Activation of permonosulfate by Co-Fe3O4 composite catalyst for amino acid removal: Performance and mechanism of Co-Fe3O4 nanoparticles

Dissolved organic nitrogen (DON) derived from amino acids has been a major concern in drinking water treatment because of its potential to form nitrogenous disinfection byproducts (N-DBPs). The degradation performance of amino acids by peroxymonosulfate (PMS) activated by Co-Fe3O4 composite catalyst in heterogeneous catalytic process was elucidated in our study. The sole and combined catalytic performance of PMS and Co-Fe3O4 were evaluated for two amino acid species (i.e., histidine and phenylalanine) separately and validated under varying levels of PMS dose, Co-Fe3O4 dose, initial pH. The removal of histidine (62%) and phenylalanine (33%) was achieved with 0.1 g/L Co-Fe3O4, 1.5 mM PMS in the PMS/Co-Fe3O4 system. In contrast, only 19% and 16% histidine removal were obtained under individual application of PMS and Co-Fe3O4, respectively, confirming the preferable performance in the Co-Fe3O4/PMS system. Moreover, the reusability of the Co-Fe3O4 was elucidated after four successive runs. Radical quenching experiments revealed •OH and SO4•− were active while SO4•− was the dominant radical species. Examination of degradation intermediates and N-DBPs in Co-Fe3O4/PMS system showed that the increase of DCAN in histidine was attributed to histamine formation which produced more DCAN. Finally, the mechanism by the Co-Fe3O4/PMS system for the degradation of amino acids was proposed. The catalyst Co-Fe3O4 exhibited a unique adsorption of amino acids and the electron donor ability of Fe2+ enhanced the Co3+/Co2+ cycle which promoted the generation of free radicals according to the conversion of Fe and Co valence states.