Three-dimensional composite of Co3O4 nanoparticles and nitrogen-doped reduced graphene oxide for lignin model compound oxidation

Article abstract of DOI:10.1039/c8nj01533c

A three-dimensional composite of Co₃O₄ nanoparticles and nitrogen-doped reduced graphene oxide (3D Co₃O₄/N-rGO) with a unique 3D porous structure was prepared, and its catalytic activity in lignin model compound oxidation was explored. The 3D Co₃O₄/N-rGO composite exhibits improved catalytic performance as compared to Co₃O₄ nanoparticles or 3D N-rGO in the oxidation of lignin model compounds. The higher catalytic activity of the 3D Co₃O₄/N-rGO composite is attributed to the combination of its porous structural features, large surface area that is provided by the 3D N-rGO matrix, and active Co₃O₄ nanoparticles doped on the N-rGO surface. The structural features of the 3D Co₃O₄/N-rGO are beneficial to reactant and product diffusion and transportation, and also are helpful in preventing aggregation of Co₃O₄ nanoparticles. In addition, the introduction of N atoms in rGO is also favorable for the formation of active oxygen species for the oxidation of model compounds. Given the high activity and the easy recovery from the reaction system, the 3D Co₃O₄/N-rGO composite should be applicable to non-noble metal catalytic systems for lignin model compounds.

Full text of DOI:10.1039/c8nj01533c

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Zhang, F.
Zhang, S. Guo and J. Zhang, New J. Chem., 2018, DOI: 10.1039/C8NJ01533C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Volume 40 Number
1 January 2016 Pages 1–846
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Please do not adjust margins
New Journal of Chemistry
Page 1 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
NJC
ARTICLE
Three-dimensional Composite of Co3O4 Nanoparticles and
Nitrogen Doped Reduced Graphene Oxide for Lignin Model
Compounds Oxidation
Received 00th January 20xx,
Accepted 00th January 20xx
Jiali Zhang,§ Fangwei Zhang,§a Shouwu Guo*a and Jingyan Zhang*b
a
DOI: 10.1039/x0xx00000x
www.rsc.org/
Three dimensional composite of Co3O4 nanoparticles and nitrogen doped reduced graphene oxide (3D Co3O4/N-rGO) with
unique 3D porous structure is prepared and its catalytic activity in lignin model compounds oxidation is explored. The 3D
Co3O4/N-rGO composite exhibits better catalytic performance than Co3O4 nanoparticles or 3D N-rGO in the oxidation of
lignin model compounds. The higher catalytic activity of the 3D Co3O4/N-rGO composite attributes to the combination of
their porous structural feature, large surface area that provided by 3D N-rGO matrix, and active Co3O4 nanoparticles doped
on the N-rGO surface. The structural feature of the 3D Co3O4/N-rGO is beneficial to the reactant and product diffusion and
transportation, and also is helpful in preventing aggregation of Co3O4 nanoparticles. In addition, the introduction of N
atoms in GO also is favorable to the formation of active oxygen species for the oxidation of model compounds. Given the
high activity and the easy recovery from the reaction system, the 3D Co3O4/N-rGO composite should be applicable non-
noble metal catalytic system for lignin model compounds.
catalytic systems, cobalt-based catalysts have been relatively
popular.24 However, oxidation reactions with cobalt-based catalysts
usually require the use of organic solvents, high oxygen pressure,
Introduction
The decomposition of lignin can produce value-added chemicals
2
high temperature or long reaction time.
and fuel,1, but, owing to the complicacy, the decomposing
Recently, three dimensional (3D) graphene-based materials,
including graphene foams and aerogels, are found to be robust
matrices for accommodating metals, metal oxides, and metal
complexes for various applications.25-35 We have demonstrated that
nitroarene compound can be reduced efficiently using graphene
quantum dots (GQDs) anchored on 3D reduced graphene oxide (3D
rGO) as catalyst.36 The porous motif of 3D rGO offers a large surface
area and mass transfer pathways for reactant and product, thus 3D
GQDs/rGO exhibits better performance in substrate adsorption as
well as product diffusion. However, the activity of 3D GQDs/rGO
composite is relatively low, originated from the limited
surface/edge defects of GQDs which are hard to control through
the synthesis. Recently, it was found that the nitrogen-doped
graphene exhibits excellent catalytic performance possibly due to
the incorporation of N heteroatoms into the backbone lattice of
processes and also the underneath chemical mechanisms are
4
studied usually using lignin model compounds.3, Lignin model
compounds, such as veratryl alcohol (VA) can be selectively oxidized
to veratraldehyde in the presence of catalysts, including enzymes,5,
6 metal complexes,7-11 and many others. However, the poor stability
and recyclability of these homogeneous catalysts limit deadly their
practical applications. Accordingly, owing to their inherent
advantages in recovery, recycling and amenability for continuous
processing as compared to the homogeneous counterparts,
heterogenous catalysts for lignin decomposition become more
attractive. Heterogeneous catalysts for lignin transformation were
designed using metals or metal oxide as active components, metal
oxide, metal organic framework (MOF), or mineral as matrices. For
instances, Ru/Al2O3,12 Ru/PG,13 Pd/PG,13 Pd/SiO2,14 Au/Al2O3,15
20
Au/CeO2,16 Co3O4,17, 18 MnOX,19, RGO-MnCoO,21 Co-ZIF-9,22 and
graphene nanosheets as pyridinic, pyrrolic, and quaternary N
Ru@ZIF-8+CuO23 systems have been developed. Among these
38
complexes.37,
More detailed researches showed that the
introduction of nitrogen species could enhance the electron donor
property of the carbon matrix, resulting in an improvement of the
interaction between carbon and substrate molecules.30, 39 In this
work, the composite of Co3O4 nanoparticles and porous 3D N-rGO
was prepared, and its catalytic property in the decomposition of
lignin model compounds was explored.
