Layered Sodium Titanate Research Articles

Outstanding rate capability and long cycle stability induced by homogeneous distribution of nitrogen doped carbon and titanium nitride on the surface and in the bulk of spinel lithium titanate

N-doped carbon and TiN composite conductive structure with homogeneous distribution on the surface and in the bulk of spinel lithium titanate (Li4Ti5O12) nanoparticles is prepared via a simple one-step chemical vapor deposition assisted solid-state route in the presence of layered structure sodium titanate nanotubes as the titanium source and ethylenediamine as the carbon and nitrogen source. Results indicate that as-fabricated Li4Ti5O12 samples containing N-doped carbon and TiN composite conductive structure exhibit markedly improved electrochemical properties as compared with pristine Li4Ti5O12. Particularly, the electrode made from Li4Ti5O12 containing N-doped carbon and TiN composite conductive structure obtained after 60min of treatment in the presence of ethylenediamine has a high capacity of 162 mAh·g−1 at a charge/discharge rate of 20C as well as a substantial capacity of 92% and a capacity retention of 75% after 2500 cycles at 10C, showing superior electrochemical performance and great potential as an anode material for high-rate lithium-ion batteries. The enhanced electrochemical performance of the composite electrodes can be attributed to the small size of Li4Ti5O12 nanoparticles as well as the uniform distribution of N-doped carbon and TiN composite conductive structure on the surface and in the bulk of Li4Ti5O12 nanoparticles.

Mildly Alkaline Preparation and Methylene Blue Adsorption Capacity of Hierarchical Flower-like Sodium Titanate

The hydrothermal preparation of flower-like layered sodium titanate architectures in a weakly alkaline medium is reported. NaCl was used as a morphology-directing agent, and a growth mechanism was proposed. The hierarchical structure is assembled from one-dimensional nanoribbons and exhibits an excellent removal capacity toward methylene blue (MB). A pseudo-second-order kinetic model was found to well describe the adsorption kinetics. Kinetic studies demonstrated that the overall rate of MB adsorption was controlled by surface adsorption and intraparticle diffusion. Results of this work are of great significance for environmental applications of flower-like layered sodium titanate architectures as a promising adsorbent material used for water purification.

New Materials Based On a Layered Sodium Titanate for Dual Electrochemical Na and Li Intercalation Systems

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Layered sodium titanate nanostructures as a new electrode for high energy density supercapacitors

A flower-shaped hydrated layered sodium titanate material, Na2Ti2O4(OH)2, have been synthesized through a facile hydrothermal method and subsequently converted into sodium free titania (anatase). Potential application of the Na2Ti2O4(OH)2 as an electrode for supercapacitors under pseudo-capacitance storage mode is evaluated. The Na2Ti2O4(OH)2 showed sixfold higher specific capacitance (CS ∼ 300 F g−1) in an aqueous electrolyte than the anatase and demonstrated stable electrochemical cycling. This high CS is originated from a combination of electrochemical double layer and pseudo-capacitance storage mechanisms. The presence of hydrated layered within some loose interlayer plays an important role in assisting the diffusion process of ions as confirmed in electrical impedance spectroscopy analysis.

New materials based on a layered sodium titanate for dual electrochemical Na and Li intercalation systems

The electrochemical properties of materials derived from NaTi3O6(OH)·2H2O have been investigated for the first time. The parent compound has a corrugated layered structure consisting of {Ti6O14}4− units with hydrated sodium cations and protons in the interlayer spaces. Upon heating to 600 °C, water is removed irreversibly, the interlayer distances become smaller, and connecting bonds between the octahedral layers form. It was found that this material can reversibly intercalate both lithium and sodium. The initial specific discharge capacities, as measured in half-cells, varied with the state of hydration and the nature of the counter electrode (Na or Li). The electrochemical potential showed a non-linear sloping dependence with degree of intercalation, indicative of a solid-solution mechanism of intercalation. The process was centered at a low average potential of about 0.3 V vs. Na or Li, the lowest ever reported for titanate-based Li hosts. The higher density and potential for higher rate capability of this compound, in comparison to carbonaceous materials with similar voltage and reversible capacities, make a compelling case for its development as an anode material, for both lithium and sodium ion batteries.

In situ Sn2+-incorporation synthesis of titanate nanotubes for photocatalytic dye degradation under visible light illumination

Sn2+-incorporated titanate nanotubes, prepared by washing a layered sodium titanate with a SnCl2 solution for tube formation, exhibit noticeable photocatalytic activity under visible light irradiation. This in situ synthesis results in a Sn/Ti ratio of approximately 0.6. Because of the introduction of Sn2+ ions, the Sn 5s orbital replaces the O 2p orbital as the top level of the valence band of titanate nanotubes. Optical absorption analysis shows that Sn doping reduces the bandgap of titanate nanotubes from 3.5 to 2.6eV. Oxidation of the Sn2+-incorporated titanate nanotubes leads to oxidation of Sn2+ to Sn4+, hence, widening the bandgap. Under visible light irradiation, Sn2+-incorporated titanate nanotubes effectively degrade methylene blue in an aqueous solution, whereas the bare titanate nanotubes exhibit substantially lower photocatalytic activity. Photoluminescence analysis demonstrates that the induced charges from excitation of the Sn2+ ions tend to be relaxed through chemical interactions, rather than irradiative recombination.

