Photofragmentation of mass-selected titanium oxide cluster cations

In this paper we present the photofragmentation spectra of mass-selected positive titanium oxide cluster ions Ti _x O _y ⁺. The clusters are generated by the combination of laser ablation of a titanium target and the supersonic nozzle expansion of oxygen and are detected by time-of-flight mass spectrometry. Small clusters are mass-selected and photodissociated at a wavelength of 308 nm. The recorded photofragmentation spectra indicate that for all parent clusters the main fragment is TiO⁺ and, in some cases, Ti₂O₃ ⁺ is also observed. This is consistent with the assumption that small Ti _x O _y ⁺ clusters are built from a TiO⁺ core with TiO₂ building blocks.     

Chromium-doped titanium dioxide thin-film photoanodes in visible-light-induced water cleavage

A new method for the synthesis of nanocrystalline anatase Cr-doped TiO₂ colloids from nanotubes utilizing the hydrothermal ion-intercalation (HII) method has been devised using hydrothermal treatment in an acidic environment. To investigate the photoelectrochemical reaction that occurs when water is split into H₂ and O₂ under visible light, a Cr-doped TiO₂ thin film served as a model photoelectrode. The photoelectrochemical activity of Cr-doped TiO₂ was higher than that of the undoped sample. The photoelectrochemical activity of photoelectrodes increased drastically with increased chromium doping. A red shift in the band gap was induced by Cr doping of TiO₂. It was revealed that the Cr-doped TiO₂ photoelectrode was able to utilize a wide range of light in the visible region of the spectrum. At high Cr concentrations, the lower photoelectrochemical activity is attributed to the effect of Cr³⁺ ion recombination and excess Cr³⁺ ions forming secondary phase Cr₂O₃.     

Synthesis and photocatalytic activity of polyaniline–TiO<Subscript>2</Subscript> composites with bionic nanopapilla structure

Polyaniline (PANI)–TiO₂ nanocomposites possessing both nano and microscale structures were prepared through a facile hydrothermal route in the presence of PANI. The nanopapilla particles were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectra, X-ray diffraction, FTIR spectra, UV–Vis spectroscopy, and N₂ adsorption analysis, etc. The results show that the composites possess both nano and microscale structures. The TiO₂ nanorods are dispersed on PANI with one end fixed to the surface. The photocatalytic properties of the powders were verified by the photodegradation of gaseous acetone under UV (λ = 254 nm) and visible-light irradiation (λ > 400 nm). In fact, the photocatalytic effects exhibited by the composite particles were superior to that of pure TiO₂ and P25 samples. This excellent behavior is attributed to the structural features of PANI–TiO₂ microspheres and the synergistic effect between PANI and TiO₂ which facilitates a larger amount of surface active sites. This in turn causes a faster charge separation and slower charge recombination which results in a more efficient decomposition of gaseous pollutants.     

Preparation of TiO2-carbon surface composites with high photoactivity by supercritical pretreatment and sol-gel processing

TiO₂-carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol-gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol-gel method, the small nanosize TiO₂ particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti³⁺ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO₂ nanoparticles, baffles the agglomeration of TiO₂ nanoparticles and easily produces Ti³⁺ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO₂-carbon (TC) composites and pure TiO₂. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO₂ in comparison with TC and pure TiO₂, because their surface area are greater than that of TC and pure TiO₂.     

Dispersion of Nano TiO2 in Ethylene Glycol and Poly(ethylene terephthalate)

Nano TiO₂ was dispersed in ethylene glycol (EG) by the replacement of dispersion medium from water sol. EG/TiO₂ suspension was well stabilized by the electrostatic repulsive force when pH value of suspension was less than 4.3. In situ polymerization starting from bis(2-hydroxyethyl) terephthalate (BHET) and EG/TiO₂ suspension was carried out to prepare a series of poly(ethylene terephthalate) (PET)/TiO₂ nanocomposites. Under highly acidic conditions, 97% particles dispersed in PET matrix had the size less than 100 nm. With the increase of pH value, aggregation occurred and larger size particles appeared. A tensile test showed that Young's modulus of PET was increased by the addition of nano TiO₂     

