键阻断原理构建中孔A型沸石

采用不同类型的有机硅烷化SiO₂作为基本合成单元, 制备了具有晶内中孔的A型沸石。考察了反应碱度、Si/Al比、晶化时间等合成条件对产品的影响。结果表明, 甲氨基丙基三甲氧基硅烷是合成中孔A型沸石的最佳硅烷化试剂;硅烷化试剂的应用, 使中孔沸石晶化过程可以通过“键阻断原理”有效控制;沸石的中孔尺寸可以通过不同类型的有机硅烷化试剂进行调控; 一定范围内, 其外比表面积、中孔体积随SiO₂表面硅烷化度的增加而增加。通过沸石晶化过程中的“键阻断”, 可以制备具有晶内中孔的A型沸石。     

键阻断原理构建中孔A型沸石

采用不同类型的有机硅烷化SiO2作为基本合成单元,制备了具有晶内中孔的A型沸石。考察了反应碱度、Si/Al比、晶化时间等合成条件对产品的影响。结果表明,苯胺基丙基三甲氧基硅烷是合成中孔A型沸石的最佳硅烷化试剂;硅烷化试剂的应用,使中孔沸石晶化过程可以通过"键阻断原理"有效控制;沸石的中孔尺寸可以通过不同类型的有机硅烷化试剂进行调控;一定范围内,其外比表面积、中孔体积随SiO2表面硅烷化度的增加而增加。通过沸石晶化过程中的"键阻断",可以制备具有晶内中孔的A型沸石。     

Incorporation of CoS nanoparticles into ZSM-5 zeolite by hydrothermal and ion exchange methods

Cobalt sulfide nanoparticles were introduced into the medium-pore zeolite ZSM-5 (Zeolite Scony Mobil Five) by ion exchange in aqueous suspension and also by the addition of cobalt sulfate to the synthesis gel in hydrothermal zeolite synthesis. The latter method was systematically studied in the presence of tetraethylammonium ions as organic agents. The materials were characterized by chemical analysis, x-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), energy dispersion x-ray (EDX), IR, BET and diffuse reflectance spectroscopy (DRS). SEM picture and BET were used to discriminate between CoS nanoparticles in the zeolite pores and on the outer crystal surface. Their crystalline structure and morphology were studied by XRD and scanning electron microscopy. The results showed that in hydrothermal method zeolite acts as a template. CoS nanoparticles with an approximate size of 22 nm grow on the surface of zeolite. In ion exchange method, however, the majority of CoS nanoparticles are about 6 nm in diameter, located on the surface of the MFI (type materials ZSM-5) structure. Exciton absorption peaks at higher energy than the fundamental absorption edge of bulk CoS indicate quantum confinement effect in nanoparticles as a consequence of their small size. The absorption spectra show that the optical band gap for CoS nanoparticles produced by hydrothermal and ion exchange methods is 3.68 and 4.1 eV, respectively.     

Laser Control of Zeolite Nucleation

Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd‐YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X‐ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite‐1), following a hydrothermal treatment. The average crystal size (in the 0.6–3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.     

Green Synthesis of Magnetic Zeolite LTA using NaOH Activated Fly Ash

The magnetic zeolite LTA was successfully synthesized using NaOH activated fly ash. The properties of the magnetic zeolite LTA were characterized by XRD, FTIR, SEM, TEM, BET, and VSM. We can be concluded that the synthesized composite consists of zeolite LTA and magnetic Fe₃O₄ nanoparticle. The nitrogen adsorption technique confirmed that the magnetic zeolite LTA exhibits a specifific surface area of 10.0183 m² · g^–1, which is much larger than that of the fly ash. VSM result confirms that the magnetization saturation value of the magnetic zeolite LTA is 10.06 emu · g^–1. Therefore, the magnetic zeolite LTA could be easily separated from the liquid phase using a magnet.     

