Chitin-Derived Mesoporous, Nitrogen-Containing Carbon for Heavy-Metal Removal and Styrene Epoxidation

Article abstract of DOI:10.1002/cplu.201500293

The production of a series of mesoporous, nitrogen-containing (N-containing) carbon materials directly from pure chitin by means of carbonization at different temperatures under template-free conditions is reported. Thermogravimetric analysis combined with infrared spectroscopy was applied to follow the temperature-dependent chemical events during the carbonization process, thereby shedding light on the automated pore formation mechanism. The physicochemical properties of the N-containing carbon materials have been extensively investigated, which provided guidance and rational understanding of the application of these materials. It was found that the N-containing carbon materials obtained at lower temperatures (400-600°C) were enriched with amine, amide, and pyrrolic functionalities, which enables their very high efficiency as adsorbents to remove toxic heavy metals, such as Cr^VI, Hg^II, and Pd^II, from water. In contrast, N-containing carbon materials prepared at higher temperatures (800-1000°C) were enriched with graphitic N, which exhibited excellent catalytic activity in the epoxidation of styrene. Coming out of their shells: Mesoporous nitrogen-containing carbon materials were prepared by carbonizing chitin at different temperatures. The carbon products prepared at 400-600°C exhibited good performance in the removal of heavy metals from water owing to nitrogen-containing groups such as amine, amide, and pyrrolic functionalities. The graphitic nitrogen atoms in the carbon products prepared at 800-1000°C endowed them with excellent catalytic activity for the epoxidation of styrene (see figure).

Full text of DOI:10.1002/cplu.201500293

DOI: 10.1002/cplu.201500293
Full Papers
Chitin-Derived Mesoporous, Nitrogen-Containing Carbon
for Heavy-Metal Removal and Styrene Epoxidation
[
a]
Yongjun Gao, Xi Chen, Jiaguang Zhang, and Ning Yan*
The production of a series of mesoporous, nitrogen-containing
N-containing) carbon materials directly from pure chitin by
of the application of these materials. It was found that the N-
containing carbon materials obtained at lower temperatures
(400–6008C) were enriched with amine, amide, and pyrrolic
functionalities, which enables their very high efficiency as ad-
(
means of carbonization at different temperatures under tem-
plate-free conditions is reported. Thermogravimetric analysis
combined with infrared spectroscopy was applied to follow
the temperature-dependent chemical events during the car-
bonization process, thereby shedding light on the automated
pore formation mechanism. The physicochemical properties of
the N-containing carbon materials have been extensively inves-
tigated, which provided guidance and rational understanding
VI
II
sorbents to remove toxic heavy metals, such as Cr , Hg , and
II
Pd , from water. In contrast, N-containing carbon materials pre-
pared at higher temperatures (800–10008C) were enriched
with graphitic N, which exhibited excellent catalytic activity in
the epoxidation of styrene.
Introduction
Mesoporous carbon materials, which possess a high surface
area, large pore volume, and special physicochemical proper-
ly corroded after the carbonization, which leads to increased
synthetic complexity and enhanced product cost. Finally, some
methods lack the tunability to modify the nitrogen content
and the types of N-containing groups on the surface, which
limits the scope of application.
[1]
[2]
ties, have been widely applied in the fields of adsorbents,
[
3]
[4]
[5]
fuel cells, gas separation and storage, and catalysis. To im-
prove the performance of mesoporous carbon materials, sur-
face functionality incorporation and heteroatom doping are
Chitin, the second most abundant biopolymer on earth, is
a N-containing biomass material existing in the exoskeletons
[
3]
often used. Generally, the introduction of nitrogen atoms to
the carbon matrix not only adjusts the surface polarity and
electron-donor ability, but also influences its neighboring
[
14]
of insects and crustaceans. Chitin has long been considered
as a starting material for the production of functional poly-
[6]
[15]
carbon atoms leading to improved properties. And the intro-
duction of nitrogen atoms into the carbon framework can en-
hance the adsorption capacity and catalytic performance. The
synthesis of N-containing carbon materials commonly includes
carbonizing N-containing precursors (such as N-containing
mers. Apart from that, it finds little application. Indeed, the
vast majority of the waste chitin material is either dumped
back into the sea or transported to special landfills without uti-
[
16]
lization. Considering the biologically fixed 7 wt% nitrogen
(see Table 1 for the chemical structure), chitin provides
a cheap and renewable resource to synthesize N-containing
chemicals and materials. Very recently, the transformation of
chitin into a series of chemicals has been conducted, but the
[
7]
[8]
[9]
ionic liquids, amino sugar, melamine, N-containing poly-
[10]
mer ), or treating pre-synthesized carbon materials with N-
[11]
[12]
containing compounds (such as ammonia or acetonitrile ).
Despite the considerable advances in the field, the current pro-
tocols for the manufacture of N-containing, porous carbon
have some limitations. First of all, the nitrogen source is often
based on non-renewable and/or toxic chemicals, which is not
[
17]
product yields were typically low.
Simple, effective, and
value-added transformation of chitin into chemicals and mate-
rials, in particular those containing nitrogen, is highly desira-
ble.
[13]
compatible with the principles of green chemistry. In addi-
tion, template agents are commonly needed to obtain meso-
porous structures. Some of the templates have to be chemical-
There are several previous studies pertinent to the transfor-
mation of chitin to N-containing carbon materials. Prawn
[
18]
[19]
shells and crawfish shell were carbonized at 7508C to gen-
erate N-doped porous carbon/CaCO3 composites, as well as
[
a] Dr. Y. Gao, X. Chen, Dr. J. Zhang, Prof. Dr. N. Yan
Department of Chemical and Biomolecular Engineering
National University of Singapore
purified porous carbon upon removal of CaCO by an acid. In
3
another study, chitin was heated to temperatures between 170
and 4508C, and the resulting biochar was used to absorb poly-
4
Engineering Drive 4, 117585 Singapore (Singapore)
[
20]
cyclic aromatic hydrocarbons. Chitin was also transformed
into N-containing carbon materials following a three-step pro-
cedure including sequential deacetylation, hydrolysis, and final-
E-mail: ning.yan@nus.edu.sg
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201500293.