Formation and photodecomposition of cationic titanium oxide clusters

In this paper we report on the titanium oxide cluster cations Ti _x O _y ⁺, generated by laser ablation of a titanium target in the region of the nozzle expansion of oxygen. The mass distribution of the clusters produced is recorded with a time-of-flight mass spectrometer. Three different series, namely TiO(TiO₂) _n ⁺ , TiO(TiO₂) _n O₂⁺, and (TiO₂) _n ⁺, appear in the spectra. Two different ablation wavelengths (infrared at 1064 nm and ultraviolet at 308 nm) are used to generate the titanium oxide clusters. At the shorter wavelength the maximum size of the clusters formed decreases. The interaction of the UV photons with the Ti _x O _y ⁺ clusters is further investigated in a separate two-laser arrangement with an IR laser for ablation and after some mm downstream with an UV system for the cluster beam irradiation. These studies indicate that the intensity of the T _x O _y ⁺ clusters with x≥4, y≥7 is strongly influenced by the absorption of UV photons. This is attributed mainly to dissociation into smaller ones.     

Study on preparation and properties of molybdenum alloys reinforced by nano-sized ZrO<Subscript>2</Subscript> particles

The nano-sized ZrO₂-reinforced Mo alloy was prepared by a hydrothermal method and a subsequent powder metallurgy process. During the hydrothermal process, the nano-sized ZrO₂ particles were added into the Mo powder via the hydrothermal synthesis. The grain size of Mo powder decreases obviously with the addition of ZrO₂ particles, and the fine-grain sintered structure is obtained correspondingly due to hereditation. In addition to a few of nano-sized ZrO₂ particles in grain boundaries or sub-boundaries, most are dispersed in grains. The tensile strength and yield strength have been increased by 32.33 and 53.76 %.     

Hydrothermal synthesis of flower-like TiO2 nanocrystals/graphene oxide nanocomposites

A facile hydrothermal method has been developed to be capable of decorating graphene oxide (GO) with flower-like TiO₂ nanocrystals without using any bridging species. The flower-like TiO₂ nanocrystals were uniformly self-assembled on the surface of GO nanosheets. The photocatalytic activity experiment indicated that the prepared TiO₂/GO nanocomposites exhibited a higher photocatalytic activity for the photocatalytic degradation of rhodamine B (RB) aqueous solution under the UV illumination, this methodology made the synthesis of TiO₂/GO nanocomposites possible and may be further extended to prepare more complicated nanocomposites based on GO for technological applications.     

Electromigration with enhanced green emission in the titanium dioxide nanotube/graphene composite

One of the most studied photoluminescence emission peaks of anatase titanium dioxide (TiO₂) is green, located at about 520 nm, which is assigned to the radiative recombination between a mobile electron in the conduction band and oxygen vacancy defect as a trapped hole in the bandgap. Composite materials of TiO₂ with graphene are normally shown by the gradual quenching of photoluminescence intensity as a result of carrier lifetime extension, which is important to enhance photocatalytic activity. Herein we report an observation of the intensity enhancement of the green PL emission in a composite TiO₂ nanotube (TNT) and graphene produced through facile hydrothermal synthesis. The heterojunction formation of graphene and TNT makes the excited photoelectrons easy to diffuse from TNT to graphene. Hence, the recombination rate of mobile electrons in graphene and trapped holes located on the nanotube surface is enhanced due to the high mobility of electrons in graphene.     

