巯丙基功能化介孔纳米二氧化硅的合成

用三种不同的方法将巯基丙基三甲氧基硅烷(MPTMS)引入二氧化硅网络中, 合成了粒径为50-200 nm的巯丙基功能化的介孔纳米二氧化硅, 并利用透射电子显微镜, 热重分析等手段对其形貌与性能进行了表征. 在巯丙基官能团的作用下介孔纳米二氧化硅的形貌发生了重大改变, 由非常规则的六角形变为纳米棒. 控制反应时间可以调节介孔纳米二氧化硅的粒径大小, 用三乙醇胺代替氢氧化钠可以合成直径在100 nm以下的功能化介孔二氧化硅粒子. 为了保护巯基官能团, 选用了酸醇提取法去除模板. 另外, 对介孔二氧化硅粒子的形成机制也进行了探讨.     

Fabrication and characterization of mesoporous Co3O4 core/mesoporous silica shell nanocomposites

A mesoporous Co(3)O(4) core/mesoporous silica shell composite with a variable shell thickness of 10-35 nm was fabricated by depositing silica on Co(3)O(4) superlatticed particles. The Brunauer-Emmett-Teller (BET) surface area of the composite with a shell thickness of ca. 2.0 nm was 238.6 m(2)/g, which varied with the shell thickness, and the most frequent pore size of the shell was ca. 2.0 nm. After the shell was eroded with hydrofluoric acid, mesoporous Co(3)O(4) particles with a pore size of ca. 8.7 nm could be obtained, whose BET surface area was 86.4 m(2)/g. It is proposed that in the formation of the composite the electropositive cetyltrimethylammonium bromide (CTAB) micelles were first adsorbed on the electronegative Co(3)O(4) particle surface, which directed the formation of the mesoporous silica on the Co(3)O(4) particle surface. Electrochemical measurements showed that the core/shell composites exhibited a higher discharge capacity compared with that of the bare Co(3)O(4) particles.     

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.     

Mesoporous Silica Microspheres Composited with SBA-15s for Resonance Frequency Reduction in a Miniature Loudspeaker

Microspheres composited with mesoporous SBA-15 particles and silica were investigated as fillers in miniature loudspeakers to study the factors influencing the resonance frequency offsets(RFOs). Mesoporous silica microspheres(MSMs) were prepared by self-assembling SBA-15 mesoporous silica in a microemulsion synthesis system. The formation process involved the fabrication of a stable O/W microemulsion of tetrabutyl orthosilicate(TBOS) and hexadecyltrimethylammonium bromide(C₁₆TAB) and encapsulation of SBA-15s. The RFO increased and then decreased with increasing particle size(in the length range of 0.7-5.5 μm and in the width range of 0.2-0.45 μm), increased with increasing pore size(in the range of 7.0-9.4 nm) of SBA-15s, and increased with decreasing particle size(105-900 μm) of MSMs.     

Highly aminated mesoporous silica nanoparticles with cubic pore structure

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3?n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.     

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.     

Facile method to synthesize platelet SBA-15 silica with highly ordered large mesopores

Highly ordered mesoporous SBA-15 silica with large pore diameter of 18 nm (nominal BJH pore diameter ~22 nm) and short pore length (~500 nm) was synthesized using a micelle expander 1,3,5-triisopropylbenzene in the absence of ammonium fluoride by employing short initial stirring time at 17 °C followed by static aging at low temperature. Scanning and transmission electron microscopies revealed that the material comprised of platelet particles in which large mesopores were nearly flawlessly arranged within uniform domains up to 3 μm in size. The platelet SBA-15 had the (100) interplanar spacing of 17 nm, high surface area (~470 m(2) g(-1)) and large pore volume (~1.6 cm(3) g(-1)). The hydrothermal treatment at 130 °C for 2 days was employed to eliminate constrictions from the pore channels. The control experiment showed that a sample prepared with prolonged stirring had very similar mesoporous properties, but the particle size was smaller and the domains were irregular, proving that the static conditions facilitate the formation of SBA-15 with platelet particle morphology. The absence of ammonium fluoride was also critical in attaining the platelet particle shape.     

