Titanate Nanosheets Research Articles

Growth of Lithium Lanthanum Titanate Nanosheets and Their Application in Lithium-Ion Batteries.

In this work, lithium-doped lanthanum titanate (LLTO) nanosheets have been prepared by a facile hydrothermal approach. It is found that with the incorporation of lithium ions, the morphology of the product transfers from rectangular nanosheets to irregular nanosheets along with a transition from La2Ti2O7 to Li0.5La0.5TiO3. The as-prepared LLTO nanosheets are used to enhance electrochemical performance of the LiCo1/3Ni1/3Mn1/3O2 (CNM) electrode by forming a higher lithium-ion conductive network. The LiCo1/3Ni1/3Mn1/3O2-Li0.5La0.5TiO3 (CNM-LLTO) electrode shows better a lithium diffusion coefficient of 1.5 × 10(-15) cm(2) s(-1), resulting from higher lithium-ion conductivity of LLTO and shorter lithium diffusion path, compared with the lithium diffusion coefficient of CNM electrode (5.44 × 10(-16) cm(2) s(-1)). Superior reversibility and stability are also found in the CNM-LLTO electrode, which retains a capacity at 198 mAh/g after 100 cycles at a rate of 0.1 C. Therefore, it can be confirmed that the existence of LLTO nanosheets can act as bridges to facilitate the lithium-ion diffusion between the active materials and electrolytes.

Bottom-up synthesis of titanate nanoflakes and nanosheets in ionic liquid solvents

The bottom-up synthesis of titanate nanoflakes in ionic liquid solvents was carried out by heating mixtures of titanium isopropoxide (TIP), 40% tetrabutylammonium hydroxide (TBAOH) aqueous solution, and ionic liquids with a molar ratio of 1TIP : xTBAOH : (10 − x)ionic liquid : 22xH2O. Using tetrabutylammonium chloride (TBACl) as an ionic liquid, layered titanate crystals with TBA+ as an interlayer cation were synthesized by the acid–base reaction of TBAOH and titanic acid, which was formed by the hydrolysis of TIP, in the range of 0.5 ≤ x ≤ 2.5. The use of 1,2,3-trimethylimidazolium (mmmIm+) methylsulfate as an ionic liquid also led to the formation of layered titanate with mmmIm+ ions as an interlayer cation, although the amount of layered titanate was smaller than that in the case using TBACl. The solvent exchange from ionic liquids to aqueous solution by dialyzing the products caused the exfoliation of layered titanate, providing titanate nanoflakes with a lateral size of about 3 nm. Moreover, by comparing the bottom-up syntheses of layered titanate in ionic liquids and in water, the crystallization behavior of layered titanate was examined. The amount of TBA+ or mmmIm+, which acts as an interlayer cation of layered titanate, influenced the nucleation of layered titanate rather than the solubility of titanate. A significant amount of TBA+ or mmmIm+ in the ionic liquid solvents accelerated the nucleation of layered titanate crystals, providing small titanate nanoflakes. Furthermore, the formed titanate species existed as exfoliated nanosheets or nanoflakes in water solvent, but were present as layered titanate crystals in ionic liquids. However, this difference in the state of titanates had little influence on the growth rates of layered titanate crystals. Thus, the bottom-up synthesis of layered titanates in ionic liquids was useful for the formation of very small titanate nanoflakes.

Improving the stability of titania nanosheets by functionalization with polyelectrolytes

Highly stable suspensions of titanate nanosheets were designed by surface functionalization with P(AAm-co-DADMAC) copolymer.

Hydrothermal synthesis of sodium titanate nanosheets using a supercritical flow reaction system

Hydrothermal synthesis of sodium titanate nanosheets using a supercritical flow reaction system

Preparation of titanate nanosheets and nanoribbons by exfoliation of amine intercalated titanates.

Amine intercalated titanates were synthesized by direct exchange of potassium ions of K2Ti4O9 by alkyl ammonium ions of various alkyl chain lengths. These intercalated solids exfoliate well in alcohols of different alkyl chain lengths and non-polar solvents such as toluene and hexane to yield colloidal dispersions of titanate nanosheets. The longer the alkyl chain of the intercalated amine the better the exfoliation of the intercalated titanate in long chain alcohols and non-polar solvents. While non-uniform rectangular nanosheets were obtained when aggressive sonication was employed for exfoliating the solids, nanoribbons were obtained when the exfoliation was carried out by gently stirring the solids in the solvent.