a.Department of Electronic Engineering, School of Electronic Information and
Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R.
China. E-mail: swguo@sjtu.edu.cn
b.State Key Laboratory of Bioreactor Engineering, Shanghai Key Laboratory of New
Drug Design, School of Pharmacy, East China University of Science and
Technology, Shanghai 200237, P. R. China. E-mail: jyzhang@ecust.edu.cn
§
Authors contributed equally.
† Electronic Supplementary Information (ESI) available. See DOI:
10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 2 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
ARTICLE
Journal Name
Technologies, USA) with 60% acetic acid buffer (A) and 40%
methanol (B) as mobile phase at a column temperature of 30 oC
with flow rate of 1 ml/min. The products and substrates were
Experimental
Materials
Cobalt (II) acetate tetrahydrate (Co(CH3COO)2·4H2O, AR),
detected using the UV detector at λmax= 235 nm. Product
benzyl alcohol and ethanol absolute (AR) were purchased from
Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Veratryl
alcohol (VA, 98%), 4-methoxyl benzyl alcohol (99%) and 3,4,5-
trimethoxyl benzyl alcohol (98%) were bought from Saen Chemical
Technology, Co., Ltd, Shanghai, China. Vanillyl alcohol (99%) was
bought from Molbase Biotechnology Co, Ltd, Shanghai, China. 4-
Methyl benzyl alcohol (98%) was obtained from Aladdin Industrial
Co., Ltd, Shanghai, China. Ammonium Hydroxide (NH3·OH, 25-28%,
AR) was obtained from Shanghai Lingfeng Chemical Reagent Co.,
Ltd., Shanghai, China. All chemicals were used as received without
further purification. Graphene oxide (GO) was prepared following
the procedures described in our previous work.40
identification was achieved by comparison of retention times to
those of standard solutions of pure compounds. Conversions of
lignin model compounds and yields of product were determined by
HPLC using external standard method.
The catalyst turnover frequency (TOF), the milligrams of VA
consumed 1 mg of catalyst (active metal/metal oxide loading) per
hour was calculated under the same reaction condition.
Reusability of Catalyst
After catalytic reaction, the 3D Co3O4/N-rGO composite was
separated from the reaction system centrifugation (8000 rpm, 10
min). Then, it was washed three times with ethanol, dried at 60oC
for 12h in a vacuum oven to reuse.
Synthesis of 3D N-rGO
Instrumental
Typically, 15 ml of aqueous dispersion of GO (2 mg/ml) was
added to an autoclave (40 ml size), ammonia solution (1 ml) was
added and stirred for 5 min. The autoclave was then transferred to
an oven at 180 oC for 6 h. The product with cylinder-like bulk
morphology was collected and was immersed into deionized water
to remove the residual NH3·H2O (as shown in Scheme 1). The
cylinder-like 3D N-rGO bulk product was ground into powder for
analysis.
Atomic Force Microscopic (AFM) image of graphene oxide was
taken on a MultiMode Nanoscope V scanning probe microscopy
(SPM) system (Veeco, USA), and AN-NSC 10AFM cantilever tips
(SHNIT Co., Russia) with a force constant of ~ 37 N/m and
resonance vibration frequency of ~ 330 kHz were used. Sample for
AFM was prepared by dropping aqueous suspension (~ 0.02 mg/mL)
of GO on freshly cleaved mica surface and dried in air, respectively.
