Synthesis, structure, and reactivity of a new Ti-containing microporous/mesoporous material

A new class of porous, mixed phase titanosilicate materials containing a microporous TS-1 phase and a mesoporous Ti-MCM-48 phase has been successfully synthesized. A novel, one-pot synthesis method was used in which the organic templates for the mesoporous and microporous phases were added sequentially to the same reaction mixture, followed by crystallization at 150 degrees C. The gemini surfactant 18-12-18 was used to form the Ti-MCM-48 mesophase; subsequent addition of tetrapropylammonium cation (TPA+) led to the formation of TS-1. The relative amounts of the two phases within the final products were controlled by optimizing the crystallization time. Crystallization times between 12 and 50 h gave materials containing both phases, with an increasing amount of microphase formed at longer crystallization times. These materials, called "Ti-MMM-2" (microporous/mesoporous materials) were characterized using powder XRD, N2 physisorption, TEM, FTIR, DR-UV/Vis spectroscopy, and 29Si MAS NMR. In the epoxidation of cyclohexene with tert-butyl hydroperoxide (TBHP), Ti-MMM-2 samples exhibited higher catalytic activity (approximately 61%) than either TS-1 (16%) or Ti-MCM-48 (42%), with a very high selectivity (97%) for formation of cyclohexene oxide.     

Thermal behavior of silicophosphate gels obtained from different precursors

Phosphosilicate glasses are of great interest in important fields, such as optical active systems, energy generating systems, humidity sensors, and as materials for biomedical applications. Many studies were accomplished to establish the influence of different reaction parameters on the evolution and final structure of sol–gel prepared phosphosilicate gels. In the present work, we studied the thermal behavior of the silicophosphate gels obtained starting with different phosphorous precursors, the influence of these precursors on the composition and structure of the resultant gels, and their evolution with thermal treatment. By Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and thermodifferential analysis (DTA/TG), and Differential Scanning calorimetry coupled with Mass Spectrometry (DSC-MS), it was established that the type of the precursors essentially influences the composition and structure and consequently the thermal behavior of the obtained gels. In the case of triethylphosphate precursor, all used methods of investigation have shown that the ester is trapped in the silica matrix and it is eliminated during the thermal treatment. Triethylphosphite partially hydrolizes and reacts with the silica network during post-preparation thermal treatment. Only in the case of H₃PO₄, an interaction with TEOS takes place and leads to Si–O–P bond formation. By thermal treatment, the gels with different composition and structure lead to materials with different properties.     

Parametric analysis of the extraction of depth profile information from ARXPS data obtained on a silicon wafer sample

In this study a silicon wafer was analysed by angle‐resolved x‐ray photoelectron spectroscopy and the data compared with a calculation based upon a simple model of the sample surface. The parameters in the mathematical model were varied in groups of three and the sum‐squared difference between the calculation and the experimental results was plotted as an error surface. Most of the error surfaces were found to exhibit a well‐constrained minimum, indicating an optimum set of values for the parameters in question, but important examples of co‐dependency were also noted. Copyright © 2003 John Wiley & Sons, Ltd.     

Chemical assembly of a titanium oxide layer on microporous silica

Russian Journal of General Chemistry - The chemical assembly of a titanium oxide coating on a regular microporous silica surface by the atomic layer deposition method was considered. The change in...     

Particle distribution in a microporous material: experiments with zeolite A.

The theory on particle distribution and exchange equilibria in a microporous material is applied to experimental ion-exchange data involving zeolite Na-A and zeolite K-A, with silver ions as the exchanging species. The presented method enables direct evaluation of the measured data and consideration of nonequivalent particle sites. The isotherms of the K+ versus Ag+ exchange in zeolite K-A rise much more steeply, at low exchange degrees, than those of the Na+ versus Ag+ exchange in zeolite Na-A. This result implies a different course of the ion-exchange reactions. Spectroscopic measurements on dehydrated, partly silver-exchanged zeolites Na-A and K-A do indeed show that in zeolite Na-A, the Na+ ions occupying four-ring positions are exchanged faster for Ag+ than the Na+ ions occupying eight- and six-ring positions, while in zeolite K-A the exchange does not start with the four-ring ion but with six-ring ions, followed by the four-ring ion. These findings are consistent with the results obtained from evaluation of the ion-exchange data. The resulting thermodynamic quantities significantly differ from published reference values, which we suggest should be revised.     

