Plasma Electrochemistry: How to Control the Size and Size Distribution of Au Nanoparticles

Metal nanoparticles (NPs) have attracted a great deal of interest for their unique optical and catalytic properties. These novel materials are normally prepared in solution as colloids by chemically reducing metal salts in the presence of a stabilizer (i.e. surfactant). Recently, we have developed a green chemical approach based on plasma electrochemical reduction (PER). A novel microplasma source that plasmas formed at sub-millimeter spatial scale allows a non-thermal, atmospheric-pressure plasma to be stably formed at the surface of aqueous ionic electrolytes and thin polymeric films. This has enabled 1) charge transfer reactions at the plasma-liquid and plasma film interface [1] and 2) electrochemical applications of plasmas for novel materials synthesis [2-6]. However, although controlling the size and size distribution of nanoparticles is a primary requirement for their application potential in diversified area, still remained question is how to control the size and size distribution in plasma electrochemical approach.

Here, we present plasma electrochemical approach to control the size and size distribution of Au nanoparticles.  We initially prepared an aqueous solution including HAuCl₄ and carried out PER (single-step process).  In order to grow Au nanoparticles, we synthesized Au seed by PER. Afterwards, Au precursor was slowly added to grow Au seed (multi-step process). As the results, multi-step process successfully synthesized the size of Au nanoparticles at the range from ~60 nm to ~1 um

To characterize the nanoparticle films, we have employed Ultraviolet-Visible absorbance spectroscopy, Nanoparticle size and Stability Analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Acknowledgment

This work was supported by R&D Program of ‘Plasma Convergence & Fundamental Research’ through the National Fusion Research Institute of Korea (NFRI) funded by the Government funds.

References

[1] C. Richmonds, M. Witzke, B. Bartling, S. W. Lee, J. Wainright, C.-C. Liu, R. Mohan Sankaran, J. Am. Chem. Soc. 133, 17582 (2011).

[2] C. Richmonds and R. M. Sankaran , Appl. Phys. Lett. 93, 131501 (2008).

[3] S. W. Lee, D. Liang , X. P. A. Gao , and R. M. Sankaran  Adv. Func. Mater. 21, 2155  (2011).

[4] S. W. Lee, H. Zamani, P. X. L. Feng, and R. M. Sankaran,J. Vac. Sci. Technol. A, 30, 010603, (2011).

[5] S. W. Lee, J. R. Kumpfer, P. A. Lin, G. Li, X. P. A. Gao, S. J. Rowan, R. M. Sankaran, Macromolecules  45, 8201 (2012)

[6] S. W. Lee, M. Janyasupab, C.-C. Liu, R. M. Sankaran, Catal.Today, 211 137 (2013)

Figure: Photo and particle size analysis of Au nanoparticles after single-step and multi-step plasma electrochemical reduction .