A microfluidic-based controllable synthesis of rolled or rigid ultrathin gold nanoplates

Article abstract of DOI:10.1039/c5ra02461g

A continuous, microfluidic-based, seed-mediated synthesis of high-purity gold nanoplates with different thicknesses was developed. The thickness of the nanoplates can be fairly tuned from less than 1 nm to a few nm by varying the flow rate. Depending on the thickness, the obtained nanoplates could be rigid and flat-surfaced with thicknesses larger than 2 nm or flexible with crumpled or rolled shapes when the thickness is around 1 nm. These nanoplates are poly-crystalline with different crystal faces and show high electrochemical activity towards glucose oxidation.

Full text of DOI:10.1039/c5ra02461g

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A microfluidic-based controllable synthesis of
rolled or rigid ultrathin gold nanoplates†
Cite this: RSC Adv., 2015, 5, 37512
Qiang Fu, Guangjun Ran and Weilin Xu*a
ab
a
A continuous, microfluidic-based, seed-mediated synthesis of high-purity gold nanoplates with different
thicknesses was developed. The thickness of the nanoplates can be fairly tuned from less than 1 nm to a
few nm by varying the flow rate. Depending on the thickness, the obtained nanoplates could be rigid
and flat-surfaced with thicknesses larger than 2 nm or flexible with crumpled or rolled shapes when the
thickness is around 1 nm. These nanoplates are poly-crystalline with different crystal faces and show
high electrochemical activity towards glucose oxidation.
Received 8th February 2015
Accepted 9th April 2015
DOI: 10.1039/c5ra02461g
www.rsc.org/advances
thicknesses of tens of nanometers, with mixed shapes including
obtuse triangles, hexagons, and quasi-rounds. Furthermore, the
Introduction
The control of metal nanostructure morphology (size, shape, evitable production of a large number of ball-like nanoparticles
and surface structure) has attracted considerable attention in during these preparations is really a waste of gold sources,
recent years due to the interest in precise tuning of electronic, which are limited on the earth.
1
–4
optical, and catalytic properties. Consequently, a variety of
nonspherical gold nanocrystals with different shapes such as synthesis of Au supraparticles. In that work, it was revealed
Recently, we reported a continuous microuidic-based
43
5,6
7,8
9,10
10
11,12
rods, wires, belts,
combs, plates and prisms,
poly- that a type of exible, thin Au nanoplate is in fact the rst
13–17
18
19
20–24
hedra,
cages and frames, caps, stars and owers,
as intermediate for the growth of Au supraparticles. Herein, by
25–29
well as dendrites
have been achieved. However, these varied varying the ow rate in the microuidic device, we obtained a
types of nanocrystals were obtained by bench top batch series of Au nanoplates with controllable thickness and found
preparative methods, which are successful in the laboratory. that the morphology (rolled or rigid) of the Au nanoplates could
These methods are not convenient for the synthesis of aniso- be tuned by controlling the thickness of the nanoplates. In
tropic nanocrystals on a large scale. Therefore, microuidic addition, the electrochemical test shows that the electro-
methods have been regarded as suitable alternative protocols catalytic activity of the nanoplates toward glucose oxidation
with a high probability of continuously gaining large quantities depends on the morphology of the nanoplates: the rolled ones
30,31
of particles with a uniform size and shape.
Moreover, among show considerably higher catalytic activity than the at ones.
the gold nanocrystals discussed above, microuidic protocols
have been used to prepare various shapes of nanoparticles with
different sizes (e.g. spherical nanoparticles, nanorods, and
Experimental section
Chemicals
30,32–39
hexagonal and triangular nanoplates).
