Immobilization of nanoscale zero-valent iron and its application for the degradation of chlorinated chemicals

Abstract

Immobilization of nanoscale zero-valent iron (nZVI) in cationic exchange membrane (CEM) and alginate bead was investigated for the degradation of trichloroethylene (TCE). Using a commercial CEM as a support, it was possible to immobilize the ZVI (Fe(0)-CEM) and palladium-doped ZVI (Fe/Pd-CEM). According to SEM (scanning electron microscopy) analysis, the 30 - 40 nm of nZVI particles were formed on the surface of CEM after immobilization. By using both ferric ions and barium ions as the cross-linking cations, the palladium-doped and nZVI-immobilized alginate bead (Fe/Pd-Alginate) was synthesized. According to TEM (transmission electron microscopy), the size of nZVI was as small as a few nanometers. From the surface analysis of the nZVI-immobilized supports, it was found that the immobilized nZVI shave the core-shell structure. The core is composed of single crystal $Fe^0$, while most of irons on the surface are oxidized to $Fe^{3+}$. Both Fe(0)- and Fe/Pd-CEM and Fe/Pd-Alginate removed TCE from aqueous solution by > 99%. Moreover, the release of metal from the support was < 5% of the loaded iron in both cases. In Fe(0)- and Fe/Pd-CEM, the removal of TCE was accomplished by sorption on the membrane matrix and degradation, while alginate bead did not adsorb TCE. In both cases, the removal of TCE followed pseudo-first-order kinetics. The observed pseudo-first-order reaction constants ( $k_{obs}$ ) of Fe(0)- and Fe/Pd-CEM were 0.44 and 0.41 $h^{-1}$ , respectively. Because the metal loading of Fe(0)- and Fe/Pd-CEM differs fairly from the other papers, it was inappropriate to compare the surface area normalized rate constant ( $k_{SA}$ ) values with the reported values. The $k_{obs}$ of Fe/Pd-Alginate was 6.11 $h^{-1}$ and the mass normalized rate constant ( $k_m$ ) was 1.6 $Lh^{-1}g^{-1}$ . The Fe(0)- and Fe/Pd-CEM can be recycled after re-reduction without loss of bound metal and Fe/Pd-Alginate also can be used repeatedly without deactivation. Although the removal ...