HR: 1340h
AN: B23B-1043    [Abstracts]
TI: Cu2+ as a Probe for Nanomineral Surface Chemistry
AU: * Madden, A S
EM: maddenas@ornl.gov
AF: Oak Ridge National Laboratory, Environmental Sciences Division P.O. Box 2008, Oak Ridge, TN 37831-6036 United States
AU: Hochella, M F
EM: hochella@vt.edu
AF: Virginia Tech, NanoGeoscience and Technology Laboratory Department of Geosciences, Blacksburg, VA 24061 United States
AB: Recent field-based studies have shown that minerals with diameters less than approximately 10-15 nanometers, including highly crystalline materials, are common and important in the transport of toxic metals released as a result of mining activities. Through the scientific discipline of nanoscience, it is expected that materials will experience size-property-reactivity relationships in this size range. These relationships are almost entirely unknown in mineralogical and biogeochemical systems. As such, model systems were utilized to explore nanomineral reactivity as a function of mineral size. Size-dependent geochemical reactivity of hematite nanoparticles has been measured in experimental systems, including heterogeneous Mn2+ oxidation and photochemical reduction. In general, those particles with average diameters of 7 nm have significantly greater reactivity compared to particles with average diameters greater than approximately 10 nm, even after surface area normalization. It was hypothesized that the increased reactivity of the smallest particles could be most easily interpreted as a change in the arrangement and/or coordination of surface atoms. Sorption experiments at low Cu2+ loading demonstrated an enhanced affinity of Cu2+ to the 7 nm average diameter particles relative to larger sizes, suggesting an abundance of binding sites which stabilize the Jahn-Teller distorted Cu2+ ion that are not as significant on larger sized particles. In addition, FTIR spectra of dried hematite nanominerals are consistent with an increased proportion of bidentate vs. monodentate carbonate surface complexes, representing a change in the dominant type of adsorption complex between the carbonate ion and the smallest and larger hematite particles. FTIR results along with zeta potential measurements lend further support to the hypothesis that the greater affinity of Cu2+ for the smallest particles is due to changes in the nature and reactivity of surface functional groups unique to that size range. The results imply that natural nanomaterials (<10 nm) can control the distribution of toxic metals in a different manner than that expected through consideration of the reactivity of larger particles, over and above the increased surface area.
DE: 0499 New fields (not classifiable under other headings)
SC: Biogeosciences [B]
MN: Fall Meeting 2005