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1.
Core–shell carboxyl‐functionalized multiwall carbon nanotube (c‐MWCNT)/poly(m‐aminophenol) (PmAP) nanocomposite were prepared through in‐situ polymerization of m‐aminophenol (m‐AP) in the presence of MWCNTs, and explicated as a dielectric material for electronic applications. The formation of thin PmAP layer on individual c‐MWCNT with excellent molecular level interactions at interfaces was confirmed by morphological and spectroscopic analyses. Here we conducted a comparative study of the dielectric performances of PmAP based nanocomposite films with pristine MWCNTs and c‐MWCNTs as fillers. Compared to PmAP/MWCNT nanocomposites, the PmAP/c‐MWCNT nanocomposites exhibited higher dielectric permittivity and lower dielectric loss. The well dispersed c‐MWCNTs in PmAP/c‐MWCNT nanocomposite produce huge interfacial area together with numerous active polarized centers (crystallographic defects), which in turn intensified the Maxwell‐Wagner‐Sillars (MWS) effect based on excellent molecular level interactions and thus, produce large dielectric permittivity (8810 at 1 kHz). The percolation threshold of PmAP/c‐MWCNT nanocomposites is found lower than that of the PmAP/MWCNT nanocomposites, which could be attributed to homogeneous distribution of c‐MWCNTs and strong c‐MWCNT//PmAP interfacial interactions in the nanocomposites. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

2.
Poly(L ‐lactide)/multiwalled carbon nanotubes (PLLA/MWCNTs) nanocomposite recently attracts much attention because of its excellent comprehensive properties including improved thermostability, tensile strength, and conductivity. However, the nanocomposite exhibits similar brittleness compared with unmodified PLLA. In this work, a polar elastomer, that is, ethylene‐co‐vinyl acetate (EVA), was introduced into PLLA/MWCNTs nanocomposite. The selective distribution of MWCNTs and the effects of EVA on crystalline structure of PLLA were investigated using scanning electron microscope, transmission electron microscope, differential scanning calorimetry, and wide angle X‐ray diffraction. The results show that the presence of EVA induces the change of the distribution of MWCNTs in the nanocomposites, and consequently, the cold crystallization of PLLA is prevented. With the increase of EVA content, both the ductility and the impact resistance of PLLA/FMWCNTs are improved greatly, indicating the toughening effect of EVA on PLLA/MWCNTs nanocomposite. The decreased tensile strength and modulus can be compensated through annealing treatment. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011  相似文献   

3.
The ability to obtain a maximum loading of inorganic nanoparticles while maintaining uniform dispersion in the polymer is the key to the fabrication of mixed‐matrix membranes with high pervaporation performance in bioalcohol recovery from aqueous solution. Herein, we report the simultaneous spray self‐assembly of a zeolitic imidazolate framework (ZIF)–polymer suspension and a cross‐linker/catalyst solution as a method for the fabrication of a well‐dispersed ZIF‐8–PDMS nanohybrid membrane with an extremely high loading. The ZIF‐8–PDMS membrane showed excellent biobutanol‐permselective pervaporation performance. When the ZIF‐8 loading was increased to 40 wt %, the total flux and separation factor could reach 4846.2 g m−2 h−1 and 81.6, respectively, in the recovery of n‐butanol from 1.0 wt % aqueous solution (80 °C). This new method is expected to have serious implications for the preparation of defect‐free mixed‐matrix membranes for many applications.  相似文献   

4.
《化学:亚洲杂志》2017,12(7):753-758
Hybrid nanocrystals of PVBA‐b ‐PS/ZIF‐8 were prepared by the growth of ZIF‐8 on the surface of the self‐assembled structures from poly(p ‐vinylbenzoic acid)‐block‐polystyrene. Two different morphologies—micelles and vesicles—were obtained in selective solvents owing to the different ratios of PVBA to PS blocks. The structure and morphology of the PVBA‐b ‐PS/ZIF‐8 composites were characterized by Fourier transform IR spectroscopy, thermogravimetric analysis, X‐ray diffraction, transmission electron microscopy and scanning electron microscopy. PVBA‐b ‐PS/ZIF‐8 showed high catalytic performance in Knoevenagel condensation reactions at room temperature, which were attributed to the more exposed active sites of the small ZIF‐8 nanocrystals grown in a confined space and a high concentration of reactants in the polymeric aggregates.  相似文献   

