Selected-control fabrication of multifunctional fluorescent-magnetic core-shell and yolk-shell hybrid nanostructures

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(2)O(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(2)O(3):Eu core-shell and yolk-shell nanostructures can be precisely tuned. Importantly, as-prepared SPIO@Y(2)O(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(2)O(3):Eu core-shell nanoparticles and yolk-shell NCs. The combined magnetic manipulation and optical monitoring of magnetic-fluorescent SPIO@Y(2)O(3):Eu yolk-shell NCs will open up many exciting opportunities in dual imaging for targeted delivery and thermal therapy.     

微波热解法制备Cu/Cu2O纳米材料

在二乙二醇溶剂体系中利用微波介电加热分解醋酸铜前体,进一步还原得到Cu2O和Cu纳米粒子以及Cu/Cu2O核壳结构。 采用X射线衍射、透射电子显微镜、扫描电子显微镜和紫外吸收光谱测试技术对产物的形貌、结构和组成进行了研究,结果表明,得到的Cu/Cu2O核壳结构直径为500 nm左右。 对比实验研究了不同聚合度乙二醇系列溶剂、反应时间以及表面活性剂或配位剂对产物形貌、组成的影响,表明低聚合度乙二醇和长的反应时间有利于醋酸铜还原形成铜。     

Revisiting the Stöber method: inhomogeneity in silica shells

We demonstrate that the silica shell on nanoparticles formed by a typical St?ber method is inhomogeneous in nature. The outer layer of the shell is chemically more robust than the inner layer, which can be selectively etched by hot water. Methods are developed to "harden" the soft silica shells. These new understandings are exploited to develop versatile and template-free approaches for fabricating sophisticated yolk-shell nanostructures.     

Magnetic MOF microreactors for recyclable size-selective biocatalysis

In this contribution we report a synthetic strategy for the encapsulation of functional biomolecules within MOF-based microcapsules. We employ an agarose hydrogel droplet Pickering-stabilised by UiO-66 and magnetite nanoparticles as a template around which to deposit a hierarchically structured ZIF-8 shell. The resulting microcapsules are robust, highly microporous and readily attracted to a magnet, where the hydrogel core provides a facile means to encapsulate enzymes for recyclable size-selective biocatalysis.     

Catalytically Active Hollow Fiber Membranes with Enzyme-Embedded Metal–Organic Framework Coating

Metal–organic frameworks (MOFs) are suitable enzyme immobilization matrices. Reported here is the in situ biomineralization of glucose oxidase (GOD) into MOF crystals (ZIF-8) by interfacial crystallization. This method is effective for the selective coating of porous polyethersulfone microfiltration hollow fibers on the shell side in a straightforward one-step process. MOF layers with a thickness of 8 μm were synthesized, and fluorescence microscopy and a colorimetric protein assay revealed the successful inclusion of GOD into the ZIF-8 layer with an enzyme concentration of 29±3 μg cm⁻². Enzymatic activity tests revealed that 50 % of the enzyme activity is preserved. Continuous enzymatic reactions, by the permeation of β-d -glucose through the GOD@ZIF-8 membranes, showed a 50 % increased activity compared to batch experiments, emphasizing the importance of the convective transport of educts and products to and from the enzymatic active centers.     

Selective dimerization of higher cycloolefins in the presence of micro- and micromesoporous zeolite catalysts

Selective synthesis of dimers of cycloolefins C₆-C₈ was carried out in the presence of highly dispersed zeolite catalysts HY, HBeta, and HZSM-12 and granulated zeolite HY-WB, which differ in acidic properties and pore structure. The high selectivity of microporous zeolite HZSM-12 in cyclohexene dimerization (100%) and micromesoporous zeolite HY-WB in cycloheptene and cyclooctene dimerization (90–95%) was established.     

潜手性Schiff碱不对称催化还原反应研究进展

对近年来潜手性Schiff碱的不对称催化氢化的发展状况按照均相、非均相及氢转移催化氢化三种类型进行了较为详尽的综述.     

