Heterogeneous activation of peroxymonosulfate with Fe3O4 magnetic nanoparticles for degradation of Reactive Black 5: Batch and column study

In the present study, magnetite nanoparticles (Fe3O4) were used to activate peroxymonosulfate (PMS) in the degradation of Reactive Black 5 (RB5) from aqueous solutions. 94.86% of RB5 was degraded using Fe3O4 dosage of 250 mg L−1, PMS of 2 mM at pH of 7 after 60 min. The RB5 degradation rate was improved with temperature, and the activation energy was obtained to be 13.36 kJ mol−1. The presence of chloride, carbonate, nitrate, and bicarbonate in the solution reduced the rate of RB5 degradation due to the scavenging effect and the production of reactive species with low oxidation potential. Fe3O4 exhibited excellent stability for 240 min in a column reactor. The scavenging experiments emphasized that both SO4•- and •OH play an important role in the tests; however, SO4•- was the dominant species for RB5 degradation. The possible mechanism of PMS decomposition into reactive species by Fe3O4 was proposed. The column reactor showed a degradation efficiency of 95.65%, 80%, and 50% for RB5 in the synthetic sample, surface water, and textile wastewater, respectively. Toxicity was assessed by culturing Escherichia coli (E. coli) under the optimal condition. Five RB5 degradation products were identified by gas chromatography-mass spectrometry (GC-MS), and SO42-, NH4+, NO3-, CO2 and H2O were produced as the final mineralized products in the Fe3O4/PMS system. Comparative experiments have shown that the Fe3O4 catalyst has high efficiency in PMS activation and RB5 degradation; however, the presence of ultrasound, heat, and ultraviolet in the catalytic system can be beneficial to increase the degradation rate during fewer reaction times.