Flexible and iridescent chiral nematic mesoporous organosilica films

Nanocrystalline cellulose (NCC) has been used to template ethylene-bridged mesoporous organosilica films with long-range chirality and photonic properties. The structural color of the organosilica films results from their chiral nematic ordering, can be varied across the entire visible spectrum, and responds to the presence of chemicals within the mesopores. To synthesize these materials, acid hydrolysis was used to remove the NCC template without disrupting the organosilica framework. The resulting mesoporous organosilica films are much more flexible than brittle mesoporous silica films templated by NCC. These materials are the first of a novel family of chiral mesoporous organosilicas with photonic properties.     

仿生介孔二氧化硅用于高效液相色谱拆分手性化合物

仿生介孔硅是以有机物作为模板,可有效复刻模板的独特形貌,从而得到其相同或相似结构孔径的介孔硅。本文从仿生的观点出发,从蟹壳中提取得到几丁质膜,将其用作模板制备了仿生手性向列型介孔二氧化硅,并用其制备了液相色谱柱,进行了手性化合物拆分实验。结果表明,该色谱固定相对10个手性化合物有一定的手性分离效果。     

Fluorescence Emission from 2,6‐Naphthylene‐Bridged Mesoporous Organosilicas with an Amorphous or Crystal‐Like Framework

We report that 2,6‐naphthylene‐bridged periodic mesoporous organosilicas exhibit unique fluorescence behavior that reflects molecular‐scale periodicities in the framework. Periodic mesoporous organosilicas consisting of naphthalene–silica hybrid frameworks were synthesized by hydrolysis and condensation of a naphthalene‐derived organosilane precursor in the presence of a template surfactant. The morphologies and meso‐ and molecular‐scale periodicities of the organosilica materials strongly depend on the synthetic conditions. The naphthalene moieties embedded within the molecularly ordered framework exhibited a monomer‐band emission, whereas those embedded within the amorphous framework showed a broad emission attributed to an excimer band. These results suggest that the naphthalene moieties fixed within the crystal‐like framework are isolated in spite of their densely packed structure, different from conventional organosilica frameworks in which only excimer emission was observed for both the crystal‐like and amorphous frameworks at room temperature. This key finding suggests a potential to control interactions between organic groups and thus the optical properties of inorganic/organic hybrids.     

Hard templating of nanocrystalline titanium dioxide with chiral nematic ordering

Anatase TiO(2) nanocrystals have been organized into high-surface-area (150-230 m(2) g(-1)) mesoporous films with long-range chiral nematic ordering. The chiral structure of the anatase films causes them to selectively reflect circularly polarized light and appear iridescent. These materials show replication of structural features found in the silica template on nanometer to millimeter length scales.     

Periodic Mesoporous Organosilica Materials: Self‐Assembly of Carbamothioic Acid‐Bridged Organosilane Precursors

A new series of carbamothioic acid‐containing periodic mesoporous organosilica (PMO) materials has been synthesized by a direct cocondensation method, in which an organosilica precursor N,S‐bis[3‐(triethoxysilyl)propyl]carbamothioic acid (MI) is treated with tetraethyl orthosilicate (TEOS), and the nonionic surfactant Pluronic 123 (P123) is used as a template under acidic conditions in the presence of inorganic additives. Moreover, the synthesis of the PMO material consisting of the MI precursor without TEOS has been realized. These novel PMO materials have large surface areas, well‐ordered mesoporous structures, hollow fiberlike morphologies, and thick walls. They are also structurally well‐ordered with a high organosilica precursor content, and the carbamothioic acid groups are thermally stable up to 250 °C. Furthermore, the organosilica materials exhibit hydrothermal stability in basic solution.     

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.     

Responsive Mesoporous Photonic Cellulose Films by Supramolecular Cotemplating

Cellulose‐based materials have been and continue to be exceptionally important for humankind. Considering the bioavailability and societal relevance of cellulose, turning this renewable resource into an active material is a vital step towards sustainability. Herein we report a new form of cellulose‐derived material that combines tunable photonic properties with a unique mesoporous structure resulting from a new supramolecular cotemplating method. A composite of cellulose nanocrystals and a urea–formaldehyde resin organizes into a chiral nematic assembly, which yields a chiral nematic mesoporous continuum of desulfated cellulose nanocrystals after alkaline treatment. The mesoporous photonic cellulose (MPC) films undergo rapid and reversible changes in color upon swelling, and can be used for pressure sensing. These new active mesoporous cellulosic materials have potential applications in biosensing, optics, functional membranes, chiral separation, and tissue engineering.     