Elaboration of monodisperse spherical hollow particles with ordered mesoporous silica shells via dual latex/surfactant templating: radial orientation of mesopore channels

Monodisperse spherical hollow nanoparticles of mesoporous silica featuring mesopores with a radial orientation in the silica shell were synthesized via a dual-templating method. Specifically designed polystyrene latexes with anionic or cationic surface charges acted as the core templates, while cetyltrimethylammonium bromide served as a co-template to structure the mesopore formation during tetraethoxysilane hydrolysis/condensation. The particles were well-separated and presented homogeneous mesoporous silica shells. Average particle diameters were less than 200 nm, and the particles displayed high values of specific surface area and pore volume. The shell thickness and the hollow core diameter could be tuned independently while the radial pore structure was preserved. A detailed analysis of the nitrogen adsorption-desorption isotherms proved that the central cavity was completely isolated from the external medium, that is, only accessible through the radial mesopores of the shell. Consequently, our particles gather the advantages of a well-defined structure, straight penetrating channels across the silica shell, and a high accessible porous volume of the central core. These properties make them far better candidates than simple mesoporous particles for any storage and/or controlled release applications.     

The role of pore size and structure on the thermal stability of gold nanoparticles within mesoporous silica

Highly dispersed gold particles (<2 nm) were synthesized within the pores of mesoporous silica with pore sizes ranging from 2.2 to 6.5 nm and different pore structures (2D-hexagonal, 3D-hexagonal, and cubic). The catalysts were reduced in flowing H2 at 200 degrees C and then used for CO oxidation at temperatures ranging from 25 to 400 degrees C. The objective of this study was to investigate the role of pore size and structure in controlling the thermal sintering of Au nanoparticles. Our study shows that sintering of Au particles is dependent on pore size, pore wall thickness (strength of pores), and pore connectivity. A combination of high-resolution TEM/STEM and SEM was used to measure the particle size distribution and to determine whether the Au particles were located within the pores or had migrated to the external silica surface.     

Facile fabrication of hollow mesoporous silica nanospheres for superhydrophilic and visible/near-IR antireflection coatings

A series of hierarchically mesostructured silica nanoparticles (MSNs) less than 100 nm in size were fabricated by means of a one-step synthesis using dodecanethiol (C(12)-SH) and cetyltrimethylammonium bromide (CTAB) as the dual template, and trimethylbenzene (TMB) as the swelling agent. Silica nanoparticles with varied morphologies and structures, including mesoporous silica nanoparticles with tunable pore size, mesoporous silica nanoparticles with a thin solid shell, hollow mesoporous silica nanoparticles with tunable cavity size, and hollow mesoporous silica nanoparticles with a thin solid shell, were obtained by regulating the TMB/CTAB molar ratio and the stirring rate with the assistance of C(12)-SH. Silica particulate coatings were successfully fabricated by using MSNs with varied morphologies and structures as building block through layer-by-layer dip-coating on glass substrates. The thickness and roughness of the silica particulate coatings could be tailored by regulating the deposition cycles of nanoparticles. The silica particulate coatings composed of hollow mesoporous silica nanoparticles with a thin shell (S2) increased the maximum transmittance of slide glass from 90 to 96%, whereas they reduced its minimum reflection from 8 to 2% at the optimized wavelength region that could be adjusted from visible to near-IR with a growing number of deposition cycles. The coatings also exhibited excellent superhydrophilic and antifogging properties. These mesostructured silica nanoparticles are also expected to serve as ideal scaffolds for biological, medical, and catalytic applications.     

High-surface-area catalyst design: Synthesis, characterization, and reaction studies of platinum nanoparticles in mesoporous SBA-15 silica

