Carbothermal synthesis of carbon-supported nanoscale zero-valent iron particles for the remediation of hexavalent chromium

Nanoscale, zero-valent iron is a promising reagent for in situ reduction of a variety of subsurface contaminants, but its utility in full-scale remediation projects is limited by material costs. Iron. nanoparticles (20-100 nm diameter) supported on carbon) were synthesized by reacting iron salts, adsorbed or (C-Fe-0) 80 m(2)/g carbon black, impregnated from aqueous solutions onto at 600-800 degrees C under Ar. Similar products were obtained by heating the reactants under air in a covered alumina crucible. X-ray powder diffraction patterns show that Fe3O4 particles are formed at 300-500 degrees C in the initial stage of the reaction and that these particles are reduced to a mixture of (alpha- and gamma-Fe nanoparticles above 600 degrees C. When C-Fe-0 was combined with carboxymethylcellulose in a 5:1 weight ratio in water, the resulting material had similar transport properties to previously optimized nanoiron/polyanion suspensions in water-saturated sand columns. At a 10:3 Fe/Cr mole ratio, C-Fe-0 reduced a 10 ppm Cr(VI) solution to similar to 1 ppm within three days. The surface area normalized first-order Cr removal rate was 1.2 h(-1) m(-1) under these conditions. These results demonstrate that reactive nanoiron with good transport properties in water-saturated porous media c an be made in a scalable process from inexpensive starting materials by carbothermal reduction.