The SEM and TEM images were acquired using Ultra 55 field
emission scanning electron microscope (Zeiss, Germany) with the
working voltage of 10.0 kV, and JEOL JEM-2100F transmission
electron microscope (JEOL, Japan) with the operation voltage of 200
kV, and the high-resolution TEM (HRTEM) image was measured on
the same instrument. The TEM specimen was prepared by placing
the ethanol suspensions on the lacey support films and drying
under ambient condition. The FT-IR spectra were acquired on a
EQUINOX 55 FT-IR spectrometer (Bruker, Germany). The specimens
for FT-IR measurement were prepared by grinding the dried powder
of GO or 3D Co3O4/N-rGO with KBr together, and then compressing
them into thin pellets. X-ray diffraction (XRD) patterns were
recorded on a Bruker D8 Advance PC diffractometer (Bruker,
Germany) using Cu/Kα radiation (λ = 1.55406 Å), with the 2θ range
of 10 to 80° and the scan rate of 0.2° s-1. The surface area was
determined using the Brunauer-Emmett-Teller (BET) method by
ASAP 2020 M (Micromeritics, USA). X-ray photoelectron spectra
(XPS) was recorded on Krotos AXIS-Ultra DLD (SHIMADZU, Japan).
The mass ratio of Co3O4 in the hybrid was determined iCAP 7600
ICP-OES (Thermo Fisher Scientific, USA). 10 mg specimen for ICP-
OES measurement was dissolved in 6 ml mixture of HNO3 and HClO4
with volume ratio of 3:1, then the mixture was heated at 120-150
oC to remove C and N in composite. After cooling, the solid was
dissolved in 1 ml mixture of HCl and HNO3 with volume ratio of 3:1,
then the mixture solution was diluted by H2O to the constant
volume of 100 ml. The reaction by-products of lignin model
compounds oxidation were analyzed by ACQUITY UPLC & Q-TOF MS
Premier (Waters) with water (A) and acetonitrile (B) as mobile
phase under gradient elution conditions.
For comparison, 3D rGO was prepared by hydrothermal
reaction of the GO under similar condition without using NH3·H2O.
Synthesis of 3D Co3O4/N-rGO Composite
Sixty mg of Co(CH3COO)2·4H2O was added into 1.24 ml of H2O,
6.26 ml of ethanol and stirred for 5 min, followed by the addition of
0.5 ml of NH3·H2O and stirred for 5 min. Subsequently, the mixture
was transferred to a 40 ml size autoclave. The as-prepared cylinder
3D N-rGO (30 mg) was immersed into the above solution at RT for 2
h. The autoclave was solvothermally treated at 150 oC for 3 h. After
cooling down to room temperature, the product was obtained by
centrifugation and washed 3 times with deionized water, dried for
24 h by lyophilization. The product is named as 3D Co3O4/N-rGO.
Except for SEM measurement, the cylinder 3D Co3O4/N-rGO
composite was ground into powder for testing and analyses.
Control sample Co3O4 NPs were also prepared through the
same method as 3D Co3O4/N-rGO without adding 3D N-rGO.
Catalytic Oxidation of Lignin Model Compounds using 3D Co3O4/N-
rGO
Oxidation of the lignin model compounds was studied using VA
as an example, other lignin model compounds were oxidized under
the same conditions. Generally, the oxidation reaction of VA was
carried out in a 10 ml quartz reactor containing 2 mg of 3D
Co3O4/N-rGO composite and 100 μl of VA (0.1 M) in 2.5 ml of H2O,
then filled with 0.5 MPa O2 and closed with septum. The reaction
solution was stirred at 140 oC for 4 h. After cooling to room
temperature, the catalyst was separated by centrifugation. The
supernatant was directly analyzed by 1220 HPLC (Agilent
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 3 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
Journal Name
ARTICLE
Scheme l. Illustration of the preparation process of the 3D
Co3O4/N-rGO composite.
Results and discussion
Preparation and Characterization of 3D Co3O4/N-rGO Composite
3D Co3O4/N-rGO composite is synthesized through a three-
step procedure as schematically shown in Scheme 1. Single-layer
GO sheets (AFM image in Figure S1) are first reduced and self-
assembled to 3D N-rGO through a hydrothermal treatment in the
Figure 2. (a) The survey XPS spectra of the 3D Co3O4/N-rGO. (b-d) C
o
presence of NH3·H2O at 180 C. Subsequent hydrothermal reaction
1s, N 1s, and Co 2p XPS spectra of the composite.
