Enhanced photocatalytic activity of titanium oxide nanotubes after heating treatment

Titanium oxide nanotubes were obtained by an electrochemical anodization method. Scanning electron microscope results demonstrate that the diameter of the tubes is about 120 nm and the length of the tubes is around 13 μm. Transmission electron microscope results indicate that the nanotubes are assembled by numerous nanoparticles and tube-like structure remains well after heat treatment at 400-600 °C. The photocatalysis performance of the nanotubes was evaluated in terms of the decomposition rate of methyl orange under UV irradiation. The results show that the photocatalytic activity was enhanced through the heating treatment of the nanotubes, and the nanotubes heated at 600 °C exhibits the best photocatalytic activity. X-ray diffraction patterns indicate that there is no phase transformation during the heat treatment. Therefore, the enhanced activity can be attributed to the improvement of nanotubes crystallinity, which may provide more insights about the effect of the crystallinity on the photocatalytic performance.

Synthesis, characterization and photocatalytic activity of MxCe1-xVO4 (M = Li, Ca and Fe)

Non-stoichiometric substituted cerium vanadates, MxCe1-xVO4 (M = Li, Ca and Fe), were synthesized by solid-state reactions. The crystal structure was analyzed by powder X-ray diffraction and it exhibits a tetragonal zircon Structure, crystallizing in the space group I4(1)/amd with a = 7.3733(4) and c = 6.4909(4) angstrom and Z = 4. Particle sizes were in the range of 600-800 nm, as observed by scanning electron microscopy. The thermal analysis of the compounds showed phase stability up to 1100 degrees C. The UV diffuse reflectance spectra indicated that the compounds have band gaps in the range of 2.6-2.9 eV. The photocatalytic activity of these Compounds was investigated for the first time for the degradation of different dyes, and organics, the oxidation of cyclohexane and the hydroxylation of benzene. The degradation of dyes was modeled using the Langmuir-Hinshelwood kinetics, while the oxidation of cyclohexane and hydroxylation of benzene were modeled using a free radical mechanism and a series reaction mechanism, respectively.

Photocatalytic activity of Ag-substituted and impregnated nano-TiO2

Ag-substituted (Ag sub) and Ag-impregnated (Ag imp), anatase phase nano-TiO2 have been synthesized by solution combustion technique and reduction technique, respectively. The catalysts were characterized extensively by powder XRD, TEM, XPS, FT-Raman, UV absorption, FT-IR, TGA, photoluminescence, BET surface area and isoelectric pH measurements. These catalysts were used for the photodegradation of dyes and for the selective photooxidation of cyclohexane to cyclohexanone. The photoactivities of the combustion-synthesized catalysts were compared with those of commercial Degussa P 25 (DP 25) TiO2, and Ag-impregnated DP 25 (Ag DP). For the photocatalytic degradation of dyes, unsubstituted combustion-synthesized TiO2 (CS TiO2) exhibited the highest activity, followed by 1% Ag imp and 1% Ag sub. For the photoconversion of cyclohexane, the total conversion of cyclohexane and the selectivity of cyclohexanone followed the order: 1% Ag sub > DP 25 > CS TiO2 > 1% Ag imp > 1% Ag DP. The kinetics of the photodegradation of dyes and of the photooxidation of cyclohexane were modeled using Langmuir–Hinshelwood rate equation and a free radical mechanism, respectively, and the rate coefficients were determined. The difference in activity values of the catalysts observed for these two reactions and the detailed characterization of these catalysts are described in this study.

Photocatalytic activity of tin-substituted TiO2 in visible light

Ultrafine powders of (Ti1-xSnx)O2, 0photocatalytic activity (after platinization) in the visible light region (420-550 nm) for H2 production from aqueous solutions containing sacrificial donors such as hypophosphite. The spectral sensitization is shown to be due to peroxotitanium species present in the lattice.

Photocatalytic Activity of Microwave Plasma-Synthesized TiO2 Nanopowder

Nanocrystalline TiO2 was synthesized using the microwave plasma technique and characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, laser particle size analyzer, UV-vis spectroscopy and BET surface area analyzer. The synthesized TiO2 powder crystallized in anatase phase and the crystallite sizes were in nanometers. The photocatalytic activity of the compound was determined and compared against the activity of the commercial Degussa P-25 TiO2 catalyst. The degradation rates of the dyes were found to be higher over the synthesized TiO2 as compared to that over commercial Degussa P-25 TiO2.

