Preparation of organomodified aluminosilicates for purification of biological solutions

Organomodified aluminosilicates for purification of biological solutions were prepared from a natural zeolite. The synthesis was performed by chemical deposition of chitosan on the zeolite surface followed by successive treatment with a solution of copper sulfate and a solution of potassium ferricyanide. The composition of sorbents was determined by elemental analysis. The physicochemical properties of the starting and modified zeolites were studied by the positron annihilation spectroscopy, IR spectroscopy, powder X-ray diffraction, and scanning electron microscopy, while the adsorption properties were examined by sorption of brilliant green. The adsorption behavior of the zeolites toward endotoxins was assessed. The sorbent containing the ferricyanide-chitosan complex was found to have the highest sorption capacity for lipopolyssacharides (endotoxins).     

Use of Biopolymers for the Removal of Metal Ion Contaminants from Water

Summary: Naturally abundant biosorbants such as chitin and chitosan are recognized as excellent metal ligands, forming stable complexes with many metal ions, and serving as effective protein coagulating agents. Chitosan is a heteropolymer made of D-glucosamine and a small fraction of N-acetyl-D-glucosamine residues. Therefore, the adsorption ability of chitosan is found to be much higher than that of chitin, which has relatively fewer amino groups. Zeolites are crystalline microporous aluminosilicates with ion exchange properties suitable for a wide range of applications in catalysis and separation of liquid and gaseous mixtures. Incorporation in chitosan membranes is an effective method to control the diffusion outside the zeolite crystals and appropriately designed composite systems can find numerous opportunities for applications in wastewater treatment. In this paper we present the synthesis of zeolite-chitosan and zeolite-ethyl cellulose composites by encapsulation of clinoptilolite using a gelling solution of chitosan or an ethyl cellulose solution in ethyl acetate. The adsorption process of Cu²⁺ and Cd²⁺ on some adsorbents was investigated: clinoptillolite tuff (0.05 mm), chitosan flakes, ethyl cellulose, zeolite-chitosan and zeolite- ethyl cellulose composites. Zeolite-chitosan composites have been prepared by encapsulation of zeolites by a gelling solution of chitosan. Micrometric crystals of clinoptillolite were dispersed in a 3% chitosan solution in 1% aqueous acetic acid. The chitosan gel was formed and the zeolite crystals were encapsulated during the gelling process. The same procedure was used to obtain zeolite – ethyl cellulose composites. Study of the metal ion retention properties of different adsorbent materials was carried out using a steady state regime. The concentration of heavy metal ions in supernatant was determined by the atomic absorption spectrophotometric method. Adsorption isotherms of metal ions on adsorbents were determined and correlated with common isotherm equations such as Langmuir and Freundlich models.     

In situ SAXS/WAXS of zeolite microwave synthesis: NaY, NaA, and beta zeolites.

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.     

Unveiling the elusive role of tetraethyl orthosilicate hydrolysis in ionic-liquid-templated zeolite synthesis

Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1-butyl-3-methylimidazolium ([BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization.     

The Link between ZSM-5 Zeolite Crystallization and Mesopore Formation by Leaching

Acid or base leaching are well-established tools in the synthesis of mesoporous zeolites. Previous studies suggest an inherent link between the structure-property relationship of mesoporous zeolites, that is, chemical resistance, pore diameter and distribution, with zeolite synthesis or crystallization conditions. The exact nature and/or origin of this link is currently however, poorly established. Here, we provide evidence how zeolite crystallization conditions influence the leaching behavior and thus structure of mesoporous zeolites. Electron microscopy and in situ small angle X-ray scattering both confirmed the crystallization of ZSM-5 to utilize both nanoparticles and oligomers as elemental building blocks. Utilization of these species is highly depended on supersaturation. The precursor solution of decreased water content favored a faster consumption of nanoparticles compared to its oligomers at the early stage of crystallization. Then the addition of oligomers can heal the surface imperfections and thus the resulting zeolite showed a higher resistance against acid leaching. In contrast, within the precursor solution of increased water content the slower consumption of nanoparticles led to crystals with a less robust rim. Defects existed in the rim due to limited healing by oligomers and, as such, mesopores can be created by the following post-treatment. Precise control over selected crystallization conditions can therefore further aid the design of optimized mesoporous zeolites.     

