Titania Nanotube Layer Research Articles

Atomic Layer Deposition of Noble Metal Nanoparticles for Electrocatalytic Applications

Noble metals such as Pt, Ru, Pd, Ir, etc., have superior performance for various catalytic applications [1]. Due to their scarcity, efforts were being made to reduce the mass/loading or replace these noble metals. Atomic Layer Deposition (ALD) is one among the best technique to facilitate lowering of loading mass on a support of interest [2,3]. Due to the governing surface energy variations between noble metals and support surfaces, the growth initiates as nanoparticles (NP) and with a further increase in ALD cycles the agglomeration among NP’s dominates over the individual NP size increase, thus developing thin films of relatively higher thickness.For electrocatalytic applications, it is important to choose the right substrates. Among available substrates, carbon papers and titania nanotube layers are best choices considering their physio-chemical properties, availability and low costs incurred.The uniform decoration of these substrates by NPs of catalysts proved to be highly efficient in electrocatalysis, as shown in our recent papers [3-5].The presentation will introduce and describe the synthesis of different noble metal NPs by ALD on important substrates. It will also include the corresponding physical and electrochemical characterization and encouraging results obtained in electrocatalysis.

Laser-Treated MXene as an Electrochemical Agent to Boost Properties of Semitransparent Photoelectrode Based on Titania Nanotubes.

In this study, Ti3C2Tx underwent laser treatment to reshape it, resulting in the formation of a TiO2/Ti3C2Tx heterojunction. The interaction with laser light induced the formation of spherical TiO2 composed of an anatase-rutile phase on the Ti3C2Tx surface. Such a heterostructure was loaded over a titania nanotube (TNT) layer, and the surface area was enhanced through immersion in a TiCl4 solution followed by thermal treatment. Consequently, the photon-to-electron conversion efficiency exhibits a 10-fold increase as compared to bare TNT. Moreover, for the sample produced with optimized conditions, five times higher photoactivity is observed in comparison to bare TNT. It was shown that under visible light irradiation the most photoactive heterojunction based on the tubular layer reveals a substantial drop in the charge transfer resistance of about 32% with respect to the dark condition. This can be attributed to the narrower band gaps of the modified material and improvement of the separation efficiency of the photogenerated electron-hole pairs. Overall results suggest that this investigation underscores TiO2/Ti3C2Tx as a promising noble-metal-free material that enhances both the electrochemical and photoelectrochemical performances of electrode materials based on TNT that can be further used in light-harvesting applications.

Osteoimmune-modulating and BMP-2-eluting anodised 3D printed titanium for accelerated bone regeneration.

3D printing of titanium (Ti) metal has potential to transform the field of personalised orthopaedics and dental implants. However, the impacts of controlled surface topographical features of 3D printed Ti implants on their interactions with the cellular microenvironment and incorporation of biological growth factors, which are critical in guiding the integration of implants with bone, are not well studied. In the present study, we explore the role of surface topological features of 3D printed Ti implants using an anodised titania nanotube (TiNT) surface layer in guiding their immune cell interaction and ability to deliver bioactive form of growth factors. TiNT layers with precisely controlled pore diameter (between 21and 130 nm) were anodically grown on 3D printed Ti surfaces to impart a nano-micro rough topology. Immune biomarker profiles at gene and protein levels show that anodised 3D Ti surfaces with smaller pores resulted in classical activation of macrophages (M1-like), while larger pores (i.e., >100 nm) promoted alternate activation of macrophages (M2-like). The in vitro bone mineralisation studies using the conditioned media from the immunomodulatory studies elucidate a clear impact of pore diameter on bone mineralisation. The tubular structure of TiNTs was utilised as a container to incorporate recombinant human bone morphogenetic protein-2 (BMP-2) in the presence of various sugar and polymeric cryoprotectants. Sucrose offered the most sustainable release of preserved BMP-2 from TiNTs. Downstream effects of released BMP-2 on macrophages as well as bone mineralisation were assessed showing bioactivity retention of the released rhBMP-2. Overall, the TiNT surface topography in combination with controlled, sustained, and local release of bioactive growth factors can potentially enhance the osseointegration outcomes of custom 3D printed Ti implants in the clinic.

