Supporting Information Synthesis and Purification of Silver Nanowires ...
Supporting Information Synthesis and Purification of Silver Nanowires to Make Conducting Films with a Transmittance of 99% Bo Li, Shengrong Ye, Ian E. Stewart, Samuel Alvarez, Benjamin J. Wiley*
Materials. Ethylene glycol was purchased from J.T. Baker. Polyvinylpyrrolidone (MW = 130K, 55K or 29K, PVP), Fe(NO3)3, NaCl, AgNO3, ethyl acetate, pentyl acetate, and toluene were purchased from Sigma-Aldrich. Ethyl cellulose (Standard 300) was
donated from the Dow Chemical Company. Ethanol and isopropanol were purchased from VWR. All chemicals were used without further purification.
Synthesis of Ag Nanowires. Three stock solutions were prepared: (A) 220.0 mM NaBr, (B) 210.0 mM NaCl, (C) 505.0 mM PVP in ethylene glycol (EG, J.T. Baker). EG (7.7 mL), solution A (0.1 mL), solution B (0.2 mL), solution C (1.0 mL), and fresh AgNO3 (265.0 mM, 1.0 mL) in EG were then added into a 50 ml flask placed in an oil bath at room temperature. After vigorous magnetic stirring for 30 min, the flask was then slowly heated to 170 oC in 15 min. Nitrogen gas was bubbled through the reaction during heating. Thereafter, the flask was stoppered and allowed to react for 1 hr without stirring. Upon the completion of the reaction, the flask was removed from the oil bath and 30 mL of water was added. The amount of solution A that is added can be varied to control the diameter of NWs.
Purification of Ag Nanowires by Selective Precipitation. The light green reaction mixture was first diluted with 30 mL deionized (DI) water. Acetone (80-160 ml, or 2 – 4 × by volume) was slowly added into this solution with gentle mixing. During the mixing, the dispersion turned pale yellow, which indicated that the NWs aggregated. At this point no additional acetone was added, and the aggregates settled to the bottom of the cylinder within 10 minutes, leaving the particles suspended in solution. The supernatant was removed by a pipette. Subsequently, the aggregated NWs were redispersed in 20 mL DI water containing 0.5 wt % PVP, and then precipitated by 40-80 mL acetone. The aggregates formed and settled within 10 min, and the supernatant was again removed. NWs with high purity can be obtained after this procedure was repeated 2-4 times. Finally, the NWs were dispersed in ethyl alcohol and collected by centrifugation to remove the extra PVP.
Instrumentation and Characterization. To prepare the samples for SEM (FEI XL30 SEM-FEG), a small chip of a silicon (Si) wafer (5 mm × 5 mm) was cut for each sample, placed on a piece of double sided tape in a Petri dish, and 5 μL of the suspension of Ag products dispersed in ethanol was placed on a Si chip. To prepare the AgCl/AgBr samples for TEM (FEI Tecnai G² Twin), the copper grid was placed on top of a Whatman filter, and 3 μL of the solution (without heating) was pipetted onto the grid. The solution was absorbed into the filter paper underneath the grid, leaving the majority of the precipitation on the grid. Optical microscopy images were taken with an
Olympus BX51 microscope. UV-Vis absorbance spectra were measured at room temperature using a UV-Vis spectrophotometer (Cary 6000i). The mass of the products was determined by an atomic absorption spectrometer (AAS).
Preparation of Transparent Conducting Nanowire Films. Transparent conducting films were made in a manner similar to our previous reports.1,2 The ink formulation was made by dissolving ethyl cellulose (0.03 g) in ethyl alcohol (2.70 g), before addition of ethyl acetate (0.24 g), pentyl acetate (0.5 g), isopropanol (0.5 g), and toluene (1.14 g). After the Ag NWs were washed with ethyl alcohol, the ink formulation (1 mL) was added to the Ag NWs, and this suspension was vortexed. The dispersion was centrifuged at a low speed (~500 rpm) so that a well-dispersed Ag NW ink could be pipetted from the solution. To make conductive films, glass microscope slides (purchased from VWR, 25 mm × 75 mm × 1 mm ) were placed onto a clipboard to hold them down while the NW ink (50 µL) was pipetted in a line at the top of the slide. A Meyer rod (Gardco) was then quickly (< 1 second) pulled down over the NW ink by hand, spreading it across the glass into a thin, uniform film. Different densities of NWs on the surface of the substrate were obtained by varying the concentration of the NWs in the ink. The slides coated with Ag NWs were dried in air for 10 minutes at 80 oC. Once the slides returned to room temperature, they were dipped in a mixture of ethyl alcohol and acetone (v/v = 4:1) for 10 seconds to remove the organic material and dried under N2 gas. Finally, the slides were put into an 80 oC oven in air for 30 minutes. The transmittance and sheet
resistance of each NW film was measured using a UV-Vis spectrophotometer (Cary 6000i) and a four-point probe (Signatone SP4-50045TBS). Each data point in Figure 5 is the average of 5 measurements. REFERENCES (1) Rathmell, A. R.; Wiley, B. J. Adv. Mater. 2011, 23, 4798. (2) Rathmell, A. R.; Nguyen M.; Chi M. F.; Wiley, B. J. Nano Lett. 2012, 12, 3193.
