Anodic TiO2 Nanotubes Research Articles

What happens if anodic TiO2 nanotubes are soaked in H3PO4 at room temperature for a long time?

We have found that anodized amorphous TiO2 nanotubes can be transformed into rutile phase TiO2, resulting in the formation of a flower-like structure, when soaked in H3PO4 solution at room temperature for 2–4 days. The presence of PO43− ions in the soaking solution is believed to play a key role in the formation of the flower-like TiO2 structure. The resulting TiO2 flower-like material can be used as a binder-free electrode and exhibits obvious redox activity in AlCl3 solution and superior supercapacitive performance compared to conventional TiO2 nanotubes. The presented technique offers a simple, scalable, energy-saving, and cost-effective way to tailor the morphology and properties of anodized TiO2 nanotubes for different applications.

Effect of proton irradiation on anatase TiO2 nanotube anodes for lithium-ion batteries

The role of defects in the charge transfer and transport properties of electrode materials for lithium-ion batteries has recently garnered increased interest. It is widely recognized that ion irradiation promotes the formation of defects within a crystalline solid. Among all ion species used for irradiation, protons are expected to create primarily simple Frenkel pair point defects without significantly changing the stoichiometry of the damaged region of the target material. This work investigates the effect of proton irradiation at varying temperatures on the electrochemical properties of anatase TiO2 nanotube (TiO2-NT) electrode for lithium-ion battery applications. Anatase TiO2-NTs are irradiated at both room temperature (25 °C) and 250 °C and compared with non-irradiated control specimens. Characterization by Raman spectroscopy and XRD suggests that the irradiation at both temperatures does not alter the long-range order of the nanotubes. However, high-resolution TEM reveals that defect clusters are formed upon irradiation and increase in size with increasing temperature. Both irradiated samples exhibit increased capacity and enhanced rate capability compared with the non-irradiated control, which can be explained by increased storage sites as well as improved Li+ diffusivity due to the presence of irradiation-induced defects. This study presents a unique perspective on pathways to engineer functional nanostructured electrode materials by tailoring irradiation conditions.

Effect of different hole scavengers on the photoelectrochemical properties and photocatalytic hydrogen evolution performance of pristine and Pt-decorated TiO2 nanotubes

TiO2 nanotubes have been investigated in photoelectrochemistry and photocatalysis for more than a decade. However, up to now, a systematic investigation of different hole scavengers is still lacking. Here we investigate the effect of the most relevant sacrificial hole scavengers on the photoelectrochemical properties and photocatalytic H2 evolution performance of pristine and Pt-decorated anodic TiO2 nanotubes. We examine methanol, isopropanol, ethylene glycol, EDTA-Na2, as well as Na2SO3 and H2O2 and find that the incident photocurrent conversion efficiency (IPCE) of the TiO2 nanotubes in 0.1 M Na2SO4 electrolytes increases by 1.8–3.1 times, depending on the used hole scavenger. The efficiency increases in the sequence H2O2 < Na2SO3 < isopropanol < methanol < ethylene glycol < EDTA-Na2. In presence of any hole scavenger, for nanotubes in the length-range of 2–10 μm, the photocurrent spectra and the IPCE magnitude are independent of the tube length. The photocurrent onset potential (optical flatband potential) is significantly affected by the different type of scavengers, in line with their red-ox potential. Under open circuit conditions (photocatalytic conditions), organic hole scavengers lead to a 10.0–28.8 times higher H2 production by TiO2 nanotubes than the scavenger-free case, with a sequence MeOH > i-PrOH > EDTA-Na2 > EG, while little or even detrimental effects of Na2SO3 and H2O2 are observed (note, this inactivity is in contrast to photoelectrochemical H2 generation). These results are compared to results obtained for TiO2 particles, and discussed in terms of various concepts in the literature.

