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We have performed first-principles electronic structural calculations to investigate the nature and origin of ferromagnetism in Ti_1-xCo_xO₂ with cobalt concentrations x being 0.0625 and 0.125 in the interesting experimental range. In x being 0.125, when all possible arrangements of two Co atoms within a large supercell are considered, the clustering of Co atoms at nearst-neighbour Ti sites is energetically preferred. Also the interplay between clustering and exchange interactions in Co-doped anatase TiO₂ is discussed. It is predicted that the exchange coupling constant increases up to a value corresponding to lower Co concentrations by decreasing the distance between Co atoms.

We present in this paper the synthesis of rutile TiO₂ nanorods using an efficient microwave hydrothermal method. The product was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the results indicated the growth of high quality rutile nanorods along the c-axis of rutile TiO₂ and the radial aggregation of them into spherical secondary nanoparticles.

High-orderly nanotubes of titania were fabricated by anodic oxidation of pure titanium substrate in different electrolytes containing fluoride. Different morphological nanotubes of titania were obtained through controlling the different pH value of inorganic electrolytes, and it was found that nanotubes of titanium oxide would not formed when pH value was above 6. The morphological and structural properties of nanotublar products were characterized by SEM. The synthesized nanotubes of titania in organic electrolytic solutions containing fluoride was of 60 μm in length. The experiments demonstrated the length and orderliness of nanotubes of titanium oxide in organic solutions were much better than those in inorganic solutions.

Titanium dioxide coatings were deposited by utilizing atmospheric plasma-spraying system. The agglomerated P25/20 nano-powder and different spraying parameters (e.g., Argon flow rate and spray distance) were used to determine their influences on the microstructure, crystalline structure, photo-absorption, and photo-catalytic performance of the coatings. The microstructure and phases of as-sprayed TiO₂ coatings were characterized by scanning electron microscope SEM and X-ray diffraction, respectively. Surface characteristics were investigated by Fourier Transform Infrared. Photo-catalytic efficiency of the elaborated samples was also determined in an environmental test chamber set-up and evaluated from the conversion rate of ethanol. The photo-absorption was determined by UV–Vis spectrophotometer. The as-sprayed TiO2 coating was photo-catalytically reactive for the degradation of ethanol. The photo-catalytic activity was influenced by spray conditions. It is found that the photo-catalytic activity is significantly influenced by anatase content, surface area, and surface state. The results showed that the argon flow rate has an influence on the microstructure, anatase content, and photo-catalytic activity of the TiO₂ coatings.

Electronic structures and optical properties of C–N-codoped anatase TiO₂ were calculated by using GGA+U method based on the density functional theory. The calculated results showed that the N-doped, C-doped and C–N-codoped TiO₂ produced 2p states in band gap, and the band gaps of the three doped systems decreased compared with the pure TiO₂. According to the optical results, the band edges of the three doped systems shifted to the long wavelength region, and the visible optical absorption from 450 nm to 800 nm was observed. Moreover, the visible light response of C–N-codoped TiO₂ was better than the C or N single doped TiO₂, indicating that there was a synergistic effect for the C–N-codoped TiO₂, which offseted the deficiencies of C- or N-doped TiO₂.

This work studies the photocatalytic activity of zinc oxide (ZnO) nanopowder to recover silver (Ag) metal from low Ag⁺ concentrated solution under artificial ultraviolet (UV) light. Benchmark titanium dioxide (P25 TiO₂) was used for comparison purpose. Experimental results indicated that ZnO exhibited superior performance for Ag recovery compared to TiO₂. Under optimal catalyst loading, the achieved Ag removal efficiencies were 100% and 99.94% at 0.2 g/L ZnO (1 h) and 2 g/L TiO₂ (2 h), respectively. An induction period at low concentration of TiO₂ (0.1 g/L) was observed and a mechanism was proposed. The photodissolution of ZnO was assessed and proved to be negligible. Recovered pure Ag metal was characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM), showing a promising effective Ag recovery technology using ZnO photocatalyst.

