A facile solution route to deposit TiO2 nanowire arrays on arbitrary substrates

Nanostructured TiO2 Arrays for Energy Storage

Because of their extensive specific surface area, excellent charge transfer rate, superior chemical stability, low cost, and Earth abundance, nanostructured titanium dioxide (TiO₂) arrays have been thoroughly explored during the past few decades. The synthesis methods for TiO₂ nanoarrays, which mainly include hydrothermal/solvothermal processes, vapor-based approaches, templated growth, and top-down fabrication techniques, are summarized, and the mechanisms are also discussed. In order to improve their electrochemical performance, several attempts have been conducted to produce TiO₂ nanoarrays with morphologies and sizes that show tremendous promise for energy storage. This paper provides an overview of current developments in the research of TiO₂ nanostructured arrays. Initially, the morphological engineering of TiO₂ materials is discussed, with an emphasis on the various synthetic techniques and associated chemical and physical characteristics. We then give a brief overview of the most recent uses of TiO₂ nanoarrays in the manufacture of batteries and supercapacitors. This paper also highlights the emerging tendencies and difficulties of TiO₂ nanoarrays in different applications.

Advanced titanium dioxide fluidizable nanowire photocatalysts

In photocatalytic water splitting, fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distribution, parasitic back-reactions and photocatalyst handling difficulties, which limit the scalability of immobilized-film and suspended slurry photocatalysts. Fluidization of one-dimensional TiO₂ photocatalyst particles, such as nanorods, -wires and -ribbons, is highly desired as it further enhances the efficiency of photocatalytic reaction, due to their peculiar photo-electrochemical characteristics that result in more effective separation of photo-generated charges and absorption of photons. However, the harsh physical environment of a fluidized bed reactor does not readily allow for nanostructured TiO₂ photocatalysts, as the fine features would be quickly removed from the particle surface. Here, we propose a scalable method for fabrication of rutile TiO₂ nanorods on porous glass beads as a 3D protective substrate to reduce the attrition rate caused by fluidization. The quality of the synthesized nanorod films was optimized through controlling a growth quality factor, R_q, allowing for good quality films to be grown in different batch amounts and different hydrothermal reactor sizes. The utilization of porous glass beads substrate has reduced the attrition rate, and the protective features of the particles reduced the rate of attrition by an order of magnitude, compared to a particulate photocatalyst, to near negligible levels. Such considerably reduced attrition makes the as-developed porous glass beads supported rutile TiO₂ nanorods a viable fluidizable photocatalyst candidate for various applications, including water splitting and degradation of organic compounds.

Fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distribution, parasitic back-reactions and photocatalyst handling, which limit the scalability of immobilized-film and suspended slurry photocatalysts.

Modulation of titania nanoflower arrays transformed from titanate nanowire arrays to boost photocatalytic Cr(vi) detoxification

The integration of the N/S co-doping, anatase/rutile junction construction, and morphology regulation of TiO2 arrays is achieved by a simple method to improve photocatalytic activity.

Surface-Induced Desolvation of Hydronium Ion Enables Anatase TiO2 as an Efficient Anode for Proton Batteries

Hydrogen ion is an attractive charge carrier for energy storage due to its smallest radius. However, hydrogen ions usually exist in the form of hydronium ion (H₃O⁺) because of its high dehydration energy; the choice of electrode materials is thus greatly limited to open frameworks and layered structures with large ionic channels. Here, the desolvation of H₃O⁺ is achieved by using anatase TiO₂ as anodes, enabling the H⁺ intercalation with a strain-free characteristic. Density functional theory calculations show that the desolvation effects are dependent on the facets of anatase TiO₂. Anatase TiO₂ (001) surface, a highly reactive surface, impels the desolvation of H₃O⁺ into H⁺. When coupled with a MnO₂ cathode, the proton battery delivers a high specific energy of 143.2 Wh/kg at an ultrahigh specific power of 47.9 kW/kg. The modulation of the interactions between ions and electrodes opens new perspectives for battery optimizations.

Spacing prior to decorating TiO2 nanowires with dewetted Au nanoparticles for boosting photoelectrochemical water oxidation

Dewetted Au nanoparticles are used as masks to space out TiO2 nanowires, which restrict the planar coalescence of nanowires and favor the successive decoration of Au nanoparticles by dewetting, thus boosting the PEC water oxidation performance.

