Quaternized POSS modified rGO-supported Pd nanoparticles as a highly efficient catalyst for reduction and Suzuki coupling reactions

Article abstract of DOI:10.1039/c9nj04491d

Functionalized two-dimensional graphene oxide sheets and their inorganic-organic nanohybrids have aroused great interest because of their excellent synergetic effect on metal-based nanocatalyst PdNPs supported on highly hydrophilic quaternized polyhedral oligomeric silsesquioxane (QPOSS) functionalized reduced graphene oxide (rGO) and were successfully constructed as a nanohybrid catalyst for efficient heterogeneous catalytic reactions. Octaammonium POSS (OAPOSS) was first covalently grafted to carboxylated GO nanosheets through an amidation reaction, and then the OAPOSS decorated on rGO nanosheets was quaternized with glycidyltrimethylammonium chloride (GDTMAC) via an epoxide ring-opening reaction to obtain a highly functional hydrophilic QPOSS@rGO hybrid. Finally, the PdNPs were loaded onto QPOSS@rGO nanosheets through an in situ reduction route. The quaternary ammonium groups on QPOSS@rGO can strongly coordinate with PdNPs, making it particularly advantageous for stabilizing PdNPs and preventing the leaching of Pd metals. Compared to the PdNPs@rGO catalyst without modification with hydrophilic QPOSS, the low-dose PdNPs@QPOSS@rGO nanocatalysts exhibited outstanding catalytic efficiency in the reduction of methylene blue and nitrophenols. In addition, the as-designed nanocatalysts also showed high catalytic activity for the Suzuki coupling reaction when utilizing pure water as a green solvent. It was proved that QPOSS and rGO can synergistically catalyze and promote the diffusion of reactants. In particular, the PdNPs@QPOSS@rGO nanohybrid catalyst showed no significant loss of catalytic activity after reusing it five times. Our results demonstrated that highly hydrophilic QPOSS endows the resulting PdNPs@QPOSS@rGO nanohybrid with good dispersibility and stability in water, which remarkably further improves the catalytic activity of the nanocatalyst.

Full text of DOI:10.1039/c9nj04491d

NJC
View Article Online
View Journal | View Issue
PAPER
Quaternized POSS modified rGO-supported Pd
nanoparticles as a highly efficient catalyst for
reduction and Suzuki coupling reactions†
Cite this: New J. Chem., 2019,
43, 18601
Siwen Xia, Yu Yang and Changli Lu
*
¨
Functionalized two-dimensional graphene oxide sheets and their inorganic–organic nanohybrids have
aroused great interest because of their excellent synergetic effect on metal-based nanocatalyst PdNPs
supported on highly hydrophilic quaternized polyhedral oligomeric silsesquioxane (QPOSS) functionalized
reduced graphene oxide (rGO) and were successfully constructed as a nanohybrid catalyst for efficient
heterogeneous catalytic reactions. Octaammonium POSS (OAPOSS) was first covalently grafted to
carboxylated GO nanosheets through an amidation reaction, and then the OAPOSS decorated on rGO
nanosheets was quaternized with glycidyltrimethylammonium chloride (GDTMAC) via an epoxide ring-
opening reaction to obtain a highly functional hydrophilic QPOSS@rGO hybrid. Finally, the PdNPs were
loaded onto QPOSS@rGO nanosheets through an in situ reduction route. The quaternary ammonium
groups on QPOSS@rGO can strongly coordinate with PdNPs, making it particularly advantageous
for stabilizing PdNPs and preventing the leaching of Pd metals. Compared to the PdNPs@rGO catalyst
without modification with hydrophilic QPOSS, the low-dose PdNPs@QPOSS@rGO nanocatalysts exhibited
outstanding catalytic efficiency in the reduction of methylene blue and nitrophenols. In addition, the
as-designed nanocatalysts also showed high catalytic activity for the Suzuki coupling reaction when utilizing
pure water as a green solvent. It was proved that QPOSS and rGO can synergistically catalyze and promote
the diffusion of reactants. In particular, the PdNPs@QPOSS@rGO nanohybrid catalyst showed no significant
loss of catalytic activity after reusing it five times. Our results demonstrated that highly hydrophilic QPOSS
endows the resulting PdNPs@QPOSS@rGO nanohybrid with good dispersibility and stability in water, which
remarkably further improves the catalytic activity of the nanocatalyst.
Received 31st August 2019,
Accepted 23rd October 2019
DOI: 10.1039/c9nj04491d
rsc.li/njc
the easy aggregation of metal nanoparticles leads to the inhibition
of their catalytic activity, which greatly limits the development
Introduction
Noble metal nanoparticles (NMNPs) are widely used in the fields prospects of metal nanoparticles.9 As is known to all, this is still
of catalytic coupling reactions, degradation of organic dyes, bio- a scientific challenge that homogeneous metal catalysts are
optical sensing and medical diagnosis, due to their unique expensive to prepare, low in yield, and difficult to separate
structural morphology, high specific surface area, excellent resulting in poor reusability. So many studies have shown that
stability, and good catalytic performance.1,2 Since the palladium fixing metal NPs on various support materials as heterogeneous
(Pd)-catalyzed Suzuki–Miyaura reaction was recognized by the catalysts to improve the dispersion of metal nanoparticles and
award of the Nobel Prize in Chemistry in 2010,3–5 Pd-based catalytic activity is an effective technique to settle the above
catalysts have important strategic significance in synthetic question.10 Multiple materials, such as inorganic triiron tetroxide,11
chemical catalysis and industrial applications, and have received silica,12 organic polymers,13 carbon materials,14 and metal–organic
great attention from researchers. PdNPs have been confirmed as frameworks (MOFs),15 have be developed as the efficient supports of
efficient nanocatalysts in various catalysis fields, such as aerobic metal nanocatalysts.
alcohol oxidation, organic synthesis, low-temperature CO oxidation,
Among the many catalyst carriers, it is known that recently
catalytic reduction of organic dyes and multiple coupling developed novel graphene oxide (GO) is one of the most studied
reactions.5–8 One of the main problems in these aspects is that carbon nanomaterials. GO is the most promising candidate for
catalyst carriers due to its unique structure and surface properties.
