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b取向MFI型分子筛膜能够显著促进分子的传输效率, 被广泛应用于混合物分离及催化领域. 虽然传统的原位水热晶化法已较为成熟, 然而仍难以调控膜层的b轴取向生长. 本文以304不锈钢片为基底, 采用经典的原位水热晶化法研究了基底表面物化性质、 前驱液配比及晶化条件对钛硅分子筛膜b轴取向生长的影响. 结果表明, TiO2中间层表面的羟基能够定向诱导分子筛晶粒的吸附, 进而提高钛硅分子筛膜的b轴取向程度. 同时, 前驱液中模板剂和水含量对晶粒的大小及膜层的定向生长具有显著影响, 即仅在合适的碱度下才能形成高b轴取向的钛硅分子筛膜. 相似文献
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b轴取向MFI型分子筛膜因其在膜分离、膜催化反应器研究领域的重要应用引起了广泛关注。本文综述了二次生长法合成b轴MFI型分子筛膜的最新研究进展,从晶种的合成、晶种涂覆方式以及二次生长溶液的组成等方面详细总结了调控b取向MFI型分子筛膜合成的方法;比较了不同分子筛膜合成策略的优缺点,及这些合成策略对不同体系的分离效果(分离因子与通量)和催化性能的影响。本文还介绍了近年来二维(2D)分子筛和分子筛纳米片的监测与生长控制方法,自下而上直接合成纳米片与高通量、高选择性分子筛膜合成方面的最新突破。通过深入探讨各种分子筛膜制备策略,对b轴取向分子筛膜制备的发展趋势进行了展望。 相似文献
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采用新型薄片状MFI沸石晶体作为晶种,通过无凝胶蒸汽辅助晶化法(gel-less steam-assisted crystallization,GLSAC)在烧结氧化硅多孔载体上制备了致密平整、b轴取向的MFI沸石膜。考察了GLSAC中模板剂浓度、釜底水量、生长温度及时间对MFI沸石膜的影响。扫描电子显微镜和X射线衍射结果显示,适量的模板剂和釡底水量能抑制晶种的面外生长。成功制备了厚度750 nm、致密平整的MFI沸石膜。制备的对丁烷异构体气体分离测试表明,25℃时,等物质的量的丁烷异构体的分离因子(SFA/B)可达36,对正丁烷的渗透速率为1.5×10-7mol·m-2·s-1·Pa-1。 相似文献
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我们通过自下而上(bottom-up)的方法制备了高宽深比、高结晶度的b轴方向上超薄的MFI沸石纳米片,为制备b轴取向MFI沸石薄膜提供了基础。采用滑动涂覆法(slip coating method)在玻璃片载体上制备了厚度约为100 nm的b轴取向MFI纳米片晶种层。采用无模板剂二次生长法,抑制晶种层面外孪晶生长,实现了晶种层的面内外延生长。在合成体系的nSiO2:nNa2O:nC2 H5 OH:nH2 O=1:0.03:1.3:0.89、晶化时间48 h、晶化温度180℃时,制备了厚度约为200 nm的连续致密的b轴取向MFI沸石膜,与基于四丙基氢氧化铵(TPAOH)的常规合成溶液水热二次生长制备的MFI沸石膜相比,厚度降低了90%,并且保持了晶种层的b轴取向性。 相似文献
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MFI型沸石分子筛,由于其具有较宽合成条件、合适均的一孔径、可修饰和改 性的骨架和孔道系统,高的热稳定性、水热稳定性、化学稳定性和机械强度,不仅 广泛应用于传统的催化和分离领域,而且也广泛地应用于膜的制备。由于MFI型沸 石晶体体型和晶内孔道系统 的各向异性,控制晶体在载体表面的定向生长对于膜 分离、膜催化、膜传感等都极其重要的。文献中报道的c轴取向MFI型沸石膜层的制 备方法有:(1)晶体在强电场作用下在载体表面上进行定向排 列,然后在排列好 的晶体间喷镀或电镀一层金属膜;(2)在有刻蚀槽的微结构硅片表面进行组装; (3)水热合成法;(4)晶种层的二次生长法等。 相似文献
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MFI型沸石分子筛,由于其具有较宽合成条件、合适均的一孔径、可修饰和改 性的骨架和孔道系统,高的热稳定性、水热稳定性、化学稳定性和机械强度,不仅 广泛应用于传统的催化和分离领域,而且也广泛地应用于膜的制备。由于MFI型沸 石晶体体型和晶内孔道系统 的各向异性,控制晶体在载体表面的定向生长对于膜 分离、膜催化、膜传感等都极其重要的。文献中报道的c轴取向MFI型沸石膜层的制 备方法有:(1)晶体在强电场作用下在载体表面上进行定向排 列,然后在排列好 的晶体间喷镀或电镀一层金属膜;(2)在有刻蚀槽的微结构硅片表面进行组装; (3)水热合成法;(4)晶种层的二次生长法等。 相似文献
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采用旋涂法在粗糙的α-Al2O3载体片上制备出较完备的分子筛晶种层;以四丙基氢氧化铵(TPAOH)为有机模板剂,通过调控合成液的H2O/Si摩尔比,实现了对分子筛晶体面内优先生长的调控;经过三次水热合成得到致密交联的h0h-轴取向高硅MFI分子筛膜,膜厚约为8 μm(包括~5 μm致密层和~3 μm过渡层)。采用先低温加氢裂解后低温空气氧化的两步法脱除工艺,有效脱除了分子筛膜内的有机模板剂。相比于传统高温煅烧法,该法可以避免分子筛膜因脱除模板剂而形成的较大晶间缺陷。因而采用低温两步法脱除模板剂的分子筛膜片在30 ℃时具有较好的CO2分离效果,其CO2/N2分离因子达到5.2, CO2渗透通量高达5.8 × 10-7mol·m-2·s-11·Pa-1。 相似文献
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MFI型分子筛膜在分离、催化等领域具有广阔的应用前景,受到了国内外学者的普遍关注。全硅的MFI型分子筛膜具有很强的疏水性,表现出优良的乙醇/水混合物分离性能。本文综述了用于该体系渗透汽化分离的MFI型分子筛膜的研究进展,详细阐述了合成方法(原位水热合成法和晶种法)、不同类型的载体、合成液的原料及配方、合成条件(温度及时间)和焙烧条件对所制备的MFI型分子筛膜的分离性能的影响,归纳了实验研究和理论模拟对该体系分离机理的探讨,并介绍了其对膜制备的指导作用。在深入分析不同合成条件优缺点的基础上,对用于乙醇/水分离体系的MFI型分子筛膜制备的发展趋势进行了展望。 相似文献
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Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride 下载免费PDF全文
Dr. Yong Peng Xiaofei Lu Prof. Dr. Zhengbao Wang Prof. Dr. Yushan Yan 《Angewandte Chemie (International ed. in English)》2015,54(19):5709-5712
