Graphdiyne oxides as excellent substrate for electroless deposition of Pd clusters with high catalytic activity

Article abstract of DOI:10.1021/ja5131337

Graphdiyne (GDY), a novel kind of two-dimensional carbon allotrope consisting of sp- and sp²-hybridized carbon atoms, is found to be able to serve as the reducing agent and stabilizer for electroless deposition of highly dispersed Pd nanopartic

Full text of DOI:10.1021/ja5131337

Communication
pubs.acs.org/JACS
Graphdiyne Oxides as Excellent Substrate for Electroless Deposition
of Pd Clusters with High Catalytic Activity
Hetong Qi, Ping Yu, Yuexiang Wang, Guangchao Han, Huibiao Liu, Yuanping Yi, Yuliang Li,
and Lanqun Mao*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems, Key Laboratory of
Organic Solids, Institute of Chemistry, the Chinese Academy of Sciences, Beijing 100190, China
S
* Supporting Information
deposition of metals onto carbon nanotubes through
spontaneous reduction of metal ions on nanotubes.5a Dai et
ABSTRACT: Graphdiyne (GDY), a novel kind of two-
dimensional carbon allotrope consisting of sp- and sp2-
al. reported an elegant general approach to electroless
hybridized carbon atoms, is found to be able to serve as
the reducing agent and stabilizer for electroless deposition
of highly dispersed Pd nanoparticles owing to its low
reduction potential and highly conjugated electronic
structure. Furthermore, we observe that graphdiyne oxide
(GDYO), the oxidation form of GDY, can be used as an
even excellent substrate for electroless deposition of
ultrafine Pd clusters to form Pd/GDYO nanocomposite
that exhibits a high catalytic performance toward the
reduction of 4-nitrophenol. The high catalytic performance
is considered to benefit from the rational design and
electroless deposition of active metal catalysts with GDYO
as the support.
deposition of various metals onto carbon nanotubes based on
substrate-enhanced electroless deposition of metals.5b Recently,
Xie et al. observed electroless deposition of Pd onto graphene
oxides.5c
As a new carbon allotrope, graphyne family has been
theoretically proposed to possibly feature as assembled layers of
sp- and sp2-hybridized carbon atoms with striking applications
in device and energy materials such as lithium ion batteries.8
More remarkably, graphdiyne (GDY) is first synthesized
through cross-coupling on the surface of copper foil using
hexaethynylbenzen.9 GDY, comprising benzene rings and
carbon−carbon triple bonds in the structure and each benzene
ring is connected to six adjacent benzene rings through two
carbon−carbon triple bonds, resulting in a flat porous structure
(Scheme 1).9,10 The structure of GDY is related to that of
eveloping highly efficient and stable metal catalysts has
Dbecome one of the increasingly important goals in
chemistry and materials science owing to both economic and
environmental reasons.1 To accomplish this goal, metal
catalysts with small sizes are preferred since they can provide
a high accessible surface area for efficient catalysis. However,
the surface energy increases with the decreasing particle size,
which usually leads to serious aggregation of the metal particles,
resulting in the gradual decrease of the catalytic activity.2 For
this problem, using supporting substrate is a possible solution,
especially for nanometer sized metal catalysts.3 The catalytic
activity per surface metal atom of the metal catalysts strongly
depends on the nature of supporting materials when particle
size is smaller than 6 nm.4 For this reason, extensive interests
have been drawn to the uses of sp2-hybridized carbon materials
as the supporting materials because they have lower reduction
potentials than some kinds of metal ions and could enable
electroless deposition of metals5 in a technically simple way
without the use of surfactants or extra reducing agents or
catalysts but with capability for large-scale production.6
Moreover, the sp2-hybridized carbons could interact with and
thereby bind with metal atoms strongly since more interaction
states and transmission channels are generated between both,
as predicted theoretically.7 These properties enable the
formation of carbon-supported metal catalysts with remarkably
enhanced activity and stability.5c So far, carbon nanotubes and
graphene have been used for electroless deposition of
metals.5,6b For instance, Dai et al. first reported electroless
Scheme 1. Schematic Illustration of Formation of Pd/GDYO
through Electroless Deposition of Pd onto GDYO
graphene, but with the introduction of butadiyne linkages
(−CC−CC−) to form 18-C hexagons. It comprises sp2-
and sp-hybridized carbon atoms and exhibits unique electronic
structure, and high chemical stability and electrical con-
ductivity.11 Very recently, self-catalyzed growth of large-area
nanofilms of GDY and the applications of GDY in various
research fields have been reported.12 The unique atomic
arrangement and electronic structure of GDY practically inspire
Received: December 25, 2014
Published: April 14, 2015
© 2015 American Chemical Society
5260
DOI: 10.1021/ja5131337
J. Am. Chem. Soc. 2015, 137, 5260−5263

Journal of the American Chemical Society
Communication
the present investigation on the uses of GDY to develop high
efficient catalysts in this study.
