Two-dimensional RuO₂ nanosheets as robust catalysts for peroxymonosulfate activation

This study explored for the first time the application of two-dimensional (2D) ruthenium oxide (RuO₂) nanosheets (NSs) for organic decomposition through peroxymonosulfate (PMS) activation. RuO₂ NSs outperformed not only the corresponding RuO₂ nanoparticles (NPs) but also other common PMS activators such as transition metal oxides and carbonaceous nanomaterials, which is ascribed to facile electron transfer on 2D nanosheets, higher surface area and porosity, and favorable interaction with PMS on the hydrophilic surface. Aside from the higher PMS activation efficiency, the potential advantages of RuO₂ NSs include (i) optimized performance under weakly acidic and neutral conditions and (ii) capability to utilize both PMS and PDS as radical precursors unlike Co₃O₄. In addition, RuO₂ NSs/PMS could decompose both aromatic (e.g., bisphenol A, benzoic acid, and ranitidine) and non-aromatic compounds (e.g., dichloroacetate) to a significant extent, which is in marked contrast to the carbon nanotube-PMS system of which the efficiency sensitively depends on the kind of substrate. The generation of a sulfate radical (SO₄^-) as a main oxidant (from PMS decomposition) was corroborated by not only an outstanding inhibition effect of methanol (a sulfate radical scavenger) but also the formation of the sulfate radical adduct in the electron paramagnetic resonance (EPR) spin-trapping test. As a practical method of utilizing RuO₂ NSs, RuO₂ NSs could be coupled with magnetic Fe₃O₄, which enabled not only the facile recovery of the catalyst after use but also the robust catalytic performance without losing the activity during repeated use. Despite the high material cost of RuO₂, such superiorities can make it an effective, stable, and reusable PMS activator.