Two-dimensional (2D) GO nanosheets possess high specific
College of Chemistry, Northeast Normal University, Changchun, 130024, China.
surface area, excellent electron transport ability, and good
E-mail: lucl055@nenu.edu.cn
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c9nj04491d chemical stability, which can generate the synergy between
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 18601--18610 | 18601

View Article Online
Paper
NJC
metal nanoparticles and GO and further enhance the stability solar cells.31–33 Recently, researchers have exploited POSS in
and versatility of nanocomposite catalysts.16,17 All of these various catalytic reactions and achieved good catalytic results.
features make GO an interesting option to support Pd nano- For instance, Lu et al. combined aminopropyl-POSS with
catalysts. In addition, the PdNPs are immobilized on the support terephthalaldehyde (TPA) by a Schiff base chemical reaction.34
material of GO as a catalyst, the structures of the catalysts are A porous covalent network catalyst was formed by coordination
stable, and it is more convenient for the catalyst separation and of containing-nitrogen groups in POSS-TPAX and Pd(II), which
recycling in the catalytic systems, but because of the p–p stacking can be utilized in the Suzuki coupling reaction. Arsalani et al.
or van der Waals interactions between PdNPs and GO, the used an octaAmmonium POSS (OA-POSS) nano-crosslinked
as-prepared metal particles heavily aggregate, and the catalytic poly(ethylene glycol) hydrogel as the carrier of Ag nanoparticles
activity is also very low, which limits their application in organic to prepare organic–inorganic hybrid catalysts for reducing 4-NP
catalysis.18,19
to 4-NA.35 Akbari et al. dispersed PdNPs on a carrier material
In order to improve the chemical stability, aqueous dispersion based on TAP-POSS and poly(acrylamide-co-hydroxyethyl metha-
and catalytic activity, surface modification of GO is an essential crylate) (AAm-co-HEMA) as a heterogeneous catalyst in the Heck
approach to overcome the above problems. At present, there are coupling reaction in the aqueous phase.36 In particular, in the
a few reports on small molecules or polymer modified GO above catalytic reaction, using POSS-based polymer composites
nanosheet-supported PdNPs as catalysts. For instance, Correia as a metal nanoparticle carrier, it can be found that the
et al. immobilized Pd nanoparticles on organosilane containing introduction of POSS improves the dispersion of nanoparticles.
amine or thiol group functionalized GO to catalyze Heck and Ervithayasuporn et al. utilized methyl methacrylate functionalized
Suzuki reactions.20 The strong interaction between the metal POSS (MMA-POSS-Tn) as a comonomer to prepare new porous
particles and the carrier allows the Pd particle size to be smaller polymer-silsesquioxane hybrids, which stabilized Pd nanoparticles
than that of the non-functionalized GO. Although the small for the oxidation of aerobic alcohol in water.37 Chang et al. used
molecule functionalized GO inhibited the serious growth of Pd the thiolated POSS to encapsulate amorphous palladium
particles, the small molecules easily fall off to cause the leaching nanoclusters as a catalyst for the Heck reaction.38 The large
of Pd nanoparticles to increase, resulting in catalyst deactivation gaps between POSS molecules also provide a transport channel
and catalytic cycles to be significantly reduced. Yu et al. proposed for the input of the reactants. Gruttadauria et al. prepared
a wet chemical method to prepare GO@polydopamine(PDA)@Pd a novel imidazolium tetrachloropalladate salt catalyst immo-
nanocomposites toward degradation of MB.21 However, it should bilized on a POSS nanocage and demonstrated the effect of
be noted that the macromolecule modified GO by mussel- the POSS nanocage structure on the yield in the Suzuki
inspired chemistry as nanocatalysts did not exhibit outstanding reaction as compared with the 1-butyl-3-methylimidazolium
catalytic activity. Wang et al. used polyethyleneimine (PEI) to tetrachloropalladate catalyst.39 Simone et al. introduced
couple PdNPs and Fe3O4 NPs onto graphene nanosheets for the functionalized POSS into polylactic acid composite fibers,
Tsuji–Trost reaction.22 Yoon et al. demonstrated the preparation and surprisingly found no changes in the structure of the
of ultrafine Pd supported by ionic block copolymer decorated polymers, while the supported palladium nanoclusters achieved
rGO nanosheets as a catalyst for efficiently degrading methylene good catalytic effects in the Heck coupling reaction.40 It can be
blue.23 Although polymer-modified rGO significantly has become seen that the unique cubic cage structure and functionalization
a facile strategy as the support of metal nanocatalysts, the reaction sites of POSS are favored by many researchers. There-
composition of the polymers is complex and the Pd nanoparticles fore, the introduction of the ideal modifier POSS has been
are located between the graphene and the polymer or on the proven to be an effective approach in the design of functional
surface of the polymer brushes, which hinders the diffusion rate composites.
from the hydrophobic reactants to the surface of the metal
Although POSS has been used to good effect in the field of
catalytic center in the Suzuki coupling reaction.24 Therefore, it catalysis, the application of PdNPs supported by POSS modified
is necessary to promote the diffusion of the reactants to the graphene oxide nanohybrid materials in catalysis is less reported.
catalyst surface, at the same time, fine-tune the size of metal NPs In this work, the 2D GO surface was functionalized with highly
and improve their dispersibility and catalytic activity, but this still hydrophilic QPOSS which was utilized as a carrier for the in situ
remains a challenge.
growth of PdNPs to successfully construct an efficient multi-
Polyhedral oligomeric silsesquioxane (POSS) is an inorganic– phase nanohybrid catalyst in Scheme 1. The catalytic activity of
organic hybrid depicted by the criterion (RSiO1.5)n.25,26 A hydro- the as-designed nanocatalyst Pd@QPOSS@rGO was systemati-
phobic cage-shaped inorganic core in POSS is joined by a Si–O–Si cally investigated using the reduction of methylene blue (MB)
bond and eight highly reactive organic groups. Compared with and nitrophenol (NP) as model reactions. The performance of
additional inorganic hybrid nanoparticles, nano-sized POSS has PdNPs@QPOSS@rGO as a catalyst for the green catalysis of the
many functionalized reaction sites, excellent thermal stability, Suzuki–Miyaura coupling reaction in the aqueous phase was
and chemical stability, and is highly soluble in many organic/ also evaluated. Due to the synergistic catalysis of QPOSS@rGO
inorganic solvents. These unique properties make POSS become and PdNPs, the PdNPs@QPOSS@rGO nanohybrid as a catalyst
an ideal modification reagent.27–31 So POSS has been used at with good dispersion stability in water was demonstrated to possess
present in numerous fields, such as drug delivery, medical outstanding catalytic performance in various heterogeneous
devices, low dielectric constant materials, optical devices and catalysis reactions.
18602 | New J. Chem., 2019, 43, 18601--18610 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
by centrifugation, then washed three times with deionized water,
and finally vacuum-dried to obtain carboxylation graphene oxide.
Preparation of OAPOSS@rGO
20 mg of GO, 32 mg of EDC, and 12 mg of NHS were evenly
dispersed in 10 mL of distilled water and sonicated for 30 min;
40 mg POSS and 41.4 mg triethylamine were dissolved in 10 mL
N,N-dimethylformamide. Then, the above two dispersions were
mixed before being stirred for 24 h at 25 1C. The product was
separated by centrifugation and washed twice with methanol
and water, respectively. The obtained crude product was collected
by centrifugation, washed three times with ethanol and water
to remove unreacted OAPOSS and vacuum-dried at room tem-
perature to obtain the final sample.
Scheme 1 Schematic depiction of the preparation and catalytic application
of the PdNPs@QPOSS@rGO catalyst.
