Nanocrystalline Titania Particles Research Articles

Photocatalytic activity of mixed-phase of TiO2 synthesized by non-aqueous methodology

A mix-phase (anatase-rutile) nanocrystalline titania particles were successfully synthesized in a non-aqueous solvent medium using a novel approach of controlled hydrolysis of titanium isopropoxide. The hydrolysis was carried out by the controlled release of water molecules from simple Schiff base formation reaction of anisaldehyde employing aniline as an amine component in isopropanol solvent medium. The excess aniline used, and the imine formed acts as directing agents. The photocatalytic activities of the catalysts prepared were compared with Degussa P25 for methylene blue degradation in direct sunlight. The photocatalytic activity was found to increase with decreasing availability of water molecules formed during the Schiff base formation (imination) reaction. Also, it was found to affect the phase and shape selection. TEM images show sphere-like to hexagonal to a rod-shaped formation of particulates.

Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques

AbstractThe mechanical behavior of nanostructured spherical submicrometer titania particles was studied by in situ uniaxial compression experiments in the scanning and transmission electron microscope (SEM and TEM). Mesoporous and amorphous titania particles were prepared by a wet chemical sol‐gel approach. To obtain nanocrystalline (nc) single‐phase anatase and rutile particles the amorphous particles were crystallized by high‐temperature annealing. For each sample the deformation behavior of at least 50 particles was investigated by in situ compression experiments in the SEM. In all cases an elastic – predominantly plastic deformation behavior accompanied by crack initiation at exceptionally high engineering strain values of several percent were observed. Crack propagation presumably along grain boundaries and a Weibull distributed fracture stress was shown for all nc particles. Complementary in situ TEM experiments and ex situ analysis of focused ion beam prepared particle cross‐sections were carried out to identify the underlying deformation mechanisms. Grain rotations and grain sliding are observed for nc anatase particles during in situ compression and are further identified to be linked to a densification of the mesoporous particle structure. Our dedicated preparation and quantitative in situ characterization methodology provides an excellent basis for a better understanding of the mechanical behavior of advanced ceramics.

Inelastic neutron scattering study of the coordination of para-amino benzoic acid molecules to the surface of nanocrystalline titania particles

The interaction of para-amino benzoic acid (PABA) with nanocrystalline titania particles has been studied with inelastic neutron scattering. The vibrational spectra of hybrid TiO 2/PABA, with different amounts of PABA, are compared with the spectrum obtained for solid PABA and to spectra derived from ab initio calculations for the isolated and dimer molecules. The absence of the OH bending modes of the carboxylic acid group for the chemisorbed species supports the formation of Ti–O–C bonds with the carboxyl group of the molecule.

Efficient gas phase photodecomposition of acetone by Ru-doped Titania

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by homogenous hydrolysis of TiOSO4 in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and surface area (BET) and porosity determination (BJH). The photocatalytic activity of Ru-doped titania samples was determined in the gas phase by decomposition of acetone during irradiation at 365nm and 400nm. The Ru-doped titania samples demonstrated enhanced photocatalytic activity under visible light. Ruthenium oxide causes the anatase to rutile transformation to occur at lower temperatures and decreasing of band-gap energy of Ru-doped samples.

Integrated blocking layers for hybrid organic solar cells

In hybrid organic solar cells a blocking layer between transparent electrode and nanocrystalline titania particles is essential to prevent short-circuiting and current loss through recombination at the electrode interface. Here we report the preparation of a thin, uniform and crack free hybrid blocking layer composed of conducting titania nanoparticles embedded in an insulating polymer derived ceramic. To do so we combine sol–gel chemistry with novel poly(dimethylsiloxane) containing amphiphilic block copolymer, poly(ethyleneglycol) methyl ether methacrylate–block–poly(dimethylsiloxane)–block–poly(ethyleneglycol) methyl ether methacrylate as the templating agent. Conductive probe scanning force microscopy proved that the existing percolating titania networks are separated by an insulating ceramic matrix. The structural uniformity of the percolating structures was investigated by microbeam grazing incidence small angle X-ray scattering making the integrated blocking layer suitable for hybrid organic solar device applications. Preliminary tests with the integrated blocking layer showed reasonable comparison to conventional TiO2 blocking layer containing devices mentioned in the literature.

Demonstration of a novel, flexible, photocatalytic oxygen-scavenging polymer film

The preparation of a novel, flexible, photocatalytic, oxygen-scavenging polymer film is described. The film incorporates nanocrystalline titania particles in an ethyl cellulose polymer film, with or without an added sacrificial electron donor of triethanolamine. When coated on the inside of a glass vessel its UV-driven light-scavenging action is demonstrated by platinum octaethyl porphyrin coated glass beads sealed inside, since their luminescence increases with increasing UV-irradiation time. When used as a flexible film, work with an oxygen electrode shows that the film is able to scavenge oxygen at an average rate of 0.017 cm 3 O 2 h −1 cm −2 over a 24 h period, which compares favourably to other, well-established oxygen-scavenger systems. The potential of using such as system for oxygen scavenging in packaging is discussed briefly.