GaN@ZIF-8: selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework

The microporous zeolitic imidazolate framework [Zn(MeIM)(2); ZIF-8; MeIM = imidazolate-2-methyl] was quantitatively loaded with trimethylamine gallane [(CH(3))(3)NGaH(3)]. The obtained inclusion compound [(CH(3))(3)NGaH(3)]@ZIF-8 reveals three precursor molecules per host cavity. Treatment with ammonia selectively yields the caged cyclotrigallazane intermediate (H(2)GaNH(2))(3)@ZIF-8, and further annealing gives GaN@ZIF-8. This new composite material was characterized with FT-IR spectroscopy, solid-state NMR spectroscopy, powder X-ray diffraction, elemental analysis, (scanning) transmission electron microscopy combined with electron energy-loss spectroscopy, photoluminescence (PL) spectroscopy, and N(2) sorption measurements. The data give evidence for the presence of GaN nanoparticles (1-3 nm) embedded in the cavities of ZIF-8, including a blue-shift of the PL emission band caused by the quantum size effect.     

Preparation of metallodielectric composite particles with multishell structure

In this article, we demonstrated the synthesis of metallodielectric composite particles comprising a metal shell on a dielectric core and an outer coating of an insulating dielectric layer by depositing silver on silica supporting cores followed by coating of titania. A combination of surface reaction and surface seeding techniques is exploited for the formation of a complete silver shell on silica spheres. The additional outer coating of titania on silver shell particles is then performed by hydrolyzing tetra-n-butyl titanate in ethanol at room temperature. The morphologies of silver shells and titania coating are studied with electron microscopy, and their existences are confirmed with X-ray diffraction and energy-dispersive X-ray measurement.     

Au@ZIF-8核壳结构中金纳米粒子分布的调控及其在荧光分子光致发光传感中的应用

控制金属@MOF核壳纳米结构中金属纳米粒子的分布不容易实现。我们应用了合成MOF胶体粒子所用到的配位调制方法来合成Au@ZIF-8核壳纳米结构。通过使用过量的2-甲基咪唑和不同用量的1-甲基咪唑可获得不同的Au@ZIF-8。该合成方法可在ZIF-8纳米晶体中灵活调整Au纳米粒子（Au NPs）的分布。此外,我们分别研究了2种不同尺寸的荧光分子与Au@ZIF-8结合后的光致发光光谱和寿命。ZIF-8的孔径可以决定这2种分子是否可通过多孔壳结构接近Au NPs。分子光学特性对Au NPs近场的发光增强和荧光猝灭的竞争非常敏感。     

Diffusion through the Shells of Yolk-Shell and Core-Shell Nanostructures in the Liquid Phase

Easy in, easy out: Mass transport through TiO(2) and SiO(2) shells was probed in the liquid phase with IR spectroscopy by detecting carbon monoxide adsorption in Pt@void@TiO(2) yolk-shell and Pt@SiO(2) core-shell nanostructures (see picture; C?green, O?red, Pt?pale red). Adsorption was observed on the surface of Pt nanoparticle cores, and on the inner face of the TiO(2) shells in the yolk-shell case.     

CoPd Nanoalloys with Metal–Organic Framework as Template for Both N-Doped Carbon and Cobalt Precursor: Efficient and Robust Catalysts for Hydrogenation Reactions

In this work, a series of metal–organic framework (MOF)-derived CoPd nanoalloys have been prepared. The nanocatalysts exhibited excellent activities in the hydrogenation of nitroarenes and alkenes in green solvent (ethanol/water) under mild conditions (H₂ balloon, room temperature). Using ZIF-67 as template for both carbon matrix and cobalt precursor coating with a mesoporous SiO₂ layer, the catalyst CoPd/NC@SiO₂ was smoothly constructed. Catalytic results revealed a synergistic effect between Co and Pd components in the hydrogenation process due to the enhanced electron density. The mesoporous SiO₂ shell effectively prevented the sintering of hollow carbon and metal NPs at high temperature, furnishing the well-dispersed nanoalloy catalysts and better catalytic performance. Moreover, the catalyst was durable and showed negligible activity decay in recycling and scale-up experiments, providing a mild and highly efficient way to access amines and arenes.     

