Micro/Nanomaterials With Controllable Morphology Prepared By Electrospray And Its Properties Research

Micro/nanomaterials with multilevel interior structures have a wide range of applications in the aerospace, automatic control, catalysis, communications, biomedical and other fields. Electrospray is a simple and efficient method which can be used to prepare micro/nanomaterials with multilevel interior structures such as hollow, core-shell and janus structure. In this thesis, micro/nanomaterials with multilevel interior structures are successfully prepared by calcinating electrosprayed precursor spheres. We also investigate the photocatalytic properties of porous and rattle-type TiO2particles and exchange bias phenomenon of ferromagnetic (γ-Fe2O3)/antiferromagnetic (NiO) janus particles.Firstly, porous and rattle-type mischcrystal TiO2submicrospheres are successfully synthesized by rational calcination of precursor microspheres prepared by electrospray. In the case of low heating rate, the degradation of Ti(OH)4leads to a TiO2skeleton, and then after PVP is completely decomposed, the porous structure are obtained. While in the case of high heating rate, a dense shell is formed due to loss of PVP and degradation of Ti(OH)4rapidly at same time in the outside of the precursor. After the loss of inner PVP, a core is formed in the shell, so the rattle-type structure are obtained. The precursor microspheres have an average diameter of about700nm. After calcination at500℃for2h, the average diameters of the as-obtained porous and rattle-type TiO2products reduces to about200nm and600nm, respectively. X-Ray Diffraction shows that the as-obtained TiO2products are a mixture of anatase and rutile phase. Nitrogen absorption-desorption curve with a type of H3hysteresis loop manifests that the samples have mesoporous structure. The surface area of porous and rattle-type TiO2submicrospheres is38m2/g and32m2/g, and pore volume is0.107cm3/g and0.063cm3/g, respectively. Photocatalytic activity toward the decomposition of Rhodamine B under the irradiation of UV lights was investigated. The rate constant for porous and rattle-type spheres is more than2.5and1.6times higher than that of the Degussa P25titania, respectively. The high catalytic activity is contributed the multilevel interior structures and stable interface between rutile and anatase,Furthermore, γ-Fe2O3/NiO janus particle with exchange bias effect are made by electrospray method and heat treatment. The ferromagnetic and antiferromagnetic precursor solutions were injected to two paralleled capillarys, respectively. Under proper voltage, Fe2O3/NiO precursors are obtained. After heat treatment with different heating rate, we got the samples with different morphology. With a slow heating rate, the microspheres transform to bowl-sharp particles due to the asymmetric shrinkage. With high heating rate, the sample transforms to spherical ball. Meanwhile, the size of crystal increases with the heating rate. EDS shows the element distribution in the particle is not uniform, demonstrating that the samples have a janus structure. M-H curve shows that saturation magnetization, residual magnetization and coercivity increase with the increasing heating rate. However, only after the janus particles are solidification and cooled down from Neel temperature at magnetic field, an obvious exchange bias are observed. The exchange-bias field Hex is biggest in the5℃/min samples due to the larger interface between the ferromagnetic and antiferromagnetic nanoparticles. It is weakest in the sample which is heated to500℃immediately because of a small interface due to porous structure.