Opto-electronic properties of anodized TiO2 nanotube arrays investigated using electron energy loss spectroscopy

A study of the nanoscale crystallinity of anodized TiO2 nanotubes is reported with the aim of demonstrating its influence on the localized optical and electronic properties of the structure. By employing scanning transmission electron microscopy, coupled with electron energy loss spectroscopy, x-ray diffraction and electron energy filtered jump-ratio imaging to probe changes in the electron near edge fine structure of the Ti L3,2 ionization edge, it is found that nanotubes annealed at 450 °C in air for 3 h crystallize in the anatase polymorph along their walls, with the underlying thick oxide barrier layer being predominantly rutile. An increase in annealing temperature to 600 °C results in the co-existence of anatase and rutile along the nanotube length with the nanotube top and bottom showing crystallization in anatase and rutile, respectively. Valence EELS shows that the localized energy band-gap is inconsistent along the nanotube length, deviating between that typically measured for anatase (3.2 eV) and rutile (3.0 eV). The obtained band-gap of 3.21 eV at the nanotube top and 3.44 eV at nanotube bottom is attributed to the co-existence of anatase and rutile phases even at a low annealing temperature of 450 °C.

Microstructure and properties of TiO2 nanotube coatings on bone plate surface fabrication by anodic oxidation

TiO2 nanotube coatings with different structures were prepared on bone plate surface by anodic oxidation at different voltages or time and in an ethylene glycol solution containing 0.3 wt% ammonium fluoride (NH4F) and 2 vol% deionized water. Subsequently, the morphology, elemental composition, crystalline structure, surface roughness, microhardness, contact angle, adhesion force, corrosion resistance and wear resistance of the as-prepared coatings were characterized. At the optimized oxidation voltage of 60 V in microstructural, biocompatibility and properties of coatings considerations, the prolonged oxidation within a certain range led to increasing nanotube thickness and inner diameter, which further improved the properties of TiO2 nanotube coating samples. Specifically, surface roughness and adhesion force of the coatings increased progressively, the maximum adhesion force was (12.10 ± 0.50) N, while their contact angle and microhardness decreased gradually. Moreover, the coatings also exhibited the enhanced corrosion resistance in simulated body fluid (SBF), with the corrosion potential or the corrosion current increased by 56.91% or decreased by 79.45% to the largest extent. During dry friction, both friction coefficient and wear groove depth declined, corresponding reduction rates up to 22.52% and 49.01% evidenced the improved wear resistance. Besides, the major wear mechanism of the coating was a combination of abrasive and adhesive wear. Accordingly, the voltage of oxidation at 60 V and the oxidation time of 6 h were determined as the optimum processing parameters for preparing TiO2 nanotube coating on the bone plate surface, and the nanotube inner diameter and coating thickness were (118 ± 3.5) nm and (34 ± 2.8) μm, respectively.The novelties of the present study are:1.A uniform and neat TiO2 nanotube coatings were fabricated using the anodic oxidation method. The effects of oxidation voltage and oxidation time on the microstructure of TiO2 nanotube array were further examined, and the relationship between oxidation parameters and coating morphology was concluded. On that basis, the changes in the structural parameters of TiO2 nanotube coatings under other oxidation parameters can be inferred.2.The morphology, elemental composition, crystalline structure, surface roughness, microhardness, contact angle, adhesion force, corrosion resistance and wear resistance of TiO2 nanotube coatings were systematically studied, and the relationship between roughness and hydrophilicity of the coatings was discussed.3.The wear process of anodized TiO2 nanotube coatings under dry friction conditions was explained according to the friction coefficient curves, and the wear mechanism of the coating was clarified based on the wear morphology and the energy spectrum analysis of the coatings.4.The optimum oxidation voltage and oxidation time for preparing of TiO2 nanotube coating on the bone plate surface by anodization were determined as 60 V and 6 h, respectively, when the electrolyte was an ethylene glycol solution containing 0.3 wt% NH4F and 2 vol% deionized water.

Low-Temperature Ammonia Oxidation in a Microchannel Reactor with Wall-Loaded X(X = Pt, Pd, Rh, PtPdRh)/TiO2 Nanotube Catalysts

In this research, wall-loaded X(X = Pt, Pd, Rh, PtPdRh)/TiO2 nanotube (NT) catalysts were prepared by deposition via photoreduction with anodized TiO2 nanotubes and were assembled in a microchannel...

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 13 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet. Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials. One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4]. The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

Granulation and Photocatalytic Performance of Anodized TiO&lt;sub&gt;2 &lt;/sub&gt;Nanotubes with Microwave-Assisted Annealing

The present work investigates the effects of microwave-assisted annealing on the granulation and photocatalytic performance of anodic TiO2 nanotubes. The results indicate that although microwave-assisted heating can transform the amorphous TiO2 nanotubes into completely anatase one within 5min, it brings the collapse and granulation of TiO2 nanotubes, which weaken their photocatalytic activity. Meanwhile, the detachment and evolution of F- rich layer to a layer of TiO2 membrane with rounding-off surface, and the stripping of TiO2 nanotube bottom from its body are also observed.

