Search results for "NATAS"
showing 10 items of 159 documents
Titania nanotubes modeled from 3- and 6-layered (101) anatase sheets: Line group symmetry and comparative ab initio LCAO calculations
2010
Abstract The formalism of line groups for one-periodic (1D) nanostructures with rotohelical symmetry has been applied for construction of TiO 2 nanotubes (NTs). They are formed by rolling up the stoichiometric two-periodic (2D) sheets cut from the energetically stable (1 0 1) anatase surface, which contains either six (O–Ti–O_O–Ti–O) or three (O–Ti–O) layers. After optimization of geometry the former keeps the centered rectangular symmetry of initial slab while the latter is spontaneously reconstructed to the hexagonal fluorite-type (1 1 1) sheet. We have considered the four sets of TiO 2 NTs with optimized 6- and 3-layered structures, which possess the two pairs of either anatase (− n , n …
Ab initio calculations of doped TiO2 anatase (101) nanotubes for photocatalytical water splitting applications
2016
Abstract TiO 2 (titania) is one of the promising materials for photocatalytic applications. In this paper we report on recently obtained theoretical results for N and S doped, as well as N+S co-doped 6-layer (101) anatase nanotube (NT). First principles calculations in our study have been performed using a modified B3LYP hybrid exchange-correlation functional within density functional theory (DFT). Here we discuss the energy of defect formation mechanism and electronic band structure for nanotubes under study. We also report on influence of dopant concentration on the NT's band structure and discuss the defect–defect interactions.
Water Adsorption on Clean and Defective Anatase TiO2 (001) Nanotube Surfaces: A Surface Science Approach
2018
We use ab initio molecular dynamics simulations to study the adsorption of thin water films with 1 and 2 ML coverage on anatase TiO2 (001) nanotubes. The nanotubes are modeled as 2D slabs, which consist of partially constrained and partially relaxed structural motifs from nanotubes. The effect of anion doping on the adsorption is investigated by substituting O atoms with N and S impurities on the nanotube slab surface. Due to strain-induced curvature effects, water adsorbs molecularly on defect-free surfaces via weak bonds on Ti sites and H bonds to surface oxygens. While the introduction of an S atom weakens the interaction of the surface with water, which adsorbs molecularly, the presence…
Photo-Activity Research of Nano-Structured TiO2Layers
2011
Titania with anatase structure is investigated due to its photo-active properties that can be used in the water photocatalysis applications and in the organic photovoltaic devices. In this work the anodization conditions are described to obtain stable thin film TiO2 layers formed from vertically oriented nanotubes with approximate height 358 nm, inner tube diameter 48 nm and wall thickness 20 nm, but centre to centre distance 100 nm. Annealed at 500 o C TiO2 layer mostly consists from oxide with anatase structure, though XRD spectroscopy shows rutile impurities as well. Obtained nanotube layers are sensitive mostly to UV light.
Comparison of the Photoelectronic and Photocatalytic Activities of Various Anatase and Rutile Forms of Titania in Pure Liquid Organic Phases and in A…
1996
Various titania samples of industrial origin (Degussa and Tioxide) have been characterized by electrical photoconductance measurements and tested as photocatalysts in various liquid media (either pure organic liquids or aqueous solutions) as a function of their structure (anatase versus rutile). Anatase was constantly found more active than rutile, whatever the reaction chosen (mild oxidation of pure cyclohexane and 2-propanol; total degradation of phenol and nitrophenol isomers in water). In identical conditions, Degussa was found more active, but the intrinsic activity, expressed in moles converted per hour and per square meter of active surface, was found slightly higher for anatase Tiox…
Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques
2011
Abstract Typical red–brown (Fe-rich) and high-quality white–grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to 228Ac (232Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to 228Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO2 polymorphs). SEM-EDS indicated the presence of Ti–Fe–containing phases (e.g.…
The solubility of Co in TiO2 anatase and rutile and its effect on the magnetic properties
2009
Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are found to be paramagnetic at room-temperature. Only further annealing in Ar/H{sub 2} gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope studies reveal for low doping levels =4%. The observed Co oxides are reduced by Ar/H{sub 2} to Co metal. The room-temperature ferromagnetism can therefore be traced back to a segregation of metallic Co. - Graphical abstract: Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are paramagnetic at room-temperature. Further annealing in Ar/H{sub 2} gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope…
Preparation and photoactivity of nanostructured TiO2 particles obtained by hydrolysis of TiCl4
2005
This work reports the preparation of nanostructured polycrystalline TiO2 photocatalysts obtained by hydrolysis of TiCl4 in very mild conditions. Several samples were prepared as suspensions or colloidal dispersions by using TiCl4/H2O volume ratios ranging between 1:1 and 1:100. The samples were characterised by X-ray diffraction analysis, specific surface area determination, diffuse reflectance spectroscopy and scanning electron microscopy. 4-Nitrophenol photodegradation was used as probe reaction to test the photoactivity of the catalysts. Some samples revealed a photoactivity higher than that of Degussa P25 in similar experimental conditions and the most photoactive one was that prepared …
Synergistic effect between hydrodynamic conditions during Ti anodization and acidic treatment on the photoelectric properties of TiO2 nanotubes
2015
In the present work, the combined influence of controlled hydrodynamic conditions during Ti anodization and the acidic treatment with HClO4 on the photoelectric properties of mixed anatase/rutile TiO2 nanotubes has been studied. Anodized samples were analyzed by means of Field Emission Scanning Electronic Microscopy (FE-SEM), Confocal Raman Microscopy, electrochemical measurements (electrochemical impedance spectroscopy and Mott-Schottky analysis) and photoelectrochemical measurements. It has been observed that the use of hydrodynamic conditions increases the surface area of nanotubes, while acidic treatment enhances their conductivity. Besides, there is a clear synergistic effect between t…
Photoelectrocatalytic oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B3 by TiO2 nanotubes
2020
In this paper, the first photoelectrocatalytic (PEC) 3-pyridinemethanol oxidation to 3-pyridinemethanal and vitamin B-3 was investigated. To meet this aim, efficient nanotube structured TiO2 on a Ti plate as a photoanode was prepared by an anodic oxidation method in ethylene glycol and characterized by XRD, SEM, and photocurrent techniques. The effect of nanotube morphology, applied potential, Na2SO4 concentration, stirring speed of solution, and pH on the reaction activity and product selectivities were investigated. The TiO2 phase of all of the anodes was mainly the anatase one. The PEC activity, the intensity of the XRD peak and the photocurrent increased by increasing the nanotube lengt…