Anatase Nanotubes Research Articles

Evidence of the Electrochemical Ca2+ Intercalation in Anatase Nanotubes

AbstractHere, we demonstrate the electrochemical intercalation of Ca2+ ions within the lattice of anatase nanotubes (a‐NTs) synthesized by hydrothermal treatment of TiO2/NaOH precursors followed by Na+/H+ ion exchange and H2O‐loss at high temperature in air. Scanning electron microscopy, X‐ray diffraction, and Raman spectroscopy confirm the formation of nanosized anatase, whereas transmission electron microscopy highlights the formation of nanotubular morphologies with an average diameter of 10 nm. TiO2 electrodes are able to deliver reversible specific capacities in aprotic batteries vs. calcium metal or in hybrid configurations vs. capacitive activated carbon using aprotic electrolytes (i. e., Ca(BH4)2 in tetrahydrofuran or Ca(TFSI)2 in dimethoxyethane, respectively). The electrochemical intercalation of Ca2+ ions into the anatase lattice is confirmed by X‐ray absorption spectroscopy in close comparison with Na+ and Li+ intercalations. Ca2+ incorporation leads to the partial amorphization of the TiO2 lattice despite the limited Ca/Ti ratio (i. e., 0.09) obtained in discharge. The analysis of the extended X‐ray absorption fine structure region allows the determination of the local structure of the incorporated Ca2+ ions and confirms that a disordered environment is obtained after the electrochemical reaction.

Surface modification of TiO2 nanotubes via pre-loaded hydroxyapatite towards enhanced bioactivity

Anodic TiO2 nanotubes (NTs) are widely established in biomedical applications, as the sub-100 nm morphology significantly impacts their biological activity. In this study, we examine the use and surface functionalization of TiO2 nanotube layers on titanium substrates to facilitate the formation of hydroxyapatite, a crucial ability for implant applications. TiO2 NT layers are grown by electrochemical anodization and the focus is on as-formed and anatase NTs with 100- and 15-nm-diameters, the latter amorphous and available in double-wall (DT) or single-wall (ST) structures. Surface modification of the TiO2 NTs is achieved through an alternate immersion method (AIM) or a simple CaCl2 immersion. The former deposits hydroxyapatite (HA) coatings on/in the NT layers, while the latter forms a thin Ca-surface-modified layer on the TiO2 surface. Both methods effectively induce the formation of an HA layer on 100-nm-diameter NTs after five days of immersion in simulated body fluid (SBF). The chemical composition of NTs is a deciding factor, as the 100-nm-diameter NTs that already contain phosphates (from the anodizing electrolyte) also lead to HA formation by modification via Ca-functionalization (CaCl2 immersion). Whereas, for smaller diameter NTs, the surface nanotopography of the DT and ST NTs is key for the HA nucleation and formation via the AIM approach, but not via immersion in a calcium-containing solution. This promising approach accelerates the growth of HA on TiO2 nanomaterials by initiating apatite nucleation on TiO2 NTs and, thus, has significant implications for increasing their bioactivity in biomedical applications.

Structural and Electromagnetic Signatures of Anatase and Rutile NTs and Sheets in Three Different Water Models under Different Temperature Conditions.

Experimental studies of TiO2 nanotubes have been conducted for nearly three decades and have revealed the remarkable advantages of this material. Research based on computer simulations is much rarer, with research using density functional theory (DFT) being the most significant in this field. It should be noted, however, that this approach has significant limitations when studying the macroscopic properties of nanostructures such as nanosheets and nanotubes. An alternative with great potential has emerged: classical molecular dynamics simulations (MD). MD Simulations offer the possibility to study macroscopic properties such as the density of phonon states (PDOS), power spectra, infrared spectrum, water absorption and others. From this point of view, the present study focuses on the distinction between the phases of anatase and rutile TiO2. The LAMMPS package is used to study both the structural properties by applying the radial distribution function (RDF) and the electromagnetic properties of these phases. Our efforts are focused on exploring the effect of temperature on the vibrational properties of TiO2 anatase nanotubes and an in-depth analysis of how the phononic softening phenomenon affects TiO2 nanostructures to improve the fundamental understanding in different dimensions and morphological configurations. A careful evaluation of the stability of TiO2 nanolamines and nanotubes at different temperatures is performed, as well as the adsorption of water on the nanosurface of TiO2, using three different water models.