TiO2 nanotubes modified with Au nanoparticles for visible-light enhanced antibacterial and anti-inflammatory capabilities

Titanium and the corresponding alloys are the most widely used material used in implant. However, the infection associated with the orthopedic implant is the main cause of the orthopedic implant failure. In this study, the anodized TiO2 nanotubes (TNT) on Ti substrate were used as scaffolds for a controlled layer-by-layer Au nanoparticle deposition. Owing to the surface plasmon resonance (SPR) of Au, the hierarchical nanotubes show improved absorption and visible-light-induced phtocatalytical activity. The TNT-Au samples with the optimized amount of Au nanoparticle exhibit high antibacterial activity and high anti-inflammatory efficiency under visible-light irradiation. The non-decorated TNT samples do not show any of these interesting properties. Therefore, due to the enhanced antibacterial and anti-inflammatory properties, the prepared Au-decorated TNT is promising materials to increase the success rates of dental implants.

Homogeneous Anodic TiO2 Nanotube Layers on Ti–6Al–4V Alloy with Improved Adhesion Strength and Corrosion Resistance

AbstractHexagonal TiO2 nanotubes (TNTs) arrays are generally fabricated on Ti‐based substrates for some biomedical purposes, but the TNT layers constructed on conventionally processed Ti alloys are usually inhomogeneous because the substrates typically contain both the α and β phases. In this work, high‐pressure torsion (HPT) is applied to obtain a saturated single α‐phase microstructure in Ti–6Al–4V alloys via strain‐induced β phase dissolution. Homogeneous anodic TNT layers with three different morphologies, one‐step nanoporous, one‐step nanotubular, and two‐step nanoporous structures, are electrochemically fabricated on the ultrafine‐grained (UFG) Ti–6Al–4V alloy substrates after HPT processing, whereas the TNT layers prepared on coarse‐grained substrates are normally inhomogeneous. More notably, the TNT layers show significantly improved adhesion strength to the UFG substrate as well as better corrosion resistance compared to those on the conventionally processed Ti–6Al–4V substrates. X‐ray diffraction analysis, scanning electron microscopy in combination with electron backscatter diffraction, and transmission electron microscopy indicate that the improvement is due to a larger dislocation density in the UFG substrate as well as strain‐induced β phase dissolution.

High-performance UV photodetector of anodic rutile TiO2 nanotube arrays

Anodic rutile TiO2 nanotube arrays on Ti foil annealed at 850 °C was successfully synthesized without annihilating the nanotubular structures using novelty annealing approach. The significant morphological characteristics of the rutile nanotube arrays were employed to fabricate excellent-photoresponse characteristics of UV photodetector. The performance of electrical and photoresponse was investigated and the findings demonstrated that UV photodetector under illumination (395 nm, 2.62 mW/cm2) exhibited a high sensitivity (3600), rapid response time (0.8 s) and rapid recovery time (0.81 s) at bias voltage 5 V. The photodetector demonstrated remarkable stability and reproducibility emergence with time. In addition, the photoresponse characteristics were performed at distinct bias voltages and light intensities. As illustrated above, the photodetector based on rutile nanotube arrays is an encouraging nano-optoelectronic device that is excellently applicable for UV spectrum.

TiCr alloy anodization for Cr-doped TiO2 nanotube array with improved photocatalytic activity

Cr-doped anodic TiO2 nanotube array has been prepared with increased photocurrent compared to pristine titania. However, detailed effect of Cr-addition in titanium on the growth and photocatalytic property of anodic nanotube is still indistinct. To clarify this point, we initially compared the morphology, crystallinity and chemical composition of anodic nanotube arrays on various TiCr alloys. The results indicated that tube length and diameter were increased by TiCr alloy anodization, and Cr atoms were doped inside TiO2 in the form of Cr2+, Cr4+ and Cr2O3. Because of Cr-doping, anatase crystallization of nanotube was inhibited. The photocatalytic activities were next evaluated. Compared to pristine Ti, Ti0.2Cr and Ti0.5Cr, Ti0.1Cr anodization was found to be optimum for preparing nanotube array with improved photocatalytic activity. The reason could be the improved UV-visible light absorption and photo-generated carriers utilization efficiency due to appropriate Cr doping. For Ti0.2Cr and Ti0.5Cr anodization, excess Cr2O3 could be formed, cause the recombination of photo-generated carriers, and reduce the photocatalytic property. The results presented in this work may offer useful guidelines for Ti alloy anodization towards preparation of nanostructured photocatalysts with promising applications.