A Simple Drop-and-Dry Approach to Grass-Like Multifunctional Nanocoating on Flexible Cotton Fabrics Using In Situ-Generated Coating Solution Comprising Titanium-Oxo Clusters and Silver Nanoparticles

Multifunctional nanocoatings have been of central importance in various technological fields, yet their fabrication, especially on flexible substrates, still remains a persistent challenge to date. We herein demonstrate a mild single-step drop-and-dry approach to the in situ growth of hierarchical grass-like nanostructures on flexible cotton fabrics. A precursor solution comprising titanium-oxo clusters [Ti₁₈MnO₃₀(OEt)₂₀(MnPhen)₃] (Phen = 1,10-phenanthroline) and AgNO₃ is employed wherein Ag⁺ cations are in situ-reduced to silver nanoparticles (AgNPs). Drop-casting onto cotton fabrics under mild conditions induces the in situ growth of the heterogeneous grass-like assembly, and each constituent nanofibrous 'grass leaf' incorporates AgNPs both on the surface and embedded in the interior. The hierarchical morphology and heterogeneous composition of these grass-like nanostructures impart the coated cotton fabrics with enhanced antibacterial properties, robust hydrophobicity, and UV-blocking capability, which are features desired in textile materials but lacking in natural cotton.

Facet-dependent decoration of TiO2 mesocrystals on TiO2 microcrystals for enhanced photoactivity

Bottom-up constructions of hierarchical TiO₂ are effective to enhance their photoactivity towards degradations of organic pollutants. Thanks to highly active facets, {001} exposed anatase TiO₂ microcrystals attract much attention in photocatalysis; yet their efficiency is limited by the large crystal size. Herein, we report a facile solution approach to deposit anatase TiO₂ mesocrystals only on {101} facets of anatase TiO₂ microcrystals. The selective surface decoration enhances the photoactivity through replacing the less active {101} facets with more active TiO₂ mesocrystals; whilst the highly active {001} facets remain untouched. When utilized to assist photodegradation of phenol in water under UV light illumination, the hierarchical TiO₂ exhibited a reaction rate constant doubled that of the pristine {001} exposed TiO₂ microcrystals. The present tactic to selectively decorate TiO₂ microcrystals may give hints to other applications involving facet-dependent properties.

Sheet-on-belt branched TiO2(B)/rGO powders with enhanced photocatalytic activity

TiO2(B) is usually adopted to construct phase junctions with anatase TiO2 for applications in photocatalysis to facilitate charge separation; its intrinsic photocatalytic activity, especially when in the form of one- or three-dimensional nanostructures, has been rarely reported. In this study, a sheet-on-belt branched TiO2(B) powder was synthesized with the simultaneous incorporation of reduced graphene oxide (rGO). The monophase, hierarchically nanostructured TiO2(B) exhibited a reaction rate constant 1.7 times that of TiO2(B)/rGO and 2.9 times that of pristine TiO2(B) nanobelts when utilized to assist the photodegradation of phenol in water under UV light illumination. The enhanced photocatalytic activity can be attributed to the significantly increased surface area and enhanced charge separation.

Self-supported one-dimensional materials for enhanced electrochromism

A reversible, persistent electrochromic change in color or optical parameter controlled by a temporarily applied electrical voltage is attractive because of its enormous display and energy-related applications. Due to the electrochemical and structural advantages, electrodes based on self-supported one-dimensional (1D) nanostructured materials have become increasingly important, and their impacts are particularly significant when considering the ease of assembly of electrochromic devices. This review describes recent advances in the development of self-supported 1D nanostructured materials as electrodes for enhanced electrochromism. Current strategies for the design and morphology control of self-supported electrodes fabricated using templates, anodization, vapor deposition, and solution techniques are outlined along with demonstrating the influences of nanostructures and components on the electrochemical redox kinetics and electrochromic performance. The applications of self-supported 1D nanomaterials in the emerging bifunctional devices are further illustrated.

Titania nanowires functionalized polyester fabrics with enhanced photocatalytic and antibacterial performances

Flexible organic fabrics coated with titania find wide applications in pollutant degradations and antibiosis. Because of the enhanced charge separations, TiO₂ with one-dimensional nanostructures exhibits photocatalytic activity superior to that of nanoparticulate films; however, only the later has been achieved on organic substrates through commonly sol-gel techniques till now. In this study, radially aligned TiO₂ nanowires were precipitated on polyester fabrics through multi-steps of surface roughening, sol-gel TiO₂ seeding, hydrogen titanate nanobelts precipitation, and finally sulfuric acid treatment. Both mesoporous anatase TiO₂ nanowires and single-crystalline rutile TiO₂ nanorods have been achieved, which, together with some unchanged titanate nanobelts, exhibited an overall narrowed band gap of ca. 2.50eV. The TiO₂ nanowires on flexible PET fabrics showed higher photocatalytic activity towards degradations of not only rhodamine B in water but also toluene gas in air under UV light illumination, when compared with either TiO₂ nanotube array or commercial Degussa P25 nanoparticulate films on metallic Ti substrates. Remarkable sterilization of E. coli and S. epidermidis under visible light irradiation was also achieved. The excellent photocatalytic and antibacterial performances were attributed to the unique mixed 1D nanostructures, phase junctions, abundant surface hydroxyl groups, and the narrowed band gap.