Experimental Studies on TiO2 NT with Metal Dopants through Co-Precipitation, Sol-Gel, Hydrothermal Scheme and Corresponding Computational Molecular Evaluations.

In the last decade, TiO2 nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO2 nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO2 nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO2 nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO2 hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO2 nanotubes with metal doping for ion storage devices such as batteries.

Removal of contaminants of emerging concern by photocatalysis with a highly ordered TiO2 nanotubular array catalyst

In this work, the treatment of wastewater polluted with contaminants of emerging concern is evaluated by heterogeneous photocatalysis with TiO2. Titanium plates are anodized by different experimental conditions, and the influence of these conditions on the catalytic performance is evaluated by factorial design of experiments. The formation of TiO2 nanotubes in the anatase form is sought for photocatalysts with high active surface. Thus, electrolyte used in the anodization process (NH4F/H2O in ethylene glycol or H2SO4 in water), potential ramp (2 – 4 V min−1), maximal applied potential (20 – 60 V) and heat treatment are evaluated as influencing factors of the experimental design. The activity of these catalysts is tested by ofloxacin (pharmaceutical compound used as model of contaminant of emerging concern) degradation in wastewater treatment, obtaining the kinetic constant of the process, parameter chosen as response variable of the experimental design. Results show that NH4F/H2O as electrolyte, 2 V min−1, 40 V and a heat treatment are the optimum conditions for the formation of TiO2–anatase nanotubes with a good disposition and arrangement, observing the higher efficiency in the wastewater treatment process. In addition, wastewater treatment conditions are evaluated (UV wavelength, irradiance and initial concentration of ofloxacin), and it is found that UV-B, maximal irradiance and minimal initial concentration of the pollutant are the optimal factors for a higher process efficiency. This is a work that opens the door to the removal of contaminants of emerging concern from wastewater with a technology of low cost, with easy implantation and environmental compatibility, making possible to use only sunlight as a reagent.

Stable and Reversible Lithium Storage Properties of LiTiOx Nanotubes for Electrochemical Recovery from Aqueous Solutions

AbstractIn the present work, an easy and scalable method to prepare lithium titanium oxide nanotubes with stable and reversible lithium storage properties is reported. This material could be an excellent candidate for lithium recovery from aqueous solutions or have a direct application as Li‐ion batteries electrodes in a circular economy perspective. Vertically oriented anatase nanotubes are grown by anodic oxidation in an ethylene glycol‐based electrolyte. Then, the nanotubes are hydrothermally converted into a mixed lithium titanate. Morphological and crystallographic characterizations confirm the successful shape‐preserving conversion after which the nanotubes are subjected to electrochemical cycling. XRD and XPS analyses confirm a significant lithium uptake after cycling, and its recovery is investigated by means of an acidic treatment. While allowing for an almost complete recovery of the lithium integrated in their structure, the nanotubes also showed excellent morphological and structural stability proving to be excellent candidates for lithium recovery purposes.

Space charge limited conduction in anatase and mixed-phase (anatase/rutile) single TiO2 nanotubes

