Zhenkun Sun

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/

Sol–Gel Design Strategy for Ultradispersed TiO2 Nanoparticles on Graphene for High-Performance Lithium Ion Batteries

The rational design and controllable synthesis of strongly coupled inorganic/graphene hybrids represents a long-standing challenge for developing advanced catalysts and energy-storage materials. Here, we report a simple sol-gel method toward creating ultradispersed TiO2 nanoparticles on graphene with an unprecedented degree of control based on the precise separation and manipulation of nanoparticles nucleated, grown, anchored, and crystallized and the reduction of graphene oxide (GO). The hybrid materials show ultradispersed anatase nanoparticles (~5 nm), ultrathin thickness (≤3 layers), and a high surface area of ~229 m(2)/g and exhibit a high specific capacity of ~94 mA h g(-1) at ~59 C, which is twice as that of mechanically mixed composites (~41 mA h g(-1)), demonstrating the potential of strongly synergistic coupling effects for advanced functional systems.

Free-Standing Mesoporous Carbon Thin Films with Highly Ordered Pore Architectures for Nanodevices

We report for the first time the synthesis of free-standing mesoporous carbon films with highly ordered pore architecture by a simple coating-etching approach, which have an intact morphology with variable sizes as large as several square centimeters and a controllable thickness of 90 nm to ∼3 μm. The mesoporous carbon films were first synthesized by coating a resol precursors/Pluronic copolymer solution on a preoxidized silicon wafer and forming highly ordered polymeric mesostructures based on organic-organic self-assembly, followed by carbonizing at 600 °C and finally etching of the native oxide layer between the carbon film and the silicon substrate. The mesostructure of this free-standing carbon film is confirmed to be an ordered face-centered orthorhombic Fmmm structure, distorted from the (110) oriented body-centered cubic Im3̅m symmetry. The mesoporosity of the carbon films has been evaluated by nitrogen sorption, which shows a high specific BET surface area of 700 m(2)/g and large uniform mesopores of ∼4.3 nm. Both mesostructures and pore sizes can be tuned by changing the block copolymer templates or the ratio of resol to template. These free-standing mesoporous carbon films with cracking-free uniform morphology can be transferred or bent on different surfaces, especially with the aid of the soft polymer layer transfer technique, thus allowing for a variety of potential applications in electrochemistry and biomolecule separation. As a proof of concept, an electrochemical supercapacitor device directly made by the mesoporous carbon thin films shows a capacitance of 136 F/g at 0.5 A/g. Moreover, a nanofilter based on the carbon films has shown an excellent size-selective filtration of cytochrome c and bovine serum albumin.

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.

Solvent Evaporation Induced Aggregating Assembly Approach to Three-Dimensional Ordered Mesoporous Silica with Ultralarge Accessible Mesopores

A solvent evaporation induced aggregating assembly (EIAA) method has been demonstrated for synthesis of highly ordered mesoporous silicas (OMS) in the acidic tetrahydrofuran (THF)/H(2)O mixture by using poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) as the template and tetraethylorthosilicate (TEOS) as the silica precursor. During the continuous evaporation of THF (a good solvent for PEO-b-PMMA) from the reaction solution, the template molecules, together with silicate oligomers, were driven to form composite micelles in the homogeneous solution and further assemble into large particles with ordered mesostructure. The obtained ordered mesoporous silicas possess a unique crystal-like morphology with a face centered cubic (fcc) mesostructure, large pore size up to 37.0 nm, large window size (8.7 nm), high BET surface area (508 m(2)/g), and large pore volume (1.46 cm(3)/g). Because of the large accessible mesopores, uniform gold nanoparticles (ca. 4.0 nm) can be introduced into mesopores of the OMS materials using the in situ reduction method. The obtained Au/OMS materials were successfully applied to fast catalytic reduction of 4-nitrophenol in the presence of NaHB(4) as the reductant. The supported catalysts can be reused for catalytic reactions without significant decrease in catalysis performance even after 10 cycles.

Synthesis of dual-mesoporous silica using non-ionic diblock copolymer and cationic surfactant as co-templates.

