Sergei A. Khainakov

Intercalation of α,ω-Alkyldiamines into Layered α-Titanium Phosphate from Aqueous Solutions

Abstract This paper reports a study on the mechanism of intercalation of α,ω-alkyldiamines, NH 2 (CH 2 ) n NH 2 (n = 2–9), into layered α-titanium phosphate, α-Ti(HPO 4 ) 2 ·H 2 O. The intercalates synthesis was performed by titrating the host with aqueous solutions of alkyldiamine at 25%C. Crystalline phases showing a general formula α-Ti(HPO 4 ) 2 ·xNH 2 (CH 2 ) n NH 2 ·H 2 O (x ≤ 1) have been obtained. In every case, a monolayered arrangement of α,ω-alkyldiamine molecules into the host layers is formed. The average inclination angle of the alkyldiamine molecules to the phosphate layer and the intercalates packing density have been determined.

SYNTHESIS AND ION EXCHANGE PROPERTIES OF NOVEL INORGANIC ADSORBENTS TINaV)-NITRILOTRIS(METHYLENE)TRIPHOSPHONATES

ABSTRACT Several new tin(IV) nitrilotris(methylene)triphosphonates of different composition have been synthesized by the reaction of a tin tetrachloride and nitrilotris(methylene)triphosphonic acid [N(CH2PO(O)OH)3] and a gel method of their preparation in granular form (as spherical beads) was developed. The solids were characterized by elemental analysis, TGA, FT-IR, MAS 31PNMR and X-ray spectroscopy. The ion exchange behavior of tin(IV) nitrilotris(methylene)triphosphonates towards alkali, alkaline earth and some transition metal ions in individual and complex solutions were studied. It was found that these exchangers contain highly acidic adsorption sites, which enables them to operate efficiently even at pH close to 0, High affinity of the tin(IV) nitrilotris(rnethylene)triphosphonates for lead, cadmium, copper in acid solutions makes them promising for treatment of some technological solutions and waste.

Hydrothermal synthesis and structural characterization of framework microporous mixed tin–zirconium silicates with the structure of umbite

Abstract A novel framework mixed tin–zirconium silicate, K2Sn0.25Zr0.75Si3O9·H2O (1), was synthesized under mild hydrothermal conditions. The unit cell is orthorhombic, a=10.260(2) A, b=13.272(2) A, c=7.174(1) A, space group P212121, Z=4. Isotypic with the mineral umbite, the structural formula may be written as K 2 ( Sn , Zr ){ uB ,1 ∞ 1 }[ 3 Si 3 O 9 ] . In a topotactical process, the K+ ions in compound 1 were replaced by Na+ ions, thus obtaining compound 2: Na2Sn0.25Zr0.75Si3O9·H2O (2), a=10.500(1) A, b=13.354(2) A, c=7.2731(9) A.

Exceptional thermal stability of undoped anatase TiO2 photocatalysts prepared by a solvent-exchange method

A new solvent-exchange technique to prepare anatase nanoparticles with exceptional thermal stability and photocatalytic activity is described here. The process of preparation is accomplished by using organic solvents to precipitate hydrous titania particles from a basic aqueous medium containing a titanium peroxo complex. Undoped titanium dioxide formed via a solvent exchange method has unprecedented thermal stability against transformation to the rutile phase, as opposed to TiO2 prepared by the common method of the gelation of an aqueous titanium peroxo complex. On the basis of X-ray thermodiffraction experiments, it has been established that the thermal treatment at 1000 °C of the titania prepared by ethanol precipitation contains 100% pure anatase phase. The stabilization of anatase is induced by the high defectiveness of the TiO2 nanostructure, which is evidenced from band-gap energy estimation, PXRD and HRTEM studies. The prepared TiO2 nanoparticles show an outstanding photocatalytic activity comparable to the commercial Aeroxide P25 photocatalyst in the UV-assisted decomposition of methylene blue.

A hydrothermal peroxo method for preparation of highly crystalline silica-titania photocatalysts

A new completely inorganic method of preparation of silica-titania photocatalyst has been described. It has been established that the addition of silica promotes crystallinity of TiO2 anatase phase. Relative crystallinity and TiO2 crystal size in the silica-titania particles increase with the silica content until SiO2/TiO2 molar ratio of 0.9, but at higher molar ratios they start to decrease. The single-source precursor containing peroxo titanic (PTA) and silicic acids has been proved to be responsible for high crystallinity of TiO2 encapsulated into amorphous silica. It has been proposed that peroxo groups enhance rapid formation of crystalline titania seeds, while silica controls their growth. It has been concluded from the TEM that the most morphologically uniform anatase crystallites covered with SiO2 particles are prepared at SiO2/TiO2 molar ratio of 0.4. This sample, according to (29)Si NMR, also shows the high content of hydroxylated silica Q(3) and Q(2) groups, and it is the most photocatalytically active in UV-assisted decomposition of methylene blue among the tested materials. It has been determined that the increase in the amount of the condensed Q(4) silica in the mixed oxides leads to the decrease in photocatalytic performance of the material, despite its better crystallinity. High crystallinity, low degree of incorporation of Ti atoms in SiO2 in the mixed oxide and adsorption of methylene blue in the vicinity of photoactive sites on the hydroxylated silica have been considered as the main factors determining the high degradation degree of methylene blue in the presence of silica-titania.

