Rutile TiO2 Nanorod Arrays Research Articles

Self-powered SnSx/TiO2 photodetectors (PDs) with dual-band binary response and the applications in imaging and light-encrypted logic gates

In this work, we report the design and fabrication of self-powered binary response PDs based on II-type heterostructures consisting of SnSx nanoflakes (NFs) and rutile TiO2 nanorod arrays (NRs). The TiO2 NRs effectively block light with wavelengths below 400 nm from reaching SnSx. Under 385 nm light, the photoelectrons in TiO2 recombine with holes in SnSx at the interface due to the energy band bending, resulting in a positive photocurrent. Under 410 nm light, the photoelectrons in SnSx and the photogenerated holes in TiO2 accumulate at the interface, overcoming the interfacial potential barriers induced by the higher Fermi levels of SnSx and inducing a negative photocurrent. Based on the bipolar response, the dual-band imaging capability without external filters and the light-encrypted OR, AND, and NOT logic gates using a single device are demonstrated. This work provides a blueprint for the development of multifunctional self-powered PDs that can simplify system architecture, reduce the energy consumption, and improve accuracy for applications, such as visual systems, light-controlled logic circuits, and encrypted optical communications.

Multifunctional engineering on the ultrasensitive driven-dual plasmonic heterogenous dimer system of 1D semiconductor for accurate SERS sensitivity and quantitation

Self-assembled functional nanomaterials with electromagnetic (EM) hot spots and chemical (CM) enhancement have been recognized as a key in surface-enhanced Raman scattering (SERS) analysis. Herein, a dual-hybrid plasmonic coupling SERS sensor composed of rutile TiO2 nanorod arrays (r-TNRs), Au nanospheres (AuNSs), and Ag nanocubes (AgNCs) has been designed to achieve ultrasensitive detection and obtain unique molecular fingerprints. The AgNCs/AuNSs/r-TNRs-based SERS chip shows an extremely promising SERS enhancement factor (EF) of 1.2 ×1011, detectability at sub-picomolar concentrations (down to the single-molecule level, 10-13 M), and excellent signal reproducibility with a relative standard deviation (RSD) of 3.4 %. Furthermore, this system has been applied for fingerprint detection in complex mixtures, demonstrating impressive specificity and accuracy. The photocatalytic decomposition efficiency of the AgNCs/AuNSs/r-TNRs platform reaches approximately ∼99 % within 20 min. Additionally, the Raman intensity of crystal violet only declined by 15 % after 21 days, illustrating the outstanding stability of the as-proposed ternary SERS sensor.

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.

Constructing the Vo-TiO2/Ag/TiO2 Heterojunction for Efficient Photoelectrochemical Nitrogen Reduction to Ammonia

Photoelectrochemical (PEC) nitrogen (N2) fixation technology provides the possibility to produce ammonia (NH3) under mild conditions, but the efficiency of N2 reduction in this process is greatly limited due to the high bond energy and ionic potential of N2. Herein, the Vo-TiO2/Ag/TiO2 photoelectrode consisting of rutile TiO2 nanorod arrays, Ag nanoparticles, and anatase TiO2 nanosheets with oxygen vacancies (Vo-TiO2) was constructed for accelerating the PEC reduction of N2 into ammonia. The separation of photogenerated carriers can be promoted by the heterojunction among TiO2 nanorods, Ag nanoparticles, and Vo-TiO2 nanosheets. Furthermore, the photogenerated electrons from the conduction band of TiO2 and the hot electrons from Ag nanoparticles’ local surface plasmon resonance (LSPR) effect were injected into the conduction band of Vo-TiO2, and they were further captured by Vo-TiO2 oxygen vacancy and can reduce N2 that adsorbed on the catalyst to NH3. Without any sacrificial agent, the average NH3 production rate can reach 51.2 μg h–1 cm–2. The catalyst exhibited excellent stability even after multiple uses. The LSPR effect of Ag nanoparticles and heterojunction structure promote the better PEC performance of TiO2 nanorod arrays.

