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1.
A novel, one‐step synthesis of a highly stable mesoporous molecular sieve (MMS‐H), which has a structure analogous to MCM‐48 but which contains zeolite building units, is reported. A variety of experimental techniques—X‐ray diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), Fourier‐transform infrared (FTIR) spectroscopy, hyperpolarized 129Xe NMR, and solid‐state 27Al and 31P magic‐angle spinning (MAS) NMR spectroscopies—have been used to characterize the framework structure, porosity, and acidity of this novel mesoporous/microporous composite material, which is also found to possess superior thermal, hydrothermal, steam, and mechanical stabilities.  相似文献   

2.
Magnetite nanoparticles modified covalently with triethoxysilane having a quaternary dicetyl ammonium ion are used together with tetraethylorthosilicate as building blocks to prepare a mesoporous material. Cetyltrimethylammonium bromide is used as a structure‐directing agent under conditions typically used for mesoporous MCM‐41 silicas. The resulting mesoporous material (MAG‐MCM‐41), containing up to 15 wt % of magnetite is characterized by transmission electron microscopy (TEM), isothermal gas adsorption, and X‐ray diffraction. In contrast to siliceous MCM‐41, mesoporous MAG‐MCM‐41 exhibits a remarkable hydrothermal stability. The magnetic properties of MAG‐MCM‐41 are characterized by DC and AC magnetic susceptibility, and by isothermal hysteresis cycles, confirming the long‐range magnetic ordering above 400 K. As evidenced by atomic force microscopy and TEM, the ability to respond to magnetic fields is used to orient films of MAG‐MCM‐41 with the channels perpendicular to a support.  相似文献   

3.
Hierarchical macro‐/mesoporous titania is prepared without the addition of templates or auxiliary additives at room temperature by the simple dropwise addition of tetrabutyl titanate to pure water, and then calcined at various temperatures. The products are characterized by X‐ray diffraction, N2‐adsorption–desorption analysis, scanning electron microscopy, and the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of acetone in air. The results reveal that hierarchical macro‐/mesoporous structures of titania can spontaneously form by self‐assembly in alkoxide–water solutions in the absence of organic templates or auxiliary additives. The calcination temperature has a strong effect on the structures and photocatalytic activity of the prepared titania. At 300 °C, the calcined sample shows the highest photocatalytic activity. At 400 and 500 °C, the photocatalytic activity slightly decreases. When the calcination temperature is higher than 500 °C, the photocatalytic activity greatly decreases because of the destruction of the hierarchical macro‐/mesoporous structure of the titania and the drastic decrease of specific surface area. The hierarchically macro‐/mesostructured titania network with open and accessible pores is well‐preserved after calcination at 500 °C, indicating especially high thermal stability. The macroporous channel structures are even preserved after calcination at 800 °C. This hierarchical macro‐/mesostructured titania is significant because of its potential applications in photocatalysis, catalysis, solar‐cell, separation, and purification processes.  相似文献   

4.
Hydrothermally stable thioether‐bridged mesoporous materials have been synthesized by one‐step co‐condensation of 1,4‐bis(triethoxysily)propane tetrasulfide (TESPTS) with tetramethoxysilane (TMOS) using cetyltrimethylammonimum bromide (CTAB) as the surfactant in basic conditions. The ordered mesoporous materials can be formed with a wide range of thioether concentrations in the mesoporous framework, as is seen by X‐ray diffraction (XRD) characterization. The results of N2 sorption and transmission electron microscopy (TEM) reveal that the materials synthesized with TESPTS/TMOS molar ratios in the range 1:8–1:3 have extensive structural defect holes in the nanochannels. All materials exhibit enhanced hydrothermal stability, which is in proportion to the concentration of thioether bridging in the mesoporous framework. The thioether‐functionalized mesoporous materials are efficient adsorbents for removing Hg2+ and phenol from waste water. The Hg2+‐adsorption capacity of the material can be as high as 1500 mg g–1.  相似文献   

