Thermal treatment and environment effect on transient photoconductivity behavior of anatase TiO2 with dominant {0 0 1} facets

Nanosized anatase TiO2 powders with dominant {0 0 1} facets were prepared by solvothermal reaction of titanium isopropoxide in the presence of hydrofluoric acid as a capping agent. Two kinds of samples, as prepared and calcinated at 600 °C were fabricated and their UV-Visible and transient photoconductivity were investigated in vacuum and in air. The photoconductivity reaches high values and is sensitive on the environment. Thermal treatment improves the crystalline quality and enhances the amount of created excess charge carriers

Electrical conductivity studies of anatase TiO2 with dominant highly reactive {0 0 1} facets

Nanostructured powders of titanium dioxide anatase nanoplates with dominant highly reactive {0 0 1} facets were fabricated using a solvothermal method. Two kinds of samples, as prepared and calcinated at 600 °C, were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrical conductivity in vacuum and in air. The dependence of the conductivity versus the inverse of temperature in the temperature range 150-440 K indicated the contribution of at least two conduction mechanisms in vacuum. The electron transport was controlled by partially depleted of charge carriers grains and adiabatic small polaron conduction in the high temperature regime and by Mott variable-range hopping (VRH) at lower temperatures. The environment was found from the experimental results to influence significantly the electrical conductivity values and its temperature dependence. A decrease with temperature in air is observed in the ranges 290-370 and 285-330 K for the as prepared and the calcinated sample respectively. Potential barriers caused by partial depletion of carriers at grain boundaries control the electrical conductivity behavior in air at high temperatures and VRH in the lower temperature regime

Solvothermal synthesis and photocatalytic performance of Mn4+-doped anatase nanoplates with exposed {001} facets

The photocatalytic activity of TiO2 and manganese doped TiO2 nanoplates with various manganese atomic percentages, in the range of 2-7%, was studied. The undoped and doped nanoplates with exposed {001} facets were produced by a solvothermal method. The crystal structure as well as the shape of the TiO2 and Mn4+/TiO2 anatase nanoparticles was determined with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Both techniques revealed that the nanocrystals are in the form of plates. Moreover, the anisotropic peak broadening of the X-ray diffraction patterns was studied using the Rietveld refining method. Chemical analysis of the photocatalyst that was carried out with X-ray photoelectron spectroscopy (XPS) showed the presence of manganese ions in the TiO2 anatase matrix. The Density Functional Theory (DFT) calculations exhibited a decrease in the energy gap and an increase in the density of the electronic stated inside the gap for the doped TiO2. These observations were in agreement with the results of the UV-visible diffuse reflectance spectroscopy (DRS) that demonstrated an adsorption shift towards the visible region for the same samples. The photocatalytic activity of the synthesized catalysts was investigated by the photocatalytic oxidation of the gaseous nitric oxide (NO) and decomposition of the gaseous acetaldehyde (CH3CHO) under visible light irradiation. The optimal concentration of dopant that improves the photocatalytic activity of the nanoplates was determined. © 2014 Elsevier B.V

Preparation of fluorine-doped TiO2 photocatalysts with controlled crystalline structure

Recommended by M. Sabry Abdel-Mottaleb Nanocrystalline F-doped TiO 2 powders were prepared by sol-gel route. The thermal behavior of the powders was recorded by DTA/TG technique. The crystalline phase of the fluorinated TiO 2 powders was determined by X-ray diffraction technique. It was demonstrated that F-doping using CF 3 COOH favors the formation of rutile along with anatase phase even at low temperature. Moreover, the rutile's phase content increases with the increase of the quantity of the fluorine precursor in the starting solution. The surface area of the powders and the pore size distribution were studied by N 2 adsorption-desorption using BET and BJH methods. X-ray photoelectron spectroscopy (XPS) revealed that the fluorine is presented in the TiO 2 powders mainly as metal fluoride in quantities ∼16 at %. The F-doped TiO 2 showed a red-shift absorption in UV-vis region which was attributed to the increased content of rutile phase in the powders. The powders exhibited enhanced photocatalytic activity in decomposition of acetone

