Bingdi Chen

Facile Ultrasonic Synthesis of CoO Quantum Dot/Graphene Nanosheet Composites with High Lithium Storage Capacity

In this paper, we report a facile ultrasonic method to synthesize well-dispersed CoO quantum dots (3-8 nm) on graphene nanosheets at room temperature by employing Co(4)(CO)(12) as cobalt precursor. The prepared CoO/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (1592 mAh g(-1) after 50 cycles), high Coulombic efficiency (over 95%), excellent cycling stability, and high rate capability (1008 mAh g(-1) with a total retention of 77.6% after 50 cycles at a current density of 1000 mA g(-1), dramatically increased from the initial 50 mA g(-1)). The extraordinary performance arises from the structure advantages of the composites: the nanosized CoO quantum dots with high dispersity on conductive graphene substrates supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions, which are beneficial for high capacity and rate capability. Meanwhile, the isolated CoO quantum dots anchored tightly on the graphene nanosheets can effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction during discharge/charge processes, which is good for high capacity as well as cycling stability. Moreover, regarding the anomalous behavior of capacity increase with cycles (activation effect) observed, we proposed a tentative hypothesis stressing the competition between the conductivity increase and the amorphorization of the composite electrodes during cycling in determining the trends of the capacity, in the hope to gain a fuller understanding of the inner working of the novel nanostructured electrode-based lithium-ion batteries.

Metal oxide and sulfide hollow spheres: layer-by-layer synthesis and their application in lithium-ion battery.

A novel layer-by-layer approach has been developed to synthesize polycrystalline SnO(2) hollow spheres with tunable shell thickness and size using SiO(2) spheres as a template. The surface of the SiO(2) spheres has been first modified by the polyelectrolyte, and subsequently, the compact SnO(2) layer has deposited on the surface of the SiO(2) spheres through a redox reaction because of the electrostatic attraction between the charged species. After HF etching treatment, the uniform SnO(2) hollow spheres have been obtained. The approach presented herein has been extended to synthesize other metal oxide and sulfide hollow spheres such as In(2)O(3) and ZnS. Moreover, the as-synthesized SnO(2) hollow spheres have been applied in lithium-ion battery and show improved performance compared with SnO(2) nanoparticles. The high surface area and stable hollow structure of the SnO(2) hollow spheres may be responsible for the improved performance.

Carbon nanotube-based magnetic-fluorescent nanohybrids as highly efficient contrast agents for multimodal cellular imaging

We developed a simple and novel layer-by-layer (LBL) assembly in combination with covalent connection strategy for the synthesis of multifunctional carbon nanotubes (CNTs)-based magnetic-fluorescent nanohybrids as multimodal cellular imaging agents for detecting human embryonic kidney (HEK) 293T cells via magnetic resonance (MRI) and confocal fluorescence imaging. Superparamagnetic iron oxide nanoparticles (SPIO) and near-infrared fluorescent CdTe quantum dots (QDs) were covalently coupled on the surface of CNTs in sequence via LBL assembly. It was indicated that the SPIO layer acted not only as a contrast agent for MRI, but also as a spacer between CdTe QDs and CNTs for prohibiting fluorescence quenching of QDs on the surface of the CNTs. The multifunctional CNT-based magnetic-fluorescent nanohybrids showed an enhanced MRI signal as contrast agent for detecting 293T cells in comparison with the pure SPIO. This is due to the magnetic coupling between the orderly arrayed SPIO, the function of CNTs for lowering the transverse relaxation and the ability of CNTs for penetrating into cells. Moreover, the multifunctional CNT-based magnetic-fluorescent nanohybrids exhibited the higher intracellular labeling efficiency due to the ability of CNTs for penetrating into cells in comparison with pure SPIO-CdTe nanoparticles.

Bioinspired synthesis of gadolinium-based hybrid nanoparticles as MRI blood pool contrast agents with high relaxivity

A unique biomineralization approach was developed to synthesize gadolinium-based hybrid (GH) nanoparticles for effective blood pool contrast agents. This approach is bioinspired, environmentally benign, and straightforward. As-prepared GH nanoparticles are biocompatible and well stable in serum. They exhibit much higher longitudinal relaxivity and transverse relaxivity in water (r1 and r2 values of 15.0 and 19.7 s−1 per mM of Gd3+, respectively) than those measured for Gd–DTPA solution (r1 and r2 values of 3.7 and 4.6 s−1 per mM of Gd3+, respectively). In vivo T1-weighted magnetic resonance imaging (MRI) in living mice shows that the GH nanoparticles have an intravascular half-life up to 1 h, much longer than that of Gd–DTPA (about 10 min). As the GH nanoparticles were found to be cleared gradually via hepatobiliary (HB) processing, they can also serve as ideal candidates for liver specific MR contrast agents. In particular, these GH nanoparticles are bioinspired and environmentally benign, therefore promising for medical imaging applications.

Synergistic removal of Pb(II), Cd(II) and humic acid by Fe3O4@mesoporous silica-graphene oxide composites.

