Pore size engineering in mesoporous silicas using supercritical CO2

In this paper we investigate the use of supercritical carbon dioxide (sc-CO(2)) for synthesizing calcined mesoporous silicas with tunable pore sizes, wall thickness, and d spacings. Small angle neutron scattering was used to probe the controlled swelling of the triblock copolymer surfactant templating agents, P123 (PEO(20)PPO(69)PEO(20)), P85 (PEO(26)PPO(39)PEO(26)), and F127 (PEO(106)PPO(70)PEO(106)), as a function of CO(2) pressure. The transition from the liquid crystal phase to the calcined mesoporous silicas, formed upon condensation and drying, was also studied in detail. Powder X-ray diffraction, transmission electron microscopy, and nitrogen adsorption techniques were used to establish pore diameters, silica wall widths, and the hexagonal packing of the pores within the calcined silicas. Using a direct templating method, the diameters of mesopores and the spacing between the pores could be tuned with a high level of precision. The swelling process was observed to have no detrimental effects on the quality of silica formed, a distinct advantage over conventional swelling techniques, and all of the silicas synthesized in this study were highly ordered over distances of at least 2000 A.     

Encapsulation method for the dispersion of NiO onto ordered mesoporous silica, SBA-15, using polyethylene oxide (PEO)

An effective method for dispersing NiO onto ordered mesoporous silica, SBA-15, is described. The procedure involves the use of polyethylene oxide (PEO) as an encapsulating agent. It can be expected that encapsulation between PEO and Ni2+ ions mainly involves complexes between PEO and Ni2+ ions. Both N2 adsorption/desorption isotherm and TEM analyses indicate that a 2-dimensionally hexagonal pore structure with a distinct pore symmetry (space group P6mm) is maintained throughout the procedure, even though both Ni2+ ions and PEO are present in the middle of the self-assembly of mesostructured silica. The particle size of the NiO increases slightly as a function of PEO concentration. When the ratio of PEO to the templating agent (triblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide) reaches a value of 4.5, ordered mesoporous silica with NiO is hardly formed.     

Shape- and size-controlled synthesis in hard templates: sophisticated chemical reduction for mesoporous monocrystalline platinum nanoparticles

Here we report a novel hard-templating strategy for the synthesis of mesoporous monocrystalline Pt nanoparticles (NPs) with uniform shapes and sizes. Mesoporous Pt NPs were successfully prepared through controlled chemical reduction using ascorbic acid by employing 3D bicontinuous mesoporous silica (KIT-6) and 2D mesoporous silica (SBA-15) as a hard template. The particle size could be controlled by changing the reduction time. Interestingly, the Pt replicas prepared from KIT-6 showed polyhedral morphology. The single crystallinity of the Pt fcc structure coherently extended over the whole particle.     

Vanadium-containing mesoporous silica of high photocatalytic activity and stability even in water

Vanadium-containing mesoporous silica molecular sieve (V proportional HMS) with tetrahedrally coordinated V-oxide species (VVO4) has been prepared by a modified surfactant-templating method, consisting of an addition of surfactant to a mixture of water, alcohol, and Si and V precursors followed by calcination. The V proportional HMS demonstrates high photocatalytic activity even in the presence of water, while other V proportional HMS's prepared by conventional templating methods and V/HMS prepared by an impregnation method show almost no activity owing to hydrolysis of the VVO4 species. ESR and photoluminescence measurements reveal that the modified templating method creates VVO4 species confined within a silica layer, while other methods create VVO4 species exposed on silica surface. The former VVO4 species are highly stabilized by the confinement within the silica, thus suppressing the hydrolysis. Another notable property of the confined VVO4 species is the higher photocatalytic activity even without water, despite their confined structure. This is explained by higher electrophilicity and longer lifetime of the excited-state VVO4 species (VIVO4*) derived from their distorted structure. The obtained findings suggest potential use of the modified surfactant-templating method for synthesis of stable and recyclable V-containing mesoporous silica with high photocatalytic activity.     

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.     

