Formation of Double‐Walled TiO<sub>2</sub> Nanotubes and Robust Anatase Membranes

Albu, Sergiu P.; Ghicov, Andrei; Aldabergenova, S.B.; Drechsel, Peter; LeClere, Darren J.; Thompson, G.E.; Macák, Jan M.; Schmuki, Patrik

doi:10.1002/adma.200801189

Cited by 459 publications

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“…This leads to a twin-wall morphology of TiO 2 nanotubes [46]. Typically the inner shell of TiO 2 nanotubes is of inferior quality.…”

Section: Specific Other Morphologies and Factorsmentioning

confidence: 99%

“…refs [1,44,45]. It should be noted though that the as-formed tubes are amorphous and contain significant amount of fluorides and typically carbon, and for many applications need to be thermally crystallized to anatase or mixed anatase/rutile structures [46]. Furthermore, it is worth mentioning that using dilute fluoride electrolytes, similar aligned oxide tubes or pore-morphologies can be grown on a full range of other metals (Zr [47][48][49], Hf [50], Ta [51][52][53], Fe [54][55][56], Nb [57,58], Co [59], V [60]) and many alloys, see e.g.…”

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Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

Zhou

Nguyen

Özkan

et al. 2014

Electrochemistry Communications

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The present review gives an overview of the highlights of more than 10 years of research on synthesis and applications of ordered oxide structures (nanotube layers, hexagonal pore arrangements) that are formed by self-organizing anodization of metals. In particular we address the questions after the critical factors that lead to the spectacular self-ordering during the growth of anodic oxides that finally yield morphologies such as highly ordered TiO 2 nanotube arrays and similar structures. Why are tubes and pores formed -what are the key parameters controlling these processes?Link to the published article: http://dx.doi.org/10.1016/j.elecom.2014.06.021 1 Over the past decade, the formation and application of anodic, self-organized TiO 2 nanotube arrays grown from a Ti metal (as illustrated in Fig.1) and similar oxide structures have attracted wide scientific and technological interest [1][2][3][4][5][6][7]. Self-organization during anodization has been observed already more than 70 years ago for aluminum that, when anodized in acidic electrolytes, forms hexagonally ordered porous structures [8] -such ordering can peak in a virtually perfect arrangement, as demonstrated by Masuda et al. in 1995 [9], by a meticulous optimization of the electrochemical growth conditions. These alumina structures since then have been widely used for templating (i.e., to fill the pores by a secondary material to form nanorods or nanowires, in combination with stripping the template or not), as well as for numerous other applications -excellent overviews on growth and applications of porous alumina are available; see e.g. refs. [2][3][4]10,11].In the past few years, however, research activities on ordered TiO 2 nanotube layers have in numbers of paper-output surpassed porous alumina; in the past decade, more than three thousand papers have been published dedicated to anodic TiO 2 nanotubes [1,[5][6][7]. The main reason for this enormous interest is the anticipated impact of such nanotube layers in functional applications of titanium dioxide; such as dye sensitized solar cells [12][13][14][15], photocatalysis [16,17] (including water splitting for the generation of hydrogen, pollution degradation, or the reduction of CO 2 ), biomedicine [18][19][20] (biomedical coatings of implants, drug delivery systems), ion-insertion batteries, electrochromics, etc. [21][22][23][24] These applications are, to a large extent, based on a number of almost unique features of TiO 2 [1,[25][26][27][28]: it is a semiconductor of a band-gap of 3.0 eV (rutile) -3.2 eV (anatase), with a considerably large electron diffusion length (mainly anatase), relative band-edge positions suitable to trigger a wide range of photocatalytic reactions; the material is highly biocompatible, and shows considerably good ion intercalation properties. Many of these features can be exploited in a nanotubular form even more beneficially than in powder assemblies (e.g. directional charge transport, orthogonal carrier separation, optimized and directional diffusion profile...

