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1.
    
SBA‐15 (2D hexagonal structure) and KIT‐6 (3D cubic structure) silica materials are used as templates for the synthesis of two different crystalline mesoporous WO3 replicas usable as NO2 gas sensors. High‐resolution transmission electron microscopy (HRTEM) studies reveal that single‐crystal hexagonal rings set up the atomic morphology of the WO3 KIT‐6 replica, whereas the SBA‐15 replica is composed of randomly oriented nanoparticles. A model capable of explaining the KIT‐6 replica mesostructure is described. A small amount of chromium is added to the WO3 matrix in order to enhance sensor response. It is demonstrated that chromium does not form clusters, but well‐distributed centers. Pure WO3 KIT‐6 replica displays a higher response rate as well as a lower response time to NO2 gas than the SBA‐15 replica. This behavior is explained by taking into account that the KIT‐6 replica has a higher surface area as demonstrated by Brunauer–Emmett–Teller analyses and its mesostructure is fully maintained after the screen‐printing step involved in sensors preparation. The presence of chromium in the material results in a shorter response time and improved sensor response to the lowest NO2 concentrations tested. Electrical differences related to mesostructure are reduced as a result of additive introduction.  相似文献   

2.
    
A novel, heterogeneous approach to “naked‐eye” colorimetric and spectrophotometric anion sensing is demonstrated, employing the molecular receptor alizarin complexone adsorbed onto a nanocrystalline, mesoporous TiO2 film. pH buffer action intrinsic to the TiO2 film allows dip sensing in aqueous solutions. This heterogeneous sensing system exhibits a high selectivity to F– and CN– anions, high sensitivity, a rapid response time, and excellent reusability.  相似文献   

3.
    
One of the most challenging tasks encountered in developing highly efficient electro‐optic (EO) devices is to find a material system that possesses all desirable properties such as large EO coefficients, good thermal and mechanical stability, and low optical loss. In order to meet this stringent requirement, we have developed a series of crosslinkable EO dendrimers using the standardized AJL8 ‐type chromophore as the center core and the furyl‐ and anthryl‐containing dendrons as the periphery. Upon adding a trismaleimide ( TMI ) dienophile, these dendrimers could be in‐situ crosslinked via the Diels–Alder cycloaddition and efficiently poled under a high electric field. Through this dynamic process, the spatially voided and π‐electron‐rich surrounding of the chromophore core changes into a dense and more aliphatic network, with the dipolar chromophore embedded and aligned inside. The resultant materials exhibit large EO coefficients (63–99 pm V–1 at 1.31 μm), excellent temporal stability (the original r33 values remain unchanged at 100 °C for more than 500 h), and blue‐shifted near‐IR absorption. With these combined desirable properties, a poled EOD2/TMI film could be processed through multiple lithographic and etching steps to fabricate a racetrack‐shaped micro‐ring resonator. By coupling this ring resonator with a side‐polished optical fiber, a novel broadband electric‐field sensor with high sensitivity of 100 mV m–1 at 550 MHz was successfully demonstrated.  相似文献   

4.
    
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   

5.
    
The synthesis of a faujasite–Metglas composite material that can be used in gas‐sensing applications is presented. A continuous faujasite film was synthesized on a Metglas magnetoelastic strip using the secondary growth method. The ability of the new composite to remotely sense carbon dioxide in a nitrogen atmosphere at room temperature over a wide range of concentrations is demonstrated by monitoring the changes in the resonance frequency of the strip. The novel sensor combines the electromagnetic properties of the magnetoelastic material with the adsorption properties of the faujasite crystals. Experiments performed over a period of a few months showed that the composite sensor remained fully operational, thus indicating its long‐term stability. Furthermore, the present work demonstrates that a zeolite–Metglas composite can be used as a sensor of an analyte in a mixture as long as it adsorbs selectively larger amounts of the particular analyte than other compounds present in the mixture.  相似文献   

6.
    