TiO2 nanotube arrays are used for several applications; however, in-depth analysis of charge conduction through an individual nanotube is necessary to predict the behavior of devices and to achieve higher efficiency. Here we report successful isolation and charge transport study through individual nanotubes annealed at different conditions. Anatase or anatase/rutile mixed-phase nanotubes are obtained by annealing in air or nitrogen at temperatures 450 and 650 °C, respectively. Current-voltage measurements in the range of 213 K–413 K indicate that the charge transport through single nanotubes follows Ohmic conduction in lower voltage and trap-assisted space charge limited conduction (SCLC) at higher voltage. Charge transport is controlled by two thermal activation processes resulting in two different values of activation energy, which changes with applied voltage. The activation energy in mixed-phase sample is higher than in the anatase nanotube. Calculated values of trap density vary from 9.28 × 1013/cm3 for anatase nanotubes to 6.60 × 1015/cm3 for mixed-phase (∼52% rutile) and 3.34 × 1016/cm3 in mixed-phase nanotubes (∼76% rutile). The variation of trap density with an increase in rutile phase is attributed to electron trapping by rutile regions arising from a corresponding band alignment. This is also reflected in room temperature conductivity which decreases with increase in rutile content.

Direct Electrochemical Visualization of the Orthogonal Charge Separation in Anatase Nanotube Photoanodes for Water Splitting

Photoelectrochemical (PEC) water splitting is an important and rapidly developing technology that produces H2 as a renewable resource, but local surface investigations remain a major challenge. Using scanning electrochemical cell microscopy (SECCM), the PEC catalytic effects of anatase TiO2-nanotube arrays grown on Ti felt are explored. The SECCM imaging is performed both perpendicular and parallel to the nanotube growth direction. In contrast to bulk cyclic voltammetry measurements, SECCM measures only the upper region of the nanotubes that remain in contact with the electrolyte, which provides a better understanding of the phenomena connected to the longitudinal charge transport. Despite the presence of regions with higher and lower photocurrent, the PEC reactivities of the nanotube tops and walls are roughly comparable with each other. The data support the model of orthogonal electron–hole separation. This model facilitates the photogenerated hole diffusion over the short distance to the electrolyte interface due to the sufficient transport of photoexcited electrons along the long axial direction of TiO2 nanotubes and is often applied to one-dimensional systems. Observed results were additionally supported by the nanotube decoration with photoelectrochemically deposited PbO2 particles.

Anatase TiO2 nanotubes as Li-ion battery anodes: A molecular dynamics study of Li-ion adsorption on anatase nanotubes

Lithium ion batteries are widely used in many electronic devices to store energy and release it when needed. Higher storage capacities and higher charge/discharge rates necessitates use of advanced materials. One way of increasing this rate is surface storage rather than bulk storage of Li-ions. This is facilitated by nanosizing the electrodes. One of the potential candidates for this task as the Li-ion battery anode is TiO2 nanotubes. In this research we studied the adsorption of Li-ions on anatase nanotubes using molecular dynamics simulations. Li-ions are dispersed in a simulation box around a TiO2 nanotube and due to the non-bonding interactions, they adsorb on the nanotubes. Our results showed that the volume change of the nanotubes due to this adsorption is negligible which enhances the cycle life of these anodes. And with increasing the temperature to 1000 K, the number of adsorbed ions increases and remains close to the maximum, but With further increase in temperature, the number of adsorbed ions decreases over time. We have also confirmed that the Li-ions adsorb in tetrahedral sites of anatase and molecular dynamics simulations in the range of nanoseconds cannot capture the hopping of these ions within the tetrahedral sites. In addition, using the adsorption isotherms we showed that when the surface coverage is small the adsorptions obey a Langmuir-type isotherm.

Removal of chemical oxygen demand from industrial estate sewage over hybridized anatase-graphene oxide-carbon nanotubes nanocomposite under solar irradiation

The aim of present work was to investigate the performance of hybridized materials, containing anatase, graphene oxide (GO), and carbon nanotubes (CNTs) in the photocatalytic treatment of sewages discharged from the industrial estate. The obtained results demonstrated the ability of hybridized nanocomposite for the solar treatment of sewages collected from different stages of industrial recovery process, between upstream of anaerobic system, and downstream of sand filter. The appropriate proportions of GO, and CNTs were determined, as 3.33 %. The effects of variables like initial COD, irradiation time, sewage collection position, and pH were evaluated on the treatment performance. If the initial COD is controlled at the level of 780 mg.l−1, the COD removal efficiency reaches to ∼90 % which is the prohibitive condition in the industrial scale. The maximal photoactivity was achieved within 20 min by the control of sewage pH at the level of 8. The COD removal kinetics were related to the load of anatase nanoparticles, < 20 nm, specific surface area, 60 m2. g−1, and band gap energy, 2.1 eV, of prepared nanocomposite which is a promising material for the wastewater cleaning in the real condition.

