Precise Control of the Oriented Layered Double Hydroxide Nanosheets Growth on Graphene Oxides Leading to Efficient Catalysts for Cascade Reactions

Article abstract of DOI:10.1002/cctc.201901208

In recent years, great attention has been paid to cascade reactions, which can improve efficiency and reduce waste production by implementing several consecutive reactions. Herein, two bifunctional catalysts were successfully prepared by precise control of the oriented layered double hydroxides (LDHs) growth on graphene oxides (GO) using a single-drop and co-precipitation method, respectively. The resultant Ru/LDH-GO-P and Ru/LDH-GO-V composites were characterized by EXAFS, FT-IR, XRD, TG-DTA, BET, XPS, TEM, CO₂-TPD, O₂-TPD, etc. The catalytic performance of Ru/LDH-GO-P and Ru/LDH-GO-V for one-pot oxidation-Knoevenagel condensation reaction showed significant difference under the same experimental conditions, in which the Ru/LDH-GO-P showed 99 % conversion and 99 % selectivity, in marked contrast of 60.7 % conversion and 47.9 % selectivity using Ru/LDH-GO-V as catalyst. The large enhancement of the catalytic performance using Ru/LDH-GO-P can be attributed to the following reasons: 1) the Co³⁺ centers in Ru/LDH-GO-P can promote the formation of surface oxygen vacancies that can adsorb and activate O₂ to get better performance; 2) the Ru/LDH-GO-P exhibited larger BET surface and more medium-strong basic active sites than the Ru/LDH-GO-V. Moreover, the Ru/LDH-GO-P catalyst can be easily recovered from the reaction system and reused for at least five times without obvious deterioration of its catalytic activity or structural integrity.

Full text of DOI:10.1002/cctc.201901208

Accepted Article
Title: Precise control of the oriented layered double hydroxide
nanosheets growth on graphene oxides leading to efficient
catalysts for cascade reactions
Authors: Yu-Fei Song, Wei Zhang, Zelin Wang, Yufei Zhao, and
Haralampos N. Miras
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201901208
Link to VoR: http://dx.doi.org/10.1002/cctc.201901208
A Journal of
www.chemcatchem.org

10.1002/cctc.201901208
ChemCatChem
Precise control of the oriented layered double hydroxide
nanosheets growth on graphene oxides leading to efficient
catalysts for cascade reactions
Wei Zhang,a Zelin Wang,a Yufei Zhao,a Haralampos N. Miras,b* and Yu-Fei Songa*
[a] W. Zhang, Z. Wang, Prof. Y. Zhao and Prof. Y.-F. Song*
State Key Laboratory of Chemical Resource Engineering, Beijing Advanced Innovation Center for Soft
Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
*Email: songyf@mail.buct.edu.cn; Tel/Fax: +86 10- 64431832
[b] Dr. H. N. Miras
WestCHEM, School of Chemistry, University of Glasgow, Glasgow G12 8QQ, U.K.
*E-mail: charalampos.moiras@glasgow.ac.uk; Tel: +44 (0)141-3304375
Abstract: In recent years, great attention has been paid to cascade reactions, which can
improve efficiency and reduce waste production by implementing several consecutive
reactions. Herein, two bifunctional catalysts were successfully prepared by precise control of
the oriented layered double hydroxides (LDHs) growth on graphene oxides (GO) using a
single-drop and co-precipitation method, respectively. The resultant Ru/LDH-GO-P and
Ru/LDH-GO-V composites were characterized by EXAFS, FT-IR, XRD, TG-DTA, BET,
XPS, TEM, CO2-TPD, O2-TPD, etc. The catalytic performance of Ru/LDH-GO-P and
Ru/LDH-GO-V for one-pot oxidation-Knoevenagel condensation reaction showed significant
difference under the same experimental conditions, in which the Ru/LDH-GO-P showed 99%
conversion and 99% selectivity, in marked contrast of 60.7% conversion and 47.9%
selectivity using Ru/LDH-GO-V as catalyst. The large enhancement of the catalytic
performance using Ru/LDH-GO-P can be attributed to the following reasons: 1) the Co3+
centers in Ru/LDH-GO-P can promote the formation of surface oxygen vacancies that can
adsorb and activate O2 to get better performance; 2) the Ru/LDH-GO-P exhibited larger BET
surface and more medium-strong basic active sites than the Ru/LDH-GO-V. Moreover, the
Ru/LDH-GO-P catalyst can be easily recovered from the reaction system and reused for at
least five times without obvious deterioration of its catalytic activity or structural integrity.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Introduction
In recent years, the cascade reaction systems have attracted wide attention since it can
improve efficiency of chemical processes and reduce the waste production.[1] As a result,
rational design of catalysts with well-defined and spatially isolated multiple active sites plays
a significant role in the optimization of cascade reaction systems. Since many of the
employed homogeneous catalytic systems are known to suffer from separation issues from
the reaction medium,[2] research efforts mainly focus on the development of heterogeneous
systems such as UiO-66-Ru,[3] NH2-MIL-101,[4] Au@Cu(II)-MOF,[5] Tris-LDH-Zn4(PW9)2,[6]
Pd/COF-TpPa-Py,[7] and Ni3Ga-LDH,[8] which have demonstrated good catalytic activity in
one-pot cascade reactions. Although these catalysts were efficient for the cascade reactions,
they are largely restricted by the facts such as the requirement of excessive amounts of
oxygen donor reagents, the addition of soluble base, and the use of high temperature. As
such, the development of effective catalytic systems tailored for cascade reactions under mild
conditions is highly desirable and challenging.
Layered double hydroxides (LDHs) are composed of brucite-like two-dimensional sheets
3+
and interlayer anions with general chemical formula [M2+
M
x(OH)2]x+[Ax/n]n-·mH2O,[9]
1-x
where M2+ and M3+ represent di- and trivalent metal cations, An− is the counterion.[10] Due to
fascinating properties that can be finely tuned by appropriate choice of the metal ions and
guest anions,[11] LDHs have been widely used in various fields.[12] In addition, LDHs can
efficiently catalyze Knoevenagel condensation reactions owing to the presence of abundant
and accessible hydroxyl groups.[13,6] LDH materials ensure immobilization and high
dispersion of metal particles due to its excellent adsorption capacity within the gallery of the
LDH.[14] Previously reported examples of LDH-supported catalysts, such as the Ru-LDH,[15]
Pd-LDH,[16] Au-LDH[17] showed significantly higher catalytic activity than those immobilized
on other supports.