In this communication, we demonstrate that GDY can be
agent among all the carbon materials for electroless deposition
of metals.
To demonstrate the electroless deposition of Pd onto GDY,
in a typical synthesis, homogeneous suspension of GDY was
mixed with an aqueous solution of PdCl42− and the mixture was
put into an ice bath for 30 min under vigorous stirring. The
resulting sample was then collected by centrifugation and
washing for several times with water. X-ray photoelectron
spectroscopy (XPS) spectra of the sample indicates the
presence of Pd (Figure S2A); the peaks at 337.4 and 342.7
eV correspond to 3d5/2 and 3d3/2 components of the metallic
Pd,15 revealing the formation of metallic Pd(0) and thereby
indicating the successful electroless deposition of Pd onto
GDY. Transmission electron microscopy (TEM) image of the
sample (Figure 2A,B) suggests that the as-formed Pd NPs have
used for electroless deposition of Pd nanoparticles (NPs)
2−
through the direct redox reaction between GDY and PdCl4
,
in which GDY acts as the reducing agent and stabilizer.
Moreover, we observe that GDY oxides (GDYO) can be used
as an even excellent substrate for electroless deposition of
ultrafine Pd clusters. The as-formed Pd/GDYO nanocomposite
is found to show a high catalytic performance toward the
reduction of 4-nitrophenol (4-NP) with sodium borohydride
(NaBH4) as a reductant.
The GDY used here was synthesized on the surface of copper
via a cross-coupling reaction using hexaethynylbenzene
precursors, as reported in our early study (for more details,
Supporting Information).9 As schematically shown in Scheme
1, GDY is 2D network with the connecting units consisting of a
six-membered carbon ring in the center and six carbon triple
bonds attached to each of the ring carbon atoms. The flat
carbon networks contain only sp- and sp2-hybridized carbon
atoms with a high π-conjunction.9,10 To explore the direct
2−
redox reaction property of GDY and GDYO with PdCl4 ion,
Ecutoff values of GDY and GDYO were measured with
ultraviolet photoelectron spectra (UPS) (Figure 1). The work
Figure 1. UPS spectra of GDY (A), GDYO (B), and Pd/GDYO (C).
Figure 2. TEM (A, C) and HRTEM (B, D) images of Pd/GDY (A, B)
and Pd/GDYO (C, D).
functions (Φ) were thus calculated with the equation,13 Φ = hν
− EFermi + Ecutoff, where hν, EFermi, and Ecutoff are the photo
energy of the excitation light (21.22 eV), the Fermi level edge
(21.08 eV in this case), and the inelastic secondary electron
cutoff measured in Figure 1, respectively. The reduction
potential was obtained from the equation,5a,14 Φ/e = E(vs SHE)
+ 4.44 V, where Φ is the work functions, E is the reduction
potential versus standard hydrogen electrode (SHE). On the
basis of these equations, the parameters for GDY, GDYO and
Pd/GDYO were calculated and the results were summarized in
Table 1. The reduction potential of GDY was estimated to be
a uniform size of 4 0.5 nm and are well dispersed on the
surface of GDY. High-resolution Transmission electron
microscopy (HRTEM) image (Figure 2B, inset) shows that
the interplanar spacing of the particle lattice is 0.220 nm, which
agrees well with the (111) lattice spacing of face-centered cubic
Pd (0.224 nm).5c These results revealed that the GDY could
serve as excellent substrate for electroless deposition of Pd NPs.
