Jia Liu

Multifunctional Mesoporous Composite Microspheres with Well-Designed Nanostructure: A Highly Integrated Catalyst System

The precise control of the size, morphology, surface chemistry, and assembly process of each component is important to construction of integrated functional nanocomposites. We report here the fabrication of multifunctional microspheres which possess a core of nonporous silica-protected magnetite particles, transition layer of active gold nanoparticles, and an outer shell of ordered mesoporous silica with perpendicularly aligned pore channels. The well-designed microspheres have high magnetization (18.6 emu/g), large surface area (236 m(2)/g), highly open mesopores (approximately 2.2 nm), and stably confined but accessible Au nanoparticles and, as a result, show high performance in catalytic reduction of 4-nitrophenol (with conversion of 95% in 12 min), styrene epoxidation with high conversion (72%) and selectivity (80%), especially convenient magnetic separability, long life and good reusability. The unique nanostructure makes the microsphere to be a novel stable and approachable catalyst system for various catalytic industry processes.

Highly Water-Dispersible Biocompatible Magnetite Particles with Low Cytotoxicity Stabilized by Citrate Groups†

The synthesis of functional nanoparticles with controllable size and shape is of great importance because of their fundamental scientific significance and broad technological applications. Magnetic nanocrystals have attracted much attention in the past few decades owing to their unique magnetic features and important applications in biomedicine and therapeutics. In particular, superparamagnetic nanoparticles have been extensively pursued for bioseparation, drug delivery, 20] and detection of cancer. 21–22] Among various magnetic nanoparticles, iron oxides, such as magnetite (Fe3O4) or maghemite (g-Fe2O3), have been considered as ideal candidates for these bio-related applications owing to their good biocompatibility and stability in physiological conditions and low cytotoxicity. Many methods have been developed to prepare iron oxide nanocrystals. The thermal decomposition of organometallic and coordination compounds in nonpolar solution has been used successfully for the synthesis of monodisperse magnetic nanocrystals with high crystallinity and small size on the nanometer scale. However, the magnetic nanocrystals synthesized by these methods are usually hydrophobic, stabilized by nondegradable surfactants, and have a low magnetization, which hampers their applications extremely in bio-related fields, where water-dispersible particles with high magnetic field responsiveness are in demand. Therefore, much effort has focused on the fabrication of water-soluble iron oxide nanocrystals with controllable sizes, fast magnetic response, and desirable surface properties. Although many ligand-exchange strategies have been explored to offer them hydrophilic surface and aqueous dispersibility, their magnetic field responsiveness has not been effectively improved. Li and co-workers reported a convenient synthesis of hydrophilic magnetite microspheres by a solvothermal reaction by reduction of FeCl3 with ethylene glycol (EG), but the resultant magnetite microspheres are ferromagnetic and not water dispersible. Recently, they synthesized magnetic microspheres using a microemulsion of oil droplets in water as confined templates. These magnetic nanoparticles are assembled with the evaporation of low-boiling-point solvents. More recently, by a using high-temperature reduction reaction with poly(acrylic acid) (PAA) as a stabilizer, FeCl3 as a precursor, and diethylene glycol as a reductant, Ge et al. directly fabricated water-dispersible superparamagnetic nanocrystal clusters with controllable diameters of 30– 180 nm. These nanoclusters are composed of small nanocrystals of 6–8 nm. However, the polyelectrolyte PAA attached on the magnetic clusters is not biodegradable and biocompatible, and thus may limit their applications. Herein, we report a facile synthesis of highly water-dispersible magnetite particles with tunable size by a modified solvothermal reaction. The magnetite particles were synthesized by a modified solvothermal reaction at 200 8C by reduction of FeCl3 with EG in the presence of sodium acetate as an alkali source and biocompatible trisodium citrate (Na3Cit) as an electrostatic stabilizer. The excess EG acts as both the solvent and reductant. Na3Cit was chosen because the three carboxylate groups have strong coordination affinity to Fe ions, which favors the attachment of citrate groups on the surface of the magnetite nanocrystals and prevents them from aggregating into large single crystals as occurred previously. Moreover, Na3Cit is widely used in food and drug industry and citric acid is one of products from tricarboxylic acid cycle (TAC), a normal metabolic process in human body. Typically, the 250 nm magnetite particles were synthesized with the composition of FeCl3/Na3Cit/NaOAc/EG = 1:0.17:36.5:89.5 at 200 8C for 10 h (see the Supporting Information for experimental details). Scanning electron microscopy (SEM) images show that when the FeCl3 concentration is in the range of 0.05 to 0.25 molL , all of the magnetite particles obtained have a nearly spherical shape and uniform size (Figure 1). The diameter of the spheres dramatically increases from 80 to 410 nm with the increase of FeCl3 concentration, indicating that higher FeCl3 concentrations can lead to a larger particle size. Transmission electron microscopy (TEM) (Figure 2 a) reveals that the magnetite particles prepared from 0.2 molL 1 of FeCl3 have a nearly uniform size of about 250 nm and spherical shape, which is in good agreement to the SEM results (Figure 1c). A TEM image at higher magnification [*] J. Liu, Z. K. Sun, Dr. Y. H. Deng, Y. Zou, C. Y. Li, Dr. X. H. Guo, L. Q. Xiong, Y. Gao, Prof. Dr. F. Y. Li, Prof. Dr. D. Y. Zhao Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials and Advanced Materials Laboratory, Fudan University Shanghai 200433 (China) Fax: (+ 86)21-6564-1740 E-mail: yhdeng@fudan.edu.cn dyzhao@fudan.edu.cn Homepage: http://homepage.fudan.edu.cn/~dyzhao/

A simple approach to the synthesis of hollow microspheres with magnetite/silica hybrid walls

In this paper, we report a simple approach for templating synthesis of magnetic hollow composite microspheres with magnetite/silica walls. This approach is based on the co-sedimentation of polymer microspheres and magnetic colloids followed by impregnation with silica oligomer from tetraethyl orthosilicate and the further removal of the polymer microspheres by pyrolysis. The diameter of the hollow microspheres can be adjusted in range of 300 nm-2.0 microm by using polymer microspheres of different sizes and the wall thickness is tunable from 10-50 nm by controlling ratio of magnetite to the polymer microspheres. Magnetic characterizations show that the hollow microspheres have superparamagnetism with magnetization saturation of 10-30 emu/g. HRTEM and N(2) adsorption-desorption isotherms reveal that the hollow microspheres have numerous nanopores in the walls with a broad distribution in the range of 2 to 80 nm, which results in a high BET surface (67.6 m(2)/g) and pores volume (0.14 cm(3)/g).

A novel approach to the construction of 3-D ordered macrostructures with polyhedral particles

A novel and facile approach was developed for the fabrication of 3-D ordered macrostructures of polyhedral particles through coating and packing of monodisperse polystyrene-co-poly[3-(trimethoxylsilyl)propyl methacrylate] (St-co-TMSPM) microspheres with the amphiphilic triblock copolymer F127 and phenolic resol by centrifugation, and subsequent thermosetting treatment of the deposited microspheres. The polyhedral particles possess a regular shape of rhombic dodecahedra (∼1 µm) due to the spontaneous deformation of the fcc packed polymeric microspheres coated with resol–F127 composites during the thermosetting process. The amphiphilic triblock copolymer F127 plays a vital role in the formation of the ordered macrostructured polyhedral particles with compatible poly(St-co-TMSPM)–resin composites. The simplicity of the fabrication method should open up a new door to the synthesis of nonspherical particles and the construction of ordered macrostructures that possess unique properties for potential application in various fields such as photonic crystals.