Double Z-scheme Co3O4/Bi4O7/Bi2O3 composite activated peroxymonosulfate to efficiently degrade tetracycline under visible light.

Co3O4/Bi4O7/Bi2O3 (CBB) composites were prepared, in which Co3O4 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 Co3O4 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 (·O2-), and singlet oxygen (1O2) 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.