Graphene oxides (GO) exhibits a two-dimensional honeycomb sp2 carbon lattice with
extremely large surface area and fast electron transfer properties due to its high
conductivity.[18] However, the graphene-based materials tend to stack together due to π-π
interactions, largely limiting their application. Thus, GO’s physical and chemical properties
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
renders it an excellent support system for the immobilization of catalysts and development of
composite nanomaterials with superior functionality. Immobilization of LDH nanosheets on
the surface of GO, exhibits the following advantages: 1) the presence of the LDH and
interaction with the GO’s nanosheets can decrease the π-π interactions and prevent their
aggregation;[19] 2) the large specific surface area of GO disperses effectively the LDH’s active
sites.[20]
In this work, we reported the preparation and characterization of two bifunctional
catalysts Ru/LDH-GO-P and Ru/LDH-GO-V by in-situ synthesis and immobilization of LDH
on GO surface by single-drop method and co-precipitation method, respectively.
Investigation of their catalytic efficiency in one-pot oxidation-Knoevenagel condensation
reaction under the same experimental conditions revealed significant differences between the
two catalytic systems which greatly depends on the morphology of the composite. The
Ru/LDH-GO-P exhibited much better activity and selectivity in the cascade reaction between
cinnamyl alcohol and ethyl cyanoacetate to produce cinnamylidene ethyl cyanoacetate under
mild conditions. Moreover, the heterogeneous catalyst of Ru/LDH-GO-P can be easily
recovered and reused for at least five times without obvious deterioration of their structural
integrity and activity.
Experimental Section
All chemicals were of analytical grade and were used as received without any further
purification. RuCl3·3H2O, CoCl2·6H2O, AlCl3·6H2O, NaOH, and Na2CO3, were obtained
from Energy Chemical in Shanghai. Ethyl cyanoacetate (98%), malononitrile (97%),
cinnamyl alcohol (98%) and other alcohols were purchased from Alfa Aesar. Graphite was
purchased from Chengdu Organic Chemicals Co. Ltd, Chinese Academy of Sciences.
Powder XRD patterns were recorded on a Rigaku XRD-6000 diffractometer under the
following conditions: 40 kV, 30 mA, CuKα radiation (l = 0.154 nm). FT-IR spectra were
recorded on a Bruker Vector 22 infrared spectrometer using KBr pellets. Diffuse reflectance
Fourier transform infrared (DRIFT) spectra were recorded on a Bruker Tensor 27
spectrometer. Raman measurements were recorded on a Renishaw Raman spectrometer using
a laser excitation wavelength of 532 nm. The N2 adsorption-desorption isotherms were
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
measured on a Quantachrome Autosorb-1 system at the liquid-nitrogen temperature, and the
o
samples were degassed at 120 C for 6 h before the measurements. TG-DTA was performed
on a TGA/DSC 1/1100 SF from Mettler Toledo in flowing N2 with a heating rate of 10
o
o
oC/min from 33 C to 900 C. XPS measurements were performed on a PHI Quantera SXM
using monochromatized AlKα exciting X-radiation. Temperature-programmed desorption
(TPD) was probed by using a PCA-1200 Chemical adsorption apparatus 1100 analyzer
equipped with a thermal conductivity detector (TCD). The 1H-NMR spectra were recorded on
a Bruker AV400 NMR spectrometer at resonance frequency of 400 MHz, and the chemical
shifts were given relative to TMS as the internal reference. The K-edge XANES
measurements were performed at the 1W1B beamline of Beijing Synchrotron Radiation
Facility. Fourier transform EXAFS (FT-EXAFS) shell fitting was carried out with Artemis
Software.
The transition metal stock solution: In a typical experiment, the transition metal stock
solution was prepared by mixing RuCl3·3H2O (98.05 mg, 0.375 mmol), CoCl2·6H2O (892.24
mg, 3.75 mmol) and AlCl3·6H2O (301.79 mg, 1.25 mmol) in distilled water (25 mL).
The alkali metal stock solution: it was prepared by mixing Na2CO3 (530 mg, 2.5 mmol)
and NaOH (800 mg, 10 mmol) in 50 mL of distilled water.
Synthesis of Ru/LDH-sd: This compound was prepared using single-drop method as
following. The alkali metal stock solution was added dropwise into the transition metal stock
solution with vigorous stirring at room temperature until pH = 10.0. The resulting suspension
was aged at 363 K for 6 h. After that, the solution was filtered and the precipitate was washed
with deionized water (3 20 mL). The obtained solid sample was dried at 333 K overnight
under vacuum to obtain Ru/CoAl-LDH (Ru/LDH-sd).
Synthesis of Ru/LDH-cp: This compound was prepared using co-precipitation method.
The transition metal stock solution and the alkali metal solution were added dropwise
simultaneously into the 25 mL distilled water with vigorous stirring at room temperature and
the pH of the mixture was controlled to 10.0. Then, the resulting suspension was aged at 363
K for 6 h. After that, the mixture was filtered and the resultant precipitate was washed with
deionized water (3  20 mL). The obtained solid was dried at 333 K overnight in a vacuum
oven to obtain Ru/CoAl-LDH (Ru/LDH-cp).
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
GO was synthesized and characterized according to previously reported method.[21]
Synthesis of Ru/LDH-GO-P: The transition metal stock solution was added into the GO
suspension and the mixture was sonicated for 30 min, to which the alkali metal stock solution
was added dropwise with vigorous stirring at room temperature until pH = 10.0. The resulting
suspension was aged at 363 K for 6 h, and the mixture was filtered and the precipitate was
washed with deionized water (3  20 mL). The obtained solid sample was dried at 333 K
overnight under vacuum, and it was denoted as Ru/LDH-GO-P due to the presence of LDH in
parallel growth on the GO.
