Low-Loss Dielectric Mirror with Ion-Beam-Sputtered TiO 2-SiO 2 Mixed Films

Ion-beam-sputtered TiO(2)-SiO(2) mixed films with 17% SiO(2) concentration were used as high-refractive-index layers in a multilayered-stack dielectric mirror. Experimental results indicated that total loss of the as-deposited mirror was 34% lower than that of the as-deposited conventional mirrors with pure TiO(2) films used as high-refractive-index layers. In addition, annealing reduced total loss of the mirrors. Although decreasing with an increasing annealing temperature, total loss of the conventional mirrors dramatically increased above ~200 degrees C annealing temperature, owing to increased scattering from an amorphous-to-crystalline phase transition in the TiO(2) films. In addition, total loss of the mirrors with the mixed films continuously decreased with an increasing annealing temperature up to 400 degrees C without the phase transition. Total loss was reduced 88% by means of decreasing absorption in the mixed films. Moreover, the annealed mirror with mixed films was better than both the as-deposited mirror and the conventional mirror with pure films in terms of laser-damage resistance.     

Development of photocatalytic TiO2 nanofibers by electrospinning and its application to degradation of dye pollutants

We have developed photocatalytic TiO2 nanofibers for the treatment of organic pollutants by using electrospinning method. We found that the optimized electrospinning conditions (electric field and flow rate) were 0.9 kV cm(-1) and 50 microL min(-1). After annealing at 550 degrees C for 30 min, we fabricated TiO2 nanofibers (average 236 nm thick) with anatase crystalline phase. To increase photocatalytic activity and effective surface area, we coated photocatalytic TiO2 particles on the TiO2 nanofibers by using sol-gel method. The degradation rate (k'=85.4x10(-4) min(-1)) of composite TiO2 was significantly higher than that (15.7x10(-4) min(-1)) of TiO2 nanofibers and that (14.3x10(-4) min(-1)) of TiO2 nanoparticles by the sol-gel method. Therefore, we suggested that the composite TiO2 of nanofibers and nanoparticles be suitable for the degradation of organic pollutants.     

Photocatalytic ozonation of dimethyl phthalate with TiO2 prepared by a hydrothermal method

TiO(2) was prepared by a hydrothermal method at a low temperature and used to degrade and mineralize dimethyl phthalate (DMP). TiO(2) was characterized by XRD, TEM, BET and UV-vis techniques. The characteristics of TiO(2) prepared by a hydrothermal method (h-t TiO(2)) included a good crystalline anatase phase, greater surface area, stronger absorption to UV light wavelength and lower agglomeration than TiO(2) prepared by a classic sol-gel method (s-g TiO(2)). The photocatalytic activity of h-t TiO(2) prepared under optimal hydrothermal condition (180°C for 10h) was 2.5 times higher than that of s-g TiO(2) in degrading DMP. The process of photocatalysis combined with UV irradiation and ozonation (TiO(2)/UV/O(3)) considerably improved the mineralization and degradation of DMP compared to photocatalysis combined with UV irradiation (TiO(2)/UV), ozonation combined with UV irradiation (UV/O(3)), and ozonation alone (O(3)). A kinetic study showed the mineralization in TiO(2)/UV/O(3) followed the Langmuir-Hinshelwood model.     

Synthesis of Fe(2)O(3)/TiO(2) nanorod-nanotube arrays by filling TiO(2) nanotubes with Fe

Synthesis of hematite (α-Fe(2)O(3)) nanostructures on a titania (TiO(2)) nanotubular template is carried out using a pulsed electrodeposition technique. The TiO(2) nanotubes are prepared by the sonoelectrochemical anodization method and are filled with iron (Fe) by pulsed electrodeposition. The Fe/TiO(2) composite is then annealed in an O(2) atmosphere to convert it to Fe(2)O(3)/TiO(2) nanorod-nanotube arrays. The length of the Fe(2)O(3) inside the TiO(2) nanotubes can be tuned from 50 to 550?nm by changing the deposition time. The composite material is characterized by scanning electron microscopy, transmission electron microscopy and diffuse reflectance ultraviolet-visible studies to confirm the formation of one-dimensional Fe(2)O(3)/TiO(2) nanorod-nanotube arrays. The present approach can be used for designing variable one-dimensional metal oxide heterostructures.     

