Electrochemical properties of rutile TiO2 nanorods as anode material for lithium-ion batteries

In this paper, we synthesized rutile TiO₂ nanorods by hydrolysis of TiCl₄ ethanolic solution in water at 50?°C. Scanning electron microscopy and transmission electron microscopy images show that the as-prepared sample was consisted of nanoflowers of about 500?nm in sizes, and each petal of nanoflowers was assembled by several nanorods. We tested the electrochemical properties of the rutile TiO₂ nanorods as an anode material for lithium-ion batteries. The rutile TiO₂ nanorods exhibited a large initial discharge capacity of 223?mA?h?g^?1, and the stabilized capacity was as high as 170?mA?h?g^?1 after 100 cycles. These improved electrochemical performances may be attributed to the shorter diffusion length for both the electron and Li⁺, and the large electrode?Celectrolyte contact area offered by the nanorods with a large specific surface area, which facilitated the lithium ions insertion and extraction.     

Growth of branched rutile TiO2 nanorod arrays on F-doped tin oxide substrate

Branched rutile TiO₂ nanorod arrays were directly synthesized on the F-doped tin oxide (FTO) substrate through a two-step hydrothermal treatment by a seeding method with TiO₂-nanorods as seeds. The samples were characterized respectively by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FESEM). Results showed that TiO₂ nanorods with nanobranches (TiO₂-NB) grew vertically on the FTO substrate. XRD and HRTEM results confirmed that the TiO₂-NB arrays were single-crystalline rutile. The optical properties of the samples were studied with a UV-vis spectrometer. The photocatalytic activity of the TiO₂-NB film is better than that of P25 particulate film. Direct electrical pathway and improved light-harvesting efficiency were crucial for the superior photocatalytic activity of the TiO₂-NB arrays.     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

TiO2 Wedgy Nanotubes Array Flims for Photovoltaic Enhancement

In this study, TiO₂ wedgy nanotubes with rectangular cross-sections were fabricated on transparent conductive substrates by using TiO₂ nanorods as the precursor via the anisotropic etching route. TiO2 nanotubes with V-shaped hollow structure and the special crystal plane exposed on the tube wall possess nature of high surface area for more dye molecules absorption, and the strong light scattering effects and dual-channel for effective electron transport of the TiO₂ V-shaped nanotubes based dye-sensitized solar cell exhibit a remarkable photovoltaic enhancement compared with the TiO₂ nanorods. The photoanode based on our V-shaped TiO₂ nanotubes with a length of 1.5 μm show a 123% increase of the dye loading and a 182% improvement in the overall conversion efficiency when compared with 4 μm rutile TiO₂ nanorods photoanode.     

Evolution of zirconia coating layer on rutile TiO2 surface and the pigmentary property

Zirconia-coated rutile TiO₂ composites were prepared by the chemical liquid deposition method starting from rutile TiO₂ and ZrOCl₂. The amorphous zirconia coating layers were anchored at the TiO₂ surface via Zr-O-Ti bond. The formation of continuous and dense zirconia coating layers was dependent on the pH value of the reaction solution and the mole ratio of ZrOCl₂ to TiO₂. As compared to the naked rutile TiO₂, the water dispersibility, whiteness, brightness, and relative light scattering index of the zirconia-coated rutile TiO₂ composites were increased.     

Hybrid ultraviolet photodetectors with high photosensitivity based on TiO2 nanorods array and polyfluorene

The highly oriented array composed of rutile TiO₂ nanorods is synthesized by the hydrothermal method on the SnO:F (FTO) substrate. The hybrid UV detector is fabricated via spin-coating a thin layer of poly (9,9-dihexylfluorene) (PFH) on the array. The device characteristics, including I-V curves under UV illumination and time response are studied. Obvious UV photoconductive effect is observed in the device and the response is fast to the switching on and off UV light illumination, which can be repeated for at least 50 times. The quick enhancement of the current origins from the large contact area between TiO₂ nanorods and PFH and the convenient charge transport in TiO₂ nanorods.     