Our present work is based on the density functional theory (DFT) studies of TiO₂ crystals doped with V impurities. Both rutile and anatase structures have been considered within the present research and different defect concentrations have been used as well. Our calculations reveal equilibrium geometry of the system showing atomic rearrangement around the point defect being mainly inward with respect to the impurity. Magnetism and electronic structure based on the density of states (DOS) patterns for both rutile and anatase crystals have been obtained and discussed in detail. It is shown that local magnetic moments arise mainly from the 3d states of the impurity atom with some admixture of 2p states from the vanadium-nearest O atoms.

A liquid fuel high velocity oxy-fuel (HVOF) thermal spray process has been used to deposit TiO₂ photocatalytic coatings utilizing a commercially available anatase/rutile nano-powder as the feedstock. The coatings were characterized in terms of the phases present, its crystallite size and coating morphology by means of X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy, respectively. The results indicate that the sprayed TiO₂ coatings were composed of both TiO₂ phases, namely anatase and rutile with different phase content and crystallite size. A high anatase content of 80% by volume was achieved at 0.00015 fuel to oxygen ratio with nanostructure coating by grain size smaller than feedstock powder.

It is found that fuel to oxygen ratio strongly influenced on temperature and velocity of particles in stream jet consequently on phase transformation of anatase to rutile and their crystallite size and by optimizing the ratio which can promote structural transformation and grain coarsening in coating.

TiO₂ thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol–gel technique. The influence of annealing temperature on the structural, morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO₂ films has also been examined by optical polaromicrograph (OPM). TiO₂ films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.

First-principles calculations based on the density functional theory (DFT) within the generalized gradient approximation (GGA) have been used to study Sc-doped TiO₂, rutile and anatase, crystals. Local defect microstructure, electronic and electrical properties have been obtained and discussed in the present work. Large radius hole polaron state found here points out to the possibility of p-type electrical conductivity in Sc-doped titania.

The transparent semiconducting copper iodide (CuI) films were deposited by pulsed laser deposition (PLD) and their structural and optoelectrical properties in the power output of TiO₂|Dye|CuI cells are reported. These CuI films exhibited optical transmittance of over 80% in the wavelength range from 400 to 900 nm and a minimum resistivity of about 2 KΩ-cm. An efficient charge generation is observed through the illumination of the TiO₂ layer of the fabricated p-CuI|Dye|n-TiO₂ cells. The cells performances have been given in the current–voltage (I–V) working curve under illumination when exposed to AM 1.5 illumination condition (100 mW/cm², 25°C). The maximum short circuit photo current density (J_sc) of about 12.2 mA/cm² and open circuit photo voltage (V_oc) of about 480 mV were obtained for the TiO₂|Dye|CuI cells with good reproducibility. The fill factor (FF) and power conversion efficiency (η) were about 47.8% and 2.8%, respectively.

The properties and optical band gap excitation of nanoporous titanium dioxide (TiO₂) and transparent semiconducting copper iodide (CuI) films prepared by a XeCl excimer laser were investigated. The CuI films exhibited optical transmittance over 80% in the wavelength range from 400 to 900 nm with minimum resistivity of about 2 KΩcm. The optical absorption of these films showed a remarkable blue shift compared to that of polycrystalline of CuI, which can be explained from the formation of ultra fine of CuI grains. The properties of pulsed laser deposited CuI and TiO₂ in power output of p-CuI|dye|n-TiO₂ cells were studied. The photoelectron generation and mechanism in fabricated p-CuI|dye|n-TiO₂ cells were also studied. An efficient charge generation was observed through the illumination of the TiO₂ layer of the fabricated p-CuI|dye|n-TiO₂ cells. The band gap excitation of TiO₂ was observed only under illumination through TiO₂ layer. The adsorbed dye molecules to the TiO₂ surface act as a relay, especially under illumination through TiO₂ layer in the wave range region of 300–400 nm.