Atomic Layer Deposition of Ru Nanoparticles on Low Surface Energy Carbon Supports for Alkaline Hydrogen Evolution Reaction

Platinum group metals such as Pt, Ru, Pd, Ir, etc., have superior performance for various catalytic applications.[1] Due to their scarcity, efforts were being made to reduce or replace these noble metals. Atomic Layer Deposition (ALD) is one among the best technique to facilitate lowering of loading mass on a support of interest.[2],[3] Furthermore, ALD is the most suitable technology that can decorate high aspect ratio and high surface area substrate architectures by noble metal nanoparticles.[4] Due to the governing surface energy variations between noble metals and support surfaces, the growth initiates as nanoparticles (NP) and with a further increase in ALD cycles the agglomeration among NP’s dominates over the individual NP size increase, thus developing thin films of relatively higher thickness. The surface energy variations are also known to increase the nucleation delay of noble metals especially for Ru considerably. In this regard our efforts were laid to improve the functionality with pretreatments on carbonaceous supports which were shown promising to reduce the nucleation delay of ALD deposited Ru.For electrocatalytic applications, it is important to choose the right substrates. Among available substrates, carbon papers (CP) and titania nanotube (TNT) layers are best choices considering their physio-chemical properties, availability, vast literature, and low costs incurred using these as support substrates in electrocatalysis and photocatalysis. Several surface modifications for CP’s and variations on morphological aspects of TNT layers had received a great attention form applied fields due to their improved surface area, conductivity and stability.[5]–[8] Uniformly decorating these CP’s and TNT layers by NPs or thin films of catalysts proved to be highly efficient with no boundaries on applications.[9] The presentation will introduce and describe the synthesis of different noble metal NPs by our ALD tool (Beneq TFS 200) on various aspect ratio TNT layers and CP substrates. It will also include the corresponding physical and electrochemical characterization and encouraging results obtained with alkaline hydrogen evolution reaction.

Cover Feature: 2D FeSx Nanosheets by Atomic Layer Deposition: Electrocatalytic Properties for the Hydrogen Evolution Reaction (ChemSusChem 11/2023)

The Cover Feature shows a scheme of the synthesis by atomic layer deposition of 2D iron sulfide nanosheets conformal and homogenously grown on titanium dioxide nanotube layers. Those composite nanotubular structures feature electrocatalytic activity toward hydrogen evolution reaction in alkaline media, originated from the synergistic interplay between in situ both morphological and chemical composition changes experienced by the 2D iron sulfide nanosheets. More information can be found in the Research Article by R. Zazpe et al.

Effects of Mode of Preparation of Titanium Dioxide Nanotube Arrays on Their Photocatalytic Properties: Application to p-Nitroaniline Degradation

The aim of this study was to investigate the photoactivity of dioxide titanium (TiO2) nanotube films depending on different structure factors including pore size, tube length, tube wall thickness and crystallinity. Aqueous p-nitroaniline was used as a probe to assess the photocatalytic activity of titanium dioxide nanotube layers under UV irradiations. Self-organized titanium dioxide nanotube thin films were prepared by electrochemical anodization of titanium (Ti) foils and Ti thin films sputtered onto silicon (Si). The amorphous as-formed titanium nanotube layers were then annealed at different temperatures ranging from 450 to 900 °C in order to form crystalline phases. The structure and the morphology of the films were characterized by surface analysis techniques and scanning electron microscopy, respectively. The photocatalytic activity of the resulting TiO2 thin films was evaluated by monitoring the UV degradation of p-nitroaniline by UV spectrophotometry and by determining nitrification yields of by ion chromatography. The highest photocatalytic activity was exhibited for titanium nanotubes annealed at 450 °C. The presence of rutile -obtained for an annealing temperature of 900 °C—appeared to reduce the photodegradation yield of p-nitroaniline. Finally, the TiO2 nanotubes obtained from Ti foils revealed the most efficient photocatalytic properties.