Synthesis of Ru/LDH-GO-V: The transition metal stock solution and the alkali metal
solution were added simultaneously dropwise into the GO suspension with vigorous stirring
at room temperature, and the pH of the solution was controlled to 10.0. The resulting
suspension was aged at 363 K for 6 h. After that, the mixture was filtered and the precipitate
was washed with deionized water (3  20 mL). The obtained solid was dried at 333 K
overnight in a vacuum, and it was denoted as Ru/LDH-GO-V because the LDH was grown
vertically on GO.
Catalytic test
In a typical One-pot oxidation-Knoevenagel condensation reaction, solid catalyst (100
mg), benzyl alcohol (1 mmol) and toluene (7 mL) were mixed in a 50 mL three-necked flask.
The reaction mixture was kept under stirring at 333 K under O2 bubble (10 mL/min for 2
hours, 0.10 MPa). After the reaction progressed for a desired period of time, ethyl
cyanoacetate (1.5 mmol) was charged into the reaction system rapidly. The mixture was left
at 333 K for an additional time period. The resulting products were extracted with CH2Cl2
and analyzed by gas chromatography equipped with a flame ionization detector (GC-FID).
The yields were calculated by using reference standards. The obtained products (purified by
rotary evaporation and silica gel column chromatography eluted with petroleum ether/EtOAc
= 5:1) were dissolved in CDCl3 and analyzed by 1H NMR spectroscopy. After completion of
the reaction, the catalyst was recovered by centrifugation, washed with acetone, and dried
under 333 K overnight.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Results and Discussion
Scheme 1. Schematic representation of the Ru/LDH-GO-V and Ru/LDH-GO-P nanocomposites.
As shown in Scheme 1, the Ru/LDH-GO-P nanocomposite was synthesized via single
drop method, while the Ru/LDH-GO-V nanocomposite was prepared using co-precipitation
method. The Ru/LDH-GO-P and Ru/LDH-GO-V revealed rather similar XRD patterns
(Figure 1a). The peaks located at 2θ = 12, 24, 35, 39, 60, and 62o can be indexed to the (003),
(006), (009), (015), (110) and (113) reflection of the LDH phase with 3R symmetry,
respectively.[21] The GO present a characteristic (001) diffraction at 2θ =11.9o, indicative of
an interlayer distance of approximately 0.74 nm,[19] which can be attributed to the formation
of oxygenated functional groups on the graphite layers. No typical diffraction peak of GO
was observed in the corresponding nanocomposites, which can be attributed to the
superimposed reflections with LDH.[22]
As shown in Figure 1b, Raman spectrum of GO revealed the G band at 1598 cm-1 and the
D band at 1342 cm-1, respectively.[23] The intensity ratio of the D to the G band (ID/IG)
provides the surface defect and the degree of lattice distortion of the graphite layer within the
carbon material. The gradual increase of the ID/IG ratio from 0.92 for GO, to 0.96 for
Ru/LDH-GO-V and 1.04 for Ru/LDH-GO-P (Table S1) was indicative of the effective
immobilization of the LDH on the GO surface. The higher ID/IG value resulted in the
conjugated carbon atoms with more structural defects.[22] The increased number of defect
sites on the surface of graphene may play an important role in promoting the in-situ
formation and immobilization of LDH on GO, which is important for the inhibition of the
agglomeration of LDH nanosheets during the growth process and consequently the high
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
dispersion of Ru active centers.
Figure 1. a) XRD patterns of GO, Ru/LDH-GO-P, and Ru/LDH-GO-V. b) Raman spectra of GO, Ru/LDH-
GO-P, and Ru/LDH-GO-V. c) TEM image of Ru/LDH-GO-P. d) TEM image of Ru/LDH-GO-V.
Interestingly, TEM and SEM images of Ru/LDH-GO-P (Figure 1c, S1, S2) exhibited
dramatic difference from those of Ru/LDH-GO-V (Figure 1d, S1, S2). In the case of
Ru/LDH-GO-P, the LDHs grew with ab-planes of the crystallites oriented parallel to GO
(Figure S3), whereas for Ru/LDH-GO-V, the ab-planes can be found to be oriented
perpendicular to GO. Such morphological difference can be assigned to be the different
concentration of LDH nucleation points formed in the synthetic process.[24] In the case of
Ru/LDH-GO-V, high concentration of LDH nucleation points were formed by simultaneous
addition of alkali and transition metal stock solution into the GO dispersion, according to the
co-precipitation method. Thus, the high concentration of LDH led to the growth and
subsequent immobilization of LDH crystallites with their ab-planes aligned perpendicular to
the GO substrate. However, in the case of Ru/LDH-GO-P which was formed using single
drop method, the transition metal stock solution and the GO dispersion were mixed before the
subsequent addition of the alkali solution. As a result, the local concentration of LDH
nucleation points on the surface of GO was much lower than in the case of co-precipitation
method. Low local concentrations promoted slower generation of nucleation points on the
GO surface and the LDH crystallites were oriented with their ab-faces parallel to the GO
film. FT-IR spectrum (Figure S4) of GO itself showed the peaks at 1722, 1624, 1058 cm-1
that can be assigned to the C=O stretching bands of COOH groups, the carbon backbone
(C=C/C-C), and the alkoxy (C-O), respectively.[25] In contrast, these bands disappeared in the
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
corresponding FT-IR spectrum of Ru/LDH-GO-P and Ru/LDH-GO-V, which was indicative
of partial reduction of the GO during the formation of LDH-GO composite.[26]
Figure 2. a) Normalized Co K-edge XANES spectra of Ru/LDH-GO-P, and Ru/LDH-GO-V. b) Locally
amplified version of Normalized Co K-edge XANES spectra. c) The k3-weighted Fourier transform spectra from
Co K edge EXAFS. d) Normalized Ru K-edge XANES spectra of Ru/LDH-GO-P, Ru/LDH-GO-V, RuCl3, and
RuO2. e) Locally amplified version of Normalized Ru K-edge XANES spectra. f) The k3-weighted Fourier
transform spectra from Ru K edge EXAFS.
