Aerosol-Assisted Production of Mesoporous Titania Microspheres with Enhanced Photocatalytic Activity: The Basis of an Improved Process

An aerosol-based process was used to prepare mesoporous TiO2 microspheres (MTM) with an average diameter in the range of 0.5-1 μm. The structural characteristics and photocatalytic properties of the synthesized materials were determined. As-prepared MTM materials and those heated in air from 400 to 600 °C exhibited mesoporous texture with a narrow size distribution and an inorganic framework that consisted of 4-13 nm anatase crystallites. Pore volumes for the MTM materials were in the range of 0.17-0.34 cm3 g-1. Microspheres heated to 400 °C presented a locally ordered mesopore structure and possessed X-ray diffraction d spacings between 9.8 and 17.3 nm. Heating above 400 °C resulted in a loss of the mesoscopic order, a decrease of the surface area, retention of the porosity, and an increase of the anatase nanoparticle size to 13 nm. The accessibility of the pore volume was measured by monitoring the uptake of gallic acid (GA) using Fourier transform IR. The MTM materials made excellent catalysts for the photodegradation of GA, with the performance being higher than that of an equivalent sample of Degussa P25. The present MTM materials are advantageous in terms of their ease of separation from the aqueous phase, and hence a novel photocatalytic process is proposed based on separate adsorption and photocatalytic decomposition steps with an improved and more rational use of both catalyst and sunlight.Fil: Araujo, Paula Zulema. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Luca, Vittorio. Australian Nuclear Science And Technology Organisation; Australia. Comisión Nacional de Energía Atómica; ArgentinaFil: Bozzano, Patricia B.. Comisión Nacional de Energía Atómica; ArgentinaFil: Bianchi, Hugo Luis. Universidad Nacional de San Martín; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Soler Illia, Galo Juan de Avila Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Blesa, Miguel Angel. Universidad Nacional de San Martín; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Evaporation-induced self-assembly of mesoscopically ordered organic/organosilica nanocomposite thin films with photoluminescent properties and improved hardness

We report the use of evaporation-induced self-assembly (EISA) to organize and chemically bind a functionalized organic material, N,N′-bis(4-tert- butylphenyl)-N,N′-bis(4-((E)-2-(triethoxysilyl)vinyl)phenyl)biphenyl-4, 4′-diamine (3), into the ordered nanochannels within an organosilica matrix based on 1,2-bis(triethoxysilyl)ethane (BTSE). Characterization techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and nitrogen absorption/desorption (BET) were used to show that the EISA derived thin films and powders are highly ordered with compound 3 occupying and chemically bound within the nanochannels. Furthermore, photoluminescent spectroscopy (PL) and nanoindentation show these materials have unique PL properties with hardness values twice of their nonordered counterparts. © 2008 American Chemical Society

X-ray Absorption Spectroscopy Study of TiO2–xThin Films for Memory Applications

Metal–insulator–metal (MIM) devices based on titanium dioxide thin films exhibit resistive switching behavior (RS); i.e., they have the ability to switch the electrical resistance between high-resistive states (HRS) and low-resistive states (LRS) by application of an appropriate voltage. This behavior makes titanium dioxide thin films extremely valuable for memory applications. The physical mechanism behind RS remains a controversial subject but it has been suggested that it could be interface-type, without accompanying structural changes of the oxide, or filament-type with formation of reduced titanium oxide phases in the film. In this work, X-ray absorption spectroscopy (XAS) at the Ti K-edge (4966 eV) was used to characterize the atomic-scale structure of a nonstoichiometric TiO2–x thin film before and after annealing and for the first time after inclusion in a MIM device based on a Cr/Pt/TiO2–x/Pt stack developed on an oxidized silicon wafer. The advantage of the XAS technique is that is element-specific. Therefore, by tuning the energy to the Ti K-edge absorption, contributions from the Pt, Cr, and Si in the stack are eliminated. In order to investigate the structure of the film after electrical switching, XAS analysis at the Ti K-edge was again performed for the first time on the Cr/Pt/TiO2–x/Pt stack in its virgin state and after switching to LRS by application of an appropriate bias. X-ray absorption near-edge structure (XANES) was employed to assess local coordination and oxidation state of the Ti and extended X-ray absorption fine structure (EXAFS) was used to assess bond distances, coordination numbers, and Debye–Waller factors. XAS analysis revealed that the as-deposited film is amorphous with a distorted local octahedral arrangement around Ti (average Ti–O distance of 1.95 Å and coordination number of 5.2) and has a majority oxidation state of Ti4+ with a slight content of Ti3+. The film remains amorphous upon insertion into the stack structure and after electrical switching but crystallizes as anatase upon annealing at 600 °C. These results do not give any indication of the appearance of conducting filaments upon switching and are more compatible with homogeneous interface mechanisms