Synergistic experimental–dft investigation into photocatalytic efficiency of M-Type XFe₁₂O₁₉ (X = Ba, Sr) hexaferrites

The XFe₁₂O₁₉ (X = Ba, Sr) M-type hexaferrites were successfully synthesized using the sol-gel auto-combustion process to examine their structural, morphological, electronic, photocatalytic, and optical properties, supported by density functional theory (DFT) calculations. This work combines comprehensive experiments with first-principles calculations to clearly and comparatively explain how substituting Sr²⁺ and Ba²⁺ into the M-type XFe₁₂O₁₉ (X = Ba, Sr) structure influences the lattice, alters the electronic and optical characteristics, and impacts the material's photocatalytic behavior. The XRD analysis confirms single-phase hexagonal magnetoplumbite structures (P63/mmc) without secondary phases, with experimentally measured crystalline sizes of 44.54 nm for BaFe₁₂O₁₉ and 33.72 nm for SrFe₁₂O₁₉. The structural properties of both hexaferrites show good agreement between theoretical and experimental results. SEM images reveal plate-like morphologies with agglomerated grains, while EDX analysis confirms a stoichiometric composition. The simulated electronic band structures show direct transitions in these compositions, and calculated values match experimental results. Optical studies identify direct energy band gaps of 2.676 eV for BaFe₁₂O₁₉ and 1.602 eV for SrFe₁₂O₁₉, as determined by UV-Vis spectroscopy. BaFe₁₂O₁₉ and SrFe₁₂O₁₉ hexaferrites degraded Methylene Blue by 81% and 97%, respectively, demonstrating that the first-order kinetic model fits well with the excellent photocatalytic oxidation. Theoretical findings align with experimental results from FTIR, UV–Vis, PL, and photocatalytic tests, confirming that these compositions are promising for photocatalytic applications.