5.
In this work, a glassy carbon electrode (GCE) was modified with multiwall carbon nanotubes/ionic liquid/graphene quantum dots (MWCNTs/IL/GQDs) nanocomposite. Then, the nanocomposite was decorated with nickel‐cobalt nanoparticles (Ni?Co NPs), and it was used as a non‐enzymatic glucose sensor. Field emission scanning electron microscopy, X‐ray diffraction spectroscopy, and energy dispersive spectroscopy were employed to prove the electrodeposition of the Ni?Co NPs on the surface of MWCNTs/IL/GQDs/GCE. Also, cyclic voltammetric and amperometric methods were utilized for the investigation of the electrochemical behaviour of the Ni?Co NPs/MWCNTs/IL/GQDs/GCE for glucose oxidation. The novel amperometric sensor displayed two linear ranges from 1.0 to 190.0 μmol L?1 and 190.0 to 4910 μmol L?1 with a low detection limit of 0.3 μmol L?1 as well as fast response time (2 s) and high stability. Also, the sensor showed good selectivity for glucose determination in the presence of ascorbic acid, citric acid, dopamine, uric acid, fructose, and sucrose, as potential interference species. Finally, the performance of the proposed sensor was investigated for the glucose determination in real samples. Ni?Co NPs/MWCNTs/IL/GQDs/GCE showed good sensitivity and excellent selectivity.  相似文献   

6.
A convenient method for the confined incorporation of highly active bimetallic PdCo nanocatalysts within a hollow and porous metal–organic framework (MOF) support is presented. Several chemical conversions occur simultaneously during the one‐step low temperature pyrolysis of well‐designed polystyrene@ZIF‐67/Pd2+ core–shell microspheres, where ZIF (zeolitic imidazolate framework) is a subclass of MOF: the polystyrene core is removed, resulting in a beneficial hollow and porous ZIF support; the ZIF‐67 shell acts as a well‐defined porous support and as a felicitous Co2+ supplier for metal nanoparticle formation; and Pd2+ and Co2+ are reduced to form catalytically active bimetallic PdCo nanoparticles in the well‐defined micropores, inducing the confined growth of PdCo nanoparticles with excellent dispersity.  相似文献   

7.
We report the synthesis of cobalt sulfide multi‐shelled nanoboxes through metal–organic framework (MOF)‐based complex anion conversion and exchange processes. The polyvanadate ions react with cobalt‐based zeolitic imidazolate framework‐67 (ZIF‐67) nanocubes to form ZIF‐67/cobalt polyvanadate yolk‐shelled particles. The as‐formed yolk‐shelled particles are gradually converted into cobalt divanadate multi‐shelled nanoboxes by solvothermal treatment. The number of shells can be easily controlled from 2 to 5 by varying the temperature. Finally, cobalt sulfide multi‐shelled nanoboxes are produced through ion‐exchange with S2? ions and subsequent annealing. The as‐obtained cobalt sulfide multi‐shelled nanoboxes exhibit enhanced sodium‐storage properties when evaluated as anodes for sodium‐ion batteries. For example, a high specific capacity of 438 mAh g?1 can be retained after 100 cycles at the current density of 500 mA g?1.  相似文献   

8.
PDMAEMA‐b‐PMAA block copolymers were prepared by the sequential RAFT polymerization of DMAEMA and tBMA, followed by hydrolysis. Phosphotungstic acid (HPW) was anchored to the PDMAEMA blocks through electrostatic interactions and the as‐obtained HPW/PDMAEMA‐b‐PMAA was added to the synthesis of ZIF‐8. During the formation of ZIF‐8, the PMAA blocks coordinated to the Zn2+ ions through their carboxy groups, along with the HPW groups that were anchored to the PDMAEMA blocks. In this way, the block copolymer could consolidate the interactions between HPW and ZIF‐8 and prevent the leakage of HPW. Finally, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite was obtained and the structure of the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 hybrid material was characterized by using powder X‐ray diffraction (PXRD), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). As a photocatalyst, the HPW/PDMAEMA‐b‐PMAA/ZIF‐8 ternary lamellar composite showed excellent photoactivity for the degradation of methylene blue (MB). The rate of degradation of MB was 0.0240 min?1, which was 7.5‐times higher than that of commercially available P25 (0.0032 min?1). In the presence of H2O2, the kinetic degradation parameters of the composite reached 0.0634 min?1, which was about 19.8‐times higher than that of P25.  相似文献   

