Synthesis,characterization of B-doped TiO<Subscript>2</Subscript> nanotubes with high photocatalytic activity

B-doped TiO₂ nanotubes (B/TiO₂ NTs) were prepared by the combination of sol–gel process with hydrothermal treatment. The prepared catalysts were characterized by XRD, TEM and XPS. The photocatalytic activity of B/TiO₂ NTs was evaluated through the photodegradation of aqueous methyl orange. The results demonstrated that the 1.5% B/TiO₂ NTs calcined at 300 °C possessed the best photocatalytic activity. Compared with pure TiO₂ nanotubes, the doping with B significantly enhanced the photocatalytic efficiency.     

The Preparation and Characterization of La Doped TiO2 Nanotubes and Their Photocatalytic Activity

La-doped TiO₂ nanotubes (La/TiO₂ NTs) were prepared by the combination of sol-gel process with hydrothermal treatment. The prepared samples were characterized by using transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectra, and ultraviolet-visible spectra. The photocatalytic performance of La/TiO₂ NTs was studied by testing the degradation rate of methyl orange under ultraviolet (UV) irradiation. The results indicated La/TiO₂ NTs calcined at 300°C consisted of anatase as the unique phase. The absorption spectra of the La/TiO₂ NTs showed a stronger absorption in the UV range and a slight red shift in the band gap transition than that of pure TiO₂ nanotubes. The photocatalytic performance of TiO₂ NTs could be improved by the doping of lanthanum ions, which is ascribed to several beneficial effects the formation of Ti-O-La bond and charge imbalance, existing of oxygen defects and Ti³⁺ species, stronger absorption in the UV range and a slight red shift in the band gap transition, as well as higher equilibrium dark adsorption of methyl orange. 0.75 wt% La/TiO₂ NTs had the best catalytic activity.     

Influences of the H2PtCl6 Solution's pH on the Photocatalytic Activities of Platinum-Loaded TiO2 Nanotubes

By using H₂PtCl₆ and titanate nanotubes as precursor, platinum-loaded TiO₂ nanotubes (Pt/TiO₂NTs) are prepared at different pH by deposition-precipitation method. The prepared materials are characterized with powder x-ray diffraction (XRD) and x-ray photoelectron spectra (XPS). Their photocatalytic performance is evaluated by the degradation rates of methyl orange solution under UV-vis light irradiation. Obtained results indicate that the pH of H₂PtCl₆ solution has obvious influence on the catalytic performance of Pt/TiO₂NTs.     

TiO2 Nanotubes as a Therapeutic Agent for Cancer Thermotherapy

We report the photothermal properties as well as the in vitro cell test results of titanium oxide nanotubes (TiO₂ NTs) as a potential therapeutic agent for cancer thermotherapy in combination with near-infrared (NIR) light. TiO₂ NTs are found to have a higher photothermal effect upon exposure to NIR laser than Au nanoparticles and single-wall carbon nanotubes, which have also attracted considerable interest as therapeutic agents for cancer thermotherapy. The temperature increase of a TiO₂ NT/NaCl suspension during NIR laser exposure is larger than that of a TiO₂ NT/D.I. water suspension due to the heat generated by the formation of Na₂TiF_6. According to the in vitro cell test results the cells exposed to NIR laser without TiO₂ NT treatment have a cell viability of 96.4%. Likewise, the cells treated with TiO₂ NTs but not with NIR irradiation also have a cell viability of 98.2%. Combination of these two techniques, however, shows a cell viability of 1.35%. Also, the cell deaths are mostly due to necrosis but partly due to late apoptosis. These results suggest that TiO₂ NTs can be used effectively as therapeutic agents for cancer thermotherapy due to their excellent photothermal properties and high biocompatibility.     

