This study systematically evaluated the effects of iron (Fe)/copper (Cu) co-impregnation on electron transfer-mediated activation of peroxymonosulfate (PMS) using spent coffee waste biochar (SCWB), which is related to PMS activation performance for the degradation of Sunset Yellow FCF (SY) and Congo Red (CR). SCWB co-impregnated with Fe/Cu (FeCu@SCWB) exhibited increased specific surface area, greater pore volume, and higher metal content than those of SCWB, which affect its electron transfer performance. Consequently, FeCu@SCWB/PMS systems demonstrated notably higher removal efficiency in degrading SY and CR than SCWB/PMS systems due to the enhanced electron transfer between PMS and SCWB. Singlet oxygen and superoxide, which are the main reactive oxygen species in FeCu@SCWB/PMS systems for the degradation of SY and CR, were generated through electron transfer at various PMS activation sites of FeCu@SCWB. FeCu@SCWB/PMS systems decomposed SY and CR efficiently despite the co-existence of anions. FeCu@SCWB/PMS systems exhibited high stability as the concentrations of leached Fe and Cu complied with the World Health Organization effluent treatment standards. FeCu@SCWB/PMS systems also showed high SY and CR removal efficiencies even after three repetitions. Hence, FeCu@SCWB/PMS systems are a promising option to effectively remove SY and CR from actual water systems.
Sung et al. (Mon,) studied this question.