Two-step growth mechanism of supported Co3O4-based sea-urchin like hierarchical nanostructures

The formation mechanism of Co3O4-based sea-urchin like nanostructures from Co-O-B layers is unveiled. In this process, promoted by oxidizing annealing, B plays a major role, inducing first a chemical reduction of Co and the formation of a metallic particle core. The growth of nano-needles from the particle surface occurs through outdiffusion and oxidation of Co from the metallic reservoir

Towards the Development of a Z-Scheme FeOx/g-C3N4 Thin Film and Perspectives for Ciprofloxacin Visible Light-Driven Photocatalytic Degradation

Thermally synthesized graphitic carbon nitride (g-C3N4) over pulsed laser deposition (PLD) produced urchin-like iron oxide (FeOx) thin films were fabricated via in situ and ex situ processes. Materials characterisation revealed the formation of the graphitic allotrope of C3N4 and a bandgap Eg for the combined FeOx/g-C3N4 of 1.87 and 1.95 eV for each of the different fabrication strategies. The in situ method permitted to develop a novel petal-like morphology, whereas for the ex situ method, a morphological mixture between FeOx bulk and g-C3N4 was observed. Given the improved optical and morphological properties of the in situ film, it was employed as a proof of concept for the direct photocatalysis and photo-Fenton removal of ciprofloxacin antibiotic (CIP) under visible light irradiation. Improved photocatalytic activity (rate constant k = 8.28 × 10−4 min−1) was observed, with further enhancement under photo-Fenton conditions (k = 2.6 × 10−3 min−1), in comparison with FeOx + H2O2 (k = 1.6 × 10−3 min−1) and H2O2 only (k = 1.3 × 10−4 min−1). These effects demonstrate the in situ methodology as a viable route to obtain working heterojunctions for solar photocatalysis in thin-film materials, rather than the more common powder materials

Production of nanoparticles from natural hydroxylapatite by laser ablation

Laser ablation of solids in liquids technique has been used to obtain colloidal nanoparticles from biological hydroxylapatite using pulsed as well as a continuous wave (CW) laser. Transmission electron microscopy (TEM) measurements revealed the formation of spherical particles with size distribution ranging from few nanometers to hundred nanometers and irregular submicronic particles. High resolution TEM showed that particles obtained by the use of pulsed laser were crystalline, while those obtained by the use of CW laser were amorphous. The shape and size of particles are consistent with the explosive ejection as formation mechanism

Laser Ablation of Aluminum Near the Critical Regime: A Computational Gas-Dynamical Model with Temperature-Dependent Physical Parameters

The complexity of the phenomena simultaneously occurring, from the very first instants of high-power laser pulse interaction with the target up to the phase explosion, along with the strong changes in chemical-physical properties of matter, makes modeling laser ablation a hard task, especially near the thermodynamic critical regime. In this work, we report a computational model of an aluminum target irradiated in vacuum by a gaussian-shaped pulse of 20 ns duration, with a peak intensity of the order of GW/cm2. This continuum model covers laser energy deposition and temperature evolution in the irradiated target, along with the mass removal mechanism involved, and the vaporized material expansion. Aluminum was considered to be a case study due to the vast literature on the temperature dependence of its thermodynamic, optical, and transport properties that were used to estimate time-dependent values of surface-vapor quantities (vapor pressure, vapor density, vapor and surface temperature) and vapor gas-dynamical quantities (density, velocity, pressure) as it expands into vacuum. Very favorable agreement is reported with experimental data regarding: mass removal and crater depth due to vaporization, generated recoil momentum, and vapor flow velocity expansion

Backscattering of Positrons from Solid Targets

As recently shown by Vicanek and Urbassek, the mean v of the large angle collisions suffered by a charged particle before slowing down to rest in a solid is a quantity that plays an important role in determining the backscattering probability from solid targets. V depends both on the range and on the transport cross section of the particles penetrating the solid. In these paper we give an analytical expression to calculate v for low energy positrons (E < 5 keV), based on a numerical code for the calculations of the differential elastic scattering cross section. Then we compare the backscattering coefficients, obtained by using the calculated values of v, to the results obtained with Monte Carlo simulations and to the available experimental data

Slow Electrons Impinging on Dielectric Systems: II. Implantation Profiles, Mobility and Recombination Processes

When an insulator is subject to electron irradiation, a fraction of electrons is absorbed while the other one is backscattered. It is easily proved that injected electrons cannot be definitely trapped but they must instead recombine with positive charges left near the irradiated surface when secondary electrons are emitted; this is justified on the basis that dielectric breakdown is not observed during specific experiments of electron irradiation of insulators. The dynamics of the absorbed electrons depend on a number of parameters: the number of trapped electrons, the charge-space distribution, the mobility, and the number of secondary electrons emitted from the region near the surface of the dielectric. The time evolution of the surface electric has been studied by integration of the continuity equation for the relevant transport processes of the injected charge by adopting, as the charge source term, the distribution of the absorbed electrons as obtained by a Monte Carlo simulation. The image charge has been also introduced in the calculation in order to take into account the change in the dielectric constant when passing from the material to the vacuum. Selected computational results are reported to illustrate the role of the relevant parameters which control the charging effects in electron-irradiated insulators

Numerical simulation of hydrogen desorption from thin metallic films

Metal–hydrogen systems are of great basic and technological interest. In fusion reactors, absorption and desorption of hydrogen isotopes by the first wall and blanket structure are open problems. Hydrogen accumulation at adiation-induced defects in steel may have serious detrimental effects on the structure of steel. In this work, we present the results of a numerical code realized for simulating the hydrogen desorption processes and point out the advantage related with the numerical approaches to the problem. Indeed, as opposed to the analytical procedures which need approximations to avoid mathematical complications to include traps coverage, the numerical approaches work without any approximation. 2006 Elsevier B.V. All rights reserved