Fe3O4@N-doped carbon derived from dye wastewater flocculates as a heterogeneous catalyst for degradation of methylene blue

The development of high-efficiency, low-cost, and easy-to-synthesize Fenton catalysts for the degradation of organic wastewater is desirable. Electrocoagulation (EC) is a practical technology for wastewater treatment because of its low cost and convenience; however, a large amount of sludge and flocculates are produced during EC that requires secondary treatment. Considering recycling of resources and turning waste materials into useful items, for the first time, we prepared an efficient Fenton catalyst, Fe3O4@N-doped carbon (Fe3O4@NC), which is a composite derived from malachite green dye wastewater flocculates, produced using EC; it was used for methylene blue (MB) degradation. Fe3O4@NC-20 exhibited remarkable catalytic activity, with nearly 100% degradation of MB dye in 50 min, which is outstanding compared to previously reported catalysts. The morphology and structural characterizations revealed that the outstanding catalytic activity of Fe3O4@NC-20 can be attributed to the synergy between the uniform Fe3O4 nanoparticles and the porous carbon matrix, which offers a large surface area, high pore volume, and large number of catalytic sites. Moreover, Fe3O4@NC-20 facilitated simple separation with 63.1 emu g(-1) saturation magnetization and could be reused over multiple cycles, retaining approximately 96% decolorization efficiency of MB and 59% removal efficiency of total organic carbon after 5 repeated cycles. Furthermore, the catalytic mechanism was discussed; the catalytic oxidation may be attributed to the hydroxyl radicals obtained via the reaction of Fe3O4@NC-20 and H2O2, which can induce the degradation of MB to produce CO2 or other colorless intermediates.