Activity Of TiO2 Nanotube Arrays Research Articles

Facile fabrication of SnO2/TiO2 nanotube arrays for efficient degradation of pollutants

Herein, an efficient Z-scheme SnO2/TiO2 nanotube arrays (NTAs) was synthesized through a facile solvothermal method. The investigation indicates that SnO2 can improve the photoelectrocatalytic (PEC) activity of TiO2 NTAs, the photocurrent density of 0.07-SnO2/TiO2 NTAs can reach 0.94 mA cm−2, which is 4.48 times higher than that of TiO2 NTAs. The PEC degradation efficiency of MB and RhB (5 mg·L−1) is 94.71% and 80.58% over 0.07-SnO2/TiO2 NTAs after 90 min under 300 W Xe lamp irradiation, and the film-shaped 0.07-SnO2/TiO2 NTAs maintains a stable PEC performance during four times of recycling without a complex separation process. Based on the energy band structures analysis and the radical trapping experiments, the boosted PEC activity is benefited from a Z-scheme charge transfer route between SnO2 and TiO2 NTAs, which can inhibit the charge recombination and maintain the strong redox capacity of electrons and holes. This work provides a simple way to construct film-shaped TiO2 based heterojunction in PEC technology for environmental pollution remediation.

Preparation and photocatalytic activity of TiO2 nanotube arrays prepared on transparent spinel substrate

TiO2 nanotubes (TNTs) were prepared on transparent spinel (MgAl2O4) ceramic material by anodic oxidation of magnetron sputtered Ti layer. The properties of TNTs were compared with nanotubes produced on other three different substrates, Si wafer, polymeric Kapton film, and Ti foil. The photocatalytic activity of TNTs was tested by the removal of two model pollutants rhodamine B (RhB) and bisphenol A (BPA). Depending on the used substrate, the efficiency of TNTs in the degradation of both pollutants increases in the order of Kapton < spinel < Si < Ti. Nanotubes grown on Ti foil exhibited the best photocatalytic activity reaching 88% for the removal of RhB and 36% for the removal of BPA. The degradation rates of RhB could be well described by the pseudo-first order reaction, while the degradation of BPA could be better fitted with fractional first-order kinetic model. The calculations of residual stresses and deformations in the prepared materials with TNT surface layer showed that the composite with spinel substrate is the most stable structure with minimal warping of the laminate.

Study on the morphology and photocatalytic activity of TiO2 nanotube arrays produced by anodizing in organic electrolyte with Ni, Na, and C as dopants

The main purpose of this research work is to investigate the effect of nickel as metal dopant on the morphology and photocatalytic activity of TiO2 nanotube arrays synthesized in the organic electrolyte by anodizing process containing sodium carbonate as an additive (TNAS). In order to characterize the synthesized nanotubes, various analyses such as FESEM, XRD, FTIR, XPS, DRS, and EIS were applied. The results of XPS and FTIR tests evaluate the participation of sodium (Na), nickel (Ni), and carbon (C) in the lattice of nanotubes as dopants. According to the DRS and UV-visible tests results, the band gap energy of TiO2 nanotube arrays decreases from 3.20 to ~ 2.64 eV as well as the absorption edge extends from UV-light region (396 nm) to visible light region (510 nm). However, the photocurrent density of doped TiO2 nanotubes increased about 10 times higher than that of the pristine compounds.

Band-gap narrowing and electrochemical properties in N-doped and reduced anodic TiO2 nanotube arrays

