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Title: Electron Mobility and Trapping in Ferrihydrite Nanoparticles

Iron is the most abundant transition metal in the Earth’s crust, and naturally occurring iron oxide minerals play a commanding role in environmental redox reactions. Although iron oxide redox reactions are well-studied, their precise mechanisms are not fully understood. Recent work has shown that these involve electron transfer pathways within the solid, suggesting that overall reaction rates could be dependent upon electron mobility. Initial ultrafast spectroscopy studies of iron oxide nanoparticles sensitized by fluorescein derivatives supported a model for electron mobility based on polaronic hopping of electron charge carriers between iron sites, but the constitutive relationships between hopping mobilities and interfacial charge transfer processes has remained obscured. In this paper, we developed a coarse-grained lattice Monte Carlo model to simulate the collective mobilities and lifetimes of these photoinjected electrons with respect to recombination with adsorbed dye molecules for essential nanophase ferrihydrite and tested predictions made by the simulations using pump–probe spectroscopy. We acquired optical transient absorption spectra as a function of the particle size and under a variety of solution conditions and used cryogenic transmission electron microscopy to determine the aggregation state of the nanoparticles. We observed biphasic electron recombination kinetics over time scales that spanned from picoseconds to microseconds,more » the slower regime of which was fit with a stretched exponential decay function. The recombination rates were weakly affected by the nanoparticle size and aggregation state, suspension pH, and injection of multiple electrons per nanoparticle. Finally, we conclude that electron mobility indeed limits the rate of interfacial electron transfer in these systems, with the slowest processes relating to escape from deep traps, the presence of which outweighs the influence of environmental factors, such as pH-dependent surface charge.« less
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [4] ; ORCiD logo [5] ;  [6]
  1. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry; Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical Sciences Division
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Foundry
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division; Polish Academy of Sciences (PAS), Warsaw (Poland). Inst. of Physical Chemistry
  4. Univ. of Minnesota, Minneapolis, MN (United States). Dept. of Chemistry
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical Sciences Division
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; 0957696; DEC-2016/22/E/ST4/00446
Type:
Accepted Manuscript
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 1; Journal Issue: 4; Journal ID: ISSN 2472-3452
Publisher:
American Chemical Society
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF); The National Science Centre (NCN) (Poland)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; charge separation; electron transfer; ferrihydrite; iron; redox
OSTI Identifier:
1435087

Soltis, Jennifer A., Schwartzberg, Adam M., Zarzycki, Piotr, Penn, R. Lee, Rosso, Kevin M., and Gilbert, Benjamin. Electron Mobility and Trapping in Ferrihydrite Nanoparticles. United States: N. p., Web. doi:10.1021/acsearthspacechem.7b00030.
Soltis, Jennifer A., Schwartzberg, Adam M., Zarzycki, Piotr, Penn, R. Lee, Rosso, Kevin M., & Gilbert, Benjamin. Electron Mobility and Trapping in Ferrihydrite Nanoparticles. United States. doi:10.1021/acsearthspacechem.7b00030.
Soltis, Jennifer A., Schwartzberg, Adam M., Zarzycki, Piotr, Penn, R. Lee, Rosso, Kevin M., and Gilbert, Benjamin. 2017. "Electron Mobility and Trapping in Ferrihydrite Nanoparticles". United States. doi:10.1021/acsearthspacechem.7b00030. https://www.osti.gov/servlets/purl/1435087.
@article{osti_1435087,
title = {Electron Mobility and Trapping in Ferrihydrite Nanoparticles},
author = {Soltis, Jennifer A. and Schwartzberg, Adam M. and Zarzycki, Piotr and Penn, R. Lee and Rosso, Kevin M. and Gilbert, Benjamin},
abstractNote = {Iron is the most abundant transition metal in the Earth’s crust, and naturally occurring iron oxide minerals play a commanding role in environmental redox reactions. Although iron oxide redox reactions are well-studied, their precise mechanisms are not fully understood. Recent work has shown that these involve electron transfer pathways within the solid, suggesting that overall reaction rates could be dependent upon electron mobility. Initial ultrafast spectroscopy studies of iron oxide nanoparticles sensitized by fluorescein derivatives supported a model for electron mobility based on polaronic hopping of electron charge carriers between iron sites, but the constitutive relationships between hopping mobilities and interfacial charge transfer processes has remained obscured. In this paper, we developed a coarse-grained lattice Monte Carlo model to simulate the collective mobilities and lifetimes of these photoinjected electrons with respect to recombination with adsorbed dye molecules for essential nanophase ferrihydrite and tested predictions made by the simulations using pump–probe spectroscopy. We acquired optical transient absorption spectra as a function of the particle size and under a variety of solution conditions and used cryogenic transmission electron microscopy to determine the aggregation state of the nanoparticles. We observed biphasic electron recombination kinetics over time scales that spanned from picoseconds to microseconds, the slower regime of which was fit with a stretched exponential decay function. The recombination rates were weakly affected by the nanoparticle size and aggregation state, suspension pH, and injection of multiple electrons per nanoparticle. Finally, we conclude that electron mobility indeed limits the rate of interfacial electron transfer in these systems, with the slowest processes relating to escape from deep traps, the presence of which outweighs the influence of environmental factors, such as pH-dependent surface charge.},
doi = {10.1021/acsearthspacechem.7b00030},
journal = {ACS Earth and Space Chemistry},
number = 4,
volume = 1,
place = {United States},
year = {2017},
month = {5}
}