Decoupling intrinsic crystalline integrity from extrinsic modifications in BiFeO3: Single-crystal-derived particles outperform high-surface-area sol-gel nanoparticles in piezo-photocatalytic ofloxacin degradation

The study compares single-crystal-derived BiFeO 3 (BFO) particles (BFOsc, from flux-TSSG bulk → cleavage-controlled ball milling) with nanoparticles BFO (BFOsg, from tartaric-acid-assisted sol-gel) under fixed nominal composition, thereby eliminating extrinsic complications from doping and heterointerfaces. It demonstrates that BFOsc delivers a mass-normalized pseudo-first-order rate of k  = 0.758 min −1  g −1 for ofloxacin under simultaneous visible light and ultrasound, which is 27% higher than that of BFOsg (0.597 min −1  g −1 ), despite a ~ 9-fold lower specific surface area (0.69 vs 6.30 m 2 /g), and affords 61.77% removal within 120 min. Rietveld XRD, PFM/KPFM, PL/TRPL, photoelectrochemistry and spin-trapping EPR collectively show that the long-range ferroelectric domains, low grain-boundary density and dilute isolated oxygen vacancies in BFOsc sustain a more coherent bulk piezoelectric built-in field, suppress non-radiative recombination and enhance ·O 2 − and ·OH generation. DFT further predicts stronger O 2 adsorption (−0.68 eV vs −0.54 eV) and larger model charge transfer (0.78|e| vs 0.67 |e| under charged injection). The work attributes the performance ceiling of BFO piezo-photocatalysis primarily to crystalline integrity and domain order rather than geometric surface area, offering an intrinsic structure-property guideline for multiferroic perovskite water remediation.