Preparation Of Magnetically Separable Composite Photocatalyst And Effect Of Magnetic Carrier On Photocatalytic Activity

Semiconductor photocatalysts have many advantages, high efficiency, low selectivity, no secondary pollution, etc. In all kinds of semiconductor materials, TiO2and ZnO nanoparticles show excellent ability in degradation of many environmental pollutants. Compared to other photocatalysts, they are low-cost, high stability, high activity. However, they are still limited in water and wastewater treatment field, mainly due to the difficult separation and reclaiming of TiO2and ZnO nanoparticles from treated water.The nanosized magnetic particles can solve the difficulty of photocatalyst separation from the treated water due to the characteristics of large surface area and magnetism property. The composite photocatalyst has both the excellent photocatalytic activity of powder photocatalyst and the characteristic of supported photocatalyst, which is easily recycled by the external magnetic field.In this study, magnetically separable photocatalysts were prepared through the combination of the nanosized magnetic particles and nanosized photocatalyst particles. The morphology and structure of the samples were characterized using analytical techniques of VSM, XRD, TEM, XPS, PL, UV-vis, BET, etc. The relationships between the microstructure and photocatalytic properties were investigated. Some conclusions were made as follows:1. NiFe2O4nanoparticles were prepared by liquid catalytic phase transformation method at low temperature. Then, the composite nanoparticles TiO2/NiFe2O4(TN) were prepared via sol-gel method. The effect of magnetic nanoparticle NiFe2O4on photocatalytic property of TiO2has been studied. The patterns of XRD indicate that adulterating a smidgen of NiFe2O4into TiO2(about0.1%) can promote the phase transformation of TiO2, however, when the doped amount of NiFe2O4surpasses1%, the introduction of NiFe2O4can inhibit the growth of TiO2crystal grain and reduce the size of TiO2crystal grain. The results of PL and the degradation experiments show that the NiFe2O4nanoparticles in photocatalyst TN play the role of the effective recombination centre of the photogenerated electrons and holes, leading to the decrease in photocatalytic activity.2. Magnetic nanospheres SiO2@NiFe2O4(SN) were prepared by reverse micelle technique, which are based on the prepared NiFe2O4nanoparticles. The results of XRD and TEM show that NiFe2O4nanoparticles were wrapped by SiO2, and then the magnetic nanosphere SN were formed. With the increasing amount of NiFe2O4nanoparticles, the dispersion and spherical degrees of SN nanosphere are getting worse.3. A magnetically separable composite photocatalyst TiO2@SiO2@NiFe2O4(TSN) was prepared by liquid phase deposition method, and characterized by X-ray diffraction and transmission electron microscopy. The results indicate that nickel ferrite core nanoparticles are completely encapsulated into silica nanospheres as carrier (SiO2@NiFe2O4), and titania nanoparticles are deposited onto the surface of SiO2@NiFe2O4nanospheres, forming a TiO2shell for photocatalysis. The degradation experiments of methyl orange indicate that when the molar ratio of H3BO3to [TiF6]2-is set at4:1, the as-prepared photocatalyst calcined at300℃presents the best photocatalytic activity.4. A magnetically separable composite photocatalyst ZSN@SiO2@NiFe2O4(ZSN) was prepared by sol-gel method. The result of VSM indicates that the composite photocatalyst shows superparamagnetic nature. XRD and TEM were used to characterize the structure of the ZSN photocatalyst. The results indicate that the magnetic nanospheres SN were wrapped by ZnO nanoparticles to form a ZnO shell. The degradation experiments of methyl orange indicate that the as-prepared ZSN calcined at500℃for3h presents the best photocatalytic activity.