Effect of Zn Substitution on the Structural, Optical Properties and Photocatalytic Activity of BiFeO3 Nanopowders

The multiferroic Zn-doped BiFeO3 materials with nominal formula BiFe1-xZnxO3 (0 <= x <= 0.08) are successfully synthesized using hydrothermal synthesis allowing to obtain powders with an average grain size of 8 nm. X-ray diffraction and Raman spectroscopy analysis prove that nanopowders are pure and homogeneous and show an increase of the unit cell volume when the amount of Zn increases attesting of the substitution of Fe site. Using temperature-dependent Raman spectroscopy, it is also found that the Neel antiferromagnetic critical temperature is weakly, if any, affected. In contrast, using UV-vis reflectance measurements, clear changes are observed in the features of the optical absorption with modifications of the crystal-field when increasing the Zn amount. The photocatalytic activity of the pure and the most doped samples is evaluated by the degradation of the methylene blue dye under visible light irradiation. The photocatalytic activity of the Zn-doped samples is found to be higher than that of BiFeO3. After 3 h of sunlight irradiation, the degradation efficiency increases from 61% to 83% for BiFeO3 and BiFe0.92Zn0.08O3, respectively. The crystal-field modification after Zn substitution is considered as the principal cause of the obvious enhanced photocatalytic activity.