(Photo) electrochemical water oxidation at anodic TiO2 nanotubes modified by electrodeposited NiFe oxy-hydroxides catalysts

Anodic TiO2 nanotubes are potential candidates for industrial scale and stable photoelectrochemical water oxidation. Major roadblocks for the realization of this technology however are the limited light absorption, as this material usually absorbs only in the UV, and the sluggish water oxidation kinetics at the electrode/electrolyte interface. Various efforts have nonetheless demonstrated absorption and photocurrent generation with visible light while a typical solution for the slow water oxidation is electrode modification via oxygen evolution catalysts; NiFe (oxy) hydroxides in particular are among the highest turn-over efficiency and low-cost catalysts. Studies about loading NiFe (oxy) hydroxides onto anodic TiO2 nanotubes by electrodeposition methods are rarely reported and the influence of the loaded catalysts on the photoanode performance is not fully understood. In this work, NiFe (oxy) hydroxides are first electrodeposited on Au substrates; the as-deposited catalysts indicate enhanced oxygen evolution catalytic activity. The same deposition method is then applied at various TiO2 nanotube systems. Specifically, mouths, walls and whole bodies of anodic TiO2 nanotubes are electrodeposited with NiFe (oxy) hydroxides and the corresponding photo response to water oxidation are investigated. We show that at relatively low applied potential (≤1.5 V vs. RHE) the NiFe (oxy) hydroxides layer significantly reduces photon absorption and facilitates interfacial recombination, leading to a decreased photocurrent density. In contrast, at relatively high bias (>1.5 V vs. RHE), the oxygen evolution is enhanced due to the intrinsic electro-catalytic properties of the loaded catalysts. Synergistic effect are not found in the three NiFe (oxy) hydroxide films deposited at TiO2 nanotube systems.

Intracellular Drug Delivery with Anodic Titanium Dioxide Nanotubes and Nanocylinders.

Titanium dioxide (TiO2) holds remarkable promises for developing current theranostic strategies. Anodic TiO2 nanostructures as a porous scaffold have offered a broad range of useful theranostic properties; however, previous attempts to generate single and uniform TiO2 one-dimensional nanocarriers from anodic nanotube arrays have resulted in a broad cluster size distribution of arbitrarily broken tubes that are unsuitable for therapeutic delivery systems due to poor biodistribution and the risk of introducing tissue inflammation. Here, we achieve well-separated, uniformly shaped anodic TiO2 nanotubes and nanocylinders through a time-varying electrochemical anodization protocol that leads to the generation of planar sheets of weakly connected nanotubes with a defined fracture point near the base. Subsequent sonication cleanly detaches the nanotubes from the base. Depending on the position of the fracture point, we can fabricate single-anodic nanocylinders that are open on both ends and nanotubes that are closed on one end. We proceed to show that anodic nanotubes and nanocylinders are nontoxic at therapeutic concentrations. When conjugated with the anticancer drug doxorubicin using a pH-responsive linker, they are readily internalized by cells and subsequently release their drug cargo into acidic intracellular compartments. Our results demonstrate that uniformly sized anodic TiO2 nanotubes and nanocylinders are suitable for subcellular delivery of therapeutic agents in cancer therapy.

Boosted photocatalytic hydrogen evolution by tuning inner pore size and co-catalyst thickness of the anodic TiO2 nanotubes

The formation of well aligned TiO2 nanotubes with suitable inner diameters is a pre-requisite for photocatalytic application. The inner diameters can be tuned by the composition of electrolyte, anodization temperature, and applied potential. Here, we have successfully formed the TiO2 nanotubes with wide inner diameters by controlling the anodization potential of the Ti metal substrate. The anodizations were performed in the aqueous solution of ethylene glycol mixed with hydrofluoric acid as an electrolyte at potentials of 150–240 V at 40 ℃. It resulted into TiO2 nanotubes with inner diameters in the range of 160–400 nm and lengths about 6–8 μm, respectively. Moreover, the TiO2 nanotubes were sputter coated with thin layers (1–5 nm) of Pt and Au nanoparticles. Finally, we compared the photocatalytic behavior of the as-prepared TiO2 nanotubes and those coated with Au and Pt nanoparticles. Interestingly, 1 nm Pt coated 300 and 400 nm inner diameter TiO2 nanotubes showed highest H2 production rate of 25 μL h−1 cm-2 under a 10 h of light illumination.