9.
The rational design of metal–organic frameworks (MOFs) with hollow features and tunable porosity at the nanoscale can enhance their intrinsic properties and stimulates increasing attentions. In this Communication, we demonstrate that methanol can affect the coordination mode of ZIF‐67 in the presence of Co2+ and induces a mild phase transformation under solvothermal conditions. By applying this transformation process to the ZIF‐67@ZIF‐8 core–shell structures, a well‐defined hollow Zn/Co ZIF rhombic dodecahedron can be obtained. The manufacturing of hollow MOFs enables us to prepare a noble metal@MOF yolk‐shell composite with controlled spatial distribution and morphology. The enhanced gas storage and porous confinement that originate from the hollow interior and coating of ZIF‐8 confers this unique catalyst with superior activity and selectivity toward the semi‐hydrogenation of acetylene.  相似文献   

10.
《化学:亚洲杂志》2018,13(18):2641-2648
Copper‐doped zeolite imidazole framework‐8 (Cu/ZIF‐8) was prepared and its peroxidase‐like oxidative catalytic activity was examined with a demonstration of its applicability for cancer‐cell imaging. Through simple solution chemistry at room temperature, Cu/ZIF‐8 nanocrystals were produced that catalytically oxidized an organic substrate of o‐phenylenediamine in the presence of H2O2. In a similar manner to peroxidase, the Cu/ZIF‐8 nanocrystals oxidized the substrate through a ping‐pong mechanism with an activation energy of 59.2 kJ mol−1. The doped Cu atoms functioned as active sites in which the active Cu intermediates were expected to be generated during the catalysis, whereas the undoped ZIF‐8 did not show any oxidative activity. Cu/ZIF‐8 nanocrystals exhibited low cell toxicity and displayed catalytic activity through interaction with H2O2 among various reactive oxygen species in a cancer cell. This oxidative activity in vitro allowed cancer‐cell imaging by exploiting the photoluminescence emitted from the oxidized product of o‐phenylenediamine, which was insignificant in the absence of the Cu/ZIF‐8 nanocrystals. The results of this study suggest that the Cu/ZIF‐8 nanocrystal is a promising catalyst for the analysis of the microbiological systems.  相似文献   

11.
A series of spray dried zeolitic imidazolate frameworks (ZIFs = ZIF‐8, ZIF‐67, and Zn/Co‐ZIF) are used as a catalyst for the bulk ring‐opening polymerization of δ‐valerolactone without any co‐catalyst to generate polyvalerolactone. Interestingly, using the same catalyst under the same reaction conditions could manipulate the structure of the product polymer, and thus its physical properties. Thus, using a dried substrate leads to the formation of the cyclic polymer while a linear polymer was formed on using the commercially available substrate. An activated monomer mechanism has been suggested where the propagating zinc alkoxide undergoes an intramolecular transesterification to release cyclic or linear polyvalerolactone. The ROP of δ‐VL without drying shows that the polymeric zwitterions have little tendency to cyclize in the presence of moisture. At 140 °C, ZIF‐8 shows a superior catalytic activity resulting in the production of cyclic polyvalerolactone having a high molecular weight as compared to ZIF‐67 or Zn/Co‐ZIF due to the presence of highly active sites. The catalyst could be recycled and reused without any significant loss of catalytic activity.  相似文献   

12.
Matrix‐polymer‐functionalized multiwalled carbon nanotubes (MWCNTs) are demonstrated as a highly efficient toughening agent for matrix polymers. With poly(vinylidene fluoride) (PVDF) as the matrix polymer, the PVDF/MWCNT‐PVDF nanocomposite films show high toughness. With a small load amount of MWCNT‐PVDF (0.07 wt %), the nanocomposite film shows a yield point and a constant‐stress extension region in stress–strain tests, compared with the typical low‐extensibility feature of neat PVDF film. The PVDF/MWCNT‐PVDF‐0.7 film exhibits a 180‐fold increase of toughness and about 38‐fold increase in strain at break compared with neat PVDF film. This toughening effect is attributed to (a) homogeneous dispersion of MWCNT‐PVDF in PVDF, (b) the high efficiency of load‐transfer across MWCNT/PVDF interface, and (c) the long length of the MWCNTs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012  相似文献   

