Hong-Mei Xiao

Template-free synthesis and characterization of novel 3D urchin-like α-Fe2O3 superstructures

Novel three-dimensional (3D) urchin-like α-Fe2O3 superstructures were successfully prepared by a template-free hydrothermal synthetic route using FeSO4·7H2O and NaClO3 as reagents. The as-obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis and vibrating sample magnetometry. It is shown that the superstructures consisted of well-aligned α-Fe2O3 nanorods growing radially from the cores of the superstructures. The α-Fe2O3 nanorods have an average length of about 800 nm and a mean diameter of about 80 nm. Magnetic hysteresis measurement reveal that the urchin-like α-Fe2O3 superstructures display weak ferromagnetic behavior with a remanence of 4.6783 × 10−3 emu g−1 and a coercivity of 92.235 Oe at room temperature. The formation mechanism of the 3D urchin-like α-Fe2O3 superstructures was also discussed.

Self-Assembled 3D Flower-Like Hierarchical β-Ni(OH)2 Hollow Architectures and their In Situ Thermal Conversion to NiO

Three-dimensional (3D) flower-like hierarchicalβ-Ni(OH)2hollow architectures were synthesized by a facile hydrothermal route. The as-obtained products were well characterized by XRD, SEM, TEM (HRTEM), SAED, and DSC-TGA. It was shown that the 3D flower-like hierarchicalβ-Ni(OH)2hollow architectures with a diameter of several micrometers are assembled from nanosheets with a thickness of 10–20 nm and a width of 0.5–2.5 μm. A rational mechanism of formation was proposed on the basis of a range of contrasting experiments. 3D flower-like hierarchical NiO hollow architectures with porous structure were obtained after thermal decomposition at appropriate temperatures. UV–Vis spectra reveal that the band gap of the as-synthesized NiO samples was about 3.57 eV, exhibiting obviously red shift compared with the bulk counterpart.

Enhanced Microwave Absorption Performance of Coated Carbon Nanotubes by Optimizing the Fe3O4 Nanocoating Structure

It is well accepted that the microwave absorption performance (MAP) of carbon nanotubes (CNTs) can be enhanced via coating magnetic nanoparticles on their surfaces. However, it is still unclear if the magnetic coating structure has a significant influence on the microwave absorption behavior. In this work, nano-Fe3O4 compact-coated CNTs (FCCs) and Fe3O4 loose-coated CNTs (FLCs) are prepared using a simple solvothermal method. The MAP of the Fe3O4-coated CNTs is shown to be adjustable via controlling the Fe3O4 nanocoating structure. The results reveal that the overall MAP of coated CNTs strongly depends on the magnetic coating structure. In addition, the FCCs show a much better MAP than the FLCs. It is shown that the microwave absorption difference between the FLCs and FCCs is due to the disparate complementarities between the dielectric loss and the magnetic loss, which are related to the coverage density of Fe3O4 nanoparticles on the surfaces of CNTs. For FCCs, the mass ratio of CNTs to Fe3+ is then optimized to maximize the effective complementarities between the dielectric loss and the magnetic loss. Finally, a comparison is made with the literature on Fe3O4-carbon-based composites. The FCCs at the optimized CNT to Fe3+ ratio in the present work show the most effective specific RLmin (28.7 dB·mm-1) and the widest effective bandwidth (RL < -10 dB) (8.3 GHz). The excellent MAP of the as-prepared FCC sample is demonstrated to result from the consequent dielectric relaxation process and the improved magnetic loss. Consequently, the structure-property relationship revealed is significant for the design and preparation of CNT-based materials with effective microwave absorption.

Lanthanum-doped ZnO quantum dots with greatly enhanced fluorescent quantum yield

The lanthanum-doped ZnO quantum dots (QDs) are synthesized by a modified sol–gel method under atmospheric conditions. The as-prepared quantum dots are characterized by X-ray powder diffraction, energy dispersion spectrum analysis and high resolution transmission electron microscopy. The optical properties of the products are studied by ultra-violet spectroscopy and fluorescent spectroscopy. The results show that the doped quantum dots exhibit greatly enhanced luminescent properties and their quantum yield centered around 495 nm is increased from 30.5% for un-doped ZnO QDs already improved by silane surface modification to 77.9% for La-doped ZnO QDs at a proper La-doping content, which is the highest reported so far for the green-emitting ZnO QDs. Positron annihilation spectroscopy is employed to probe the vacancy-type defects of ZnO QDs. Finally, anti-counterfeiting inks are prepared by incorporating La-doped ZnO QDs into the transparent oil and their possible potential applications are explored.

Wearable Electronics of Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing.

Wearable electronics used in smart clothing for healthcare monitoring or personalized identification is a new and fast-growing research topic. The challenge is that the electronics has to be simultaneously highly stretchable, mechanically robust and water-washable, which is unreachable for traditional electronics or previously reported stretchable electronics. Herein we report the wearable electronics of sliver nanowire (Ag-NW)/poly(dimethylsiloxane) (PDMS) nanocomposite which can meet the above multiple requirements. The electronics of Ag-NW/PDMS nanocomposite films is successfully fabricated by an original pre-straining and post-embedding (PSPE) process. The composite film shows a very high conductivity of 1.52 × 104 S cm−1 and an excellent electrical stability with a small resistance fluctuation under a large stretching strain. Meanwhile, it shows a robust adhesion between the Ag-NWs and the PDMS substrate and can be directly machine-washed. These advantages make it a competitive candidate as wearable electronics for smart clothing applications.

Ternary Ag/epoxy adhesive with excellent overall performance.

Excellent electrical conductivity (EC) generally conflicts with high lap shear strength (LSS) for electrically conductive adhesives (ECAs) since EC increases while LSS decreases with increasing conductive filler content. In this work, the ECAs with the excellent overall performance are developed based on the ternary hybrid of Ag microflakes (Ag-MFs), Ag nanospheres (Ag-NSs), and Ag nanowires (Ag-NWs). First, a low silver content adhesive system is determined. Then, the effects of the relative contents of Ag fillers on the EC and the LSS are studied. It is shown that a small amount of Ag-NSs or Ag-NWs can dramatically improve the EC for the Ag-MF/epoxy adhesives. The Ag-NSs and Ag-NWs with appropriate contents have a synergistic effect in improving the EC. Meanwhile, the LSS of the as-prepared adhesive with the appropriate Ag contents reaches an optimal value. Both the EC and the LSS of the as-prepared ternary hybrid ECA with a low content of 40 wt % Ag are higher than those of the commercial ECAs filled with the Ag-MF content over 60 wt %. Finally, the ternary hybrid ECA with the optimal formulation is shown to be promising for printing the radio frequency identification tag antennas as an immediate application example.

Layer-structured silver nanowire/polyaniline composite film as a high performance X-band EMI shielding material

Free-standing layer-structured Ag nanowire (Ag-NW)/polyaniline (PANI) composite films were prepared via a novel but simple two-step casting process. The as-prepared layer-structured PANI composite film with 14 vol% Ag-NWs show a very high electrical conductivity (EC) of 5300 S cm−1, a reasonably good mechanical strength of 44 MPa and an excellent electromagnetic interference (EMI) shielding efficiency of above 50 dB over a wide bandwidth of 1.2 GHz. Comparatively, the plain-structured composite counterparts prepared via the commonly used direct-mixing process exhibit a higher percolation threshold, a lower EC of 4234 S cm−1 and an inferior EMI shielding performance of above 50 dB over a narrow bandwidth of 0.4 GHz. In spite of this, the plain-structured Ag-NW/PANI composite films also display a relatively higher EMI SE when compared to other PANI based composites reported previously. This study provides a facile and effective strategy to fabricate layer-structured composite films with excellent EMI shielding efficiency in the X-band, which may find applications in electronic devices and radiation sources.

Electrical Switch for Smart pH Self-Adjusting System Based on Silver Nanowire/Polyaniline Nanocomposite Film

A sensitive pH-triggered electrical switch is demonstrated by using a layer-structured silver nanowire/polyaniline nanocomposite film fabricated via an easy vertical spinning method. The as-prepared nanocomposite film shows the high electrical conductivity of 1.03 × 10(4) S cm(-1) at the Ag-NW areal density of 0.84 mg cm(-2) and a good cycling stability. Particularly, because of the layered structure, the switch achieves a very high contrast ratio of ca. 9 × 10(8), which is 2-6 orders higher than that reported previously. The high electrical conductivity and the high switching ratio make the layer-structured nanocomposite film a sensitive switch candidate for pH-responsive systems. Finally, a smart pH self-adjusting switching system is successfully designed using the as-prepared layer-structured nanocomposite film.

Novel core–shell structured BiVO4 hollow spheres with an ultra-high surface area as visible-light-driven catalyst

In recent years, BiVO4 has been extensively studied as a promising visible-light-driven catalyst candidate due to its great visible-light absorbing ability. In this paper, novel core–shell structured (CSS) BiVO4 hollow spheres with an ultra-high specific surface area were synthesized via a one-pot, surfactant- and template-free hydrothermal route. The as-obtained products were characterized by scanning electron microscopy, X-ray diffraction, nitrogen adsorption–desorption experimentation, Raman and UV–vis absorption spectroscopy, respectively. The formation mechanism of the BiVO4 products was proposed in terms of the morphological evolution with prolonging the reaction time. The as-prepared CSS BiVO4 hollow spheres similar to Russian dolls were comprised of an inner core and an open outer shell, leading to an ultra-high specific surface area about fifty times that of solid spherical counterparts fabricated by the traditional solid-state reaction method. As a result, the CSS BiVO4 hollow spheres exhibited a superior photocatalytic activity over not only solid BiVO4 spheres but also other morphological products such as biscuits and plates in the photodegradation of rhodamine B under visible-light irradiation.

Synthesis and physical properties of electromagnetic polypyrrole composites via addition of magnetic crystals

Polypyrrole (PPy) has received great attention as an electrically conducting matrix for electromagnetic composites because of its high conductivity, relatively good environmental stability, and easy synthesis. Magnetic crystals are suitable additives for preparing electromagnetic PPy composites. In the past two decades, a great deal of research work has been done on the synthesis and physical properties of electromagnetic PPy composites owing to their promising electromagnetic properties and various potential applications. PPy composites, in various forms such as powders, films, sheets, tubes and blocks, etc., have been prepared using the four methods of simple blending, electrochemical processing, in situ polymerization and the one-step chemical method. The physical properties including electrical, magnetic, absorbing and absorption properties of electromagnetic PPy composites have been extensively studied. This highlight article provides an up-to-date review on the synthesis methods and physical properties of electromagnetic PPy composites, in which the magnetic crystal additives are either in nano-sized or micro-sized scales. A summary is given for the synthesis approaches and their advantages and disadvantages are clearly displayed. The physical properties of electromagnetic PPy composites are then surveyed as a function of the magnetic crystal content. The electromagnetic PPy composites show not only good electrical and magnetic properties but also promising absorbing and absorption properties. Especially, the composites exhibit better absorbing properties than pure PPy or magnetic additives alone; also, they show high adsorption capacities for fluoride, Cr(VI), and endocrine disrupting compounds, etc. Finally, our perspectives are provided on the future development of electromagnetic PPy composites through the combination of different magnetic crystal additives and synthesis methods.