Synthesis of quaternized OAPOSS@rGO (QPOSS@rGO)
Experimental
Materials
20 mg of OAPOSS@rGO, 41.4 mg of GDTMAC and 20 mL of
distilled water were mixed in a three-necked flask under nitrogen
gas. The black mixture was stirred for 1 h at room temperature
and next for 4 h at 80 1C. After the temperature of the reaction
system was cooled to room temperature, diethyl ether was added
to precipitate the product. The final product was centrifuged
before washing them with isopropyl alcohol many times to
remove unreacted GDTMAC and dried in a vacuum oven at 25 1C.
Graphene oxide sheets were prepared by following previously
published work (see the ESI†).41 Glycidyltrimethylammonium
chloride (GDTMAC) and octaAmmonium POSS (OAPOSS) were
provided from Aladdin. Sodium chloroacetate, methanol,
triethylamine, sodium hydroxide, isopropanol, methylene blue
(MB), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimidehydrochloride
(EDC), o-, m- and p-nitrophenols, N-hydroxysuccinimide (NHS), aryl
bromide, arylboronic acid, potassium carbonate and palladium(II)
chloride (PdCl2, 55–60%) were supplied by Shanghai Macklin
Reagent Co. Ltd.
Preparation of QPOSS@rGO supported PdNPs
(PdNPs@QPOSS@rGO)
30 mg of QPOSS@rGO in 150 mL of distilled water was sonicated
for 0.5 h to uniformly disperse QPOSS@rGO. PdCl2 (0.885 mg mLÀ1
,
Characterization
6.0 mL) was poured into the QPOSS@rGO dispersion for ultra-
sonication for 2.0 h. 6.0 mL of the freshly prepared solution of
NaBH4 (0.2 M) was poured to the above system before continuously
stirring at room temperature for 24 h. The sample was collected by
centrifugation and washed several times with ethanol and water to
remove unsupported palladium nanoparticles and PdCl2, followed
by drying in a vacuum oven at room temperature. The amount of Pd
in the PdNPs@QPOSS@rGO catalyst was determined by ICPAES to
be about 3.48 wt%.
Transmission electron microscopy (TEM) observation was
conducted utilizing a JEM-2100F electron microscope, and the
as-prepared samples were dispersed in deionized water, and
put on an ultrathin carbon supported film. The infrared
absorption spectra of the samples were obtained using a Magna
560 FTIR Fourier transform infrared (FTIR) spectrometer. The
UV-vis absorption spectra were obtained from 200 to 800 nm
utilizing a SHIMADZU UV-2550 UV-vis spectrophotometer.
Thermogravimetric analysis (TGA) of materials was performed
using a PerkinElmer TGA-2 thermogravimetric analyzer (heating
rate: 10 1C minÀ1, nitrogen atmosphere). The X-ray photoelectron
spectroscopy (XPS) spectra were obtained from the surface with a
diameter of 500 mm in area by means of a Quantum 2000
spectrometer on an X-ray photoelectron spectrometer (X-TOOL,
ULVAC-PHI) using non-monochromatized Al Ka excitation radiation.
X-ray diffraction (XRD) patterns were obtained using a Rigaku
D/max-TTR-III diffractometer with Cu Ka radiation. The Pd
metal content in the composites was measured by inductively
coupled plasma atomic emission spectroscopy (ICP-AES, USA,
Thermo Jarrel Ash, Franklin).
Catalytic reduction of methylene blue (MB)
The catalytic activity of the as-prepared nanohybrid catalyst was
evaluated using the reduction reaction of blue methylene (MB)
to colorless leuco methylene blue (LMB). In detail, 2.0 mL MB
aqueous solution (5.0 mg LÀ1) and 1.0 mL of fresh NaBH4
aqueous solution (0.5 M) were mixed in a quartz cuvette and
agitated for 5 s, and the last 20 mL of the PdNPs@QPOSS@rGO
(0.1 mg mLÀ1) catalyst was added to the above solution before
stirring for a couple of seconds. The catalytic process was
tracked using an ultraviolet-visible spectrophotometer.
Catalytic reduction of nitrophenols
Preparation of carboxylated graphene oxide
The catalytic activity of the as-prepared nanohybrid catalyst was
0.1 g of graphene oxide (GO), 100 mL of deionized water, 5.0 g also investigated using the catalytic reduction of o-, m-, and
of sodium chlorohexanoate and 5.0 g of NaOH were mixed in a p-nitrophenols. 1.0 mL of a fresh NaBH4 aqueous solution
250 mL Erlenmeyer flask, and the solution was sonicated for (0.2 M), 6.5 mL of the m-, o-, p-nitrophenol aqueous solution
2 h under ice bath conditions. The above mixture was collected (0.05 M) and distilled water (2.0 mL) were mixed in the UV
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 18601--18610 | 18603

View Article Online
Paper
NJC
quartz cell and stirred for a few seconds. Then, 30 mL of the 7.5 nm (Fig. 1d). In order to evaluate the effect of QPOSS, we
PdNPs@QPOSS@rGO (0.25 mg mLÀ1) catalyst was mixed with also prepared a composite of PdNPs supported on pure GO
the above solution and stirred for 5 s. The reduction reaction process sheets to compare the dispersibility of the catalyst (PdNPs@rGO).
was immediately monitored utilizing a UV-vis spectrophotometer.
As displayed in Fig. S1 (ESI†), PdNPs were not evenly distributed
on the PdNPs@rGO nanosheets, and there is a serious aggregation
of Pd particles with a particle size of approximately 9.3 nm. The
above analysis further confirmed that the PdNPs were uniformly
and stably dispersed on the GO nanosheets due to the introduction
of QPOSS. Compared with the PdNPs@rGO catalyst without
QPOSS modification, to further demonstrate the stability of the
catalyst, we also presented the photographs of two samples
placed at the same time and concentration. As shown in Fig. S2b
(ESI†), PdNPs@QPOSS@rGO is still stably dispersed in water
after two weeks. In contrast, a precipitate has appeared in the
bottle only for two days for PdNPs@rGO without hydrophilic
QPOSS modification (Fig. S2a, ESI†). The above results also
demonstrate that the highly hydrophilic quaternized POSS plays
an essential role in enhancing the dispersion and stabilization
of PdNPs.
Evaluation of the catalytic performance for Suzuki coupling
reactions
Phenylboronic acid (0.6 mmol), aryl halide (0.5 mmol), distilled
water (5.0 mL), K2CO3 (1.5 mmol) and the PdNPs@QPOSS@
rGO nanocatalyst (0.3 mol% Pd) were added to a round bottom
flask before stirring at 80 1C for 2 h. The obtained organic
product was collected via centrifugation and was extracted
three times with 10 mL of ethyl acetate. The finally acquired
product was analyzed by gas chromatography (GC). The PdNPs@
QPOSS@rGO nanocatalyst was also recycled by centrifugation
and washing with a large amount of water and ethyl acetate to
wash off residual salts and organics for reuse in the catalytic
procedure.
The chemical structures of GO, OAPOSS@rGO and PdNPs@
QPOSS@rGO nanohybrids were confirmed by FTIR (Fig. 2).
