Baozhong Shen

SiC–Fe3O4 dielectric–magnetic hybrid nanowires: controllable fabrication, characterization and electromagnetic wave absorption

Controllable dielectric–magnetic coaxial hybrid nanowires, having a core of SiC nanowires and a shell of Fe3O4 nanoparticles, have been synthesized using a straightforward polyol approach. The morphology, microstructure and magnetic properties of the SiC–Fe3O4 hybrid nanowires have been characterized by transmission electron microscope, powder X-ray diffractometer and vibrating sample magnetometer. The characterization confirms that monodisperse Fe3O4 nanoparticles of core size 10 nm have been successfully coated on the surface of SiC nanowires. The coverage density of the nanoparticles may be adjusted simply by changing the weight ratio of the precursors. Measurement of the electromagnetic (EM) parameters indicates that the Fe3O4 nanoparticles increase the magnetic loss and improve the impedance matching conditions compared to untreated SiC nanowires. When the coverage density of Fe3O4 is optimal, the reflection loss of an EM wave can be as low as −51 dB. By changing the loading density of Fe3O4, the best microwave absorption state was obtained in the 2–18 GHz band. These results suggest that SiC–Fe3O4 hybrid nanowires will be valuable in EM absorption applications.

Enhanced microwave absorption of Fe3O4 nanocrystals after heterogeneously growing with ZnO nanoshell

To enhance the microwave absorption of Fe3O4 nanocrystals, ZnO nanoshells with a thickness of 2 nm were grown on Fe3O4 nanocrystals by heterogeneous nucleation. After being coated with ZnO nanoshells, the material possesses a far more improved ability for microwave absorption. A minimum reflection loss of −3.31 dB for Fe3O4 nanocrystals alone was improved to a minimum reflection loss of −22.69 dB and with an effective absorption band (RL < −10 dB) covering a frequency range of 10.08–15.97 GHz. The reasons for the enhanced microwave absorption were studied by the use of X-ray absorption near-edge structures at O K-edge, electron spin resonance analysis and microwave electromagnetic parameters mapping. The results indicate that the decoration of the dielectric ZnO shell had varied the dielectric property as well as the oxidization environment and distribution of Fe ions on the surface of the Fe3O4. This well balances the permeability and the permittivity of the nanomaterials and decreases the difficulty of impedance matching the microwave absorber within the free space. This leads to the Fe3O4@ZnO nanohybrids possessing vastly improved microwave absorption as compared to Fe3O4 nanocrystals alone.

Enhanced Fluorescence Imaging Guided Photodynamic Therapy of Sinoporphyrin Sodium Loaded Graphene Oxide

Extensive research indicates that graphene oxide (GO) can effectively deliver photosensitives (PSs) by π-π stacking for photodynamic therapy (PDT). However, due to the tight complexes of GO and PSs, the fluorescence of PSs are often drastically quenched via an energy/charge transfer process, which limits GO-PS systems for photodiagnostics especially in fluorescence imaging. To solve this problem, we herein strategically designed and prepared a novel photo-theranostic agent based on sinoporphyrin sodium (DVDMS) loaded PEGylated GO (GO-PEG-DVDMS) with improved fluorescence property for enhanced optical imaging guided PDT. The fluorescence of loaded DVDMS is drastically enhanced via intramolecular charge transfer. Meanwhile, the GO-PEG vehicles can significantly increase the tumor accumulation efficiency of DVDMS and lead to an improved PDT efficacy as compared to DVDMS alone. The cancer theranostic capability of the as-prepared GO-PEG-DVDMS was carefully investigated both in vitro and in vivo. Most intriguingly, 100% in vivo tumor elimination was achieved by intravenous injection of GO-PEG-DVDMS (2 mg/kg of DVDMS, 50 J) without tumor recurrence, loss of body weight or other noticeable toxicity. This novel GO-PEG-DVDMS theranostics is well suited for enhanced fluorescence imaging guided PDT.

