Anatase Crystalline Structure Research Articles

Cu clusters modified aligned titania nanotubes for photoelectrochemical water splitting

Abstract Limited availability of the fossil fuel resources, and their environmental impact has led to a rapid increase in the scientific interest towards renewable energy sources. Photoelectrochemical water splitting to produce hydrogen is one such technology. In the current work, aligned titania nanotubes were fabricated by electrochemical anodization and surface engineered with sub-nanometer Cu clusters for the enhanced photoelectrochemical responses. The nanotubes have anatase crystalline structure and are well covered on the surface as shown by X-ray diffraction and scanning electron microscopy, respectively. The surface modification of the nanotubes using Cu clusters enhanced the photoelectrochemical responses, indicative of improving the water splitting yield. The enhancement in photocurrent could be explained due to an extended absorption range or reduced recombination. As the enhancement was limited to the UV region and no visible response was observed, it was considered unlikely the surface modification altered the materials band gap. Instead, the enhancement is considered to be due to reduced recombination.

Кристаллические микроконусные покрытия на губчатом титане.

For the first time it was shown how to obtain microcone-shaped TiO2structures by means of anodizing of porous powder materials made of titanium sponge. It was established that during anodizing in 10 %Н2SO4+ 0,15 % HF electrolyte along with the growth of the X-ray amorphous nanoporous TiO2film a set of microcones with anatase crystalline structure is formed on the surface of titanium sponge powder particles. Microcones (height is up to 7m, base diameter is up to 5m) consist of multilayer nanoscale structures. Such structures are promising for the manufacture of new nanomaterials for catalytic and sensor devices.

Effect of Sb doping and polyvinylpyrrolidone on the mesoporous TiO2 photoanodes for Sb2Se3 sensitized solar cells

Abstract Mesoporous-TiO2:Sb layers were developed by sol-gel and spin-coating techniques for their application as photoanodes in SSSCs. The effect of Sb doping (4 mol%) and PVP loading (0.2-0.4 g) on the optical, structural, morphological, and chemical properties were studied. SEM results showed that the morphology, porosity, and particle size in the mp-TiO2:Sb depend on the amount of polymer and Sb doping. In particular, the doping decreases the porosity and particle size. XRD patterns showed well-defined reflections resembling the anatase crystalline structure. The crystallite size was of 22.61 and 16.27 nm for the undoped layers with 0.2 and 0.4 of PVP, which decreased to 17.69 and 7.93 nm for the doped ones. It was not observed the presence of Sb2O3 or Sb metallic, indicating Sb ions were inserted in the TiO2 lattice by substitution of Ti ions. Analysis of XPS spectra showed the presence of Ti4+, O2-, and Sb3+ in the mp-TiO2:Sb layers. The optical bandgaps of the mp-TiO2:Sb were in the range of 3.14-3.33 eV. The evaluation of the mp-TiO2:Sb layers as photoanodes in the Sb2Se3-sensitized solar cells gives a Voc of 261 mV, a Jsc of 3.92 mA/cm2, and a PCE of 0.71%.

Fast responsive anatase nanoparticles coated fiber optic pH sensor

The sol-gel method is employed to synthesize the phenol red encapsulated anatase nanoparticles (PR/ANPs) matrix at low temperature (60 °C). Field emission scanning electron microscopy/Energy Dispersive X-Ray (FESEM/EDX) analysis shows porous nanostructures, and uniform elemental distribution. Atomic Force Microscopy exhibited that after phenol red (PR) encapsulation, average surface roughness (Ra) is increased up to ∼ 20 nm than pure anatase matrix Ra ∼14 nm. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy analysis confirmed the presence of bond ∼ 1054 cm−1 which is indicative of good PR encapsulation within the anatase matrix. X-ray diffraction analysis (XRD) shows intense peak corresponding to phenol along with anatase peaks suggested the interaction of Ti and O atoms with PR species. High resolution transmission electron micrographs (HR-TEM) analysis exhibited crystalline anatase structure before and after encapsulation along (101) direction. The average particle size is observed 5 nm for ANPs matrix which reduced to 3 nm after encapsulation. Observed high surface area 218 m2/g after encapsulation is helpful to enhance the activity of the sensing device. Thermogravimetric analysis (TGA) shows that after 422 °C, no mass weight loss is observed which confirmed the thermal stability of synthesized matrices. After encapsulation, observed low refractive index 1.8 at 550 nm indicates the porous nature of the matrix. The fiber optic pH sensor shows a linear response over the dynamic pH range 1–12, sensitivity is calculated as 1.83 counts/pH at 454 nm with determination coefficient (R2) ∼ 0.97. The proposed sensing device has fast response time 1.09s–0.42s within acidic-basic media, good reversibility, and validity. Experimental findings suggested that synthesized material has great potential in photonic devices/applications.

