Self-supporting Co-MOF@chitosan membrane with in-situ reconstructed amorphous CoO(OH) nanolayer for peroxymonosulfate activation: High activity and ultra-low cobalt leaching

Highly recoverable and stable heterogeneous catalysts are critical for peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). This work addresses the difficult separation and metal leaching issues of conventional powdered metal–organic frameworks (MOFs) by constructing a self-supporting Co-MOF@chitosan (Co-MOF@CS) composite membrane. Through in situ reconstruction during PMS activation, the low-crystallinity Co-MOF precursor transforms into an amorphous CoO(OH) nanolayer on the membrane surface. The reconstructed active phase anchors firmly on the porous CS substrate, thereby enabling efficient PMS activation by facilitating rapid electron transfer and providing abundant surface active sites. The Co-MOF@CS membrane exhibited excellent catalytic performance, degrading > 96% of the methylene blue (MB) and ∼70% of sulfadiazine (SDZ) after five consecutive cycles. Notably, the degradation efficiency increased slightly after multiple cycles due to continuous exposure of CoO(OH) active sites. The Co species effectively anchored onto the CS matrix through strong coordination, contributing to extremely low cobalt leaching (0.05 to 0.06 mg/L) and outstanding long-term reusability. Radical quenching and electron paramagnetic resonance (EPR) analyses revealed superoxide radicals (O 2 •− ) and singlet oxygen ( 1 O 2 ) as the dominant reactive species. This work elucidates the dynamic self-activation of low-crystallinity Co-MOFs in AOPs while providing a green and sustainable solution to secondary pollution caused by powdered nanocatalysts during water treatment.