TiO2 NTs Research Articles

Formation of grassy TiO2 nanotube thin film by anodisation in peroxide electrolyte for Cr(VI) removal under ultraviolet radiation

Arrays of TiO2 nanotubes (TiO2 NTs) with grassy surfaces were observed on titanium foil anodised at 60 V in fluorinated ethylene glycol (EG) with added hydrogen peroxide (H2O2). The grassy surface was generated by the chemical etching and dissolution of the surface of the TiO2 NTs walls, which was accelerated by the temperature increase on the addition of H2O2 . Upon annealing at 600 °C, the grassy part of the TiO2 NTs was found to consist of mostly anatase TiO2 whereas the bottom part of the anodic oxide comprised a mixture of anatase and rutile TiO2. The TiO2 NTs were then used to reduce hexavalent chromium (Cr(VI)) under ultraviolet radiation. They exhibited a rather efficient photocatalytic effect, with 100% removal of Cr(VI) after 30 min of irradiation. The fast removal of Cr(VI) was due to the anatase dominance at the grassy part of the TiO2 NTs as well as the higher surface area the structure may have. This work provides a novel insight into the photocatalytic reduction of Cr(VI) on grassy anatase TiO2 NTs.

High-efficiency photoelectrochemical cathodic protection performance of the iron-nitrogen-sulfur-doped TiO2 nanotube as new efficient photoanodes

Novel iron-nitrogen-sulfur-tridoped titanium dioxide nanotubes (Fe-N-S-TiO2 NTs) have been synthesized via single step anodization of titanium using potassium ferricyanide, as a suitable additive, in dimethyl sulfoxide (DMSO) electrolyte and applied as photoanodes in the photocathodic protection of stainless steel 403 (SS403). Photocurrent density, open circuit potential and Tafel polarization curves have been used to study the photocathodic protection effect of the samples prepared. Upon the addition of potassium ferricyanide to the anodizing electrolyte and titanium dioxide nanotube doping, the light absorption of the Fe-N-S-TiO2 NTs were increased to the visible region, comparable with pure TiO2 NTs, according to the results obtained. Enhanced photoelectro-response activity and photocathodic protection performance for 403 stainless steel are exhibited by Fe-N-S-TiO2 NTs under light illumination. In addition, the optimal sample electrode (FT4) potentials shifted negatively to −683 mV under illumination.

Electro- and photo-electrooxidation of 2,4,5-trichlorophenoxiacetic acid (2,4,5-T) in aqueous media with PbO2, Sb-doped SnO2, BDD and TiO2-NTs anodes: A comparative study

Abstract In this work, the 2,4,5-T degradation in aqueous media was studied by electro- (EC) and photoelectrochemical (PEC) oxidation methods, which are two of the most important advanced oxidation processes (AOPs) for wastewater treatment. Both EC and PEC experiments were carried out in a single compartment cell under galvanostatic conditions (30 mA cm−2) at 298 K by using 0.05 M Na2SO4 + 200 ppm 2,4,5-T at pH 3 and pH 9, as model solutions. EC oxidation was performed using Sb-doped SnO2, PbO2 and boron doped diamond (BDD) as anodic materials. Besides these anodes, TiO2 in a nanotubular structure (TiO2 NTs) with or without PbO2 dispersed nanoparticles (TiO2::PbO2) were also used for PEC oxidation process. In all cases, the electrolyzed solutions were periodically analyzed by UV–vis spectrophotometry (232 or 235 nm) and liquid chromatography (HPLC) for 2,4,5-T as well as the oxidation by-products. The mineralization level was occasionally measured by using total organic carbon (TOC). For PEC experiments the photocurrent response variations with potential in 0.5 M H2SO4 were obtained by the linear scanning voltammetry (LSV) method at a slow potential sweep (5 mV s−1). Results clearly showed that at 30 mA cm−2, the 2,4,5-T was 100% oxidized on Sb-doped SnO2 and 95% on PbO2 after 120 min of electrolysis, which allow to assume the EC as an adequate treatment method to remove this herbicide from wastewaters. HPLC results showed the formation of aromatic intermediates such as 2,4,5-trichlorophenol (2,4,5-TCP) and 2,5-dihydroxyquinone (2,5-DHQ) followed by the formation of carboxylic acid such as hydroxyacetic acid. For these cases, alkaline media (pH 9) was better than acidic media (pH 3) in about one magnitude order in the apparent rate constant (k). On the other hand, photochemical activity results showed that PEC on TiO2-NTs::PbO2 had higher photocurrent density values than on naked TiO2 NTs as photoanodes. These electrodes also had the better photo conversion efficiencies (η), which strongly suggests the occurrence of a “co-catalysis” effect due to an electronic transfer assisted by the closed contact between TiO2 and PbO2. This fact was supported by the PEC oxidation of 2,4,5-T in aqueous solution, whose k value was slightly lower than that observed for bulk material.