Moreover, the results demonstrated here also suggest that GDY
could act as stabilizer for Pd NPs, which may be attributed to a
strong anchoring effect between Pd nuclei and GDY,
presumably owing to the high π-conjugated structure of GDY
that can interact with the as-formed Pd NPs, which was similar
to the case of graphene.5c,7
To deposit Pd nanostructures with even smaller size, GDY
was oxidized into GDY oxides (GDYO) in a concentrated
H2SO4/HNO3 mixture (volume ratio, 3:1) containing KMnO4.
We observed that GDYO possesses a slightly higher work
function (4.23 eV) than that of GDY (4.11 eV) (Table 1) since
the acidic oxidation introduces surface oxygen-containing
groups and thereby disrupts the π-conjugation of GDY and
introduces surface dipole moments.16 The reduction potential
of GDYO was calculated to be −0.21 V vs SHE (Table 1),
suggesting that GDYO could also be used as substrate for the
electroless deposition of Pd. Moreover, compared with GDY,
GDYO was more readily stabilized in water, facilitating the
Table 1. Material Parameters: Sample, Work Function, and
Reduction Potential
samples
GYD
E
(eV)
work function (eV)
Evs SHE (V)
cutoff
3.97
4.11
4.23
−0.33
−0.21
+0.62
+0.02
GYDO
PdCl42−/Pd
4.09
Pd/GDYO
4.32
4.46
2−
about −0.33 V vs SHE, which was lower than that of PdCl4
ion (+0.62 V vs SHE), suggesting its ability as the substrate for
electroless deposition of Pd. The reduction potential of GDY is
even lower than those of other kinds of carbon allotropes such
as carbon nanotubes (+0.50 V vs SHE)5a and graphene oxides
(+0.48 V vs SCE),5c suggesting GDY is the excellent reducing
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Journal of the American Chemical Society
Communication
formation of Pd/GDYO in an aqueous solution by the
electroless deposition method. Similar to that with GDY, the
binding energy 337.6 and 342.9 eV in the XPS of the sample
prepared with GDYO and PdCl42− were observed, correspond-
ing to the 3d5/2 and 3d3/2 components of the metallic Pd(0)
(Figure S2B),15 again demonstrating the formation of Pd/
GDYO nanocomposite. The reference binding energies of the
metallic bulk Pd at 335.1 and 340.0 eV are lower than the
observed Pd values, suggesting that the values of the binding
energy of Pd clusters on a GDYO surface are influenced by the
nature of the support, as reported previously.17 TEM image
reveals that Pd particles have a uniform size of 1.3 0.1 nm
and are fairly well dispersed on the surfaces of GDYO (Figure 2
C,D). These results demonstrated that the GDYO could be
used as an excellent substrate for electroless deposition of Pd
clusters to form Pd/GDYO as well. Theoretical estimation
suggests that Pd atom tends to approach the C−C triple bonds
of GDY and GDYO (Figure S3). As could be observed in Table
1, the work function of the as-formed Pd/GDYO was measured
to be 4.46 eV, suggesting that the deposition of Pd clusters
onto the GDYO essentially lowers the reduction activity toward
Figure 3. (A) Time-dependent UV−vis absorption spectra recorded
during the catalytic reduction of 4-NP with the presence of the Pd/
GDYO nanocomposite. (B) Plots of ln(Ct/C0) as a function of the
reaction time for the reduction of 4-NP catalyzed by four different
catalysts of Pd/GDYO (red), commercial Pd/C (black), Pd/GO
(blue), and Pd/CNT (green).
NPs spontaneously on the surface of another kinds of carbon
materials including graphene oxide (GO) (Figure S6) and
multiwalled carbon nanotubes (MWNTs) through the redox
2−
PdCl4 precursor. The small size of Pd clusters deposited on
the GDYO surface further indicates that oxygen-containing
groups generated on the GDYO surface may play an important
role in controlling the formation of Pd clusters through
increasing the anchoring ability of Pd nuclei on the GDYO
surface and avoiding Ostwald ripening following nuclei.5c This
interaction may also be responsible for the good stability of the
as-formed Pd clusters/GDYO, which was reflected by almost
no change in morphology or size after the as-prepared Pd/
GDYO was dispersed in water for 3 months (Figure S4).
