Functionalized periodic mesoporous organosilicas: Hierarchical and chiral materials

The integration of organic and inorganic fragments within the pore walls of the periodic mesoporous organosilicas (PMOs) represents one of the recent breakthroughs in material science. The resulting PMOs are promising materials for applications in such areas as catalysis, adsorption, separation and drug-delivery. We summarize here the recent progress made in the synthesis of PMOs with hierarchical structures and large functional groups, with special emphasis on the chiral mesoporous organosilicas and their ...     

Periodic Mesoporous Silicas and Organosilicas: An Overview Towards Catalysis

Micelle-templated mesoporous and organic–inorganic hybrid mesoporous materials are important in many fields of material research, especially for hosting catalysts in confined space. Among this class, the recent discovery of periodic mesoporous organosilicas (PMOs) represent an exciting new group of organic–inorganic nanocomposites targeted for a broad range of applications ranging from catalysis to microelectronics. Compared to the earlier generation of organic–inorganic hybrid mesoporous samples, obtained by the cocondensation reaction or by the grafting reaction, PMOs represent the right combination of organic and inorganic groups in the frame wall positions. This article reviews the current state of art in organic–inorganic hybrid mesoporous material research with special emphasis over periodic mesoporous organosilica materials having various redox centers (Ti, V, Cr) suitable for oxidation reactions as well as acidic sites (Al, –SO₃H) for the organic transformation of bulky molecules.     

Ordered mesoporous materials at the beginning of the third millennium: new strategies to create hybrid and non-siliceous variants

In recent years, research efforts in the field of ordered mesoporous materials are shifting towards either hybrid materials, containing both inorganic (typically silica) and organic functionalities, or towards variants that do not contain silica at all. Promising examples of hybrid materials are periodic mesoporous organosilicas (PMOs); examples of non-siliceous mesoporous materials are carbons, polymers and metal oxides. They can be further tuned to obtain structures with a wide range of functional groups, and are candidates for applications in adsorption, catalysis, sensoring, microelectronics and several other applications.     

Synthesis and Characterization of Alkyl‐Imidazolium‐Based Periodic Mesoporous Organosilicas: A Versatile Host for the Immobilization of Perruthenate (RuO4−) in the Aerobic Oxidation of Alcohols

The preparation and characterization of a set of periodic mesoporous organosilicas (PMOs) that contain different fractions of 1,3‐bis(3‐trimethoxysilylpropyl)imidazolium chloride (BTMSPI) groups uniformly distributed in the silica mesoporous framework is described. The mesoporous structure of the materials was characterized by powder X‐ray diffraction, transmission electron microscopy, and N₂ adsorption–desorption analysis. The presence of propyl imidazolium groups in the silica framework of the materials was also characterized by solid‐state NMR spectroscopy and diffuse‐reflectance Fourier‐transform infrared spectroscopy. The effect of the BTMSPI concentration in the initial solutions on the structural properties (including morphology) of the final materials was also examined. The total organic content of the PMOs was measured by elemental analysis, whereas their thermal stability was determined by thermogravimetric analysis. Among the described materials, it was found that PMO with 10 % imidazolium content is an effective host for the immobilization of perruthenate through an ion‐exchange protocol. The resulting Ru@PI‐10 was then employed as a recyclable catalyst in the highly efficient aerobic oxidation of various types of alcohols.     

Functionalizing inorganic solids: towards organic-inorganic nanostructured materials for intelligent and bioinspired systems

The design, preparation, and properties of organic-inorganic hybrid compounds are described and discussed with respect to their potential uses as intelligent and bioinspired materials. Several synthesis strategies based on intercalation in 2D solids, the grafting of organic groups onto silica and silicates, and the self-assembly of organo-silica materials are presented, focusing on the soft procedures that are used to modify the functionality of the inorganic substrates. The combination of both organic and inorganic moieties at the nanometer level forms the basis for preparing multifunctional solids that are provided with specific functions in response to different types of stimuli. In some cases these resemble materials that are found in biological systems. Examples include organic-inorganic membranes that are based on intercalated macrocyclic compounds and bi-layer vesicles that consist of alkyl long-chains arranged either in the confined region of layered silicates or as self-organized organo-silica micelles. The role of certain hybrid materials such as membranes provides a different approach to the development of artificial liposomes and other mimetic systems that have an organic-inorganic composition and nanostructural organization. Their potential uses for DDS or DNA-dense phases are also discussed and novel alternatives to bioinspired systems development are proposed.     

