Titanium-containing zeolites and microporous molecular sieves as photovoltaic solar cells.

Four titanium-containing zeolites and microporous molecular sieves differing on the crystal structure and particle size (Ti/Beta, Ti/Beta-60, TS-1 and ETS-10) are prepared, and their activity for solar cells after incorporating N3 (a commercially available ruthenium polypyridyl dye) is tested. All the zeolites exhibit photovoltaic activity, and the photoresponse is quite independent of the zeolite pore dimensions or particle size. The photoresponse increases with titanium content in the range 1-7% wt. In this way, cells are obtained that have open-circuit voltage Voc=560 mV and maximum short-circuit photocurrent density Isc=100 microA, measured for 1x1 cm2 surfaces with a solar simulator at 1000 W through and AM 1.5 filter. These values are promising and comparable to those obtained for current dye-sensitized titania solar cells.     

Ortho-selectivity in aluminophosphate molecular sieves: A molecular simulation study

Monte Carlo adsorption simulations of xylenes have been performed in aluminophosphate molecular sieve structures. A new force field fitted for o-xylene in AlPO₄-5 was used. It is shown that force fields have good transferability among the aluminophosphate sieves series and the new force field adequately describes the experimentally observed adsorption isotherms for xylene/AlPO₄-5. A previous investigation of adsorption isotherms and structural analysis has been extended to AlPO₄-8 and VPI-5 sieves. In AlPO₄-8, like in AlPO₄-5, the variations in the channels diameters and the corresponding interaction energy of the molecule-crystal lattice drive all molecular positioning. In VPI-5, the modulation between wide and narrow regions becomes negligible due to the larger pore diameter, so no ortho-selectivity was observed. The simulations confirm the ortho-selectivity mechanism proposed to aluminophosphates.     

Liquid-phase synthesis of isopulegol from citronellal using mesoporous molecular sieves mcm-41 and zeolites

Isopulegol (IPG) was synthesized from citronellal (CTN) at atmospheric pressure and 40~60°C in a batch reactor by using mesoporous molecular sieves MCM-41 as well as zeolites HZSM-5 and Hβ. The catalysts were characterized by the methods of XRD, N₂ adsorption, ²⁷Al and ²⁹Si MAS-NMR and TPD of ammonia. Under our reaction conditions, Al-MCM-41 was found to be the best catalyst; it exhibited much higher activity, despite slightly lower IPG selectivity. The catalytic results depend on a variety of factors, viz. the acidity, the pore size and the pore channel of catalysts. The reaction paths were proposed and the kinetic parameters for competitive first order reactions of CTN were estimated. This revised version was published online in June 2006 with corrections to the Cover Date.     

A comparison between low background silver diammine and silver nitrate protein stains.

Several methods of silver staining of proteins after sodium dodecyl sulfate-electrophoresis in polyacrylamide gels were compared. The most rapid methods were found to be less sensitive than more time-consuming methods. Among the long methods, those using glutaraldehyde treatment of the gel and silver diammine complex as the silvering agent were found to be the most sensitive, at the expense of the use of a modified polyacrylamide matrix and higher silver concentrations.     

介孔分子筛研究新进展

介孔分子筛材料作为催化剂或催化剂载体为有机大分子参与反应提供了有利的空间构型和择形活性中心,在石油加工工业中具有潜在的应用优势。但由于介孔分子筛材料的水热稳定性比较低,且酸性较弱,极大地影响了其在催化领域中的广泛应用。本文综述了近年硅基介孔分子筛的改性研究进展,重点讨论了在提高介孔分子筛酸性和水热稳定性方面的研究工作。     

Synthetic zeolites A and X as stationary phases in thin-layer chromatography

Summary The possibility of using synthetic zeolites A and X as stationary phases in thin-layer chromatography has been investigated and the method of preparing layers from crystalline zeolites and their gels determined, as was the possibility of separating certain mixtures on the layers obtained. Experiments were performed simultaneously on layers from zeolites A and X dried at room temperature and on layers activated at 120°C, and also on layers from amorphous forms but in this case only on those dried at room temperature. Dyes and inorganic cations were used as test substances. On the basis of the results obtained it has been established that only the crystalline compounds can be successfully used as thin layers for the separation of organic compounds.     