Hydrothermal deposition of AgCl/AgBr co-sensitizers to modify TiO2 NTs for enhanced photocatalytic performance

AgCl/AgBr co-sensitizers were prepared on TiO2 nanotube arrays (TiO2 NTs/AgCl/AgBr) by the hydrothermal method. The composition, morphology, optical absorption, photoelectric and photoelectrocatalytic (PEC) performances of TiO2 NTs/AgCl/AgBr were influenced by the concentration ratio of KCl/KBr. The investigation results revealed that the TiO2 NTs/AgCl/AgBr photocatalyst exhibited dramatically strong visible light absorption and outstanding photoelectrochemical capacity. The photoelectrode produced high visible light surface photovoltage (-0.43 V), transient photocurrent (0.47 mA/cm2) and carrier concentration (4.39 × 1020 cm-3). The sample also showed high PEC activity in the organic dye and Cr(VI) removal, and the photocatalytic mechanism and charge carrier transfer path were described based on PEC results. The investigation would offer prospective insight to the sensitization of TiO2 NTs, which would result in extensive attraction in the preparation and application of semiconductor materials as photoelectrodes and photocatalysts with superior photoelectrochemical performances.

Nickel-decorated TiO2 nanotube arrays as a self-supporting cathode for lithium-sulfur batteries

Lithium-sulfur batteries are considered to be one of the strong competitors to replace lithium-ion batteries due to their large energy density. However, the dissolution of discharge intermediate products to the electrolyte, the volume change and poor electric conductivity of sulfur greatly limit their further commercialization. Herein, we proposed a self-supporting cathode of nickel-decorated TiO2 nanotube arrays (TiO2 NTs@Ni) prepared by an anodization and electrodeposition method. The TiO2 NTs with large specific surface area provide abundant reaction space and fast transmission channels for ions and electrons. Moreover, the introduction of nickel can enhance the electric conductivity and the polysulfide adsorption ability of the cathode. As a result, the TiO2 NTs@Ni-S electrode exhibits significant improvement in cycling and rate performance over TiO2 NTs, and the discharge capacity of the cathode maintains 719 mA·h·g−1 after 100 cycles at 0.1 C.

Immobilization of Cubic Silver Plasmonic Nanoparticles on TiO2 Nanotubes, Reducing the Coffee Ring Effect in Surface-Enhanced Raman Spectroscopy Applications.

Surface-enhanced Raman spectroscopy (SERS) substrates prepared by immobilizing silver cubic nanoparticles (Ag CNPs) on titanium dioxide nanotubes (TiO2 NTs) were used for investigations of the “coffee ring” (CR) effect and its impact on spatial reproducibility of measured Raman signals in comparison with flat surfaces (Ti and Si) where the CR effect is usually significant. The immobilization of nanoparticles from drops, which is a very simple technique, usually does not permit a homogeneous distribution of deposited NPs because there is significant accumulation of the material at the boundary of the drying area. Our proposed SERS substrates effectively reduced the CR effect through the use of well-ordered nanostructures where a smaller number of Ag CNPs were transferred to the boundary region. It was not only the surface morphology that was important but also the physicochemical properties of TiO2 NTs, such as wettability. The wettability of the prepared samples was determined by measuring the static water contact angle (WCA), and the chemical composition near the boundary of the drying area was studied using Auger electron spectroscopy. The morphology of the substrates obtained was characterized using scanning electron microscopy. Our studies showed that reducing the coffee ring effect increased the spatial reproducibility of the measured SERS signal in the area of the deposited CNPs. Therefore, the platforms obtained may be very useful in commercial SERS applications.

