Application of High-Angle Annular Dark Field Scanning Transmission Electron Microscopy, Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectrometry, and Energy-Filtered Transmission Electron Microscopy to the Characterization of Nanoparticles in the Environment
Journal
Environmental Science & Technology
Journal Volume
37
Journal Issue
4
Start Page
786
End Page
791
ISSN
0013-936X
1520-5851
Date Issued
2003-01-16
Author(s)
Ewing, Rodney C.
Abstract
A major challenge to the development of a fundamental understanding of transport and retardation mechanisms of trace metal contaminants (<10 ppm) is their identification and characterization at the nanoscale. Atomic-scale techniques, such as conventional transmission electron microscopy, although powerful, are limited by the extremely small amounts of material that are examined. However, recent advances in electron microscopy provide a number of new analytical techniques that expand its application in environmental studies, particularly those concerning heavy metals on airborne particulates or water-borne colloids. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-energy-dispersive X-ray spectrometry (EDX), and energy-filtered TEM (EFTEM) can be effectively used to identify and characterize nanoparticles. The image contrast in HAADF-STEM is strongly correlated to the atomic mass: heavier elements contribute to brighter contrast. Gold nanocrystals in pyrite and uranium nanocrystals in atmospheric aerosols have been identified by HAADF-STEM and STEM-EDX mapping and subsequently characterized by high-resolution TEM (HRTEM). EFTEM was used to identify U and Fe nanocrystals embedded in an aluminosilicate. A rare, As-bearing nanophase, westerveldite (FeAs), was identified by STEM-EDX and HRTEM. The combined use of these techniques greatly expands the effective application of electron microscopy in environmental studies, especially when applied to metals of very low concentrations. This paper describes examples of how these electron microbeam techniques can be used in combination to characterize a low concentration of heavy metals (a few ppm) on nanoscale particles.
Subjects
Electron Probe Microanalysis
Environmental Monitoring
Metals
Heavy
Microscopy
Electron
Scanning
Particle Size
Trace Elements
Atmospheric aerosols
Energy dispersive spectroscopy
Nanostructured materials
Scanning electron microscopy
Spectrometry
Transmission electron microscopy
heavy metal
nanoparticle
pyrite
trace metal
uranium
analytical method
analytic method
article
crystal
molecular weight
pollutant
pollution transport
scanning transmission electron microscopy
transmission electron microscopy
X ray spectrometry
Retardation mechanism
Environmental engineering
Publisher
American Chemical Society (ACS)
Type
journal article