Cesium Titanate Research Articles

Efficient p-n Heterojunction Photocatalyst Composed of Bismuth Oxyiodide and Layered Titanate.

Bismuth oxyhalides and layered alkali titanates are promising components to design high-performance hybrid photocatalysts. In this work, a hybrid photocatalyst composed of lepidocrocite-type layered cesium titanate (Cs0.7Ti1.77Li0.23O4, CsTLO) and bismuth oxyiodide (BiOI) was designed rationally based on lattice matching. BiOI formed on the layered titanate by ion exchange of CsTLO with Bi cations and subsequent growth of BiOI nanodisks (6 nm in the thickness and 125 nm in the lateral size) in an aqueous solution of cesium iodide, resulting in the hybrid where BiOI nanodisks were lying flat on the layered titanate and exposed the (001) facet predominantly. The present hybrid exhibited efficient photodegradation of methylene blue (4, 10, and 14 times higher than that of CsTLO, Bi-TLO, and BiOI, respectively), which was ascribed to the efficient charge transfer in the bulk and at the interface assisted by the built-in internal electric fields and the high activity of (001) BiOI for direct oxidation of the pollutant.

Post-synthetic particle size reduction of a layered cesium titanate (Cs2Ti5O11) for the improvement of photocatalytic H2 production

Layered cesium titanate (Cs2Ti5O11) having an elongated rectangular particle shape of size a few hundreds of nanometers has been prepared by size reduction of a macroscopic sample prepared by a previously reported solid-state reaction procedure. The as-prepared material had a particle size of 3 μm (length) and 0.5 μm (width). The described size reduction was accomplished by first pelletizing the Cs2Ti5O11 by pressing it in a mold, and then crushing it in a mortar. The Cs2Ti5O11 samples before and after size reduction were proton-exchanged to obtain H2Ti5O11, which proved to be active for photocatalytic H2 production in the presence of methanol as a sacrificial donor under UV irradiation. In this process, H2Ti5O11 derived from size-reduced Cs2Ti5O11 exhibited higher activity than that derived from the pristine Cs2Ti5O11.

Ni-Doped Protonated Layered Titanate/TiO2 Composite with Efficient Photocatalytic Activity for NO x Decomposition Reactions

A unique structural transformation of a lepidocrocite-type layered titanate, K0.8Ti1.73Li0.27O4, into a rutile-type TiO2 has recently been realized via dilute HCl treatment and subsequent drying at room temperature for producing rutile-nanoparticle-decorated protonated layered titanate exhibiting highly efficient photocatalytic activity. Herein, the authors report synthesis of a lepidocrocite-type layered cesium titanate with nominal compositions of C s 0.7 T i 1.825 ‐ x / 2 N i x □ 0.175 ‐ x / 2 O 4 ( x = 0 , 0.05, 0.1, and 0.35) through solid-state reactions of Cs2CO3, TiO2, and Ni(CH3COO)2·4H2O at different temperatures (600 or 800°C), followed by treatment with dilute HCl and subsequent drying to produce a Ni-doped protonated layered titanate/TiO2 composite. C s 0.7 T i 1.825 ‐ x / 2 N i x □ 0.175 ‐ x / 2 O 4 with an optimized Ni content obtained at a lower temperature was converted into a Ni-doped protonated layered titanate/TiO2 composite to exhibit high photocatalytic activity for NO x decomposition reactions.

Mechanochemical syntheses of all-inorganic iodide perovskites from layered cesium titanate and bismuth (and antimony) iodide.

All-inorganic iodide perovskites were prepared by a mechanochemical reaction between a layered cesium titanate and bismuth (or antimony) triiodide under ambient conditions. The layered cesium titanate was a sacrificial template and also acted as a milling media for the formation of the perovskite nanoparticles with the size of a few nanometres.

A phase separation in a protonated layered nickel titanate to form Ni-doped anatase/rutile TiO2 nanocomposite with efficient visible-light responsive photocatalytic activity

ABSTRACT We report a simple methodology for the preparation of an efficient visible-light responsive TiO2 photocatalyst through acid treatment of a lepidocrocite-type layered nickel cesium titanate (Cs0.7Ti1.65Ni0.35O4) for interlayer protonation and subsequent calcination at different temperatures (400–600°C) to induce structural transformation. The Ni-doped anatase/rutile nanocomposite possessing a morphology similar to that of protonated layered nickel titanate is obtained at all calcination temperatures. The sample obtained at 600°C exhibits the highest visible-light responsive photocatalytic activity for decomposition of the aqueous methylene blue dye under visible-light (λ > 420 nm) irradiation. The activity is 14 times higher than that of P25 (standard TiO2 photocatalyst) modified with Ni2+ and 3 times higher than that of NiTiO3 (visible-light responsive photocatalyst). The efficient visible-light responsive photocatalytic activity is ascribable to the visible-light absorption ability of the TiO2 phase owing to Ni-doping. Also, an efficient electron transfer across anatase–rutile interfaces for inhibition of charge recombination could be responsible for the activity. This methodology is a new route for efficient visible-light responsive photocatalysts based on TiO2 doped with various elemental species. This is because lepidocrocite-type layered titanates are available in a variety of chemical compositions.