In Fig. 2a, we can observe characteristic peaks at 3415, 1728,
1227 and 1050 cmÀ1 which are attributed to the stretching and
bending vibrations of –OH, CQO, C–O–C and C–O bonds on
GO nanosheets, respectively.43 In addition, the vibration peak
at 1621 cmÀ1 may be attributed to the water molecules, or
caused by the vibration of the unoxidized carbon skeleton on
the GO surface. It can be seen from Fig. 2b that the stretching
vibration absorption peaks of CQO and C–OH appeared at
1618 and 3415 cmÀ1 after carboxylation of GO, while the peaks
of the epoxy and alkoxy groups were weakened, which proved
that GO has been successfully carboxylated.44 As shown in
Fig. 2c, in contrast, the OAPOSS modified GO (OAPOSS@rGO)
showed a significant decrease in the carboxyl band at 1728 cmÀ1
and a strong peak at 1102 cmÀ1 was also observed due to the
stretching vibration of the special Si–O–Si cage structure.45
The characteristic peaks observed at 2874 and 2943 cmÀ1 are
attributed to the presence of CH2 groups on the cage of OAPOSS,
and a new peak appearing at 1570 cmÀ1 could be assigned to the
stretching vibrations of N–H and C–N bonds.44,46 The above
result indicates that OAPOSS molecules have been successfully
Results and discussion
TEM was utilized to observe the morphological characteristics
of different samples GO, OAPOSS@rGO and PdNPs@QPOSS@
rGO. Fig. 1a shows the GO morphology with a representative
corrugated thin stratified structure, which shows no difference
with the feature reported in the literature,41 indicating the
successful preparation of GO. Compared to the smooth surface
structure of GO, OAPOSS@rGO has a distinctly different mor-
phology as depicted in Fig. 1b. After grafting POSS, the primary
smooth monolayer of GO becomes rough and it can be clearly
seen that there are many dots on the surface of GO.42 This
result proves that the lattice-free POSS molecules have been
successfully anchored on the GO. Fig. 1c displays the TEM
image of PdNPs decorated on the QPOSS@rGO nanosheets. We
can clearly observe that PdNPs are evenly dispersed on the
QPOSS@rGO surface, effectively avoiding the aggregation of
PdNPs in the presence of QPOSS. The as-obtained PdNPs have a
uniform size, and the average diameter of the particles is about
Fig. 2 FTIR spectra of (a) GO, (b) GO-COOH, (c) OAPOSS@rGO,
Fig. 1 TEM images of (a) GO, (b) OAPOSS@rGO and (c) PdNPs@QPOSS@
(d) QPOSS@rGO and (e) PdNPs@QPOSS@rGO.
rGO; (d) Pd particle size distribution histogram of PdNPs@QPOSS@rGO.
18604 | New J. Chem., 2019, 43, 18601--18610 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
covalently grafted onto the surface of GO sheets. As shown in
Fig. 2d, the sample QPOSS@rGO showed a stronger and wider
O–H absorption peak at 3415 cmÀ1 after the epoxy ring-opening
reaction of GDTMAC with OAPOSS. At the same time, a new
typical peak of the quaternary ammonium groups appeared at
1640 cmÀ1, which revealed that the nanocatalyst support of
QPOSS@rGO has been successfully fabricated.47 After loading
metal Pd particles (Fig. 2e), the FTIR spectra of the as-prepared
PdNPs@QPOSS@rGO nanohybrid catalyst are basically the
same as those of QPOSS@rGO, which should be ascribed to
the lower palladium loading on the QPOSS@rGO surface.
The XRD patterns of OAPOSS, GO, QPOSS@rGO and
PdNPs@QPOSS@rGO are shown in Fig. 3. As expected, GO
showed a major peak at a low diffraction angle (2y = 11.411) in
Fig. 3b, indicating the successful synthesis of graphene oxide
with a certain degree of aggregation.48 Pure OAPOSS showed a
number of sharp diffraction peaks corresponding to the
presence of cage-type structures and amine-substituted isomers
of the POSS inorganic segment at 2y = 6.81, 111, 19.11, 21.81,
23.31, 26.91, 33.11 and 38.71 (Fig. 3a), indicating the formation
of a typical crystalline structure.49 As shown in Fig. 3b, after
QPOSS was covalently functionalized on GO nanosheets, the
typical peak of GO shifted to a lower scattering angle at 2y = 7.41
because the introduction of QPOSS increases the layer spacing
between GO sheets, which is consistent with the literature
report.50,51 The amorphous QPOSS on GO exhibited a weak
broad diffraction peak at 2y = 201. But the characteristic peak of
GO disappeared in PdNPs@QPOSS@rGO, showing that the
ordered graphitic stacking of GO has been converted to well-
disordered structures. When Pd particles were further formed
on QPOSS@rGO, as illustrated in Fig. 3d, four typical peaks
appeared at 2y = 80.41, 66.71, 46.41 and 39.21 which are ascribed
to the (311), (220), (200), and (111) diffraction planes of PdNPs,
respectively.52 These results also proved that PdNPs have been
successfully loaded on QPOSS@rGO hybrid nanosheets.
Fig. 4 XPS survey scans of (a) GO, (b) OAPOSS@rGO, (c) QPOSS@rGO
and (d) PdNPs@QPOSS@rGO.
observe that the contents of nitrogen and silicon elements
in QPOSS@rGO have decreased due to the introduction of
GDTMAC. After loading the Pd nanoparticles, additional peaks
of Pd 3d at 335.7 and 560.5 eV appeared in Fig. 4d. The C 1s
spectrum of GO in Fig. 5a showed four peaks at 288.6, 287.3,
286.8 and 284.8 eV, representing the carbon bonds of OQC–C,
CQO, C–O, and C–C, respectively. This is attributed to the rich
oxygen-containing functional groups on the GO sheets. Compared
with GO, the high-resolution C 1s XPS spectrum for OAPOSS@rGO
in Fig. 5b clearly revealed that the peak intensities of C–O (286.9 eV)
and CQO (287.2 eV) were significantly reduced and that of C–C
became dominant, together with the new appearance of the C–Si
peak (283.6 eV).53 This is because the OAPOSS was successfully
grafted onto the surface of GO by the amidation reaction and most
of the GO was reduced to rGO. The N 1s XPS spectrum (Fig. 5c) of
OAPOSS@rGO clearly indicated that the peak of nitrogen
appeared at 399.2 (C–N), 398.7 (N–H) and 401.1 eV (ÀNH–CO–),
demonstrating the formation of an amide bond, again indicating
that POSS–NH2 is covalently anchored to GO.49 For the Pd 3d XPS
The chemical structures of GO, OAPOSS@rGO, QPOSS@rGO,
PdNPs@QPOSS@rGO were further characterized by XPS. As
expected, only C 1s and O 1s peaks were observed in the XPS
spectrum of GO (Fig. 4a), but the peaks of N 1s (398.9 eV), Si 2p
(101.8 eV) and Si 2s (154.3 eV) appeared in the XPS spectrum of
OAPOSS@rGO (Fig. 4b). As shown in Fig. 4c, we can clearly
Fig. 5 High-resolution C 1s spectra of GO (a), high-resolution C 1s and N
1s spectra of OAPOSS@rGO (b and c), high-resolution Pd3d spectrum of
PdNPs@QPOSS@rGO (d).
