Crystalline Titanium Research Articles

Catalytic properties of titania nanotube prepared by simple refluxing method

Cost effective, well crystallized zigzag titania nanotubes have been prepared by utilizing a high crystalline titanium dioxide nanopowder and refluxing it into a 10M KOH solution at 160°C for 18h under atmospheric pressure. These nanotubes possess a diameter of ca. 23nm and average length of 600nm and have a rough surface all around with BET surface area of 58m2/g. The prepared nanotube shows high crystal intensity of the anatase peak (101) almost five times compared to the hydrothermally synthesized nanotubes (12nm in diameter, surface area of 87m2/g). Using a model reaction, the photocatalytic performances in aqueous solution were carried out under UV-irradiation and it was observed that nanotubes prepared by the refluxing method shows superior photocatalytic decoloration efficiency (79%) of methyl orange compared to the hydrothermally driven nanotubes and nanocrystals (45%). The prepared catalysts were analyzed by FE-SEM, XRD, UV–vis DRS spectra and BET surface area techniques.

Preparation of Nano Crystalline Titanium Dioxide by Microwave Hydrothermal Method

Titanium dioxide (TiO2) nanoparticles due to their exclusive physical, chemical and electrical properties are widely used as a heterogeneous catalyst and catalytic support in the chemical reactions, a semiconductor for photocatalysis reactions and additives in the membrane processes. The TiO2 nanoparticles are also utilized in solar cells, gas sensors, pigments and etc. Efficiency of these nanoparticles in various applications is dramatically dependent on their size. Various techniques such as combustion flame synthesis and conventional hydrothermal methods have been used to prepare TiO2 nanoparticles, but few synthesis techniques can reproducibly produce particles below 10 nm. In this study, the TiO2 nanoparticles in rutile phase were synthesized by microwave assisted hydrothermal method by controlling the crystallization time and temperature. Titanium tetrachloride (TiCl4) was used as a titanium precursor. The synthesized nanoparticles were characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. The XRD pattern showed that the rutile phase of the TiO2 nanoparticles was successfully synthesized by the proposed method with the average crystal size of 4nm. Finally, the prepared Titanium dioxide (TiO2) nanoparticles were as a hydrophobic additive in the polymeric ultrafiltration membranes in order to reduce the membrane fouling.

Toward Tunable Adsorption Properties, Structure, and Crystallinity of Titania Obtained by Block Copolymer and Scaffold-Assisted Templating

Nanostructured titania and composite titania materials were synthesized for the first time by a one-pot strategy in an aqueous solution containing Pluronic P123 block copolymer and suitable precursors. The strategy can be considered as more facile, environmentally friendly, and less expensive as compared to the existing ones that require use of organic solvents. In the case of composites, silica and alumina particles were used as a structure protecting scaffold and composite components. This synthesis strategy allowed tuning of adsorption and structural properties of the resulting materials; namely, the specific surface area was varied from 84 to 250 m(2) g(-1), total pore volume from 0.11 to 0.46 cm(3) g(-1), and the pore width from 5.6 to 11.2 nm. All samples studied but one showed exclusively anatase phase, and the composites obtained with silica scaffold showed tunable degree of crystallinity. The proposed approach to tailoring the surface and structure properties of titania is especially important for the development of high performance materials for photocatalysis, lithium-based batteries, and dye-sensitized solar cells.

A new approach to apply crystalline titania hydrosols onto a polyester cloth

A new procedure was developed to attach titania hydrosols to polyester fabrics, providing processed fibers with self-cleaning properties.

