Temperature-dependent evolution of hydroxyl radicals from peroxymonosulfate activation over nitrogen-modified carbon nanotubes

Abstract

© 2018 Elsevier B.V. Rational regulation of redox capacity in advanced oxidation processes (AOPs) by metal-free nanomaterials is appealing to extend the state-of-the-art carbocatalysis toward diverse applications. In this study, nitrogen-decorated single-walled carbon nanotubes (N-SWCNT) were fabricated using urea as a green precursor under thermal pyrolysis. We comprehensively investigated the peroxymonosulfate (PMS) activation at varying temperatures with/without the nanocarbon toward nitrobenzene (NB) oxidation. In the noncatalytic system, NB decomposition rate was impressively boosted with the raising reaction temperatures. More importantly, hydroxyl radicals (•OH) were unveiled to be the primary reactive oxygen species (ROS) and contributed to NB degradation under high temperatures in PMS/N-SWCNT system. The mechanism of PMS activation with/without N-SWCNT and impact of temperature were elucidated by both in situ electron paramagnetic resonance (EPR) technique and selectively radical quenching tests. Interestingly, the NB degradation kinetics witnessed a two-stage process with different activation energies in PMS only and PMS/N-SWCNT systems, suggesting that the reaction temperature may be able to tune the catalytic mechanism and generated ROS. Therefore, the nanocarbon-catalyzed and thermal-assisted metal-free AOPs can be featured with maneuverable oxidative potentials toward a wide range of redox processes.