Electrochemical properties of TiO2 nanoparticle/nanorod composite photoanode for dye-sensitized solar cells

A unique composite of TiO₂ nanoparticles (NPs) and nanorods (NRs) has been used to fabricate a photoelectrode for developing dye-sensitized solar cells (DSSCs) with higher sensitivity. The TiO₂ nanorods were synthesized using a mechanical process, in which electrospun TiO₂ nanofibers was grinded in a controlled way to obtain uniform size distribution. The characteristics of electron transport, recombination lifetime and charge collection were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). Photoelectrodes prepared with the composites of NRs and NPs showed significant improvements in electron transportation compared to only NP photoelectrodes, which would enhance the photovoltaic performance of DSSCs. IMPS and IMVS measurements show that fast electron transport and slightly decreased recombination lifetime resulted in the improvement of efficiency. The highest energy conversion efficiency obtained from the photoelectrodes fabricated with the as-prepared rutile TiO₂ nanofibers at 5 wt% NR content was up to 6.1% under AM1.5G solar illumination. The results demonstrate that the composite nanostructure can take advantage of both the fast electron transport of the nanorods and the high surface area of the nanoparticles.     

Immobilized TiO<Subscript>2</Subscript> nanoparticles produced by flame spray for photocatalytic water remediation

Anatase/rutile mixed-phase titanium dioxide (TiO₂) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO₂ powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO₂ powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO₂-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO₂.     

Raman study of phase transformation of TiO2 rutile single crystal irradiated by infrared femtosecond laser

Titanium dioxide (TiO₂) rutile single crystal was irradiated by infrared femtosecond (fs) laser pulses with repetition rate of 250 kHz and phase transformation of rutile TiO₂ was observed. Micro-Raman spectra show that the intensity of E_g Raman vibrating mode of rutile phase increases and that of A_1g Raman vibrating mode decreases apparently within the ablation crater after fs laser irradiation. With increasing of irradiation time, the Raman vibrating modes of anatase phase emerged. Rutile phase of TiO₂ single crystal is partly transformed into anatase phase. The anatase phase content transformed from rutile phase increased to a constant with increasing of fs pulse laser irradiation time. The study indicates the more stable rutile phase is transformed into anatase phase by the high pressure produced by fs pulse laser irradiation.     

Growth of nanocrystalline TiO2 films by pulsed-laser-induced liquid-deposition method and preliminary applications for dye-sensitized solar cells

A novel technique, the pulsed-laser-induced liquid-deposition (PLLD) method, has been employed to grow nanocrystalline TiO₂ films on fluorine-doped tin-oxide-coated (FTO) glass substrates at room temperature. The PLLD method was implemented by directing a pulsed laser into a liquid precursor and depositing the photosynthesized nanocrystalline TiO₂ on an FTO glass substrate immersed in the liquid precursor. The as-grown nanocrystalline TiO₂ films were found to have a rutile crystal structure and consist of a number of flower-like TiO₂ crystal units arrayed together on the FTO glass substrate. Each of the flower-like TiO₂ crystal units was composed of many nanostructured TiO₂ whiskers, and their building blocks were found to be bundles of TiO₂ nanorods with diameter of about 5 nm. The growth of these TiO₂ nanorods is highly anisotropic, with the preferential growth direction along [001]. As-grown nanocrystalline TiO₂ films were annealed at 450°C in air for 30 min for the applications of dye-sensitized solar cells, and the nanostructured characteristics with good porosity were preserved after annealing. A preliminary dye-sensitized solar cell was built based on the annealed nanocrystalline TiO₂ film. The results suggest that the PLLD method is a promising technique for growing nanocrystalline TiO₂ films for photovoltaic applications.     

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO₂ were prepared on glass substrates from an aqueous solution of TiCl₃ and NH₄OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO₂ transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO₂ thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.     