Pore size and liquid impregnation of microporous aluminosilicate gels and glasses

Optically clear monolithic (OCM) gels of microporous aluminosilicates have been prepared by slow hydrolysis-polycondensation of alkoxides. Subsequent heating induces transformations into OCM microporous glasses. The surface area (∼610 m²/g after drying at 300°C) and the pore volume (∼0.35 cc/g at 300°C) decrease monotonously with increasing annealing temperature. However, after heat treatment at 600°C under air (glass state) the monoliths are still microporous. Modifications of the xerogel pore distribution by an impregnation process and metal aggregate formation with pyrolysis are studied by N₂ adsorption-desorption analysis and small-angle X-ray scattering (SAXS). The microporous structure becomes mesoporous. A model of microporous impregnation in the gel or glass state is proposed.     

ACDF molecules data obtained from a spectra fitting method

Absorption and fluorescence spectra of ACDF molecules dissolved in toluene have been fitted by a procedure previously described. Interesting quantities relatives to these molecules have been obtained from the fitting parameters and comparison with experimental results was made.     

Thermal characterization of the metal-silicalites obtained from aqueous nonalkaline fluoride gels

Thermal analysis of crystalline Metallosilicalite-1 precursors with various heteroatoms was carried out in a nitrogen atmosphere. Different interactions between tetrapropylammonium species and the zeolitic environment were evidenced, depending on the type of metallic complexes in the reaction medium. The results support the mechanism of Metallosilicalite-1 formation through a condensation process from the liquid phase.Isomorphous substitution of T element in a molecular sieve material is very interesting in order to modify its acidity or redox catalytic properties [1–6].Normally zeolites are synthesized in hydrothermal mixtures. Alkaline hydroxides, TPABr, silica and water are typically required to obtain Silicalite-1. Recently, MFI zeolitic structures have been obtained from near-neutral nonalkaline reaction mixtures containing fluoride ions [7–8].Using tetrapropylammonium bromide (TPABr) as a template, molecular sieve Bi-, Ce-, Cu-, Cr-, Mo-, Pb-, Sb-, Ti-, V- and W-Silicalite-1 was the only phase obtained in the presence of fluoride ions.In this paper, it is investigated how the thermal decomposition of TPA ions is influenced by the presence of heteroatoms in the framework of crystals.     

Modification of silica gels with small admixtures of titanium ions

Microporous silica gels containing small amounts of titanium ions are synthesized. Addition of Ti ions to the silica gels during the sol-forming step is demonstrated to increase the specific surface area and decrease the volume of sorptive pores. Spectral results indicate that Ti ions uniformly distribute in the silica gel matrix and isomorphously replace Si.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2217–2222, October, 1991.     

Conformal coating of nanoscale features of microporous Anodisc membranes with zirconium and titanium oxides

We have successfully coated a nanofeatured material with ZrO2 and TiO2 using a polymer assisted deposition technique.     

新型三维微孔砷酸铟InAsO4(H2O)2的合成及结构

首次以有机胺为结构导向剂,在水热条件下合成了微孔砷酸铟材料InAsO4-1,并对其进行了结构及性质表征。X射线单晶结构解析表明InAsO4-1分子式为InAsO4(H2O)2。晶体学数据为：Pbca,a=0.9090(4)nm,b=1.0344(4)nm,c=1.0468(4)nm,α=β=Υ=90°,V=0.9843(7)nm^3,Z=8,R=0.0480,Rw=0.1045。InAsO4-1具有三维结构,其a,b方向分别有4元环及6元环的一维孔道,结构中还含有一8^16^44^2笼,热重分析显示其结构水较稳定。     

Colorimetric and gravimetric determination of silicon in titanium and titanium alloys

Improved colorimetric and gravimetric methods are proposed for the determination of silicon in titanium and titanium alloys. In the colorimetric method the sample is dissolved in hydrofluoric acid. boric acid added and the; titanium oxidized with hydrogen peroxide and permanganate. The bulk of the titanium is precipitated as a crystalline precipitate by heating in boiling water, and the molybdenum color developed. A portion of the solution is filtered and the transmittance measured. In the gravimetric method the sample is fumed with milfuric acid. the silica ignited and fused with aodium carbonate, The silica is then dehydrated with perchloric acid. Thecolorimetric method is recommended for 0.003 to 1.5% silicon, and the gravimetric method for 0.3 to 5% silicon.     

Synthesis of inorganic gels in a lyotropic liquid crystal medium. I. Synthesis of silica gels in lamellar phases obtained from non-ionic surfactants

Some lamellar phases made with aqueous lyotropic liquid crystals were used as templates for the gelation of a silica inorganic network from tetramethylorthosilicate (TMOS). The aim was to synthesize materials with an anisotropic texture.Lamellar phases were obtained by using non-ionic surfacants. At first, structural, textural and rheological properties of the lamellar phases were studied. Then, the evolution of the system after introduction of the alkoxide, i.e., during the sol-gel transition, was followed by low angle X ray diffraction and rheological measurements. Finally, a textural study of dried gels was carried out.The formation of gels with a lamellar structure was analysed by compressing the total phase diagram (quaternary system) to a ternary system. The hydrolysis and condensation reactions of the TMOS are strongly influenced by the presence of the structured lamellar phase. Gelation seems to happen around the liquid crystal microdomains. A schematic model of gelation is proposed based on experimental observations.     

Energy levels of small titanium oxide clusters obtained from SCF calculations

The energy levels of small titanium oxide clusters [(TiO₂)₂, and (TiO₂H)₃, and (TiO₂H)₂] have been calculated using ab initio SCF methods. Both crystal and relaxed geometries have been considered. Systematic changes in the valencelevel structure resulting from geometry relaxation are found, which may be related to band-gap changes experimentally observed for small titanium oxide particles. In addition, a Ti? OH local surface state is found to be well described within a limited cluster model. © 1994 John Wiley & Sons, Inc.     

Analysis of the microporous structure of the low-cost activated carbon fibres obtained from flax and jute cloth

The paper presents the results of research devoted to obtaining the low-cost activated carbon fibres from waste flax and jute cloth by carbonisation in inert atmosphere and activation with air as well as to the analysis of the microporous structure of materials obtained on the basis of the nitrogen, argon and benzene adsorption isotherms, using among others, the unique LBET method with implemented of the new models of the multilayer adsorption on the heterogeneous surfaces of the carbonaceous adsorbents. As part of the research conducted, imaging of the surface of the low-cost activated carbon fibres obtained has also been done using scanning electron microscopy.     

Synthesis and properties of a microporous carbon material as a catalyst support for fuel cells

It is stated that one-dimensional conductivity in amorphous microporous carbon material (AMCM) samples is associated with the considerable imperfection of graphene fragments in the carbon material rather than the presence of unshared electrons. It is likely that the graphene fragments are formed upon the carbonization of a carbon precursor accompanied by the partial or complete removal of precursor heteroatoms. It is hypothesized that the presence of localized unpaired electrons, which give EPR spectra, is due to the formation of local defects in carbene fragments. Thus, the effects of the value of conductivity and the concentration of unpaired electrons on the power output of a fuel cell cannot be distinguished based on the experimental data with the use of an AMCM as a catalyst support. The interaction of localized paramagnetic centers with electron gas can be interpreted in terms of the C-S relaxation model.     

Porous silicon oxycarbide glasses from organically modified silica gels of high surface area

High surface area alkyl-substituted silica aerogels and xerogels were successfully prepared by sol-gel processing and supercritical drying. The gels were further heat treated in inert atmosphere to temperatures as high as 1000°C. Surface areas and pore structure of the gels and gels pyrolyzed at high temperatures were determined by multipoint BET surface area measurement. The aerogels and xerogels exhibited surface areas of about 1100 m²/g. No significant effect of pH was found on the surface areas of gels in the two step sol-gel process, but gels of low pH showed smaller pore diameter and higher density. Xerogels showed smaller surface area, pore size, and pore volume compared to aerogels. Upon pyrolyzing in inert atmosphere, the surface areas of all the gels decreased with temperature as a result of collapse of micropores and shrinkage of mesopores. Unlike pure silica gel, which loses almost all surface area and densifies at 1000°C, the advantage of the alkyl-substituted gels is that they maintained a high surface area of 400 m²/g at 1000°C.Also with the Department of Agronomy.