TiO<Subscript>2</Subscript> nanofibers embedding single crystalline TiO<Subscript>2</Subscript> nanowires

Epitaxially grown titanium dioxide (TiO₂) nanofibers embedding single crystalline TiO₂ nanowires (NWs) were successfully fabricated by electropinning poly(vinyl pyrrolidone)/ethanol solutions mixed with hydrothermally synthesized TiO₂ NWs and titanium isopropoxide precursors and subsequently calcinating the electrospun nanofibers. Utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the morphologies of TiO₂ NWs and nanofibers were investigated. High resolution TEM (HR-TEM) and selected area electron diffraction (SAED) allowed us to indentify the fact that, during the calcination process under the optimized condition, titanium isopropoxide precursors were epitaxially crystallized on the surface of single crystalline TiO₂ NWs. Based on the X-ray diffraction (XRD) experiments, it was also realized that the crystalline structure of hydrothermally synthesized TiO₂ NWs and epitaxially crystallized TiO₂ nanofibers is anatase and that TiO₂ composite nanofibers embedding TiO₂ NWs exhibited a higher crystallinity than the pristine TiO₂ nanofibers. Additionally, ultraviolet visible (UV–Vis) spectra of nanofibers indicated that optical properties of TiO₂ nanofibers can be tuned by introducing the single crystalline TiO₂ NWs.     

TiO<Subscript>2</Subscript>-based nanopowders obtained from different Ti-alkoxides

Pure TiO₂ and S-doped TiO₂ sol–gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO₂ porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.     

Synthesis and characterization of Co(OH)<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> nanotube composites as supercapacitor materials

A novel composite of Co(OH)₂ and TiO₂ nanotubes was synthesized by a chemical precipitation method. Co(OH)₂/TiO₂ nanotube composites and its microstructure were characterized by transmission electron microscopy (TEM), X-ray diffraction pattern (XRD). The electrochemical capacitance performance of this composite was investigated by cyclic voltammetry and charge–discharge tests with a three-electrode system in 6 M KOH solution. We synthesized different weight ratios of Co(OH)₂/TiO₂ nanotubes, a maximum specific capacitance of 229 F/g was obtained for the composite. Based on these tests, we propose that TiO₂ nanotubes provide the three-dimensional nanotube network structure for the composite and make the Co(OH)₂ dispersed. For these reasons, the TiO₂ nanotubes used as a framework for Co(OH)₂ improve the utilization of Co(OH)₂ greatly.     

Diagnostics of Plasma Behavior and TiO<Subscript>2</Subscript> Properties Based on DBD/TiO<Subscript>2</Subscript> Hybrid System

Plasma catalysis is gaining increasing interest in environmental and energy applications, such as the destruction of gas pollutants and hydrocarbon conversion. In order to further improve the application of plasma catalysis, it is crucial to understand the fundamental mechanisms, especially the mutual interaction between plasma and catalyst. In this paper, a parallel-plate dielectric barrier discharge (DBD) reactor is developed to investigate the plasma behavior and TiO₂ properties in the plasma/catalytic hybrid system. The introduction of TiO₂ thin film coated on the dielectric improves the discharge intensity, which significantly contributes to the enhancement of reactive species and charges. The energy efficiency of generating ozone in DBD/TiO₂ system has been approximately raised by 38% compared to pure DBD when the applied voltage reaches 13 kV. It is fortunately found that the discharge does not change the crystal structure of the TiO₂, but the band gap increases from 3.13 to 3.39 eV, which has been proved to enhance the oxidizability of TiO₂ in the degradation of methyl orange experiment under UV light. The FTIR and XPS spectra also demonstrate that N element is doped into the structure of TiO₂. These results successfully illustrate the plasma behavior and catalyst properties in plasma/catalysis hybrid system and provide reference for the optimization of the plasma catalysis process.     

Obtaining composites Cu/TiO<Subscript>2</Subscript> by combining mechanical activation and self-propagating high temperature synthesis

The possibility of obtaining nanostructured composites Cu/TiO₂ by combining mechanical activation and self-propagating high temperature synthesis was investigated by X-ray diffraction and electron microscopy.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Photooxidation of Ethylbenzene with TiO<Subscript>2</Subscript> and Metal Coated TiO<Subscript>2</Subscript> and its Kinetics

Summary. Photooxidation of ethylbenzene with oxygen to give ethylbenzene hydroperoxide has been achieved in a stirred photochemical reactor that was cooled by a water system by irradiation with a 400W high-pressure mercury lamp and using TiO₂ powder and metal coated TiO₂. The effects of the amount of copper or silver coated on TiO₂ and of the temperature on the rate of oxidation have been investigated. It is suggested that thermal cleavage of the O–O bond and photochemically generated singlet oxygen should be considered as the initiating step in a radical chain mechanism. An optimum loading of 6% Ag or 4–5% Cu was observed for photooxidation of ethylbenzene.     

Oxidation of ammonia using modified TiO<Subscript>2</Subscript> catalyst and UV-VIS irradiation

The impact of UV and VIS irradiation and specific nitrogen modification on a 5%Cu/5%TiO₂/SiO₂ catalyst in the course of oxidation of ammonia was investigated. It was demonstrated that both UV and VIS irradiation increased the conversion of the reactant in the reaction studied. Due to a good distribution of titanium dioxide and copper on the surface of the support, higher ammonia conversion was achieved. Physico-chemical characterisation of the catalysts studied using methods such as BET, SEM-EDS, TPD (NH₃), and TPD (CO₂) was carried out.     

