Huifeng Li

High-performance piezoelectric gate diode of a single polar-surface dominated ZnO nanobelt

We report a piezoelectric gated diode that is composed of a single ZnO nanobelt with +/- (0001) polar surfaces being connected to an indium tin oxide (ITO) electrode and an atomic force microscopy (AFM) tip, respectively. The electrical transport is controlled by both the Schottky barrier and the piezoelectric barrier modulated by the applied forces. The diode exhibits a high ON/OFF current ratio (up to 1.6 x 10(4)) and a low threshold force of about 180 nN at 4.5 V bias. The electrical hysteresis is suggested to be attributed to be carrier trapping in the piezoelectric electric field.

Rapid Simultaneous Removal of Toxic Anions [HSeO3]−, [SeO3]2–, and [SeO4]2–, and Metals Hg2+, Cu2+, and Cd2+ by MoS42– Intercalated Layered Double Hydroxide

We demonstrate fast, highly efficient concurrent removal of toxic oxoanions of Se(VI) (SeO42-) and Se(IV) (SeO32-/HSeO3-) and heavy metal ions of Hg2+, Cu2+, and Cd2+ by the MoS42- intercalated Mg/Al layered double hydroxide (MgAl-MoS4-LDH, abbr. MoS4-LDH). Using the MoS4-LDH as a sorbent, we observe that the presence of Hg2+ ions greatly promotes the capture of SeO42-, while the three metal ions (Hg2+, Cu2+, Cd2+) enable a remarkable improvement in the removal of SeO32-/HSeO3-. For the pair Se(VI)+Hg2+, the MoS4-LDH exhibits outstanding removal rates (>99.9%) for both Hg2+ and Se(VI), compared to 81% removal for SeO42- alone. For individual SeO32- (without metal ions), 99.1% Se(IV) removal is achieved, while ≥99.9% removals are reached in the presence of Hg2+, Cu2+, and Cd2+. Simultaneously, the removal rates for these metal ions are also >99.9%, and nearly all concentrations of the elements can be reduced to <10 ppb, a limit acceptable for drinking water. The maximum sorption capacities for individual Se(VI) and Se(IV) are 85 and 294 mg/g, respectively. The 294 mg/g capacity for Se(IV) reaches a record value, placing the MoS4-LDH among the highest-capacity selenite adsorbing materials described to date. More interestingly, the presence of metal ions extremely accelerates the capture of the selenium oxoanions because of the reactions of the metal ions with the interlayer MoS42- anions. The sorptions of Se(VI)+Hg and Se(IV)+M (M = Hg2+, Cu2+, Cd2+) are exceptionally rapid, showing >99.5% removals for Hg2+ within 1 min and ∼99.0% removal for Se(VI) within 30 min, as well as >99.5% removals for pairs Cu2+ and Se(IV) within 10 min, and Cd2+ and Se(IV) within 30 min. During the sorption of SeO32-/HSeO3-, reduction of Se(IV) occurs to Se0 caused by the S2- sites in MoS42-. Sorption kinetics for the oxoanions follows a pseudo-second-order model consistent with chemisorption. The intercalated material of MoS4-LDH is very promising as a highly effective filter for decontamination of water with toxic Se(IV)/Se(VI) oxoanions along with heavy metals such as Hg2+, Cd2+, and Cu2+.

Synthesis, characterization and electromagnetic performance of nanocomposites of graphene with α-LiFeO2 and β-LiFe5O8

Face-centered cubic α-LiFeO2 and spinel β-LiFe5O8 with uniform size and high dispersion have been successfully assembled on 2D graphene sheets via a facile one-pot strategy under different reaction conditions. The reduction of GO by this method is effective and comparable to conventional methods, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the products can be easily controlled by changing the solvent and reaction temperature. It was shown that the as-formed β-LiFe5O8 and α-LiFeO2 nanocrystals with a diameter of ca. 5 nm and 7 nm, respectively, were densely and uniformly anchored on the graphene sheets, and as a result, the aggregation of the nanoparticles was effectively prevented. The investigation of the microwave absorbability reveals that the α-LiFeO2–GN and β-LiFe5O8–GN nanocomposites exhibit excellent microwave absorbability, which is stronger than that of the corresponding α-LiFeO2 and β-LiFe5O8 nanostructures, respectively.

