The Preparation And Photocatalytic Performances Of BiFeO₃ Based Photocatalysts

BiFeO₃ is one of the few multi-ferrous materials with ferroelectric and ferromagnetic at room temperature and has narrow band gap energy?2.1-2.8 e V?,which has been attracted more and more attention in the field of photocatalysis.However,the photocatalytic efficiency of BiFeO₃ is low due to the easily recombination of photogenerated electrons and holes.Therefore,this paper focuses on how to improve the photocatalytic efficiency of BiFeO₃,for example:1)combined with advanced oxidation technology to degrade organic pollutants;2)ion doping;3)prepared a new composite material BiFeO₃/g-C₃N₄ to reduce the recombination rate of photogenerated electrons and holes.1. The pure phase BiFeO₃ microspheres were successfully synthesized by hydrothermalmethod.The materials were characterized by X-ray diffraction,scanning electron microscopy and solid UV-vis diffuse reflectance spectroscopy.The phase,structure and optical properties were discussed,respectively.BiFeO₃ exhibits good photocatalytic activity during the degradation of Rhodamine B under the visible light.Fe³⁺in BiFeO₃ can activate potassium persulfate?PMS?to produce strong oxidative free radicals SO₄^·-,and the photocatalytic efficiency is significantly higher than that of pure phase BiFeO₃ due to the synergistic effect of visible light photocatalysis and SO₄^·-based BiFeO₃/PMS/Vis system.In addition,we studied the effect of reaction temperature,PMS concentration and other experiment conditions on the photocatalytic activity.It was found that the photocatalytic activity was enhanced with the increase of temperature and PMS concentration.In order to confirm the contribution of the oxidizing radical species,a series of quenching experiments were carried out,the synergistic mechanism between photocatalytic and oxidative degradation of organic pollutants was then proposed.2.Co doped BiFeO₃ microparticles were prepared by hydrothermal method.The photocatalytic materials were characterized by X-ray diffraction,scanning electron microscopy,hysteresis loop,solid UV-vis diffuse reflectance spectroscopy.The analysis of XRD and EDS shows that Co has been doped into the lattice of BiFeO₃,and the structure does not change due to the low doping amount.UV-vis analysis showed that the absorption range of the doped samples was extended to 400 nm⁷00 nm.Furthermore the ability of Co-BiFeO₃ activated PMS degraded Rh B enhanced significantly,because compared with Fe,Co is more favorable to activate PMS and produce SO₄^·-and SO₅^·-.At the same time,Co-BiFeO₃ can effectively reduce the recombination rate of photogenerated electrons and holes and improve the photocatalytic activity.The magnetic propertie of BiFeO₃ particles shows that the doping of Co can increase the magnetic properties of BiFeO₃.Finally,the stability of Co-BiFeO₃ was investigated.3.The BiFeO₃/g-C₃N₄ composites with different mass ratios?3%,6%,12%?were prepared by the combination of hydrothermal and high-temperature calcination methods.The samples were characterized by X-ray diffraction,transmission electron microscopy,solid UV-vis diffuse reflectance spectroscopy,and so on.XRD and TEM analysis showed that heterojunction was formed between the two materials.UV-vis analysis showed that the absorption spectrum of the composite was higher than that of the pure phase of BiFeO₃.Under the irradiation of visible light,the BiFeO₃/g-C₃N₄ composite showed stronger photocatalytic activity and stability than BiFeO₃.At the same time,in order to further improve the photocatalytic activity,H₂O₂ has been introduced into the system to form heterogeneous Fenton system,resulting in the producton of strong oxidizing·OH which will enable a more efficient degradation of organic pollutants.In addition,we investigated the effect of solution p H on the photocatalytic activity in heterogeneous Fenton reaction,and investigated the stability of the composite,The photocatalytic reaction mechanism was proposed by quenching experiment.