Formation of TiO<sub>2</sub> Thin Film on Antibacterial Metal Injection Molding Stainless Steel Orthodontic Bracket 17-4 PH Using Physical Vapor Deposition Method

This study aims to equip orthodontic bracket SS 17-4 PH fabricated using metal injection molding with antibacterial properties. This can be achieved by applying TiO2 coating on the surface of brackets using magnetron sputtering PVD method. This method is chosen due to its compatibility to be used on bulk metal and its ability to control thin-film stoichiometry. Samples were prepared using the series of following steps which comprised of metal injection molding, binder elimination with solvent and thermal debinding, sintering in vacuum and argon atmosphere, electropolishing, and magnetron sputtering PVD coatings as the final stage. Negative bias, sputtering power, and partial pressure on vacuum chamber were set as the constant parameters. The atmosphere inside the PVD chamber was controlled using oxygen and argon gases. XRD and SEM observations were carried out to obtain the information on the phase and morphology of the films. Rutile and anatase crystalline structures with 2,27 nm and 9,78 nm crystal size were measured in as-deposited PVD TiO2 respectively. The deposition films were achieved in the range of 3 μm-8 μm.

Structural Changes of TiO2 as a Result of Irradiation by E-Beam and X-Rays

Abstract The subject of this research was to monitor and evaluate the effect of X-rays and e-beam irradiation on the structure of nanoscaled TiO2 and its properties. The samples of nanoscaled TiO2 were synthesized using the sol–gel method and subsequently exposed to thermal treatment to obtain the anatase crystalline structure. X-ray powder diffraction (XRPD) and Raman spectroscopy revealed the following changes in the structure as a result of the e-beam and X-ray irradiation: a decrease in the size of the crystallite of TiO2, an increase of the distance between the crystalline planes and the lattice parameters as well as the achievement of a certain degree of amorphization. As a consequence of the structural changes, thermal stability decreased. Also, a shift of the light absorption toward the visible end of the spectrum was detected and the energy of the band gap was reduced, indicating a better photocatalytic activity, i.e., the photocatalytic action can be shifted to the region of the visible light.

Sequential RTV/(TiO2/SiO2) nanocomposite deposition for suppressing the leakage current in silicone rubber insulators

The sequential deposition method is introduced for suppressing the leakage current in silicone rubber insulators. Room temperature vulcanizing silicone and TiO2/silica nanocomposites are sequentially deposited on silicone insulators surface. TEM results showed that TiO2 nanoparticles size is about 20–30 nm, and the structural study revealed their anatase crystalline structure. Silica nanoparticles are deposited on the surface of insulators by spray deposition. The contact angle was enhanced from 104° to 149° after nanoparticles deposition, which confirms the hydrophobicity improvement. Results show that leakage current for nanocomposite samples in a contaminated environment reduced to about 0.02 mA, which was 1 mA in insulators without any coating, indicating a remarkable improvement after coating. The stability of bare and coated insulators was examined under kaolin, salt, NH4Cl-contaminated environment, and also UV radiation for more than 500 h. Results show that the sequential deposition could be utilized as a cost-effective and scalable method for enhancing the hydrophobicity and stability of insulators.

Synergetic effect of the catalytic action of plasma jet deposited TiOx coatings and atmospheric pressure plasma treatment on the degradation of RYRR

