Oxygen defect regulation and photocatalytic-peroxymonosulfate activation of Co(II)/BiPO4−x composites synergistically promoting medical waste degradation

The low regeneration rate of Co(II) is a major obstacle to the efficient activation of peroxymonosulfate (PMS) by Co in advanced oxidation technology. Herein, a Co(II)/oxygen-defect monoclinic monazite BiPO4 (Co(II)/BiPO4−x) photocatalyst was prepared. The degradation efficiency of tetracycline hydrochloride (TCH) and polyethylene terephthalate (PET) in the 25%Co(II)/BiPO4−x/PMS/UV system is up to 99.0% (within 30 min) and 40.4%, which was 1.9 and 6.5 times that of the BiPO4/PMS/UV system, respectively. The loading of Co(II) increases the oxygen defect concentration of BiPO4−x, therefore more photogenerated electrons can involve in the Co cycling to promote PMS activation. Meanwhile, simultaneous illumination X-ray photoelectron spectroscopy (SI-XPS) indicates that the electrons are transferred from BiPO4−x to Co, accelerating the regeneration rate of Co(II). DFT calculation reveals that 25%Co(II)/BiPO4−x exhibits much lower reaction energy barrier. This novel work demonstrates a new perspective to modulate the free radical and nonradical dual-pathway for treating refractory contaminants through defect engineering.