Cobalt (II)-intercalated layered double hydroxide as an efficient activator for catalytic oxidation of organic contaminants

The simultaneous optimization and design of catalysts' structure or components are extremely significant ap-proaches to further enhancing the catalytic activity. Herein, cobalt (II)-intercalated Ni-Fe layered double hy-droxide (Co-NiFe-LDH) was fabricated via a novel topological transformation process and employed as an efficient activator on peroxymonosulfate (PMS) activation for simulated sewage decontamination. Character-izations with state-of-the-art spectroscopies demonstrated Co (II) was successfully embedded in the interlayer of NiFe-LDH after reconstruction. Meanwhile, experiments manifested that the Co-NiFe-LDH possessed an enhanced catalytic performance relative to neither pristine NiFe-LDH nor ternary CoNiFe-LDH. The maximum Orange II sewage degradation (30 mg L-1, 99.5 %) could be obtained under the optimal conditions (30 min, 120 mg L-1 Co-NiFe-LDH, and 1 mM PMS) with the first-order up to 0.216 min(-1). Encouragingly, the Co-NiFe-LDH/PMS system exhibited stable performance over a wide pH range and low dissolution. It was also found that the superior performance of Co-NiFe-LDH was attributed to the clusters of Co in the interlayer, which can improve electro-chemical characteristics, thereby accelerating interfacial electron transfer. Moreover, on the basis of redox cycles of Ni (II)/Ni (III) and Fe (II)/Fe (III), a new redox cycle of Co (II)/Co (III) was discovered in Co-NiFe-LDH, therefore promoting the utilization efficiency of oxidants. Besides, quenching experiments and electron para-magnetic resonance spectroscopy (EPR) demonstrated that SO4 center dot- and center dot OH acted as the dominant active radicals for Orange II degradation. It's also encouraging that the Co-NiFe-LDH/PMS system could efficiently decompose other typical contaminants, and its catalytic activity remained unchanged after five uses. Ultimately, a reason-able catalytic mechanism of the Co-NiFe-LDH/PMS system was proposed by the comprehensive analysis. This work sheds light on the elegantly designed LDH with high performance toward activating PMS in water decontamination.