A working hypothesis for broadening framework types of zeolites in seed-assisted synthesis without organic structure-directing agent

Recent research has demonstrated a new synthesis route to useful zeolites such as beta, RUB-13, and ZSM-12 via seed-assisted, organic structure-directing agent (OSDA)-free synthesis, although it had been believed that these zeolites could be essentially synthesized with OSDAs. These zeolites are obtained by adding seeds to the gels that otherwise yield other zeolites; however, the underlying crystallization mechanism has not been fully understood yet. Without any strategy, it is unavoidable to employ a trial-and-error procedure for broadening zeolite types by using this synthesis method. In this study, the effect of zeolite seeds with different framework structures is investigated to understand the crystallization mechanism of zeolites obtained by the seed-assisted, OSDA-free synthesis method. It has been found that the key factor in the successful synthesis of zeolites in the absence of OSDA is the common composite building unit contained both in the seeds and in the zeolite obtained from the gel after heating without seeds. A new working hypothesis for broadening zeolite types by the seed-assisted synthesis without OSDA is proposed on the basis of the findings of the common composite building units in zeolites. This hypothesis enables us to design the synthesis condition of target zeolites. The validity of the hypothesis is experimentally tested and verified by synthesizing several zeolites including ECR-18 in K-aluminosilicate system.     

介孔分子筛制备技术新进展—二次合成、超分子自组装和介孔生成剂法

具有内部介孔结构的多级孔分子筛兼具微孔分子筛和介孔材料的功能, 拥有良好的传质和催化特性. 在过去的几十年内, 介孔分子筛在催化、 吸附和分离领域发展迅速. 近年来, 新型合成方法的开发在很大程度上实现了介孔分子筛孔道结构、 组分及形貌灵活可控的调节. 本综述讨论了近期出现的多种新合成路径, 重点介绍了近期发展起来的二次合成制备低硅/铝介孔分子筛、 超分子自组装合成介孔分子筛及有机小分子原位合成介孔分子筛技术. 对这些合成技术的机理进行了讨论, 以期为介孔分子筛未来的发展提供思路. 文章的最后还讨论了不同的合成策略所面临的一些关键性挑战.     

Characterization of the products obtained from alkaline conversion of tuff and metakaolin

Currently, there has been a growing interest of zeolite materials for industrial and scientific purpose. Synthetic zeolites are more often used than natural ones due to its higher purity and more uniform particle sizes. Numerous investigations are conducted in searching of inexpensive raw materials suitable for zeolite synthesis. Moreover, the temperature, pressure, times and SiO₂/Al₂O₃ ratio are the most important parameters which play key roles in the synthesis processes. Due to such a large number of factors that affect the process, zeolite synthesis has been undergoing constant development. Nowadays, researchers focus on the methods of synthesizing zeolites at ambient temperature and pressure. Metakaolin and tuff are natural raw materials which can be turned into a brand new class of synthetic zeolites. However, each requires different method of synthesis in order to obtain a material with best physical properties. This paper discusses the process of alkaline activation of synthetic zeolites from natural raw materials: volcanic tuff excavated in Filipowice and metakaolin obtained from Rominco company. Two methods: fusion and low-temperature synthesis, were used in the presented research. Moreover, the physical properties of raw materials and zeolites obtained were shown. Based on the XRD analysis, it was verified that materials after the synthesis process contained zeolites A, Na-X and faujasite-Na. Furthermore, the dehydration and thermal decomposition phenomena of the tuff and metakaolin before and after the synthesis process were determined by coupled TG/MS techniques.     

High yield method for nanocrystalline zeolite synthesis

Nanocrystalline zeolites, such as silicalite-1 and zeolite Y, were synthesized in high yield by periodically removing nanocrystals from the synthesis solution and recycling the unused reagents, including the template and T-atom sources.     

Recent advance in synthesis and application of heteroatom zeolites

Incorporation of heteroatoms into the framewo rk of zeolites has become a significant strategy to improve their performance in catalysis and adsorption,because the obtained heteroatom zeolites exhibit quite different properties from the conventional aluminosilicate zeolites in aspects of surface acidity,pore structures,particle size and so on.In this review,the progress on the heteroatom zeolites including their synthesis and application is highlighted.First,the recent advance on the design and synthesis of different heteroatom zeolites is summarized.Special emphasis is placed on the introduction and comparison of three typical methods,including the direct synthesis,post synthesis and improved direct synthesis,for the traditional heteroatom zeolites(such as TS-1,Sn-MFI,Sn-β) and newly-reported heteroatom zeolites(such as W-MFI,Mo-MFI).According to their intrinsic characteristics,the application of heteroatom zeolites in diverse fields,such as production of fine chemicals,air pollution control and biomass conversion is then discussed.Finally,the challenges and perspective on the future development of heteroatom zeolites in low-cost preparation and practical application are proposed.     