Subsequently, we utilized X-ray absorption spectroscopy (XAS) in an effort to elucidate
the chemical state and coordination environment of Co and Ru atoms. The Co K-edge X-ray
absorption near edge structure (XANES) spectra (Figure 2a-2b, S5a) suggested that the
valence state of Co in Ru/LDH-GO-P was higher than that in Ru/LDH-GO-V. The
corresponding Fourier Transformed (FT) k3χ(k) functions (Figure 2c) showed that both
Ru/LDH-GO-P and Ru/LDH-GO-V exhibited two prominent peaks at 1.6 and 2.8 Å,
corresponding to the nearest Co−OOH and the neighboring Co-Co coordination, respectively.
The peak intensity for Co−OOH and Co-Co coordination in Ru/LDH-GO-P were significantly
lower than the corresponding peaks in Ru/LDH-GO-V, suggesting that the Ru/LDH-GO-P
possessed more Co and O vacancies than the Ru/LDH-GO-V. As shown in Figure 2e and
S5b, the Ru K-edge for both nanocomposites is close to that of the RuCl3 reference,
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
suggesting that the oxidation state of Ru remained +3. As can be seen from the EXAFS
spectrum in R space (Figure 2f), the Ru/LDH-GO-P and Ru/LDH-GO-V exhibited a
prominent peak at approximately 1.6 Å from the Ru-O shell. No other typical peaks for Ru-
Ru contributions at longer distances (> 2.0 Å) were observed, indicating the high dispersion
of isolated Ru3+ through the Ru/LDH-GO nanosheets.[27]
Figure 3. a) TG-DTA profile of Ru/LDH-GO-P and Ru/LDH-GO-V. b) The N2 adsorption-desorption isotherm
and the pore size distribution (inset picture) of Ru/LDH-GO-P and Ru/LDH-GO-V. c) Co 2p XPS spectra for
Ru/LDH-GO-P, Ru/LDH-GO-V. d) C 1s+Ru 3d XPS spectra for Ru/LDH-GO-P, Ru/LDH-GO-V.
Thermogravimetric and differential thermal analysis (TG-DTA) of Ru/LDH-GO-P and
Ru/LDH-GO-V showed three distinct stages of weight loss upon temperature increase from
30 to 800 oC (Figure 3a). In the case of Ru/LDH-GO-P, the first weight loss of 15.21 % took
place between 30 and 220 oC that can be ascribed to the removal of water molecules absorbed
on the surface and the interlayer space. The second weight loss of 17.33 % between 220 and
o
440 C corresponded to the subsequent disintegration of the layered structure. The third
o
weight loss of 9.29 % between 440 and 630 C was related to the combustion of the carbon
[28]
skeleton.
In case of Ru/LDH-GO-V, the first two weight losses were similar to the ones
observed in Ru/LDH-GO-V. However, the third weight loss temperature took place at slightly
o
lower temperatures (between 390 and 560 C), which was due to the weaker interactions
between the LDH and GO. To further investigate the possibility of a porous structure and to
determine the surface area of the prepared composites, the N2 adsorption-desorption isotherm
and the Barrett-Joyner-Halenda (BJH) pore size distribution plots of Ru/LDH-GO-V,
Ru/LDH-GO-P and GO were calculated (Figure 3b, S6). All samples exhibited typical type
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
IV adsorption isotherms and H3 type hysteresis loops at a high relative pressure (P/P0 > 0.4),
which indicates the predominant presence of mesopores. Ru/LDH-GO-P showed a peak
centered at approximately 3.8 nm (Figure 3b, inset) and Ru/LDH-GO-V showed a peak
centered at approximately 3.3 nm. The larger surface area of Ru/LDH-GO-P (116.49 m2∙g-1)
than that of Ru/LDH-GO-V (94.62 m2·g-1) may have a profound effect on the adsorption of
O2 and subsequent efficiency during the catalytic processes.
XPS spectra of the Co2p, Ru3d, C1s, Ru3p, Al2p and O1s were presented in Figure 3,
S7. The Co2p core lines of the Ru/LDH-GO-P and Ru/LDH-GO-V (Figure 3c) can be split
into Co2p3/2 (∼781.1 eV) and Co 2p1/2 (∼797.3 eV) peaks along with two satellite bands
located at 786.6 and 803.4 eV, indicating the existence of high-spin Co2+ state in both
cases.[29] It was worth noting that the binding energies of Co2p3/2 and Co2p1/2 in Ru/LDH-
GO-P (781.0 and 797.1 eV) are both ∼0.3 eV lower than those in Ru/LDH-GO-V (781.3 and
797.4 eV), confirming the enhanced electron density of Co atoms, which is consistent with
the XAFS data. [30] The atomic ratios of Co3+/Co2+ in Ru/LDH-GO-P and Ru/LDH-GO-V
were found to be 0.22 and 0.16, respectively. This result indicated the presence of more Co3+
centers in Ru/LDH-GO-P that can promote the formation of surface oxygen vacancies that
can adsorb and activate O2.[15,31] As shown in Figure 3b, deconvolution of both Ru3d5/2
profiles of Ru/LDH-GO-P and Ru/LDH-GO-V showed the main binding energy peak at
282.1 eV, which can be attributed to Ru(OH)3.[32]
Table 1. Performance of different catalysts in the oxidation of cinnamyl alcohol and the subsequent
Knoevenagel condensation with ethyl cyanoacetate.[a]
Entry
Catalyst
Ru/LDH-GO-P
Ru/LDH-GO-V
Ru/LDH-sd
Ru/LDH-cp
RuCl3
Conv. A (%) Yield B (%) Yield C (%)
1
2
>99
60.7
40.9
21.5
0
0
12.8
10.6
7.9
0
99
47.9
30.3
13.6
0
3
4
5[b]
6[c]
GO
0
0
0
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
7[d]
8[e]
9
RuCl3+LDH-sd+GO
RuCl3+LDH-cp+GO
No catalyst
43.5
22.0
0
9.5
7.5
0
36.0
14.5
0
[a] Reaction conditions: catalyst (100 mg), A (1 mmol), ethyl cyanoacetate (1.5 mmol), O2,
[b]
[c]
[d]
solvent (7 mL), T=333 K, 3 h.
