Well-dispersed graphene-polydopamine-Pd hybrid with enhanced catalytic performance

Article abstract of DOI:10.1039/c5ra13361k

Inspired by the discovery of adhesive proteins in mussels, we prepared a graphene-polydopamine (GPDA) hybrid, in which the commonly used graphene oxide was replaced by graphene synthesized through physical routes. Then, the hybrid was decorated with ultra

Full text of DOI:10.1039/c5ra13361k

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: J. Ma, H. Yang, S.
Li, R. Ren, J. Li, X. Zhang and J. Ma, RSC Adv., 2015, DOI: 10.1039/C5RA13361K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
Page 1 of 11
RSC Advances
View Article Online
DOI: 10.1039/C5RA13361K
Journal Name
ARTICLE
Well-dispersive graphene-polydopamine-Pd hybrid with enhanced
catalytic performance
Jian-Xin Ma, Honglei Yang, Shuwen Li, Ren Ren, Jing Li, Xueyao Zhang and Jiantai Ma∗
Received 00th January 20xx,
Accepted 00th January 20xx
Inspired by the discovery of the adhesive proteins in mussels’ clues, we prepared a graphene-polydopamine (GPDA) hybrid,
in which the commonly used graphene oxide was replaced by graphene synthesized through physical routes. Then the
ultrafine Pd nanoparticles were decorated on the hybrid to obtain a stable and well-dispersed catalyst in polar solvents. The
Pd nanoparticles on graphene-polydopamine (GPDAP) were 2.0 nm in average and processed a good monodispersibility on
the polydopamine modified graphene, while the size of the Pd particles on unmodified graphene (GP) was larger than 4.5
nm and obviously aggregated. The catalytic activity of the catalyst was investigated in the reduction of 4-nitrophenol (4-NP),
K3[Fe(CN)6], methylene blue (MB) and rhodamine B (RhB), respectively, which are common industrial pollutants. The
comparison between Pd/C (CP) and GP, GPDA prevailed that the prepared catalyst GPDAP showed superior activity even
just tiny amount of catalyst was added.
DOI: 10.1039/x0xx00000x
www.rsc.org/
surface area and the quantity of steps and kinks on the surface
can enhance the catalytic activity of the metallic nanoparticles.
Based on the above properties, smaller size of the metal particle
is beneficial for the activities of the catalysts. However, serious
aggregation makes it hard to prepare small and monodispersed
particles. To avoid the aggregation, different kinds of supports,
1 Introduction
Dyes, which are widely used in many industries, cause serious
environmental pollution, due to their toxicity and difficulty to
degrade. As a kind of dye used in pesticides, dyeing,
pharmaceutical industry, 4-nitrophenol (4-NP) is produced in the
highest quantities among phenol derivatives in the world1. For
sake of the existence of the nitro group, the ring of the 4-NP is
further stabilized, which makes it hard to degrade in the natural
environment. Other dyes like methylene blue (MB) and
rhodamine B (RhB) are also carcinogenic and difficult to degrade.
such as Al2O3, MOF and graphene, have been used to minimize
9-13
the total surface energy and stabilize the nanoparticles
.
Graphene, a kind of marvelous two-dimensional carbon
nanosheets, with a structure of honeycomb, has attracted great
attention because of its high strength and excellent conductivity
to both heat and electricity. Since discovered by Novoselov et al.
in 2004 14, graphene has been applied in many fields, such as
transistors 15, biosensors 16, fuel cells 17, catalysts 18, 19, hydrogen
storage 20, and drug delivery 21. As a support of catalyst, it can
stabilize nanoparticles through static interaction, as well as
improve the catalytic performance through synergistic
interaction between nanoparticles and graphene 22. Though the
excessive charge makes pure graphene a good support to
stabilize nanoparticles, the static interaction is not strong enough
to prevent the aggregation effectively 23. In order to solve this
problem, the functionalization of graphene via covalent or
noncovalent method is considerably investigated. The covalent
functionalization shows strong bond intensity. Yet, the extended
aromatic structure of graphene is perturbed, just because of
binding to or generating defects on graphene 24-26. Compared to
covalent, noncovalent functionalization can attach functional
Due to their toxicity and stability, many efficient catalysts such
as noble metals are frequently used for the disposal of dyes2.
Currently, a cheaper noble metal Pd showed much higher activity
for the catalytic oxidation, catalytic hydrogenation, cross-
coupling reactions 3-5, and reduction of 4-NP compared to other
6
commonly studied noble metals . For example, Zhang et al.
reported the development of a new type of bifunctional
nanocatalyst based on three-dimensional macroscopic carbon
nanotube-graphene hydrogel supported Pd nanoparticles and
explored its practical application in catalytic reduction of p-
7
nitrophenol . In 2013, a kind of ultrafine Pd nanoparticles was
prepared, which was encapsulated by Double-shelled hollow
carbon spheres with reduced graphene oxide as inner shell and
carbon layer as outer shell and it exhibited superior performance
8
in the reduction of p-nitrophenol . Moreover, improving the
27,
groups to graphene without disturbing the aromatic structure
28. In most cases, the strength of this kind of decoration is not as
intense as that of covalent decoration. Therefore, it is crucial to
find out an approach combining advantages of both covalent and
noncovalent functionalization.