[
8]
ly carbonization. In this latter study, the real precursor is the
partially deacetylated chitosan instead of chitin. 13–36 wt%
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À1
a large peak at 1773 cm was observed firstly, which
Table 1. Carbonization yields and elements analysis of various NC products.
suggests the generation of carbonyl-group-contain-
ing compounds. This peak, together with the CÀO
À1
stretching vibration peak at 1170 cm and the OÀH
À1 [21]
stretching vibration peak at around 3000 cm ,
suggested the formation of carboxylic acids. Slightly
À1
Products Mass yield [wt%] XPS results [wt%]
Elemental analyzer results [wt%]
afterwards, a small peak located at 2145 cm and
[a]
C
N
O
C
N
H
O
À1
a moderate peak located at 2352 cm were detect-
chitin
–
54.2 5.0 40.8 47.24
78.9 8.4 12.7 73.08
6.89
8.87
7.45
7.09
4.75
6.40
4.64
2.49
1.70
1.33
39.5
13.4
8.19
8.27
5.63
ed, which corresponded to CO and CO , respective-
2
NC-400
NC-600
NC-800
22.0
18.6
18.1
[21]
À1
ly. In addition, a peak at 1511 cm ascribed to the
86.7 5.0
88.0 5.1
90.2 3.1
8.3 81.87
6.9 82.94
6.7 88.29
N=O stretching vibration and the OÀH characteristic
À1
NC-1000 18.3
vibration of water at 3729 cm
were detected.
Therefore, the weight loss at the second stage was
attributed to the degradation of the polymeric sac-
charide, including the deacetylation of chitin, fol-
lowed by decomposition of the deacetylated pyra-
[
(
a] The oxygen content is calculated based on the formula: 100ÀC (wt%)ÀH
wt%)ÀN (wt%).
Si(OCH ) was used as a co-template and was removed with
nose rings, during which some nitrogen was lost in the form
of nitrogen oxide. In fact, some organic nitrogen-containing
compounds were also generated from chitin, such as acet-
amide and 3-hydroxypyridine (see below). However, these
compounds were not detected by FTIR spectroscopy, presuma-
bly owing to their low concentration. The third weight-loss
stage is from 450 to 8708C but the weight loss is insignificant,
3
4
NaOH after carbonization at 9008C. From these, it can be seen
that chitin is a promising starting material for N-containing
carbon materials, but several important issues remain to be ad-
dressed. Only one study starting with pure chitin for carboniza-
[
20]
tion was carried out. Moreover, there has been no systemat-
ic, thorough study on the structure–carbonization temperature
relationship at a practically useful temperature range (400–
1
0008C) for chitin-derived N-containing carbon materials. Sub-
sequently, the inadequate understanding of the structural fea-
tures of N-containing carbon materials obtained at different
temperatures hampers diversified, wide application of these
materials as a rational choice. With this in mind, we tested the
production of N-containing mesoporous carbon materials di-
rectly from chitin under template-free conditions at four differ-
ent carbonization temperatures. This resulted in N-containing
carbon materials with different surface areas, nitrogen content,
and surface functionalities. They exhibited excellent per-
VI
II
formance in the removal of heavy metals such as Cr , Pb , and
II
Hg from water, and in the epoxidation of styrene.
Results and Discussion
Preparation of N-containing carbon materials from chitin
Chitin extracted from different sources has different crystal
structures and different thermal stability. In our study, a-chitin
was employed throughout. The carbonization of chitin under
nitrogen was firstly followed by on-line thermogravimetry cou-
pled with Fourier transform infrared spectroscopy (TG-IR
Figure 1). In TG analysis (Figure 1a), there are three weight-loss
stages during the entire heating process. The first stage ranges
from the starting temperature to 1408C with a weight loss of
1
.1 wt%, which reflects the evaporation of the remaining
water. The second stage is between about 300 and 4508C,
with a significant loss of 78.3 wt% and an associated exother-
mic peak centered at 4318C on the differential thermal analysis
Figure 1. (a) TGA and DTA curves and (b) three-dimensional on-line FTIR
spectra of the volatile products in chitin carbonization. The labeled peaks in
the FTIR spectrum represent: (1) CÀO stretching, (2) OÀH bending, (3) NÀH
(
DTA) curve, which corresponds to the decomposition of chitin.
The gas products as well as the low-boiling-point products
evolved during the degradation of chitin were detected by
FTIR spectroscopy (Figure 1b). According to the contour,
bending, (4) C=O stretching, (5) CO, (6) CO
2
, (7) CÀH stretching, and (8) OÀH
stretching.
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which may result from the decomposition of surface functional
groups. At this stage, there is no new peak appearing on the
FTIR spectrum. From TG-IR analysis, the decomposition of
chitin mainly occurred between 300 and 4508C and generated
a large amount of volatile products that were detected in the
system until the end of the analysis. Based on the TG analysis
of chitin, we selected 4008C as the minimal temperature to
study the carbonization of chitin in a nitrogen atmosphere.
The method for preparing N-containing carbon materials is
extremely simple. Briefly, chitin carbonization is conducted in
a tubular furnace in a nitrogen atmosphere under tempera-
À1
ture-programmed heating (108Cmin ) that is maintained for
four hours after reaching the desired temperature. Chitin was
carbonized at 400, 600, 800, and 10008C, and the products
were termed as NC-400, NC-600, NC-800, and NC-1000, respec-
tively. Table 1 shows the carbon-product mass yields at differ-
ent carbonization temperatures. From X-ray photoelectron
spectroscopy (XPS) analysis it can be seen that the carbon con-
tent increased monotonically (from 82.5 to 90.2 wt%), whereas
the oxygen (from 12.7 to 6.7 wt%) and nitrogen (from 8.4 to
3
.1 wt%) contents decreased with the increase of temperature,
which indicated the decomposition of O- and N-containing
groups on the surface at high temperature. The contents of
carbon, nitrogen, and hydrogen in these materials were also
analyzed by an elemental analyzer. The nitrogen content in
NC-400 (8.87 wt%) is higher than that in chitin (6.89 wt%), and
decreased only slightly from 400 to 8008C. Even when treated
at 10008C, a significant portion of nitrogen was maintained in
the bulk (4.75 wt%). In addition, a large amount of liquid prod-
uct (about 35–50 wt%) can be generated and collected at the
exit of the quartz tube. Analysis of the liquid product obtained
at 6008C by gas chromatography-mass spectrometry (GC-MS)
and high-performance liquid chromatography (HPLC) revealed
acetic acid and acetamide to be the two main products with
yields of 5.9 and 2.2 wt%, respectively. Ethylene glycol, glycolic
acid, 3-hydroxypyridine, and N-acetylglucosamine were also
detected but the yields were much lower (combined yield:
Figure 2. (a) XRD patterns and (b) FTIR spectra of chitin, NC-400, NC-600,
NC-800, and NC-1000.
around 24.88). With the increase of carbonization temperature,
the peak at about 24.88 became sharper, and the peak at
about 42.98 became more prominent. It illustrated that the
carbon product achieved at higher carbonization temperature
has a more regular layered structure and structural order than
1
.5 wt%). From mass balance measurements, 30–40 wt% prod-
[
23b]
ucts were in the form of gases (CO, CO , etc.).
that obtained at lower temperature.