A fast convenient method to prepare hybrid sol-gel materials with low volume-shrinkages

We present a simple and fast method for the synthesis of polyacrylates-silica hybrid materials with significantly low volume shrinkages through the sol-gel reactions of tetraethyl orthosilicate and 2-hydroxyethyl methacrylate along with the free-radical polymerization of the acrylate monomer. The volume shrinkage from the processible sol to the final product was about 6–20% for the hybrid materials having the silica contents up to about 50 wt-%. As a result of the low shrinkage, crack-free, transparent and monolithic hybrid materials of relatively large sizes can be prepared within a short period of 6 to 12 hours. The formation of covalent bonding between the organic and the silica components in the hybrid materials was demonstrated. Thermal stability of the polyacrylate component in the hybrid materials were found to be higher than that of the bulk polymer. Other vinyl polymers such as poly(methyl methacrylate) and polyacrylonitrile have also been incorporated into the inorganic silica sol-gel matrix by using this method.     

含金属笼型倍半硅氧烷的研究进展

倍半硅氧烷作为催化剂载体硅胶表面结构与性能研究的模型,可以通过表征其表面反应性质来直观认识硅胶负载型催化剂的作用机制。过去几十年来,倍半硅氧烷的研究呈现飞跃式的发展态势,开发出许多新化合物和新合成方法,并在一些催化过程中得到应用。将倍半硅氧烷作为金属化合物的配体,极大地丰富了元素化学的内容。本文重点介绍了合成含金属笼型倍半硅氧烷的相关进展,同时介绍了含金属笼型倍半硅氧烷在聚合物材料应用中的研究。     

Highly Carboxylic‐Acid‐Functionalized Ethane‐Bridged Periodic Mesoporous Organosilicas: Synthesis,Characterization, and Adsorption Properties

Functionalization of periodic mesoporous organosilicas (PMOs) with high loadings of pendant organic groups to form bifunctional PMOs with ordered mesostructures remains a challenging objective. Herein, we report that well‐ordered ethane‐bridged PMOs functionalized with exceptionally high loadings of pendant carboxylic acid groups (up to 80 mol % based on silica) were synthesized by the co‐condensation of 1,4‐bis(trimethoxysilyl)ethane (BTME) and carboxyethylsilanetriol sodium salt (CES) with Pluronic P123 as the template and KCl as an additive under acidic conditions. The bifunctional materials were characterized by using a variety of techniques, including powder X‐ray diffraction, nitrogen‐adsorption/desorption, TEM, and solid‐state ¹³C and ²⁹Si NMR spectroscopy. Zeta‐potential measurements showed that the surface negative charges increased with increasing the CES content. This property makes them potential candidates for applications in drug adsorption. The excellent adsorption capacity of these bifunctional PMOs towards an anticancer drug (doxorubicin) was also demonstrated.     

Synthesis and lysozyme adsorption of rod-like large-pore periodic mesoporous organosilica

Highly ordered rod-like large-pore periodic mesoporous organosilica (PMO) was successfully synthesized at low acid concentration with the assistance of inorganic salt using triblock copolymer P123 as a template. The roles of inorganic salt and acidity in the production of highly ordered mesostructure and the morphology control of PMOs were investigated. It was found that the inorganic salt can significantly widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rod-like PMOs can only be synthesized in a narrow range of acid and salt concentrations, which were sensitive to induction time. The adsorption of lysozyme on PMO was studied at different pH values in comparison with adsorption on pure silica material under controlled morphology and pore structure. It was found that the adsorption capacity of lysozyme on the PMO was lower than that on pure SBA-15 silica material and the adsorption amounts are larger at pH 9.6 than at 7.0 for both materials. The results show that the electrostatic interaction between lysozyme and PMO/SBA-15 surface is more dominant than the hydrophobic forces and the interaction of neighboring lysozyme molecules also plays an important role.     