Synthesis of cesium, sodium and nitrogen derived titanates using the Pechini sol-gel method

Cesium and sodium titanates with the respective stoichiometries of CsxTi2-x/4□x/4O4 (x ≈ 0.7) and Na2Ti6O13 was synthesized by making use of the Pechini sol-gel method. Direct intercalation of hydrazine hydrate in cesium and sodium titanates proved unsuccessful with the direct intercalation of ammonium into cesium titanate achieved. The protonated form of cesium titanate was successfully intercalated with hydrazine hydrate. Findings of the structural properties of the various titanates obtained from X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Fourier-Transform Infra-Red spectroscopy, Raman spectroscopy and transmission electron microscopy are presented.

An Unusually Acidic and Thermally Stable Cesium Titanate Cs xTi2- yM yO4 ( x = 0.67 or 0.70; M = vacancy or Zn).

Proton-free, alkali-containing layered metal oxides are thermally stable compared to their protonic counterparts, potentially allowing catalysis by Lewis acid sites at elevated temperatures. However, the Lewis acidic nature of these materials has not been well explored, as alkali ions are generally considered to promote basic but to suppress acidic character. Here, we report a rare example of an unusually acidic cesium-containing oxide Cs xTi2- yM yO4 ( x = 0.67 or 0.70; M = Ti vacancy □ or Zn). These lepidocrocite-type microcrystals desorbed NH3 at >400 °C with a total acidity of ≲410 μmol g-1 at a specific surface area of only 5 m2 g-1, without the need for lengthy proton-ion exchange, pillaring, delamination, or restacking. The soft and easily polarized Cs+ ion essentially drives the formation of the Lewis acidic site on the surfaces as suggested by IR of sorbed pyridine. The two-dimensional layered structure was preserved after the oxide was employed in the ethanol conversion at 380 °C, the temperature at which the protonic form could have converted to anatase. The structure was also retained after the NH3 temperature-programmed desorption measurement up to 700 °C. The production of ethylene from ethanol, well-known to occur over acid sites, unambiguously confirmed the acidic nature of this cesium titanate.

Layered Titanates (Na2Ti3O7 and Cs2Ti5O11) as Very High Capacity Adsorbents of Cadmium(II)

Abstract A layered cesium titanate (Cs2Ti5O11) and a layered sodium titanate (Na2Ti3O7) were used to concentrate Cd(II) ion from aqueous solution. The reaction of aqueous solutions of cadmium(II) acetate with the cesium titanate was examined at room temperature under varied pH. An H type adsorption isotherm was obtained, indicating strong interactions between Cd(II) and the titanate. For the reaction of the sodium titanate with aqueous solutions of cadmium(II) acetate, the formation of cadmium carbonate was observed in addition to the ion exchange of Na2Ti3O7 with Cd(II). The maximum amounts of the collected Cd(II) were 1.28 mmol/g Cs2Ti5O11 and 1.16 mmol/g Na2Ti3O7, which were superior to the values (0.08–0.39 mmol/g adsorbent) reported for other inorganic ion exchangers such as clay minerals and zeolites.

Layered cesium copper titanate for photocatalytic hydrogen production

Layered cesium copper titanate as well as the unmodified cesium titanate Cs0.68Ti1.83□0.17O4 (□: vacancy) were synthesized by a solution-based approach. The insertion of small amounts of copper into the vacancies of Cs0.68Ti1.83□0.17O4 led to a significant red shift of the band gap energy from 3.4 eV to 2.9 eV. During photocatalytic H2 production experiments, a steady increase in the evolution rate was detected, which can be referred to the in-situ reduction of incorporated copper ions to metallic Cu. The reduced copper ions leach out of the lattice to the catalyst surface and act as co-catalyst for H2 formation, considerably exceeding the activity achieved with Cs0.68Ti1.83□0.17O4 modified with 0.075 wt.-% of Rh as co-catalyst. The use of diffuse reflectance spectroscopy enabled a direct measurement of the copper nanoparticle formation by following their rising plasmon resonance at operating conditions. Characterization by X-ray diffraction (XRD) revealed a significant change in the crystal structure upon photocatalysis.

Fe-doped and ZnO-pillared titanates as visible-light-driven photocatalysts

Fe-doped cesium titanate was obtained by a solid state reaction with a mixture of Cs 2CO 3, TiO 2, and Fe 2O 3. ZnO-pillared doped titanate nanocomposite was successfully fabricated by exfoliating doped titanate and restacking its nanosheets with ZnO nanoparticles. The resulting nanocomposite was characterized by powder X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, N 2 adsorption–desorption measurement, thermogravimetric analysis and UV–vis spectroscopy. It was revealed that the present nanocomposite exhibits greatly increased specific surface area with mesoporous texture and that there exists an electronic coupling between the host sheets and the guest nanoparticles in the pillared system. The results of degradation of methylene blue under visible light radiation suggest that doping iron ions improves the material spectral response region and that hybridizing with ZnO nanopillars can suppress the recombination of photogenerated electron–hole pairs.

