Different Microstructure Of Iron Oxide Hydrothermal Synthesis And Magnetic Properties Of Study

Nanodiscs, nanocubes, nanospindles and nanoparticles of a-Fe2O3 have been synthesized via a simple hydrothermal method. Morphologies and structures of these products were characterized by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy ect. The formation process of the nanostructures was discussed, and the possible growth mechanisms were proposed. The magnetic properties of a-Fe2O3 with different structures were investigated and the intrinsic relationship between microstructure and magnetic properties was discussed.(1) Synthesis and size-dependent magnetic properties of single-crystal hematite nanodiscs:Single-crystal a-Fe2O3 nanodiscs with diameters of 132 to 150 nm were synthesized by a facile hydrothermal reaction of FeCl3 and NaOH at 200℃for 12h in the presence of NaH2PO4. The role of NaH2PO4 in the formation process of nanodiscs was discussed and theα-Fe2O3 nanodiscs are formed by the cooperative action of selective adsorption and etching of the phosphate ions. The sizes of the nanodiscs were decreased to 91-112 and 78-92 nm by introducing ethylene glycol into the system. The magnetic hysteresis loops of a-Fe2O3 nanodiscs with different sizes at room temperature were discussed and the results showed that both the remanent magnetization and the coercive force were decreased with the decreasing nanodisc sizes.(2) Controlled synthesis and size-dependent magnetic properties of uniform single-crystal a-Fe2O3 nanocubes with different sizes:Uniform single-crystal a-Fe2O3 nanocubes were synthesized by the hydrothermal reaction of FeCl3 and NaOH at 140℃for 12-15 h. Controlled synthesis of nanocubes with different sizes were achieved by tuning the concentration of FeCl3 solution and the reaction time. The formation process of the cubes was discussed and it was found that the a-Fe2O3 nanocubes were obtained by the decomposition of Fes(OOH)16Cl1.3. The magnetic properties of the as-synthesized a-Fe2O3 nanocubes were investigated. Both the remanent magnetization and the coercive force were increased with the increasing sizes of nanocubes.(3) Controlled synthesis of a-Fe2O3 nanospindles and nanoparticles and their magnetic properties:Single-crystal a-Fe2O3 nanospindles and nanoparticles were obtained by increasing mole ratio of FeCl3 to NaH2PO4 in the FeCl3-NaH2PO4-NaOH hydrothermal system at 200℃for 12 h. The roles of NaH2PO4 and Cl- in the formation process of the nanospindles and nanoparticles were studied, the formation of nanospindles and nanoparticles result from the cooperative action of NaH2PO4 and Cl-. The magnetic properties of the as-synthesized a-Fe2O3 nanostructures were investigated, and it was found that both the remanent magnetization and the coercive force of the nanospindles with stronger anisotropy were larger than that of the nanoparticles.