Layered Titanium Oxide Research Articles

Oxide Acidity Modulates Structural Transformations in Hydrogen Titanates during Electrochemical Li-Ion Insertion.

Hydrogen titanates (HTOs) form a diverse group of metastable, layered titanium oxides with an interlayer containing both water molecules and structural protons. We investigated how the chemistry of this interlayer environment influenced electrochemical Li+-insertion in a series of HTOs, H2TiyO2y+1·nH2O (y = 3, 4, and 5). We correlated the electrochemical response with the physical and chemical properties of HTOs using operando X-ray diffraction, in situ differential electrochemical mass spectroscopy, solid-state proton nuclear magnetic resonance, and quasi-elastic neutron scattering. We found that the potential for the first reduction reaction trended with the relative acidity of the structural protons. This mechanism was supported with first-principles density functional theory (DFT) calculations. We propose that the electrochemical reaction involves reduction of the structural protons to yield hydrogen gas and formation of a lithiated hydrogen titanate (H2-xLixTiyO2y+1). The hydrogen gas is confined within the HTO lattice until the titanate structure expands upon subsequent oxidation. Our work has implications for the electrochemical behavior of insertion hosts containing hydrogen and structural water molecules, where hydrogen evolution is expected at potentials below the hydrogen reduction potential and in the absence of electrolyte proton donors. This behavior is an example of electrochemical electron transfer to a nonmetal element in a metal oxide host, in analogy to anion redox.

Hybridization of Layered Titanium Oxides and Covalent Organic Nanosheets into Hollow Spheres for High-Performance Sodium-Ion Batteries with Boosted Electrical/Ionic Conductivity and Ultralong Cycle Life.

While development of a sodium-ion battery (SIB) cathode has been approached by various routes, research on compatible anodes for advanced SIB systems has not been sufficiently addressed. The anode materials based on titanium oxide typically show low electrical performances in SIB systems primarily due to their low electrical/ionic conductivity. Thus, in this work, layered titanium oxides were hybridized with covalent organic nanosheets (CONs), which exhibited excellent electrical conductivity, to be used as anodes in SIBs. Moreover, to enlarge the accessible areas for sodium ions, the morphology of the hybrid was formulated in the form of a hollow sphere (HS), leading to the highly enhanced ionic conductivity. This synthesis method was based on the expectation of synergetic effects since titanium oxide provides direct electrostatic sodiation sites that shield organic components and CON supports high electrical and ionic conductivity with polarizable sodiation sites. Therefore, the hybrid shows enhanced and stable electrochemical performances as an anode for up to 2600 charge/discharge cycles compared to the HS without CONs. Furthermore, the best reversible capacities obtained from the hybrid were 426.2 and 108.5 mAh/g at current densities of 100 and 6000 mA/g, which are noteworthy results for the TiO2-based material.

Electrochemical Properties of Titanium Oxides with Disordered Layer Stacking through Flocculation of Exfoliated Titania Nanosheets

A new type of layered titanium oxides with turbostratic stacking has been synthesized via flocculation of exfoliated titania nanosheets with HCl or LiOH. Nitrogen adsorption–desorption isotherms showed that the spray-dried flocculations had mesoporous structures composed of slit-shaped pores. Cross-sectional SEM and TEM analyses clarified that particles were composed of agglomerated highly twisted flakes. UV-Visible diffuse reflectance spectra of restacked titania nanosheets were depended on the restacking process and were significantly blue shifted compared with that for the parent layered compound. The product flocculated with HCl showed a high initial capacity of about 300 mAh g−1 (cutoff voltage: 1.0 V), whereas rechargeable capacities were gradually decreased during charge-discharge repetition. On the other hand, the heat-treated product restacked by LiOH showed a relatively good cyclability over the 50 cycles, indicating a rechargeable capacity of about 150 mAh g−1. X-ray absorption spectra and cyclic voltammograms gave the evidence of the redox reaction of titanium, and the average voltage depended on the type of layer stacking. The XRD analyses of electrodes after charge-discharge revealed that the cyclability depended on the stability of layer structure.

Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide.

The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron–hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

ChemInform Abstract: Alternate Layered Nanostructures of Metal Oxides by a Click Reaction.

AbstractAn alternating multilayer of titanium and tungsten oxides is synthesized by modifying layered titanium oxide with an alkene group and layered tungsten oxide with a thiol group, and causing a thiol—ene (click) reaction.

Alternate Layered Nanostructures of Metal Oxides by a Click Reaction

An alternating multilayer of titanium and tungsten oxides is synthesized by modifying layered titanium oxide with an alkene group and layered tungsten oxide with a thiol group, and causing a thiol—ene (click) reaction.

Mesoporous Layer-by-Layer Ordered Nanohybrids of Layered Double Hydroxide and Layered Metal Oxide: Highly Active Visible Light Photocatalysts with Improved Chemical Stability

Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical stability.