5.
A new concept is proposed to synthesize mesoporous magnetic nanocomposite particles of great scientific and technological importance. Mesoporous silica coatings were created on micrometer‐sized magnetite (Fe3O4) particles using cetyltrimethylammonium chloride micelles as molecular templates. The characterization by transmission electron microscopy (TEM), nitrogen adsorption–desorption, diffuse‐reflectance Fourier‐transform infrared spectroscopy, and zeta‐potential measurements confirmed the deposition of mesoporous silica thin layers on the magnetite particles. The synthesized particles showed a drastic increase in specific surface area with an average pore size of 2.5 nm. The coating material showed a negligible effect on the saturation magnetization of the original particles that were fully protected by silica coatings. The synthesized mesoporous magnetic nanocomposite particles have a wide range of applications in toxin removal, waste remediation, catalysis, reactive sorbents, and biological cell separations.  相似文献   

6.
Hydrogen adsorption in two different metal–organic frameworks (MOFs), MOF‐5 and Cu‐BTC (BTC: benzene‐1,3,5‐tricarboxylate), with Zn2+ and Cu2+ as central metal ions, respectively, is investigated at temperatures ranging from 77 K to room temperature. The process responsible for hydrogen storage in these MOFs is pure physical adsorption with a heat of adsorption of approximately –4 kJ mol–1. With a saturation value of 5.1 wt.‐% for the hydrogen uptake at high pressures and 77 K, MOF‐5 shows the highest storage capacity ever reported for crystalline microporous materials. However, at low pressures Cu‐BTC shows a higher hydrogen uptake than MOF‐5, making Cu‐based MOFs more promising candidates for potential storage materials. Furthermore, the hydrogen uptake is correlated with the specific surface area for crystalline microporous materials, as shown for MOFs and zeolites.  相似文献   

7.
A simple synthesis route to mesoporous carbons that contain heteroaromatic functionality is described. The sulfur‐functionalized mesoporous carbon (S‐FMC) materials that have been prepared show excellent thermal stability, as well as excellent hydrothermal stability, and stability over a wide range of pH values. These materials also show excellent mercury sorption performance over a broad range of pH, much broader than is possible with thiol‐based functionality or most silica‐based sorbents. The superior performance of these mesoporous heterocarbons as heavy‐metal sorbent material is demonstrated. These materials are shown to be stable at elevated temperatures and extreme pHs, making them ideally suited as a new class of absorbent material.  相似文献   

8.
Nanometer‐sized surfactant‐templated materials are prepared in the form of stable suspensions of colloidal mesoporous silica (CMS) consisting of discrete, nonaggregated particles with dimensions smaller than 200 nm. A high‐yield synthesis procedure is reported based on a cationic surfactant and low water content that additionally enables the adjustment of the size range of the individual particles between 50 and 100 nm. Particularly, the use of the base triethanolamine (TEA) and the specific reaction conditions result in long‐lived suspensions. Dynamic light scattering reveals narrow particle size distributions in these suspensions. Smooth spherical particles with pores growing from the center to the periphery are observed by using transmission electron microscopy, suggesting a seed‐growth mechanism. The template molecules could be extracted from the nanoscale mesoporous particles via sonication in acidic media. The resulting nanoparticles give rise to type IV adsorption isotherms revealing typical mesopores and additional textural porosity. High surface areas of over 1000 m2 g–1 and large pore volumes of up to 1 mL g–1 are obtained for these extracted samples.  相似文献   

9.
A novel mesoporous‐nanotube hybrid composite, namely mesoporous tin dioxide (SnO2) overlaying on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesoporous SnO2 on the surface of MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure‐directing agents. Nitrogen adsorption–desorption, X‐ray diffraction and transmission electron microscopy analysis techniques were used to characterize the samples. It was observed that a thin layer tetragonal SnO2 with a disordered porous was embedded on the surface of MWCNTs, which resulted in the formation of a novel mesoporous‐nanotube hybrid composite. On the base of TEM analysis of products from controlled experiment, a possible mechanism was proposed to explain the formation of the mesoporous‐nanotube structure. The electrochemical properties of the samples as anode materials for lithium batteries were studied by cyclic voltammograms and Galvanostatic method. Results showed that the mesoporous‐tube hybrid composites displayed higher capacity and better cycle performance in comparison with the mesoporous tin dioxide. It was concluded that such a large improvement of electrochemical performance within the hybrid composites may in general be related to mesoporous‐tube structure that possess properties such as one‐dimensional hollow structure, high‐strength with flexibility, excellent electric conductivity and large surface area.  相似文献   

10.
A study of electrochemical Li insertion combined with structural and textural analysis enabled the identification and quantification of individual crystalline and amorphous phases in mesoporous TiO2 films prepared by the evaporation‐induced self‐assembly procedure. It was found that the properties of the amphiphilic block copolymers used as templates, namely those of a novel poly(ethylene‐co‐butylene)‐b‐poly(ethylene oxide) polymer (KLE) and commercial Pluronic P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H), decisively influence the physicochemical properties of the resulting films. The KLE‐templated films possess a 3D cubic mesoporous structure and are practically amorphous when calcined at temperatures below 450 °C, but treatment at 550–700 °C provides a pure‐phase (anatase), fully crystalline material with intact mesoporous architecture. The electrochemically determined fraction of crystalline anatase increases from 85 to 100 % for films calcined at 550 and 700 °C, respectively. In contrast, the films prepared using Pluronic P123, which also show a 3D cubic pore arrangement, exhibit almost 50 % crystallinity even at a calcination temperature of 400 °C, and their transformation into a fully crystalline material is accompanied by collapse of the mesoporous texture. Therefore, our study revealed the significance of using suitable block‐copolymer templates for the generation of mesoporous metal oxide films. Coupling of both electrochemical and X‐ray diffraction methods has shown to be highly advisable for the correct interpretation of structure properties, in particular the crystallinity, of such sol–gel derived films.  相似文献   

11.
Herein, we demonstrate an ammonia nitridation approach to synthesize self‐supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co3O4 and Cr2O3), which were nanocastly prepared by using mesoporous silica SBA‐15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA‐15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CoN) can be obtained by the transformation of Co3O4 nanowire replica under ammonia atmosphere from 275 to 350 °C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 °C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750–1000 °C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature‐program‐decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small‐angle XRD patterns and TEM images showed the 2‐D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide‐angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70–90 m2 g?1) and large pore volumes (about 0.2 cm3 g?1).  相似文献   

12.
An ordered mesoporous tungsten‐oxide/carbon (denoted as m‐WO3?x‐C‐s) nanocomposite is synthesized using a simple one‐pot method using polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as a structure‐directing agent. The hydrophilic PEO block interacts with the carbon and tungsten precursors (resol polymer and WCl6), and the PS block is converted to pores after heating at 700 °C under a nitrogen flow. The m‐WO3?x‐C‐s nanocomposite has a high Brunauer–Emmett–Teller (BET) surface area and hexagonally ordered pores. Because of its mesoporous structure and high intrinsic density of tungsten oxide, this material exhibits a high average volumetric capacitance and gravimetric capacitance as a pseudocapacitor electrode. In comparison with reduced mesoporous tungsten oxide (denoted as m‐WO3?x‐h), which is synthesized by a tedious hard template approach and further reduction in a H2/N2 atmosphere, m‐WO3?x‐C‐s shows a high capacitance and enhanced rate performance, as confirmed by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The good performance of m‐WO3?x‐C‐s is attributed to the high surface area arising from the mesoporous structure, the large interconnected mesopores, and the low internal resistance from the well‐dispersed reduced tungsten oxide and amorphous carbon composite structure. Here, the amorphous carbon acts as an electrical pathway for effective pseudocapacitor behavior of WO3‐x.  相似文献   

13.
RuO2‐based mesoporous thin films of optical quality are synthesized from ruthenium‐peroxo‐based sols using micelle templates made of amphiphilic polystyrene‐polyethylene oxide block copolymers. The mesoporous structure and physical properties of the RuO2 films (mesoporous volume: 30%; pore diameter: ~30 nm) can be controlled by the careful tuning of both the precursor solution and thermal treatment (150–350 °C). The optimal temperature that allows control of both mesoporosity and nanocristallinity is strongly dependent on the substrate (silicon or fluorine‐doped tin oxide). The structure of the resulting mesoporous films are investigated using X‐ray diffraction, X‐ray photoelectron spectroscopy, and atomic force microscopy. Mesoporous layers are additionally characterized by transmission and scanning electron microscopy and ellipsometry while their electrochemical properties are analyzed via cyclic voltammetry. Thick mesoporous films of ruthenium oxide hydrates, RuO2 · xH2O, obtained using a thermal treatment at 280 °C, exhibit capacitances as high as 1000 ± 100 F g?1 at a scan rate of 10 mV s?1, indicating their potential application as electrode materials.  相似文献   