at 150 oC in the presence of cobalt salt leads to the growth and
crystallization of Co3O4 nanoparticles on the surface of 3D N-rGO,
forming 3D Co3O4/N-rGO composite. As shown in Figure 1a and b,
the as-prepared composite consists of the 3D interconnected
porous N-rGO nanosheets and Co3O4 nanoparticles. The size of
Co3O4 nanoparticles is in the range of 5-10 nm (Figure 1c). The
HRTEM image showed that the lattice constant of the Co3O4
nanoparticles was ca. 0.234 nm, closing to (311) facet of Co3O4,
confirming the good crystallinity of Co3O4 in the composite.41 The
formation of Co3O4 nanoparticles was further verified by X-ray
powder diffraction data. As depicted in Figure S2a, the diffraction
peaks at 2θ of 19.1, 31.5, 37.0, 45.0, 59.4 and 65.3◦ in are
contributed to (111), (220), (311), (400), (511) and (440) diffractions
of Co3O4 with spinel crystalline phase (JCPDS Card No.42-1467).39, 41
The FT-IR spectrum of the as-prepared composite shows that the
vibration bands of -OH, -C=O, -C-O groups from the starting GO
decreased dramatically, suggesting that GO was reduced to rGO
(Figure S2b).40 Meanwhile, the new absorption bands at around
1390 cm-1 and 1574 cm-1 are attributed to C-N stretching and C=N
stretching, respectively.42 Moreover, the distinct absorption bands
at 661 cm-1 and 571 cm-1 are ascribed to the symmetric and
asymmetric stretching vibrations of Co-O group comparing with
bare Co3O4 nanoparticles, which suggests the existence of cobalt
oxide in the composite.43 The chemical composition of the 3D
Co3O4/N-rGO composite is determined further by X-ray
photoelectron spectroscopy (XPS) as shown in Figure 2a. The peaks
at 284.7 eV, 285.8 eV, 286.4eV, 287.1 eV, 287.6 eV and 289.5 eV
can be assigned, respectively, to C 1s XPS of C=C/C-C, C=N, C-O, C-N,
C=O, O=C-O groups (Figure 2b).39 The N1s XPS spectrum, Figure 2c,
reveals the presence of pyridinic N, pyrrolic N, graphitic N and
pyridinic N-oxide within the N-rGO structure.44 For Co 2p XPS
spectrum (Figure 2d), two major peaks with binding energies at
779.7 and 794.9 eV are fitted, respectively, to 2p3/2 and 2p1/2 of Co
bonded with O, indicating the presence of Co3O4 in the composite.18,
41 The Co content, ∼10 wt% (∼15 wt% of Co3O4), in the composite is
quantitatively determined further by inductively coupled plasma
optical emission spectrometry (ICP-OES) analysis. The nitrogen
adsorption-desorption isotherms of the composite clearly indicate
that it assumes porous structure (Figure S3). Consequently, these
results undoubtedly confirm the formation of 3D porous Co3O4/N-
rGO composite.
Catalytic Activity of 3D Co3O4/N-rGO Composite for Oxidation of
Lignin Model Compound VA
The catalytic performance of the 3D Co3O4/N-rGO composite in
oxidation of lignin model compounds, using VA as an example, with
O2 as oxidant agent is evaluated in aqueous solution, and the results
are summarized in Table 1. The conversion of VA is generally
increased with the increase of the amount of catalyst, and can
reach 91.2% when the catalyst loading is 27.0%. Higher catalyst
Figure 1. SEM (a, b), TEM (c) and HRTEM (d) images of 3D
Co3O4/N-rGO.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 4 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
ARTICLE
Journal Name
Table 1. Effect of the 3D Co3O4/N-rGO composite loading on VA
oxidation reaction.
Entry
Catalyst (Co3O4
content/mg %)
Selectivity (%)
Conv. (%) 1a
1b
1c
—
1
2
3
4
5
none
1
>99
0.5 mg (4.5%)
1.0 mg (9.0%)
2.0 mg (18.0%)
3.0 mg (27.0%)
63.2
66.8
90.0
91.2
94.1
89.8
81.4
80.4
4.6
6.0
8.7
10.2
Figure 3. The effects of reaction time (a), temperature (b), and
oxygen pressure (c) on the conversion and product distribution of
VA oxidation using 3D Co3O4/N-rGO as catalyst. Reaction condition:
VA (0.01 mM), catalyst (2 mg, Co3O4 loading 18%), H2O (2.5 ml),
oxygen (0.5-3.0 MPa), temperature (100-140 oC), time (1-5 h).
Conversions and selectivity were determined by HPLC.
Reaction condition: VA (0.01 mM), H2O (2.5 ml), oxygen (0.5 MPa),
temperature (140 oC), time (4 h). Conversion and selectivity were
determined by HPLC.
loading facilitates the oxidation of veratraldehyde further to
veratric acid, though major product is veratraldehyde. The
oxidation of VA is probably accomplished in two steps, namely, VA
was converted to veratraldehyde first, then the veratraldehyde is
continuously oxidized to veratric acid as proposed in literature.17
The effects of the reaction time and temperature on the VA
oxidation with 3D Co3O4/N-rGO as catalyst, mainly conversion and
selectivity, were also examined. As shown in Figure 3a, the
conversion of VA increased from 38.2 to 93.5% with an increase of
reaction time from 1 to 5 h, while the selectivity to veratraldehyde
slightly decreased from 81.4 to 78.8%, and the yield of veratric acid
increased from 5.5 to 11.6%. The effect of temperature on the
conversion of VA and selectivity to veratraldehyde at the range of
100-150 oC was more obvious to the reaction time, Figure 3b. The
conversion of VA increased from 29.7 to 97.4%, while the selectivity
to veratraldehyde dropped from 86.5% to 78.1% when the reaction
temperature was raised from 100 to 150 oC. This is expected, since
at a higher temperature the reaction was accelerated, and more
veratraldehyde was further oxidized to veratric acid.
