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.
Bransfield
Stephen J
SJ
Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Cwiertny
David M
DM
Roberts
A Lynn
AL
Fairbrother
D Howard
DH
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