Synthesis, structure, and physical properties of hybrid nanocomposites for solid-state dye lasers

We report on the synthesis, structural characterization, physical properties, and lasing action of two organic dyes, Rhodamine 6G (Rh6G) and Pyrromethene 597 (PM597), incorporated into new hybrid organic-inorganic materials, where the organic component was either poly(2-hydroxyethyl-methacrylate) (PHEMA) or copolymers of HEMA with methyl methacrylate (MMA), and the inorganic counterpart consisted of silica derived from hydrolysis-condensation of methyltriethoxysilane (TRIEOS) in weight proportion of up to 30%. Lasing efficiencies of up 23% and high photostabilities, with no sign of degradation in the initial laser output after 100 000 pump pulses at 10 Hz, were demonstrated when pumping the samples transversely at 534 nm with 5.5 mJ/pulse. A direct relationship could be established between the structure of the hybrid materials, analyzed by solid-state NMR, and their laser behavior. An inorganic network dominated by di-/tri- substituted silicates in a proportion approximately 35:65, corresponding to samples of HEMA with 15 and 20 wt % proportion of TRIEOS, optimizes the lasing photostability. The thermal properties of these materials, together with the high homogeneity revealed by atomic force microscopy (AFM) images, even in compounds with high silica content, indicate their microstructure to be a continuous phase, corresponding to the polymer matrix, which "traps" the silica components at molecular level via covalent bonding, with few or no silica islands.     

Epoxide Opening versus Silica Condensation during Sol–Gel Hybrid Biomaterial Synthesis

Hybrid organic–inorganic solids represent an important class of engineering materials, usually prepared by sol–gel processes by cross‐reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3‐Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid‐material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2–11) was deeply investigated for the first time by solution‐state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy‐ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol–gel hybrid biomaterials with tuneable properties.     

Step‐Up Synthesis of Periodic Mesoporous Organosilicas with a Tyrosine Framework and Performance in Horseradish Peroxidase Immobilization

New amino‐acid‐bridged periodic mesoporous organosilicas (PMOs) were constructed by hydrolysis and condensation reactions under acid conditions in the presence of a template. The tyrosine bissilylated organic precursor (TBOS) was first prepared through a multistep reaction by using tyrosine (a natural amino acid) as the starting material. PMOs with the tyrosine framework (Tyr‐PMOs) were constructed by simultaneously using TBOS and tetraethoxysilane as complex silicon sources in the condensation process. All the Tyr‐PMOs materials were characterized by XRD, FTIR spectroscopy, N₂ adsorption–desorption, TEM, SEM, and solid‐state ²⁹Si NMR spectroscopy to confirm the structure. The horseradish peroxidase (HRP) enzyme was first immobilized on these new Tyr‐PMOs materials. Optimal conditions for enzyme adsorption included a temperature of 40 °C, a time of 8 h, and a pH value of 7. Furthermore, the novel Tyr‐PMOs materials could store HRP for approximately 40 days and maintained the enzymatic activity, and the Tyr‐PMOs–10 % HRP with the best immobilization effect could be reused at least eight times.     

Flexible inorganic–organic hybrids with dual inorganic components

Combining multiple inorganic components is an effective approach to improve the mechanical properties of inorganic–organic hybrid materials. The inorganic components can form interactions with the organic polymer matrix, and there is thus a need to understand the reinforcement mechanism under the optimal combination of organic polymer and inorganic particles. In this work, we prepared a series of dual inorganic particle–based titania/silica–poly(tetrahydrofuran)–poly(ε-caprolactone) (TiO₂/SiO₂–PTHF–PCL) hybrids by means of simultaneous cationic ring-opening polymerization and sol–gel reaction. In addition to constructing hybrid networks, the SiO₂ and TiO₂ components play important roles in multiple toughening mechanisms. The prepared dual inorganic hybrids feature enhanced thermal stability and mechanical properties when compared with the ones with a single inorganic component. The optimized mixing of such two inorganic components is identified through mechanical tests, revealing that the hybrid polymer₇₀/(Si_0.6Ti_0.4)₃₀ (70/18/12 mass ratio) has the highest compressive failure strain (80%) and compressive ultimate strength (1.3 MPa) as well as storage modulus (120 kPa), enabling elongation of up to 37% when compared with its original length. We thus find that the dual inorganic component approach is an effective strategy to enhance the mechanical properties of hybrid materials, suggesting potential applications as scaffolds for tissue engineering and soft robotics.     

