Multiply-twinned intermetallic AuCu pentagonal nanorods

Article abstract of DOI:10.1039/c3cc47254j

Monodispersed intermetallic AuCu pentagonal nanorods with controlled size and composition have been developed by a seed-mediated growth route. The AuCu/C nanomaterial catalyzed the coupling reaction of sulfonamide with benzyl alcohol in good to excellent yields.

Full text of DOI:10.1039/c3cc47254j

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Multiply-twinned intermetallic AuCu pentagonal
nanorods†
Cite this: Chem. Commun., 2014,
50, 1141
Jinhua Yang, Leng Leng Chng, Xianfeng Yang, Xiaojun Chen and Jackie Y. Ying*
Received 23rd September 2013,
Accepted 22nd November 2013
DOI: 10.1039/c3cc47254j
www.rsc.org/chemcomm
Monodispersed intermetallic AuCu pentagonal nanorods with controlled compositions.19 To the best of our knowledge, the synthesis of AuCu
size and composition have been developed by a seed-mediated growth pentagonal nanorods has remained a great challenge because of the
route. The AuCu/C nanomaterial catalyzed the coupling reaction of distinct reduction rates and the lattice mismatch of the different
sulfonamide with benzyl alcohol in good to excellent yields.
components, which would be quite different from the reported Au
and Au–Ag pentagonal nanorods with similar lattice parameters.24–26
Herein, for the first time, we report a facile approach to synthesize
Nanorods with shape anisotropy have received much attention due
to their promising applications in electronics,1,2 biomedicine,3,4 monodispersed AuCu pentagonal nanorods with controlled sizes and
chemical sensing, imaging,5 and catalysis.6–8 Among different compositions by elongating the multiply-twinned Au decahedrons in
types of nanorods, the pentagonal nanorods possess a unique the oleylamine solution containing the Cu precursor (shown in
morphology, which have many interesting composition- and shape- Scheme S1, ESI†). The simultaneous alloying of Au and Cu resulted
dependent properties, such as excellent stability and high catalytic in the growth of the AuCu nanorods. We also evaluated the catalytic
activity.9–11 Their enhanced catalytic performance is attributed to the activity of the AuCu nanorods in a carbon–nitrogen (C–N) coupling
higher activity of the surface atoms on the twins of multiply-twinned reaction. Our heterogeneous catalysts exhibit high catalytic activity
particles (MTPs).12–14 Pentagonal nanorods of one or two metals towards the C–N coupling reaction with excellent recyclability.
have been successfully developed in the past decade.15 Murphy and
co-workers prepared a high yield of Au pentagonal nanorods in pentagonal nanorods, a simple one-pot reaction was first employed
aqueous solution by seed-mediated growth method from to synthesize Au decahedral nanoparticles, which were subsequently
For a typical synthesis of multiply-twinned intermetallic AuCu
a
multiply-twinned decahedral Au nanoparticles, and postulated a used as seeds for the formation of AuCu pentagonal nanorods.
general mechanism for the pentagonal nanorod growth.16,17 These Briefly, a solution of 93 mg of HAuCl4Á3H2O in 10 mL of oleylamine
Au pentagonal nanorods showed improved plasmonic properties. For was heated at 110 1C for 4 h under nitrogen flow with rapid
bimetallic pentagonal nanorods, Song and co-workers have developed magnetic stirring. To prepare AuCu pentagonal nanorods, the above
Ag–Au–Ag heterometallic nanorods through directed anisotropic Au colloidal solution was heated to 280 1C at a rate of B20 1C minÀ1
growth from gold decahedrons.18
and then 60 mg of Cu(acac)2 was added quickly. The mixture was
,
Bimetallic AuCu nanoparticles with tunable sizes and composi- kept at 280 1C for 1 h under nitrogen flow with magnetic stirring.
tions offer a broader control over properties than single metallic The as-prepared colloidal solution was then cooled to room
nanoparticles.19–21 Spherical intermetallic AuCu multiply-twinned temperature, and the nanoparticles were precipitated, washed
nanoparticles have been successfully synthesized by a seed-based with methanol and re-dispersed in non-polar organic solvents
diffusion route.20 However, shape-controlled growth of AuCu nano- (e.g. toluene, hexane and chloroform).
particles has been rarely reported in the literature.22,23 It appeared
The transmission electron microscopy (TEM) image shows
to be very difficult due to complications in the solution phase and that the as-prepared Au nanoparticles have an average diameter of
the tendency of self-purification. Liu and Walker have reported 10.0 Æ 0.8 nm (Fig. S1A, ESI†). The multiply-twinned decahedral
monodispersed Au–Cu nanocubes with controllable sizes and structure of the nanoparticles was confirmed by the high-resolution
TEM (HRTEM) image (Fig. S1B, ESI†). These Au decahedra were
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, The Nanos,
then used as seeds for the formation of AuCu nanorods.
