A layered protonic titanate of lepidocrocite-type, HxTi2-x/4□x/4O4·H2O (x ∼ 0.7; □, vacancy), has been exfoliated on the action of an aqueous solution of tetrabutylammonium (hereafter TBA) hydroxide, which resulted in a stable colloidal suspension. A colloidal aggregate centrifuged from the suspension was examined by an in situ X-ray diffraction technique under conditions where drying speed was controlled. The diffraction immediately after separation from the liquid phase was principally amorphous except for a series of sharp reflections detected in a small angle scattering region. On the basis of the line profile analysis, the latter diffraction feature was accounted for by the fundamental intersheet interference of a spacing >10 nm, which demonstrates the existence of a novel associated pair of the titanate nanosheets accommodating a large volume of water cluster between them. These XRD data provide persuasive evidence for delamination into single layers. Upon drying, the amorphous halo disappeared and ...

Macromolecule-like Aspects for a Colloidal Suspension of an Exfoliated Titanate. Pairwise Association of Nanosheets and Dynamic Reassembling Process Initiated from It

Inorganic framework solids are no longer limited to just the silicates and phosphates. Recent research has revealed that carboxylates, arsenates, sulfates, selenates, selenites, germanates, phosphites can also form such structures. One of the emerging areas combines the rich coordination chemistry of the central metal ions of many of these structures with the flexibility and functionality of the organic linkers to give rise to organic-inorganic hybrid compounds. The compounds of the transition-metals appear to provide many variations arising from their coordination preferences, ligand geometry, and the valence state. In addition, the combination of the magnetic nature of the transition metal center with the channel structure of open frameworks suggests interesting potential applications. In this Review the synthesis, structures and properties of the various transition-metal open-framework compounds are discussed.

Open-framework structures of transition-metal compounds.

Stable microporous materials, such as zeolites, are extremely important for applications in catalysis, adsorption, ion-exchange, and separation. In this review we describe a new class of stable microporous materials that involves novel mixed octhaedral-tetrahedral framework oxides. The archetypal material is based on titanosilicates, although there is tremendous scope for introducing many other transition metals. These materials not only have potential novel applications in the fields normally associated with zeolites but also possible applications in the areas of optoelectronics, nonlinear optics, batteries, magnetic materials and sensors.

Microporous Titanosilicates and other Novel Mixed Octahedral‐Tetrahedral Framework Oxides

137Cs and 90Sr, both byproducts of the uranium and plutonium fission processes, make up the majority of high-level waste from nuclear power plants. 63Ni is a byproduct of the erosion-corrosion process of the reactor components in nuclear energy plants. The concentrations of these ions in solution determine the Waste Class (A, B, or C); thus, their selective removal in the presence of large excesses of nonradioactive ions is necessary to reduce waste volume and cut disposal costs. We report the new material K2xMgxSn3–xS6 (x = 0.5–1, KMS-2) and its application for the ion exchange of Cs+, Sr2+, and Ni2+ in varying conditions. This compound crystallizes in the hexagonal space group P63/mmc with cell parameters a = b = 3.6749(8) A and c = 16.827(4) A. The difference in crystal structure between KMS-2, the previously reported Mn analog K2xMnxSn3–xS6 (KMS-1), and their parent SnS2 is also described. Distribution coefficients for KMS-2 are high for Cs+ (7.1 × 103 mL/g) and Sr2+ (2.1 × 104 mL/g) at neutral pH (∼ ...

Selective Removal of Cs+, Sr2+, and Ni2+ by K2xMgxSn3–xS6 (x = 0.5–1) (KMS-2) Relevant to Nuclear Waste Remediation

Thin flakes of titanium dioxide have been synthesized through a novel route via exfoliation of a layered precursor. A protonic oxide of HxTi2-x/4□ x/4O4·H2O (x ∼ 0.7; □, vacancy) was delaminated into colloidal single sheets (thickness 0.75 nm) by being interacted with a bulky organic amine, (C4H9)4NOH. The resulting titania sol was freeze-dried to produce a gel in a thin filmlike texture. The gelation took place by reassembling 10−20 titanate sheets and consequently yielding lamellar aggregates. Upon heating above 400 °C, the gel was transformed into titanium dioxide (anatase) in thin flaky morphology (20−30 nm in thickness versus ∼μm in the lateral dimension). Intermediates at various stages of the synthetic process as well as the final product were examined by applying various characterization techniques such as X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM, TEM), FT-IR and Raman spectroscopies, thermogravimetry, and elemental analysis. The flaky particulates were aggregat...

