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Influence of Structural Defects on Biomineralized ZnS Nanoparticle Dissolution: An In-Situ Electron Microscopy Study Jeremy R. Eskelsen, Jie Xu, Michelle Y. Chiu, Ji-Won Moon, Branford O Wilkins, David E Graham, Baohua Gu, and Eric M. Pierce Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04343 • Publication Date (Web): 19 Dec 2017 Downloaded from http://pubs.acs.org on December 22, 2017
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Influence of Structural Defects on Biomineralized ZnS Nanoparticle Dissolution: An In-Situ Electron Microscopy Study
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Jeremy R. Eskelsena, Jie Xub, Michelle Chiua, Ji-Won Moonc, Branford Wilkinsa, David E. Grahamc, Baohua Gua, Eric M. Piercea‡*
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a
Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS 6038, Oak Ridge, TN 37831 b
Geological Sciences, University of Texas at El Paso, 500 West University Ave, El Paso, TX 79968 c
Biosciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS 6038, Oak Ridge, TN 37831
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KEYWORDS1: liquid cell electron microscopy, metal sulfides, nanoparticles, dissolution, structural defect, sphalerite, zinc blende, wurtzite.
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*
Corresponding Author: Eric M. Pierce
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Phone: (865) 574-9968
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Fax: (865) 576-8646
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Email:
[email protected] 20
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This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-publicaccess-plan).
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ABSTRACT: The dissolution of metal sulfides, such as ZnS, is an important biogeochemical
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process affecting fate and transport of trace metals in the environment. However, currently
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studies of in-situ dissolution of metal sulfides and the effects of structural defects on dissolution
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are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized
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via several abiotic and biological pathways. Specifically, the biogenic ZnS nanoparticles were
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produced by an anaerobic, metal-reducing bacterium Thermoanaerobacter sp. X513 in a Zn-
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amended, thiosulfate-containing growth medium either in the presence or absence of silver (Ag),
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whereas the abiogenic ZnS nanoparticles were produced by mixing an aqueous Zn solution with
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either H2S-rich gas or Na2S solution. The size distribution, crystal structure, aggregation
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behavior, and internal defects of the synthesized ZnS nanoparticles were examined using high-
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resolution transmission electron microscopy (TEM) coupled with X-ray energy dispersive
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spectroscopy. The characterization results show that both the biogenic and abiogenic samples
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were dominantly composed of sphalerite. In the absence of Ag, the biogenic ZnS nanoparticles
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were significantly larger (i.e., ~10 nm) than the abiogenic ones (i.e., ~3–5 nm) and contained
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structural defects (e.g., twins and stacking faults). The presence of trace Ag showed a restraining
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effect on the particle size of the biogenic ZnS, resulting in quantum-dot-sized nanoparticles (i.e.,
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~3 nm). In situ dissolution experiments for the synthesized ZnS were conducted with a liquid-
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cell TEM (LCTEM), and the primary factors (i.e., the presence or absence structural defects)
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were evaluated for their effects on the dissolution behavior using the biogenic and abiogenic ZnS
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nanoparticle samples with the largest average particle size. Analysis of the dissolution results
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(i.e., change in particle radius with time) using the Kelvin equation shows that the defect-bearing
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biogenic ZnS nanoparticles (γ = 0.799 J/m2) have a significantly higher surface energy than the
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abiogenic ZnS nanoparticles (γ = 0.277 J/m2). Larger defect-bearing biogenic ZnS nanoparticles 2
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were thus more reactive than the smaller quantum-dot-sized ZnS nanoparticles. These findings
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provide new insight into the factors that affect the dissolution of metal sulfide nanoparticles in
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relevant natural and engineered scenarios, and have important implications for tracking the fate
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and transport of sulfide nanoparticles and associated metal ions in the environment. Moreover,
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our study exemplified the use of an in-situ method (i.e., LCTEM) to investigate nanoparticle
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behavior (e.g., dissolution) in aqueous solutions.
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INTRODUCTION Solid–fluid interfacial reactions that govern the formation of fine-grained nanoparticulate
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metal sulfides have relevance to a range of areas with energy and industrial applications (e.g.,
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sedimentary sulfide ore deposit formation, geochemical cycling of elements in the earth’s crust,
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contaminated site remediation, and semiconductor research).1,
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perspective, the influence that the formation of fine-grained metal sulfides can have on the
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world’s aquatic resources and the geochemical cycling of elements cannot be overstated. For
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example, the bioavailability and transport of metals ions (e.g., Fe, Zn, and Hg) in anoxic
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environments—such as marine ecosystems near hydrothermal vents, stream biofilms, acid mine
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drainage, and the pores of anaerobic sediments—is directly controlled by the production of
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sulfides by sulfate-reducing bacteria.3-9 Sulfate-reducing bacteria are ubiquitous in natural
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systems, where they obtain electrons by oxidizing organic carbon compounds to reduce sulfate to
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sulfide, which is the dominant process for sulfide production in low-temperature (
