emulsion shows an enhanced conversion and a good stabilizing
effect to the Au nanoparticles. To further simplify the separation
process, the PHCSs loaded with both Au nanoparticles and
magnetic nanoparticles are used as the catalyst. The catalytic
activity isn’t affected and the functionalized PHCSs can be
conveniently gathered by applying a magnetic field (Fig. 2h).
All the above results indicate that the PHCS-stabilized Pickering
emulsion is a promising catalytic system to accelerate water/
organic biphasic reactions.
In summary, we present the self-assembly of amphiphilic
porous hollow carbonaceous spheres into Pickering emulsions
and their reversible pH-dependent phase-transfer behaviour in
water/oil system. Both the bare PHCSs and those functionalized
with metals and magnets are efficient catalysts for water/oil
biphasic reactions, facilitating not only the separation of the
products but also the recovery of the catalysts from the reaction
system.
This work was supported by the National Natural Science
Foundation of China (20703065, 20877097).
Fig. 2 (a) SEM image of the PHCSs. (b) SEM image of the
Au-PHCSs. (c) BSE-SEM image of the Au-PHCSs. (d) XRD pattern
of the Au-PHCSs. (e) Energy dispersive X-ray spectroscopy measure-
ments of Au-PHCSs. (f) The size distribution of gold nanoparticles on
the Au-PHCSs. (g) Kinetic profiles of the reduction of p-nitroanisole
Notes and references
1 W. A. Herrmann and C. W. Kohlpaintner, Angew. Chem., Int. Ed.
Engl., 1993, 32, 1524–1544.
4
by NaBH . (h) Photo images demonstrating the magnetic separation
2
3
4
5
C. J. Li, Chem. Rev., 1993, 93, 2023–2035.
of the magnetic Au-PHCSs by an external magnetic field.
C. M. Starks, J. Am. Chem. Soc., 1971, 93, 195–199.
J. F. Rathman, Curr. Opin. Colloid Interface Sci., 1996, 1, 514–518.
G. D. Yadav, Top. Catal., 2004, 29, 145–161.
functionalized PHCSs are prepared via direct reaction with
corresponding salt solutions of Au(III), Ag(I) and Pd(II). With
abundant reductive groups (hydroxyl, aldehyde group) on
their surfaces, the PHCSs can reduce the metal salt in situ,
which results in mono-metal or even bimetal loaded PHCSs
6 S. Baj, A. Siewniak and B. Socha, Appl. Catal., A, 2006, 309,
5–90.
G. D. Yadav and O. V. Badure, J. Mol. Catal. A: Chem., 2008,
88, 33–41.
8
7
8
9
2
J. Gao, S. Wang, Z. Jiang, H. Lu, Y. Yang, F. Jing and C. Li,
J. Mol. Catal. A: Chem., 2006, 258, 261–266.
K. M. Ho, W. Y. Li, C. H. Wong and P. Li, Colloid Polym. Sci.,
(
see ESIw). Scanning electron microscopy (SEM) images of the
Au loaded PHCSs are shown in Fig. 2a and b. It can be seen
that the shape and size of the PHCSs do not change after
coating with the Au nanoparticles. The back scattered electron
2010, 288, 1503–1523.
0 A. Nisar, J. Zhuang and X. Wang, Adv. Mater., 2011, 23,
1130–1135.
1
(
BSE) image (Fig. 2c) shows that there is a broad size
11 B. P. Binks and C. P. Whitby, Langmuir, 2004, 20, 1130–1137.
2 B. P. Binks, J. Philip and J. A. Rodrigues, Langmuir, 2005, 21,
296–3302.
13 S. Tcholakova, N. D. Denkov and A. Lips, Phys. Chem. Chem.
Phys., 2008, 10, 1608–1627.
1
distribution of particles, ranging from 10–70 nm. Adopting
2
the same protocol as we reported previously, Fe O coated
3
3
3
4
PHCSs were also synthesized, and the PHCSs could be
functionalized with both magnetic and catalytically active
metals (see ESIw).
1
4 N. Brun, S. Ungureanu, H. Deleuze and R. Backov, Chem. Soc.
Rev., 2011, 40, 771–788.
1
5 S. Crossley, J. Faria, M. Shen and D. E. Resasco, Science, 2010,
327, 68–72.
16 D. J. Cole-Hamilton, Science, 2010, 327, 41–42.
4
The catalytic reduction of p-nitroanisole by NaBH was chosen
as a model reaction for studying the catalytic performances of
24
17 D. Z. Ni, L. Wang, Y. H. Sun, Z. R. Guan, S. Yang and
K. B. Zhou, Angew. Chem., Int. Ed., 2010, 49, 4223–4227.
PHCSs with Au nanoparticles (Au-PHCSs). In one control
group, where the bare PHCSs are used as catalysts, the reduction
1
1
2
8 J. I. Amalvy, S. P. Armes, B. P. Binks, J. A. Rodrigues and
G. F. Unali, Chem. Commun., 2003, 1826–1827.
9 B. P. Binks and J. A. Rodrigues, Angew. Chem., Int. Ed., 2005, 44,
4
does not occur even with a large excess of NaBH . We set another
control test using colloidal gold as catalyst; the size of the gold
nanoparticles is about 13 nm which are prepared following
4
41–444.
0 N. X. Yan and J. H. Masliyah, J. Colloid Interface Sci., 1996, 181,
0–27.
21 G. D. Yadav, Y. B. Jadhav and S. Sengupta, Chem. Eng. Sci.,
003, 58, 2681–2689.
25
Storhoff’s method. In the first 10 min, the conversion reaches
5%, but the gold nanoparticles start to agglomerate visibly at the
2
1
2
water/toluene interface quickly, resulting in catalyst deactivation.
However, using Au-PHCSs as catalysts, the reaction proceeds well
and completes within an hour. The conversion of p-nitroanisole
varying with time is plotted in Fig. 2g. Moreover, the Au-PHCSs
can be simply separated by filtration and reused after washing.
After three cycles, the catalyst is in as good a condition as ever.
Compared to the control groups, the Au-PHCS-formed Pickering
2
2 S. K. Maity, N. C. Pradhan and A. V. Patwardhan, Appl. Catal.,
A, 2006, 301, 251–258.
23 L. Wang, D. Z. Ni, D. Yang, K. B. Zhou and S. Yang, Chem. Lett.,
010, 39, 451–453.
2
2
4 D. A. Dotzauer, S. Bhattacharjee, Y. Wen and M. L. Bruening,
Langmuir, 2009, 25, 1865–1871.
2
5 J. J. Storhoff, R. Elghanian, R. C. Mucic, C. A. Mirkin and
R. L. Letsinger, J. Am. Chem. Soc., 1998, 120, 1959–1964.
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11903–11905 11905