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Transformation of Engineered Nanomaterials through the Prism of Silver Sulfidation

Published

Author(s)

Fan Zhang, Andrew J. Allen, Aaron C. Johnston-Peck, Jingyu Liu, John M. Pettibone

Abstract

Structure transformation of engineered nanomaterials (ENMs) often dictates their efficacy, safety, and environmental impact. To address the existing significant knowledge gap regarding the fundamental kinetic rate and extent of ENMs transformation in environment, we have conducted a rigorous and comprehensive structural investigation of the transformation, aggregation, and dissolution behaviors of a PVP-coated silver nanoparticle (AgNP) suspension upon sulfidation in moderately reduced hard water with fluvic acid and dissolved Na2S, using ex situ analytical transmission electron microscopy (TEM) and in situ and ex situ synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS). We found that sulfidation of faceted AgNPs strongly depends on the crystallographic orientation of the facets, with nanometer-scale passivation layers developed on {111} and {100} facets and continuous nucleation and growth along {110} facets. Nanobeam electron diffraction and atomic resolution imaging show that Ag and Ag2S domains possess single- crystalline order. In situ SAXS and WAXS allowed simultaneous determination of the real-time morphological changes of the AgNPs and their extent of the sulfidation. SAXS and WAXS results strongly indicate sulfidation follows first-order reaction kinetics without any aggregation. Aided by their size monodispersity, we established the sulfidation rate constant at ≈ 0.013 min-1 for 68 nm diameter AgNPs. Evaluation of the long-term sulfidation product of the AgNPs under different S/Ag ratios using ex situ SAXS/WAXS reveals the silver mass in the AgNP and transformed Ag/Ag2S NP is preserved and suggests no dissolved Ag+ ion was leached into the solution. The combined nondestructive methodology developed in this work can be readily extended to probe and unfold the structure transformation pathway and the relevant kinetics in a broad range of model ENM systems.
Citation
Nanoscale Advances
Volume
1

Keywords

engineered nanomaterials, structure transformation, silver nanoparticle, sulfidation, in situ
Created January 1, 2019, Updated January 30, 2019