Crystallinity of TiO2 nanotubes and its effects on fibroblast viability, adhesion, and proliferation.

Titanium and titanium alloys are widely used as a biomaterial due to their mechanical strength, corrosion resistance, low elastic modulus, and excellent biocompatibility. TiO2 nanotubes have excellent bioactivity, stimulating the adhesion, proliferation of fibroblasts and adipose-derived stem cells, production of alkaline phosphatase by osteoblasts, platelets activation, growth of neural cells and adhesion, spreading, growth, and differentiation of rat bone marrow mesenchymal stem cells. In this study, we investigated the functionality of fibroblast on titania nanotube layers annealed at different temperatures. The titania nanotube layer was fabricated by potentiostatic anodization of titanium, then annealed at 300, 530, and 630 °C for 5 h. The resulting nanotube layer was characterized using SEM (Scanning Electron Microscopy), TF-XRD (Thin-film X-ray diffraction), and contact angle goniometry. Fibroblasts viability was determined by the CellTiter-Blue method and cytotoxicity by Lactate Dehydrogenase test, and the cell morphology was analyzed by scanning electron microscopy. Also, cell adherence, proliferation, and morphology were analyzed by fluorescence microscopy. The results indicate that the modification in nanotube crystallinity may provide a favorable surface fibroblast growth, especially on substrates annealed at 530 and 630 °C, indicating that these properties provide a favorable template for biomedical implants.

Studies on Silver Ions Releasing Processes and Mechanical Properties of Surface-Modified Titanium Alloy Implants.

Dispersed silver nanoparticles (AgNPs) on the surface of titanium alloy (Ti6Al4V) and titanium alloy modified by titania nanotube layer (Ti6Al4V/TNT) substrates were produced by the chemical vapor deposition method (CVD) using a novel precursor of the formula [Ag5(O2CC2F5)5(H2O)3]. The structure and volatile properties of this compound were determined using single crystal X-ray diffractometry, variable temperature IR spectrophotometry (VT IR), and electron inducted mass spectrometry (EI MS). The morphology and the structure of the produced Ti6Al4V/AgNPs and Ti6Al4V/TNT/AgNPs composites were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, measurements of hardness, Young’s modulus, adhesion, wettability, and surface free energy have been carried out. The ability to release silver ions from the surface of produced nanocomposite materials immersed in phosphate-buffered saline (PBS) solution has been estimated using inductively coupled plasma mass spectrometry (ICP-MS). The results of our studies proved the usefulness of the CVD method to enrich of the Ti6Al4V/TNT system with silver nanoparticles. Among the studied surface-modified titanium alloy implants, the better nano-mechanical properties were noticed for the Ti6Al4V/TNT/AgNPs composite in comparison to systems non-enriched by AgNPs. The location of silver nanoparticles inside of titania nanotubes caused their lowest release rate, which may indicate suitable properties on the above-mentioned type of the composite for the construction of implants with a long term antimicrobial activity.

Stress-generating electrochemical reactions during the initial growth of anodic titanium dioxide nanotube layers

Titanium dioxide nanotube layers are widely investigated for diverse applications as functional materials. Previously, we demonstrated the importance of mechanical stress-generating open-circuit electrochemical reactions or chemical reactions in the initiation and growth of nanotube layers. These reactions were investigated here through analysis of stress and potential transients after interrupted anodization followed by open-circuit oxide dissolution. Large tensile stress increases after complete dissolution occur at potentials near the TiH2/Ti2O3 equilibrium potential, and are attributed to cathodic hydride formation at exposed metal surfaces. Tensile increases accompanying initiation of nanotubes during anodization itself were also explained by the hydride mechanism. The observation of tensile stress changes after both complete oxide dissolution and nanotube formation supports the view that nanotube initiation involves detachment of oxide at the metal interface. Tensile stress changes during anodization were followed by compressive transients that were also found during open-circuit dissolution, but not associated with a specific range of open-circuit potentials. The compressive stress change was explained by chemical oxidation of Ti+3 ions in nanotube walls by H+ ions, along with absorption of charge-compensating anionic species. Hydrogen ion absorption is promoted by large decreases of surface pH that accompany anodization in organic-based solutions.