沸石分子筛膜缺陷的形成及修复*

分子筛膜在化学传感器、膜分离和膜催化等领域有潜在的应用前景。缺陷的存在降低了分子筛膜的筛分作用和分离选择性,从而限制了其工业应用。本文综述了沸石分子筛膜缺陷形成及修复方面的研究进展,详细介绍了沸石分子筛膜缺陷形成的原因,并按照过程机理将分子筛膜修复方法划分为多次合成法、积炭结焦法、表面涂层法、化学气相沉积法以及液相化学沉积法等。在深入分析了各种修复方法优缺点的基础上,对今后分子筛膜修复技术的发展趋势进行了展望。     

Effect of Aging on the Synthesis of Kaolin-Based Zeolite Y from Ahoko Nigeria Using a Novel Metakaolinization Technique

Zeolite Y was systematically synthesized from Ahoko Nigerian kaolin in a conventional hydrothermal system using novel metakaolinization technique. The effect of aging on the formation of zeolite phase was investigated during the course of the synthesis. A rapidly processed metakaolin at a temperature of 600°C and exposure time of 50 minutes, which is capable of reducing the energy and cost of producing it was used to study the synthesis of zeolite Y. It was found that aging conditions play a prominent role in the preparation of zeolite Y from Ahoko metakaolin. Aging played a significant role by increasing the crystallinity of the final product even though zeolite Y was obtain without aging. The outcome of zeolite Y synthesized from Ahoko kaolin in 9 hours at 100°C was different from most reports on the synthesis of zeolite Y from kaolin where longing time (72 hours) of crystallization are reported.     

Preparation of Zeolite X Membranes on Porous Ceramic Substrates with Zeolite Seeds

Zeolite X membranes were investigated by in-situ hydrothermal synthesis on porous ceramic tubes precoated with zeolite X seeds or precursor amorphous aluminosilicate, and porous α-Al2O3 ceramic tubes with a pore size of 50 200 nm were employed as supports. Zeolite X crystals were synthesized by the classic method and mixed into deionized water as a slurry with a concentration of 0.2 0.5wt%, having a range of crystal sizes from 0.2 to 2μm. Crystal seeds were pressed into the pores near the inner surface of the ceramic tubes, and crystallization took place at 95℃ for 24-96 h. It was also investigated that Boehmite sol added with zeolite X seeds was precoated on ceramic supports to form a layer of γ-Al2O3 by heating, and hydrothermal crystallization could then take place to prepare the zeolite membranes on the composite ceramic tubes. The crystal species were characterized by XRD, and the morphology of the supports subjected to crystallization was characterized by SEM. The composite zeolite membranes have zeolitic top-layers with a thickness of 10-25 μm, and zeolite crystals can be intruded into pores of the supports as deeply as 100μm. The experimental results indicate that the precoating of zeolitic seeds on supports is beneficial to crystallization by shortening the synthesis time and improving the membrane strength. The resulting zeolite X membrane shows permselectivity to tri-n-butylamine((C4H9)3N) over perfluro-tributyl-amine ((C4Fg)3N), and a permeance ratio of 57 for ((C4Hg)3N to (C4F9)3N could be reached at 350℃. Permeances of BZ, EB and TIPB through the zeolite membrane were also measured and were found to slightly increase with temperature.     

液相脉冲激光烧蚀法制备高熔点的纳米金属粒子

采用液相脉冲激光烧蚀法成功地制备了高熔点的金属Pt、Ru与Ag纳米粒子. 采用SEM、TEM、ED和紫外-可见吸收光谱表征了纳米粒子的特征. 纳米粒子的粒径基本在数个到数十个纳米的大小范围内. 发现含适量PVP(poly(vinylpyrrolidone))的水溶液有利于纳米粒子的制备, 而且还能够提高纳米粒子悬浮液的稳定性. 该制备方法较简单, 在制备高熔点的纳米金属粒子方面有着其它方法所不能比拟的优势.     

Evaluation of the dehydration performance of zeolite NaA membrane on porous alumina tube by the alumina X-ray diffraction intensity.

A zeolite NaA (A-type zeolite of ca. 0.4 nm pore size; Linde Type A, LTA) membrane for the dehydration of alcohol was characterized by X-ray diffraction analysis (XRD). Also, the relationship between the X-ray absorption and the EtOH/H2O pervaporation (PV) dehydration performance (water selectivity and permeation flux) of the LTA membrane was first investigated. The LTA membranes used here were gel-synthesized hydrothermally on an alumina porous support tube. Since diffraction lines from the alumina generate from a deeper layer than those of the LTA crystal, and are absorbed by both the surface LTA crystal and materials embedded in the alumina porous support, the alumina (113) diffraction line was intensively monitored to estimate the overall X-ray absorption by the LTA membrane. The intensity of the alumina (113) diffraction line showed a good correlation with the PV dehydration performance of the LTA membrane, that is, lower values with the water selectivity and higher values with the permeation flux. The lower diffraction intensity means stronger X-ray absorption by the LTA membrane. The major factor causing the difference in the X-ray absorption is the thickness or quantity of materials embedded in an alumina porous support, rather than those of the surface LTA crystal. These phenomena can be used conveniently (without real PV experiments) to determine the EtOH/H2O PV dehydration performance of the LTA membrane.     