Ultrathin anatase nanosheets with high energy facets exposed and related photocatalytic performances

Ultrathin anatase nanosheets with high energy (116) facets exposed were fabricated from exfoliated titanate nanosheets and exhibited high photocatalytic performance.

High power layered titanate nano-sheets as pseudocapacitive lithium-ion battery anodes

Ultra-thin layered sodium titanate nano-sheets were synthesised using a continuous hydrothermal flow process and the as-prepared materials were investigated as an anode material for lithium-ion batteries. In comparison to previous studies on similar materials, the layered titanates herein showed high electrochemical activity at lower potentials. Cyclic voltammetry measurements in the potential range of 0.05–2.1 V vs. Li/Li+, revealed that charge storage occurred from both lithium-ion intercalation as well as pseudocapacitive surface chemical processes. During electrochemical cycling tests, a high specific current of 0.5 A g−1 was applied and the cells achieved a stable specific capacity of ca. 120 mAh g−1 for over 1200 cycles. Even at an applied current of 10 A g−1, the electrode material delivered a stable specific capacity of 38 mAh g−1, which suggests that this material may be suitable for high power applications.

A Crucial Role of Rh Substituent Ion in Photoinduced Internal Electron Transfer and Enhanced Photocatalytic Activity of CdS-Ti(5.2-x)/6 Rhx /2 O2 Nanohybrids.

The photocatalytic activity and photostability of CdS quantum dot (QD) can be remarkably enhanced by hybridization with Rh-substituted layered titanate nanosheet even at very low Rh substitution rate (<1%). Mesoporous CdS-Ti(5.2-x)/6 Rhx/2O2 nanohybrids are synthesized by a self-assembly of exfoliated Ti(5.2-x)/6 Rhx/2O2 nanosheets with CdS QDs. The partial substitution of Rh(3+)/Rh(4+) ions for Ti(4+) ions in layered titanate is quite effective in enhancing an electronic coupling between hybridized CdS and titanate components via the formation of interband Rh 4d states. A crucial role of Rh substituent ion in the internal electron transfer is obviously evidenced from in situ X-ray absorption spectroscopy showing the elongation of (RhO) bond under visible light irradiation. This is the first spectroscopic evidence for the important role of substituent ion in the photoinduced electron transfer of hybrid-type photocatalyst. The CdS-Ti(5.2-x)/6 Rhx/2O2 nanohybrids show much higher photocatalytic activity for H2 production and better photostability than do CdS and unsubstituted CdS-TiO2 nanohybrid. This result is ascribable to the enhancement of visible light absorptivity, the depression of electron-hole recombination, and the enhanced hole curing of CdS upon Rh substitution. The present study underscores that the hybridization with composition-controlled inorganic nanosheet provides a novel efficient methodology to optimize the photo-related functionalities of semiconductor nanocrystal.

Visible-Light-Induced Activity Control of Peroxidase Bound to Fe-Doped Titanate Nanosheets with Nanometric Lateral Dimensions.

Catalytic performance of horseradish peroxidase (HRP) electrostatically adsorbed on nanometric and semiconducting Fe-doped titanate (FT) nanosheets was successfully manipulated by visible light illumination. A colloidal solution of FT with a narrow band gap corresponding to a visible light region was fabricated through a hydrolysis reaction of metals sources. HRP could be easily bound to the FT at pH = 4 through an electrostatic interaction between them, and the formed HRP-FT was utilized for the visible-light-driven enzymatic reaction. Under exposure to visible light with enough energy for band gap excitation of the FT, catalytic activity of HRP-FT was dramatically enhanced as compared with free (unbound) HRP and was simply adjusted by light intensity. In addition, wavelength dependence of an enzymatic reaction rate was analogous to an optical absorption spectrum of the FT. These results substantiated an expected reaction mechanism in which the photoenzymatic reaction was initiated by band gap excitation of FT followed by transferring holes generated in the valence band of irradiated FT to HRP. The excited HRP oxidized substrates (amplex ultrared: AUR) accompanied by two-electron reduction to regenerate the resting state. In addition, the catalytic activity was clearly switched by turning on and off the light source.

