Highly-ordered TiO2 Nanotube Arrays Research Articles

Preparation of TiO2 Nanotube Using Anodization Method: Charactherization and Its Application for CO Sensor

Preparation of highly ordered TiO 2 nanotube arrays (HOTNAs) by anodization of Ti foil industrial grade in ethylene glycol electrolyte containing 0.3% of ammonium fluoride and 2% of water at 30 V for 90 minutes was conducted. The morphology structure, chemical composition, functional group, crystal phase, and optical properties of HOTNAs were characterized by field emission scanning electron microscope (FE-SEM), Energy Dispersive X-Ray (EDX),Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), and ultraviolet visible diffuse reflectance spectroscopy (UV/Vis-DRS). The well-ordered nanotube with vertically oriented structure was formed in the HOTNAs having size in diameter, length, and wall thickness of 48,0 nm, 1,8 µm, and 26,7 nm, respectively. The fabricated HOTNAs were evaluated for their sensing properties for CO detection. The results show that the fabricated HOTNAs were able to detect 2500 ppm of CO gas with response about 93,429 at operation temperature 150 ° C. This preliminary study of sensing performance demonstrates that the prepared HOTNAs under this study is potential and promising as a material sensor for CO detection.

Highly sensitive and selective H2O2 sensors based on ZnO TFT using PBNCs/Pt-NPs/TNTAs as gate electrode

A highly sensitive and selective sensor is urgently needed in many practical H2O2 detection, such as water quality monitoring, quality control of food products, and so on. However, the traditional three electrode system limits its further development in recent years due to its difficulty in miniaturization and integration. To effectively improve its sensitivity and selectivity, highly-ordered TiO2 nanotube arrays (TNTAs) are modified with Pt nanoparticles and Prussian blue (PB) nanotubes and creatively combines with thin-film transistor (TFT) based on ZnO to prepare an electrochemical sensor. The sensor uses PBNCs as recognition units for the specific detection of H2O2, and the generated electrical signal is amplified by TFT. Thus, a highly sensitive and selective H2O2 sensor is achieved. The detection limit of the sensor is as low as 5.19 nM, which is three orders of magnitude lower than the conventional electrochemical detection methods using the same electrode. The sensor also possesses wider linear detection range of 0.1–50 μM and 50 μM–5 mM comparable to that of other reported H2O2 sensors. Besides, the sensor has good selectivity for H2O2 in the presence of common interferences such as ascorbic acid, uric acid, glucose, and dopamine. Furthermore, the device presents good reproducibility and exhibits good long-term stability over 27 days of continuous measurement. This study offers important insights for the rational design of sensors with high sensitivity and selectivity.

Synthesis of NiO/TNTs p-n junction for highly photocatalysis activity under sunlight irradiation

Highly-ordered TiO2 nanotube arrays (TNTs) were successfully synthesized on a Ti foil using a cost-effective two-step electrochemical anodization, into which NiO nanoparticles (NPs) were decorated uniformly using ultrasound-assisted deposition, forming NiO/TNTs p-n junctions. These nanostructures were characterized by X-ray Diffraction, Field Emission Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy, and Photoluminescence spectra. The photocatalytic activity of pure TNTs and NiO/TNTs samples was evaluated through the photodegradation of RB dye as a pollutant model under sunlight irradiation. Results demonstrated that the photodegradation efficiency of pure TNTs and NiO/TNTs samples were 77% and 97.1%, respectively. NiO/TNTs p-n junction showed higher photodegradation efficiency in comparison to pure TNTs; and this improvement may be attributed to the influence of NiO NPs that can enhance separation of charge carriers. The mechanisms of formation of NiO/TNTs p-n junctions and the influence of NiO NPs on their photocatalytic activity were also discussed.