PtOx-TiO2 anatase nanomaterials for photocatalytic reformation of methanol to hydrogen: effect of TiO2 morphology

Pure TiO2 anatase semiconductor materials with three different morphologies (nanoparticles, nanotubes and nanofibers) were used to disperse with PtOx (2.0 wt.% nominal loading) nanoparticles. Structural, electronic and morphological characteristics of the calcined materials were studied by using XRD, Raman, DR UV–vis, XPS spectroscopy, transmission electron microscopy and N2 physisorption techniques. The band gap energy values were obtained from the Tauc plots and band gap energy values were decreased after deposition of PtOx over TiO2 nanomaterials. PtOx-TiO2 anatase nanotubes (2.0 Pt–Ti-A-NT) sample possessed unique physico-chemical properties such as high Pt dispersion, high surface area, pore volume and pore diameter in the range of 10–40 nm with unimodal distribution. The photocatalytic performances of all synthesized samples were tested for hydrogen production via reforming of aqueous methanol under visible light irradiation. To optimize the reaction conditions, several parameters such as methanol concentration, mass of the catalyst, pH of solution and reaction temperature were studied. Among the synthesized samples, 2.0PtOx-TiO2 anatase nanotubes sample exhibited highest photo activity for hydrogen generation. The observed results indicated the significant role of the morphology of TiO2 anatase semiconductor; decrease of the band gap energy, increasing electron storage and delayed electron–hole recombination due to high interaction between PtOx and TiO2 nanotubes. The highest performance for 2.0 PtOx-TiO2 anatase nanotubes sample at a promising hydrogen quantity of 1489 μmolg−1 was observed at 50 °C after 3 h.

The storage mechanism difference between amorphous and anatase as supercapacitors

Although TiO2 nanotubes is a promising electrode as supercapacitors due to its high energy density, easy synthesis and chemical stability, there are draw backs such as low conductivity and capacitance. Many studies concentrated on improving its electrochemical performance itself but little attention was payed to the reason of capacitance differences caused by its different crystal structures. Herein, we prepare amorphous and anatase TiO2 nanotubes and hydrogenated them by a simple electrochemical hydrogenation method to improve their conductivity and capacitance. And then study and compare their morphology and structure differences by SEM, TEM, XRD and BET. The results show that the pore size distribution, internal structure order and internal carrier concentration are the main reasons for their electrochemical performance differences. The microporous structure less than 2 nm in amorphous nanotubes act as a trap of electrolyte ions at current density larger than 0.1 μA cm−2, leading to small charge and discharge capacitance. The long-range ordered crystal structure of anatase is more favorable for the orderly diffusion of carriers, reducing the inelastic scattering of carrier diffusion process and the electron hole-complexing probability, making anatase nanotubes exhibit higher coulomb efficiency and cycle stability than that of amorphous ones.

Effect of size and crystalline phase of TiO2 nanotubes on cell behaviors: A high throughput study using gradient TiO2 nanotubes

The research of TiO2 nanotubes (TNTs) in the field of biomedicine has been increasingly active. However, given the diversity of the nanoscale dimension and controversial reports, our understanding of the structure-property relationships of TNTs is not yet complete. In this paper, gradient TNTs with a wide diameter range of 20–350 nm were achieved by bipolar electrochemistry and utilized for a thorough high-throughput study of the effect of nanotube dimension and crystalline phase on protein adsorption and cell behaviors. Results indicated that protein adsorption escalated with nanotube dimension whereas cell proliferation and differentiation are preferred on small diameter (<70 nm) nanotubes. Large diameter anatase nanotubes had higher adsorption of serum proteins than as-prepared ones. But only as-prepared small diameter nanotubes presented slightly higher cell proliferation than corresponding annealed nanotubes whereas there was no discernible difference between as-prepared and annealed nanotubes on cell differentiation for the entire gradient. Those findings replenish previous research about how cell responses to TNTs with a wide diameter range and provide scientific guidance for the optimal design of biomedical materials.