When a Au/Cu atomic ratio of 1 : 1 was used (denoted as AuCu),
the synthesized nanoparticles were nearly uniform pentagonal
Singapore 138669, Singapore. E-mail: jyying@ibn.a-star.edu.sg; Fax: +65 6478-9020
† Electronic supplementary information (ESI) available: Experimental protocols;
synthesis scheme; TEM and HRTEM images of Au, Cu, AuCu3, and Au@Cu
nanorods with an average size of B15 nm in length and B12 nm
in diameter (shown in Fig. 1A). The HRTEM image (Fig. 1B) revealed
nanoparticles; XPS spectra; ultraviolet-visible (UV-Vis) spectra and coupling
reactions of AuCu nanorods. See DOI: 10.1039/c3cc47254j
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Fig. 1 (A) TEM, (B, C) HRTEM, and (D) HAADF-STEM images of AuCu
pentagonal nanorods. Cu and Au elemental profiles along the (E) red and
(F) blue lines, respectively, across the AuCu nanorod shown in (D).
(G) SAED pattern of the AuCu nanorods.
Fig. 2 XRD reference lines of (A) Au (JCPDS 65-2870) and (B) Cu (JCPDS
85-1326). (C) XRD pattern of AuCu pentagonal nanorods and XRD refer-
ence lines of AuCu (JCPDS 65-2798). (D) XRD pattern of AuCu2 pentagonal
nanorods. (E) XRD pattern of AuCu3 pentagonal nanorods and XRD
reference lines of AuCu3 (JCPDS 35-1357).
that the synthesized nanoparticles were predominantly multiply-
twinned with a pentagonal nanorod morphology. The ends of the
nanorods still retained the same structure as the Au decahedral grow along the {111} and {110} faces (Fig. S6C, ESI†) with oleyamine
seeds as shown in Fig. 1C. An arbitrary single particle specified in blocking the high-energy {100} surface (Fig. S6D, ESI†). The aniso-
the high-angle annular dark-field scanning transmission electron tropic growth mechanism for AuCu pentagonal nanorods was
microscopy (HAADF-STEM) image is shown in Fig. 1D. Furthermore, consistent with those of AuAg nanorods, whereby the nanorods
as shown in Fig. 1E and F, the signals of Au and Cu were detected were directly grown from well-defined multiply-twinned decahedral
across the entire particle along its length and width, which con- Au particles.8,9,18 However, the growth of the AuCu pentagonal
firmed that the nanoparticle was indeed composed of Au and Cu nanorods involved the formation of the AuCu intermetallic phase.
across the entire particle. The AuCu particles were obtained via the The growth mechanism was different from that reported for the
rapid interdiffusion of metal atoms as a result of the elevated heterometallic AuAg nanorods.
temperature, and the large number of interfacial vacancy defects.20,27
The length of the pentagonal nanorods was controlled by the
The XRD pattern of the nanorods corresponded to the AuCu amount of Au seeds at a fixed Cu precursor concentration during
intermetallic phase (JCPDS 65-2798) (see Fig. 2C), which was con- synthesis. For a Au/Cu atomic ratio of 1 : 2, pentagonal nanorods
firmed by the selected area electron diffraction (SAED) pattern denoted as AuCu2 were obtained with a uniform length of B19 nm,
(Fig. 1G). The energy dispersive X-ray (EDX) spectroscopy analysis and a similar diameter of B12 nm as that of the AuCu nanorods
showed that the AuCu nanorods have a Au/Cu atomic ratio of 47 : 53 (Fig. 3A). Although the length of the nanorods increased from
(Fig. S2A, ESI†), which was in close agreement with the precursor B15 nm to B19 nm when the Au/Cu atomic ratio was increased
composition employed. Peak deconvolution of the Cu 2p X-ray from 1 : 1 to 1 : 2, the multiply-twinned {100} faces on the side and
photoelectron spectroscopy (XPS) confirmed the zero valence of Cu the {110} and {111} faces at the two ends of the nanorods remained
in the AuCu nanorods (Fig. S3, ESI†). The peak position of the unchanged (Fig. S6B and C, ESI†). Fig. 3F and G confirmed that the
surface plasmon resonance of the AuCu nanorods remained stable, AuCu2 nanorods have a uniform Au and Cu profile across the entire
and no color change was noted in the AuCu nanorods solution after particle. The powder XRD pattern of AuCu2 nanorods (Fig. 2D)
one month (Fig. S4, ESI†). In contrast, a significant red shift of the appeared to consist of (i) a set of peaks that were intermediate of
Cu nanoparticles solution (Fig. S4, ESI†) was observed, with a color the AuCu intermetallic phase (JCPDS 65-2798) and the AuCu3
change from red to green. This illustrated the excellent stability of intermetallic phase (JCPDS 35-1357), and (ii) a set of peaks asso-
Cu in the AuCu nanorods.