Fig. 3 XRD patterns of (a) OAPOSS, (b) GO, (c) QPOSS@rGO and
(d) PdNPs@QPOSS@rGO.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 18601--18610 | 18605

View Article Online
Paper
NJC
spectrum in Fig. 5d, two signal peaks of Pd 3d3/2 and Pd 3d5/2
were observed at 340.9 and 335.4 eV. The appearance of the Pd2+
peaks (337.6 and 342.8 eV) indicated that some Pd atoms are
bonded with their carriers.23 The above analysis confirmed the
formation of PdNPs on the surface of QPOSS@rGO.
As we all know, the thermal decomposition behavior of
particular structures is different, so we studied the thermal
stabilities of GO-COOH, QPOSS@rGO, and PdNPs@QPOSS@rGO
by TGA (Fig. 6). GO-COOH displayed two stages of weightlessness in
Fig. 6a. The first stage weight loss occurred from 100 to 230 1C,
mainly caused by the loss of the hydroxyl groups of GO and the
evaporation of water adsorbed by the surface layer. The weight loss
in the second stage occurred between 600 and 700 1C, mainly
attributed to the loss of more stable oxygen-related groups.54 In
Fig. 6b, the final complete weight loss observed for QPOSS@rGO at
700 1C is 54.6% and the total mass loss is only 5% below 200 1C,
whereas pure POSS loses all weight at around 300 1C due to thermal
evaporation, indicating that GO as a carrier is very important for the
stable presence of POSS.53,55 Due to the loading of Pd NPs (Fig. 6c),
the residual amount of PdNPs@QPOSS@rGO (67.7%) is larger than
that of QPOSS modified GO (54.6%) because of PdNPs and carbon
Fig. 7 UV-vis spectra for the reduction of MB to LMB utilizing various
volumes of catalyst aqueous solutions: (a) PdNPs@QPOSS@rGO (20 mL),
(b) PdNPs@QPOSS@rGO (10 mL). The concentration of the catalyst was
fixed at 0.1 mg mLÀ1. (c) Plots of ln(Ct/C0) vs. time in the reduction of MB
using various catalysts. (d) Reusability of the PdNPs@QPOSS@rGO nano-
hybrid catalyst for MB reduction.
residues,22 which further illustrates the improvement of the thermal Although the PdNPs@rGO has catalytic activity (Fig. S4c, ESI†),
stability of the PdNPs@QPOSS@rGO nanocomposites. the catalytic efficiency is much lower than that of PdNPs@
The catalytic activity of the PdNPs@QPOSS@rGO nano- QPOSS@rGO, which proves that compared to the above control
hybrid catalyst for organic dye MB was monitored by UV-vis samples, PdNPs@QPOSS@rGO as a new nanocatalyst exhibits
absorption spectroscopy. As displayed in Fig. 7a, after the amount higher catalytic activity.
of PdNPs@QPOSS@rGO added to the reaction solution is 20 mL,
Since excess NaBH4 is used, the catalytic reduction of MB is
it was clearly seen that the maximum absorption peak at considered to be a pseudo first order reaction, assuming that
662.7 nm for methylene blue (MB) disappeared instantaneously the catalytic rate is not associated with the NaBH4 concen-
and the indicative absorption peak of leucomethylene blue (LMB) tration for the reduction reaction. Based on the above kinetics,
appeared at 291.2 nm and the solution quickly changed from we determined the catalytic reduction rate associated with the
blue to colorless within only 20 s, which also indicates that MB concentration to evaluate the apparent rate constant kapp for
was successfully reduced to LMB. When adding the PdNPs@ the reduction of MB, expressed as ln(Ct/C0) = Àkt (Fig. 7c and
QPOSS@rGO catalyst (10 mL) to the reaction system, the MB Fig. S4f, ESI†).23 According to the linear relationship between
characteristic peak continued to decrease and after 40 s a new the reaction time and ln(Ct/C0), the kapp values were calculated
LMB absorption peak appeared (Fig. 7b), indicating that PdNPs@ to be approximately 0.03, 0.01, 0.13, 5.95 and 11.69 minÀ1
QPOSS@rGO as a catalyst has significant catalytic activity. Under corresponding to GO (20 mL), OAPOSS@rGO (20 mL), PdNPs@rGO
the same conditions, the same amount (0.25 mg mLÀ1) of (20 mL), PdNPs@QPOSS@rGO (10 mL) and PdNPs@QPOSS@rGO
catalysts GO, OAPOSS@rGO, and PdNPs@rGO was used to (20 mL) respectively. The rate constant of the PdNPs@QPOSS@rGO
catalyze MB as a comparative experiment (Fig. S4, ESI†). We catalyst was much higher than those of the control samples. This
can observe that GO and OAPOSS@rGO showed almost no also showed that upon synergy of QPOSS and GO, the nanocatalyst
catalytic effect on the degradation of MB (Fig. S4a and b, ESI†). showed an excellent catalytic effect, and the hydrophilic QPOSS
cage structure had a positive influence on the catalytic reaction.
The turnover frequency (TOF) value is frequently utilized to
more accurately evaluate the catalytic activity. The TOF value is
described as the number of substrate molecules (MB) per mole
of metal (Pd) per hour or minute and the corresponding unit is hÀ1
or minÀ1. The method for determining the TOF value is given in
the ESI† (see eqn (S1)). When compared to the formerly reported
nanocatalysts for the catalytic reduction of MB, it can be stated
that the PdNPs@QPOSS@rGO nanohybrid catalyst with a TOF
value of 2431.5 minÀ1 exhibits excellent catalytic activity for the
reduction reaction compared with the control samples (Table S1,
ESI†). The recycling of nanocatalysts is also critical for practical
applications, so we tested the reusability of the nanocatalysts. As
shown in Fig. 7d, the PdNPs@QPOSS@rGO nanocatalyst maintains
Fig. 6 TGA curves of (a) GO-COOH, (b) QPOSS@rGO, and (c) PdNPs@
QPOSS@rGO.
18606 | New J. Chem., 2019, 43, 18601--18610 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
almost the high conversion rate after 5 cycles, which is sufficient to
prove that the new nanocomposite has excellent stability.
