On the Polyol Synthesis of Silver Nanostructures: Glycolaldehyde as a Reducing Agent

Transcription

1 Supporting Information for: On the Polyol Synthesis of Silver Nanostructures: Glycolaldehyde as a Reducing Agent Sara E. Skrabalak, Benjamin J. Wiley, Munho Kim, Eric V. Formo and Younan Xia* Other Analytical Tests We attempted to detect the presence of GA with proton NMR and GC mass spectrometry as well, but these methods proved unsuitable for the present study. Proton NMR spectra were acquired with a 300 MHz AV300 spectrometer (Bruker). No new peaks appeared in the NMR spectra of EG after heating at 160 o C for 1 h. Figure S4 shows the NMR spectra of 1 mm glyoxal in EG. As indicated by comparison with NMR spectra calculated with ChemDraw Ultra 10.0, only EG peaks are present in the spectra. Because the amount of glycolaldehyde measured spectrophotometrically did not exceed 0.3 mm, we conclude that the amount of glycolaldehyde generated in EG is below the detection limit of the NMR spectrometer. Mass spectra were acquired with a Shimadzu QP2010 gas chromatograph quadrupole mass spectrometer (Shimadzu Scientific Instruments, Columbia, MD). For mass spectrometry, the adherence of EG to the column and saturation of the detector across a wide temperature range, combined with the chemical similarity of the compounds, made it very difficult or impossible to differentiate the micromolar concentration of GA from the much larger amount of EG. More Experimental Details Most chemicals were purchased from Aldrich; however, EG was supplied by J. T. Baker (low Fe and Cl content) and glyoxal was supplied by Alfa Aesar. UV-Vis spectra were taken with a Cary 50 spectrophotometer (Varian) or a HP 8452A Diode Array spectrometer. ICP-AES was conducted with the following instrument: Jarrell Ash 955, Thermo Jarrell Ash Corporation, Franklin, MA. To test GA production under Ar (or O 2 ), EG (5 ml) was added to a 50 ml 3- necked round bottom with a gas inlet line, a water condenser, and a rubber septum. The EG was S1

2 sparged with Ar (purity 99.99%) for 30 min. The condenser was then turned on and the top was plugged by a rubber septum with a narrow gas outlet. The EG was sparged for another 1.5 h before heating for 1 h. For the Fe(NO 3 ) 3 test, the condenser setup was used and is consistent with the Ag nanowire synthesis. For the Na 2 S test, EG was heated in a disposable vial and is consistent with the Ag nanocube synthesis. For the CuCl 2 test, EG (5 ml) was heated in a disposable vial for 1 hr in air at 150 C then 40 µl of a 4 mm CuCl 2 -EG solution was added; an aliquot was removed at 15 min. Data Analysis Please note that the perchloric acid used during the colorimetric test could facilitate EG oxidation to GA, just as it facilitates the oxidation of GA to glyoxal. To account for this possibility, background GA production from the colorimetric test was measured and found to be low (essentially Figure 1B as-purchased EG spectrum). To aid in analysis, often this slight background GA production was subtracted from spectra, as indicated in the Figure captions. When additives (e.g., Fe(III), Cu(II), or Na 2 S) were present during analysis, background GA production from the colorimetric test in their presence was also tested and corrected for. S2

3 Figure S1. (A) Spectra of Ag nanoparticles produced after addition of AgNO 3 and PVP to EG that had been heated at a given temperature for 1 h. Heating of the EG was stopped just before addition of the solution. (B) Colorimetric tests on EG heated at different temperatures for 1 h. S3

4 Figure S2. (A) Spectra taken from suspensions of Ag nanoparticles with known concentrations for Ag. (B) Spectra of colorimetric tests on glyoxal/eg solutions of known concentrations. (C) Calibration curve for determining Ag concentration from absorbance spectra. (D) Calibration curve for determination of GA concentration from absorbance spectra. Note that the extinction cross-sections of Ag nanoparticles can vary slightly with size; this property could be responsible for the deviation between GA concentration and AgNO 3 reduced at 160 C in Figure 3B. S4

5 Figure S3. Spectra from the colorimetric tests on EG heated at 150 C for 1 h in air with and without CuCl 2 ; background from the colorimetric test was subtracted from both spectra. S5

6 Figure S4. Comparison of NMR spectrum of 1 mm glyoxal in EG with calculated spectra of EG and glyoxal indicates that 1 mm is below the detection limit of the instrument. This amount of glyoxal is more than 3 times the amount measured spectrophotometrically. Note the different scale for the calculated EG. S6