Fabrication of a multi-scale nanostructure of TiO(2) for application in dye-sensitized solar cells

We propose a highly ordered multi-scale nanostructure of TiO(2) for applications as an anode in dye-sensitized solar cells (DSSCs). The structure is composed of a TiO(2) blocking layer, a TiO(2) inverse opal main body, regularly arranged transport channels between contacting spherical voids of the TiO(2) inverse opal, and TiO(2) nanoparticles coated on the spherical surfaces of the voids. The ordered and continuous backbone of the inverse opal serves as the fast electron transport pathways while the regularly arranged transport channels enable easy transport of dye and electrolyte within the structure. A multi-cycle procedure was developed to enable fabrication of thick inverse opals and easy adjustment of the inverse opal thickness. An example structure was constructed, involving a blocking layer of 90?nm thickness, an inverse opal of 100?nm voids, transport channels of 30-50?nm openings, and nanoparticles 10-15?nm in size. An open-circuit voltage decay investigation showed a significant improvement in electron lifetime for the proposed multi-scale TiO(2) nanostructure based DSSC than that of a TiO(2) nanoparticle film based DSSC, revealing the superior electron recombination characteristic offered by the proposed TiO(2) nanostructure. The conversion efficiency of the DSSC assembled from such an anode structure can reach 4% with a short-circuit current density (J(sc)) of 8.7?mA?cm(-2) and open-circuit potential (V(oc)) of 0.76?V under AM 1.5 (100?mW?cm(-2)) illumination.     

Titanium dioxide-mediated heterogeneous photocatalytic degradation of terbufos: parameter study and reaction pathways

The photocatalytic degradation of terbufos in aqueous suspensions was investigated by using titanium dioxide (TiO(2)) as a photocatalyst. About 99% of terbufos was degraded after UV irradiation for 90 min. Factors such as pH of the system, TiO(2) dosage, and presence of anions were found to influence the degradation rate. Photodegradation of terbufos by TiO(2)/UV exhibited pseudo-first-order reaction kinetics, and a reaction quantum yield of 0.289. The electrical energy consumption per order of magnitude for photocatalytic degradation of terbufos was calculated and showed that a moderated efficiency (E(EO)=71 kWh/(m(3)order)) was obtained in TiO(2)/UV process. To obtain a better understanding of the mechanistic details of this TiO(2)-assisted photodegradation of terbufos with UV irradiation, the intermediates of the processes were separated, identified, and characterized by the solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) technique. The probable photodegradation pathways were proposed and discussed.     

Improvement in performances of dye-sensitized solar cell with SiO2-coated TiO2 photoelectrode

The pure TiO2 and the nano-porous SiO2-coated TiO2 (STO) films were deposited on the FTO substrates by spray technique for the application of dye-sensitized solar cells (DSSCs). XRD pattern shows the pure TiO2 and STO films exhibits the same structure. We found that there is no much difference in dye absorption between the STO and the pure TiO2 films. The electrochemical impedance spectra reveal that insulating nature of the porous SiO2 increases surface resistance of the TiO2 film and supresses back transfer of the photogenerated electrons to the electrolyte. The field-emission scanning electron microscopy (FE-SEM) and energy dispersion X-ray spectroscopy (EDS) reveal that the surface morphology and the existence of SiO2 layer on the surface of the TiO2 films, respectively. The photoelectrochemical results show that the short-circuit photocurrent (J(SC)) increased from 16.73 mA cm(-2) to 18.31 mA cm(-2) and the open-circuit voltage (V(OC)) value changed from 0.71 V to 0.74 V for the STO films. The efficiency of cell has been greatly improved from 8.25 to 9.3%.     

An unconventional route to high-efficiency dye-sensitized solar cells via embedding graphitic thin films into TiO2 nanoparticle photoanode

Graphitic thin films embedded with highly dispersed titanium dioxide (TiO(2)) nanoparticles were incorporated for the first time into the conventional dye-sensitized solar cells (DSSCs), resulting in a remarkably improved cell efficiency due to its superior electron conductivity. Massively ordered arrays of TiO(2) dots embedded in carbon matrix were fabricated via UV-stabilization of polystyrene-block-poly(4-vinylpyridine) films containing TiO(2) precursors followed by direct carbonization. For dye-sensitized TiO(2) based solar cells containing carbon/TiO(2) thin layers at both sides of pristine TiO(2) layer, an increase of 62.3% [corrected] in overall power conversion efficiency was achieved compared with neat TiO(2)-based DSSCs. Such a remarkably improved cell efficiency was ascribed to the superior electron conductivity and extended electron lifetime elucidated by cyclic voltammetry and impedance spectroscopy.     

