Insights into Co3O4 nano-rod/peroxymonosulfate catalytic oxidation system for chemical cleaning ultrafiltration membrane: Performance, mechanisms, and effects on the membrane stability

In this study, Co3O4 nano-rod (Co3O4-NR) with (1 1 0) crystal plane predominant exposure is prepared by a hydrothermal method, and peroxymonosulfate (PMS) was activated via them for ultrafiltration membrane (PVDF and PES membrane) cleaning. Co3O4-NR with (1 1 0) planes exposed obtained abundant oxygen vacancies (OV) and low oxidation state Co (Co2+) and therefore showed excellent ability for PMS activation. The Co3O4-NR/PMS system did not require long-term immersion in a high-concentration chemical reagent solution compared with conventional ultrafiltration membrane chemical cleaning. The cleaning process, which was conducted for only 15 min in Co3O4-NR (1.6 g/L)/PMS (2 mM) solution, was sufficient to restore almost all the permeate flux and could remove essentially all the irreversible foulants. The excellent membrane cleaning performance of the Co3O4-NR/PMS system was attributed to the generation of 1O2 and O2•−, which degraded the large-molecule, hydrophobic natural organic matter (NOM) into small-molecule, hydrophilic organic matter. Cyclic experiments showed that Co3O4-NR had excellent reusability, which offered significant cost savings. The consecutive chemical cleaning experiments indicated that the Co3O4-NR/PMS maintained the membrane stability better than the traditional chlorine cleaning method. The system effectively averts membrane damage and polymer structure changes caused by long-term exposure to oxidants. In conclusion, the Co3O4-NR/PMS system has significant advantages in membrane cleaning and broad application prospects.