Consistently, FTIR spec-
2
tra exhibit systematic changes (Figure 2b). For NC-800 and NC-
1
000, the characteristic peaks of chitin located at approximately
Structure characterization
À1
3
260, approximately 1650, 1558, and 1080 cm , which were as-
[
22]
To further probe the structural changes during carbonization,
X-ray diffraction (XRD) was used to characterize these carbon
products. Figure 2a shows the XRD patterns of chitin as well as
those of NC-400, NC-600, NC-800, and NC-1000. The peaks at
cribed to the n , nC
=
O, n , and n
stretching vibrations,
NÀH
CÀN
CÀO
disappeared and were replaced by two new vibration peaks
À1
located at approximately 1560 and 1120 cm , respectively,
2
which corresponded to the vibration of the sp C=N and/or aro-
À1
3
À1 [25]
2
q=19.1 and 9.18, representing the (101) and (020) diffraction
matic C=C (1560 cm ), and sp CÀN (1120 cm ). For NC-400,
[
22]
À1
facets of chitin, disappeared after carbonization at different
temperatures. One new peak located at 2q=24.88 was ascribed
to the diffraction of the (002) facets, which indicated that there
a weak peak located at approximately 3360 cm can be ob-
served, which indicates some primary amine groups may
[
26]
exist.
[23]
was interlayer structure in the material. A second, weak peak
appeared at 2q=42.98 corresponding to the in-plane diffraction
of (100) facets, which reflected the triperiodic order of materials
Raman spectroscopy was also used to analyze the micro-
scopic structure of the products, and the original spectra were
deconvoluted (Figure 3). Two characteristic Raman bands for
[23b,24]
À1
and the formation of a real graphitic phase.
According to
graphite, located at approximately 1330 cm (D band) and ap-
À1
[27]
the XRD patterns, the product achieved at the lowest tempera-
ture (4008C) had already fully lost the crystal structure of chitin
and showed some degree of layered structure (broad peak at
proximately 1575 cm (G band), indicated the existence of
2
a graphitic sp -hybridized carbon structure in all samples. It is
well known that the G band is due to the single-crystal graph-
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nomenon was previously ob-
served in some carbonizated
high-molecular polymers and
was ascribed to
a complex
“
throat- or cavity-type“ micropo-
rous structure, or to the property
of sorbate-induced swelling of
[
29]
micropores.
Plausibly, the N-
containing carbon materials de-
rived from chitin contained
some complex microporous
structures, which inhibited the
nitrogen contained in the com-
plex-micropore desorption at
low relative pressure. All these
isotherms belong to the type IV
isotherm, which confirms these
N-containing carbon materials
have a mesoporous structure.
Compared with chitin, which has
a
7
surface area of merely
2
À1
.4 m g ,
the
Brunauer–
Emmett–Teller (BET) surface
areas of NC-400 and NC-600 are
much higher, at 221 and
Figure 3. Deconvoluted Raman spectra of (a) NC-400, (b) NC-600, (c) NC-800, and (d) NC-1000.
ite and the D band results from the defects or the polycrystal-
line graphite in the bulk carbon. The relative intensity of the D
band to the G band, I /I , was usually used as a criterion to de-
D
G
[28]
termine the disordered extent in carbon materials. The ratio
of ID/IG for NC-600 was slightly greater than the one for NC-
4
00, which suggested that more defects or a more disordered
graphite structure was generated at higher temperature. We
deduced that the defects may be formed during the transfor-
mation of surface functional groups, such as from amino
groups (NH ) to quaternary nitrogen atoms, which partly de-
2
2
stroyed the sp -hybridized carbon structure. NC-800 and NC-
1
000 have the same value of I /I , slightly smaller than that of
D G
NC-600 though, which indicates an increase of the graphitic
structure at higher carbonization temperature.
The scanning electron microscopy (SEM) images of NC-400,
NC-600, NC-800, and NC-1000 are shown in Figure 4. Com-
pared with chitin, which has a fibrous structure (see Figure S1a
in the Supporting Information), the four N-containing carbon
materials exhibit a graphitic structure. For NC-400 and NC-600,
layered carbon sheets with pores can be observed clearly. For
samples carbonized at higher temperatures (NC-800 and NC-
Figure 4. SEM images of (a) NC-400, (b) NC-600, (c) NC-800, and (d) NC-1000.
2
À1
251 m g , respectively. At higher carbonization temperatures,
the surface area of the product began to decrease. The BET
2
À1
surface area of NC-800 is 181 m g and that of NC-1000 is
2
À1
only 18 m g , which indicates that some pore structures were
damaged at higher carbonization temperature. The pore-size
distribution based on Barrett–Joyner–Halenda (BJH) analysis
(Figure 5b, d, f, and h) suggested that the pores have already
been created at 4008C, in the range of 2–9 nm and centered
at approximately 3.3 nm. Although the surface area exhibited
no significant change among samples treated between 400
and 8008C, the pore-size distribution varied along with the in-
crease of temperature. For NC-600 and NC-800, the pore sizes
were randomly distributed in the range of 2–9 nm. In contrast,
the porous structure was almost entirely damaged for NC-
1000. We also observed the existence of micropores (<2 nm)
1
000), the layered carbon sheet is still the predominant struc-
ture but the pore size appears to be smaller. These structural
features can also be observed in lower magnification SEM
images (Figure S2). TEM images provided in Figures S1b and
S3 corroborate the layered carbon sheet structure for the NC-
6
00 and NC-800 samples.
