Nucleation and crystallization of titania nanoparticles in silica titania planar waveguides: A study by low frequency Raman scattering

SiO2 (1-x) - TiO2 (x) waveguides, with the mole fraction x in the range 0.07 - 0.20 and thickness of about 0.4 μm, were deposited on silica substrates by a dip-coating technique. The thermal treatments at 700-900°C, used to fully densify the xerogels, produce nucleation of TiO2 nanocrystals even for the lowest TiO2 content. The nucleation of TiO2 nanocrystals and their growth by thermal annealing up to 1300°C were studied by waveguide Raman spectroscopy, for the SiO2 (0.8) - TiO2 (0.2) composition. By increasing the annealing temperature, the Raman spectrum evolves from that typical of the silica-titania glass to that of anatase, but brookite phase is dominant at intermediate temperatures. In the low. frequency region (5-50 cm-1) of the Raman spectra, acoustic vibrations of the nanocrystals are observed. From the measured line shapes, we can deduce the size distribution of the particles. The results are compared with those obtained from the line widths in the X-ray diffraction patterns. Nanocrystals with a mean size in the range 4-20 nm are obtained, by thermal annealing in a corresponding range of 800-1300°C.

Effect of scandium on the structural and photocatalytic properties of titanium dioxide thin films

Pure and scandium doped-TiO2 thin films were prepared by the sol-gel process and coated by dip coating. The effects of scandium on the phase formation, optical properties and photoactivity of the TiO2 thin films were investigated. The lattice parameters and the crystallinity of the anatase phase, characterized by the Rietveld method, demonstrated that scandium doping affected the structural parameters and crystallinity of the films, modifying the absorption edge. A direct correlation was found between band gap energy and photodegradation efficiency, with lower values of band gap energy augmenting this efficiency. Moreover, a significant improvement in the catalyst's photodegradation efficiency was attained with a scandium concentration of 5.0 mol%. © 2007 Springer Science+Business Media, LLC.

A study of the precursors and photoactivity of nanostructures of Ti oxides synthesized by the alkaline hydrothermal method

The present study describes the synthesis, characterization and photocatalytic potential of Ti oxide nanostructures of various morphologies and crystalline phases that were synthesized from 4 different precursors by the alkaline hydrothermal method. The materials were characterized by mainly X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA) and X-ray absorption spectroscopy (XAS). Also, photocatalytic potential was assessed by rhodamine B photodegradation. The materials obtained from peroxytitanium complexes (PTCs) exhibited a strong dependence on the concentration of KOH ([KOH]) used for synthesis. The pre-formed sheets of the PTCs were critical to the formation of nanostructures such as nanoribbons, and they were also compatible with the rolling up process, which can be utilized to form structures such as nanorods, nanowires or nanotubes. In the rhodamine photodegradation tests, TiO2 anatase nanostructures with six-coor inated Ti were more effective than the titanate ones (five-coordinated), despite having a smaller surface area and fewer OH groups. The lower photoactivity of the titanates was attributed to the presence of five-coordinated titanium species (TiO5), which may act as electron-hole recombination centers. Furthermore, the material with a mixture of TiO2/titanate was shown to be promising for photocatalytic applications. © 2013 by American Scientific Publishers.

TiO2-Cu photocatalysts: A study on the long- and short-range chemical environment of the dopant

In this study, the short- and long-range chemical environments of Cu dopant in TiO2 photocatalyst have been investigated. The Cu-doped and undoped TiO2 specimens were prepared by the sol-gel approach employing CuSO4·5H2O and Ti(O-iPr)4 precursors and subjecting the dried gels to thermal treatment at 400 and 500 C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a significantly higher efficiency of Cu-doped samples than that of pure TiO2. The X-ray diffraction results showed the presence of anatase phase for samples prepared at 400 and 500 C. No crystalline CuSO4 phase was detected below 500 C. It was also found that doping decreases the crystallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environment of sulfate changes as a function of thermal treatment, and UV-vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 C sample. X-ray absorption fine structure measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu2+ local order is similar to that of CuSO4, containing, however, oxygen vacancies. X-ray photoelectron spectroscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO4, the presence of Cu1+ and CuO phases, indicating the active role of Cu in the TiO2 lattice. © 2013 Springer Science+Business Media New York.