The silver ionic conductivity in heterogeneous systems of AgBr:Al2O3 and AgI:Al2O3 is highly enhanced by utilizing mesoporous Al2O3 as the insulating phase. The highest Ag+ conductivity of 3.1 × 10–3 Ω–1 cm–1 (at 25 °C) has been obtained for the AgI:Al2O3 composite with an Al2O3 volume fraction of 0.3. For AgBr:Al2O3, the enhancement of the conductivity is satisfactorily explained in the framework of the ideal space‐charge model, while in the case of AgI:Al2O3 stacking disorder is also considered to contribute to the ionic conductivity.  相似文献   

7.
    
Using surfactant‐assisted synthesis, aluminas with hierarchical nanopores are produced. The hierarchical structures are composed of mesopores of 4 nm diameter, and macropores with diameters of about 300 nm. The structures were found to be stable to the thermal removal of the surfactant. Synthesis factors affecting the appearance of the hierarchically structured alumina material are presented. A potential mechanism for the formation of the uniquely structured aluminas is proposed.  相似文献   

8.
    
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   

9.
    
Hierarchical assembly of hollow microstructures is of great scientific and practical value and remains a great challenge. This paper presents a facile and one‐pot synthesis of Cu2O microspheres with multilayered and porous shells, which were organized by nanocrystals. The time‐dependent experiments revealed a two‐step organization process, in which hollow microspheres of Cu2(OH)3NO3 were formed first due to the Ostwald ripening and then reduced by glutamic acid, the resultant Cu2O nanocrystals were deposited on the hollow intermediate microspheres and organized into finally multishell structures. The special microstructures actually recorded the evolution process of materials morphologies and microstructures in space and time scales, implying an intermediate‐templating route, which is important for understanding and fabricating complex architectures. The Cu2O microspheres obtained were used to fabricate a gas sensor, which showed much higher sensitivity than solid Cu2O microspheres.  相似文献   

10.
    
Porous capsules composed of hematite, silica, and hematite–silica composites are prepared by a templated synthesis method. Polyelectrolyte multilayer‐coated particles (PEMPs) are used to synthesize goethite nanocrystals and the resulting goethite‐nanocrystal‐embedded PEMPs (PEMP–goethite) are then used as templates to form porous capsules. The surface morphology and surface area of the porous capsules can be controlled by the size of the PEMP–goethite template, which is determined by the extent of growth of the goethite nanocrystals. By controlling the surface morphology and area, it is also possible to tune the sensitivity of the hematite capsules for use as gas‐sensing materials. This surfactant‐free approach is also used to synthesize silica and silica‐based composite capsules with a controllable porous shell thickness. This straightforward approach can also be extended to the synthesis of other porous capsules or particles with a controllable surface morphology.  相似文献   

11.
    
On p. 2766, Qinshan Zhu and co‐workers report on multishell hollow Cu2O microspheres that are synthesized by a facile and one‐pot solvothermal route. A two‐step organization process, in which hollow microspheres of Cu2(OH)3NO3 are formed first followed by reduction to Cu2O by glutamic acid, leads to the special multishell and hollow microstructures. Interestingly, a Cu2O gas sensor fabricated with the multishell microspheres shows a much higher sensitivity to ethanol than solid Cu2O microspheres. Hierarchical assembly of hollow microstructures is of great scientific and practical value and remains a great challenge. This paper presents a facile and one‐pot synthesis of Cu2O microspheres with multilayered and porous shells, which were organized by nanocrystals. The time‐dependent experiments revealed a two‐step organization process, in which hollow microspheres of Cu2(OH)3NO3 were formed first due to the Ostwald ripening and then reduced by glutamic acid, the resultant Cu2O nanocrystals were deposited on the hollow intermediate microspheres and organized into finally multishell structures. The special microstructures actually recorded the evolution process of materials morphologies and microstructures in space and time scales, implying an intermediate‐templating route, which is important for understanding and fabricating complex architectures. The Cu2O microspheres obtained were used to fabricate a gas sensor, which showed much higher sensitivity than solid Cu2O microspheres.  相似文献   