Antimony Doped Tin Oxide Nanoparticles Deposited onto Nb−TiO2 Nanotubes for Electrochemical Degradation of Bio‐refractory Pollutions

To improve the service life of SnO₂?Sb electrodes in degradation of refractory wastewater, we report anodic information of tin oxide antimony on top of Nb?TiO₂ nanotubes (Nb?Ti/Nb?TiO₂?NTs/ATONPs) prepared through screen‐printing. It was found that the Nb?Ti/Nb?TiO₂?NTs/ATONPs anodes presented a significantly enhanced in electro‐catalytic oxidation performance (in Acid Red 73) compared to titanium‐based tin antimony electrodes (Ti/ATONPs). Additionally, the electrochemical properties and the stability were further studied by the electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry (CA) measurements and accelerated life test, respectively. These results indicated that Nb?TiO₂?NTs/ATONPs anode possessed Nb?TiO₂ nanotubes which exhibited a higher oxygen evolution potential (2.24 V vs. Ag/AgCl), as well as a better wettability, a larger current at constant potential and 2.1 times longer lifetime than the conventional Ti/ATONPs anode.     

Au/TiO2 nanotube catalysts prepared by combining sol–gel method with hydrothermal treatment and their catalytic properties for CO oxidation

A new preparation method for Au/TiO₂ nanotubes (NTs) by combing sol–gel with hydrothermal treatment technique was developed. The TiO₂ NTs calcined at 300 °C were nearly uniform, and the gold particles were distributed homogeneously. The possible formation mechanism was suggested. The 5 % Au/TiO₂ NTs calcined at 300 °C had the best catalytic activity for CO oxidation, and their conversion of CO remained at 100 % during 60 h on stream. This preparation method could improve the thermal stability of Au/TiO₂ nanotube catalysts.     

Controllable incorporation of CdS nanoparticles into TiO<Subscript>2</Subscript> nanotubes for highly enhancing the photocatalytic response to visible light

A constant current electrochemical deposition was employed to incorporate CdS nanoparticles into the TiO₂ nanotube arrays (TiO₂NTs). The size and amount of CdS nanoparticles in TiO₂NTs (CdS@TiO₂NTs) were controllable via modulating current, deposition time and electrolyte concentration. It was revealed, from the scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) in depth profile, that CdS nanoparticles were filled into TiO₂ nanotubes. A shift of the absorption edge toward the visible region under the optimal electrodeposition condition was observed with the diffuse reflectance spectroscopy (DRS). A 5-fold enhancement in the photocurrent spectrum for TiO₂NTs was observed and the photocurrent response range was significantly extended into the visible region because of the CdS incorporation. Compared with pure TiO₂NTs, under a visible light irradiation, CdS@TiO₂NTs exhibited a 3.5-fold improvement of photocatalytic activity, which was demonstrated by the photocatalytic decomposition of Rhodamine B (RhB).     

In Situ ATR-FTIR and UV-Visible Spectroscopy Study of Photocatalytic Oxidation of Ethanol over TiO2 Nanotubes

The photocatalytic oxidation of ethanol over TiO₂ nanotubes (NTs) was investigated by in situ attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and ultraviolet (UV)-visible spectroscopy. In the ATR-FTIR study, the TiO₂ NTs were spread in a ZnSe crystal trough that was used as the reactor. The evolution of the reaction under UV irradiation was investigated by in situ monitoring of changes in the species at the surface of the TiO₂ NTs. Ethanol adsorbed on the TiO₂ NTs surface, forming alkoxide and hydroxide groups, which were then attacked by ^?OH, with the formation of a vinyl alcohol intermediate that was finally transformed to acetic acid. In addition, the species changes in the reaction solution were also investigated by in situ UV-visible spectroscopy using a small volume flow-through cell. The UV-visible data further confirmed the oxidation mechanism of ethanol on TiO₂ NTs elucidated by ATR-FTIR data.     

Highly controlled coating of biomimetic polydopamine in TiO2 nanotubes

Highly controlled coating of biomimetic polydopamine (PDA) was achieved on titanium dioxide nanotubes (TiO₂ NTs) by exposing TiO₂ NT arrays to a slightly alkaline dopamine solution. The thin films act as photonic sensitizers (enhancing photocurrents and photodegradation) in the visible light range. The PDA coatings can furthermore be used as a platform for decorating the TiO₂ NTs with different co-catalysts and metal nanoparticles (NPs).     