Chitosan Coating of TiO2 Nanotube Arrays for Improved Metformin Release and Osteoblast Differentiation.

BackgroundIneffective integration has been recognized as one of the major causes of early orthopedic failure of titanium-based implants. One strategy to address this problem is to develop modified titanium surfaces that promote osteoblast differentiation. This study explored titanium surfaces modified with TiO2 nanotubes (TiO2 NTs) capable of localized drug delivery into bone and enhanced osteoblast cell differentiation.Materials and MethodsBriefly, TiO2 NTs were subjected to anodic oxidation and loaded with Metformin, a widely used diabetes drug. To create surfaces with sustainable drug-eluting characteristics, TiO2 NTs were spin coated with a thin layer of chitosan. The surfaces were characterized via scanning electron microscopy, atomic force microscopy, and contact angle measurements. The surfaces were then exposed to mesenchymal bone marrow stem cells (MSCs) to evaluate cell adhesion, growth, differentiation, and morphology on the modified surfaces.ResultsA noticeable increase in drug release time (3 days vs 20 days) and a decrease in burst release characteristics (85% to 7%) was observed in coated samples as compared to uncoated samples, respectively. Chitosan-coated TiO2 NTs exhibited a considerable enhancement in cell adhesion, proliferation, and genetic expression of type I collagen, and alkaline phosphatase activity as compared to uncoated TiO2 NTs.ConclusionTiO2 NT surfaces with a chitosan coating are capable of delivering Metformin to a bone site over a sustained period of time with the potential to enhance MSCs cell attachment, proliferation, and differentiation.

Solvothermal synthesis and enhanced photocatalytic hydrogen production of Bi/Bi2MoO6 co-sensitized TiO2 nanotube arrays

Bi/Bi2MoO6/TiO2 NTs photocatalysts were synthesized on the basis of TiO2 NTs by a solvothermal method using glucose as the reducing agent. The removal of organic dyes such as RhB and MB and heavy metal ions like Cr(VI) were used to simulate industrial wastewater for the photocatalytic activity assessment of Bi/Bi2MoO6/TiO2 NTs. Na2S/Na2SO3 solution was used as sacrificial agent to study the photocatalytic hydrogen generation performance of samples. The results showed that Bi3+ was successfully reduced to metal Bi and deposited on the surface of Bi2MoO6. The removal efficiencies of RhB, MB and Cr(VI) reached 73.21%, 92.98% and 70.54%, respectively, which confirmed the excellent photocatalytic activity of samples. The photocatalytic hydrogen production performance of the sample was also remarkable and the hydrogen generation rate reached 173.41 μmol·h−1·cm−2. The active species and photocatalytic mechanism of pollutant degradation and hydrogen generation were proposed based on the photoelectrochemical data. The excellent photocatalytic performances of Bi/Bi2MoO6/TiO2 NTs will exhibit prospective guidance for the preparation and photocatalytic water splitting of bismuth-based photocatalysts.

All-Solid-State Lithium Ion Batteries Using Self-Organized TiO2 Nanotubes Grown from Ti-6Al-4V Alloy.

All-solid-state batteries were fabricated by assembling a layer of self-organized TiO2 nanotubes grown on as anode, a thin-film of polymer as an electrolyte and separator, and a layer of composite LiFePO4 as a cathode. The synthesis of self-organized TiO2 NTs from Ti-6Al-4V alloy was carried out via one-step electrochemical anodization in a fluoride ethylene glycol containing electrolytes. The electrodeposition of the polymer electrolyte onto anatase TiO2 NTs was performed by cyclic voltammetry. The anodized Ti-6Al-4V alloys were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical properties of the anodized Ti-6Al-4V alloys were investigated by cyclic voltammetry and chronopotentiometry techniques. The full-cell shows a high first-cycle Coulombic efficiency of 96.8% with a capacity retention of 97.4% after 50 cycles and delivers a stable discharge capacity of 63 μAh cm−2 μm−1 (119 mAh g−1) at a kinetic rate of C/10.