Electrochemical activity of TiO2 nanotube arrays (NTAs) is restricted by a wide band gap of TiO2. To overcome this restriction, we considered systematic research on two effective methods of doping of TiO2 NTAs such as the N-doping and electrochemical reductive doping and predicting the proper application of them. Band gap narrowing was occurred from 3.16 eV for undoped TiO2 NTAs to 2.9 and 2.7 eV at N-doped and self-doped TiO2 ones respectively. The electrochemical responses of the TiO2 NTAs before and after doping were examined by cyclic Voltammetry (CV) curve. To understand the electrochemical behavior of the undoped and doped TiO2 NTAs, electrochemical impedance spectroscopy (EIS) was used and three equivalent circuit models were also built. The results showed that the undoped TiO2 NTAs is not strictly capacitive but a small quantity of N in TiO2 remarkably decreases the surface resistance of TiO2 electrode. In contrast, self-doped TiO2 NTAs resistance is reduced to very negligible contents of 0.0001322 Ωcm−2, that not only self-doped sample becomes to completely capacitive but also, it leads to the semiconductor nature of TiO2 NTAs transforms to semi-metallic one, and the two orders of enhancement in capacitance of blue TiO2 NTAs are very astonishing and it has outstanding potential for applications like supercapacitors as the electrochemical response of the self-doped TiO2 NTA sample was found to be a content of about 7 mF cm−2 that it is improved about 20 times compared with undoped one. Furthermore, it was found that doping of TiO2 NTAs with nitrogen atoms increases the carrier density about 2.82 × 1021 and self-doped TiO2 NTAs show the higher carrier density about 1.14 × 1025 compared with N-doped NTAs. These finding help to understand the mechanism of doping in two different methods and select the best one in relevant applications.

Facile Preparation and High Activity of TiO2 Nanotube Arrays toward Oxygen Reduction in Alkaline Media

Four TiO2 electrodes have been investigated for the oxygen reduction reaction (ORR) in 2 M NaOH. Anodic oxidation of Ti-foil was used as the final or the first step in the preparation of four electrodes based on TiO2: amorphous (Ti/AM-TiO2), two anatase forms (Ti/A400-TiO2 and Ti/A550-TiO2), and, finally, lithium-anatase form (Ti/A-Li0.25TiO2), all of them obtained as TiO2 nanotube arrays. The electrodes’ structure was examined by Raman spectroscopy. Cyclic voltammetry and chronoamperometry were employed for the study of kinetics of ORR. Ti/A-Li0.25TiO2 and Ti/A400-TiO2 electrodes showed the highest catalytic activity for ORR with the highest cathodic peak current density and the lowest Tafel slope values. Number of electrons exchanged during ORR at TiO2 electrodes was in the range from 2.3 to 2.8. Additionally, TiO2 electrodes showed good stability as well as acceptable selectivity in the presence of borohydride, methanol or ethanol as typical fuels for fuel cells. Thus this study introduces a simple, low-cost preparation route of TiO2-based electrodes with high efficiency for ORR for energy conversion and storage applications.

Effect of sodium carbonate as an additive on the morphology and photocatalytic activity of TiO2 nanotubes

The major purpose of this research is increasing the photocatalytic activity of TiO2 nanotube arrays by doping with sodium and carbon for using in water splitting as photoanode. The synthesized TiO2 nanotubes (TNA) were characterized using FESEM (Field Emission Scanning Electron Microscope), XRD (X-ray Diffraction), DRS (Diffraction Reflection Spectroscopy) and XPS test (X-ray Photoelectron Spectroscopy) analyses. The results of FTIR and XPS confirmed the presence of sodium and carbon in the lattice of TNA as dopants. Moreover, the DRS test showed the decrease in the band gap energy of TNA from 3.20 to ∼2.88eV; uv-visible test exhibited extension in the absorption edge of pure TiO2 nanotubes from Uv-light (396nm) to visible light (488nm). In addition, the results of photoelectrochemical measurement indicated that the photocurrent density of doped TiO2 nanotubes increased about 5 times than that of the pure compounds.

