Solvent: A Key in Digestive Ripening for Monodisperse Au Nanoparticles
Wang et al. Nanoscale Research Letters
Solvent: A Key in Digestive Ripening for Monodisperse Au Nanoparticles
Peng Wang 0
Xuan Qi 0
Xuemin Zhang 0
Tieqiang Wang 0
Yunong Li 0
Kai Zhang 0
Shuang Zhao 0
Jun Zhou 0 1
Yu Fu 0
0 College of Sciences, Northeastern University , Shenyang 110004 , China
1 School of Materials Science and Engineering, Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University , Shenyang 110004 , China
This work has mainly investigated the influence of the solvent on the nanoparticles distribution in digestive ripening. The experiments suggested that the solvents played a key role in digestive ripening of Au nanoparticles (Au NPs). For the benzol solvents, the resulting size distribution of Au NPs was inversely related to the solvent polarity. It may be interpreted by the low Gibbs free energy of nanoparticles in the high polarity medium, which was supposedly in favor of reducing the nanoparticles distribution. Through digestive ripening in the highly polar benzol solvent of p-chlorotoluene, monodisperse Au NPs with relative standard deviation (RSD) of 4.8% were achieved. This indicated that digestive ripening was an effective and practical way to prepare high-quality nanoparticles, which holds great promise for the nanoscience and nanotechnology.
Solvent polarity; Digestive ripening; Au nanoparticles; Monodispersity
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Background
Au nanoparticles (Au NPs) and their self-assemblies
have drawn intense attentions due to their unique
properties and potential applications [1, 2], such as
catalysts [3], electronic and optoelectronic nanodevices [4],
biosensors [5], and biomedicine [6]. For fully
implementing the functions of Au NPs, the uniform size distribution
is of key significance. The monodisperse nanoparticles
(relative standard deviation less than 5.0%) show unique
properties and higher performances compared with the
corresponding polydisperse ones [7, 8]. Unfortunately, it is
hard to prepare monodisperse Au NPs with simple
synthesis process and common starting materials [9–11].
Therefore, a great deal of effort has been made to obtain
monodisperse Au NPs [12]. One main strategy is direct
alteration of the synthesis method, including selection of
special metal sources and reduction agents, introduction
of nanoparticle seeds, addition of surfactants, and so on.
However, although the monodisperse Au NPs have been
achieved by direct synthesis [13], it suffers from high-cost
of starting materials, tedious separation and unsatisfied
repeatability. An alternative approach to preparing
monodisperse Au NPs is post-treatment of the prepared ones,
which could detour the issue.
Digestive ripening, discovered by Lin [14], is an
effective post-treatment method. It is carried on by refluxing
a nanoparticle suspension with an excess amount of
capping agents (called as digestive ripening agents (DRA)),
which could cause the shrink of large particles and the
growth of small particles to achieve an equilibrium size
at a stable state [11, 12]. A distinct feature of digestive
ripening is that it can obtain high reproducibility and
yield with fine control [15]. The effect factors on
digestive ripening, including capping agent, temperature,
refluxing time, field effect, and the length of digestive
ripening agent, have been explored [11, 16–20]. Solvent
is an important participant in digestive ripening.
Moreover, the study has shown the solvent plays a vital role in
the synthesis process, which implied the effect of the
solvent on digestive ripening would be remarkable.
However, the related work has been rarely reported. In
addition, thus far the monodisperse Au nanoparticles
obtained by digestive ripening mainly came from the
system reported by Lin [11]. In that system, the original
Au nanoparticles were synthesized by a
surfactantassisted method. Its process was tedious and the yield
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was low, that substantially weakened the advantage of
digestive ripening.
Based on the above consideration, digestive ripening
of Au NPsin different solvents was investigated in this
work. The experiments showed that there was no
obviously development in size distribution of Au NPs in the
solvents of linear hydrocarbon. However, there was a
dramatic change when benzol solvents were used.
Moreover, the distribution was closely related with the solvent
polarity. The higher the polarity of the used solvent is,
the lower the RSD of the resulting nanoparticles is.
When a highly polar benzol of p-chlorotoluene was used
as the reflux solvent, RSD of the Au NPs (...truncated)