On the role of triethanolamine in the charnell synthesis of zeolites

Using NMR of elements present in solutions for the synthesis of zeolites, we have investigated the state of solution components. Specific interaction of sodium aluminate with triethanolamine in the starting solution has been found, which determines the results of synthesis of NaX zeolies in the system studied.A. F. Ioffe Physico-Technical Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 67–70, July–August, 1993.Translated by L. Smolina     

Sustainable Synthesis of Pure Silica Zeolites from a Combined Strategy of Zeolite Seeding and Alcohol Filling

Currently, the synthesis of pure silica zeolites always requires the presence of organic structure‐directing agents (OSDAs), which direct the assembly pathway and ultimately fill the pore space. A sustainable route is now reported for synthesizing pure silica zeolites in the absence of OSDAs from a combined strategy of zeolite seeding and alcohol filling, where the zeolite seeds direct crystallization of zeolite crystals from amorphous silica, while the alcohol is served as pore filling in the zeolites. Very importantly, the alcohol could be fully washed out from zeolite pores by water at room temperature, which completely avoids calcination at high temperature for removal of OSDAs in the synthesis of pure silica zeolites.     

Synthesis and Properties of Zeolites from Autoclaved Aerated Concrete (AAC) Waste

Syntheses routes for the conversion of autoclaved aerated concrete (AAC) waste into aluminosilicate zeolites like LTA and related phases were developed. The procedures always started with leaching steps of the pure AAC waste by combinations of strong alkaline (NaOH) and mild acid (citric acid) treatments, before the real crystallization process was performed separately under addition of sodium aluminate. All products were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive X‐ray analysis (EDX‐analysis) and Fourier‐transform infrared spectroscopy (FTIR). Zeolites LTA and related phases basic sodalite (SOD), hydrosodalite (SOD), cancrinite (CAN) and an intermediate phase between SOD and CAN were observed. Depending on the preparation route tailor made synthesis of pure phase zeolite LTA with crystal sizes up to 5 μm was worked out. In addition to syntheses procedures important properties of the zeolites were discussed with respect to the treatment procedure of AAC. It is shown, that the special synthesis pathway is not only responsible for the product composition and formation of a certain structure type but also exhibits a strong influence on the crystallinity, crystal size, and morphology. The water sorption capacity and the hydrothermal stability of the products were selected for those further investigations. Whereas adequate water sorption capacity up to 272 mg · g^–1 were measured for zeolites LTA obtained from two different reaction routes, limited hydrothermal stabilities were revealed for other products. Under the conditions of strong hydrothermal treatment at a temperature of 473 K for 72 h, a more or less extended phase transformation into ANA‐Type zeolites occurred. This process was least extensive for pure phase zeolite LTA obtained from the alkaline solution of AAC leaching.     

ZSM-5分子筛酸性质对甲醛合成三聚甲醛催化性能的影响

ZSM-5分子筛是合成三聚甲醛的有效催化剂。本工作通过XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等手段对一系列不同SiO₂/Al₂O₃物质的量比的ZSM-5分子筛催化剂进行了表征,研究了ZSM-5分子筛中Brønsted酸中心和Lewis酸中心对其甲醛合成三聚甲醛催化性能的影响。结果表明,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有合适的Brønsted酸中心用于催化甲醛缩聚为三聚甲醛的反应,同时其Lewis酸中心量极少,可有效抑制Cannizzaro或Tishchenko等副反应,提高三聚甲醛的选择性,因而具有最佳的合成三聚甲醛催化性能。寿命实验评价结果显示,SiO₂/Al₂O₃物质的量比为250的ZSM-5分子筛具有良好的催化稳定性,单程寿命长达114 h,并且可通过550℃焙烧再生恢复其催化活性。     

硅铝沸石分子筛晶化过程再思考

目前针对沸石分子筛的晶化过程已经进行了大量研究, 但是近年来硅铝分子筛的合成显示其晶化过程超出了传统的沸石分子筛晶化理论, 特别表现在硅铝沸石分子筛的模板作用、 水的作用以及沸石晶体之间的转化等. 本文讨论了上述作用的本质, 并通过研究模板法作用提出了无有机模板法合成硅铝沸石的策略, 通过了解水的作用提出了无溶剂法合成沸石分子筛, 通过表征沸石之间的转化过程发现不仅低骨架密度可以向高骨架密度晶体转化, 而且高骨架密度也可以向低骨架密度晶体转化.     

