Nanoscale iron particles for complete reduction of chlorinated ethenes

This paper examines the potential for using laboratory synthesized nanoscale Pd/Fe bimetallic particles to reduce chlorinated ethenes. Rapid and complete dechlorination was achieved for six chlorinated ethenes: tetrachloroethene (PCE, C2Cl4), trichloroethene (TCE, C2HCl3), 1,1-dichloroethene (1,1-DCE, C2H2Cl2), cis- and trans-1,2-dichloroethene (c-DCE, t-DCE, C2H2Cl2), and vinyl chloride (VC, C2H3Cl). The chlorinated ethenes (20 mg l−1) were completely reduced within 90 min at a metal loading of 5 g l−1. Ethane was the primary product from these reactions, amount to 60–90% of the total carbon. Ethene (3–20%) was produced during the transformation of TCE, DCEs and VC. No chlorinated intermediates or final products were detected above the method detection limit (<5 μg l−1). The remarkable performance of the nanoscale particles can be attributed to: (1) High specific surface area of the nanoscale metal particles, approximately 35 m2 g−1, tens to hundreds of times higher than commercial grade micro- or milli-scale iron particles; (2) Increased reactivity per unit metal surface area, largely due to the presence of the noble metal (Pd) on the surface. Values of the surface-area-normalized rate coefficients (kSA) were two orders of magnitude higher than those reported in the literature for larger iron particles. Due to their small particle size and high reactivity, the nanoscale bimetallic particles may be useful in a wide array of environmental applications including subsurface injection for groundwater treatment.