As for gold nano-
plates, to the best of our knowledge, no one has already Hydrogen tetrachloroaurate trihydrate (HAuCl $3H O) was
4
2
successfully prepared gold nanoplates with different thickness purchased from Sigma-Aldrich. Cetyltrimethylammonium
by the microuidic protocol, although a similar protocol has chloride (CTAC), sodium borohydride (NaBH ), and ascorbic
4
been used for the synthesis of different-sized gold nano- acid (AA) were purchased from Shanghai Sinopharm Chemical
36
particles. Although various bench top batch preparative Reagent Co., Ltd. Sodium bromide (NaBr), b-D-glucose, sul-
methods have been reported for the synthesis of gold nano- phuric acid (H SO ), and potassium hydrogen phosphate
2
4
12,40–42
plates with or without a bending contour,
these gold (KH PO and K HPO ) were purchased from Beijing Chemical
2 4 2 4
nanoplates mainly have sizes in the micrometer range and Co. All chemicals were used as received without further puri-
cation. Ultrapure distilled water (18.2 MU cm) was used for all
solution preparations.
a
State Key Laboratory of Electroanalytical Chemistry, Jilin Province Key Laboratory of
Low Carbon Chemical Power, Changchun Institute of Applied Chemistry, Chinese
Academy of Science, 5625 Renmin Street, Changchun 130022, P. R. China. E-mail:
Synthesis of gold seeds
weilinxu@ciac.ac.cn
À4
b
10 mL aqueous solution containing 2.5 Â 10 M HAuCl and
4
Graduate University of Chinese Academy of Science, Beijing, 100049, China
0
.10 M CTAC was prepared rst. Then, 0.45 mL of the NaBH
4
solution (0.02 M, ice-cold) was added into the above mentioned
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c5ra02461g
1
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solution with stirring. The resulting solution turned brown Instrumentation
immediately, indicating the formation of gold seeds, which
were aged for 1 h at 30 C to decompose excess borohydride. The
seed particles have a size of about 4 nm (Fig. S1†).
UV-vis absorption spectra were taken using a JASCO V-570
spectrophotometer. Transmission electron microscopy (TEM),
high resolution transmission electron microscopy (HRTEM)
and selected area electron diffraction (SAED) characterization
was performed using JEOL JEM-2100 electron microscopes with
an operating voltage of 200 kV. Digital HRTEM images were
analyzed to determine the crystallinity of the nanoplates using a
digital micrograph 3.7. Atomic force microscopy (AFM) images
were generated with a Veeco Multimodel NanoScope 3D in the
tapping AFM mode. All electrochemical experiments were per-
formed using a CHI 750E electrochemical workstation (CH
Instruments, Chenhua Co., Shanghai, China). A conventional
three-electrode system was employed with a modied GCE (3.0
mm in diameter) as working electrode, a platinum sheet as
auxiliary electrode and a saturated calomel electrode (SCE) as
reference electrode.
ꢀ
Microuidic synthesis of gold nanoplate
The microuidic chip consists of a microchannel (400 mm Â
4
00 mm cross-section and 3 cm long) with three inlets and one
4
3
outlet. As shown in Scheme 1 and Fig. S2,† the reaction
regime was divided into three different solutions: solution 1:
3
75 mL of 0.01 M HAuCl4 solution, 15 mL of 0.01 M NaBr
solution and 4.6 mL of 0.1 M CTAC solution were mixed
together; solution 2: 135 mL of 0.04 M ascorbic acid solution
and 4.8 mL of 0.1 M CTAC solution were added together; and
solution 3: 150 mL seed solution and 4.8 mL of 0.1 M CTAC
solution were added together. Then, these three different
solutions were injected into the microuidic chip through
three independent channels at the same rate. Moreover, the
effluent from the chip was collected into a centrifugal tube
with a large amount of ice-cold ultrapure water to terminate
the growth. The solution in the tube was then centrifuged at
Results and discussion
First, the sample of folded or rolled nanoplate is prepared at 70
1
2 000 rpm for at least 15 min. To remove the excess surfac-
À1
mL min
based on our previous report. The detailed
tant, the precipitate was washed by water twice through
centrifugation at 12 000 rpm for not less than 15 min. By
varying the ow rate of the solution, nanoplates with different
thicknesses were obtained.
43
morphology of the sample was characterized as before. Fig. 1a
and S3(a–e)† show clearly that the well-dened nanoplates are
rolled or folded to different extents. In addition, a thickness of
about 1 nm could be predominantly seen from the rolled edge
of the nanoplate (Fig. S3b†). The HRTEM image of an individual
nanoplate (Fig. 1b) displays clear lattice fringes with fringe
spacing of about 0.235 nm, indicating that the entire nanoplate
is crystalline with the (111) facet running across the main
surface of the nanoplate. The SAED pattern (Fig. 1c) shows a set
Preparation of the gold nanoplate-modied electrode
A glassy carbon electrode (GCE) was polished before each
experiment with 1, 0.3 and 0.05 mm alumina slurry and then
successively washed with diluted nitric acid, acetone and
distilled water in an ultrasonic bath. The original solution
containing nanoplates (ca. 15 mL) was concentrated to 1 mL,
and then 100 mL of the condensed solution was dropped onto
the pretreated GCE and dried in the air. Aer that, 4 mL Naon
(0.1%) was cast onto the electrode. Such a modied electrode
was used for electrochemical characterization. The modied
ꢀ
electrode was stored at 4 C when not in use.
Fig. 1 (a) Typical TEM image of rolled Au nanoplates. (b) Typical
HRTEM image of the surface of a Au nanoplate shown in (a). (c)
Scheme 1 The setup of the flow-based microfluidic system for Correlated SAED pattern for sample shown in (a). (d) Absorption
synthesis of the ultrathin gold nanoplate.
spectra of ultrathin crumpled gold nanoplates shown in (a).
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of diffraction spots indexed to the (111), (200), (220), (311) and nanoplates were tested in 0.5 M H
2
SO
4
. As shown in Fig. 3a, the
(
(
222) reections of the gold fcc structure. The UV-vis spectrum cyclic voltammetry (CV) curves show that the rolled nanoplate
Fig. 1d) shows a relatively narrow absorption band with the (obtained with ow rate of 70 mL min ) modied electrode
À1
maximum absorption at about 590 nm, revealing that rolled displays a considerably higher peak current, which is associated
40
nanoplates have a relatively uniform size.
with surface oxide reduction events, than that of the rigid ones.
Furthermore, to investigate the mechanism of such a rapid Therefore, it is expected that the rolled nanoplates may show a
growth process, a series of microuidic experiments at different better performance in electrochemical oxidation of glucose

ow rates were performed (data shown in Fig. S4†). To our than the rigid at-surfaced nanoplates. Fig. 3b shows CV curves
surprise, it can be concluded that the rolled ultrathin gold for glucose oxidation in a phosphate buffered solution on these
nanoplates mentioned before can be obtained at a relatively two modied GCEs. Two main regions can be observed. The
high ow rate, whereas at a low rate, the rigid, at-surfaced rst peak is at 0.2 V vs. SCE, an oxidation peak (peak A, which
nanoplates could be obtained. Fig. 2a and b show that the cannot be seen clearly in the rolled nanoplate modied GCE),
À1
products acquired at 5 mL min are just the rigid nanoplates which is assigned to the dehydrogenation of the anomeric
with the fringe spacing of 0.235 nm (indexed to the (111) facet), carbon of the glucose molecule. The current corresponding to
which is consistent with that of the rolled nanoplate shown in this process is higher for rolled nanoplates than rigid ones. This
Fig. 1b. Atomic force microscopy (AFM) was utilized to certify dehydrogenation leads to the formation of gluconolactone. The
the thickness of rigid nanoplates. As shown in Fig. 2c and d, the second peak presents the main oxidation peak centered at
thickness of the nanoplates obtained with a ow rate of 5 mL around 0.3 V vs. SCE (peak B), which corresponds to the further
À1
44,45
min is about 5.5 nm, which is considerably thicker than that oxidation of gluconolactone.
