Activation of sulfite by different Fe0-based nanomaterials for oxidative removal of sulfamethazine in aqueous solution

In this work, bare nanoscale zero-valent iron (NZVI) and the modified NZVI (sulfide-modified NZVI, Ni/NZVI and activated carbon supported NZVI) were utilized to activate sulfite for the removal of the target pollutant sulfamethazine (SMT). Some critical factors influencing the removal process were investigated, including dosage of sulfite and nanoparticles (NPs), ratios of modifier/NZVI, dissolved oxygen, initial pH values, groundwater components and aging time of NPs. Under the optimal conditions, in terms of the dosage of sulfite/NPs and the ratio of modifier/NZVI, all the modified NZVI showed a better performance than the bare NZVI. Dissolved oxygen was determined to be an essential factor for producing reactive radicals in all the activation processes. The active radicals were identified to be SO4 center dot and HO center dot and HO center dot was evidenced as the principal reactive species. Initial pH value significantly affected the SMT removal, which was obviously inhibited under alkaline condition. In such case, Ni/NZVI showed a better performance than the other NPs due to the catalysis effect of Ni. It was also found that the groundwater components (e.g., HCO3-, Ca2+, SO42-, and humic acid) could restrain the removal process because of the buffering effect, the radical scavenging effect and some other effects (e.g., surface precipitation). Spectroscopic analysis of the fresh and aged (30 d) NPs illustrated that both bare and modified NZVI were slightly oxidized in the air, and could still be employed for the activation of sulfite.