Inspired by the highly dispersed and surfactant-free nature of
Pd clusters and the unique structure of GDYO, we chose the
reduction of 4-nitrophenol (4-NP) by NaBH4 as a model
reaction to investigate into the catalytic activity of the Pd/
GDYO nanocomposite. The aqueous solution of 4-NP itself
exhibits a strong absorption peak at 317 nm (Figure S5A).
Upon the addition of NaBH4 into the solution, the absorption
peak at 317 nm disappears along with the appearance of a new
peak at 400 nm (Figure S5A) due to the formation of 4-
nitrophenolate ion, at the same time the color of the solution
changed from light yellow to bright yellow (Figure S5A), which
was consistent with the previous report.18 Upon the addition of
Pd/GDYO into the mixture of 4-NP and NaBH4, the
absorption peak at 400 nm significantly decreases as the
reaction proceeds. Meanwhile, a new peak appears at 300 nm
(Figure 3 and Figure S5), revealing the reduction of 4-NP and
formation of 4-AP, according to the previous report.19 Since the
concentration of NaBH4 largely exceeds that of 4-NP, the
reduction was considered as a pseudo-first-order reaction with
regard to 4-NP only. The absorbance was proportional to the
concentration of 4-NP in this system and the value of ln(At/A0)
reflects that of ln(Ct/C0), where Ct and C0 are the
concentrations of 4-NP at time t and 0, respectively. Therefore,
the reaction rate constant k was calculated from the rate
equation, ln[Ct/C0] = kt. To follow the kinetics of the reaction,
UV−vis spectra of the reaction mixture were monitored at 1
min intervals regularly. Figure 3B shows the time-dependent
UV−vis spectra of 4-NP catalyzed by the Pd/GDYO and the
rate constant k was calculated to be 0.322 min−1, according to
the slope of the fitted line (Figure 3B, red line). To further
investigate into the influence of the supporting materials on the
catalytic activity for the reduction of 4-NP, we deposited Pd
2−
reaction between PdCl4 ion and carbon materials. The rate
constant k values were calculated to be 0.029, 0.008, and 0.058
min−1 for the Pd/GO, Pd/MWNT, and the commercial Pd/C
catalysts, respectively. The rate constant on Pd/GDYO was
about 40-fold higher than that of Pd/MWNT, 11-fold higher
than that of Pd/GO, and 5-fold higher than the commercial
Pd/C. Such excellent catalytic performance of the Pd/GDYO
could be mainly attributed to synergistic effects from the highly
dispersed and surfactant-free nature of Pd clusters benefited
from the electroless deposition method and the unique
structure of the GDYO. These results suggest that the smaller
size of Pd clusters and lager π-conjugated structure of GDYO
are mainly responsible for the more efficient catalysis of 4-NP
as compared with those of Pd/GO, Pd/MWNT, and
commercial Pd/C.
In summary, we have first demonstrated that GDY can be
used as the reducing agent and stabilizer for electroless
deposition of highly dispersed and surfactant-free Pd clusters
owing to its low reduction potential and highly conjugated
electronic structure. Further, GDYO, the oxidation form of
GDY is observed to be an even excellent substrate for
depositing ultrafine Pd clusters to form Pd/GDYO nano-
composite that shows a high catalytic performance toward the
reduction of 4-nitrophenol. The high performance could be
considered to arise from synergetic effects that occur at the Pd/
GDYO nanocomposite. This work is believed to be significantly
beneficial to the design and development of active metal
catalysts as advanced catalytic systems for practical applications.
ASSOCIATED CONTENT
* Supporting Information
Experimental details and additional figures as noted in the text.
T This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*lqmao@iccas.ac.cn
■
Notes
The authors declare no competing financial interest.
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Journal of the American Chemical Society
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(16) Ago, H.; Kugler, T.; Cacialli, F.; Salaneck, W. R.; Shaffer, M. S.