RuCl3 (19.6 mg), GO (10 mg). RuCl3 (19.6 mg),
LDH-sd (80.4 mg), GO (10 mg). [e] RuCl3 (19.6 mg), LDH-cp (80.4 mg), GO (10 mg)
The catalytic activity of Ru/LDH-GO-P, and Ru/LDH-GO-V in the one-pot tandem
synthesis of cinnamylidene ethyl cyanoacetate (abbreviated as C) from cinnamyl alcohol
(denoted as A) was investigated in toluene under oxygen atmosphere. The results were
summarized in Table 1. The one-pot synthesis of cinnamylidene ethyl cyanoacetate was
realized through the oxidation of cinnamyl alcohol followed by Knoevenagel condensation
with ethyl cyanoacetate. Cinnamyl aldehyde (denoted as B) was produced as an intermediate
in all cases. The cascade reaction proceeded smoothly with 99% conversion and 99%
selectivity of cinnamylidene ethyl cyanoacetate using Ru/LDH-GO-P as catalyst (Table 1,
entry 1). In contrast, Ru/LDH-GO-V did not promote the reaction as efficiently as Ru/LDH-
GO-P with the conversion of 47.9 % (entry 2). Moreover, the control experiments using
Ru/LDH-sd and Ru/LDH-cp as catalysts showed considerably lower conversion of A (entries
3, 4), indicating that the introduction of GO can decrease the π-π interactions and aggregation
of LDH nanosheets and facilitate the dispersion of active sites. Bare GO and RuCl3 also
showed no activity for the cascade reaction. Finally, the physical mixture of GO and LDH
showed inferior efficiency (entries 6, 7) since both activity and selectivity were considerably
lower than those using Ru/LDH-GO-P as catalyst.
The CO2-TPD measurements were performed in order to obtain information about the
number of basic sites present on the solids. As shown in Figure 4a, the broad peak for CO2
desorption between 100 and 200 °C can be deconvoluted into two contributions in the range
of 100-170 °C and 170-200 °C, which were identified as weak and medium-strong basic
sites, respectively. [33] Moreover, the Ru/LDH-GO-P showed substantially more (weak and
medium-strong) basic sites than Ru/LDH-GO-V, which was consistent with the fact that the
Ru/LDH-GO-P performed more efficiently than the Ru/LDH-GO-V for the above cascade
reaction.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Figure 4. a) CO2-TPD of Ru/LDH-GO-P and Ru/LDH-GO-V, b) in situ CO2-IR of Ru/LDH-GO-P and
Ru/LDH-GO-V, c) O2-TPD of Ru/LDH-GO-P and Ru/LDH-GO-V.
In order to demonstrate further the difference between the basic sites of the two catalysts,
we employed the in-situ CO2-IR technique (Figure 4b). Three species of adsorbed CO2 were
detected, which can be assigned to bicarbonates, bidentate carbonates, and monodentate
carbonates (Table S2). This result confirmed the presence of three different types of surface
basic sites. Bicarbonates were formed from the interaction of CO2 with OH groups, while
bidentate carbonates and monodentate carbonates can be originated from the interaction of
CO2 with M-O ion pairs and surface O2− ions, respectively.[30,34] The IR spectrum of
Ru/LDH-GO-P was noticeably more complex than that of Ru/LDH-GO-V. For Ru/LDH-GO-
P, the characteristic peak of bidentate carbonates at 1618 cm-1 indicated the presence of M-O
ion pairs than that in Ru/LDH-GO-V, which was consistent with the CO2-TPD studies. To
examine the mobility of oxygen species, we conducted O2-TPD tests. For both Ru/LDH-GO-
P and Ru/LDH-GO-V, the broad peaks located in the range of 150 and 350 oC were assigned
2-
-
to the chemisorbed oxygen O2 and surface-active oxygen species O2 , respectively.[30,35] In
addition, the peaks in Ru/LDH-GO-P showed higher intensity than that in Ru/LDH-GO-V,
-
indicating higher abundance of O22- and O2 species.
Kinetic study of cascade oxidation–Knoevenagel condensation reaction
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Figure 5. Yields vs reaction time of cinnamyl aldehyde and cinnamylidene ethyl cyanoacetate using a)
Ru/LDH-GO-P and b) Ru/LDH-GO-V as catalysts, respectively.
To describe directly the different reaction pathway between Ru/LDH-GO-P and
Ru/LDH-GO-V, the tandem synthesis of cinnamylidene ethyl cyanoacetate (denoted as C)
from cinnamyl alcohol (denoted as A) was performed at different reaction times. When
Ru/LDH-GO-P was used as catalyst (Figure 5a, S8), the product cinnamyl aldehyde (denoted
as B) yield gradually increased to reach maximum within 120 min. Subsequent addition of
ethyl cyanoacetate into the reaction mixture led to a rapid decrease of the intermediate B,
whereas the yield of C increased rapidly within 30 min. In contrast, when Ru/LDH-GO-V
was applied as catalyst (Figure 5b, S8), the observed increase of B and C was considerably
lower than Ru/LDH-GO-P.
Figure 6. a) Effect of the solvent on the one-pot oxidation-Knoevenagel condensation reaction by
Ru/LDH-GO-P. b) Recycling test of the Ru/LDH-GO-P catalyst for 5 times. c) Hot filtration experiments,
red line: in the presence of Ru/LDH-GO-P; green line: Ru/LDH-GO-P was filtrated at 30min. Reaction
conditions: catalyst (100 mg), A (1 mmol), ethyl cyanoacetate (1.5 mmol), O2, solvent (7 mL), T=333 K, 3
h.
