A green and energy-saving microwave-based method to prepare magnetic carbon beads for catalytic wet peroxide oxidation

A green and energy-saving method was proposed to fabricate magnetic carbon (Fe@CS) beads (diameter: 0.5–1 mm) as Fenton-like catalyst and to simultaneously regenerate saturated activated carbon. Chitosan (CS) was used as the precursor of carbon, and tremendous heat produced during the regeneration of activated carbon by microwave irradiation (600 W) was utilized for carbonization within 2 min. The effects of microwave irradiation time and iron/CS mass ratio on Fe@CS were evaluated through various characterization methods, such as iron content, phase, microstructure, degree of graphitization, and associated Fenton-like catalytic activity. Fe3O4 and slight Fe(0) were the main iron species in Fe@CS beads. The microstructure of Fe@CS beads presented a hollow nanosphere structure and the Fe3O4 nanoparticles were uniformly embedded in the carbon layer. The Fe@CS/H2O2 Fenton-like system managed to efficiently degrade acid orange II even in a wide pH range of 3–9. Hydroxyl radical was proven by electron spin resonance spectroscopy as the dominant active species. The crystal or catalytic activity of Fe@CS hardly changed after five cycles. Moreover, the catalytic activity was enhanced after each cycle because the surface bound iron and increased iron leaching (<2 mg/L in first four cycles). The stability could be restored (decreased iron leaching) easily through a convenient regeneration process. In conclusion, this study proposed a novel and facile method for preparing reusable heterogeneous Fenton-like particle catalysts, providing valuable insights for the green, energy-saving and reusable applications of catalysts.