Bose-Einstein Condensation of Light in a Semiconductor Quantum Well Microcavity

When particles with integer spin accumulate at low temperature and high density they undergo Bose-Einstein condensation (BEC). Atoms, solid-state excitons and excitons coupled to light all exhibit BEC, which results in high coherence due to massive occupation of the respective system's ground state. Surprisingly, photons were shown to exhibit BEC much more recently in organic dye-filled optical microcavities, which, owing to the photon's low mass, occurs at room temperature. Here we demonstrate that photons within an inorganic semiconductor microcavity also thermalise and undergo BEC. Although semiconductor lasers are understood to operate out of thermal equilibrium, we identify a region of good thermalisation in our system where we can clearly distinguish laser action from BEC. Based on well-developed technology, semiconductor microcavities are a robust system for exploring the physics and applications of quantum statistical photon condensates. Notably, photon BEC is an alternative to exciton-based BECs, which dissociate under high excitation and often require cryogenic operating conditions. In practical terms, photon BECs offer their critical behaviour at lower thresholds than lasers. Our study shows two further advantages of photon BEC in semiconductor materials: the lack of dark electronic states allows these BECs to be sustained continuously; and semiconductor quantum wells offer strong photon-photon scattering. We measure an unoptimised interaction parameter, $\tilde{g}=0.0023\pm0.0003$, which is large enough to access the rich physics of interactions within BECs, such as superfluid light or vortex formation.Comment: 15 pages, 4 figure

Study of the photocatalytic activity of anatase TiO2 nano-microstructures with exposed {001} facets

TiO2 anatase nanoplates, hollow microspheres and microcrystals with exposed {001} crystal facets were fabricated via a solvothermal- hydrothermal method at 180 °C for 24 hours using titanium isopropoxide or titanium tetrafluoride as a titanium precursor, ethanol or distilled water as a solvent and lastly hydrofluoric acid as the enhancer for the formation of the TiO2 anatase {001} crystal facets. All samples were calcined at 600 °C in order to remove the fluoride atoms adsorbed on the photocatalysts surface. This paper presents the influence of different TiO2 anatase structures in their photocatalytic activity. The photocatalytic evaluation of all TiO2 anatase structures with exposed {001} crystal facets was obtained by oxidizing the NO gas to NO2 and NO3- and then calculating their photonic efficiency. Commercial TiO 2 photocatalyst P25 by Evonik Degussa was used as a reference. The TiO2 anatase nanoplates were the structure that exhibited the best photocatalytic activity of all TiO2 anatase structures, including the used reference P25 by Evonik Degussa

Electrical conductivity mechanisms in titania hollow microspheres with dominant {0 0 1} facets

Anatase titania hollow microspheres with dominant {0 0 1} facets were synthesized by a solvotherrmal-hydrothermal method. Two kinds of samples, as prepared and calcinated at 600 C, were fabricated. The temperature dependence of their electrical conductivity in vacuum and in air, in the temperature range 113-440 K, was investigated. The conductivity data were fitted using the grain boundary model (GB), the small polaron hopping (SPH) model and the Mott's variable range hopping model in the different temperature regimes, suggesting the contribution of several conduction mechanisms. A significant decrease of conductivity values in air is observed, indicating the influence of environment on titania hollow microspheres. In the temperature region 274-294 K a metal-like behavior in air is shown for the as prepared sample. © 2013 Elsevier B.V. All rights reserved

Salivary metal levels of orthodontic patients: A novel methodological and analytical approach

The purpose of this study was to qualitatively and quantitatively assess the nickel, chromium, and ferrous levels in a population of 17 orthodontic patients undergoing treatment, compared with seven untreated individuals, employing a novel methodological approach and a new analytical technique. Salivary samples obtained from patients before and after rinsing with double distilled water were processed for Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) for simultaneous estimation of the concentration of the metallic elements. No statistically significant difference was detected between control and patient groups with respect to salivary metal content, regardless of element. The range of salivary metal levels found did not exceed those of daily intake through food and air. The lack of a continuous monitoring scheme for salivary metal concentrations in real time may impose substantial obstacles to defining the release rate of metals in vivo. The results of this study emphasize the necessity of incorporating the dimension of time in assessing the release potential of orthodontic alloys. © 2003 European Orthodontic Society