Nitrogen-adsorption experiments further demonstrated that
these materials have a high surface area and mesoporous
structure. Except for NC-1000, all of the isotherms exhibited an
unclosed hysteresis loop with the desorption curve lying
above the adsorption line (Figure 5a, c, e, and g). This phe-
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proved that the carbonization occurred even at
4
008C, and the extent of graphitization increased
along with increased temperature. The peak at
85.8 eV suggested that there were some N-contain-
2
ing groups on the surface of the materials. Some
other carbon atoms bearing oxygen-containing
groups located at 286.7, 287.6, and 289.2 eV may
have resulted from the partial decomposition of the
polysaccharide structure. In addition, in the NC-400 C
1
s XPS spectrum, there is another peak at 283.5 eV,
which could not be ascribed to any of the above.
From the XPS handbook, it appears that it may
belong to a carbide carbon, however, considering the
extremely low metal content (from inductively cou-
pled plasma atomic emission spectroscopy (ICP-OES)
analysis), the peak cannot be ascribed to carbide. We
tentatively assign the peak to be the amorphous
carbon from partial carbonization of chitin at 4008C,
which can be transformed into graphitized carbon at
[
31]
a higher temperature.
shown in Figure 6b, d, f, and h, at least four peaks at
98.6, 400.6, 401.2, and 402.5 eV, which correspond
to pyridinic N, pyrrolic N, graphitic N, and nitrogen in
For the XPS N 1s spectra
3
[
12,18,27,32]
oxidation states,
were taken into consider-
ation during deconvolution. For NC-400, the N 1s
spectrum is much more complex than the other
three N-containing carbon materials. Other than the
four main nitrogen species, there are other nitrogen
species such as amide (400.1 eV), amino (398.8 eV),
[
33]
and other unknown nitride (397.3 eV) forms, which
is in accordance with the FTIR analysis revealing the
À1
NÀH stretching vibration at about 3260 cm in NC-
4
00. Along with the increase of carbonization tem-
perature, these complex nitrogen species were incor-
porated into the framework of the carbonizated
carbon. Indeed, graphitic N and pyridinic N are the
major forms of nitrogen in NC-800 and NC-1000. XPS
analysis confirmed that not only the nitrogen con-
tent, but also the types of major nitrogen species,
can be modified by changing the carbonization tem-
Figure 5. Nitrogen-adsorption isotherms of N-containing carbon: (a) NC-400, (c) NC-600,
e) NC-800, (g) NC-1000, and the pore-size distribution based on BJH analysis of adsorp-
tion isotherm data: (b) NC-400, (d) NC-600, (f) NC-800, (h) NC-1000.
(
perature.
A detailed component distribution of
in NC-400, NC-600, and NC-800, which further suggest the exis-
tence of micropores in the N-containing carbon materials. On
considering the TG-IR analysis, most volatile products were
generated from the decomposition of chitin at around 4008C.
Plausibly, the large amount of vapor (78 wt% of the starting
material) is responsible for the creation of the mesopores
when escaping from the bulky solid.
carbon and nitrogen types based on XPS fitting results is pro-
vided in Table S1 in the Supporting Information.
Heavy-metal adsorption
Mesoporous carbon materials are usually used as adsorbents
[
34]
to remove contaminants from water. We expect our N-con-
taining carbon materials from chitin to be superior in heavy-
metal removal from water owing to the strong binding effect
between nitrogen and metal ions. To evaluate the metal-re-
moval effect of N-containing carbon materials prepared at dif-
ferent temperatures, three sample solutions containing a kind
of metal ion at a concentration of 10 ppm were treated in the
presence of NC-400, NC-600, NC-800, and NC-1000, respective-
ly, over a period of 12 hours with stirring (Figure 7a). The ad-
sorption capabilities of N-containing carbon materials for these
To clarify the changes of the electronic state of nitrogen and
carbon atoms in chitin after carbonization, the C 1s and N 1s
XPS spectra were collected and analyzed in detail (Figure 6).
The C 1s XPS spectra shown in Figure 6a, c, e, and g were de-
convoluted to at least five components at 284.9, 285.8, 286.7,
2
2
87.6, and 289.2 eV attributed to sp C, CÀN, CÀO, C=O, and
[27,30]
C(O)OH, respectively.
Among these peaks, the peak at
2
84.9 eV was the main peak and gradually became sharp
along with the increase of carbonization temperature. This
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NC-400 was selected for further evaluation. The
VI
effect of pH on Cr adsorption is shown in Figure 7b.
VI
Interestingly, the adsorption ability towards Cr is
higher at a lower pH. For example, at pH 3.0, the re-
VI
moval efficiency for Cr is 92% whereas at pH 10.0,
NC-400 almost completely lost its capability to
VI
remove Cr . This can be rationalized by considering
the surface charge state of NC-400 at different pH.
Amino groups and other nitrogen species would be
protonated at lower pH so that the adsorbent is posi-
VI
tively charged. Under this condition, Cr ions exist
À
À
either in the form of HCrO4 or CrO4 . The electro-
VI
static attractions between the adsorbent and Cr
anion species enhanced the adsorption efficiency of
VI
Cr on NC-400. Figure 7c shows the time profile of
VI
Cr adsorption on NC-400 under neutral conditions.
The adsorption amount (q) increased with the ad-
sorption time and reached adsorption equilibrium
after five hours. This indicates NC-400 exhibited rela-
VI
tively fast adsorption kinetics in Cr removal, compa-
[
35]
rable with other materials.
The adsorption iso-
VI
therms of Cr is illustrated in Figure 7d, at the initial
metal-ion concentration of 1–100 ppm. The qe
À1
IV
reached a remarkable 47.8 mgg , at a Cr equilibri-
um concentration of 88 ppm (which corresponds to
a 100 ppm initial concentration), which is considera-
bly larger than the data achieved by other adsorb-
À1 [36]
ents such as sawdust (3.3 mgg ), chitosan cross-
À1 [37]
linked with epichlorohydrin (11.3 mgg ), and mag-
À1 [35a]
netic graphene (4.9 mgg ),
under similar condi-
tions, which indicates that NC-400 is a very promising
material in the preconcentration and/or removal of
heavy-metal ions from aqueous solutions.
Catalytic activity
It is well established that N-doped carbon materials
exhibit excellent catalytic oxidation activity because
the doped nitrogen can impact the electronic state
[
12,38]
of carbon.
