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1.
Iron oxide (Fe 3O 4) magnetic nanoparticles as movable cores were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first more common route, Fe 3O 4 nanoparticles were coated with silica layer via the Stöber process to yield Fe 3O 4@SiO 2 core–shell nanoparticles, subsequently used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe 3O 4@SiO 2@P(AA‐EGDMA). The silica layer was selectively removed through alkali etching to yield Fe 3O 4@air@P(AA‐EGDMA). In the second route, Fe 3O 4 nanoparticles without any stabilization were used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe 3O 4@P(AA‐EGDMA) core–shell nanoparticles. The nanoparticles were subsequently dispersed in acidic medium of pH = 2. Yolk–shell Fe 3O 4@air@P(AA‐EGDMA) nanoparticles were formed through deswelling of crosslinked PAA because of protonation of carboxyl groups at low pH values. Various techniques were utilized to investigate the characteristics of the synthesized core–shell nanoparticles. Formation of yolk–shell nanostructure was observed for both synthesis routes, namely etching of silica layer and deswelling approaches, from vibrating sample magnetometry and transmission electron microscopy results. Both types of nanoparticles showed pH‐responsive behaviour, i.e. decrease in absorption with increase in pH, as examined using UV–visible spectroscopy. 相似文献
2.
The preparation of Ni@Pd core–shell nanoparticles immobilized on yolk–shell Fe 3O 4@polyaniline composites is reported. Fe 3O 4 nanoclusters were first synthesized through the solvothermal method and then the SiO 2 shell was coated on the Fe 3O 4 surface via a sol–gel process. To prepare Fe 3O 4@SiO 2@polyaniline composites, polyvinylpyrrolidone was first grafted on to the surface of Fe 3O 4@SiO 2 composites and subsequently polymerization of aniline was carried out via an ultrasound‐assisted in situ surface polymerization method. Selective etching of the middle SiO 2 layer was then accomplished to obtain the yolk–shell Fe 3O 4@polyaniline composites. The approach uses polyaniline (PANI) conductive polymer as a template for the synthesis of Ni@Pd core–shell nanoparticles. The catalytic activity of the synthesized yolk–shell Fe 3O 4@PANI/Ni@Pd composite was investigated in the reduction of o‐nitroaniline to benzenediamine by NaBH 4, which exhibited conversion of 99% in 3 min with a very low content of the catalyst. Transmission electron microscopy, X‐ray photoelectron spectroscopy, TGA, X‐ray diffraction, UV–visible, scanning electron microscopy, X‐ray energy dispersion spectroscopy and FT‐IR were employed to characterize the synthesized nanocatalyst. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
A simple, efficient and eco‐friendly procedure has been developed using Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe 2O 3@TiO 2 (γ‐Fe 2O 3@TiO 2‐EG‐Cu(II)) for the synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles, via the condensation reactions of various aldehydes with benzil and ammonium acetate or ammonium acetate and amines, under solvent‐free conditions. High‐resolution transmission electron microscopy analysis of this catalyst clearly affirmed the formation of a γ‐Fe 2O 3 core and a TiO 2 shell, with mean sizes of about 10–20 and 5–10 nm, respectively. These data were in very good agreement with X‐ray crystallographic measurements (13 and 7 nm). Moreover, magnetization measurements revealed that both γ‐Fe 2O 3@TiO 2 and γ‐Fe 2O 3@TiO 2‐EG‐Cu(II) had superparamagnetic behaviour with saturation magnetization of 23.79 and 22.12 emu g ?1, respectively. γ‐Fe 2O 3@TiO 2‐EG‐Cu(II) was found to be a green and highly efficient nanocatalyst, which could be easily handled, recovered and reused several times without significant loss of its activity. The scope of the presented methodology is quite broad; a variety of aldehydes as well as amines have been shown to be viable substrates. A mechanism for the cyclocondensation reaction has also been proposed. 相似文献
4.
A facile and efficient method for fabrication of magnetic composite microspheres CoFe2O4@TiO2@Au is demonstrated. The shells of anatase TiO2 were coated onto a magnetic CoFe2O4 core via liquid-phase deposition procedure, and then Au nanoparticles were deposited onto CoFe2O4@TiO2 microspheres through seed-mediated growth. XRD, TEM, and VSM were used to investigate the structure, morphology and magnetic properties of the samples, their photocatalytic activity were also tested. Heterostructure of CoFe2O4@TiO2@Au was confirmed by different measurements. Compared to unmodified CoFe2O4@TiO2 microspheres, CoFe2O4@TiO2@Au microspheres showed higher photocatalytic activity for Rhodamine B (RhB) degradation in water. 相似文献
5.
