Nanotechnology and the Environment - American Chemical Society

Chapter 11 Nanoscale Heavy Metal Phases on Atmospheric and Groundwater Colloids 1

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Satoshi Utsunomiya, Kathy Traexler, LuMin Wang, and RodneyC.Ewing 1,2

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Nuclear Engineering and Radiological Science, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109-2104 Geological Sciences, University of Michigan, 2534C.C.Little Building, 425 East University, Ann Arbor, MI 48109 ([email protected])

Downloaded by TUFTS UNIV on October 29, 2017 | http://pubs.acs.org Publication Date: December 14, 2004 | doi: 10.1021/bk-2005-0890.ch011

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Introduction Nano-particles are ubiquitous in the ambient environments; atmosphere and groundwater. The effects offine-to ultra-fine particles in atmosphere on human being (1,2) and global climate have been increasing the importance recently (3). In groundwater, fine-grain particles (1umare characterized well by some analytical methods using X-ray and ion microprobe, a transmission electron microscopy (TEM) is the best technique to characterized nano-particles (< 1um) in environments. However there is still a challenge to investigate trace element phases, which frequently occur in dispersed nano-particles, because the contrast in TEM is usually not correlated to the compositional variety. The recently developed, scanning TEM with high-angle annular detector (HAADF-STEM), allows a compositional imaging in near atomic level, in which the contrast is related to atomic mass and the specimen thickness (6). In this study, the atmospheric particulates from Detroit urban area and the colloids from Nevada Test Site.

© 2005 American Chemical Society

Karn et al.; Nanotechnology and the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

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Karn et al.; Nanotechnology and the Environment ACS Symposium Series; American Chemical Society: Washington, DC, 2004. 2+x

Figure 1. The occurrence of uranium by HAADF-STEM and HRTEM image of U-bearing nanoparticles encapsulated in a "cage" of carbonaceous fulleroid. The particles were subsequently identified as uraninite, U0 .



Figure 2, Ground water colloids from Nevada test site. Left picture is a HAADF-STEM image with elemental map of Co-bearing colloids. Inset is the SAED pattern. Right picture shows a Cs-bearing particle.


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Experimental method


The samples were characterized using Field Emission SEM (FE-SEM: Philips XL-30), and high resolution TEM (HRTEM: JEOL 2010F). Nano-scale elemental mapping on nanocrystals containing heavy metals was conducted using HAADF-STEM with EDX mapping system (Emispec, ES Vision ver. 4.0) (7). TEM specimens were prepared by dispersing the samples from the filters onto holey carbon grids. Before STEM analysis, the TEM specimen holder was cleaned with plasma (Fischione Model CI020) to minimize a contamination. A drift correction acquisition system was used for the STEM-EDX mapping.

Results and discussion In Detroit aerosol sample, uranium nanocrystals were detected by HAADFSTEM and subsequently the phase was identified as uraninite, U 0 . In addition, the uraninite nanocrystals were often encapsulated by well-crystalline carbon forming "cage-like" structure. The structure possibly retards the uraninite from alteration in the ambient atmosphere (5). In the same sample, trace elements; Pb, As, La, Ce, Sr, Ti, Zn, Cr, Se, Sn, Y , Zr, Au, and Ag, were detected and the elemental distributions were directly mapped in nano-scale. The structure of the particles bearing Pb, Sr, Ti, Zn, and Au were successfully determined by the diffraction pattern. The size of most particles bearing trace elements detected in this study was distributed within the range of 0.01-1.0 μπι, which has the longest residence time, -100 days, in any particle sizes. In the groundwater sample from Nevada Test Site, the three important potentially radionuclide elements, Co, Cs, and Eu were identified. Cobalt occurred in awaruite (Ni Fe) structure with Mo and Cr. The Cs-bearing phase consisted of Cs, Ο and U possibly forming a Cs-uranate. An Eu-bearing phase was monazite. The three elements were present, not as absorbed species, but as incorporated in the minerals structure. 2

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References 1. Pope, C. Α., III; Burnett, R. T.; Thun, M . J.; Galle, Ε. Ε.; Krewski, D., Ito, K.; Thurston. G. D. J. Am.Med.Assoc. 2002, 287, 1132-1142. 2. Oberdörster, G. Phil. Trans. R. Soc. Lond. A 2000, 358, 2710-2740.

3. Andreae, M . O. Nature 1996, 380, 389-390.


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4. McCarthy, J. F.; Zachara, J. M . Environ. Sci. Technol. 1989, 23, 496-502. 5. Kersting A, B. et al. Nature 1999, 397, 56-59. 6. Pennycook, S. J.; Jesson, D. E. Phys. Rev. Lett. 1990, 64, 938-941. 7. Utsunomiya, S.; Ewing, R. C. Environ. Sci.Technol.2003, 37, 786-791. 8. Utsunomiya, S.; Jensen, Κ. Α.; Keeler, G. J.; Ewing, R. C. Environ. Sci. Technol. 003, 36, 4943-4947.


Nanotechnology and the Environment - American Chemical Society

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