Fabrication of titanium dioxide thin flakes and their porous aggregate

A sodium titanosilicate of ideal composition Na{sub 2}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}2H{sub 2}O was synthesized hydrothermally in highly alkaline media. Its crystal structure was solved from X-ray powder data by ab initio methods. The compound is tetragonal, a = 7.8082(2), c = 11.9735(4) {angstrom}, space group P4{sub 2}/mcm, Z = 4. The titanium atoms occur in clusters of four grouped about the 4{sub 2} axis and are octahedrally coordinated by oxygen atoms. The silicate groups serve to link the titanium clusters into groups of four arranged in a square of about 7.8 {angstrom} in length. These squares are linked to similar ones in the c direction by sharing corners to form a framework which encloses a tunnel. Half the Na{sup +} ions are situated in the framework coordinated by silicate oxygen atoms and water molecules. The remaining sodiums are present in the cavity, but evidence indicates that some of them are replaced by protons. The composition is then closer to Na{sub 1.64}H{sub 0.36}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}1.8H{sub 2}O. The sodium ions within the tunnels are exchangeable. Exhaustive exchange with CsNO{sub 3} yielded a Cs{sup +} phase of composition Na{sub 1.49}Cs{sub 0.2}H{sub 0.31}Ti{sub 2}O{sub 3}SiO{sub 4}{center_dot}H{sub 2}O whose structure was revealed from applicationmore » of Rietveld methods to X-ray powder data. 19 refs., 7 figs., 5 tabs.« less

Synthesis, Crystal Structures, and Ion-Exchange Properties of a Novel Porous Titanosilicate

Pillaring of Layered Tetravalent Metal Phosphates and Oxides Using (3-Aminopropyl)trimethoxysilane

A novel layered sodium titanium silicate Na2TiSi2O7 2H2O has been synthesized by the reaction of a titanium-hydrogen peroxide complex and silicic acid in alkaline media under mild hydrothermal conditions (200°C). The product was characterized by elemental analysis. TGA, FT-IR. MAS 29Si and 23Na NMR and X-ray spectroscopy. The intercalation reaction of n-alkylamines from the gaseous phase and the ion exchange behavior of Na2TiSi2O7 2H2O towards alkali, alkaline earth and some transition metal ions in model individual and complex solutions were studied. It was found that the layered sodium titanium silicate contains acidic hydroxyl functional groups, which results in cation uptake at pH>1.5. The high affinity of the exchanger for cesium in weakly acid and neutral solutions makes it a promising material for the treatment of some types of nuclear wastes, contaminated ground water and different biological liquors.

SYNTHESIS AND CHARACTERIZATION OF A NOVEL LAYERED SODIUM TITANIUM SILICATE Na2TiSi2O7 2H2O.

Presented is a preliminary study of the adsorption of lanthanides on several types of inorganic ion exchangers. The exchangers used are a proton form of Na4Ti9O20, Zr(C6H4P2O6)x(HPO4)2−2x·xH2O (ZrMPP), and Zr(C12H8P2O6)x(HPO4)2−2x·xH2O (ZrBPP). The distribution coefficient for some of the lanthanide ions on these materials suggest that they can be used to remove lanthanide ions from solutions containing alkali and alkaline earth metal ions, and can also be used for separation of the individual lanthanide ions by column experiments.

Use of Selective Inorganic Ion Exchangers for the Separation of Rare Earths

A novel nickel interstratified α-zirconium phosphate (α-ZrP) of approximate composition Zr(PO4)2Ni4(OH)5(C2H3O2)·2H2O has been synthesized by forming the nickel polymers in situ between the layers of zirconium phosphate to yield materials with d spacings ranging from 18.4 to 19.5 A. X-ray powder structure refinement has shown that the resulting composite has unit cell dimensions a = 9.298(2), b = 5.389(1), and c = 37.61(5) A, β = 103.40(2)°, Z = 4 and consists of layers of the original zirconium phosphate with two layers of nickel atoms bonded directly to the phosphate layers and a third layer of nickel hydroxide situated between the bonded Ni layers. Calcination of these materials led to a decrease in the d spacing of up to 4.7 A to produce a nickel oxide three layers thick between the lamellae of the α-ZrP. These composites have surface areas ranging from 63 to 158 m2 g-1 depending upon the temperature of calcination. Pore size analysis showed the materials to be predominantly microporous with pores of ...

Roy A. Cahill

Papers

Synthesis, Crystal Structures, and Ion-Exchange Properties of a Novel Porous Titanosilicate

Pillaring of Layered Tetravalent Metal Phosphates and Oxides Using (3-Aminopropyl)trimethoxysilane

SYNTHESIS AND CHARACTERIZATION OF A NOVEL LAYERED SODIUM TITANIUM SILICATE Na2TiSi2O7 2H2O.

Use of Selective Inorganic Ion Exchangers for the Separation of Rare Earths

Nickel Oxide Interstratified and Pillared α-Zirconium Phosphate