Photo-electrochemical properties of TiOs2 nanotube arrays: effect of different polishing method of Ti substrate prior to anodization in fluoride-H2O2-containing electrolyte

The comparison of two pre-treatment methods, such as mechanical polishing and chemical polishing, prior to anodization of titanium surface in the ethylene glycol based electrolyte containing H2O2, were carried out to investigate their effects on photo-electrochemical property of produced highly ordered TiO2 nanotube arrays (HOTNAs). The Ti-chemical polishing was conducted in electrolyte containing H2O2 (0.6% H2O2/1.4% H2O). The prepared HOTNAs were characterized by FT-IR, UV-Vis DRS and SEM. The obtained FTIR spectrum, showed vibration band at 1100 and 425 cm−1, give strong indication on the existent of a -Ti-O-Ti-network. While from UV-Vis DRS spectra, the band gap of the fabricated HOTNAs were found in the range of 3.10-3.22 eV, which are characteristics for anatase phase. In addition, obtained SEM image indicates the existence of quite good ordered nanotube arrays morphology. Linear sweep voltammetry (LSV) measurement showed that the steady state photocurrent density of HOTNAs fabricated by Ti-chemical polishing were greater than that of prepared by Ti-mechanical polishing. The increasing of H2O2 content in electrolyte (1.5% H2O2/3.5% H2O) affected to the enhancement of steady state photocurrent density of HOTNAs. Thus pre-treatment of the Ti foils using chemical polish method does enhance its photo-electrochemical property.

Enhanced photoelectrochemical performance of TiO2 nanotube arrays with coexisted Pt nanoparticles and Co-Pi cocatalysts

Highly-ordered TiO2 nanotube arrays (TNTAs) were prepared by electrochemical anodization. Cobalt-phosphate (Co-Pi) film fabricated by electrodeposition and Pt nanoparticles (Pt NPs) fabricated by photochemical reduction were decorated onto TNTAs to enhance the photoelectrochemical (PEC) performance together. The photocurrent density of the TNTAs/Co-Pi/Pt photoelectrode could reach 0.185mA/cm2 at 1.23V versus reversible hydrogen electrode under UV lamp illumination (1mW/cm2), which is 2.65 times compared to that of the pure TNTAs photoelectrode. Electrochemistry impedance spectroscopy and Mott-Schottky analysis were conducted to explore the reasons for the enhancement of the PEC performance. Pt NPs could promote the reduction of Co(Ⅳ)-oxo intermediate to Co(II) or Co(Ⅲ) which facilitated the charge transfer in the PEC performance. The result provides a promising guideline to design a simple and efficient photoelectrode for the PEC water-splitting system.

Visible light active Ce/Ce2O/CeO2/TiO2 nanotube arrays for efficient hydrogen production by photoelectrochemical water splitting

Highly-ordered TiO2 nanotube arrays (TNTs) were fabricated by Ti sheet by electrochemical anodization. Ce and its oxide could be loaded on TNTs as cocatalysts for water splitting electrode. SEM, XRD and XPS indicated that the Ce and its oxide were a mixture of Ce, Ce2O3 and CeO2 and dispersed upper and inner TNTs. The Ce/Ce2O3/CeO2/TiO2 nanotube arrays showed stronger photocurrent response, higher photoconversion efficiency (PCE) for hydrogen generation and lower flat band potential (Efb) than TiO2 nanotube arrays. The photoelectrochemical cell (PEC) with anode and cathode separate compartments was implied for hydrogen generation. Photoelectrochemical hydrogen production from pure water was demonstrated without external voltage using Ce/Ce2O3/CeO2/TNTs semiconductor electrode. By adding ethylene glycol in anode electrolyte and at E = 0.7 V (vs. open circuit potential) bias voltage, the photocurrent density reached 11.2 mA cm−2, PCE for 6.1% and the average hydrogen production rate for 5 mL h−1 cm−2 under 450 W Xe lamp illumination. Moreover, a stable H2 generation property was studied in the visible light region. Meanwhile, the respective modification mechanism of Ce/Ce2O3/CeO2 cocatalysts for improving hydrogen production rate of TNTs was discussed in detail.

