Search results for "medium"
showing 10 items of 3746 documents
Effect of titanium dioxide crystalline structure on the photocatalytic production of hydrogen
2011
The effect of the crystalline phase of TiO 2 (anatase, rutile and brookite) on its photocatalytic activity in hydrogen production from methanol-water vapours has been investigated by testing a series of both home-made and commercial TiO 2 photocatalysts, either bare or surface-modified by deposition of a fixed amount, i.e. 1 wt%, of platinum as co-catalyst. For all of the TiO 2 samples the rate of hydrogen production increased by one order of magnitude upon Pt deposition, because of the ability of Pt to enhance the separation of photoproduced electron-hole pairs. Under irradiation in the 350-450 nm wavelength range, brookite and anatase showed similar photoactivities, both superior to that …
The effect of the surface disordered layer on the photoreactivity of titania nanoparticles
2017
It is well known that the surface of metal oxide catalysts presents, usually, non-crystalline species containing impurities and low coordinated cations, which are observed in HRTEM images as a disordered layer of amorphous phase. Despite of being these species more accessible and less stable than the crystalline catalysts components, they have been rarely considered when analysing the catalyst activity. In this work, we have studied the effect of a treatment with HCl solution at pH = 0 on the characteristics of the disordered layer in two commercial anatase TiO2 samples, using techniques such as TGA, 1H MAS-NMR and HRTEM, and by determining these sample photocatalytic activity for the 4-nit…
Preparation and photoactivity of nanostructured anatase, rutile and brookite TiO2 thin films
2006
Photoactive films consisting of pure anatase, brookite or rutile TiO2 were prepared by dip coating from water dispersions obtained by using TiCl4 as the precursor under similar mild experimental conditions
Reduced grey brookite for noble metal free photocatalytic H2evolution
2021
Herein we introduce for the first time a reduced “grey” brookite TiO2 photocatalyst, produced by thermal hydrogenation of brookite nanoparticles, that shows a remarkable noble metal free photocatalytic H2 evolution. Its activity is substantially higher than that of other TiO2 polymorphs, i.e. anatase or rutile, comparably sized and activated by hydrogenation under optimized conditions. Along with brookite powders, an oriented brookite single crystal was investigated as a defined surface to confirm the effects of the hydrogenation treatment. By a combination of electron paramagnetic resonance (EPR), electron and X-ray characterization techniques applied to the powders and single crystal, we …
Investigation of TiO<sub>2</sub> Ceramic Surface Conductivity Using Conductive Atomic Force Microscopy
2012
Dense TiO2 (rutile) ceramic samples were prepared by sintering compacts of titanium dioxide anatase powder at 1500 °C for 5h. Sintered samples were polished and annealed in vacuum at 1000 °C for 1h. Structural properties of the samples were studied by X-ray diffraction, polarized light and scanning electron microscopy. The surface topography and local electrical conductivity of the samples were investigated by atomic force microscopy technique under atmospheric conditions. Enhanced electrical conductivity was observed at grain boundaries while the polished, vacuum annealed grains surface showed non-homogeneous conductivity.
Hydrothermal synthesis of nanostructured inorganic powders by a continuous process under supercritical conditions
2005
Abstract In this study, using a prototype of hydrothermal synthesis in subcritical and supercritical water working in a continuous way, nanometric ceramic precursors with perfectly defined composition are produced: spinel ferrites such as Fe2CoO4, TiO2 with anatase structure and also perovskite structures such as BaZrO3. The as-prepared powders are fully characterized by complementary experiments: X-ray diffraction, electron microscopies, EDX spectrometry, surface area measurement, etc. Thus, particles size, morphology, aggregation state, crystal structure, composition are investigated. Moreover, magnetic properties of the ferrites products are studied. The powders obtained are pure phases …
Preparation and photoactivity of samarium loaded anatase, brookite and rutile catalysts
2011
Abstract Pure and samarium loaded anatase, brookite and rutile nanopowders were synthesized by thermohydrolysis of TiCl 4 . The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (SSA) determination, UV–vis diffuse reflectance spectroscopy (DRS), atomic force microscopy (AFM), contact angle (CA) measurements and photoluminescence (PL) spectroscopy. The photocatalytic activity of pure and Sm-loaded TiO 2 polymorphs was investigated by employing the photodegradation of 4-nitrophenol as probe reaction in a liquid-solid system. Loading with Sm resulted in an improvement of the photoreactivity of the three TiO 2 polymorphs. The benefi…
Partial photoelectrocatalytic oxidation of 3-pyridinemethanol by Pt, Au and Pd loaded TiO2 nanotubes on Ti plate
2021
Abstract The photoelectrocatalytic (PEC) oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B3 was investigated by using Pt, Au and Pd loaded (as single or bimetallic) nanotube structured TiO2 on Ti plate in water under UVA irradiation. Nanotube structured TiO2 on Ti plate samples were prepared as anode by anodic oxidation method in ethylene glycol solution in different times, and then they were calcined at 500 °C to be obtained in crystalline form. The anodes were loaded with noble metals by electrochemical reduction method and characterized by XRD, XPS, SEM, and photocurrent techniques. The TiO2 on the plates was in the anatase phase. The loaded metals were in metallic form…
A recipe for the use of rutile in sedimentary provenance analysis
2012
Abstract Rutile has received considerable attention in the last decade as a valuable petrogenetic indicator mineral. Based on both new and previously published data, we carve out advantages and pitfalls regarding TiO 2 -minerals in sedimentary provenance analysis. This results in a recipe for the use of rutile in provenance studies. The main points are: Rutile geochemistry from different grain size fractions does not differ systematically, and hence rutiles should be extracted from the fraction containing the most rutile grains (usually 63–200 μm). Similarly, different magnetic susceptibility of rutile does not systematically imply different trace element composition. Before interpretation …
Photocatalytic Selective Oxidation of 5-(Hydroxymethyl)-2-furaldehyde to 2,5-Furandicarbaldehyde in Water by Using Anatase, Rutile, and Brookite TiO2…
2013
5-(Hydroxymethyl)-2-furaldehyde (HMF) was selectively oxidized to 2,5-furandicarbaldehyde (FDC) in; aqueous medium by using home prepared (HP) anatase, rutile, and brookite TiO2 nanoparticles. HP samples were prepared via a sol-gel method by using TiCl4 as the TiO2 precursor. Commercial TiO2 catalysts were also used for, comparison. All samples were characterized by BET specific surface area, XRD, TGA, and SEM, and the reactivity results showed that HP catalysts are predominantly amorphous and give rise to selectivities toward FDC more than twice that of commercial and well crystallized catalysts.