Roles of mechanical stress and lower-valent oxide in the formation of anodic titanium dioxide nanotube layers

Self-organized TiO2 nanotube arrays are characterized by gaps that separate the layers of oxide surrounding cylindrical pores. Nanotube layer growth is thought to involve oxide flow induced by mechanical stress associated with anodization. The mechanism of TiO2 nanotube initiation was studied with in situ stress measurements during anodization in ethylene glycol-water-fluoride solutions. Compressive stress changes due to initial growth of barrier oxide films were detected, along with significantly larger tensile and compressive stress changes that followed the appearance of gaps between nanotubes at the metal-oxide interface. Interrupted anodizing experiments revealed that the latter stress changes are due to chemical processes or open-circuit electrochemical reactions. Further evidence for such reactions was deduced from the calculation of apparent Ti valences below four from measurements of Ti metal consumption during anodization. The gaps between nanotubes are thought to result from local oxide delamination at the metal interface induced by oxide flow, and the large compressive stress change is attributed to chemical oxidation of Ti+3 ions in the nanotube walls. This previously unrecognized chemical oxidation reaction may suggests new avenues to control nanotube layer growth and properties.

Photoelectrochemical ultraviolet photodetector by anodic titanium dioxide nanotube layers

A prototype ultraviolet (UV) photodetector based on photoelectrochemical (PEC) cell from material synthesis up to assembly was demonstrated in this work. Self-organized titanium dioxide (TiO2) nanotube layers (1 and 5 μm thicknesses) prepared by electrochemical anodization were applied as the sensing layer in the photodetector. A printed circuit board (PCB) platform with physical size of 2 cm × 2 cm was designed to mount the sensing layer. The photodetector system comprised of a sandwich structure can be described as glass/ITO/electrolyte/TiO2 nanotube layer/Ti/PCB platform. For this system, a low applied voltage of 0.5–1 V was required to drive the photodetector. TiO2 nanotube layers have shown positive photoresponse in the entire UV spectral region (λ = 250–400 nm, classified as UV-A, B and C). In particular, the highest response with >850 sensitivity, and responsivity of ≈740 mA/W had been achieved by the 5 μm TiO2 nanotube layer for detection in the UV-A region, and the respective rise and decay time were 0.88 and 1.28 s. This work shows that the sandwich structure PEC cell UV photodetector with TiO2 nanotube layer as sensing layer is stable, highly sensitive and provides rapid response. Such platform can be potentially applied for other sensing materials as an efficient photodetector.

Boosted Photoactivity of Titania Nanotube Layers Doped with a Suspension of Gold Nanoparticles

In the present work, we report on the behavior of synthesized gold nano-particles suspension, incorporated in titanium dioxide nanotube layers (TiO2- NT) and fabricated by electrochemical anodization in 0.4 wt% hydrofluoric acid solution and we study its photocatalytic response. Gold nanoparticles were characterized using Transmission electron microscopy and X-ray diffraction. Scanning electron microscopy was used to study the morphology of TiO2 nanotube layers doped by gold nanoparticles. Boosted photocatalytic performances on the degradation of an azo dye were obtained by using TiO2 nanotube layers doped by gold nanoparticles (Au/TiO2-NT), compared to undoped TiO2 nanotube layer (TiO2-NT) catalysts. Under UV irradiation, this new nanomaterial, with noble metal-semi conductor heterojunction (Au/ TiO2-NT) exhibits a synergetic effect in accelerating the electron transfert, resulting in an enhanced photoactivity recorded in the kinetics of degradation of Acid Orange 7 (AO7). Chronoamperometry was used to highlight higher photocurrent produced by gold-titania interface submited to UV irradiation.

