TiO2 Nanorod Array Films Research Articles

Pt-modified TiO2 nanorod array films on FTO with enhanced CO sensitivity: A combined experimental and first-principle study

In this work, highly regular TiO2 array films consisting of nanorods with a diameter of ∼119 nm were grown on FTO via a facile hydrothermal method. Then Pt nanoparticles with a size of ∼5 nm were modified on the surface of TiO2 nanorods via an in-situ reduction process. The gas-sensing performances of pristine TiO2 and Pt-modified TiO2 samples were systematically tested. The introduction of Pt nanoparticles could enhance the response and stability toward CO gas and decrease the optimal operating temperature from 400 °C to 360 °C. And the Pt/TiO2-based sensor with a Pt content of 1.5 wt% exhibits the maximum CO sensitivity. Furthermore, the adsorption energies of Pt-modified or Pt-doped TiO2 for CO molecules were calculated using first-principles calculations. The chemical sensitivity of Pt to CO molecules may be responsible for the improved CO sensitivity. Additionally, the unique nanorod array structure of Pt/TiO2 and the nano-Schottky junction generated between them are helpful in enhancing the gas-sensing property.

Core-shell TiO2/ZnO nanorod array films on FTO: Two-step synthesis and improved ethanol sensing performance

In this work, highly regular TiO2 nanorod array films were synthesized in situ on FTO by a facile hydrothermal method, and then ZnO shell layers were grown on the surface of the nanorods to form a core-shell structure via an ion-layer adsorption-reaction way. Compared to the TiO2 nanorods, the prepared TiO2/ZnO nanocomposites exhibited enhanced ethanol sensing performances, including a low working temperature, higher sensitivity, and faster response capability. The optimum sensor based on 2c-TiO2/ZnO exhibited the maximum response value of 30.85 toward 50 × 10−6 C2H5OH at 340 °C, which was almost 4.15 times higher than that of the TiO2 sensor. The improved ethanol sensing mechanism was discussed in relation to the unique nanorod array structure and the heterojunctions between TiO2 and ZnO.

Characteristics of diluted magnetic semiconductor based on Mn-doped TiO2 nanorod array films

In this work, un-doped and Mn-doped TiO2 nanorod (NR) array films were successfully prepared by hydrothermal method that deposited on FTO substrate at different molar ratios (x = 0, 0.025, 0.05, 0.075, and 0.1). The prepared samples were examined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). XRD illustrates the pure rutile phase in all samples. The preferred orientation along [001] for pure sample convert to [101] direction with increasing doping content. Lattice constants increase with increasing doping content. The top view of FESEM images show the uniformly distributed nanorod arrays. The nanorods’ length decrease, and their diameters increase with increasing doping content. The nanorods start to bevel from its vertical direction after doping. The crystal size of TiO2 NRs with different manganese doping has calculated using the Williamson-Hall plot. The saturation magnetism appeared in pure titanium oxide has been attributed to the oxygen vacancies, while it changed to diluted magnetic semiconductor after doped with Mn.

Anatase TiO2 nanorod arrays as high-performance electron transport layers for perovskite solar cells

One-dimensional nanorod arrays show great potential as electron transport layers of perovskite solar cells due to their unique characteristic of oriented electron transport. Herein, anatase phase TiO2 nanorod arrays are successfully grown on FTO conductive glass by a facile hydrothermal method using tetrabutyl titanate as precursor. By regulating the concentration of tetrabutyl titanate, TiO2 nanorods with the length of 50, 200, 300 and 1000 nm are synthesized. XRD and Raman spectra show that the nanorods are pure anatase phase, while SEM and TEM images reveal that they are polycrystalline structure. The anatase TiO2 nanorod array films have homogeneous surface morphologies, which are beneficial to deposit compact and pinhole-free perovskite films. The light absorption, photoluminescence quenching and trap densities of the films are systematically investigated. Consequently, the perovskite solar cells based on 50 nm anatase TiO2 nanorod arrays show the best photoelectric conversion efficiency of 15.3%, and those based on 200, 300, 1000 nm nanorod arrays achieve the photoelectric conversion efficiencies of 14.5%, 13.8% and 12.1%, respectively.

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).

