Highly Conducting Spaced TiO2 Nanotubes Enable Defined Conformal Coating with Nanocrystalline Nb2 O5 and High Performance Supercapacitor Applications

Red-light-excited TiO2/Bi2S3 heterojunction nanotubes and photoelectric hydrogels mediate epidermal-neural network reconstruction in deep burns

Inspired by the strong light absorption of carbon nanotubes, we propose a fabrication approach involving one-dimensional TiO2/Bi2S3 QDs nanotubes (TBNTs) with visible red-light excitable photoelectric properties. By integrating the construction of heterojunctions, quantum confinement effects, and morphological modifications, the photocurrent reached 9.22 µA/cm2 which is 66 times greater than that of TiO2 nanotubes (TNTs). Then, a red light-responsive photoelectroactive hydrogel dressing (TBCHA) was developed by embedding TBNTs into a collagen/hyaluronic acid-based biomimetic extracellular matrix hydrogel with good biocompatibility, aiming to promote wound healing and skin function restoration. This approach is primarily grounded in the recognized significance of electrical stimulation in modulating nerve function and immune responses. Severe burns are often accompanied by extensive damage to epithelial-neural networks, leading to a loss of excitatory function and difficulty in spontaneous healing, while conventional dressings inadequately address the critical need for nerve reinnervation. Furthermore, we highlight the remarkable ability of the TBCHA photoelectric hydrogel to promote the reinnervation of nerve endings, facilitate the repair of skin substructures, and modulate immune responses in a deep burn model. This hydrogel not only underpins wound closure and collagen synthesis but also advances vascular reformation, immune modulation, and neural restoration. This photoelectric-based therapy offers a robust solution for the comprehensive repair of deep burns and functional tissue regeneration. STATEMENT OF SIGNIFICANCE: We explore the fabrication of 1D TiO2/Bi2S3 nanotubes with visible red-light excitability and high photoelectric conversion properties. By integrating heterojunctions, quantum absorption effects, and morphological modifications, the photocurrent of TiO2/Bi2S3 nanotubes could reach 9.22 µA/cm², which is 66 times greater than that of TiO2 nanotubes under 625 nm illumination. The efficient red-light excitability solves the problem of poor biosafety and low tissue penetration caused by shortwave excitation. Furthermore, we highlight the remarkable ability of the TiO2/Bi2S3 nanotubes integrated photoelectric hydrogel in promoting the reinnervation of nerve endings and modulating immune responses. This work proposes an emerging therapeutic strategy of remote, passive electrical stimulation, offering a robust boost for repairing deep burn wounds.

Less known facts and findings about TiO2 nanotubes

Anodic TiO₂ nanotubes that are grown on Ti substrates by a simple anodization in various types of fluoride containing electrolytes have attracted scientific and technological interest due to their wide potential applications, and therefore, numerous research efforts have been dedicated to these self-ordered oxide structures in the past decade. The present mini-review highlights less known but important aspects, such as the formation of spaced nanotubes with adjustable interspacing that is achieved in a few specific organic electrolytes, and strong effects of the metallic Ti substrate which significantly affect the growth of the tubes. We discuss the formation of oxide nanotubes grown from adequately alloyed substrates and noble metal nanoparticle decoration of tubes. We describe how specific heat-treatment can introduce a nanotwinned boundary in the oxide tube walls of single-walled nanotubes obtained by a decoring process. All the facts and findings were studied in recent years and TiO₂ nanotubes can be upgraded with more optimized functionalities for their applications.