Preparation of TiO2/Al-MCM-41 mesoporous materials from coal-series kaolin and photodegradation of methyl orange

TiO2/Al-MCM-41 mesoporous materials were prepared via sol-gel method by loading titania onto Al-MCM-41 mesoporous molecular sieve by hydrothermal treatment from coal-series kaolin as raw material. The TiO2/Al-MCM-41 mesoporous materials were characterized by XRD, FT-IR, HRTEM, N2 adsorption-desorption and the photocatalytic degradation of methyl orange solution under visible light irradiation. The results showed that the TiO2/Al-MCM-41 mesoporous materials possessed a high surface area of 369.9–751.3 m2/g and a homogeneous pore diameters of 2.3–2.8 nm. The titania crystalline phase was anatase, and the particles size of TiO2 increased with TiO2 content. The Al-MCM-41 mesoporous materials exhibited excellent photodegradation activity under visible-light irradiation for methyl orange.

Stable Protein Device Platform Based on Pyridine Dicarboxylic Acid-Bound Cubic-Nanostructured Mesoporous Titania Films

Here we shortly report a protein device platform that is extremely stable in a buffer condition similar to human bodies. The protein device platform was fabricated by covalently attaching cytochrome c (cyt c) protein molecules to organic coupler molecules (pyridine dicarboxylic acid, PDA) that were already covalently bound to an electron-transporting substrate. A cubic nanostructured mesoporous titania film was chosen as an electron-transporting substrate because of its large-sized cubic holes (∼7 nm) and highly crystalline cubic titania walls (∼0.4 nm lattice). Binding of PDA molecules to the mesoporous titania surface was achieved by esterification reaction between carboxylic acid groups (PDA) and hydroxyl groups (titania) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediator, whereas the immobilization of cyt c to the PDA coupler was carried out by the EDC-mediated amidation reaction between carboxylic acid groups (PDA) and amine groups (cyt c). Results showed that the 2,4-position isomer among several PDAs exhibited the highest oxidation and reduction peak currents. The cyt c-immobilized PDA-bound titania substrates showed stable and durable electrochemical performances upon continuous current-voltage cycling for 240 times (the final current change was less than 3%) and could detect superoxide that is a core indicator for various diseases including cancers.

Electrochemical properties of all-solid-state lithium batteries with amorphous titanium sulfide electrodes prepared by mechanical milling

Amorphous titanium trisulfide (TiS3) active materials were prepared by ball milling of an equimolar mixture of crystalline titanium disulfide (TiS2) and sulfur. A high-resolution transmission electron microscope image revealed no periodic lattice fringes on the amorphous TiS3. The all-solid-state lithium secondary batteries using a sulfide solid electrolyte and the amorphous TiS3 electrode showed high capacity of greater than 300 mAh g−1 for 10 cycles. The amorphous TiS3 had a higher capacity than the mixture of crystalline TiS2 and S, which was used as the starting material of amorphous TiS3. The X-ray diffraction patterns and the Raman spectra of the amorphous TiS3 electrode after the first and tenth charge–discharge measurements were similar to those before the measurement. The amorphous structure of TiS3 did not change greatly during the first few cycles. The all-solid-state cells with the amorphous TiS3 electrode showed higher initial coulombic efficiency because the amorphous TiS3 active material retained its structure during the initial electrochemical test.

Precise Size Control over Ultrafine Rutile Titania Nanocrystallites in Hierarchical Nanotubular Silica/Titania Hybrids with Efficient Photocatalytic Activity

Hierarchical-structured nanotubular silica/titania hybrids incorporated with particle-size-controllable ultrafine rutile titania nanocrystallites were realized by deposition of ultrathin titania sandwiched silica gel films onto each nanofiber of natural cellulose substances (e.g., common commercial filter paper) and subsequent flame burning in air. The rapid flame burning transforms the initially amorphous titania into rutile phase titania, and the silica gel films suppress the crystallite growth of rutile titania, thereby achieving nano-precise size regulation of ultrafine rutile titania nanocrystallites densely embedded in the silica films of the nanotubes. The average diameters of these nanocrystallites are adjustable in a range of approximately 3.3-16.0 nm by a crystallite size increment rate of about 2.4 nm per titania deposition cycle. The silica films transfer the electrons activated by crystalline titania and generate catalytic reactive species at the outer surface. The size-tuned ultrafine rutile titania nanocrystallites distributed in the unique hierarchical networks significantly improve the photocatalytic performance of the rutile phase titania, thereby enabling a highly efficient photocatalytic degradation of the methylene blue dye under ultraviolet light irradiation, which is even superior to the pure anatase-titania-based materials. The facile stepwise size control of the rutile titania crystallites described here opens an effective pathway for the design and preparation of fine-nanostructured rutile phase titania materials to explore potential applications.