Uniform FexNiy Nanospheres: Cost-Effective Electrocatalysts for Nonaqueous Rechargeable Li–O2 Batteries

Uniform FexNiy nanospheres were synthesized via a simple solvothermal method and used as electrocatalysts for Li–O2 batteries. Fe7Ni3 nanospheres exhibited relatively high catalytic activities in the electrochemical tests. They delivered a reversible capacity of more than 7000 mAh/gKB and gave a discharge–charge voltage gap reduction of 250 mV compared with Ketjen Black.

In Situ Preparation of Cobalt Nanoparticles Decorated in N-Doped Carbon Nanofibers as Excellent Electromagnetic Wave Absorbers

Electrospinning and annealing methods are applied to prepare cobalt nanoparticles decorated in N-doped carbon nanofibers (Co/N-C NFs) with solid and macroporous structures. In detail, the nanocomposites are synthesized by carbonization of as-electrospun polyacrylonitrile/cobalt acetylacetonate nanofibers in an argon atmosphere. The solid Co/N-C NFs have lengths up to dozens of microns with an average diameter of ca. 500 nm and possess abundant cobalt nanoparticles on both the surface and within the fibers, and the cobalt nanoparticle size is about 20 nm. The macroporous Co/N-C NFs possess a hierarchical pore structure, and there are macropores (500 nm) and mesopores (2-50 nm) existing in this material. The saturation magnetization ( Ms) and coercivity ( Hc) of the solid Co/N-C NFs are 28.4 emu g-1 and 661 Oe, respectively, and those of the macroporous Co/N-C NFs are 23.3 emu g-1 and 580 Oe, respectively. The solid Co/N-C NFs exhibit excellent electromagnetic wave absorbability, and a minimum reflection loss (RL) value of -25.7 dB is achieved with a matching thickness of 2 mm for solid Co/N-C NFs when the filler loading is 5 wt %, and the effective bandwidth (RL ≤ -10 dB) is 4.3 GHz. Moreover, the effective microwave absorption can be achieved in the whole range of 1-18 GHz by adjusting the thickness of the sample layer and content of the dopant sample.

High-purity production of ultrathin boron nitride nanosheets via shock chilling and their enhanced mechanical performance and transparency in nanocomposite hydrogels

A simple, highly efficient, and eco-friendly method is prepared to divide bulk boron nitride (BN) into boron nitride nanosheets (BNNSs). Due to the anisotropy of the hexagonal BN expansion coefficient, bulk BN is exfoliated utilizing the rapid and tremendous change in temperature, the extreme gasification of water, and ice thermal expansion pressure under freeze drying. The thickness of most of the BNNSs was less than ∼3 nm with a yield of 12-16 wt%. The as-obtained BNNS/polyacrylamide (PAAm) composite hydrogels exhibited outstanding mechanical properties. The tensile strength is fives times the bulk of the BN/PAAm composite hydrogels and the elongations are more than nine-fold the bulk of the BN/PAAm composite hydrogels. The BNNS/PAAm nanocomposite hydrogels also exhibited excellent elastic recovery, and the hysteresis of the BNNS nanocomposite hydrogels was negligible even after 30 cycles with a maximum tensile strain (ε max) of 700%. This work provides new insight into the fabrication of BN/polymer nanocomposites utilizing the excellent mechanical properties and transparency of BN. The results confirm that a few layers of BNNSs can also efficiently and directly improve the mechanical properties of composite polymer due to its stronger surface free energy and better wettability.