Enhanced removal of trace Cr(VI) ions from aqueous solution by titanium oxide–Ag composite adsorbents

Titanium oxide–Ag composite (TOAC) adsorbents were prepared by a facile solution route with Ag nanoparticles being homogeneously dispersed on layered titanium oxide materials. The as-synthesized TOAC exhibited a remarkable capability for trace Cr(VI) removal from an aqueous solution, where the concentration of Cr(VI) could be decreased to a level below 0.05 mg/L within 1 h. We have systematically investigated the factors that influenced the adsorption of Cr(VI), for example, the pH value of the solution, and the contact time of TOAC with Cr(VI). We found that the adsorption of Cr(VI) was strongly pH-dependent. The adsorption behavior of Cr(VI) onto TOAC fitted well the Langmuir isotherm and a maximum adsorption capacity of Cr(VI) as 25.7 mg/g was achieved. The adsorption process followed the pseudo-second-order kinetic model, which implied that the adsorption was composed of two steps: the adsorption of Cr(VI) ions onto TOAC followed by the reduction of Cr(VI) to Cr(III) by Ag nanoparticles. Our results revealed that TOAC with high capacity of Cr(VI) removal had promising potential for wastewater treatment.

Layered Titanium Oxide Nanosheet and Ultrathin Nanotubes: A First-Principles Prediction

We propose stable layered structures and ultrathin tubular configurations of titanium oxide (TiO2) nanomaterials on the basis of first-principles calculations within density functional theory. The thinnest TiO2 nanosheet is characterized by a reconstructed (001) bilayer of rutile TiO2, while ultrathin TiO2 nanotubes can be built by rolling up a TiO2NS. These nanotubes are predicted to have high stability, large Young’s modulus, and tunable electronic properties. A possible synthetic route toward these nanostructures is also presented.

PH Dependence of the Photoluminescence of Eu3+-Intercalated Layered Titanium Oxide

We investigated the pH dependence of Eu3+ emissions from Eu3+-intercalated layered titanium oxide (Eu/TiO) and evaluated the local structure of the intercalated Eu3+ at varying pH values using lifetime measurements and EXAFS. A red Eu3+ emission was observed under radiation by UV light with a higher energy than the band gap of the host TiOx layer. The emission is based on energy transfer from the host TiOx layer to Eu3+. The emission intensity of Eu/TiO in 0.01 M NaOH aqueous solution was stronger than that in 0.01 M HCl aqueous solution, and the emission response of the Eu/TiO film was relatively stable to pH cycling. Two phenomena may provide a mechanism for the change in emission from Eu/TiO. One is a change in the efficiency of energy transfer from the TiOx nanosheet to Eu3+, and the other is a fine hydration state change of Eu3+ without a change in the total water amount.

Effects of hydronium intercalation and cation substitution on the photocatalytic performance of layered titanium oxide

We have investigated the effects of hydronium (H 3O +) intercalation and transition metal substitution on the photocatalytic activity of layered titanate. The basal spacings of the cesium titanate and Fe-/Ni-substituted titanates are notably expanded by 1 M HCl treatment, indicating the intercalation of hydronium ion. Diffuse reflectance UV–vis spectroscopic results clearly demonstrate that, in contrast to the hydronium intercalation, the substitution of transition metal ions gives rise to a remarkable narrowing of bandgap energy down to ∼1.9–2.3 eV. According to Fe K- and Ni K-edge X-ray absorption spectroscopic analysis, the substituted iron and nickel ions are stabilized in octahedral titanium sites with trivalent and divalent oxidation states, respectively. The photodegradation tests for organic dye molecules reveal that the hydronium intercalation enhances remarkably the photocatalytic performance of cesium titanate under UV irradiation and the substitution of Fe or Ni endows wide bandgap titanate with visible light driven photocatalytic activity.

Preparation and Thermoelectric Properties of the Layered Titanium Oxide and Effect of Metal-ion Substitution

Preparation and Thermoelectric Properties of the Layered Titanium Oxide and Effect of Metal-ion Substitution

Structure and Raman Spectra of Layered Titanium Oxides

The Raman spectra of layered titanium oxides, NaLnTiO4, Na2Ln2Ti3O10, HLnTiO4, and HLnTiO4·xH2O (Ln=lanthanides), were investigated. The assignment of the Raman bands was based on the structural data. The characteristic major band around 900 cm−1of parent sodium compounds, which is assigned to the symmetric stretching mode of a short Ti–O bond, was not observed for proton-exchanged derivatives but instead a broad weak band around 820 cm−1appeared. Such a change is proposed to result from the replacement of an ionic Ti–O−Na+bond by a covalent Ti–O–H bond. The difference in Brønsted acidity between titanium oxides and niobium oxides with similar structure could be explained by comparison of their Raman spectra before and after proton exchanges. A structural rearrangement by the intercalation of a water molecule into a proton layer gave two bands around 770 and 900 cm−1, which were assigned to two types of terminal Ti–O bonds with different bond orders. In addition, several characteristic modes of layered-type titanium oxides were systematically compared and assigned.

Synthesis and characterization of layered titanium oxides NaRTiO 4 (R = La, Nd and Gd)

The layered titanium oxides NaRTiO 4 (R = La, Nd and Gd) have been synthesized at 850 °C. The lattice parameter a decreases with decreasing of the ionic size of R, in contrast to the results previously reported for samples synthesized at higher temperature, 1050 °C. X-ray Rietveld refinement of NaNdTiO 4 confirmed the ordering of Na and R and the large displacement of Ti from the center of the oxygen coordination octahedra, resulting in one strong and one weak TiO bonds along c-axis. Magnetic susceptibility of the rocksalt-type (NdO) 2 layer in NaNdTiO 4 resembles that of the fluorite-type Nd 2O 2 layer in Nd 2CuO 4.