Table 2. Comparison of the oxidation of VA with different catalysts.
Entry
Catalyst
metal/metal oxide
Conv. (%)h
Selectivityh (%)
TOFi (h-1)
Ref.
content (wt%)
1b
1c
1a
1
2
Co3O4 NPsa
3D rGOa
120.0
—
29.7
91.9
2.4
0.062
—
this work
this work
this work
this work
this work
this work
15, 16
17
46.2
61.2
43.7
56.8
90.0
85.0
90.0
47.0
74.0
93.0
73.0
93.5
90.0
90.6
91.7
81.4
96.0
98.0
98.0
84.0
72.0
83.0
1.3
1.1
4.1
4.0
8.7
4.0
—
3
3D N-rGOa
—
—
4
N-rGOa
—
—
5
Co3O4 NPs+3D N-rGOa
3D Co3O4/N-rGOa
59.2
18.0
40.0
20.0
7.4
0.24
1.26
0.30
2.20
1.60
2.04
3.72
17.8
6
b
7
Nano spinel Co3O4
c
8
MnOx
9
Co-ZIF-9d
20
—
10
11
12
RGO-MnCoOe
18.3
5.0
6.0
—
19
f
Ru/Al2O3
10
g
Au/CeO2
0.6
14
—
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 5 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
Journal Name
ARTICLE
a Reaction condition: VA (0.01 mM), catalyst (2 mg), H2O (2.5 ml), oxygen (0.5 MPa), temperature (140 oC), time (4 h). Conversion and selectivity were determined by
HPLC. b Reaction condition: substrate (0.5 g), water (70 ml), catalyst loading (0.2 g), temperature (140 oC), oxygen (4 MPa), time (7 h). c Reaction condition: VA (0.5 g),
catalyst (0.1 g), temperature (120 oC), acetonitrile (60 ml), air (2.1 MPa), time (1.5 h). d Reaction condition: toluene (5.0 g), Co-ZIF-9 (0.05 g), NaOH (0.04 g), VA (0.68 g),
oxygen(0.5 MPa), temperature (150 oC). e Reaction condition: aromatic alcohol (3.24 mmol), RGO-MnCoO catalyst (0.1 g), temperature (140 °C), acetonitrile (70 ml), air
f
g
(2.1 MPa), time (2 h). Reaction condition: VA (100 mg), catalyst (100 mg, 5 wt % metal), water (10 ml), temperature (160 °C), air (0.5 MPa), time (5 h). Reaction
condition: Substrate (4.85 mmol), Au/CeO2 (0.5 mol%), temperature (80 °C), oxygen (0.1 MPa) (flow rate: 25 ml min-1), time (7h).h Some conversion and selectivity
were estimated or calculated from data provided in the original articles. i TOF were estimated or calculated from data provided in the original articles.
In order to find optimal oxygen pressure, the VA oxidation was of the 3D N-rGO is apparently more favorable to mass transfer of
carried out with the identical amount of catalyst, but different the substrate and products.45
conversion of VA slightly increased from 90.0 to 94.7% with an
The better catalytic performance of the 3D Co3O4/N-rGO
increase of partial pressure of oxygen from 0.5 to 3.0 MPa, while composite over Co3O4 nanoparticles might be assigned to the 3D
selectivity to veratraldehyde almost unchanged. The reaction rate porous structure of N-rGO matrix. This assumption is confirmed by
remains the same with the increase of oxygen pressure. The minor their nitrogen adsorption-desorption isotherm (Figure S3). The N2
oxygen pressures of 0.5-3.0 MPa at 140 oC. As shown in Figure 3c, physisorption measurements show that Co3O4 nanoparticles and 3D
the influence of oxygen pressure to the reaction rate and selectivity Co3O4/N-rGO both exhibit the hysteresis phenomenon that belong
suggests that oxygen pressure of 0.5 MPa seems high enough for to the type IV isotherms with H2 loops and H3 loops, respectively,
VA oxidation. Therefore, the conditions for VA oxidation used in the suggesting that 3D Co3O4/N-rGO has mesoporous structural feature.
following experiments are as following: catalyst loading is 18%, However, BET specific surface area of the 3D Co3O4/N-rGO is up to
o
reaction time is 4 h, temperature is 140 C, and oxygen pressure is ~197 m2/g with a pore size of 2.5 nm and 4 nm, while it is only ~74
