Redox Dynamics of Mixed Metal (Mn, Cr, and Fe) Ultrafine Particles
The impact of particle composition on metal oxidation state, and on changes in oxidation state with simulated atmospheric aging, are investigated experimentally in flame-generated nanoparticles containing Mn, Cr, and Fe. The results demonstrate that the initial fraction of Cr(VI) within
the particles decreases with increasing total metal concentration in the flame. In contrast, the initial Mn oxidation state was only partly controlled by metal loading, suggesting the importance of other factors. Two reaction pathways, one reductive and one oxidative, were found to be operating
simultaneously during simulated atmospheric aging. The oxidative pathway depended upon the presence of simulated sunlight and O3, whereas the reductive pathway occurred in the presence of simulated sunlight alone. The reductive pathway appears to be rapid but transient, allowing the oxidative
pathway to dominate with longer aging times, i.e., greater than ∼8 hours. The presence of Mn within the particles enhanced the importance of the oxidative pathway, leading to more net Cr oxidation during aging, implying that Mn can mediate oxidation by removal of electrons from other particulate
metals.
Document Type: Research Article
Affiliations: 1: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA 2: Department of Mechanical and Aeronautical Engineering, University of California, Davis, California, USA 3: Department of Land, Air & Water Resources, University of California, Davis, California, USA
Publication date: 01 January 2009
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