Single-crystalline Rutile TiO2 Research Articles

Synthesis of uniformly ordered single-crystalline TiO2 nanorods on flexible Ti substrate

With high conductivity and ionic mobility, one-dimensional (1D) titanium dioxide (TiO2) nanoarrays have attracted great interest in the photoanode of solar cells and the cathode of lithium-ion/sodium-ion batteries. However, the synthesis of TiO2 nanoarrays often requires highly toxic or corrosive solution circumstances. Meanwhile, the case that most TiO2 nanoarrays are grown on rigid conductive substrate can’t satisfy the demand for application in the space of complex shape. In this work, we developed a simple method to prepare highly ordered single crystalline rutile TiO2 nanorod arrays with high density on flexible metal Ti substrate in relatively weak acid solution, and the orientation of the nanorods were more uniform than those by other means ever before. Based on detailed analysis, an ion-assisted and concentration-limited epitaxial growth mechanism by H+ and is proposed for this uniformly ordered rutile TiO2 nanorod array. This work can promote the research and application of flexible solar cells and lithium-ion batteries, especially their integration.

Single crystalline rutile TiO2 nanorods synthesis by onestep catalyst-free vapor transport method

In this report, a novel one-step approach to grow highly crystalline rutile TiO2 nanorods on bare silicon substrate by a simple vapor transport technique without a catalyst is discussed. The crystal structure of the nanorod ensemble was examined by X-ray diffraction. The structure and morphology of the nanorods were analyzed by scanning electron microscopy and transmission electron microscopy and the one dimensional growth direction was observed to be along (110) plane. Chemical composition of the individual nanorods was examined by X-ray energy-dispersive spectrometry. A possible growth mechanism for the nanorods has been proposed. As the synthesis was catalyst-free, the resulting nanorods were of high purity. These nanorods are expected to have a variety of applications.

Spindle Single-Crystalline Rutile TiO2 with Excellent Cyclability for Low-Cost Li-Storage Materials

We investigated the Li storage properties of spindle single-crystalline rutile TiO2 fine particles synthesized by a large-scale sulfate process. Their anode properties were compared with those of p...

Single-crystalline rutile TiO2 nanorod array on flexible Ti substrates for efficient photoelectrocatalytic degradation of phenol in water

Single-crystalline nanorods are intrinsic highways for charge transfer and hence ideal nanofeatures for efficient photoelectrochemical (PEC) degradations of pollutants in wastewater. Photocatalytic thin films on flexible substrates avoid the nuisance catalysts-recovering procedure and also allow for the flexible design in photocatalytic apparatus. We therefore directly deposited single-crystalline rutile TiO2 nanorod arrays on flexible and conductive Ti substrates through a hydrothermal technique and optimized the synthetic parameters to achieve an extremely high PEC activity towards phenol removal in water under UV light illumination. In the presence of tetrabutyltitanate (TBT) and HCl reactants under a hydrothermal environment, a balance in the erosion of the Ti substrate and the precipitation of TiO2 nanorods is found to be the key to tune the nanofeatures of the TiO2 thin films and in turn the PEC efficiency. The decreasing TBT concentration achieved a more sparsely distributed nanorod array, which significantly contributes to the PEC activity; yet too little TBT resulted in total dissolution of Ti plates. The PEC activity increased with increasing hydrothermal duration because of more loaded TiO2. The maximum reaction rate constant is 2.74 h−1, which is 39 times that of a commercial P25 TiO2 nanoparticulate film. The photocurrent stabilized at 0.9 mA/cm2 under the illumination of AM1.5G simulated solar light, suggesting a high separation efficiency of photogenerated holes and electrons along the single-crystalline rutile TiO2 nanorod arrays.