This study explores the synergetic effect of the photocatalytic behavior of TiOx plasma-deposited coatings and atmospheric pressure plasma treatment on the degradation of remazol yellow-RR (RYRR) in aqueous solution. Therefore, the first part of this paper was dedicated to the development of TiOx coatings on substrates with various geometries and dimensions via a non-thermal atmospheric pressure plasma assisted polymerization using tetraisopropyl orthotitanate (TIOT) as a precursor. The plasma deposition processes were performed as a function of the deposition potential. The surface chemistry, morphology, structural and hydrophilic properties of the obtained TiOx coating were investigated by means of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and water contact angle (WCA) analysis. Results revealed the formation of TiOx characteristic chemical groups in a process that is highly dependent on the deposition parameters. TiOx coating were super-hydrophilic and exhibited a cauliflower-like morphology in which the anatase crystalline structure is predominated over the rutile phase. In the second part of the study, the photocatalytic nature of TiOx coatings and the simultaneous effect of an array of multi-jet plasma treatment on the degradation efficiency of RYRR molecules in aqueous solution are examined. The reactive species involved during the TiOx deposition and degradation processes were examined via optical emission spectroscopy (OES). The degradation efficiency was investigated using Uv–Vis spectroscopy. RYRR degradation and the formation of degradation products were further confirmed by high-performance liquid chromatography (HPLC). The variation in pH, total organic carbon (TOC) and electrical conductivity of the plasma treated RYRR was also assessed. Furthermore, the generation of reactive oxygen species (ROS) such as OH radicals and H2O2 in the solution was also studied spectroscopically. Overall, results showed that the degradation rate after the concurrent plasma-TiOx photocatalytic reactions was significantly higher than after plasma treatment alone due to the formation of higher concentrations of various ROS.

TiO2 Sol-gel Coating as a Transducer Substrate for Impedimetric Immunosensors

Given the importance of the transducer elements in the performance of sensors for various applications, as well as the growing search for devices that are capable of providing the response in shorter time, in this work, titanium dioxide was examined as a candidate for application in an electrochemical biosensor. A TiO2 coating deposited by sol-gel method on a silicon wafer was obtained with an anatase crystalline structure, as an n-type<br /> semiconductor with donor density equal to 2.954 · 1017 cm–3. Its surface was functionalized to be tested as a biosensor to detect snake venom of the Bothrops genera, and each step of the functionalization was investigated using Electrochemical Impedance Spectroscopy (EIS) and Cyclic voltammetry. Despite being less sensitive than the reference method ELISA, the TiO2-based biosensor was also capable of detecting the analyte of interest at 20 μg mL–1, revealing an increase in its leakage resistance and phase shift after incubation in this solution. Furthermore, the total time for carrying out the biodetection with the TiO2-coated device (41.24 ± 0.05 min) was estimated to be approximately 80 % shorter than that required by the labelled standard assay, which indicates that TiO2 is a promising electrochemical transducer for biosensing applications.

Anticorrosion of WO<sub>3</sub>-Modified TiO<sub>2</sub> Thin Film Prepared by Peroxo Sol-Gel Method

The aim of this study was to develop a method to prepare WO3-TiO2 film which has high anticorrosion property when it was coated on type 304 stainless steel. A series of WO3-modified TiO2 sols were synthesized by peroxo-sol gel method using TiCl4 and Na2WO4 as the starting materials. TiCl4 was converted to Ti(OH)4 gel. H2O2 and Na2WO4 were added in Ti(OH)4 solution and heated at 95°C. The WO3-TiO2 sol was transparent, in neutral (pH~7) solution, stable suspension without surfactant, nano-crystallite and no annealing is needed after coating, and very stable for 2 years in stock. WO3-TiO2 sol was formed with anatase crystalline structure. These sols were characterized by XRD, TEM, and XPS. The sol was used to coat on stainless steel 304 by dip-coating. The WO3-TiO2 was anatase in structure as characterized by X-ray diffraction. There were no WO3 XRD peaks in the WO3-TiO2 sols, indicating that WO3 particles were very small, possibly incorporating into TiO2 structure, providing the amount of WO3 was very small. The TiO2 particles were rhombus shape. WO3-TiO2 had smaller size area than pure TiO2. The SEM results showed that the film coated on the glass substrate was very uniform. All films were nonporous and dense films. Its hardness reached 2 H after drying at 100°C, and reached 5 H after annealing at 400°C. The WO3-TiO2 film coated on 304 stainless steel had better anticorrosion capability than the unmodified TiO2 film under UV light illumination. The optimum weight ratio of TiO2: WO3 was 100:4.

Glycerol-Mediated Facile Synthesis of Colored Titania Nanoparticles for Visible Light Photodegradation of Phenolic Compounds.