Hydrogen plasma-treated 1D/3D TiO2 nanorod array photoanode for efficient photoelectrochemical water splitting

The rutile phase titanium oxide (TiO2) based photoanode exhibits less energy conversion efficiency, as compared to anatase phase TiO2 photoanode. Enhancing the performance of the rutile phase TiO2 photoanode in a photoelectrochemical cell for water splitting is a significant challenge. In this study, we have grown the rutile phase 1D/3D nanorod array structure by using a one-step hydrothermal process. To enhance the surface properties of 1D/3D TiO2 nanorod array films, the as-grown films were treated in a hydrogen plasma atmosphere created using an electron cyclotron resonance (ECR) plasma system. The crystalline phases of the untreated and Hydrogen plasma treated films are confirmed by XRD and Raman studies. We found that, hydrogen plasma treatment creates Ti3+ sites and oxygen vacancies, leading to an increment in optical absorbance and reducing the band gap from 3.17 to 2.89 eV. Additionally, a significant enhancement in photocurrent density (0.369 mAcm−2 at 1 V versus Ag/AgCl) was observed in hydrogen plasma-treated 1D/3D TiO2 nanorod array photoanodes compared to untreated films (0.034 mAcm−2 at 1 V). The enhancement is attributed to the increase in carrier concentration induced by oxygen vacancy formation and the improved electron-hole pair separation. Further, the hydrogen plasma-treated 1D/3D TiO2 nanorod array photoanode exhibited high Photostability for long time duration.

Improved photoelectric performance of DSSCs based on TiO2 nanorod array/Ni-doped TiO2 compact layer composites film

In spite of the TiO2 compact layer (TCL) being widely used, it still needs more study. This paper took Ni-doped TCLs as the research target, using an innovative two-step method perfectly prepared Ni-doped TCLs with different thicknesses. And then on the basis of Ni-doped TCLs, the TiO2 nanorod array (TNA) films were successfully prepared. The effects of Ni-doped TCLs with different thicknesses on the morphology, structure, and photoelectric performance of TNA films were investigated. The results indicated that Ni-doped TCLs with appropriate thickness can significantly improve performance of TNA films and obtain satisfactory PCE stability with time. Compared with the TNA films based on Ni:TCL5, Ni:TCL10, and Ni:TCL30, the TNA film with Ni:TCL20 exhibited better comprehensive photoelectric performance, the DSSCs based on this TNA film achieved the highest Jsc (10.191 mA cm−2), Voc (0.574 V), PCE (4.42%), and the most excellent PCE stability with time.

A novel in situ synthesis of TiO2/CdS heterojunction for improving photoelectrochemical water splitting

We report a novel hydrothermal in situ synthesis route for the CdS-sensitized TiO2 nanorod array films and their photoelectrochemical (PEC) performance are investigated in this paper. Although heterojunctions have been well recognized for enhancing the PEC performance of TiO2 nanostructures, the specific synthesis methodology of high production quality, low preparation cost, and high controllability over the heterojunction structures is still a hot and open topic. In this work, controllable nanoscale TiO2/CdS heterojunctions have been successfully realized through hydrothermal synthesis. The absorption spectrum is shown to be broadened from ~350 nm to ~570 nm, and the photocurrent density increases from 0.35 to 2.03 mA/cm2, corresponding to photo-conversion efficiency of ~0.88%. The method is considered as an efficient and facile choice in the fabrication of TiO2-based PEC hydrogen production functional materials.

Enhanced morphology and photoelectric properties of one-dimensional TiO2 nanorod array films

Abstract One-dimensional TiO2 nanorod array films (1D TNA films) were prepared by the two-step process. The results show that the density of 1D TNA films is significantly improved with the presence of TiO2 compact layer (TCL) and the hydrothermal reaction time of 15 h. The TiO2 crystallinity is improved. The utilization efficiency of the visible light is increased with the lower concentration of crystal defects. The charge recombination center caused by the defects decreased, while the electrons and holes were effectively separated, thus the charge recombination rate was lowered, and better charge transport performance caused the transient photocurrent to increase significantly.

