One-pot synthesis of ordered mesoporous carbon–silica nanocomposites templated by mixed amphiphilic block copolymers

Mixed amphiphilic block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO–PPO–PEO) and polydimethylsiloxane-poly(ethylene oxide) (PDMS–PEO) have been successfully used as co-templates to prepare ordered mesoporous polymer–silica and carbon–silica nanocomposites by using phenolic resol polymer as a carbon precursor via the strategy of evaporation-induced self-assembly (EISA). The ordered mesoporous materials of 2-D hexagonal (p6m) mesostructures have been achieved, as confirmed by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and nitrogen-sorption measurements. Experiments show that using PDMS–PEO as co-template can enlarge the pore sizes and reduce the framework shrinkage of the materials without evident effect on the specific surface areas. Ordered mesoporous carbons can then be obtained with large pore sizes of 6.7 nm, pore volumes of 0.52 cm³/g, and high surface areas of 578 m²/g. The mixed micelles formed between the hydrophobic PDMS groups and the PPO chains of the F127 molecules should be responsible for the variation of the pore sizes of the resulting mesoporous materials. Through the study of characteristics of mesoporous carbon and mesoporous silica derived from mother carbon–silica nanocomposites, we think mesoporous carbon–silica nanocomposites with the silica-coating mesostructure can be formed after the pyrolysis of the PDMS–PEO diblock copolymer during surfactant removal process. Such method can be thought as the combination of surfactant removal and silica incorporation into one-step. This simple one-pot route provides a pathway for large-scale convenient synthesis of ordered mesostructured nanocomposite materials.     

Elucidation of interactive effects of synthesis conditions on the characteristics of mesoporous silicas templated using polyoxide surfactant

A series of mesoporous silicas (MS-1–MS-9) were synthesized at different gel compositions using a triblock copolymer (TCP), poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), as the surfactant. The interactive effects of acidity, the contents of tetraethyl orthosilicate (TEOS) and the surfactant, and the gelling temperature on the characteristics of the final material were simultaneously characterized. Increasing acidity favored mesopore formation. A material with a surface area of 760 m²/g, mostly in the mesoporous range, was obtained at 1.0(TEOS):0.017(TCP):7.3HCl:115.7H₂O. Mesopore formation was predominantly determined by the TEOS:TCP ratio and was promoted with its increase from 1.56:1 to 2.09:1. A further increase to 2.61:1 was detrimental. Whereas increasing the TCP content to 3.5% w/w improved micellization, a further increase to 4.6% should be avoided. Mesoporous silicas showed low crystallinity but a high degree of hexagonal mesoscopic organization. The weak surface acidity was attributed to surface silanols, the number of which was proportional to mesoporosity.     

Synthesis and characterization of ordered mesoporous silica by using polystyrene microemulsion as templates

A simple room temperature synthesis of pure mesoporous silica by using a homemade and functional template: polystyrene microemulsion is reported. The process consists of HCl-catalysed sol-gel reactions of tetraethyl orthosilicate (TEOS) in polystyrene microemulsion, followed by removal of the template via solvent extraction or calcining. X-ray diffraction, Transmission Electron Microscope and N₂ adsorption-desorption isotherms are then used to characterize the mesostructure. The results indicate that the synthesized mesoporous silica has a large BET surface area with more than 900 m²/g, large pore volume with more than 0.8 cm³/g and ordered mesopore-structure. This provides a possible way to control the meso-structure and pore size of mesoporous materials via potential functional templates.     

Elucidation of interactive effects of synthesis conditions on the characteristics of mesoporous silicas templated using polyoxide surfactant

A series of mesoporous silicas (MS-1-MS-9) were synthesized at different gel compositions using a triblock copolymer (TCP), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), as the surfactant. The interactive effects of acidity, the contents of tetraethyl orthosilicate (TEOS) and the surfactant, and the gelling temperature on the characteristics of the final material were simultaneously characterized. Increasing acidity favored mesopore formation. A material with a surface area of 760 m²/g, mostly in the mesoporous range, was obtained at 1.0(TEOS):0.017(TCP):7.3HCl:115.7H₂O. Mesopore formation was predominantly determined by the TEOS:TCP ratio and was promoted with its increase from 1.56:1 to 2.09:1. A further increase to 2.61:1 was detrimental. Whereas increasing the TCP content to 3.5% w/w improved micellization, a further increase to 4.6% should be avoided. Mesoporous silicas showed low crystallinity but a high degree of hexagonal mesoscopic organization. The weak surface acidity was attributed to surface silanols, the number of which was proportional to mesoporosity.     

