Haisheng Qian

Magnetic-field induced formation of 1D Fe3O4/C/CdS coaxial nanochains as highly efficient and reusable photocatalysts for water treatment

We report a novel strategy for fabrication of one-dimensional (1D) Fe3O4/C/CdS coaxial nanochains via a magnetic field-induced assembly and microwave-assisted deposition method. First, 1D pearl chain-like Fe3O4/C core–shell nanocables are successfully assembled via the hydrothermal reaction of Fe3O4 nanospheres and glucose in water in the presence of an external magnetic field. The carbonaceous layer is about 10 nm in thickness, and it acts as the stabilizer for the Fe3O4 nanochains. Afterwards, CdS nanoparticles are facilely deposited onto the 1D Fe3O4/C nanochains via a rapid microwave-irradiation route to form 1D Fe3O4/C/CdS coaxial nanochains. Further investigation has revealed that these magnetic nanocomposites possess significantly improved activity as a recyclable photocatalyst for the degradation of organic pollutants when exposed to visible light irradiation. This new synthesis strategy is not restricted to the specific material discussed in this work and should be versatile for a wide range of magnetically separable photocatalysts containing 1D magnetic nanochains as the support and an outer layer of active semiconductor nanocrystals.

A novel ternary composite: fabrication, performance and application of expanded graphite/polyaniline/CoFe2O4 ferrite

Expanded graphite–polyaniline microparticles (EG/PANI), synthesized by the emulsion polymerization of aniline in the presence of expanded graphite, were coated with CoFe2O4 ferrite (CF) to form ternary composites of EG/PANI/CoFe2O4 (EG/PANI/CF). The phase composition, morphology, electrical and magnetic performances of the composites were characterized by means of modern measurement technology. The results indicated that the electrical and magnetic performances of the ternary composites were related to their composition, and were better than those of binary composites. The EG/PANI/CF composites with a mCF/mEG/PANI of 0.2 had the best conductivity (86.207 S cm−1) of all ternary composites. The EG/PANI/CF composites with a mCF/mEG/PANI of 0.8 at a thickness of 0.5 mm had the minimum reflection loss of −19.13 dB at 13.28 GHz and an available bandwidth of 5.94 GHz. Hence, the obtained composites had potential and valuable applications in microwave shielding and absorption fields.

Submicrometer-sized NiO octahedra: facile one-pot solid synthesis, formation mechanism, and chemical conversion into Ni octahedra with excellent microwave-absorbing properties

A facile template-free and one-pot thermal decomposition approach was used for the mass preparation of submicrometer-sized NiO octahedra. Ni octahedra with tailored crystallization and texture characteristics are easily achieved through H2-annealing of NiO octahedra at various temperatures. The good morphology retention of Ni octahedra is due to the principle of minimum surface free energy as well as the similar crystallographic system to that of NiO. Studies on static magnetic and microwave electromagnetic properties reveal the relationships among the reactivity, shape, and resultant properties of the nanomaterials. Because of their high BET specific surface area and favorable crystal size, porous Ni octahedra produced at 300 °C exhibit excellent matching and absorbing properties with a minimum RL value of −37.93 dB at 12.80 GHz and 11.60 GHz bandwidth (below −20 dB). Thus the Ni octahedra described here are believed to have a wide range of applications, including catalysis, electromagnetic shielding, and absorption.

Flower-like Co superstructures: Morphology and phase evolution mechanism and novel microwave electromagnetic characteristics

Flower-like Co superstructures composed of leaf-like flakes were synthesized via a facile hydrothermal approach independent of surfactants or complex precursors. The evolution of the morphology and crystal phase was closely related to the variation of the electrode potentials, in which NaOH and hydrazine hydrate played crucial roles. The microwave electromagnetic and absorbing properties of the flower-like Co/wax composites varied strongly with the mass ratios (λ) of Co powder to wax. At the low λ of Co powder to wax, flower-like Co superstructures functioned as the random distributed patches in wax matrix and, therefore composites exhibited frequency selective surface (FSS) behaviors. Owing to high conductance and eddy current losses, however, composites with high λ showed excellent microwave absorption performances, with a minimum reflection loss (RL) of −40.25 dB observed at 6.08 GHz, corresponding to a matching thickness of 2.5 mm. In particular, the absorption bandwidth (RL ≤ −20 dB) was 13.28 GHz. The current work provides insights into the absorption mechanism of flower-like complex absorption materials.

