Photoelectrochemical study of electrodeposited TiO<Subscript>2</Subscript> thin films onto F:SnO<Subscript>2</Subscript> substrates

TiO₂ thin films have been effectively fused onto F:SnO₂ (FTO) substrates via the electrodeposition method. The influence of deposition temperature on the synthesis of F:SnO₂ substrates and relative information of as-deposited and annealed TiO₂ thin films have been studied. Novel TiO₂ microspheres are detected on F:SnO₂ substrates at an optimized electrodeposition potential. Raman bands approve the creation of single-anatase-phase TiO₂. The optimized deposition surroundings show a decrease in the band gap of F:SnO₂ substrates and TiO₂ thin films. The determined photoelectrochemical properties of annealed TiO₂ thin films indicate a fill factor of 51% and power conversion efficiency of 0.15% for application in solar cells.     

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.     

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.     

Entrapment of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in TiO<Subscript>2</Subscript> nanotubes for visible light-driven photocatalysis

In this study, we prepared nanoparticles of the visible light-responsive photocatalyst, Bi₂O₃ entrapped in anatase TiO₂ nanotubes (Bi₂O₃-in-TNTs) via a vacuum-assisted precursor-filling process followed by annealing. Owing to the unique tubular electronic structure of TiO₂ nanotubes, the interior of the nanotube is in an electron-deficient state, which was confirmed by XPS spectra and H₂-TPR. Electrochemical impedance studies showed that the Bi₂O₃-in-TNTs demonstrated a more efficient separation of photogenerated carriers than when Bi₂O₃ nanoparticles were deposited on the outer wall of TiO₂ nanotubes (Bi₂O₃-out-TNTs). Due to the confinement effect of TiO₂ nanotubes, which inhibits photogenerated carriers’ recombination, the Bi₂O₃-in-TNTs exhibited a better photocatalytic performance for the photo-degradation of methyl orange under visible light compared to Bi₂O₃-out-TNTs.     

Synthesis,characterization of B-doped TiO<Subscript>2</Subscript> nanotubes with high photocatalytic activity

B-doped TiO₂ nanotubes (B/TiO₂ NTs) were prepared by the combination of sol–gel process with hydrothermal treatment. The prepared catalysts were characterized by XRD, TEM and XPS. The photocatalytic activity of B/TiO₂ NTs was evaluated through the photodegradation of aqueous methyl orange. The results demonstrated that the 1.5% B/TiO₂ NTs calcined at 300 °C possessed the best photocatalytic activity. Compared with pure TiO₂ nanotubes, the doping with B significantly enhanced the photocatalytic efficiency.     

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.     

Interfacial properties of self-organized TiO<Subscript>2</Subscript> nanotubes studied by impedance spectroscopy

The semiconductor properties of the interface TiO₂/electrolyte in high organized porous oxide structures were analyzed by means of impedance spectroscopy near the flat band potential. The impedance and capacitance studies performed on the as-anodized and thermally treated samples (anatase) indicate the presence of a duplex structure formed by (1) the oxide at the bottom of the pores and (2) the walls of pores with different donor densities and surface state concentrations.     

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.     

TiO<Subscript>2</Subscript>/WO<Subscript>3</Subscript> photoanodes with enhanced photocatalytic activity for air treatment in a polymer electrolyte cell

The application of electrochemically enhanced photocatalysis in air treatment using a Nafion-based photoelectrochemical cell and TiO₂/WO₃ photoanodes for organic vapor photooxidation under both UV and visible light irradiation is briefly presented. In that direction, the obtained results regarding the preparation and characterization of the TiO₂/WO₃ photoanodes with enhanced photocatalytic activity are reviewed. Particular emphasis is given in the comparison of the photocatalytic behavior of bilayer TiO₂/WO₃ coatings, electrosynthesized on stainless steel mesh and powder C + mixed (WO₃ + TiO₂) photoanodes. The advantages of using a high surface area C + mixed (WO₃ + TiO₂) powder catalysts as photoanodes against their plain TiO₂ + C and WO₃ + C analogues are discussed.     

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.     

Study of Fe-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalyst for an enhanced NH<Subscript>3</Subscript>-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NO_X. Novel Fe-doped V₂O₅/TiO₂ catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NO_X conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H₂-TPR, NH₃-TPD) techniques showed that the iron existed in the form of Fe³⁺ and Fe²⁺ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO₂ and H₂O.     

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.     

Preparation of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> and N co-doped TiO<Subscript>2</Subscript> photocatalysts and their enhanced photocatalytic activities under visible light

Niobium pentaoxide (Nb₂O₅) and nitrogen co-doped TiO₂ photocatalysts were prepared by mechanical alloying with Nb₂O₅, TiO₂ and urea as raw materials. The pure TiO₂ powders of Degussa P25 were chosen as precursor. Chemical and physical properties of the Nb₂O₅ and N co-doped TiO₂ photocatalysts were investigated, including XRD patterns, XPS spectra, DRS spectra, FT-IR spectra and N₂ adsorption-desorption isotherms. Experiments on photodegradation of methylene blue (MB) and sulfosalicylic acid (SSA) under visible light were carried out to evaluate the photoactivities of the prepared samples, and the chemical oxygen demand (COD) analysis was also conducted as a comparison.     

Electrochemical preparation of PMeT/TiO<Subscript>2</Subscript> nanocomposite electrochromic electrodes with enhanced long-term stability

In this work, 3-methylthiophene (MeT) was electrochemically incorporated with nano- and mesoporous TiO₂ films to form poly(3-methylthiophene) (PMeT)/TiO₂ nanocomposite electrochromic electrodes. TiO₂ films, which were previously coated on the ITO glass sheets through a well-established technique, were introduced to enhance the adhesion of the polymers to the substrates and thus increase the long-term stability of the devices. With this effort, the nanocomposite electrodes were found to retain up to 60% of their optical response after 3,500 deep and double potential steps and retain up to 50% of their electroactivity after 10⁴ same steps, exhibiting enhanced long-term stability. Switching time and the maximum optical contrast (ΔT%) of the nanocomposite electrodes were found to be 0.6 s and 45%, respectively. Moreover, our work showed that electrochemically incorporating conductive polymers (CPs) with TiO₂ mesoporous films was an effective method to form high-quality CP/TiO₂ nanocomposite electrodes, which can be used widely in battery cathodes, photovoltaic cells, photocatalytic reaction, and photoelectrochromic cells and were supposed to enhance their performances.     

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.     

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.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Supercapacitive performance of homogeneous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> nanotube arrays enhanced by carbon layer and oxygen vacancies

Self-supported and binder-free electrodes based on homogeneous Co₃O₄/TiO₂ nanotube arrays enhanced by carbon layer and oxygen vacancies (Co₃O₄/co-modified TiO₂ nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co₃O₄ nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co₃O₄ nanoparticles, a maximum specific capacitance of 662.7 F g^?1 can be achieved, which is much higher than that of Co₃O₄ decorated on pristine TNAs (Co₃O₄/TNAs; 166.2 F g^?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g^?1, revealing the excellent long-term electrochemical cycling stability of Co₃O₄/m-TNAs. Thus, this kind of heterostructured Co₃O₄/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.