The influence of surface roughness and high pressure torsion on the growth of anodic titania nanotubes on pure titanium

Anodic titanium dioxide nanotube (TNT) arrays have wide applications in photocatalytic, catalysis, electronics, solar cells and biomedical implants. When TNT coatings are combined with severe plastic deformation (SPD), metal processing techniques which efficiently improve the strength of metals, a new generation of biomedical implant is made possible with both improved bulk and surface properties. This work investigated the effect of processing by high pressure torsion (HPT) and different mechanical preparations on the substrate and subsequently on the morphology of TNT layers. HPT processing was applied to refine the grain size of commercially pure titanium samples and substantially improved their strength and hardness. Subsequent anodization at 30V in 0.25wt.% NH4F for 2h to form TNT layers on sample surfaces prepared with different mechanical preparation methods was carried out. It appeared that the local roughness of the titanium surface on a microscopic level affected the TNT morphology more than the macroscopic surface roughness. For HPT-processed sample, the substrate has to be pre-treated by a mechanical preparation finer than 4000 grit for HPT to have a significant influence on TNTs. During the formation of TNT layers the oxide dissolution rate was increased for the ultrafine-grained microstructure formed due to HPT processing.

Interface Storage and Diffusion in Titania-Based Na-Ion Battery Negative Electrodes

Ordered, nanostructured transition metal oxides are currently in the spotlight of battery research. To exploit, however, the full potential of self-assembled titania nanotube layers in Na-ion battery technology we need to close the gap in knowledge about the underlying storage mechanisms as well as ion dynamics. For this purpose, amorphous TiO2 nanotubes (70-130 nm in diameter, 4.5 – 17 µm in length) were fabricated by anodization, i.e., electrochemical oxidation. The electrochemical behaviour with respect to sodium insertion was studied by cyclic voltammetry and galvanostatic cycling with potential limitation. It turned out that the nanotubes are very resilient to cycling, some being able to withstand more than 300 charge-discharge cycles without significant loss of capacity. Compared to classical insertion reactions, the mechanism of reversible electrochemical storage of Na+ in the nanotubes seems to differ significantly. There is strong evidence that a large amount of the Na+ ions is stored on the surface or in the surface-influenced regions while only a smaller fraction is inserted in the walls of the tubes. The interfacial Na+ storage is governed by a faradaic adsorption phenomena, which is essentially different from the (pseudo-)capacitive model hitherto used in the literature. The finding that, in the case of sodium, interfacial storage is more important than ion insertion into the crystal lattice is supported by the very low Na+ diffusion coefficients determined at various electrode potentials (in the order of 4 · 10-20 - 10-21 cm2/s). This dominant interfacial storage mechanism may explain the high specific capacity and the very good cycling performance recently reported for some nanostructured titania phases as well as for other nanosized titanate materials. Figure A. Chemical diffusion coefficient of Na+ into amorphous TiO2 at room temperature (23 ±1°C) after subtracting the interfacial storage contributions for different sample types. Figure B. Pseudo-capacitance values corresponding to the interfacial storage of Na+ ions on various nanotube layers plotted as a function of the electrode potential. Figure 1

Application of coupled substrate aging and TiO2 nanotube crystallization heat treatments in cold-rolled Ti–Nb–Sn alloys

Among titanium alloys, the β-type is the most indicated for orthopedic implants due to the reduced elastic modulus compared with α + β alloys. To improve osseointegration, the growth of a self-ordered titania nanotube layer onto the surface of titanium alloy implant pieces is a strategy used to accelerate bone growth. In this paper, the effects of heat treatment for titania nanotube crystallization on Ti–Nb and Ti–Nb–Sn alloys on the phase transformation, the Vickers hardness, and the elastic modulus of the substrate were investigated. TiO2 layers were grown onto cold-rolled Ti alloy substrates by anodization, and crystallization to anatase was followed by glazing-angle high-temperature X-ray diffraction with a heating ramp of 288 K/min to 623 K, where the samples were held for up to 4 h. The dynamic of the α- and ω-phase formation/dissolution was followed by X-ray diffraction. Transmission electron microscopy was used to confirm the presence of the α- and ω-phases and their volumes and dimensions. As a result of the TiO2 crystallization heat treatment, a continuous increase in the hardness was observed for the Ti–35Nb and Ti–35Nb–2Sn alloys, which is attributed to dissolution of α″ and the formation of ω precipitates. The same feature was observed for the elastic modulus. In the Ti–35Nb–4Sn alloy, the reverse decomposition of martensite resulted in the β phase and later in α phase precipitation. The aging of this alloy resulted in a homogeneous distribution of a high volumetric fraction of fine and dispersed α phase, which resulted in a hardness increase from 220 to 270 HV. This coupled heat treatment resulted in high hardness, low elastic modulus, and a nanotube with an anatase crystal phase.