Figure S1. (A) Length and (B) diameter histograms of the Ag NWs obtained from the reaction with 2.2 mM NaBr after purification.
Figure S2. SEM images of Ag NWs obtained from the reaction with 0 mM NaBr before (A) and after (B) purification. (C&D) Histograms showing the distribution of NW lengths and diameters after purification.
Figure S3. (A) SEM images of Ag NWs obtained from the reaction with 1.1 mM NaBr before (A) and after (B) purification. (C&D) Histograms showing the distribution of NW lengths and diameters after purification.
Figure S4. Dark field optical microscope image and SEM image of unpurified reaction products obtained from the reaction with 8.8 mM NaBr.
Table S1. The effect of [Br-] on the products. [Br] (mM)
0
1.1
2.2
Mass of Ag ion (mg)
28.6
28.6
28.6
Mass of products (Ag nanoparticles
22.2
20.2
16.8
Conversion of Ag+ to Ag (%)
77.7
70.5
58.6
Mass of Ag NWs
15.0
12.3
9.7
Percentage of Ag NWs in products
68.2
60.9
57.7
D (nm)
72 ± 15
36 ± 7
20 ± 2
L (m)
63 ± 17
48 ± 15
40 ± 13
Numer of NWs (×1012)
5.6
24.0
73.5
and NWs) (mg)
(%)
Figure S5. Camera pictures of the reaction flasks taken after mixing the indicated chemicals before heating.
Figure S6. Corresponding extinction spectra of the solutions in Figure S5.
Figure S7. TEM images of (A) AgCl, (B) AgBr, (C) AgCl and AgBr nanoparticles present in the solutions in Figure S5. (B) Histograms showing the distribution of the diameters of the (D) AgCl, (E) AgBr, (F) AgCl/AgBr nanoparticles.
Figure S8. (A) SEM image of purified reaction product obtained with 55K PVP and 2.2 mM NaBr, keeping the other reaction conditions the same. (B) Histograms showing the distribution of NW diameters after purification. (C) SEM image of the purified reaction product obtained with 29K PVP and 2.2 mM NaBr, keeping the other reaction conditions the same.
Figure S9. (A&B) SEM images of purified reaction product obtained with 55K PVP and 2.75 mM NaBr, keeping the other reaction conditions the same. (B) Histogram of the diameter of the NWs.
Materials. Ethylene glycol was purchased from J.T. Baker. Polyvinylpyrrolidone (MW = 130K, 55K or 29K, PVP), Fe(NO3)3, NaCl, AgNO3, ethyl acetate, pentyl acetate, and toluene were purchased from Sigma-Aldrich. Ethyl cellulose (Standard 300) was
donated from the Dow Chemical Company. Ethanol and isopropanol were purchased from VWR. All chemicals were used without further purification.
Synthesis of Ag Nanowires. Three stock solutions were prepared: (A) 220.0 mM NaBr, (B) 210.0 mM NaCl, (C) 505.0 mM PVP in ethylene glycol (EG, J.T. Baker). EG (7.7 mL), solution A (0.1 mL), solution B (0.2 mL), solution C (1.0 mL), and fresh AgNO3 (265.0 mM, 1.0 mL) in EG were then added into a 50 ml flask placed in an oil bath at room temperature. After vigorous magnetic stirring for 30 min, the flask was then slowly heated to 170 oC in 15 min. Nitrogen gas was bubbled through the reaction during heating. Thereafter, the flask was stoppered and allowed to react for 1 hr without stirring. Upon the completion of the reaction, the flask was removed from the oil bath and 30 mL of water was added. The amount of solution A that is added can be varied to control the diameter of NWs.
Purification of Ag Nanowires by Selective Precipitation. The light green reaction mixture was first diluted with 30 mL deionized (DI) water. Acetone (80-160 ml, or 2 – 4 × by volume) was slowly added into this solution with gentle mixing. During the mixing, the dispersion turned pale yellow, which indicated that the NWs aggregated. At this point no additional acetone was added, and the aggregates settled to the bottom of the cylinder within 10 minutes, leaving the particles suspended in solution. The supernatant was removed by a pipette. Subsequently, the aggregated NWs were redispersed in 20 mL DI water containing 0.5 wt % PVP, and then precipitated by 40-80 mL acetone. The aggregates formed and settled within 10 min, and the supernatant was again removed. NWs with high purity can be obtained after this procedure was repeated 2-4 times. Finally, the NWs were dispersed in ethyl alcohol and collected by centrifugation to remove the extra PVP.