DFT Investigations of Aun Nano-Clusters Supported on TiO2 Nanotubes: Structures and Electronic Properties

TiO₂ nanotubes (TiO₂NTs) are beneficial for photogenerated electron separation in photocatalysis. In order to improve the utilization rate of TiO₂NTs in the visible light region, an effective method is to use Au_n cluster deposition-modified TiO₂NTs. It is of great significance to investigate the mechanism of Au_n clusters supported on TiO₂NTs to strengthen its visible-light response. In this work, the structures, electronic properties, Mulliken atomic charge, density of states, band structure, and deformation density of Au_n (n = 1, 8, 13) clusters supported on TiO₂NTs were investigated by DMOL3. Based on published research results, the most stable adsorption configurations of Au_n (n = 1, 8, 13) clusters supported with TiO₂NTs were obtained. The adsorption energy increased as the number of Au adatoms increased linearly. The Au_n clusters supported on TiO₂NTs carry a negative charge. The band gaps of the three most stable structures of each adsorption system decreased compared to TiO₂NTs; the valence top and the conduction bottom of the Fermi level come mainly from the contribution of 5d and 6s-Au. The electronic properties of the 5d and 6s impurity orbitals cause valence widening and band gap narrowing.     

Direct Electrochemistry of Hemoglobin on Vertically Aligned Carbon Hybrid TiO2 Nanotubes and Its Highly Sensitive Biosensor Performance

The present work is focused on developing a novel biomaterial platform to achieve enhanced direct electron transfer (DET) of hemoprotein and higher biosensor performance on vertically aligned carbon hybrid TiO₂ nanotubes (C‐TiO₂ NTs). Using a simple surfactant‐assisted method, controllable hybridization of TiO₂ NTs with conductive amorphous carbon species is realized. The obtained C‐TiO₂ NTs is ingeniously chosen to serve as an ideal "vessel" for protein immobilization and biosensor applications. Results show that the appropriate hybridization of C into TiO₂ NTs leads to a much better conductivity of TiO₂ NTs without destroying their preponderant tubular structures or damaging their excellent biocompatibility and hydrophilicity. When used in loading proteins, the C‐TiO₂ NTs can be used as a super vessel for rapid and substantive immobilization of hemoglobin (Hb), with a large surface electroactive Hb coverage ( Γ ??) of 3.3×10^?9 mol·cm^?2. Enhanced DET of Hb is commendably observed on the constructed Hb/C‐TiO₂ NTs biosensor with a couple of well‐defined redox peaks in a fast electron transfer process. The biosensor further exhibits fast response, high sensitivity and stability for the amperometric biosensing of H₂O₂ with the detection limit as low as 3.1×10^?8 mol/L.     

浸渍-分解法制备高可见光催化活性的Bi2O3/TiO2纳米管阵列

用浸渍-分解法将Bi₂O₃纳米颗粒沉积在TiO₂纳米管壁上, 制备了Bi₂O₃/TiO₂纳米管阵列. 用电感耦合等离子体发射光谱(ICP-AES)测定了Bi₂O₃/TiO₂ 纳米管阵列的化学组分, 利用X 射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和紫外-可见(UV-Vis)吸收光谱表征了所制备的样品. 通过在可见光下(λ>400 nm)降解甲基橙(MO)水溶液来评价样品的光催化活性. 结果表明, Bi₂O₃纳米颗粒均匀地沉积在TiO₂纳米管中. Bi₂O₃/TiO₂纳米管阵列具有比纯Bi₂O₃膜和N-TiO₂纳米管阵列高得多的可见光催化活性. Bi₂O₃/TiO₂纳米管阵列活性的增强是其强可见光吸收和Bi₂O₃与TiO₂之间形成的异质结的协同作用的结果.     