State Key Laboratory of Applied Organic Chemistry, Gansu Provincial Engineering
Laboratory for Chemical Catalysis, College of Chemistry and Chemical
Engineering, Lanzhou University, Lanzhou 730000, PR China
E-mail: majiantai@lzu.edu.cn; Fax: +86-931-8912582; Tel: +86-931-8912577
Electronic Supplementary Information (ESI) available. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 11
ARTICLE
Recently, polymers with aromatic structures have been 500~1000, Electrical resistivity (Ω.cm):
Journal Name
0.30)VipewreAprtaicrleedOnlbinye
≦
29,
employed to functionalize graphene
30. The discovery of physical method was purchased from Nanjing XFNano Materials
DOI: 10.1039/C5RA13361K
adhesive proteins in mussels’ clues, which are rich in 3,4- Tech Co., Ltd., Dopamine was purchased from Energy Chemical
dihydroxy-L-phenylalanine as the main role to interact with of Sun Chemical Technology (Shanghai) Co., Ltd., Tris (99.8%)
substrates 31, propelled a new strategy of surfaces modification. was purchased from Pengcheng Biological Technology
Inspired by this versatile adhesives of invertebrate mussels, in Development Co., Ltd., K2PdCl4 (99.9%) was purchased from
32
2007, Lee et al.
reported a method to functionally modify J&K Scientific Ltd., KCl was purchased from Cheng Du Ke
material surfaces with polydopamine (PDA), a kind of structure Long Chemical Co., Ltd., NaBH4 was purchased from
similar to DOPA, interacting with surfaces by intensive covalent Sinopharm Chemical reagent Co., Ltd., Ethenol was purchased
and noncovalent binding33. For this reason, PDA is a promising from Rionlon Development Co., Ltd.
alternative to functionalize graphene which combines
2.2 Preparation of Graphene-PDA (GPDA)
advantages of both covalent and noncovalent functionalization.
Xu et al. reduced GO with dopamine to obtain polydopamine HCl (5 M) was added to the solution of Tris to obtain 10 mM
functionalized reduced graphene oxide (rGO) 34. Ye et al. Tris-Cl buffer (pH=8.5) and 50 mg of dopamine hydrochloride
designed a route to synthesize
a polydopamine (PDA)-Ag- was dissolved in 10 mL DI water. Subsequently, 50 mg
reduced graphene oxide (RGO) hybrid and hybrid was applied to Graphene was added to 100 mL Tris-Cl buffer and the solution
the oxidation of hydroquinone to benzoquinone in the presence was sonicated for 30 min in an ice-salt bath. The suspension was
of H2O2 35. Furthermore they synthesized flowerlike Pt stirred vigorously for 10 min. Then
nanocrystals on poly-dopamine (PDA) functionalized reduced hydrochloride was added to the flask. The reaction was stirred at
oxide graphene (RGO) 36. The Pt(F)-PDA/RGO catalyst showed 60
for 24 hours. In the end, the product was filtrated with 400
improved catalytic activity and stability toward methanol nm nanofiltration membrane, washed by water and alcohol for
5 mL dopamine
℃
electrooxidation. Zhao et al. immobilized Cu2+ on magnetic several times and dried reduced pressure at 60
graphene@polydopamine (magG@PDA@Cu2+) composites and Black powders were obtained.
applied the novel nanocomposites to the enrichment and
℃ overnight.
2.3 Preparation of Graphene-PDA-Pd (GPDAP)
37
identification of low-concentration standard peptides
.
However, strong oxidizer and concentrated acid are needed to 20 mg GPDA was dispersed in 40 mL DI water and sonicated for
prepare GO, which consumes a large quantity of dangerous 30 min, followed by adding 3.77mL K2PdCl4 (5 mM) and
reagent and produces environmental pollutants. Paton et al.38 keeping stirring for 1 h. After that 40mL NaBH4 (2.5mM) was
exfoliated graphite in solution to prepare graphene large-scale added dropwise in 30 min. After being stirred for 3 h, the product
directly, which means graphene prepare with physical route was obtained by filtration, thoroughly rinsed with water and
could be more available and cheaper than traditional GO in the alcohol and dried in reduced pressure desiccator for 24h.
near future. But fewer -OH and -COOH on it than GO made it
2.4 Preparation of Graphene-Pd (GP)
hard to disperse in polar solvent without the aid of surfactants.
To mimic the directly exfoliated graphene, we chose 20 mg graphene was dispersed in 40 mL DI water. Then 3.77mL
commercialized graphene prepared through physical route which K2PdCl4 (5mM) was added and kept stirring for 1 h. After that,
is also short of -OH and -COOH to proceed the experiment.
GP was prepared similarly to the former process.