To identify the best solvent medium for the one-pot oxidation-Knoevenagel condensation
reaction, we investigated the effects of a series of solvents on the catalytic efficiency (Figure
6a). The cascade reaction proceeded efficiently with the conversion of A reaching 95% in
DMSO and 93% in DMF, respectively. If toluene was used, we observed almost complete
conversion of A (99%) and selectivity of C >99%. On the other hand, the catalytic activity
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
decreased if water, methanol, ethanol, and acetonitrile were used as solvents in the cascade
reaction. Based on the above screening, we selected toluene as the most appropriate solvent
medium. As shown in Figure 6b, Ru/LDH-GO-P used for the promotion of the cascade
reaction can be easily recovered by filtration and recycled for at least 5 times without obvious
deterioration of its catalytic activity. In addition, the characterization of the recycled catalyst
using powder XRD and FT-IR (Figure S9) confirmed its structural integrity.
To prove whether the cascade reaction followed heterogeneous or homogeneous
pathway, we conducted the following experiment. When the cascade reaction was half-way
through (the conversion reached 53 % after 30 min), the Ru/LDH-GO-P catalyst was filtered
off. And the remaining reaction mixture was kept under the same experimental conditions. As
a result, it showed that no additional conversion of the reactant to the product can be
observed (Figure 6c). This experiment demonstrates further the efficiency and robustness of
the Ru/LDH-GO-P heterogeneous catalyst.
Comparison with other reported heterogeneous catalysts
Table 2. Performance of different catalysts in the oxidation of cinnamyl alcohol and the subsequent
Knoevenagel condensation with malononitrile.
Entry
catalyst
oxidant
T
t
Conv. [%] Yield [%]
Ref.
1
2
3
4
5
6
UiO-66-Ru(3.6mol % Ru)
CuBr+FL2
O2
373K
32h
13h
34h
4h
94.6
66
51.2
-
3
TEMPO 313K
TBHP 343K
36
37
Au/NH2-UiO-66
30%HPW/mpg-C3N4
MNP@PIL/W
79
77
-
H2O2
H2O2
O2
363K
363K
333K
97.6
99
38
7h
95
98.0
39
Ru/LDH-GO-P
2.5h
98.0
This work
The one-pot oxidation-Knoevenagel condensation reactions using a variety of substrates
and catalysts reported previously were summarized in Table 2, Table S3 and S4. The
Ru/LDH-GO-P exhibited very good catalytic activity using O2 as oxidant under mild reaction
conditions compared with previously reported catalysts. In addition, the Ru/LDH-GO-P
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
showed considerably better catalytic activity compared with other noble metal-based
catalysts, such as UiO-66-Ru and Au/NH2-UiO-66 for cinnamyl alcohol and the subsequent
Knoevenagel condensation with malononitrile reaction (Table 2, entries 1, 3). Also in the case
where the substrate was replaced with benzyl alcohol and malononitrile, Ru/LDH-GO-P still
exhibited superior reactivity compared to other reported catalysts (Table S3, entries 2,7,13,
Table S4, entries 1, 2, 5). The observed physical and chemical properties (activity, stability
and regeneration) renders the Ru/LDH-GO-P composite catalyst an exceptional catalytic
material for the one-pot oxidation-Knoevenagel condensation reaction.
Scheme 2. Reaction pathway of the one-pot reaction over the Ru/LDH-GO-P catalyst.
Based on the discussed experimental evidence, we proposed a possible pathway for the
one-pot reaction over the Ru/LDH-GO-P catalyst (Scheme 2). At the beginning of the
reaction, the substrate of cinnamyl alcohol interacted primarily with the basic Ru–OH active
sites coupled with elimination of hydroxyl protons from cinnamyl alcohol, leading to the
formation of an alkoxide intermediate.[1a] Subsequently, the intermediate formed a highly
reactive metal–alcoholate moiety that was able to eliminate H, forming cinnamaldehyde.
Then, the basic sites of the LDH catalyzed the Knoevenagel condensation of nitriles with
aldehydes to form cinnamylidene ethyl cyanoacetate. The final step involved the rapid
oxidation of the Ru–H species by the molecular O2 to form Ru-OH active sites that completed
the catalytic cycle.
In order to evaluate the general applicability and efficiency of the Ru/LDH-GO-P as
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
heterogeneous catalyst in one-pot oxidation-Knoevenagel condensation reactions, we
investigated the conversion of various benzyl alcohol derivatives and active methylene
compounds (Table 3). The Ru/LDH-GO-P proved to be effective for a variety of benzyl
alcohols with either an electron-withdrawing or an electron-donating group (entries 5-9).
Herein, p-Cl, p-Br, p-methyl, p-nitro, and p-methoxy substituted benzyl alcohols were
transformed to the desired products with high yields (entries 5-9), although nitro group, Cl,
and Br were strong electron withdrawing groups and methoxy and methyl groups exhibited
electron-donating properties. In addition, malononitrile, which was used as the active
methylene compound in the condensation reactions with benzyl alcohol derivatives, was also
converted to the corresponding condensation products in high yields (entries 2, 4). It should
be noted that malononitrile showed higher reactivity compared to the ethyl cyanoacetate in
the condensation reaction with the carbonyl substrates.
Table 3. One-pot oxidation-Knoevenagel cascade reactions towards different substrates using Ru/LDH-
GO-P as the catalyst.
Entry
A
R2
Time
Conv. (%)
Yield (%)
1
COOEt
3h
99.5
99.5
2
3
4
5
6
7
8
9
CN
2.5h
2h
2h
2h
2h
2h
2h
2h
98.0
96.5
99.0
95.0
93.9
90.7
94.6
92.1
98.0
96.5
99.0
95
COOEt
CN
COOEt
COOEt
COOEt
COOEt
COOEt
93.9
90.7
94.6
92.1
Conclusion
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Two new heterogeneous catalysts of Ru/LDH-GO-P and Ru/LDH-GO-V were
successfully synthesized by single-drop method and co-precipitation method, respectively.
Experimental data revealed that in the case of Ru/LDH-GO-P, LDH layers were developed
with their ab-planes parallel to the GO surface, whereas the ab-planes were found to be
oriented perpendicular to GO surface for Ru/LDH-GO-V. XANES studies indicated that the
Ru/LDH-GO-P incorporated more Co and O vacancies than Ru/LDH-GO-V.
