Enhanced piezo-photocatalysis degradation of ofloxacin using Gd/Ni co-doped BiFeO3 magnetic nanoparticles

To address rapid carrier recombination and low magnetic separation efficiency in piezocatalysis, Gd/Ni co-doped BiFeO3 nanoparticles were synthesized via a sol–gel method. Rietveld refinement confirmed lattice distortion and secondary phase formation at high doping levels. Gd/Ni doping induces a phase transition in BFO from rhombohedral to orthorhombic, with the Pnma proportion reaching 84.15% at x = 0.09. Gd/Ni co-doping induced 12.7% oxygen vacancy concentration, suppressing electron–hole recombination, while enhanced Dzyaloshinskii–Moriya interaction increased saturation magnetization by 17.85-fold (magnetic recovery > 95%). The optimized sample (x = 0.09) achieved 80.94% ofloxacin degradation in 120 min (twice that of pristine BiFeO3), retaining 71.53% efficiency after 4 cycles. Radical trapping and EPR identified ˙OH and ˙O2− as dominant species, revealing a ferroelectric–piezoelectric synergistic mechanism. This work provides a strategy for designing magnetically recoverable piezocatalysts for complex wastewater treatment.