Influence of copper loading and surface coverage on the reactivity of granular iron toward 1,1,1-trichloroethane.
Although iron-based bimetallic reductants offer promise in treating organohalides, the influence of additive mass loading and two-dimensional surface coverage on reductant reactivity has not been fully elucidated. In this study we examine 1,1,1-trichloroethane reduction by Cu/Fe bimetals as a function of Cu loading and surface coverage. Information from a suite of complementary techniques (X-ray photoelectron spectroscopy, Auger electron spectroscopy, and cross-sectional energy-dispersive X-ray spectroscopy) indicates that displacement plating produces a heterogeneous metallic copper overlayer on iron. The dependence of pseudo-first-order rate constants (k(obs) values) for 1,1,1-trichloroethane reduction on Cu loading exhibits two distinct regimes. At Cu loadings less than 1 monolayer equivalent (approximately 10 micromol Cu/g Fe), a pronounced increase in k(obs) is associated with a corresponding increase in the two-dimensional surface coverage of Cu. A weaker dependence of k(obs) on Cu mass is exhibited at loadings in excess of 1 monolayer equivalent, which we ascribe to an increase in the volume of the metallic overlayer. The observed relationship between k(oba) and loading suggests that 1,1,1-trichloroethane reduction occurs on the Cu surface rather than at the interface between the Cu overlayer and the iron substrate.
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Stephen J
SJ
Bransfield
David M
DM
Cwiertny
A Lynn
AL
Roberts
D Howard
DH
Fairbrother
D003300:Copper / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D013057:Spectrum Analysis / Q000379:methods; D014240:Trichloroethanes / Q000737:chemistry*; D014965:X-Rays
D014240:Trichloroethanes; C024566:1,1,1-trichloroethane; D003300:Copper; D007501:Iron