Mesoporous molecular sieves and nanoperiodic materials

A review is given of literature data and some results of the authors on different approaches to the synthesis and the physicochemical properties of mesoporous molecular sieves and nanoperiodic structures made from inorganic oxides, phosphates, heteropolyacids, and surfactants. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 33, No. 5, pp. 322–337, September–October, 1997.     

用3A分子筛作模板构建灵敏的表面增强拉曼光谱银基底

成功地制备了一种灵敏的表面增强拉曼散射(SERS)银基底。即以3A分子筛为模板,以葡萄糖为还原剂,通过改善的银镜反应在分子筛上建构银壳,再用稀氢氟酸去掉分子筛核制备由带有平的内表面的平板堆砌而成的聚集体。通过扫描电子显微镜观测了其大小和形貌,通过X-射线粉末衍射仪研究了其结构。以4-羟基苯硫酚(4-MPH)为探针分子,考察了其SERS活性,与在玻璃基底上构建的银纳米粒子和商品微米银粉末相比,吸附在该平板银聚集体上的4-MPH在~1078 cm-1处谱带的SERS峰强度是吸附在以玻璃为基底的银纳米粒子的40倍左右,是吸附在商品微米银粉末的13倍左右。通过计算,该SERS活性基底的增强因子约为2.8×105。这种灵敏的SERS基底容易制备,成本合适,在设计、开发SERS光谱探针装置等方面有很好的应用前景。     

A heterogeneous model for gas transport in carbon molecular sieves

A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.     

A new TMA adsorptive expansion test for molecular sieves

Until recently, it has been believed that during adsorption and desorption cycles of molecular sieve pellets, the pellets have been passive participants in the process. It has lately been shown by others using X-ray diffraction technique that the molecular sieve structure undergoes expansion and contraction as a result of moisture content changes.A new thermomechanical analyzer (TMA) technique has been developed that allows the dimensional change to be measured continuously as a function of time and, concurrently, moisture content, thus creating an unique method for measuring adsorption rates.The instrument modifications (DuPont 990 and 943), collection and evaluation of data, and the sensitivity of the adsorption rate due to various parameters are discussed in the paper.

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Zusammenfassung Bis vor kurzem wurde angenommen, dass wÄhrend der Adsorptions- und Desorptionszyklen an Molekularsiebpellets, diese sich als passive Teilnehmer an dem Vorgang beteiligen. Durch andere Autoren wurde unter Anwendung der Röntgendiffraktionstechnik gezeigt, da\ die Molekularsiebstruktur infolge von Änderungen des Feuchtigkeitsgehalts Expansionen und Kontraktionen ausgesetzt ist.Eine neue thermomechanische Analysentechnik wurde entwickelt, welche die kontinuierliche Messung der DimensionsÄnderung als Funktion der Zeit unter gleichzeitiger Messung des Feuchtigkeitsgehalts gestattet und somit eine einzigartige Methode zur Ermittlung von Adsorptionsgeschwindigkeiten schafft.Die Varianten des Instrumentes (DuPont 990 und 943), die Datensammlung und -Verarbeitung, sowie die durch verschiedene Parameter bedingte Empfindlichkeit der Adsorptionsgeschwindigkeit werden in der Veröffentlichung erörtert.

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Résumé Jusqu'à tout récemment on pensait que lors des cycles d'adsorption et de désorption des tamis moléculaires, les particules des tamis étaient des participants passifs. Depuis peu de temps des auteurs ont montré, en se servant de la technique de diffraction des rayons X, que par suite à des variations de l'humidité, la structure des tamis moléculaires subit des dilatations et des contractions.On a développé une nouvelle technique d'analyse thermomécanique qui permet de mesurer, en continu, les variations de dimension en fonction du temps simultanément avec la teneur en humidité, créant ainsi une méthode unique de mesure des vitesses d'adsorption.Les modifications apportées à l'appareil (Du Pont 990 et 943), l'acquisition et l'évaluation des données, ainsi que la sensibilité de la vitesse d'adsorption due à divers paramètres sont discutées.