12.
RuO2@SiO2 nanomaterials are prepared using hybrid mesostructured silica (EtO)2P(O)(CH2)3SiO1.5/x SiO2 (x = 9, 16) by anchoring the metal precursor [Ru(COD)(COT)] (COD is 1,3‐cyclooctadiene, COT is 1,3,5‐cyclooctatriene) inside the pores of the organized silica matrix through the phosphonate moieties. Following this task, the nanoparticles are fabricated by i) decomposing the metal precursor with hydrogen at room temperature in tetrahydrofuran to achieve ruthenium nanoparticles and ii) thermally treating the ruthenium particles in silica at 450 °C in air to fabricate RuO2. The materials containing Ru and RuO2 nanoparticles are characterized by elemental analysis, transmission electron microscopy (TEM), X‐ray diffraction (XRD), nitrogen sorption measurements, and 31P and 13C NMR. The obtained RuO2@SiO2 nanomaterials are evaluated as catalytic filters when deposited onto gas sensors for the preferential detection of propane in the multicomponent gas mixture propane/carbon monoxide/nitrogen dioxide.  相似文献   

13.
    
Two novel porous nitrosamine traps have been synthesized in order to eliminate carcinogens from the environment. A functional mesoporous material, CuO/SBA‐15, has been synthesized by using an in‐situ coating method, with the addition of a guest salt to the reaction system to modify the porous materials before the particles of SBA‐15 were incubated; the synthesis and modification processes were performed in a single step. The resulting mesoporous composites selectively adsorb N‐nitrosopyrrolidine (NPYR), a typical volatile nitrosamine, and are potential cigarette additives that can be used for the removal of nitrosamines from cigarette smoke, thereby protecting public health and the environment. In another reaction, silica gel is modified by being coated with magnesia and then corroded by NaOH solution.The magnesia is dispersed onto the silica by impregnating it with a magnesium acetate solution, followed by calcination. After corrosion of the calcined sample with caustic soda, only the silica particles that are completely covered by magnesia remain. This material exhibits a similar ability to SBA‐15 and zeolite NaY in its selective adsorption of NPYR.  相似文献   

14.
    
Because of its high activity and selectivity toward the reduction of hydrogen peroxide and oxygen, Prussian blue (PB) is usually considered as an “artificial enzyme peroxidase” and has been extensively used in the construction of electrochemical biosensors. In this study, we report on the construction of amperometric biosensors via grafting PB nanoparticles on the polymeric matrix of multiwalled carbon nanotubes (MWCNTs) and poly(4‐vinylpyridine) (PVP). The MWCNT/PVP/PB composite films were synthesized by casting films of MWCNTs wrapped with PVP on gold electrodes followed by electrochemical deposition of PB on the MWCNT/PVP matrix. The electrode modified with the MWCNT/PVP/PB composite film shows prominent electrocatalytic activity toward the reduction of hydrogen peroxide, which can be explained by the remarkable synergistic effect of the MWCNTs and PB. Therefore, fast amperometric response of this sensor to hydrogen peroxide was observed with a detection sensitivity of 1.3 μA μM –1 of H2O2 per square centimeter area and a detection limit of 25 nM . These results are much better than those reported for PB‐based amperometric sensors. In addition, a glucose biosensor fabricated by casting an additional glucose oxidase (GOD) containing Nafion film above the MWCNT/PVP/PB composite film shows promise for the sensitive and fast detection of glucose. The observed high stability, high sensitivity, and high reproducibility of the MWCNT/PVP/PB composite films make them promising for the reliable and durable detection of hydrogen peroxide and glucose.  相似文献   

15.
    
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   

16.
    
Among the mesoporous silica micellar templated structures (MTSs), MSU‐X silica, obtained through an N0I0 assembly between non‐ionic polyethyleneoxide‐based surfactants (N0) and silica neutral inorganic precursors (I0), exhibits a regular ordered structure with a 3D wormhole porous framework and an easily controlled pore size. These materials have been tested for applications requiring both a narrow mesopore size distribution and isotropic properties. A specific double‐step synthesis that we developed recently for MSU‐X materials has allowed us to prepare mesoporous silica particles with the required shape, size, and properties. Both the particles’ synthesis and comparative HPLC separation tests with a commercial ungrafted silica HPLC powder of identical shape and size are reported.  相似文献   

17.
    