As such, we carried out preliminary
tests on the catalytic activity of chitin-derived N-con-
taining carbon materials in the epoxidation of styrene
Figure 6. XPS C 1s spectra of N-containing carbon (a) NC-1000, (c) NC-800, (e) NC-600,
g) NC-400, and XPS N 1s spectra of (b) NC-1000, (d) NC-800, (f) NC-600, (h) NC-400.
using tert-butyl hydroperoxide (TBHP) as the oxidant.
(
Indeed, these materials effectively promoted the oxi-
dation reaction. In the absence of catalyst the con-
II
II
VI
three heavy-metal ions followed the order of Hg >Pb >Cr . It
is clear that the temperature at which the N-containing carbon
material is produced has a strong effect on the adsorption abil-
ity. NC-400 exhibited the highest capability to remove heavy-
metal ions, and the capability dropped monotonically as the
carbonization temperature increased. NC-1000 exhibited
almost no ability to remove these heavy-metal ions. From
these, we conclude that the amino groups and pyrrolic N in
the NC material are mainly responsible for the excellent heavy-
metal removal, as XPS and IR analysis indicated that the
version is very low (2.7%) with only 2 mol% of epoxide ob-
tained after one hour (Table 2, entry 1). When 10 mg NC-400
was used, both the styrene conversion and epoxide yield in-
creased considerably (Table 2, entries 2–5). Among the four N-
containing carbon materials, NC-1000 exhibits the highest cata-
lytic activity; whereas NC-400 exhibited the worst catalytic ac-
tivity under the same reaction conditions. The performances of
NC-600 and NC-800 were moderate. When the reaction time
was prolonged to 12 hours, the conversion of styrene and the
yield of styrene increased accordingly. NC-1000 still exhibited
the highest catalytic activity (67% conversion) compared to
the other three carbon materials, whereas NC-800 and NC-600
degree of NH and pyrrolic groups in NC dropped with increas-
2
ing carbonization temperature.
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Therefore, NC-800 is the most
suitable catalyst for the reaction
among the four N-containing
carbon catalysts, which enables
the highest yield for the desired
product. Compared with other
N-containing carbon materials,
such as nitrogen-doped onion-
[
38b]
like carbon (N-OLC),
nitrogen-
doped carbon nanotubes (N-
[
38b]
CNTs),
and N-doped gra-
[
39]
phene, the catalytic activity of
the N-containing carbon derived
from chitin was slightly lower
but the selectivity to styrene
oxide was higher. To demon-
strate the function of nitrogen
atoms in the material for cataly-
sis, a nitrogen-free carbon mate-
rial was prepared by carbonizing
VI
II
II
Figure 7. (a) The adsorption ability of N-containing carbon materials for Cr , Pb , and Hg . (b) The pH effect on
microcrystalline
cellulose
at
VI
VI
Cr adsorption by NC-400. (c) The time profile of Cr adsorption on NC-400. (d) The adsorption ability of NC-400
for Cr at different equilibrium concentrations. Conditions: (a) 5 mg NC, 20 mL solution (pH 7, metal ion concen-
VI
10008C (termed as C-1000). The
poor catalytic activity and low
selectivity for epoxide were ob-
served under the same reaction
conditions (Table 2, entry 10).
Combining the XPS fitting re-
tration=5 ppm), 12 h, stirring; (b) 5 mg NC-400, 20 mL solution (pH was adjusted by HNO
3
and NaOH,
VI
VI
C
2
0
(Cr )=5 ppm), 12 h, stirring; (c) 5 mg NC-400, 20 mL solution (pH 7, C
0
(Cr )=5 ppm), stirring; (d) 5 mg NC-400,
VI
VI
À1
0 mL solution (pH 7, C
0
(Cr )=1–100 ppm,), stirring. C
e
is the equilibrium concentration of Cr . q
e
[mgg ] is the
equilibrium amount of heavy metal adsorbed per gram of adsorbent.
[a]
Table 2. Catalytic activity of carbon materials in the epoxidation of styrene.
sults with the reaction performances, it is clear that
the surface area and the nitrogen content are not
the determining factors for a superior catalytic activi-
ty. The content of graphitic carbon and graphitic ni-
trogen are plausibly the main factors responsible for
styrene epoxidation. Therefore, the higher carboniza-
tion temperature is critical to achieve a kind of N-
containing carbon material with excellent catalytic
activity for oxidation reactions. Although more active
carbon-based catalysts are known, including in epoxi-
Entry Catalyst t [h] Conv. [%]
Selectivity [mol%]
1
2
3
4
5
none
1
1
1
1
1
2.7
5.7
10.7
11.2
14.9
74.1
57.9
53.3
67.9
65.1
22.2
7.0
11.2
11.6
10.7
0.0
1.8
1.9
1.8
2.0
0.0
0.0
0.0
0.0
0.0
NC-400
NC-600
NC-800
NC-
1
000
[39]
dation, the simple procedure for the catalyst syn-
6
7
8
9
NC-400 12 29.7
NC-600 12 41.9
NC-800 12 46.1
74.4
87.8
87.6
62.9
6.7
7.2
5.2
6.1
1.3
1.2
1.1
0.7
4.0
1.9
1.1
thesis from an abundant, renewable material makes
chitin-derived NC attractive for catalytic applications.
NC-
000
C-1000 12 19.5
12 66.8
20.1
1
1
11
0
23.1
46.0
5.6
1.0
35.9
Conclusion
[
b]
N-OLC-
3
4
88.4
all others 54.0
In conclusion, a simple, scalable, and affordable car-
bonization method, in the absence of any additional
reagent, for the preparation of mesoporous, N-con-
taining carbon materials from chitin was developed.
The pore structure, surface area, and types of nitro-
gen in the resulting material can be easily adjusted
by changing the carbonization temperature, leading
to materials suitable for different applications. A low
carbonization temperature is beneficial to achieve
[
b]
1
1
2
3
N-CNTs
4
75.1
11.1
72.8
all others 88.9
all others 27.2
[
c]
NG-800 24 87.6
[
a] Reaction conditions: styrene 0.5 mmol, catalyst 10 mg, TBHP 1.5 mmol, 3 mL
CH Cl , 1008C, 1 h, after reaction, 30 mg dodecane was added as an internal standard
and products were analyzed by GC-7890 equipped with HP-5 column.
b] Ref. [38b]: 908C, catalyst 10 mg, styrene/TBHP=1:3. [c] Ref. [39]: 1008C, catalyst
0 mg, styrene/TBHP=1:3.