Construction of Ag@AgCl decorated TiO2 nanorod array film with optimized photoelectrochemical and photocatalytic performance

A novel Ag@AgCl/TNR film photocatalyst was successfully obtained by a facile multistep route. Using a well-organized TiO2 nanorod array (TNR) film as the starting material, Ag nanoparticles were uniformly deposited on the TNR film via a photochemical reduction, and in situ oxidation of Ag by FeCl3 solution resulted in the formation of Ag@AgCl/TNR film. The structure, morphology, composition, optical, photocatalytic and photoelectrochemical properties of the obtained films were investigated in detail. The results showed that core-shell Ag@AgCl can effectively promote the transfer of photo-generated electron-hole pairs, suppress their recombination, and enhance the visible light absorption. The Ag@AgCl/TNR film with 60 min oxidation time (S60) showed the highest photocurrent and best transfer performance of interfacial electrons in the electrochemical impedance spectroscopy (EIS) Nyquist plots. For the photodegradation of methyl orange (MO), the S60 exhibited the highest photocatalytic efficiency (90.8%) and good stability under visible light irradiation, which can be comparable and even better than the previous reports. A detailed photocatalytic mechanism was proposed on the basis of the fact that Ag nanoparticles with surface plasma resonance (SPR) can be excited by visible light and this unique structure effectively transfers photo-generated electrons from Ag to TiO2 conduction band, accomplished by the transfer of compensative electrons from a donor (Cl−) to Ag nanoparticles.

Enhanced photoelectrochemical performance of TiO2 nanorod array films based on TiO2 compact layers synthesized by a two-step method.

An innovative two-step method perfectly prepared TCLs with different thicknesses, and then the TNA films based on TCLs were successfully prepared. The effects of different thicknesses of TCLs on the morphology and photoelectrochemical performance of TNA films were investigated. The results indicated that TCLs with appropriate thickness could effectively improve the morphology and photoelectrochemical performance of TNA films. Compared with the TNA films based on TCL5, TCL10 and TCL30, the TNA film based on TCL20 exhibited more ideal and comprehensive photoelectrochemical performance. Moreover, dye-sensitized solar cells (DSSCs) based on this TNA film achieved the highest Jsc (10.2054 mA cm−2), Voc (0.5737 V), PCE (3.3%) and Pout (3.31 mW cm−2).

Enhanced photocatalytic activity of AgVO<SUB align="right">3/TiO<SUB align="right">2 nanorod array composite film under visible light irradiation

The novel AgVO3/TiO2 nanorod array composite film (NACF) has been prepared by the hydrothermal and subsequent successive ionic layer adsorption methods. The photocatalytic films were characterised by the scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and UV-vis diffuse reflectance spectra (UV-vis DRS). The SEM result showed that AgVO3/TiO2 NACF exhibited a well nanorod array structure, and some AgVO3 nanocrystals were deposited on the TiO2 nanorods. The novel AgVO3/TiO2 NACF showed the enhanced visible photocatalytic activity for degradation of methyl orange (MO) compared with the pure TiO2 nanorod array film. The deposition of AgVO3 nanocrystals on the TiO2 nanorod array led to the improved visible light absorption of the composite film due to the narrow bandgap of AgVO3 (less than 2.5 eV). The contact of AgVO3 and TiO2 resulted in the formation of semiconductor heterostructure, which led to the enhanced separation of photogenerated carriers. The improved visible absorption and efficient separation of photogenerated electron-hole pairs should result in the higher visible activity of composite film compared with pure TiO2 nanorod array film.

TiO2 nanorod array film decorated with rGO nanosheets for enhancing photocatalytic and photoelectrochemical properties

A well-aligned TiO2 nanorod array film decorated with reduced graphene oxide(rGO/TNR) was constructed on fluorine-doped tin oxide (FTO) via a one-pot hydrothermal route with the aim of improving the photocatalytic and photoelectrochemical performances. The optimal ratio of components was investigated by changing the GO content that was added to the TiO2 precursor solution. The structure, morphology, composition, optical, photocatalytic and photoelectrochemical properties of the rGO/TNR films were investigated in detail. The resulting rGO/TNR films had a unique microstructure, apparent red shift of the absorption edge and low recombination rate of photoinduced charge carriers. For the degradation of methylene orange (MO) under UV light, the 5 wt%-rGO/TNR film exhibited the best photogradation efficiency of 95.8% in 120 min compared to bare TNR, which had a photogradation efficiency of 41.4%. Moreover, the 5 wt%-rGO/TNR film also showed the highest photocurrent of 110 μA/cm2, which was 6 times higher than that of bare TNR (16 μA/cm2). The excellent performance of the rGO/TNR film may be caused by the synergistic effect of the extended photoresponse range, high adsorption of target molecules and effective photogenerated electron-hole separation via rGO nanosheets as electron collectors and transporters.