Mesoporous nanoparticles composed of γ‐Al 2O 3 cores and α‐Fe 2O 3 shells were synthesized in aqueous medium. The surface charge of γ‐Al 2O 3 helps to form the core–shell nanocrystals. The core–shell structure and formation mechanism have been investigated by wide‐angle XRD, energy‐dispersive X‐ray spectroscopy, and elemental mapping by ultrahigh‐resolution (UHR) TEM and X‐ray photoelectron spectroscopy. The N 2 adsorption–desorption isotherm of this core–shell materials, which is of type IV, is characteristic of a mesoporous material having a BET surface area of 385 m 2 g ?1 and an average pore size of about 3.2 nm. The SEM images revealed that the mesoporosity in this core–shell material is due to self‐aggregation of tiny spherical nanocrystals with sizes of about 15–20 nm. Diffuse‐reflectance UV/Vis spectra, elemental mapping by UHRTEM, and wide‐angle XRD patterns indicate that the materials are composed of aluminum oxide cores and iron oxide shells. These Al 2O 3@Fe 2O 3 core–shell nanoparticles act as a heterogeneous Fenton nanocatalyst in the presence of hydrogen peroxide, and show high catalytic efficiency for the one‐pot conversion of cyclohexanone to adipic acid in water. The heterogeneous nature of the catalyst was confirmed by a hot filtration test and analysis of the reaction mixture by atomic absorption spectroscopy. The kinetics of the reaction was monitored by gas chromatography and 1H NMR spectroscopy. The new core–shell catalyst remained in a separate solid phase, which could easily be removed from the reaction mixture by simple filtration and the catalyst reused efficiently. 相似文献
6.
Core–shell structured Fe 3O 4/SiO 2/TiO 2 nanocomposites with enhanced photocatalytic activity that are capable of fast magnetic separation have been successfully synthesized by combining two steps of a sol–gel process with calcination. The as‐obtained core–shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO 2, and an outer layer of TiO 2 nanocrystals with a tunable average size. The convenient control over the size and crystallinity of the TiO 2 nanocatalysts makes it possible to achieve higher photocatalytic efficiency than that of commercial photocatalyst Degussa P25. The photocatalytic activity increases as the thickness of the TiO 2 nanocrystal shell decreases. The presence of SiO 2 interlayer helps to enhance the photocatalytic efficiency of the TiO 2 nanocrystal shell as well as the chemical and thermal stability of Fe 3O 4 core. In addition, the TiO 2 nanocrystals strongly adhere to the magnetic supports through covalent bonds. We demonstrate that this photocatalyst can be easily recycled by applying an external magnetic field while maintaining their photocatalytic activity during at least eighteen cycles of use. 相似文献
7.
Hollow mesoporous SiO 2 (mSiO 2) nanostructures with movable nanoparticles (NPs) as cores, so‐called yolk‐shell nanocapsules (NCs), have attracted great research interest. However, a highly efficient, simple and general way to produce yolk‐mSiO 2 shell NCs with tunable functional cores and shell compositions is still a great challenge. A facile, general and reproducible strategy has been developed for fabricating discrete, monodisperse and highly uniform yolk‐shell NCs under mild conditions, composed of mSiO 2 shells and diverse functional NP cores with different compositions and shapes. These NPs can be Fe 3O 4 NPs, gold nanorods (GNRs), and rare‐earth upconversion NRs, endowing the yolk‐mSiO 2 shell NCs with magnetic, plasmonic, and upconversion fluorescent properties. In addition, multifunctional yolk‐shell NCs with tunable interior hollow spaces and mSiO 2 shell thickness can be precisely controlled. More importantly, fluorescent‐magnetic‐biotargeting multifunctional polyethyleneimine (PEI)‐modified fluorescent Fe 3O 4@mSiO 2 yolk‐shell nanobioprobes as an example for simultaneous targeted fluorescence imaging and magnetically guided drug delivery to liver cancer cells is also demonstrated. This synthetic approach can be easily extended to the fabrication of multifunctional yolk@mSiO 2 shell nanostructures that encapsulate various functional movable NP cores, which construct a potential platform for the simultaneous targeted delivery of drug/gene/DNA/siRNA and bio‐imaging. 相似文献
8.