13.
The zeolitic imidazolate framework ZIF‐4 has recently been shown to exhibit large structural flexibility as a response to hydrostatic pressures, going from an open pore phase ( ZIF ‐ 4 ( Zn )‐ op ) to a closed pore phase ( ZIF ‐ 4 ( Zn )‐ cp ). The use of diamond anvil cell (DAC) setups has so far restricted thorough experimental insight into the evolution of lattice parameters at pressures below p < 0.1 GPa. Here we revisit the high‐pressure properties of ZIF‐4(Zn) by applying a new high‐pressure powder X‐ray diffraction setup that allows for tracking the evolution of lattice parameters in pressure increments as small as Δp = 0.005 GPa in the pressure range p = ambient – 0.4 GPa; a pressure resolution that cannot be achieved by using traditional DACs. We find ZIF‐4(Zn) has a bulk modulus of K( ZIF ‐ 4 ( Zn )‐ op ) = 2.01 ± 0.05 GPa and K( ZIF ‐ 4 ( Zn )‐ cp ) = 4.39 ± 0.20 GPa, clarifying and confirming some ambiguous results that have been reported previously.  相似文献   

14.
The present work describes the development of a selective and sensitive voltammetric sensor for simultaneous determination of catechol (CC) and hydroquinone (HQ), based on a glassy carbon (GC) electrode modified with manganese phthalocyanine azo‐macrocycle (MnPc) adsorbed on multiwalled carbon nanotubes (MWCNT). Scanning electron microscopy and scanning electrochemical microscopy were used to characterize the composite material (MnPc/MWCNT) on the glassy carbon electrode surface. The modified electrode showed excellent electrochemical activity towards the simultaneous oxidation and reduction of CC and HQ. On the MnPc/MWCNT/GC electrode, both CC and HQ can generate a pair of quasi‐reversible and well‐defined redox peaks. Under optimized experimental and operational conditions, the cathodic peak currents were linear over the range 1–600 µmol L?1 for both CC and HQ, with limits of detection of 0.095 and 0.041 µmol L?1, respectively. The anodic peak currents were also linear over the range 1–600 µmol L?1 for both CC and HQ, with limits of detection of 0.096 and 0.048 µmol L?1, respectively. The proposed method was effectively applied for the simultaneous detection of hydroquinone and catechol in water samples and the results were in agreement with those obtained by a comparative method described in the literature.  相似文献   

15.
In this communication, the synthesis, characterization, and properties of highly conductive core–shell nanocomposites of poly(N‐vinylcarbazole) (PNVC)–polypyrrole (PPY) copolymers with multi‐walled carbon nanotubes (MWCNTs) are described. A unique free‐radical coupling reaction between PNVC and PPY cation radicals in chloroform solvent, using feric chloride as an oxidant, in the presence of suspended MWCNTs in the reaction medium, was used for the synthesis of nanocomposite. Field‐emission scanning and transmission electron microscopy studies showed the formation of the core–shell nanocomposite. Raman spectrocopy results as well as thermogravimetric analysis supported the electron microscopic observations. The resulting PNVC–PPY copolymer‐coated MWCNTs showed an unprecedentedly increased value of direct electrical conductivity (bulk) compared to the conductivity of all samples even with pure MWCNTs.

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16.
A novel nanocomposite coating of poly(o‐toluidine) and oxidized multiwalled CNTs (MWCNTs, where CNTs is carbon nanotubes) was electrochemically prepared on a stainless‐steel wire. The applicability of the fiber was assessed for the headspace solid‐phase microextraction of benzene, toluene, ethylbenzene, and xylenes in aqueous samples followed by GC with flame ionization detection. In order to obtain an adherent and stable composite coating, several experimental parameters related to the coating process, such as polymerization potential and time, and the concentration of o‐toluidine and oxidized MWCNTs were optimized. The combination of MWCNTs and polymer in a nanocomposite form presents desirable opportunities to produce materials for new applications. The effects of various parameters on the efficiency of the headspace solid‐phase microextraction process, such as desorption temperature and time, extraction temperature and time, and ionic strength were also investigated. At the optimum conditions, LODs were 0.03–0.06 μg/L. The method showed linearity in the range of 0.5–300 μg/L with coefficients of determination >0.99. The intraday and interday RSDs obtained at a 5 μg/L concentration level (n = 5) using a single fiber were 1.2–5.2 and 3.2–7.5%, respectively. The fiber‐to‐fiber RSD (%; n = 3) at 5 μg/L was 6.1–9.2%.  相似文献   