Enhanced interfacial adhesion and osseointegration of anodic TiO2 nanotube arrays on ultra-fine-grained titanium and underlying mechanisms

The poor adhesion of anodic TiO₂ nanotubes (TNTs) arrays on titanium (Ti) substrates adversely affects applications in many fields especially biomedical engineering. Herein, an efficient strategy is described to improve the adhesion strength of TNTs by performing grain refinement in the underlying Ti substrate via high-pressure torsion processing, as a larger number of grain boundaries can provide more interfacial mechanical anchorage. This process also improves the biocompatibility and osseointegration of TNTs by increasing the surface elastic modulus. The TNTs in length of 0.4 µm have significantly larger adhesion strength than the 2.0 µm long ones because the shorter TNTs experience less interfacial internal stress. However, post-anodization annealing reduces the fluorine concentration in TNTs and adhesion strength due to the formation of interfacial cavities during crystallization. The interfacial structure of TNTs/Ti system and the mechanism of adhesion failures are further investigated and discussed. STATEMENT OF SIGNIFICANCE: Self-assembled TiO₂ nanotubes (TNTs) prepared by electrochemical anodization have a distinct morphology and superior properties, which are commonly used in photocatalytic systems, electronic devices, solar cells, sensors, as well as biomedical implants. However, the poor adhesion between the TNTs and Ti substrate has hampered wider applications. Here in this study, we describe an efficient strategy to improve the adhesion strength of TNTs by performing grain refinement in the underlying Ti substrate via high-pressure torsion (HPT) processing. The interfacial structure of TNTs/Ti system and the mechanism of adhesion failure are systematically studied and discussed. Our findings not only develop the knowledge of TNTs/Ti system, but also provide new insights into the design of Ti-based implants for orthopedic applications.

Ti-rich TiO2 Tubular Nanolettuces by Electrochemical Anodization for All-Solid-State High-Rate Supercapacitor Devices

Supercapacitors store charge by ion adsorption or fast redox reactions on the surface of porous materials. One of the bottlenecks in this field is the development of biocompatible and high-rate supercapacitor devices by scalable fabrication processes. Herein, a Ti-rich anatase TiO₂ material that addresses the above-mentioned challenges is reported. Tubular nanolettuces were fabricated by a cost-effective and fast anodization process of Ti foil. They attained a large potential window of 2.5 V in a neutral electrolyte owing to the high activation energy for water splitting of the (1 0 1) facet. Aqueous and all-solid-state devices showed diffusion time constants of 46 and 1700 ms, as well as high maximum energy (power) densities of 0.844 (0.858) and 0.338 μWh cm^-2 (0.925 mW cm^-2 ), respectively. The all-solid-state device showed ultrahigh stability of 96 % in capacitance retention after 20 000 galvanostatic charge/discharge cycles. These results open an avenue to fabricate biochemically inert supercapacitor devices.

TiO2 Nanomembranes Fabricated by Atomic Layer Deposition for Supercapacitor Electrode with Enhanced Capacitance

TiO₂ is a promising environment friendly, low cost, and high electrochemical performance material. However, impediments like high internal ion resistance and low electrical conductivity restrict its applications as electrode for supercapacitor. In the present work, atomic layer deposition was used to fabricate TiO₂ nanomembranes (NMs) with accurately controlled thicknesses. The TiO₂ NMs were then used as electrodes for high-performance pseudocapacitors. Experimental results demonstrated that the TiO₂ NM with 100 ALD cycles had the highest capacitance of 2332 F/g at 1 A/g with energy density of 81 Wh/kg. The enhanced performance was ascribed to the large surface area and the interconnectivity in the case of ultra-thin and flexible NMs. Increased ALD cycles led to stiffer NMs and decreased capacitance. Moreover, one series of two supercapacitors can light up one light-emitting diode with a working voltage of ~ 1.5 V, sufficiently describing its application values.

Construction of 3D Si@Ti@TiN thin film arrays for aqueous symmetric supercapacitors

We report the preparation of 3D binder-free Si@Ti@TiN thin film array electrodes for supercapacitors using deep silicon etching and magnetron sputtering for the first time. This work not only offers the 3D array structure of Si@Ti@TiN thin films, but also paves a promising way for the construction of high-energy storage systems.