The synthesis and characterization of a novel silicon–silica nanocomposite material are reported. A self‐assembly method allows the encapsulation of silicon nanoclusters within the channels of a periodic mesoporous silica thin film. The result is the formation of a silicon–silica nanocomposite film with bright, room‐temperature photoluminescence in the visible range, and a nanosecond luminescence lifetime. The properties of the nanocomposite material have been studied by several analytical techniques, which collectively show the existence within the channels of non‐diamondoid‐structure‐type silicon nanoclusters with various hydrogenated silicon sites. It is estimated that the silicon nanoclusters in the silica mesoporous films occupy up to 39 % of the accessible pore volume. The nanocomposite film shows improved resistance to air oxidation compared to crystalline silicon. The high loading and chemical stability to oxidation under ambient conditions are important advantages in terms of the development of silicon‐based light‐emitting diodes from this class of materials.  相似文献   

18.
    
A new class of bifunctional periodic mesoporous organosilicas (PMOs) composed of organosilicate building blocks with two different silicon sites have been synthesized from the single‐source bifunctional organosilica precursors tris(triethoxysilylethyl)ethoxysilane and bis(triethoxysilylethyl)diethoxysilane, respectively denoted MT3‐PMO and DT2‐PMO. The synthesis of these PMOs is achieved by the co‐assembly of a triblock‐copolymer Pluronic P123 template with the bifunctional organosilica precursor under acid‐catalyzed and inorganic‐salt‐assisted conditions. After template removal through solvent extraction, the MT3‐PMO and DT2‐PMO so obtained show well‐ordered mesopores and display large pore diameters (6–7 nm) and pore volumes (0.6–0.8 cm3 g–1) with a narrow pore‐size distribution and high surface areas (700–800 m3 g–1).  相似文献   

19.
    
A variety of alkyl hydroperoxides such as tert‐butyl‐, tert‐octyl‐, 1‐cyclopentyl‐, 1‐cyclohexyl‐, 3,4‐disubstituted‐1‐cyclohexyl‐, n‐propyl, and n‐undecyl‐hydroperoxides have been functionalized onto ordered mesoporous silica, SBA‐15, from the corresponding covalently anchored synthons. All the tert‐hydroperoxides are prepared by autoxidation using molecular O2 and an initiator, whereas other hydroperoxides are obtained by reaction with H2O2. For autoxidation, the use of a combination of an azoinitiator (AIBN) and N‐hydroxyphthalimide increased the hydroperoxide yield compared with using the azoinitiator alone. Synthons containing two or more tert‐ and sec‐hydrogens lead to higher peroxide yield compared to synthons with a single reactive site. Oxidation of Si–OH (silanol groups) with acidic H2O2 at low temperature produces Si–OOH. Reusability of these alkyl hydroperoxides is carried out by oxidation of alcohols obtained from the corresponding alkyl hydroperoxides using H2O2. Both the covalently anchored synthons and the resulting hydroperoxides are thoroughly characterized by powder X‐ray diffraction, 13C cross‐polarized magic angle spinning NMR, TG/DTA, Fourier transform IR spectroscopy, sorption, and surface area measurements. The quantification of the amount of alkyl hydroperoxide was carried out by iodometric titration using a thio solution. The hydroperoxides exhibit high activity for the epoxidation of styrene to styrene oxide and exhibit reasonably high efficiency for oxygen transfer.  相似文献   

20.
    
In this study we report the synthesis of a new class of materials called hybrid periodic mesoporous organosilicas (HPMOs). By coupling a silsesquioxane precursor through at least two chemical linkages to the mesopore walls of a pre‐existing periodic mesoporous silica (PMS) or periodic mesoporous organosilica (PMO). Many of the problems of a conventional PMO material can be avoided while ensuring efficient use of the bridging organic functional groups of the silsesquioxane. We demonstrate this concept for PMS by anchoring various silsesquioxanes, such as ethene and ethane silsesquioxanes, to the mesopore walls of the PMS. The addition of anchored silsesquioxane monolayers and multilayers to the mesopore walls also allows for the strict control of the diameter of the mesopore as well as the mesopore wall thickness in the final HPMO material. Additionally it is shown that having the silsesquioxane located solely on the surface of the mesopores in HPMOs gives increased chemical accessibility of the organic bridge‐bonded moiety when compared with their PMO counterparts containing the bridge‐bonded organic both on the surface and within the pore walls.  相似文献   

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