ZnO modified TiO2 nanotube array supported Pt catalyst for HCHO removal under mild conditions

Highly-ordered pore-through TiO2 nanotube arrays (TiNT) are modified with ZnO and then used as the support for a Pt/ZnO/TiNT catalyst. The Pt/ZnO/TiNT is applied to the trace HCHO oxidation under mild conditions. In comparison with the Pt/TiNT without ZnO modification, monolith-like Pt/ZnO/TiNT shows higher activity under parallel preparation and test conditions. A HCHO conversion of 95% with more than 100h stable performance is achieved over 0.2wt.% Pt/ZnO/TiNT at 30°C. The effect of ZnO modification on the structural properties and catalytic performance of Pt/ZnO/TiNT are investigated. The superior performances are related to the enhanced HCHO storage capacity of ZnO/TiNT support, the specific monolith-like structure and the modified metal–support interaction in Pt/ZnO/TiNT.

Optical and Morphological Properties of TiO<sub>2</sub> Nanotubes for Sensor Applications

Highly-ordered TiO2 nanotube arrays were fabricated by electrochemical anodizing, using titanium foils as the anode and cathode and changing the amount of fluoride (NH4F) in the solution. The effect of synthesis parameters, such as, ethylene glycol solutions containing different amounts of water, NH4F, anodizing voltage, and current density were studied on the optical and morphological properties. It was observed from XRD espectra, that Anatase and Rutile phases were influenced by annealing, between 300 and 723 K, for all the samples, while morphological changes were not observed. Nanotubes diameters varying beteween 20 and 50 nm with diferent length sizes were observed from SEM micrographics. A high absorption for the UV region and a gap band round of 3.1 eV were obtained from spectrophotometry measurements. The correlation between the synthesis parameters and the optical properties presented are an excellent indicator for the TiO2 nanotubes application as optical sensors.

Synthesis of highly-ordered TiO2 nanotube arrays with tunable sizes

Vertically-oriented one-dimensional TiO2 nanotube (TNT) arrays have been fabricated by anodic oxidation using different electrolyte solvents, including ethylene glycol (EG), diethylene glycol (DEG), and dimethyl sulfoxide (DMSO), in the presence of hydrofluoric acid (HF) or ammonium fluoride (NH4F). The influence of synthetic conditions, including the nature of the electrolyte and anodization voltage, on nanotube microstructure has been systematically investigated. Highly-ordered TNTs with tube length of ∼0.5–26.7 μm, inner diameter of ∼13–201 nm, and outer diameter of ∼28–250 nm have been obtained. The conversion of as-prepared TNT arrays from amorphous phase to crystalline structure has been achieved by a post-synthetic annealing at 500 °C for 3 h in oxygen ambient. The TNT arrays with tunable sizes and structures are attractive for use as electrode materials in fabrication of thin film solar cells and highly active photocatalysts.

Fabrication and photoluminescence properties of ridged TiO2 nanotube arrays

Highly-ordered ridged TiO2 nanotube (TNT) arrays have been fabricated by a simple anodic method. Their structures have been systematically investigated using X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer and HRTEM, and the results clearly presented the ridged morphologies with the outer diameters of about 200 nm. We also found that the annealing procedure induced the phase transformation from amorphous phase to anatase phase. The room-temperature photoluminescence (PL) properties were studied, and the much stronger PL emission for the anatase phase was observed compared to the amorphous counterparts. Furthermore, the broad emission for the anatase phase could be decomposed of three peaks locating at 540, 622 and 773 nm, respectively. The oxygen vacancies and the trapping of free excitons by TiO6 octahedra near defects are the key factors to cause these peaks.

Influence of Pt deposition on water-splitting hydrogen generation by highly-ordered TiO2 nanotube arrays

Highly-ordered TiO2 nanotube arrays (TNTAs) were fabricated on Ti sheets by electrochemical anodization. Uniform Pt nanoparticles with an average diameter of 3 nm could be successfully located on the TiO2 nanotubes on only one side (Pt/TNTAs) or both sides of the Ti sheet (Pt/TNTAs/Pt). Pt/TNTAs, the single-sided Pt deposited TNTAs, could be directly used to split water without a counter electrode. The hydrogen evolution rate can reach 120 μmol h−1 cm−2 in a mixed solution of 0.5 M Na2SO4 and 0.5 M ethylene glycol without any applied bias, which is six times of that by the pure TNTAs. In comparison to the traditional three electrode system, this single-sided Pt deposited TNTAs is a much more simple and efficient water splitting system. Meanwhile, the photoelectrical conversion mechanism has been investigated in detail.

