Elucidating the Degradation of Naphthalene in Fenton-like Processes Coupled with Various Sulfur-Iron Materials: Performance and Mechanisms

In this work, three sulfur-iron materials (sulfide-modified nanoscale zerovalent iron (S-nZVI), ferrous sulfide (FeS), and pyrite (FeS2)) were employed to enhance the Fenton process for naphthalene (NAP) degradation. The enhancement performance and mechanisms of S-nZVI, FeS, and FeS2 were investigated and compared. The results showed that NAP removal was enhanced from 56.4% in the H2O2/Fe(II) system to 88.6%, 83.0%, and 89.1% with the addition of S-nZVI, FeS, and FeS2, respectively. Three sulfur-iron materials could all reduce Fe(III) produced in aqueous solution, regenerate Fe(II), and slow down the precipitation of dissolved iron. In addition, the addition of sulfur-iron materials could promote the generation of hydroxyl radical (HO•), thus intensifying the degradation of NAP. The results of scavenging tests indicated that HO• was the dominant reactive oxygen species (ROS) for NAP removal, while superoxide radical (O2−•) also participated. The effect of complex water matrices on NAP degradation was evaluated, showing that sulfur-iron material-enhanced techniques had a wide pH application range and had great tolerance to inorganic ions and humic acid. Moreover, NAP degradation intermediates and their toxicity were elucidated. Finally, the obvious removal of various pollutants in sulfur-iron material-enhanced systems demonstrated that these technologies could be used to remediate organic-polluted groundwater.