Single-crystalline TiO2 Nanorod Arrays Research Articles

Hybrid Lithographic Arbitrary Patterning of TiO2 Nanorod Arrays

In this work, we report a hybrid lithographic method that combines the top–down soft lithography and the bottom–up hydrothermal approach for growing single-crystalline TiO2 nanorod arrays with arbitrary patterns. The arbitrary patterns of TiO2 seeds were obtained through the microcontact printing of the TiO2 seed precursor onto Si substrates using prepatterned poly(dimethylsiloxane) (PDMS) as stamps, followed by a baking process. Afterward, TiO2 nanorod arrays were selectively grown on patterned TiO2 seeds through conventional hydrothermal methods. By controlling the TiO2 seed precursor concentration, the hydrothermal reaction time and temperature and the patterns, the morphology and density of the TiO2 nanorods can be tuned in a controllable manner. Overall, this work provides a new strategy for the low-cost and facile preparation of patterned TiO2 nanorod arrays that has potential applications in micro–nano-optoelectronic devices and other fields.

Enhanced optical and photoelectrochemical performance of single-crystalline TiO2 nanorod arrays with exposed {001} facets sensitized with CdS nanosheets

Single-crystalline TiO2 nanorod arrays (TiO2 NRAs) with dominant {001} facets sensitized with CdS nanosheets were prepared on fluorine-doped tin oxide (FTO) substrate by a simple combination of hydrothermal and successive ion layer absorption and reaction (SILAR) methods. The amount of CdS nanosheets was controlled by changing reaction time (0, 2, 6, and 10 min) in SILAR process. The effects of SILAR time on the microstructure, morphology, and optical and photoelectrochemical properties of TiO2 NRAs were investigated. Changing of SILRA times are accompanied by significant variations of optical properties including a decrease of the band gap from 2.98 to 2.41 eV and a red absorption peak shift from ultraviolet to visible region. Notably, the photoelectrochemical performance of TiO2 NRAs after 6 min SILAR deposition of CdS nonosheets improved significantly, displaying an optimal photocurrent density of 1.5 mA cm−2, which is about 15 times higher than that of pure TiO2 NRAs. This enhanced photoelectrochemical properties due to the synergistic effect of CdS nanosheets and rutile TiO2 NRAs with highly reactive {001} facets.

Core-Shell Nanorod Arrays of Crystalline/Amorphous TiO2 Constructed by Layer-by-Layer Method for High-Performance Electrochromic Electrodes

In this paper, core-shell nanorod arrays of crystalline/amorphous TiO2 (c/a-TiO2) are demonstrated for the comprehensive enhancement of electrochromic performance. The amorphous TiO2 (a-TiO2) shell was conformally deposited on the surface of single-crystalline TiO2 nanorod arrays (c-TiO2) core via a facile layer-by-layer method, which ensures the high-quality contact between the core and shell. The optimal c/a-TiO2 core-shell structure with 13nm a-TiO2 layer combines the assets of distinct porous morphology in c-TiO2 and high charge density in a-TiO2, possessing notably larger optical contrast (43%) and higher coloration efficiency (16.2cm2C−1) than c-TiO2 (18%, 8.8cm2C−1) at 800nm. Compared to the pristine c-TiO2, c/a-TiO2 shows lower threshold voltage and faster response speed due to the low energy barrier and rapid ion migration in the a-TiO2 shell during lithium insertion/extraction. Moreover, the c/a-TiO2 nanostructures can offer outstanding cycling stability in different potential windows upon extensive electrochemical cycling.

