2 laser annealing. Raman spectroscopy and AFM results showed that after an adapted pulsed CO2 laser annealing, the resulting materials showed a crystalline environment in which the phase of the crystalline GeO2 varies with varying irradiation time.

Improvement of the electron collection efficiency in porous hematite using a thin iron oxide underlayer: towards efficient all-iron based photoelectrodes

Abstract: Different approaches have been explored to increase the water oxidation activity of nanostructured hematite (α-Fe2O3) photoanodes, including doping with various elements, surface functionalization with both oxygen evolving catalysts (OEC) and functional overlayers and, more recently, the introduction of ultrathin oxide underlayers as tunneling back contacts. Inspired by this latter strategy, we present here a photoanode design with a nanometric spin-coated iron oxide underlayer coupled with a mesoporous hematite film deposited by electrophoresis. The electrodes equipped with the thin underlayer exhibit a four-fold improvement in photoactivity over the simple hematite porous film, reaching a stable photocurrent density of ca. 1 mA cm−2 at 0.65 V versus the saturated calomel electrode (SCE) at pH 13.3 (NaOH 0.1 M) under air mass (AM) 1.5G illumination. A further improvement to 1.5 mA cm−2 is observed after decoration of the hematite surface with a Fe(III)-OEC. These results demonstrate that by combining different iron oxide morphologies, it is possible to improve the selectivity of the interfaces towards both electron collection at the back contact and hole transfer to the electrolyte, obtaining an efficient all-iron based photoelectrode entirely realized with simple wet solution scalable procedures.