P.; Windle, A. H.; Friend, R. H. J. Phys. Chem. B 1999, 103, 8116.
(17) (a) Priolkar, K. R.; Bera, P.; Sarode, P. R.; Hegde, M. S.; Emura,
S.; Kumashiro, R.; Lalla, N. P. Chem. Mater. 2002, 14, 2120.
(b) Wojcieszak, R.; Genet, M. J.; Eloy, P.; Ruiz, P.; Gaigneaux, E. M. J.
Phys. Chem. C 2010, 114, 16677.
ACKNOWLEDGMENTS
■
We acknowledge financial support from the National Natural
Science Foundation of China (21321003, 21210007, and
21435007), the National Basic Research Program of China
(2013CB933704), and The Chinese Academy of Sciences.
(18) (a) Pradhan, N.; Pal, A.; Pal, T. Langmuir 2001, 17, 1800.
(b) Deng, Y.; Cai, Y.; Sun, Z.; Liu, J.; Liu, C.; Wei, J.; Li, W.; Liu, C.;
Wang, Y.; Zhao, D. J. Am. Chem. Soc. 2010, 132, 8466. (c) Ge, J.;
Zhang, Q.; Zhang, T.; Yin, Y. Angew. Chem., Int. Ed. 2008, 47, 8924.
(d) Li, A.; Luo, Q.; Park, S. J.; Cooks, R. G. Angew. Chem., Int. Ed.
2014, 53, 3147.
(19) (a) Dai, Y.; Liu, S.; Zheng, N. J. Am. Chem. Soc. 2014, 136, 5583.
(b) Lu, N.; Chen, W.; Fang, G.; Chen, B.; Yang, K.; Yang, Y.; Wang,
Z.; Huang, S.; Li, Y. Chem. Mater. 2014, 26, 2453.
REFERENCES
■
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169. (b) Farmer, J. A.; Campbell, C. T. Science 2010, 329, 933.
(c) Wang, X.; Peng, Q.; Li, Y. Acc. Chem. Res. 2007, 40, 635.
(2) (a) White, R. J.; Luque, R.; Budarin, V. L.; Clark, J. H.;
MacQuarrie, D. J. Chem. Soc. Rev. 2009, 38, 481. (b) Astruc, D.; Lu, F.;
Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852.
(3) (a) Li, X.; Yuan, Z.; He, S. J. Am. Chem. Soc. 2014, 136, 3617.
(b) Lee, Y.; Garcia, M. A.; Frey Huls, N. A.; Sun, S. Angew. Chem., Int.
Ed. 2010, 49, 1271. (c) Li, Z.; Yuan, Z.; Li, X.; Zhao, Y.; He, S. J. Am.
Chem. Soc. 2014, 136, 14307.
(4) (a) Campbell, C. T. Acc. Chem. Res. 2013, 46, 1712. (b) Ishida,
T.; Kinoshita, N.; Okatsu, H.; Akita, T.; Takei, T.; Haruta, M. Angew.
̌ ́
Chem., Int. Ed. 2008, 47, 9265. (c) Prieto, G.; Zecevic, J.; Friedrich, H.;
de Jong, K. P.; de Jongh, P. E. Nat. Mater. 2013, 12, 34. (d) Cargnello,
M.; Doan-Nguyen, V. V. T.; Gordon, T. R.; Diaz, R. E.; Stach, E. A.;
Gorte, R. J.; Fornasiero, P.; Murray, C. B. Science 2013, 341, 771.
(5) (a) Choi, H. C.; Shim, M.; Bangsaruntip, S.; Dai, H. J. Am. Chem.
Soc. 2002, 124, 9058. (b) Qu, L.; Dai, L. J. Am. Chem. Soc. 2005, 127,
10806. (c) Chen, X.; Wu, G.; Chen, J.; Chen, X.; Xie, Z.; Wang, X. J.
Am. Chem. Soc. 2011, 133, 3693.
(6) (a) Song, J. H.; Wu, Y.; Messer, B.; Kind, H.; Yang, P. J. Am.
Chem. Soc. 2001, 123, 10397. (b) Qu, L.; Dai, L.; Osawa, E. J. Am.