Essential influence of electrode and electrolyte temperatures on the anodizing process of Ti

Abstract Recently, anodic TiO2 nanotubes have attracted increasing attention. Most studies only consider electrolyte temperature, but few consider electrode temperature, and no one has analyzed effects of the two temperatures on electronic current and ionic current. According to the constant-voltage current-fitting formula, effects of electrolyte and electrode temperature on ionic and electronic current are discussed quantitatively, respectively. It is concluded that electrolyte temperature mainly affects ionic current while the increase of the electrode temperature can accelerate the generation and rise rate of the electronic current. In addition, “spherical explosion” morphology formed at high temperature is proposed and schematically explained.

Controllable Synthesis of MoS2@TiO2 Composite Nanostructure by Anodic Oxidation-Hydrothermal Technique

MoS2@TiO2 composite nanostructure arrays consisting of thin MoS2 nanosheets on the surface of anodized TiO2 nanotube arrays were successfully synthesized with a facile anodic oxidation-hydrothermal technique. In this study, x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer and ultraviolet–visible spectroscopy (UV–Vis) were used to characterize the samples. On this basis, the photocatalytic property of MoS2@TiO2 composite nanostructure in the degradation of methylene blue was investigated. XRD results indicate that MoS2 nanosheets on the surface of anodized TiO2 nanotube arrays were in a hexagonal phase. FESEM shows that MoS2 nanosheets have a uniform distribution and low agglomeration because of the regular lamellar structure with tight arrangement. Meanwhile, the MoS2@TiO2 composite nanostructure shows the high light absorption intensity both in the ultraviolet and visible region. And the photodegradation efficiency for methylene blue is 92.10%, thus, it has potential applications in the field of photocatalysis.

Growth orientation mechanism of TiO2 nanotubes fabricated by anodization

TiO2 nanotubes (TNTs) fabricated by anodization have been extensively researched in recent years. However, the mechanism that controls the growth orientation of anodic TNTs is still not clear. Here, we firstly examine their growth orientation systematically. Combined with the previous literature, the results of anodization on rotated Ti foil and thin Ti wire confirm that almost all of the TNTs grow vertically to the local Ti substrate surface. Their growth orientation predominantly depends on the local electric field around the bottom of the nanotube. The distribution of the local electric field is regulated by the shape of the initial nano-scale local Ti substrate surface (INLTSS). Most of the INLTSS is nearly flat, which leaves vertical, circular, and straight TNTs. In terms of the evolution of TNTs fabricated on a micron-scale convex surface, the vertical growth of TNTs leads to a continuous decrease in the oxide/substrate (O/S) interface area, and a few TNTs are periodically crushed and detached from the O/S interface. For a micron-scale concave surface, due to the ever-increasing O/S interface area, Y-branched TNTs occurred periodically as a response to avoid a vacancy on the oxide/substrate interface.

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing.

The present work presents a strategy to stabilize amorphous anodic self-organized TiO2 nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO2 nanotube layers uniformly coated by thin TiO2 using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced. We investigated the soaking effects of ALD TiO2 coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO2 coatings (≈8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F− ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO2 nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment.

Bamboo shoot nanotubes with diameters increasing from top to bottom: Evidence against the field-assisted dissolution equilibrium theory

The formation mechanism of anodic TiO2 nanotubes remains controversial. To further explore the growth of nanotubes, we compared the difference between galvanostatic and potentiostatic anodizing processes, and discovered that the electric current kept dropping in the final phase of the potentiostatic process, whereas the voltage kept rising in the final phase of the galvanostatic process. Therefore, the so-called steady growth state of the field-assisted dissolution equilibrium model was not observed in either anodizing process. Furthermore, during galvanostatic anodization, we discovered for the first time that the diameters of the nanotubes gradually increased from top to bottom (from 134.9 nm to 202.0 nm). Bamboo shoot nanotubes with increasing diameters were fabricated through one-step and multi-step galvanostatic anodizations. These experimental observations cannot be explained by the field-assisted dissolution equilibrium theory. However, the electronic current model provides a reasonable explanation for the results obtained in this paper.