π–π Interactions Between Aromatic Groups in Amphiphilic Molecules: Directing Hierarchical Growth of Porous Zeolites

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.     

Characterization of defects and surface structures in microporous materials by HRTEM, HRSEM, and AFM.

High-resolution transmission (HRTEM) and high-resolution scanning electron microscopy as well as atomic force microscopy (AFM), X-ray diffraction, and electron diffraction were used for studying the zeolites MFI, MEL, and the MFIMEL intergrowth system. All three zeolites consisted of individual particles having a size in the range of approximately 0.5 m to 5 m. The particle habits varied from rather cubelike to almost spherelike with many intermediate habits. Typically, the particles of these three zeolites were assembled by many individual blocks that differed in the dimension from about 25 nm to 140 nm as well as in the shape from very frequently almost rectangular (for MFI, MEL, and MFIMEL) to sometimes roundish or irregular habits (mainly for MFIMEL). An estimate shows that some 104 up to more than 106 densely packed blocks typically may assemble each individual zeolite particle or, related to the corresponding unit cell dimension, about 108 up to 1010 unit cells. The fine surface structure of zeolite particles was terracelike with steps between adjacent terraces typically in the range of 20 nm to 60 nm; the minimum step measured was approximately 4 nm. A detailed study of the surface topography was performed by AFM, detecting organic molecules at the block intersections. The presence of topological defects was observed by HRTEM and electron diffraction.     

Minimization of Surface Energies and Ripening Outcompete Template Effects in the Surface Growth of Metal–Organic Frameworks

As well‐oriented, surface‐bound metal–organic frameworks become the centerpiece of many new applications, a profound understanding of their growth mode becomes necessary. This work shows that the currently favored model of surface templating is in fact a special case valid only for systems with a more or less cubic crystal shape, while in less symmetric systems crystal ripening and minimization of surface energies dominate the growth process.     

Vernier‐Templated Synthesis,Crystal Structure,and Supramolecular Chemistry of a 12‐Porphyrin Nanoring

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier‐templated synthesis of a 12‐porphyrin nanoring. NMR and small‐angle X‐ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo‐oligomerization reaction. UV/Vis/NIR titrations show that the three‐component assembly of the 12‐porphyrin nanoring figure‐of‐eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single‐crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular C?H???N contacts involving the tert‐butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12‐porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition.     

Silicalite crystal growth investigated by atomic force microscopy

Atomic force microscopy has been used to image the various facets of two morphologically distinct samples of silicalite. The smaller (20 microm) sample A crystals show 1 nm high radial growth terraces. The larger (240 microm) sample B crystals show growth terraces 1 to 2 orders of magnitude higher than the terraces on sample A with growth edges parallel to the crystallographic axes. Moreover, the terraces on the (010) face are significantly higher than the terraces on the (100) face - inconsistent with the previously proposed 90 degrees intergrowth structure. Sample A highlights that under certain synthetic conditions, silicalite grows in a manner akin to zeolites Y and A, via the deposition of layers comprising, in the case of silicalite, pentasil chains. It is probable that the rate of terrace advance is identical on the (010) and (100) faces, and it is the rate of terrace nucleation that dictates the overall growth rate of each facet and hence the relative size expressed in the final crystal morphology. Analysis of the growth terraces of sample B and detailed consideration of the structures of both MFI, and a closely related material MEL, lead to the proposal of a generalized growth mechanism for silicalite including the incorporation of defects within the structure. These defects are thought to be responsible for both the relative and the absolute terrace heights observed and may also explain the hourglass phenomenon observed by optical microscopy. The implications of this growth mechanism, supported by results of infrared microscopy, generate a new dimension to the continuing debate on the existence of intergrowths within one of the most important structures relevant to zeolite catalysis.     

Lyotropic Liquid Crystal Templating of Groups 11 and 12 Metal Films

Liquid crystal templating has been used to produce metal films with nanometer‐sized pores. While successful templating procedures have been reported for metals from some groups of elements (e.g., groups 9 and 10), no such reports are available for other groups. This work investigates liquid crystal templating procedures for metals from groups 11 and 12. TEM indicates that permanent mesoporous structures are obtained for templated cadmium while copper forms mesoporous structures only temporarily. Silver, gold and zinc could not be templated at all. Reasons for these observations are briefly discussed, underlining the importance of various factors influencing the templating process.     

