Surface chemistry and electrochemistry of supported zerovalent iron nanoparticles in the remediation of aqueous metal contaminants

The microstructure, physical characteristics, corrosion behavior, and react ivity of zerovalent iron nanoparticles synthesized on a support (primarily a nonporous, hydrophobic polymer resin) were studied. The remediation of gr oundwater by zerovalent iron in in situ permeable reactive barriers relies on the redox reaction between metallic iron and a reducible contaminant. De creasing the size of the iron particles and dispersing them on a support in creases the specific surface area of the iron, as well as the ratio of surf ace to bulk iron atoms, and should thereby increase both the reaction rate and the fraction of iron atoms available for the reaction. Borohydride redu ction of aqueous ferrous sulfate gives supported iron nanoparticles, 10-30 nm in diameter, which consist of 85% zerovalent iron by weight. These mater ials ("ferragels") are stable in air and have corrosion behavior comparable to iron filings. Interestingly, the presence or absence of a support, as w ell as the boron remaining from the borohydride reduction process, influenc es the electrochemical corrosion rate of the composite materials. Supported and unsupported zerovalent iron nanoparticles are superior to iron filings in both terms of initial rates of reduction and total moles of contaminant s (Cr(VI), Pb(II), TcO4-) reduced per mole of iron. The enhanced reactivity and passive corrosion behavior of these materials should make them good ca ndidates for use in permeable reactive barriers.