Heterogeneous activation of peroxymonosulfate by GO-CoFe2O4 for degradation of reactive black 5 from aqueous solutions: Optimization, mechanism, degradation intermediates and toxicity

Abstract

The magnetic cobalt ferrite (CoFe2O4) loaded on graphene oxide (GO) was synthesized by the co-precipitation method and used to activate peroxymonosulfate (PMS) in the degradation of the reactive black 5 (RB5). The response surface methodology (RSM) was used to optimize the laboratory parameters and the interaction between them. The maximum degradation efficiency with R2 > 99% was obtained at pH of 7, the GO-CoFe2O4 dose of 125 mg/L, the RB5 concentration of 50 mg/L, the PMS dose of 2.49 mM, and the reaction time of 3.49 min. Under optimal conditions, the degradation efficiency of the PMS/GO-CoFe2O4 process (100%) was much higher than that of GO (33%), GO-CoFe2O4 (43.12%), and PMS (14.05%) at 30 min. The RB5 degradation rate was improved with temperature, and the activation energy was calculated to be 12.47 kJ/mol. Nitrate and carbonate reduced the degradation efficiency of RB5 by reacting with the main radicals. The PMS/GO-CoFe2O4 system showed good performance for the treatment of raw water. However, it does require a longer treatment time for real wastewater. GO-CoFe2O4 showed excellent stability and reusability in five consecutive reaction cycles to remove chemical oxygen demand (COD) and total organic carbon (TOC). The proposed PMS activation mechanism based on scavenging experiments showed that SO4•- plays a dominant role in the RB5 degradation. The gas chromatography–mass spectrometry (GC–MS) analysis showed that RB5 was degraded through the pathways, including desulfonation, dechlorination, deamination, hydroxylation, dehydrogenation, and chain/ring cleavage. Toxicity tests were performed with Daphnia pulex, and the results showed that the treated effluent required more catalytic treatment and better stabilization due to the presence of cobalt ions and intermediates.