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Synthesis and characterization of mesoporous molecular sieves

In the synthesis of mesoporous molecular sieves of the type MCM-41, different cationactive surfactants and sources of silicon were used. Moreover, Al-MCM-41 samples with different content of aluminium were synthesized. MCM-41 and Al-MCM-41 were synthesized at elevated temperature in stainless-steel autoclaves. Prepared mesoporous molecular sieves were characterized by powder X-ray diffraction (XRD), physical adsorption of nitrogen at the temperature of −197°C, sorption capacity of benzene, and by infrared spectroscopy (FTIR). Acidity was measured for Al-MCM-41 by temperature programmed desorption of ammonia (TPDA) and by FTIR of adsorbed pyridine. Acid catalytic activity of Al-MCM-41 was tested by isomerization of o-xylene. Influence of the synthesis reproducibility, surfactant used, source of silicon, synthesis time, source of aluminium, and Si to Al mole ratio on the properties of mesoporous molecular sieves were evaluated.     

Stabilisation of reactive intermediates in molecular sieves

This paper presents studies on paramagnetic intermediates, free atoms and radicals produced in γ-irradiated molecular sieves and their reactions with adsorbate molecules or exchangeable cations. Four different systems have been investigated using EPR spectroscopy, Na-A/CH₄, AgNa-A/CH₃OH, Ag-SAPO-11/C₂H₄ and AgCs-rho/NH₃. It was found that methyl radicals are formed in two different sites in Na-A/CH₄ and in one of them they are stable at room temperature. The formation of Ag·CH₂OH⁺ radical cation with one-electron bond between silver and carbon has been established in AgNa-A/CH₃OH by EPR experiments with [¹³C]CH₃OH and DFT calculations. In Ag-SAPO-11/C₂H₄ the stabilisation of biligand silver/ethylene complex, Ag⁰(C₂H₄)₂ was postulated based on EPR and DFT results. Tetrameric silver clusters (Ag ₄ ³⁺ ) produced radiolytically in AgCs-rho/NH₃ strongly interact with two ammonia molecules as was deduced from the changes in superhyperfine structure of high-field EPR line of Ag ₄ ³⁺ pentet for zeolite exposed to [¹⁴N]NH₃ and [¹⁵N]NH₃. The presented examples clearly show that the combination of radiation methods with EPR technique is very useful to study the structure and reactivity of paramagnetic intermediates.     

Silicoaluminophosphate molecular sieves: Characterization of textural and acidic properties

The silicoaluminophosphate SAPO-37 as well as ZSM-20 zeolite have a faujaside-like structure and are potentially useful as catalysts. We report in this work different procedures to decompose the organic template occluded in SAPO-37. The texture of the final products was analyzed by means of nitrogen adsorption. The acid properties of SAPO-37 and ZSM-20 were also compared by IR measurements of adsorbed pyridine and related to the acidic properties of the presently commonly used cracking catalyst zeolite Y.

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The response of halide ion-selective electrodes to redox systems : A comparison between silver/silver halide electrodes and silver sulphide- based halide ion-selective electrodes

Silver/silver chloride and bromide electrodes, prepared by anodizing ordinary silver electrodes, and the corresponding ion-selective electrodes based on silver sulphide, were tested for their susceptibility towards redox systems. It proved that the latter type of electrode responded significantly to strong oxidants. In contrast, the silver/silver halide types were highly resistant to redox interference provided that the silver halide layer was free from open pores. This could be achieved by generation of sufficiently thick layers and by selection of suitable current densities during electrodeposition (<20 mA cm^-2). The interrelation between the conditions of silver chloride film generation and redox resistance of the resulting electrodes is described in detail.     