By taking the one-pot oxidation-Knoevenagel condensation of cinnamyl alcohol and
ethyl cyanoacetate as a probe reaction, the Ru/LDH-GO-P showed excellent catalytic
performance with the conversion and selectivity >99% for the cascade reactions at 333 K
under O2 atmosphere within 3 h, while the Ru/LDH-GO-V showed 60.7% conversion and
47.9% selectivity under the same experimental condition. The observed dramatic difference
of the catalytic performance can be attributed to the following reasons. Firstly, the Co3+
centers in Ru/LDH-GO-P can promote the formation of surface oxygen vacancies that can
adsorb and activate O2 to get better performance; Secondly, the Ru/LDH-GO-P exhibited
larger BET surface and more medium-strong basic active sites than the Ru/LDH-GO-V.
Moreover, the Ru/LDH-GO-P catalyst exhibited wide-range applicability in a variety of
aromatic alcohols and it can be easily recovered and reused at least five times without
obvious deterioration of its catalytic activity. The observed exceptional robustness and
efficiency render the Ru/LDH-GO-P catalyst an exceptional candidate for industrial
applications in fine-chemical synthesis.
Conflicts of interest
The authors declare there are no conflicts of interest.
Acknowledgements
This research was supported by the National Nature Science Foundation of China (U1707603,
21625101), Beijing Natural Science Foundation (2182047) and the Fundamental Research
Funds for the Central Universities (XK1802-6, XK1902, 12060093063). H.N.M
acknowledges the financial support from The University of Glasgow. We would like to thank
1W1B beam line of Beijing Synchrotron Radiation Facility (BSRF).
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
Keywords: alcohols, cascade reation, graphene oxides, heterogeneous catalysis,
layered double hydroxides.
References
[1]
a) K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem. Soc. 2005,
127, 9674-9675. b) M. Platon, R. Amardeil, L. Djakovitch, J. C. Hierso, Chem. Soc. Rev. 2012,
41, 3929-3968. c) R. C. Wende, P. R. Schreiner, Green Chem. 2012, 14, 1821-1849.
a) D. B. Ramachary, S. Jain, Org. Biomol. Chem. 2011, 9, 1277–1300. b) Y. Jiang, X. Y. Tang, M.
Shi, Chem. Commun. 2015, 51, 2122–2125.
[2]
[3]
[4]
[5]
Q. M. Yang, H. Y. Zhang, L. P. Wang, Y. C. Zhang, J. Q. Zhao, ACS Omega 2018, 3, 4199-4212.
D. K. Wang, Z. H. Li, Catal. Sci. Technol. 2015, 5, 1623-1628.
J. S. Wang, F. Z. Jin, H.-C. Ma, X.-B. Li, M.-Y. Liu, J.-L. Kan, G.-J. Chen, Y.-B. Dong, Inorg.
Chem. 2016, 55, 6685-6691.
[6]
[7]
[8]
K. Liu, Y. Q. Xu, Z. X. Yao, H. N. Miras, Y.-F. Song, ChemCatChem 2016, 8, 929-937.
Q. Sun, B. Aguila, S. Q. Ma, Mater. Chem. Front. 2017, 1, 1310-1316.
W. Y. Zhou, S. Y. Zhai, J. G. Pan, A. J. Cui, J. F. Qian, M. Y. He, Z. X. Xu, Q. Chen, Asian J. Org.
Chem. 2017, 6, 1536-1541.
[9]
a) G. L. Fan, F. Li, D. G. Evans, X. Duan, Chem. Soc. Rev. 2014, 43, 7040-7066. b) S. Omwoma,
W. Chen, R. Tsunashima, Y. F. Song, Coord. Chem. Rev. 2014, 258-259, 58-71. c) R. Y. Yang, Y.
S. Gao, J. Y. Wang, Q. Wang, Dalton Trans. 2014, 43, 10317-10327.
[10] Y. Q. Jia, Y. J. Fang, Y. K. Zhang, H. N. Miras, Y. F. Song, Chem. Eur. J. 2015, 21, 14862-14870.
[11] S. Zhao, J. H. Xu, M. Wei, Y. F. Song, Green Chem. 2011, 13, 384-389.
[12] Q. Wang, D. O’Hare, Chem. Rev. 2012, 112, 4124-4155.
[13] a) E. Angelescu, O. D. Pavel, R. Birjega, R. Zavoianu, G. Costentin, M. Che, Appl. Catal. A.
2006, 308, 13-18. b) M. Yang, J. Liu, Z. Chang, G. R. Williams, D. O’Hare, X. Zheng, X. Sun, X.
Duan, J. Mater. Chem. 2011, 21, 14741-14746. c) Y. Kuwahara, K. Tsuji, T. Ohmichi, T.
Kamegawa, K. Mori, H. Yamashita, ChemSusChem. 2012, 5, 1523-1532.
[14] J. T. Feng, Y. F. He, Y. N. Liu and D. Q. Li, Chem. Soc. Rev. 2015, 44, 5191-5319.
[15] a) K. Kaneda, T. Yamashita, T. Matsushita, K. Ebitani, J. Org. Chem. 1998, 63, 1750-1751. b) T.
Matsushita, K. Ebitani, K. Kaneda, Chem. Commun. 1999, 265-266. c) N. Zhang, Y. Y. Du, M.
Yin, C. Y. Guan, J. T. Feng, D. Q. Li, RSC Adv. 2016, 6, 49588-49596.
[16] N. Kakiuchi, Y. Maeda, T. Nishimura, S. Uemura, J. Org. Chem. 2001, 66, 6620.
[17] T. Mitsudome, A. Noujima, T. Mizugaki, K. Jitsukawa, K. Kaneda, Adv. Synth. Catal. 2009, 351,
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
1890-1896.
[18]
a) J. Y. hang, Y. C. Ding, X. B. Cai, Y. L. Chen, M. Peng,Z. H. Jia, Z. Jiang, P. J. Ren, S. Y. Yao, J.
L. Xie, D. Q. Xiao, X. D. Wen, N. Wang, H. Y. Liu, D. Ma, ACS Catal. 2019, 9, 5998−6005. b) L.
X. Xia, D. Li, J. Long, F. Huang, L. N. Yang, Y. S. Guo, Z. M. Jia, J. P. Xiao, H. Y. Liu, Carbon
2015, 145, 47-52. c) F. Huang, Y. C. Deng, Y. L. Chen, X. B. Cai, M. Peng, Z. M. Jia, P. J. Ren, D.