Non‐surfactant template‐directed synthesis of SiO2‐polyimide hybrid self‐standing films with ordered mesoporous structure

The silica‐PI hybrid self‐standing films with ordered mesoporous structure have been prepared by using dibenzoyl‐L ‐tartaric acid (L ‐DBTA) as non‐surfactant template under mild sol–gel route. Polyimide matrix was obtained from polyamic acid (PAA) via thermal imidization process and the template was removed in this process. The PI‐based hybrid film with 20 wt% SiO₂ obtained from DBTA presented the ordered mesoporous channels with average pore size of about 2.0 nm and BET surface area of 1167 m²/g. FTIR and SEM studies indicated that the hydrogen bond interaction between the carboxylic groups of DBTA and benzamide bonds of PAA made the PAA possibly participate in the assembly process of the aggregates of the non‐surfactant template molecules. The mechanical, thermal and some physical properties of these hybrid films materials were also characterized. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of N‐Doped Mesoporous Carbon Nanorods through Nano‐Confined Reaction: High‐Performance Catalyst Support for Hydrogenation of Phenol Derivatives

Traditional hard‐template methods for the preparation of mesoporous carbon structures have been well developed, but there are difficulties associated with complete filling of the organic precursors in ordered mesochannels and exact replication of the templates. Herein, mesoporous carbon nanorods (meso‐CNRs) were synthesized through thermal condensation of furfuryl alcohol followed by the nano‐confined decomposition of polyfurfuryl alcohol in silica nanotubes (SiO₂ NTs) with porous shells. Limited and slow release of gaseous water through the porous shells and finite polyfurfuryl precursor inside silica nanotubes are responsible for the formation of the mesoporous structures. Nitrogen can be doped into the meso‐CNRs by adding guanidine hydrochloride to the precursors. The nitrogen dopant not only stabilizes the ultrasmall and active Pd nanocatalyst in the meso‐CNRs but also increases the electron density of Pd and accelerates the dissociation of H₂, both of which increase the catalytic activity of the Pd catalyst in hydrogenation reactions.     

Periodic Mesoporous Organosilicas as Efficient Nanoreactors in Cascade Reactions Preparing Cyclopropanic Derivatives

In this work, three organosilica precursors functionalized with carbamate moieties were synthesized by condensing of 3‐isocyanatopropyltriethoxysilane and coupling regents of either hydroquinone (HQ), bisphenol A (BPA), or 1,1′‐bi‐2‐naphthol (BN). These organosilica precursors were covalently bonded in the framework of periodic mesoporous organosilicas by co‐condensation and hydrolysis with tetraethyl orthosilicate (TEOS) under hydrothermal treatment. The compositions and physical properties were characterized with FTIR, XRD, thermogravimetric/differential thermal analysis (TG/DTA), ²⁹Si NMR, ¹³C NMR spectroscopies, SEM, TEM, and BET technologies. These characterizations suggest that three different structures were formed as the result of different sizes and compositions of the organosilica precursors. The three mesoporous organosilicas were applied as heterogeneous catalysts in the one‐pot cascade Knoevenagel and Michael cyclopropanic reactions for the synthesis of cyclopropanic derivatives and showed excellent activity and selectivity. The highest conversion was obtained with mesoporous catalyst (MC)‐HQ owing to its ordered mesostructure, highest surface area, and weakest stereo effect of the organic linking groups compared with MC‐BAP and MC‐BN. This methodology employed cheaper and more easily obtainable raw materials as reagents over the traditional alkene additive system and these heterogeneous catalysts exhibit superior performance and recyclability than typical homogeneous organic catalysts.     

嵌段共聚物与阳离子表面活性剂混合模板合成介孔SiO_2

利用三嵌段共聚物EO_(20)PO_(70)EO_(20)与阳离子表面活性剂CTAB作为混合 模板合成了内部孔结构与外观形貌同时受到调控的介孔氧化硅。与使用单一共聚物 模板制备的介孔氧化硅相比，在混合模板作用下得到的介孔氧化硅的孔结构有序度 降低，而孔径则随混合模板中共聚物的质量分数的降低而减小。在EO_(20)PO_(70) EO_(20)与CTAB质量比为1:1时可得到形貌完好、表面光滑的介孔氧化硅微米球，其 平均孔径为3.2nm，比表面积为972m~2/g。     

电解质诱导聚集初级粒子制备介孔SiO_2材料

在无模板剂的条件下,通过在Stber合成过程中引入外加电解质成功地制备了具有介孔结构的SiO2粒子.实验结果表明,通过电解质的加入可以诱导Stber过程中初级SiO2粒子的聚集,从而得到了具有介孔结构和较强表面吸附能力的SiO2粒子.     

