Search

Herein, we report the optimization of nitrogen (N) doping in TiO 2 nanotubes to achieve the enhanced photocatalytic efficiencies in degradation of dye and H 2 gas evolution under solar light exposure. TiO 2 nanotubes have been produced via hydrothermal process and N doping has been tuned by varying the concentration of urea, being the source for N, by solid-state dispersion process. The structural analysis using XRD showed the characteristic occupancy of N into the structure of TiO 2 and the XPS studies showed the existence of Ti-N-Ti network in the N-doped TiO 2 nanotubes. The obtained TEM images showed the formation of 1D tube-like structure of TiO 2 . Diffuse reflectance UV-Vis absorption spectra demonstrated that the N-doped TiO 2 nanotubes can efficiently absorb the photons of UV-Vis light of the solar light. The optimized N-doped TiO 2 nanotubes (TiO 2 nanotubes vs urea @ 1:1 ratio) showed the highest degradation efficiency over methyl orange dye (∼91% in 90 min) and showed the highest rate of H 2 evolution (∼19,848 μmol h -1 .g -1 ) under solar light irradiation. Further, the recyclability studies indicated the excellent stability of the photocatalyst for the durable use in both the photocatalytic processes. The observed efficiency was ascribed to the optimized doping of N-atoms into the lattices of TiO 2 , which enhanced the optical properties by forming new energy levels of N atoms near the valence band maximum of TiO 2 , thereby increased the overall charge separation and recombination resistance in the system. The improved reusability of photocatalyst is attributed to the doping-induced structural stability in N-doped TiO 2 . From the observed results, it has been recognized that the established strategy could be promising for synthesizing N-doped TiO 2 nanotubes with favorable structural, optical and photocatalytic properties towards dye degradation and hydrogen production applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Electrochemical anodization of low-concentration (0.02-0.2 at% Au) TiAu alloys in a fluoride electrolyte leads to self-organized TiO2 nanotubes that show a controllable, regular in situ decoration with elemental Au nanoclusters of ≈5 nm in diameter. The degree of self-decoration can be adjusted by the Au concentration in the alloy and the anodization time. Such Au particle decorated tubes show a high activity for photocatalytic H2 production from ethanol solutions., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The fabrication of self-organized VO(2) nanotubular/nanoporous layers is demonstrated by self-organizing anodization, followed by a suitable heat treatment. These VO(2) layers show a reversible metal to insulator transition (MIT) at 70 and 44 °C, when heating and cooling, respectively., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The present article reviews the current status of using TiO(2) nanotubes in Grätzel-type, dye-sensitized solar cells and extends the overview with the latest results and findings. Critical factors in tube geometry (length, diameter, top morphology), crystal structure (amorphous, anatase, rutile) as well as factors affecting dye loading or electron mobility are addressed. The highest solar cell efficiencies today for pure nanotube systems reach approximately 4% while for some mixed systems, around 7% has been reported. For both systems significant room for enhancement is anticipated and some key points and strategies for improvement are outlined.

Herein, we report a single‐step anodization process for WO3‐doped TiO2 nanotubes in an aqueous electrolyte containing the tungsten precursor Na2WO4 ⋅ 2H2O and fluoride ions. The single‐step anodization allows for homogeneous doping of WO3 into the TiO2 nanotube structures. The doping concentration depends on the concentration of the tungsten precursor in the electrolyte, demonstrating that the reported anodizing process is the most efficient approach for metal oxide doping in TiO2. Moreover, compared to bare TiO2, the WO3‐doped TiO2 nanotubes shows better proton intercalation, which leads to enhanced electrochromic performance. Single‐step performance boost: the feasibility of obtaining WO3‐doped TiO2 nanotubes by single‐step anodization of Ti in a tungstate‐containing electrolyte is demonstrated. The doping concentrations are controlled by concentration of tungstate salt in the electrolyte. The doped TiO2 nanotubes allow for higher electrochromic activity as compared with that of bare TiO2 structures. [ABSTRACT FROM AUTHOR]