Ordered Mesoporous Carbons

Ordered mesoporous carbons have recently been synthesized using ordered mesoporous silica templates. The synthesis procedure involves infiltration of the pores of the template with appropriate carbon precursor, its carbonization, and subsequent template removal. The template needs to exhibit three‐dimensional pore structure in order to be suitable for the ordered mesoporous carbon synthesis, otherwise disordered microporous carbon is formed. MCM‐48, SBA‐1, and SBA‐15 silicas were successfully used to synthesize carbons with cubic or hexagonal frameworks, narrow mesopore size distributions, high nitrogen Brunauer–Emmett–Teller (BET) specific surface areas (up to 1800 m² g^–1), and large pore volumes. Ordered mesoporous carbons are promising in many applications, including adsorption of large molecules, chromatography, and manufacturing of electrochemical double‐layer capacitors.     

Synthesis and characterization of ordered and cubic mesoporous silica crystals under a moderately acidic condition

Ordered and cubic mesoporous silica materials were synthesized by using poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer as template under a moderately acidic condition of 0.5 mol/l HCl solution. These mesoporous materials were characterized by Fourier transform (FT) IR spectroscopy, thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption measurements. The three-dimensional cage-like microporosity of the prepared mesoporous silica having ordered hexagonal mesoporous structure was evidenced by the well-defined XRD patterns combined with TEM photographs. SEM observation shows a highly regular cubic crystal structure for the prepared mesoporous silica. The size of these crystallites was maintained within the range between 4 and 6 μm, which is fairly important for the application to the stationary phase for separation. The nitrogen adsorption–desorption analysis reveals that the prepared mesoporous silica possesses a small pore diameter of 3.68 nm, a total surface area of 363.648 m²/g, a total pore volume of 0.379 cm³/g, and a pore-wall thickness of 6.63 nm. These features may lead to higher thermal and hydrothermal stability, excellent microporosity, and good connectivity. The mesoporous silica prepared in this study exhibits potential applications to catalysis, sensoring, and separation.     

缓冲溶液中制备掺杂高度隔离铁物种的介孔氧化硅(英文)

使用P123作为模板剂,采用不同的硅源(正硅酸甲酯,正硅酸乙酯,硅酸钠)在弱酸性的条件下(pH=4.4,乙酸-乙酸钠缓冲溶液)合成掺杂铁的介孔氧化硅材料.正硅酸甲酯和硅酸钠形成有序的二维六方相的介孔结构,而正硅酸乙酯形成了囊泡结构.紫外可见漫反射光谱和紫外共振拉曼光谱表明,在环境友好的条件下,采用硝酸铁和硅酸钠可以合成出高度隔离的铁物种.缓冲溶液提供了一条便捷的途径,通过简单改变硅源来控制介孔结构.掺杂铁的介孔氧化硅材料在苯酚的羟化反应中表现出优异的催化性能,主要由于铁物种高度分散在氧化硅载体上,介孔结构使铁活性位更易于接近反应物分子.     