Characterization Studies on the Ionic Liquid-Templated Mesoporous Silica with Wormlike Pores

This article reports a novel preparation of wormlike mesoporous silica with 1-hexadecane-3-methylimidazolium bromide (C₁₆MIM)Br, a kind of room-temperature ionic liquids (RTILs), as a template via a sol-gel nanocasting technique. The characterization studies were carried out in contrast with that of the mesoporous silica with cetyltrimethylammonium bromide (CTAB), a usually used template, which has the same alkyl chain length with (C₁₆MIM)Br. The structures of the silica materials have been characterized by Transmission electron microscopy (TEM), High-resolution TEM (HRTEM) and N₂ adsorption-desorption measurements. The results show that both the mesoporous materials prepared with different templates respectively can form regular wormlike mesopores with ca. 2 nm in pore diameter. They also have large BET surface areas with narrow size distribution. Compared to the CTAB-template mesoporous silica, the material with (C₁₆MIM)Br as a template has highly uniform pore size and larger surface area. In addition, the formation mechanism of the wormlike mesopores with RTIL has been proposed by an electrostatic charge matching assembly-pathway and steric factor.     

苯官能化MCM-41的合成、表征、磺酰化及与二胺的反应

以三乙氧基硅基苯((C₂H₅O)₃Si-Ph，（(triethoxysilyl)benzene，TESB)以及正硅酸乙酯（TEOS）的混合液为硅源，以溴代十六烷基吡啶(CPBr)为模板剂，在HCl介质中合成了苯官能化的有机-无机杂化介孔分子筛MCM-41。对合成的分子筛用FT-IR、PXRD、TEM、N₂吸附-脱附等手段进行了表征。结果表明，合成的苯官能化的有机-无机杂化介孔分子筛具有良好的介孔孔道结构。用三甲基氯硅烷对分子筛表面的Si-OH进行了封端处理，用氯磺酸对合成的苯官能化的有机-无机杂化介孔分子筛进行了磺酰化，并与各种二胺进行了反应。     

气-液界面有序介孔SiO2无机膜的仿生合成

早在几百万年以前,自然界就通过生物矿化过程形成了结构高度有序的有机/无机复合材料,如哺乳动物的牙床、骨骼以及贝壳珍珠层等[1]。随着对天然生物材料生物矿化过程研究的逐渐深入,材料研究者从中得到极为重要的启示:先形成有机物自组装体,无机先驱物在自组装聚集体与溶液相的界面处发生化学反应,在有机自组装体的模板作用下,形成有机/无机复合体,再将有机模板去除即可得到具有一定形状与组织结构的无机材料。这种模仿生物矿化中无机物在有机物调制下形成过程的材料合成,称为仿生合成(biomimetic synthesis)[2]。仿生合成过程中,通过选择有…     

Functionalized Periodic Mesoporous Organosilica: A Highly Enantioselective Catalyst for the Michael Addition of 1,3‐Dicarbonyl Compounds to Nitroalkenes

A functionalized periodic mesoporous organosilica with incorporated chiral bis(cyclohexyldiamine)‐based Ni^II complexes within the silica framework was developed by the co‐condensation of (1R,2R)‐cyclohexyldiamine‐derived silane and ethylene‐bridge silane, followed by the complexation of NiBr₂ in the presence of (1R,2R)‐N,N′‐dibenzylcyclohexyldiamine. Structural characterization by XRD, nitrogen sorption, and TEM disclosed its orderly mesostructure, and FTIR and solid‐state NMR spectroscopy demonstrated the incorporation of well‐defined single‐site bis(cyclohexyldiamine)‐based Ni^II active centers within periodic mesoporous organosilica. As a chiral heterogeneous catalyst, this functionalized periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in the asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes, comparable to those with homogeneous catalysts. In particular, this heterogeneous catalyst could be recovered easily and reused repeatedly up to nine times without obviously affecting its enantioselectivity, thus showing good potential for industrial applications.     

Photonic Patterns Printed in Chiral Nematic Mesoporous Resins

Chiral nematic mesoporous phenol‐formaldehyde resins, which were prepared using cellulose nanocrystals as a template, can be used as a substrate to produce latent photonic images. These resins undergo swelling, which changes their reflected color. By writing on the films with chemical inks, the density of methylol groups in the resin changes, subsequently affecting their degree of swelling and, consequently, their color. Writing on the films gives latent images that are revealed only upon swelling of the films. Using inkjet printing, it is possible to make higher resolution photonic patterns both as text and images that can be visualized by swelling and erased by drying. This novel approach to printing photonic patterns in resin films may be applied to anti‐counterfeit tags, signage, and decorative applications.     