2.5 Characterization
Based on the reasons above, we functionalized graphene
synthesized through physical routes, instead of traditional GO, The structure of our catalyst was analyzed with Raman
with polydopamine through self-polymerization of dopamine spectrometer (inViaRenishaw confocal spectrometer with 633
directly, which is facile and more useful for large scale nm laser excitation). The morphology, size, and size
preparation in the future. Furthermore, ultrafine Pd nanoparticles distributions of the Pd particles were investigated using
were decorated on graphene-polydopamine (GPDA) hybrid with transmission electron microscopy (TEM, Tecnai G2 F30 electron
simple method with no surfactant added. To evaluate the microscope operating at 300 kV). X-ray diffraction (XRD)
catalytic activity of our catalyst, it was used in the reduction of measurements were carried out with a high-resolution X-ray
4-NP and K3[Fe(CN)6] by borohydride ions compared with diffractometer (Rigaku D/max2400 diffractometer). The
commercial grade palladium on carbon (CP) and graphene-Pd concentration of Pd in our catalyst was analyzed using inductive
(GP) prepared with similar process to that of graphene-PDA-Pd coupled plasma atomic emission spectrometer (ICP-AES),
(GPDAP) 39. Further application of two famous dyes (MB and which was conducted with PerkinElmer (Optima-4300DV). The
RhB) for degradation was studied. The processes were recorded reaction was investigated with UV-VIS absorption spectra
in situ by UV-VIS spectrophotometer.
(HP/Agilent 8453 UV/Vis Spectrophotometer).
2.6 Catalytic reduction of 4-nitrophenol
2 Experimental
200 µL of 4-notriphenol (1 mM) was mixed with 1.2mM DI
water and 1.5 mL of fresh NaBH4 (10 mM) solution in a quartz
cuvette. And 1 mg catalyst was dispersed into 10 mL DI water.
As soon as 100 µL catalyst solution was added, monitoring the
2.1 Materials
Graphene (Diameter: 0.5~2 µm, Thickness: ~0.8 nm, Single
Layer Ratio: ~80%, Purity: ~99%, BET surface area (m2/g):
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 11
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
reaction with UV-VIS spectroscopy at 25
was measured at a wavelength of 400 nm.
℃
. And the kinetics
View Article Online
DOI: 10.1039/C5RA13361K
2.7 Catalytic reduction of hexacyanoferrate (III)
200 µL of hexacyanoferrate (III) (10 mM) was mixed with
1.25mL DI water and 1.5 mL of fresh NaBH4 (10 mM). After
that, 50 µL catalyst solution (0.1 mg/mL) was added. the
catalytic reduction of dyes, time-dependent absorption spectra
were recorded at 15
℃.
2.8 Catalytic degradation of organic dyes
1 mg of catalyst was ultrasonically dispersed in 10 mL DI water.
Then 10 µL catalyst solution was added to 50 µL MB (2 mM)
solution, followed by the addition of 1.5 mL freshly prepared
NaBH4 solution (10 mM). 1.45mL DI water was added to keep
the reaction system in proper concentration. The extent of the
reaction was monitored by UV-VIS spectrophotometer in situ.
The degradation of RhB was studied under same condition,
except the quantity of catalyst solution was 50 µL.
3 Result and discussion
Fig.1 Schematic illustration for the preparation of GPDAP.
Inspired by the fabulous adherence of mussels, we designed a
simple method for functionalization of pure graphene. The
chelation of Pd(II) ions on catechol structure leads to good
monodispersity of reduced Pd nanoparticles and that kind of
strong interaction can prevent particles from aggregation, as
illustrated in the Fig.1. Furthermore, the coordination of amino
groups to Pd is also strong to improve the stability 40, 41. And
dispersibility of our catalyst was highly boosted. It is believed
that the mussel-inspired polydopamine decoration have a
promising future. The contents of nitrogen in graphene-PDA
hybrid was 2.4 wt% characterized by ICP-AES. Therefore, the
percentage of PDA in GPDA was 26.25%. Furthermore, 7.9wt%
of Pd was disposed on GPDA in GPDAP and 7.3wt% was
disposed on graphene in GP, indicated by the ICP-AES analysis.
The content of Pd in GPDAP was higher than GP even excessive
NaBH4 added, due to the coordination of Pd ions with catechol
structures and amino groups.
The TEM of GPDAP compared with Graphene Pd were given in
Fig.3. The fabulous feature was that the Pd particles on GPDA
were monodispersed and well-distributed, while the size of Pd
without PDA not was as homogenous as the former. The high
resolution TEM (HRTEM) obviously visualized the aggregation
of Pd without PDA and good monodispersity when PDA was
added. By statistical analyzing the particle size distribution, as
seen in the inserts of Fig.3 (A) and (B),the mean particle size of
Pd in GPDAP was 2.0 nm and processed better
monodispersibility, most of which distributed in a narrow range
from 1 to 3 nm. However, the diameter of Pd nanoparticles in GP
was as large as 4.5 nm in average and disperses from 1 to 9 nm.
This could be ascribed to catechol and amino groups stabilizing
the particles and lowing the energy 41. In the image of HRTEM,
the interplanar spacing of Pd lattice could be distinguished
clearly to be 0.226 nm, which matched well with the (111) lattice
of spacing of Pd (0.225 nm) 45. Based on the results of TEM,
GPDAP had a larger surface area and more Pd atoms were
exposed.
