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 (O_V) 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.