Ordered mesoporous materials, ever since their discovery, have attracted considerable interest owing to their outstanding physicochemical properties (such as high surface area, large pore volume, variety of pore structures, easily modifiable surface, diverse framework compositions) and broad potential applications in, for example, adsorption, separation, catalysis, drug delivery and fuel cells. Considerable efforts have recently been devoted to fabricating ordered porous materials with hierarchical pore structures, such as macro-/meso-, meso-/micro-, and macro-/microporous materials. Additionally, in order to further increase the surface area for enhanced interactions with adsorbents and reduced transport limitations, much research has been conducted on the synthesis of ordered mesoporous materials with a bimodal pore structure which are highly desirable for applications in catalysis, sensing, and drug delivery. According to the templating synthesis concept for mesoporous materials, the bimodal mesopore system can be achieved by using two templates of different molecular weights that lead to pores of corresponding pore sizes. In fact, various template pairs have been employed to synthesize mesoporous materials with bimodal pores, including a nonionic copolymer and an ionic surfactant, a non-ionic copolymer and a non-ionic surfactant, an ionic block copolymer and an ionic surfactant, and mixed templates of two block copolymers with different molecular weights. However, in most cases dual-mesoporous materials with welldefined pore arrangements (specifically, with small mesopores surrounding the large mesopores) and tunable pore sizes could not be synthesized because of difficulties in controlling the assembly process in the dual-templating system. From a general thermodynamic point of view, the creation of a hierarchical micellar system is usually unfavorable; the two template molecules tend to form either mixed micelles or they form separate macroscopic phases. In light of this theoretical consideration, to achieve a hierarchical mesostructure, it is necessary for one set of template molecules to form stable micelles first before interaction with the second set of template molecules during the synthesis process. Consequently, to obtain ordered dual-mesoporous materials with two well-arranged sets of mesopores, two obstacles must be overcome. One is forming distinct large micelles of high-molecular-weight block copolymers and small micelles of low-molecular-weight surfactants. The second obstacle is triggering the independent co-assembly of the two kinds of micelles into an organized “alloy” phase, with small surfactant molecules filling the interstitial voids of the ordered mesostructure built up by large block copolymers. However, to date, it is a challenge to control the assembly process in the synthesis of dual-mesoporous silica with two kinds of template molecules. We report herein on a solvent-evaporation-induced stepby-step aggregating approach for the synthesis of ordered dual-mesoporous silica materials by using poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) and alkyltrimethylammonium bromide (CnTAB) as co-templates and tetraethyl orthosilicate (TEOS) as a silica source in an acidic tetrahydrofuran (THF)/H2O solution. It is found that, at the early stage of THF solvent evaporation, PEO-bPMMA copolymers with associated silicate oligomers first formed stable composite micelles in the solution. With the further evaporation of THF, the increased concentration and strong electrostatic attraction induce CnTAB molecules to move toward the negatively charged spherical composite micelles. Further evaporation of THF causes the composite micelles to assemble into large particles (0.5–6.0 mm) with a face-centered-cubic (fcc) structured mesophase. Meanwhile, the ultrahigh concentration of CnTAB molecules located in the interstitial space of the aggregated composite micelles assemble into curving rod-shaped micelles, resulting in a unique ordered mesostructure constructed of spherical large micelles and wormlike small micelles bound with silicate species (Scheme 1). After the templates were removed by simple calcination in air, unique ordered dual-mesoporous silica materials were obtained with large mesopores (ca. 20 nm) packed in an Fm 3m structure and small wormlike mesopores (ca. 2.5 nm) homogeneously distributed in the wall of the large pores. Because the non-ionic EO125-MMA174 has a very long hydrophobic segment, a mixture of THF and aqueous hydrochloric acid solution (3:1 v/v) was used to dissolve this template, the ionic surfactants, and the silica source (TEOS), yielding a homogeneous starting solution. It was found that, similar to our previous report, as the THF evaporated, the reaction system underwent a dramatic change from a clear solution, to a blue colloidal dispersion, to a white turbid [*] J. Wei, Q. Yue, Z. K. Sun, Prof. Dr. Y. H. Deng, Prof. Dr. D. Y. Zhao Department of Chemistry and Advanced Materials Laboratory Fudan University, Shanghai 200433 (P.R. China) E-mail: yhdeng@fudan.edu.cn dyzhao@fudan.edu.cn Homepage: http://www.mesogroup.fudan.edu.cn/

Magnetic yolk–shell mesoporous silica microspheres with supported Au nanoparticles as recyclable high-performance nanocatalysts

Correction for ‘Magnetic yolk–shell mesoporous silica microspheres with supported Au nanoparticles as recyclable high-performance nanocatalysts’ by Yonghui Deng et al., J. Mater. Chem. A, 2015, DOI: 10.1039/c4ta06967f.

An Interface-Directed Coassembly Approach To Synthesize Uniform Large-Pore Mesoporous Silica Spheres

A facile and controllable interface-directed coassembly (IDCA) approach is developed for the first time to synthesize uniform discrete mesoporous silica particles with a large pore size (ca. 8 nm) by using 3-dimensional macroporous carbon (3DOMC) as the nanoreactor for the confined coassembly of template molecules and silica source. By controlling the amount of the precursor solution and using Pluronic templates with different compositions, we can synthesize mesoporous silica particles with diverse morphologies (spheres, hollow spheres, and hemispheres) and different mesostructure (e.g., 2-D hexagonal and 3D face centered cubic symmetry), high surface area of about 790 m(2)/g, and large pore volume (0.98 cm(3)/g). The particle size can be tunable from submicrometer to micrometer regimes by changing the macropore diameter of 3DOMC. Importantly, this synthesis concept can be extended to fabricate multifunctional mesoporous composite spheres with a magnetic core and a mesoporous silica shell, large saturated magnetization (23.5 emu/g), and high surface area (280 m(2)/g). With the use of the magnetic mesoporous silica spheres as a magnetically recyclable absorbent, a fast and efficient removal of microcystin from water is achieved, and they can be recycled for 10 times without a significant decrease of removal efficiency for microcystin.

In-Situ Crystallization Route to Nanorod-Aggregated Functional ZSM-5 Microspheres

Herein, we develop a reproducible in situ crystallization route to synthesize uniform functional ZSM-5 microspheres composed of aggregated ZSM-5 nanorods and well-dispersed uniform Fe(3)O(4) nanoparticles (NPs). The growth of such unique microspheres undergoes a NP-assisted recrystallization process from surface to core. The obtained magnetic ZSM-5 microspheres possess a uniform size (6-9 μm), ultrafine uniform Fe(3)O(4) NPs (~10 nm), good structural stability, high surface area (340 m(2)/g), and large magnetization (~8.6 emu/g) and exhibit a potential application in Fischer-Tropsch synthesis.