We formed various TiO 2 nanotube layers by anodizing Ti metal under various conditions of anodization temperature and time. By controlling these conditions, we could adjust the morphology of the TiO 2 nanotubes in terms of length and wall thickness. Subsequent annealing converted the TiO 2 nanotubes into crystallized nanostructures. TiO 2 nanotubes of different crystalline phases had different mechanical properties. To evaluate the mechanical properties of the TiO 2 nanotubes in detail, they were subjected to Vickers hardness testing. The TiO 2 nanotube layers showed wide variations in hardness depending upon the anodization and annealing temperatures. [ABSTRACT FROM AUTHOR]

Self-organized TiO 2 nanotubes (NTs) can be formed by electrochemical anodization. Anodization is generally performed in aqueous or organic electrolytes containing halogen ions, such as Cl− and F−. However, these electrolytes lead to less ordered structures or carbon remnants, thus suppressing the electrical properties and limiting the applications. To overcome these limitations, new anodization approaches were performed in carbon-free electrolyte-based electrolyte. In this review, we summarizes the short history of TiO 2 NTs, general mechanisms of growing NTs, properties, and applications of classic TiO 2 NTs. Then, a new-generation of anodization approach conducted in molten orhto-phosphoric acid is elucidated based on anodization parameters, concluding the optimized condition to form highly ordered TiO 2 NT arrays. Finally, the review addresses further modifications such as heat-treatment, noble metal deposition, thermal dewetting, and double anodization to enhance the optical and electrical properties for use in various applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work we investigate the photocatalytic hydrogen production (water splitting) activity of different Pt loaded TiO 2 nanotube layers. Therefore, we fabricate free standing membranes and fix them in four different configurations: top up (with initiation layer “grass” or without) and bottom up (bottom closed or open), then decorate the tubes with various amounts of Pt and measure the open-circuit photocatalytic H 2 production rate. We find a strong influence of the configuration with the open top morphology showing the highest photocatalytic hydrogen production efficiency, these nanotubes yield 3.5 times more H 2 than the least efficient structure (bottom closed). The work therefore provides valuable guidelines for optimizing TiO 2 nanotube layers for photocatalytic applications. [ABSTRACT FROM AUTHOR]

We optimize the deposition of CH3NH3PbI3 perovskite into mesoporous electrodes consisting of anodic TiO2 nanotube layers. By a simple spin-coating approach, complete filling of the tube scaffolds is obtained, which leads to interdigitated perovskite structures in conformal contact with the TiO2 tube counterparts. Such assemblies can be used as solid-state solar cells in a hole-transporting-material-free configuration, that is, the tube scaffold serves as electron collector and blocking layer, while the perovskite acts as visible-light absorber and hole-transporting material. We show that the complete filling of the tube scaffold with the perovskite is essential to improve the solar cell efficiency. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we fabricate TiO2 nanotubes that are self-decorated with Au nanoparticles by anodizing low concentration (0.02 and 0.2at.% Au) TiAu alloys. After formation, the TiO2 tube walls carry regularly dispersed self-decorated Au particles with ~5nm in diameter which cause significant surface plasmon resonances. This plasmon resonance effect can be exploited to achieve visible photoresponse and can be used for photocatalytic H2 production under visible light illumination. [Copyright &y& Elsevier]

Nearly 100 % filling of TiO2 nanotubes with metals, including Ag, Cu, Au, and Pt, was achieved by defect‐sealing treatment at the bottom of the nanotubes, followed by metal deposition using nuclei formation/coalescence. The resulting short‐circuit‐free interdigitated electrode configurations can, for example, be used to fabricate memristive electrodes. [ABSTRACT FROM AUTHOR]