A yolk–shell-structured sphere composed of a superparamagnetic Fe 3O 4 core and a carbon shell (Fe 3O 4@HCS) was etched from Fe 3O 4@SiO 2@carbon by NaOH, which was synthesized through the layer-by-layer coating of Fe 3O 4. This yolk–shell composite has a shell thickness of ca. 27 nm and a high specific surface area of 213.2 m 2 g ?1. Its performance for the magnetic removal of tetracycline hydrochloride from water was systematically examined. A high equilibrium adsorption capacity of ca. 49.0 mg g ?1 was determined. Moreover, the adsorbent can be regenerated within 10 min through a photo-Fenton reaction. A stable adsorption capacity of 44.3 mg g ?1 with a fluctuation <10% is preserved after 5 consecutive adsorption–degradation cycles, demonstrating its promising application potential in the decontamination of sewage water polluted by antibiotics. 相似文献
9.
A facile and effective approach to preparation of dual‐responsive magnetic core/shell composite microspheres is reported. The magnetite(Fe 3O 4)/poly(methacrylic acid) (PMAA) composite microspheres were synthesized through encapsulating γ‐methacryloxypropyltrimethoxysilane (MPS)‐modified magnetite colloid nanocrystal clusters (MCNCs) with crosslinked PMAA shell. First, the 200‐nm‐sized MCNCs were fabricated through solvothermal reaction, and then the MCNCs were modified with MPS to form active vinyl groups on the surface of MCNCs, and finally, a pH‐responsive shell of PMAA was coated onto the surface of MCNCs by distillation‐precipitation polymerization. The transmission electron microscopy (TEM) and vibrating sample magnetometer characterization showed that the obtained composite microspheres had well‐defined core/shell structure and high saturation magnetization value (35 emu/g). The experimental results indicated that the thickness and degree of crosslinking of PMAA shell could be well‐controlled. The pH‐induced change in size exhibited by the core/shell microspheres reflected the PMAA shell contained large amount of carboxyl groups. The carboxyl groups and high saturation magnetization make these microspheres have a great potential in biomolecule separation and drug carriers. Moreover, we also demonstrated that other magnetic polymeric microspheres, such as Fe 3O 4/PAA, Fe 3O 4/PAM, and Fe 3O 4/PNIPAM, could be synthesized by this approach. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
10.
The Fe 3O 4/TiO 2/Bi 2O 3 composites were synthesized by a sol–gel method and used as improved photocatalysts for the degradation of methyl orange (MO) under simulated sunlight at room temperature. The as-prepared Fe 3O 4/TiO 2/Bi 2O 3 composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). TEM analysis reveals that the composite has a core–shell structure and diameters of Fe 3O 4 core is about 200 nm. DRS results reveal that all composites showed red shift in optical absorption. TiO 2, Fe 3O 4, and Bi 2O 3 exist mainly as separate phases in the Fe 3O 4/TiO 2/Bi 2O 3 composites based on XPS analysis. The photocatalytic degradation of MO with the prepared photocatalysts was studied under simulated sunlight illumination. Photocatalytic reactivity test indicated that the removal efficiency of MO with the Fe 3O 4/TiO 2/Bi 2O 3 photocatalyst was higher than that of pure TiO 2 and Fe 3O 4/TiO 2. Recovery rate of Fe 3O 4/TiO 2/Bi 2O 3 photocatalysts achieved 80 % after five times reuse. 相似文献
11.
Magnetic core–shell titanium dioxide nanoparticles (Fe 3O 4@SiO 2@TiO 2) were applied for the efficient preparation of 1,2,4,5‐tetrasubstituted imidazole derivatives by the one‐pot multi‐component condensation of benzil with aldehydes, primary amines and ammonium acetate under solvent‐free conditions. The catalyst was synthesized and studied using several techniques including X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
12.
Magnetic silica‐coated magnetite (Fe 3O 4) sub‐microspheres with immobilized metal‐affinity ligands are prepared for protein adsorption. First, magnetite sub‐microspheres were synthesized by a hydrothermal method. Then silica was coated on the surface of Fe 3O 4 particles using a sol–gel method to obtain magnetic silica sub‐microspheres with core‐shell morphology. Next, the trichloro(4‐chloromethylphenyl) silane was immobilized on them, reacted with iminodiacetic acid (IDA), and charged with Cu 2+. The obtained magnetic silica sub‐microspheres with immobilized Cu 2+ were applied for the absorption of bovine hemoglobin (BHb) and the removal of BHb from bovine blood. The size, morphology, and magnetic properties of the resulting magnetic micro(nano) spheres were investigated by using scanning microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and a vibrating sample magnetometer (VSM). The measurements showed that the magnetic sub‐microspheres are spherical in shape, very uniform in size with a core‐shell, and are almost superparamagnetic. The saturation magnetization of silica‐coated magnetite (Fe 3O 4) sub‐microspheres reached about 33 emu g ?1. Protein adsorption results showed that the sub‐microspheres had a high adsorption capacity for BHb (418.6 mg g ?1), low nonspecific adsorption, and good removal of BHb from bovine blood. This opens a novel route for future applications in removing abundant proteins in proteomic analysis. 相似文献
13.