π–π Interactions Between Aromatic Groups in Amphiphilic Molecules: Directing Hierarchical Growth of Porous Zeolites

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.     

Ordered macroporous quercetin molecularly imprinted polymers: Preparation,characterization, and separation performance

Ordered macroporous molecularly imprinted polymers were prepared by a combination of the colloidal crystal templating method and the molecular imprinting technique by using SiO₂ colloidal crystal as the macroporogen, quercetin as the imprinting template, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker and tetrahydrofuran as the solvent. Scanning electron microscopy and Brunauer–Emmett–Teller measurements show that the ordered macroporous molecularly imprinted polymers have a more regular macroporous structure, a narrower pore distribution and a greater porosity compared with the traditional bulk molecularly imprinted polymers. The kinetic and isothermal adsorption behaviors of the polymers were investigated. The results indicate that the ordered macroporous molecularly imprinted polymers have a faster intraparticle mass transfer process and a higher adsorption capacity than the traditional bulk molecularly imprinted polymers. The ordered macroporous molecularly imprinted polymers were further employed as a sorbent for a solid‐phase extraction. The results show that the ordered macroporous molecularly imprinted polymers can effectively separate quercetin from the Gingko hydrolysate.     

Texture of MFI films grown from seeds

This review describes how the texture of MFI films grown from seed crystal is developed during film preparation. Reports published during the last 5 years are in focus. Relative growth rates in various crystallographic directions, competitive growth, properties of the seed layer, defects, grain boundaries and other parameters influencing the film properties are discussed. Mathematical models describing competitive growth are also discussed. Suitable characterization methods for defects are described. The last part of the review is devoted to diffusion. Diffusion models accounting for texture in MFI films and the influence of texture on diffussion are discussed.     

Synthesis of Fe‐loaded MFI zeolite using silatrane as precursor and its CO activity

Fe‐MFI zeolite was successfully synthesized using silatrane as precursor and tetrapropyl ammonium bromide as template via the sol–gel process and microwave heating technique. The effects of ageing time, heating temperature, heating time and iron concentration were investigated, and it was found that Fe‐MFI synthesis favors higher heating temperatures, but is limited by the degradation of the incorporation of a template molecule. Moreover, longer ageing and heating times promote the incorporation of higher amounts of iron atom in the MFI structure. However, too long an ageing time decreases the incorporation of iron. The lower the percentage Fe loading, the greater the percentage of Fe³⁺ ions incorporated into the MFI framework. The catalytic activity of Fe‐MFI catalyst for the oxidation of CO was studied and it was found that these synthesized catalysts catalyzed the oxidation of CO very well. Copyright © 2005 John Wiley & Sons, Ltd.     

Further studies of a simple atomistic model of silica: thermodynamic stability of zeolite frameworks as silica polymorphs

We have applied our previously reported model of silica based on low coordination and strong association [J. Chem. Phys. 121, 8415 (2004)], to the calculation of phase stability of zeolite frameworks SOD, LTA, MFI, and FAU as silica polymorphs. We applied the method of Frenkel and Ladd for calculating free energies of these solids. Our model predicts that the MFI framework structure has a regime of thermodynamic stability at low pressures and above approximately 1400 K, relative to dense phases such as quartz. In contrast, our calculations predict that the less dense frameworks SOD, LTA, and FAU exhibit no regime of thermodynamic stability. We have also used our model to investigate whether templating extends the MFI regime of thermodynamic stability to lower temperatures, by considering templates with hard-sphere repulsions and mean-field attractions to silica. Within the assumptions of our model, we find that quartz remains the thermodynamically stable polymorph at zeolite synthesis temperatures (approximately 400 K) unless unphysically large template-silica attractions are assumed. These predictions suggest that some zeolites such as MFI may have regimes of thermodynamic stability even without template stabilization.     

Recent Progress in Inorganic Anions Templated Silver Nanoclusters: Synthesis,Structures and Properties

Over recent years, research on the ligand‐protected silver clusters have gained significant interest owing to their unique potential applications in catalysis, organic optoelectronics, and luminescent materials. However, the synthesis of structurally precise high‐nuclearity silver nanoclusters is still challenging and become one of the prime interests of chemists. The controllable synthesis of high‐nuclearity silver nanoclusters involves the ingenious use of capping ligands or/and templating agents. Thereinto, the main role of the templating agents is to promote the order arrangement of silver ions around them to form discrete molecules. Our lab has performed comprehensive studies on the ligand‐protected silver clusters in the past eight years. This review highlights recent progress in the use of inorganic template anions, silver precursors, solvents, and the ligand types in synthesizing high‐nuclearity silver nanoclusters. Furthermore, some interesting photo‐ and electrochemical properties revealed by silver clusters including luminescent thermochromism, electrical conductivity, and electrochemical reduction of H₂O₂ have been also summarized.     