2
2
a
a
[
1
exhibited the highest selectivity towards epoxide (88%)
Table 2, entries 6–9). The lower selectivity for the NC-1000 cat-
a carbon material with large surface area and high nitrogen
content enriched with amine and pyrrolic functionalities, which
are beneficial to the removal of heavy-metal ions from water.
In contrast, a higher carbonization temperature increases the
content of graphitic nitrogen and carbon, which are essential
(
alyst is due to the formation of styrene glycol (20% selectivity).
These results indicate that NC-1000 can not only catalyze the
epoxidation of styrene but also the hydrolysis of styrene oxide.
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for excellent catalytic activity in oxidation reactions such as sty-
rene epoxidation. This study highlights the potential of utiliz-
ing chitin, the second most abundant biomaterial on earth, to
manufacture functionalized N-containing carbon materials.
More applications of these novel carbon materials as catalysts,
adsorbents, and beyond are currently under development in
the group.
D and G bands and the ratios of the two peak intensities were cal-
culated based on the height of the two deconvoluted peaks.
Protocols for preparing N-containing carbon from chitin
Chitin (1 g) was loaded into a quartz tube that was placed in a tub-
À1
ular furnace and nitrogen gas with the flow rate of 50 mLmin
was connected. The furnace was heated at a rate of 108Cmin
À1
from room temperature to the target temperature. Then the fur-
nace was held at this temperature for 4 hours before cooling
down. The liquid product was collected in a two-necked flask
Experimental Section
(
10 mL) connected to one end of the quartz tube, cooled by air.
Chemicals
The quartz tube was taken out the furnace and the product in the
tube was collected and analyzed further.
a-Chitin was purchased from Wako Pure Chemical Industry. Styrene
(
ꢀ99%), 4-tert-butylhydroperoxide solution (TBHP, 70 wt% in
water), HgCl (ACS reagent, ꢀ99.5%), and dodecane (ꢀ99%) were
2
purchased from Sigma–Aldrich. K Cr O (ꢀ99.9%) was produced
Quantification of calcium in chitin
2
2
7
by Fisons Scientific Equipment. Dichloromethane (analytical re-
agent grade) was produced by Fisher Scientific Company. Pb(NO3)2
was purchased from Merck Chemicals. All chemicals were used
without further treatment.
Chitin (0.0512 g) was digested in concentrated nitric acid (65 wt%,
1
0 mL) at 1208C for 12 hours. The solution was transferred to
a volumetric flask (25 mL) and the flask was topped up to the
mark line by the addition of pure water. Then the solution was an-
alyzed by ICP-OES.
Characterization
GC-MS and GC analysis of liquid products
XPS spectra were recorded on a VG ESCALAB 220I-XL system
equipped with two types of X-ray sources: the twin anode (Mg/Al)
and the twin-crystal monochromated Al source, producing spectra
from areas ranging from 8 mm down to 20 mm in diameter. The
data were calibrated by the C 1s signal (285.0 eV) and processed
further. XRD analysis was carried out on a Bruker D8 Advanced dif-
fractometer using CuKa (l=1.5406 Š) radiation (40 kV voltage,
The liquid products generated during the carbonization process
were analyzed and quantified by the pre-column derivatization
method, by employing hexamethyldisililazane to silylate the hy-
[40]
droxyl groups. The liquid product (0.1 g), a small magnetic stir-
ring bar, and derivatization reagents, including pyridine (1.5 mL),
hexamethyldisilazane (1.5 mL), and trifluoroacetic acid (0.1 mL),
were added into a small flask (10 mL). The flask was sealed and
heated under stirring in a water bath at 608C for 1 h. After silyla-
tion, dedecane (8 mg) was added into the system and the mixture
was analyzed on a GC-MS (Agilent 7890A GC system with a 7693
Autosampler, 5975C inert MSD with triple-axis detector, and an Agi-
lent HP-5 column). After the structures of all the peaks were deter-
mined on a GC-MS spectrum, the sample was analyzed further and
quantified on a GC (Agilent 7890) equipped with a FID detector.
3
0 mA cathodic current). Diffraction patterns were recorded within
a 2q range of 5–808. SEM images were taken with a JSM-6700F
field-emission microscope. The carbon materials powder was di-
rectly immobilized on a copper holder by conducting resin without
platinum coating before characterization. TEM images were taken
on a JEOL JEM-2010 microscope. The samples were dispersed in
ethanol by ultrasonication and then dropped on a copper grid.
Gas sorption isotherms were measured using a Nova 4200e sur-
face-area analyzer. The materials were degassed at 1508C for at
least 17 hours. The BET specific surface areas were calculated by
VI
II
II
using the adsorption data in the relative pressure (P/P ) range of
Adsorption of Cr , Pb , and Hg by N-containing carbon ma-
terials
0
0
.05–0.35. The pore-size distribution for each sample was based on
BJH analysis of adsorption isotherm data. FTIR were achieved on
a Bruker Equinox 55 infrared spectrometer. The number of scans
VI
II
II
Stock solutions (100 ppm) of Cr , Pb , and Hg were prepared in ul-
trapure water. In the experiments, heavy-metal solutions (20 mL,
1–20 ppm) were prepared by diluting the stock solution and then
the N-containing carbon material (5 mg) was added. Then the solu-
tion was stirred by a magnetic stirring bar at 1000 rpm for 0.25–
À1
was 16 with a resolution of 4 cm over the range of 4000–
À1
4
00 cm under transmittance mode. A sample (about 2 mg) was
diluted by KBr (98 mg) and then pressed into a wafer before mea-
surement. Thermogravimetric analysis was conducted on a DTG-
1
2 hours. At the end of the adsorption, the adsorbent was re-
6
0A thermogravimetry analyzer (Shimadzu) under a nitrogen at-
moved by filtration and the solution was acidified by nitrate acid
and analyzed by ICP-OES. All adsorption experiments were carried
out in triplicate and the results were presented in the form of aver-
age values and relative percentage deviations. The amount of the
heavy metals adsorbed per unit mass of adsorbent was calculated
according to Equation (1):
mosphere and the volatile products were detected by a coupled
Fourier transform infrared spectrophotometer (IR Prestige-21, Shi-
madzu) online. Raman analysis was conducted on an XploRA PLUS
Raman microscope (Horiba/JY, France). The samples were placed
on a glass slide and measured directly. All spectra were obtained
with a laser wavelength of 532 nm and laser power of 25 mW. The
À1
scan range was between 500 and 3500 cm and the scan time
was 60 seconds. All the original Raman spectra had their linear
background subtracted and deconvoluted by using PeakFit version
q ¼ ðC ÀC ÞV=M
ð1Þ
e
0
f
À1
4
2
.12 software. The range of the processed spectrum was 900–
000 cm with the best baseline mode and Gaussian–Lorentzian
in which q [mgg ] is the adsorption amount of heavy metal per
e
À1
mass of adsorbent, C and C are the initial and final concentration
0
f
area mode with a multipeak best fit. The deconvoluted peaks at
approximately 1330 and approximately 1575 cm along with the
[ppm] of heavy metal ions, respectively, V is solution volume [mL],
and M is the mass of adsorbent [g].
