Nano ZIF-8-decorated flower-shaped cobalt–nickel catalyst for p-nitrophenol degradation via peroxymonosulfate activation: A new insight into the mechanism

Novel flower-shaped Co:Ni@zeolitic imidazolate framework (ZIF)-8 catalysts with different molar ratios of Co:Ni decorated with nano ZIF-8 metal–organic frameworks (MOFs) were prepared using a simple hydrothermal process followed by simple co-precipitation method to enhance the efficiency of Co:Ni toward peroxymonosulfate (PMS) activation for p-nitrophenol (PNP) degradation. The performance of the catalysts was investigated under different optimal conditions, including the Co:Ni ratio, temperature, catalyst dose, pH, and PMS dose, and the mechanism are extensively discussed. The calcined sample NiCo₂O₄@ZIF-8 exhibited an outstanding degradation efficiency for PNP after 60 min through the activation of PMS, which in turn generated active sulfate radicals (SO₄^•−). Importantly, NiCo₂O₄@ZIF-8 improved the mineralization rate of PNP to approximately 98 % within 4 h and was successfully applied to actual sample analysis. The presence and relative concentrations of other various reactive oxygen species (ROS), including sulfate radical (SO₄^•−), hydroxyl radicals (^•OH), and superoxide radicals (O₂^•−), were determined through a trapping experiment. The prepared NiCo₂O₄@ZIF-8 composite exhibited excellent stability and reusability over five successive cycles.