One‐pot synthesis of thermoresponsive magnetic composite microspheres with a poly( N‐isopropylacrylamide) (PNIPAM) shell and a Fe 3O 4 core is demonstrated. Temperature sensitivity of PNIPAM was adopted to design the novel synthesis pathway. The as‐prepared composite microspheres have an obvious core‐shell structure with a mean size of approximately 250 nm. The Fe 3O 4 core is approximately 5 nm and the thickness of the PNIPAM shell is approximately 10 nm. The content of Fe 3O 4 in the composite microspheres can be controlled by this method. The composite microspheres experience a swelling and shrinking process in water by adjusting the temperature below and above the lower critical solution temperature (LCST) around 32 °C. These microspheres also show fine response to an external magnetic field. This work presents a platform to synthesize organic/inorganic composite microspheres in a facile and efficient approach. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2702–2708 相似文献
14.
The thermal decomposition approach, reverse micro-emulsion system and surface modification technique had been successfully used to synthesis single magnetic core Fe 3O 4@Organic Layer@SiO 2–NH 2 complex microspheres. The magnetization of the magnetic microspheres core could be easily tuned between 28 and 56 emu/g by adjusting the amount of 2-mercaptobarbituric acid. It was found that the Organic Layer to some extent had a protective effect on avoiding Fe 3O 4 being oxidized into Fe 2O 3. Each Fe 3O 4@Organic Layer microsphere could be coated uniformly by about 30 nm of silica shell. The average diameter of the Fe 3O 4@Organic Layer@SiO 2 composites was about 538 nm. The saturation magnetization of the Fe 3O 4@Organic Layer@SiO 2 complex microspheres was 12.5% less than magnetic microspheres cores. The Fe 3O 4@Organic Layer@SiO 2–NH 2 composites possessed a huge application potentiality in specificity enriching and separating biological samples. 相似文献
15.
通过溶剂热和溶胶-凝胶涂层法, 设计并制备了具有分级多孔结构和光催化性质的核-壳纳米球(HP-Fe 2O 3@TiO 2). 透射电子显微镜(TEM)照片证明所得HP-Fe 2O 3@TiO 2样品具备分级多孔结构, 这是因为HP-Fe 2O 3@TiO 2的内核-Fe 2O 3具有大孔空隙, 同时外壳-TiO 2具有介孔空隙. 此外, 通过X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)以及氮气吸附-脱附曲线深入研究了HP-Fe 2O 3@TiO 2的结构及其性质. 分别在可见及紫外光照下, 研究了样品在H 2O 2体系下的光催化降解亚甲基蓝(MB)的性质. 所观察到的HP-Fe 2O 3@TiO 2纳米球的光催化性能, 可归因于核-壳结构的协同作用, 这进一步表明, TiO 2外壳对α-Fe 2O 3的光催化活性有重要影响作用. 在可见光照射下, HP-Fe 2O 3@TiO 2 (1 mL Ti(OC 4H 9) 4 (TBT))具有较优异的光催化活性. 同时, HP-Fe 2O 3@TiO 2 (4mL TBT)具备优异的单分散形貌, 并在紫外光照射下, 表现出最优的光催化活性. 相似文献
16.
Three‐dimensional (3D) flowerlike hierarchical Fe 3O 4@Bi 2O 3 core–shell architectures were synthesized by a simple and direct solvothermal route without any linker shell. The results indicated that the size of the 3D flowerlike hierarchical microspheres was about 420 nm and the shell was composed of several nanosheets with a thickness of 4–10 nm and a width of 100–140 nm. The saturation magnetization of the superparamagnetic composite microspheres was about 41 emu g ?1 at room temperature. Moreover, the Fe 3O 4@Bi 2O 3 composite microspheres showed much higher (7–10 times) photocatalytic activity than commercial Bi 2O 3 particles under visible‐light irradiation. The possible formation mechanism was proposed for Ostwald ripening and the self‐assembled process. This novel composite material may have potential applications in water treatment, degradation of dye pollutants, and environmental cleaning, for example. 相似文献
17.
