Soluble Starch-Assisted Preparation And Photocatalytic Properties Of ZnO

As a typical wide band gap multifunction semiconductor, Znic oxide (ZnO) has been used in many fields. Semiconductor photocatalytic technology has been employed in phtotocatalytic decomposition of water and degradation of organic pollutants, so it was widely utilized in environmental waste treatment and protection. ZnO is one of the most widely used effective photocatalyst, and has attracted the public concern from home and abroad. But the photocatalytic efficiency of ZnO always was relatively low for the reason of energy barrier. The doping of other elements or semiconductors into ZnO was used to change the properties, such as defect concentration, particle sizes, which had been verified to enhance the photocatalytic property of ZnO. So, how to fabricate ZnO and ZnO mixed oxide of high photocatalytic efficiency has become the hotspot of research. In this paper, we have adapted soluble starch-assisted aqueous solution method to fabricate uniform ZnO spheres, and sol-gel method to obtain M-Zn-0 (M= Fe, Mn, Cr, Co, Ni) mixed oxide. The final photocatalysts had been analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Field-emission scanning electron microscopy (FESEM), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and Ramon spectra (Raman).SEM and FESEM show that the morphology of ZnO spheres is very uniform and have good monodispersity. And SEM analysis revealed the size of single ZnO decreased from 200-450 nm to 150-300 nm after calcination at 500℃. FESEM revealed the single ZnO sphere is composed of many nano-ZnO particles. The sizes of ZnO nanoparticles increased from 5 nm to 15-30 nm after calcination at 500℃. Ramon spectra showed the ZnO sphere fabricated by aqueous solution method is a mixed of starch and ZnO. The starch was removed by calcination at 500℃. The DRS analysis revealed the absorption band of ZnO compound were red shift compared with the pure ZnO.We investigated the photocatalytic properties of ZnO and ZnO mixed oxide by degradation of rhodamine B (RhB) and 4-nitrophenol (4-NP) under ultra-visible light. The results showed that the ZnO spheres had high photocatalytic efficiency of RhB and 4-NP. The Cr-Zn-O (1:40) mixed oxide, which was obtained by sol-gel method, had much better photocatalytic property than single ZnO under the same photocatalytic condition. And the photocatalytic degradation efficiency of RhB (5 mg/L) reached 92% after one hour of illumination. Compared with that, it was only 70% for the single ZnO. The photocatalytic property of ZnO had been enhanced a lot after doping of Cr. But the doping of the other metal (Fe, Mn, Ni, Co) elements did not play the same role in improving the photocatalytic property of ZnO.