High-efficiency photocatalysis in Ca-Cr doped BiFeO₃ nanoparticles via bandgap tuning

The growing environmental threat posed by synthetic dye pollution has accelerated the search for effective semiconductor-based photocatalysts for scalable and sustainable wastewater treatment. This study reports the greatly enhanced visible-light photocatalytic activity of Bi_0.97Ca_0.03Fe_1-x Cr _x O₃ (x = 0.00, 0.01, 0.03, 0.05) nanoparticles synthesized via a modified sol-gel method. Structural analysis confirmed the formation of a distorted rhombohedral perovskite phase, with doping leading to reduced lattice parameters and crystallite size. The bandgap narrowed from 2.13 eV in pure BiFeO₃ (BFO) to 1.80 eV in the co-doped sample. Elemental analysis confirmed improved stoichiometric balance and reduced bismuth volatilization in the co-doped samples. Under xenon lamp illumination, methylene blue degradation reached 93% for Bi_0.97Ca_0.03Fe_0.95Cr_0.05O₃ at neutral pH, approaching the upper limits of reported efficiencies for BFO-based systems. The reaction followed pseudo-first-order kinetics, with the rate constant rising from 0.01358 to 0.03038 min^-1. Moreover, the formation of an antiferromagnetic-ferromagnetic core-shell structure in the co-doped samples is proposed to notably improve dye degradation by promoting surface charge separation and suppressing recombination. This work highlights the potential of Ca and Cr co-substituted BFO nanoparticles as high-performance, visible-light-driven photocatalysts for dye remediation under environmentally relevant pH conditions.