Two-dimensional molecular sieves: structure design by computer simulations

Nanoporous molecular networks formed spontaneously by organic molecules adsorbed on solid substrates are promising materials for future nanotechnological applications related to separation and catalysis. With their unique ordered structure comprising nanocavities of a regular shape planar networks can be treated as 2D analogs of bulk nanoporous materials. In this report we demonstrate how the Monte Carlo simulation method can be effectively used to predict morphology of self-assembled porous molecular architectures based on structural properties of a building block. The simulated results refer to the assemblies created by cross-shaped organic molecules which are stabilized by different intermolecular interactions, including hydrogen bonding and van der Waals interactions. It is demonstrated that tuning of size and aspect ratio of the building block enables the creation of largely diversified extended structures comprising pores of a square and rectangular shape. Our theoretical predictions can be helpful in custom design of functional adsorbed overlayers for controlled deposition, sensing and separation of guest molecules.     

A low cost route to hexagonal mesostructured carbon molecular sieves

A mesoporous carbon molecular sieve with a hexagonal framework structure (denoted C-MSU-H) has been prepared using a MSU-H silica template that can be assembled from a low cost soluble silicate precursor at near-neutral pH conditions.     

Hydrogen storage in low silica type X zeolites

Low silica type X zeolites (LSX, Si/Al = 1) fully exchanged by alkali-metal cations (Li(+), Na(+), and K(+)) were studied for their hydrogen storage capacities. Hydrogen adsorption isotherms were measured separately at 77 K and <1 atm, and at 298 K and <10 MPa. It was found that the hydrogen adsorption capacity of LSX zeolite depended strongly on the cationic radius and the density of the cations that are located on the exposed sites. The interaction energies between H(2) and the cations follow the order Li(+) > Na(+) > K(+), as predicted based on the ionic radii. Oxygen anions on zeolite framework were minor adsorption sites. Li-LSX had an H(2) capacity of 1.5 wt % at 77 K and 1 atm, and a capacity of 0.6 wt % at 298 K and 10 MPa, among the highest of known sorbents. The hydrogen capacity in LSX zeolite by bridged hydrogen spillover was also investigated. A simple and effective technique was employed to build carbon bridges between the H(2) dissociation catalyst and the zeolite to facilitate spillover of hydrogen atoms. Thus, the hydrogen storage capacity of Li-LSX zeolite was enhanced to 1.6 wt % (by a factor of 2.6) at 298 K and 10 MPa. This is by far the highest hydrogen storage capacity obtained on a zeolite material at room temperature. Furthermore, the adsorption rates were fast, and the storages were shown to be fully reversible and rechargeable. Further optimization of the bridge building technique would lead to an additional enhancement of hydrogen storage.     

Hysteresis and scanning behavior of mesoporous molecular sieves

Sorption hysteresis is a widely studied phenomenon whose predicted behavior is well documented and researched. On the other hand, there is much less known about the region that lies between sorption isotherms, believed to be a metastable region. Scanning curves are a way of understanding the mechanism of hysteresis and a tool for hysteresis model validation. Scanning curves were produced for mesoporous materials: SBA-15 and MCM-41 for N(2) sorption at 77 K and Ar sorption at 87 K. A limited set of different scanning behaviors is identified. Like most hysteresis theories, it was found that a single model for scanning behavior cannot be extended to all materials under the same or different experimental conditions. Two behaviors are consistent with recent theories and simulations; however, several are not. The implications as to the characterization of pore dimensions and structure are discussed.     

A comparison between parallelization approaches in molecular dynamics simulations on GPUs

We test the relative performances of two different approaches to the computation of forces for molecular dynamics simulations on graphics processing units. A “vertex‐based” approach, where a computing thread is started per particle, is compared to an “edge‐based” approach, where a thread is started per each potentially non‐zero interaction. We find that the former is more efficient for systems with many simple interactions per particle while the latter is more efficient if the system has more complicated interactions or fewer of them. By comparing computation times on more and less recent graphics processing unit technology, we predict that, if the current trend of increasing the number of processing cores—as opposed to their computing power—remains, the “edge‐based” approach will gradually become the most efficient choice in an increasing number of cases. © 2014 Wiley Periodicals, Inc.