Anatase TiO2 Nanotubes Research Articles

TiO₂ Nanostructures for Photoelectrocatalytic Degradation of Acetaminophen.

Advanced oxidation processes driven by renewable energy sources are gaining attention in degrading organic pollutants in waste waters in an efficient and sustainable way. The present work is focused on a study of TiO2 nanotubes as photocatalysts for photoelectrocatalytic (PEC) degradation of acetaminophen (AMP) at different pH (3, 7, and 9). In particular, different TiO2 photocatalysts were synthetized by stirring the electrode at different Reynolds numbers (Res) during electrochemical anodization. The morphology of the photocatalysts and their crystalline structure were evaluated by field emission scanning electron microscopy (FESEM) and Raman confocal laser microscopy (RCLM). These analyses revealed that anatase TiO2 nanotubes were obtained after anodization. In addition, photocurrent densities versus potential curves were performed in order to characterize the electrochemical properties of the photocatalysts. These results showed that increasing the Re during anodization led to an enhancement in the obtained photocurrents, since under hydrodynamic conditions part of the initiation layer formed over the tubes was removed. PEC degradation of acetaminophen was followed by ultraviolet-visible absorbance measurements and chemical oxygen demand tests. As drug mineralization was the most important issue, total organic carbon measurements were also carried out. The statistical significance analysis established that acetaminophen PEC degradation improved as hydrodynamic conditions linearly increased in the studied range (Re from 0 to 600). Additionally, acetaminophen conversion had a quadratic behavior with respect to the reaction pH, where the maximum conversion value was reached at pH 3. However, in this case, the diversity of the byproducts increased due to a different PEC degradation mechanism.

Highly Hydrophilic TiO₂ Nanotubes Network by Alkaline Hydrothermal Method for Photocatalysis Degradation of Methyl Orange.

High-density and highly cross-coated anatase TiO2 nanotubes networks have been successfully prepared on the surface of Ti foil by alkaline hydrothermal using NaOH and Ti foil as the precursors. The nanotubes networks were analyzed using X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), transmission electron microscope (TEM), scanning electron microscopy (SEM), optical contact angle tester, and ultraviolet (UV) fluorescence spectrophotometer, respectively. The results showed that the nanotubes network with diameters of 30–50 nm were obtained on the Ti foil surface. The morphology of the nanotubes network possessed the three-dimensional network structure, The TiO2 nanotubes network grew along the (101) direction of the tetragonal anatase crystal. The morphology and crystal phase of the TiO2 nanotubes network were better at the conditions of NaOH concentration 7–10 mol/L and temperature 160–170 °C. The best contact angle of TiO2 nanotubes network after UV-light irradition was only 5.1 ± 2.9°. Under the irradiation of mercury lamp, the nanotubes network exhibited excellent photocatalytic performance and the degradation ratio of methyl orange solution reached to 80.00 ± 2.33%. Thus, the anatase TiO2 nanotubes network has great potential in applications for pollution photocatalytic degradation.

Carbon-Coated and Interfacial-Functionalized Mixed-Phase Mox Ti1-x O2-δ Nanotubes as Highly Active and Durable PtRu Catalyst Support for Methanol Electrooxidation.

A synchronous carbon-coating and interfacial-functionalizing approach is proposed for the fabrication of Mo-doped Mox Ti1-x O2-δ nanotubes (C@IF-MTNTs) under mild hydrothermal reaction with subsequent annealing as advanced catalyst supports for PtRu nanoparticles (NPs) towards methanol electrooxidation. The carbonation of glucose and Mo-doping takes place simultaneously at the interface of pristine anatase TiO2 nanotubes (TNTs), generating a unique concentric multilayered one-dimensional (1D) structure with crystalline an anatase/rutile mixed-phase TiO2 core and Mo-functionalized interface and subsequently a carbon shell. The obtained PtRu/C@IF-MTNTs catalyst exhibits an over 2 times higher mass activity with comparable durability than that of the unmodified PtRu/C@TNTs catalyst and over 1.7 times higher mass activity with over 20 % higher stability than that of PtRu/C catalyst. Such superior catalytic performance towards methanol electrooxidation is ascribed to the Mo-functionalized interface, concentric multilayered 1D architecture, and anatase/rutile mixed-phase core, which facilitates the charge transport through 1D structural support and electronic interaction between C@IF-MTNTs and ultrafine PtRu NPs. This work reveals the critical application of a 1D interfacial functionalized architecture for advanced energy storage and conversion.