Influence of growth acidic solution and etching time on rutile TiO2 nanorod arrays synthesized by hydrothermal method in dye-sensitized solar cells

Titanium butoxide (Ti(OBu)4) precursor was used to prepare titanium dioxide (TiO2) nanorods as a photoanode by hydrothermal method directly on FTO glass with different hydrochloric acid (HCl) – water (H2O) ratio (12.5-7.5, 10-10, 7.5-12.5 and 5-15) ml and etching times (24, 48, and 72)h. The (XRD) results show good crystallinity of TiO2 with rutile phase and preferred orientations (101) and (002) for all samples. The grain size of the TiO2 nanorods increases with decrease the HCl concentration. The (FESEM) images show that an increase in HCl concentration leads to an increase in the rod diameter of the TiO2 NRs and a decrease in their length. The optimum efficiency (η) of DSSC based on TiO2 NRs was 3.255% at sample ET, where the preparation condition (7.5 ml HCl + 12.5 H2O) with a 48 h etching time.

High-efficient hole-transport-material-free carbon-based all-inorganic perovskite solar cells using Cs-doped TiO2 nanorods array as the electron transport layer

Vertical-oriented Cs-doped rutile TiO2 nanorod (Cs-TiO2 NR) arrays were prepared without a seed layer through the hydrothermal method. One-dimension TiO2 nanorod (TiO2 NR) arrays not only provide a direct and fast channel for charge transfer but also increase the perovskite loading amount. Further research shows that the conduction band minimum of Cs-TiO2 NRs increases from − 3.94 eV to − 3.86 eV when compared with the pristine TiO2 NRs, which favors the positive band alignment at the ETL/perovskite interface and reduces the carrier recombination and energy loss. Furthermore, we simultaneously replaced the expensive and unstable organic hole transport layer and noble metal electrode with a carbon electrode for the purpose of reducing the cost of the PSCs. The study proves that Cs-TiO2 NRs not only improve the energy level arrangement at the ETL/perovskite interface but also reduce the density of defect states at the interface and increase carrier lifetime. The hole-transport-material-free carbon-based all-inorganic FTO/Cs-TiO2 NRs/CsPbI2.25Br0.75/C solar devices exhibited a high-power conversion efficiency (PCE) of 12.72%, showing a 16% increase in PCE when compared with the control device. This work opens the door to the preparation of high-efficiency hole-transport-material-free carbon-based all-inorganic PSCs via the energy level calibration engineering.

Solution chemistry quasi-epitaxial growth of atomic CaTiO3 perovskite layers to stabilize and passivate TiO2 photoelectrodes for efficient water splitting

Perovskite oxides with unique crystal structures and high defect tolerance are promising as atomic surface passivation layers for photoelectrodes for efficient and stable water splitting. However, controllably depositing and crystalizing perovskite-type metal oxides at the atomic level remains challenging, as they usually crystalize at higher temperatures than regular metal oxides. Here, we report a mild solution chemistry approach for the quasi-epitaxial growth of an atomic CaTiO3 perovskite layer on rutile TiO2 nanorod arrays. The high-temperature crystallization of CaTiO3 perovskite is overcome by a sequential hydrothermal conversion of the atomic amorphous TiOx layer to CaTiO3 perovskite. The atomic quasi-epitaxial CaTiO3 layer passivated TiO2 nanorod arrays exhibit more efficient interface charge transfer and high photoelectrochemical performance for water splitting. Such a mild solution-based approach for the quasi-epitaxial growth of atomic metal oxide perovskite layers could be a promising strategy for both fabricating atomic perovskite layers and improving their photoelectrochemical properties.

Tailored TiO2 nanorod arrays for dye sensitized solar cell applications

A TiO2 layer using titanium (IV) butoxide on fluorine doped tin oxide (FTO) substrate is used as a seed layer for the growth of TiO2 nanorod arrays (TRA). TRAs with length of ∼1 to 2 μm were grown on seed layer (SL) by two step method. In the first step TiO2 SLs were deposited by sol-gel assisted spin coating method and the second step involved the typical hydrothermal technique to grow rutile TRAs. Most of the TRAs grown on FTO substrate without SL were randomly oriented and TRAs with 0.025 M SL was oriented vertically from the substrate. Whereas TRAs grown on 0.05 M SL showed hierarchical nanoflower clusters composed of a bunch of TRAs as petals blooming from the core. The XRD pattern showed all the three TRAs to be crystallized in a tetragonal rutile phase. Photo luminescence spectra revealed that the TRAs on 0.05 M SL have comparatively low intense blue emission band, predicting the suppressed electron-hole recombination rate. The power conversion efficiency of the dye sensitized solar cell (DSSC) with TRAs grown on 0.05 M SL was recorded as 3.18%, which is 3 times greater than that without SL and 1.6 times greater than that with 0.025M SL in our observations.