用高效NaY沸石导向剂快速合成A型沸石

提出了应用高效NaY沸石导向剂快速合成A型沸石的新方法. 在合成过程中, NaY沸石导向剂提供了全部硅源(无需另加硅源). 与用水玻璃提供硅源的合成方法相比, 该法晶化速度快, 合成温度低, 并可在低碱度条件下合成超细A型沸石. 29Si NMR表征和UV Raman研究表明, 高效NaY沸石导向剂中含有大量的六元环等低分子量硅铝酸根前驱体, 它们有利于A型沸石成核与晶体生长.     

Synthesis of Compact NaA Zeolite Membrane by Microwave Heating Method

A continuous and dense NaA zeolite membrane was synthesized by microwave heating method while employing a multi-step seeding LTA zeolite with the average size of 120 rim. The gas H2/N2 mixture separating results indicated that the mixture selectivity increased with increasing of synthesis times. In addition, selectivity of the three-step synthesis was higher than the value(3.74) expected from Kundsen diffusion.     

In situ observation of homogeneous nucleation of nanosized zeolite A

The formation of zeolite A (LTA) in the presence of tetramethylammonium cations is studied using in situ small angle and wide angle X-ray scattering (SAXS/WAXS) techniques. The SAXS measurements show the formation of homogeneous precursors 10 nm in size prior to the crystallization of LTA which were consumed during the crystallization. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. However, although such temperature dependence is noted for the final crystal size, the initial precursor particles size appears to be closely similar (ca. 10 nm) irrespective of the synthesis temperature.     

Sub-40 nm Zeolite Suspensions via Disassembly of Three-Dimensionally Ordered Mesoporous-Imprinted Silicalite-1

Zeolite nanocrystals were prepared from three-dimensionally ordered mesoporous-imprinted (3DOm-i) silicalite-1 by a fragmentation method involving sonication and dissolution within a certain pH range. 3DOm-i silicalite-1 with spherical elements with diameters ranging from 10 to 40 nm and a wide range of crystal sizes (100-200 nm, 500-600 nm, and 1-2 μm) was used as the starting material. The highest yield (57%) of isolated nanocrystals was obtained for 3DOm-i silicalite-1 with a crystal size of 100-200 nm and a spherical element diameter of 40 nm. The smallest nanocrystals obtained, albeit in very low yields, had a 10 nm diameter. Preparation of stable silicalite-1 nanocrystal suspensions fragmented from 20 and 40 nm 3DOm-i silicalite-1 was demonstrated. Cryogenic transmission electron microscopy showed that the isolated zeolite nanocrystals can be used as seeds for the epitaxial growth of silicalite-1. An application of these findings was demonstrated: silicalite-1 nanocrystal suspensions were used to deposit seed layers on porous α-alumina disks, which were converted to continuous thin (300-400 nm) films by secondary growth that exhibited both high permeances and separation factors (3.5 × 10(-7) mol m(-2) s(-1) Pa(-1) and 94-120, respectively, at 150 °C) for p- and o-xylene.     

3D Raman Spectroscopy of Large Zeolite ZSM-5 Crystals

Hydrothermal treatment is a common method used to modify the physicochemical properties of zeolite-based catalyst materials. It alters the number and type of acid sites through dealumination and increases molecular diffusion by mesopore formation. Steaming also reduces the structural integrity of zeolite frameworks. In this study, Raman microscopy has been used to map large zeolite ZSM-5 crystals before and after steaming. 3D elemental maps of T−O (T: Al or Si) sites of the zeolite were obtained. The Raman active vibrational bands were determined, which are indicative of (non-) framework Al, as well as of structural integrity. Zeolite steaming caused the introduction of additional heterogeneities within the zeolite framework. Al migration and the formation of extra-framework Al species were observed. The described experiments demonstrate the capability of 3D Raman spectroscopy as a valuable tool to obtain information on the spatial distributions of framework elements as well as defects within a zeolite-based material.     

A new strategy for the controlled deposition of gold nanoparticle aggregates on two-dimensional polystyrene arrays and its application in glucose oxidase immobilization

Zeolite 4A (LTA) has been successfully synthesized by a hydrothermal method, where kaolin was used as silica and alumina source. The synthesized zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser granulometry, and FTIR spectroscopy. XRD data from the Rietveld refinement method confirmed only one crystallographic phase. Zeolite A morphology was observed by SEM analysis, and it showed well-defined crystals with slightly different sizes but with the same cubic shape. Particle size distribution of the crystals was confirmed by laser granulometry, whereas FTIR spectroscopy revealed significant structural differences between the starting material and the final zeolite product used as water softener.     