Abstract: Highly ordered TiO2 nanotube stump-[TiO2 NS]-layers, prepared by anodization of Ti in HF/H3PO4 solutions, were used as a substrate for a thermal dewetting of Au thin films. Depending on the initial Au sputter-deposited layer thickness, various sizes and densities of gold nanoparticles [Aunp] could be obtained on the TiO2 NS. Under certain conditions, very homogeneously distributed Aunp (with diameters in the range of 2–15nm) can be generated. Such Aunp/TiO2 NS combinations show a high efficiency for H2 production from H2O/EtOH solutions. A maximum H2 production efficiency could be obtained from a 2nm thick Au layer (57.03μl H2 for 9h) that was dewetted to ≈28,000particles/μm2 with individual particle diameters of ≈5nm. [Copyright &y& Elsevier]

Abstract: In the present work, we produce highly ordered and defined short aspect ratio self-organized TiO2 nanotubes – so called titania nanotube stumps [TNS] – by anodizing Ti in a HF/H3PO4 electrolyte. These TNS-layers are ideal for a conformal filling by metal sputter deposition. After decorating amorphous TNS with a Pt top contact, we investigate the solid-state current–voltage behavior and find a strongly pronounced memristic behavior. We ascribe the finding to the high vacancy density present in TNS bottoms prepared under high ion flux conditions. [Copyright &y& Elsevier]

Abstract: We report on the formation of self-organized nanotubular oxide structures by anodization of zinc in a sulfide based electrolyte. Under optimized experimental conditions, successful growth of a several micrometer long self-organized tubular structure is achieved. The anodized samples were characterized using FE-SEM, XPS, XRD and SAED. The key to formation of tubular ZnO is a protective sulfide containing initial layer. In contrast to other self-ordered tubular geometries, ZnO anodic layers consist of a particular tube wall structure. The resulting double hierarchy layers show a considerable efficiency for photoelectrochemical splitting of water when used in a sacrificial polysulfide electrolyte. [Copyright &y& Elsevier]

Gleichförmigkeit perfektioniert: Ein hochorientierter Aunp@TiO2 ‐ Photokatalysator wurde durch selbstorganisierende Anodisierung eines Ti ‐ Substrats und anschließende Entnetzung eines Gold ‐ Dünnfilms erhalten. Das Ergebnis: genau ein Au ‐ Nanopartikel (np) pro TiO2 ‐ Nanokavität. Solche Anordnungen sind hocheffiziente Photokatalysatoren für die Wasserstofferzeugung aus Ethanol. [ABSTRACT FROM AUTHOR]

Abstract: Over the past years, the photoelectrochemical behavior of anodic TiO2 nanotubes has intensively been investigated. However, comparably little attention has been paid to the large influence of growth parameters on the phtoelectrochemical tube properties. In the present work we investigate nanotubes of comparable geometry but using either aqueous electrolytes or different organic electrolytes. We show that very drastic differences in their photoresponse can be obtained. Moreover, we show that a recently introduced tube bottom sealing treatment has a very different effect on different tube types and strongly affects the performance of nanotube layers in dye sensitized solar cells. [Copyright &y& Elsevier]

A little dopey: Ta‐doped titania (TiO2) nanotube (NT) arrays can be grown by electrochemical anodization onto low‐Ta‐concentration (0.03–0.4 at % Ta) Ti–Ta alloys. Under optimized conditions (0.1 at % Ta, annealing at 650 °C and 7 μm thickness), Ta‐doped TiO2 NT arrays show a significantly enhanced activity in photoelectrochemical water splitting under simulated sunlight conditions (see figure). [ABSTRACT FROM AUTHOR]

Get attached: The mechanical attachment of TiO2 nanotube layers to a substrate can be a determining factor for the performance of these layers in dye‐sensitized solar cells (DSSCs). Self‐organized TiO2 nanotube layers grown in an electrolyte that contained lactic acid are shown to have considerably improved anchoring on the Ti metal substrate, which allows the construction of stable and efficient solar cells with >50 μm nanotube length (see figure). [ABSTRACT FROM AUTHOR]

