Double Z-scheme Co 3 O 4 /Bi 4 O 7 /Bi 2 O 3 composite activated peroxymonosulfate to efficiently degrade tetracycline under visible light.

Co 3 O 4 /Bi 4 O 7 /Bi 2 O 3 (CBB) composites were prepared, in which Co 3 O 4 was synthesized from Co-MOF as precursor. The peroxymonosulfate (PMS) activated by CBB catalyst under visible light was used to degrade tetracycline (TC). Owing to the synergistic effect of photocatalysis and PMS activation, 98.4% of TC was removed within 60 min. The optimal loading of Co 3 O 4 was determined, and the influence of PMS dosage, initial pH, and disturbing anions on the degradation effect were investigated. The "CBB + Vis + PMS" system showed good reusability, and the degradation was only reduced by 1.7% after 5 cycles. This system also had a good degradation of other five pollutants. The quenching experiment showed that holes (h + ), superoxide radicals (·O 2 - ), and singlet oxygen ( 1 O 2 ) were the main active species. The degradation products of TC were determined by liquid chromatography-mass spectrometry, and the degradation pathway was proposed. Finally, a double Z-scheme degradation mechanism was proposed in the "CBB + Vis + PMS" system. The peroxymonosulfate activated by CBB under visible light to degrade organic pollutants has widespread application prospects in environmental remediation.