Niobium doped tungsten oxide mesoporous film with enhanced electrochromic and electrochemical energy storage properties

Exploring high performance cathode materials is of great means for the development of bi-functional electrochromic energy storage devices. Herein, Nb-doped WO₃ mesoporous films as integrated high-quality cathode are successfully constructed via a facile sol-gel method. Chemical state and crystallinity of the WO₃ based films are significantly influenced by doping concentration. Compared with the pure WO₃, the optimal Nb-doped film shows improved optical-electrochemical properties with high specific capacity (74.4 mAh g^-1 at 2 A g^-1), excellent high-rate capability, large optical contrast (61.7% at 633 nm), and ultra-fast switching speed (3.6 s and 2.1 s for coloring and bleaching process, respectively). These positive features suggest the potential application of Nb-doped WO₃ mesoporous cathode. Our research paves the way for the development of multifunctional photoelectrochemical energy devices.

Spaced TiO2 Nanotubes Enable Optimized Pt Atomic Layer Deposition for Efficient Photocatalytic H2 Generation

In the present work, we report the use of TiO2 nanotube (NT) layers with a regular intertube spacing that are decorated by Pt nanoparticles through the atomic layer deposition (ALD) of Pt. These Pt-decorated spaced (SP) TiO2 NTs are subsequently explored for photocatalytic H2 evolution and are compared to classical close-packed (CP) TiO2 NTs that are also decorated with various amounts of Pt by using ALD. On both tube types, by varying the number of ALD cycles, Pt nanoparticles of different sizes and areal densities are formed, uniformly decorating the inner and outer walls from tube top to tube bottom. The photocatalytic activity for H2 evolution strongly depends on the size and density of Pt nanoparticles, driven by the number of ALD cycles. We show that, for SP NTs, a much higher photocatalytic performance can be achieved with significantly smaller Pt nanoparticles (i.e. for fewer ALD cycles) compared to CP NTs.

Surface Characteristic Effect of Ag/TiO2 Nanoarray Composite Structure on Supercapacitor Electrode Properties

Ag-ion-modified titanium nanotube (Ag/TiO2-NT) arrays were designed and fabricated as the electrode material of supercapacitors for electrochemical energy storage. TiO2 nanotube (NT) arrays were prepared by electrochemical anodic oxidation and then treated by Ag metal vapor vacuum arc (MEVVA) implantation. The Ag amount was controlled via adjusting ion implantation parameters. The morphology, crystallinity, and electrochemistry properties of as-obtained Ag/TiO2-NT electrodes were distinguished based on various characterizations. Compared with different doses of Ag/TiO2-NTs, the electrode with the dose of 5.0 × 1017 ions·cm-2 exhibited much higher electrode capacity and greatly enhanced activity in comparison to the pure TiO2-NTs. The modified electrode showed a high capacitance of 9324.6 mF·cm-3 (86.9 mF·g, 1.2 mF·cm-2), energy density of 82.8 μWh·cm-3 (0.8 μWh·g, 0.0103 μWh·cm-2), and power density of 161.0 mW·cm-3 (150.4 μW·g, 2.00 μW·cm-2) at the current density of 0.05 mA. Therefore, Ag/TiO2-NTs could act as a feasible electrode material of supercapacitors.

TiO2 nanotubes with different spacing, Fe2O3 decoration and their evaluation for Li-ion battery application

In the present work, we report on the use of organized TiO₂ nanotube (NT) layers with a regular intertube spacing for the growth of highly defined α-Fe₂O₃ nano-needles in the interspace. These α-Fe₂O₃ decorated TiO₂ NTs are then explored for Li-ion battery applications and compared to classic close-packed (CP) NTs that are decorated with various amounts of nanoscale α-Fe₂O₃. We show that NTs with tube-to-tube spacing allow uniform decoration of individual NTs with regular arrangements of hematite nano-needles. The tube spacing also facilitates the electrolyte penetration as well as yielding better ion diffusion. While bare CP NTs show a higher capacitance of 71 μAh cm^-2 compared to bare spaced NTs with a capacitance of 54 μAh cm^-2, the hierarchical decoration with secondary metal oxide, α-Fe₂O₃, remarkably enhances the Li-ion battery performance. Namely, spaced NTs with α-Fe₂O₃ decoration have an areal capacitance of 477 μAh cm^-2, i.e. they have nearly ∼8 times higher capacitance. However, the areal capacitance of CP NTs with α-Fe₂O₃ decoration saturates at 208 μAh cm^-2, i.e. is limited to ∼3 times increase.