Morphological control on SBA-15 mesoporous silicas via a slow self-assembling rate

Pluronic 123-templated mesoporous SBA-15 silica rods with a length of ca. 3.0–4.0 μm were easily synthesized in a dilute silicate solution with a pH value of 2.0 at room temperature. Through a good control on the synthetic condition and the chemical components, a high homogeneity (>95%) of the hexagonal SBA-15 silica rods can be achieved. In addition, the effect of the synthetic conditions including acid source, weight ratio of the P123/sodium silicate, temperature, water content, pH value, and applying shearing flow were explored in detail to tailor the morphologies of the SBA-15 mesoporous silicas. In this paper, we also focused on the counterion effect on the synthesis of the SBA-15 mesoporous silicas. It was found that the SO₄ ²⁻ counterion from H₂SO₄ has higher affinity to induce the formation of P123 rod-like micelles than that of Cl⁻, NO₃ ⁻. Meanwhile, we postulated that the self-assembly pathway of the silica species and the neutral tri-block copolymer micelles in a dilute solution with a pH value of 2.0 would occur through an S⁰···I⁰ rather than the S⁰X^−…I⁺ one as previously discussed. We further employed the SAB-15 mesoporous silica rods as the templates to synthesize high-quality CMK-3 mesoporous carbon rods by using commercially available phenol–formaldehyde (PF) resin as the carbon source.     

Aligned bioactive mesoporous silica coatings for implants

Ongoing research is reported aimed at preparing mesoporous silica coatings on various substrates for medical applications by a biomimetic approach (self-assembling of organic/inorganic sol-gel systems into ordered structures). Tetraethylorthosilicate (TEOS) was selected as the silica precursor, and amphiphilic triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), and the cationic surfactant cetyltrimethyl ammonium chloride (CTAC), as structure-directing agents. The mesochannels diameter could be adjusted by changing the directing agent, and a preferred alignment of the mesostructure was observed independently of the used substrate (glass, silicon, Ti or Ti6Al4V). Three different treatments (thermocalcination, photocalcination, and solvent extraction) have been also studied to remove the organic templates, of which photocalcination showed to be the most versatile. When soaked in a simulated body fluid, mesoporous silica coatings induced apatite formation after seven days.     

Facile synthesis of ordered mesoporous silica with high γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> loading via sol-gel process

A series of ordered mesoporous silica loaded with iron oxide was synthesized by facile one-step sol-gel route using Pluronic P123 as the template, tetraethylorthosilicate as the silica source, and hydrated iron nitrite as the precursor under acid conditions. The as-synthesized materials with Fe/Si molar ratio ranging from 0.1 to 0.8 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and N₂ adsorption porosimetry. All samples possess ordered hexagonal mesoporous structure similar to SBA-15, with a high surface area, large pore volume, and uniform pore size. Although higher iron content causes a distortion of hexagonal ordering structure to some extent, the materials still maintain the ordered mesopore structure even with Fe/Si molar ratio as high as 0.8. Pore structure and TEM data suggest that iron oxide nanoparticles are buried within the silica wall, and increasing the iron oxide loading has little effects on the pore structure of the mesoporous silica. VSM results show as-synthesized samples exhibit superparamagnetic behavior.     

Gelatin-assisted porous expansion of mesoporous silica

In this study, we report the pore expansion effect of gelatin, a common amphoteric biological protein, on the hexagonal mesoporous silica materials. Tetraethyl orthosilicate (TEOS) was used as silica source and the nonionic surfactant P123 (EO₂₀PO₇₀EO₂₀) as template. The microstructure characters of products were investigated by low-angle X-ray diffraction (LAXRD), transmission electron microscope (TEM), and N₂ adsorption–desorption measurements. The results show that the products prepared with gelatin have the mild expansion ratios of 29–39% and 5–22% in pore diameter and pore volume, respectively. The specific surface area of products ranges from 445 to 590 m² g⁻¹. Moreover, it is revealed that the presence of gelatin did not change the intact 2D-hexagonal mesoporous structure of materials. The ultraviolet–visible absorption spectroscopy (UV–Vis) analysis indicates that there is an interaction between the oxygen atoms of P123 and gelatin molecules. The pore expansion may be because the gelatin can interact with the hydrophilic sides of P123 micelles via hydrogen bonds interaction, which is different from the reported pore expansion mechanisms for other systems.     