Chem. Soc. 2006, 128, 5523. (c) Chu, H.; Wang, J.; Ding, L.; Yuan, D.;
Zhang, Y.; Liu, J.; Li, Y. J. Am. Chem. Soc. 2009, 131, 14310.
(d) Dasgupta, N. P.; Liu, C.; Andrews, S.; Prinz, F. B.; Yang, P. J. Am.
Chem. Soc. 2013, 135, 12932.
(7) (a) Wang, Q. J.; Che, J. G. Phys. Rev. Lett. 2009, 103, No. 066802.
́
(b) Cabria, I.; Lopez, M. J.; Alonso, J. A. Phys. Rev. B 2010, 81,
035403. (c) Metz, K. M.; Goel, D.; Hamers, R. J. J. Phys. Chem. C
2007, 111, 7260.
(8) (a) Haley, M. M.; Brand, S. C.; Pak, J. J. Angew. Chem., Int. Ed.
1997, 36, 835. (b) Hwang, H. J.; Koo, J.; Park, M.; Park, N.; Kwon, Y.;
Lee, H. J. Phys. Chem. C 2013, 117, 6919. (c) Koo, J.; Hwang, H. J.;
Huang, B.; Lee, H.; Lee, H.; Park, M.; Kwon, Y.; Wei, S. H.; Lee, H. J.
Phys. Chem. C 2013, 117, 11960. (d) Haley, M. M. Pure. Appl. Chem.
2008, 80, 519. (e) Hwang, H. J.; Kwon, Y.; Lee, H. J. Phys. Chem. C
2012, 116, 20220.
(9) Li, G.; Li, Y.; Liu, H.; Guo, Y.; Li, Y.; Zhu, D. Chem. Commun.
2010, 46, 3256.
(10) Li, Y.; Xu, L.; Liu, H.; Li, Y. Chem. Soc. Rev. 2014, 43, 2572.
(11) (a) Long, M.; Tang, L.; Wang, D.; Li, Y.; Shuai, Z. ACS Nano
2011, 5, 2593. (b) Luo, G.; Zheng, Q.; Mei, W. N.; Lv, J.; Nagase, S. J.
Phys. Chem. C 2013, 117, 13072.
(12) (a) Qian, X.; Liu, H.; Huang, C.; Chen, S.; Zhang, L.; Li, Y.;
Wang, J.; Li, Y. Sci. Rep. 2015, 5, 7756. (b) Xiao, J.; Shi, J.; Liu, H.; Xu,
Y.; Lv, S.; Luo, Y.; Li, D.; Meng, Q.; Li, Y. Adv. Energy Mater. 2015,
DOI: 10.1002/aenm.201401943. (c) Huang, C.; Zhang, S.; Liu, H.; Li,
Y.; Cui, G.; Li, Y. Nano Energy 2015, 11, 481.
(13) (a) Shin, H. J.; Choi, W. M.; Choi, D.; Han, G. H.; Yoon, S. M.;
Park, H. K.; Kim, S. W.; Jin, Y. W.; Lee, S. Y.; Kim, J. M.; Choi, J. Y.;
Lee, Y. H. J. Am. Chem. Soc. 2010, 132, 15603. (b) Kim, K. K.; Bae, J.
J.; Park, H. K.; Kim, S. M.; Geng, H. Z.; Park, K. A.; Shin, H. J.; Yoon,
S. M.; Benayad, A.; Choi, J. Y.; Lee, Y. H. J. Am. Chem. Soc. 2008, 130,
12757.
(14) (a) Reiss, H.; Heller, A. J. Phys. Chem. 1985, 89, 4207.
(b) Memmingm, R. Top. Curr. Chem. 1994, 169, 105.
(15) (a) Bhuvana, T.; Gregoratti, L.; Heun, S.; Dalmiglio, M.;
Kulkarni, G. U. Langmuir 2008, 25, 1259. (b) Wan, Y.; Wang, H.;
Zhao, Q.; Klingstedt, M.; Terasaki, O.; Zhao, D. J. Am. Chem. Soc.
2009, 131, 4541.
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