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Water-driven structure transformation in nanoparticles
at room temperature – Supplementary Information
Hengzhong Zhang, Benjamin Gilbert, Feng Huang, Jillian F. Banfield.
The size of ZnS nanoparticles:
To determine the average size of the ZnS nanoparticles used in this work (both before
and after the addition of water) we used two approaches: the position of the UV-vis
absorption onset; and direct high-resolution transmission electron microscopy (TEM)
imaging. First, we sought an empirical relationship between the average size of ZnS
nanoparticles and the onset of UV absorption, compiled from a review of the literature
(Suppl. Fig. 1, below). We observed that when particle size had been measured by
TEM, a good correlation is obtained between particle size and absorption onset (red
line). When XRD was used for size determination, no sensible correlation is obtained
(blue points) because the strain contribution to peak broadening cannot be neglected. To
estimate the size of the nanoparticles used in this work, we compare our UV-vis data
with the reliable TEM-based data, obtaining an estimated average size of 2.8 +/- 0.2 nm.
We also performed HRTEM imaging of nanocrystalline ZnS, deposited onto grids for
analysis. Representative images are given in Suppl. Fig. 2. HRTEM analysis of the
nanoparticles gave an average size of 3.0 +/- 0.3 nm based on the sizes of 20-30
individual ZnS nanoparticles, in reasonable agreement with the UV-vis approach. No
size change was observed following the addition of water, despite the dramatic
structural change.
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Supplementary Figure 1. The empirical relationship between the average size of ZnS
nanoparticles and the onset of UV absorption, compiled from a review of the literature
(red and blue points). We digitized the UV-vis spectra from reports in the literature,
choosing only those in which the full threshold regions of the UV-vis spectrum was
displayed, and in which the average nanoparticle size was determined by independent
means, either with TEM [refs. S1-S3] or XRD [refs. S4-S6]. We plot the point of
inflection in the UV-vis spectrum vs. particle diameter, obtaining a reasonably
continuous curve only when the average particle size was determined by TEM. Hence,
this subset of the compiled data (dashed red line) was used to estimate the average size
distribution of the ZnS nanoparticles studied in this work. The position of the absorption
onset measured in this is shown as a black point, plus error bars. The resulting estimated
average size was 2.8 +/- 0.2 nm.
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Supplementary Figure 2. Representative high resolution TEM of ZnS nanoparticles
deposited from methanol, a, before and b, after water binding. Direct images of
individual nanoparticles in these and other images were used for size determination.
Scale bar = 10 nm.
Supplementary references:
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absorption fine structure analysis of ZnS nanocrystallites in N,Ndimethylformamide. An effect of counterions on the microscopic structure of a
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S4. Vogel, W., Borse, P. H., Deshmukh, N. & Kulkarni, S. K. Structure and stability of
monodisperse 1.4-nm ZnS particles stabilized by mercaptoethanol. Langmuir 16,
2032-2037 (2000).
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S5. van Dijken, A., Janssen, A. H., Smitsmans, M. H. P., Vanmaekelbergh, D. &
Meijerink, A. Size-selective photoetching of nanocrystalline semiconductor
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