TiO2 Nanorod Films Research Articles

Superhydrophilic TiO2 nanorod films with variable morphology grown on different substrates

Rutile TiO2 nanorods were allowed to grow on FTO or glass substrate under the assistance of an anatase TiO2 nanoparticle/SiO2 primary film through a hydrothermal process. The component of TiO2 nanoparticle was expected to be dissolved and then to induce the growth of rutile TiO2 nanorods during the hydrothermal process and the component of SiO2 was designed to play two roles in providing landing site for rutile TiO2 nucleuses and improving the wettability of the nanorod films. The morphology of the nanorod films could also be varied with the primary film. The nanorod films derived from the primary film performed an enhanced superhydrophilicity as compared with that directly formed on the FTO surface, and showed superhydrophobicity after surface modification.

Bi-layer of nanorods and three-dimensional hierarchical structure of TiO2 for high efficiency dye-sensitized solar cells

A novel bi-layer structure assembled by nanorods and three-dimensional hierarchical TiO2 is synthesized by a facile two step hydrothermal method. By adjusting the acid concentration, the morphology of three-dimensional hierarchical TiO2 can be well controlled. This bi-layer structure combines the merits of one-dimensional nanorods which can serve as direct electrons transport pathways and three-dimensional hierarchical structure supplying light scattering ability and large specific surface area for dye loading. Hence, the photovoltaic performance of the dye-sensitized solar cells based on the bi-layer TiO2 is greatly enhanced compared to that of single nanorods film. The maximum short-circuit current and power conversion efficiency of the DSSCs based on bi-layer TiO2 structure reach 12.55 mA/cm2 and 5.61% respectively, which are remarkably larger than those of 5.00 mA/cm2 and 2.38% for the DSSC based on a single layer TiO2 nanorods film. The superior performance of bi-layer TiO2 structure is attributed to the large dye loading amount and light scattering properties due to the unique hierarchical structure.

Initial reactant controlled synthesis of double layered TiO2 nanostructures and characterization of its spectra of absorption and photoluminescence

Double layered titanium dioxide (TiO2) nanostructures were synthesized on fluorine-doped tin oxide (FTO) substrates using a low-cost and convenient hydrothermal method. The prepared TiO2 nanostructures were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The SEM images showed that the double layered TiO2 nanostructure composed of one layer of TiO2 nanorods film on FTO and one layer of TiO2 nanoflowers on the TiO2 nanorods film. The results of XRD indicated that the prepared TiO2 nanostructures were rutile TiO2. The band gap of the prepared TiO2 nanostructures was calculated by ultraviolet–visible (UV–vis) absorption spectrum. Optical properties of the samples were investigated by photoluminescence (PL) spectroscopy. The results indicated that all of the prepared samples had the same luminescence center. And the luminescence intensity of double layered TiO2 increased with increasing the excitation wavelength.

Synergistic effect of Pt0 and M2+ (Cu2+, Ni2+, Co2+) on photo(electro)catalytic activity of TiO2 nanorod array thin films

M2+ (Cu2+, Ni2+, Co2+) and Pt0-M2+ loaded TiO2 nanorod film samples were prepared on transparent conducting oxide glass (FTO/F:SnO2). Two step method was used consisting a hydrothermal method to grow TiO2 nanorods on the surface and an ultrasonic-assisted sequential cation adsorption method to modify the nanorods. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry, photocatalytic activities were tested by methylene blue degradation under visible light. M2+-TiO2/FTO samples were compared with Pt0-M2+-TiO2/FTO samples; the synergistic effect of Pt0 and M2+ was discussed. Pt0-Ni2+-TiO2/FTO showed superior photoelectrocatalytic activity with 1.358 mA cm−2 and 78.3% methylene blue degradation under visible light. Quantum yields were calculated separately as a sign for H2 generation rate and as a conversion of methylene blue molecule per absorbed light.