RuO2-doping into high-aspect-ratio anodic TiO2 nanotubes by electrochemical potential shock for water oxidation

A novel method for homogenous incorporation of Ru (RuO₂, or RuO₃) into high aspect ratio anodic TiO₂ NTs was studied. TiO₂ NTs were prepared by anodization in HF based electrolyte, after which very short high applied potential, referred to as potential shock, was imposed on the TiO₂ NTs in KRuO₄ electrolyte. The high potential shock induced massive flow of RuO₄⁻ to positively-biased TiO2 NTs, resulting in the incorporation of Ru as a form of Ru, RuO₂, and RuO₃ in the TiO₂ NTs. Optimal potential shock, which allowed the most suitable amount and incorporation state of Ru catalysts in TiO₂ NTs, was determined by SEM, TEM, EDS, XPS, and LSV. It was demonstrated that electrochemical potential shock (simply imposed on the anodic TiO₂ for a few seconds in the electrolyte of KRuO₄) resulted in homogenous incorporation of Ru into the whole nanotubes without the need for any complicated steps or facilities.     

Enhancement of ethanol electrooxidation on plasmonic Au/TiO2 nanotube arrays

Novel electrocatalysts Au/TiO₂ nanotube arrays (Au/TiO₂NTs) were prepared by loading low-content(1.9 at.%) of Au nanoparticles (AuNPs) onto highly ordered TiO₂ nanotube arrays (TiO₂NTs). Ethanol electrooxidation indicates that visible-light (λ > 400 nm) irradiation can significantly enhance the activity as well as resistpoisoning of Au/TiO₂NTs electrocatalysts that are activated by plasmon resonance. Au/TiO₂NTs catalysts calcinated at 300 °C display the highest performance due to the strong synergistic interactions between TiO₂ and Au NPs. The combination of visible-light irradiation with a controllable potential offers a new strategyfor enhancing the performance of anodes in direct ethanol fuel cell (DEFC).     

Enhanced Visible‐Light‐Induced Photoelectrocatalytic Degradation of Methyl Orange by CdS Sensitized TiO2 Nanotube Arrays Electrode

In this work, CdS sensitized TiO₂ nanotube arrays (CdS/TiO₂NTs) electrode was synthesized with the CdS deposition on the highly ordered titanium dioxide nanotube arrays (TiO₂NTs) by sequential chemical bath deposition method (S‐CBD). The as‐prepared CdS/TiO₂NTs was characterized by field‐emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD). The results indicated that the CdS nanoparticles were effectively deposited on the surface of TiO₂NTs. The amperometric I‐t curve on the CdS/TiO₂NTs electrode was also presented. It was found that the photocurrent density was enhanced significantly from 0.5 to 1.85 mA/cm² upon illumination with applied potential of 0.5 V at the central wavelength of 253.7 nm. The photoelectrocatalytic (PEC) activity of the CdS/TiO₂NTs electrode was investigated by degradation of methyl orange (MO) in aqueous solution. Compared with TiO₂NTs electrode, the degradation efficiencies of CdS/TiO₂NTs electrode increased from 78% to 99.2% under UV light in 2 h, and from 14% to 99.2% under visible light in 3 h, which was caused by effective separation of the electrons and holes due to the effect of CdS, hence inhibiting the recombination of electron/hole pairs of TiO₂NTs.     

TiO2 nanotubes fabricated by electrochemical anodization in molten o-H3PO4-based electrolyte: Properties and applications

Self-organized TiO₂ nanotubes (NTs) can be formed by electrochemical anodization. Anodization is generally performed in aqueous or organic electrolytes containing halogen ions, such as Cl⁻ and F⁻. However, these electrolytes lead to less ordered structures or carbon remnants, thus suppressing the electrical properties and limiting the applications. To overcome these limitations, new anodization approaches were performed in carbon-free electrolyte-based electrolyte. In this review, we summarizes the short history of TiO₂ NTs, general mechanisms of growing NTs, properties, and applications of classic TiO₂ NTs. Then, a new-generation of anodization approach conducted in molten orhto-phosphoric acid is elucidated based on anodization parameters, concluding the optimized condition to form highly ordered TiO₂ NT arrays. Finally, the review addresses further modifications such as heat-treatment, noble metal deposition, thermal dewetting, and double anodization to enhance the optical and electrical properties for use in various applications.     