Synthesis of highly ordered mesoporous crystalline WS(2) and MoS(2) via a high-temperature reductive sulfuration route

A high-temperature reductive sulfuration method is demonstrated to synthesize highly ordered mesoporous metal sulfide crystallites by using mesoporous silica as hard templates. H2S gas is utilized as a sulfuration agent to in situ convert phosphotungstic acid H3PW12O40.6H2O to hexagonal WS2 crystallites in the silica nanochannels at 600 degrees C. Upon etching silica, mesoporous, layered WS2 nanocrystal arrays are produced with a yield as high as 96 wt %. XRD, nitrogen sorption, SEM, and TEM results reveal that the WS2 products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure (space group, p6mm) and rodlike morphology, analogous to the mother template. The S-W-S trilayers of the WS2 nanocrystals are partially oriented, parallel to the mesochannels of the SBA-15 template. This orientation is related with the reduction of the high-energy layer edges in layered metal dichalcogenides and the confinement in anisotropic nanochannels. The mesostructure can be 3-D cubic bicontinuous if KIT-6 (Iad) is used as a hard template. Mesoporous WS2 replicas have large surface areas (105-120 m2/g), pore volumes ( approximately 0.20 cm3/g), and narrow pore size distributions ( approximately 4.8 nm). By one-step nanocasting with the H3PMo12O40.6H2O (PMA) precursor into the mesochannels of SBA-15 or KIT-6 hard template, highly ordered mesoporous MoS2 layered crystallites with the 2-D hexagonal (p6mm) and 3-D bicontinuous cubic (Iad) structures can also be prepared via this high-temperature reductive sulfuration route. When the loading amount of PMA precursor is low, multiwalled MoS2 nanotubes with 5-7 nm in diameter can be obtained. The high-temperature reductive sulfuration method is a general strategy and can be extended to synthesize mesoporous CdS crystals and other metal sulfides.     

Surfactant‐directed one‐pot preparation of novel Ti‐containing mesomaterial with improved catalytic activity and reusability

Titanium was incorporated in ionic liquid based periodic mesoporous organosilica to prepare a nanostructured catalyst (Ti@PMO‐IL) with high activity. Procedure for the synthesis of Ti@PMO‐IL was followed according the simultaneous hydrolysis and condensation of alkylimidazolium ionic liquid, tetramethoxysilane (TMOS) and tetrabutylorthotitanate (TBOT) where a surfactant template was used together with a simple acid‐based catalytic aproach. N₂ adsorption isotherm of the Ti@PMO‐IL was studied to measure its mean pore volume, pore size distribution and specific surface area. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was applied to identify the chemical bonds present in Ti@PMO‐IL. The morphology of this nanomaterial was investigated by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) image was used to study mesoporosity and structure order of the catalyst. The catalytic activity of Ti@PMO‐IL was then studied and found to be efficient and reusable to catalyze Hantzsch reaction.     

Organorhodium‐Functionalized Periodic Mesoporous Organosilica: High Hydrophobicity Promotes Asymmetric Transfer Hydrogenation in Aqueous Medium

Three organosilica‐bridged periodic mesoporous organosilicas were prepared by the immobilization of a chiral N‐sulfonylated diamine‐based organorhodium complex within their silicate network. Structural analysis and characterization confirmed their well‐defined single‐site active rhodium centers, whilst electron microscopy revealed their highly ordered hexagonal mesostructures. Among these three different organosilica‐bridged periodic mesoporous organosilicas, the ethylene‐bridged periodic mesoporous organosilica catalyst exhibited excellent heterogeneous catalytic activity and high enantioselectivity in the aqueous asymmetric transfer hydrogenation of aromatic ketones. This superior catalytic performance was attributed to its salient hydrophobicity, whilst its comparable enantioselectivity relative to the homogeneous catalyst was derived from the confined nature of the chiral organorhodium catalytic sites. Furthermore, this ethylene‐bridged periodic mesoporous organosilica could be conveniently recovered and reused at least 12 times without the loss of its catalytic activity. This feature makes this catalyst attractive for practical organic synthesis in an environmentally friendly manner. This study offers a general way of optimizing the bridged organosilica moiety in periodic mesoporous organosilicas, thereby enhancing its catalytic activity in heterogeneous catalysis.