Preparation And Characterization Of Mn_xZn_1-xFe₂O₄/Bi₂O₃ Magnetic Composite Photocatalyst

Environmental pollution especially water pollution is getting worse with the acceleration of industrialization. There are some defects such as higher energy consumption and longer processing cycle in traditional wastewater treatment methods. Semiconductor photocatalysis possess the characteristics of high efficiency and energy-saving in the process of degradation of organic pollutants in water, receiving extensive attention. As a representative of semiconductor photocatalysts, Ti O2 has become a hotspot of energy and environmental scholar for its non-toxic and good stability. Due to wide band gap and weak response to visible light of Ti O2, more and more researchers were turning to explore new photocatalyst such as Ag3PO4 and their composites, sulfides as well as bismuth compounds and so on. Bi2O3 of Bismuth compounds got attention for its narrower band gap and larger absorption wavelength, and became one of the development hot points in new optical catalyst. However, this kind of photocatalyst is hard to separate and recover after reaction, and it’s likely to result in secondary pollution for the incomplete recovery. Load the appropriate amount of magnetic material can not only improve the photocatalytic activity of the photocatalyst itself, but also realize recycling and reuse by an external magnetic field. Solving the above problems, it accorded with the concept of green chemistry.In this paper, α-Bi2O3 was prepared by chemical precipitation. As it was used as photocatalyst, the Rh B(10mg/L) degradation rate reached 50.7% under the simulated sunlight for 4h. Composites magnetic photocatalyst MnxZn1-xFe2O4/α-Bi2O3 were synthesized by impregnation sintering method by using manganese zinc ferrite as magnetic substrate. Effects of composite mass ratio, reaction time and calcination temperature on the photocatalytic activity were discussed. The as-prepared MnxZn1-xFe2O4/α-Bi2O3 composites were characterized by X-ray diffraction(XRD), Fourier transforms infrared(FTIR), diffuse reflectance spectroscopy(DRS), scanning electron microscope(SEM) and Vibrating sample magnetometer(VSM). The results showed that the Rhodamine B degradation rate of MnxZn1-xFe2O4/α-Bi2O3, which prepared with mass ratio of 20% and the reaction time of 3h aswell as the calcination temperature of 500℃, reached 99.6% under simulated sunlight for 4h. And it was higher than that of pure α-Bi2O3 under the same conditions.The β-Bi2O3 was prepared by chemical precipitation, and its Rh B(10mg/L) degradation rate reached 83.6% under the simulated sunlight for 2.5h. Composites magnetic photocatalyst MnxZn1-xFe2O4/β-Bi2O3 were synthesized by impregnation sintering method using manganese zinc ferrite as magnetic substrate. We discussed the effects of composite mass ratio, reaction time and calcination temperature on the photocatalytic activity. The as-prepared MnxZn1-xFe2O4/β-Bi2O3 composites were characterized by XRD, FTIR, DRS, SEM and VSM. The results showed that the Rhodamine B degradation rate of MnxZn1-xFe2O4/β-Bi2O3, which prepared with mass ratio of 15% and the reaction time of 2h as well as the calcination temperature of 380℃, reached 99.1% under simulated sunlight for 2.5 h. It was higher than tha of pure β-Bi2O3 under the same conditions.The MnxZn1-xFe2O4/α-Bi2O3 and MnxZn1-xFe2O4/β-Bi2O3 were recovered, and the recovery ratios were 84.1% and 89.3%, respectively. After five recycling, the degradation rate of Rh B for the former was still up to 86.2% irradiating 4h, and the later was up to 82.7% irradiating 2.5h. It revealed that composites magnetic photocatalyst were with high stability and reusability.Under a radiation source of xenon lamp, the landfill leachate was degradated with MnxZn1-xFe2O4/β-Bi2O3 as photocatalyst. Effects of leachate’s initial concentration, illumination time and leachate’s p H on degradation rate were researched. The results showed that the removal efficiency of COD in landfill leachate reached 63.0% under the conditions of 250mg/L of the initial leachate’s concentration, 250 min of the illumination time, 5 of the p H.