0.5 MPa.
m2/g for the bare Co3O4 nanoparticles (Table 3). The porous
In order to understand further the catalytic property of the 3D structure and the large surface area of the 3D Co3O4/N-rGO
Co3O4/N-rGO composite, VA oxidations were also performed with composite are apparently more favorable to substrate adsorption
Co3O4, 3D rGO, 3D N-rGO, N-rGO and the physical mixture of Co3O4 and product diffusion in VA oxidation. Besides, the catalytic activity
and 3D N-rGO (named as Co3O4 + 3D N-rGO) as catalysts, and the of 3D Co3O4/N-rGO composite is remarkably higher than physical
results are summarized in Table 2. Overall, the 3D Co3O4/N-rGO mixture of Co3O4 and 3D N-rGO (Co3O4 NPs+3D N-rGO), implying
composite exhibits higher activity than the others under the same that the catalytic activity of the composite should be from the
condition. 3D N-rGO alone can catalyze the oxidation of VA with a combination of the unique 3D structure of N-rGO and the Co3O4
relatively low activity, but more active than 3D rGO. The catalytic nanoparticles anchored on it. Taken together, 3D N-rGO might not
activity of 3D N-rGO may be partially contributed by the nitrogen only plays a metal-free catalyst, but also the excellent support for
species as pyridinic, pyrrolic, and graphitic N complexes into Co3O4 nanoparticles in the catalytic reaction.
skeleton lattice of rGO (Figure 2c).30, 39 Nitrogen-doped chemically
The better catalytic performance of the 3D Co3O4/N-rGO is also
reduced GO (N-rGO) show lower activity than 3D N-rGO (table 2, reflected by their higher turnover frequency (TOF) comparing to
entry 4), indicating that 3D porous morphology of 3D N-rGO might bare Co3O4 nanoparticles under the same reaction condition (Table
also contribute to their activity. The assumption is supported by the 2). However, TOF of the 3D Co3O4/N-rGO composite is still lower
large specific surface area of 3D N-rGO (~255 m2/g) vs N-rGO (~220 than those noble metal catalysts, such as Au/CeO2, a very efficient
16, 19-22
m2/g) determined by nitrogen adsorption/desorption isotherm catalyst for VA oxidation in the absence of solvent.12,
curves vs (Table 3). The porous structure and the large surface area However, most of the oxidation reactions with those catalysts
(listed in Table 2) were accomplished in organic solvents, except for
Ru/Al2O3 (TOF, 3.72),12 and Au/CeO2 (TOF, 17.8).16
Table 3. Textual parameters of different catalysts.
Catalytic Activities of 3D Co3O4/N-rGO in the Oxidations of Other
Lignin Model Compounds
Catalysts
SBET
SExt
VTotal
Vmicro
Vmeso
(m2/g)
(m2/g)
(cm3/g)a
(cm3/g)b
(cm3/g)c
To evaluate further the catalytic performance of 3D Co3O4/N-
rGO in the oxidations of other lignin model compounds, benzyl
alcohol and its derivatives were investigated under the same
reaction condition, and the results are summarized in Table 4. In
general, 3D Co3O4/N-rGO can catalyze the oxidization of all these
lignin model compounds, but shows different conversion rates.
Comparably, the benzyl alcohols with more substitution groups can
be oxidized quickly. The reason might be that certain electron-
donating group enhances the oxidation process. For instances, the
conversion rate of vanillyl alcohol is much higher than that of VA,
and selectivity is much lower (entry 1 vs 6), and 4-methoxybenzyl
alcohol can be oxidized a little easier than 4-methylbenzyl alcohol
Co3O4 NPs
3D N-rGO
N-rGO
74.09
70.06
0.15
0.32
0.30
0.22
0
0.15
255.32
220.57
196.89
233.54
177.91
144.44
0.01
0.02
0.03
0.31
0.28
0.19
3D Co3O4/
N-rGO
SBET: BET surface area, SExt: External surface area, VTotal: Total pore volume,
Vmeso: Mesopore volume, Vmicro: Micropore volume.
a Total pore volume at P/P0= 0.95.
b t-plot.
c Vmeso=VTotal-Vmicro
.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 6 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
ARTICLE
Journal Name
provides with diffusion and transportation space for reactant
substrate and products. It was demonstrated that the 3D
Co3O4/N-rGO composite has better catalytic performance than
the individual Co3O4 nanoparticle or 3D N-rGO in the oxidation
of lignin model compounds. The catalytic activity of the
composite should be attributed to the unique 3D morphology
of N-rGO, the as-doped N heteroatom, and the inherent
catalytic activity of Co3O4 nanoparticles. Given the higher
catalytic activity of the 3D Co3O4/N-rGO, coupled with ease
recovery and good stability, the 3D Co3O4/N-rGO composite
should be potentially useful catalyst for the oxidation of lignin.
Table 4. Catalytic activity of 3D Co3O4/N-rGO in oxidation of
lignin model compounds.
Entry
R
Conv. (%)
Selectivity (%)
1a
1b
1c
1
2
3
4
5
6
3,4-dimethoxyl
4-methoxyl
3,4,5-trimethoxyl
4-methyl
90.0
81.4
8.7
55.0
66.9
82.3
75.6
77.6
82.4
20.7
17.7
18.2
21.7
15.8
4.2
46.5
Conflicts of interest
H
33.0
There are no conflicts to declare.