Lifetime and regeneration of immobilized titania for photocatalytic removal of aqueous hexavalent chromium

Immobilized titania (TiO2) batch reactors reduced hexavalent chromium (Cr(VI)) in the form of potassium dichromate (K2Cr2O7) to trivalent chromium (Cr(III)) in aqueous solution at pH 3 under 171 W/m2 light intensity. The light source was a 125-W ultraviolet (UV) lamp. The Cr(VI) reduction showed zero-order kinetics (k0), while the Cr(VI) adsorption fitted with first-order kinetics (k(1st)). Adsorption capacity increased with increasing initial Cr(VI) concentration, and the area of immobilized TiO2 limited the reduction efficiency. The lifetime of fresh immobilized TiO2 was approximately 14 h. In addition, the regeneration of TiO2 with 3M sodium hydroxide (NaOH) was necessary to improve adsorption reaction.     

Synthesis of a CNT-grafted TiO(2) nanocatalyst and its activity triggered by a DC voltage

Carbon nanotube (CNT)-grafted TiO(2) (CNT/TiO(2)) was synthesized as an electrically conductive catalyst that exhibits redox ability under electrical excitation besides ultraviolet (UV) irradiation. The CNT/TiO(2) material was synthesized by a two-step process. Ni nanoparticles were photodeposited onto TiO(2) first. The Ni nanoparticles then served as seeds for the growth of CNTs using the chemical vapor deposition (CVD) of C(2)H(2). The CNT/TiO(2) nanocomposite exhibits strong oxidation activity toward NO gas molecules via both photocatalysis under UV irradiation and electrocatalysis under a DC?voltage of 500?V in dark conditions.     

Titania-germanium nanocomposite for photo-thermo-electric application

The introduction of germanium (Ge) into titania (TiO(2)) creates an attractive semiconductor. The new semiconductor is named titania-germanium (TiO(2)-Ge). Ge dots are dispersed in the distorted TiO(2) matrix of TiO(2)-Ge. The quantum Bohr radius of Ge is 24.3?nm, and hence the properties of the Ge dot can be varied by tailoring its size if it is smaller than its Bohr radius due to the quantum confinement effect (QCE). Therefore, simply by changing the Ge concentration, the morphology of TiO(2)-Ge can be varied within a wide range. Consequently, the optical, electronic and thermal properties of TiO(2)-Ge can be tailored. TiO(2)-Ge becomes a promising material for the next generation of photovoltaics as well as thermoelectric devices. It could also be used for photo-thermo-electric applications.     

TiO2 nanorod arrays functionalized with In2S3 shell layer by a low-cost route for solar energy conversion

We report the fabrication and characterization of a TiO(2)-In(2)S(3) core-shell nanorod array structure for application of semiconductor-sensitized solar cells. Hydrothermally synthesized TiO(2) nanorod arrays on FTO glass substrates are functionalized with a uniform In(2)S(3) shell layer by using the successive ion layer adsorption and reaction (SILAR) method. This low-cost technique promotes a uniform deposition of In(2)S(3) nanoshells on the surface of TiO(2) nanorods, thus forming an intact interface between the In(2)S(3) shell and TiO(2) core. Results show that the thickness of In(2)S(3) shell layers as well as the visible light absorption threshold can be effectively controlled by varying the coating cycles during the SILAR process. The best reproducible performance of the sandwich solar cell using the TiO(2)-In(2)S(3) core-shell nanorod arrays as photoelectrodes was obtained after 30 SILAR cycles, exhibiting a short-circuit current (I(sc)) of 2.40 mA cm(-2), an open-circuit voltage (V(oc)) of 0.56 V, a fill factor (ff) of 0.40 and a conversion efficiency (η) of 0.54%, respectively. These results demonstrate a feasible and controllable route towards In(2)S(3) coating on a highly structured substrate and a proof of concept that such TiO(2)-In(2)S(3) core-shell architectures are novel and promising photoelectrodes in nanostructured solar cells.     