Preparation and drug release behavior of TiO2 nanorod films with incorporating mesoporous bioactive glass

For orthopedic implant coatings, excellent biological performance and anti-infective property have been both increasingly required for implantation surgery. In this work, TiO2 nanorod films with good cellular responses and mesoporous bioactive glass (MBG) with good drug loading and release ability were adopted, and MBG-incorporated TiO2 nanorod films were prepared by the sol–gel technique. The effects of TiO2 nanorod density and MBG composition on the formation of the incorporated films were investigated. The results show that T-MBG (SiO2/CaO/P2O5/TiO2=80/5/5/10) tightly cohered to TiO2 nanorods in the films, and the degree of T-MBG incorporation ranged from about 100nm to 300nm of exposed TiO2 nanorods in height. T-MBG incorporation had a positive role in the cytocompatibility of the films. Importantly, T-MBG incorporation improved greatly the drug release behavior of the TiO2 nanorod films. The present work provides an approach to build organized nanostructure films on implant surfaces with satisfactory biological performance and essential anti-infective ability.

Floating growth of large-scale freestanding TiO2 nanorod films at the gas-liquid interface for additive-free Li-ion battery applications.

The floating growth process of large-scale freestanding TiO2 nanorod films at the gas-liquid interface was investigated. On the basis of the experiments, a self-templated growth scenario was developed to account for the self-assembly process. In the scenario, titanium complexes function not only as the Ti source for the growth of TiO2 but also as a soft template provider for the floating growth. According to the scenario, several new recipes of preparing freestanding TiO2 nanorod films at the gas-liquid interface were developed. The freestanding film was applied to a lithium ion battery as a binder-free and conducting agent-free anode, and good cyclability was obtained. This work may pave a new way to floating and freestanding TiO2 and other semiconductor materials, which has great potential not only in basic science but also in the applications such as materials engineering, Li-ion battery, photocatalyst, dye-sensitized solar cell, and flexible electronics.

Growth of the [110] Oriented TiO2 Nanorods on ITO Substrates by Sputtering Technique for Dye-Sensitized Solar Cells

TiO2 films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. It has been found that the sputtering pressure is a very important parameter for the structure of the deposited TiO2 films. When the pressure is lower than 1 Pa, the deposited film has a dense structure and shows a preferred orientation along the [101] direction. However, the nanorod structure has been obtained as the sputtering pressure is higher than 1 Pa. These nanorods structure TiO2 film shows a preferred orientation along the [110] direction. The phases of the deposited TiO2 films have been characterized by the x-ray diffraction and the Raman scattering measurements. All the films show an anatase phase and no other phase has been observed. The results of the SEM show that these TiO2 nanorods are perpendicular to the ITO substrate. The TEM measurement shows that the nanorods have a very rough surface. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorod films prepared at different sputtering pressures as photoelectrode. And the effect of the sputtering pressure on the properties of the photoelectric conversion of the DSSCs has been studied.

Au@SiO2 core/shell nanoparticle-decorated TiO2 nanorod arrays for enhanced photoelectrochemical water splitting

To improve the separation efficiency of photoinduced charge carries, Au@SiO2 nanoparticles (NPs) with core–shell structure were loaded onto the surface of TiO2 nanorods grown on fluorine-doped tin oxide substrate by a facile two-step process. The resulted Au@SiO2/TiO2 photoanodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, as well as photoelectrochemical measurements. Compared with pristine TiO2 nanorod film, the Au@SiO2/TiO2 films showed remarkable enhancement in photoelectrochemical water splitting, with incident photon-to-current conversion efficiency increasing from 31 % to 37 % at 380 nm at 0.7 V versus saturated calomel electrode. This could be interpreted by the effect of metallic surface plasmon resonance of Au@SiO2 NPs, which would generate an intense electromagnetic field with spatially nonhomogenous distributed intensity. As a result, the charge carriers generated in the near-surface region of TiO2 nanorods could be easily separated. This modification method based on the effect of metallic surface plasmon resonance for promoted charge carrier separation provides a promising way to develop semiconductor photoelectrodes with high solar water-splitting performance.