14.
An oxidation‐resistant and elastic mesoporous carbon, graphene mesosponge (GMS), is prepared. GMS has a sponge‐like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single‐layer graphene walls, which realizes a high electric conductivity and a large surface area (1940 m2 g?1). Moreover, the graphene‐based framework includes only a very small amount of edge sites, thereby achieving much higher stability against oxidation than conventional porous carbons such as carbon blacks and activated carbons. Thus, GMS can simultaneously possess seemingly incompatible properties; the advantages of graphitized carbon materials (high conductivity and high oxidation resistance) and porous carbons (large surface area). These unique features allow GMS to exhibit a sufficient capacitance (125 F g?1), wide potential window (4 V), and good rate capability as an electrode material for electric double‐layer capacitors utilizing an organic electrolyte. Hence, GMS achieves a high energy density of 59.3 Wh kg?1 (material mass base), which is more than twice that of commercial materials. Moreover, the continuous graphene framework makes GMS mechanically tough and extremely elastic, and its mean pore size (5.8 nm) can be reversibly compressed down to 0.7 nm by simply applying mechanical force. The sponge‐like elastic property enables an advanced force‐induced adsorption control.  相似文献   

15.
Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C2H5O)3Si–R–Si(OC2H5)3 or R′–[Si(OC2H5)3]3 with R = methene (–CH2–), ethylene (–C2H2–), ethene (–C2H4–), 1,4‐phenylene (C6H4), and R′ = 1,3,5‐phenylene (C6H3). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and 29Si and 13C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH2 and C2H4 compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.  相似文献   

16.
Direct synthesis (co‐condensation reaction) and post‐synthesis reaction (grafting) are combined for the first time to efficiently fabricate bifunctionalized ordered mesoporous materials (OMMs). Ethylenediamine‐containing OMMs (ED‐MCM‐41) were first synthesized via direct synthesis and then further modified by the phenyl (PH) group in a supercritical fluid (SCF) medium via grafting reaction, resulting in OMMs with ED and PH groups (PH‐ED‐MCM‐41). X‐ray diffraction (XRD) patterns, N2 sorption properties, transmission electron microscopy (TEM), 29Si and 13C magic angle spinning (MAS) NMR, chemical analysis, and hydrothermal treatment were used to characterize the bifunctionalized materials. Experiments show that bifunctionalized OMMs can be efficiently prepared by modifying the directly synthesized monofunctionalized OMMs via grafting reaction in a supercritical fluid medium. Both functional groups are distributed uniformly at the surfaces. The advantage of bifunctionalized OMMs over monofunctionalized OMMs was illustrated by introducing thiol groups into ED‐MCM‐41 materials and the subsequent formation of CdS nanocrystals inside thiol‐ and ED‐functionalized MCM‐41 (HS‐ED‐MC‐41). Because of the variety of the functional groups that can be introduced into OMMs by direct synthesis or post‐synthesis reaction, it is expected that the present strategy could provide a generally applicable approach to the design of OMMs with two functional groups.  相似文献   