New Triblock Copolymer Templates,PEO‐PB‐PEO,for the Synthesis of Titania Films with Controlled Mesopore Size,Wall Thickness,and Bimodal Porosity

The synthesis and properties of a series of new structure‐directing triblock copolymers with PEO‐PB‐PEO structure (PEO = poly(ethylene oxide) and PB = polybutadiene) and their application as superior pore‐templates for the preparation of mesoporous titania coatings are reported. Starting from either TiCl₄ or from preformed TiO₂ nanocrystalline building blocks, mesoporous crystalline titanium oxide films with a significant degree of mesoscopic ordered pores are derived, and the pore size can be controlled by the molecular mass of the template polymer. Moreover, the triblock copolymers form stable micelles already at very low concentration, i.e., prior to solvent evaporation during the evaporation‐induced self‐assembly process (EISA). Consequently, the thickness of pore walls can be controlled independently of pore size by changing the polymer‐to‐precursor ratio. Thus, unprecedented control of wall thickness in the structure of mesoporous oxide coatings is achieved. In addition, the micelle formation of the new template polymers is sufficiently distinct from that of typical commercial PPO‐PEO‐PPO polymers (Pluronics; PPO = poly(propylene oxide)), so that a combination of both polymers facilitates bimodal porosity via dual micelle templating.     

Template-directed synthesis of mesoporous silicas containing phosphonic acid derivatives in the surface layer

A template-directed process, using 1-dodecylamine as a template, is developed for the synthesis of mesoporous silicas containing the phosphonic acid derivatives ≡Si(CH₂)₂P(O)(OC₂H₅)₂ and ≡Si(CH₂)₃P(O)(CH₃)(ONa) in the surface layer. The porous materials obtained by removing the template with boiling methanol have specific surfaces of 854 and 505 m²/g, accessible pore volumes of 0.42 and 0.37 cm³/g, and pore diameters of 2.2 and 2.5 nm, respectively. As shown by scanning electron microscopy and x-ray diffraction, the mesoporous silicas are nonuniform in particle shape and size, and their structure is less ordered than that of classic mesoporous silicas, such as MCM-41. IR and ¹³C, ³¹P, and ²⁹Si CP/MAS NMR spectroscopy data indicate that, in the surface layer of the mesoporous silica prepared with the use of ≡Si(CH₂)₂P(O)(OC₂H₅)₂, the functional groups are present in the form of T ² and T ³ structural units. In addition, the surface layer contains alkoxy groups and water, which participates in hydrogen bonding.     

PEG-directed hydrothermal synthesis of alumina nanorods with mesoporous structure via AACH nanorod precursors

Al₂O₃ nanorods with mesoporous structures are successfully synthesized from a hydrothermal and thermal decomposition process via the ammonium aluminum carbonate hydroxide (denoted as AACH) precursors. TEM images show that the average diameter of Al₂O₃ nanorods is about 60 nm, and the length is around 1–2 μm. The experimental results show that well-crystallized mesopores with hierarchically distributed pore sizes are embedded in the Al₂O₃ nanorods. The N₂ adsorption–desorption experiment indicates that the as-synthesized alumina nanorods have large surface area (ca. 176 m²/g) and narrow pore-size distributions. At the same time, the as-prepared Al₂O₃ nanorods exhibit strong photoluminescent properties at room temperature. A plausible surfactant-induced nanorod formation mechanism using the poly ethylene glycols as the template agent for the nanorod assembly is also proposed.     

Synthesis of mesoporous silica materials (MCM-41) from iron ore tailings

Highly ordered mesoporous materials were successfully synthesized by using the iron ore tailings as the silica source and n-hexadecyltrimethyl ammonium bromide as the template. The samples were detail characterized by powder X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and N₂ physisorption. The as-synthesized materials had high surface area of 527 m² g⁻¹ and the mean pore diameter of 2.65 nm with a well-ordered two-dimensional hexagonal structure. It is feasible to prepare mesoporous MCM-41 materials using the iron ore tailings as precursor.     