Platinum nanoparticles in the size range of 1.7-7.1 nm were produced by alcohol reduction methods. A polymer (poly(vinylpyrrolidone), PVP) was used to stabilize the particles by capping them in aqueous solution. The particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM investigations demonstrate that the particles have a narrow size distribution. Mesoporous SBA-15 silica with 9-nm pores was synthesized by a hydrothermal process and used as a catalyst support. After incorporation into mesoporous SBA-15 silica using low-power sonication, the catalysts were calcined to remove the stabilizing polymer from the nanoparticle surface and reduced by H2. Pt particle sizes determined from selective gas adsorption measurements are larger than those determined by bulk techniques such as XRD and TEM. Room-temperature ethylene hydrogenation was chosen as a model reaction to probe the activity of the Pt/SBA-15 materials. The reaction was shown to be structure insensitive over a series of Pt/SBA-15 materials with particle sizes between 1.7 and 3.6 nm. The hydrogenolysis of ethane on Pt particles from 1.7 to 7.1 nm was weakly structure sensitive with smaller particles demonstrating higher specific activity. Turnover rates for ethane hydrogenolysis increased monotonically with increasing metal dispersion, suggesting that coordinatively unsaturated metal atoms present in small particles are more active for C2H6 hydrogenolysis than the low index planes that dominate in large particles. An explanation for the structure sensitivity is suggested, and the potential applications of these novel supported nanocatalysts for further studies of structure-activity and structure-selectivity relationships are discussed.     

Facile synthesis of mesoporous silica sublayer with hierarchical pore structure on ceramic membrane using anionic polyelectrolyte

A facile method for introducing mesoporous silica sublayer onto the surface of a ceramic membrane for use in liquid-phase separation is described. To reduce the electrostatic repulsion between the mesoporous silica sol and the ceramic membrane in highly acidic conditions (pH < 2), thus facilitating the approach of hydrolyzed silica sol to the surface of the membrane, poly(sodium 4-styrenesulfonate) (Na+PSS-, denoted as PSS-) was used as an ionic linker. The use of PSS- led to a significant reduction in positive charge on the ceramic membrane, as confirmed by experimental titration data. Consistent with the titration results, the amount of mesoporous silica particles on the surface of the ceramic membrane was low, in the absence of PSS- treatment, whereas mesoporous silica sublayer with hierarchical pore structure was produced, when 1 wt % PSS- was used. The results show that mesoporous silica grows in the confined surface, eventually forming a multistacked surface architecture. The mesoporous silica sublayer contained uniform, ordered (P6 mm) mesopores of ca. 7.5 nm from mesoporous silica as well as macropores ( approximately mum) from interparticle voids, as evidenced by transmission electron microscopy and scanning electron microscopy analyses. The morphologies of the supported mesoporous silica could be manipulated, thus permitting the generation of uniform needlelike forms or uniform spheroid particles by varying the concentration of PSS-.     

Production of porous silica microparticles by membrane emulsification

A method for the production of near-monodispersed spherical silica particles with controllable porosity based on the formation of uniform emulsion droplets using membrane emulsification is described. A hydrophobic metal membrane with a 15 μm pore size and 200 μm pore spacing was used to produce near-monodispersed droplets, with a mean size that could be controlled between 65 and 240 μm containing acidified sodium silicate solution (with 4 and 6 wt % SiO(2)) in kerosene. After drying and shrinking, the final silica particles had a mean size in the range between 30 and 70 μm. The coefficient of variation for both the droplets and the particles did not exceed 35%. The most uniform particles had a mean diameter of 40 μm and coefficient of variation of 17%. By altering the pH of the sodium silicate solution and aging the gel particles in water or acetone, the internal structure of the silica particles was successfully modified, and both micro- and mesoporous near-monodispersed spherical particles were produced with an average internal pore size between 1 and 6 nm and an average surface area between 360 and 750 m(2) g(-1). A material balance and particle size analysis provided identical values for the internal voidage of the particles, when compared to the voidage as determined by BET analysis.     

可用于色谱固定相的介孔氧化硅球材料的合成

采用非离子型嵌段高分子表面活性剂EO₂₀PO₃₀EO₂₀ (P65)为结构导向剂, 正硅酸乙酯为硅源, 在酸性介质中, 静置法制备了微米级介孔氧化硅球. 通过改变合成温度、反应时间或者无机盐KCl的加入量, 可以调节介孔氧化硅球的直径(9.0～17.6 μm); 加入1,3,5-三甲苯(TMB)或者调节水热温度, 可以调节介孔氧化硅球的孔径(2.3～4.8 nm). 采用X射线衍射(XRD)、N₂吸附-脱附、扫描电镜(SEM)、激光散射粒度分布和对溶菌酶的吸附等方法, 对介孔氧化硅球的结构、孔性质、形貌、吸附性质等进行了表征. 实验发现, 孔径较小的介孔氧化硅球(≤4.3 nm)对溶菌酶的吸附不明显(≤42 mg/g), 而孔径(4.8 nm)大于溶菌酶直径的材料对溶菌酶有较大的吸附量(192 mg/g), 说明孔径均匀可调的介孔氧化硅球材料可以很好地用作体积排阻色谱柱的固定相.     