Electrochemical Investigation on the Interface between Electronically Conducting Polymer and Titania Nanotube Arrays

Electronically conducting polymers (ECP) can be deposited on different types of substrate such as metals[1] or semiconductors. Heterostructures made from inorganic oxides and ECP have been widely exploited with the aim of diverse applications (photovoltaic cells, photocatalysis[2], Li-ion batteries[3], etc.). Among metal oxides, titanium (IV) dioxide is of particular interest. In addition to its ability to store reversibly Li+ and its chemical stability, TiO2can be easily nanostructured by anodization of a Ti foil.A way to improve metal oxide performances is to control their morphology at the nanoscale[4]. In fact, using highly-ordered TiO2 nanotube arrays (TiO2-NTAs) as the substrate for electropolymerization does provide a high surface area for polymer deposit, vertical pathways for electron transport and leads to the formation of a high density of surface states that influences the interfacial electron-transfer process[5].TiO2 is a n-type semiconductor with an energy band gap of about 3.2 eV. Under UV illumination, it generates charges and especially holes that can oxidize species adsorbed at its surface. Consequently, electrodeposition of polymers such as polypyrrole is a photo-assisted process. Moreover, when exposed to UV light in an aqueous solution, the doping level of TiO2 increases and so does its conductivity[5,6].Physicochemical properties of deposited layers depend on the substrate, the method of synthesis, the solvent, the doping anion and the pH of the solution [7]. In the present communication, we describe the photo-assisted synthesis of electroactive polypyrrole films in TiO2-NTAs under different conditions. The resulting heterostructures have been subjected to cyclic voltammetry measurements, electrochemical impedance spectroscopy, FEG-SEM and Raman spectroscopy.The results of this work emphasize the role of UV light illumination during electropolymerization and the role of the electrolyte anion. It is also shown that a 3D hybrid junction can be achieved between TiO2-NTAs and polypyrrole which is an ECP. Both electrochemical impedance spectroscopy and cyclic voltammetry evidence the fact that the two materials may form an ohmic junction. Moreover, the polypyrrole growth implies a thickening of the film without any further spreading out on the TiO2-NTAs substrate, the TiO2/PPy junction providing a preferential path for electron transfer. References (1) Hien, N.T.L.; Garcia, B.; Pailleret, A. ; Deslouis, C. Electrochimica Acta (2005), 50, 1747-1755.(2) Luo Q, Li X, Wang D, Wang Y, An J. Journal of Materials Science (2011), 46(6):1646-1654.(3) Gemeay, A.H.; Nishiyama, H.; Yoneyama, H. J. Electrochem. Soc. (1995), 142, 4190-4195.(4) Allam N.K., Shankar K., Grimes C.A. Advanced Materials (2008), 20, 3942-3946.(5) Pu, P.; Cachet, H.; Ngaboyamahina, E.; Sutter, E.M.M. J. Solid State Electrochem. (2013), 17, 817-828.(6) Pu, P.; Cachet, H.; Laidani, L.; Sutter, E.M.M. J. Phys. Chem. C (2012), 116, 22139.(7) Castagno, K.R.L.; Dalmoro, V.; Azambuja, D.S. Materials chemistry and Physics (2011), 130, 721-726.

Effect of irradiation on deposition of CdS in fabricating co-axial heterostructure of TiO2 nanotube arrays via chemical deposition

Highly-ordered TiO2 nanotube arrays were synthesized electrochemically. Effect of irradiation on deposition of CdS in fabricating co-axial heterogeneous structure via chemical deposition was investigated. The field emission measurements revealed that irradiation with higher energy will help to achieve not only more CdS, but also neater and more intimate heterostructure through exerting influences on ion migration into the tubes and attachment of ions onto the tube walls. The XRD measurements revealed that the deposited nanotubes are composed of anatase TiO2, metallic Ti, and CdS. The optical characterization revealed that the photoabsorption and absorption activity are correlated with the energy of irradiation. The photoelectrochemical measurements revealed that the photocurrent density are also correlated with the energy of the irradiation. The stability of the obtained structures was governed by the contact between CdS and TiO2 as well as the amount of CdS.