用工业固体废料合成沸石分子筛的研究进展

系统总结了以工业固体废料为原料合成沸石分子筛材料的最新研究进展, 讨论了以粉煤灰、 珍珠岩工业废料、 煤矸石、 流体催化裂化(FCC)废催化剂、 锂矿渣、 铝土矿渣、 废瓷料和废弃玻璃等工业固体废料为原料, 合成LTA, FAU, MFI, CHA, GIS, SOD, ANA和KFI沸石分子筛材料的工艺方法, 及其在污水中重金属离子的脱除、 空气中CO₂的捕获、 氮氧化物的选择性还原等实际应用中的性能, 并对未来工业固体废料合成沸石分子筛的发展趋势进行了展望.     

二维分子筛的制备及其催化应用研究进展

沸石分子筛是一种具有独特孔道结构的硅铝酸盐晶体,因其具有较大的比表面积、优异的孔道择形性、良好的热稳定性以及适宜的酸性质等特点,被广泛应用于催化、吸附、分离等领域。与常规三维沸石分子筛相比,二维分子筛由于其独特的形貌结构带来的可调变的多级孔结构、适宜的表面酸性以及良好的扩散传质性能等优点,已在吸附和催化领域显示出巨大的应用潜力。本文系统总结了二维MFI、SAPO-34、MCM-n、Y型分子筛等的合成以及此类分子筛催化应用研究方面的最新进展。最后,对二维沸石分子筛材料的新合成方法及新应用领域进行了展望。     

New polyaniline/chitosan composite systems: Synthesis,structure, and functional properties

Electroconductive and mechanically strength composite systems based on polyaniline and chitosan on the polyethylene porous substrate were obtained. A method to synthesize the conductive form of polyaniline in the solution of chitosan was developed. Molecular characteristics of chitosan in the solutions of acetic and hydrochloric acids and in their mixtures have been investigated. Optimal composition of solvent for the synthesis of polyaniline in a chitosan solution was determined. Electrical conductivity and mechanical characteristics of polyaniline/chitosan composite systems on porous polyethylene film were measured.     

微孔-微孔复合分子筛的结构特征及应用

微孔-微孔复合分子筛是指两种(或多种)微孔分子筛的复合晶体,不仅具备单一分子筛的特性,而且由于复合过程中产生的结构畸变使其具有独特的孔道结构和酸性质,进而体现出优异的催化反应特性,成为当今分子筛领域的研究热点。微孔-微孔复合分子筛可分为共晶分子筛和共生分子筛两种,前者通过两种分子筛晶体的无限成分单元重排,有利于构成新的完整的晶体结构,后者则是两种分子筛共生长过程中得到的两相交错生长的复合体,产生微结构畸变和界面效应。本文对微孔-微孔复合分子筛进行归纳和分类,并系统介绍了微孔-微孔复合分子筛的研究进展,着重阐述了共晶分子筛和共生分子筛的合成与微结构特点以及在催化反应领域中的应用。     

Atomic-Scale Designing of Zeolite Based Catalysts by Atomic Layer Deposition

Zeolite-supported catalysts have been widely used in the field of heterogeneous catalysis. Atomic-scale governing the metal or acid sites on zeolites still encounters great challenge in controllable synthesis and developing of novel catalysts. Atomic layer deposition (ALD), owing to its unique character of self-limiting surface reactions, becomes one of the most promising and controllable strategies to tailor the metallic deposition sites in atomic scale precisely. In this review, we present a comprehensive summary and viewpoint of recent research in designing and engineering the structural of zeolite-based catalysts via ALD method. A prior focus is laid on the deposition of metals on the zeolites with emphasis on the isolated states of metals, followed by introducing the selected metals into channels of zeolites associates with identifying the location of metals in and/or out of the channels. Subsequently, detailed analysis of tailoring the acid sites of different zeolites is provided. Assisted synthesis of zeolite and the regioselective deposition of metal on special sites to modify the structures of zeolites are also critically discussed. We further summarize the challenges of ALD with respect to engineering the active sites in heterogeneous zeolite-based catalysts and provide the perspectives on the development in this field.