Plasma Nitriding of TiO2 Nanotubes: N-Doping in Situ Investigations Using XPS.

The nitrogen doping of titanium dioxide nanotubes (TiO2 NTs) was investigated as a result of well-controlled plasma nitriding of TiO2 NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO2 NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N–TiO2 NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO2 band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO2 NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti–N bonds in the TiO2 lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO2 NTs after each step of the nitriding and annealing treatments.

Enhanced Photoelectrochemical Water-Splitting Property on TiO2 Nanotubes by Surface Chemical Modification and Wettability Control.

We report a simple method to control the photoelectrochemical (PEC) water-splitting performance of TiO2 nanotube arrays (NTs) by surface chemical modification. Four types of modifier molecules with different surface energy and functional groups, including amine (-NH2), n-alkane (-CnH2n+1), perfluoroalkyl (-F), and polymer molecule (-polymer), were self-assembled to the surface of TiO2 NTs, which could change the surface chemical composition and wettability from superhydrophilicity to hydrophobicity. Interestingly, different from expected results, photoelectrochemical measurement results show that the n-octadecyltrichlorosilane-modified TiO2 nanotube arrays with a contact angle of about 134° present the highest PEC property with doubled photocurrent density and more negative onset potential. And the total PEC performance order of the monolayers-modified TiO2 NTs is (-CnH2n+1) > (-F) > (-NH2) > (-OH, pristine TiO2) > (-polymer), which is due to the molecular monolayers modification being able to suppress the recombination of photogenerated electrons and holes and facilitate water oxidation by regulating the interface electric double layer, whereas a thick polymer layer on the photoelectrode surface would affect the light absorbance and decrease the PEC performance. Further investigation indicates that the surface energy and wettability of the TiO2 photoelectrode adjusted by surface modification also have an important influence on the interface reaction of water oxidation and the adsorption/desorption of newly formed oxygen, which also provides a new method for controlling the surface photocatalytic reactions.

TiO2 Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid.

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO2 nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO2 nanotubes (TiO2 NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO2 NTs, forming ‘rings’ and agglomerates. A part of metal nanoparticles decorated also TiO2 NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO2 NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO2 NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst—Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO2 NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO2 NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO2 catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy—XPS; Auger electron spectroscopy—AES).

Corrosion Behavior of Titanium Dioxide Nanotubes in Alkaline Solution

In this study, titanium dioxide nanotubes (TiO2–NTs) are prepared by using anodization method on commercial pure titanium (Ti) by applying constant voltage of 60 V to the electrolysis system for 15 min, one and two hours. Highly ordered and quality TiO2–NTs layers are formed on Ti electrode. To investigate the corrosion behavior of TiO2–NTs in 1 M KOH solution, electrochemical and surface analysis methods such as anodic and cathodic current-potential curves, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX) are used. Effect of long immersion time is also studied. Obtained results showed that the corrosion behavior of TiO2–NTs is more improved when compared to bare Ti electrode. Very stable, durable and excellent protective TiO2–NT layer is obtained at anodization time of 1 h. This oxide layer resisted the aggressive solution attack. It is suggested that this oxide layer is used in many industrial applications to reduce the corrosion of commercial pure Ti.

One-Step Decoration of TiO2 Nanotubes with Fe3O4 Nanoparticles: Synthesis and Photocatalytic and Magnetic Properties

This paper presents an effective hydrothermal route to decorate various types of anodic 1D TiO2 nanotubes (TiO2 NTs) with magnetite nanoparticles (Fe3O4 NPs), yielding a magnetically guidable and a...