Highly crystalline and silica-embedded titania rhombic shaped nanoparticles with mesoporous structure and its application in photocatalytic degradation of organic compound

Highly crystalline and silica-embedded titania rhombic shaped nanoparticles with mesoporous structure are successfully obtained via a facile solvothermal method using Ti(OC4H9)4 as precursor, acetic acid as solvent and Si(OC2H5)4 (TEOS) as stabilizer. Various characterization techniques, including Transmission electron microscopy(TEM), X-ray diffraction(XRD), UV–vis diffuse reflection spectroscopy, Raman spectroscopy, N2 adsorption–desorption isotherms and X-ray photoelectron spectra (XPS), have been applied to investigate the physical–chemical properties and the formation process of silica-embedded titania. The photocatalytic performances of all the silica-embedded titania samples are also studied by the degradation of methylene blue (MB) dye under UV irradiation. The results indicate that the mesoporous silica-embedded titania nanocrystals exhibit rhombic or truncated rhombic shapes and have extremely high special surface area of 260.7 m2 g−1. All the highly crystalline and mesoporous silica-embedded titania samples show better photocatalytic activity than that of the pure titania. The maximum photocatalytic activity is obtained on the silica-embedded titania nanoparticles with 0.6 ml TEOS, which is 6.7 times that achieved on the pure titania sample and 1.5 times that performed on the Degussa P25 powders. This is attributed to high crystallinity, increased surface area by embedding amorphous silica and proper assembly of TiO2 nanoparticles.

Photophysical properties of hybrid complexes of quantum dots and reaction centers of purple photosynthetic bacteria Rhodobacter sphaeroides adsorbed on crystalline mesoporous TiO2 films

Complexes of CdSe/ZnS and CdTe quantum dots (QDs) with proteins of reaction centers (RCs) of purple bacteria Rhodobacter sphaeroides have been obtained. An efficient energy transfer from QDs (a donor of electron excitation energy) to RCs (acceptor) is observed for them both in the solution and in the films of crystalline mesoporous titanium oxide. The design of such hybrid structures allows us to increase the absorptive ability of the RC many times and, respectively, increase the efficiency of the light energy conversion into the electrical potential. Such hybrid structures can be used for the development of high-performance solar cells.

Porous Titania with Heavily Self-Doped Ti3+ for Specific Sensing of CO at Room Temperature

Semiconductor-based sensors have played an important role in efficient detection of combustible, flammable, and toxic gases, but they usually need to operate at elevated temperatures (200 °C or higher). Although reducing the operation temperature down to room temperature is of practical significance, it is still a huge challenge to fabricate room temperature sensors with a low cost. Here we show a novel "self-doping" strategy to overcome simultaneously both difficulties of "high resistance" and "low reaction rate", which have always been encountered for room-temperature operation of semiconductor-based sensors. In particular, a porous crystalline titania with heavily self-doped Ti(3+) species has been prepared by using a porous amorphous TiO2 and urea as the starting materials. The resulting Ti(3+) self-doped TiO2 material serves as an efficient room-temperature gas-sensing material for specific CO detection with fast response/recovery. The self-dopant (Ti(3+)) in the titania material has proved to decrease the resistance of TiO2 significantly on the one hand and to increase the chemisorbed oxygen species substantially, thus enhancing the surface reaction activity on the other. Such a self-doping concept is anticipated to give a fresh impetus to rational design of room-temperature sensing devices with low costs.