Quantum Dot Sensitized Solar Cells Based on TiO2/AgInS2

Quantum dot heterojunctions with type-II band alignment can efficiently separate photogenerated electron-hole pairs and, hence, are useful for solar cell studies. In this study, a quantum dot sensitized solar cell (QDSSC) made of TiO2/AgInS2 is achieved to boost the photoconversion efficiency for the TiO2-based system by varying the AgInS2 layer’s thickness. The TiO2 nanorods array film is prepared by using a simple hydrothermal technique. The formation of a AgInS2 QD-sensitized TiO2-nanorod photoelectrode is carried out by successive ionic layer adsorption and reaction (SILAR) technique. The effect of the QD layer on the performance of the solar cell is studied by varying the SILAR cycles of the QD coating. The synthesized electrode materials are characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy and solar cell performances. The results indicate that the nanocrystals have effectively covered the outer surfaces of the TiO2 nanorods. The interfacial structure of quantum dots (QDs)/TiO2 is also investigated, and the growth interface is verified. A careful comparison between TiO2/AgInS2 sensitized cells reveals that the trasfer of electrons and hole proceeds efficiently, the recombination is suppressed for the optimum thickness of the QD layer and light from the entire visible spectrum is utilised. Under AM 1.5G illumination, a high photocurrent of 1.36 mAcm−2 with an improved power conversion efficiency of 0.48% is obtained. The solar cell properties of our photoanodes suggest that the TiO2 nanorod array films co-sensitized by AgInS2 nanoclusters have potential applications in solar cells.

Visible light responsive CdS sensitized TiO2 nanorod array films for efficient photocatalytic reduction of gas phase CO2

Abstracts In this letter, an effective photocatalytic reduction of CO2 by using CdS-Cu2+/TiO2 nanorod array films photocatalyst under visible light was studied. TiO2 nanorod array films were prepared by the hydrothermal method, after which Cu2+ ions and CdS quantum dots (QDs) were deposited on the TiO2 nanorod arrays using the ultrasonic-assisted sequential cation adsorption method and successive ionic layer adsorption and reaction (SILAR) method respectively. The composition, morphology and optical property of the samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectric spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS). The loading amount of CdS QDs was regulated by controlling the deposition cycles which demonstrates correspondingly optical behaviors. Their photocatalytic activities were evaluated by reduction of gas-phase CO2 to estimate the ethanol yield under various operating parameters, including the CdS QDs concentration, CO2 flow rate and reaction temperature. The experiment results showed that when the SILAR method cycle deposition was two, the reaction product yield reached the maximum, and the ethanol yield was 109.12 μmol/g-cat h at a flow rate of 4 mL/min and under the reaction system temperature of 80 °C. The highly efficient photocatalytic activities of CdS-Cu2+/TiO2 nanorod array films in the reduction process of CO2 were attributed to the combination of one-dimensional (1D) nanostructure with decorating Cu2+ ions and CdS QDs, which restrain recombination of the electron hole pairs and broaden the visible-light response. In addition, the photocatalytic mechanism was discussed to understand the experimental results over the CdS-Cu2+/TiO2 nanorod array films.

Improved photovoltaic performance of perovskite solar cells based on three-dimensional rutile TiO2 nanodendrite array film.

In order to explore high performance and stable perovskite solar cells (PSCs), the design and optimization of electron transport layer (ETL) have been paid more and more attention. Vertically oriented, one-dimensional (1D) TiO2 nanostructured array films are considered superior ETLs because of their rapid electron transporting property and open pore architectures. In this study, a three-dimensional (3D) rutile TiO2 nanodendrite array (RTNDA) film containing 1D trunks and branches was fabricated through second hydrothermal treatment of 1D rutile TiO2 nanorod array (RTNRA) film hydrothermally grown on a fluorine tin oxide (FTO) conductive glass. The resulting 3D-RTNDA film not only facilitates close contact with mixed-ion perovskite (Cs0.05(FA0.83MA0.17)0.95Pb(I0.9Br0.1)3) film, but also promotes the formation of a perovskite layer with larger crystal grain sizes. Both can efficiently retard the interface charge recombination, and thus result in a significantly improved power conversion efficiency (PCE) of 18.0%, improved by 20% as compared to that (15.0%) of the device fabricated with the 1D-RTNRA film. Spectroscopic, electrochemical and photoelectrochemical measurements indicate that the improved photovolatic performance can be mainly ascribed to the largely suppressed hysteresis effect, the increased open-circuit voltage and fill factor stemming from the more effective hole blocking and electron transport. The results presented here demonstrate that 3D-RTNDA film with 3D rutile TiO2 hierarchical nanoarchitecture is a promising ETL selection in designing high-performance PSCs.

