We have studied the interaction of engineered and natural NPs, including Ag(0), ZnO, CuO, and 2-line ferrihydrite (2L-Fh), with aqueous solutions, natural organic matter (NOM), and E. coli bacteria, to understand their transformations and reactivity in complex natural environments. Engineered Ag(0) NPs commonly coated by polyvinylpyrrolidone (PVP) are readily transformed to Ag2S and AgCl NPs or aqueous Ag-Cl species when exposed to aqueous solutions containing inorganic sulfide and chloride ions, respectively. Using solubility measurements, XPS, TEM, and high energy synchrotron x-ray total scattering and pair distribution function analysis, we found that PVP-coated Ag(0) NPs transform to Ag2S, forming a core-shell structure, which results in significantly lower release of Ag+ ions and thus lower toxicity to a variety of organisms. ZnO NPs when exposed to sulphide in aqueous solutions forms ZnS NPs; the transformation mechanism is dissolution followed by re-precipitation which differs from that for Ag(0) NP sulfidation. When exposed to inorganic sulphide CuO transforms to CuS, which results in higher release of Cu2+ to solution and higher toxicity. 2L-Fh NPs from acid mine drainage environments are often associated with NOM and high concentrations of Al and Si. We used the same methods as above in addition to 27Al NMR and STXM to study the structure and strain of 2L-Fh NPs and their interactions with Si and Al and found that Al can substitute for Fe3+, whereas no observable substitution of Si into Fh structural sites was found. We have also found that synthetic 2L-Fh (Fe8.2O8.5(OH)7.4�3H2O) transforms to a more ordered form of different stoichiometry (Fe10O14(OH)2�~1H2O) and ultimately to hematite (alpha-Fe-2O3) when exposed to citrate at elevated temperature (175�C). The effects of NOM coatings on the reactivity of 2L-Fh were examined by EXAFS studies of Zn(II)- and U(VI)-reacted 2L-Fh with and without NOM coatings and will be reviewed.

Interaction of engineered and natural nanoparticles (NPs) at solid-water, solid-organic matter, and solid-microbe interfaces

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.