Instrumentation and Characterization. To prepare the samples for SEM (FEI XL30 SEM-FEG), a small chip of a silicon (Si) wafer (5 mm × 5 mm) was cut for each sample, placed on a piece of double sided tape in a Petri dish, and 5 μL of the suspension of Ag products dispersed in ethanol was placed on a Si chip. To prepare the AgCl/AgBr samples for TEM (FEI Tecnai G² Twin), the copper grid was placed on top of a Whatman filter, and 3 μL of the solution (without heating) was pipetted onto the grid. The solution was absorbed into the filter paper underneath the grid, leaving the majority of the precipitation on the grid. Optical microscopy images were taken with an
Olympus BX51 microscope. UV-Vis absorbance spectra were measured at room temperature using a UV-Vis spectrophotometer (Cary 6000i). The mass of the products was determined by an atomic absorption spectrometer (AAS).
Preparation of Transparent Conducting Nanowire Films. Transparent conducting films were made in a manner similar to our previous reports.1,2 The ink formulation was made by dissolving ethyl cellulose (0.03 g) in ethyl alcohol (2.70 g), before addition of ethyl acetate (0.24 g), pentyl acetate (0.5 g), isopropanol (0.5 g), and toluene (1.14 g). After the Ag NWs were washed with ethyl alcohol, the ink formulation (1 mL) was added to the Ag NWs, and this suspension was vortexed. The dispersion was centrifuged at a low speed (~500 rpm) so that a well-dispersed Ag NW ink could be pipetted from the solution. To make conductive films, glass microscope slides (purchased from VWR, 25 mm × 75 mm × 1 mm ) were placed onto a clipboard to hold them down while the NW ink (50 µL) was pipetted in a line at the top of the slide. A Meyer rod (Gardco) was then quickly (< 1 second) pulled down over the NW ink by hand, spreading it across the glass into a thin, uniform film. Different densities of NWs on the surface of the substrate were obtained by varying the concentration of the NWs in the ink. The slides coated with Ag NWs were dried in air for 10 minutes at 80 oC. Once the slides returned to room temperature, they were dipped in a mixture of ethyl alcohol and acetone (v/v = 4:1) for 10 seconds to remove the organic material and dried under N2 gas. Finally, the slides were put into an 80 oC oven in air for 30 minutes. The transmittance and sheet
resistance of each NW film was measured using a UV-Vis spectrophotometer (Cary 6000i) and a four-point probe (Signatone SP4-50045TBS). Each data point in Figure 5 is the average of 5 measurements. REFERENCES (1) Rathmell, A. R.; Wiley, B. J. Adv. Mater. 2011, 23, 4798. (2) Rathmell, A. R.; Nguyen M.; Chi M. F.; Wiley, B. J. Nano Lett. 2012, 12, 3193.
Figure S1. (A) Length and (B) diameter histograms of the Ag NWs obtained from the reaction with 2.2 mM NaBr after purification.
Figure S2. SEM images of Ag NWs obtained from the reaction with 0 mM NaBr before (A) and after (B) purification. (C&D) Histograms showing the distribution of NW lengths and diameters after purification.
Figure S3. (A) SEM images of Ag NWs obtained from the reaction with 1.1 mM NaBr before (A) and after (B) purification. (C&D) Histograms showing the distribution of NW lengths and diameters after purification.
Figure S4. Dark field optical microscope image and SEM image of unpurified reaction products obtained from the reaction with 8.8 mM NaBr.
Table S1. The effect of [Br-] on the products. [Br] (mM)
0
1.1
2.2
Mass of Ag ion (mg)
28.6
28.6
28.6
Mass of products (Ag nanoparticles
22.2
20.2
16.8
Conversion of Ag+ to Ag (%)
77.7
70.5
58.6
Mass of Ag NWs
15.0
12.3
9.7
Percentage of Ag NWs in products
68.2
60.9
57.7
D (nm)
72 ± 15
36 ± 7
20 ± 2
L (m)
63 ± 17
48 ± 15
40 ± 13
Numer of NWs (×1012)
5.6
24.0
73.5
and NWs) (mg)
(%)
Figure S5. Camera pictures of the reaction flasks taken after mixing the indicated chemicals before heating.
Figure S6. Corresponding extinction spectra of the solutions in Figure S5.
Figure S7. TEM images of (A) AgCl, (B) AgBr, (C) AgCl and AgBr nanoparticles present in the solutions in Figure S5. (B) Histograms showing the distribution of the diameters of the (D) AgCl, (E) AgBr, (F) AgCl/AgBr nanoparticles.
Figure S8. (A) SEM image of purified reaction product obtained with 55K PVP and 2.2 mM NaBr, keeping the other reaction conditions the same. (B) Histograms showing the distribution of NW diameters after purification. (C) SEM image of the purified reaction product obtained with 29K PVP and 2.2 mM NaBr, keeping the other reaction conditions the same.
Figure S9. (A&B) SEM images of purified reaction product obtained with 55K PVP and 2.75 mM NaBr, keeping the other reaction conditions the same. (B) Histogram of the diameter of the NWs.
