Yonghui Deng

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 versatile kinetics-controlled coating method to construct uniform porous TiO2 shells for multifunctional core-shell structures.

The development of a simple and reproducible route to prepare uniform core@TiO(2) structures is urgent for realizing multifunctional responses and harnessing multiple interfaces for new or enhanced functionalities. Here, we report a versatile kinetics-controlled coating method to construct uniform porous TiO(2) shells for multifunctional core-shell structures. By simply controlling the kinetics of hydrolysis and condensation of tetrabutyl titanate (TBOT) in ethanol/ammonia mixtures, uniform porous TiO(2) shell core-shell structures can be prepared with variable diameter, geometry, and composition as a core (e.g., α-Fe(2)O(3) ellipsoids, Fe(3)O(4) spheres, SiO(2) spheres, graphene oxide nanosheets, and carbon nanospheres). This method is very simple and reproducible, yet important, which allows an easy control over the thickness of TiO(2) shells from 0 to ~25, ~45, and ~70 nm. Moreover, the TiO(2) shells possess large mesoporosities and a uniform pore size of ~2.5 nm, and can be easily crystallized into anatase phase without changing the uniform core-shell structures.

A general chelate-assisted co-assembly to metallic nanoparticles-incorporated ordered mesoporous carbon catalysts for Fischer-Tropsch synthesis.

The organization of different nano objects with tunable sizes, morphologies, and functions into integrated nanostructures is critical to the development of novel nanosystems that display high performances in sensing, catalysis, and so on. Herein, using acetylacetone as a chelating agent, phenolic resol as a carbon source, metal nitrates as metal sources, and amphiphilic copolymers as a template, we demonstrate a chelate-assisted multicomponent coassembly method to synthesize ordered mesoporous carbon with uniform metal-containing nanoparticles. The obtained nanocomposites have a 2-D hexagonally arranged pore structure, uniform pore size (~4.0 nm), high surface area (~500 m(2)/g), moderate pore volume (~0.30 cm(3)/g), uniform and highly dispersed Fe(2)O(3) nanoparticles, and constant Fe(2)O(3) contents around 10 wt %. By adjusting acetylacetone amount, the size of Fe(2)O(3) nanoparticles is readily tunable from 8.3 to 22.1 nm. More importantly, it is found that the metal-containing nanoparticles are partially embedded in the carbon framework with the remaining part exposed in the mesopore channels. This unique semiexposure structure not only provides an excellent confinement effect and exposed surface for catalysis but also helps to tightly trap the nanoparticles and prevent aggregating during catalysis. Fischer-Tropsch synthesis results show that as the size of iron nanoparticles decreases, the mesoporous Fe-carbon nanocomposites exhibit significantly improved catalytic performances with C(5+) selectivity up to 68%, much better than any reported promoter-free Fe-based catalysts due to the unique semiexposure morphology of metal-containing nanoparticles confined in the mesoporous carbon matrix.

Ordered mesoporous materials based on interfacial assembly and engineering.

Ordered mesoporous materials have inspired prominent research interest due to their unique properties and functionalities and potential applications in adsorption, separation, catalysis, sensors, drug delivery, energy conversion and storage, and so on. Thanks to continuous efforts over the past two decades, great achievements have been made in the synthesis and structural characterization of mesoporous materials. In this review, we summarize recent progresses in preparing ordered mesoporous materials from the viewpoint of interfacial assembly and engineering. Five interfacial assembly and synthesis are comprehensively highlighted, including liquid-solid interfacial assembly, gas-liquid interfacial assembly, liquid-liquid interfacial assembly, gas-solid interfacial synthesis, and solid-solid interfacial synthesis, basics about their synthesis pathways, princples and interface engineering strategies.

Core-shell Ag@SiO2@mSiO2 mesoporous nanocarriers for metal-enhanced fluorescence

A novel mesoporous nanocarrier consisting of a silver core, a silica spacer with controlled thickness and a fluorophores-loaded mesoporous silica shell was fabricated for the metal-enhanced fluorescence (MEF) and Förster resonance energy transfer (FRET) effects.

Synthesis and microwave absorption of uniform hematite nanoparticles and their core-shell mesoporous silica nanocomposites

