Systematic Performance Comparison of Fe/Fe/Peroxymonosulfate and Fe/Fe/Peroxydisulfate Systems for Organics Removal.

Activated zero-valent iron (Ac-ZVI) coupled with Fe was employed to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) for acid orange 7 (AO7) removal. Fe was used to promote Fe liberation from Ac-ZVI as an active species for reactive oxygen species (ROS) generation. The factors affecting AO7 degradation, namely, the Ac-ZVI:Fe ratio, PMS/PDS dosage, and pH, were compared. In both PMS and PDS systems, the AO7 degradation rate increased gradually with increasing Fe concentration at fixed Ac-ZVI loading due to the Fe-promoted liberation of Fe from Ac-ZVI. The AO7 degradation rate increased with increasing PMS/PDS dosage due to the greater amount of ROS generated. The degradation rate in the PDS system decreased while the degradation rate in the PMS system increased with increasing pH due to the difference in the PDS and PMS activation mechanisms. On the basis of the radical scavenging study, sulfate radical was identified as the dominant ROS in both systems. The physicochemical properties of pristine and used Ac-ZVI were characterized, indicating that the used Ac-ZVI had an increased BET specific surface area due to the formation of FeO nanoparticles during PMS/PDS activation. Nevertheless, both systems displayed good reusability and stability for at least three cycles, indicating that the systems are promising for pollutant removal.