4-hydroxyl-3-
methoxyl
> 99.0
Reaction condition: aromatic alcohol (0.01 mM), catalyst (2 mg, Co3O4
loading 18%), H2O (2.5 ml), oxygen (0.5 MPa), temperature (140 oC), time (4
h). Conversions and selectivity were determined by HPLC.
Acknowledgements
The work was financially supported by China Postdoctoral
Science Foundation (Nos.2017M611567), the National “973
Program” of China (Nos. 2014CB260411 and 2015CB931801).
(entry 2 vs 4). The residual selectivity for the oxidation of VA is
ascribed to the formation of veratrole as a by-product,12 which was
confirmed by ultra-performance liquid chromatography quadrupole
time-off-light mass spectrometer (UPLC-Q-TOF-MS) (Figure S4). The
by-product of the oxidation of 3,4,5-trimethoxyl benzyl alcohol is
1,2,3-trimethoxybenzene. We believe the high conversion of vanillyl
alcohol, but lower selectivity was also due to the formation of by-
products, like as 2-methoxy-1,4-benzoquinone and 2-methoxy-
phenol (Figure S5). Nevertheless, these results indicate that 3D
Co3O4/N-rGO can catalyze lignin model compounds, and can be
used in the oxidation of these compounds. The success of the
oxidation of lignin model compounds also motivate us examine
other substrate. The preliminary result shows that 3D Co3O4/N-rGO
composite can catalyze the epoxidation of styrene. However, the
optimization of catalytic performance of composite need to be
explored further.
References
1. X. Zhang, Q. Zhang, T. Wang, L. Ma, Y. Yu and L. Chen,
Bioresource Technol., 2013, 134, 73-80.
2. Y. Liu, L. Chen, T. Wang, Q. Zhang, C. Wang, J. Yan and L. Ma,
ACS Sustain. Chem. Eng., 2015, 3, 1745-1755.
3. H. Lange, S. Decina and C. Crestini, Eur. Polym. J., 2013, 49,
1151-1173.
4. C. Li, X. Zhao, A. Wang, G. W. Huber and T. Zhang, Chem. Rev.,
2015, 115, 11559-11624.
5. M. A. Eisenstadt and K. G. Bogolitsyn, Russ. J. Bioorg. Chem.,
2010, 36, 802-815.
6. T. M. Larson, A. M. Anderson and J. O. Rich, Biotechnol. Lett.,
2013, 35, 225-231.
7. F. Cui and D. Dolphin, Can. J. Chem., 1992, 70, 2314-2318.
8. A. Haikarainen, J. Sipila¨, P. Pietika¨inen and I. M. Mutikainen,
Bioorgan. Med. Chem., 2001, 9, 1633-1638.
9. K. Kervinen, P. Lahtinen, T. Repo, M. Svahn and M. Leskelä,
Catal. Today, 2002, 75, 183-188.
10. K. Kervinen, H. Korpi, M. Leskelä and T. Repo, J. Mol. Catal. A-
Chem., 2003, 203, 9-19.
11. V. O. Sippola and A. O. I. Krause, J. Mol. Catal. A-Chem., 2003,
194, 89-97.
12. M. Melián-Rodríguez, S. Saravanamurugan, S. Kegnæs and A.
Riisager, Top. Catal., 2015, 58, 1036-1042.
13. Z. Yang, X. Zhao, T. Li, W. Chen, Q. Kang, X. Xu, X. Liang, Y.
Feng, H. Duan and Z. Lei, Catal. Commun., 2015, 65, 34-40.
14. A. Kim, H. S. Bae, J. C. Park, H. Song and K. H. Park, New J.
Chem., 2015, 39, 8153-8157.
We also examined the reusability of the composite, one of the
key properties that determine the practical applicability of a
catalyst. Figure 3d showed that the conversion of VA decreased by
18% after
nanoparticles was observed (Figure S6a). However, the specific
surface area of 3D Co3O4/N-rGO (~98 m2/g) used
times
5 cycles, and no obvious aggregation of Co3O4
5
determined by nitrogen adsorption/desorption isotherm curves is
lower than that of as-prepared catalyst (~197 m2/g) (Figure S6b),
which may lead to the decrease of catalyst activity. Moreover, the
metal leaching test showed that cobalt content in the residual
reaction solution is about 18.8 ppm, suggesting that the decent
reusability of the composite as catalyst.
15. P. D. Giorgi, N. Elizarov and S. Antoniotti, ChemCatChem, 2017,
9, 1830-1836.
16. A. Abad, P. Concepción, A. Corma and H. García, Angew.
Chem., 2005, 117, 4134-4137.
17. V. R. Mate, M. Shirai and C. V. Rode, Catal. Comm., 2013, 33,
66-69.
Conclusions
To pursue an applicable catalyst for lignin decomposition,
3D Co3O4/N-rGO composite was designed and prepared
through a simple hydrothermal method. The as-prepared 3D
Co3O4/N-rGO composite assumes a 3D porous structure that
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 7 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
Journal Name
ARTICLE
18. V. R. Mate, A. Jha, U. D. Joshi, K. R. Patil, M. Shirai and C. V.
Rode, Applied Catalysis A: General, 2014, 487, 130-138.