(
Compared with that of the rigid
À1
<1 nm) prepared at 70 mL min mentioned above (HRTEM nanoplate modied GCE, the rolled nanoplate modied GCE
image shown in Fig. S3b†). Moreover, the sample gained at 5 mL exhibited considerably larger oxidation currents, which clearly
À1
min is thicker than the at-surfaced sample (with thickness demonstrate the better electrocatalytic activity of the rolled
À1
ꢁ
2.5 nm) prepared at 10 mL min (Fig. S5†). In addition, AFM nanoplates towards the glucose oxidation than the rigid ones.
was used to characterize the samples prepared at 30 and 50 mL Moreover, the electrocatalytic activities of gold nanoplates
min . Unfortunately, the exact height of rolled nanoplates prepared at 10 mL min , 30 mL min and 50 mL min were
cannot be measured directly by AFM due to their complicated evaluated. As shown in Fig. S7,† their electrocatalytic activity is
rolling mode (Fig. S6†). Based on these facts, we can conclude between that of rigid nanoplates (prepared at 5 mL min ) and
that, when the ow rate is low, the nanoplates could grow thick rolled nanoplates (prepared at 70 mL min ). In addition, their
À1
À1
À1
À1
À1
À1
due to a long growth time before they owed out from the chip electrocatalytic activity is increased with increasing ow rate
and then were quenched by the iced water in the tube shown in (shown in Fig. S7†).
Scheme 1. As the ow rate increases, the growth time decreases, Moreover, the electrodeposition method is one of the most
which then leads to thinner Au nanoplates. When they are thin useful approaches to prepare various types of gold nano-
4
6,47
48
enough, they tend to roll up to reduce the high surface energy. structures such as nanorods,
nanocubes and spherical
49
Glucose oxidation in a phosphate buffered electrolyte is used nanoparticles. Nanoparticles with different shapes and sizes
to produce electricity in fuel cells, and similar experimental can be facilely synthesized on the conducting surfaces by
conditions are adopted here to evaluate the electrocatalytic altering the conditions of electrochemical deposition. It is
50–52
activities of different gold nanoplates. Before that, GCEs benecial to synthesize the hybrid material.
The isolated
modied by the rolled (red curve) and rigid (black curve) nanoparticle has to be acquired by an additional separation
46
process. As for the microuidic-based method, a higher
surface to volume ratio and a lower sample consumption enable
the chemical reaction processing in a continuous model to be
completed within a short time and give a relatively uniform
35–39
reaction environment.
Moreover, microuidic protocols
Fig. 2 (a) Typical TEM image of flat-surfaced Au nanoplates prepared
À1
at the rate of 5 mL min , (b) typical HRTEM image of the surface of a
nanoplate shown in (a), (c) typical AFM image of sample shown in (a), Fig. 3 (a) The cyclic voltammograms of two types of (rigid/rolled)
and (d) height profile along the colored line of a rigid gold nanoplate nanoplate modified electrodes in (a) 0.5 M H SO , (b) in PBS (pH 7.4) in
2
4
À1
ꢀ
shown in (c).
the presence of 10 mM glucose recorded at 50 mV s and at 20 C.
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offer the capability to automate a multi-step synthesis with less 19 N. Zhao, L. Li, T. Huang and L. Qi, Nanoscale, 2010, 2, 2418–
human operation.
2423.
2
0 H.-G. Liao, Y.-X. Jiang, Z.-Y. Zhou, S.-P. Chen and S.-G. Sun,
Angew. Chem., Int. Ed., 2008, 47, 9100–9103.
1 P. S. Kumar, I. Pastoriza-Santos, B. Rodriguez-Gonzalez,
F. J. G. de Abajo and L. M. Liz-Marzan, Nanotechnology,
2008, 19, 015606.
Conclusions
2
We have developed a continuous seed-mediated method for the
preparation of high-purity gold nanoplates with tunable thick-
ness, which are rolled or rigid depending on their sizes. These 22 S. Barbosa, A. Agrawal, L. Rodr ´ı guez-Lorenzo, I. Pastoriza-
nanoplates are poly-crystalline with different crystal faces and
Santos, R. n. A. Alvarez-Puebla, A. Kornowski, H. Weller
show a high electrochemical activity toward glucose oxidation.
and L. M. Liz-Marz ´a n, Langmuir, 2010, 26, 14943–14950.
