Hollow ZSM‐5 with Silicon‐Rich Surface,Double Shells,and Functionalized Interior with Metallic Nanoparticles and Carbon Nanotubes

Hollow ZSM‐5 single crystals with silicon‐rich exterior surface are prepared by a “dissolution–recrystallization” strategy in tetrapropylammonium hydroxide solution. Selective dissolution and exterior recrystallization cause the silicon components to migrate from the inside to outside, resulting in a regular void in the interior of the crystal, increased Brönsted acid sites and a silicon‐rich external surface. The as‐prepared hollow ZSM‐5 exhibits excellent acid catalysis with enhanced shape selectivity, as shown in biphenyl methylation as a probe reaction, which is attributed to the silicon‐rich external surface and thus the inhibition of isomerization on external surface. More interestingly, hollow ZSM‐5 single crystals with double shells are successfully prepared by layer‐by‐layer technique followed with dissolution–recrystallization strategy. Furthermore, hollow ZSM‐5 encapsulating iron and carbon nanotubes are successfully synthesized. Furthermore, hollow ZSM‐5 nanosized crystals with the interior functionalized as bimetallic (oxide) nanoparticles such as CuO‐Pd are also successfully synthesized.     

Beyond Creation of Mesoporosity: The Advantages of Polymer‐Based Dual‐Function Templates for Fabricating Hierarchical Zeolites

Direct synthesis of hierarchical zeolites currently relies on the use of surfactant‐based templates to produce mesoporosity by the random stacking of 2D zeolite sheets or the agglomeration of tiny zeolite grains. The benefits of using nonsurfactant polymers as dual‐function templates in the fabrication of hierarchical zeolites are demonstrated. First, the minimal intermolecular interactions of nonsurfactant polymers impose little interference on the crystallization of zeolites, favoring the formation of 3D continuous zeolite frameworks with a long‐range order. Second, the mutual interpenetration of the polymer and the zeolite networks renders disordered but highly interconnected mesopores in zeolite crystals. These two factors allow for the synthesis of single‐crystalline, mesoporous zeolites of varied compositions and framework types. A representative example, hierarchial aluminosilicate (meso‐ZSM‐5), has been carefully characterized. It has a unique branched fibrous structure, and far outperforms bulk aluminosilicate (ZSM‐5) as a catalyst in two model reactions: conversion of methanol to aromatics and catalytic cracking of canola oil. Third, extra functional groups in the polymer template can be utilized to incorporate desired functionalities into hierarchical zeolites. Last and most importantly, polymer‐based templates permit heterogeneous nucleation and growth of mesoporous zeolites on existing surfaces, forming a continuous zeolitic layer. In a proof‐of‐concept experiment, unprecedented core–shell‐structured hierarchical zeolites are synthesized by coating mesoporous zeolites on the surfaces of bulk zeolites.     

Hierarchically Structured Zeolite Bodies: Assembling Micro‐, Meso‐, and Macroporosity Levels in Complex Materials with Enhanced Properties

Engineering levels of porosity in hierarchical zeolites is a vibrant area of research with remarkable application potential. To gain practical relevance, the superior properties observed for the as‐synthesized powders have to be preserved when they are shaped into suitable technical geometries. Herein, mechanically stable millimeter‐sized bodies are prepared by granulation of mesoporous ZSM‐5 zeolite powders using an attapulgite clay binder. Alkaline treatment of conventional zeolite granules is demonstrated to be unsuitable for this purpose. Multiple techniques are applied to characterize mesoporous zeolite granules with respect to their conventional zeolite counterparts, thus establishing the impact of binder inclusion and granulation on their respective properties. The intrinsic structure and acidity of the zeolite are retained post‐structuring. Gas adsorption and mercury porosimetry confirm the presence of interconnected micro‐, meso‐, and macropores. A wide range of imaging techniques permits visualization of the particle properties, phase distribution, and consequent origins of the distinct levels of porosity within the zeolite granules. The superior adsorption properties of the hierarchical ZSM‐5 zeolite granules are demonstrated using cyclohexane, toluene, and isopropyl alcohol as probe molecules.     