In this study, we developed a glycerol-mediated safe and facile method to synthesize colored titania nanoparticles (NPs) via solution route. Our method is considerably effective and greener than other options currently available. Colored titania NPs were produced by hydrolyzing TiCl4 precursor in aqueous solution containing different concentrations of glycerol (0.0, 1.163, 3.834, and 5.815 mol/L) and subsequent calcination at 300 °C for 1 h. Our results highlight firstly that glycerol-mediated synthesis is unlikely to affect the anatase crystalline structure of TiO2, and secondly, that it would lead to coloration, band gap narrowing, and a remarkable bathochromic redshift of the optical response of titania. More importantly, the synthesized colored titania have Ti3+ ions, which, at least in terms of our samples, is the major factor responsible for its coloration. These Ti3+ species could induce mid gap states in the band gap, which significantly improve the visible light absorption capability and photocatalytic performance of the colored titania. The photocatalytic experiments showed that the colored TiO2 NPs prepared in 1.163 mol/L aqueous glycerol solution displayed the best photocatalytic performance. Almost 48.17% of phenolic compounds and 62.18% of color were removed from treated palm oil mill effluent (POME) within 180 min of visible light irradiation.

Photocatalytic Degradation of Different VOCs in the Gas-Phase over TiO2 Thin Films Prepared by Ultrasonic Spray Pyrolysis

In this study, we deposited TiO2 thin films onto borosilicate glass by ultrasonic spray pyrolysis at 350 and 450 °C. The aim of study is to determine the effect of deposition temperature on photocatalytic activity of TiO2 thin films and to investigate the performance of TiO2 thin films on photocatalytic degradation of methyl tert-butyl ether (MTBE), acetone, acetaldehyde, and heptane as functions of different operating parameters. TiO2 thin films deposited at 350 and 450 °C have a thickness value of 190 and 330 nm, respectively. All as-prepared TiO2 films possess an anatase crystalline structure. According to the X-ray photon spectroscopy (XPS) study, the TiO2 thin film deposited at 350 °C showed a higher amount of oxygen vacancies and hydroxyl groups on the film surface after UV treatment. The aged-TiO2 thin film deposited at 350 °C showed a water contact angle (WCA) value of 0° after 10 min UV irradiation, showing superhydrophilic surface behavior. The TiO2 film deposited at 350 °C exhibited the highest amount of conversion of MTBE (100%). The results also showed that TiO2 films are capable of photocatalytic degradation of MTBE (100%) and acetaldehyde (approx. 80%) in humid air conditions and high airflow rate. The visible-light-activity of TiO2 thin films was tested with 5 ppm MTBE and acetone. TiO2 thin films deposited at 350 °C with a surface area of 600 cm2 showed 60% of MTBE and 33% of acetone degradation under VIS light.

Raman spectroscopic study of the influence of voltage-time on titania growth-fast anodized nanostructures

Many studies, focused in TiO2 nanotubes obtained by anodization, uses frequently a NH4F salt concentration from 0.3 – 0.5 wt% and the information about how voltage and time affects to nanotubes morphology, are valid for these concentration, moreover, this range induces a long time of anodized. TiO2 nanotubes were prepared by anodization process of a set of titanium foils in order to study the influence of time and voltage on the morphology of them. The anodization process consists of an organic media of ethylene glycol and 1.2 wt% of NH4F salts, voltage from 5 to 30 V for a time period from 1 to 6 hours, constant potential of 30 V for a time lapse from 10 to 360 minutes and 5 to 480 seconds. All anodized samples are rinsed and annealed to 400 °C by 3 hours to obtain an anatase crystalline structure. The morphological characterization was carried out by Field Emission Scanning Electron Microscopy (FESEM) to verify the presence of the nanostructures: nanopores, nanotubes and nanograss, these nanostructures were identified to appear for a time period from 5 to 480 seconds, 10 to 60 minutes and 1 to 6 hours, respectively. The surface morphology, inner diameter and length of the nanotubes varied with the electrochemical anodization parameters. Raman spectroscopy was used for optical characterization in order to identify the changes in signal intensity and Eg mode Shift and it was observed that intensity suffers an increment and Eg mode suffers a blue shift as a thickness function.

Insight into the Degradation Mechanisms of Atomic Layer Deposited TiO2 as Photoanode Protective Layer.