This protocol is fast, reproducible and adaptable to microuidic 23 P. R. Sajanlal and T. Pradeep, Nano Res., 2009, 2, 306–320.
synthesis without any additional batch processing steps and 24 Z. Wang, J. Zhang, J. M. Ekman, P. J. Kenis and Y. Lu, Nano
probably could be extended to the synthesis of other types of
ultrathin nanoplates.
Lett., 2010, 10, 1886–1891.
25 Y. Qin, Y. Song, N. Sun, N. Zhao, M. Li and L. Qi, Chem.
Mater., 2008, 20, 3965–3972.
2
2
6 T. Huang, F. Meng and L. Qi, Langmuir, 2009, 26, 7582–7589.
7 X. Xu, J. Jia, X. Yang and S. Dong, Langmuir, 2010, 26, 7627–
7631.
Acknowledgements
This work was funded by the National Basic Research Program
of China (973 Program, 2012CB932800 and 2014CB932700), the 28 W. Ye, J. Yan, Q. Ye and F. Zhou, J. Phys. Chem. C, 2010, 114,
National Natural Science Foundation of China (21273220 and 15617–15624.
1422307), and “the Recruitment Program of Global youth 29 H. Hian ´a Teo, Chem. Commun., 2010, 46, 7112–7114.
2
Experts” of China.
30 S. E. Lohse, J. R. Eller, S. T. Sivapalan, M. R. Plews and
C. J. Murphy, ACS Nano, 2013, 7, 4135–4150.
3
1 D. Kumar, A. Kulkarni and B. Prasad, Colloids Surf., A, 2014,
References
443, 149–155.
1
2
3
4
5
Y. Xia and N. J. Halas, MRS Bull., 2005, 30, 338–348.
C. J. Murphy, Science, 2002, 298, 2139–2141.
P. V. Kamat, J. Phys. Chem. B, 2002, 106, 7729–7744.
M. A. El-Sayed, Acc. Chem. Res., 2001, 34, 257–264.
32 C. Bullen, M. J. Latter, N. J. D'Alonzo, G. J. Willis and
C. L. Raston, Chem. Commun., 2011, 47, 4123–4125.
33 V. Sebasti ´a n, S.-K. Lee, C. Zhou, M. F. Kraus, J. G. Fujimoto
and K. F. Jensen, Chem. Commun., 2012, 48, 6654–6656.
N. R. Jana, L. Gearheart and C. J. Murphy, Adv. Mater., 2001, 34 J. Boleininger, A. Kurz, V. Reuss and C. S ¨o nnichsen, Phys.
3, 1389. Chem. Chem. Phys., 2006, 8, 3824–3827.
B. Nikoobakht and M. A. El-Sayed, Chem. Mater., 2003, 15, 35 C.-H. Weng, C.-C. Huang, C.-S. Yeh, H.-Y. Lei and G.-B. Lee, J.
1
6
1957–1962.
Micromech. Microeng., 2008, 18, 035019.
7
8
C. Wang and S. Sun, Chem.–Asian J., 2009, 4, 1028–1034.
H. Feng, Y. Yang, Y. You, G. Li, J. Guo, T. Yu, Z. Shen, T. Wu
and B. Xing, Chem. Commun., 2009, 1984–1986.
J. Zhang, J. Du, B. Han, Z. Liu, T. Jiang and Z. Zhang, Angew.
Chem., Int. Ed., 2006, 45, 1116–1119.
36 V. Sebastian Cabeza, S. Kuhn, A. A. Kulkarni and
K. F. Jensen, Langmuir, 2012, 28, 7007–7013.
37 L. L. Lazarus, A. S.-J. Yang, S. Chu, R. L. Brutchey and
N. Malmstadt, Lab Chip, 2010, 10, 3377–3379.
38 D. Shalom, R. C. Wootton, R. F. Winkle, B. F. Cottam, R. Vilar
and C. P. Wilde, Mater. Lett., 2007, 61, 1146–1150.
