Robust Synthesis of Gold-Based Multishell Structures as Plasmonic Catalysts for Selective Hydrogenation of 4-Nitrostyrene

Article abstract of DOI:10.1002/anie.201910836

A robust self-template strategy is used for facile and large-scale synthesis of porous multishell gold with controllable shell number, sphere size, and in situ surface modification. The process involved the rapid reduction of novel Au-melamine colloidal templates with a great amount of NaBH₄ in presence of poly(sodium-p-styrenesulfonate) (PSS). After soaking the templates in other metal salt solution, the obtained bimetallic templates could also be generally converted into bimetallic multishell structures by same reduction process. In the hydrogenation of 4-nitrostyrene using NH₃BH₃ as a reducing agent, the porous triple-shell Au with surface modification (S-PTSAu) exhibited excellent selectivity (97 %) for 4-aminostyrene in contrast with unmodified triple-shell Au. Furthermore, it also showed higher enhancement of catalytic activity under irradiation of visible light as compared to similar catalysts with fewer shells.

Full text of DOI:10.1002/anie.201910836

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Accepted Article
Title: Robust synthesis of Au-based multishell structures as plasmonic
catalysts for selective hydrogenation of 4-nitrostyrene
Authors: Shuyan Song, Jian Li, Yu Liu, Lingling Zhang, Qishun Wang,
Xiao Wang, Hongjie Zhang, and Yan Long
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201910836
Angew. Chem. 10.1002/ange.201910836
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Robust synthesis of Au-based multishell structures as plasmonic
catalysts for selective hydrogenation of 4-nitrostyrene
Jian Li,[a,b] Yan Long,[a] Yu Liu,[a] Lingling Zhang,[a] Qishun Wang,[a,b] Xiao Wang,[a] Shuyan Song,*[a,b]
and Hongjie Zhang[a,b]
Abstract: In this paper, we describe a robust self-template strategy
for facile and large-scale synthesis of porous multishell Au with
controllable shell number, sphere size and in-situ surface
modification. The process involved the rapid reduction of novel Au-
melamine colloidal templates with a great amount of NaBH4 in
presence of poly(sodium-p-styrenesulfonate) (PSS). After soaking
the templates in other metal salt solution, the obtained bimetallic
templates could also be generally converted into bimetallic multishell
structures by same reduction process. In the hydrogenation of 4-
nitrostyrene using NH3BH3 as a reducing agent, the porous triple-
shell Au with surface modification (S-PTSAu) exhibited excellent
selectivity (97 %) for 4-aminostyrene in contrast with unmodified
triple-shell Au. Furthermore, it also showed higher enhancement of
catalytic activity under irradiation of visible light as compared to
similar catalysts with less shell number. This work opens up a new
route in designing and synthesizing Au-based multishell structures
for various applications.
shells.[12,13] These preparation procedures are tedious, especially
for shell number above two, and the obtained products show low
reproducibility, which hinders their further applications.
Interestingly, multishell structure of metal oxide can be facile
formation by controlling decomposition of metal-organic
template.[14,15] However, successful examples in noble metal
have yet to be reported,[16,17] largely due to the lack of suitable
template and the corresponding conversion strategy. On one
hand, there are limited reports about metal-organic colloidal
particles of noble metal, especially containing Au ions.[18,19] On
the other hand, unlike metal oxide clusters, the Au clusters
generated by the decomposition of a template can rapidly
aggregate and regrow into bulk materials owing to their high
surface free energies,[20] which would increase difficulty in
controlling morphology.
Herein, we synthesized novel Au-melamine colloidal spheres
by directly heating aqueous solution of Au3+ and melamine at 70
oC. By rapidly adding a great amount of NaBH4 into mixed
solution containing colloidal sphere and PSS, the multishell Au
with in-stiu modification of reducing PSS could be obtained. The
scanning electron microscopy (SEM) images (Figure 1a and b)
and the transmission electron microscopy (TEM) images (Figure
1c) reveal that the solid template spheres with average
diameters of 400 nm (Figure S1a) possess uniform structure and
smooth surfaces. The X-ray powder diffraction (XRD) pattern
(Figure S1b) and the high-resolution X-ray photoelectron
spectroscopy (XPS) spectrum (Figure S1c) of Au display the
Fabricating metal catalysts with attractive structure and
excellent performance have received much attention in recent
years.[1-3] To evaluate their performance, the catalytic selectivity
plays an important role for specific organic reaction. Chemical
modification is one of effective strategy for tuning electronic
states and steric environment of metal catalysts and further
improving their selectivity.[4,5] However, the greatly reduced
activity was also observed in these modified catalysts due to the
influence of modifier.[6,7] Plasmonic catalysis has emerged as
effective routes to accelerate chemical reactions under mild and
environmentally friendly conditions.[8,9] As one of excellent
plasmonic catalysts, Au materials can not only catalyze a series
of organic reactions, but also harvest and utilize visible light
energy to promote these reactions.[8,9] Constructing multishell
structures of Au may further increase their plasmonic catalytic
activity, since the porous multiple shells can provide larger
specific surface area, enable molecules to access to the interior
of structures and increase light-harvesting.[10-11]
For the synthesis of multishell noble metal, current methods
have mainly focused on the use of galvanic replacement
reactions, involving multiple growing and etching of sacrificial
[a]
[b]
J. Li, Y. Long, Y. Liu, L. L. Zhang, Q. S. Wang, Dr. X. Wang, Prof. S.
Y. Song, and Prof. H. J. Zhang
State Key Laboratory of Rare Earth Resource Utilization,
Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun 130022, P. R. China.