Synthesis of large-pore methylene-bridged periodic mesoporous organosilicas and its implications

In this article, we report the synthesis of methylene-bridged periodic mesoporous organosilicas (PMOs) of the SBA-15 type. The materials were characterized by SAXS, BET, NMR, FESEM, and TEM. It was found that the synthesis of methylene-bridged SBA-15 PMOs requires more rigorous conditions than that of SBA-15 PMOs bearing organic bridges other than methylene. A mild acidic environment, which slows down the hydrolysis and condensation rates of the precursor, with the assistance of a salt, which enhances precursor-template interaction, should be used to synthesize high-quality large-pore methylene-bridged PMOs. We attributed this to the fast hydrolysis and condensation rates and the rigid backbone of precursor 1,2-bis(triethoxysilyl)methylene. By examining and comparing the synthesis of three large-pore PMOs with different bridges, we concluded that the inductive, bridging, and conformation effects of the organic bridging group play an important role in the synthesis of large-pore PMO materials.     

无机材料的仿生合成

生物矿化重要的特征之一是细胞分泌的有机基质调制无机矿物的成核和生长, 形成具有特殊组装方式和多级结构特点的生物矿化材料(如骨、牙和贝壳)。仿生合成就是将生物矿化的机理引入无机材料合成, 以有机物的组装体为模板, 去控制无机物的形成,制备具有独特显微结构特点的无机材料, 使材料具有优异的物理和化学性能。仿生合成已成为无机材料化学的研究前沿。本文综述了无机材料仿生合成的发展现状。     

Syntheses, properties and applications of periodic mesoporous organosilicas prepared from bridged organosilane precursors

Periodic mesoporous organosilicas (PMOs) prepared by surfactant-directed polycondensation of bridged organosilane precursors are promising for a variety of next-generation functional materials, because their large surface areas, well-defined nanoporous structures and the structural diversity of organosilica frameworks are advantageous for functionalization. This critical review highlights the unique structural features of PMOs and their expanding potential applications. Since the early reports of PMOs in 1999, various synthetic approaches, including the selection of hydrolytic reaction conditions, development of new precursor compounds, design of templates and the use of co-condensation or grafting techniques, have enabled the hierarchical structural control of PMOs from molecular- and meso-scale structures to macroscopic morphology. The introduction of functional organic units, such as highly fluorescent π-conjugates and electroactive species, into the PMO framework has opened a new path for the development of fluorescent systems, sensors, charge-transporting materials and solid-state catalysts. Moreover, a combinational materials design approach to the organosilica frameworks, pore wall surfaces and internal parts of mesopores has led to novel luminescent and photocatalytic systems. Their advanced functions have been realized by energy and electron transfer from framework organics to guest molecules or catalytic centers. PMOs, in which the precise design of hierarchical structures and construction of multi-component systems are practicable, have a significant future in a new field of functional materials (93 references).     