Fabrication of Pd-TiO2 nanotube photoactive junctions via Atomic Layer Deposition for persistent pesticide pollutants degradation

The design of nano-structured heterogeneous catalytic junctions with high interface to volume ratio and discrete surface distribution is critical to promote the photoelectron activity in the catalytic degradation of organic pollutants. In this work, photocatalytic palladium‑titanium dioxide nano-junctions were fabricated via Atomic Layer Deposition (ALD) of palladium nanoparticles over the surface of titanium dioxide nanotubes. The Pd catalytic interface and resulting active site density was tailored by varying the nanoparticle growth and coalescence via ALD, leading to Pd-TiO2 junctions with distinctive morphological aspects and interface properties. The visible light response of the Pd-TiO2 junctions was attributed to the Surface Plasmon Resonance effect and correlated to the variation of the catalyst morphology tuned by ALD. Uniform, discrete distribution of Pd nanoparticles with diameter lower than 5 nm led to high catalytic interface to deposited volume ratio. The nano-engineered Pd-TiO2 junctions showed enhanced photocatalytic activity towards the degradation of methylene blue selected as a model contaminant and 2,4 D, with a kinetic constant 4.5 higher than as-annealed anatase TiO2 nanotubes. The design of well-defined catalytic junctions obtainable by a scalable, accurate deposition technique such as ALD represents a promising route to develop cutting-edge photoactive devices with high performance and minimum noble-metal loading.

Photoelectrochemical water vapor splitting using an ionomer-coated rutile TiO2 thin layer on titanium microfiber felt as an oxygen-evolving photoanode

Rutile TiO2 thin layers on a titanium microfiber electrode split water vapor into hydrogen and oxygen via a proton exchange membrane.

Design of New Al Photoanode Composite for Cathodic Protection Based on Photocatalytic Material and Sacrificial Anode

A new kind of Al photoanode composite based on photocatalytic material and sacrificial anode was proposed and designed to provide new ideas for cathodic protection in marine environment. Fabricated with the traditional Al-Zn-In-Mg-Ti sacrificial anode and Co(OH)2 modified anatase TiO2 nanotubes, a new Al photoanode composite with good photoelectrochemical cathodic protection property was obtained. To compare with the traditional sacrificial anode, the cathodic protective properties of both the sacrificial anode and this Al photoanode composite were evaluated by electrochemical measurements in aqueous 3.5 wt.% NaCl solution. By means of scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectrophotometer morphologies, crystal structures, surface compositions and light response range of the Al photoanode composite during the immersion were characterized, respectively. The generated protective current density of the Al photoanode composite is found to be greater under illumination than that of the traditional Al-Zn-In-Mg-Ti sacrificial anode. Co(OH)2@TiO2 plays an important role in supplemental protection for Q235 carbon steel and improves the current efficiency.

Thermal conductivity of TiO2 nanotube: a molecular dynamics study

The thermal conductivity of anatase TiO2 nanotubes was investigated using equilibrium molecular dynamics simulations based on Green-Kubo formalism. The calculated thermal conductivity of for anatase crystal at room temperature agrees well with experimental value of ~8.5 W K−1 · m−1, demonstrating that the method used in our calculation can provide a good description for the thermal transport of TiO2. The dependence of the thermal conductivity of TiO2 nanotubes with temperature, tube size and chirality were studied in detail. The relationship between the thermal conductivity and the vibrational density-of-states of the nanotubes was also investigated.