Understanding the effect of plasmonic enhancement on photocatalytic activity of TiO2 nanotube arrays

Plasmonic effects in wide-bandgap photocatalysts loaded with noble metal nanoparticles (NPs) have been shown to enhance visible light absorption as well as charge transfer. TiO2 owing to its superior photostability, abundance and non-toxcitiy, especially in form of nanotube arrays (NTAs) to maximize surface interactions, has been often used as a photoactive template. However systematic studies of photoelectrochemical properties in plasmonic TiO2 NTAs are rare and usually involve Au NPs only. Here, we examine the effect of Ag NP loading of TiO2 NTAs via photoreduction of different concenrations of AgNO3 (20mM–1100mM) in order to establish the optimum value at which photoactivity is maximal. Remarkably, the system prepared from 200mM aqueous solution were found to exhibit an unprecedented 680-fold increase in photocurrent density as compared to the bare anatase NTAs (0.041mA·cm−2 versus 0.06μA·cm−2). Furthermore, hydrogen evolution under AM 1.5G illumination was improved by 350% from 40μL·cm−2 in pristine anatase NTAs to 180μL·cm−2 in optimally decorated NTAs.

Effect of irradiation intensity and initial pollutant concentration on gas phase photocatalytic activity of TiO2 nanotube arrays

Well-organized TiO2 nanotube arrays were fabricated via one-step anodization process. The as-prepared TiO2 nanotubes were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM). Photocatalytic activity of obtained photocatalyst was studied in reaction of toluene degradation in the gas phase using low powered and low cost light-emitting diodes (UV LEDs) as an irradiation source. The effect of irradiation intensity and initial pollutant concentration on gas phase photoactivity of TiO2 nanotubes was analyzed. Obtained TiO2 nanotubes were smooth and vertically oriented with a length of about 1.7±0.05μm. The inner diameter and the wall thickness were 65±2nm and 6±0.4 nm, respectively. The results showed that the initial toluene degradation rate increased (from 0.0062 up to 0.0567μmol/min) with raising initial toluene concentration (50–400ppm), while too high dose of irradiation (about 50mW/cm2) reduced photocatalytic toluene degradation rate. The best stability of TiO2 nanotubes in three subsequent irradiation cycles was observed for irradiation intensity of 38mW/cm2. Moreover, it was found that photocatalytic toluene degradation over TiO2 nanotubes showed first order kinetic behavior.

The Synthesis and Photocatalytic Properties of TiO2 Nanotube Array by Starch-Modified Anodic Oxidation.

In this study, the characterization and photocatalytic activity of TiO2 nanotube arrays prepared by anodization process with starch addition were investigated in detail. The results suggested that the optimum mass fraction of starch added in anodization process was 0.1%, with which TiO2 nanotube arrays owning good tubular structure were synthesized. The tube length and average inner diameter of nanotubes were approximately 4μm and 30nm, respectively. Through the characterization of TiO2 nanotube arrays by energy dispersive spectrometer, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy, it was found that the as-prepared nanotubes possessed well uniformed and higher photodegradation responsive than the pure TiO2 . Moreover, it was expected that the as-prepared nanotubes exhibited good photocatalytic activity for the degradation of RhB under UV-light irradiation, which could be ascribed to their good morphology, enhanced UV-light absorption property and electron transmission ability during the photocatalytic reaction. In addition, the nanotubes were not significantly regenerated during the cycling runs experiment. Overall, this study could provide a principle method to synthesize TiO2 nanotube arrays with enhanced photocatalytic activity by anodization process with starch addition for environmental purification.

The influence of geometrical characteristics on the photocatalytic activity of TiO2 nanotube arrays for degradation of refractory organic pollutants in wastewater.

The effects of geometrical characteristics such as surface area (SA) and porosity of TiO2 nanotube arrays (TNAs) on its photocatalytic activity were investigated by applying variable voltages and reaction times for the anodization of Ti substrates. While larger SA of nanotubes was observed under higher applied potential, the porosity of TNAs decreased by increasing anodizing voltage. Under applied potential of 80 V, the SA of TNAs increased from 0.164 to 0.471 m2/g as anodization time increased from 1 to 5 hours, respectively. However, no significant effect on the porosity of TNAs was observed. On the other hand, both SA and porosity of TNAs, synthesized at 60 V, increased by augmenting the anodization time from 1 to 3 hours. But further increasing of anodization time to 5 hours resulted in a decreased SA of TNAs with no effect on their porosity. Accordingly, the TNAs with SA of 0.368 m2/g and porosity of 47% showed the highest photocatalytic activity for degradation of 4-chlorobenzoic acid (4CBA). Finally, the degradation of refractory model compounds such as carbamazepine and bisphenol-A was tested and more than 50% of both compounds could be degraded under UV-A irradiation (λmax=365 nm).