Experimental and theoretical approach of nanocrystalline TiO2 with antifungal activity

Using a solvothermal method for this research we synthesized nanocrystalline titanium dioxide (nc-TiO2) anatase particles with a mean diameter of 5.4 nm and evaluated their potential antifungal effect against planktonic cells of Candida albicans without UV radiation. To complement experimental data, we analyzed structural and electronic properties of both the bulk and the (1 0 1) surface of anatase by first-principles calculations. Based on experimental and theoretical results, a reactive O2H- and OH- species formation mechanism was proposed to explain the key factor which facilitates the antifungal activity. © 2013 Published by Elsevier B.V.

Soft-chemical synthesis, characterization and humidity sensing behavior of WO3/TiO2 nanopowders

Tungsten oxide/titania (WO3/TiO2) nanopowders were synthesized by the polymeric precursor method which varied the WO3 content between 0 and 10 mol%. The powders were thermally treated in a conventional furnace and their structural, microstructural and electric properties were evaluated by X-ray diffraction (XRD), Raman spectrometry, N 2 physisorption, NH3 chemisorption, temperature-programmed reduction (TPR), X-ray absorption near-edge spectroscopy (XANES) in situ XANES and extended X-ray absorption fine structure spectroscopy (EXAFS) and transmission electron microscopy (TEM). XRD and Raman spectrometry confirmed the homogeneous distribution of an amorphous WO3 phase in the TiO 2 matrix which stabilized the anatase phase through the generation of [TiO5·V0] or [TiO5·V 0] complex sites. Conventional TPR-H2 (temperature programmed reduction) along with XANES TPR-H2 and XANES TPR-EtOH showed that WO3/TiO2 sample reduction occurs through the formation of these complex clusters. Moreover, the addition of WO3 promoted an increase in the surface acidity of doped samples as revealed by NH3 chemisorption. The WO3/TiO2 bulk-ceramic samples were further used to estimate their potential application in a humidity sensor in the range of 15-85% relative humidity. Probable reasons that lead to the different humidity sensor responses of samples were given based on the structural and surface characterizations. Correlation between the sensing performance of the sensor and its structural features are also discussed. Although all samples responded as a humidity sensor, the W2T sample (2 mol% added WO3) excelled for sensitivity due to the increase in acid sites, optimum mean pore size and pore size distribution. © 2013 Elsevier B.V.

TiO2 synthesized by microwave assisted solvothermal method: Experimental and theoretical evaluation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Propriedades estruturais e eletrônicas de nanofilmes de TiO2 anatase: cálculos B3LYP-D* em sistemas periódicos bidimensionais

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Titanate nanotubes produced from microwave-assisted hydrothermal synthesis: Photocatalytic and structural properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparation of TiO2/SnO2 Thin Films by Sol-Gel Method and Periodic B3LYP Simulations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo do desempenho de filmes de Ti02 como aceptor de elétrons e obtenção de fases puras de nanopartículas de Ti02: anatase e rutila, sintetizado por uma nova rota química

Pós-graduação em Ciência dos Materiais - FEIS

Photocatalytic decomposition of rhodamine-B using scandium and silver-modified TiO2 Powders

Semiconductor-mediated photocatalytic oxidation is an interesting method for water decontamination and a specially modified TiO2 is said to be a promising material. This study verified that the synthesis of 1wt%Ag modified-Sc0.01Ti0.99O1.995 powder samples prepared by Polymeric Precursor Method is capable of forming a mixture of anatase-rutile phase with high photocatalytic performance. This kind of material is found to have a lower bandgap compared to the TiO2-anatase commercial powders, which can be associated to an innovative hybrid modification. The simultaneous insertion of scandium in order to generate a p-type semiconductor and a metallic silver nanophase acting as an electron trapper demonstrated being capable of enhancing the degradation of rhodamine B compared to the commercial TiO2. In spite of the different thermal treatments or phase amounts, the hybrid modified powder samples showed higher photocatalytic activity than the commercial ones.

Biomarker evaluation in fish after prolonged exposure to nano-TiO2: influence of illumination conditions and crystal phase

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pigments based on Cr and Sb doped TiO2 prepared by microemulsion-mediated solvothermal synthesis for inkjet printing on ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A relationship between structural and electronic order-disorder effects and optical properties in crystalline TiO2 nanomaterials

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)