Understanding the Behavior and Mechanism of Oxygen-Deficient Anatase TiO2 toward Sodium Storage.

TiO2 has drawn increasing research attention as negative electrode material in sodium ion battery because of its natural abundance, low cost, nontoxicity, and facile preparation. Despite tremendous studies carried out, the sodium storage mechanism is still under discussion, and the electronic and local structures of TiO2 during sodiation/desodiation process are not well understood either. Herein, we reported a mechanism study of graphene-supported oxygen-deficient anatase TiO2 nanotubes (nanowires) as the negative electrode material for sodium ion batteries. Different from the previous reports, the insertion/extraction of Na+ ions leads to almost no changes of titanium valence state but there is a charge redistribution of O 2p orbitals which alters the hybridization between O 2p and Ti 3d states, suggested by the combined electrochemical and X-ray spectroscopic study. Both the electronic and local structures of TiO2 during the reversible sodiation/desodiation process are revealed from the Ti L-edge and O K-edge spectra. This detailed study would shed light on the material design and structural optimization of TiO2 as energy storage material in different systems.

Evaluation of Antimicrobial Properties of Conventional Poly(Methyl Methacrylate) Denture Base Resin Materials Containing Hydrothermally Synthesised Anatase TiO2 Nanotubes against Cariogenic Bacteria and Candida albicans.

The purpose of this study was to investigate the antimicrobial properties of a conventional poly methyl methacrylate (PMMA) modified with hydrothermally synthesised titanium dioxide nanotubes (TNTs). Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentrations (MFC) for planktonic cells of the TiO2 nanotubes solution against Lactobacillus acidophilus, Streptococcus mutans and Candida albicans were determined. The powder of conventional acrylic resin was modified using 2.5% and 5% by weight synthesised titanium dioxide (TiO2) nanotubes, and rectangular-shaped specimens (10 mm × 10 mm × 3 mm) were fabricated. The antimicrobial properties of ultraviolet (UV) and non-UV irradiated modified, and non-modified acrylic resins were evaluated using the estimation of planktonic cell count and biofilm formation of the three microorganisms mentioned above. The data were analysed by one-way analysis of variance (ANOVA), followed by a post-hoc Tukey's test at a significance level of 5%. MIC, for Streptococcus. mutans, Lactobacillus. acidophilus, and Candida. albicans, MBC for S. mutans and L. acidophilus and MFC for Candida. albicans were obtained more than 2100 µg/mL. The results of this study indicated a significant reduction in both planktonic cell count and biofilm formation of modified UV-activated acrylic specimens compared with the control group (p = 0.00). According to the results of the current study, it can be concluded that PMMA/TiO2 nanotube composite can be considered as a promising new material for antimicrobial approaches.

Exceptional behavior of anatase TiO2 nanotubes in axial loading: A molecular dynamics study of the effect of surface wrinkles

Anatase TiO2 nanotubes have interesting properties which makes them a candidate for various applications. In this way, they may be exposed to different mechanical loadings. The aim of this research is to elucidate the mechanical behavior of anatase TiO2 nanotubes in axial loading using molecular dynamics simulations. Nanotubes with different radii and lengths are studied in 300 K both in stretching and compression. Our results show an interesting phenomenon occurring on the surface of these structures. As the radius of the nanotubes increases, their surface begins to wrinkle axially. This causes their axial behavior change dramatically. The threshold radius is observed to be 50 Å for length of 300 Å. This structural change softens the nanotubes in stretch loading while increasing the toughness by bestowing the structures more deformability. On the other hand, the nanotubes may entirely lose their stability in compression as the wrinkles form. As the radius or length of the anatase nanotubes increases, the possibility of wrinkle formation increases, strengthening these effects. Our results are important for the design of structures in which the anatase nanotubes are axially loaded, especially if the loading is compressive, to avoid structural failure.