新型囊泡状二氧化硅中孔分子筛的合成与表征

中孔分子筛能适应人们有效利用重组分油的需要，因此自从1992年美国Mobil公司的研究者们。用烷基季铵盐阳离子表面活性剂做模板剂，合成出M41S系列中孔分子筛之后，中孔分子筛的合成与应用已成为人们研究的热点之一。近几年来。人们根据不同的组装路线，利用不同的表面活性剂做模板剂已合成出多种新型中孔分子筛，如以静电组装路线合成的FSM-16、M41S、SBA-n系列、KIT-1等，以氢键组装路线合成的HMS，MSU-X，MSU-V，MSU-G等。     

Design and synthesis of ordered mesoporous silica materials with high degree of silica condensation at high temperature from a mixture of polymer surfactant with small organic ammonium

Thermal stability on a mixture of triblock polymer (P123) and fluorocarbon surfactant (FC-4) in acidic media for synthesis of ordered mesoporous materials has been carefully investigated by NMR spectroscopy at various treated temperatures (RT-180 degrees C) and the templating mechanism of the mixture on high-temperature synthesis has been proposed. Accordingly, we have designed fluorocarbon-free templates for syntheses of ordered mesoporous silica materials at high temperatures. As expected, ordered mesoporous silica materials with high degree of silica condensation are synthesized at high temperatures from these designed templates.     

A simple approach to prepare monodisperse mesoporous silica nanospheres with adjustable sizes

A new and facile approach has been developed to prepare monodisperse mesoporous silica nanospheres (MMSNs) with controlled particle sizes and pore structures. In our approach, MMSNs were synthesized simply in a sodium acetate solution without adding any other alkali or alcohol additives. MMSNs have a spherical shape and uniform particle sizes, which can be adjusted from 50 to 110 nm by increasing the reaction temperature from 40 to 80 °C. By performing a subsequent hydrothermal treatment (HT) under basic condition (pH=~11.5) at 130 °C, the mesoporous pore volume and surface area can be enhanced, while keeping the mono-dispersion characteristics and the mesopore size almost unchanged. The pore sizes of MMSNs can be adjusted from 2.8 to 4.0 nm under acidic solutions by changing the HT temperature from 100 to 130 °C. The formation process of MMSNs has been investigated by transmission electron microscopy (TEM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) techniques. A spherical micelle templating mechanism is proposed to explain the formation of MMSNs in our system, which is different from that of traditional highly ordered mesoporous silica nanoparticles (MCM-41).     

Hydrothermal growth of mesoporous SBA-15 silica in the presence of PVP-stabilized Pt nanoparticles: synthesis, characterization, and catalytic properties

A novel high surface area heterogeneous catalyst based on solution phase colloidal nanoparticle chemistry has been developed. Monodisperse platinum nanoparticles of 1.7-7.1 nm have been synthesized by alcohol reduction methods and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis. Characterization of the Pt/SBA-15 catalysts suggests that Pt particles are located within the surfactant micelles during silica formation leading to their dispersion throughout the silica structure. After removal of the templating polymer from the nanoparticle surface, Pt particle sizes were determined from monolayer gas adsorption measurements. Infrared studies of CO adsorption revealed that CO exclusively adsorbs to atop sites and red-shifts as the particle size decreases suggesting surface roughness increases with decreasing particle size. Ethylene hydrogenation rates were invariant with particle size and consistent with a clean Pt surface. Ethane hydrogenolysis displayed significant structure sensitivity over the size range of 1-7 nm, while the apparent activation energy increased linearly up to a Pt particle size of approximately 4 nm and then remained constant. The observed rate dependence with particle size is attributed to a higher reactivity of coordinatively unsaturated surface atoms in small particles compared to low-index surface atoms prevalent in large particles. The most reactive of these unsaturated surface atoms are responsible for ethane decomposition to surface carbon. The ability to design catalytic structures with tunable properties by rational synthetic methods is a major advance in the field of catalyst synthesis and for the development of accurate structure-function relationships in heterogeneous reaction kinetics.     

Facile synthesis of monodisperse microspheres and gigantic hollow shells of mesoporous silica in mixed water-ethanol solvents

Mesoporous silica materials with a variety of morphologies, such as monodisperse microspheres, gigantic hollow structures comprising a thin shell with a hole, and gigantic hollow structures consisting of an outer thin shell and an inner layer composed of many small spheres, have been readily synthesized in mixed water-ethanol solvents at room temperature using cetyltrimethylammonium bromide (CTAB) as the template. The obtained mesoporous silica generally shows a disordered mesostructure with typical average pore sizes ranging from 3.1 to 3.8 nm. The effects of the water-to-ethanol volume ratio (r), the volume content of tetraethyl orthosilicate TEOS (x), and the CTAB concentration in the solution on the final morphology of the mesoporous silica products have been investigated. The growth process of gigantic hollow shells of mesoporous silica through templating emulsion droplets of TEOS in mixed water-ethanol solution has been monitored directly with optical microscopy. Generally, the morphology of mesoporous silica can be regulated from microspheres through gigantic hollow structures composed of small spheres to gigantic hollow structures with a thin shell by increasing the water-to-ethanol volume ratio, increasing the TEOS volume content, or decreasing the CTAB concentration. A plausible mechanism for the morphological regulation of mesoporous silica by adjusting various experimental parameters has been put forward by considering the existing state of the unhydrolyzed and partially hydrolyzed TEOS in the synthesis system.     