Photocatalytic antibacterial performance of Sn(4+)-doped TiO(2) thin films on glass substrate

Pure anatase, nanosized and Sn(4+) ion doped titanium dioxide (TiO(2)) particulates (TiO(2)-Sn(4+)) were synthesized by hydrothermal process. TiO(2)-Sn(4+) was used to coat glass surfaces to investigate the photocatalytic antibacterial effect of Sn(4+) doping to TiO(2) against gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus). Relationship between solid ratio of TiO(2)-Sn(4+) in coatings and antibacterial activity was reported. The particulates and the films were characterized using particle size analyzer, zeta potential analyzer, Brunauer-Emmett-Teller (BET), X-ray diffractometer (XRD), SEM, AAS and UV/VIS/NIR techniques. The results showed that TiO(2)-Sn(4+) is fully anatase crystalline form and easily dispersed in water. Increasing the solid ratio of TiO(2)-Sn(4+) from 10 to 50% in the coating solution increased antibacterial effect.     

Nitrogen-doped TiO2 nanotube array films with enhanced photocatalytic activity under various light sources

Highly ordered nitrogen-doped titanium dioxide (N-doped TiO(2)) nanotube array films with enhanced photocatalytic activity were fabricated by electrochemical anodization, followed by a wet immersion and annealing post-treatment. The morphology, structure and composition of the N-doped TiO(2) nanotube array films were investigated by FESEM, XPS, UV-vis and XRD. The effect of annealing temperature on the morphology, structures, photoelectrochemical property and photo-absorption of the N-doped TiO(2) nanotube array films was investigated. Liquid chromatography and mass spectrometry were applied to the analysis of the intermediates coming from the photocatalytic degradation of MO. The experimental results showed that there were four primary intermediates existing in the photocatalytic reaction. Compared with the pure TiO(2) nanotube array film, the N-doped TiO(2) nanotubes exhibited higher photocatalytic activity in degradating methyl orange into non-toxic inorganic products under both UV and simulated sunlight irradiation.     

The effect of erbium on the adsorption and photodegradation of orange I in aqueous Er3+-TiO2 suspension

Pure TiO(2) and erbium ion-doped TiO(2) (Er(3+)-TiO(2)) catalysts prepared by the sol-gel method were characterized by means of XRD and diffusive reflectance spectra (DRS). The XRD results showed that erbium ion doping could enhance the thermal stability of TiO(2) and inhibit the increase of the crystallite size, and the DRS results showed that the optical absorption edge slightly shifted to red direction owing to erbium ion doping and the Er(3+)-TiO(2) catalysts had three typical absorption peaks located at 490, 523 and 654 nm owing to the transition of 4f electron from (4)I(15/2) to (4)F(7/2), (2)H(11/2) and (4)F(9/2). With a purpose of azo dyes degradation, orange I was used as a model chemical. And the adsorption isotherm, degradation and mineralization of orange I were investigated in aqueous suspension of pure TiO(2) or Er(3+)-TiO(2) catalysts. The results showed that Er(3+)-TiO(2) catalysts had higher adsorption equilibrium constants and better adsorption capacity than pure TiO(2). The adsorption equilibrium constants (K(a)) of Er(3+)-TiO(2) catalysts were about twice of that of pure TiO(2). The maximum adsorption capacity (Q(max)) of 2.0% Er(3+)-TiO(2) catalyst was 13.08x10(-5)mol/g, which was much higher than that of pure TiO(2) with 9.03x10(-5)mol/g. Among Er(3+)-TiO(2) catalysts, 2.0% Er(3+)-TiO(2) catalyst achieved the highest Q(max) and K(a) values. The kinetics of the orange I degradation using different Er(3+)-TiO(2) catalysts were also studied. The results demonstrated that the degradation and mineralization of orange I under both UV radiation and visible light were more efficient with Er(3+)-TiO(2) catalyst than with pure TiO(2), and an optimal dosage of erbium ion at 1.5% achieved the highest degradation rate. The higher photoactivity under visible light might be attributable to the transitions of 4f electrons of Er(3+) and red shifts of the optical absorption edge of TiO(2) by erbium ion doping.     

Synthesis and electrical properties of (Bi(1/2)Na(1/2))TiO3 (BNT) ferroelectric thin films by liquid sprayed mist chemical vapor deposition technique

This study aims to synthesize lead-free ferroelectric material, (Bi(1/2)Na(1/2))TiO3 using the Liquid Sprayed Mist Chemical Vapor Deposition (LSMCVD) technique. The mist of precursor solution was vaporized and deposited on two different substrates of Si(100) and (111)Pt/TiO2/SiO2/Si(100) in an oxygen atmosphere. The deposition temperature and time were varied in the range of 400-600 degrees C and 30-90 min. (Bi(1/2)Na(1/2))TiO3 thin film had preferred orientations of (110). The thickness of the thin film deposited was 35-162 nm. The remnant polarization (2Pr) and the dielectric constant were 4.6-16.8 microC/cm2, 325-350, respectively.     

