(737c) Aerosol Assisted Synthesis of Gold Nanoparticles | AIChE

(737c) Aerosol Assisted Synthesis of Gold Nanoparticles


Jokiniemi, J. - Presenter, VTT Fine Particles
Lähde, A., University of Eastern Finland
Koshevoy, I., University of Eastern Finland
Karhunen, T., University of Eastern Finland
Torvela, T., University of Eastern Finland
Pakkanen, T. A., University of Joensuu

nanoparticles (AuNPs) also called gold colloids are
the most stable metal nanoparticles [Daniel and Astruct 2004]. AuNPs are known to have some unique properties
including the surface plasmon resonance (SPR), which arises from the collective
oscillation of conduction electrons and, dominates the optical spectra of
metallic nanoparticles (NPs) [de la Garza et
al. 2010]. This makes them attractive for many potential
applications in the fields of biotechnology (e.g. biosensors, cell and tissue
engineering, open MR imaging), energy (e.g. high-K capacitors, solar cells) and
information technology (e.g. fiber-optic communications systems, printable
electronics) [Wu et al. 2008]. However, the properties and applicability of AuNPs are strongly dependent on the
particles size, interparticle distance, nature of the protecting organic shell,
and shape of the nanoparticles.

There are a
number of methods used for the preparation of AuNPs including sol-gel and other
solvent based methods, layer-by-layer self-assembly, and aerosol assisted
methods [Daniel and Astruct 2004, Majumdar et al. 1996]. In particular, aerosol
assisted methods like spray pyrolysis are promising as they can produce
submicron-sized particles with high elemental and phase purity. However, the
preparation of AuNPs with aerosol methods typically require high pressures,
temperatures and/or the use of strong acids like HCl and HNO3 [de la
Garza et al. 2010]. Furthermore, the particle size, concentration, chemical
stability and degree of aggregation need to be controlled, since these
properties strongly affect the optical, electrical, chemical and biological
properties of the gold nanoparticles [Amendola and Meneghetti 2009].

In this paper we
present an atmospheric pressure aerosol assisted synthesis of nanocolloidal
gold. The aim of the study was to prepare plasmomic
nanoparticles with well determined size, shape, morphology and composition
using a single-stage, continuous aerosol synthesis route. Homoleptic cluster of (AuC2R)10
(R=2,6-dimethyl-4-heptanol) was synthesized [Koshevoy et al. 2012] and used as
the precursor for the studies. The particle formation is based on the thermal transformation
of the precursor in a high-temperature reactor (T=200 ? 800 ºC). A systematic
investigation of the influence of process parameters on powder characteristics,
including particle and crystallite size, and surface properties, has been
carried out.

The particle
properties including particle size, shape and crystallinity could be altered by
changing the reactor conditions. Phase-pure gold nanoparticles with the
crystallite size between 2.4 and 4.2 nm were obtained depending on the process
conditions. The result is very different from typical spray pyrolysis product
where only one particle is formed from one starting droplet as here many nanosized Au particles are obtained from one droplet. A dramatic change in the color from bright yellow to very dark
red of the collected powder was observed as the temperature increased (Figure 1
inserts). In addition, a clear transformation of droplet like particles formed
at 200 ºC to solid gold nanoclusters obtained at 800 ºC was observed. At 200 ºC
spherical liquid like particles were observed indicating that the particles
were formed mainly by droplet drying (Figure 1 A-B). At the intermediate
temperature, 400 ºC, spherical gold particle clusters were formed by thermal
reactions taking place within the droplet (Figure 1 C-D). Finally, irregular
agglomerates of gold nanoparticles with the primary size below 5 nm were
obtained at 800 ºC (Figure 1 E-F). No significant sintering of the primary Au
nanoclusters was observed even at the temperatures above 400 ºC. This can be
partly explained by the steric hindrance of the side chains. In addition, at
800 ºC a surface layer was observed around the particles in TEM images. Based
on the Raman measurements the surface layer consisted of carbonaceous material
originating from the thermal decomposition of the precursor compound.

Figure 1. TEM images of AuNPs prepared at (A-B) T=200 ºC, (C-D) T=400 ºC and (E-F)
800 ºC. The particles collected on the filter are shown as inserts.


This work was
supported by the strategic funding of the University of Eastern Finland under
the NAMBER spearhead project.


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