Sequestration of CO2 using Cu nanoparticles supported on spherical and rod-shape mesoporous silica

The CO₂ sequestration is one of the most promising solutions to tackle global warming. In this study, spherical mesoporous silica particles (MPS-S) and rod-shaped mesoporous silica particles (MPS-R) loaded with Cu nanoparticles were selectively prepared and employed for CO₂ adsorption. For the first time uniform Cu nanoparticles were incorporated into the rod-shaped mesoporous silica particles by post-synthesis modification using both N-[3-(trimethoxysilyl)propyl]ethylenediamine (PEDA) and ethylenediamine (EDA) as coupling agents. The physiochemical properties of the mesoporous and copper grifted silica composites were investigated by CHN elemental analysis, FTIR spectroscopy, thermogravimetric analysis, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), surface area analysis, scanning, transmission electron microscopy and gas analysis system (GSD 320, TERMO). The mesoporous silica shows highly ordered mesoporous structures, with the rod-shaped particles having a higher surface area than the spherical ones. Copper nanoparticles with an average diameter of 6.0 nm were uniformly incorporated into the MPS-S and MPS-R. Moreover, Cu-loaded mesoporous silica exhibits up to 40% higher CO₂ adsorption capacity than the bare MPS. The MPS-R modified with Cu nanoparticles showed a maximum CO₂ adsorption capacity of 0.62 mmol/g and the humidity showed a slight negative effect on CO₂ uptake process. The enhancement of CO₂ adsorption onto transition metal/mesoporous substrates provides basis for imminent CO₂ sequestration.     

Synthesis and characterization of monodisperse, mesoporous, and magnetic sub-micron particles doped with a near-infrared fluorescent dye

Recently, multifunctional silica nanoparticles have been investigated extensively for their potential use in biomedical applications. We have prepared sub-micron monodisperse and stable multifunctional mesoporous silica particles with a high level of magnetization and fluorescence in the near infrared region using an one-pot synthesis technique. Commercial magnetite nanocrystals and a conjugated-NIR-dye were incorporated inside the particles during the silica condensation reaction. The particles were then coated with polyethyleneglycol to stop aggregation. X-ray diffraction, N₂ adsorption analysis, TEM, fluorescence and absorbance measurements were used to structurally characterize the particles. These mesoporous silica spheres have a large surface area (1978 m²/g) with 3.40 nm pore diameter and a high fluorescence in the near infrared region at λ=700 nm. To explore the potential of these particles for drug delivery applications, the pore accessibility to hydrophobic drugs was simulated by successfully trapping a hydrophobic ruthenium dye complex inside the particle with an estimated concentration of 3 wt%. Fluorescence imaging confirmed the presence of both NIR dye and the post-grafted ruthenium dye complex inside the particles. These particles moved at approximately 150 μm/s under the influence of a magnetic field, hence demonstrating the multifunctionality and potential for biomedical applications in targeting and imaging.     

Polyelectrolyte-surfactant complex as a template for the synthesis of zeolites with intracrystalline mesopores

Mesoporous zeolite silicalite-1 and Al-ZSM-5 with intracrystalline mesopores were synthesized with polyelectrolyte-surfactant complex as the template. Complex colloids were first formed by self-assembly of the anionic polymer poly(acrylic acid) (PAA) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in basic solution. During the synthesis procedure, upon the addition of the silica source, microporous template (tetrapropylammonium hydroxide), and NaCl, these PAA/CTA complex colloids underwent dissociation and gave rise to the formation of hollow silica spheres with mesoporous shells templated by CTAB micelles and PAA domains as the core. Under hydrothermal treatment, the hollow silica spheres gradually merged together to form larger particles with the PAA domains embedded as the space occupant, which acted as a template for intracrystalline mesopores during the crystallization of the zeolite framework. Amphiphilic organosilane was used to enhance the connection between the PAA domain and the silica phase during the synthesis. After calcination, single crystal-like zeolite particles with intracrystalline mesopores of about 5-20 nm were obtained, as characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N(2) adsorption measurements. With the addition of an aluminum source in the synthesis, mesoporous zeolite Al-ZSM-5 with intracrystalline mesopores was also synthesized, and enhanced catalytic property was observed with mesoporous Al-ZSM-5 in acetalization of cyclohexanone with methanol.     