Synthesis of TiO2-based nanocomposites by anodizing and hydrogen annealing for efficient photoelectrochemical water oxidation

Black TiO2 based nanomaterials have shown considerable potential towards photoelectrochemical water oxidation due to their low cost, raw material availability and operational stability. In this work, thermal annealing of anatase TiO2 nanotube arrays under hydrogen-argon atmosphere at high temperatures (>600 °C) is employed to induce significant oxygen deficiency and phase transitions to substoichiometric structures (Magnéli phases), with the aim to limit interfacial recombination processes and increase the density of charge carriers. Particle-nanowire porous TiO2 sub-stoichiometries are formed at 800 °C, which is quantitatively investigated via X-ray diffraction and Rietveld refinement. The photocurrent of this Ti-O compounds is increased by 2.4-fold at 1.23VRHE and the photoconversion efficiency is enhanced by 2.8-fold at a reduced bias under simulated solar illumination in comparison with pristine TiO2 nanotube arrays. The improved performance is owed to slower interfacial recombination, resulting in the increase of water oxidation selectivity from 65% to 92%, and by the increase in charge carrier density up to two orders of magnitude, as evaluated via electrochemical impedance spectroscopy. Finally, this method is compared to electrochemical hydrogen doping, with the latter exhibiting a significantly lower energy conversion efficiency.

Effect of DI Water Content on the Growth of Anatase TiO<sub>2</sub> Nanotubes Synthesized by Anodization Process

Vertically aligned anatase TiO2 nanotubes (NTs) were fabricated by anodization of a pureTi foil in ethylene glycol solutions containing different concentrations of deionized (DI) water. Themorphology, elemental composition, and crystallization of TiO2 nanostructures were analyzed byfield emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Ramanspectroscopy, and X-ray spectroscopy (XPS), respectively. The diameter and length of TiO2 NTswere controlled by varying concentrations of DI water. Furthermore, we found that TiO2 NTs in DIwater 12 wt. % was suitable for further applications in UV photodetector due to it has a high volumeto surface area ratio and long tube. TiO2 NTs have a high potential in various applications such as UVphotodetectors, gas sensor, dye sensitized solar cells, and photocatalysts.

Synthesis and characterization of ZnO nanorice decorated TiO2 nanotubes for enhanced photocatalytic activity

In present study, we report on the synthesis of TiO2/ZnO nanocomposite (TZN) films for potential applications as photocatalyst in heterogeneous photo-degradation of Rhodamine B under UVA irradiations. ZnO nano-rice decorated TiO2 nanotubes were successfully synthesized via a facile and effective two-step route. Firstly, TiO2 nanotube arrays were grown by anodic oxidation. Afterwards, ZnO rice shaped nanostructures were decorated by successive chemical bath deposition cycles of 2, 4, 6 and 8. The XRD, FESEM, XPS and μ-XRF results showed that the rice-shaped wurtzite ZnO nanoparticles with dimensions of ca. 1μm × 100 nm were homogeneously distributed on the anatase TiO2 nanotube arrays with highly uniform in the presence of in zinc nitrate hexahydrate and hexamethylenetetramine precursors with 1:4 M ratios. The photodegradation results showed that the photocatalytic activity of TZN films were gradually increased in parallel with the number of ZnO deposition cycles and the best performance was found for TNZ8 film. The RhB photodegradation efficiency was determined to be 65% for bare TiO2 whereas 95% degradation of Rhodamine B was occurred for TNZ8 film which follow pseudo-first-order kinetic. In addition, TZN films exhibited good photostability after four reuses. Also, photocatalytic activity of TZN were tested under UVC, UVB, UVA and visible region irradiations for comparative purposes.

