Application of nano-scale zero-valent iron adsorbed on magnetite nanoparticles for removal of carbon tetrachloride: Products and degradation pathway

Nano-scale zero-valent iron (nZVI) attached to Fe3O4 nanoparticles (Fe-0@Fe3O4), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe-0@Fe3O4 composites with different ratios of the two components were compared. Under optimum conditions, when the Fe-0/Fe3O4 ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe-0/Fe3O4 ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe3O4 alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe-0@Fe3O4 system: both Fe2+ and Fe3+ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe2+ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe-0 to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe2+ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe-0@Fe3O4 nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds.