Novel activation of peroxymonosulfate by an easily recyclable VC@Fe3O4 nanoparticles for enhanced degradation of sulfadiazine

An easily recyclable nanocomposite ascorbic acid-modified Fe3O4 (VC@Fe3O4) was synthesized, characterized, and evaluated as a green heterogeneous catalyst for activation of peroxymonosulfate (PMS). The structures of fresh and used VC@Fe3O4 were well characterized by TEM, XRD, FTIR, and XPS. The catalytic activity comparison between Fe3O4 and VC@Fe3O4 was performed under different parameters for depletion of sulfadiazine (SD). Additionally, scavenging tests and in-situ electron paramagnetic resonance (EPR) tests were applied to discern the primary radicals generated in the VC@Fe3O4/PMS system. The results indicate that the VC@Fe3O4 possesses a higher catalytic activity towards PMS compared with Fe3O4 for SD removal, and the observed pseudo first rate constant (k(obs)) were 7.24 x 10(-2) min(-1) for the VC@Fe3O4/PMS system and 1.05 x 10(-2) min(-1) for the Fe3O4/PMS system, correspondingly. 56.6% SD removal efficiency was obtained with 0.3 mM PMS and 0.8 g/L VC@Fe3O4 under pH 7.0. A large amount of hydroxyl radicals (OH) and a few number of sulfate radicals (SO4-center dot) were discerned by the hyperfine splitting constant values and scavenging results. Mechanisms on the peroxymonosulfate activation and radical generation in the VC@Fe3O4/PMS system were supposed. Results indicate that VC would obviously boost the cycle of Fe2+-Fe3+ on surface of VC@Fe3O4 nanoparticles and newly generated Fe2+ can continuously be consumed to activate PMS, which is answer for the rapid generation of reactive radicals (OH center dot, SO4-center dot). At last, mineralization and degradation pathway were also investigated. The findings of this study suggest that VC@Fe3O4 is a novel effective catalyst in activation of peroxymonosulfate under neutral pHs.