Effect of TiO₂ Additives on the Stabilization of h-YbFeO₃ and Promotion of Photo-Fenton Activity of o-YbFeO₃/ h-YbFeO₃/ r-TiO₂ Nanocomposites

Nanostructured hexagonal rare-earth orthoferrites (h-RfeO₃, R = Sc, Y, Tb-Lu) are well known as a highly effective base for visible-light-driven heterojunction photocatalysts. However, their application is limited by metastability, leading to difficulties in synthesis due to the irreversible transformation to a stable orthorhombic structure. In this work, we report on a simple route to the stabilization of h-YbFeO₃ nanocrystals by the synthesis of multiphase nanocomposites with titania additives. The new I-type heterojunction nanocomposites of o-YbFeO₃/h-YbFeO₃/r-TiO₂ were obtained by the glycine-nitrate solution combustion method with subsequent heat treatment of the products. An increase in the mole fraction of the h-YbFeO₃ phase in nanocomposites was found with the titanium addition, indicating its stabilizing effect via limiting mass transfer over heat treatment. The complex physicochemical analysis shows multiple contacts of individual nanocrystals of o-YbFeO₃ (44.4-50.6 nm), h-YbFeO₃ (7.5-17.6 nm), and rutile r-TiO₂ (~5 nm), confirming the presence of the heterojunction structure in the obtained nanocomposite. The photocatalytic activity of h-YbFeO₃/o-YbFeO₃/r-TiO₂ nanocomposites was evaluated by the photo-Fenton degradation of the methyl violet under visible light (λ ≥ 400 nm). It was demonstrated that the addition of 5 mol.% of TiO₂ stabilizes h-YbFeO₃, which allowed us to achieve a 41.5 mol% fraction, followed by a three-time increase in the photodecomposition rate constant up to 0.0160 min^-1.