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Title: Reduction of HAuCl 4 by Na 2S revisited: The case for Au nanoparticle aggregates and against Au 2S/Au core/shell particles

Abstract

The reaction of sodium sulfide with chloroauric acid has been surrounded by a controversy over the structure of the resulting product. The original report proposed a Au 2S/Au core/shell structure based on strong near-IR resonance and limited transmission electron microscopy. Subsequent reports used the same model without further attempts to determine the structure of the products. With a significant body of experimental work compiled over a period of several years, we have shown that the major product of this reaction is aggregated spherical nanoparticles of gold with a minority component consisting of triangular and rod-like structures. This is in contradiction to the core/shell structures as originally proposed. Recently, there have been additional reports that again suggest a Au 2S/Au core/shell structure or irregularly shaped Au nanoparticles as an explanation for the near-IR resonance. To help resolve this issue, we have carried out further experiments to determine how the reaction products may depend on experimental conditions such as concentration and aging of the reactants, particularly Na 2S. It has been determined that sodium thiosulfate is the likely product from Na 2S aging. In addition, persistent spectral hole burning experiments have been conducted on gold nanoparticle aggregate (GNA) samples at excitation intensitiesmore » that are lower than that required to melt the nanostructures. We have observed a decrease in optical absorption on resonance with the excitation laser wavelength, with simultaneous increases in absorption to the blue and red of this wavelength region. However, in the presence of the stabilizer poly(vinyl pyrrolidone) (PVP), no increase in absorbance was observed but rather a blue shifting and decrease in intensity of the near-IR plasmon resonance. These results imply that the non-stabilized GNAs are able to break apart and reform into off resonant aggregate structures. In contrast, this behavior is suppressed in PVP stabilized GNAs because of the presence of polymer which quickly passivates the individual nanoparticles that comprise the GNAs after they are disrupted by laser irradiation. These results would be very difficult to explain if the nanostructures were core/shell. Furthermore, these new results again support the model of GNAs as the best possible explanation for the product of the HAuCl 4 and Na 2S reaction.« less

Authors:
 [1];  [2];  [2];  [3]
  1. Univ. of California, Santa Cruz, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Univ. of California, Santa Cruz, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1343002
Report Number(s):
UCRL-JRNL-227541
Journal ID: ISSN 1932-7447
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 111; Journal Issue: 25; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; gold; nanoparticle; aggregates; SERS; surface enhanced Raman scattering; femtosecond; transient absorption; metal nanoparticle; oscillations; persistent spectral hole burning; sodium sulfide; sodium thiosulfate; nanoshell; gold sulfide; core/shell

Citation Formats

Schwartzberg, A. M., Grant, C. D., van Buuren, Tony, and Zhang, J. Z. Reduction of HAuCl4 by Na2S revisited: The case for Au nanoparticle aggregates and against Au2S/Au core/shell particles. United States: N. p., 2007. Web. doi:10.1021/jp067697g.
Schwartzberg, A. M., Grant, C. D., van Buuren, Tony, & Zhang, J. Z. Reduction of HAuCl4 by Na2S revisited: The case for Au nanoparticle aggregates and against Au2S/Au core/shell particles. United States. doi:10.1021/jp067697g.
Schwartzberg, A. M., Grant, C. D., van Buuren, Tony, and Zhang, J. Z. Sat . "Reduction of HAuCl4 by Na2S revisited: The case for Au nanoparticle aggregates and against Au2S/Au core/shell particles". United States. doi:10.1021/jp067697g. https://www.osti.gov/servlets/purl/1343002.
@article{osti_1343002,
title = {Reduction of HAuCl4 by Na2S revisited: The case for Au nanoparticle aggregates and against Au2S/Au core/shell particles},
author = {Schwartzberg, A. M. and Grant, C. D. and van Buuren, Tony and Zhang, J. Z.},
abstractNote = {The reaction of sodium sulfide with chloroauric acid has been surrounded by a controversy over the structure of the resulting product. The original report proposed a Au2S/Au core/shell structure based on strong near-IR resonance and limited transmission electron microscopy. Subsequent reports used the same model without further attempts to determine the structure of the products. With a significant body of experimental work compiled over a period of several years, we have shown that the major product of this reaction is aggregated spherical nanoparticles of gold with a minority component consisting of triangular and rod-like structures. This is in contradiction to the core/shell structures as originally proposed. Recently, there have been additional reports that again suggest a Au2S/Au core/shell structure or irregularly shaped Au nanoparticles as an explanation for the near-IR resonance. To help resolve this issue, we have carried out further experiments to determine how the reaction products may depend on experimental conditions such as concentration and aging of the reactants, particularly Na2S. It has been determined that sodium thiosulfate is the likely product from Na2S aging. In addition, persistent spectral hole burning experiments have been conducted on gold nanoparticle aggregate (GNA) samples at excitation intensities that are lower than that required to melt the nanostructures. We have observed a decrease in optical absorption on resonance with the excitation laser wavelength, with simultaneous increases in absorption to the blue and red of this wavelength region. However, in the presence of the stabilizer poly(vinyl pyrrolidone) (PVP), no increase in absorbance was observed but rather a blue shifting and decrease in intensity of the near-IR plasmon resonance. These results imply that the non-stabilized GNAs are able to break apart and reform into off resonant aggregate structures. In contrast, this behavior is suppressed in PVP stabilized GNAs because of the presence of polymer which quickly passivates the individual nanoparticles that comprise the GNAs after they are disrupted by laser irradiation. These results would be very difficult to explain if the nanostructures were core/shell. Furthermore, these new results again support the model of GNAs as the best possible explanation for the product of the HAuCl4 and Na2S reaction.},
doi = {10.1021/jp067697g},
journal = {Journal of Physical Chemistry. C},
number = 25,
volume = 111,
place = {United States},
year = {2007},
month = {3}
}

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