Synthesis of Anodic TiO2 Nanotube Arrays Annealed at 700°C for UV Photodetector

Anodic titanium dioxide (TiO2) nanotube arrays on Ti foil were synthesized using electrochemical anodization technique and annealed at 700 °C without annihilating the nanotubular assemblies. The nanotubular structure was used to fabricate UV photodetection device based on Metal-Semiconductor-Metal. The photodetection device exhibited UV-sensitive photoresponse characteristics due to the mixed anatase and rutile phases of the TiO2 nanotube arrays. The photoresponse analysis showed good sensitivity to UV light irradiation with excellent stability and reproducibility. Moreover, the UV photodetector revealed the current gain is 7, response time is 0.77 s and decay time is 0.79 s, respectively at biased voltage 4 V. As mentioned above, the UV photodetector based on mixture of anatase and rutile phase nanotube arrays is a recommended nano-optoelectronic apparatus that is remarkably applicable over Ultraviolet band.

Self-Activation of TiO2 Nanotubes for Photocatalytic H2 Generation

TiO2 and particularly its anatase form, is one of the most widely studied oxide semiconductors for photocatalytic production of H2 from aqueous solutions.In anatase, the conduction band is situated at an energetic position that allows the transfer of photogenerated electrons to aqueous media and thus the conversion of H+ into H2. Moreover, TiO2 provides an almost unique high resistance against chemical and photocorrosion. On the other hand, photocatalytic H2 production from aqueous electrolytes shows very slow kinetics on all TiO2 surfaces. Therefore, typically decoration of titania with co-catalysts is used to accelerate the H2 evolution kinetics. Most effective co-catalysts are costly noble metals, such as Pt, Pd, or Au. Economically it is of great interest to develop means and approaches to reduce the use of such costly co-catalyst. In the presentation, we discuss efficient noble-metal-free approaches for catalyzing photocatalytic hydrogen generation. A particularly interesting approach is provided by defined defect engineering of anatase. Specific shallow Ti3+ states can promote the generation of photocatalytic H2. Most spectacular is that these catalytic sites can be formed by photoinduced reduction. In other words, under suitable illumination conditions it is possible to create, in situ, energetically suitable Ti3+ states that then act as an intrinsic co-catalyst for photocatalytic H2 evolution. As a result, both co-catalytic formation of active sites and photocatalytic H2 formation is observed. I.e., with increasing illumination time, a light‐induced self‐amplification of the photocatalytic H2 production rate occurs. The effect is characterized by electron paramagnetic resonance (EPR) spectroscopy, reflectivity, and photoelectrochemical techniques. The origin of the self‐activation and amplification behavior observed for anatase nanoparticles and nanotubes will be discussed in the presentation.

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.

Scaling up Photoelectrocatalytic Reactors: A TiO2 Nanotube-Coated Disc Compound Reactor Effectively Degrades Acetaminophen

Multiple discs coated with hierarchically-organized TiO2 anatase nanotubes served as photoelectrodes in a novel annular photoelectrocatalytic reactor. Electrochemical characterization showed light irradiation enhanced the current response due to photogeneration of charge carriers. The pharmaceutical acetaminophen was used as a representative water micropollutant. The photoelectrocatalysis pseudo-first-order rate constant for acetaminophen was seven orders of magnitude greater than electrocatalytic treatment. Compared against photocatalysis alone, our photoelectrocatalytic reactor at &lt;8 V reduced by two fold, the electric energy per order (EEO; kWh m−3 order−1 for 90% pollutant degradation). Applying a cell potential higher than 8 V detrimentally increased EEO. Acetaminophen was degraded across a range of initial concentrations, but absorbance at higher concentration diminished photon transport, resulting in higher EEO. Extended photoelectrocatalytic reactor operation degraded acetaminophen, which was accompanied by 53% mineralization based upon total organic carbon measurements. This proof of concept for our photoelectrocatalytic reactor demonstrated a strategy to increase photo-active surface area in annular reactors.