TiO2 nanorods with CdS quantum dots for optical applications

We combine CdS semiconductor quantum dots and single-crystalline rutile TiO2 nanorod arrays to produce a practical quantum dot sensitized solar cell. A facile wet-chemical approach was implemented for growth of this CdS@TiO2 architecture. Rutile TiO2 nanorod arrays with lengths of 1–2 mm and diameters of 40–60 nm was synthesized on fluorine-doped tin oxide glass by a hydrothermal process in a titanium tetrachloride precursor solution. CdS quantum dots with a size of 5–10 nm was deposited onto a TiO2 nanorod surface using an ultrasonic-assisted chemical bath deposition method. The resulting CdS quantum dots and TiO2 nanorods formed a type-II heterojunction and showed increased absorption over visible light range. Incident photon-to-current conversion efficiencies (IPCE) as high as 85% and power conversion efficiencies of 2.54% were obtained using a polysulfide electrolyte

TiO2 nanorods with CdS quantum dots for optical applications

We combine CdS semiconductor quantum dots and single-crystalline rutile TiO2 nanorod arrays to produce a practical quantum dot sensitized solar cell. A facile wet-chemical approach was implemented for growth of this CdS@TiO2 architecture. Rutile TiO2 nanorod arrays with lengths of 1–2 mm and diameters of 40–60 nm was synthesized on fluorine-doped tin oxide glass by a hydrothermal process in a titanium tetrachloride precursor solution. CdS quantum dots with a size of 5–10 nm was deposited onto a TiO2 nanorod surface using an ultrasonic-assisted chemical bath deposition method. The resulting CdS quantum dots and TiO2 nanorods formed a type-II heterojunction and showed increased absorption over visible light range. Incident photon-to-current conversion efficiencies (IPCE) as high as 85% and power conversion efficiencies of 2.54% were obtained using a polysulfide electrolyte.

Photoelectrochemical Cathodic Protection Effect of Bi2S3/TiO2 nanorod Array Composite Film for Stainless Steel

TiO2 nanomaterials have long been a topic of interest for applications in various fields due to their special photoelectrochemical properties. However, there are some problems for practical applications of a pure TiO2 film. TiO2 can only be excited by ultraviolet light and its photoelectric conversion efficiency is low due to the high electron-hole recombination rate. In order to overcome these problems, many methods have been developed to modify TiO2 films for improving their photoelectrochemical properties. In this work, we fabricated a Bi2S3 modified rutile TiO2 nanorod array film on FTO conductive glass for achieving a good photoelectrochemical cathodic protection effect on 403 stainless steel (403SS) in a NaCl solution. A single crystalline rutile TiO2 nanorod array film was prepared by a typical hydrothermal reaction method. A FTO substrate (10 mm × 15 mm × 2.2 mm) was immersed in a TiCl4 solution and thermally treated in an electric oven at 70 ℃ for 30 min. After that, the FTO specimen was annealed at 550 ℃ in air for 1 h. Then the specimen with the TiO2 seed layer was immersed a mixed aqueous solution of TiCl4 and HCl, and heated in an electric oven at 150 ℃ for 10 h. Bi2S3 nanoparticles was prepared on the TiO2 film by a typical chemical bath deposition method. The TiO2 film sample was alternately immersed in the Bi(NO3)3 ethylene glycol solution and the Na2S aqueous solution for 1 min. After each immersion, the film sample was dried at 80 ℃ for 5 min. This operation cycle was repeated for 15 times. Finally, the film sample was annealed at 240 ℃ for 4 h in a N2 atmosphere. The prepared films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their photoelectrochemical properties and photocathodic protection effects were investigated. The results indicated that the prepared TiO2 film was composed of the nanorod array. The TiO2 in the film was highly crystallized and agreed well with the rutile phase, and Bi2S3 nanoparticles were successfully deposited on the TiO2 film. The photoresponse of the Bi2S3/TiO2 composite film was extended into the visible light region, and its photoelectrochemical properties were enhanced. Under white light illumination, the Bi2S3/TiO2 composite film as a photoanode could make the potential of 403SS in a 0.5 M NaCl solution decrease by 695 mV (relative to its corrosion potential), showing a more effective photoelectrochemical cathodic protection effect than the pure rutile TiO2 nanorod film, which is of significance for environmentally friendly corrosion control of metals. This work was supported by the National Natural Science Foundation of China (Nos. 21573182, and 21173177).