孔道中杂合-β-环糊精的有机-无机手性固定相的制备及手性分离性能

制备了β-环糊精-6-单取代氨乙基氨丙基三甲氧基硅烷手性单体(β-CD siloxane),以该手性单体和1,2-双(三乙氧基硅基)乙烷(BTEE)为硅源,十六烷基三甲基溴化铵(CTAB)为模板,采用水热合成法直接制得孔道中含有环糊精的手性介孔材料。 再对该产物进行苯基异氰酸酯化得到杂合β-环糊精的有机-无机介孔分离材料(β-CD PMOs)。 在正相HPLC及反相HPLC条件下,分别考察该填料柱对常见含氮碱性药物对映体的拆分效果。 结果表明,不管在反相或正相分离模式下,采用常见的流动相在pH=4.15条件实现了11个碱性药物的手性分离,手性选择因子(α)最高可达2.42。 孔道中直接杂合β-环糊精的手性固定相制备方法简便、快速和成本低,进一步优化成孔条件后有一定应用前景。     

介孔分子筛的酸性和水热稳定性

介孔分子筛材料在催化、吸附与分离以及化学组装制备先进材料和分子器件等方面具有潜在的应用价值.但是,由于介孔分子筛材料较低的水热稳定性和较弱的酸性,极大地影响了其在催化研究中的广泛应用.本文系统地综述了最近几年在提高介孔分子筛酸性和水热稳定性的研究工作.其中包括:(1)将超酸组份负载于介孔分子筛的孔道中以达到提高介孔分子筛材料的酸强度的目的;(2)通过在合成介孔分子筛的过程中加入无机盐和有机胺等助剂或采用合适的后处理方法以提高介孔分子筛的水热稳定性;(3)通过新型模板剂来合成具有较高水热稳定性的介孔分子筛材料;(4)利用具有沸石分子筛基本结构单元的沸石分子筛导向剂与表面活性剂自组装来合成具有强酸中心和高温水热稳定的介孔分子筛材料.     

Synthesis and properties of 1,3,5-benzene periodic mesoporous organosilica (PMO): novel aromatic PMO with three point attachments and unique thermal transformations

A new aromatic periodic mesoporous organosilica material containing benzene functional groups that are symmetrically integrated with three silicon atoms in an organosilica mesoporous framework is reported. The material has a high surface area, well-ordered mesoporous structure and thermally stable framework aromatic groups. The functional aromatic moieties were observed to undergo sequential thermal transformation from a three to two and then to a one point attachment within the framework upon continuous thermolysis under air before eventually being converted to periodic mesoporous silica devoid of aromatic groups at high temperatures and longer pyrolysis times. The mesoporosity of the material was characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and nitrogen porosimetry, whereas the presence and transformation of the aromatic groups in the walls of the materials were characterized by solid-state NMR spectroscopy, mass spectrometry, and thermogravimetric analysis. The attachment of a benzene ring symmetrically onto three siloxanes of the framework was used advantageously as a cross-linker to enhance the thermal stability of the organic group. Some of these properties are investigated in comparison with other aromatic PMOs that have only two point attachments and an amorphous phenylsilica gel that has only one point attachment. The successful synthesis of the first aromatic PMO with its organic group attached within the framework through more than two points is an important step toward the synthesis of PMOs having organic groups with more complex and multiple attachments within the framework.     

Imide-siloxane block copolymer/silica hybrid membranes: preparation, characterization and gas separation properties

Imide-siloxane block copolymer/silica hybrid membranes with covalent bonds were prepared via sol–gel reaction. The structural informations of these hybrid membranes were obtained by using Fourier transform-infrared spectrometry (FT-IR), ²⁹Si nuclear magnetic resonance (²⁹Si NMR), XPS and thermogravimetric analysis (TGA). The gas separation properties of the hybrid membranes were also investigated in terms of organosiloxane (PDMS) or silica content at various temperatures. In the hybrids, the addition of PDMS phase increased the permeabilities of gases such as He, CO₂, O₂, and N₂, indicating that the gas transport occurred mainly through rubbery organic matrix. Meanwhile, the PDMS phase contributed the decreased gas selectivities to nitrogen but the reduction in selectivities was very small in comparison with other siloxane containing polymeric membranes. This might be due to the restriction of chain mobility by the existence of inorganic component such as silica network in the hybrids. Additionally, the increase of silica content in these hybrid membranes considerably retarded the falling-off of gas selectivity at elevated temperature. The increase of silica content in hybrid membranes resulted in well-formed silica networks and hence these inorganic components restricted the plasticization of organic matrix by the thermal segmental motion of organic components, leading to preventing the large decrease of the gas selectivity.