A comparative study on the activation of persulfate by bare and surface-stabilized nanoscale zero-valent iron for the removal of sulfamethazine

Abstract In this study, bare nanoscale zero-valent iron (NZVI) and that modified by starch, carboxymethyl cellulose (CMC) and sodium dodecyl benzene sulfonate (SDBS) were compared for their ability in activating persulfate to degrade sulfamethazine (SMT) in aqueous solution. The influencing factors, i.e., mass ratio of stabilizer/NZVI, pH, groundwater components (e.g., Ca2+, HCO3−, SO42− and humic acid) and particle aging, on SMT removal were examined. The results showed that there was an optimal mass ratio of stabilizer/NZVI for the stabilized NZVI (50 wt%, 0.1 wt% and 0.5 wt%, respectively, for starch-, SDBS- and CMC-stabilized NZVI) in order to achieve a faster removal rate of SMT than the bare NZVI. There was no significant difference among different nanoparticles in SMT removal in pure water at pH 5 and 9. While in simulated groundwater, the SMT removal in the bare NZVI system was more inhibited than the stabilized NZVI system. Compared with that in pure water, the removal rate of SMT was markedly decreased in simulated groundwater, especially at pH 9, which might be due to the radical scavenging effect of groundwater components (e.g., HCO3−, humic acid, SO42−) and the buffering effect of HCO3−. The aging of nanoparticles decreased the reaction rate. After aging for 15 d, SMT removal was decreased from 71.6%, 83.2%, 81.9% and 72.4% to 58.8%, 61%, 59.1% and 52.9%, respectively, for bare, starch-, SDBS- and CMC-stabilized NZVI in the first 5 min. However, SMT could still be completely removed in all systems when the reaction time was prolonged to 1 h. XRD analysis of the aged nanoparticles indicated that both bare and stabilized NZVI were not significantly oxidized in the air, and could still be employed for the activation of persulfate.