HR: 09:10h
AN: B31F-05 INVITED    [Abstracts]
TI: Nucleation and Growth of Environmental Nanomaterials at Water-Mineral Interfaces
AU: * Jun, Y
EM: ysjun@seas.wustl.edu
AF: Washington University, One Brookings Drive, Box 1180, Missouri, St. Louis, MO 63130, United States
AU: * Jun, Y
EM: ysjun@seas.wustl.edu
AF: Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, United States
AU: Waychunas, G A
EM: GAWaychunas@lbl.gov
AF: Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, United States
AU: Lee, B
EM: blee@aps.anl.gov
AF: Argonne National Lab, Bldg 433E006, 9700 S.Cass Ave., Argonne, IL 60439, United States
AB: The nucleation and growth of metal oxide nanoparticles and films on mineral surfaces can markedly affect aqueous metal contaminant transport and other surface-controlled reactions. Recently, grazing incidence small angle x-ray scattering (GISAXS) has been used to analyze the size, shape, and distribution of quantum dots and polymers on substrates. However, no work has been attempted thus far using GISAXS for in situ observations of environmental interfacial processes---such as the nucleation, growth, or aggregation of nanoparticles on mineral surfaces. In this work, we devised the first environmental application of GISAXS in aqueous systems and studied the kinetics of nucleation and growth of iron oxide nanoparticles at water-quartz interfaces, using in situ time- resolved simultaneous SAXS/GISAXS technique. The changes in the sizes and shapes of nuclei and the interspacing between nuclei on quartz surfaces are determined as a function of exposure time, iron concentration, ionic strength, and presence of steps at the mineral surfaces. The iron oxide nuclei started to grow close to steps rather than on terraces (diameter 5.3 ± 0.5 nm, height 1.9 ± 0.2 nm, at 4 min reaction time with [Fe³⁺] = 10^-4 M). At 31 min, the nuclei began to coalesce with each other and form larger surface clusters. We found that the surface steps direct the iron oxide nucleation and affect the kinetics of nucleation and growth of iron oxide nanoparticles at water-quartz interfaces. In addition, we were able to distinguish the quantitative contribution between homogeneous and heterogeneous nucleation under different ionic strength and aqueous iron concentrations. For comparison, we generated simulations of the nanoparticle scattering and conducted measurements with AFM and TEM. GISAXS can provide statistically improved morphological information about the early stages of environmental nanoparticle growth compared with AFM and TEM, and allows real-time geochemical kinetic analysis of nanoparticle growth and reactions.
DE: 0330 Geochemical cycles (1030)
DE: 0400 BIOGEOSCIENCES
DE: 0452 Instruments and techniques
DE: 0489 Trace element cycling (4875)
DE: 1094 Instruments and techniques
SC: Biogeosciences [B]
MN: 2007 Fall Meeting