Q. Xiao, X. D. Wen, N. Wang, H. Y. Liu, D. Ma, J. Am. Chem. Soc. 2018, 140, 13142−13146. d)
Z. M. Jia, F. Huang, J. Y. Diao, J. Y. Zhang, J. Wang, D. S. Su, H. Y. Liu, Chem. Commun. 2018,
54, 11168-11171. f) J. Wang, R. Huang, Y. J. Zhang, J. Y. Diao, J. Y. Zhang, H. Y. Liu, D. S. Su,
Carbon 2017, 111, 519-528.
[19] S. Huang, G.-N. Zhu, C. Zhang, W. W. Tjiu, Y.-Y. Xia, T. X. Liu, ACS Appl. Mater. Interfaces
2013, 4, 2242-2249.
[20] B. Li, Y. F. Zhao, S. T. Zhang, W. Gao, M. Wei, ACS Appl. Mater. Interfaces 2013, 5, 10233-
10239.
[21] a) Y. F. Zhao, P. Y. Chen, B. S. Zhang, D. S. Su, S. T. Zhang, L. Tian, J. Lu, Z. X. Li, X. Z. Cao, B.
Y. Wang, M. Wei, D.G. Evans, X. Duan, Chem. Eur. J. 2012, 18, 11949-11958. b) Y. Lee, J. H.
Choi, H. J. Jeon, K. M. Choi, J. W. Lee, J.K. Kang, Energy Environ. Sci. 2011, 4, 914-920.
[22] T. N. Lambert, C. A. Chavez, B. Hernandez-Sanchez, P. Lu, N. S. Bell, A. Ambrosini, T.
Friedman, T. J. Boyle, D. R. Wheeler, D. L. Huber, J. Phys. Chem. C 2009,113 , 19812-19823.
[23] a) V. Chandra, J. Park, Y. Chun, J. W. Lee, I. C. Hwang, K. S. Kim, ACS Nano 2010, 4, 3979-
3986. b) Y. W. Zhu, S. Murali, W. W. Cai, X. S. Li, J. W. Suk, J. R. Potts, R. S. Ruoff, Adv. Mater.
2010, 22, 3906-3924.
[24] S. Huang, G.-N. Zhu, C. Zhang, W. W. Tjiu, Y.-Y. Xia, T. X. Liu, ACS Appl. Mater. Interfaces
2012, 4, 2242-2249.
[25] a) C. Nethravathi, T. Nisha, N. Ravishankar, C. Shivakumara and M. Rajamathi, Carbon 2009, 47,
2054-2059. b) A. B. Bourlinos, D. Gournis, D. Petridis, T. Szabo, A. Szeri and I. Dekany,
Langmuir 2003, 19, 6050-6055.
[26] R. F. Xie, G. L. Fan, Q. Ma, L. Yang, F. Li, J. Mater. Chem. A 2014, 2, 7880-7889.
[27] Z. L. Wang, S. M. Xu, Y. Q. Xu, L. Tan, X. Wang, Y. F. Zhao, H. H. Duan,Y. F. Song, Chem. Sci.,
2019, 10, 378–384.
[28] Z. B. Lei, L. Lu, X. S. Zhao, Energy Environ. Sci. 2012, 5, 6391-6399.
[29] a) P Li, P. P. Huang, F. F. Wei, Y. B. Sun, C. Y. Cao, W. G. Song, J. Mater. Chem. A 2014, 2,
12739-12745. b) R. Z. Ma, J. B. Liang, K. Takada, T. Sasaki, J. Am. Chem. Soc. 2011, 133, 613-
620.
[30] Q. Wang, L. F. Chen, S. L. Guan, X. Zhang, B. Wang, X. Z. Cao, Z. Yu, Y. F. He, D. G. Evans, J.
T. Feng, D. Q. Li, ACS Catal. 2018, 8, 3104-3115.
[31] a) T. L. Stuchinskaya, M. Musawir, E. F. Kozhevnikova, I. V. Kozhevnikov, J. Catal. 2005, 231,
41-47. b) Y. B Yu, T. Takei, H. Ohashi, H. He, X. L. Zhang and M. Haruta, J. Catal. 2009, 267,
121-128.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201901208
ChemCatChem
[32] D. J. Morgan, Surf. Interface Anal. 2015, 47, 1072–1079.
[33] a) J. Zhang, W. J. Yan, Z. An, H. Y. Song, J. He, ACS Sus. Chem. Eng. 2018, 6, 7313-7324. b) H.
Chen, S. He, M. Xu, M. Wei, D. G. Evans, X. Duan, ACS Catal. 2017, 7, 2735-2743. c) O. D.
Pavel, D. Tichit, I. C. Marcu, Appl. Clay Sci. 2012, 61, 52-58.
[34] a) J. C. Lavalley, Catal. Today 1996, 27, 377-401. b) J. Di Cosimo, V. Díez, M. Xu, E. Iglesia, C.
R. Apesteguía, J. Catal. 1998, 178, 499-510.
[35] Y. T. Chen, H. J. Zheng, Z. Guo, C. M. Zhou, C. Wang , A. Borgna , Y. H. Yang, J. Catal. 2011,
283, 34-44.
[36] W. J. Ang, Y. S. Chng, Y. Lam, RSC Adv. 2015, 5, 81415-81428.
[37] C. S. Hinde, W. R. Webb, B. K. J. Chew, H. R. Tan, W.-H. Zhang, T. S. Andy Horbd, R. Raja,
Chem. Commun. 2016, 52, 6557-6560.
[38] H. F. Wang, C. Y. Wang, Y. F. Yang, M. Zhao, Y. J. Wang, Catal. Sci. Technol. 2017, 7, 405-417.
[39] N. Zohreh, M. Tavakolizadeh, S. H. Hosseini, A. Pourjavadi, C. Bennett, Polymer 2017, 112, 342-
350.
This article is protected by copyright. All rights reserved.