Bio-inspired design of strong self-standing cathode toward highly stable reversible Li-CO2 batteries

The hysteresis kinetics of carbon dioxide reduction reaction (CDRR) and evolution reaction (CDER) reaction are major barriers toward the practical implementation of lithium-carbon dioxide (Li-CO2) batteries. Herein, a free-standing and binder-free cathode composed of rutile TiO2 nanorod arrays (TiO2 NAs) and carbonized natural sponge was designed and realized by a simple seeds-assisted construction. The novel air cathode was found to exhibits a high specific capacity of 4.38 mAh cm−2 and long cycle life of more than 1600 h, as well as the discharge products, which would deposit at the surface of the TiO2 NAs rather than carbon substrate during the discharge process. The improved performance can be ascribed to the interconnected conductive sponge framework with macropore and mesoporous channels that can house more discharge products, and the reactant molecules can unrestricted contact with the active sites. Furthermore, the good adhesion to the carbon substrate and the numerous available catalytic sites of the TiO2 NAs contribute intimate contact of the discharge products with the TiO2 NAs, improving CDRR and CDER kinetics effectively and boosting the electrochemical reactions. This TiO2/Sponge represents a promising design in the development of a nature-inspired, self-standing, and binder-free electrode for high-performance Li-CO2 batteries.

Facile Synthesis of Fluorine Doped Rutile TiO2 Nanorod Arrays for Photocatalytic Removal of Formaldehyde

Facile Synthesis of Fluorine Doped Rutile TiO2 Nanorod Arrays for Photocatalytic Removal of Formaldehyde

High-Efficiency All-Inorganic Perovskite Solar Cells Tailored by Scalable Rutile TiO2 Nanorod Arrays with Excellent Stability.

Tailored optimization of perovskite solar cells (PSCs) is a persistent objective to achieve the ultimate commercialization purpose, in which the electron/hole transport layer with thickness on the nanometer scale is generally required to maximize the charge collection and minimize the series resistance. Therefore, precise control on the fabrication technology of the charge transport layer is important. Herein, one-dimensional (1D) rutile TiO2 nanorod arrays with a thickness of 1.8 μm have been fabricated and employed as a potential electron extraction layer for high-efficiency all-inorganic CsPbBr3 PSCs for the first time. Arising from the sufficient carrier mobility, excellent conductivity, and superior charge extraction ability by means of regulating the donor concentration with nitrogen atoms, a champion efficiency of 8.50% has been achieved with excellent long-term stability after 50 days storage in air conditions, which is comparable to that of the 200 nm-thick TiO2 layer tailored device. The primary results demonstrate that the TiO2 layer with micrometer scale thickness is also feasible to effectively collect the photogenerated carriers and realize considerable solar-to-electric conversion ability, providing multifarious technologies to fabricate the electron extraction layer.

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.

Bi2Se3, Bi2Te3 quantum dots-sensitized rutile TiO2 nanorod arrays for enhanced solar photoelectrocatalysis in azo dye degradation

Rutile TiO2 nanorod arrays vertically aligned on conductive fluorine-doped tin oxide glass are optimized for photocatalysis in terms of the density and diameter of nanorods by tuning the concentration of Ti precursor and reaction time during the hydrothermal process. Quantum dots (QDs) of V2VI3( V = Bi; VI = Se, Te) topographic insulators are then employed as sensitizers to enhance the visible-light response of TiO2. Electrochemical measurements show that the decoration of Bi2Se3 or Bi2Te3 significantly increases the photocurrent due to the enhanced light harvesting properties and the charge carrier separation capability mediated by the topographic isolation effect of V2VI3 QDs. Photoelectrocatalytic (PEC) activity evaluation is conducted towards the decoloration of azo dyes, including methyl orange and methylene blue under the sunlight irradiation. The elaborated Bi2Se3/TiO2 nanorod array exhibits the superior PEC performances, presenting shows great potentials in environmental remediation.