19. A. Jha, T. Chandole, R. Pandya, H.-S. Roh and C. V. Rode, RSC
Adv., 2014, 4, 19450-19455.
20. A. Kamimura, H. Komatsu, T. Moriyama and Y. Nozaki,
Tetrahedron, 2013, 69, 5968-5972.
21. A. Jha, D. Mhamane, A. Suryawanshi, S. M. Joshi, P. Shaikh, N.
Biradar, S. Ogale and C. V. Rode, Catal. Sci. Technol., 2014, 4,
1771-1778.
22. J. Zakzeski, A. Dębczak, P. C. A. Bruijnincx and B. M.
Weckhuysen, Appl. Catal. A-Gen., 2011, 394, 79-85.
23. H. Fan, Y. Yang, J. Song, G. Ding, C. Wu, G. Yang and B. Han,
Green Chem., 2014, 16, 600-604.
24. R. Behling, S. Valange and G. Chatel, Green Chem., 2016, 18,
1839-1854.
25. M. Li, J. Hu and H. Lu, Catal. Sci. Technol., 2016, 6, 7186-7192.
26. Z. Wang, Y. Pu, D. Wang, J. Shi, J. Wang and J.-F. Chen, AICHE
J., 2017, 0, 1-9.
27. M. Dabiri, M. Kasmaei, P. Salari and S. K. Movahed, RSC Adv.,
2016, 6, 57019-57023.
28. Z. Ma, Y. Qiu, Y. Huang, F. Gao and P. Hu, RSC Adv., 2015, 5,
79456-79462.
29. Z. Zhang, T. Sun, C. Chen, F. Xiao, Z. Gong and S. Wang, ACS
Appl. Mater. Interfaces, 2014, 6, 21035-21040.
30. M. Mahyari, M. S. Laeini and A. Shaabani, Chem. Commun.,
2014, 50, 7855-7857.
31. S. Zhang, X. Shen, Z. Zheng, Y. Ma and Y. Qu, J. Mater. Chem. A,
2015, 3, 10504-10511.
32. P. Kumar Sahoo, B. Panigrahy, D. Thakur and D. Bahadur, New
J. Chem., 2017, 41, 7861-7869.
33. J. Liu, X. Yan, L. Wang, L. Kong and P. Jian, J. Colloid Interface
Sci., 2017, 497, 102-107.
34. X. Liu, X. Zhao, Y. Cao, T. Li, S. Qiu and Q. Shi, New J. Chem.,
2017, 41, 865-872.
35. W. Zhong, X. Tian, C. Yang, Z. Zhou, X. Liu and Y. Li, Int. J.
Hydrogen Energ., 2016, 41, 15225-15235.
36. J. Zhang, F. Zhang, Y. Yang, S. Guo and J. Zhang, ACS Omega,
2017, 2, 7293-7298.
37. J. Long, X. Xie, J. Xu, Q. Gu, L. Chen and X. Wang, ACS Catal.,
2012, 2, 622-631.
38. Y. Gao, G. Hu, J. Zhong, Z. Shi, Y. Zhu, D. S. Su, J. Wang, X. Bao
and D. Ma, Angew. Chem. Int. Ed. Engl., 2013, 52, 2109-2113.
39. R. Nie, J. Shi, W. Du, W. Ning, Z. Hou and F.-S. Xiao, J. Mater.
Chem. A, 2013, 1, 9037-9045.
40. J. Zhang, H. Yang, G. Shen, P. Cheng, J. Zhang and S. Guo,
Chem. Commun. , 2010, 46, 1112-1114.
41. C. Wang, P. Shi, X. Cai, Q. Xu, X. Zhou, X. Zhou, D. Yang, J. Fan,
Y. Min, H. Ge and W. Yao, J. Phys. Chem. C, 2015, 120, 336-344.
42. S. Suresh Balaji, M. Karnan and M. Sathish, Int. J. Hydrogen
Energ., 2018, 43, 4044-4057.
43. R. K. Das and A. K. Golder, Electrochim. Acta, 2017, 251, 415-
426.
44. F. Yang, C. Chi, C. Wang, Y. Wang and Y. Li, Green Chem., 2016,
18, 4254-4262.
45. X. Fan, G. Zhang and F. Zhang, Chem. Soc. Rev., 2015, 44, 3023-
3035.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

New Journal of Chemistry
Page 8 of 8
View Article Online
DOI: 10.1039/C8NJ01533C
Three-dimensional Composite of Co3O4 Nanoparticles and Nitrogen Doped
Reduced Graphene Oxide for Lignin Model Compounds Oxidation
Table of contents
3D composite of Co3O4 nanoparticles and N-doped reduced graphene oxide can
catalyze effectively oxidation of lignin model compounds.