Probing the interphase HO• zone originated by carbon nanotube during catalytic ozonation

Carbon nanotube (CNT) is an attractive metal-free catalyst that can be explored in combination with ozone treatment. Using fluorescence microscopy image analysis, we investigated the production of hydroxyl radicals (HO') within the solid-liquid interphase for CNT-mediated catalytic ozonation. The visualized results suggest that HO center dot was vastly generated via catalysis and accumulated within a surface region of the CNT (we defined this region as the interphase HO center dot zone). In this region, using 7-hydroxycoumarin as a HO center dot marker, the radical abundance was at least 1000 times higher than that in the aqueous bulk phase. Owing to the observed inhomogeneity of HO center dot, the CNT/ozone system effectively decomposed perfluorooctane sulfonate that was fairly resistant to non-catalytic ozonation, and the decomposition kinetics was not much inhibited by tert-butanol as bulk-phase HO' scavenger due to the remaining HO center dot zone at surface region available for reaction. A longevity trial revealed the sustained formation of the interphase HO center dot zone and strongly indicated that the graphitic structure may optimize the density of surface active sites responsible for the proliferation and local concentration of HO center dot. CNT, with good catalytic efficiency, longevity and stability, is anticipated as the basis of future nanomaterials able to promote HO center dot exposure in ozone treatment for advanced oxidation process. (C) 2017 Elsevier Ltd. All rights reserved.