A Rational Repeating Template Method for Synthesis of 2 D Hexagonally Ordered Mesoporous Precious Metals

A repeating template method is presented for the synthesis of mesoporous metals with 2D hexagonal mesostructures. First, a silica replica (i.e., silica nanorods arranged periodically) is prepared by using 2D hexagonally ordered mesoporous carbon as the template. After that, the obtained silica replica is used as the second template for the preparation of mesoporous ruthenium. After the ruthenium species are introduced into the silica replica, the ruthenium species are then reduced by a vapor‐infiltration method by using the reducing agent dimethylamine borane. After the ruthenium deposition, the silica is chemically removed. Analysis by transmission and scanning electron microscopies, a nitrogen‐adsorption–desorption isotherm, and small‐angle X‐ray scattering revealed that the mesoporous ruthenium had a 2D hexagonal mesostructure, although the mesostructural ordering is decreased compared to that of the original mesoporous carbon template. This method is widely applicable to other metal systems. By changing the metal species introduced into the silica replica, several mesoporous metals (palladium and platinum) can be synthesized. Ordered mesoporous ruthenium and palladium, which are not easily attainable by the soft‐templating methods, can be prepared. This study has overcome the composition variation limitations of the soft‐templating method.     

Hybrid lamellar silica: combined template extraction and hydrophilic silanation

The surface modification of lamellar silica prepared by liquid crystal templating has been investigated. Two hydrophilic surface modifier agents, 2-glycidoxypropyltrimethoxysilane and 2-[methoxy(polyethyleneoxy)propyl)]trimethoxysilane, have been tested. Characterizations of the modified silica include thermal analysis, (13)C and (29)Si solid state NMR, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The different characterizations confirmed the preservation of the lamellar morphology and the successful surface modification with both silanes along with the template elimination. The results also indicate that the structure and length of the silanes influence the final lamellar organization as well as the grafting yields and mechanisms.     

Comparison of Templating Abilities of Urea and Thioruea During Photodimerization of Bipyridylethyelene and Stilbazole Crystals

Photodimerization of cocrystals of four bispyridylethylenes and two stilbazoles with urea as a template in the solid state has been investigated following our success with thiourea. Four investigated olefins photodimerized quantitatively to a single dimer in the crystalline state only. The reactivity of urea–olefin crystals is understood on the basis of their packing arrangements in the crystalline state. In reactive crystals the adjacent reactive molecules are within 4.2 Å and parallel, whereas the unreactive ones have their adjacent molecules are farther than 4.6Å and nonparallel. Thus, with the knowledge of crystal packing the reactivity of urea–olefin crystals is predictable on the basis of Schmidt's topochemical postulates. The templating property of urea, similar to thiourea, derives from its ability to form hydrogen bonds with itself and the guest olefins. Despite the similarities in molecular structures of urea and thiourea their subtle electronic properties, yet to be fully understood, affect the crystal packing and consequently their reactivity in the crystalline state. Further work is needed to fully exploit the templating properties of urea.     

Quantitation of melatonin and n‐acetylserotonin in human plasma by nanoflow LC‐MS/MS and electrospray LC‐MS/MS

Melatonin (MEL) and its chemical precursor N‐acetylserotonin (NAS) are believed to be potential biomarkers for sleep‐related disorders. Measurement of these compounds, however, has proven to be difficult due to their low circulating levels, especially that of NAS. Few methods offer the sensitivity, specificity and dynamic range needed to monitor MEL and its precursors and metabolites in small blood samples, such as those obtained from pediatric patients. In support of our ongoing study to determine the safety, tolerability and PK dosing strategies for MEL in treating insomnia in children with autism spectrum disorder, two highly sensitive LC‐MS/MS assays were developed for the quantitation of MEL and precursor NAS at pg/mL levels in small volumes of human plasma. A validated electrospray ionization (ESI) method was used to quantitate high levels of MEL in PK studies, and a validated nanospray (nESI) method was developed for quantitation of MEL and NAS at endogenous levels. In both assays, plasma samples were processed by centrifugal membrane dialysis after addition of stable isotopic internal standards, and the components were separated by either conventional LC using a Waters SymmetryShield RP18 column (2.1 × 100 mm, 3.5 µm) or on a polyimide‐coated, fused‐silica capillary self‐packed with 17 cm AquaC18 (3 µm, 125 Å). Quantitation was done using the SRM transitions m/z 233 → 174 and m/z 219 → 160 for MEL and NAS, respectively. The analytical response ratio versus concentration curves were linear for MEL (nanoflow LC: 11.7–1165 pg/mL, LC: 1165–116500 pg/mL) and for NAS (nanoflow LC: 11.0–1095 pg/mL). Copyright © 2012 John Wiley & Sons, Ltd.     