Fig.2 showed Raman spectra of Graphene, polydopamine and
Graphene-PDA hybrid (GPDA). In the spectrum of graphene,
there were two strong featured bands, the vibrational D band at
1350 cm-1 and the G band at 1580 cm-1. D band arose from the
defects at the edge of graphene and interaction with the substrate
42. Polydopamine also showed two broad bands at 1350 cm-1,
1580 cm-1, coming from vibration of aromatic rings and aliphatic
C-C and C-O stretching43. The sum of two constitutions was
observed in GPDA. The ratios of intensity of peaks (ID/IG) before
and after the modification were calculated, which changed from
1.46 to 1.18 after PDA modified, inferring the less defects after
decoration with PDA. That is because the defects on graphene
was covered by polydopamine which also possesses aromatic
structures 44
.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 11
ARTICLE
Journal Name
View Article Online
DOI: 10.1039/C5RA13361K
Fig.2 Raman spectra of PDA, graphene and GPDA.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 11
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
Typical XPS spectra of GP and GPDAP wDeOreI:d10e.p1i0c3t9e/dC5inRAF13ig3.615K.
The existence of N 1s (400.8eV) further confirmed that the
graphene was decorated by PDA through π-π interaction. Peaks
at 335.4 eV which was for 3d5/2 of Pd nanoparticles indicated the
41,
existence of Pd in our catalysts
47. Comparing the high
resolution XPS spectra of Pd in GPDAP with that in GP, the peak
of Pd 3d5/2 of GP is 335.51 eV and that of GPDAP is 337.95 eV.
An obvious shift of 2.44 eV was recognized after the decoration
of PDA, which may due to the strong interaction between amino
group or catechol structure and Pd nanoparticles.
Fig.3 TEM image of GP (A and C) and GPDAP (B and D). Insert: particle size distribution
graphs of Pd nanoparticles in GP (A) and GPDAP (B) and HRTEM of GP (C) and GPDAP (D).
XRD was measured to study the structure of our catalysts. In
consideration of the GP, the peaks in the Fig.4 demonstrated the
existence of both Graphite-like crystalline and Pd particles. The
broad diffraction peak at 26.3 ° came from the (002) crystal face
of graphene. The other four peaks at 40.4 °, 46.8 °, 68.4 ° and
82.4 ° corresponded to the (111), (200), (220) and (311)
crystalline plane of Pd particles 46. For GPDAP, similar features
were presented. The average particle size of Pd in GPDAP
calculated from the Pd (111) peak according to the Scherrer’s
Formula was 2.1 nm, which agreed well with the TEM result.
The XRD result confirmed the Pd particle was successfully
immobilized on graphene-polydopamine hybrid.
Fig. 5 (A) XPS wide-scan spectra of GPDAP and GP. (B) N 1s core level spectra of GPDAP
and GP. (C) Pd 3d core level spectra of GPDAP and GP
Fig.4 XRD spectra of GPDAP, GP and the standard bar graph of Pd and pure graphene.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 11
ARTICLE
Journal Name
after 7 days. Obviously, the dispersibility of GPDAP was well
View Article Online
DOI: 10.1039/C5RA13361K
For heterogeneous catalysts, the dispersibility in solution plays a improved by polydopamine.
key role in the activity of catalysis. Based on the properties of
hydroxyl groups on the surface, our catalyst showed fabulous So as to accurately demonstrated catalytic ability of our catalyst,
dispersibility. Catalysts with and without polydopamine added our catalysts (GPDAP, GP and CP) were used in two widely used
were compared. As shown in Fig.6, the photos were taken after catalytic model reactions 39, 48, viz. the reduction of 4-NP by
0 h (A), 2 h (B), 5 h (C) and 7 h (D). The concentrations of both sodium borohydride and the reduction of ferrocyanate(III) 49,as
solution are 0.5mg/mL and the solution started to precipitate shown in Fig.6 (E).
Fig.6 Photographs of (a) GP and of (b) GPDAP dispersed in DI water after 0 h(A), 2 h (B), 5 h (C) and 7 h (D). the concentration of both solution is 0.5 mg/mL. (E) The illustration of the
reduction of 4-NP, K3[Fe(CN)6], RhB and MB catalyzed by GPDAP.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 11
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
View Article Online
DOI: 10.1039/C5RA13361K
Fig. 7 UV-visible absorption spectra of the reduction of 4-NP (A), K3[Fe(CN)6] (C), MB (E), RhB (G) catalysed by GPDAP. Plot of ln(Ct/C0) versus time spectra for the reduction of 4-NP
(B), K3[Fe(CN)6] (D), MB (F), RhB (H) catalyzed by GPDAP, GP, CP and nothing added.
When studying the former model reaction, the extent of reactions we could treat the reduction as pseudo-first-order with respect to
was monitored in situ by measuring the UV-VIS absorption the concentration of 4-NP 54, 55. That is, ln(A/A0) and time shows
spectra of the reactant mixture to ensure the precision of good linear relationship, so we can write the kinetic equation for
surveillance, because the reaction was so fast that to separate the the reaction as follows:
products in such short time was infeasible. A peak of the reactant
푑퐶푡 푑퐴
퐶푡
= ln ( ) = ln ( ) = −푘푡
푑푡 퐶0 퐴0
퐴푡
4-NP was showed at 400 nm and that of the product 4-
aminophenol (4-AP) at 315 nm 50
=
푑푡
.