模板剂对全硅MCM-41介孔分子筛结构的影响

分别采用十六烷基三甲基溴化铵和十六烷基三乙基溴化铵作为模板剂,硅溶胶为硅源,用水热晶化法在碱性（NaOH）介质中合成了MCM-41介孔分子筛样品.通过XRD、N2吸附-脱附、TG-DTA、IR等测试手段对这两种样品进行了对比表征分析.考察了两种不同模板剂对其晶体结构、比表面及孔径大小的影响.实验结果表明,相对于十六烷基三甲基溴化铵做模板剂,采用大头基的十六烷基三乙基溴化铵可以合成较大孔径和孔容（分别为4.72 nm和1.14 cm3•g-1）的MCM-41介孔分子筛,而且具有较窄的孔径分布,因此对于合成大孔径的介孔分子筛MCM-41,十六烷基三乙基溴化铵是一种很好的模板剂.     

Thermally stable polymer composites with improved transparency by using colloidal mesoporous silica nanoparticles as inorganic fillers

The colloidal mesoporous silica nanoparticles with small particle sizes (namely, CMS) are used as inorganic fillers of polymers (i.e. epoxy and silicone). From simple calculation, almost all polymers are estimated to be confined in the mesopores. To clarify the superiority of CMS over nonporous silica particles and mesoporous silica particles with much larger size (TMPS-4) as inorganic fillers, a systematic study on mechanical strength and transparency of polymer-silica nanocomposites was conducted. Compared with nonporous silica particles, similar to TMPS-4, CMS shows a greater effect on lowering the CTE. In addition, obtained polymer-CMS nanocomposites show improved transparency than polymer-TMPS-4 nanocomposites.     

氧化钨介孔材料的制备与表征

以介孔二氧化硅(KIT-6)为硬模板, 硅钨酸为钨源, 用硬模板法制备WO3-SiO2复合材料, 再利用HF除去二氧化硅, 得到了介孔三氧化钨材料. 用X射线衍射(XRD)、能量扩散X射线(EDX)、高分辨透射电镜(HRTEM)、N2吸附-脱附等表征手段, 对制备复合材料的物料比、煅烧温度以及不同分散剂等条件进行了考察. 结果表明, 硅钨酸与硅介孔的物料比(m(WO3)/m(SiO2))在3:1到4:1之间, 在600-750 ℃下煅烧, 能制备结构较好的介孔氧化钨. 乙醇和蒸馏水为分散剂时, 用乙醇为分散剂所得的介孔WO3材料具有更高的比表面积和孔体积.     

Mesoporous Silica Materials Synthesized via Sol-Gel Methods Modified with Ionic Liquid and Surfactant Molecules

Mesoporous silica materials were synthesized via a sol-gel method employing a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, bmimBF4) as a new solvent medium and further modified with surfactant (hexadecyl-trimethyl-ammonium bromide, CTAB) as a pore templating material. The synthesized samples were characterized by the transmission electron microscopy, X-ray diffraction, and N2 adsorption-desorption techniques. The results indicated that the mesoporous silica synthesized by using bmimBF4 and CTAB as mixed templates showed better mesostructural order and smaller pore size, compared with mesoporous silica materials synthesized by using single bmimBF4 as template under the same conditions. This indicates that the presence of surfactant can affect the microstructures of silica prepared by the present synthesis method.     

载有量子点的介孔二氧化硅微球的制备与性能研究

采用自组装方法制备了一种磁核/介孔二氧化硅壳的微球, 调节体系中C₁₈TMS的加入量可控制介孔硅球的比表面积; 并通过化学修饰的方法对介孔微球表面进行巯基功能化修饰. 利用巯基与量子点之间的相互作用可将一定尺寸的量子点吸附于介孔二氧化硅球的孔中, 令介孔微球具有荧光效应; 同时可以利用吸附不同粒径的量子点的荧光光谱对介孔二氧化硅微球孔径的大小进行近似考察.     