As shown in Scheme 2, the excellent catalytic activity of the
PdNPs@QPOSS@rGO nanocatalyst for reducing MB probability
is attributed to the synergistic effect of functionalized GO and
the outstanding hydrophilicity of nanohybrids: (i) rGO nano-
sheets have a high adsorption capacity for MB. Due to the
layered structure GO, a larger specific surface area is imparted
to the nanocatalyst and the reactant MB is rapidly adsorbed by
the p–p stacking and van der Waals forces.56 (ii) The synergy
between QPOSS and GO accelerates the electron transfer
among the PdNPs and MB. This is beneficial for MB molecules
to absorb electrons thereby increasing the catalytic activity.57
(iii) Highly hydrophilic quaternized POSS plays a vital role in
enhancing the dispersibility of the nanocatalyst in the catalytic
system, and excellent hydrophilicity also results in the efficient
contact of the catalyst with MB.21 (iv) Functionalization of GO
with QPOSS effectively prevents aggregation and overgrowth of
PdNPs, resulting in higher interaction efficiency between PdNPs
and MB molecules, which improves catalytic activity.22,57 In
Fig. 8 Successive UV-vis absorption spectra for the catalytic reduction of
(a) o-NP, (b) m-NP, and (c) p-NP utilizing PdNPs@QPOSS@rGO as a catalyst.
(d) Plots of ln(Ct/C0) versus reaction time for the reduction of three isomeric
nitrophenols catalyzed by the PdNPs@QPOSS@rGO catalyst.
particular, compared to PdNPs@rGO, the hydrophilicity of the the rate constants of these control catalysts are determined to
QPOSS modified catalyst can further ameliorate the catalyst be 0.025, 0.008, and 0.003 minÀ1, which are significantly lower
dispersibility in pure water, maximizing the amount of surface than that of the PdNPs@QPOSS@rGO nanocatalyst. PdNPs@
exposed to metal atoms, thereby enhancing the accessibility of QPOSS@rGO showed different TOF values for m-, o- and p-NP,
the reactants to the metal active center.58,59 These characteristics which are determined to be 244.8, 49.0 and 30.6 minÀ1 respectively.
are beneficial for the wide applicability of the nanocatalyst in In addition, the nanocatalyst for the catalytic reduction of p-NP
heterogeneous catalysis.
maintained high conversion rates after five cycles in Fig. S6 (ESI†).
The degradation properties of different nitrophenol derivatives Therefore, the PdNPs@QPOSS@rGO nanocatalysts designed by
(m-NP, o-NP, and p-NP) were also investigated to further evaluate us exhibited high catalytic activity and stability, and presented
the catalytic performance of the as-prepared PdNPs@QPOSS@rGO significant advantages over other reported catalysts for the
nanohybrid.10 The UV-visible spectra in Fig. 8a–c show the reduction of p-NP (Table S2, ESI†).
reduction process and reaction time of p-NP, o-NP, and m-NP
We further studied the catalytic performance of PdNPs@
catalyzed by the PdNPs@QPOSS@rGO nanohybrid catalyst QPOSS@rGO as an environmentally benign nanohybrid catalyst
respectively. It can be seen that after the addition of the for Suzuki coupling reactions. We chose the most common
catalyst, the maximum absorption peaks of m-, p- and o-NPs phenylboronic acid and bromobenzene as the basic reaction
at 392, 400 and 414 nm were observed to decrease and model to optimize the Suzuki coupling reaction conditions
disappear completely after about 0.5, 4.0, and 2.5 minutes, including solvent, temperature and reaction time (Table 1).
respectively. As shown in Fig. 8d, the rate constants (kapp) for
m-, o- and p-NPs are determined to be 3.69, 1.31 and
0.95 minÀ1, respectively. The excellent catalytic activity of the
Table 1 Influence of solvents and reaction conditions on Suzuki cross-
coupling reactions catalyzed by the PdNPs@QPOSS@rGO nanocatalyst
(0.3 mol% Pd)a
PdNPs@QPOSS@rGO nanocatalyst for the reduction of nitrophenol
is also demonstrated. For comparison with the as-designed
PdNPs@QPOSS@rGO nanocatalyst, we used control catalysts
PdNPs@rGO, OAPOSS@rGO and GO to evaluate the reducing ability
of p-NP under the same conditions. As shown in Fig. S5 (ESI†),
Entry R1
X
Solvent
Reaction conditions Conversionc (%)
1
2
3
4
5
6
7
8
9
H
H
H
H
H
H
H
H
H
Br H2O
Br H2O
Cl H2O
RT, 12 h
RT, 24 h
RT, 24 h
RT, 24 h
60 1C, 2 h
60 1C, 4 h
24.5
98.5
37.0
98.5
40.8
97.3
99.9
98.9
99.9
I
H2O
Br H2O
Br H2O
Br EtOH/H2Ob 60 1C, 4 h
Br H2O
Br EtOH/H2O
80 1C, 2 h
80 1C, 2 h
a
Reaction conditions: bromobenzene (0.5 mmol), chlorobenzene
(0.5 mmol), iodobenzene (0.5 mmol), phenylboronic (0.6 mmol), and
b
Scheme 2 Catalytic reduction mechanism of MB with PdNPs@QPOSS@
rGO as the catalyst.
K2CO3 (1.5 mmol), water (5.0 mL). Volume ratio of EtOH/H2O is 1 : 1.
c
Conversion was measured by GC analysis.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 18601--18610 | 18607

View Article Online
Paper
NJC
We used K2CO3 as a base to investigate the effect of different
solvents on the model reaction, and it was observed that the
best yield was obtained in both EtOH/H2O (v1/v2 = 1 : 1) and pure
water (Table 1, entries 6–9). From the perspective of environ-
mental protection, we finally chose water as the green solvent.
In addition, the effect of temperature and time (Table 1, entries
1, 2 and 5–9) was also investigated and it was found that the
yield was the highest at 80 1C for 2 h. Although the conversion
rate at room temperature for 24 h (Table 1, entries 2 and 4) was
as high as 98.5%, under the same conditions, the reaction effect
of the catalyst on iodobenzene and phenylboronic acid was
not satisfactory (Table 1, entry 3). According to the above
comparison conditions, we found that the catalyst PdNPs@QPOSS@
rGO (0.3 mol% Pd) showed the best conversion rate in the
presence of water at 80 1C for 2.0 h. This optimal condition
serves as a basis for subsequent investigation of the Suzuki
coupling reaction.
Under the optimal reaction conditions, we also evaluated
the applicability of PdNPs@QPOSS@rGO catalysts for Suzuki
coupling reactions of phenylboronic acid and various aryl
halides. In general, most of the reactants have achieved good
conversion rates in the Suzuki reaction. The PdNPs@QPOSS@rGO
catalyst showed excellent catalytic activity in the presence of aryl
iodide with phenylboronic acid (Table 2, entries 9–12), followed by
a slight decrease in aryl bromide (Table 2, entries 4–8), whereas for
the reaction of aromatic chlorides, the related coupled product
conversions were relatively low (Table 2, entries 1–3), which was
basically consistent with previous studies.60–63 Interestingly, it was
found that the reaction of a substituted aryl halide having electron-
withdrawing groups (–CN, –CHO) afforded satisfactory yields
(96.1–98.8%) (Table 2, entries 7, 8, and 12).
Fig. 9 The reusability of PdNPs@QPOSS@rGO catalysts for the Suzuki
coupling reaction of bromobenzene with phenylboronic acid at 80 1C
for 2 h.
Suzuki coupling reactions (Table S3, ESI†). On the whole, the
above results reveal that our PdNPs@QPOSS@rGO nanohybrid
catalyst has excellent catalytic efficiency in the Suzuki coupling
reactions.