Abstract: Ta doped TiO2 nanotube layers were fabricated by anodization of different Ti–Ta alloys with Ta contents of 0.03, 0.1 and 0.4at.%. For all layers well defined nanotubular structures could be formed. The layers were then characterized in dye-sensitized solar cells. Under optimized conditions, that is for a 0.1at.% Ta alloy, the solar cell efficiency could be enhanced by 25% compared to non-doped TiO2 nanotubes. Intensity modulated photocurrent spectra (IMPS) and intensity modulated photovoltage spectra (IMVS) measurements performed with the solar cells indicate that the beneficial effect is due to suppression of recombination effects. [Copyright &y& Elsevier]

Abstract: The present work investigates the photocatalytic performance of TiO2 nanotubes with different tube top morphologies. Such morphological variations are obtained when growing self-organized nanotube arrays under different (but widely used) anodization conditions. We compare the most typical appearances of tube tops that are: i) “grassy” tubes, ii) tubes with initiation layers, iii) doubled anodized and iv) “open” tubes. The results show that tubes with an open, defined mouth have a significantly enhanced photocatalytic performance in open circuit, dye degradation experiments as well as when used as a photoanodes for photoelectrochemical water splitting. [Copyright &y& Elsevier]

Abstract: Ti alloys with low Nb contents (0.1at.% and 0.5at.%) were used to grow self-organized Nb-doped TiO2 nanotube arrays. These layers were partially converted to SrTiO3 using a hydrothermal treatment. Various factors, such as hydrothermal temperature, hydrothermal duration, and annealing conditions, were investigated in view of the photocatalytic water splitting performance of the formed Nb-doped TiO2/SrTiO3 heterostructure nanotubes. Photoelectrochemical characterization shows that Nb-doping efficiently enhances the photocatalytic water splitting performance of TiO2/SrTiO3 heterostructure nanotubes. [Copyright &y& Elsevier]

Abstract: Highly ordered nanoporous and nanotubular TiO2 geometries can be anodically grown on Ti substrates in fluoride containing ethylene glycol electrolytes using different water contents. Here we fabricate 1μm thick layers consisting of arrayed tubes or pores with an open diameter of 15nm. We compare these small diameter structures to classical 100nm diameter TiO2 nanotubes for their application in Grätzel-type solar cells. The results show clearly that a small diameter nanotube geometry significantly enhances the solar cell conversion efficiency. [Copyright &y& Elsevier]

Herein, we report the optimization of nitrogen (N) doping in TiO 2 nanotubes to achieve the enhanced photocatalytic efficiencies in degradation of dye and H 2 gas evolution under solar light exposure. TiO 2 nanotubes have been produced via hydrothermal process and N doping has been tuned by varying the concentration of urea, being the source for N, by solid-state dispersion process. The structural analysis using XRD showed the characteristic occupancy of N into the structure of TiO 2 and the XPS studies showed the existence of Ti–N–Ti network in the N-doped TiO 2 nanotubes. The obtained TEM images showed the formation of 1D tube-like structure of TiO 2. Diffuse reflectance UV–Vis absorption spectra demonstrated that the N-doped TiO 2 nanotubes can efficiently absorb the photons of UV–Vis light of the solar light. The optimized N-doped TiO 2 nanotubes (TiO 2 nanotubes vs urea @ 1:1 ratio) showed the highest degradation efficiency over methyl orange dye (∼91% in 90 min) and showed the highest rate of H 2 evolution (∼19,848 μmol h−1.g−1) under solar light irradiation. Further, the recyclability studies indicated the excellent stability of the photocatalyst for the durable use in both the photocatalytic processes. The observed efficiency was ascribed to the optimized doping of N-atoms into the lattices of TiO 2 , which enhanced the optical properties by forming new energy levels of N atoms near the valence band maximum of TiO 2 , thereby increased the overall charge separation and recombination resistance in the system. The improved reusability of photocatalyst is attributed to the doping-induced structural stability in N-doped TiO 2. From the observed results, it has been recognized that the established strategy could be promising for synthesizing N-doped TiO 2 nanotubes with favorable structural, optical and photocatalytic properties towards dye degradation and hydrogen production applications. Image 1 • Hydrothermal route to develop TiO 2 nanotubes from TiO 2 bulk powders. • Optimization of N-doping to tune the physio-chemical properties of TiO 2 nanotubes. • Confirmation of Ti–N–O–Ti network in N–TiO 2 via XRD, XPS and FT-IR. • Achievement of 91% degradation of methyl orange dye in 90 min. • Achievement of a highest rate of H 2 evolution ∼19,848 μmol h−1.g−1. This study demonstrates the development of N-doped TiO 2 nanotubes from bulk TiO 2 powder and their enhanced photocatalytic dye degradation and H 2 production under solar light. [ABSTRACT FROM AUTHOR]