Synthesis of Hollow SiO2 Nanoparticles from Dy2O3@SiO2 Core–Shell Nanocomposites via a Recyclable Sonochemical Method

Hollow silica nanoparticles were prepared from Dy₂O₃@SiO₂ core–shell nanocomposites, for the first time, by a simple ultrasonic assisted sol–gel method. The Dy₂O₃@SiO₂ core–shell nanocomposites were prepared by the deposition of a SiO₂ layer onto the surface of Dy₂O₃ nanoparticles using a three-step coating process. The hollow SiO₂ nanostructures were obtained by selective removal of the Dy₂O₃ cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction, Fourier transfom infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results indicated that hollow SiO₂ nanostructures were sphere-like shape with the average size of 20?nm and had an amorphous crystal structure. The important advantage of this process is the recyclability of the Dy₂O₃ nanoparticles as the starting material of the reaction.     

Thermosensitive Au-PNIPA yolk-shell particles as “nanoreactors” with tunable optical properties

We demonstrate that Au-silica-poly(N-isopropylacrylamide) (PNIPA) trilayer composite particles with controllable thickness of PNIPA out-layer can be developed via free radical polymerization using Au-silica core-shell particles as seed. The presence of Au-silica particles does not influence of thermosensitivity of PNIPA shell, which exhibits a similar swelling behavior as pure PNIPA microgels. The etching of silica midlayer by NaOH treatment leads to Au-PNIPA particles with yolk-shell structure. The obtained yolk-shell particles can work as “nanoreactors” for the further growth of Au core within the PNIPA shell via seeded growth approach, which is followed with interesting optical properties. In addition, the optical properties of the Au cores can be modulated by the volume transition of the PNIPA shell.     

低共熔溶剂中原位合成ZIF-8膜及其气体分离性能

在α-氧化铝载体上,采用原位合成法,在尿素/氯化胆碱低共熔溶剂中合成了ZIF-8膜。采用X射线衍射(XRD)和扫描电子显微镜(SEM)对合成的ZIF-8膜进行了表征。考察了反应溶液浓度、降温速率对ZIF-8膜合成的影响。通过优化合成条件合成了表面平整致密,厚度为8 μm的ZIF-8膜。采用Wicke-Kallenbach技术对优化条件下合成的ZIF-8膜进行了单组分气体渗透和双组分混合气体分离性能表征。在室温(293 K)下,ZIF-8膜对H2/CO2、H2/O2、H2/N2、H2/CH4双组分气体的分离系数分别为7.4、5.2、9.1、13.8,均大于相应的努森扩散分离系数,说明合成的ZIF-8膜具有分子筛分性能。     

Synthesis and Characterization of Pd@MxCu1−x (M=Au,Pd, and Pt) Nanocages with Porous Walls and a Yolk–Shell Structure through Galvanic Replacement Reactions

This paper describes the synthesis of Pd@M_xCu_1?x (M=Au, Pd, and Pt) nanocages with a yolk–shell structure through galvanic replacement reactions that involve Pd@Cu core–shell nanocubes as sacrificial templates and ethylene glycol as the solvent. Compared with the most commonly used templates based on Ag, Cu offers a much lower reduction potential (0.34 versus 0.80 V), making the galvanic reaction more easily to conduct, even at room temperature. Our structural and compositional characterizations indicated that the products were hollow inside, and each one of them contained porous M–Cu alloy walls and a Pd cube in the interior. For the Pd@Au_xCu_1?x yolk–shell nanocages, they displayed broad extinction peaks extending from the visible to the near‐IR region. Our mechanistic study revealed that the dissolution of the Cu shell preferred to start from the slightly truncated corners and then progressed toward the interior, because the Cu {100} side faces were protected by a surface capping layer of hexadecylamine. This galvanic approach can also be extended to generating other hollow metal nanostructures by using different combinations of Cu nanostructures and salt precursors.     