Fabrication and Electrochemical Properties of Highly Ordered Titania Nanotubes Modified with Boron Nanocrystalline Diamond

Recently, we reported on the phenomena of the formation of the novel composite material based on titania nanotubes (TiO2 NTs) over-grown by thin boron-doped diamond (BDD) produced in microwave plasma enhanced chemical vapor deposition (MW PE CVD) [1,2]. Under microwave plasma treatment, the structure TiO2 NTs underwent transformation from stoichiometric anatase into non-stochiometric oxide with Ti(III) phase and some rutile phase arises. Furthermore, obtained material was characterized with a significantly enhanced conductivity and capacitance comparing to pristine titania. The electrochemical studies showed that the specific areal capacitance of TiO2/BDD raised up to 7.46 mF cm-2 whereas for the pure BDD it reached only 0.11 7.46 mF cm-2. Because of such strong modification of titania and application potential in energy storage devices we decided to initiate growth of boron nanocrystalline diamond (B-NDC) on the highly ordered TiO2 nanotube arrays. TiO2 NTs are fabricated via two-step anodization of titanium metal plate followed by a short immersion in diluted HF in order to remove any surface debris [3]. Titanium plate covered by uniform titania nanotube layer provides a large specific surface area as well as a direct pathway for charge transport, thus holding promising capabilities of being support for another materials deposition. Afterwards, similarly to formation of TiO2NTs/BDD material, the deposition of boron nanocrystalline diamond will be also realized under microwave plasma conditions and Ti/TiO2 NTs will act as a substrate. The morphology and the structure of obtained composite material will be investigated using scanning electron microscopy and Raman spectroscopy. Electrochemical activity will be identified applying cyclic voltammetry and electrochemical impedance spectroscopy techniques performed in aqueous electrolyte. The influence of boron-doping level will be observed as a change in registered capacitive current and impedance behaviour.

Influence of Anodization Time and Voltage on the Parameters of TiO2 Nanotubes

A vertically aligned titania nanotube layer was obtained by electrochemical anodic oxidation in the electrolyte contained 0.4 wt% solution of NH4F in 54 ml of ethylene glycol and 5 ml of deionized water, after titanium was chemically cleaned/etched with a mixture of HCl, H2O and HNO3 solution for removing the natural oxide films. The morphology and composition of the titania nanotube layer were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The anodization of TiO2 nanotubes was done using 60 V for 240 min and 30 min, and 30 V for 30 min. The diameter of the titania nanotubes was about 52-156 nm, the wall thickness about 32-53 nm and the height about 0.9-6.3 μm. The pore size of TiO2 nanotubes influences the dissolution rate of CaP thin films and Young's modulus, which is significantly lower than that of the Ti substrate. Our future challenge will be investigation of the microstructure and mechanical behavior of titania nanotubes with CaP film.