New insights into the photo-enhanced electrocatalytic reduction of carbon dioxide on MoS2-rods/TiO2 NTs with unmatched energy band

In this paper, the highly-ordered TiO2 nanotube arrays (TiO2 NTs) were obtained by improved anodic oxidation method and the MoS2-rods were assembled to the TiO2 NTs by a facile hydrothermal method, obtained the MoS2-rods/TiO2 NTs heterojunction. According to the UV–vis DRS and XPS analysis, the obtained MoS2-rods/TiO2 NTs exhibited excellent absorption in the visible area (400–600nm) and its energy band gap was 1.55eV, but its conduction band (−0.15eV) was more positive than the CO2 reduction potential, it indicated that MoS2-rods/TiO2 NTs had no ability for photocatalytic reduction of CO2. Electrocatalysis could reduce CO2, but the products yield was very low and the faraday efficiency gradually reduced with reaction going on. Interestingly, when illumination was introduced into the electrocatalytic process, the light greatly enhanced the CO2 electrocatalytic reduction ability of the MoS2-rods/TiO2 NTs. Furthermore, the faraday efficiency increased to 2.65 times from 42.20% (electrocatalysis) to 111.58% (photo-enhanced electrocatalysis), and the methanol yield increased to 2.29 times from 6.32mmolL−1 to 14.49mmolL−1. The new insights for how light enhanced electrocatalytic reduction of CO2 was elaborated systematically from three aspects, that is, reduction overpotential, enhanced electron transmission ability, and generated p–n heterojunction. Furthermore, the generation mechanism of methanol with photo-enhanced electrocatalysis was also deduced. Especially, we deduced that the protons involving into the CO2 reduction came from two aspects, one was from the electrocatalytic oxidation water on the anode, and the other was from the in situ photocatalytic oxidation water on the cathode.

Fabrication of TiO<sub>2</sub> Nanotube Arrays in Ethylene Glycol Electrolyte by the Electrochemical Anodization Method

Highly-ordered TiO2 nanotube arrays were successfully fabricated by electrochemical anodization of titanium. The morphology of TiO2 nanotube arrays, the length and pore size were represented by field emission scanning electron microscopy (FE-SEM). The parameters of various anodization including F- concentration, reaction temperature and anodization voltage were investigated in detail. The results show that as-prepared TiO2 nanotube arrays possess good uniformity and well-aligned morphology in mixture of ethylene glycol and 0.3 wt% NH4F electrolyte at 40 V for 25 °C. The growth rates of TiO2 nanotube arrays can show activation energy.

Highly-ordered dye-sensitized TiO2 nanotube arrays film used for improving photoelectrochemical electrodes

Thin titanium oxide nanotube arrays (TNAs) films were synthesized by anodization of titanium foil in an aqueous dimethyl sulfoxide solution using a platinum foil counter electrode. TNAs up to 6.8 μm in length, 120 nm in inner pore diameter, and 20 nm in wall thickness were obtained by 40 V potentials anodization for 24 h. Their microstructures and surface morphologies were characterized by XRD, TEM, SAED and UV-vis spectroscopy. The photoelectrochemical properties of as-prepared unsensitized and dye-sensitized TNAs electrodes were examined under simulated solar light (AM 1.5, 100 mW/cm2) illumination. The results showed that the photocurrent of the dye-sensitized TNAs electrodes reached 6.9 mA/cm2, which was 6 times more than that of the dye-sensitized TiO2 nanoparticles (TNPs) electrodes. It implied that the electron transport process and the charge recombination suppression within TNAs electrodes were much more favorable in comparison with that in the TNPs electrodes. Electrodes applying such kind of titania nanotubes will have a potential to further enhance the efficiencies of TNAs-based dye-sensitized solar cells.

