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Robust Fe3O4/SiO2-Pt/Au/Pd Magnetic Nanocatalysts with
Multifunctional Hyperbranched Polyglycerol Amplifiers
Li Zhou,†,‡ Chao Gao,*,‡ and Weijian Xu*,†
†Institute of Polymer Science and Engineering, College of Chemistry and Chemical Engineering,
Hunan University, Changsha 410082, P. R. China, and ‡MOE Key Laboratory of Macromolecular Synthesis
and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, 38 Zheda Road,
Hangzhou 310027, P. R. China
Received February 5, 2010. Revised Manuscript Received April 1, 2010
Here we report a facile approach to prepare multicarboxylic hyperbranched polyglycerol (HPG)-grafted SiO2-coated
iron oxide (Fe3O4/SiO2) magnetic hybrid support. This support combined the both features of Fe3O4 and HPG, facile
magnetic separation, and favorable molecular structure with numerous functional groups. With the use of the grafted-
HPGs as templates, various noble metal nanocatalysts such as Pt, Au, and Pd were directly grown on the surfaces of
magnetic support with ultrasmall and nearly monodisperse sizes (e.g., the average sizes of Pt, Au, and Pd are 4.8 ( 0.5,
6.0 ( 0.6, and 4.0 ( 0.4 nm, respectively) and high coverage densities. Because of the amplification effect of HPG, high
loading capacities of the nanocatalysts, around 0.296, 0.243, and 0.268 mmol/g for Pt, Au, and Pd, respectively, were
achieved. Representative catalytic reactions including reduction of 4-nitrophenol, alcohol oxidation, and Heck reaction
demonstrated the high catalytic activity of the noble metal nanocatalysts. Because of the stabilization of HPG templates,
the nanocatalysts can be readily recycled by a magnet and reused for the next reactions with high efficiencies. The robust
multifunctional magnetic hybrids will find important applications in catalysis and other fields such as drug delivery and
bioseparations.
Introduction
catalyst with nanoscale size and large surface areas immobilized
on an appropriate support can also show comparable catalytic
efficiency of the homogeneous catalyst to some extent.9,10 Re-
cently, immobilizing noble metal nanocatalysts on Fe3O4 mag-
netic support has drawn a great deal of attention due to the facile
recycle process of the catalyst by an external magnetic field.11-13
In addition, the Fe3O4 particles can be easily produced through
precipitation of ferrite with the basic solution. Considering the
Fe3O4 particles are reactive especially in an acid environment and
thereby to lose their magnetic properties, silica as a protecting
shell was usually utilized to coat the Fe3O4 particles to form a
core-shell (Fe3O4/SiO2) structure.14 Meanwhile, the silica shell
can prevent the aggregation of the Fe3O4 particles and provide
numerous surface Si-OH groups for further modification.15
The metal nanocatalysts can be immobilized on the magnetic
support through two approaches. The one is to deposit the
presynthesized metal nanoparticles onto the support by chemical
adsorption.16,17 This approachallows the finecontrol over the size
and shape of the metal nanoparticles, but the whole operation-
steps are tedious; and moreover, the adsorbed nanocatalysts are
With the development of nanoscience and nanotechnology,
the combination of different nanomaterials to afford a multi-
functional integrated nanosystem that simultaneously possesses
optical, catalytic, electronic, and magnetic properties becomes
possible.1,2 This kind of nanosystem is significantly fascinating
because of its potential applications in biomedicine, optical
devices, and catalysis.3-5
For catalysis, it is well-known that homogeneous catalysts
show higher catalytic activities than their heterogeneous counter-
parts because they can dissolve in reaction media making all
catalytic sites accessible to the substrate.6,7 However, the expen-
sive noble metal catalysts are difficult to be recycled and thus
cause huge waste and also contaminate the products. In practical
industrial applications, homogeneous catalysis has a share of less
than 20%, significantly lower than that of heterogeneous cata-
lysis.8 Therefore, the high catalytic activity is not the sole factor
for an excellent catalyst, but a recyclable system in which the
catalyst can be easily separated from the products and recycled
through a separate rejuvenation procedure is also needed. On
the other hand, for heterogeneous catalysis, the noble metal
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*To whom correspondence should be addressed. E-mail: chaogao@
zju.edu.cn (C.G.); weijxu@hnu.cn (W.X.).
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Langmuir 2010, 26(13), 11217–11225
Published on Web 04/13/2010
DOI: 10.1021/la100556p 11217