Impact of Annealing Treatment on the Behaviour of Titanium Dioxide Nanotube Layers

In this work, we study the influence of the annealing treatment on the behaviour of titanium dioxide nanotube layers. The heat treatment protocol is actually the key parameter to induce stable oxide layers and needs to be better understood. Nanotube layers were prepared by electrochemical anodization of Ti foil in 0.4 wt% hydrofluoric acid solution during 20 minutes and then annealed in air atmosphere. In-situ X-ray diffraction analysis, coupled with thermogravimetry, gives us an inside on the oxidation behaviour of titanium dioxide nanotube layers compared to bulk reference samples. Structural studies were performed at 700°C for 12 h in order to follow the time consequences on the oxidation of the material, in sufficient stability conditions. In-situ XRD brought to light that the amorphous oxide layer induced by anodization is responsible for the simultaneous growths of anatase and rutile phase during the first 30 minutes of annealing while the bulk sample oxidation leads to the nucleation of a small amount of anatase TiO2. The initial amorphous oxide layer created by anodization is also responsible for the delay in crystallization compared to the bulk sample. Thermogravimetric analysis exhibits parabolic shape of the mass gain for both anodized and bulk sample; this kinetics is caused by the formation of a rutile external protective layer, as depicted by the associated in-situ XRD diffractograms. We recorded that titanium dioxide nanotube layers exhibit a lower mean mass gain than the bulk, because of the presence of an initial amorphous oxide layer on anodized samples. In-situ XRD results also provide accurate information concerning the sub-layers behavior during the annealing treatment for the bulk and nanostructured layer. Anatase crystallites are mainly localized at the interface oxide layer-metal and the rutile is at the external interface. Sample surface topography was characterized using scanning electron microscopy (SEM). As a probe of the photoactivity of the annealed TiO2 nanotube layers, degradation of an acid orange 7 (AO7) dye solution and 4-chlorophenol under UV irradiation (at 365 nm) were performed. Such titanium dioxide nanotube layers show an efficient photocatalytic activity and the analytical results confirm the degradation mechanism of the 4-chlorophenol reported elsewhere.

Optimization of electrochemical doping approach resulting in highly photoactive iodine-doped titania nanotubes

The paper focuses on the optimization procedure concerning the synthesis method resulting in highly ordered titania nanotubes doped with iodine atoms. The doping process was based on the electrochemical treatment of a titania nanotube layer immersed in a potassium iodide (KI) solution acting as an iodine precursor. A number of endeavors were undertaken in order to optimize the doping conditions. Electrolyte concentration, reaction voltage, and time/duration were the main factors that influenced the iodine (I)-doping effect on the photoactivity. The parameters of electrochemical doping that result in a material characterized by the highest photocurrent density are as follows: reaction voltage of 1.5 V, duration of 15 min, and 0.1 M KI. Different spectroscopic techniques, i.e., UV–Vis spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the absorbance capability and the crystalline phase, to confirm the presence of iodine atoms and to study the nature of chemical compounds. The morphology inspection performed by means of scanning electron microscopy shows that the doping process does not affect the ordered tubular architecture. The photocurrent densities of the I-doped sample were six times higher in comparison to those generated by the pure titania nanotube electrode. Moreover, doped samples act as a much better catalyst in the photodegradation process of methylene blue and formation of hydroxyl radicals (•OH) than undoped samples.

Long-Cycle-Life Na-Ion Anodes Based on Amorphous Titania Nanotubes--Interfaces and Diffusion.

Amorphous self-assembled titania nanotube layers are fabricated by anodization in ethylene glycol based baths. The nanotubes having diameters between 70-130 nm and lengths between 4.5-17 μm are assembled in Na-ion test cells. Their sodium insertion properties and electrochemical behavior with respect to sodium insertion is studied by galvanostatic cycling with potential limitation and cyclic voltammetry. It is found that these materials are very resilient to cycling, some being able to withstand more than 300 cycles without significant loss of capacity. The mechanism of electrochemical storage of Na(+) in the investigated titania nanotubes is found to present significant particularities and differences from a classical insertion reaction. It appears that the interfacial region between titania and the liquid electrolyte is hosting the majority of Na(+) ions and that this interfacial layer has a pseudocapacitive behavior. Also, for the first time, the chemical diffusion coefficients of Na(+) into the amorphous titania nanotubes is determined at various electrode potentials. The low values of diffusion coefficients, ranging between 4 × 10(-20) to 1 × 10(-21) cm(2)/s, support the interfacial Na(+) storage mechanism.