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SUMMARY:IMX Seminar Series - Nanoscale mechanism of uranium reduction by m
 agnetite
DTSTART:20231120T131500
DTEND:20231120T141500
DTSTAMP:20260916T194624Z
UID:edc9bd50ce4c70d200169fd7cab2fb1fa164bcdb057bf011999aa302
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Rizlan Bernier-Latmani\, EPFL\nUranium (U) is a ubiquito
 us element in the Earth’s crust and its biogeochemical behavior is large
 ly constrained by its redox transformation from soluble uranium hexavalent
  species (U(VI)) to sparingly soluble tetravalent species ((U(IV)). U(VI) 
 reduction by mineral phases has been shown to produce crystalline U in the
  form of U(IV)O2\, but also to form persistent pentavalent U (U(V)). Magne
 tite (Fe3O4) is an Fe(II)-bearing iron oxide and experimental studies have
  shown that the co-precipitation of U(VI) and magnetite resulted in the fo
 rmation of a stable U(V) coordination in the iron oxide mineral phases [1]
 . A study [2] reported the formation of single U oxide nanocrystals (1-5 n
 m) followed by the formation of nanowires that extended away the magnetite
  surface. Over time\, the nanowires collapsed into ordered UO2 nanocluster
 s. Numerous questions arise from the transient formation of uranium oxide 
 nanoparticle nanowires. The most salient are: (a) why do these nanowires f
 orm? (b) why do they persist? and (c) why do they collapse? The current hy
 pothesis is that the nanoparticles harbor pentavalent uranium (as mixed va
 lence uranium oxides) that is slowly reduced further to tetravalent uraniu
 m. Thus\, the formation and persistence of nanowires is linked to that of 
 U(V). Here\, we present O K-edge and U N-edge electron energy loss spectro
 scopy spectra from individual uranium oxide nanoparticles within the nanow
 ires in order to characterize the valence state of individual nanocrystals
  by comparing their fine structure to references mixed valence oxides\nmea
 sured under the same conditions.\nThe mechanism that emerges at the scale 
 of individual nanoparticles (1-5 nm) is the initial reduction of U(VI) to 
 U(V) at the magnetite surface\, producing mixed valence oxides UO2+x that 
 self-assemble into nanowires. These nanowires are stable as long as no fur
 ther reduction occurs but reduction to UO2 results in the collapse of nano
 wires into nanoclusters. The reduction of U(VI) by magnetite represents an
  example of heterogeneous reductive precipitation that\, due to the proper
 ties of uranium\, can be resolved at the near atomic scale and reveal the 
 complexity of electron transfer from mineral to metal.\n[1] Pidchenko et a
 l. Environ. Sci. Technol.\, 51\, 2217–2225 (2017).\n[2] Pan et al.\, Nat
 . Commun.\, 11\, 4001 (2020)\n\nBio: Rizlan Bernier-Latmani is a geo-micro
 biologist with interests in geochemical and microbial processes in the env
 ironment\, particularly microbially-mediated transformations in subsurface
  environments and in the mammalian gut. She studied in the United States a
 nd came to Switzerland as a tenure-track assistant professor in 2005. She 
 is now a full professor in the Environmental Engineering Institute. Her wo
 rk spans molecular-scale mechanistic understanding to the interrogation of
  field-scale processes and makes use of a large array of tools ranging fro
 m spectroscopy and microscopy to meta-omics and sampling soil and water in
  remote areas. Today\, she will talk about her work on uranium reduction b
 y the iron oxide magnetite and its surprising mechanism.\n 
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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