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

Abstract

• Efficient removal of TCs was achieved by the catalyst/sunlight/PMS systems. • The double Z-scheme heterojunction structure was proved by multiple characterizations and DFT calculation. • 1 O 2 was the dominant species for TCs degradation rather than SO 4 ·− or ·OH. • Photocatalytic and non-photocatalytic processes were distinguished. • Radical and non-radical pathways were also elucidated. A series of environmental-friendly and cost-effective 0D/2D/2D ZnFe 2 O 4 /Bi 2 O 2 CO 3 /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 ZnFe 2 O 4 and 2.6–2.9 times higher than those of Bi 2 O 2 CO 3 /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 2 − , and Fe(II)/Fe(III) pathway, and active species including · O 2 − , 1 O 2 , SO 4 · − , · OH, and h + participated in the catalytic processes. Unexpectedly, 1 O 2 , and · OH were determined to be the primary species during the degradation processes instead of SO 4 · − . 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.