The synergistic adsorption of heavy metal ions and humic acid can be very challenging. This is largely because of their competitive adsorption onto most adsorbent materials. Hierarchically structured composites containing polyethylenimine-modified magnetic mesoporous silica and graphene oxide (MMSP-GO) were here prepared to address this. Magnetic mesoporous silica microspheres were synthesized and functionalized with PEI molecules, providing many amine groups for chemical conjugation with the carboxyl groups on GO sheets and enhanced the affinity between the pollutants and the mesoporous silica. The features of the composites were characterized using TEM, SEM, TGA, DLS, and VSM measurements. Series adsorption results proved that this system was suitable for simultaneous and efficient removal of heavy metal ions and humic acid using MMSP-GO composites as adsorbents. The maximum adsorption capacities of MMSP-GO for Pb(II) and Cd (II) were 333 and 167 mg g−1 caculated by Langmuir model, respectively. HA enhances adsorption of heavy metals by MMSP-GO composites due to their interactions in aqueous solutions. The underlying mechanism of synergistic adsorption of heavy metal ions and humic acid were discussed. MMSP-GO composites have shown promise for use as adsorbents in the simultaneous removal of heavy metals and humic acid in wastewater treatment processes.

Preparation of novel magnetic hollow mesoporous silica microspheres and their efficient adsorption

Magnetic hollow mesoporous silica microspheres (MHMSs) were successfully prepared by employing yolk-shell magnetic silica spheres as the template together with the coating of tetraethoxysilane (TEOS)/hexadecyl trimethoxysilane (C(16)TMS) hybrid. The microstructure and properties of MHMSs were studied by TEM, SEM, XRD, BET, and VSM characterizations. The average diameter of MHMSs was about 300 nm and the mesoporous shell thickness was totally around 70 nm. The 11 nm magnetite nanoparticles were homogeneously embedded in the mesoporous silica shell. Meanwhile, the adsorption and separation process of Rhodamine B were carried out to demonstrate that the material could be used for the adsorbent.

Targeting Negative Surface Charges of Cancer Cells by Multifunctional Nanoprobes

A set of electrostatically charged, fluorescent, and superparamagnetic nanoprobes was developed for targeting cancer cells without using any molecular biomarkers. The surface electrostatic properties of the established cancer cell lines and primary normal cells were characterized by using these nanoprobes with various electrostatic signs and amplitudes. All twenty two randomly selected cancer cell lines of different organs, but not normal control cells, bound specifically to the positively charged nanoprobes. The relative surface charges of cancer cells could be quantified by the percentage of cells captured magnetically. The activities of glucose metabolism had a profound impact on the surface charge level of cancer cells. The data indicate that an elevated glycolysis in the cancer cells led to a higher level secretion of lactate. The secreted lactate anions are known to remove the positive ions, leaving behind the negative changes on the cell surfaces. This unique metabolic behavior is responsible for generating negative cancer surface charges in a perpetuating fashion. The metabolically active cancer cells are shown to a unique surface electrostatic pattern that can be used for recovering cancer cells from the circulating blood and other solutions.

Low-temperature chemical solution route for ZnO based sulfide coaxial nanocables: general synthesis and gas sensor application

A novel chemical solution approach has been developed to synthesize ZnO based sulfide coaxial nanocables such as ZnO/ZnS and ZnO/CdS by chemical reaction in tetrahydrofuran (THF; C4H8O), in which sulfur, NaBH4 and ZnCl2 or CdCl2 were used as reactants and ZnO nanorods were used as the template at room temperature. The morphology and structure of ZnO/ZnS and ZnO/CdS coaxial nanocables have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), x-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analysis. Furthermore, the as-prepared ZnO/CdS coaxial nanocables have been applied as NH3 gas sensors at room temperature with superior sensitivity, good reproducibility and a short response/recovery time. Finally, a first explanation for the improved performance of the ZnO/CdS coaxial nanocable based gas sensors has been presented.

One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels

We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530–600 nm). Moreover, the PL emission peak of CdSe/CdS core–shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core–shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.

Preparation of highly fluorescent magnetic nanoparticles for analytes-enrichment and subsequent biodetection.

Bifunctional nanoparticles with highly fluorescence and decent magnetic properties have been widely used in biomedical application. In this study, highly fluorescent magnetic nanoparticles (FMNPs) with uniform size of ca. 40 nm are prepared by encapsulation of both magnetic nanoparticles (MNPs) and shell/core quantum dots (QDs) with well-designed shell structure/compositions into silica matrix via a one-pot reverse microemulsion approach. The spectral analysis shows that the FMNPs hold high fluorescent quantum yield (QY). The QYs and saturation magnetization of the FMNPs can be regulated by varying the ratio of the encapsulated QDs to MNPs. Moreover, the surface of the FMNPs can be modified to offer chemical groups for antibody conjugation for following use in target-enrichment and subsequent fluorescent detection. The in vitro immunofluorescence assay and flow cytometric analysis indicate that the bifunctional FMNPs-antibody bioconjugates are capable of target-enrichment, magnetic separation and can also be used as alternative fluorescent probes on flow cytometry for biodetection.