Physical basis for the formation and stability of silica nanoparticles in basic solutions of monovalent cations

The colloidal stability, phase behavior, and solubility of silica nanoparticles (3-10 nm) that are formed in basic solutions of monovalent cations (primarily tetrapropylammonium) are investigated using a combination of chemical equilibria and electrostatic models. The free-energy gain associated with the formation of an electric double layer surrounding the nanoparticle was obtained by solving the Poisson-Boltzmann equation. This free energy is an important contribution to the total free energy of the particle and is second only to the formation of Si-O-Si bonds. The free energy of formation of the nanoparticles becomes increasingly negative with an increase in particle size and density, which explains the lower solubility of nanoparticles compared to that of amorphous silica. There is a minimum in the free energy of condensation as a function of size that qualitatively explains why the formation of small particles with a uniform size (<5 nm) is energetically favorable. The electrostatic models provide an estimate for the nanoparticle surface potential, which is significantly higher (-120 to -170 mV) than that of zeolite silicalite-1 (-60 to -80 mV) prepared in similar solutions. This result explains the stability of such small particles in solution. It is also shown that a condensation model that is based on silica solubility can describe the phase diagram for nanoparticle formation reported by Fedeyko et al. (J. Phys. Chem. B 2004, 108, 12271) over a wide range of pH and, in conjunction with a complexation model, provides an approximate equilibrium constant (pKa = 8.4) for the dissociation of nanoparticle silanol groups.     

利用FraGen程序预测沸石分子筛的骨架结构

沸石分子筛是一类广泛应用于各种化工领域的微孔材料. 利用计算机方法搭建理论上合理的沸石骨架模型, 即沸石分子筛的结构预测, 不仅可以用来对已合成的沸石材料进行结构解析, 而且可以用来设计尚未被合成的具有新颖结构的沸石材料, 为未来实现沸石分子筛的定向合成提供靶向结构. 目前, 沸石材料的结构预测面临着许多亟待解决的难题, 其中最突出的问题是现有的结构预测方法产生合理结构的效率仍然非常低. 针对这一问题, 我们课题组开发了一套专门用于预测无机晶体结构的计算机程序——FraGen. FraGen程序可以在指定的晶胞内产生原子, 并根据平行回火的Monte Carlo 原理调整晶胞内原子的位置, 以产生合理的晶体结构. 在本文中, 我们首次利用FraGen 程序, 以已知的AET沸石结构为模板, 通过单独控制每个原子的Wyckoff点对称性, 预测出一系列新颖的沸石结构. 对比已有的结构预测方法, 我们的新方法在相同的条件下能够预测出更多化学上合理的沸石结构.     

Fabrication of Zeolite A Rods with Irregular Macropores by Self-assembly of Zeolite A Microcrystals Using Microwave-assisted Hydrothermal Synthesis

Zeolite A rods by self-assembly of zeolite A microcrystal were successfully synthesized by microwave-assisted hydrotherrnal synthesis. The average size of zeolite crystals consisting of self-assembling materials was about 300 nm and the length of zeolite rods was in the range of 15--30μm.     

Synthesis of zeolite nanocrystals at room temperature

Zeolite A nanoparticles were synthesized under room-temperature conditions from a very reactive organic-template-free gel system. The optimization of the syntheses parameters, namely, the composition of the initial system and the careful choice of the reactants, allowed the crystallization to be accomplished within 3 days. At this stage the individual zeolite crystals were in the range of 100-300 nm without well-developed crystal faces. The prolongation of the synthesis time up to 10 days led to formation of larger well-faceted cubic crystals averaging about 400-500 nm in size. The high-resolution transmission electron microscopy (HRTEM) study revealed that a thin layer of amorphous material covers the zeolite particles acting as a binder between individual zeolite crystals. The postsynthesis treatment of the product in NH(3) media under ultrasonic radiation disintegrated the loosely attached zeolite particles and decreased the fraction of zeolite A particles with low colloidal stability. The employed approach, however, did not result in complete disintegration of aggregated crystals. The zeolite crystals obtained under ambient conditions were characterized by XRD, SEM, dynamic light scattering, and N(2) adsorption measurements.