Single-crystal α-iron oxide (denoted as FO) particles with uniform sub-micrometer size and polyhedron-like shape have been successfully fabricated by using polyvinylpyrrolidone (PVP) capping agent-mediated hydrolysis of iron nitrate under mild hydrothermal conditions (200 °C). The hematite products were characterized via combined techniques including scanning electronic microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The single-crystal hematite particles have relatively uniform sizes of 180–360 nm and octahedron-shaped structures with comparatively smooth surfaces. Furthermore, the as-made hematite particles can be used as cores to prepare core-shell mesoporous silica composites. The intermediate nonporous silica layer was coated first via a sol-gel process, and then the mesoporous silica structure was coated as the outer shell layer by a surfactant-assembly method, resulting in uniform core-shell mesoporous silica FO@nSiO2@mSiO2 composites. TEM images show that the FO@nSiO2@mSiO2 composites possess distinct two-layer coating core-shell structures with ordered hexagonal mesostructure in the outer silica shell layer. N2 sorption measurements show that the uniform accessible mesochannel size for the FO@nSiO2@mSiO2 nanocomposites is ∼2.10 nm, the surface area is as high as ∼445 m2/g, and the pore volume is as large as ∼0.29 cm3/g. Furthermore, the reflection loss (dB) spectra measured in the frequency range 2–18 GHz showed that the FO@nSiO2@ mSiO2 composites have improved electromagnetic interference (EMI) shielding effectiveness (SE) compared to that of pure hematite materials. This is mainly attributed to the better impedance match and multiple-interfacial polarization among the FO@nSiO2@mSiO2 nanocomposites.

Highly Ordered Mesoporous Tungsten Oxides with a Large Pore Size and Crystalline Framework for H2S Sensing

An ordered mesoporous WO3 material with a highly crystalline framework was synthesized by using amphiphilic poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers as a structure-directing agent through a solvent-evaporation-induced self-assembly method combined with a simple template-carbonization strategy. The obtained mesoporous WO3 materials have a large uniform mesopore size (ca. 10.9 nm) and a high surface area (ca. 121 m(2)  g(-1)). The mesoporous WO3-based H2S gas sensor shows an excellent performance for H2S sensing at low concentration (0.25 ppm) with fast response (2 s) and recovery (38 s). The high mesoporosity and continuous crystalline framework are responsible for the excellent performance in H2S sensing.

An Interface Coassembly in Biliquid Phase: Toward Core-Shell Magnetic Mesoporous Silica Microspheres with Tunable Pore Size.

Core-shell magnetic mesoporous silica microspheres (Magn-MSMs) with tunable large mesopores in the shell are highly desired in biocatalysis, magnetic bioseparation, and enrichment. In this study, a shearing assisted interface coassembly in n-hexane/water biliquid systems is developed to synthesize uniform Magn-MSMs with magnetic core and mesoporous silica shell for an efficient size-selective biocatalysis. The synthesis features the rational control over the electrostatic interaction among cationic surfactant molecules, silicate oligomers, and Fe3O4@RF microspheres (RF: resorcinol formaldehyde) in the presence of shearing-regulated solubilization of n-hexane in surfactant micelles. Through this multicomponent interface coassembly, surfactant-silica mesostructured composite has been uniformly deposited on the Fe3O4@RF microspheres, and core-shell Magn-MSMs are obtained after removing the surfactant and n-hexane. The obtained Magn-MSMs possess excellent water dispersibility, uniform diameter (600 nm), large and tunable perpendicular mesopores (5.0-9.0 nm), high surface area (498-623 m(2)/g), large pore volume (0.91-0.98 cm(3)/g), and high magnetization (34.5-37.1 emu/g). By utilization of their large and open mesopores, Magn-MSMs with a pore size of about 9.0 nm have been demonstrated to be able to immobilize a large bioenzyme (trypsin with size of 4.0 nm) with a high loading capacity of ∼97 μg/mg via chemically binding. Magn-MSMs with immobilized trypsin exhibit an excellent convenient and size selective enzymolysis of low molecular proteins in the mixture of proteins of different sizes and a good recycling performance by using the magnetic separability of the microspheres.

Mesoporous Silica Encapsulating Upconversion Luminescence Rare-Earth Fluoride Nanorods for Secondary Excitation

Mesoporous silica encapsulating upconversion luminescence NaYF(4) nanorods with uniform core-shell structures have been successfully synthesized by the surfactant-assistant sol-gel process. The thickness of ordered mesoporous silica shells can be adjusted from 50 to 95 nm by varying the amount of hydrolyzed silicate oligomer precursors from tetraethyl orthosilicate (TEOS), which further influences the BET surface area, pore volume, and the luminescence intensity. After coated with mesoporous silica shells, the hydrophobic nanorods is rendered to hydropholic simultaneously. The obtained beta-NaYF(4)@SiO(2)@mSiO(2) core-shell nanorods possess high surface area (71.2-196 m(2) g(-1)), pore volume (0.07-0.17 cm(3) g(-1)), uniform pore size distribution (2.3 nm), and accessible channels. Furthermore, the uniform core-shell nanorods show strong upconversion luminescence property similar to the hexagonal upconversion cores. The open mesopores can not only provide convenient transmission channels but also offer the huge location for accommodation of large molecules, such as fluorescent dyes and quantum dots. The secondary-excitation fluorescence of Rhodamine B is generated from the upconversion rare-earth fluoride nanorods cores to the fluorescent dyes loaded in the mesoporous silica shells.