Elucidating the Role of AgCl in the Nucleation and Growth of Silver Nanoparticles in Ethylene Glycol

Transcription

1 Supplementary Data and Descriptions Elucidating the Role of AgCl in the Nucleation and Growth of Silver Nanoparticles in Ethylene Glycol Suyue Chen, Jesse L. Carey III, David R. Whitcomb, Philippe Bühlmann, and R. Lee Penn* Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States Carestream Health, Inc., 1 Imation Way, Oakdale, Minnesota 55128, United States * rleepenn@umn.edu Potentiometric measurement of Ag + concentration and K sp measurement for AgCl in ethylene glycol The Ag + concentration in ethylene glycol solution was measured using potentiometry, and the apparent K sp of AgCl in ethylene glycol was measured by titration (Figure S1). Additional measurements were performed to determine whether the PVP concentration influenced the K sp of AgCl in ethylene glycol, and the results demonstrate that the K sp does not significantly change with PVP concentration (Table S1). Figure S1. Plot of (a) potential between Ag wire and free flow electrode vs. log 10 a(ag + ) in ethylene glycol without PVP for the calibration of potentiometric measurements, and (b) log 10 a(ag + ) vs. the difference between the concentrations of NaCl and AgNO 3 resulting from the addition of the ethylene glycol solution containing 5 mm NaCl into the ethylene glycol solution containing 0.1 mm AgNO 3, both without PVP. The K sp of AgCl is determined by (b) to be M 2. 1 / 9

2 Table S1. Apparent K sp of AgCl measured in ethylene glycol with different concentrations of PVP* c(pvp) (mm) K sp (M 2 ) log 10 (K sp /M 2 ) * PVP concentrations are defined as the concentration of monomers in solution with a standard deviation of 0.02 based on triplicate measurements 2 / 9

3 Product Composition As discussed in the main paper and shown in Figure 3, the reaction produced both isolated particles, which were identified as Ag NPs, and head-tail particles, which were identified as Ag-AgCl NPs. The supporting observations are: 1) The typical reaction produces both Ag and AgCl crystals, and the Ag to AgCl ratio increases as a function of reaction time. Figure S2 shows the selective area electron diffraction (SEAD) patterns from samples captured at different time intervals. The general trend is that the product contains predominantly AgCl crystals with a small amount of Ag at the early stages, and the product contains only Ag crystals, with no detectable AgCl observed after 45 min. 2) Head-tail particles are composed of Ag and AgCl crystals. SAED patterns from areas with predominately head-tail particles (e.g. Figure S3 a) show comparable intensities for the rings consistent with diffraction by the Ag and AgCl crystals. 3) Isolated particles contain only Ag crystals. When the reaction product consists predominately of isolated particles, the X-ray powder diffraction (Figure 2) and SAED (Figure S2) show signal from Ag only. 4) The head-tail particles are composed of Ag heads and AgCl tails, which appear darker and lighter, respectively, in the electron micrographs (figure S3a). The energy dispersive X-ray spectra exhibit a strong Ag peak and a weak Cl peak (Ag to Cl atom ratio 93:7) when the electron beam is focused as in (b) and comparable peaks from Ag and Cl (atom ratio 68:32) when focused as in (c). The theoretical 1:0 and 1:1 Ag to Cl atom ratios for Ag crystal and AgCl are not observed because it is virtually impossible to obtain X-rays solely from the head or tail area using the microscope employed for this work. a, 3 min Ag {311} b, 12 min Ag {311} c, 45 min Ag {220} Ag {220} Ag {200} Ag {111} Ag {200} Ag {111} Ag {311} Ag {220} Ag {200} Ag {111} d, 3 h AgCl {111} AgCl {200} AgCl {220} AgCl {111} AgCl {200} AgCl {220} e, 6 h f, 12 h g, 18 h h, 24 h 3 nm -1 Figure S2. Representative SAED patterns from samples taken at (a) 3 min, (b) 12 min, (c) 45 min, (d) 3 h, (e) 6 h, (f) 12 h, (g) 18 h, and (h) 24 h from the typical Ag NP synthesis (scale bars represent 3 nm -1 ). The decrease of AgCl diffraction intensity is consistent with the decrease of head-tail Ag-AgCl NPs. 3 / 9

4 a b c 50 nm Figure S3. TEM images of a representative head-tail nanoparticle: (a) the whole particle, and when the electron beam was condensed on an area dominated by (b) the head or (c) the tail (scale bars represent 50 nm). The energy dispersive X-ray spectrum exhibits a strong Ag peak and a weak Cl peak (Ag to Cl atom ratio 93:7) when the electron beam is focused as in (b), and comparable peaks from the two elements (Ag to Cl atom ratio 68:32) when focused as in (c). 4 / 9