Effect of NH4F concentration in electrolyte on the fabrication of TiO2 nanotube arrays prepared by anodisation

Highly-ordered TiO2 nanotube arrays (TNTs) were prepared by anodisation in ethylene electrolytes containing 0.2–0.7 wt% NH4F. The dimension, chemical composition and optical characterisation of prepared TNTs were determined by the field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy, respectively. Both the length and inner diameter of the prepared TNTs were increased with increasing NH4F concentration of electrolyte because of the faster electrochemical dissolution rate of TiO2. However, dimension of TNTs approached stable lengths and inner diameters as the NH4F concentration was higher than 0.3 wt%. The presence of Ti3+ state was observed for TNTs prepared with increasing NH4F concentration because of the charge compensation of the substitution of fluoride ions for oxygen ions. TNTs prepared in the electrolytes containing higher NH4F concentrations exhibited superior performance on the photocatalytic decomposition of Acid Red 4 possibly because more fluorides incorporated with TNTs to inhibit the recombination of electron–hole pairs.

Highly-ordered TiO2 nanotube arrays with double-walled and bamboo-type structures in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) based on free-standing, double-walled TiO2 nanotubes with bamboo-like morphology have been prepared by a sequence of alternating voltage and two-step anodization treatments. The combination of double-walled and bamboo-like morphologies led to an increase in dye loading and an improvement in photoconversion performance. Subsequently, the fabricated dye-sensitized nanotubes used to prepare DSSCs that operate in a frontside illumination mode yielded a significantly high power conversion efficiency of 3.46%, which was approximately two times higher than DSSCs that were fabricated using traditional single-walled TiO2 nanotube arrays with smooth surfaces. In addition, DSSCs fabricated from nanotubes with higher bamboo ring densities exhibited better conversion efficiencies than those prepared from nanotubes with lower bamboo ring densities. The improved conversion efficiency can be attributed to increased dye loading in the combined double-walled and bamboo-like titania nanostructures.

Enhanced Visible Light Activity of Ag-Loaded TiO<sub>2</sub> Nanotube Arrays by AC Electrodeposition

In this work, highly-ordered TiO2 nanotube arrays were prepared by constant-voltage anodization, followed by electrodeposition of Ag to obtain Ag-loaded TiO2 (Ag-TiO2) nanotube arrays via alternating current (AC) process. The results of SEM and XRD show that the morphology and crystal structure of Ag-TiO2 layer depend greatly on the electrodeposition parameters. Ag-TiO2 nanotube arrays prepared in 2.5 mmol/L AgNO3 solution by electrodeposition with applied voltage of 12 V for 1 minute performed the best photoelectrochemical current response and photocatalystic activity. The photocurrent density of Ag-TiO2 is 43.32 μA/cm2 under sunlight irradiation (70 mW/cm2), which is 4.2 times as that of unloaded TiO2 nanotube arrays. Methyl orange (MO) degradation rate with the Ag-TiO2 nanotube arrays achieves 52.13% after 90 min sunlight irradiation which is obvious higher than that of TiO2 nanotube arrays. The mechanism of enhancing photoelectrochemical activity of decorating titania with Ag has also been discussed in the view of energy band theory.

阳极氧化法制备Y型TiO2纳米管

Highly-ordered Y-branched TiO2 nanotube arrays were fabricated on the Ti foils in ethylene glycol containing 0.5% NH4F(mass fraction)and 5% H2O(volume fraction) by a three-step electrochemical anodic oxidation via increasing the electrolyte temperature.The effect of pretreatment process on surface morphology and the growth mechanism of Y-branched TiO2 nanotubes were discussed.Four samples were fabricated by anodic oxidation at different temperature ranges of 20~60 ℃.The results show that phenomena such as annular nanowires,nanotube breach or length reduction etc.will appear in the surface morphology of Y-branched TiO2 nanotubes when electrolyte temperature is set at 40 ℃ or more in the third step of anodic oxidation,which is not conducive to ensuring the overall quality of Y-branched TiO2 nanotube arrays.However,the ideal temperature range is 30~40 ℃ in the third step during the anodizing process.