Porous NiCo₂O₄ Sheet Catalysts for the Microwave-Assisted Fenton Reaction

Environmental pollution caused by persistent organics has drawn intensive attention. Microwave-assisted Fenton reaction (MAFR) was a rapid and effective technique for their removal. Herein, a sponge-templated method was introduced for the scalable preparation of two-dimensional (2D) porous NiCo2O4 sheet. Its surface area was 4.0 times higher than that of NiCo2O4 aggregate prepared without a sponge template. Control experiments revealed that the hydrophilic surface and restricted growth effect of sponge were essential for shaping sheetlike morphology. According to the response surface methodology, the optimal condition in MAFR was 10 mg of catalyst, 10 mg of peroxymonosulfate, 300 W of microwave power, and 70 °C of temperature, under which 50 mg/L of rhodamine B (RhB) was degraded within 1.5 min. The degradation rate constant was as high as 0.45 min–1, which was about 2.0 times higher than the reaction catalyzed by NiCo2O4 aggregate. SO4•– was identified as the main active species, as 62.2% of RhB removal was inhibited in their absence. The 2D porous NiCo2O4 sheet also exhibited good reusability and stability, Co3+ leaching in NiCo2O4 was only 1/14 that in Co3O4, and 81.7% of degradation efficiency was maintained even after five successive cycles.