Pb(II) adsorption to hydrated α-Fe2O3 (1-102), studied via density functional theory

 

Author: Cynthia S. Lo

Mentor: Anne M. Chaka

Division: Physical and Chemical Properties (838)

Laboratory: CSTL

Building/Room: 221/B332

Mail Stop: 8380

Telephone: (301) 975-5478

Fax: (301) 869-4020

E-mail: cynthia.lo@nist.gov

Sigma Xi member: Yes

Category: Chemistry

 

The adsorption of contaminant metals at mineral/solution interfaces plays an important role in controlling their transport and bioavailability in soil and aqueous environments.  Lead is of particular importance due to its prevalence as a contaminant associated with the oxidation of mine tailings from Pb-Zn mineral deposits as well as its wide spread association with domestic and industrial waste streams.  However, both the stability of the sorbed species and the preferred mode of adsorption are highly dependent on the structure of the metal oxide surface, including the composition of the bulk material, crystallographic orientation, and the types of functional groups present at the surface.  For example, the contaminant metal ion may bind strongly to the surface as an “inner-sphere” complex through direct bonding and potentially multidentate association.  Else, it may bind weakly as an “outer-sphere” complex through hydrogen bonding and other electrostatic interactions with the surface.  Pb(II)/α-Fe2O3 is a simple model system suitable for detailed experimental (CTR, GI-XAFS, XSW) and theoretical characterization.  In this work, we present density functional theory results on Pb(II) binding, including the sorption modes and binding geometries, to hydrated α-Fe2O3 (1-102).  We will also discuss the modification of the mineral surface structure upon water physisorption, heterolytic water dissociation, and Pb(II) binding.