CoFe2O4 Nanocrystals Mediated Crystallization Strategy for Magnetic Functioned ZSM‐5 Catalysts

Zeolites have many applications in the petrochemical and fine chemical industry and their functionalization does expand the spectrum of potentials. However, the integration of functional nanocrystals into zeolite frameworks with controlled size, dispersion, and crystallization behavior still remains a significant challenge. Here, a new synthesis of magnetic functioned ZSM‐5 zeolite catalysts via a CoFe₂O₄ nanocrystal mediated crystallization strategy is reported. It is found that high crystallinity of CoFe₂O₄ nanocrystals results in a well‐dispersed encapsulation of them into a single‐crystal of ZSM‐5 due to non‐further‐grown nanocrystals during the fast ZSM‐5 growth. On the contrary, low crystallinity of CoFe₂O₄ nanocrystals leads to the polycrystalline zeolite growth due to the secondary growth of nanocrystals accompanied by the zeolite crystallization and large lattice mismatch between them. The successful encapsulation of small CoFe₂O₄ nanocrystals (≈4 nm) into single crystals lies on the preattachment of them into solid silica gel. During the growth of ZSM‐5 crystals, no secondary growth of nanocrystals happens and its motion is restricted. The encapsulation of magnetic CoFe₂O₄ nanocrystals not only endows magnetic function into zeolites for the first time, but also does not impact catalytic performance of ZSM‐5 in acetalization of cyclohexanone with methanol, which is highly promising in catalytic industries.     

Zeolite Catalysts with Tunable Hierarchy Factor by Pore‐Growth Moderators

The design of hierarchical zeolite catalysts is attempted through the maximization of the hierarchy factor (HF); that is, by enhancing the mesopore surface area without severe penalization of the micropore volume. For this purpose, a novel desilication variant involving NaOH treatment of ZSM‐5 in the presence of quaternary ammonium cations is developed. The organic cation (TPA⁺ or TBA⁺) acts as a pore‐growth moderator in the crystal by OH^?‐assisted silicon extraction, largely protecting the zeolite crystal during the demetallation process. The protective effect is not seen when using cations that are able to enter the micropores, such as TMA⁺ Engineering the pore structure at the micro‐ and mesolevel is essential to optimize transport properties and catalytic performance, as demonstrated in the benzene alkylation with ethylene, a representative mass‐transfer limited reaction. The hierarchy factor is an appropriate tool to classify hierarchically structured materials. The latter point is of wide interest to the scientific community as it not only embraces mesoporous zeolites obtained by desilication methods but it also enables to quantitatively compare and correlate various materials obtained by different synthetic methodologies.     

Shape Selectivity in Adsorption of n‐ and Iso‐alkanes on a Zeotile‐2 Microporous/Mesoporous Hybrid and Mesoporous MCM‐48

The adsorption of linear and branched C5–C9 alkanes in the temperature range 50–250 °C on mesoporous MCM‐48 material and its microporous/mesoporous variant Zeotile‐2 at low surface coverage is investigated using the pulse chromatographic technique. On MCM‐48, the differences in adsorption between linear and branched alkanes are merely a result of differences in volatility, indicating that the MCM‐48 material does not present shape‐selective adsorption sites. On Zeotile‐2, there is a preferential adsorption of linear over branched alkanes. The difference arises from a difference in adsorption entropy rather than enthalpy. Upon their adsorption on Zeotile‐2 branched alkanes lose relatively more entropy than their linear isomers do. Zeolitic molecular pockets embedded in the walls of the mesoporous Zeotile‐2 impose steric constraints on the bulky isoalkanes. Zeotile‐2 combines adsorption properties from microporous and mesoporous materials. Compared to the nitrogen molecule, linear and branched C5–C9 alkanes are superior probes for investigating micropores and micropockets in hierarchical materials.     

In Situ Growth of Mesoporous SnO2 on Multiwalled Carbon Nanotubes: A Novel Composite with Porous‐Tube Structure as Anode for Lithium Batteries

A novel mesoporous‐nanotube hybrid composite, namely mesoporous tin dioxide (SnO₂) overlaying on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesoporous SnO₂ on the surface of MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure‐directing agents. Nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analysis techniques were used to characterize the samples. It was observed that a thin layer tetragonal SnO₂ with a disordered porous was embedded on the surface of MWCNTs, which resulted in the formation of a novel mesoporous‐nanotube hybrid composite. On the base of TEM analysis of products from controlled experiment, a possible mechanism was proposed to explain the formation of the mesoporous‐nanotube structure. The electrochemical properties of the samples as anode materials for lithium batteries were studied by cyclic voltammograms and Galvanostatic method. Results showed that the mesoporous‐tube hybrid composites displayed higher capacity and better cycle performance in comparison with the mesoporous tin dioxide. It was concluded that such a large improvement of electrochemical performance within the hybrid composites may in general be related to mesoporous‐tube structure that possess properties such as one‐dimensional hollow structure, high‐strength with flexibility, excellent electric conductivity and large surface area.     