Photoelectrochemical activity and its mechanism of mesoporous TiO2 nanotube arrays prepared with chemical etching method

Mesopores are etched in the tube walls of TiO2 nanotubes, which can enhance the photoelectrochemical activities of TiO2 nanotube arrays (NTAs).

Construction of Mn0.5Zn0.5Fe2O4 modified TiO2 nanotube array nanocomposite electrodes and their photoelectrocatalytic performance in the degradation of 2,4-DCP

Mn0.5Zn0.5Fe2O4 contributes to the enhanced photoelectrochemical properties and photoelectrocatalytic activity of TiO2 nanotube arrays.

An insight into the influence of morphology on the photoelectrochemical activity of TiO2 nanotube arrays

In this study, we demonstrate the evolution of morphology and band gap tuning of TiO2 nanotube (TNT) arrays by an electrochemical anodization method. Both XRD and Raman spectra confirm the crystallinity of TNT arrays in a phase pure anatase form. The crystallinity of TNT increases up to the anodization time of 60min and with further increase in time, the crystallinity decreases due to the destruction of tubular structures. By increasing the anodization time, the optical absorption of TiO2 is extended up to the visible region. The well defined visible light photoluminescence emissions reveal the structural defects, oxygen vacancies (F or F2+, F+) and radiative recombination sites created within the band gap. The nanotubes fabricated at an anodization time of 60min show the highest photoconversion efficiency of 11.86% in the potassium hydroxide (KOH) electrolyte containing ethylene glycol.

Significance of crystallinity on the photoelectrochemical and photocatalytic activity of TiO2 nanotube arrays

Abstract We report the significance of crystallinity on photoelectrochemical and the photocatalytic degradation of methyl orange of titanium dioxide (TiO2) nanotube arrays. The TiO2 nanotube arrays are fabricated by electrochemical anodization of titanium substrates in fluoride based aqueous electrolyte for various anodization time. The degree of crystallinity and phase purity (anatase) is confirmed from X-ray diffraction and Raman spectra. High resolution scanning electron microscope is used to analyze the surface morphology of forming nanotubes. The UV–vis absorption spectrum shows the enhanced absorption in the visible region which is further confirmed using photoluminescence spectra. The photoelectrochemical properties of the prepared samples are studied from linear sweep photovoltammetry measurements and a maximum photocurrent density of 1.32 mA/cm2 is observed. The enhanced photoelectrochemical activity is attributed to the higher crystallinity which increases the charge carrier separation and extends its light absorption from ultraviolet to visible region owing to lower band gap of 2.751(7) eV.

Enhanced visible light photocatalytic activity of TiO2 nanotube arrays modified with CdSe nanoparticles by electrodeposition method

Highly ordered TiO2 nanotube arrays (NTAs) were fabricated on titanium substrate via electrochemical anodization method. CdSe nanoparticles were deposited on the TiO2 NTAs through the electrodeposition process. The influence of electrolyte concentration and deposition time on the visible light photocatalytic performance of CdSe/TiO2 NTAs was studied systematically. The photocatalytic activity of as-prepared samples was evaluated by degradation of methyl orange under visible light irradiation. The results indicated that the CdSe nanoparticles distributed uniformly on the surface of TiO2 NTAs when deposited in the electrolyte containing 0.02M CdCl2, 2mM SeO2 and 0.02M Na2SO4 with time of 600s. After irradiation under visible light for 2h, the degradation rate of CdSe/TiO2 NTAs composite material reached 94.4%, while the degradation rate of unmodified TiO2 NTAs was only 6.2 % under the same condition, demonstrating that the CdSe/TiO2 NTAs exhibited higher photocatalytic activity in visible light region. In addition, a reasonable degradation rate of 80.96% was achieved even after being used for 5 times.