Scalable Synthesis of Triple-Core-Shell Nanostructures of TiO2 @MnO2 @C for High Performance Supercapacitors Using Structure-Guided Combustion Waves

Core-shell nanostructures of metal oxides and carbon-based materials have emerged as outstanding electrode materials for supercapacitors and batteries. However, their synthesis requires complex procedures that incur high costs and long processing times. Herein, a new route is proposed for synthesizing triple-core-shell nanoparticles of TiO₂ @MnO₂ @C using structure-guided combustion waves (SGCWs), which originate from incomplete combustion inside chemical-fuel-wrapped nanostructures, and their application in supercapacitor electrodes. SGCWs transform TiO₂ to TiO₂ @C and TiO₂ @MnO₂ to TiO₂ @MnO₂ @C via the incompletely combusted carbonaceous fuels under an open-air atmosphere, in seconds. The synthesized carbon layers act as templates for MnO₂ shells in TiO₂ @C and organic shells of TiO₂ @MnO₂ @C. The TiO₂ @MnO₂ @C-based electrodes exhibit a greater specific capacitance (488 F g^-1 at 5 mV s^-1 ) and capacitance retention (97.4% after 10 000 cycles at 1.0 V s^-1 ), while the absence of MnO₂ and carbon shells reveals a severe degradation in the specific capacitance and capacitance retention. Because the core-TiO₂ nanoparticles and carbon shell prevent the deformation of the inner and outer sides of the MnO₂ shell, the nanostructures of the TiO₂ @MnO₂ @C are preserved despite the long-term cycling, giving the superior performance. This SGCW-driven fabrication enables the scalable synthesis of multiple-core-shell structures applicable to diverse electrochemical applications.

Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe₂ nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe₂ in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe₂ has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe₂ delivers a high specific capacitance of 759.5 F g^-1 at 1 mA cm^-2 , which is much larger than that of CoO nanocones (319.5 F g^-1 ). In addition, the CoSe₂ electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm^-2 . An asymmetric supercapacitor using the CoSe₂ as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg^-1 at a power density of 1914.7 W kg^-1 , and maintains 24.9 Wh kg^-1 when power density increased to 7354.8 W kg^-1 . Moreover, the CoSe₂ electrode also exhibits better oxygen evolution reaction activity than that of CoO.

Porous TiO₂-Based Gas Sensors for Cyber Chemical Systems to Provide Security and Medical Diagnosis

Gas sensors play an important role in our life, providing control and security of technical processes, environment, transportation and healthcare. Consequently, the development of high performance gas sensor devices is the subject of intense research. TiO₂, with its excellent physical and chemical properties, is a very attractive material for the fabrication of chemical sensors. Meanwhile, the emerging technologies are focused on the fabrication of more flexible and smart systems for precise monitoring and diagnosis in real-time. The proposed cyber chemical systems in this paper are based on the integration of cyber elements with the chemical sensor devices. These systems may have a crucial effect on the environmental and industrial safety, control of carriage of dangerous goods and medicine. This review highlights the recent developments on fabrication of porous TiO₂-based chemical gas sensors for their application in cyber chemical system showing the convenience and feasibility of such a model to provide the security and to perform the diagnostics. The most of reports have demonstrated that the fabrication of doped, mixed and composite structures based on porous TiO₂ may drastically improve its sensing performance. In addition, each component has its unique effect on the sensing properties of material.