Influence of anions stabilizing the sols in synthesis of powders of highly dispersed titanium dioxide and three-dimensional nanocomposites based on SiO2/TiO2

This paper reports on the results of investigations into the influence of anions (Cl^?, SO ₄ ^2? ,NO ₃ ^? ), which stabilize the sol-gel synthesis of highly dispersed titanium dioxide, on the crystallization and phase transition of TiO₂ upon dehydration. The effect of the size factor on the phase composition of TiO₂ in SiO₂/TiO₂ nanocomposites has been investigated using a three-dimensional opal matrix as a set of nanoreactors for the sol-gel synthesis of TiO₂ · nH₂O. It has been shown that there is a possibility of extending the region of the existence of a thermodynamically metastable modification of TiO₂ (anatase) to the temperature of 1100°C due to the changes in the conditions of the sol-gel synthesis of TiO₂ · nH₂O.     

Hydrothermal Synthesis of Metal Oxide Nanoparticles at Supercritical Conditions

Hydrothermal synthesis of CeO₂ and AlO(OH) were conducted using a flow type apparatus over the range of temperature from 523 to 673 K at 30 MPa. Nanosize crystals were formed at supercritical conditions. The mechanism of nanoparticle formation at supercritical conditions was discussed based on the metal oxide solubility and kinetics of the hydrothermal synthesis reaction. The reaction rate of Ce(NO₃)₃ and Al(NO₃)₃ was evaluated using a flow type reactor. The Arrhenius plot of the first order rate constant fell on a straight line in the subcritical region, while it deviated from the straight line to the higher values above the critical point. The solubility of Ce(OH)₃ and AlO(OH) was estimated by using a modified HKF model in a wide range of pH and temperature. In acidic conditions, where hydrothermal synthesis reaction is concerned, solubility gradually decreased with increasing temperature and then drastically dropped above the critical point. The trend of the solubility and the kinetics around the critical point could be explained by taking account of the dielectric constant effect on the reactions. There are two reasons why nanoparticle are formed at supercritical conditions. Larger particles are produced at subcritical conditions due to Ostwald ripening; that could not be observed in supercritical water because of the extremely low solubility. Second reason is the faster nucleation rate in supercritical water because of the lower solubility and the extremely fast reaction rate.     

Application limitedness of the model of spheroidal scatterers for describing scattering properties of titanium dioxide

The results of measurements of the scattering matrix of an aqueous suspension of titanium dioxide at a wavelength of 0.63 μm in the scattering angle range of 10°–150° are presented. The results of the measurements are compared with calculation data for scatterers having the shape of prolate ellipsoids. It is shown that, even when the size parameter equals 4, the experimental and calculated values of the matrix elements f ₂₂ and f ₁₂ significantly differ, which is caused by a complex form of TiO₂ particles, and that the determination of the parameters of the distribution of TiO₂ suspension particles in the interpretation of the measurement data in the context of the considered model is possible with an error of 27% in the effective size and 16% in the distribution width.     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Formation of microcapsules containing titanium dioxide nanoparticles by pulse expansion of a supercritical solution into a background gas

The formation of microcapsules with a core of TiO₂ nanoparticles in a shell of polyethylene glycol by pulse expansion (pulse duration of 400 µs) of a supersonic jet of TiO₂-suspension in a supercritical solution of polyethylene glycol (PEG 8000) in CO₂ into a background gas (He) is studied. It is shown that the size of capsules and the content of TiO₂ in them depend on the pressure of the background gas in the inlet chamber in the range from 0.125 to 3 atm. The upper (1.5 atm) and the lower (0.25 atm) limits of the pressure range, in which microcapsules with a relatively high content of titanium dioxide are formed, are determined.     

Activation energy of hydrogen desorption from high-performance titanium oxide carrier-selective contacts with silicon oxide interlayers

The impact of hydrogen desorption on the electrical properties of TiO_x on crystalline silicon (c-Si) with SiO_y interlayers is studied for the development of high-performance TiO_x carrier-selective contacts. Compared with the TiO_x/c-Si heterocontacts, a lower surface recombination velocity of 9.6 cm/s and lower contact resistivity of 7.1 mΩ cm² are obtained by using SiO_y interlayers formed by mixture (often called SC2). The hydrogen desorption peaks arising from silicon dihydride (α1) and silicon monohydride (α2) on the c-Si surface of the as-deposited samples are observed. The α1 peak pressure of as-deposited heterocontacts with SiO_x interlayers is lower than that of heterocontacts without a SiO_y interlayer. Furthermore, the hydrogen desorption energies are found to be 1.76 and 2.13 eV for the TiO_x/c-Si and TiO_x/SC2-SiO_y/c-Si heterocontacts, respectively. Therefore, the excellent passivation of the TiO_x/SC2-SiO_y/c-Si heterocontacts is ascribed to the relatively high rupture energy of bonding between Si and H atoms.     