The importance of silica morphology in silica–titania composites with dye sensitized solar functionality

Silica–titania composite dye sensitized solar cells were prepared by synthesizing crystalline titania around silica particles to test dye sensitized solar cell performance under conditions where current would flow primarily in surface regions. Three different commercial silica particles were used in this study — each with a different mean particle size and pore structure to give information about the coverage and connectedness of the chemically-derived surface titania layer. The silica–titania composite materials were characterized using scanning electron microscopy, X-ray diffraction and other techniques. The effect of surface area and porosity of the host silica particles on the morphology of the silica–titania layers and the performance in dye sensitized solar cells is discussed.

Formation of Titanium Nitride on the GaN(0001) Surface: A Density Functional Theory Study

We have carried out density functional theory (DFT) calculations to study the role of titanium impurity atoms during gallium nitride (GaN) growth. Adsorption and incorporation of Ti atoms on GaN(0001) surface is examined and it is shown that Ti atoms preferentially adsorb at the T4 sites at low and high coverage. In addition, calculating the formation energy of multiple-impurity configurations, we constructed a surface phase diagram showing the energetically most stable structures as a function of Ti and Ga chemical potentials. Based on these, we find that incorporation of Ti atoms in the Ga-substitutional site is energetically more favorable compared with the Ti surface adsorption on the top layers. This effect leads to the formation of an interfacial crystalline titanium nitride (TiN) compound on the GaN(0001) surface, which can offer a good interfacial combination between Ti and GaN substrates.

Low-Temperature Crystalline Titanium Dioxide by Atomic Layer Deposition for Dye-Sensitized Solar Cells

Low-temperature processing of dye-sensitized solar cells (DSCs) is crucial to enable commercialization with low-cost, plastic substrates. Prior studies have focused on mechanical compression of premade particles on plastic or glass substrates; however, this did not yield sufficient interconnections for good carrier transport. Furthermore, such compression can lead to more heterogeneous porosity. To circumvent these problems, we have developed a low-temperature processing route for photoanodes where crystalline TiO2 is deposited onto well-defined, mesoporous templates. The TiO2 is grown by atomic layer deposition (ALD), and the crystalline films are achieved at a growth temperature of 200 °C. The ALD TiO2 thickness was systematically studied in terms of charge transport and performance to lead to optimized photovoltaic performance. We found that a 15 nm TiO2 overlayer on an 8 μm thick SiO2 film leads to a high power conversion efficiency of 7.1% with the state-of-the-art zinc porphyrin sensitizer and cobalt bipyridine redox mediator.

Fabrication of nanostructured hollow TiO2 nanofibers with enhanced photocatalytic activity by coaxial electrospinning

Two types of hollow crystalline titanium dioxide (TiO2) nanofibers were successfully fabricated through a facile coaxial electrospinning technique, with titanium sol and titanium precursor respectively as the materials for the shell. The two types of hollow TiO2 nanofibers possessed a similar tubular feature on the nanometer scale, but different morphology on surface nanostructures and size on shell thickness. Hollow nanofibers prepared by using titanium sol demonstrated that a small amount of water in core could prevent efficiently the diffusion of the core and shell solutions. For the titanium precursor without spinnability, it could be coated on the poly(vinyl pyrrolidone) core nanofibers as shell templates during the coaxial electrospinning process and properly developed into nanostructured TiO2 wall of the hollow nanofibers. Both of hollow TiO2 nanofibers exhibited higher photocatalytic activity for degradation methylene blue in comparison with the solid TiO2 nanofibers prepared by normal electrospinning due to their unique hollow structure.