E-mail: songsy@ciac.ac.cn
J. Li, Q. S. Wang, Prof. S. Y. Song, and Prof. H. J. Zhang
School of Applied Chemistry and Engineering, University of Science
and Technology of China, Hefei 230026, Anhui, P. R. China.
Figure 1. (a-b) SEM images with different magnification, (c) TEM images for
Au-melamine spheres; (d-e) SEM images, (f-h) TEM images with different
magnification, and (i) HRTEM image of S-PTSAu.
Supporting information for this article is given via a link at the end of
the document.
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formation of amorphous colloidal sphere containing Au3+. The
Fourier transform infrared (FT-IR) spectra (Figure S1f) show that
the colloidal sphere might be formed by complicated hydrogen-
bond interaction. The colloidal sphere with average size of 400
nm can be adjusted to 254 nm and 130 nm by changing
experiment conditions (Figure S2). Unlike templates, the
reduced samples illustrate vesicle-like morphology with rough
surfaces and decreased average diameter of 288 nm (Figure 1d,
e and S3a). The TEM images (Figure 1f, g and S3b) reveal that
the spheres possess a clear triple-shell structure. These porous
shells consist of Au branches, which are formed by mutual
fusion of small Au nanoparticles. A large number of interstices
between branches with size below to 10 nm are distributed
throughout the shells (Figure 1h). The high resolution TEM
(HRTEM) image illustrates that the lattice distances are 0.205
nm (Figure 1i), corresponding to the (200) planes of metal Au.
Figure 3. TEM images of (a) S-PSSAu, (b) S-PDSAu and (c) S-PTSAu. (d)
UV-Vis-NIR absorption spectra of different samples with same Au
concentration (90 ppm).
faster than separation rate of MBPs, the formation of multishell
Au is limited within the MBPs, which not only weakens the
uncontrollable regrowth of small Au nanoparticles but also
prevents their departure to form free nanoparticles. Therefore,
the relatively slow separation of MBPs effectively assists the
formation of completed multishell structures. The addition of
PSS to original solution can obtain the dispersive samples. The
XPS spectrum of S 2p (Figure 2e) shows presence of three
-
types of sulfur species in final sample, including sulfonate (–SO3
), sulfinate (–SO2 ) and the sulfide (-S-). These results display
that part of –SO3- in PSS is reduced into –SO2- and -S- by highly
-
active hydrogen in NaBH4 to form reducing PSS, which is similar
2-
to the formation of S2- and S2 from SO3
.
2- [21] These reducing
PSS with a stronger coordinated capability will stabilize the Au
sphere to form S-PTSAu. Additionally, XRD patterns (Figure 2f)
of samples reacting for different time and the TEM images in
Figure S7 indicate that the initial reduction stage can obtain
MBPs-protected shells consisting of small Au nanoparticles.
Along with gradual separation of MBPs, these small Au
nanoparticles will regrow via mutual fusion process, finally
leading to form porous shells. The more detailed formation
process can be found in supporting information.
Figure 2. (a) Schematic. (b) TEM image of Au-melamine sphere. (c) TEM
image of triple shell Au after reaction for one minute without the addition of
PSS. (d) TEM image of S-PTSAu, (e) XPS spectrum of S 2p for S-PTSAu. (f)
XRD patterns of S-PTSAu after reaction for different time.
Furthermore, we discovered that changing reaction
temperature could effectively tune shell numbers. For example,
the single, double and triple-shell Au with surface modification
(S-PSSAu, S-PDSAu and S-PTSAu) formed at the temperature
of 0 oC, 10 oC and 25 oC, respectively (Figure 3a-c). It is
postulated that increased reaction temperature can decrease
In order to weaken the diffusion and growth of small Au
nanoparticles, the mixed solvents of water and ethylene glycol
with high viscosity were used in reduction process (Figure S4). If
no PSS was added in reactions, the only aggregated multishell
Au spheres were obtained (Figure S5a-b). The TEM images of
sample after reaction for one minute show that the completed
multishell structures already form at this time (Figure 2c and
S6a). However, the whole sphere is covered by the residual
melamine-based polymers (MBPs) (Figure 2c and S6). Most of
MBPs would separate from the Au surfaces with further reaction
(Figure S5). Because the reduction rate of colloidal sphere is
－
viscosity of solvent and greatly accelerate BH4 to diffuse into
the interior of colloidal sphere (Figure 2a). As a result, the
－
inward diffusion of BH4 is much faster than outward diffusion of
Au species. These diffusion rate distinctions finally lead to
formation of multishell structures.[22-24] UV–Vis–NIR spectra
(Figure 3d) of three samples (S-PSSAu, S-PDSAu and S-PTSAu)
with same Au concentration were determined to investigate their
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Table 1. Selective Hydrogenation of 4-nitrostyrene over PTSAu/ZrO2, S-PTSAu, S-PDSAu and S-PSSAu under Visible Light Irradiation and in the Dark.