Where, Ct and C0 are the concentration of 4-NP at time t and the
start separately. A in the equation stands for the absorption of 4-
NP. As seen in the Fig.7(B), the rate constants k calculated from
the slopes was 4.7098×10-3 s-1, 1.8349×10-3 s-1, 1.2937 ×10-4 s-1
and 1.0153×105 s-1 attributed to GPDAP, GP, CP and no catalyst
added respectively. The content of Pd in our catalyst (GPDAP
7.9%, GP 7.3% and CP 10%) was analyzed using ICP-AES. To
compare with the activity of catalysts in literatures reported
before, a factor k* defined as the rate constant over the weight of
catalyst (k*=k/m) was calculated. Then we got
k*(GPDAP)=4.7098×102 s-1g-1, k*(GP)=1.8349×102 s-1g-1 and
k*(CP)=12.937 s-1g-1. Compared with k* of catalyst reported in
literatures in Table s1, our catalyst showed higher activity. The
excellent activity of GPDAP probably came from (1) better
dispersibility developed by hydroxyl of polydopamine (Fig.6),
(2) good monodispersity and smaller size of Pd which means
larger active surface (Fig.3) and (3) π-π interaction between
graphene and aromatic reactant to highly improve the
Initially, a blank experiment was tried, during which no catalyst
was added. The 4-NP solution showed yellowish, while it turned
dark yellow after NaBH4 was added. After that, the peak of 4-NP
at 400 nm remained unchanged. That indicated that it can’t react
in the absence of catalysts. Then with catalysts (GPDAP, GP and
CP) added in other experiments, the intensity of the peak of 4-
NP at 400 nm decreased as the reaction extended and a new peak
of 4-AP appeared gradually at 315 nm. An interesting
phenomenon was observed that the peak at 315 nm did not
always increase as the 4-NP was reduced. The abnormality might
be attributed to the absorption of products on graphene 51, 52, or
cumulation of intermediates 53
.
When 10 µL GPDAP was added, the intensity of absorption at
400 nm decreases sharply and the system turned transparent
within 600 s, as Fig.7 (A) showed. However, the other catalyzed
with GP became yellowish after 1000 s (Fig. s2). And we also
tried one with CP, the colour of which remained almost
unchanged owing to low quantities of catalysts. Only in the
spectra can we distinct the decrease of the peak at 400 nm.
concentration of 4-NP on the surface of catalysts 22
.
Another famous reaction we used was the reduction of
hexacyanoferrate (III) by borohydride. What is interesting of this
reaction is both states of the ions are stable and possess the same
chemical composition. Because of these particularities, no
induction period, which was often observed in reduction of
organic dyes such as 4-NP reduction, had been observed in this
-
The concentration of the BH4 exceeded 100 times than that of 4-
-
NP and catalysts, so we could ignore the degradation of BH4
-
ions and treated the concentration of BH4 as constant.
Furthermore, since the concentration of NaBH4 was so high that
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 8 of 11
ARTICLE
Journal Name
reaction, as shown in Fig.7 (C). Like the former reaction, the
reduction of hexacyanoferrate (III) was carried out on condition
Table 1 Summary of the constants for the catalytic reductions
View Article Online
DOI: 10.1039/C5RA13361K
Catalyst dosing
Catalyst
GPDAP
GP
Substance
4-NP
4-NP
4-NP
4-NP
K3[Fe(CN)6] 2.330×10-2
K3[Fe(CN)6] 4.260×10-3
K3[Fe(CN)6] 2.650×10-3
K3[Fe(CN)6] 4.310×10-4
k (s-1)
k* (s-1g-1)
4.7098×102
1.8349×102
12.937
-
4.660×103
8.520×102
5.300×102
-
-
that the BH4 was far more excessive than [Fe(CN)6]3- to
4.7098×10-3
1.8349×10-3
1.2937×10-4
1.0153×10-5
10 μg
10 μg
10 μg
-
5 μg
5 μg
5 μg
-
1 μg
1 μg
1 μg
-
5 μg
5 μg
5 μg
-
-
minimalize the influence of the concentration of BH4 and to
-
inhabit the hydrolysis of BH4 . The rate of reaction was
CP
monitored in situ by spectrophotometer with the decrease of the
absorption at 420 nm. Interestingly, the presence of the catalysts
changed the order of the reaction, as reported, from zero order
kinetics to first order kinetics 49. In order to compare the rates
before and after the addition of the catalysts and to simplify the
experiment, we treated the reaction with no catalyst added as a
first order reaction, which did not affect the result of the
experiment.
None
GPDAP
GP
CP
None
GPDAP
GP
MB
MB
MB
MB
RhB
RhB
RhB
RhB
2.146×10-2
1.550×10-4
6.553×10-5
2.926×10-5
2.040×10-2
2.146×10-4
1.452×10-4
7.066×10-5
2.146×104
1.550×102
65.53
CP
None
GPDAP
GP
CP
None
-
4.080×103
42.92
The rate constants for the reductions were k(GPDAP)=2.330×10-
2 s-1, k(GP)=4.260×10-3 s-1 and k(CP)=2.650×10-3 s-1, as the Fig.7
(C, D), and factor k* was calculated (k*(GPDAP)=4.660×103 s-
1g-1, k*(GP)=8.520×102 s-1g-1 and k*(CP)=5.300×102 s-1g-1) that
indicated the catalyst GPDAP showed higher catalytic activity
than the GP and CP. The remarkably high activity may come
from the high accessible surface area of the ultrafine Pd
nanoparticles.