In the present work, a combined route involving first doping of iron or neodymium ions via sol–gel method followed by acidification of the metal-doped TiO₂ particles for the improvement of the photocatalytic capability of TiO₂ was reported. The obtained metal-doped/acidified TiO₂ photocatalysts were thoroughly characterized by X-ray diffraction, Fourier transform infrared analysis, and photoluminescence emission spectra. At the same time, their photocatalytic activities were evaluated in simulant photodegradation of methylene blue (MB). The results based on these characterizations showed that not only a rutile layer formed on the surface of original TiO₂ particles after surface cladding, but also the doped Fe or Nd ion had a favorable effect on suppression of the electron–hole recombination in the titania under ultraviolet light irradiation. Furthermore, the photocatalytic activity of the material obtained by Fe doping and acidification was substantially improved in comparison to the untreated TiO₂. However, the sample prepared from Nd-doping and acidification of TiO₂ showed decreased capability relative to the untreated TiO₂ in degradation of MB under similar conditions. Finally, the reason why the photocatalytic activities of the obtained catalysts are sensitive to the metal-doping was discussed in details.

A systematic study of unrelaxed and relaxed surface characters on the TiO₂ (101) surface has been carried out by first-principles calculations using plane-wave pseudopotential method. We find that O_2c atoms have an inward relaxation of 0.012 Å and Ti_5c atoms have an outward relaxation of 0.155 Å by taking a 24-layer slab with 5 Å vacuum width to consider the atomic relaxations, in good agreement with other theoretical values. The slab thickness has significant effect on the quality of band structure and density of states, and 24-layer slab is sufficient to present the electronic properties of TiO₂ (101) surface. Atomic relaxations result in a large transfer of surface charges from outermost layer to inner layer, and the surface bonds have a rehybridization, which makes the ionization reduce and the covalence increase; we believe that it causes the surface bond shorten. A fine analysis of band structure and density of states of the TiO₂ (101) surface shows that the surface relaxation induces the transformation from semi-metallic to semiconducting characteristic.

In this work, nanocrystalline TiO₂/ITO electrodes were prepared by sol–gel method starting from tetrabutyl orthotitanate (Ti(OBuⁿ)₄) reacted with hydrogen peroxide in the ice-water bath. The sol–gel derived TiO₂ films were characterized by XRD, SEM, BET, and UV/Vis absorption spectroscopic techniques. The preparation conditions, including the number of coats and calcination temperature, were also investigated. Furthermore, PEC cells were constructed for testing the activities of prepared TiO₂/ITO photoelectrodes. The photo-currents for hydrogen production via the PEC reaction were measured under UV irradiation (λ_max = 253.7 nm). The experimental results showed that the sol–gel derived TiO₂ films calcined at 300°C–600°C were anatase structure and they showed a maximum UV/Vis absorption at about 380 nm. Moreover, from the result of PEC reactions, it was found that the TiO₂/ITO photoelectrode (calcined at 600°C, with the thickness of TiO₂ layer of about ~0.2 μm) demonstrated a large saturation current (0.326 mA/cm²) with a quite high photoelectrochemical conversion efficiency of 2.39%.

Titanium dioxide doped Fe³⁺ and La³⁺ nano-composite films were prepared using the sol–gel method. The photo-catalytic properties were evaluated by photo-degradation of methyl orange in solution. Scanning electron microscope, X-ray diffraction, and energy dispersive spectrometer were used to characterize the TiO₂ film doped Fe³⁺ and La³⁺, indicating that the film has nano-structure, and mainly anatase crystal. It is proved that co-doped Fe³⁺ and La³⁺ can improve significantly the photo-catalytic properties of TiO₂ film due to the synergistic effect of the two ions.