Entrapment of Bi2O3 nanoparticles in TiO2 nanotubes for visible light-driven photocatalysis

In this study, we prepared nanoparticles of the visible light-responsive photocatalyst, Bi2O3 entrapped in anatase TiO2 nanotubes (Bi2O3-in-TNTs) via a vacuum-assisted precursor-filling process followed by annealing. Owing to the unique tubular electronic structure of TiO2 nanotubes, the interior of the nanotube is in an electron-deficient state, which was confirmed by XPS spectra and H2-TPR. Electrochemical impedance studies showed that the Bi2O3-in-TNTs demonstrated a more efficient separation of photogenerated carriers than when Bi2O3 nanoparticles were deposited on the outer wall of TiO2 nanotubes (Bi2O3-out-TNTs). Due to the confinement effect of TiO2 nanotubes, which inhibits photogenerated carriers’ recombination, the Bi2O3-in-TNTs exhibited a better photocatalytic performance for the photo-degradation of methyl orange under visible light compared to Bi2O3-out-TNTs.

MoS2 Decorated on Different Metal Oxide Nanotubular Structures with a High Density of Reactive Sites for HER Reactions

MoS2 is intensively investigated for decades owing to some unique chemical and physical properties. 1 For many applications, the use of nanoscale geometries is highly advantageous owing to the high specific surface area and short carrier and ion diffusion pathways that can be established.2 This is to a large extent due to the weak van der Waals force between the stacked S-Mo-S units giving it a graphene-like layer structure. 3 This is not only the origin of outstanding lubrication properties but also the key to the insertion and extraction of small foreign ions into the free space of the S-Mo-S layers.4 In this study, we report the self-organized formation of anodic molybdenum oxide nanotube arrays.5 The amorphous tubes can be crystallized to MoO2 or MoO3 and be converted fully or partially into molybdenum sulfide. Vertically aligned MoOx/MoS2 nanotubes can be formed with defined MoS2 sheets in a layer by layer arrangement. These provide a high density of reactive stacking misalignments (defects). These core–shell nanotube arrays consist of a conductive suboxide core and a functional high defect density MoS2 coating. Such structures are investigated for applications in electrocatalysis (hydrogen evolution). Furthermore, nanoscaled MoS2 has a gap broadens up to 1.8 eV when reaching monolayer thickness with a conduction band more negative to the conduction band of TiO2. In our experiments, MoS2 can be decorated on the top of anodic anatase TiO2 nanotubes (TiNTs) site-selectively. 6 The layers can be used as co-catalysts for photocatalytic hydrogen evolution. A strongly enhanced H2 evolution activity can be observed using only a nominal 1 nm thick MoS2 decoration on top of a 6 μm thick TiNT layer. We ascribe this strong beneficial effect to two factors: (i) the thin molybdenum sulfide on the top acts as an electron transfer mediator, i.e. as an H2 evolution co-catalyst; and (ii) the underlying tube layer acts as a light-to-electron harvester.

Water Adsorption on Clean and Defective Anatase TiO2 (001) Nanotube Surfaces: A Surface Science Approach

We use ab initio molecular dynamics simulations to study the adsorption of thin water films with 1 and 2 ML coverage on anatase TiO2 (001) nanotubes. The nanotubes are modeled as 2D slabs, which consist of partially constrained and partially relaxed structural motifs from nanotubes. The effect of anion doping on the adsorption is investigated by substituting O atoms with N and S impurities on the nanotube slab surface. Due to strain-induced curvature effects, water adsorbs molecularly on defect-free surfaces via weak bonds on Ti sites and H bonds to surface oxygens. While the introduction of an S atom weakens the interaction of the surface with water, which adsorbs molecularly, the presence of an N impurity renders the surface more reactive to water, with a proton transfer from the water film and the formation of an NH group at the N site. At 2 ML coverage, a further surface-assisted proton transfer takes place in the water film, resulting in the formation of an OH- group and an NH2+ cationic site on the surface.