Fabrication of Au‐Nanoparticle/TiO2‐Nanotubes Electrodes Using Electrochemical Methods and Their Application for Electrocatalytic Oxidation of Hydroquinone

Gold nanoparticle (Au‐NPs)‐Titanium oxide nanotube (TiO₂‐NTs) electrodes are prepared by using galvanic deposition of gold nanoparticles on TiO₂‐NTs electrodes as support. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy results indicate that nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm diameters and gold nanoparticles are well‐dispersed on the surface of TiO₂‐NTs support. The electrooxidation of hydroquinone of Au‐NPs/TiO₂‐NTs electrodes is investigated by different electrochemical methods. Au‐NPs/TiO₂‐NTs electrode can be used repeatedly and exhibits stable electrocatalytic activity for the hydroquinone oxidation. Also, determination of hydroquinone in skin cream using this electrode was evaluated. Results were found to be satisfactory and no matrix effects are observed during the determination of hydroquinone content of the “skin cream” samples.     

Degradation of ofloxacin by UVA-LED/TiO<Subscript>2</Subscript> nanotube arrays photocatalytic fuel cells

The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO₂ nanotube arrays photocatalytic fuel cells (UVA-LED/TiO₂ NTs PFCs) was investigated. TiO₂ nanotube arrays (TiO₂ NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO₂ NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO₂ NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min^?1) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO₂ NTs PFC. The main reactive species of OFX degradation are positive holes (h⁺) and superoxide ion radicals (O ₂ ^·? ) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.     

Pyrite (FeS2)-decorated 1D TiO2 nanotubes in a bilayer as a sustainable photoanode for photoelectrochemical water splitting activity

Herein, FeS₂@TiO₂ nanotubes photocatalyst was prepared by electrochemical anodization method followed by successive ionic layer adsorption and reaction method, and then finally annealed in a tube furnace for homogenous crystallization. The surface morphology, elemental composition, optical properties, and crystalline structure of the prepared FeS₂@TiO₂ nanocomposite were found out by performing scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, and fluorescence spectroscopy, respectively, while bonds vibrations and various functional groups' presence were analyzed using Raman and Fourier transform infrared spectroscopy. A higher photocurrent density of 1.59 mA/cm² at 0.3 V versus reference electrode of Ag/AgCl (1.23 V versus reversible hydrogen electrode) using 100 mW/cm² intensive light source was shown by 15-FeS₂@TiO₂ nanotubes (uniformly loaded photoanode) while donor density (N_D) of 3.68 × 10⁻¹³ cm⁻³ as compared to pure TiO₂ NTs (0.09 mA/cm²), 05-FeS₂@TiO₂ NTs (0.19 mA/cm²), 10-FeS₂@TiO₂ NTs (0.53 mA/cm²) and 20-FeS₂@TiO₂ NTs (0.61 mA/cm²), respectively. The exceptional photoelectrochemical activity results were attributed to the homogenous integration of FeS₂ that not only increase the charge separation but also, intensively interacted with the substrate (TiO₂ nanotubes), which results in an excellent photoelectrochemical activity.     

Photocatalytic activities of C–N-doped TiO2 nanotube array/carbon nanorod composite

A C–N-doped TiO₂ nanotube (NT)/carbon nanorod composite is fabricated by chemical vapor deposition (CVD). Carbon nanorods are grown from the TiO₂ NTs, and partly graphitized, while TiO₂ is in the mixture of anatase and rutile. The C–N doping shifts the absorption edge of TiO₂ NTs to the visible light region; the formed carbon nanorods promote the charge carrier transfer from the TiO₂ surface to the electrolyte. Under the simulated solar light irradiation, the C–N-doped TiO₂ NTs show higher photocatalytic activity in the degradation of methyl orange (MO) than the undoped TiO₂ NTs.