Enhanced performance of carbon dots and Mn3O4 composite by phosphate in peroxymonosulfate activation

A composite of nitrogen-doped carbon dots and Mn 3 O 4 (CMO) was synthesized using a facile hydrothermal and precipitation method for peroxymonosulfate (PMS) activation. Surprisingly, high concentrations of H 2 PO 4 − (DP, above 20 mM) significantly enhanced the degradation efficiency of bisphenol A (BPA). The improvement was not attributed to the accelerated cleavage of PMS or pH variation. Instead, DP could directly form a complex with CMO, generating Mn(III)-DP with a high potential (0.64 V vs. SCE, 100 mM of DP). Simultaneously, it decreased the oxidative potential of BPA from 0.69 to 0.38 V vs. SCE. The degradation pathways of BPA differed in the CMO/PMS and CMO/DP systems. These findings inspire further exploration of carbon dots-based catalysts in persulfate activation and unveil the origin of enhanced performances by phosphate.