Hydrophilic and Antimicrobial Zeolite Coatings for Gravity‐Independent Water Separation

Condensing heat exchangers onboard manned spacecraft require hydrophilic fin surfaces to facilitate wetting and wicking of condensate to achieve gravity‐independent water separation in the zero‐ or micro‐gravity environment of space. In order to prevent the proliferation of microbes, the coating must also be biocidal. Here we show for the first time that zeolite A and ZSM‐5 coatings deposited via in‐situ crystallization on stainless steel and aluminum alloys have excellent hydrophilicity, biocidal properties, and adhesion. Water contact angles below 5° were obtained on most substrates tested. When silver‐ion exchange is carried out on the zeolite A coating, it becomes highly antibacterial. This biocidal capability of zeolite A is regenerative by repeated ion exchange. All coatings exhibit the highest rating of 5B as determined by adhesion test ASTM D‐3359‐02 (American Society for Testing and Materials). These properties, in addition to zeolite coating's low‐temperature crystallization process and demonstrated corrosion resistance, make zeolite coatings advantageous over the current sol–gel coatings and well suited for use in condensing heat exchangers onboard manned spacecraft.     

A Silicon–Silica Nanocomposite Material

The synthesis and characterization of a novel silicon–silica nanocomposite material are reported. A self‐assembly method allows the encapsulation of silicon nanoclusters within the channels of a periodic mesoporous silica thin film. The result is the formation of a silicon–silica nanocomposite film with bright, room‐temperature photoluminescence in the visible range, and a nanosecond luminescence lifetime. The properties of the nanocomposite material have been studied by several analytical techniques, which collectively show the existence within the channels of non‐diamondoid‐structure‐type silicon nanoclusters with various hydrogenated silicon sites. It is estimated that the silicon nanoclusters in the silica mesoporous films occupy up to 39 % of the accessible pore volume. The nanocomposite film shows improved resistance to air oxidation compared to crystalline silicon. The high loading and chemical stability to oxidation under ambient conditions are important advantages in terms of the development of silicon‐based light‐emitting diodes from this class of materials.     

Hydrogen‐Bonded Liquid Crystals in Confined Spaces—Toward Photonic Hybrid Materials

A series of hybrid materials based on chiral nematic mesoporous organosilica (CNMO) films infiltrated with liquid crystalline hydrogen‐bonded assemblies is prepared and characterized with respect to the mutual manipulation of the photonic properties of the host and the liquid‐crystalline behavior of the guest. Detailed differential scanning calorimetry studies reveal the impact of confinement on the mesomorphic behavior of the liquid crystalline assemblies in the pores of the CNMO films. The photonic properties of the chiral nematic mesoporous host can be controlled by changing the temperature or irradiating the films with UV light. These stimuli‐induced phase transitions are accompanied by changes in the orientational order of the mesogens as revealed by ¹⁹F NMR spectroscopy. The combination of confinement and changes in the molecular orientation in a unique hybrid material based on hydrogen‐bonded liquid crystals and a porous host with a chiral nematic mesostructure is an interesting concept for the design of optical sensors, reflectors, or filters.     

Novel Three Dimensional Cubic Fm3m Mesoporous Aluminosilicates with Tailored Cage Type Pore Structure and High Aluminum Content

Novel three dimensional cubic Fm3m mesoporous aluminosilicates (AlKIT‐5) with very high structural order and unprecedented loadings of Al in the silica framework have been successfully prepared for the first time by using non ionic surfactant as a template in a highly acidic medium. The obtained materials have been unambiguously characterized in detail by several sophisticated techniques such as XRD, N₂ adsorption, HRTEM, HRSEM, EDS, elemental mapping, ²⁷Al MAS NMR, and NH₃‐TPD. We also demonstrate that the nature, and the amount of Al incorporation in the silica framework can easily be controlled by simply varying the n_H2O/n_HCl and the n_Si/n_Al ratios, and the Al sources in the synthesis gel. Among the Al sources examined, the Al isopropoxide (AiPr) is superior over other Al sources. ²⁷Al MAS NMR results reveal that the amount of tetrahedral Al in the framework can be controlled by simply adjusting the n_Si/n_Al ratio in the synthesis gel, which increases with increasing the Al incorporation. One of the interesting findings in the work is the increase of the specific surface area, specific pore volume and the pore diameter of AlKIT‐5 with increasing the Al incorporation in the silica framework (up to n_Si/n_Al ratio of 10) while retaining the well‐ordered three dimensional cage type porous structure, and the mechanism for the unusual behavior has been discussed in detail. Finally, the acidity and the catalytic activity in the acetylation of veratrole of the AlKIT‐5 catalysts have been studied and the results have been compared with the several zeolites catalysts. Among the catalysts examined, AlKIT‐5(10) is found to be superior over the zeolites catalysts such as mordenite, zeolite H‐Y, zeolite H‐β, and ZSM‐5.     