Tailoring titanium dioxide by silver particles for photocatalysis

Titanium dioxide-silver (TiO₂–Ag) composites are synthesized by using the hydrothermal method with different weight ratios for photocatalyst applications. With the introduction of Ag, the composites exhibited absorbance in visible region, and the bandgap also decreased by 0.45 eV. The TiO₂–Ag composite with 5:7 ratio shows the best photocatalytic degradation of methylene blue, the highest photocurrent response, and the lowest electrochemical impedance, thus exhibiting the best photocatalytic performance. The introduction of Ag into TiO₂ retards the recombination time of the photo-generated electrons and holes as well as increases the charge transfer rate at interfaces of the composites.     

Studies on pore morphology of titanium and its oxide by small angle neutron scattering

Titanium metal bodies have been prepared from the sintered powder compacts of TiO₂ by a novel molten salt electrochemical approach, known as FFC Cambridge process. The phase and compositional characterizations of both Ti and TiO₂ have been carried out by X-ray diffraction. The pore morphologies of sintered TiO₂ pellet and the metallic Ti pellet, obtained after electrochemical reduction have been studied by SANS over a scattering wave vector q range of 0.003–3.5 nm⁻¹ using a double crystal diffractometer and a pin-hole collimated SANS instrument. In the case of reduced metal pellet, average pore size was found to be larger than that of the oxide pellet as the voids left behind after the oxygen atoms left the oxide matrix, could not coalesce.      

Thickness dependent optical properties of titanium oxide thin films

TiO₂ thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60°, 70°, and 75°, respectively. The whole spectra have been fitted by Forouhi–Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO₂ thin film have positive correlation to the film thickness. The refractive indices of TiO₂ thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO₂ thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO₂ thin film growth can be used to explain these phenomena.     

Fe fine particles encapsulated by titanium oxides with high magnetization for biomedical application

Iron (Fe) fine particles encapsulated by titanium oxide (TiO₂) were synthesized through a solid-phase reaction. The structure of Fe cores and TiO₂ shells consisted of α-Fe and rutile TiO₂, respectively. The average particle size was 0.8 μm, in which a Fe particle with a diameter of ∼750 nm was encapsulated by a TiO₂ shell with a thickness of ∼100 nm. The Fe particles had a high saturation magnetization of 127 Am²/kg and low coercivity of 1.6 kA/m. They also exhibited excellent corrosion resistance, similar to Fe₃O₄ in a soaking test.     

Synthesis and characterization of nitrogen-doped TiO2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity

Nitrogen-doped TiO₂ coatings on reduced graphene oxide were prepared via a sonochemical synthesis and hydrothermal process. The nanocomposites showed improved photocatalytic activity due to their large specific surface areas (185–447 m²/g), the presence of TiO₂ in the anatase phase, and a quenched photoluminescence peak. In particular, GN3-TiO₂ (nitrogen-doped TiO₂ coatings on rGO with 3 ml of titanium (IV) isopropoxide) exhibited the best photocatalytic efficiency and degradation rate among the materials prepared. With nitrogen-doped on the reduced graphene oxide surface, the photocatalytic activity is enhanced approximately 17.8 times compared to that of the pristine TiO₂. The dramatic enhancement of activity is attributed to the nitrogen contents and rGO effectively promoting charge-separation efficiency and providing abundant catalytically active sites to enhance the reactivity. The composites also showed improved pollutant adsorption capacity, electron–hole pair lifetime, light absorption capability, and absorbance of visible light.