0D/2D/2D ZnFe2O4/Bi2O2CO3/BiOBr double Z-scheme heterojunctions for the removal of tetracycline antibiotics by permonosulfate activation: Photocatalytic and non-photocatalytic mechanisms, radical and non-radical pathways

A series of environmental-friendly and cost-effective 0D/2D/2D ZnFeO/BiOCO/BiOBr double Z-scheme heterojunctions (abbreviated as xZnCB) were fabricated by a hydrothermal method using an electrostatic self-assembly strategy. The removal efficiencies toward tetracycline (TC), oxytetracycline (OTC), and doxycycline (DOX) were 93%, 90.1%, and 89.4% in 10ZnCB/sunlight/permonosulfate (PMS) systems within 20 min, and the degradation rate constants of 10ZnCB were 5.7–8.2 times higher than those of ZnFeO and 2.6–2.9 times higher than those of BiOCO/BiOBr (CB) under the same conditions. XPS valence band spectra, quenching experiments, EPR measurements, and density functional theory (DFT) calculations demonstrated the existence of the double Z-scheme heterojunctions. The coexistence of radical and non-radical pathways caused by photocatalytic and non-photocatalytic degradation mechanisms was also elucidated. PMS was effectively activated by a photoinduced e, ·O, and Fe(II)/Fe(III) pathway, and active species including ·O, O, SO, ·OH, and h participated in the catalytic processes. Unexpectedly, O, and ·OH were determined to be the primary species during the degradation processes instead of SO. Recycling experiments, metal leaching measurements, and TC degradation experiments in the secondary effluent demonstrated the excellent catalytic and structural properties of these xZnCB hybrid materials.