Manipulation of precession modes in all-permalloy nanostripe-nanopillar structured spin torque nano-oscillator driven by direct current.

We investigated the dynamical behaviors of an all-permalloy structured spin-torque nano-oscillator (STNO) composed of a nanostripe with in-plane magneto-anisotropy and a free magnetized nanopillar in the absence of a non-magnetic spacer via a micro-magnetic simulation. It is found the newly-devised STNO exhibits two stable precession modes of magnetization in the nanopillar: out-of-plane precession mode and in-plane precession mode under varying applied DC current densities. The switching between the two modes is generated in a certain current density, depending on geometries of the nanopillar as well as the nanostripe. Given a special nanopillar geometry, both modes demonstrate stable oscillation properties in a certain range of current densities. Pulsed magnetic field can effectively realize transformation of the two modes under application of a proper current density. The realization of synchronous oscillations to significantly enhance the output power is verified in this new type of STNO by etching plenty of nanopillars on the nanostripe to build STNOs array.

Novel recyclable BiOBr/Fe3O4/RGO composites with remarkable visible-light photocatalytic activity.

Magnetic BiOBr/Fe3O4/RGO composites with remarkable photocatalytic capability were prepared by a simple hydrothermal method to load 3D flower-like microspherical BiOBr onto the surface of Fe3O4/RGO. Under visible-light irradiation (λ > 420 nm), the BiOBr/Fe3O4/RGO composite with 56% mass percentage of Fe3O4/RGO shows the optimal removal ability for Rhodamine B, and the total removal efficiency is 96%. The coupling of Fe3O4/RGO and BiOBr elevates the conduction band of BiOBr, which enhances the reduction level of BiOBr/Fe3O4/RGO composites. Ultimately, based on experiments and theoretical calculations, an n-type Schottky contact formed at the heterojunction interface between RGO doped with Fe3O4 and BiOBr is proposed for photoexcited charge transfer. The RGO with great adsorptivity plays a major role in the photocatalysts composed of BiOBr, RGO and Fe3O4. Further, BiOBr/Fe3O4/RGO composites with permanent-magnetism can be recovered and reused easily by external magnetic field and maintain a total removal efficiency of 90% after four cycles.

Hydrothermal Synthesis of Ultra-Light Coal-Based Graphene Oxide Aerogel for Efficient Removal of Dyes from Aqueous Solutions.

A novel carboxymethyl cellulose (CMC)-supported graphene oxide aerogel (CGOA) was fabricated from a cost-effective and abundant bituminous coal by a mild hydrothermal process and freeze-drying treatment. Such an aerogel has cross-linked graphene oxide layers supported by CMC, and therefore, displays high mechanical strength while having ultra-low density (8.257 mg·cm-3). The CGOA has a 3D interconnected porous structure, beneficial graphene framework defects and abundant oxygen-containing functional groups, which offer favorable diffusion channels and effective adsorption sites for the transport and adsorption of dye molecules. The adsorption performance of rhodamine B by an optimized CGOA shows a maximum monolayer adsorption capacity of 312.50 mg·g-1, as determined by Langmuir isotherm parameters. This CGOA exhibited a better adsorption efficiency (99.99%) in alkaline solution, and satisfactory stability (90.60%) after three cycles. In addition, adsorption experiments on various dyes have revealed that CGOA have better adsorption capacities for cationic dyes than anionic dyes.