New insights into the photocatalytic and magnetic activity of Co-doped BiFeO3 nanoparticles via competing structures

Cobalt was chosen as the doping element for BiFeO3 (BFO), and pure BFO and a series of BiFe1-x Co (x) O-3 (x = 0.03, 0.05, 0.07, 0.09) nanoparticles, correspondingly labeled as nBFCO (n = 3, 5, 7, 9), were successfully prepared and investigated based on the sol-gel method in this paper. The synthesized nanoparticles were characterized by x-ray diffraction, field emission scanning electron microscopy, Brunauer-Emmett-Teller surface area, x-ray photoelectron spectroscopy and ultraviolet-visible light absorption. With the increase in the doping level of cobalt in BFO, a competing structure wandering between rhombohedral and orthorhombic structures was observed in the experiment. For instance, the microstructure characterization clearly indicates coexistence of the rhombohedral and orthorhombic structures in 7BFCO. Meanwhile, the bandgap of BFO was significantly reduced from 2.04 eV to 1.78 eV. The photocatalytic degradation of Rhodamine B of samples in an aqueous solution was investigated under different wavelengths of light. We found that 7BFCO was the optimal proportion for acquiring the photocatalytic and magnetic activity in this work, e.g. the photocatalytic efficiency can reach 98.2%. The underlying physics based on the lattice structure, size effects and energy gap is also discussed.