Xiaohui Guo

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/

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.

Facile Synthesis of Hierarchically Mesoporous Silica Particles with Controllable Cavity in Their Surfaces

Novel and uniform mesoporous silica particles with controllable cavities in their surface have been fabricated using PAA and CTAB as dual templates in a mild reaction system. Herein, a series of hierarchically distinct silica particles can be obtained by simply adjusting the mass ratios (R) of PAA to CTAB. When the R value continues to decrease, the corresponding number and opening size of these cavities are also increased. However, if no PAA added, only unique monodisperse mesoporous silica spheres with uniform size of approximately 400 nm can be obtained. These specific silica particles were characterized by means of small-angle X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) spectra, and nitrogen adsorption-desorption measurements. Results show that these unique mesoporous silica particles totally behave as an hexagonally ordered mesophase. The maximum BET surface area can be as high as 891 m(2)/g, and the maximum pore volumes can be as large as 0.27 cm(3)/g. Notably, the specific cavity features including opening size and cavity number almost do not change after calcination treatment. Moreover, a possible formation mechanism of the hierarchically distinct silica particles has been put forward, considering that the specific interface instability effect, the reduction in the surface free energy, and the synergic self-assembly of PAA and CTAB in solution can play a key role in mediating the formation of the hierarchical silica nanostructures. In general, the synthesis route is simple and straightforward for the preparation of the other biomineral nanostructures and may play an important role in microencapsulation.

Controlled crystallization of hierarchical and porous calcium carbonate crystals using polypeptide type block copolymer as crystal growth modifier in a mixed solution

Various kinds of nearly spherical calcium carbonate (CaCO3) crystals with hierarchical and porous structures can be prepared using poly(ethylene glycol)-b-poly(aspartic acid) (PEG-b-pAsp) as a crystal growth modifier in a mixed solvent composed of N,N-dimethylformamide (DMF) and cyclohexanol. The results reveal that the porosity or specific surface area of these CaCO3 crystals can be tuned by altering the volume ratio (R) of DMF/cyclohexanol in solution, and the pore size of the obtained spherical particles can be ranged from several tens to hundreds of nanometres. Additionally, most of the obtained calcium carbonate samples can be assigned to vaterite or a mixture of calcite and vaterite, which are well crystalline and are influenced by the R value. Interestingly, unique hierarchical and porous microspheres can be prepared at polymer concentrations of ∼ 0.5 g L−1 and an R value of ∼ 1.0, respectively. It has been proposed that the formation of the specific CaCO3 crystals with hierarchical and porous structures could be ascribed to the collodial aggregation transition and self-assembly of calcium carbonate precursor in a desirable mixed solvent. This specific synthesis strategy in a mixed solvent again emphasizes that it is possible to synthesize other inorganic/organic hybrid materials with exquisite morphology and specific textures.

Cobalt‐Doping‐Induced Synthesis of Ceria Nanodisks and Their Significantly Enhanced Catalytic Activity

High-quality cobalt-doped ceria nanostructures with triangular column, triangular slab, and disklike shapes are synthesized by tuning the doping amount of cobalt nitrate in a facile hydrothermal reaction. The cobalt-doped ceria nanodisks display significantly enhanced catalytic activity in CO oxidation due to exposed highly active crystal planes and the presence of numerous surface defects.

Controlled synthesis of hydroxyapatite crystals templated by novel surfactants and their enhanced bioactivity

In this paper, we report that hydroxyapatite (HAP) nanocrystals with various shape and size have been successfully prepared by a dual template-assisted hydrothermal synthesis approach in isopropanol/water mixed solvents. Herein, we chose 4-aminobenzenesulfonic acid (ABSA) and polyethylene glycol 4000 (PEG-4000) as structure-directed templates, respectively. By gradually changing the mass ratios (R) of PEG-4000 to ABSA, the obtained HAP samples can undergo distinct morphological evolution accordingly. A class of unique sheet-like HAP sample could be formed when only using ABSA as template. Moreover, when the R value was changed to 1/4, uniform and high-yielding HAP plate-shaped structure can be obtained. When only using PEG-4000 as a template, almost novel and wedge-shaped HAP samples can be obtained. The results demonstrated that the obtained plate-like HAP sample has single-crystalline behavior and uniform distribution in both size and shape. Additionally, we perform and evaluate the bioactivity of HAP in simulated body fluid (SBF), indicating that the two obtained HAP samples can possess apparently improved bioactivity compared to previous literature reports, and bone-like apatite could be readily formed on the HAP surface through different soaking periods in SBF. Notably, for the first time, a novel method for evaluating the in vitro bioactivity of HAP has been proposed. Therefore, the presented synthetic route for HAP is well-controlled and facilitated, which could be extended to the preparation of other biomaterials with specific morphologies and architectures.