Around 100 nm thick TiO2 layers deposited by atomic layer deposition (ALD) have been investigated as anticorrosion protective films for silicon-based photoanodes decorated with 5 nm NiFe catalyst in highly alkaline electrolyte. Completely amorphous layers presented high resistivity; meanwhile, the ones synthesized at 300 °C, having a fully anatase crystalline TiO2 structure, introduced insignificant resistance, showing direct correlation between crystallization degree and electrical conductivity. The conductivity through crystalline TiO2 layers has been found not to be homogeneous, presenting preferential conduction paths attributed to grain boundaries and defects within the crystalline structure. A correlation between the conductivity atomic force microscopy measurements and grain interstitials can be seen, supported by high-resolution transmission electron microscopy cross-sectional images presenting defective regions in crystalline TiO2 grains. It was found that the conduction mechanism goes through the injection of electrons coming from water oxidation from the electrocatalyst into the TiO2 conduction band. Then, electrons are transported to the Si/SiOx/TiO2 interface where electrons recombine with holes given by the p+n-Si junction. No evidences of intra-band-gap states in TiO2 responsible of conductivity have been detected. Stability measurements of fully crystalline samples over 480 h in anodic polarization show a continuous current decay. Electrochemical impedance spectroscopy allows to identify that the main cause of deactivation is associated with the loss of TiO2 electrical conductivity, corresponding to a self-passivation mechanism. This is proposed to reflect the effect of OH- ions diffusing in the TiO2 structure in anodic conditions by the electric field. This fact proves that a modification takes place in the defective zone of the layer, blocking the ability to transfer electrical charge through the layer. According to this mechanism, a regeneration of the degradation process is demonstrated possible based on ultraviolet illumination, which contributes to change the occupancy of TiO2 electronic states and to recover the defective zone's conductivity. These findings confirm the connection between the structural properties of the ALD-deposited polycrystalline layer and the degradation mechanisms and thus highlight main concerns toward fabricating long-lasting metal-oxide protective layers for frontal illuminated photoelectrodes.

Growth of a TiO2 nanotubular layer without presence of nanograss in a short time

Many studies, focused in TiO2 anodized, uses frequently a NH4F salt concentration from 0.3 – 0.5 wt% and the whole information about how voltage, time and even pH affects to nanotubes morphology, are effective just for these concentration range. It is known, increasing salt concentration, the electrolyte increases their conductivity and anodization speed (oxidation-dissolution) suffer also an increment and for a specifically concentration 1.2wt%, there is no data about morphology repercussions. A TiO2 nanotubular matrix is synthesized, in order to identify the range of time where it is possible to obtain with no presence of nanograss. The anodization process consists of an organic electrolyte of ethylene glycol, deionized water and 1.2 wt% NH4F salts, constant potential of 30 V and a time lapse from 10 to 60 minutes (short time). All anodized samples are rinsed and annealed to 400 °C by 4 hours to obtain an anatase crystalline structure; no samples are cleaned in ultrasonic bath to preserve the nanograss structure. Optical characterization was performed by Raman Spectroscopy to identify the increases in signal intensity, associated with thickness. The morphological characterization was carried out by Scanning Electron Microscopy to verify the presence and density of the nanograss and nanotubes.

One-step hydrothermal synthesis of Ag decorated TiO2 nanoparticles for dye-sensitized solar cell application

Over the past few years, many efforts have been made to develop efficient visible light-activated photovoltaic materials. In this study, the Ag-TiO2 nanoparticles were synthesized by using the hydrothermal method. Ag-TiO2 nanoparticles showed significantly higher visible light absorption and better photovoltaic activity than anatase TiO2. TiO2 nanoparticles were decorated with different concentrations of Ag to improve their photovoltaic properties. All the as-prepared TiO2 and Ag-TiO2 nanoparticles showed a pure anatase crystalline structure. In addition, the Ag-doped nanoparticles showed broader absorption edges (which shifted to higher wavelengths) than the undoped nanoparticles. The solar conversion efficiency (η) of 0.1M Ag-decorated (Ag0.1-TiO2) nanoparticle-based dye-sensitized solar cell (DSSC) was 6.44%, which is ∼22% higher than that of the TiO2 nanoparticle-based DSSC (η of 5.05%).