39 J. Wagner and J. M. K ¨o hler, Nano Lett., 2005, 5, 685–691.
9
1
1
1
0 N. Zhao, Y. Wei, N. Sun, Q. Chen, J. Bai, L. Zhou, Y. Qin, M. Li
and L. Qi, Langmuir, 2008, 24, 991–998.
1 R. Jin, Y. Cao, C. A. Mirkin, K. Kelly, G. C. Schatz and 40 S. Yang, T. Zhang, L. Zhang, S. Wang, Z. Yang and B. Ding,
J. Zheng, Science, 2001, 294, 1901–1903.
Colloids Surf., A, 2007, 296, 37–44.
2 A. Miranda, E. Malheiro, E. Skiba, P. Quaresma, 41 Y. Shao, Y. Jin and S. Dong, Chem. Commun., 2004, 1104–
P. A. Carvalho, P. Eaton, B. de Castro, J. A. Shelnutt and
E. Pereira, Nanoscale, 2010, 2, 2209–2216.
3 F. Kim, S. Connor, H. Song, T. Kuykendall and P. Yang,
1105.
42 B. Cao, B. Liu and J. Yang, CrystEngComm, 2013, 15, 5735–
5738.
1
1
1
1
1
1
Angew. Chem., Int. Ed., 2004, 43, 3673–3677.
4 D. Seo, C. I. Yoo, J. C. Park, S. M. Park, S. Ryu and H. Song,
Angew. Chem., Int. Ed., 2008, 47, 763–767.
5 G. H. Jeong, M. Kim, Y. W. Lee, W. Choi, W. T. Oh, Q. H. Park
and S. W. Han, J. Am. Chem. Soc., 2009, 131, 1672–1673.
6 C. Li, K. L. Shuford, M. Chen, E. J. Lee and S. O. Cho, ACS
Nano, 2008, 2, 1760–1769.
43 Q. Fu, Y. Sheng, H. Tang, Z. Zhu, M. Ruan, W. Xu, Y. Zhu and
Z. Tang, ACS Nano, 2015, 9, 172–179.
44 M. Pasta, F. La Mantia and Y. Cui, Electrochim. Acta, 2010, 55,
5561–5568.
45 J. Wang, J. Gong, Y. Xiong, J. Yang, Y. Gao, Y. Liu, X. Lu and
Z. Tang, Chem. Commun., 2011, 47, 6894–6896.
46 B. M. I. van der Zande, M. R. B ¨o hmer, L. G. J. Fokkink and
C. Sch ¨o nenberger, Langmuir, 2000, 16, 451–458.
47 B. M. Van der Zande, M. R. B ¨o hmer, L. G. Fokkink and
C. Sch ¨o nenberger, J. Phys. Chem. B, 1997, 101, 852–854.
7 M. S. Yavuz, W. Li and Y. Xia, Chem.–Eur. J., 2009, 15, 13181–
13187.
8 S. E. Skrabalak, J. Chen, Y. Sun, X. Lu, L. Au, C. M. Cobley
and Y. Xia, Acc. Chem. Res., 2008, 41, 1587–1595.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 37512–37516 | 37515

View Article Online
RSC Advances
Paper
4
4
5
8 J. Hern ´a ndez, J. Solla-Gull ´o n, E. Herrero, A. Aldaz and 51 Y. Hu, J. Jin, P. Wu, H. Zhang and C. Cai, Electrochim. Acta,
J. M. Feliu, J. Phys. Chem. C, 2007, 111, 14078–14083. 2010, 56, 491–500.
9 H. Zhang, J.-J. Xu and H.-Y. Chen, J. Phys. Chem. C, 2008, 112, 52 A. D. Franklin, D. B. Janes, J. C. Claussen, T. S. Fisher and
3886–13892. T. D. Sands, Appl. Phys. Lett., 2008, 92, 013122.
1
0 J. C. Claussen, M. M. Wickner, T. S. Fisher and
D. M. Portereld, ACS Appl. Mater. Interfaces, 2011, 3,
1765–1770.
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