Catalytic Ozonation of Ketoprofen with In Situ N-Doped Carbon: A Novel Synergetic Mechanism of Hydroxyl Radical Oxidation and an Intra-Electron-Transfer Nonradical Reaction

A novel synergetic mechanism of hydroxyl radical ((OH)-O-center dot) oxidation and an intra-electron-transfer nonradical reaction was found in the catalytic ozonation of ketoprofen (KTP) with the in situ N-doped hollow sphere carbon (NHC). Outperforming the conventional (OH)-O-center dot-based catalytic ozonation process, O-3/NHC not only realized an enhancement of the pseudo first -order rate constant of 11 times in comparison with that of O-3 alone, but was also endowed with a high stability over a wide pH (4-9) and temperature (15-35 degrees C) range for the degradation of KTP. The high graphitization degree (I-D/I-G = 0.78-0.88) and low unsaturated oxygen content (0.10-1.38%) of NHC highlighted the dominant role of N-heteroatoms in the O-3/NHC system. The specific effects of different N species were confirmed by a relationship study (N property vs catalytic activity) and X-ray photoelectron spectroscopy characterization. The graphitic N forming in the bulk of the graphitic structure served as the electron-mobility region to promote KTP degradation with the transfer of electrons from the KTP molecule to O-3 via a nonradical reaction process. The pyrrolic and pyridinic N located at defects of the graphitic structure acted as the radical-generation region to decompose O-3 into (OH)-O-center dot for degrading KTP by a radical oxidation process. This finding provided a brand new insight into engineering N-doped carbonaceous catalysts precisely in the catalytic ozonation process for the efficient treatment of organic-contaminated water.