Microwave Assisted Synthesis of Nanostructured Titanium Dioxide with High Photocatalytic Activity

TiO2 (anatase) was synthesized using a microwave-irradiation-assisted chemical method. The reaction conditions were varied to obtain unique nanostructures of TiO2 comprising nanometric spheres giving the materials a very porous morphology. The oxide was characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The specific surface area and porosity were quantified by the BET method, and the degradation of dyes was carried out using these materials. The photocatalytic activity of the nanometric TiO2 was significantly higher than that of commercially available TiO2 (Degussa P25) for the degradation of the dyes.

Nanoscale ZnO/CdS heterostructures with engineered interfaces for high photocatalytic activity under solar radiation

Semiconductor based nanoscale heterostructures are promising candidates for photocatalytic and photovoltaic applications with the sensitization of a wide bandgap semiconductor with a narrow bandgap material being the most viable strategy to maximize the utilization of the solar spectrum. Here, we present a simple wet chemical route to obtain nanoscale heterostructures of ZnO/CdS without using any molecular linker. Our method involves the nucleation of a Cd-precursor on ZnO nanorods with a subsequent sulfidation step leading to the formation of the ZnO/CdS nanoscale heterostructures. Excellent control over the loading of CdS and the microstructure is realized by merely changing the initial concentration of the sulfiding agent. We show that the heterostructures with the lowest CdS loading exhibit an exceptionally high activity for the degradation of methylene blue (MB) under solar irradiation conditions; microstructural and surface analysis reveals that the higher activity in this case is related to the dispersion of the CdS nanoparticles on the ZnO nanorod surface and to the higher concentration of surface hydroxyl species. Detailed analysis of the mechanism of formation of the nanoscale heterostructures reveals that it is possible to obtain deterministic control over the nature of the interfaces. Our synthesis method is general and applicable for other heterostructures where the interfaces need to be engineered for optimal properties. In particular, the absence of any molecular linker at the interface makes our method appealing for photovoltaic applications where faster rates of electron transfer at the heterojunctions are highly desirable.

Photocatalytic Activity of Combustion Synthesized Nanocrystalline CeAlO3

The photocatalytic activity of combustion synthesized nanocrystalline CeAlO3 was determined for the degradation of four anionic and four cationic dyes. The perovskite oxide showed high-photocatalytic activity and a complete degradation of all the dyes was possible within 2 h. The photocatalytic activity of the compound was comparable with the activity of the commercial Degussa P-25 TiO2 catalyst. The degradation of dyes was found to follow first order kinetics and the first order degradation rate constants were determined.

Nanoparticles of SrTiO3 prepared by gel to crystallite conversion and their photocatalytic activity in the mineralization of phenol

Nanometre-sized powders of SrTiO3 were prepared at 70-100 degrees C by the wet-chemical method of gel to crystallite (G-C) conversion. The crystallite sizes obtained were in the range 5-13 nm, as estimated by transmission electron microscopy (TEM) studies. The photocatalytic activities of these powders in the mineralization of phenol were evaluated in comparison with Degussa P25 (TiO2). The maximum photocatalytic activity was observed for powders annealed in the range 1100-1300 degrees C. The optical spectra of the particle suspensions in water showed broadened absorption around the band gap region, together with the appearance of an absorption maximum in the UV region. The effect of inorganic oxidizing species as electron scavengers on the rate of the photocatalytic degradation of phenol was studied. The influence of bulk and surface defects, which participate in the charge transfer process during photocatalysis, was investigated systematically.

Solution combustion synthesis of gamma(L)-Bi(2)MoO(6) and photocatalytic activity under solar radiation

The facile method of solution combustion was used to synthesize gamma(L)-Bi(2)MoO(6). The material was crystallized in a purely crystalline orthorhombic phase with sizes varying from 300 to 500 nm. Because the band gap was 2.51 eV, the degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (< 1 m(2)/g) of the synthesized material, gamma(L)-Bi(2)MoO(6) showed high photocatalytic activity under solar radiation due to its electronic and morphological properties. (C) 2011 Elsevier Ltd. All rights reserved.

Photocatalytic activity of ZnO nanostructured film grown by activated reactive

ZnO nanostructured films were deposited at room temperature on glass substrates and cotton fabrics by activated reactive evaporation in a single step without using metal catalyst or templates. Morphological observation has shown that the nanostructured film contains seaurchin-like structures, and this seaurchin containing large number of randomly grown ZnO nanoneedles. Microstructural analysis revealed the single crystalline nature of the grown nanoneedles and their growth direction was indentified to be along [0002]. PL spectrum of nanostructured films has shown a relatively weak near-band-edge emission peak at 380 nm, and a significant broad peak at 557 nm due to the oxygen vacancy-related emission. ZnO nanostructured films grown on glass substrates and cotton fabrics have shown good photocatalytic activity against rhodamine B.