Influence of Rutile-TiO2 nanorod arrays on Pb-free (CH3NH3)3Bi2I9-based hybrid perovskite solar cells fabricated through two-step sequential solution process

The organic–inorganic perovskite compound (CH3NH3)3Bi2I9 (MBI) has lower toxicity and higher stability than lead-based perovskite. In this work, we fabricated MBI perovskite-based solar cells (PSCs) through a two-step sequential-solution process by using rutile TiO2 nanorod array (NRA) films as the electron transporting layer (ETL) for the first time. The thickness, roughness, and crystal structure of the rutile TiO2 NRAs prepared by hydrothermal method with different reaction times were thoroughly characterized and correlated with the photovoltaic performance of PSCs. Results of morphological and structural analyses, as well as time-resolved photoluminescence studies, indicated the effect of TiO2 NRA film thickness on the carrier recombination and photovoltaic performance of MBI-based PSCs. The MBI-based device was also stable in an environment with >50% humidity for more than 67 days.

Cu2O clusters decorated on flower-like TiO2 nanorod array film for enhanced hydrogen production under solar light irradiation

Abstract In this work, the TiO2 nanorod arrays (TNAs), TNAs/Cu2O-10CYC, and TNAs/Cu2O-30CYC composites photo-catalysts for solar water splitting anode was successfully prepared via cyclic impregnation growth method. The structure, surface morphology and element chemical states have been investigated and discussed in detail. The UV–vis and PL results confirm that interaction has been formed between TNAs and Cu2O in the composite photo-catalysts and the TNAs/Cu2O composites exhibit broad spectrum absorption. Three factors affecting on the enhancement of solar light hydrogen production efficiency, e.g. enhanced UV-light absorption in solar spectrum, massive charge carrier generation and improved surface-interface reaction due to the absorbing visible light by the narrow band gap Cu2O and the injecting electrons into TiO2 conduction band, are proposed based on the experimental results. The TNAs/Cu2O-10CYC composite samples exhibit highest enhanced photocatalytic activities in the hydrogen production, which H2 evolution efficiency is about 4-fold higher than that of pure TNAs. It indicates that the efficient photo generated electron-hole transformation and separation in TNAs/Cu2O-10CYC composite sample leads to the improvement of photocatalytic performance. The present study provides a new light to prepare TNAs/Cu2O of novel configuration with promising potential applications.

Synergistic Effect of Si Doping and Heat Treatments Enhances the Photoelectrochemical Water Oxidation Performance of TiO2 Nanorod Arrays

TiO2 is a very promising photocatalytic material due to its merits including low cost, nontoxicity, high chemical stability, and photocorrosion resistance. However, it is also known that TiO2 is a wide bandgap material, and it is still challenging to achieve high photocatalytic performance driven by solar light. In this paper, silicon‐doped TiO2 nanorod arrays are vertically grown on fluorine‐doped tin oxide substrates and then are heat treated both in air and in vacuum. It is found that the silicon doping together with the heat treatment brings synergic effect to TiO2 nanorod films by increasing the crystallinity, producing abundant oxygen vacancies, enhancing the hydrophilicity as well as improving the electronic properties. When used as photoanodes in photoelectrochemical water splitting, under the condition of AM 1.5G simulated solar irradiation and without using any cocatalysts, these nanorod films show photocurrent density as high as 0.83 mA cm−2 at a potential of 1.23 V versus reversible hydrogen electrode, which is much higher than that of the TiO2 nanorod films without doping or heat treating. The silicon‐doped TiO2 nanorod array films described in this paper are envisioned to provide valuable platforms for supporting catalysts and cocatalysts for efficient solar‐light‐assisted water oxidation and other solar‐light‐driven photocatalytic applications.

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.