“Signal-off” photoelectrochemical DNA sensing strategy based on target dependent DNA probe conformational conversion using CdS quantum dots sensitized TiO2 nanorods array as photoactive material

Abstract In this work, a “signal-off” photoelectrochemical DNA sensing strategy was proposed on the basis of the DNA hybridization induced conformational conversion using CdS quantum dots (QDs) sensitized titanium oxide (TiO2) nanorod array as photoactive material. Highly oriented, single-crystalline TiO2 nanorod arrays were grown directly on fluorine doped tin oxide (FTO) substrate by the hydrothermal method and employed as matrix for immobilization of capturing hairpin DNA probe, whereas CdS QDs as visible light antennae were successively labeled on the terminal of capturing hairpin DNA probe. Compared with pure TiO2 nanorods array, CdS QDs sensitized TiO2 nanorods array evidently extended the absorption edge and exhibited enhanced photoelectrochemical response in the visible region. In the absence of the target DNA, the direct attachment of CdS QDs to TiO2 nanorod array could reduce charge recombination and hence amplify photocurrent intensity. While in the presence of target DNA, the specific recognition of the target DNA with the capturing hairpin DNA–CdS probe would trigger the conformational conversion of capturing hairpin DNA–CdS probe leading to the quenching of photocurrent. Under optimized conditions, this “signal-off” photoelectrochemical sensing strategy shows a linear relationship between photocurrent variation and the logarithm of target DNA concentration in the range from 10 aM to 100 pM with a detection limit of 5.2 aM. Moreover, it exhibits good performance of excellent specificity, high stability, and acceptable fabrication reproducibility. This present strategy opens an alternative avenue for photoelectrochemical signal transduction and expands the applications of photoelectrochemical biosensing and clinical diagnosis.

Significant enhancement of power conversion efficiency for dye sensitized solar cell using 1D/3D network nanostructures as photoanodes.

The single–crystalline TiO2 nanorod arrays with rutile phase have attracted much attention in the dye sensitized solar cells (DSSCs) applications because of their superior chemical stability, better electron transport properties, higher refractive index and low production cost. However, it suffers from a low surface area as compared with TiO2 nanoparticle films. In order to enlarge the surface area of TiO2 nanorod arrays, the 1D nanorods/3D nanotubes sample was synthesized using a facile two-step hydrothermal process involving hydrothermal growth 1D/3D nanorods and followed by post-etching treatment. In such bi-layer structure, the oriented TiO2 nanorods layer could provide direct pathway for fast electron transportation, and the 3D nanotubes layer offers a higher surface area for dye loading, therefore, the 1D nanorods/3D nanotubes photoanode exhibited faster electron transport and higher surface area than either 1D or 3D nanostructures alone, and an highest efficiency of 7.68% was achieved for the DSSCs based on 1D nanorods/3D nanotubes photoanode with further TiCl4 treatment.

Single-crystalline rutile TiO2 nanorod arrays with high surface area for enhanced conversion efficiency in dye-sensitized solar cells

Vertically ordered single-crystalline TiO2 nanorod arrays (NRAs) grown directly on transparent conductive substrates are of considerable interest for overcoming the limitations of current nanoparticle-based dye-sensitized solar cells (DSSCs) with the disordered network structure. However, the synthesis of such structures with high internal surface area is still challenging and desirable for highly efficient DSSCs. Herein, by introduction of a TiO2 nanocrystal seed layer, growth of long single-crystalline rutile TiO2 NRAs with high surface area has been demonstrated by a mild hydrothermal method combined with a chemical etching route. The chemical etching treatment developed here can effectively enlarge the surface area of rutile TiO2 NRAs for more dye-loading by splitting of original TiO2 nanorods into secondary nanowires with a reduced diameter. Accordingly, a DSSC constructed by 7 h-etched rutile TiO2 NRAs exhibits markedly enhanced efficiency of 4.69 %, compared to that of 1.30 % in the DSSCs based on un-etched TiO2 NRAs.

Photoelectrochemical behavior of TiO2 nanorod arrays decorated with CuInS2 quantum dots

One-dimensional single crystalline TiO2 nanorod arrays with different lengths were prepared by controlling the hydrothermal cycles, which were successfully sensitized with CuInS2 quantum dots by assembly linking cycles, and their optical absorption properties and photoelectrochemical properties were investigated. 6μm-TiO2 nanorod electrodes with the CuInS2 quantum dots sensitization of three linking cycles had the best photoelectrochemical properties and short-circuit current density, such as the short-circuit current density are 27.3 times higher than that of pure 6μm-TiO2 nanorod electrodes. The reason may be attributed to the suitable internal surface area of TiO2 nanorod, with the increasing of the adsorption content of CuInS2 quantum dots to generate much more photo-induce electrons. Moreover, it will also enhance the interface connection between TiO2 nanorod and FTO conducting substrate, which favors to reduce the recombination of photo-induced electron–hole pairs.