Photo(electro)catalytic Activity of Cu2+-Modified TiO2 Nanorod Array Thin Films under Visible Light Irradiation

In the present study, a two-step method was applied to synthesise Cu2+-modified TiO2 nanorod array thin films for photocatalytic processes. TiO2 nanorod array thin films were synthesised by a hydrothermal method and then modified with an ultrasonic-assisted sequential cation adsorption method. The samples were characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and inductively coupled plasma mass spectroscopy (ICP-MS) analysis. The photoelectrochemical properties of the samples were evaluated by linear sweep voltammetry and Mott–Schottky analysis; photocatalytic activities were tested by methylene blue degradation under visible light. The photocurrent density of the TiO2/FTO sample modified with 50mM Cu2+ solution was 26 times higher than that of the unmodified TiO2/FTO sample. Additionally, methylene blue degradation efficiency under visible light was increased 40% with respect to the efficiency of the unmodified sample. The mechanism of the photocatalytic activity enhancement of Cu2+-modified TiO2 nanorod films was discussed.

Electrospun Hierarchical TiO2 Nanorods with High Porosity for Efficient Dye-Sensitized Solar Cells

Ultraporous anatase TiO2 nanorods with a composite structure of mesopores and macropores fabricated via a simple microemulsion electrospinning approach were first used as photoanode materials for high-efficiency dye-sensitized solar cells (DSSCs). The special multiscale porous structure was formed by using low-cost paraffin oil microemulsion droplets as the soft template, which can not only provide enhanced adsorption sites for dye molecules but also facilitate the electrolyte diffusion. The morphology, porosity, and photovoltaic and electron dynamic characteristics of the porous TiO2 nanorod based DSSCs were investigated in detail by scanning electron microscopy (SEM), N2 sorption measurements, current density-voltage (J-V) curves, UV-vis diffuse reflectance spectra, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), and open-circuit voltage decay (OCVD) measurements. The results revealed that, although fewer amounts of dyes were anchored on the porous TiO2 nanorod films, they exhibited stronger light scattering ability, fast electrolyte diffusion, and extended electron lifetime compared to the commercial P25 nanoparticles. A power conversion efficiency of 6.07% was obtained for the porous TiO2 nanorod based DSSCs. Moreover, this value can be further improved to 8.53% when bilayer structured photoanode with porous TiO2 nanorods acting as the light scattering layer was constructed. This study demonstrated that the porous TiO2 nanorods can work as promising photoanode materials for DSSCs.

Growth and surface treatment of TiO2 nanorods using stearic acid solution

Titanium dioxide (TiO2) nanorods were deposited on silicon substrates using titanium tetra-isopropoxide as a precursor via a metal-organic chemical vapor deposition method. TiO2 nanorod film thickness was about 3.8μm, and the observed contact angles of the TiO2 surface were very low due to their super-hydrophilic properties. As a next step, TiO2 nanorods were treated for 24h with stearic acid molecules. Surface wettability changed from hydrophilic to hydrophobic by stearic acid treatment and the contact angle of TiO2 nanorod film after treatment was approximately 119°.

Improvement of nonlinear response for the power conversion efficiency with light intensities in cobalt complex electrolyte system

A vertically aligned TiO2 photoelectrode with sufficient space between TiO2 nanorods was synthesized by sacrificial templating of ZnO nanorods grown on a dense TiO2 layer/FTO film. The more expanded pore space in the TiO2 nanorod film than conventional mesoscopic TiO2 film greatly reduces the mass transport problem of cobalt electrolyte in the vicinity of the Sb2S3 sensitizer in Sb2S3-sensitized photoelectrochemical solar cells. Therefore, the nonlinearity of the power conversion efficiency (PCE) under illumination intensity was greatly relieved to 5.0% (0.1sun), 4.7% (0.5sun), and 3.7% (1sun) in a TiO2-nanorod-based Sb2S3-sensitized solar cell, whereas the efficiency of a mesoscopic-TiO2-based solar cell was significantly degraded to 5.3% (0.1 sun), 3.8% (0.5sun), and 2.3% (1sun).