17.
High‐performance non‐noble electrocatalysts for oxygen reduction reaction (ORR) are the prerequisite for large‐scale utilization of fuel cells. Herein, a type of sandwiched‐like non‐noble electrocatalyst with highly dispersed FeNx active sites embedded in a hierarchically porous carbon/graphene heterostructure was fabricated using a bottom‐up strategy. The in situ ion substitution of Fe3+ in a nitrogen‐containing MOF (ZIF‐8) allows the Fe‐heteroatoms to be uniformly distributed in the MOF precursor, and the assembly of Fe‐doped ZIF‐8 nano‐crystals with graphene‐oxide and in situ reduction of graphene‐oxide afford a sandwiched‐like Fe‐doped ZIF‐8/graphene heterostructure. This type of heterostructure enables simultaneous optimization of FeNx active sites, architecture and interface properties for obtaining an electron‐catalyst after a one‐step carbonization. The synergistic effect of these factors render the resulting catalysts with excellent ORR activities. The half‐wave potential of 0.88 V vs. RHE outperforms most of the none‐noble metal catalyst and is comparable with the commercial Pt/C (20 wt %) catalyst. Apart from the high activity, this catalyst exhibits excellent durability and good methanol‐tolerance. Detailed investigations demonstrate that a moderate content of Fe dopants can effectively increase the intrinsic activities, and the hybridization of graphene can enhance the reaction kinetics of ORR. The strategy proposed in this work gives an inspiration towards developing efficient noble‐metal‐free electrocatalysts for ORR.  相似文献   

18.
Simultaneous determination of dihydroxybenzene isomers in neutral condition was successfully realized by a simple and easy prepared modified electrode without previous chemical or physical separations. The multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE), which was prepared by the drop-coating method, was characterized by FE-SEM and TEM. Then, the electrochemical behavior of dihydroxybenzene isomers at MWCNTs/GCE was systematically studied at different temperature and pH conditions. The oxidation peak potentials were separated in neutral condition with 105 mV to hydroquinone (HQ) and catechol (CC) and 390 mV to CC and resorcinol (RS). And in neutral condition, the amperometric current were found to be linear with concentration of HQ, CC, and RS (20–140 μM) with the presence of 100 μM other isomers. Furthermore, excellent anti-interference, stability, and reproducibility were also presented by this modified electrode.  相似文献   

19.
The unique features of high porosity, shape selectivity, and multiple active sites make metal–organic frameworks (MOFs) promising as novel stationary phases for high‐performance liquid chromatography (HPLC). However, the wide particle size distribution and irregular shape of conventional MOFs lead to lower column efficiency of such MOF‐packed columns. Herein, the fabrication of monodisperse MOF@SiO2 core–shell microspheres as the stationary phase for HPLC to overcome the above‐mentioned problems is reported. Zeolitic imidazolate framework 8 (ZIF‐8) was used as an example of MOFs due to its permanent porosity, uniform pore size, and exceptional chemical stability. Unique carboxyl‐modified silica spheres were used as the support to grow the ZIF‐8 shell. The fabricated monodisperse ZIF‐8@SiO2 packed columns (5 cm long × 4.6 mm i.d.) show high column efficiency (23 000 plates m?1 for bisphenol A) for the HPLC separation of endocrine‐disrupting chemicals (bisphenol A, β‐estradiol, and p‐(tert‐octyl)phenol) and pesticides (thiamethoxam, hexaflumuron, chlorantraniliprole, and pymetrozine) within 7 min with good relative standard deviations for 11 replicate separations of the analytes (0.01–0.39, 0.65–1.7, 0.70–1.3, and 0.17–0.91 % for retention time, peak area, peak height, and half peak width, respectively). The ZIF‐8@SiO2 microspheres combine the advantages of the good column packing properties of the uniform monodisperse silica microspheres and the separation ability of the ZIF‐8 crystals.  相似文献   

20.
This communication describes the morphology and DC conductivity of poly(N‐vinylcarbazole) (PNVC)/multi‐walled carbon nanotubes (MWCNTs) nanocomposite. The nanocomposite has been synthesized by solid state in situ polymerization of N‐vinylcarbazole (NVC) monomer in the presence of MWCNTs at an elevated temperature. Fourier transform infrared (FT‐IR) spectroscopy studies reveal the ability of MWCNTs to promote the in situ polymerization of the NVC monomer. Field‐emission scanning electron microscopy (FE‐SEM) observations show the homogeneous wrapping of MWCNTs' outer surface by PNVC polymer. Transmission electron microscopy (TEM) images and Raman spectroscopy results support the SEM observations. Thermogravimetric analyses reveal a significant improvement of thermal stability of the nanocomposite sample in the higher temperature region. The resulting nanocomposite material exhibits a dramatic improvement of the DC conductivity inherent to the PNVC. For example, the DC conductivity increases from ≈5.9 × 10−13 S · cm−1 for PNVC to ≈12 S · cm−1 for the nanocomposite, an increase of about 1013 in the electrical conductivity.

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