In order to investigate the recyclability of the PdNPs@
QPOSS@rGO catalyst, we chose phenylboronic acid and bromo-
benzene as a model for the Suzuki coupling reaction at 80 1C for
2 h. After each reaction was completed, the recovered catalysts
finally were washed with ethanol and dried for the next reaction
cycle. It is apparent from Fig. 9 that there was no significant loss
in the catalytic reaction conversion after five cycles. Moreover,
we tested and calculated the loss of the metal in the catalyst
after five cycles via ICP analysis. The results clearly indicate that
there is less leakage (about 0.39 ppm metal Pd) in the reaction
system and the loss of Pd was calculated to be 0.367% in the
total catalyst content in Table S4 (ESI†). This can be attributed
to the highly hydrophilic cage QPOSS modified GO which allows
the PdNPs to be stably dispersed in water. In general, this clearly
indicates that PdNPs@QPOSS@rGO shows high catalytic activity
and excellent stability as a green nanocatalyst.
However, for the aryl halide having electron-donating groups
(–CH3, –OCH3), the yield dropped significantly as expected
(Table 2, entries 2, 3, 5, 6, 10, and 11). It is worth noting that
the catalytic performance of the PdNPs@QPOSS@rGO nano-
catalyst is more outstanding than those previously reported for
Conclusions
Table 2 Substrate study for the PdNPs@QPOSS@rGO-catalyzed Suzuki
In summary, we fabricated QPOSS modified rGO supported
PdNPs (PdNPs@QPOSS@rGO) for the first time via a convenient
and effective route. The as-designed PdNPs@QPOSS@rGO
nanohybrid has high catalytic activity due to the synergistic
catalysis of QPOSS and GO. The highly hydrophilic QPOSS as a
stabilizer for PdNPs significantly improved the dispersibility
and stability of PdNPs@QPOSS@rGO in aqueous solution. In
addition, the pure QPOSS cage size is small and inconvenient to
recycle and reuse, but covalent grafting of QPOSS onto the high
specific surface area of GO makes the catalytic reaction recycl-
able. Therefore, PdNPs@QPOSS@rGO with good stability and
reusability exhibited superior catalytic activity for the reduction of
MB and nitrophenol isomers, and the Suzuki–Miyaura reactions
in green solvent water. Obviously, QPOSS plays a crucial role in
the preparation of PdNPs@QPOSS@rGO nanocomposites with
high catalytic activity and good stability. Therefore, our strategy
for fabricating POSS-based nanohybrid catalysts with highly
active metal nanoparticles has potential value in the field of
cross-coupling reactiona
Entry
R1
X
Time (h)
Conversionb (%)
1
2
3
4
5
6
7
8
H
Cl
Cl
Cl
Br
Br
Br
Br
Br
I
2
2
2
2
2
2
2
2
2
2
2
2
90.5
73.5
o10
99.8
90.8
38.9
96.1
96.6
99.5
75.9
70.3
98.8
4-CH3
4-OCH3
H
4-CH3
4-OCH3
4-CN
4-CHO
H
9
10
11
12
4-CH3
4-OCH3
4-CN
I
I
I
a
Reaction condition: aryl halide (0.5 mmol), phenylboronic (0.6 mmol),
K2CO3 (1.5 mmol), water (5.0 mL), and the PdNPs@QPOSS@GO catalyst
b
(0.3 mol% Pd). Conversion was determined by GC analysis.
18608 | New J. Chem., 2019, 43, 18601--18610 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019

View Article Online
NJC
Paper
19 R. Arukula, M. Vinothkannan, A. R. Kim and D. J. Yoo,
J. Alloy. Compd., 2019, 771, 477–488.
20 R. L. Oliveira, C. S. Oliveira, R. Landers and C. R. D. Correia,
ChemistrySelect, 2018, 3, 535–543.
heterogeneous catalysis, and the results of this research lay a
good foundation for the development of multifunctional nano-
hybrid materials in a wide range of catalytic applications.
21 L. Fu, G. Lai, D. Zhu, B. Jia, F. Malherbe and A. Yu,
ChemCatChem, 2016, 8, 2975–2980.
22 J. Liu, X. Huo, T. Li, Z. Yang, P. Xi, Z. Wang and B. Wang,
Chem. – Eur. J., 2014, 20, 11549–11555.
Conflicts of interest
There are no conflicts of interest to declare.
23 K. Y. Cho, Y. S. Yeom, H. Y. Seo, P. Kumar, A. S. Lee and K. Y.
Baekbc, and H. G. Y, J. Mater. Chem. A, 2015, 3, 20471–20476.
24 Y. Cheng, Y. Fan, Y. Pei and M. Qiao, Catal. Sci. Technol.,
2015, 5, 3903–3916.
25 J. E. Mark, Acc. Chem. Res., 2004, 37, 946–953.
26 K. Tanaka and Y. Chujo, J. Mater. Chem., 2012, 22, 1733–1746.
27 J. B. Carroll, A. J. Waddon, H. Nakade and V. M. Rotello,
Macromolecules, 2003, 36, 6289–6291.
28 H. Xu, S. W. Kuo, J. S. Lee and F. C. Chang, Macromolecules,
2002, 35, 8788–8793.
29 B. Y. Xue, H. Wang, Y. Zhao, L. Dai, L. Feng, X. Wang and
T. Lin, Adv. Mater., 2010, 22, 4814–4818.
Acknowledgements
We would like to appreciate the financial support of the National
Natural Science Foundation of China (21574017).
Notes and references
1 S. Navalon, J. R. Herance, M. Alvaroa and H. Garcia, Mater.
Horiz., 2018, 5, 363–378.
2 M. B. Gawande, A. Goswami, F. X. Felpin, T. Asefa, X. Huang,
R. Silva, X. Zou, R. Zboril and R. S. Varma, Chem. Rev., 2016,
116, 3722–3811.
30 S. H. Phillips, T. S. Haddad and S. J. Tomczak, Curr. Opin.
Solid. St. M., 2004, 8, 21–29.
31 A. J. Waddon and E. B. Coughlin, Chem. Mater., 2003, 15,
4555–4561.
3 G. Ding, W. Wang, T. Jiang and B. Han, Green Chem., 2013,
15, 3396–3403.
32 R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuki, Chem.
Rev., 1995, 95, 1409–1430.
4 P. R. Boruah, A. A. Ali, B. Saikia and D. Sarma, Green Chem.,
2015, 17, 1442–1445.
33 D. B. Cordes, P. D. Lickiss and F. Rataboul, Chem. Rev.,
2010, 110, 2081–2173.
5 P. R. Boruah, A. A. Ali, M. Chetia, B. Saikia and D. Sarma,
Chem. Commun., 2015, 51, 11489–11492.
34 C. Zhang, Y. Leng, P. Jiang and D. Lua, RSC Adv., 2016, 6,
57183–57189.
6 W. Niu, Y. Gao, W. Zhang, N. Yan and X. Lu, Angew. Chem.
Int. Ed., 2015, 127, 8389–8392.