Selective preparation and enhanced microwave electromagnetic characteristics of polymorphous ZnO architectures made from a facile one-step ethanediamine-assisted hydrothermal approach

The current study describes a facile one-step ethanediamine (en)-assisted hydrothermal approach for the selective synthesis of ZnO architectures with morphologies that evolve from nanocones, to twinned nanoroses, to dispersed microneedles, and even to complex, flower-shaped architectures. Kinetic factors, such as time, temperature, en-to-Zn(NO3)2 molar ratio (δ), [Zn2+], and Zn sources can be easily utilized to control the oriented attachment growth of [Zn(OH)4]2− on the (0001) polar surface, thereby regulating the morphology and growth direction of the ZnO architectures. Time lengthening as well as increases in temperature, δ, and [Zn2+] can promote the morphological evolution from needle-like to flower-shaped and can change the structurally oriented growth from along the c-axis to along the a-axis. The flower-shaped ZnO–wax composites exhibit enhanced permittivity and microwave-absorbing properties as mass fraction increases. However, this distinct morphology is prone to high dielectric loss. Thus, the flower-shaped ZnO showed stronger microwave absorption performances than the needle-like ZnO, with a minimum reflection loss (RL) of −21.85 dB at 8.4 GHz, corresponding to a matching thickness of 3.0 mm. In particular, interesting nesting microwave absorption peaks can be observed in the reflection loss plots of the flower-shaped ZnO. The current work provides insights into the absorption mechanism of flower-shaped ZnO absorption materials.

Facile microemulsion route to coat carbonized glucose on upconversion nanocrystals as high luminescence and biocompatible cell-imaging probes

Surface modification of lanthanide-doped upconversion nanocrystals is crucial to make them useful for various biological applications. Unfortunately, the current methods available to achieve a desirable surface exhibiting both high luminescence and good biocompatibility are limited. In this work, we present a facile microemulsion route to coat carbonized glucose on hydrophobic NaYF(4) nanocrystals. Owing to the particular structure of the carbonized shell, glucose coating on these UCNs is not only able to preserve strong fluorescence from the core nanocrystals, but it also confers good water solubility and bears various functional groups for conjugating to biomolecules. Compared to 10 nm silica-coated UCNs, these glucose-coated nanocrystals possess better cell biocompatibility, and can be rapidly internalized into cells. Such unique features of glucose-coated UCNs may find promising applications in imaging, diagnosis and therapeutic purposes. Besides, this facile surface-modification route has the potential to be extended to a broad range of other hydrophobic nanocrystals.

A facile and generic strategy to synthesize large-scale carbon nanotubes

An easy method to prepare carbon nanotubes (CNTs) has been demonstrated using a two-step refluxing and calcination process. First, a readily available inorganic salt, Ni(NO3)2 ˙ 6H2O, used as the catalyst precursor was dissolved in the high-boiling-point organic solvents (alcohols or polyhydric alcohol) by refluxing at 190°C for 3 hours. After refluxing, NiO nanoparticles obtained in the solution act as the catalyst, and the organic refluxing solvents are used as the carbon source for the growth of CNTs. Second, CNTs are prepared by calcining the refluxed solution at 800°C in an N2 atmosphere for 3 hours. Results show that CNT growth possibly originates from carbon rings, with the nanotube walls growing perpendicular to these rings and forming a closed tube at the end.

Mesoporous silica-coated NaYF4 nanocrystals: facile synthesis, in vitro bioimaging and photodynamic therapy of cancer cells

Up-conversion nanoparticles (UCNPs) that emit high-energy photons upon excitation by low-energy near-infrared (NIR) radiation are emerging as new optical nanoprobes useful in biomedicine. Herein, the one pot facile synthesis of mesoporous silica-coated NaYF4:Yb/Er nanoparticles has been achieved successfully. The as-prepared product was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM) and Brunauer–Emmet–Teller (BET) surface area analyses, respectively. The resulting nanoparticles with a BET area of 800 m2 g−1 and an average pore size of 2.6 nm were spherical, highly monodispersed and stable in an aqueous system. Furthermore, the NaYF4:Yb/Er@mesoporous silica nanoparticles also displayed good biocompatibility and could be used for bio-labeling or bio-imaging. Additionally, the results of preliminary photodynamic therapy (PDT) of cancer cells indicated the NaYF4:Yb/Er@mesoporous silica nanoparticles could be used as important photosensitizer carriers for tumor therapy.

Decoration of ZnO nanocrystals on the surface of shuttle-shaped Mn2O3 and its magnetic-optical properties

A new type of magnetic-fluorescent bifunctional nanocomposites, shuttle-shaped Mn2O3 decorated by ZnO nanocrystals has been successfully prepared by a facile two-step, wet-chemical strategy.

Self-assembly of TiO2 composite microspheres: Facile synthesis, characterization and photocatalytic activities

A mild solution route has been designed for the synthesis of uniform TiO2/SiO2 composite microspheres with octadecyltrimethoxysilane (C18TMS) and tetrabutyl titanate at low temperature via a self-assembly process. The TiO2 composite microspheres consisted of TiO2 nanoparticles with several nanometers in diameter; and the size and morphology of the composite microspheres can be well controlled by controlling the reaction conditions. Octadecyltrimethoxysilane and reaction temperature play key roles in the formation of the composite microspheres. In particular, the synthesized composite microspheres exhibit strong anatase phase stability and good performance on photodegradation of RhB dye from the pollutant solution. All the results reveal that the self-assembly strategy represents a facile method for controlling the crystallinity and size of TiO2 photocatalysts and for their excellent photocatalytic activity, which is also of great importance to the potential applications in solar cells and lithium ion batteries etc.