| The problem of environment pollution and health safety has been a growingconcern for the last few decades. A lot of photocatalyst based on nanometersemiconductor materials has been widely studied in various fields. ZnO is a kind ofimportant semiconductor materials, which owns a wide band gap width(3.37eV) andlarge exciton binding energy. ZnO is a kind of promising photocatalytic material dueto its chemical stability, non-toxic, effective photocatalytic activity and the low cost ofsynthetic methods. ZnFe2O4is semiconductor material of spinel strcture with a narrowband gap width (1.9eV). After combined with ZnO semiconductor, the ZnO/ZnFe2O4heterojunction broaden the scope of visible light absorption and enhanced the intensityof visible light absorption, so as to improve the photocatalytic activity of thematerials.In this paper, the large area actinomorphic ZnO nanotubes budles were preparedby the chemical bath method at the temperature of90℃. We synthesizeactinomorphic ZnO/ZnFe2O4nanocomposites through coprecipitated method at60℃.The chemical composition and structure were characterized by X-ray diffractometer(XRD), scanning electron microscopy (FESEM), transmission electron microscopy(TEM), and high-resolution transmission electron microscopy (HRTEM). Theultraviolet absorption properties were characterized by ultraviolet spectrophotometerinstrument. And we studied the degradation of rhodamine B performance of ZnOnanotubes budles and ZnO/ZnFe2O4nanocomposites. From the X-ray diffractionpatterns of the pure ZnO, we can see that ZnO is hexagonal wurtzite structure, which indicates a high crystallinity of ZnO samples. From the X-ray diffraction patterns ofthe ZnO/ZnFe2O4nanocomposites, the diffraction peaks of both ZnO and ZnFe2O4canbe seen clearly, ZnFe2O4belongs to typical spinel structure. The FESEM imageindicates that large area actinomorphic ZnO nanotubes budles can be prepared by thechemical bath method. ZnO nanotubes were coated evenly by ZnFe2O4nanoparticlesfilm. The TEM image indicates that the thickness of ZnFe2O4nanoparticles film isabout80nm. From HRTEM image we can see that the crystal faces of both ZnOnanotubes and ZnFe2O4nanoparticles interlace and grow together, and the size ofZnFe2O4nanoparticles are about10nm. The result of ultraviolet-visible absorptionspectrum shows that the absorption edge of ZnO/ZnFe2O4nanocomposites redshiftobviously compared with the absorption edge of ZnO, which broaden the sunlightabsorption to visible light area and improve the photocatalytic activity of the sample.From the image of degradation of Rhodamin B we can see that the trend ofphotocatalytic efficiency increases at first then decreases with the decrease of ZnOmass fraction, and the photocatalytic efficiency of ZnO/ZnFe2O4nanocomposites ishigher than pure ZnO obviously and pure ZnFe2O4. This is because the combinationsof the two kinds of semiconductor materials form heterojunction, which improve theutilization of sunlight of the samples and improve the photocatalytic activity. Whenthe mass fraction of ZnO is60%, the photodegradation efficiency has reached99.1%under the light for100min.In recent years, the electromagnetic wave absorption materials get more attentionbecause of the electromagnetic interference problem. At present, we require thatabsorbing agent has not only strong microwave absorption performance and wideabsorption frequency, but also small thickness, light quality, antioxidant, etc. Themicrowave absorbing properties of the traditional ferrite absorbing agent are strong,but it requires that the thickness of absorbing agent is too large. Therefore, a lot ofmaterials of nanoscale structure are widely used in the application of electromagneticwave loss. It has been found that the material of one-dimensional core-shell is formedby two different kinds of functional materials. The heterojunction at the interfaceshows the novel physical properties. So we will prepare promising microwave absorption materials for choosing ZnFe2O4as shell structure and ZnO as nuclearstructure of the heterojunction.The magnetic test of samples shows that the magnetic property of sampledeclines compared with pure ZnFe2O4after combined with nonmagnetic ZnO. Thetest of microwave absorbing properties shows that the microwave absorbingproperties increase at first then decline with the decrease of ZnO mass fraction. Thebest reflection loss reaches18.4dB when ZnO mass fraction is60%because thematch degree between dielectric constant and magnetic permeability is optimal.Compared with that of pure ZnO nanotubes and pure ZnFe2O4nanoparticles,enhanced electromagnetic wave absorption of actinomorphic ZnO/ZnFe2O4nanocomposites at2-18GHz was observed and the possible mechanism wasdiscussed. First, electromagnetic wave absorber with high dielectric constant isharmful for impedance matching, which leads to strong reflection and weakabsorption. ZnFe2O4nanoparticles with relatively low dielectric constant reduced thedielectric constant of ZnO effectively after compounded with ZnO nanotubes. Second,the absorbing agent remains relatively low dielectric constant, while it will benefitelectromagnetic wave loss to improve its electrical conductivity. The heterojunction ofZnO/ZnFe2O4nanocomposites improves concentration and mobility of the carriers,and improves its conductivity. Finally, the combination between ZnO nanotubes andZnFe2O4nanoparticles can get more crystal interfaces, which make the interfacepolarization effect and relaxation more obvious. |
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