The present work establishes a process for the anodic growth of self-organized TiO2 nanotubes with a single-walled morphology. This yields not only a much more defined tube geometry but also provides a significant increase in properties and prospect for a wide range of TiO2 nanotube applications. [ABSTRACT FROM AUTHOR]

Self-ordered TiO2/Nb2O5“superlattice” nanotube arrays are successfully fabricated by electrochemical anodization from a commercially available Ti–Nb metal multilayer. The oxide nanotube walls then consist of alternating ∼4 nm TiO2 and ∼7 nm Nb2O5 rings. Such “superlattice” nanotube layers exhibit a much higher structural cycling stability for reversible Li-intercalation processes than pure TiO2 nanotubes. [ABSTRACT FROM AUTHOR]

Nb-doped TiO2nanotube (with CNb< 1 wt%) layers were successfully fabricated by self-ordered electrochemical anodization of Ti–Nb alloys. When used in dye-sensitized solar cells the efficiency enhanced by up to 30% compared to non-doped TiO2nanotubes. IMVS measurements indicate the beneficial effect to be due to lower recombination losses. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2) space nanotubes (SPNTs) have attracted considerable attention in the fields of photocatalysis and photoelectrochemical energy conversion because of their large surface area and good physical and chemical stability. However, their large bandgap (3.0–3.2 eV) and poor charge-carrier separation and transport properties lead to unsatisfactory photo-conversion efficiency. To overcome these drawbacks, we performed in vivo and in vitro deposition of BiVO 4 (BVO) on SPNTs, obtaining a sophisticated BVO/SPNTs heterojunction via electrochemical anodization and microwave-assisted synthesis. Unlike conventional TiO 2 nanotube structures, TiO 2 SPNTs possess empty spaces between the tubes (tube-to-tube interface), which can effectively admit BVO particles and generate worm-like BVO, yielding an intimate heterojunction interface and enlarged surface area. The prepared BVO/SPNTs exhibited a narrow bandgap (2.32 eV), small charge-transfer resistance, and accelerated reaction kinetics, as confirmed by incident-photon-to-current conversion efficiency, ultraviolet diffuse reflectance spectroscopy, and electrochemical impedance spectroscopy. These salient features, together with a strong response to visible light, resulted in a photocurrent density of 0.68 mA/cm2 without any co-catalyst at 1.23 V vs. a reversible hydrogen electrode in 0.5 M Na 2 SO 4 , which is 14 times higher than that of the pure SPNT electrode film. Thus, this study highlights that the integration of the materials with different dimensions by tailoring the surface properties may yield efficient and stable catalysts for multiple applications, particularly for hydrogen production at a significantly improved rate. [ABSTRACT FROM AUTHOR]