Mesoporous indium oxide synthesized via a nanocasting route

The synthesis of crystalline mesoporous indium oxide by using a mesoporous carbon (CMK-3) as hard template is described. Transmission electron microscopy (TEM) exhibits the presence of mesoporous structure in our sample and the corresponding wide-angle X-ray diffraction (XRD) pattern confirmed the crystalline wall of sample. N₂ adsorption measurement exhibits the synthesized crystalline mesoporous indium oxide possesses a specific surface area of 39 m²/g and the total pore volume of 0.17 cm³/g, and the corresponding pore size distribution curve reveals the presence of a mesopore of 7.0 nm in maximum. Our work demonstrates that the maintenance of the ordered structure of carbon template is very significant for obtaining high quality replicas via the nanocasting route.     

Silica‐Templated Synthesis of Ordered Mesoporous Tungsten Carbide/Graphitic Carbon Composites with Nanocrystalline Walls and High Surface Areas via a Temperature‐Programmed Carburization Route

Ordered mesostructured tungsten carbide and graphitic carbon composites (WC/C) with nanocrystalline walls are fabricated for the first time by a temperature‐programmed carburization approach with phosphotungstic acid (PTA) as a precursor and mesoporous silica materials as hard templates. The mesostructure, crystal phase, and amount of deposited graphitic carbon can be conveniently tuned by controlling the silica template (SBA‐15 or KIT‐6), carburizing temperature (700–1000 °C), the PTA‐loading amount, and the carburizing atmosphere (CH₄ or a CH₄/H₂ mixture). A high level of deposited carbon is favorable for connecting and stabilizing the WC nanocrystallites to achieve high mesostructural regularity, as well as promoting the carburization reaction. Meanwhile, large pore sizes and high mesoporosity of the silica templates can promote WC‐phase formation. These novel, ordered, mesoporous WC/C nanocomposites with high surface areas (74–169 m² g^?1), large pore volumes (0.14–0.17 cm³ g^?1), narrow pore‐size distributions (centered at about 3 nm), and very good oxidation resistance (up to 750°C) have potential applications in fuel‐cell catalysts and nanodevices.     

Fabrication of superparamagnetic hydroxyapatite with highly ordered three-dimensional pores

Hydroxyapatite (HA) with highly ordered three-dimensional pores, whose size is about 300 nm, was prepared by colloidal template method. The effect of the surface modification of silica spheres on the order degree of porous structure was investigated by field emission scanning electron microscopy (FESEM). Then, superparamagnetic Fe₃O₄ nanoparticles were fabricated via redox reaction, followed by coating with silica via a sol–gel process, in which a certain amount of TEOS was used in order to control the thickness of the silica shell. X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetometry were applied to characterize the properties. Finally, Fe₃O₄ magnetic nanoparticles coated with silica were adsorbed in the mesopores of HA with highly ordered three-dimensional pores by capillarity. The influence of dispersing agent on the adsorption results has been studied. Magnetometry was applied to characterize the magnetic properties of superparamagnetic HA. The quantities of adsorbed SiO₂/Fe₃O₄ nanoparticles with core–shell have been compared by variation of saturation magnetization before and after adsorption.     

聚乙二醇模板剂制备介孔材料的研究进展

聚乙二醇作为模板剂被广泛用于介孔材料的制备。介绍了使用单一聚乙二醇模板剂合成硅基、非硅基、复合类介孔材料的研究工作,探讨了聚乙二醇与表面活性剂、非表面活性剂类物质作复合模板剂制备介孔材料的方法。综述了聚乙二醇单一模板剂及复合模板剂制备介孔材料的机理。     

Synthesis and characterization of surface-modified and organic-functionalized MCM-41 type ordered mesoporous materials

A new and efficient method for the preparation of MCM-41 type ordered mesoporous phases using phosphate as promoter under reflux conditions is reported. The various mesoporous materials studied were: silica (Si-MCM-41), alumino-silicate (Al-MCM-41), and titanium-silicate (Ti-MCM-41). Our concept of promoter-assisted synthesis of zeolites and related microporous materials was found to be applicable in the synthesis of ordered mesoporous materials as well. The addition of small catalytic quantity of phosphate ions (PO ₄ ³⁻ ), used as promoters, significantly reduced the synthesis time (by a factor of 3–4) of all these mesoporous materials. The synthesis of new MCM-41 type organic-inorganic composite materials with unique properties is also reported.