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“…This leads to a twin-wall morphology of TiO 2 nanotubes [46]. Typically the inner shell of TiO 2 nanotubes is of inferior quality.…”

Section: Specific Other Morphologies and Factorsmentioning

confidence: 99%

mentioning

confidence: 99%

Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

Zhou

Nguyen

Özkan

et al. 2014

Electrochemistry Communications

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138

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“…2a and 2b) show for the non-implanted reference sample the typical anatase pattern of conventionally annealed TiO 2 nanotubes [26].…”

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“Black” TiO₂ Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H₂-Evolution

et al. 2015

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Abstract:We apply high-energy proton ion-implantation to modify TiO 2 nanotubes selectively at their tops. In the proton-implanted region we observe the creation of intrinsic co-catalytic centers for photocatalytic H 2 -evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO 2 nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained. Keywords:nanotubes; photocatalysts; water-splitting; titania; self-organization; ion-implantation 2 Ever since 1972, when Honda and Fujishima introduced photolysis of water using a single crystal of TiO 2 , photocatalytic water splitting has become one of the most investigated scientific topics of our century [1]. The concept is strikingly simple: light (preferably sunlight) is absorbed in a suitable semiconductor and thereby generates electron-hole pairs. These charge carriers migrate in valence and conduction bands to the semiconductor surface where they react with water to form O 2 and H 2 , respectively. Thus hydrogen, the energy carrier of the future, could be produced using just water and sunlight.Key factors for an optimized conversion of water to H 2 are i) as complete as possible absorption of solar light (small band gap) while ii) still maintaining the thermodynamic driving force for water splitting (sufficiently large band-gap), including suitable band-edge positions relative to the water red-ox potentials, and iii) possibly most challenging -a sufficiently fast carrier transfer from semiconductor to water to obtain a reasonable reaction kinetics as opposed to carrier recombination or photo-corrosion [2][3][4][5][6][7].In spite of virtually countless investigations on a wide range of semiconductor materials that in many respects are superior to titania (mostly in view of solar light absorption and carrier transport), TiO 2 still remains one of the most investigated photocatalysts. This is only partially due to suitable energetics but more so because of its outstanding (photo-corrosion) stability [2][3][4][5][6][7].In general, the main drawbacks of TiO 2 are on the one hand its too large band-gap of 3-3.2 eV that allow only for about 7% of solar light absorption, and on the other hand that although a charge transfer to aqueous electrolytes is thermodynamically possible, the kinetics of these processes at the TiO 2 /water interface are extremely slow if no suitable co-catalysts such as Pt, Au, Pd or similar are used [8][9][10]. Mao demonstrated a significantly increased photocatalytic activity for water splitting when black TiO 2 was loaded with a Pt co-catalyst and used under bias-free conditions (i.e. used directly as a nanoparticle suspension in an aqueous/methanol solution under sunlight (AM 1.5) conditions). The high catalyst activity was attributed to a thin amorphous TiO 2 hydrogenated layer that was formed under high pressure tre...

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“…These TiO 2 tubes are usually amorphous after growing but can be converted to anatase by annealing at temperatures (T) higher than 300 C. 14,15 After annealing, the nanotubes are polycrystalline with an average grain size of 10 to 50 nm. 16,17 We have used impedance spectroscopy in order to discern between the mechanisms of conduction given by the possible electron pathways in the sample. 18 To characterize the contact resistance we have also studied the current-voltage (I-V) characteristics using two points measurements as recently reported for single TiO 2 nanotubes.…”

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Transport properties of single TiO2 nanotubes

Stiller

Barzola‐Quiquia

Lorite

et al. 2013

Applied Physics Letters

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We investigated the electric transport properties of single TiO2 nanotubes separated from an anodic titania nanotube array. The temperature dependence of the resistance measured with the conventional four point method of all investigated samples show a Mott variable range hopping behavior. The results obtained with two contacts indicate the existence of a potential barrier between the Cr/Au contacts and samples surfaces, which influence is clearly observable at temperatures <150 K. Impedance spectroscopy in the frequency range of 40 Hz to 1 MHz carried out at room temperature indicates that the electronic transport of these polycrystalline tubes is dominated by the grain cores.

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Formation of Double‐Walled TiO₂ Nanotubes and Robust Anatase Membranes

Cited by 459 publications

References 50 publications

Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

“Black” TiO₂ Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H₂-Evolution

Transport properties of single TiO2 nanotubes

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Formation of Double‐Walled TiO2 Nanotubes and Robust Anatase Membranes

Cited by 459 publications

References 50 publications

Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

Anodic TiO2 nanotube layers: Why does self-organized growth occur—A mini review

“Black” TiO2 Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H2-Evolution

Transport properties of single TiO2 nanotubes

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Formation of Double‐Walled TiO₂ Nanotubes and Robust Anatase Membranes

“Black” TiO₂ Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H₂-Evolution