Tuning Physical and Photochemical Properties of Perovskite Oxides via B-Site Co-Substitution with Fe and Nb

Perovskite-structured oxides exhibit excellent performance across a range of applications; however, their widespread adoption is often constrained by wide bandgap energies and high charge recombination rates. To address these limitations, this study introduces iron (Fe) and niobium (Nb) ions into the B-site of the ABO3 lattice to construct the half-metallic double perovskites of the formula A2FeNbO6 (A = Ca, Sr, or Ba). The materials were synthesized using a facile one-step molten salt method, and their physical, photochemical, and optical properties were systematically investigated. UV-vis DRS, XPS-VB, and UPS analyses suggest that the as-prepared A2FeNbO6 compounds possess narrower band gaps compared to their single perovskite counterparts, ATiO3 (A = Ca, Sr, or Ba). Remarkably, the double perovskite materials A2FeNbO6 demonstrated exceptional photocatalytic activity for the degradation of TC under visible light illumination (λ = 420 nm). Among the synthesized compounds, Ba2FeNbO6 exhibited the highest performance, achieving a TC degradation rate of 92.0% within 40 min─significantly surpassing the rates observed for Ca2FeNbO6 and Sr2FeNbO6. Furthermore, the dominant reactive species and plausible reaction pathways involved in the TC degradation reaction over Ba2FeNbO6 were elucidated through radical quenching experiments, EPR spectroscopy, and LC-MS analysis. This work highlights the potential of A2FeNbO6 double perovskites as a novel class of efficient and stable photocatalysts for the degradation of organic pollutants.