Nickel-Nickel oxide nanocomposite as a magnetically separable persulfate activator for the nonradical oxidation of organic contaminants

The nanocomposite of metallic nickel and nickel oxide (denoted as Ni-NiO), synthesized by a simple sol-gel method, was found to activate peroxydisulfate (PDS), resulting in the effective oxidation of phenolic compounds and selected pharmaceuticals. A nonradical mechanism was proposed to explain the activation of PDS by Ni-NiO, in which organic contaminants are believed to be oxidized through an electron abstraction pathway mediated by the reactive complexes formed between PDS and the Ni-NiO surface. This mechanism was supported by multiple lines of evidence including radical scavenger experiments, the oxidation products, linear sweep voltammetry, and electron paramagnetic resonance spectroscopy. The Ni-NiO/PDS system exhibited a PDS utilization efficiency (expressed by the ratio of degraded organic contaminant to decomposed PDS) that was over 80%, and Ni-NiO showed a greater activity for PDS activation than a commercial nanoparticulate nickel oxide. This improved performance of Ni-NiO was attributed to the disproportioned incorporation of the metallic Ni into the NiO matrix, creating more sites with oxygen vacancy. Also owing to the metallic Ni, Ni-NiO possessed magnetic properties and therefore could be easily separated and reused.