The Photocatalytic And Magnetic Properties Of BiFeO₃through Three Kinds Of Methods

BiFeO₃is one of rare single phase multiferroic materials, which show simultaneouslyferroelectric ordering and ferromagnetic ordering at room temperature. And recently, hugeamount of investigations have been performed on the narrow band gapsemiconductor-BiFeO₃because of their potential applications in solar energy conversionand easy recycle.Three different synthesis routes （sol-gel, molten salt and hydrothermal method） havebeen taken to successfully prepare the BiFeO₃particles with the different morphologiesand average size in50nm,500nm, and15m, respectively. The crystal structure isrecognized to be a distorted rhombohedral one with the space group R3c. With thedecrease in particle size, obvious decrease in peak intensity and redshift in peak positionare observed for the Raman active bands. The narrow band gap of².1eV is determinedfrom the UV-Vis absorption spectra, indicating the semiconducting nature of the BiFeO₃particles. BFO-SG nanopowders are annealed in air at600℃for1h and5h to induce thegrowth in particle size, and BFO-SG-A1（200nm） and BFO-SG-A2（400nm） are obtained.So, all the samples exhibit efficient photodegradation of the organic due to their narrowband gap. For photodegradation of dyes under visible irradiation in the presence ofBiFeO₃particles, the particle size plays a major role in the photolysis, and thephotocatalytic efficiency increases quickly with the decrease in size. By reducing the sizeto several nanometers the BiFeO₃particles are expected as efficient photocatalyst.The magnetic properties of BFO-SG nanopowders and BFO-HP should be investigateddue to their pure phase. The precursory sol-gel nanoparticles were pressed into ahexahedral anvil high-pressure annealing apparatus with800℃for2h at a pressure of5Gpa, which were named as BFO-HP. Whereas the particle size of BFO-HP is farly largerthan62nm, BFO-HP exhibits enhanced ferromagnetism than BFO-SG from the hysteresisloops at various temperatures, and there is a minimal value of coercivity at120K.Specifically, magnetization as a function of temperature （M-T） measurements, we notethat an apparent sharp cusp observed at120K in the ZFC and FC curves, which is thetemperature of spin glass transition.