基于棒状介孔SiO_2剪切增稠流体的流变行为

以三嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯(PEO-PPO-PEO,P123)为模板剂,采用溶胶-凝胶法合成了介孔SiO_2-P123复合物,经煅烧除去P123得到不同长径比的棒状介孔SiO_2粒子,将其分散于聚乙二醇(PEG)中制成剪切增稠流体(STF),利用旋转流变仪对STF的流变性能进行了表征。结果表明:在稳态条件下,STF的剪切增稠效应随介孔SiO_2质量分数的增加而增强,随介孔SiO_2粒子长径比的增加而减弱;在动态条件下,STF的剪切增稠效应随介孔SiO_2质量分数的增加而减弱,随介孔SiO_2粒子长径比的增加而增强。     

新型介孔二氧化硅囊泡结构的调变

本文采用水热合成法,利用非离子表面活性剂聚环氧乙烷-聚环氧丙烷-聚环氧乙烷(P123)对有机溶剂均三甲苯(TMB)的增容作用,合成了大孔径介孔二氧化硅囊泡材料,首次通过控制有机溶剂TMB与无机硅源正硅酸四乙酯(TEOS)的投料时间间隔t,实现对介孔二氧化硅囊泡材料结构的调变。通过小角X射线衍射和高分辨透射电镜(HTEM)检测技术对酸性P123模板体系中的材料结构转变过程进行了表征。结果表明,改变TMB与TEOS的投料时间间隔,能够实现介孔囊泡结构的调变,同时提出"协同囊泡模板"(cooperative vesicle templating,CVT)和"协同作用机制"(cooperative formation mechanism,FM)共存。通过简单合理的设计合成不同结构的介孔材料,以期开拓其在催化、分离以及医学等领域的潜在应用,也为合成其他介孔材料提供简单合理的设计思路。     

Synthesis and characterization of pore size-tunable magnetic mesoporous silica nanoparticles

Magnetic mesoporous silica nanoparticles (M-MSNs) are emerging as one of the most appealing candidates for theranostic carriers. Herein, a simple synthesis method of M-MSNs with a single Fe(3)O(4) nanocrystal core and a mesoporous shell with radially aligned pores was elaborated using tetraethyl orthosilicate (TEOS) as silica source, cationic surfactant CTAB as template, and 1,3,5-triisopropylbenzene (TMB)/decane as pore swelling agents. Due to the special localization of TMB during the synthesis process, the pore size was increased with added TMB amount within a limited range, while further employment of TMB lead to severe particle coalescence and not well-developed pore structure. On the other hand, when a proper amount of decane was jointly incorporated with limited amounts of TMB, effective pore expansion of M-MSNs similar to that of analogous mesoporous silica nanoparticles was realized. The resultant M-MSN materials possessed smaller particle size (about 40-70 nm in diameter), tunable pore sizes (3.8-6.1 nm), high surface areas (700-1100 m(2)/g), and large pore volumes (0.44-1.54 cm(3)/g). We also demonstrate their high potential in conventional DNA loading. Maximum loading capacity of salmon sperm DNA (375 mg/g) was obtained by the use of the M-MSN sample with the largest pore size of 6.1 nm.     

Synthesis of Olive‐Shaped Mesoporous Platinum Nanoparticles (MPNs) with a Hard‐Templating Method Using Mesoporous Silica (SBA‐15)

Well‐ordered mesoporous Pt nanoparticles (MPNs) with uniform olive shapes are synthesized by using two‐dimensional (2D) hexagonal mesoporous silica (SBA‐15) as a hard template. The average particle sizes are controllable in the range of 150 to 230 nm by changing the reduction time. Low‐angle XRD profiles for the obtained MPNs show three distinct peaks assignable to the (10), (11), and (20) planes of a highly ordered 2D hexagonal symmetry. From high‐magnification SEM images, periodically arranged Pt nanowires are observed clearly, which are a negative replica of the 2D hexagonally ordered mesoporous silica (SBA‐15). Furthermore, the single crystallinity of the Pt fcc structure coherently extends over the whole particles. As a result of such unique character as well as high surface area, the obtained MPNs show distinctly enhanced electrocatalytic properties for methanol oxidation reaction compared to other Pt samples, such as Pt black.     

不同酸对介孔二氧化硅球表面形貌和介相结构的影响

在室温、不同酸性条件下合成出微米级球形介孔二氧化硅材料，通过XRD、SEM以及氮气吸附等手段对介孔二氧化硅材料进行了表征。用TEM跟踪不同反应时间介孔二氧化硅球的形成，对这些球颗粒的合成机理进行了讨论，同时探讨了不同酸性条件下介孔二氧化硅表面形貌和介相结构的变化。