Fabrication of Tunable, High‐Refractive‐Index Titanate–Silk Nanocomposites on the Micro‐ and Nanoscale

The combination of water-based titanate nanosheets dispersion and silk fibroin solution allows the realization of a versatile nanocomposite. Different fabrication techniques can be easily applied on these nanocomposites to manipulate the end form of these materials on the micro- and nanoscale. Easy tunability of the refractive index from n = 1.55 up to n = 1.97 is achieved, making it attractive for flexible, biopolymer-based optical devices.

Evaluation and comparison of layered titanate nanosheets using TOF‐SIMS and g‐ogram analysis

The evaluation of nanostructure is important to develop the highly controlled nanomaterials. In this study, two kinds of layered titanate nanosheets, which were produced by using hexylamine and laurylamine, respectively, as surfactants were investigated by Gentle Secondary Ion Mass Spectrometry Gentle‐SIMS (G‐SIMS) and g‐ogram, which is the latest Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS) data analysis method for detecting more intact ions and obtaining the information on original chemical structures of samples precisely from complicated TOF‐SIMS spectra. As a result, molecular related ions of the surfactants were detected from each sample, and the structural information of samples was obtained. From both samples, surfactant molecular ions connected with hydrocarbon were detected as more intact ions rather than molecular ions of themselves. It was suggested that hydrophobic domains of their lamellar mesostructure are formed robustly by more than two surfactant molecules connected with each other linearly. After all, important information on the chemical structure of the layered titanate nanosheets, which would be difficult to be found by using typical structural analysis methods such as X‐ray diffraction and transmission electron microscopy, were obtained using G‐SIMS and g‐ogram. Therefore, it was shown that g‐ogram and G‐SIMS are helpful to evaluate the nanostructured materials. And it was also shown that g‐ogram is applicable to organic–inorganic materials which contain long hydrocarbon structures. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Enzyme-mimetic activity of Ce-intercalated titanate nanosheets.

Colloidal solutions of Ce-doped titanate nanosheets (Ce-TNS) with tiny dimensions (<10 nm) were fabricated through a hydrolysis reaction of titanium tetraisopropoxide and Ce(NO3)3, and their annihilation activity for reactive oxygen species (ROS) was investigated. The obtained Ce-TNS had an akin crystal structure to layered tetratitanate (Ti4O9(2-)) and Ce ions occupied interlayer space between the host layers with a negative charge. The Ce-TNS possessed a superoxide dismutase (SOD) mimetic activity for disproportionation of superoxide anion radicals (O2(-)) as target ROS. It was explained that the annihilation of O2(-) caused a valence fluctuation of Ce ions existing in the interlayer. Moreover, the activity of Ce-TNS exceeded that of CeO2 nanoparticles recently attracting much attention as an inorganic SOD mimic. The superior performance was explained mainly by a high dispersion stability of the Ce-TNS bringing about a huge reaction area. Moreover, the Ce-TNS protected DNA molecules from ultraviolet light induced oxidative damage, demonstrating effectiveness as one of the new inorganic protecting agents for biomolecules and tissues.

Amine-Functionalized Titanate Nanosheet-Assembled Yolk@Shell Microspheres for Efficient Cocatalyst-Free Visible-Light Photocatalytic CO2 Reduction.

Exploiting advanced semiconductor photocatalyst with superior activity and selectivity for the conversion of CO2 into solar fuels and valuable chemicals is of worldwide interest. In this report, hierarchical amine-functionalized titanate nanosheets based yolk@shell microspheres were synthesized via one-pot organic amine mediated anhydrous alcoholysis of titanium(IV) butoxide. The selected organic amine, diethylenetriamine, played multiple roles. First, it was essential for the crystallographic, morphological and textural control of the synthesized titanate nanoarchitectures. Second, it was crucial for the in situ functionalization of titanate nanosheets by concurrent interlayer intercalation and surface grafting, which gave rise to the strong visible-light absorption ability and high CO2 adsorption capacity. As a consequence of the synergetic tuning in multilevel microstructures, an integrated engineering of the multifunctional modules of the titanate-based photocatalysts was achieved for efficient CO2 reduction toward solar fuels.

