Carbon Materials Inhibit Formation of Nitrated Aromatic Products in Treatment of Phenolic Compounds by Thermal Activation of Peroxydisulfate in the Presence of Nitrite.

Recent studies have reported that toxic nitrated aromatic products are generated during treatment of phenolic compounds by thermally activated peroxydisulfate (thermal/PDS) in the presence of nitrite (NO2-). This work explored the potential of carbon materials on controlling the formation of nitrated aromatic products using phenol as a model compound. In the presence of selected carbon materials including diverse carbon nanotubes (CNT) and powdered activated carbon (PAC), the transformation kinetics of phenol was significantly enhanced, primarily attributed to nonradical activation of PDS by carbon materials. Nitrophenols (NPs) including 2-NP and 4-NP were formed in phenol oxidation by the thermal/PDS/NO2- process, due to the reaction of phenol with reactive nitrogen species generated from NO2- oxidation. The addition of carbon materials obviously inhibited NPs formation under various experimental conditions. The bonding of nitro groups on the CNT surface was clearly confirmed by means of various characterizations, probably resulting from the competitive reaction of reactive nitrogen species with CNT vs phenol. The controlling effect of carbon materials was also verified in the cases of other phenolic compounds. Therefore, the addition of carbon materials may be a promising approach to control the formation of undesirable nitrated byproducts by the thermal/PDS process in the presence of NO2-.