Thermal behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> mesoporous gels

Summary Titania-based photocatalytic materials were prepared by sol-gel method using Fe³⁺ and polyethyleneglycol (PEG₆₀₀) as additives. Thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA) with MS detection were used to elucidate processes that take place during heating of Fe³⁺ containing titania gels. The microstructure development of the Fe₂O₃/TiO₂ gel samples with and without PEG₆₀₀ admixtures was characterized by emanation thermal analysis (ETA) under in situ heating in air. A mathematical model was used for the evaluation of ETA results. Surface area and porosity measurements of the samples dried at 120&deg;C and the samples preheated for 1 h to 300 and 500&deg;C were compared. From the XRD measurements it was confirmed that the crystallization of anatase took place after thermal heating up to 600&deg;C.     

Optimized photocatalytic degradation of pefloxacin by TiO<Subscript>2</Subscript>/UV process

The photocatalytic degradation of pefloxacin was studied using modified TiO₂ as a photocatalyst. The effect of various parameters such as the amount of the photocatalyst, the initial concentration of pefloxacin, initial pH value on the process were investigated, and the optimal conditions were determined. The optimal amount of the photocatalyst is 0.3 g/L. The photodegradation rate of pefloxacin decreases with the increase of initial concentration. Alkaline medium is favorable for the photocatalytic degradation process. The primary photo-degradation products were analyzed by HPLC-ESI-MS/MS and thus the process mechanism was discussed.     

Compatibility of TiO<Subscript>2</Subscript> with a CaO-CaCl<Subscript>2</Subscript> melt

Interaction of TiO₂ with a CaO-CaCl₂ melt was studied to determine whether electrolytic production of titanium from oxide raw materials is possible.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Photoelectrochemical processes at interfaces of nanostructured TiO<Subscript>2</Subscript>/carbon black composites studied by scanning photoelectrochemical microscopy

The local photoelectrochemical response of TiO₂/carbon black photocatalysts was studied by means of scanning photoelectrochemical microscopy performed under UV illumination and external polarization. Catalysts obtained by sol-gel techniques showed a uniform response that improved under anodic polarization, in contrast to the non-uniform response of mixtures that show enhancement under cathodic polarization. To explain the differences in photoelectrochemical activity, we performed electrochemical and capacitive studies under dark condition, finding a larger positive shift in the rest potential of sol-gel composites plus evidence of Fermi-level pinning. We propose the last is related to the presence of carbon states with a strong acceptor character formed during the sol-gel synthesis. An energy band diagram of the composites were sketched based on the data obtained.     

Influence of ThO<Subscript>2</Subscript> on the photocatalytic activity of TiO<Subscript>2</Subscript>

Microcomposites consisting of TiO₂ (or Ce-doped TiO₂) and ThO₂ (0.5–2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of ThO₂. X-ray diffraction study reveals the effects of ThO₂ (compared to the ThO₂-free TiO₂, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO₂ obtained at 550°C and containing 1% ThO₂. The composite exhibits activity in dark, also. The presence of Ce⁴⁺ ions is not an obligatory requirement for the realization of the ThO₂ effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO₂.      

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

Photocatalytic reduction of CO<Subscript>2</Subscript> over TiO<Subscript>2</Subscript> based catalysts

At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing literature related to photocatalytic CO₂ reduction over TiO₂ based catalysts and the effects of important parameters on the process performance including light wavelength and intensity, type of reductant, metal-modified surface, temperature and pressure. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Interactions in the Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>-Ti<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Interactions in the Al₂TiO₅-Ti₂O₃ system were studied and the regions of existence of Al_2?2xTi _2x ³⁺ Ti⁴⁺O₅ solid solutions with a pseudobrookite structure were determined.     

Charge separation by tetrahexahedron-SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> heterojunction as an efficient photocatalyst

Charge separation plays a key role in the conversion of solar energy into chemical energy for use in the redox reaction and as well as in the photocatalytic activity. In this study, SrTiO₃ particles with different morphologies including irregular, tetrahexahedron, and cube were synthesized by an in situ solvothermal method. The photocatalytic activity of the synthesized nanoparticles was investigated in the photocatalytic decomposition of methylene blue under UV light irradiation. Tetrahexahedron SrTiO₃ particles exhibited high decomposition activity (70 %), which is about two times higher than those of the irregular and cubic SrTiO₃ particles. The high decomposition activity of tetrahexahedron SrTiO₃ particles could be attributed to the improvement of charge separation achieved on different crystal facets. To reach a good charge separation, tetrahexahedron SrTiO₃/TiO₂ coupled nanoparticles were fabricated by impregnation method. Results showed that coupling tetrahexahedron SrTiO₃ with TiO₂ could produce efficient charge separation between tetrahexahedron SrTiO₃ and TiO₂ due to their matched band edges. In order to achieve better charge separation, the tetrahexahedron SrTiO₃/90 %TiO₂ sample was calcined at different temperatures in the 450–750 °C range. Tetrahexahedron SrTiO₃/90 %TiO₂ coupled nanoparticles calcined at 650 °C show high photocatalytic activity compared with other samples. The prepared samples were characterized by using various techniques such as X-ray diffraction, scanning electron microscopy, photoluminescence emission spectra, and UV–Vis diffuse reflectance spectroscopy.