Sandwich-structured composite from the direct coassembly of layered titanate nanosheets and Mn porphyrin and its electrocatalytic performance for nitrite oxidation

MnTMPyP–Ti4O9 nanocomposite was prepared by the direct coassembly of oppositely charged building blocks, exfoliated titanate nanosheets and 5,10,15,20-tetrakis(N-methylpyridinium-4-yl) porphyrinato manganese(III), MnTMPyP cations. XRD, IR, SEM, and TEM revealed that Mn porphyrin has been successfully inserted into the lamellar spacing of layered titanate. The metalloporphyrin molecules incorporated within the nanocomposite were found to be tilted approximately 42° against the titanate nanosheets. Further, the obtained MnTMPyP–Ti4O9 nanocomposite has been examined for the electrochemical detection of nitrite using cyclic voltammetry and differential pulse voltammetry techniques. The electrochemical studies demonstrated that MnTMPyP–Ti4O9 nanocomposite detects nitrite linearly over a concentration range of 2.0×10−6–1.57×10−3M with the detection limit of 1.25×10−6M at a signal-to-noise ratio of 3.

Bottom-Up Synthesis of Titanate Nanosheets in Aqueous Sols and Their Morphology Change by the Addition of Organic Ligands and Dialysis

The size, shape, and stacking of titanate nanosheets synthesized by heating aqueous mixtures of titanium complexes and tetrabutylammonium hydroxide were dependent on the type and amount of organic ligands and the amount of tetrabutylammonium ion (TBA+). When titanium isopropoxide was used as the titanium source, most titanate crystals were smaller than 10 nm in lateral size. However, the use of titanium complexes provided a lateral size of about 100 nm. The titanate crystals were synthesized by the acid–base reaction of titanic acid and TBAOH. The decrease in titanic acid concentration by titanium complex formation led to larger titanate crystals by the inhibition of crystal nucleation. Moreover, the use of triethanolamine and lactic acid as an organic ligand provided round and hexagonal titanate crystals, respectively. However, when the concentration of organic ligands was decreased by the dialysis of the titanate sols, the form of titanate crystals was changed to a rhombic shape. Thus, the adsorption of...

Prominently photocatalytic performance of restacked titanate nanosheets associated with H2O2 under visible light irradiation

In this work, an extremely high activity for visible light driven photocatalytic degradation of organic dyes was achieved on a restacked titanate nanosheets (rs-TNSs) material with the assistance of hydrogen peroxide (H2O2). The photocatalyst was obtained via exfoliating layered titanate precursor and the following flocculation by acidic solution, and its porous structure was further characterized with these technologies of scan electron microscopy, X-ray diffraction and nitrogen sorption. This rs-TNSs material exhibited prominent activity for photodecomposing Rhodamine B, ~90% dyes being removed in the first 5min, and the photocatalytic efficiency was much higher than those of the layered precursor and commercial Degussa P25 TiO2 under the same condition. The possible mechanism for enhanced photocatalytic activity was proposed: enlargement of the absorption spectrum to visible region by the surface modification of peroxide groups; acceptance of photogenerated electrons by H2O2 to reduce the recombination of electron–hole pairs and produce oxidative species of hydroxyl radicals. Additionally, the influences of H2O2 dosage, dye concentration and the reusability of photocatalyst were further investigated.

Free-standing films of titanate nanosheets as efficient visible-light-driven photocatalysts for environmental application

We herein report the reassembly of individual titanate nanosheets (TNSs) that were exfoliated from layered titanates to form a free-standing photocatalytic film by vacuum filtration. This TNSs film was characterized with high orientation, as well as excellent light transparency and flexibility. With the presence of H2O2, an extremely high activity and stability of the TNSs film were achieved for photo-decomposing Rhodamine B (RhB) using a 9W fluorescent lamp. A possible mechanism was proposed that the modification of –OOH groups enlarged the spectral region to visible light and high separation rate of photogenerated carriers was realized by transferring electrons on conduction band to H2O2. The trapping experiments of active species demonstrated that holes on valence band are the main oxidant species.

Titanate nanosheets as highly efficient non-light-driven catalysts for degradation of organic dyes.

A novel non-light-driven catalysis by the delaminated two dimensional titanate nanosheets (TNSs) has been explored for degradation of organic dyes with hydrogen peroxide (H2O2). This catalyst can efficiently remove dyes at high concentration and over a wide pH range, as well as with a long cycle number and superior universality.

Enhanced catalytic activity of enzymes interacting with nanometric titanate nanosheets

Enzymatic activity of horseradish peroxidase (HRP) at diluted conditions is highly increased under the presence of nanometric titanate nanosheets (TNS).

An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets.

Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.