Biphasic synthesis of Au@SiO2 core-shell particles with stepwise ligand exchange

We report the synthesis of well-dispersed core-shell Au@SiO(2) nanoparticles with minimal extraneous silica particle growth. Agglomeration was suppressed through consecutive exchange of the stabilizing ligands on the gold cores from citrate to L-arginine and finally (3-mercaptopropyl)triethoxysilane. The result was a vitreophilic, stable gold suspension that could be coated with silica in a biphasic mixture through controlled hydrolysis of tetraethoxysilane under L-arginine catalysis. Unwanted condensation of silica particles without gold cores was limited by slowing the transfer across the liquid-liquid interface and reducing the concentration of the L-arginine catalyst. In-situ dynamic light scattering and optical transmission spectroscopy revealed the growth and dispersion states during synthesis. The resulting core-shell particles were characterized via dynamic light scattering, optical spectroscopy, and electron microscopy. Their cores were typically 19 nm in diameter, with a narrow size distribution, and could be coated with a silica shell in multiple steps to yield core-shell particles with diameters up to 40 nm. The approach was sufficiently controllable to allow us to target a shell thickness by choosing appropriate precursor concentrations.     

Mesopore-free hollow silica particles with controllable diameter and shell thickness via additive-free synthesis

Mesopore-free hollow silica particles with a spherical shape, smooth surface, and controllable diameter (from 80 to 300 nm) and shell thickness (from 2 to 25 nm) were successfully prepared using an additive-free synthesis method. Different from other hollow particle developments, a mesopore-free shell was produced because of the absence of additive. Although common reports pointed out the importance of the additional additive in pasting and growing silica on the surface of a template, here we preferred to exploit the effect of the template charge in gaining the silica coating process. To form the silica, basic amino acid (i.e., lysine) was used as a catalyst to replace ammonia or hydrazine, which is harmless and able to control the silica growth and produce hollow particles with smooth surfaces. Control of the particle diameter was drastically achieved by altering the size of the template. The flexibility of the process in controlling the shell thickness was predominantly attained by varying the compositions of the reactants (i.e., silica source and catalyst). The present mesopore-free hollow particles could be efficiently used for various applications, especially for thermal insulator and optical devices because of their tendency not to adsorb large molecules, as confirmed by adsorption analysis.     

Solvent evaporation induced aggregating assembly approach to three-dimensional ordered mesoporous silica with ultralarge accessible mesopores

A solvent evaporation induced aggregating assembly (EIAA) method has been demonstrated for synthesis of highly ordered mesoporous silicas (OMS) in the acidic tetrahydrofuran (THF)/H(2)O mixture by using poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) as the template and tetraethylorthosilicate (TEOS) as the silica precursor. During the continuous evaporation of THF (a good solvent for PEO-b-PMMA) from the reaction solution, the template molecules, together with silicate oligomers, were driven to form composite micelles in the homogeneous solution and further assemble into large particles with ordered mesostructure. The obtained ordered mesoporous silicas possess a unique crystal-like morphology with a face centered cubic (fcc) mesostructure, large pore size up to 37.0 nm, large window size (8.7 nm), high BET surface area (508 m(2)/g), and large pore volume (1.46 cm(3)/g). Because of the large accessible mesopores, uniform gold nanoparticles (ca. 4.0 nm) can be introduced into mesopores of the OMS materials using the in situ reduction method. The obtained Au/OMS materials were successfully applied to fast catalytic reduction of 4-nitrophenol in the presence of NaHB(4) as the reductant. The supported catalysts can be reused for catalytic reactions without significant decrease in catalysis performance even after 10 cycles.