Preparation of nitrogen-doped TiO2 nanotube deposited with gold nanoparticles for photocatalytic phenol degradation under visible light

One of the many functions of TiO2 photocatalysts is degrading organic compounds. TiO2 photocatalysts have a band gap of 3.2 eV, which is equivalent to the energy of ultraviolet (UV) photons with a wavelength of 388 nm and allows them to be effectively activated only by UV light. However, they are less effective under visible (Vis) light. Researchers have developed many ways to use the photocatalytic properties of TiO2 under visible light via nitrogen doping. Further, the photocatalytic activity of N-doped TiO2 can be improved via surface plasmon resonance. In this study, N-doped TiO2 nanotubes (N-TiO2 NTs) are prepared and deposited with Au nanoparticles (Au/N–TiO2 NTs) via electrodeposition. The TiO2 NTs and Au/N-TiO2 NTs are characterized using UV-VIS spectrometry, Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), and linear sweep voltammetry (LSV). The photocatalytic test under tungsten lamp illumination of a 20-ppm phenol solution in a batch reactor shows a phenol degradation of 60 %, whereas a 20-ppm bisphenol A (BPA) solution is degraded by 40 %.

Novel mineralized electrospun chitosan/PVA/TiO2 nanofibrous composites for potential biomedical applications: computational and experimental insights.

Electrospun nanofibrous materials serve as potential solutions for several biomedical applications as they possess the ability of mimicking the extracellular matrix (ECM) of tissues. Herein, we report on the fabrication of novel nanostructured composite materials for potential use in biomedical applications that require a suitable environment for cellular viability. Anodized TiO2 nanotubes (TiO2 NTs) in powder form, with different concentrations, were incorporated as a filler material into a blend of chitosan (Cs) and polyvinyl alcohol (PVA) to synthesize composite polymeric electrospun nanofibrous materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nanoindentation, Brunauer–Emmett–Teller (BET) analysis, and MTT assay for cell viability techniques were used to characterize the architectural, structural, mechanical, physical, and biological properties of the fabricated materials. Additionally, molecular dynamics (MD) modelling was performed to evaluate the mechanical properties of the polymeric PVA/chitosan matrix upon reinforcing the structure with TiO2 anatase nanotubes. The Young's modulus, shear and bulk moduli, Poisson's ratio, Lame's constants, and compressibility of these composites have been computed using the COMPASS molecular mechanics force fields. The MD simulations demonstrated that the inclusion of anatase TiO2 improves the mechanical properties of the composite, which is consistent with our experimental findings. The results revealed that the mineralized material improved the mechanical strength and the physical properties of the composite. Hence, the composite material has potential for use in biomedical applications.

Li+ Pre‐Insertion Leads to Formation of Solid Electrolyte Interface on TiO2 Nanotubes That Enables High‐Performance Anodes for Sodium Ion Batteries

AbstractRecently, sodium ion batteries (SIBs) have been widely investigated as one of the most promising candidates for replacing lithium ion batteries (LIBs). For SIBs or LIBs, designing a stable and uniform solid electrolyte interphase (SEI) at the electrode–electrolyte interface is the key factor to provide high capacity, long‐term cycling, and high‐rate performance. In this paper, it is described how a remarkably enhanced SEI layer can be obtained on TiO2 nanotube (TiO2 NTs) arrays that allows for a strongly improved performance of sodium battery systems. Key is that a Li+ pre‐insertion in TiO2 NTs can condition the SEI for Na+ replacement. SIBs constructed with Li‐pre‐inserted NTs deliver an exceptional Na+ cycling stability (e.g., 99.9 ± 0.1% capacity retention during 250 cycles at a current rate of 50 mA g−1) and an excellent rate capability (e.g., 132 mA h g−1 at a current rate of 1 A g−1). The key factor in this outstanding performance is that Li‐pre‐insertion into TiO2 NTs leads not only to an enhanced electronic conductivity in the tubes, but also expands the anatase lattice for facilitated subsequent Na+ cycling.