Growth of Aligned Single-Crystalline TiO2 Nanorod Arrays on Transparent Conducting Oxide Coated Glass

In this work, we report a simple hydrothermal method for growth of aligned TiO2 nanorod arrays directly on SnO2:F (FTO) coated glass substrates without any seed layer. The rectangular nanorod is single crystalline with a tetragonal rutile structure. The diameter, length and density of the nanorods are determined by the synthesis temperature. When synthesis temperature increases from 110 to 190 °C, the diameter increases from 53 to 249 nm, and the length increases from to 324 to 1904 nm. However, the highest density is obtained at 150 °C due to nuclei coalescence at the high synthesis temperature. The activation energy for formation of TiO2 nanorod arrays is 102 kJ/mol obtained by using an Arrhenius equation.

Significant effects of reaction temperature on morphology, crystallinity, and photoelectrical properties of rutile TiO2 nanorod array films

Oriented single-crystalline TiO2 nanorod arrays have been extensively studied as the electrode of photoelectrochemical cells due to their unique properties. In this study, oriented rutile TiO2 nanorod arrays were directly synthesized on fluorine-doped tin oxide glass substrates by a facile hydrothermal method, and the effects of growth conditions (i.e. reaction temperature, growth time and titanium precursor) on their morphologies, crystal structures and photoelectrical properties were investigated. Reaction temperature played a more critical role in tailoring the surface morphology, crystal structures (i.e. length, diameter and crystallinity of nanorods) and photoelectrical properties of the nanorods than growth time did. With the increase in reaction temperature from 140 °C to 200 °C, both photocurrent density and external quantum efficiency (EQE) increased initially and then decreased, with a maximum value of 5.6 × 10−2 mA cm−2 at 170 °C and 2.7% at 160 °C, respectively. In addition, photoelectric measurements demonstrated that TiO2 nanorod arrays synthesized from TiCl4 at a relatively low reaction temperature exhibited a much higher EQE value than those obtained from titanium isopropoxide.

Annealing Effect on Photovoltaic Performance of CdSe Quantum-Dots-Sensitized TiO2Nanorod Solar Cells

Large area rutile TiO2nanorod arrays were grown on F:SnO2(FTO) conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs) were deposited onto single-crystalline TiO2nanorod arrays by a chemical bath deposition (CBD) method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO2nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dots-sensitized TiO2nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing treatment. At the same time, an improved photovoltaic performance was obtained for quantum-dots-sensitized solar cell using the annealed CdSe-TiO2nanostructure electrode. The power conversion efficiency improved from 0.59% to 1.45% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by annealing treatment.

Heterogeneous flammulina velutipes-like CdTe/TiO2 nanorod array: A promising composite nanostructure for solar cell application

Core–shell heterogeneous CdTe/TiO2 nanorod arrays have been prepared by a two-step synthesis route through combined hydrothermal growth and magnetron sputtering. The composition and microstructure of the arrays were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), which show that CdTe nanograins coated on the surface of the single-crystalline TiO2 nanorod arrays to form a type-II heterostructure. Compared with TiO2 nanorod arrays, the spectrum absorption region of CdTe/TiO2 core–shell nanostructure is broadened from ultraviolet light to visible light. The photoelectrodes of CdTe/TiO2 nanorod arrays show better photoelectric properties than those of bare TiO2 nanorod arrays. The output power of CdTe/TiO2 nanorod arrays is 25 times higher than that of a bare TiO2 nanorod array. These results indicate that the photoelectrode of CdTe/TiO2 nanorod array has a promising application in solar cell.