A novel synthetic method for nanosized crystalline titania for use in the decomposition of dyes

Photocatalytically active nanocrystalline titania particles were prepared using a hydrothermal process, by controlling the particle size and crystallinity. The crystalline structures and morphologies of the particles were characterized by X-ray diffraction and transmission electron microscopy. The BET method was used to determine the surface area and verify the grain size. To estimate the photocatalytic activity of the synthesized particles, a dye photodegradation experiment was carried out and the activity of the particles was compared with that of conventional titania. The results show that synthesized nanocrystalline titania particles had a higher photocatalytic activity than that of conventional titania. These findings provide a basis for the preparation of more effective and usef ul materials for use in AOP applications.

Low-temperature synthesis and microstructural control of titania nano-particles

Nanocrystalline titania powders were synthesized at low temperature (⩽100°C) by a sol–gel method that achieved fine control of particle size and polymorph fraction. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–Vis spectroscopy were used to characterize the phase assemblages, crystal size and band gap of the powders. It was demonstrated that larger, well-ordered titania crystals can be obtained by increasing aging temperature and time. These processing parameters can be adjusted to select specific polymorphs from the gel precursors with particular size and shape. The quantum size effect was observed in the size-controlled nanocrystalline titania particles, leading to a blue shift in UV absorption with decreasing in particle size. The anatase to rutile transformation, which may proceed with brookite as a transition phase, is dependent on both particle size and surface structure of the nascent crystals.

Synthesis of Titania coated Alumina Particles by a Hybrid Sol-gel Method

ABSTRACTModifying their surface with a coating of another ceramic material can dramatically alter the properties of ceramic particles. In the present work we have demonstrated that the Al2O3 particles can be successfully coated by TiO2 using a novel sol-gel technique. The nature of these coatings was predicted on the basis of scanning electron microscopy imaging in conjunction with the micro-Raman scattering measurements. The surface morphology of these particles shows that either individual or group of sub-micron alumina particles are coated with the nano-crystalline titania particles. The thickness of the titania coating could be varied by changing the precursor sol concentration. Amorphous titania was converted to anatase phase at 400°C and upon further heating it started transforming to rutile phase, and both these phases coexisted in the coated particles that were heat treated up to 800°C. The mechanical strength of the titania coating was measured qualitatively by ultrasonicating the coated powders for longer duration to observe that titania coatings are strongly adhered with the alumina particles.

Nanocrystalline Titania Films and Particles by Chemical Vapor Synthesis

Thick crystalline titania films with grain sizes below 30 nm, as well as nanocrystalline titania particles with sizes below 10 nm, are prepared by a modified CVD method called chemical vapor synthesis (CVS). Pyrolysis of titanium tetraisopropoxide (TTIP) is performed in a hot-wall reactor, in a mixed helium/oxygen atmosphere, using liquid precursor delivery. Film thicknesses of up to 150 μm on silicon (100) substrate materials are achieved. The influence of process parameters (particularly reactor position) on the microstructure and growth rate is examined. Process temperatures, starting at film-forming (CVD) conditions and going up to exclusive particle formation (CVS) are investigated. Grain size, particle size, and crystallographic phases are determined by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Enhanced Adsorption of Molecules on Surfaces of Nanocrystalline Particles

Quantitative measurements of adsorption from solution show up to a 70-fold increase in the adsorption coefficient when a variety of organic acids are adsorbed onto 6 nm compared to 16 nm nanocrystalline titania particles. A Langmuir adsorption model modified to include the dependence of interfacial tension (interfacial free energy) on particle size predicts an increase in the adsorption constant (Kads) as the crystallite size decreases, in agreement with the experimental results. The increase in Kads arises predominantly from the increased molar surface free energy of the nanocrystalline particles. The rapid increase in adsorption as particle size decreases has important implications for understanding and modeling natural and experimental systems.

Synthesis and Characterization of Surface-Protected Nanocrystalline Titania Particles

Monodisperse nonaggregated nanoparticles of titania are obtained through hydrolysis at 60 °C of titanium butoxide in the presence of acetylacetone and para-toluenesulfonic acid. After the particles are dried, the resulting xerosols can be dispersed without aggregation in water−alcoholic or alcoholic solutions at concentrations higher than 1 M. The characterizations of the nanoparticles were carried out in solution by using quasi-elastic light scattering (QELS); FTIR; 13C, 17O, and 1H NMR and in solid state by X-ray diffraction, transmission electron microscopy (TEM), FTIR, thermogravimetry−dynamic thermal analysis (TG−DTA), 13C cross-polarization−magic angle spinning (CP−MAS) NMR. The mean size of the anatase oxide core can be adjusted in the 1−5 nm range by a careful tuning of the synthetic conditions. The protection of these particles toward aggregation is ensured through the complexation of the surface by acetylacetonato ligands and through an adsorbed hybrid organic−inorganic layer made with acetylacetone, para-toluenesulfonic acid, and water.