| One-dimensional(1D) iron-based magnetic nanomaterials have been considered as one of the most important issues in the materials science and condensed matter physics, and the important constituents of the new generation of electro-magnetic and optical multifunction devices. Owing to not only their various physical effects just like magnetic particles, but also their specific shape anisotropy effectively conquering the magnetoelectronic limition of the particle-shaped materials, they can be expected to appled in the high-density magnetic recording, spin electronic devices, electromagnetic wave absorption, magnetic sensors, catalysis and biomedicine. In practical studies and applications, the preparation of 1D magnetic nanomatials with mass production should be sample and low cost, and their nanostructures should be uniformi, continuous and controllable.Herein, magnetic nanoribbons of Sr Fe12O19, Co Fe2O4, Fe-Co alloy and Fe-Ni alloy and Si O2-modified Co Fe2O4 nanotubes with controllable structures were successfully synthesized via polyvinylpyrrolidone(PVP)-sol assisted electrospinning route followed by heat treatment, and their microstructures and magnetic properties were investigated systematically. Furthermore, using Cu Fe2O4 porous nanotubes and Ni Fe2O4/Sr Ti O3 composite nanotubes as example, we deeply discussed the huge photocatalytic effects of spinel ferrites during the photodegradation of organic pollutants. The main conclusions are listed as follows:1. Consecutive and width-controlled Sr Fe12O19 nanoribbons were self-assembled by abundant single-domain Sr Fe12O19 nanoparticles. Each nanoribbon was uniform on width, highly crystalline and chemical pure. With PVP concentration increasing in the spinning solution, the ribbon-width was increased but the particle-size was reduced. The nanoparticles distributed on a same ribbon more intensively. The magnetic performance investigation revealed that considerable large Ms and Hc were obtained for all Sr Fe12O19 nanoribbons, and both of them increased with the ribbon-width broadening. The maximum Ms(67.9 emu·g-1) and Hc(7.31 k Oe) were concurrently acquired for Sr Fe12O19 nanoribbons with the maximum ribbon-width. Among the all values reported for pure Sr Fe12O19 nanostructures, so far, our value was the largest, which was mainly attributed to their single-domain particles, high magneto-crystalline anisotropy and unique shape anisotropy as well as the exchange-interactions between Sr Fe12O19 nanoparticles and between nanoribbons. Finally, the Stoner-Wohlfarth curling model was suggested to qualitatively analysize the magnetization reverse process of Sr Fe12O19 nanoribbons.2. Co Fe2O4 nanoribbons not only possessed high crystallinity and purity, but also exhibited excellent ferromagnetism behavior. The Ms increased with increasing annealing temperature but the Hc decreased monotonically. The sample annealed at 750 oC obtained the maximum Ms(80.3 emu·g-1), which was basically equal to the bulk value. The sample annealed at 450 oC obtained the maximum Hc(1802 Oe), which was larger than most of Hc values reported for other 1D Co Fe2O4 nanostructures by far. Furtermore, it suggested that the magnetization reverse processes of the Co Fe2O4 nanoribbons annealed at 450 and 550 oC were dominated by the coherent rotation model, but that of the Co Fe2O4 nanoribbons annealed at 650 and 750 oC were dominated by the growth of a reverse magnetic domain.3. Fe-Co alloy and Fe-Ni alloy nanoribbons were respectively prepared for the first time by deoxidizing the electrospun Co Fe2O4 and Ni Fe2O4 nanoribbons in H2 at a series of temperatures. All of the obtained samples not noly possessed novel ribbon-shape structure, but also exhibited excellent soft ferromagnetism. Moreover, the microstructures and magnetic properties of samples were significantly depended on the deoxidization temperature. For Fe-Co alloy nanoribbons, with increasing the deoxidization