Covalent interaction enhanced electromagnetic wave absorption in SiC/Co hybrid nanowires

The interaction between components in hybrids is an indispensable factor in designing and fabricating composites with distinguished electromagnetic (EM) absorption performances. Herein, covalently bonded SiC/Co hybrid nanowires (NWs) have been fabricated, which present significantly enhanced EM absorption compared to a simple physical mixture of SiC and Co. The hybrids are characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, vector network analysis, and X-ray absorption near-edge spectroscopy at the Si K-edge, C K-edge, Co L3,2-edge and O K-edge. Microstructure analysis indicates the formation of Si–O–Co bonds between SiC NWs and magnetic Co nanocrystals. Charge transfer takes place in the covalently bonded SiC/Co hybrid NWs. The induced synergistic coupling interaction in SiC/Co leads to an effective EM absorption band (RL < −10 dB) covering the frequency range of 10–16.6 GHz when the Co content is 25.1 wt% in the hybrid.

Fabrication of core–multishell MWCNT/Fe3O4/PANI/Au hybrid nanotubes with high-performance electromagnetic absorption

Core–multishell MWCNT/Fe3O4/polyaniline (PANI)/Au hybrid nanotubes are synthetized by a facile layer-by-layer technique which well integrates the dielectric components (MWCNT and PANI) and the magnetic absorber (Fe3O4) as well as the electromagnetic (EM) wave reflector (Au) into one unit. The hybrid nanotubes are characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and vector network analysis. Microstructure analysis indicates that the coverage of the gold nanoparticles could be adjusted simply by varying the weight ratio of the precursors. When gold is introduced into the hybrid nanotubes, the EM absorption is sharply enhanced. The lowest reflection loss value reduces from −22 dB to −60 dB. This may be ascribed to the fact that the introduction of gold nanoparticles is beneficial for the multi-reflection of EM waves within the absorbers, balances the impedance matching between the absorbers and free space, and induces charge redistribution within the hybrid nanotubes generating significant interfacial polarization.

Large-scale gold nanoparticle superlattice and its SERS properties for the quantitative detection of toxic carbaryl

Large scale and well-ordered gold nanoparticle superlattices were fabricated by self-assembly as an active substrate for surface-enhanced Raman scattering (SERS) that can quantitatively detect carbaryl with a detection limit of 1 ppm. These fabricated superlattices with a dimension of several hundred micrometers exhibited high, reproducible SERS activity.

Durian-like multi-functional Fe3O4–Au nanoparticles: synthesis, characterization and selective detection of benzidine

A novel durian-like multi-functional water soluble Fe3O4–Au nanocomposite is fabricated via a facile layer-by-layer technology in which a mercapto-silica shell is utilized as a functional coating on the central Fe3O4 nanoparticle cluster. Then gold nanoparticles are loaded onto the surface of Fe3O4, stabilized by Au–S chemical bonding. The fabricated nanocomposites inherit excellent physical and chemical properties from their building blocks, simultaneously exhibiting superparamagnetic, surface plasmon resonance and surface enhanced Raman scattering (SERS) active properties. Based on the magnetic separability of the inner Fe3O4 nanoparticle clusters and the SERS active properties of the suface gold, a selective detection method for benzidine has been developed for rapid detection and ease of operation with a low detection limit of 0.18 ppm.

Enhanced electrochemical reduction of CO2 to CO on Ag electrocatalysts with increased unoccupied density of states

CO2 conversion through catalytic processes in a selective and efficient manner is an essential technology for a sustainable carbon economy at present and in the future. Here, we fabricated five nanostructured Ag electrocatalysts and studied their CO2 electro-reduction properties compared to commercial Ag. Ag L-edge X-ray absorption near-edge spectroscopy was employed to characterize the electronic structure variation among the catalysts. It is found that an increased unoccupied density of states (DOS) of d-character of Ag endows the electrocatalyst with a higher selectivity and efficiency for CO2 reduction. The introduction of Ni into the Ag matrix reduces the unoccupied DOS of d-character as there is charge redistribution between Ag and Ni, worsening the active efficiency of CO production. Density functional theory calculations show that an increased unoccupied DOS optimizes the affinity of the catalyst surface to the intermediate COOH and CO, closer to the activity volcano, which facilitates CO formation. The nanoporous Ag electrocatalyst, made through anodization–reduction, possesses the highest unoccupied DOS of d-character among the samples, showing the best catalytic performance in the reduction of CO2 to CO. Meanwhile, its onset overpotential is 0.19 V and the highest faradaic efficiency reaches 90%. The electrocatalyst stays at this level for 10 h without any noticeable activity change, possessing great potential for applications in industry. This research provides a useful insight on the structure–property relationships of CO2 reduction catalysts, and a guideline for designing high-performance electrocatalysts.