The fabrication of MFI zeolite films with particular b‐axis orientation is especially fascinating. Unlike the conventional alkaline or hydrofluoric acid (HF) assisted neutral synthesis route, here we develop a novel neutral synthesis solution system of TPABr/fumed silica/H2O without the use of HF and successfully synthesize highly b‐oriented MFI zeolite films on glass‐plate substrates by secondary growth. The localized weak alkaline environment created by the dissolved Na2O species from the substrate is identified as the key factor for the depolymerization of fumed silica and subsequently the in‐plane growth of zeolite seed layers. Continuous b‐oriented MFI films can also be synthesized on other substrates in the presence of a glass plate or a trace amount of NaOH, which making our neutral synthesis route promising for the direct synthesis of MFI zeolite films and membranes on various substrates. 相似文献
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Twin growth in the synthesis of b-oriented MFI films is successfully suppressed by applying microwave irradiation on a b-oriented MFI seed layer, relying on the nucleation-related bottleneck effect. Electrochemical oxidation experiments demonstrated the importance of twin suppression in enhancing the diffusion of guest molecules in MFI films. 相似文献
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Neel Rangnekar Meera Shete Dr. Kumar Varoon Agrawal Dr. Berna Topuz Prashant Kumar Dr. Qiang Guo Issam Ismail Prof. Abdulrahman Alyoubi Prof. Sulaiman Basahel Dr. Katabathini Narasimharao Prof. Christopher W. Macosko Prof. K. Andre Mkhoyan Prof. Shaeel Al‐Thabaiti Prof. Benjamin Stottrup Prof. Michael Tsapatsis 《Angewandte Chemie (International ed. in English)》2015,54(22):6571-6575
Stable suspensions of zeolite nanosheets (3 nm thick MFI layers) were prepared in ethanol following acid treatment, which partially removed the associated organic structure‐directing agent. Nanosheets from these suspensions could then be dispersed at the air–water interface and transferred to silicon wafers using Langmuir–Schaefer deposition. Using layer‐by‐layer deposition, control on coating thickness was demonstrated. In‐plane X‐ray diffraction (XRD) revealed that the deposited nanosheets contract upon calcination similar to bulk MFI crystals. Different methods for secondary growth resulted in preferentially oriented thin films of MFI, which had sub‐12‐nm thickness in certain cases. Upon calcination, there was no contraction detectable by in‐plane XRD, indicating well‐intergrown MFI films that are strongly attached to the substrate. 相似文献
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In this study, single‐mode microwave heating was applied in epitaxial growth of b‐oriented MFI seed monolayer prepared by facile manual assembly, resulting in the formation of well‐intergrown and highly b‐oriented MFI film with few twins. It exhibited a precise molecular sieving property at a reaction temperature no higher than 100 °C within 2 hours, therefore making it possible for easy operation in an open environment. The capability for concurrent suppression of undesired out‐of‐plane twin growth and promotion of in‐plane epitaxial growth rate under mild reaction conditions was attributed to the obvious superiority of single‐mode microwave heating in comparison with conventional multi‐mode microwave heating in aspects of microwave field uniformity and intensity. Our research indicated that the single‐mode microwave heating technique could potentially be a useful tool for improving the microstructure and therefore the performance of diverse zeolite films. 相似文献
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利用乙二胺-水蒸汽进行气相转化(VPT)制备超薄、取向MFI沸石膜,通过将MFI纳米片沉积层转化为致密的沸石膜,实现了膜厚度的有效控制。扫描电子显微镜和X射线衍射表明,制备的沸石膜膜厚度约为280 nm,具有高度b轴取向的致密结构。丁烷异构体双组分分离测试结果表明,在333 K下,等物质的量的正丁烷/异丁烷混合物的正丁烷渗透速率和分离因子分别为1.5×10-7 mol·m-2·s-1·Pa-1和14.8。Na2SiO3作为低聚硅源在MFI沸石纳米片二次生长过程中能够提供硅源和碱度,通过在胺类蒸汽中实现MFI沸石纳米片间的融合生长,进一步提高了膜的取向度和致密性。 相似文献