胶粒晶体模板法制备三维有序大孔材料

使用胶粒模板法制备三维有序大孔材料（three-dimensional ordered macroporous material,3DOM）是一个快速发展的领域。本文综述了3DOM的合成技术,包括各种填充模板的方法、模板的去除方法以及它们在光子晶体、催化材料、生物传感器以及医学等方面的应用前景。     

Oriented Chiral DNA–Silica Film Guided by a Natural Mica Substrate

The formation of highly ordered chiral organic/inorganic films with high density and long‐range orientation is important in constructing chiral devices, such as broadband polarization devices, liquid‐crystal displays, or negative‐reflection materials. A feasible strategy is presented to fabricate three‐dimensional mesostructured chiral DNA–silica assemblies into large‐scale oriented arrangements. The highly ordered film was aligned by a mica crystal substrate with the bridging effect of suitable divalent metal ions, followed by the growth of the DNA–silica composite by bottom‐up assembly with a “quartet templating” method. This simple and effective route would perform well in the alignment and arrangement of highly charged biomolecules, such as polypeptides, proteins, viruses, and their inorganic assemblies, and furthermore could allow the fabrication of chiral optical materials with long‐range ordering.     

MFI/MFI核壳分子筛的合成及催化性能研究

通过对核相ZSM-5的预处理步骤和在温和水热条件下的二次生长, 合成了壳层硅铝比高、核相硅铝比低、纳米晶壳层致密的MFI(核)/MFI(壳)型核壳分子筛材料. 考察了晶化温度和晶化时间对高硅壳层MFI/MFI核壳型沸石分子筛的合成的影响, 其适宜的合成条件为晶化温度高于130 ℃, 晶化时间19 h. 核相ZSM-5的预处理步骤对于成功合成此特殊核壳型分子筛材料十分关键. 与普通ZSM-5沸石分子筛相比, MFI/MFI核壳分子筛在催化甲苯甲基化反应时的失活效率显著降低.     

Controlling the shape and alignment of mesopores by confinement in colloidal crystals: designer pathways to silica monoliths with hierarchical porosity

Monolithic pieces of hierarchically structured silica, containing both periodic macropores and mesopores with well-controlled architecture, are synthesized by dual templating methods. Colloidal crystal templating with close-packed arrays of poly(methyl methacrylate) spheres yields regular, highly interconnected macropores a few hundred nanometers in diameter, and templating with nonionic surfactants produces mesoporosity (2.5-5.1 nm pore diameters) in the macropore walls. Several distinct mesostructures can be achieved within the silica skeleton, depending on the choice of surfactant, co-surfactant, and processing conditions. In the three-dimensional (3D) confinement of the colloidal crystal template, wormlike channels, cubic (Pm3n), or two-dimensional (2D) hexagonal (P6mm) mesostructures are produced with the surfactant Brij 56 (C16H33(OCH2CH2)nOH (n approximately 10) and dodecane as cosurfactant. In the 2D hexagonal structure, channels are oriented perpendicular to the polymer spheres, thereby connecting adjacent macropores through the silica walls. This orientation contrasts with channel alignment parallel to latex spheres when the polymeric surfactant Pluronic P123 (EO20PO70EO20) is used. On the basis of high-resolution 3D transmission electron microscopy, scanning electron microscopy, small-angle X-ray scattering, and nitrogen sorption measurements, structural and textural properties of the monoliths are described in detail as a function of the synthesis parameters. The control over the mesoarchitecture of these silica-surfactant systems in 3D confinement is explained by considering the relative dimensions of the mesostructures with respect to the interstitial space in the latex template, interfacial interactions, entropic effects, and structural frustration.