17.
Aluminum‐containing plugged mesoporous silica has been successfully prepared in an aqueous solution that contains triblock copolymer templates, nitrates, and silica sources but without using mineral acid. The acidity of the solution can be finely tuned from pH 1.4 to 2.8 according to the amount of the introduced aluminum species which ranged from an Al/Si molar ratio of 0.25/1 to 4.0/1. The aluminum nitrate additive in the starting mixture, along with the weak acidity produced by the nitrates, contributes to the formation of plugged hexagonal structures and the introduction of different amounts of aluminum species into the mesostructure. Characterization by X‐ray diffraction, transmission electron microscopy, and N2 sorption measurements show that the Al‐containing plugged silicas possess well‐ordered hexagonal mesostructures with high surface areas (700–860 m2 g–1), large pore volume (0.77–1.05 cm3 g–1) and, more importantly, combined micropores and/or small mesopores in the cylindrical channels. Inductively coupled plasma–atomic emission spectrometry results show that 0.7–3.0 wt % aluminum can be introduced into the final samples. 27Al MAS NMR results display that about 43–60% aluminum species are incorporated into the skeleton of the Al‐containing silicas and the amount of the framework aluminum increases as the initial added nitrates rises. Scanning electron microscopy images reveal that the directly synthesized Al‐containing plugged silica has a similar morphology to that of traditional SBA‐15. Furthermore, the Al‐containing plugged samples have excellent performances in the adsorption and the catalytic decomposition of isopropyl alcohol and nitrosamine. Finally, the direct synthesis method is used to produce plugged mesoporous silicas that contain other metals such as chromium and copper, and the resultant samples also show good catalytic activities.  相似文献   

18.
The optoelectronic response of a material governs its suitability for a wide range of applications, from photon detection to photovoltaic conversion. To conquer the material limitations and achieve improved optoelectronic responses, nanotechnology has been employed to arrange subunits with specific size‐dependent quantum mechanical properties in a hierarchically organized structure. However, building a functional optoelectronic system from nano‐objects remains a formidable challenge. In this paper, the fabrication of a new artificially engineered optoelectronic material by the preferential growth of silicon nanocrystals on the bottom of the pore‐channels of mesoporous silica is reported. The nanocrystals form highly stable interface structures bonded on one side; these structure show strong electron–phonon coupling and a ferroelectric‐like hysteretic switching property. A new class of multifunctional materials is realized by invoking a concept that employs semiconductor nanocrystals for optical sensing and utilizes interfacial polar layers to facilitate carrier transport and emulate ferroelectric‐like switching.  相似文献   

19.
As an anode material for lithium‐ion batteries, titanium dioxide (TiO2) shows good gravimetric performance (336 mAh g?1 for LiTiO2) and excellent cyclability. To address the poor rate behavior, slow lithium‐ion (Li+) diffusion, and high irreversible capacity decay, TiO2 nanomaterials with tuned phase compositions and morphologies are being investigated. Here, a promising material is prepared that comprises a mesoporous “yolk–shell” spherical morphology in which the core is anatase TiO2 and the shell is TiO2(B). The preparation employs a NaCl‐assisted solvothermal process and the electrochemical results indicate that the mesoporous yolk–shell microspheres have high specific reversible capacity at moderate current (330.0 mAh g?1 at C/5), excellent rate performance (181.8 mAh g?1 at 40C), and impressive cyclability (98% capacity retention after 500 cycles). The superior properties are attributed to the TiO2(B) nanosheet shell, which provides additional active area to stabilize the pseudocapacity. In addition, the open mesoporous morphology improves diffusion of electrolyte throughout the electrode, thereby contributing directly to greatly improved rate capacity.  相似文献   

20.
A new poly(p‐phenylenevinylene) (PPV) composite material has been developed by the incorporation of insoluble PPV polymer chains in the pores of monodisperse mesoporous silica spheres through an ion‐exchange and in situ polymerization method. The polymer distribution within the resultant colloidal particles is characterized by electron microscopy, energy dispersive X‐ray microanalysis, powder X‐ray diffraction, and nitrogen adsorption. It was found that the polymer was selectively incorporated into the mesopores of the silica host and was well distributed throughout the body of the particles. This confinement of the polymer influences the optical properties of the composite; these were examined by UV–vis and fluorescence spectroscopy and time‐correlated single‐photon counting. The results show a material that exhibits an extremely high fluorescence quantum yield (approaching 85%), and an improved resistance to oxidative photobleaching compared to PPV. These enhanced optical properties are further complemented by the overall processability of the colloidal material. In marked contrast to the insolubility of PPV, the material can be processed as a stable colloidal dispersion, and the individual composite spheres can be self‐assembled into opaline films using the vertical deposition method. The bandgap of the opal can be engineered to overlap with the emission band of the polymer, which has significant ramifications for lasing.  相似文献   

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