Secondary battery inspired NiO nanosheets with rich Ni(III) defects for enhancing persulfates activation in phenolic waste water degradation

Sulfate radicals (center dot SO4-) with broad pH tolerance and strong oxidation capacity are promising for Fenton-like reaction degradation of phenolic waste water. Ni-based catalysts and its compounds have been seldom reported as catalysts for the sulfate radical activation from persulfates (PDS) due to its inappropriate redox potential windows. A secondary battery inspired NiO nanosheets with rich Ni(III) defects were developed for Fenton-like catalysis via the charge/discharge process of NiOx/NiOx(OH)(y) redox cycle. The redox potential of Ni(II)/Ni(III) in NiOx/Ni-x(OH)(y) cycle is high enough to activate S2O82- for the generation of center dot SO4-. The Fenton-like performance of the defect-rich NiO nanosheets is most robust among the well-known sulfate radical activation catalysts of Co3O4, alpha-Fe2O3 , MnOOH, and CuO. The enhancement effect of NiO was attributed to the formed Ni (III) defects, which could facilitate the discharge process of Ni(III) to Ni(II) and then enhance the Ni(III)/Ni(II) cycle during the Fenton-like process. The stability and recovery of defect-rich NiO nanosheets was also studied. Its high stability in chemical structure contributed to the low Ni leaching during the reaction process in basic or neutral condition. The recovery of defect-rich NiO nanosheets could be easily realized via the annealing treatment. In all, the secondary battery inspired defect-rich NiO nanosheets with outstanding sulfate radical activation would be a promising Fenton-like catalyst for environmental remediation.