5 Reaction kinetics using higher initial Ag + and Cl - concentrations Using the typical reaction conditions (c 0 (Ag + ) = c 0 (Cl - ) = 0.05 mm), the Ag + concentration drops below K sp /c 0 (Cl - ) = M after 45 min reaction time, suggesting that the AgCl completely dissolved in ethylene glycol thereafter. Reactions with higher initial Ag + and Cl - concentrations result in quicker drops in [Ag + ], as measured by Ag + activity (Figure S4), as compared to the typical reaction. Mixtures of Ag and AgCl crystals are observed throughout the 24 h reaction time (Figure S5). Most Ag-AgCl attached structures do not have one-on-one attachment between Ag and AgCl particles of similar sizes, which is different from those observed from the typical reaction. For reaction conditions with c 0 (Ag + ) and c 0 (Cl - ) of 0.5 mm or 5 mm, the K sp /c 0 (Cl - ) values are equal to or M, respectively. Since the Ag + concentration detection limit in this experiment is around M, we could not provide conclusive data to demonstrate that a(ag + ) does not drop below the value predicted by K sp. Figure S4. Plot of log 10 a(ag + ) vs. reaction time in reaction mixtures during typical synthesis and similar reactions with higher initial Ag + and Cl - concentration: c 0 (Ag + ) = c 0 (Cl - ) = 0.05 mm, 0.5 mm or 5 mm. Error bars represent standard deviations. 5 / 9

6 a1, 12 min a2, 3h a3, 12 h a4, 24 h b1, 12 min b2, 3 h b3, 12 h b4, 24 h c1, 12 min c2, 3 h c3, 12 h c4, 24 h d1, 12 min d2, 3 h d3, 12 h d4, 24 h Figure S5. Representative TEM images and SAED patterns of products sampled at (1) 12 min, (2) 3 h, (3) 12 h, (4) 24 h from reactions using initial Ag + and Cl - concentrations of 0.5 mm or 5 mm: (a1-a4, b1-b4) 0.5 mm for both Ag + and Cl -, and (c1-c4, d1-d4) 5 mm for both Ag + and Cl -. Scale bars represent 50 nm in TEM images and 3 nm -1 in SAED patterns. 6 / 9

7 Size distribution of nanoparticles from polyol synthesis: The typical reaction produces Ag NPs with bimodal size distributions (Figure S6). The size distributions of the >5 nm Ag NPs from the typical reaction are similar to those of the Ag heads in the Ag-AgCl NPs (Figure S7), which supports the hypothesis that Ag NPs originate from Ag-AgCl intermediate NPs. However, the particles sizes are sensitive to the ratio between Ag + and Cl -. The particle size distributions are broader and less consistent throughout the course of reaction when using the 1:2 or 2:1 Ag + to Cl - ratio (Figure S8). Figure S6. Histograms showing the percent of particles as a function of increasing diameter. The bimodal size distributions are observed at all stages of the reaction. The open histograms are magnified versions of the closed histograms over the diameter range of 5 to 35 nm, and the number in the upper right corner of each panel is the average diameter of the > 5 nm Ag NPs and the Ag heads in the Ag-AgCl NPs. 7 / 9

8 Figure S7. Histograms showing the similar size distributions of isolated Ag NPs, Ag heads, and AgCl tails in Ag-AgCl NPs in samples from different stages of the typical reaction (0.05 mm initial Ag + and Cl - concentrations. Note that the y-axes are scaled differently to achieve comparable peak heights. Figure S8. Histograms of percent particles residing in each diameter range. These histograms show the size distributions of the isolated Ag NPs and Ag heads of the Ag-AgCl NPs from syntheses using 0.05 mm Ag + and (a) mm Cl - or (b) 0.10 mm Cl -. The open and closed columns account for Ag heads in Ag-AgCl structures and isolated Ag NPs, representatively. 8 / 9

9 Microstructures of Ag nanocrystals from typical synthesis (0.05 mm initial Ag + and Cl - concentrations) In Figure S9, bright-field (figure S9a) and dark-field TEM images using different diffraction beams from the Ag {111} and {200} planes (figure S9 b-d) were taken from the same sample area. Each crystal domain strongly diffracts electrons into specific spots on each diffraction ring; domains with parallel orientations have strong diffraction into the same direction while those with different orientations may not. Therefore, the different contrast among crystal domains in (a) and the alternating brightness among crystal domains in (b-d) demonstrate that crystal domains within the same particle have varied relative orientations. a b c d 50 nm Figure S9. Bright-field (a) and dark-field (b-d) TEM images of the same group of particles (scale bars represent 50 nm). Image (b-d) were collected using different diffracted beams; the diffraction contrast facilitates the microstructure classification of the particles. 9 / 9