BiFe_0.5Cr_0.5O₃ nanocatalysts for sustainable solar-light-driven purification of pharmaceutical wastewater

Pharmaceutical wastewater contamination, particularly from antibiotics, poses severe environmental and health risks due to antibiotic-resistant bacteria and the inefficacy of conventional treatments. In this study, BiFe_0.5Cr_0.5O₃ (BFCO) nanoparticles were synthesized <i>via</i> the sol-gel method and investigated as a visible-light-driven photocatalyst for ciprofloxacin (CIP) and levofloxacin (LFX) degradation under solar irradiation. The structural analysis confirmed a single-phase perovskite structure with Cr³⁺ incorporation, enhancing charge separation and visible-light absorption. The presence of oxygen vacancies, identified through XPS and Raman spectroscopy, played a crucial role in charge transfer and reactive oxygen species (ROS) generation. Comprehensive electrochemical and photoelectrochemical analyses, including CV, LSV, and EIS, confirmed enhanced charge transport and reduced interfacial resistance under illumination. BFCO, with a bandgap of 1.87 eV, exhibited efficient solar energy utilization, achieving 70.35% CIP and 94% LFX degradation within 240 minutes, following pseudo-first-order kinetics. The activation energy decreased from 33.61 ± 5.88 to 19.69 ± 3.94 kJ mol^-1 K^-1, confirming enhanced catalytic efficiency. An apparent quantum yield (AQY) of 34.9% for LFX further underscored its superior activity. Scavenger studies identified electron (e^-) and superoxide (˙O₂ ^-) radicals as key ROS driving antibiotic degradation, while oxygen vacancies improved charge separation and ROS formation. Reusability tests confirmed BFCO's stability across multiple cycles, maintaining its structural, morphological, and optical integrity. The degradation mechanism involves solar-induced electron-hole pair generation, charge transfer to oxygen vacancies, and subsequent redox reactions that break down antibiotics into non-toxic byproducts. The synergistic effects of Cr substitution, oxygen vacancies, and mixed-valence states significantly enhanced photocatalytic efficiency, demonstrating BFCO's potential for large-scale environmental remediation.