Holographically defined TiO2 electrodes for dye-sensitized solar cells

We describe a multibeam interference lithography for creating 3D polymeric porous structures. The coating of a TiO(2) shell and subsequent removal of the template produce holographically defined TiO(2) (h-TiO(2)) electrodes. We analyze the morphological features of the h-TiO(2) electrodes and consider their applicability to dye-sensitized solar cells (DSSCs). Specifically, the performance of the h-TiO(2) electrode was evaluated by comparison with a macroporous TiO(2) electrode produced from colloidal crystals. The h-TiO(2) structure possesses a larger specific area than the inverted colloidal crystals because of a bicontinuous air network with the TiO(2) shell. Consequently, the h-TiO(2) electrode can produce a 30% higher photogenerated electron current.     

The fabrication of CNTs/TiO(2) photoanodes for sensitive determination of organic compounds

Titanium dioxide (TiO(2)) and carbon nanotubes (CNTs) are the two most popular functional materials in recent years. In this study, CNTs/TiO(2) composite and TiO(2) photoanodes were fabricated by a dip-coating technique, followed by subsequent calcination. The resultant photoanodes were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-visible spectroscopy (UV-vis). The results suggest that the carbon nanotubes were successfully incorporated with the TiO(2) nanoparticulates without damage and that the resultant TiO(2) nanoparticles consisted of anatase and rutile. The CNTs/TiO(2) photoanodes were capable of oxidizing various types of organic compounds (e.g.?glucose, potassium hydrogen phthalate, and phenol) in aqueous solutions in a photoelectrochemical bulk cell. In comparison with the pure TiO(2) photoanode, the sensitivity of the photoanode for the detection of organic compounds has been improved by 64%, while the background current was reduced by 80% due to the introduction of the CNTs. These advantages can be ascribed to the improved adsorptivity to organic compounds, increased absorption of UV light and enhanced electron transport at the CNTs/TiO(2) photoanode due to the introduction of the CNTs.     

Enhancement of the bleaching and degradation of textile wastewaters by Gliding arc discharge plasma in the presence of TiO2 catalyst

The degradation of two polluted textile wastewaters from SOITEX (silk and textile) industry using the plasma-catalytic process, has been studied by non-thermal Gliding arc technique coupled to Degussa P25 titanium dioxide (TiO(2)) as photo-catalyst. Experiments were carried out to optimise the amount of phtoto-catalyst. The results showed that maximum degradation was attained for 3 g L(-1) TiO(2) concentration. For wastewater (1) degradation was 95% at the end of 60 min of treatment time. The same wastewater was completely decolourised after only 30min of plasma-catalytic treatment time. In parallel, the biodegradability was significantly enhanced through 20 min of exposure to the plasmagenous source for both wastewater samples. Turbidity of wastewater (1) and wastewater (2) decreased with rate constants of 0.015 and 0.017m in(-1), respectively. The TiO(2)-mediated Gliding Arc discharge (GAD(TiO(2)) showed potential application for the treatment of liquid wastes, resulting in the mineralization of the wastewater samples confirmed by chloride, sulphate and phosphate ions formation. In both cases of GAD treatments, with and without photo-catalyst, the plasmagenous process proves efficient in the field of wastewaters degradation.     

Synthesis of carbon nanotube-TiO(2) nanotubular material for reversible hydrogen storage

A material consisting of multi-walled carbon nanotubes (MWCNTs) and larger titania (TiO(2)) nanotube arrays has been produced and found to be efficient for reversible hydrogen (H(2)) storage. The TiO(2) nanotube arrays (diameter ～60?nm and length ～2-3?μm) are grown on a Ti substrate, and?MWCNTs a few μm in length and ～30-60?nm in diameter are grown inside these TiO(2) nanotubes using chemical vapor deposition with cobalt as a catalyst. The resulting material has been used in H(2) storage experiments based on a volumetric method using the pressure, composition, and temperature relationship of the storage media. This material can store up to 2.5?wt% of H(2) at 77?K under 25?bar with more than 90% reversibility.