Reports on the defective anodic titanium dioxide (TiO 2) that harvests solar energy to perform photochemical reactions generating value-added chemicals and/or energy are scarce. In this study, we synthesize TiO 2 with two different morphologies (i.e., nanotube and compact layer) on a Ti substrate in a fluoride- and sulfide-containing electrolyte by using the electrochemical anodization method. The effect of high-temperature annealing on various TiO 2 structures and substrates in comparison with commercial TiO 2 nanoparticles coated on fluorine-doped tin oxide substrate under different gaseous environments (i.e., Ar, air, and O 2) is investigated herein by virtue of crystallinity, optoelectronic-physical properties, and photoelectrochemical performances. Unlike traditional TiO 2 nanoparticles, which are only active in ultraviolet illumination and with severe aggregation, the anodic TiO 2 nanotubes endow the effect of the oxygen vacancy and the self-doping of F− and S− ions upon annealing under the Ar environment, which is crucial to extending the photoresponse to the visible region. The gray anodic TiO 2 obtained through thermal annealing at 450 °C crystallizes in the anatase phase and maintains an intact surface morphology under different gaseous environments. The electron paramagnetic spectra are used to confirm the presence of Ti3+ or oxygen vacancy. The entrapment of the F− and S− ions within TiO 2 is determined by X-ray photoelectron spectroscopy and energy-dispersive spectroscopy introducing intrinsic defect states, which can resolve the bottlenecks in materials and encourages new paradigms beyond solar light-induced photocatalysis. [Display omitted] • Different morphologies of TiO 2 nanostructures are fabricated. • The TiO 2 nanostructure defect is controlled by annealing in gaseous environments. • Comparison of visible photoresponse according to different TiO 2 structures. [ABSTRACT FROM AUTHOR]

Abstract: The present work compares different annealing treatments for TiO2 nanotubes in terms of their photoelectrochemical performance. First, self-organized TiO2 nanotubes were grown in a most typical electrolyte of 0.5wt% NH4F+2wt% H2O in ethylene glycol to length of ≈15μm. These “as-formed” tubes are amorphous. Then the layers were either thermally annealed, thermally and hydrothermally annealed or “water annealed”. All these treatments show conversation of the tubes to anatase but with a considerably different level of crystallinity. Water annealing leads to strong tube wall roughening with corresponding area increase. In all investigated cases, the photocurrent properties (including dye sensitized solar cells (DSSCs)) and photocatalysis (decomposition of organics and water splitting), either in a two electrode configuration or under OCP, thermal annealing results in by far the best performance, followed by hydrothermal approaches. Water annealing turns out to be only of a minor improvement over using “as-formed” amorphous tubes. [Copyright &y& Elsevier]

Abstract: In the present work, we show how TiO2 nanotube layers that are decorated with a Pt-nanoparticle coating can be fabricated and operated as a reusable glucose sensing system. A critical amount of Pt coating is essential not only to provide an effective catalyst for glucose oxidation but also to establish a sufficient conductivity along TiO2 nanotube walls to allow an efficient amperometric operation of the electrode. On such an electrode the self-cleaning photocatalytic features of TiO2 can be maintained and used to re-establish poisoned activity of the Pt particles. [Copyright &y& Elsevier]

• TiO 2 nanotubes with 160–400 nm inner diameters are formed using anodization method. • Thin Au and Pt layers are sputtered onto TiO 2 nanotubes for photocatalytic application. • The Pt sputtered 300 and 400 nm TiO 2 nanotubes showed good photocatalytic activity. The formation of well aligned TiO 2 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 TiO 2 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 TiO 2 nanotubes with inner diameters in the range of 160–400 nm and lengths about 6–8 μm, respectively. Moreover, the TiO 2 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 TiO 2 nanotubes and those coated with Au and Pt nanoparticles. Interestingly, 1 nm Pt coated 300 and 400 nm inner diameter TiO 2 nanotubes showed highest H 2 production rate of 25 μL h−1 cm-2 under a 10 h of light illumination. [ABSTRACT FROM AUTHOR]

