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. Author manuscript; available in PMC: 2015 Nov 13.
Published in final edited form as: Environ Sci Technol. 2015 Jun 24;49(13):8078–8086. doi: 10.1021/acs.est.5b01496

Figure 1.

Figure 1

UV–visible extinction spectra show that NOM improves the colloidal stability of citrate-capped AgNPs more significantly than PVP-capped AgNPs, and that the degree of colloidal stabilization conferred by NOM for both particle types was SRFA < SRHA << PLFA. Spectra of citrate-capped (top) and PVP-capped (bottom) AgNPs in pH 7.5 phosphate buffer were collected after incubation of AgNPs with NOM type specified. Shown are spectra measured at 1–6 (red), 11, 20, 24, 30, and 46 h (violet) after particle redispersion; arrows indicate directions of peak intensity changes. The peak near 390 nm corresponds to extinction by the primary (12-nm-diameter) particle population and peaks at longer wavelengths correspond to aggregates. Agregate settling decreases peak intensities as it removes particles from the probed sample volume. The feature observed around 650 nm is an instrumental artifact. Results were duplicated in independent experiments.