Preparation And Photocatalytic Properties Of Magnetically Separable Photocatalyst Nanospheres

Nanosized TiO2 is of great advantage due to high catalysis efficiency, no-pollution, energy-saving and stability in semiconducting materials. It can degrade all kinds of organic pollutants in water effectively. However, aggregation and difficulty in the separation and recovery of TiO2 powders from wastewater often limit their commercial applications. So, it is an urgent and important task to develop a photocatalyst with highly catalytic activity and easily reclaiming from 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 nano-TiO2 photocatalyst has both the excellent photocatalytic activity of TiO2 powder and the characteristic of supported TiO2 photocatalyst, which is easily recycled by the external magnetic field. In this study, magnetically separable photocatalysts have been prepared through the combination of the nanosized magnetic particles and nanosized photocatalyst particles by several different methods. The morphology and structure of the samples have been characterized using analytical techniques of XRD, TEM, EDS and FT-IR, etc. The relationship between the microstructure and photocatalytic properties was investigated. Some conclusions have been made as follows:1. NiFe2O4 nanoparticles were prepared by liquid catalytic phase transformation method at low temperature. The prepared samples show the characteristics of excellent dispersion, high magnetic property, stable crystalline phase and the superparamagnetic nature. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of NiFe2O4 nanoparticles. The results indicated that the structure of NiFe2O4 nanoparticles is spinel, and the size of particle is less than 20 nm.2. Magnetic SiO2/NiFe2O4 (SN) nanospheres were prepared by reverse micelle technique, which is based on the NiFe2O4 nanoparticles. The results of XRD and TEM analysis show that NiFe2O4 nanoparticles were wrapped by SiO2, and then the magnetic nanosphere SN were formed. With the increasing amount of NiFe2O4 nanoparticles (reduction in the amount of TEOS), the dispersion and spherical degrees of SN nanosphere are getting worse. Given that the greater amount of NiFe2O4 nanoparticles, the SN nanosphere will have stronger the magnetism, so the weight ratio of NiFe2O4/SiO2 is 15 wt%.3. A magnetically separable photocatalyst nanosphere TiO2/SiO2/NiFe2O4 (TSN) was prepared by acid catalyzed sol-gel method. X-ray diffractometer (XRD) and transmission electron microscope (TEM) were used to characterize the structure of the TSN photocatalyst nanosphere. The result indicated that the magnetic nanosphere -SiO2/NiFe2O4 (SN) was wrapped by Nano-TiO2 particles to form a TiO2 shell. The degradation experiments of methyl orange indicated that a thin amorphous SiO2 layer between NiFe2O4and TiO2 shell can improve significantly the photocatalytic acticity of the sample.4. A magnetically separable photocatalyst nanosphere TiO2/SiO2/NiFe2O4 (TSN-E) was prepared by electrostatic self-assembly method. It indicated from Zeta potential that it has the possibility of self-assembly. X-ray diffractometer (XRD), transmission electron microscope (TEM) and Fourier transformation infrared spectroscope (FT-IR) were used to characterize the structure of the TSN-E photocatalyst nanosphere. The result indicated that the magnetic nanosphere-SiO2/NiFe2O4 (SN) was wrapped by Nano-TiO2 particles to form a TiO2 shell. This photocatalyst nanosphere shows superparamagnetic nature and has a strong photocatalytic activity, which can be separated and recycled conveniently through an external magnetic field.5. A magnetically separable photocatalyst nanosphere TiO2/SiO2/NiFe2O4 (TSN-E-C) was prepared by electrostatic self-assembly method with the self-assembly media of C16H33(CH3)3NBr (CTAB). It indicated from Zeta potential that it has the possibility of self-assembly. X-ray diffractometer (XRD), transmission electron microscope (TEM) and Fourier transformation infrared spectroscope (FT-IR) were used to characterize the structure of the photocatalyst nanosphere TSN-E-C. The result indicated that the magnetic nanosphere-SiO2/NiFe2O4 (SN) was wrapped by Nano-TiO2 particles to form a TiO2 shell. In the photocatalyst nanosphere TSN-E-C, SiO2 served as a barrier between NiFe2O4 and TiO2, which inhibited effectively the injection of charges from TiO2 particles to NiFe2O4, leading to the increase in photocatalytic activity. The TSN-E-C exhibited a good photocatalytic activity for removal of organic pollutants in water under UV irradiation, it's one of promising candidates for photocatalytic treatment of wastewater.