We present one of the central and basic factors related to the TiO₂ photoanodes of optimal absorption site. Binder is of particular importance for surfaces and interfaces that involve organic dye and TiO₂ layer. We introduced monodispersed liquid copolymer binders; poly(ethylene glycol)-ethyl ether methacrylate (PEG-EEM) instead of solid PEG to increase TiO₂ electrode's surface area. We attempt to investigate the morphology of the photoanodes and photovoltaic effects using field emission scanning electron microscopy (FE-SEM), BET and photovoltaic properties under illumination with AM 1.5 simulated sunlight. We achieve 167% enhanced power conversion efficiency when the optimal content of liquid PEG-EEM binder was 4 wt.% than that of PEG binder. We show that the performance of Dye-sensitized solar cell (DSSC) can be strongly improved using liquid type binder.

The photocatalytic activity of metal-deposited TiO₂ was investigated with different surface coverage of nanosized noble metals (Ag and Au). The sonochemical deposition of nanosized metals on the TiO₂ matrix was prepared by adjusting the loading volumes of silver and gold precursors in an ultrasound-driven cell. Non-annealed Ag-TiO₂ exhibited the maximal activity in the optimal loading ranges of silver precursor (e.g. 0.2–0.3 ml of 1.0 wt.% AgNO₃), displaying the enhanced efficiency of electron–hole separation. The addition of nanosized Au on Ag-TiO₂ proved to be undesirable to improve the photocatalytic activity of Au/Ag-TiO₂, except for the excessive loading of metal precursors (0.3 ml of 1.0 wt.% AgNO₃ + 0.2 ml of 1.0 wt.% HAuCl₄). XRD and XPS analysis confirmed the co-existence of Ag and Au species, and the reduction of PL (photoluminescence) intensity indicated the efficient separation of electron–hole pairs for optimal doping of nanosized metals on the TiO₂ matrix.

RO-Al₂O₃-B₂O₃-SiO₂(R = Ca, Mg) glasses containing different concentrations of TiO₂ (ranging from 0 to 9 mol.%) were prepared by conventional melting method. When TiO₂ was present in lower concentrations (≤ 6 mol.%), Fourier-transform infrared spectroscopy (FTIR) indicated that titanium ions took part in network forming positions. However, for further increase in the concentration of TiO₂ (> 6 mol.%), FTIR data indicated the formation of TiO₄ tetrahedrons and TiO₆ octahedrons. The glass transition temperatures (T_g) were determined using a differential scanning calorimetry (DSC). The T_g variation with the concentration of TiO₂ showed an increasing trend up to 6 mol.% of TiO₂ and beyond this concentration, T_g was found to decrease. The dielectric constant ε_r and loss tan δ continued to decrease with the concentration of TiO₂ up to 6 mol.% and beyond that ε_r and tan δ were found to increase. This behavior was mainly explained in terms of the rigidity of glass network.

Two TiO₂/SnO₂:F/substrate hetero-structures (HS) with different geometry were deposited by spray pyrolysis. The thickness for the TiO₂ and SnO₂:F films was 3.8 μm and 2.3 μm, and the band gap energy 3.3 eV and 3.6 eV, respectively. Both films have a transmittance greater than 70% in most of the visible spectrum. The electrical resistivity of the SnO₂:F film was ρ = (1.7)×10^-4Ω ⋅ cm. The surface morphology of the TiO₂ film shows hemispheric agglomerates formed by nano-metric needle/platy shaped particles that give them a porous texture much like a "ball of wool," the length of the needles is from 100 nm and its thickness close to 20 nm. The geometry of HS has an important influence on its efficiency as photocatalyst under low-powered UV radiation. One of the geometry for this HS, in which the TiO₂/SnO₂:F interface is exposed, showed greater efficiency than the TiO₂ and SnO₂:F films separately, or than the common "sandwich" type HS geometry. Specifically, a decrease by 62% of the initial concentration of a watery solution of methylene blue (mb) of 20 ppm in approximately 5 h of UV radiation is observed for the exposed interface HS compared with less than 30% reduction observed for the common sandwich type HS.