Enhancement of photocatalytic and photoelectrochemical properties of TiO2 nanotubes sensitized by SILAR - Deposited PbS nanoparticles

The aim of this work is to improve the photocatalytic and photoelectrochemical properties of TiO2 nanotubes (TiO2-NTAs) by sensitizing them with PbS nanoparticles (NPs) prepared by the Successive Ionic Layer Adsorption and Reaction method (SILAR). The Microstructure, surface morphology, phase composition and optical properties of the prepared structure were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM and High-resolution mode HRTEM) and X-ray photoelectron spectroscopy (XPS). The TiO2 NTAs were loaded by PbS NPs, which contents increase by increasing the number of SILAR cycles. The PbS NPs, which have a size in the order of ∼20 nm, were found to be uniformly distributed in the TiO2 NTAs without damaging the tubular ordered structure. The photocatalytic activity of the PbS/TiO2 NTAs system, toward Amido Black (AB), showed significant enhancement compared to the bare untreated TiO2 NTs. At 30 SILAR deposition cycles the PbS-NPs/TiO2 NTAs structure is able to remove 75% of BA under simulated solar light, considerably higher than the 40% removal obtained with unloaded TiO2 NTAs. A significant improvement of the Photoelectrochemical (PEC) efficiency has been also demonstrated for the PbS-NPs/TiO2 NTAs hybrid system. This improvement is mainly related to visible-light harvesting and reduced recombination of photo-generated electron-hole pairs due to the synergistic effect of the heterojunction and to the well-organized morphology of the TiO2 NTAs.

Vertical grown BiOI nanosheets on TiO2 NTs/Ti meshes toward enhanced photocatalytic performances

Vertical grown BiOI nanosheets were fabricated by the solvothermal deposition on the surface of TiO2 nanotube arrays (TiO2 NTs)/Ti meshes for the enhanced photocatalytic removal of organic dyes and heavy metal ions. The BiOI nanosheets with different size and distribution were prepared by changing the reagent concentration. The photoelectrochemical results illustrated that the TiO2 NTs/BiOI (0.05) prepared with Bi3+ concentration of 0.05 mol/L showed the uniform nanosheet structure, strong solar absorption, high photocurrent generation, low interface resistance and outstanding photocatalytic property. The visible light photocurrent and photovoltage achieved 114.33 μA/cm2 and -0.24 V, and the photocatalytic removal efficiencies of MO, RhB, MB and Cr (VI) achieved 92.22%, 97.28%, 96.57% and 70.51%, respectively. Moreover, the photocatalytic stability, active group and electron transfer mechanism were also investigated. The TiO2 NTs/BiOI heterojunction provided the effective charge carrier transportation path, which dramatically inhibited the combination and consumption of electrons. The design and construction of TiO2 NTs/BiOI electrodes identified the strategy for the efficient photocatalytic pollution treatment.

Microstructures and optical properties of TiO2/ZrO2 nanotube/nanoporous heterofilm prepared by anodizing of Ti/Zr/Ti multilayer films

This paper reports a novel method for preparing TiO2/ZrO2 nanotube/nanoporous (TiO2 NTs/ZrO2 NPs) heterofilm by directly anodizing Ti/Zr/Ti multilayer films deposited on silicon substrates. The as-deposited multilayer and anodized films were characterized by scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction to further investigate the microstructures. The whole upper Ti and partial lower Ti layers were transformed into highly ordered TiO2 nanotubes under an optimized anodizing condition, in contrast the middle Zr layer was transformed into ZrO2 with nanoporous structure. Photo-absorption performance of the P25, TiO2 nanotubes (TiO2 NTs) array and TiO2 NTs/ZrO2 NPs heterofilm were investigated by ultraviolet-visible diffuse reflection spectra. The TiO2 NTs/ZrO2 NPs heterofilm has strong absorption in the ultraviolet region and extends the absorption range to the visible light. Compared with TiO2 NTs, the TiO2 NTs/ZrO2 NPs heterofilm exhibited stronger absorbance in the range of 300-475 nm due to the synergistic effect produced by the nanoscale interaction of two metal oxide semiconductors with different structures. The energy band gap values are 2.98 and 3.01 eV for TiO2 NTs and TiO2 NTs/ZrO2 NPs heterofilm, respectively. These results are of great significance in the preparation of metal oxide with designable heterostructure on desired substrates.