Peroxymonosulfate activation by carbon-encapsulated metal nanoparticles: Switching the primary reaction route and increasing chemical stability

This study explores the technical merits of carbon encapsulation via an electrical wire explosion method to enhance the peroxymonosulfate activation performance of metals. Reflecting the nature of core-shell structures, the outer carbon layers hampered the reductive conversion of peroxymonosulfate to sulfate radicals by the inner metal cores, whereas the metal cores increased the overall electrical conductivity as a pivotal factor in non-radical activation. Hence, the impact of carbon wrapping hinged on the peroxymonosulfate reduction capability of the metals, i.e., kinetic retardation in organic degradation with reactive Cu, Fe, and Ni-Fe, but acceleration with unreactive Ni. Further, composite fabrication switched the major degradative pathway from radical-induced oxidation to mediated electron transfer, as determined from the effects of methanol and chloride, formaldehyde and bromate formation yields, reactivity toward multiple organics, and electron paramagnetic resonance spectral features. The protective carbon shells enabled pH-insensitive peroxymonosulfate activation, prevented metal ion leaching, and alleviated catalyst deactivation.