.
Experiment conditions: 4-nitrostyrene (0.2 mmol), NH3 BH3 (0.5 mmol), Au (1.5 mol%), Xe lamp at 0.5 W·cm-2 with 420 nm cutoff filter at 298 K. The reaction time
is 2 h.
light absorption property. Accompanied by the increasing shell
number, increased light-harvesting is observed, which may be
caused by the presence of additional incident light reflections in
the structures with more shells.[10,11] Moreover, converting 254
nm and 130 nm colloidal spheres can obtain 160 nm and 90 nm
(Figure S8) Au spheres, respectively. Because of the robust
conversion process, these multishell Au spheres could be easily
synthesized by expanding the synthetic scale by a factor of 20,
and the samples still maintained high quality (Figure S9). More
importantly, such a simple strategy is also suitable for generally
fabricating Au-based bimetallic multishell structures. For
example, the Au-Ag, Au-Cu and Au-Pt multishell structures were
synthesized by soaking the templates in corresponding salt
solution and further reducing the obtained templates (Figure
S10).
Selective reduction of Ar-NO2 in the presence of Ar-C=C can
lead to the formation of functional amines, which are important
industrial intermediates for pharmaceuticals, fine chemicals, and
polymers.[25,26] NH3BH3 with advantages of high hydrogen
storage capacity and long-term stability is a new candidate as a
hydrogen donor for hydrogenation reactions.[27] We chose the
hydrogenation of 4-nitrostyrene as the probe reaction to
investigate the influence of surface modification and multishell
structure on catalytic performance of Au sphere. The catalytic
reaction was implemented using NH3BH3 as a reducing agent.
The ZrO2 supported triple-shell Au (PTSAu/ZrO2) as unmodified
contrast sample was also synthesized without addition of PSS
(Figure S11a). Catalytic results under visible light irradiation and
in the dark are provided for comparison. As shown in Table 1
(entry 1), the PTSAu/ZrO2 showed >99 % conversion in both
light and dark conditions. However, their poor selectivity of 4-
aminostyrene (77 % in the light and 84 % in the dark) were also
observed. In contrast, the S-PTSAu displayed only 14 %
conversion in the dark, but >99 % conversion in visible light
irradiation. At the same time, it also possessed 97 % of
selectivity for 4-aminostyrene (Table 1, entry 2). Their selectivity
could maintain at 97 %, even though the reaction time was
prolonged to 12 h. The influence of ZrO2 can be ignored, since
the selectivity of ZrO2 supported S-PTSAu is the same as S-
PTSAu. We further tested time profiles of both modified and
unmodified sample. The time profiles of PTSAu/ZrO2 (Figure
S12a) displayed rapid reduction of –NO2, and slow
overhydrogenation could also be observed. For S-PTSAu/ZrO2,
the catalytic activity was greatly weakened (Figure S12b), which
is not surprising as the poison ability of sulfhydryl group in
reducing PSS.[4,32] More importantly, the overhydrogenation
reaction was prevented in S-PTSAu/ZrO2 system (Figure S12b).
.
The NH3 BH3-initiated hydrogenation of
a
mixture of
nitrobenzene and styrene was further tested using two catalysts.
The results (Table S1) show that PTSAu/ZrO2 are active towards
reduction of Ar-NO2 and Ar-C=C, while the S-PTSAu/ZrO2
activate only Ar-NO2, not Ar-C=C. The transfer hydrogenation
processes have been proposed in AB-initiated hydrogenation
reactions.[28-30] In these processes, the polarized hydrogen atom
.
in NH3 BH3 would transfer to unsaturated groups.[28-31] The
modification of sulfhydryl species on Au surface might influence
polarized hydrogen transfer towards -C=C, finally resulting in
their high selectivity. The unmodified Au/ZrO2 was also
synthesized (Figure S11c) by simple reduction of HAuCl4 and
ZrO2 nanoparticles mixture solution with NaBH4. In order to
confirm the influence of sulfhydryl species modification, the
Au/ZrO2 was further treated with L-cystine to obtain modified
sample (S-Au/ZrO2). The catalytic results (Table S2) show that
selectivity (96 %) of S-Au/ZrO2 is obviously higher than Au/ZrO2
(71 %).
The catalytic results of entries 2-4 in Table 1 indicate that Au
spheres with more shell number exhibit obvious higher
photocatalytic activity. Specifically, the conversion (> 99 %) of S-
PTSAu in same light conditions was higher than those of S-
PDSAu (84 %) and S-PSSAu (65 %). When reactions are
implemented under irradiation of visible light, S-PTSAu can
absorb light energy by localized surface plasmon resonance
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