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

Superstrate type CZTS solar cell with all solution processed functional layers at low temperature

A new molecular precursor for Cu2ZnSnS4 (CZTS) has been explored for the fabrication of efficient superstrate type solar cells with all solution processed functional layers at low temperature. The CZTS film made at low temperature (250 °C), without sulfurization was employed in the heterojunction device with a thin interface layer of CdS and the one-step hydrothermally processed rutile TiO2 nanorod arrays. The quality of the CZTS film was optimized by varying the composition of Cu and Zn in the precursor solution. Initial devices with (FTO/TiO2/CdS/CZTS/Au) structure exhibited the power conversion efficiency up to 1.04%, on par with the best in the relevant literature.

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).

Niobium doped TiO2 nanorod arrays as efficient electron transport materials in photovoltaic

One-dimensional (1-D) rutile TiO2 nanorod arrays (NRAs) synthesized by a hydrothermal method suffer from low electrical conductivity and large amounts of surface defects, hindering their further applications. Nb doping is thus introduced to modify their electronic properties. Results indicate that light Nb doping reduces rod nanosizes, increases electron concentrations, decreases surface defective oxides and lowers conduction band of the TiO2 NRAs, while heavy doping induces transformations of morphologies and crystalline orientations as well as occurrences of compositional deviations and low oxidative states of Ti3+. After 0.1 mol% and 1 mol% Nb incorporations, device efficiencies are substantially improved by ~16% and ~33% for the model perovskite and dye-sensitized solar cells, respectively, which are ascribed to reduced recombination at the perovskite/TiO2 interfaces (e.g. charge lifetime increasing from 62 μs to 107 μs) and improved electron transport through the photoanode of TiO2 NRAs (e.g. electron diffusion length increasing from ~14 μm to ~50 μm). Our study verifies that Nb doped 1-D TiO2 NRAs are versatile electron transporting materials in different kinds of emerging solar cells, and are also potential for other fields including photocatalysis, sensors and batteries etc.

Shell thickness dependent photocatalytic activity of TiO2/ZnS core-shell nanorod arrays

Rutile TiO2 nanorod arrays (NRAs) were first fabricated via solvothermal route using Ti foil as both substrate and titanium source, then TiO2/ZnS core-shell heterostructure NRAs were synthesized by successive ionic layer adsorption and reaction (SILAR) method using the TiO2 NRAs as a sacrificial template. The diameters of TiO2 nanorods ranged from 20 to 200 nm, and the thickness of ZnS shell varied from 3 to 20 nm. The photocatalytic activities of the samples were compared by the degradation of rhodamine B (RhB) water solution under simulated sunlight irradiation. All TiO2/ZnS NRAs exhibited higher photocatalytic activities than bare TiO2 NRAs, and the optimal ZnS shell thickness of TiO2/ZnS NRAs was 10 nm. Furthermore, TiO2/ZnS NRAs possessed excellent reusability.

Dual quantum dots decorated TiO2 nanorod arrays for efficient CO2 reduction

To meet the demand of CO2 reduction, we designed a Z-type composite photocatalyst based on vertically aligned rutile TiO2 (r-TiO2) nanorod arrays. The composite photocatalyst was obtained by decorating g-C3N4 and Au quantum dots on the r-TiO2 nanorods. Benefiting from the high charge separation efficiency of C3N4/TiO2 heterojunction and the electron capture effect of Au quantum dots, the composite catalyst indicates a significantly enhanced hydrocarbon yield efficiency. The yield rate of CO can increase to 0.138 μmol cm−2 h−1 and the yield rate of CH4 can reach 0.032 μmol cm−2 h−1 without any sacrificial agents, which is almost 5 times than that of pristine r-TiO2 nanorod arrays. This work provides an efficient strategy to rationally design high-performance photocatalysts by using quantum dots and nanorods (or nanowires) as building blocks.