Two step synthesis of CaP/TiO2 nanorod composite coatings with improved protein adsorption

Titanium dioxide (TiO2) nanorods and calcium phosphate (CaP) composite coatings were prepared and characterized. TiO2 nanorod films were grown on titanium substrates via a hydrothermal method. Then, calcium phosphate was deposited into TiO2 nanorod films electrochemically in an aqueous electrolyte containing calcium and phosphorus species. As a result, CaP/TiO2 nanorod coatings were obtained. The amount of calcium phosphate deposited could be controlled through varying temperature, voltage and duration. It was found that both the presence of calcium phosphate and UV treatment could affect the surface wettability of the composite coatings. A bovine serum albumin adsorption test showed that the protein adsorption ability of the composite coatings was also improved with the presence of calcium phosphate and UV treatment. Moreover, the presence of calcium phosphate could promote the deposition of bone-like minerals. It is suggested that such coatings may exhibit promising initial cellular responses and thus be a good alternate for bioactive coatings.

Influence of rod-surface structure on biological interactions between TiO2 nanorod films and proteins/cells

We investigated the use of TiO2 nanorod films to construct an instructive microenvironment for regulation of biological activity. Rutile TiO2 nanorod films were fabricated via a hydrothermal method. Heat treatment was used to adjust the atomic arrangement order degree of the nanorod surfaces. The influence of changes in the nanorod surface on the films was characterized. The results show that heated nanorod films were well crystallized and the nanorod surfaces had a regular atomic arrangement. Unheated nanorod films had a higher contact angle and lower sensitivity to UV illumination, and showed good capacity for protein adsorption at an early stage, which may lead to better cytocompatibility. The results provide an insight into construction of an appropriate microenvironment for interaction between biomaterials and cells.

Structural Modification of TiO2 Nanorod Films with an Influence on the Photovoltaic Efficiency of a Dye-Sensitized Solar Cell (DSSC)

TiO2 nanorod films have been deposited on ITO substrates by dc reactive magnetron sputtering technique. The structures of these nanorod films were modified by the variation of the oxygen pressure during the sputtering process. Although all these TiO2 nanorod films deposited at different oxygen pressures show an anatase structure, the orientation of the nanorod films varies with the oxygen pressure. Only a very weak (101) diffraction peak can be observed for the TiO2 nanorod film prepared at low oxygen pressure. However, as the oxygen pressure is increased, the (220) diffraction peak appears and the intensity of this diffraction peak is increased with the oxygen pressure. The results of the SEM show that these TiO2 nanorods are perpendicular to the ITO substrate. At low oxygen pressure, these sputtered TiO2 nanorods stick together and have a dense structure. As the oxygen pressure is increased, these sputtered TiO2 nanorods get separated gradually and have a porous structure. The optical transmittance of these TiO2 nanorod films has been measured and then fitted by OJL model. The porosities of the TiO2 nanorod films have been calculated. The TiO2 nanorod film prepared at high oxygen pressure shows a high porosity. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorod films prepared at different oxygen pressures as photoelectrode. The optimum performance was achieved for the DSSC using the TiO2 nanorod film with the highest (220) diffraction peak and the highest porosity.

One-pot synthesis of peacock-shaped TiO2 light scattering layer with TiO2 nanorods film for dye-sensitized solar cells

A titanium dioxide (TiO2) film, showing distinctive functions and morphology, was prepared using the hydrothermal method by controlling the ratio of HCl:CH3COOH in acidic medium. A one-dimensional (1-D) TiO2 nanorod (NR) film was synthesized with a length of 2μm using a 1:2 ratio of HCl:CH3COOH, whereas a 1-D TiO2 NR film with peacock shaped TiO2 nanobundles as a light scattering layer (LSL) was acquired by employing a 2:1 ratio of HCl:CH3COOH. This LSL exhibited remarkable dual functions with respect to high light harvesting, which was attributable to the large surface area of the micrometer-sized TiO2 nanobundles, consisting of small-sized TiO2 NRs of 30–40nm in diameter and a light scattering effect in the long wavelength region of 550–700nm. Accordingly, the dual functions of the LSL resulted in a sharp increase in conversion efficiency (3.93%) that was about twice that (1.49%) of TiO2 NR film synthesized using a 1:2 ratio of HCl:CH3COOH. In particular, a considerably enhanced short-circuit photocurrent (Jsc) was mainly responsible for the resulting increase in overall efficiency with a moderate increase in fill factor and slightly reduced open-circuit voltage.

