Insight into (Electro)magnetic Interactions within Facet-Engineered BaFe₁₂O₁₉/TiO₂ Magnetic Photocatalysts

A series of facet-engineered TiO₂/BaFe₁₂O₁₉ composites were synthesized through hydrothermal growth of both phases and subsequent deposition of the different, faceted TiO₂ nanoparticles onto BaFe₁₂O₁₉ microplates. The well-defined geometry of the composite and uniaxial magnetic anisotropy of the ferrite allowed alternate interfaces between both phases and fixed the orientation between the TiO₂ crystal structure and the remanent magnetic field within BaFe₁₂O₁₉. The morphology and crystal structure of the composites were confirmed by a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses together with the detailed study of BaFe₁₂O₁₉ electronic and magnetic properties. The photocatalytic activity and magnetic field effect were studied in the reaction of phenol degradation for TiO₂/BaFe₁₂O₁₉ and composites of BaFe₁₂O₁₉ covered with a SiO₂ protective layer and TiO₂. The observed differences in phenol degradation are associated with electron transfer and the contribution of the magnetic field. All obtained magnetic composite materials can be easily separated in an external magnetic field, with efficiencies exceeding 95%, and recycled without significant loss of photocatalytic activity. The highest activity was observed for the composite of BaFe₁₂O₁₉ with TiO₂ exposing {1 0 1} facets. However, to prevent electron transfer within the composite structure, this photocatalyst material was additionally coated with a protective SiO₂ layer. Furthermore, TiO₂ exposing {1 0 0} facets exhibited significant synergy with the BaFe₁₂O₁₉ magnetic field, leading to 2 times higher photocatalytic activity when ferrite was magnetized before the process. The photoluminescence emission study suggests that for this particular combination, the built-in magnetic field of the ferrite suppressed the recombination of the photogenerated charge carriers. Ultimately, possible effects of complex electro/magnetic interactions within the magnetic photocatalyst are shown and discussed for the first time, including the anisotropic properties of both phases.