Efficient silver modification of TiO2 nanotubes with enhanced photocatalytic activity

In this paper, Ag(CH3NH2)2+, Ag(NH3)2+ and Ag+ with different radii have been used as silver sources to find out the distribution of Ag ions on the H-TNT surface, which is critical to the final performance. The influence of this distribution on visible photocatalytic activity is further studied. The results indicate that, when Ag+ used as silver source with low concentration, these small sized silver ions mainly distribute on interlayer spacing of H-TNT. After heat-treatment and photo-reduction, the generated silver nanoparticles uniformly embed in the anatase TiO2 nanotube walls, and bring large interfacial area between Ag particles and TiO2 nanotubes. The separation effect of photogenerated electron-hole pair in TiO2 is enhanced by Ag particles, and achieves the best at 0.15 g/L, much higher than P25, TiO2/0, Ag-N@TiO2 and Ag-C-N@TiO2. This paper provides new ideas for the modification of TiO2 nanotubes.

Ultraviolet detector with ultrahigh responsivity based on Anatase TiO2 nanotubes array modified with (001) exposed nanofacets

In this paper, partial density of states and band structures of Anatase's (001) and (101) facets were studied by first-principles calculation. Based on partial density of states, electrons in the (001) facet of Anatase have much higher transition probability to be excited from valence band maximum to conduction band minimum compared with those in an (101) facet, which shows a stronger electronic activity of (001) facet. Besides, the (001) and (101) facets of Anatase have a direct and indirect band structure, respectively, based on the first-principle calculation results. The direct band structure of the (001) facet makes it more suitable to be used in optical detection. Anatase TiO2 nanotubes array modified with (001) exposed nanofacets were grown on Ti substrates by anodization, hydrothermal, and then post annealing. An ultrahigh responsivity as high as 1575.97μA/mW·cm2 under 365 nm ultraviolet light wavelength and 5 V bias was achieved.

Metal–Phosphate Bilayers for Anatase Surface Modification

Compared to many other metal oxides, anatase TiO2 shows relatively lower reactivity toward carboxylic acid anchor groups. The latter is crucial for applications, for example, in dye-sensitized solar cells (DSSCs), where the most used dyes bind to the metal oxide surface through carboxylic acid terminations. To improve the surface reactivity, metal-phosphate bilayers of Ni or Co were synthesized on anatase TiO2 compact oxide and nanotubes. In both cases, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) results showed that the bilayers were successfully formed and that the phosphate layer works as an intermediate between TiO2 and the other species. ToF-SIMS depth profiles of modified nanotubes showed that Ni and Co are present through the whole tube length and reduce in content after heat treatment, in agreement with XPS results. Phosphate groups, on the other hand, are more present in the tubes' depth, and their content on the surface is reduced upon exposure to temperature. The reactivity of the modified surfaces toward carboxylic acid-terminated molecules, as stearic acid and Ru-based N719 dye, was evaluated. Contact angle measurements together with dye desorption experiments demonstrated that the Co-phosphate bilayers heat-treated at 300 °C resulted in the largest enhancement compared to the reference. Bilayer-modified compact anatase TiO2 and anatase TiO2 nanotubes were utilized as photoanodes in DSSCs. An increase in efficiency was observed for all modified electrodes with phosphate-Co treatment, leading to the highest JSC values and an efficiency improvement of 48%.

Preparation of Au nanoparticles modified TiO2 nanotube array sensor and its application as chemical oxygen demand sensor

Au nanoparticles (AuNPs) were electrodeposited at the highly ordered anatase TiO2 nanotube array (TiO2NA) electrode under sonicating, and the AuNP-TiO2NA sensor was characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD). The photoelectrochemical experiments indicate the AuNP-TiO2NA sensor has lower photoelectro-resistance, higher photoelectrocatalytical activity and stability than that of pure TiO2NA sensor under the same conditions. The as-prepared sensor can be used for the determination of chemical oxygen demand (COD) in real samples, and the obtained results are comparable well with those of by standard K2Cr2O7 method. The method proposed is simple, fast, cost effective, and environmentally friendly.