Reproducible resistive switching in hydrothermal processed TiO2 nanorod film for non-volatile memory applications

In this study, we examined the resistive switching characteristics of the TiO2 nanorod film based resistance random access memory (RRAM). TiO2 nanorod film is grown on FTO substrate by simple hydrothermal process. The grown TiO2 film is characterized using SEM, XRD, EDAX and FTIR for its morphological, structural and compositional studies. XRD result confirms the anatase phase of TiO2. The analysis of I–V results reveals that the switching property of our device originates from the oxidation/reduction reaction occurred at the interface of Ti/TiO2. The device exhibited high ON/OFF ratio (>104), long retention and good endurance performance at RT.

Preparation and surface wettability of TiO2 nanorod films modified with triethoxyoctylsilane

Nanostructured TiO2 arrays were prepared through a facile and environmentally friendly hydrothermal method on fluorine-doped tin oxide coated glass substrates with tunable surface morphologies without using any catalysts, seeds or templates. Their crystal structure, surface morphology, compositions and wettability were investigated by X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectroscope and contact angle measurements, respectively. It is found that the concentration of hydrochloric acid has a great influence on the morphology and wettability of TiO2 nanorod films. Typically, the film prepared with 7.0M HCl exhibits a high water contact angle of 157.3±1.5° with an advancing contact angle of 154.2±1.3° and a receding contact angle of 161.2±1.3° and a small sliding angle of 7° after hydrophobic treatment. The Cassie theory was used to analyze the hydrophobic phenomenon of the as-prepared film, and it reveals that only about 9% of the water surface is contacted with the TiO2 film and the remaining 91% is contacted with the air cushion, which is reasonable for the hydrophobicity of a TiO2 nanorod film.

CuInS2 quantum dot-sensitized TiO2 nanorod array photoelectrodes: synthesis and performance optimization

CuInS2 quantum dots (QDs) were deposited onto TiO2 nanorod arrays for different cycles by using successive ionic layer adsorption and reaction (SILAR) method. The effect of SILAR cycles on the light absorption and photoelectrochemical properties of the sensitized photoelectrodes was studied. With optimization of CuInS2 SILAR cycles and introduction of In2S3 buffer layer, quantum dot-sensitized solar cells assembled with 3-μm thick TiO2 nanorod film exhibited a short-circuit current density (Isc) of 4.51 mA cm−2, an open-circuit voltage (Voc) of 0.56 V, a fill factor (FF) of 0.41, and a power conversion efficiency (η) of 1.06%, respectively. This study indicates that SILAR process is a very promising strategy for preparing directly anchored semiconductor QDs on TiO2 nanorod surface in a straightforward but controllable way without any complicated fabrication procedures and introduction of a linker molecule.

A facile low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells

Titania (TiO2) nanorods have been synthesized with controlled size for dye-sensitized solar cells (DSSCs) via hydrothermal route at low hydrothermal temperature of 100 °C for 24 h. The titania nanorods were characterized using XRD, SEM, TEM/HRTEM, UV-vis Spectroscopy, FTIR and BET specific surface area (S BET), as well as pore-size distribution by BJH. The results indicated that the bulk traps and the surface states within the TiO2 nanorods films have enhanced the efficiency of DSSCs. The size of the titania nanorods was 6.7 nm in width and 22 nm in length. The high surface area can provide more sites for dye adsorption, while the fast photoelectron-transfer channel can enhance the photogenerated electron transfer to complete the circuit. The specific surface area S BET was 77.14 m2 g−1 at the synthesis conditions. However, the band gap energy of the obtained titania nanorods was 3.2 eV. The oriented nanorods with appropriate lengths are beneficial in improving the electron transport property and thus leading to the increase of photocurrent, together enhancing the power conversion efficiency. A nearly quantitative absorbed photon-to-electrical current conversion achieved upon excitation at wave length of 550 nm and the power efficiency was enhanced from 5.6 % for commercial TiO2 nanoparticles Degussa (P25) cells to 7.2 % for TiO2 nanorods cells under AM 1.5 illumination (100 mW cm−2). The TiO2 cells performance was improved due to their high surface area, hierarchically mesoporous structures and fast electron-transfer rate compared with the Degussa (P25).