temperature, their Ms increased from 122 to 210 emu·g-1 but the corresponding Hc decreased from 296 to 173 Oe. For Fe-Ni alloy nanoribbons, when the deoxidization temperature is in the range of 300 oC ~ 500 oC, although all samples owned their respective morphology features, all of them intact reserved the ribbon-like structures. When the deoxidization temperature was further increased to 600 oC, the Fe-Ni alloy nanoribbons were sharply evolved into Fe-Ni alloy nanochains. With the deoxidization temperature increasing, the cubic Ni Fe2O4 was firstly deoxidized into the body-centered cubic(bcc) Fe-Ni alloy and then transformed into the face-centered cubic(fcc) Fe-Ni alloy. Additionally, the Ms of samples firstly increased, then decreased, and increased with the deoxidization temperature increasing, but the Hc decreased monotonously firstly and then basically stayed unchanged. And the largest Ms(145.7 emu·g-1) and the moderate Hc(132 Oe) were obtained for the Fe-Ni alloy nanoribbons with a mixed configuration of bcc and fcc phases deoxidized at 400 oC.4. For Si O2-modified Co Fe2O4 nanotubes annealed at 1000 oC, it revealed that nonmagnetic Si O2 uniformly distributed around Co Fe2O4 nanoparticles as amorphous and played significant influence on the microstructure, crystalline size and magnetic performance of the sample. The pure Co Fe2O4 sample showed a particle chain with rod-shape but the Si O2-modified Co Fe2O4 sample showed a robust nanotube structure. With increasing Si O2 content, increase at first and then decrease in Hc and monotonously decrease in Ms have been determined in the obtained modified Co Fe2O4 nanotubes. The maximum Ms(80 emu·g-1) and Hc(1477 Oe) were obtained for the pure Co Fe2O4 nanorods and the modified Co Fe2O4 nanotubes with about 14.9 wt% Si O2, respectively. It confirmed that amorphous materials can effectively improving the structure endurance of 1D electrospun inorganic oxide nanostructures treated under high temperatures.5. Homogeneously porous Cu Fe2O4 nanotubes with an average diameter of 272±2 nm were assembled by abundant spinel Cu Fe2O4 single-crystal nanoparticles with regular polyhedron structure. They got uniform component distribution, strong light response in the UV-Visible light range, considerable specific surface area of 12.8 m2/g and porosity of 15.5 nm, enough Ms(18 emu·g-1) and Hc(1531 Oe). During the photodecomposition of acid fuchsin dye in aqueous solution under a simulated sunlight source, the Cu Fe2O4 nanotubes showed an excellent catalytic activity and durability. Finally, they could be efficiently separated from the residual solution by a magnet, which not only was conductive to the recycling but also prevented the second pollution.6. The Sr Ti O3/Ni Fe2O4 porous heterogenous nanotubes(PNTs) and the Sr Ti O3/Ni Fe2O4 particles-in-tubes(PITs) were respectively prepared by a single-spinneret electrospinning and a modified side-by-side-spinneret electrospinning. And their chemical components, microstructures, magnetic performance, magnetic separations and photocatalytic performance were investigated systemly. The results indicated that Sr Ti O3/Ni Fe2O4 PNTs were the heterojunction nanotubes by connecting perovskite Sr Ti O3 and spinel Ni Fe2O4 nanoparticles, but Sr Ti O3/Ni Fe2O4 PITs were the self-assembled core/shell nanostructures by embedding Sr Ti O3 nanoparticles into Ni Fe2O4 nanotube. The two Sr Ti O3/Ni Fe2O4 composites exhibited a powerful light response and excellent room temperature ferromagnetism. The magnetic separations revealed that such amazing recycling efficiencies of 95% for Sr Ti O3/Ni Fe2O4 PNTs and 99.5% for Sr Ti O3/Ni Fe2O4 PITs were obtained. Both of the two magnetic composites performed the considerable photocatalytic activity in the degradation of rhodamine B. This work provides a feasible way to assemble the core/shell nanostructures of different materials. |
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