Synthesis and photochemical properties of HTaWO6/ (Pt,TiO2) nanocomposite under visible light irradiation

A new layered nanocomposite, HTaWO₆/(Pt, TiO₂) was synthesized using n-type semi-conductor HTaWO₆ as a host material. HTaWO₆ and HTaWO₆/TiO₂were white, while both HTaWO₆/Pt and HTaWO₆/(Pt, TiO₂) were yellow. The yellow color might be attributed to H_1-xTaWO_6-x/2 formed by the photo-induced phase transformation promoted by Pt. Although HTaWO₆/Pt showed absorption in visible light region (λ > 400 nm), the hydrogen evolution activity was negligibly small. On the other hand HTaWO₆/(Pt, TiO₂) showed excellent photocatalytic activities even under visible light irradiation. The sample containing rutile type titania such as TiO₂(P-25) also showed hydrogen evolution activity, but the activity was smaller than that of HTaWO₆/(Pt, TiO₂). These results suggested that rutile type titania, which can be excited by visible light of wavelength less than 413 nm, played an important role in the visible light-induced photocatalytic activity. The improvement of the hydrogen evolution activity of rutile type titania by intercalating into HTaWO₆/Pt may be due to the depression of the recombination of photoinduced electrons and holes by the heterogeneous electron transfer from rutile type TiO₂ to HTaWO₆/Pt.     

Gold nanoparticle shape effects on human serum albumin corona interface: a molecular dynamic study

Three-dimensional (3D) hierarchical rutile TiO₂ microspheres composed of nanorods with diameter of several-tens of nanometers, with different morphologies and with average size ranging from 1.3 to 1.8 μm, were successfully synthesized through a surfactant-free solvothermal route. The effects of the solvents n-hexane, chloroform, and cyclohexane on the microstructures of 3D hierarchical TiO₂ nanostructures were investigated. Results of scanning electron microscopy showed that 3D sea-urchin like hierarchical TiO₂ composed of nanorods with a diameter of ~10 nm can only be prepared in the cyclohexane-water system. The growth mechanism of 3D sea-urchin like hierarchical TiO₂ composed of numerous nanorods was further examined and found to differ from the well-known “growth → assembly” mode. The effects of surface tension and polarity of solvents on the morphology and crystal strength of 3D hierarchical TiO₂ nanostructure were also investigated. In addition, the prepared 3D sea-urchin like hierarchical TiO₂ showed highest photocatalytic activity compared with other 3D hierarchical TiO₂ nanostructures in this study and Degussa P25 for the degradation of Rhodamine B solution under UV light irradiation, which could be attributed to its special hierarchical superstructure, the increase of surface catalytic sites and its special composition units.     

Effect of phase structures on the formation rate of hydroxyl radicals on the surface of TiO2

To study the relationship between the phase structures of TiO₂ and the photoinduced hydroxyl radicals (OH), TiO₂ nanocrystallines were synthesized by a hydrolysis-precipitate method using tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 450, 600, 700, 800 and 900 °C for 2 h, respectively. The calcined samples were characterized by X-ray diffraction and N₂ sorption. The formation rate of OH on the surface of UV-illuminated TiO₂ was detected by the photoluminescence (PL) technique using terephthalic acid as a probe molecule. The results show that with increasing calcined temperatures, the amorphous (Am) TiO₂ precursor begins to turn into anatase (A) at 450 °C and rutile (R) phase appears at 600 °C, which is completely turned into the rutile phase at 900 °C. The BET specific surface areas of the catalyst decrease as the calcined temperatures increase. TiO₂ sample calcined at 600 °C, with a mixed phase of anatase and rutile, shows the highestOH formation rate, and the order of the OH formation rate is as follows: A+R>A>R>Am. Phase structures of TiO₂ play a more important role than specific surface areas in the OH formation rate. Two phase structure of anatase and rutile with a proper ratio is beneficial to the OH formation due to decrease of the combination rate of photo-generated electrons and holes. Our experimental result implies that the mixed phase of anatase and rutile can markedly enhance the photocatalytic activity of TiO₂.     