Green synthesis of porous Au–Nx-TiO2 nanospheres for solar light induced photocatalytic degradation of diazo and triazo dyes and their eco-toxic effects

The photocatalytic activity of Au–N_x-TiO₂ nanospheres evaluated under natural sunlight; 91% mineralization of azo dyes is achieved without toxic intermediates.

A Photocatalytic Rotating Disc Reactor with TiO₂ Nanowire Arrays Deposited for Industrial Wastewater Treatment

A photocatalytic rotating disc reactor (PRD-reactor) with TiO₂ nanowire arrays deposited on a thin Ti plate is fabricated and tested for industrial wastewater treatment. Results indicate that the PRD-reactor shows excellent decolorization capability when tested with methyl orange (>97.5%). Advanced oxidation processes (AOP), including photocatalytic oxidation and photolytic reaction, occurred during the processing. Efficiency of the AOP increases with reduction in light absorption pathlength, which enhanced the photocatalytic reaction, as well as by increasing oxygen exposure of the wastewater thin film due to the rotating disc design. It is found that, with a small dosage of hydrogen peroxide, the mineralization efficiency of industrial biodegraded wastewater can be enhanced, with a superior mineralization of >75% total organic carbon (TOC) removal. This is due to the fact that the TiO₂ photocatalysis and hydrogen peroxide processes generate powerful oxidants (hydroxyl radicals) that can strongly improve photocatalytic oxidation efficiency. Application of this industrial wastewater treatment system is benefited from the TiO₂ nanowire arrays, which can be fabricated by a mild solvothermal method at 80 °C and under atmospheric pressure. Similar morphologies and microstructures are found for the TiO₂ nanowire arrays deposited on a large metal Ti disc, which makes the wastewater treatment process more practical and economical.

Tailored performance of layered transition metal dichalcogenides via integration with low dimensional nanostructures

Transition metal dichalcogenides (TMDs) with a unique sandwich structure have attracted tremendous attention in recent years due to their distinctive electrical and optical properties.

A transparent TiO2–C@TiO2–graphene free-standing film with enhanced visible light photocatalysis

A transparent TiO₂–C@TiO₂–graphene free-standing film with graphene wrapped flower-like TiO₂ particles on C–TiO₂ fibers is synthesized for visible light photocatalysis.

One-pot low-temperature synthesis of TiO2 nanowire/rGO composites with enhanced photocatalytic activity

In situ growth of TiO₂ nanowires on graphene oxide was achieved at 80 °C in an open atmosphere. The optimized TiO₂/rGO hybrid exhibited a reaction rate constant 5.5 times that of TiO₂ nanowires towards photodegradations of rhodamine B in water under the UV light illumination.

Hybrid paper–TiO2 coupled with a Cu2O heterojunction: an efficient photocatalyst under sun-light irradiation

Hybrid paper–TiO₂, paper–Cu₂O–TiO₂ and paper–TiO₂–Cu₂O photocatalysts were prepared via a non-hydrolytic sol–gel process followed by mild hydrothermal treatment to generate the TiO₂ layer, and a reduction process to form the Cu₂O nanoparticles.

Photoelectrochemical properties of PbS quantum dot sensitized TiO2 nanorods photoelectrodes

Cross-sectional view FESEM images of (a) TiO₂ NRs, (b) PbS(4)/TiO₂ NRs (the insets show the top-view of the corresponding cross-sectional view FESEM images). 3D schematic diagrams of (c) TiO₂ NRs, (d) PbS(4)/TiO₂ NRs.

A facile solution-based approach to a photocatalytic active branched one-dimensional TiO2 array

Branched one-dimensional TiO₂ array with enhanced photocatalytic activity was fabricated via a facile solution-based strategy.

Sandwich-like titania thin films with one/three-dimensional nanostructures for photocatalytic applications

Appropriate layer-by-layer alignment of titania thin films with one/three-dimensional nanostructures resulted in enhanced photocatalytic activity.

K2TiO(C2O4)2-mediated synthesis of rutile TiO2 mesocrystals and their ability to assist photodegradation of sulfosalicylic acid in water

Flower-like rutile TiO₂ mesocrystals were synthesized by a K₂TiO(C₂O₄)₂-mediated low temperature solution route under the atmospheric pressure, which exhibited high photocatalytic activity because of the large specific surface area as well as the high charge separation rate inherent from the single crystal nature.

A facile synthesis of hierarchical TiO2for dye adsorption and photocatalysis

Hierarchical flower-like H₂Ti₅O₁₁·3H₂O assembled with radial nanowires was fabricated through a template-free solution-based method, which could be converted to TiO₂with controllable morphologies and phases by a subsequent acid-treating or annealing process.