Influence of calcination temperature on the properties and photocatalytic efficiencies of BiFe0.9Cu0.1O3 nanoparticles

BiFe₀.₉Cu₀.₁O₃ nanoparticles were synthesized via a simple solution combustion method, and the effect of calcination temperature (500–800 °C) on their properties and photocatalytic performance was systematically investigated. The nanoparticles were characterized using XRD, FTIR, FE-SEM, BET surface area analysis, XPS, UV-Vis diffuse reflectance, photoluminescence, and VSM. XRD analysis confirmed a primary rhombohedral BiFeO₃ phase alongside a secondary orthorhombic Bi₂Fe₄O₉ phase. The results revealed a complex interplay between calcination temperature and material properties: the crystallite size increased with temperature up to 700 °C, then decreased slightly. At the same time, the specific surface area was maximized at 500 °C. The optical band gap reached a minimum of 3.30 eV at 500 °C, then widened at higher temperatures. VSM measurements revealed ferromagnetic behavior at room temperature, with the saturation magnetization peaking at 600 °C due to the suppression of the spin spiral structure and the presence of oxygen vacancies. The photocatalytic activity for methylene blue (MB) degradation under visible light was maximized at 500 °C, achieving 72.75% degradation efficiency after 160 min. This optimal performance is attributed to the synergistic combination of the highest specific surface area, a favorable band gap, and a high concentration of defect sites that suppress charge carrier recombination. The optimal sample demonstrated good stability and reusability over five cycles. Scavenger tests indicated that the hydroxyl radicals (HO•) were the primary reactive species. The results confirm that solution combustion is an effective route for producing Cu-doped BFO nanoparticles, with the calcination temperature being a critical parameter for optimizing their photocatalytic performance.