Visible photocatalytic degradation of methylene blue on magnetic SrFe12O19

Methylene blue (MB) is representative of a class of dyestuffs that are resistant to biodegradation. In this study, MB was degraded in an aqueous suspension of SrFe12O19 powder under visible illumination. SrFe12O19 is a type of traditional magnet and its semiconductor characteristics were elucidated based on the ultraviolet-visible spectrum. The direct and indirect bandgap energies were determined as 1.70 eV and 0.83 eV, respectively. This magnetic compound exhibited excellent photocatalytic activity during the degradation of MB. The color of the MB solution gradually changed from deep blue to pale white as the duration of the photodegradation reaction increased, and the absorption intensity decreased rapidly to zero. However, five absorption bands did not exhibit any blue shifts during the reaction period, thereby suggesting that the degradation of MB was completed in a one-step manner, which makes SrFe12O19 a unique magnetic catalyst that differs from TiO2 and other conventional catalysts.