Efficient degradation of Rhodamine B in water by CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems: A comparative study

In this work, a comparative study of efficient degradation of Rhodamine B (RhB) in CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems was performed. Batch experiments indicated that the RhB degradation rate of CoFe₂O₄/H₂O₂ system reached 95.5% at 90 min under the condition of 0.5 g L^-1 of CoFe₂O₄ dosage, 10 mM of H₂O₂ concentration and 3.0 of initial pH. At certain conditions of initial pH = 7.0, 0.3 g L^-1 of CoFe₂O₄ dosage, 7 mM of PMS concentration, CoFe₂O₄/PMS system could completely degrade RhB within 90 min. EPR and quenching experiments indicated that •OH was the main active species of CoFe₂O₄/H₂O₂ system, and •OH, SO₄•^-, •O₂^- and ¹O₂ participated in RhB degradation of CoFe₂O₄/PMS system. The circulate of Co(II)/Co(III) and Fe(II)/Fe(III) on the CoFe₂O₄ surface promoted the formation of free radical species in the two system. In CoFe₂O₄/PMS system, the formed •O₂^- and SO₅•^- realized the generation of non-free radical species (¹O₂). The LC-MS results indicated that N-de-ethylation, chromophore cleavage, opening rings and mineralization were the main steps for the RhB degradation of the two systems. After five cycles of degradation experiment, the CoFe₂O₄/H₂O₂ and CoFe₂O₄/PMS systems still maintained the high degradation rate (85.2% and 92.4%) and low mass loss (2.7% and 3.09%). In addition, CoFe₂O₄/PMS system had better potential value for the actual water and multi-pollutant degradation than CoFe₂O₄/H₂O₂ system. Finally, the toxicity analysis and cost assessment of the two oxidation systems were preliminarily evaluated.