Formation of gold and platinum nanostructures on rutile TiO2(001) by thermal treatment of thin films in vacuum

The studies are giving an answer to the question whether noble metals undergo reversible segregation and form nanostructures on TiO2(001). It was found out that Au and Pt nanostructures (AuNSs and PtNSs) can be formed on a single-crystalline rutile TiO2(001) substrate. They were obtained by thermal treatment at 1073 K in ultra-high vacuum of thin Au and Pt films deposited by ion sputtering technique. The properties of nanostructures on TiO2(001) were analysed basing on XPS, STM, SEM and GI-XRD data. It is shown that AuNSs and PtNSs, although prepared in similar manner, exhibited significant differences in concentration, size, distribution and calculated polydispersity index. AuNSs appeared to be hemispherical-like and close to monodisperse with lateral size of 13 ± 4 nm. In contrast, PtNSs revealed the existence of two populations in size i.e. 11 ± 4 nm and 39 ± 11 nm and they possessed nanocrystalline structure with clearly exposed Pt(111) facets. Also, compared to previous findings for lighter metals (Fe, Co and Ni), the experiments showed no reversible segregation of Au and Pt on TiO2(001). Thus, the role of diffusion coefficients and masses of the selected ions was discussed to explain the differences in reversible segregation of various metals on TiO2(001) substrate.

Growth, Single-Crystalline Rutile TiO2 Nanorod Thin Film By Hydrothermal Technique

A facile, hydrothermal technique was developed to growth, single-crystalline rutile TiO2 nanorod thin films on transparent conductive fluorine-doped tin oxide (FTO) substrates. In this study, the deferent periods(6, 9, 12, 15, and 18 hour) were selective with constant temperature at 160 oC to growth this films and growth in deferent temperature (130, 150,170,190, and 210 oC) with constant period of deposition at 6h. SEM image showed all the films were nanorodand the EDX measurement was given the portion of element that contribution in rutile TiO2 nanorod thin films. The diameter, length, and density of the nanorods could be varied by changingthe growth parameters. The XRD to determine the structure properties, and optical properties were measured of these rutile TiO2 nanorod thin films and obtained the absorbance and energy gap.

Improved photoelectrical performance of single crystalline rutile TiO2 nanorod arrays incorporating α-alumina for high efficiency dye-sensitized solar cells

Novel architecture like TiO2 nanorod arrays (TNR) incorporating α-alumina (ATNR) thin film have been fabricated on the fluorine-doped tin oxide (FTO) by a modest and flexible doctor-blade technique based hydrothermal method. α-Al2O3, TNR and ATNR were used as a photoanode in dye-sensitized solar cells (DSSCs) and their photovoltaic performance was evaluated. The crystallinity, presence of α-Al2O3 on TNR and morphology of the photoanodes were characterized by X-ray diffraction, field emission scanning microscopy and high-resolution transmission scanning microscopy. DSSCs fabricated with 1.0 wt% α-Al2O3 added TNR exhibited an improved open-circuit photo voltage of 0.68 V, short-circuit current density of 15.23 mA cm−2, fill factor of 0.63 and photo-electric conversion efficiency (PCE) of 6.5%.

Influence of titanium tetrachloride concentration and multiple growth cycles of TiO2 nanorod on photoanode performance in dye sensitized solar cell

