A Model for Nucleation When Nuclei Are Nonstoichiometric: Understanding the Precipitation of Iron Oxyhydroxide Nanoparticles

Journal Article · Thu Aug 25 00:00:00 EDT 2016 · Crystal Growth and Design

DOI:https://doi.org/10.1021/acs.cgd.6b00809· OSTI ID:1474973

Legg, Benjamin A. ^[1]; Zhu, Mengqiang ^[2]; Zhang, Hengzhong ^[3]; Waychunas, Glenn ^[4]; Gilbert, Benjamin ^[4]; Banfield, Jillian F. ^[5]

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1. Univ. of California, Berkeley, CA (United States). Earth and Planetary Science; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Geosciences Division; Univ. of Wyoming, Laramie, WY (United States). Ecosystem Science and Management
3. Univ. of California, Berkeley, CA (United States). Earth and Planetary Science; Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China)
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Geosciences Division
5. Univ. of California, Berkeley, CA (United States). Earth and Planetary Science

Despite years of study, quantitative models for the nucleation and growth of metal oxyhydroxide nanoparticles from aqueous solution have remained elusive. The problem is complicated by surface adsorption, which causes the stoichiometry of the nucleus to differ from that of the bulk precipitate and causes the surface tension of the precipitate-water interface to depend upon solution chemistry. We present a variation of classical nucleation theory that can accommodate surface adsorption, and apply it to understand the nucleation of β-FeOOH (akaganeite) nanoparticles from aqueous FeCl₃ solutions. We use small-angle X-ray scattering (SAXS) to quantify nucleation rates over a range of concentrations (5-200 mM FeCl₃) and temperatures (47-80°C), then apply our model to estimate the critical nucleus size and surface tension at each condition. The surface tension varies from 0.07 J/m² in 200 mM solutions to 0.16 J/m² in 5 mM solutions. This behavior indicates that the nuclei contain an excess of Cl^- and H⁺ relative to the ideal FeOOH stoichiometry, and the coadsorption of Cl^- and H⁺ is critical for reducing surface tension into a range where classical nucleation pathways can operate. Furthermore, we find that the surface tension can be roughly estimated from aqueous solubility data alone, which may help to understand systems where surface tension data is unavailable.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 1474973
• Journal Information: Crystal Growth and Design, Vol. 16, Issue 10; Related Information: © 2016 American Chemical Society.; ISSN 1528-7483
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY