Synthesis of FeCo alloy encapsulated nitrogen-doped graphitized carbon: High catalytic activation and low metal ion leaching in microwave assisted Fenton reaction

As an efficient non-precious metal catalyst, FeCo alloy was widely used in various catalytic reactions. Owing to the organic pollution in ecosystem, it has attracted much attention in heterogeneous Fenton reaction. Unfortunately, their application was restricted by slow process and high leaching. To overcome these shortcomings simultaneously, herein, FeCo@nitrogen-doped graphitized carbon (NGC) core/shell composite was synthesized via one-step annealing Prussian blue analogue. In microwave assisted Fenton reaction (MAFR), malachite green (MG) degradation time was only 2.5 min, and the rate constant was 2.0 min⁻¹, about 20 times higher than heterogeneous Fenton reaction. Synergistic index was 3.88, meaning extra 288% of removal efficiency was yield in peroxymonosulfate (PMS)+MW+FeCo@NGC system. The effect of microwave-activation was divided into thermal effect and non-thermal effect. SO₄ ^·− produced through thermal effect occupied 73% ± 8% of total number. The contribution of thermal effect was estimated to be 65% ± 7% for MG removal. Non-thermal effect was clarified by hotspots effect theory. Due to protection of NGC shell, Co^3+/2+ leaching in composite was only one-tenth of pure FeCo. FeCo@NGC composite could be rapidly recycled due to ferromagnetic behavior with saturation magnetization of 98.7 emu/g. 89.3% of degradation efficiency was maintained after the 5^th cycle.