Silicon is regarded as one of the most promising anode materials for next generation lithium-ion batteries. For use in practical applications, a Si electrode must have high capacity, long cycle life, high efficiency, and the fabrication must be industrially scalable. Here, we design and fabricate a yolk-shell structure to meet all these needs. The fabrication is carried out without special equipment and mostly at room temperature. Commercially available Si nanoparticles are completely sealed inside conformal, thin, self-supporting carbon shells, with rationally designed void space in between the particles and the shell. The well-defined void space allows the Si particles to expand freely without breaking the outer carbon shell, therefore stabilizing the solid-electrolyte interphase on the shell surface. High capacity (∼2800 mAh/g at C/10), long cycle life (1000 cycles with 74% capacity retention), and high Coulombic efficiency (99.84%) have been realized in this yolk-shell structured Si electrode.

/pdf/a-yolk-shell-design-for-stabilized-and-scalable-li-ion-3fnjmb43uo.pdf

A yolk-shell design for stabilized and scalable li-ion battery alloy anodes.

In the past decade, non-invasive and biocompatible mesoporous silica materials as efficient drug delivery systems have attracted special attention. Great progress in structure control and functionalization (magnetism and luminescence) design has been achieved for biotechnological and biomedical applications. This review highlights the most recent research progress on silica-based controlled drug delivery systems, including: (i) pure mesoporous silica sustained-release systems, (ii) magnetism and/or luminescence functionalized mesoporous silica systems which integrate targeting and tracking abilities of drug molecules, and (iii) stimuli-responsive controlled release systems which are able to respond to environmental changes, such as pH, redox potential, temperature, photoirradiation, and biomolecules. Although encouraging and potential developments have been achieved, design and mass production of novel multifunctional carriers, some practical biological application, such as biodistribution, the acute and chronic toxicities, long-term stability, circulation properties and targeting efficacy in vivo are still challenging.

Functionalized mesoporous silica materials for controlled drug delivery

During the past two decades, extensive research has been carried out on the biomedical applications of nanostructured materials. Among these various nanomaterials, mesoporous silica materials have been intensively investigated for their potential application as delivery vehicles for small-molecule drugs, DNA, and proteins, owing to their uniform pore size, large surface area, and high accessible pore volume. However, to date, there are only a few reports on the in vivo application of mesoporous silica materials administrated by intravenous injection, because it is difficult to synthesize discrete and monodisperse mesoporous silica particles smaller than around 100 nm that possess high colloidal stability in a physiological environment and small enough size to allow a long blood circulation. In general, bigger nanoparticles (NPs) result in more rapid uptake by the reticuloendothelial system (RES), such as liver and spleen, but smaller NPs can escape from phagocytes in RES and circulate through blood vessels with a long blood half-life. Although there have been several reports on the synthesis of uniform mesoporous silica particles smaller than 200 nm observed in TEM, the particles are not discrete but aggregated. Consequently, it is still a challenge to synthesize discrete, monodisperse, and size-controllable mesoporous silica NPs for in vivo applications. Recently, multifunctional nanostructured materials have been applied to multimodal imaging and simultaneous diagnosis and therapy. In this context, the integration of mesoporous silica with superparamagnetic monodisperse nanocrystals to form uniform core–shell composite particles has great potential for simultaneous bioimaging and drug delivery. Although there have been several reports on composite materials of magnetic nanocrystals and mesoporous silica materials, these materials have not been used for in vivo applications because of their size and aggregation. Herein, we present discrete, monodisperse, and precisely sizecontrollable core–shell mesoporous silica NPs smaller than 100 nm by using single Fe3O4 nanocrystals as cores (designated as Fe3O4@mSiO2). We also demonstrate the multifunctional bioapplications of the core–shell NPs for simultaneous magnetic resonance (MR) and fluorescence imaging, and for drug delivery. The synthetic protocol is represented in Scheme 1. Cetyltrimethylammonium bromide (CTAB) serves not only as the stabilizing surfactant for the transfer of hydrophobic Fe3O4 nanocrystals [10] to the aqueous phase but also as the organic template for the formation of mesopores in the sol– gel reaction. After removing the CTAB templates from the as-synthesized materials by heating them at reflux in acidic ethanol solution (pH 1.4), we collected the Fe3O4@mSiO2 particles. When we decreased the pH value of the extraction solution below 1.0, Fe3O4 nanocrystals as well as CTAB were fully removed from the as-synthesized Fe3O4@mSiO2, resulting in hollow mesoporous silica NPs (designated as H-mSiO2). Finally, for biomedical applications, the surface of the NPs was modified with PEG to render them biocompatible by

Multifunctional Uniform Nanoparticles Composed of a Magnetite Nanocrystal Core and a Mesoporous Silica Shell for Magnetic Resonance and Fluorescence Imaging and for Drug Delivery

An overview on limitations of TiO2-based particles for photocatalytic degradation of organic pollutants and the corresponding countermeasures

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/

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

Superparamagnetic microspheres with an Fe3O4@SiO2 core and a perpendicularly aligned mesoporous SiO2 shell were synthesized through a surfactant-templating sol−gel approach. The microspheres possess high magnetization (53.3 emu/g), high surface area (365 m2/g), large pore volume (0.29 cm3/g), and uniform mesopore (2.3 nm). By using the unique core−shell microspheres with accessible large pores and excellent magnetic property, a fast removal of microcystins with high efficiency (>95%) can be achieved.

Superparamagnetic high-magnetization microspheres with an Fe3O4@SiO2 core and perpendicularly aligned mesoporous SiO2 shell for removal of microcystins.

Xiang-Ming Zhang

Papers

Superparamagnetic high-magnetization microspheres with an Fe3O4@SiO2 core and perpendicularly aligned mesoporous SiO2 shell for removal of microcystins.