29.04
-
For further application of the catalyst, we applied our catalyst
GPDAP in the reductive degradation of two major toxics in many
industries, MB and RhB, as Fig.7(E-H) showed, compared with
GP, CP and no catalyst was added.
First, reductive degradation of MB was studied. The absorption
band appeared at 665 nm corresponded to the n-π* transition of
MB and the MB was reduced to leuco methylene blue (LMB) 55-
-
57. For reason of the excessive BH4 , the reactions were also
treated as first order reaction and the ratios of ln(At/A0) to time
were calculated as shown in Fig.7 (F). The ratio of the reaction
without catalysts is k(blank)=7.066×10-5 s-1. The reaction
proceeded faster after adding GP and CP. To our surprise, by
adding GPDAP, the reduction was greatly enhanced
(k(GPDAP)=2.040×10-2 s-1). The degradation of MB to LMB
was accomplished in less than 300 s in the presence of ultrafine
Pd catalysts, GPDAP. An inductive time of about 150 s was
observed during the reduction, owing to surface restructuring of
the catalyst 58, 59
.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 11
RSC Advances
Please do not adjust margins
Journal Name
ARTICLE
3.
4.
V. Mazumder and S. Sun, J. Am. Chem. SoVci.e,w2A0rt0ic9le,O1n3lin1e,
The reduction degradation of another organic toxic RhB to leuco
Rh B (LRhB) which had often been used as fluorescence dye was
then studied 60, 61. The ratios of ln(At/A0) to time were calculated
and the result was similar to that of MB. The activity of catalyst
GPDAP was much higher than that of GP or CP with induced
time of about 180 s. Respectively, it was shown in the Fig.7 (H)
4588-4589.
DOI: 10.1039/C5RA13361K
R. Long, Z. Rao, K. Mao, Y. Li, C. Zhang, Q. Liu, C. Wang, Z.-
Y. Li, X. Wu and Y. Xiong, Angew. Chem., 2015, 127, 2455-
2460.
N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457-2483.
Y. Gao, X. Ding, Z. Zheng, X. Cheng and Y. Peng, Chem.
Commun. (Camb.), 2007, DOI: 10.1039/b706490j, 3720-
3722.
Z. Zhang, T. Sun, C. Chen, F. Xiao, Z. Gong and S. Wang, ACS
Appl. Mater. Interfaces, 2014, 6, 21035-21040.
Z. Zhang, F. Xiao, J. Xi, T. Sun, S. Xiao, H. Wang, S. Wang and
Y. Liu, Sci. Rep., 2014, 4, 4053.
M. Heemeier, A. F. Carlsson, M. Naschitzki, M. Schmal, M.
Bäumer and H.-J. Freund, Angew. Chem. Int. Ed., 2002, 41,
4073-4076.
5.
6.
(k(GPDAP)=2.146×10-2
s-1,
k(GP)=1.550×10-4
s-1,
k(CP)=6.553×10-5 s-1 and k(blank)=2.926×10-5 s-1). A summary
of the constants for the catalytic actions in this paper was
presented in Table 1. Compared with the results reported in other
papers in Table s1, our catalysts showed higher catalytic activity.
It can been seen from Fig.8 that the recovered catalysts still kept
good catalytic activity for the reduction of 4-NP even after five
circles in 9 min with a small decrease of conversion from 99%
to 93%, which might owe to the loss of Pd. This result indicated
the good stability of the catalyst which attributed to the strong
interaction between PDA and Pd.
7.
8.
9.
10.
11.
D. Esken, X. Zhang, O. I. Lebedev, F. Schroder and R. A.
Fischer, J. Mater. Chem., 2009, 19, 1314-1319.
S. Royer, D. Duprez, F. Can, X. Courtois, C. Batiot-Dupeyrat,
S. Laassiri and H. Alamdari, Chem. Rev., 2014, 114, 10292-
10368.
12.
13.
M. B. Gawande, P. S. Branco and R. S. Varma, Chem. Soc.
Rev., 2013, 42, 3371-3393.
M. Ayán-Varela, J. I. Paredes, L. Guardia, S. Villar-Rodil, J.
M. Munuera, M. Díaz-González, C. Fernández-Sánchez, A.
Martínez-Alonso and J. M. D. Tascón, ACS Appl. Mater.
Interfaces, 2015, 7, 10293-10307.
14.
15.
K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y.
Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov,
Science, 2004, 306, 666-669.
S. Bae, H. Kim, Y. Lee, X. Xu, J.-S. Park, Y. Zheng, J.
Balakrishnan, T. Lei, H. Ri Kim, Y. I. Song, Y.-J. Kim, K. S. Kim,
B. Ozyilmaz, J.-H. Ahn, B. H. Hong and S. Iijima, Nat Nano,
2010, 5, 574-578.
16.
17.
S. Alwarappan, A. Erdem, C. Liu and C.-Z. Li, J. Phys. Chem.
C, 2009, 113, 8853-8857.