Generation of Monodisperse Mesoporous Silica Microspheres with Controllable Size and Surface Morphology in a Microfluidic Device

A one‐step in situ method, termed microfluidic diffusion‐induced self‐assembly, for the synthesis of monodisperse ordered mesoporous silica microspheres, is reported. The method combines microfluidic generation of uniform droplets and subsequent in situ rapid solvent diffusion‐induced self‐assembly within the microfluidic channel. The mesoporous silica microspheres prepared in this way reveal well‐ordered 2D hexagonal mesostructures with unprecedented corrugated surface morphology of disordered mesopores that are larger than 15 nm. It is speculated that the formation of an interfacial subphase and rapid diffusion of solvent to oil are attributed to the formation of the unique surface morphology. It is also shown that the surface morphology and the particle size of the mesoporous silica microspheres can be systematically controlled by adjusting fluidic conditions.     

Cover Picture: Generation of Monodisperse Mesoporous Silica Microspheres with Controllable Size and Surface Morphology in a Microfluidic Device (Adv. Funct. Mater. 24/2008)

A one‐step in situ method, termed microfluidic diffusion‐induced self‐assembly, for the synthesis of monodisperse ordered mesoporous silica microspheres, is reported. The method combines microfluidic generation of uniform droplets and subsequent in situ rapid solvent diffusion‐induced self‐assembly within the microfluidic channel. The mesoporous silica microspheres prepared in this way reveal well‐ordered 2D hexagonal mesostructures with unprecedented corrugated surface morphology of disordered mesopores that are larger than 15 nm. It is speculated that the formation of an interfacial subphase and rapid diffusion of solvent to oil are attributed to the formation of the unique surface morphology. It is also shown that the surface morphology and the particle size of the mesoporous silica microspheres can be systematically controlled by adjusting fluidic conditions.     

Hybrid Periodic Mesoporous Organosilicas

In this study we report the synthesis of a new class of materials called hybrid periodic mesoporous organosilicas (HPMOs). By coupling a silsesquioxane precursor through at least two chemical linkages to the mesopore walls of a pre‐existing periodic mesoporous silica (PMS) or periodic mesoporous organosilica (PMO). Many of the problems of a conventional PMO material can be avoided while ensuring efficient use of the bridging organic functional groups of the silsesquioxane. We demonstrate this concept for PMS by anchoring various silsesquioxanes, such as ethene and ethane silsesquioxanes, to the mesopore walls of the PMS. The addition of anchored silsesquioxane monolayers and multilayers to the mesopore walls also allows for the strict control of the diameter of the mesopore as well as the mesopore wall thickness in the final HPMO material. Additionally it is shown that having the silsesquioxane located solely on the surface of the mesopores in HPMOs gives increased chemical accessibility of the organic bridge‐bonded moiety when compared with their PMO counterparts containing the bridge‐bonded organic both on the surface and within the pore walls.     

Organosilica Materials with Bridging Phenyl Derivatives Incorporated into the Surfaces of Mesoporous Solids

An interesting class of materials is mesoporous organosilica materials containing a bridging, organic group along the pore‐surface. Such materials are prepared from silsesquioxane precursors of the type (R′O)₃Si‐R‐Si(OR′)₃ where R is the bridging organic group of interest, in combination with a lyotropic phase as a template for the generation of the pores. A new silsesquioxane precursor, 1,3‐bis‐(trialkoxysilyl)‐5‐bromobenzene, and the related mesoporous organosilica material containing bromobenzene groups located at the pore walls are presented in the current publication. The latter precursor allows access to the derivatization reactions known for halogenated aromatic compounds. Materials containing phenyl derivatives can be obtained either by chemical modifications starting from the mentioned precursor on the molecular scale, or the modifications can be performed directly at the surfaces of the porous material. Materials with surfaces containing benzoic acid, styrene, and phenylphosphonic acid are described.     

