A singlet oxygen dominated process through photocatalysis of CuS-modified MIL-101(Fe) assisted by peroxymonosulfate for efficient water disinfection

Singlet oxygen (1O2) is an effective reactive oxygen species in disinfection due to its long lifetime and sensitivity to bacteria. This study tried to develop a 1O2 dominated process for bacterial inactivation by visible light (vis) photocatalysis assisted by PMS. A novel CuS-modified MIL-101(Fe) (CSMF) photocatalyst was synthesized for the first time. Compared with MIL-101(Fe), CuS-modified MIL-101(Fe) enhanced the photocatalytic performance by increasing absorption of visible light, narrowing down the bandgap and promoting photo carrier separation efficiency. 7.5-log Gram-negative Escherichia coli (E. coli) could be inactivated by Vis/CSMF/PMS system within 40 min, showing much better performance of 3.5-log E. coli inactivated by Vis/PMS system. The Vis/CSMF/PMS system is applicable in a broad pH range from 3.0 to 9.0, remaining quite steady disinfection efficiency after regenerations of the catalyst. Quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated 1O2 was the dominated ROS rather than OH• and SO4•−. Three pathways, including photo-generated electrons (e−) and O2 dependent pathway, photo-generated holes (h+) dependent pathway and CSMF enhanced PMS dissociation pathway, were evidenced to responsible for 1O2 formation by aeration experiments and specific 1O2 fluorescence probe. 1O2 in water attacked the bacterial cell membranes first, got inside the cell and up-regulated the level of intracellular ROS, which further led to cell membrane damage and DNA degradation so as to irreversible cell death. In addition, the developed Vis/CSMF/PMS system could also efficiently inactivate gram-positive bacteria Staphylococcus aureus and fecal coliform bacteria in practical wastewater, suggesting its wide applicability as a promising alternative to conventional disinfection process.