G. Girishkumar, T. D. Hall, K. Vinodgopal and P. V. Kamat, J.
Phys. Chem. B, 2005, 110, 107-114.
Fig. 8 Reusability of GPDAP for the reduction of 4-NP.
18.
19.
J. Pyun, Angew. Chem. Int. Ed., 2011, 50, 46-48.
R. Ren, S. Li, J. Li, J. Ma, H. Liu and J. Ma, Catal. Sci. Technol.,
2015, 5, 2149-2156.
C. Ataca, E. Aktürk, S. Ciraci and H. Ustunel, Appl. Phys. Lett.,
2008, 93.
Y. Pan, H. Bao, N. G. Sahoo, T. Wu and L. Li, Adv. Funct.
Mater., 2011, 21, 2754-2763.
T. Zeng, X.-l. Zhang, Y.-r. Ma, H.-y. Niu and Y.-q. Cai, J.
Mater. Chem., 2012, 22, 18658-18663.
Y. Li, X. Fan, J. Qi, J. Ji, S. Wang, G. Zhang and F. Zhang, Nano
Research, 2010, 3, 429-437.
D. V. Kosynkin, A. L. Higginbotham, A. Sinitskii, J. R. Lomeda,
A. Dimiev, B. K. Price and J. M. Tour, Nature, 2009, 458,
872-876.
Y. Liu, J. Zhou, X. Zhang, Z. Liu, X. Wan, J. Tian, T. Wang and
Y. Chen, Carbon, 2009, 47, 3113-3121.
X. Zhong, J. Jin, S. W. Li, Z. Y. Niu, W. Q. Hu, R. Li and J. T.
Ma, Chem. Commun., 2010, 46, 7340-7342.
X. Qi, K.-Y. Pu, H. Li, X. Zhou, S. Wu, Q.-L. Fan, B. Liu, F. Boey,
W. Huang and H. Zhang, Angew. Chem. Int. Ed., 2010, 49,
9426-9429.
4 Conclusion
20.
21.
22.
23.
24.
In conclusion, an ultrafine Pd catalyst propelled by the fantastic
property of polydopamine had been successfully prepared
through a facile method. The obtained catalyst possessed 2.0 nm
of average size for Pd nanoparticles, and showed a good
monodisipersity. This catalyst (GPDAP) was evaluated through
catalyzing the reduction of 4-NP, K3[Fe(CN)6], methylene blue
(MB) and rhodamine B (RhB) which are common toxics in many
fields and demonstrated much higher activity compared with GP
and CP. Further applications for other catalysis are currently
being processed and will be reported soon.
25.
26.
27.
References
1.
J. Noh and R. Meijboom, in Application of Nanotechnology
in Water Research, John Wiley & Sons, Inc., 2014, DOI:
10.1002/9781118939314.ch13, pp. 333-405.
28.
S. W. Li, S. J. Guo, H. L. Yang, G. L. Gou, R. Ren, J. Li, Z. P.
Dong, J. Jin and J. T. Ma, J. Hazard. Mater., 2014, 270, 11-
17.
2.
Y. Wang, D. Zhao, W. Ma, C. Chen and J. Zhao, Environ. Sci.
Technol., 2008, 42, 6173-6178.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 10 of 11
ARTICLE
29.
Journal Name
Y. Xu, H. Bai, G. Lu, C. Li and G. Shi, J. Am. Chem. Soc., 2008, 56.
130, 5856-5857.
Y. Zhang, P. L. Zhu, L. Chen, G. Li, F. R. Zhou, D. Q. Lu, R. Sun,
F. Zhou and C. P. Wong, J Mater. Chem. A, 2V0i1ew4,A2rti,c1le1O9n6lin6e-
DOI: 10.1039/C5RA13361K
30.
J. Liu, J. Tang and J. J. Gooding, J. Mater. Chem., 2012, 22,
11973.
12435-12452.
57.
58.
59.
60.
61.
L. Wang, Y. Zeng, A. Shen, X. Zhou and J. Hu, Chem.
Commun., 2015, 51, 2052-2055.
S. Wunder, F. Polzer, Y. Lu, Y. Mei and M. Ballauff, J. Phys.
Chem. C, 2010, 114, 8814-8820.
X. Zhou, W. Xu, G. Liu, D. Panda and P. Chen, J. Am. Chem.
Soc., 2009, 132, 138-146.
J. Zhang, Z. Xiong and X. S. Zhao, J. Mater. Chem., 2011, 21,
3634-3640.
31.
J. H. WAITE and M. L. TANZER, Science, 1981, 212, 1038-
1040.
H. Lee, S. M. Dellatore, W. M. Miller and P. B. Messersmith,
Science, 2007, 318, 426-430.
H. Lee, N. F. Scherer and P. B. Messersmith, Proc. Natl Acad.
Sci., 2006, 103, 12999-13003.
L. Q. Xu, W. J. Yang, K.-G. Neoh, E.-T. Kang and G. D. Fu,
Macromolecules, 2010, 43, 8336-8339.
32.
33.
34.
Y. Li, G. Lu and S. Li, J. Photochem. Photobiol. A Chem., 2002,
152, 219-228.
35.