Effects of organic modifiers on the size-controlled synthesis of hydroxyapatite nanorods

Size-controlled synthesis of hydroxyapatite nanorods were carried out by chemical precipitation method using polyethylene glycol (MW 600), Tween 20, trisodium citrate, and d-sorbitol as organic modifiers and starting from calcium nitrate, phosphoric acid, and ammonia solution. The influence of the organic modifiers on the sizes of the resultant HAP nanorods was investigated under different synthesis temperatures. It was found that polyethylene glycol was beneficial to the formation of HAP nanorods with a larger aspect ratio (average length/average diameter) at high synthesis temperature, Tween 20 and trisodium citrate favored the formation of small-sized HAP nanorods, and d-sorbitol helped the formation of HAP nanorods with long length at low synthesis temperatures.     

Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.     

Effect of heat treatment on the structure and morphology of ZnO nanorod array and its composite with titania precursor

ABSTRACT

Effects of the elevated temperature on the structure evolution of the ZnO nanorod array (ZNA) and their hybrid nanocomposite with layered (tetramethyl)ammonium titanate (LTMAT) prepared by the liquid phase deposition were investigated. The vertically oriented ZnO nanorods were deposited on a quartz plate by a chemical bath deposition method and then they were penetrated by the LTMAT using the dip-coating method from the water solution. As a result of such an experimental procedure, an assembly composed of the ZNA with LTMAT was obtained and called hybrid nanocomposite. Since the LTMAT converts to TiO₂ upon subsequent sintering at 350 °C, it can be regarded as TiO₂ precursor for the thermal treatment experiments. The experiments with ZNA and their hybrid nanocomposite at the elevated temperature revealed coalescence of the deposited ZnO nanorods and crystallization of zinc titanate with Zn₂TiO₄ stoichiometry.     

Investigation on SERS of different phase structure TiO2 nanoparticles

In this paper, anatase and rutile TiO₂ nanoparticles as well as their mixed crystal phase structure TiO₂ nanoparticles were synthesized by a sol‐hydrothermal method, and were served as active substrates for surface‐enhanced Raman scattering (SERS) study. The results show that the 4‐mercaptobenzoic acid probe molecules exhibit different degree SERS enhancements on the surface of different phase structure TiO₂ nanoparticles. The mixed crystal structure TiO₂ with an appropriate proportion of anatase and rutile phase is favourable to SERS enhancement of adsorbed molecules. These are mainly attributed to the contributions of the TiO₂‐to‐molecule charge transfer mechanism and the mixed crystal effect. Copyright © 2015 John Wiley & Sons, Ltd.     

Optical investigation on sulfur-doping effects in titanium dioxide nanoparticles

The sulfur-doping (S-doping) effects in TiO₂ nanoparticles are investigated by means of Raman spectroscopy and UV–Vis spectroscopy with different S-doping levels (10 and 50%). Raman spectra indicate that the rutile and anatase phases dominate for the low S-doped (10%) and high S-doped (50%) TiO₂ nanoparticles, respectively. The variation of phase with different S-doping levels has been ascribed to the different S-doping processes into TiO₂ nanoparticles. In addition, an extra absorption band is observed in both the S-doped TiO₂ nanoparticles. With increasing S-doping level from 10 to 50%, the extra absorption band shows a blue-shift from 470 to 445 nm, which may be ascribed to the variation of phase from rutile to anatase for TiO₂.     

Study on transformation mechanism of lithium titanate modified with hydrochloric acid

The effects of the concentration of hydrochloric acid and treatment time on the transformation of Li₂TiO₃ were studied in detail. The results demonstrate that lithium ions are easily removed from the (?133) and (?206) planes. In contrast, Li⁺ extraction requires a longer time for the (002) and (?131) planes. A mixture of the anatase and rutile phases, pure rutile, and pure anatase can be generated by treating Li₂TiO₃ with a suitable concentration of hydrochloric acid for an appropriate amount of time. The phase(s) that are present significantly affect the cyclic adsorption performance of a titanium lithium ion sieve and the dissolution of Ti. The transformation from H₂TiO₃ particles to TiO₂ primarily occurs via the dissolution-recrystallization process. The electrophilic H⁺ and highly electronegative Cl^? affect the Ti–O bond, resulting in the destruction of the Ti–O bond in TiO₆ octahedrons, promoting the structural rearrangement of anatase to rutile TiO₂.