À1
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Catalytic activity evaluation
[18] R. J. White, M. Antonietti, M. M. Titirici, J. Mater. Chem. 2009, 19, 8645–
8650.
The catalytic activity evaluation was conducted in a thick-walled
glass tube equipped with a Teflon lid. In general, N-containing
[19] L. Wang, Y. L. Zheng, X. H. Wang, S. H. Chen, F. G. Xu, L. Zuo, J. L. Wu,
L. L. Sun, Z. Li, H. Q. Hou, Y. H. Songt, ACS Appl. Mater. Interfaces 2014,
6, 7117–7125.
carbon materials (10 mg), styrene (1 mmol), CH Cl2 (2 mL), and
2
[
[
[
[
20] M. Zhang, L. Shu, X. F. Shen, X. Y. Guo, S. Tao, B. S. Xing, X. L. Wang, Envi-
ron. Pollut. 2014, 195, 84–90.
21] D. Wang, R. Xiao, H. Zhang, G. He, J. Anal. Appl. Pyrolysis 2010, 89, 171–
TBHP (460 mL) were added into the reaction tube in turn. Then the
tube was sealed with the Teflon lid and placed into a metal heater
at 1008C for 1 or 12 hours. After the reaction, dodecane (30 mg)
was added as an internal standard and dichloromethane (5 mL)
was added as the dilution solvent. After filtration, the solution was
analyzed by a Agilent 7890 gas chromatograph equipped with HP-
1
77.
22] G. Cµrdenas, G. Cabrera, E. Taboada, S. P. Miranda, J. Appl. Polym. Sci.
004, 93, 1876–1885.
2
23] a) A. Primo, A. Forneli, A. Corma, H. García, ChemSusChem 2012, 5,
2207–2214; b) L. Zhao, N. Baccile, S. Gross, Y. Zhang, W. Wei, Y. Sun, M.
Antonietti, M.-M. Titirici, Carbon 2010, 48, 3778–3787.
5
capillary column and flame ionization detector, and then the con-
version of styrene and the yields of the products were calculated
according to the peak area and calibration curve.
[24] a) K. S. Subrahmanyam, S. R. C. Vivekchand, A. Govindaraj, C. N. R. Rao, J.
Mater. Chem. 2008, 18, 1517–1523; b) L. Yu, C. Falco, J. Weber, R. J.
White, J. Y. Howe, M.-M. Titirici, Langmuir 2012, 28, 12373–12383; c) Q.
Zhao, T.-P. Fellinger, M. Antonietti, J. Yuan, J. Mater. Chem. A 2013, 1,
Acknowledgements
5113–5120.
[
[
25] a) T. V. Khai, H. G. Na, D. S. Kwak, Y. J. Kwon, H. Ham, K. B. Shim, H. W.
Kim, J. Mater. Chem. 2012, 22, 17992–18003; b) H. Kaczmarek, J. Za-
wadzki, Carbohydr. Res. 2010, 345, 941–947.
This study was financially supported by A*Star, PSF funding
through WBS: R-279-000-403-305. We thank Michael Joyes for
the proofreading.
26] a) T. Ramanathan, F. T. Fisher, R. S. Ruoff, L. C. Brinson, Chem. Mater.
2005, 17, 1290–1295; b) M. H. Ahmed, J. A. Byrne, J. A. D. McLaughlin,
A. Elhissi, W. Ahmed, Appl. Surf. Sci. 2013, 273, 507–514.
Keywords: adsorption
epoxidation · mesoporous materials
·
biomass
·
carbohydrates
·
[27] P. Hao, Z. Zhao, Y. Leng, J. Tian, Y. Sang, R. I. Boughton, C. P. Wong, H.
Liu, B. Yang, Nano Energy 2015, 15, 9–23.
[
[
28] A. C. Ferrari, J. Robertson, Phys. Rev. B 2000, 61, 14095–14107.
29] a) P. M. Budd, A. Butler, J. Selbie, K. Mahmood, N. B. McKeown, B.
Ghanem, K. Msayib, D. Book, A. Walton, Phys. Chem. Chem. Phys. 2007,
[
1] a) J. Lee, J. Kim, T. Hyeon, Adv. Mater. 2006, 18, 2073–2094; b) C. Liang,
Z. Li, S. Dai, Angew. Chem. Int. Ed. 2008, 47, 3696–3717; Angew. Chem.
9, 1802–1808; b) F. J. Liu, C. J. Li, L. M. Ren, X. J. Meng, H. Zhang, F. S.
2
2
008, 120, 3754–3776; c) T.-Y. Ma, L. Liu, Z.-Y. Yuan, Chem. Soc. Rev.
013, 42, 3977–4003; d) R. J. White, V. Budarin, R. Luque, J. H. Clark,
Xiao, J. Mater. Chem. 2009, 19, 7921–7928.
[
30] S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y.
Jia, Y. Wu, S. T. Nguyen, R. S. Ruoff, Carbon 2007, 45, 1558–1565.
31] J. Nakamura, I. Toyoshima, K.-i. Tanaka, Surf. Sci. 1988, 201, 185–194.
32] S. Biniak, G. Szymanski, J. Siedlewski, A. Swiatkowski, Carbon 1997, 35,
D. J. Macquarrie, Chem. Soc. Rev. 2009, 38, 3401–3418.
[
[
2] Y. Li, J. Fu, S. Deng, X. Lu, J. Colloid Interface Sci. 2014, 424, 104–112.