W. Ye, X. Shi, J. Su, Y. Chen, J. Fu, X. Zhao, F. Zhou, C. Wang
and D. Xue, Appl. Catal. B- Environ., 2014, 160–161, 400-
407.
36.
37.
38.
W. Ye, Y. Chen, Y. Zhou, J. Fu, W. Wu, D. Gao, F. Zhou, C.
Wang and D. Xue, Electrochim. Acta, 2014, 142, 18-24.
M. Zhao, C. Deng and X. Zhang, ACS Appl. Mater. Interfaces,
2013, 5, 13104-13112.
K. R. Paton, E. Varrla, C. Backes, R. J. Smith, U. Khan, A.
O’Neill, C. Boland, M. Lotya, O. M. Istrate, P. King, T. Higgins,
S. Barwich, P. May, P. Puczkarski, I. Ahmed, M. Moebius, H.
Pettersson, E. Long, J. Coelho, S. E. O’Brien, E. K. McGuire,
B. M. Sanchez, G. S. Duesberg, N. McEvoy, T. J. Pennycook,
C. Downing, A. Crossley, V. Nicolosi and J. N. Coleman, Nat
Mater, 2014, 13, 624-630.
39.
40.
41.
42.
43.
44.
P. Herves, M. Perez-Lorenzo, L. M. Liz-Marzan, J. Dzubiella,
Y. Lu and M. Ballauff, Chem. Soc. Rev., 2012, 41, 5577-5587.
M. A. White, J. A. Johnson, J. T. Koberstein and N. J. Turro,
J. Am. Chem. Soc., 2006, 128, 11356-11357.
L. Xu, J. Liao, L. Huang, D. Ou, Z. Guo, H. Zhang, C. Ge, N. Gu
and J. Liu, Thin Solid Films, 2003, 434, 121-125.
A. Gupta, G. Chen, P. Joshi, S. Tadigadapa and Eklund, Nano
Lett., 2006, 6, 2667-2673.
B. Fei, B. Qian, Z. Yang, R. Wang, W. C. Liu, C. L. Mak and J.
H. Xin, Carbon, 2008, 46, 1795-1797.
S. W. Li, H. L. Yang, Z. P. Dong, S. J. Guo, J. H. Zhao, G. L.
Gou, R. Ren, J. W. Huang, J. Jin and J. T. Ma, Catal. Sci.
Technol., 2013, 3, 2303-2310.
45.
46.
47.
48.
49.
50.
51.
B. E. Koel, A. Sellidj and M. T. Paffett, Phys. Rev. B, 1992, 46,
7846-7856.
M. Simões, S. Baranton and C. Coutanceau, Appl. Catal. B-
Environ., 2010, 93, 354-362.
M. Brun, A. Berthet and J. C. Bertolini, J. Electron. Spectrosc.
Relat. Phenom., 1999, 104, 55-60.
M. Schrinner, M. Ballauff, Y. Talmon, Y. Kauffmann, J. Thun,
M. Möller and J. Breu, Science, 2009, 323, 617-620.
S. Carregal-Romero, J. Pꢀrez-Juste, P. Hervꢀs, L. M. Liz-
Marzꢁn and P. Mulvaney, Langmuir, 2009, 26, 1271-1277.
N. Pradhan, A. Pal and T. Pal, Colloid Surf. A-Physicochem.
Eng. Asp., 2002, 196, 247-257.
Y. Li, Q. Du, T. Liu, J. Sun, Y. Jiao, Y. Xia, L. Xia, Z. Wang, W.
Zhang, K. Wang, H. Zhu and D. Wu, Mater. Res. Bull., 2012,
47, 1898-1904.
52.
X. Yang, X. Zhang, Y. Ma, Y. Huang, Y. Wang and Y. Chen, J.
Mater. Chem., 2009, 19, 2710-2714.
53.
54.
H.-U. Blaser, Science, 2006, 313, 312-313.
K. Esumi, R. Isono and T. Yoshimura, Langmuir, 2003, 20,
237-243.
55.
C. Deraedt, L. Salmon, S. Gatard, R. Ciganda, R. Hernandez,
J. Ruiz and D. Astruc, Chem. Commun., 2014, 50, 14194-
14196.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 11
RSC Advances
View Article Online
DOI: 10.1039/C5RA13361K
Graphical Abstract
Well-dispersive graphene-polydopamine-Pd hybrid with
enhanced catalytic performance
Jian-Xin Ma, Honglei Yang, Shuwen Li, Ren Ren, Jing Li, Xueyao Zhang and Jiantai Ma*
We reported a method to functionalize Graphene prepared by physical routes with
polydopamine. Then a catalyst of ultrafine Pd nanoparticles which were stable and
dispersed well in the polar solvents was prepared. The Pd nanoparticles were as small
as 2.8 nm in average and had good monodispersibility in water by virtue of
polydopamine modified graphene. In comparison with Palladium on carbon (CP) and
Graphene-Pd (GP), the Pd nanoparticles dispersed with the help of polydopamine
modified graphene (GPDAP) showed enhanced activity even with tiny amounts of
catalysts added for the reduction of 4-nitrophenol (4-NP), K3[Fe(CN)6], methylene
blue (MB) and rhodamine B (RhB).