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 ZnFe2O4/Bi2O2CO3/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 ZnFe2O4 and 2.6–2.9 times higher than those of Bi2O2CO3/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−, ·O2−, and Fe(II)/Fe(III) pathway, and active species including ·O2−, 1O2, SO4·−, ·OH, and h+ participated in the catalytic processes. Unexpectedly, 1O2, and ·OH were determined to be the primary species during the degradation processes instead of SO4·−. 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.