Synthesis of bimetallic nanoshells by an improved electroless plating method

In the Letter, we demonstrate an improved electroless plating method for the synthesis of bimetallic shell particles. The procedure involves a combination of surface reaction, seeding growth, and removal of supporting cores. We modified ammonical AgNO3 in ethanol with a controlled amount of HCHO in the seeding process and a uniform and relatively dense coverage of silver nanoparticle seeds on colloid cores was achieved. Following the second kind of metal plating, we extended this method to prepare continuous bimetallic core-shell and hollow particles with a submicrometer diameter. The morphologies of the bimetallic Cu/Ag and Pt/Ag particles were studied with transmission electron microscopy and scanning electron microscopy, and their crystallinity and chemical composition were confirmed by X-ray diffraction. The prepared materials may be of applied value in areas such as catalysis, optics, and plasmonics.     

On Metal Blocking in Micropores of Carbon Supports

Platinum catalysts prepared on activated carbon supports of different origin are compared in the hydrogenation of cyclohexene and cyclooctene, which differ much in their reactivity. A decrease in the catalytic activity upon decreasing the dimensions of the micropores in the support and the size of the supported metal particles has been confirmed. The results give evidence against a trivial role of the diffusional factor in such an effect and indicate complete blocking of part of the metal surface in narrow pores.     

ZIF-8 based polysulfone hollow fiber membranes for natural gas purification

Mixed matrix membranes (MMMs) have received worldwide attention for natural gas purification due to their superior performance in terms of permeability and selectivity. The zeolitic imidazole framework-8 (ZIF-8) blended polysulfone (PSf) membranes have been fabricated for natural gas purification. ZIF-8 was selected due to its low cost, remarkable thermal and chemical stabilities, and tunable microporous structure. The neat PSf hollow fiber membrane and mixed matrix hollow fiber membranes incorporated with the various ZIF-8 loadings up to 1.25% were fabricated. The prepared membranes were evaluated using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and gas separation performance. The low loading of ZIF-8 nanoparticles to the MMM improved thermal stability and glass transition temperature and yielded low surface roughness. MMMs were tested using pure gases with a significant improvement of 36% in CO₂ permeability and 28% in CO₂/CH₄ selectivity compared to the neat membrane. However, the high ZIF-8 loading reduced the separation performances. Moreover, CO₂/CH₄ selectivity decreased at elevated pressure (8 and 10 bar) due to CO₂-induced plasticization. Previously, the incorporation of ZIF-8 particles has primarily been subjected to the fabrication of flat sheet membranes, whereas this work focused on hollow fiber membranes which are rarely investigated. Hence, the promising results obtained at low feed pressure in this study demonstrated the potential of ZIF-8 based hollow fiber membrane for natural gas purification.     

Porosity control of Pd@SiO2 yolk-shell nanocatalysts by the formation of nickel phyllosilicate and its influence on Suzuki coupling reactions

The surface of Pd@SiO(2) core-shell nanoparticles (1) was simply modified by the formation of nickel phyllosilicate. The addition of nickel salts formed branched nickel phyllosilicates and generated pores in the silica shells, yielding Pd@SiO(2)-Niphy nanoparticles (Niphy = nickel phyllosilicate; 2, 3). By removal of the silica residue, Pd@Niphy yolk-shell nanoparticles (4) was uniformly obtained. The four distinct nanostructures (1-4) were employed as catalysts for Suzuki coupling reactions with aryl bromide and phenylboronic acid, and the conversion yields were in the order of 1 < 2 < 3 < 4 as the pore volume and surface area of the catalysts increased. The reaction rates were strongly correlated with shell porosity and surface exposure of the metal cores. The chemical inertness of nickel phyllosilicate under the basic conditions rendered the catalysts reusable for more than five times without loss of activity.