A flow-through reaction cell for in situ X-ray diffraction and absorption studies of heterogeneous powder–liquid reactions and phase transformations

A portable powder-liquid high-corrosion-resistant reaction cell has been designed to follow in situ reactions by X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. The cell has been conceived to be mounted on the experimental stations for diffraction and absorption of the Spanish CRG SpLine-BM25 beamline at the European Synchrotron Radiation Facility. Powder reactants and/or products are kept at a fixed position in a vertical geometry in the X-ray pathway by a porous membrane, under forced liquid reflux circulation. Owing to the short pathway of the X-ray beam through the cell, XRD and XAS measurements can be carried out in transmission configuration/mode. In the case of the diffraction technique, data can be collected with either a point detector or a two-dimensional CCD detector, depending on specific experimental requirements in terms of space or time resolution. Crystallization processes, heterogeneous catalytic processes and several varieties of experiments can be followed by these techniques with this cell. Two experiments were carried out to demonstrate the cell feasibility: the phase transformations of layered titanium phosphates in boiling aqueous solutions of phosphoric acid, and the reaction of copper carbonate and L-isoleucine amino acid powders in boiling aqueous solution. In this last case the shrinking of the solid reactants and the formation of Cu(isoleucine)(2) is observed. The crystallization processes and several phase transitions have been observed during the experiments, as well as an unexpected reaction pathway.

Hydrothermal synthesis and X-ray powder structure determination of a novel layered tin(IV) phosphate, Sn(HPO4)2·(NH3)0.4(H2O)0.6

Abstract A novel layered tin(IV) phosphate, Sn(HPO4)2·(NH3)0.4(H2O)0.6, was synthesized under mild hydrothermal conditions. The unit cell is trigonal, a=4.9751(2) A , c=22.5983(8) A , space group R 3 , Z=3. The interlayer water and ammonia molecules are disordered and were both located on the same crystallographic site. This compound is the first example within the well-known family of α-metal(IV) phosphates of a non monoclinic phase stable at room temperature. The polymorphism of these compounds would explain several of the bibliographical discrepancies detected in the description of its physical–chemical properties.

Photocatalytic degradation of 2-(4-methylphenoxy)ethanol over TiO2 spheres

The photocatalytic TiO2-assisted decomposition of 2-(4-methylphenoxy)ethanol (MPET) in aqueous solution has been studied for the first time. The intermediate compounds of MPET photodegradation have been also determined. A toxic p-cresol is formed in significant quantities during the photocatalytic reaction. A solvent-exchange approach for a template-free preparation of spherical TiO2 particles has been described, which is based solely on precipitation of hydrous titania from aqueous titanium peroxo complex by using organic solvents. The proposed method favours the formation of spherical titania particles with a mean size varying from 50 to 260nm depending on the choice of solvent. The procedure for converting nonporous titania spheres into mesoporous material maintaining the same spherical morphology has been developed. The synthesized TiO2 spheres demonstrate a degree of MPET photo-degradation close to that of the commercial titania Aeroxide P25, besides being successfully recovered and reused for four reaction cycles without loss of photocatalytic activity. The effectiveness of the commercial Aeroxide P25 in MPET photodegradation, on the other hand, suffers 10-time drop during the third reaction cycle, which is attributed to its poor recoverability because the photocatalyst is composed of small particles of 20nm size.

Intercalation of Cyclic Amines into α-Titanium Phosphate

The intercalation of some amines (aniline, benzylamine, cyclohexylamine,piperidine, pyridine, pyrazine and piperazine) into α-titaniumphosphate, Ti(HPO4)2×H2O,has been investigated by the batch method and/or by exposing the host to thevapour of the amines. The changes in the interlayer distance of the solidduring the intercalation process was followed by X-ray powder diffraction.The new intercalates were characterised by chemical and thermal analysis.Materials with a monolaminar and/or bilaminar arrangement of amine moleculesin the phosphate interlayer region are obtained depending on the nature ofthe amine. Due to steric hindrance, saturated phases are not obtained forall amines studied. The thermal decomposition of the intercalates (nitrogenatmosphere), takes place in three stages: dehydration, removal of amines andcondensation of the hydrogenphosphate to pyrophosphate groups.

MODIFIED TITANIUM PHOSPHATES AS CESIUM SELECTIVE ION EXCHANGERS

ABSTRACT Two synthetic methods for the preparation of spherically granulated titanium phosphates (TiP), as cesium selective exchangers, have been carried out. The first method uses the “ion memory” effect for the formation of specific adsorption sites in the matrix of TiP, whereas the second method results in the preparation of granular titanium phosphate - ammonium molybdophosphate (TiP-AMP) composites by a gel technique. The efficiency of the new materials has been studied in complex systems. The cesium distribution coefficients for some of the sorbents prepared are higher than 40,000 mL/g. It was found that, due to high exchange capacity, regenerability and high selectivity for cesium, TiP materials with “ion memory” effect can be used for radiocesium recovery from ground and surface waters, whereas granular composite TiP-AMP exchangers are useful for the treatment of cesium containing acid nuclear wastes with a high content of background electrolytes.