Synthesis of N-F-codoped TiO2/SiO2 nanocomposites as a visible and sunlight response photocatalyst for simultaneous degradation of organic water pollutants and reduction of Cr (VI)

A new N-F-codoped TiO2/SiO2 nanocomposite was prepared by simple sol-gel method, and strongly stabilized on a substrate used in a fabricated photoreactor. The prepared photocatalysts were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, diffuse reflectance UV/Vis, photoluminescence, field emission scanning electron microscope, energy dispersive X-ray, transmission electron microscope, and N2 adsorption/desorption methods. The effective parameters of pH, flow rate of the incoming current, and the photoreactor tubes angle against sunlight were optimized. The photocatalytic performance of prepared photocatalysts was evaluated by studying the simultaneous removal of a mixture containing three azo dyes and Cr (VI) in the fabricated continuous-flow photoreactor under visible and solar irradiation. The performance of the designed system was also proved under various outdoor climate conditions. Total organic carbon and flame atomic absorption spectroscopy analysis were performed on the treated sample to confirm the decontamination of the model pollutant mixture. It was found that doping N and F in TiO2/SiO2 nanoparticles caused least agglomeration, enhanced activity under visible and solar irradiation, and fully anatase crystalline structure in the as-synthesized nanoparticles.

Silica-coated nanocrystalline TiO2 with improved thermal stability

Deposition of a SiO2 coating on anatase TiO2 nanocrystals is shown to improve their thermal stability. As low as 0.5% Si was shown to preserve the small anatase crystallite size after calcination at 600 °C. Such treatment led to considerable sintering of TiO2 nanocrystals without the silica with the average particle size growth from 9 to 50 nm, surface area decrease from 135 to 22 m2/g and partial anatase conversion to rutile. The phase composition, crystallite size, and surface area of 5%Si-TiO2 samples were largely preserved till the temperatures as high as 800 °C whereas the anatase phase was mostly stably even after calcination at 1000 °C. The phase transformation from anatase to rutile in xerogel TiO2 and TiO2@SiO2 samples apparently did not occur until the crystallites grew larger than the critical size about 50 nm. Electron-acceptor sites capable of ionizing perylene to its radical cations were observed on all samples with anatase crystalline structure. So, the silica shell deposition improves the TiO2 thermal stability without limiting access to the surface active sites.

Photocatalytic oxidation of nitrogen oxides over {001}TiO2: the influence of F- ions.

A series of anatase TiO2 nanosheets with different percentage of {001} facets ({001}TiO2) were synthesized through a hydrothermal route using tetrabutyltitanate as a titanium precursor and HF as a shape controlling agent. The amount of HF exhibits an obvious influence on the structures and activities of TiO2 samples. The adsorbed surface F- ions on the {001} facets of the anatase TiO2 were removed by washing them with NaOH solution. The as-prepared catalysts were characterized by X-ray diffraction, Brunner-Emmet-Teller measurements, ultraviolet-visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy techniques, and X-ray photoelectron spectroscopy analysis. The results indicated that all the as-prepared catalysts showed an anatase crystalline and nanosheet structure, as well as a strong ultraviolet light absorbance. With the increase of HF content, the crystallite size and the percentage of {001} facets increased first and later decreased, state the opposite change observed in BET. When the content of HF was 4.4mL, the percentage of {001} facets reached the maximum up to 61.62%. After all samples were treated with 0.1M NaOH solution, the percentage of {001} facets increased to a maximum of 64.46%. All the samples washed by NaOH solution exhibited much higher photocatalytic activity for NOx oxidation under UV light irradiation than P25, {101}TiO2, and {001}TiO2 without NaOH washing, suggesting that the surface F- ions inhibited the photocatalytic NOx oxidation. Moreover, the results showed that the NaOH-washed {001}TiO2 has a high humidity tolerance.

Low temperature amorphous to anatase phase transition of titanium oxide nanotubes

This work reports a systematic investigation on the effects of time and temperature of hydrothermal vapor treatment (HVT) induced phase transition of amorphous TiO2 nanotube (NT) to anatase. We find that upon HVT, nanoparticles (NPs) appear to aggregate on the tops and sides of the NTs resulting in surface roughening and in the most severe case, the collapse of the NT to ordered NP arrays while retaining their highly crystalline anatase structure. Interestingly, we also find that a modest temperature of 130 °C is sufficient for inducing crystallization of anatase with the integrity of the NT array remaining intact. Increasing HVT duration results in larger crystallites of anatase with high degree of crystallinity. X-ray absorption near edge structure (XANES) spectroscopy recorded in total electron yield and partial fluorescence yield enables the tracking of the phase transition at the surface and in the bulk of the NT; that is, that bulk crystallizes more readily than the surface. The aggregated NPs on the surface are found to comprise of a core-shell structure where the core is anatase and the shell remains amorphous. The phase transition proceeds outward from the bulk.