First-principles investigation of atomic structures and stability of proton-exchanged layered sodium titanate

Atomic structures and ionic substitutions in sodium titanate $({\text{Na}}_{2\ensuremath{-}x}{\text{H}}_{x}{\text{Ti}}_{3}{\text{O}}_{7})$, having ${\text{Ti}}_{3}{\text{O}}_{7}$ sheetlike layers with ${\text{Na}}^{+}$ and ${\text{H}}^{+}$ in between, were investigated by first-principles calculations. The formation energies via ion exchange of ${\text{Na}}^{+}$ and ${\text{H}}^{+}$ were analyzed by using the supercell total energies and ionic chemical potentials determined with the aid of experimental thermodynamic data. It was found that ionic substitutions of ${\text{Na}}^{+}$ by ${\text{H}}^{+}$ take place even in alkaline solution conditions as found in previous experiments. In addition, the bonding strength between the ${\text{Ti}}_{3}{\text{O}}_{7}$ layers tends to decrease with more ${\text{Na}}^{+}$ substitutions by ${\text{H}}^{+}$, which is related to $p\text{H}$ effects on exfoliation events of ${\text{Ti}}_{3}{\text{O}}_{7}$ sheetlike layers from layered titanate prior to the nanotube formation.

Solvent-controlled synthesis of TiO 2 1D nanostructures: Growth mechanism and characterization

One-dimensional (1D) anatase TiO 2 nanostructures such as nanorods, nanowires and nanotubes with different aspect ratios were synthesized by a simple solvothermal process. The influence of the different organic solvents and the reaction time on the morphology, size and the formation of the nanostructures were investigated. The anatase TiO 2 precursor powder reacted with highly alkaline aqueous solution, yielding layered sodium titanate nanosheets. These nanosheets transformed to different 1D sodium titanates nanostructures like nanorods, nanowires and nanotubes in the different solvents i.e. highly alkaline aqueous solution, highly alkaline water–ethanol and highly alkaline water–ethylene glycol mixed solvent, respectively. Acid treatment of these 1D sodium titanates resulted hydrated titanates and finally dehydration by calcinations at 500 °C in air gave the products retaining the morphology. The synthesized samples were characterized with XRD, SEM and TEM. All the 1D nanostructures showed intense and sharp absorption spectra indicated that the products were almost defect free. Photoluminescence studies of the nanostructures showed photostable UV emission properties that arise from the band-edge free excitation.

Layered sodium titanate nanofiber and microsphere synthesized from peroxotitanic acid solution

In this paper, we report titania and titanate nanofiber synthesized by using peroxotitanic acid solution as a titanium source. The peroxotitanic acid solution was mixed with NaOH aqueous solution, followed by the hydrothermal treatment with or without vigorous agitation. In TEM and SEM images for solids obtained by the synthesis with vigorous agitation, nanofibers are observed. On the other hand, microspheres as well as nanofibers were observed in solids obtained by the synthesis without agitation. The microspheres are composed of nanofibers and nanosheets. EDX analysis for the obtained solids detected Ti and Na, indicating that the obtained solids are sodium titanate. As a reference, synthesis by using TiO 2 particles instead of the peroxotitanic acid solution was also performed. The Na to Ti mole ratio for the peroxotitanic acid based solid determined by EDX was 0.55 which is twice the value of 0.26 for the TiO 2 particle based solid. The obtained sodium titanate could be converted into anatase-type titania by the HCl treatment of the sodium titanate and the subsequent calcination.

Titanate Nanotubes and Nanorods Prepared from Rutile Powder

Various sized hollow nanotubes and solid nanorods are synthesized from rutile powder (particle size ≈ 120–280 nm) using a relatively simple chemical approach in alkaline solution. The nanotubes and nanorods occur as hydrated phases: TiO2·1.25H2O and TiO2·1.0H2O, respectively. The rutile particles react in concentrated NaOH solution under hydrothermal conditions, yielding layered sodium titanate in the form of either polycrystalline nanotubes or single-crystal nanorods. The form of the product depends on the temperature and time of hydrothermal reaction: Therefore, this is a report of the template-free control of the degree of crystallinity, crystal structure, and morphology of these types of nanoscale sodium titanate products. By treating the nanotubes and nanorods with dilute HCl, the sodium ions within them could be exchanged for protons, and the morphology of the nanotubes and nanorods is retained, resulting in hydrogen titanate nanotubes and nanorods. The electrochemical performance of dehydrated hydrogen titanate nanotubes and nanorods is explored in terms of their potential performance as anode materials for lithium-ion batteries. The discharge capacity is higher for thin anatase nanorods converted from hydrogen titanate nanotubes when compared to the calcined (at 500 °C and 700 °C) products of hydrogen titanate nanorods. The significance of these findings is the possibility of fabricating delicate, nanostructured materials directly from industrial raw materials, because the natural mineral of titanium dioxide and most of the raw industrial TiO2 products exist in the rutile phase.

無機イオン交換体の新展開 層状チタン酸ナトリウム（Ｎａ２Ｔｉ３Ｏ７）の多価イオンによるイオン交換反応

無機イオン交換体の新展開 層状チタン酸ナトリウム（Ｎａ２Ｔｉ３Ｏ７）の多価イオンによるイオン交換反応