35 F. Kazeminava, N. Arsalani and A. Akbari, Appl. Organome-
tal. Chem., 2018, 32, 1–10.
7 Y. Wang, S. De and N. Yan, Chem. Commun., 2016, 52,
6210–6224.
36 N. Arsalani, A. Akbari, M. Amini, E. Jabbari, S. Gautam and
K. H. Chae, Catal. Lett., 2017, 147, 1086–1094.
37 P. Sangtrirutnugul, T. Chaiprasert, W. Hunsiri, T. Jitjaroendee,
P. Songkhum, K. Laohhasurayotin, T. Osotchan and
V. Ervithayasuporn, ACS Appl. Mater. Interfaces, 2017, 9,
12812–12822.
38 C. H. Lu and F. C. Chang, ACS Catal., 2011, 1, 481–488.
39 L. A. Bivona, F. Giacalone, E. Carbonell, M. Gruttadauria
and C. Aprile, ChemCatChem, 2016, 8, 1685–1691.
40 O. Monticelli, M. Putti, L. Gardella, D. Cavallo, A. Basso,
M. Prato and S. Nitti, Macromolecules, 2014, 47, 4718–4727.
41 W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc., 1958,
80, 1339.
8 I. P. Beletskaya and A. V. Cheprakov, Chem. Rev., 2000, 100,
3009–3066.
9 C. Wang, J. Yin, S. Han, T. Jiao, Z. Bai, J. Zhou, L. Zhang and
Q. Peng, Catalysts, 2019, 9, 559.
10 J. Zhu, R. Wang, R. Geng, X. Zhang, F. Wang, T. Jiao, J. Yang,
Z. Bai and Q. Peng, RSC Adv., 2019, 9, 22551–22558.
11 X. Huang, R. Wang, T. Jiao, G. Zou, F. Zhan, J. Yin, L. Zhang,
J. Zhou and Q. Peng, ACS Omega, 2019, 4, 1897–1906.
12 X. Fei, W. Kong, X. Chen, X. Jiang, Z. Shao and J. Y. Lee, ACS
Catal., 2017, 7, 2412–2418.
13 Y. Liu, C. Hou, T. Jiao, J. Song, X. Zhang, R. Xing, J. Zhou,
L. Zhang and Q. Peng, Nanomaterials, 2018, 8, 35.
14 C. J. Shearer, A. Cherevan and D. Eder, Adv. Mater., 2014, 26,
2295–2318.
42 W. Bai, Q. Sheng, X. Ma and J. Zheng, ACS Sustainable Chem.
Eng., 2015, 3, 1600–1609.
43 Q. Cheng, M. Wu, M. Li, L. Jiang and Z. Tang, Angew. Chem.,
Int. Ed., 2013, 52, 3750–3755.
15 X. Chen, P. Qian, T. Zhang, Z. Xu, C. Fang, X. Xu, W. Chen,
P. Wu, Y. Shen, S. Li, J. Wu, B. Zheng, W. Zhang and F. Huo,
Chem. Commun., 2018, 54, 3936–3939.
44 Y. Bai, Y. Yuan, L. Miao and C. Lu¨, J. Membr. Sci., 2019, 570–571,
481–493.
16 R. Kannan, A. R. Kim, K. S. Nahm, H. K. Lee and D. J. Yoo,
Chem. Commun., 2014, 50, 14623–14626.
45 L. Valentini, S. B. Bon, O. Monticelli and J. M. Kenny,
J. Mater. Chem., 2012, 22, 6213–6217.
17 R. Kumar, D. J. Yoo, A. R. Kim and G. G. Kumar, New
J. Chem., 2018, 42, 14386–14393.
46 W. Bai, Q. Sheng and J. Zheng, Talanta, 2016, 150, 302–309.
47 S. Singh, A. Jasti, M. Kumar and V. K. Shahi, Polym. Chem.,
2010, 1, 1302–1312.
18 V. Georgakilas, J. N. Tiwari, K. C. Kemp, J. A. Perman,
A. B. Bourlinos, K. S. Kim and R. Zboril, Chem. Rev., 2016,
116, 5464–5519.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019 New J. Chem., 2019, 43, 18601--18610 | 18609

View Article Online
Paper
NJC
48 Z. Zhang, J. Zhang, B. Zhang and J. Tang, Nanoscale, 2013, 5, 56 G. Fu, L. Tao, M. Zhang, Y. Chen, Y. Tang, J. Lin and T. Lu,
118–123. Nanoscale, 2013, 5, 8007–8014.
49 Y. Lu, S. Zhang, Z. Geng, K. Zhu, M. Zhang, R. Na and 57 N. Liu, W. Zhang, X. Li, R. Qu, Q. Zhang, Y. Wei, L. Feng and
G. Wang, New J. Chem., 2017, 41, 3089–3096. L. Jiang, J. Mater. Chem. A, 2017, 5, 15822–15827.
50 L. Tan, A. Wan and H. Li, ACS Appl. Mater. Interfaces, 2014, 58 E. Seo, J. Kim, Y. Hong, Y. S. Kim, D. Lee and B. S. Kim,
6, 18–23. J. Phys. Chem. C, 2013, 117, 11686–11693.
51 W. Yu, J. Fu, X. Dong, L. Chen and L. Shi, Compos. Sci. 59 F. Jiang, R. Li, J. Cai, W. Xu, A. Cao, D. Chen, X. Zhang,
Technol., 2014, 92, 112–119. C. Wang and C. Shu, J. Mater. Chem. A, 2015, 3, 19433–19438.
52 H. Zhou, C. Wu, Q. Wu, B. Guo, W. Liu, G. Li, Q. Su and 60 S. E. Hooshmand, B. Heidari, R. Sedghi and R. S. Varma,
Y. Mu, Polym. Chem., 2017, 8, 1488–1494. Green Chem., 2019, 21, 381–405.
53 Y. Xue, Y. Liu, F. Lu, J. Qu, H. Chen and L. Dai, J. Phys. 61 S. Zhang, J. Li, W. Gao and Y. Qu, Nanoscale, 2015, 7,
Chem. Lett., 2012, 3, 1607–1612. 3016–3021.
54 H. Feng, W. Ma, Z. K. Cui, X. Liu, J. Gu, S. Lina and 62 X. Le, Z. Dong, Y. Liu, Z. Jin, T. D. Huy, M. Leb and J. Ma,
Q. Zhuang, J. Mater. Chem. A, 2017, 5, 8705–8713. J. Mater. Chem. A, 2014, 2, 19696–19706.
55 H. Zhou, C. Wu, Q. Wu, B. Guo, W. Liu, G. Li, Q. Su and 63 B. Qi, X. Li, L. Sun, B. Chen, H. Chen, C. Wu, H. Zhang and
Y. Mu, Polym. Chem., 2017, 8, 1488–1494. X. Zhou, Nanoscale, 2018, 10, 19846–19853.
18610 | New J. Chem., 2019, 43, 18601--18610 This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2019