In this work, the NiFe 2O 4@TiO 2/reduced graphene oxide (RGO) ternary nanocomposites with high saturation magnetization and catalytic efficiency have been synthesized through the following steps. First, graphene oxide was prepared using the modified Hummer's method. Second, the NiFe 2O 4 nanoparticles were successfully prepared using the hydrothermal method. Third, the core shell‐structured NiFe 2O 4@TiO 2/RGO nanocomposite precursors were easily obtained through hydrolysis reaction. The morphology of NiFe 2O 4@TiO 2/RGO nanocomposites was characterized from scanning electron microscope (SEM) and transmission electron microscope (TEM) images. Moreover, the results of X‐ray diffraction (XRD) patterns proved that the TiO 2 coating shell consisted of anatase. The vibrating sample magnetometer (VSM) measurements showed that the saturation magnetization value of NiFe 2O 4@TiO 2/RGO ternary nanocomposites was 25 emu/g. The X‐ray photoelectron spectroscopy (XPS) analysis confirmed that only part of the graphite oxide (GO) was reduced to RGO in the ternary nanocomposite. The degradation experiments proved that NiFe 2O 4@TiO 2/RGO nanocomposite exhibited the high catalytic efficiency and outstanding recyclable performance for rhodamine B (RhB). 相似文献
18.
A facile strategy is reported for the fabrication of Pt‐loaded core–shell nanocomposite ellipsoids (Fe 2O 3‐Pt@DSL) consisting of ellipsoidal Fe 2O 3 cores, double‐layered La 2O 3 shells and deposited Pt nanoparticles (NPs). The formation of the doubled‐shelled structure uses Fe 2O 3‐Pt@mSiO 2 as template sacrificial agent and it involves the re‐deposition of silica and self‐assembly of metal oxide units. The preparation methods of double‐shelled metal oxides avoid repeated coating and etching and could be utilized to fabricate other shaped double‐shelled composites. Characterization results indicated that the Fe 2O 3‐Pt@DSL nanocomposites possessed mesoporous structure and tunable shell thickness. Moreover, due to the formation of Fe 2O 3 and La 2O 3 composites, Pt NPs can also be stabilized via deposition on chemically active oxides with a synergistic effect. Therefore, as a catalyst for the reduction of 4‐nitrophenol, Fe 2O 3‐Pt@DSL showed superior catalytic activity and reusability due to structural superiority and enhanced composite synergy. Finally, well‐dispersed Pt NPs were encapsulated into the void between the shell layers to construct the Fe 2O 3‐Pt@DSL‐Pt catalyst. 相似文献
19.
The selected‐control preparation of uniform core–shell and yolk–shell architectures, which combine the multiple functions of a superparamagnetic iron oxide (SPIO) core and europium‐doped yttrium oxide (Y 2O 3:Eu) shell in a single material with tunable fluorescence and magnetic properties, has been successfully achieved by controlling the heat‐treatment conditions. Furthermore, the shell thickness and interior cavity of SPIO@Y 2O 3:Eu core–shell and yolk–shell nanostructures can be precisely tuned. Importantly, as‐prepared SPIO@Y 2O 3:Eu yolk–shell nanocapsules (NCs) modified with amino groups as cancer‐cell fluorescence imaging agents are also demonstrated. To the best of our knowledge, this is the first report on the selected‐control fabrication of uniform SPIO@Y 2O 3:Eu core–shell nanoparticles and yolk–shell NCs. The combined magnetic manipulation and optical monitoring of magnetic–fluorescent SPIO@Y 2O 3:Eu yolk–shell NCs will open up many exciting opportunities in dual imaging for targeted delivery and thermal therapy. 相似文献
20.
The novel three-component Fe 3O 4/TiO 2/Ag composite mircospheres were prepared via a facile chemical deposition route. The Fe 3O 4/TiO 2 mircospheres were first prepared by the solvothermal method, and then Ag nanoparticles were anchored onto the out-layer of TiO 2 by the tyrosine-reduced method. The as-prepared magnetic Fe 3O 4/TiO 2/Ag composite mircospheres were applied as photocatalysis for the photocatalytic degradation of methylene blue. The results indicate that the photocatalytic activity of Fe 3O 4/TiO 2/Ag composite microspheres is superior to that of Fe 3O 4/TiO 2 due to the dual effects of the enhanced light absorption and reduction of photoelectron–hole pair recombination in TiO 2 with the introduction of Ag NPs. Moreover, these magnetic Fe 3O 4/TiO 2/Ag composite microspheres can be completely removed from the dispersion with the help of magnetic separation and reused with little or no loss of catalytic activity. 相似文献
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