ciated with Cu (JCPDS 85-1326), suggesting the segregation of a
TEM showed that the side surface of the AuCu pentagonal separate Cu phase. The surface plasmon resonance of AuCu2
nanorods was the {100} face and multiply twinned between faces nanorods solution remained stable after one month (Fig. S4, ESI†).
(Fig. S6B, ESI†), while the two ends of the AuCu nanorods have the By further decreasing the ratio of Au : Cu to 1 : 3, pentagonal
same {110} and {111} faces (Fig. S6C, ESI†) as the decahedral Au nanorods termed AuCu3 were obtained with a greater length
seeds (Fig. S6A, ESI†). This indicated that the intermetallic AuCu (B24 nm) and a similar diameter of B12 nm (Fig. S7, ESI†). These
pentagonal nanorods were directly grown from well-defined nanorods showed an XRD pattern that corresponded to the AuCu3
multiply-twinned decahedral Au seeds by elongating the {100} face. intermetallic phase (JCPDS 35-1357) (Fig. 2E).
Oleylamine is required to form the AuCu pentagonal nanorods,
In order to further understand the growth mechanism, we
presumably to stabilize the faces during anisotropic growth, where also studied the effect of the capping agent on the formation of
Cu deposition on Au decahedral seeds led to the formation of high- AuCu nanoparticles. In a strong capping agent, such as oleic
energy surfaces such as the {100} faces (Fig. S6B, ESI†). Cu could acid/tri-n-octylamine solution,20 spherical multiply-twinned
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Good to excellent yields (71–98%) were obtained for substituted
benzyl alcohols or sulfonamides with either electron-donating
or electron-withdrawing substituents in the substrates.
In conclusion, monodispersed AuCu pentagonal nanorods with
controlled size and composition were successfully synthesized
by seed-mediated growth using oleylamine. AuCu pentagonal
nanorods were grown from well-defined multiply-twinned Au
decahedral seeds. With the growth of pentagonal nanorods, the
intermetallic AuCu phase was formed. The length and compo-
sition of the AuCu pentagonal nanorods could be controlled by
changing the amount of Au decahedral seeds at a fixed Cu
precursor concentration. The strength of capping agents and
synthesis temperature were key factors in the formation of
AuCu pentagonal nanorods instead of spherical MTPs. AuCu
nanorods demonstrated very good catalytic activity in C–N coupling
reactions with p-toluenesulfonamide and benzyl alcohol as the
model substrates at a fairly low reaction temperature.
Fig. 3 (A) TEM, (B, C) HRTEM, and (D) HAADF-STEM images of AuCu2
pentagonal nanorods. (E) EDX spectrum of a single AuCu2 nanorod
specified in (D). Cu and Au elemental profiles along the (F) red and
(G) blue lines, respectively, across the AuCu2 nanorod shown in (D).
This work was funded by the Institute of Bioengineering and
Nanotechnology (Biomedical Research Council, Agency for
Science, Technology and Research, Singapore).
AuCu nanoparticles with a monodispersed size distribution
(B14 nm) were obtained under the otherwise similar synthesis
conditions as those for the AuCu pentagonal nanorods (Fig. S8,
ESI†). The formation of spherical MTPs instead of pentagonal
nanorods in the solution of strong capping agents could be
due to unselective adsorption of the capping agents on the
different seed faces.
Besides the capping agents, the synthesis temperature also
played an important role in the anisotropic growth of the penta-
gonal nanorods. At a lower synthesis temperature of 180 1C,
spherical core–shell Au@Cu nanoparticles were obtained with a
Au/Cu atomic ratio of 1 : 1. The core–shell Au@Cu structure was
confirmed by the EDX spectroscopy analysis of an arbitrary single
particle marked in the HAADF-STEM image (Fig. S9(C), ESI†).
The HRTEM image (Fig. S9(B), ESI†) revealed that the Au@Cu
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