Electrochemical reduction on nanostructured TiO2 for enhanced photoelectrocatalytic oxidation

The influence of an electrochemical treatment method was investigated for two different TiO2 nanostructured materials, anatase nanotubes (TNT) and rutile nanorods (TNR). The treatment was done by performing cyclic voltammetry in acidic media. XPS measurements revealed a shift in Ti 2p peaks, suggesting the presence of Ti3+ after the partial reduction, as well as an increased peak associated to a higher hydroxylation degree of the surface. The treatment leads to an increase in the maximum photocurrent density, confirmed from linear sweep voltammograms and photon-to-electron conversion efficiencies (IPCE). The treatment is assumed to modify the charge carrier separation kinetics by inducing partial reduction of the TiO2. A markedly increased of two and three-fold in the IPCE was obtained for the reduced TNT and TNR, respectively, up to a maximum of 77% for TNR. This electrochemical treatment represents a facile and systematic approach to modify TiO2 nanostructured electrodes to achieve enhanced photoelectrocatalytic properties, as demonstrated by the current doubling experiments with MeOH.

Elastic properties of anatase titanium dioxide nanotubes: A molecular dynamics study**Project supported by the Key Research and Development Program of Hainan Province, China (Grant No. ZDYF2017098) and the Hainan Provincial Natural Science Foundation, China (Grant No. 519MS025).

The elastic properties of anatase nanotubes are investigated by molecular dynamics (MD) simulations. Youngʼs modulus, Poisson ratio, and shear modulus are calculated by transversely isotropic structure model. The calculated elastic constants of bulk rutile, anatase, and Youngʼs modulus of nanotube are in good agreement with experimental values, respectively, demonstrating that the Matsui and Akaogi (MA) potential function used in the simulation can accurately present the elastic properties of anatase titanium dioxide nanotubes. For single wall anatase titanium dioxide nanotube, the elastic moduli are shown to be sensitive to structural details such as the chirality and radius. For different chirality nanotubes with the same radius, the elastic constants are not proportional to the chiral angle. The elastic properties of the nanotubes with the chiral angle of 0° are worse than those of other chiral nanotubes. For nanotubes with the same chirality but different radii, the elastic constant, Youngʼs modulus, and shear modulus decrease as the radius increases. But there exist maximal values in a radius range of 10 nm–15 nm. Such information can not only provide a deep understanding of the influence of geometrical structure on nanotubes mechanical properties, but also present important guidance to optimize the composite behavior by using nanotubes as the addition.

Voids in walls of mesoporous TiO2 anatase nanotubes by controlled formation and annihilation of protonated titanium vacancies

Amorphous TiO2 nanotubes (TNTs) grown anodically on Ti metal in aqueous electrolytes show a crystallization behaviour strongly dependent on the atmosphere used during annealing at high temperature. In wet oxidizing conditions, the amorphous TNTs walls transform into relatively large and well crystallized anatase-like domains permeated by prismatic voids. On the other hand, crystallization of the amorphous nanotubes under dry reducing conditions induces nanocrystalline aggregates that do not show prismatic voids and exhibit different electronic properties. Supported by density functional theory calculations, it is argued that the formation or absence of voids can be understood in terms of formation and condensation of protonated titanium vacancies. Tunable morphology through defect chemical engineering as such, enables TNTs with increased surface area and catalytic activity, which find potential application in supercapacitors, sensors, photocatalysis, photoelectrochemistry, and dye-sensitized solar cells.