Enhanced photocatalytic activity in Mn-doped multiferroic BiFeO₃

Enhancing the performance of multiferroic BiFeO3 in different applications via Mn doping has a long history. However, the underlying mechanisms are still not understood. Here we study the contribution of multiple factors amplifying the photocatalytic activity of Mn-doped BiFeO3 towards rhodamine B degradation. The structural, optical, functional, and photocatalytic properties of BiFeO3 were found to be maximized upon 5 mol% Mn doping, also yielding enhanced photocatalytic activity. This level of doping optimized the lattice structure while maintaining phase purity, shifting the absorption edge to the near infra-red region, narrowing the bandgap energy, increasing the lifetime of photogenerated charges and surface photovoltages by a factor of two, and enhancing the spontaneous polarization to efficiently drive the photogenerated charges. We investigated the relationship between the enhanced PC activity and the structural, optical, and functional properties. The higher photocatalytic activity of Mn-doped BiFeO3 was attributed to the synergistic effect of (1) enhanced band bending on the surface as a result of internal screening of charges and (2) formation of inter-band energy levels while shifting the energy bands close to each other. Our results provide a unique opportunity for designing BiFeO3-based photocatalysts for applications in energy conversion and environmental remediation.