Visible-Light Illumination Enhanced Hydrogen Evolution on CuO Modified TiO&lt;sub&gt;2&lt;/sub&gt; Nanotube Arrays/Ti Electrocatalyst

TiO2 nanotube arrays (TNAs) modified by CuO (CuO-TNAs) catalysts were prepared by an impregnating-calcinating method using the electrochemically prepared TNAs and Cu (NO3)2 as precursors and were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction spectroscopy and UV-visible spectroscopy. The electrocatalytic properties of the CuO-TNAs samples for hydrogen evolution reaction (HER) were investigated by linear sweep curves, electrochemical impedance spectrum and current-time curves. The results showed that the electrocatalytic activity of TNAs for hydrogen evolution reaction (HER) was significantly enhanced by CuO modification, and the electrocatalytic activity of CuO-TNAs catalysts could be further promoted by visible-light illumination. The combination of visible-light irradiation with applying a controlled potential may provide new insight into enhancing the performances of the cathode for hydrogen evolution reaction.

A Novel Approach to Well‐Aligned TiO2 Nanotube Arrays and Their Enhanced Photocatalytic Performances

A simple route has been developed to prepare well‐aligned TiO2 nanotube arrays, which is based on outward coating of TiO2 and inward etching of Cu(OH)2 nanorod templates. Effects of annealing temperature and time on the crystal size and crystallinity of TiO2 nanotube arrays and photocatalytic activities of TiO2 nanotube arrays for degradation of Rhodamine B in aqueous solution have been investigated. The results indicate that the TiO2 nanotube arrays annealed at 500°C for 2 h possessed an enhanced photocatalytic activity in comparison with the TiO2 nanotube arrays without post heating and commercial anatase TiO2 nanoparticle film and presented a good life cycle performance. Scale‐up of the process has also been demonstrated. Our work opens a new avenue to fabricate free‐standing TiO2 nanotube arrays and demonstrates an excellent photocatalytic performance of the anatase TiO2 nanotube arrays for wastewater treatment. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2134–2144, 2013

Theoretical Kinetic Analysis of Heterogeneous Photocatalysis by TiO2 Nanotube Arrays: the Effects of Nanotube Geometry on Photocatalytic Activity

TiO2 nanotube arrays are important functional materials in photocatalysis. Compared with other TiO2 materials, the geometrical parameters of the nanotubes in an array significantly affect photocatalytic activity, but how they do this remains unclear. In the present work, a simple theoretical kinetic model to study the effects of nanotube diameter, wall thickness, and length on the photocatalytic activity of TiO2 nanotube arrays is developed, in which reactant (O2) transport is considered. The photocatalytic activity first increases and then decreases as the diameter and wall thickness of the nanotubes increase because of changes in light absorption, surface area, and reactant transport. The photocatalytic activity increases, and then reaches saturation as the nanotube length increases, which is mainly influenced by the change of light absorption along the nanotube. The present kinetic model agrees well with experimental results and clearly explains the photocatalytic activity of TiO2 nanotubes, helping us...

X-ray photoelectron spectroscopic studies of anodically synthesized self aligned TiO2 nanotube arrays and the effect of electrochemical parameters on tube morphology

Self aligned TiO2 nanotube arrays, compared to other TiO2 nanostructures, have better electron transport properties that will enhance the efficiency of photo catalysis, hydrogen generation by photo-electrolysis and dye sensitized solar cells. Optimization of process parameters by tuning of electrochemical parameters allows the synthesis of TiO2 nanotube arrays of desired aspect ratio, wall thickness and morphology. In this study TiO2 nanotube arrays were synthesized at various electrochemical parameters and characterized using field emission scanning electron microscopy (FESEM), Fourier transform infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS). From the results of the study optimum potential range, electrolyte compositions and duration of anodization for the fabrication of smooth walled nanotube arrays of desired aspect ratio are delineated. Presence of surface hydroxyl groups and non-stochiometry in the as prepared and annealed TiO2 nanotubes were found from FTIR and XPS studies respectively, thus providing rationalization for the enhanced photo catalytic activity of TiO2 nanotube arrays.