Single crystalline rutile TiO2 nanorod arrays (NRAs) have been grown on fluorine doped tin oxide (F: SnO2) coated glass substrate by using hydrothermal technique. The influence of precursor concentration on the morphological, structural, optical and electrical properties of TiO2 nanorods (NRs) was studied. X-ray diffraction studies show that the TiO2 NRs are highly oriented with respect to the substrate surface. FESEM measurements of TiO2 films display that the length of the rods are ranged from (1.54 to 2.44) μm. The transmittance, absorption coefficient, and energy gap at different precursor concentration were measured and calculated. Results show that rods length decreased the transmittance and energy gap, whereas it increased the absorption coefficient. The electrical measurements of TiO2 exhibit the effect of rods length on the resistivity of single crystalline rutile TiO2 nanorod array. The sample with optimum precursor concentration and with 2.44 μm in length was employed as photoanode in Dye sensitized solar cell (DSSC).The effect of multiple growth cycles of TiO2 NR on Photoanode Performance in DSSC was investigated. The spectral response of Dye sensitized solar cell showed one peak of response and its maximum value approaching 0.16 A/W at λ = 500 nm. The prepared DSSC reveals a conversion efficiency of 2.15% under illumination of 100 mW cm−2 by one time of growth cycle.

Morphology Conserving High Efficiency Nitrogen Doping of Titanate Nanotubes by NH3 Plasma

Titanate nanotubes offer certain benefits like high specific surface area, anisotropic mesoporous structure and ease of synthesis over other nanostructured titania forms. However, their application in visible light driven photocatalysis is hindered by their wide band-gap, which can be remedied by, e.g., anionic doping. Here we report on a systematic study to insert nitrogen into lattice positions in titanate nanotubes. The efficiency of N2+ bombardment, N2 plasma and NH3 plasma treatment is compared to that of NH3 gas synthesized in situ by the thermal decomposition of urea or NH4F. N2+ bombarded single crystalline rutile TiO2 was used as a doping benchmark (16 at.% N incorporated). Surface species were identified by diffuse reflectance infrared spectroscopy, structural features were characterized by scanning electron microscopy and powder X-ray diffraction measurements. The local chemical environment of nitrogen built into the nanotube samples was probed by X-ray photoelectron spectroscopy. Positively charged NH3 plasma treatment offered the best doping performance. This process succeeded in inserting 20 at.% N into nanotube lattice positions by replacing oxygen and forming Ti–N bonds. Remarkably, the nanotubular morphology and titanate crystal structure were both fully conserved during the process. Since plasma treatment is a readily scalable technology, the suggested method could be utilized in developing efficient visible light driven photocatalysts based on N-doped titanate nanotubes.

Effects of deposition temperature on the structural and optical properties of single crystalline rutile TiO2 films

Rutile phase titanium dioxide (TiO2) thin films were grown on α-Al2O3 (100) substrates at different deposition temperatures (500–650 °C) by the metalorganic chemical vapor deposition method. The analyses of X-ray diffraction θ-2θ scan indicated that the deposition temperature had an obvious influence on the crystal quality of the TiO2 films. Single crystalline rutile TiO2 films can be obtained from a relatively low deposition temperature of 500 °C–600 °C, and the film grown at 550 °C exhibited the best crystallinity, for which the composition and epitaxial relationship were identified. The effects of deposition temperature on the deposition rate and optical properties of the films have been investigated in detail.

Tunable photovoltaic performance of preferentially oriented rutile TiO2 nanorod photoanode based dye sensitized solar cells with quasi-state electrolyte

Photoanodes made of highly oriented TiO2 nanorod (NR) arrays with different aspect ratios were synthesized via a one-step hydrothermal technique. Preferentially oriented single crystalline rutile TiO2 was confirmed by the single peak in an XRD pattern (2θ = 63°, (0 0 2)). FESEM images evidenced the growth of an array of NRss having different geometries with respect to reaction time and solution refreshment rate. The length, diameter and aspect ratio of the NRs increased with reaction time as 4 h (1.98 μm, 121 nm, 15.32), 8 h (4 μm, 185 nm, 22.70), 12 h (5.6 μm, 242 nm, 27.24) and 16 h (8 μm, 254 nm, 38.02), respectively. Unlike a conventional dye-sensitized solar cell (DSSC) with a liquid electrolyte, DSSCs were fabricated here using one-dimensional rutile TiO2 NR based photoanodes, N719 dye and a quasi-state electrolyte. The charge transport properties were investigated using current–voltage curves and fitted using the one-diode model. Interestingly the photovoltaic performance of the DSSCs increased exponentially with the length of the NR and was attributed to a higher surface to volume ratio, more dye anchoring, and channelized electron transport. The higher photovoltaic performance (Jsc = 5.99 mA cm−2, Voc = 750 mV, η = 3.08%) was observed with photoanodes (16 h) made with the longer, densely packed TiO2 NRs (8 μm, 254 nm).