This work shows that highly ordered and mechanically stable micrometer-long Ta 2 O 5 nanotube arrays can be fabricated by galvanostatic anodization in a few seconds. Typically, ~ 7.7 μm long nanotubes can be grown at 1.2 A cm − 2 in only 2 s. Such nanotubes can be converted to Ta 3 N 5 nanotube arrays by nitridation. Photoelectrochemical (PEC) water splitting using AM 1.5G illumination yields for the Ta 3 N 5 nanotube photoanode modified with cobalt phosphate (Co–Pi) remarkable photocurrents of 5.9 mA cm −2 at 1.23 V RHE and 12.9 mA cm −2 at 1.59 V RHE and after Ba-doping a value of 7.5 mA cm −2 at 1.23 V RHE is obtained. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we study the modification of ordered TiO2 nanotube layers by flame annealing. We investigate different type of nanotubes (with variation in tube length, diameter, and grown in different electrolytes). We vary flame annealing parameters and analyze the morphology, phase composition and the resulting photoelectrochemical properties of the modified TiO2 nanotubes. The results show that flame annealing allows the crystallization of TiO2 nanotubes to anatase or rutile within seconds. The crystallization times strongly depend on the nanotube length and flame parameters. Samples from the outer cone show typically carbon burn off, while in the inner cone carbon accumulation occurs. The resulting photo electrochemical properties are to a large extent determined by the phase composition of the nanotubes (and not by the carbon content). Additionally, it may be noted that although the flame annealing process is fast and cheap, we could not achieve a maximum UV photoelectrochemical response comparable to classic furnace annealing. [Copyright &y& Elsevier]

• 1-μm-thick TiO 2 nanotube arrays are prepared in different types of electrolytes. • Effect of the degree of mass transfer on PEC properties is investigated. • Facile mass transfer enhancing degree of mass transfer are important for PEC. In this study, 1-μm-thick TiO 2 nanotubes array was prepared through anodization in aqueous or organic electrolytes, and their photoelectrochemical properties were compared. TiO 2 nanotubes array prepared in an aqueous electrolyte exhibited better intrinsic characteristics for water oxidation, including larger naked surface area, higher oxygen vacancies leading to improved electrical conductivity, higher donor density, and lower valence band edge position, compared to those prepared in an organic electrolyte. However, a higher photocurrent density was observed in the TiO 2 nanotubes array prepared in an organic electrolyte because of facile mass transfer, resulting in effective interaction between the generated holes and reactant. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anodization of TiO 2 nanotube arrays with various geometries was demonstrated. • The inner diameter and length of TiO 2 nanotubes can be altered by adjusting anodization parameters. • Long nanotube arrays exhibited high performance for 2,4,6-TNT detection in ambient conditions. • LOD and LOQ were 6.49 and 21.6 ppm, respectively, using optimized nanotube arrays. In this study, we investigated how the geometric design of anodic one-dimensional (1D) TiO 2 nanotube arrays affected their performance in the electrochemical reduction of 2,4,6-trinitrotoluene (2,4,6-TNT) in aqueous solutions and ambient conditions. Two main geometric parameters were considered: the inner diameter and length of TiO 2 nanotubes. The various TiO 2 nanotubes were fabricated using an anodization technique performed in four types of fluoride-containing organic solvents by adjusting various anodization parameters. All as-prepared samples successfully detected 2,4,6-TNT in an aqueous solution using cyclic voltammetry and linear sweep voltammetry. Three peaks corresponding to the reduction of each nitro group in 2,4,6-TNT were observed between − 0.5 and − 1.0 V (versus Ag/AgCl, 3 M KCl). Further, we discovered that nanotube length affected 2,4,6-TNT reduction performance. We also performed experiments at various concentrations of 2,4,6-TNT and determined the sensitivity to be 1.78 × 10-3 mA cm−2 ppm−1, the limit of detection to be 6.49 ppm, and the limit of quantitation to be 21.6 ppm 2,4,6-TNT over a linear range of 20 – 100 ppm using an electrode with nanotube inner diameter of 75 nm and length of 6 µm. A simple and fast fabricated composite-free 1D TiO 2 nanotube arrays electrode can form the basis for future studies in enhancing the detection sensitivity. Electrochemical detection of other nitro-based compounds, such as nitroglycerin, nitrocellulose, picric acid, and their mixtures, require further investigation. [ABSTRACT FROM AUTHOR]