Application of Electrochemical Impedance Spectroscopy in Characterization of Mass- and Charge Transfer Processes in Dye-Sensitized Solar Cells

Electrochemical impedance spectroscopy (EIS) technique was performed to study electronic and ionic processes in dye-sensitized solar cells (DSCs), and consequently, to evaluate the dye degradation mechanism. DSCs based on nano crystalline titanium dioxide (TiO2) sensitized by N719 dye and a liquid electrolyte system, were assembled. The fabrication of cell components such as anode and cathode, and cell assembling were studied and improved. By analyzing the impedance data, the electron transport rate, electron lifetime in the mesoscopic TiO2 film and parameters of ionic diffusion process in the electrolyte, have been derived. The fabricated DSCs were treated with 4-tert-butylpyridine and nicotinic acid by injection technique. The effect of 4-tert-butylperidine and nicotinic acid on the DSC performance has been interpreted by analysis of impedance data. The degradation of DSC performance under prolonged thermal ageing and light soaking was found to be correlated with the decrease of both diffusion rate of electron in the TiO2 film and diffusion rate of ions in the electrolyte. The degradation rate of DSC performance parameters under light soaking was higher than under thermal ageing. 4-TBP-treated DSCs show high performance just after fabrication but rapidly degraded during light ageing and thermal stress. Nicotinic acid treatment slowed the thermal degradation of DSCs in the dark.

Plasma electrolytic oxidation of a Ti–15Mo alloy in silicate solutions

The influence of the parameters used in the plasma electrolytic oxidation of Ti–15Mo alloy on the microstructure and chemical composition of the obtained oxide layer was determined, and the bioactivity of the modified alloy was measured. The obtained oxide layers are composed of crystalline titanium oxides and incorporated silicon species.

Microwave-Assisted Synthesis of Porous Carbon–Titania and Highly Crystalline Titania Nanostructures

Porous carbon-titania and highly crystalline titania nanostructured materials were obtained through a microwave-assisted one-pot synthesis. Resorcinol and formaldehyde were used as carbon precursors, triblock copolymer Pluronic F127 as a stabilizing agent, and titanium isopropoxide as a titania precursor. This microwave-assisted one-pot synthesis involved formation of carbon spheres according to the recently modified Stöber method followed by hydrolysis and condensation of titania precursor. This method afforded carbon-titania composite materials containing anatase phase with specific surface areas as high as 390 m(2) g(-1). The pure nanostructured titania, obtained after removal of carbon through calcination of the composite material in air, was shown to be the anatase phase with considerably higher degree of crystallinity and the specific surface area as high as 130 m(2) g(-1). The resulting titania, because of its high surface area, well-developed porosity, and high crystallinity, is of great interest for catalysis, water treatment, lithium batteries, and other energy-related applications.

Single Crystalline Oxygen-free Titanium Nitride by XPS

X-ray photoelectron spectroscopy (XPS) spectra are presented, which are obtained from an oxygen-free single crystalline (sc-) titanium nitride (TiN) sample. The investigated film has been grown on a magnesium oxide (MgO) single crystal with the (001) orientation. Unbalanced Reactive Magnetron Sputter deposition was used to deposit the TiN film in an argon/nitrogen atmosphere at 5 × 10−3 mbar and a temperature of 800 °C. The sample has been transferred in situ from the deposition chamber to the XPS device in order to prevent surface oxidation of the sample. Atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering (RBS) and angle resolved (AR-) XPS have been used to characterize the sample in detail. This work is dedicated to the XPS characterization of a representative oxygen-free sc-TiN sample. Detailed scans are presented and discussed for the Ti 2p, O 1s, N 1s, Ti 2s, valence band and Ti LMM regions. The spectra contain shake-ups, surface and bulk plasmons, that can be separated and quantified by the presented evaluation procedure.

Performance improvement of phase-change memory cell using AlSb3Te and atomic layer deposition TiO2 buffer layer

A phase change memory (PCM) cell with atomic layer deposition titanium dioxide bottom heating layer is investigated. The crystalline titanium dioxide heating layer promotes the temperature rise in the AlSb3Te layer which causes the reduction in the reset voltage compared to a conventional phase change memory cell. The improvement in thermal efficiency of the PCM cell mainly originates from the low thermal conductivity of the crystalline titanium dioxide material. Among the various thicknesses of the TiO2 buffer layer, 4 nm was the most appropriate thickness that maximized the improvement with negligible sacrifice of the other device performances, such as the reset/set resistance ratio, voltage window, and endurance.