Improved photocatalytic activity and adsorption ability of mesoporous potassium-intercalated layered titanate

Mesoporous potassium-intercalated layered titanate has been synthesized through a reassembling of exfoliated titanate nanosheets and potassium cations. According to powder X-ray diffraction, electron microscopy, and N 2 adsorption–desorption isotherm analyses, the intercalation of potassium ions gave rise not only to a slight basal expansion of the layered titanate but also to the formation of mesoporous assembly of the layered crystallites. In comparison with the pristine cesium titanate and its protonated derivative, the mesoporous potassium-intercalated titanate showed better photocatalytic activity for the photodegradation of organic molecules and higher adsorption capability for organic dye and CO 2 molecules, as well.

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.

Electrochemical immobilization of Cs in single-crystalline SYNROC

The development of a disposal technique for the radiotoxic 137Cs in nuclear wastes is one of the most urgent issues in nuclear fuel technology. An effective disposal method of 137Cs is to immobilize it in a synthetic rock (SYNROC) material: cesium titanate hollandite, 137Cs x Ti 8O 16 ( I4/ m, a = 10.2866 ( 3 ) Å , c = 2.9669 ( 1 ) Å ). Practical applications of 137Cs x Ti 8O 16 have been restricted so far because the conventional synthetic method requires strong chemical reducers and reaction temperatures higher than 1250 °C. In this report, we present a milder preparation method of Cs x Ti 8O 16 by electrolysis of a mixture of Cs 2MoO 4 and TiO 2 in ambient atmosphere at 900 °C. The Cs content in the resultant single-crystalline Cs 1.35Ti 8O 16 is competitive with the highest value in polycrystalline Cs 1.36±0.03Ti 8O 16 prepared by the conventional synthetic method. The electrochemical preparation of Cs 1.35Ti 8O 16 is a promising way to immobilize a high quantity of 137Cs ions in a stable form of single-crystalline SYNROC.

A New Nanohybrid Photocatalyst between Anatase (TiO2) and Layered Titanate

A new microporous TiO2-pillared layered titanate has been successfully prepared by hybridizing the exfoliated titanate with the anatase TiO2 nano-sol. According to the X-ray diffraction analysis and N2 adsorption-desorption isotherms, the TiO2-pillared layered titanate showed a pillar height of ~2 nm with a high surface area of ~460 m2/g and a pore size of ~0.95 nm, indicating that a microporous pillar structure is formed. Its photocatalytic activity was evaluated by measuring the photodegradation rate of 4-chlorophenol during irradiation of catalyst suspensions in an aqueous solution. An enhancement in activity of ca. 170% was obtained for TiO2-pillared layered titanate compared to that of the pristine compound such as layered cesium titanate.

Preparations and characterisations of ceramics based on cesium titanate

Abstract Preparations of cesium titanates have been made by several routes: co-grinding, sol-gel and spray-drying. The results obtained with these different methods are compared. Electrical characterisations of pure CsAlTiO4 have shown that this compound is not a conductor at room temperature. Another phase, Cs2Ti6O13, has been prepared. This last material has a slight conductivity (about 2×10−7 S cm−1 at 200°C). Nevertheless, it is not stable in aqueous solution and it cannot be used in electrochemical applications in a water medium. If CsAlTiO4 is synthesised without precautions, sizeable Cs2Ti6O13 traces appear in the samples. Conductivity and stability in water of the mixed compound are intermediate between the characteristics of both pure materials.

Identifying characteristics of the fibrous cesium titanate Cs 2Ti 5O 11

Electron microscopic studies of the fibrous cesium titanate Cs 2Ti 5O 11 reveal characteristic features not readily apparent using standard methods of phase analysis (optical microscopy, X-ray diffraction). Its fibrous needle-like laths give characteristic diffuse scattering, complicating the indexing of electron diffraction patterns. The hydrated form Cs 2Ti 5O 11 · (1 + x)H 2O (0.5 < x < 1) is typically grossly distorted, resembling pyrolytic graphite. Cs 2Ti 5O 11 is unstable when stored under ambient conditions at room temperature for ∼1 year when disproportionation into Cs 2Ti 4O 9 and Cs 2Ti 6O 11 · nH 2O occurs. The structure of Cs 2Ti 5O 11 and intergrowth defects in the unstable forms have been studied by high-resolution electron microscopy. It is evident that these phases would be undesirable in titanate ceramics such as SYNROC, which are designed for immobilization of radioactive 137C s.

A CESIUM IMMOBILIZATION FROM AN AQUEOUS SOLUTION USING THE CRYSTALLINE ADSORBER OF HYDROUS TITANIUM DIOXIDE FIBERS

Abstract The immobilization of Cs+ ions in a CsOH solution was studied by using the adsorber of crystalline TiO2·nH2O fibers. The adsorbed cesium contents were in a compositional range of CsxTi6O12+x⁄2(1.5&amp;lt;x≤2). This cesium titanate was remade to the Cs-priderite(CsxAlxTi8−xO16:1.5&amp;lt;x≤2) of the hollandite structure type by heating after the addition of Al2O3. The most stable immobilizer of Cs+ ions was obtained by sintering the mixed phases of Cs-priderite and rutile.