Balsam-pear-like rutile/anatase core/shell titania nanorod arrays for photoelectrochemical water splitting

In this work, a solution combustion followed by dissolution in hydrogen peroxide is adopted to achieve a precursor for decorating anatase TiO2 nanosheets along single-crystalline rutile TiO2 nanorods, which achieves balsam-pear-like core/shell nanorod arrays with enhanced photoelectrochemical water splitting. The enhanced photoelectrochemical performance is attributed to the novel nanoarchitecture, which can simultaneously offer a high surface area, enhanced light-harvesting, a rutile/anatase junction for charge carrier separation and a conductive pathway for charge carrier collection. The photoanode design can also give hints to other functional materials.

Titania nanowires functionalized polyester fabrics with enhanced photocatalytic and antibacterial performances

Flexible organic fabrics coated with titania find wide applications in pollutant degradations and antibiosis. Because of the enhanced charge separations, TiO2 with one-dimensional nanostructures exhibits photocatalytic activity superior to that of nanoparticulate films; however, only the later has been achieved on organic substrates through commonly sol-gel techniques till now. In this study, radially aligned TiO2 nanowires were precipitated on polyester fabrics through multi-steps of surface roughening, sol-gel TiO2 seeding, hydrogen titanate nanobelts precipitation, and finally sulfuric acid treatment. Both mesoporous anatase TiO2 nanowires and single-crystalline rutile TiO2 nanorods have been achieved, which, together with some unchanged titanate nanobelts, exhibited an overall narrowed band gap of ca. 2.50eV. The TiO2 nanowires on flexible PET fabrics showed higher photocatalytic activity towards degradations of not only rhodamine B in water but also toluene gas in air under UV light illumination, when compared with either TiO2 nanotube array or commercial Degussa P25 nanoparticulate films on metallic Ti substrates. Remarkable sterilization of E. coli and S. epidermidis under visible light irradiation was also achieved. The excellent photocatalytic and antibacterial performances were attributed to the unique mixed 1D nanostructures, phase junctions, abundant surface hydroxyl groups, and the narrowed band gap.

Perspective: A controversial benchmark system for water-oxide interfaces: H2O/TiO2(110).

The interaction of water with the single-crystalline rutile TiO2(110) surface has been the object of intense investigations with both experimental and computational methods. Not only is TiO2(110) widely considered the prototypical oxide surface, its interaction with water is also important in many applications where this material is used. At first, experimental measurements were hampered by the fact that preparation recipes for well-controlled surfaces had yet to be developed, but clear experimental evidence that water dissociation at defects including oxygen vacancies and steps emerged. For a perfect TiO2(110) surface, however, an intense debate has evolved whether or not water adsorbs as an intact molecule or if it dissociates by donating a proton to a so-called bridge-bonded surface oxygen atom. Computational studies agree that the energy difference between these two states is very small and thus depends sensitively on the computational setup and on the approximations used in density functional theory (DFT). While a recent molecular beam/STM experiment [Z.-T. Wang et al., Proc. Natl. Acad. Sci. U. S. A. 114(8), 1801-1805 (2017)] gives conclusive evidence for a slight preference (0.035 eV) for molecular water and a small activation energy of (0.36 eV) for dissociation, understanding the interface between liquid water and TiO2(110) arises as the next controversial frontier.