3] P. Xu, D. Wu, L. Wan, P. Hu, R. Liu, J. Colloid Interface Sci. 2014, 421,
[
[
1
60–164.
1799–1810.
[
[
[
4] L. Schlapbach, A. Zuttel, Nature 2001, 414, 353–358.
5] F. Rodríguez-Reinoso, Carbon 1998, 36, 159–175.
6] a) S. Navalon, A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem. Rev.
[
33] a) H. P. Mungse, O. P. Khatri, J. Phys. Chem. C 2014, 118, 14394–14402;
b) A. M. Alswieleh, N. Cheng, I. Canton, B. Ustbas, X. Xue, V. Ladmiral,
S. J. Xia, R. E. Ducker, O. El Zubir, M. L. Cartron, C. N. Hunter, G. J. Leg-
gett, S. P. Armes, J. Am. Chem. Soc. 2014, 136, 9404–9413; c) J. F. Mould-
er, W. F. Stickle, P. E. Sobol, K. D. Bomben, Handbook of X Ray Photoelec-
tron Spectroscopy: A Reference Book of Standard Spectra for Identification
and Interpretation of XPS Data (Edited by Jill Chastain) PerkinElmer Copo-
ration Physical Electronic Division 1992, p. 43.
2014, 114, 6179–6212; b) W. J. Lee, U. N. Maiti, J. M. Lee, J. Lim, T. H.
Han, S. O. Kim, Chem. Commun. 2014, 50, 6818–6830; c) P. Chen, T. Y.
Xiao, Y. H. Qian, S. S. Li, S. H. Yu, Adv. Mater. 2013, 25, 3192–3196.
7] a) J. S. Lee, X. Wang, H. Luo, G. A. Baker, S. Dai, J. Am. Chem. Soc. 2009,
[
1
31, 4596–4597; b) S. Zhang, K. Dokko, M. Watanabe, Chem. Mater.
014, 26, 2915–2926.
8] T.-D. Nguyen, K. E. Shopsowitz, M. J. MacLachlan, J. Mater. Chem. A
014, 2, 5915–5921.
9] H. Zhong, H. Zhang, S. Liu, C. Deng, M. Wang, ChemSusChem 2013, 6,
07–812.
2
[
[
34] A. MuÇoz García, A. J. Hunt, V. L. Budarin, H. L. Parker, P. S. Shuttleworth,
G. J. Ellis, J. H. Clark, Green Chem. 2015, 17, 2146–2149.
35] a) G. Gollavelli, C.-C. Chang, Y.-C. Ling, ACS Sustainable Chem. Eng. 2013,
[
[
2
1, 462–472; b) H. Jabeen, V. Chandra, S. Jung, J. W. Lee, K. S. Kim, S. B.
8
Kim, Nanoscale 2011, 3, 3583–3585.
[
[
[
10] H.-g. Wang, Z. Wu, F.-l. Meng, D.-l. Ma, X.-l. Huang, L.-m. Wang, X.-b.
Zhang, ChemSusChem 2013, 6, 56–60.
11] X. L. Li, H. L. Wang, J. T. Robinson, H. Sanchez, G. Diankov, H. J. Dai, J.
Am. Chem. Soc. 2009, 131, 15939–15944.
12] Y. Gao, G. Hu, J. Zhong, Z. Shi, Y. Zhu, D. S. Su, J. Wang, X. Bao, D. Ma,
Angew. Chem. Int. Ed. 2013, 52, 2109–2113; Angew. Chem. 2013, 125,
[
[
[
36] H. C. P. Srivastava, R. P. Mathur, I. Mehrotra, Environ. Technol. Lett. 1986,
7
, 55–63.
37] S. Qian, G. Huang, J. Jiang, F. He, Y. Wang, J. Appl. Polym. Sci. 2000, 77,
216–3219.
38] a) Y. Gao, J. Zhang, X. Chen, D. Ma, N. Yan, ChemPlusChem 2014, 79,
25–834; b) Y. Lin, X. Pan, W. Qi, B. Zhang, D. S. Su, J. Mater. Chem. A
3
8
2
163–2167.
2
2
014, 2, 12475–12483; c) Y. Cao, H. Yu, F. Peng, H. Wang, ACS Catal.
014, 4, 1617–1625; d) L. Zhao, R. He, K. T. Rim, T. Schiros, K. S. Kim, H.
[
[
[
13] J. H. Clark, Nat. Chem. 2009, 1, 12–13.
14] K. W. Buck, M. A. Obaidah, Biochem. J. 1971, 125, 461–471.
15] a) E. Khor, L. Y. Lim, Biomaterials 2003, 24, 2339–2349; b) M. Rinaudo,
Prog. Polym. Sci. 2006, 31, 603–632.
Zhou, C. GutiØrrez, S. P. Chockalingam, C. J. Arguello, L. Pµlovµ, D. Nor-
dlund, M. S. Hybertsen, D. R. Reichman, T. F. Heinz, P. Kim, A. Pinczuk,
G. W. Flynn, A. N. Pasupathy, Science 2011, 333, 999–1003.
39] W. Li, Y. Gao, W. Chen, P. Tang, W. Li, Z. Shi, D. Su, J. Wang, D. Ma, ACS
Catal. 2014, 4, 1261–1266.
[
[
16] F. M. Kerton, Y. Liu, K. W. Omari, K. Hawboldt, Green Chem. 2013, 15,
[
[
8
60–871.
17] a) Y. Pierson, X. Chen, F. D. Bobbink, J. Zhang, N. Yan, ACS Sustainable
Chem. Eng. 2014, 2, 2081–2089; b) X. Chen, S. L. Chew, F. M. Kerton, N.
Yan, Green Chem. 2014, 16, 2204–2212; c) X. Chen, N. Yan, Catal. Surv.
Asia 2014, 1–13; d) K. W. Omari, J. E. Besaw, F. M. Kerton, Green Chem.
40] S. H. Langer, S. Connell, I. Wender, J. Org. Chem. 1958, 23, 50–58.
2
012, 14, 1480–1487; e) F. D. Bobbink, J. Zhang, Y. Pierson, X. Chen, N.
Manuscript received: June 24, 2015
Revised: July 22, 2015
Final Article published: August 12, 2015
Yan, Green Chem. 2015, 17, 1024–1031; f) X. Chen, Y. Liu, F. M. Kerton,
N. Yan, RSC Adv. 2015, 5, 20073–20080.
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