Graphene‐Based Mesoporous SnO2 with Enhanced Electrochemical Performance for Lithium‐Ion Batteries

Graphene‐based metal oxides generally show outstanding electrochemical performance due to the superior properties of graphene. However, the aggregation of active metal oxide nanoparticles on the graphene surface may result in a capacity fading and poor cycle performance. Here, a mesostructured graphene‐based SnO₂ composite is prepared through in situ growth of SnO₂ particles on the graphene surface using cetyltrimethylammonium bromide as the structure‐directing agent. This novel mesoporous composite inherits the advantages of graphene nanosheets and mesoporous materials and exhibits higher reversible capacity, better cycle performance, and better rate capability compared to pure mesoporous SnO₂ and graphene‐based nonporous SnO₂. It is concluded that the synergetic effect between graphene and mesostructure benefits the improvement of the electrochemical properties of the hybrid composites. This facile method may offer an attractive alternative approach for preparation of the graphene‐based mesoporous composites as high‐ performance electrodes for lithium‐ion batteries.     

Synthesis of a Hydrothermally Stable,Periodic Mesoporous Material Containing Magnetite Nanoparticles,and the Preparation of Oriented Films

Magnetite nanoparticles modified covalently with triethoxysilane having a quaternary dicetyl ammonium ion are used together with tetraethylorthosilicate as building blocks to prepare a mesoporous material. Cetyltrimethylammonium bromide is used as a structure‐directing agent under conditions typically used for mesoporous MCM‐41 silicas. The resulting mesoporous material (MAG‐MCM‐41), containing up to 15 wt % of magnetite is characterized by transmission electron microscopy (TEM), isothermal gas adsorption, and X‐ray diffraction. In contrast to siliceous MCM‐41, mesoporous MAG‐MCM‐41 exhibits a remarkable hydrothermal stability. The magnetic properties of MAG‐MCM‐41 are characterized by DC and AC magnetic susceptibility, and by isothermal hysteresis cycles, confirming the long‐range magnetic ordering above 400 K. As evidenced by atomic force microscopy and TEM, the ability to respond to magnetic fields is used to orient films of MAG‐MCM‐41 with the channels perpendicular to a support.     

Ultrathin Mesoporous NiCo2O4 Nanosheets Supported on Ni Foam as Advanced Electrodes for Supercapacitors

A facile two‐step method is developed for large‐scale growth of ultrathin mesoporous nickel cobaltite (NiCo₂O₄) nanosheets on conductive nickel foam with robust adhesion as a high‐performance electrode for electrochemical capacitors. The synthesis involves the co‐electrodeposition of a bimetallic (Ni, Co) hydroxide precursor on a Ni foam support and subsequent thermal transformation to spinel mesoporous NiCo₂O₄. The as‐prepared ultrathin NiCo₂O₄ nanosheets with the thickness of a few nanometers possess many interparticle mesopores with a size range from 2 to 5 nm. The nickel foam supported ultrathin mesoporous NiCo₂O₄ nanosheets promise fast electron and ion transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with an ultrahigh specific capacitance of 1450 F g^?1, even at a very high current density of 20 A g^?1, and excellent cycling performance at high rates, suggesting its promising application as an efficient electrode for electrochemical capacitors.     

Sulfur‐Functionalized Mesoporous Carbon

A simple synthesis route to mesoporous carbons that contain heteroaromatic functionality is described. The sulfur‐functionalized mesoporous carbon (S‐FMC) materials that have been prepared show excellent thermal stability, as well as excellent hydrothermal stability, and stability over a wide range of pH values. These materials also show excellent mercury sorption performance over a broad range of pH, much broader than is possible with thiol‐based functionality or most silica‐based sorbents. The superior performance of these mesoporous heterocarbons as heavy‐metal sorbent material is demonstrated. These materials are shown to be stable at elevated temperatures and extreme pHs, making them ideally suited as a new class of absorbent material.     

Cd1–xMnxS Diluted Magnetic Semiconductors as Nanostructured Guest Species in Mesoporous Thin‐Film Silica Host Media

Recently, we demonstrated the possibility of synthesizing ordered nanowires of diluted magnetic II/VI semiconductors inside the channels of mesoporous silica host structures. Here, we expand this procedure from mesoporous powders to mesoporous thin films. Diluted magnetic semiconductors Cd_1–xMn_xS were synthesized within the pores of mesoporous thin‐film silica host structures by a wet‐impregnation technique using an aqueous solution of the respective metal acetates, followed by drying steps and a conversion to sulfide by thermal H₂S treatment. The presence of Cd_1–xMn_xS nanoparticles inside the pores was proved by powder X‐ray diffraction, infrared and Raman spectroscopy, and transmission electron microscopy. Photoluminescence excitation measurements clearly demonstrate the quantum size effect of the incorporated nanostructured guest species. The quality of the nanoparticles incorporated into the mesoporous films is comparable to that of those inside the mesoporous powders.