Synthesis of partially graphitic nanoflake-like carbon/Fe3O4 magnetic composites from chitosan as high-performance electrode materials in supercapacitors

In this study, we report the preparation of partially graphitic nanoflake-like carbons derived from chitosan and their magnetic composites via a hydrothermal reaction, followed by a high-temperature carbonization process. The prepared iron oxide particles are well dispersed on the surface of the carbon support and display good single-crystalline features. In addition, the carbon/iron oxide composite serves as an electrode material in supercapacitors. Electrochemical results demonstrated that the carbon/iron oxide based electrode can deliver high specific capacitance ∼299 F g−1 at a current density of 0.5 A g−1 with excellent recycling durability, which is probably due to the fast electron and ion transport, the enhanced conductivity and the generated pseudocapacitance that resulted from the sufficient faradaic redox reaction. More importantly, the synthetic approach is green and reproducible, which can facilitate the designing and fabrication of other carbon-based advanced function materials and devices.

Mineralization of unique barium carbonate crystal superstructures controlled by a liquid crystalline phase polymer

Barium carbonate (BaCO3) crystals with unique hierarchical superstructures have been fabricated through a facile and controlled solution self-assembly mode in the presence of a tri-block copolymer PEO70–PPO20–PEO70 (P123). The powder X-ray diffraction (XRD) results revealed that the obtained BaCO3 product was indexed to pure orthorhombic phase. Notably, BaCO3 samples with well-defined hierarchical morphologies, including spherical, rod, hexangular prism, and porous spherical aggregates can be prepared by simply adjusting the polymer P123 concentrations and the ratios of [Ba2+]/[P123]. Specifically, layered screw cap, double-taper, and shuttle-shaped superstructures were formed through choosing N,N-bimethylformamide (DMF), tetrahydrofuran (THF), and/or toluene mixed with de-ionised water (DIW) as the reaction media in the current system, respectively. It is clearly demonstrated that varying liquid crystal-phase aggregating structures of the polymer P123 and using different solvents can indeed exert a significant influence over the selective nucleation, crystal facets preferable adsorption, and consequent over-growth for the BaCO3 primary particles. Moreover, a possible formation process for the hierarchical superstructures of BaCO3 crystals is proposed.

Facile synthesis of porous NiCo2O4 nanoflakes as magnetic recoverable catalysts towards the efficient degradation of RhB

In this work, a class of flake-shaped magnetic NiCo2O4 material is fabricated by a facile hydrothermal reaction followed by a calcination treatment process. The prepared flake-like NiCo2O4 displays porous features that endow it with a large specific surface area (142.48 m2 g−1) and a narrow pore size distribution (3.70 nm). Furthermore, the NiCo2O4 samples were used as high-performance heterogeneous catalysts in the activation of peroxymonosulphate (PMS) to produce active radicals SO4−˙ and HO˙. Then, the produced SO4−˙ and HO˙ can further attack and degrade organic dyes. The catalytic results show that the magnetic flake-like NiCo2O4 catalyst can completely degrade rhodamine B (RhB) dye within 30 min with the assistance of PMS. In addition, the catalysts could be magnetically recovered, displayed high catalytic activity and excellent cycling stability. It is believed that the specific porous features, including high specific surface area and tailored pore size distributions, and surface defects can ensure the high activation of PMS for the catalytic oxidation of RhB. More importantly, the present synthetic method is facile, controllable and scalable, which highlights its potential in energy-storage, environmental treatment, and biology-related fields.

Facile In Situ Synthesis of Hierarchical Porous Ni/Ni(OH)2 Hybrid Sponges with Excellent Electrochemical Energy-Storage Performances for Supercapacitors

Herein, we report the in situ growth of single-crystalline Ni(OH)2 nanoflakes on a Ni support by using facile hydrothermal processes. The as-prepared Ni/Ni(OH)2 sponges were well-characterized by using X-ray diffraction (XRD), SEM, TEM, and X-ray photoelectron spectroscopy (XPS) techniques. The results revealed that the nickel-skeleton-supported Ni(OH)2 rope-like aggregates were composed of numerous intercrossed single-crystal Ni(OH)2 flake-like units. The Ni/Ni(OH)2 hybrid sponges served as electrodes and displayed ultrahigh specific capacitance (SC=3247 F g(-1)) and excellent rate-capability performance, likely owing to fast electron and ion transport, sufficient Faradic redox reaction, and robust structural integrity of the Ni/Ni(OH)2 hybrid electrode. These results support the promising application of Ni(OH)2 nanoflakes as advanced pseudocapacitor materials.