Bi2S3 modified single crystalline rutile TiO2 nanorod array films for photoelectrochemical cathodic protection

A combined hydrothermal reaction and sequential chemical bath deposition method is developed for fabricating a Bi2S3 modified single crystalline rutile TiO2 nanorod array film on transparent conductive glass. The results indicate that the modification of Bi2S3 nanoparticles extends the photoresponse of the Bi2S3/TiO2 composite film into the visible light region, and enhances its photoactivity. The Bi2S3/TiO2 film can serve as a photoanode in a photoelectrochemical cell and provide more effective photogenerated cathodic protection for 403 stainless steel in a corrosion cell with a 0.5M NaCl solution under white or visible light illumination compared with the pure TiO2 film.

Synthesis and Characterization of Photocatalytic Performance of Rutile-Tio2 Nanorod Arrays for Solar Hydrogen Generation

Single crystalline rutile TiO2 nanorods (TNRs) films have been grown on the fluorine doped tin oxide (FTO) substrates using a one pot hydrothermal method, have attracted great attention because of favorable applications in the photoelectrochemical water splitting system. The effect of the reaction conditions on the morphology, crystal orientation and photocatalytic activity has been systematically investigated. The X-ray diffraction (XRD) pattern shows that two diffraction peaks at 36.3° and 63.2° correspond to the (101) and (002) planes of the tetragonal rutile TiO2 nanorod, respectively. The scanning electron microscope (SEM) of the samples indicates that the TiO2 array surface morphology and orientation are highly dependent on the reaction parameters, such as temperature, reaction time and the titanium precursor concentration. In a typical condition of the hydrothermal method at 0.3ml of TBO and 160°C for 3 hr, a small diameter and short length 190 nm and 2.2 µm of TiO2 nanorods respectively, are grown on florien doped tin oxide (FTO) substrate. When synthesized TiO2 nanorods photocatalyst was irradiated under illumination of simulated AM 1.5G solar light (100 mW cm−2) achieves an overall Photocurrent density of 1.80 mA/cm2 with a maximum photoconversion efficiency of ~1.6%. The results suggest that these dense and aligned one-dimensional TiO2 nanorods are promising for hydrogen generation from water splitting based on PEC cells.

Adsorption of Dye Molecules on Single Crystalline Semiconductor Surfaces: An Electrochemical Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy Study

Adsorption of dye molecules on semiconductor surfaces dictates the interaction at and thus the electron transfer across the interface, which is a crucial issue in dye-sensitized solar cells (DSSCs). However, despite that surface enhanced Raman spectroscopy (SERS) has been employed to study the interface, information obtained so far is gathered from surfaces of irregularly arranged nanoparticles, which places complexities for precise attribution of adsorption configuration of dye molecules. Herein, we employ single crystalline rutile TiO2(110) for Raman spectroscopic investigation of TiO2–dye interfaces under electrochemical control by utilizing the enhancement of Au@SiO2 core–shell nanoparticles. FD-TD simulation is performed to evaluate the localized electromagnetic field (EM) created by the core–shell nanoparticles while Mott–Schottky measurements are used to determine the band structure of the semiconductor electrode. Comparative investigations are carried out on nanoporous P25 TiO2 electrodes. The potential-dependent Raman shift of ν(N═C═S) suggests that the binding of the SCN group of N719 to the TiO2 surface is the intrinsic nature of the TiO2–N719 interaction, after removing the possible bonding complexity by surface roughness. Nevertheless, hydrogen bonding between COOH and the TiO2 appears to be more favorable on the atomic flat rutile TiO2(110) surface than on the surface of nanoporous P25 nanoparticle as revealed by the stronger Raman shift of ν(C═O) (COOH) on the former. Electrochemical SERS (EC-SERS) results show that photoinduced charge transfer (PICT) occurs for both the P25 and rutile(110) TiO2 surfaces, and the potential to achieve PICT resonance depends on the band structure of the semiconductor. Our work demonstrates that EC-SERS can be applied to study the single crystalline semiconductor–molecule interfaces using core–shell based surface plasmonic resonance (SPR) enhancement strategy, which would promote fundamental investigations on interfaces of photovoltaic and photocatalytic systems.