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利用乙二胺-水蒸汽进行气相转化(VPT)制备超薄、取向MFI沸石膜,通过将MFI纳米片沉积层转化为致密的沸石膜,实现了膜厚度的有效控制。扫描电子显微镜和X射线衍射表明,制备的沸石膜膜厚度约为280 nm,具有高度b轴取向的致密结构。丁烷异构体双组分分离测试结果表明,在333 K下,等物质的量的正丁烷/异丁烷混合物的正丁烷渗透速率和分离因子分别为1.5×10-7 mol·m-2·s-1·Pa-1和14.8。Na2SiO3作为低聚硅源在MFI沸石纳米片二次生长过程中能够提供硅源和碱度,通过在胺类蒸汽中实现MFI沸石纳米片间的融合生长,进一步提高了膜的取向度和致密性。 相似文献
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Zhou M Liu X Zhang B Zhu H 《Langmuir : the ACS journal of surfaces and colloids》2008,24(20):11942-11946
The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique. 相似文献
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TEM investigation of formation mechanism of monocrystal-thick b-oriented pure silica zeolite MFI film 总被引:3,自引:0,他引:3
Li S Li Z Bozhilov KN Chen Z Yan Y 《Journal of the American Chemical Society》2004,126(34):10732-10737
The first direct transmission electron microscopic (TEM) observation has been carried out on the continuous monocrystal-thick b-oriented pure silica zeolite MFI films produced by in situ crystallization. The self-supporting film samples for TEM study were fabricated by dissolving the steel substrate with acid. This TEM study is free of those artifacts that are typically associated with TEM sample preparations, and allows us to investigate the "true" structure and texture of a very large area of the film and at the same time to focus at will on each individual zeolite crystal in the film. Abundant TEM information including crystallographic orientation relationships among crystals in the film (both out-of-plane and in-plane), grain boundaries, and each crystal grain was obtained. This TEM investigation provides direct unambiguous new evidence to support the homogeneous nucleation mechanism, by which the films form through homogeneous nucleation and crystal growth in the bulk to form equal-sized disk-shape crystals, followed by self-assembly of these crystals onto the substrate to produce a two-dimensional close-packed structure. The last stage of the film formation involves simultaneous space-limited growth and rotation of the individual crystals to realize the in-plane crystallographic control within the film. 相似文献
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Yunjuan Zhang Prof. Dr. Shunai Che 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):50-60
The development of hierarchical macro- or mesoporous zeolites is essential in zeolite synthesis because the size of the micropores limits mass transport and their use as industrial catalysts for bulky molecules. Although major breakthroughs have been achieved, fabricating crystallographically ordered mesoporous zeolites using a templating strategy is still an unsolved challenge. This minireview highlights our recent efforts on the self-assembly of amphiphilic molecules to obtain ordered hierarchical MFI zeolites by introducing aromatic groups into the hydrophobic tail of the amphiphilic molecules. Owing to the geometric matching between the self-assembled aromatic tails and the MFI framework, a) single-crystalline mesostructured zeolite nanosheets (SCZNs), b) SCZNs with a 90° rotational intergrowth structure, c) a hierarchical MFI zeolite with a two-dimensional square P4mm mesostructure, and d) a single-crystalline mesoporous ZSM-5 with three-dimensional pores and sheetlike mesopores layered along the a-axis were successfully synthesized. 相似文献