Facile Construction of Mesoporous N-Doped Carbons as Highly Efficient 4-Nitrophenol Reduction Catalysts

Article abstract of DOI:10.1002/cctc.201500807

Herein we propose a novel in situ N-doping method to develop a new type of mesoporous N-doped carbons constructed by direct pyrolysis of properly rigid strut N-rich metal-organic frameworks at 950 °C. This facile fabrication method creates doped N that is evenly dispersed on mesoporous carbons (≈4.0 nm) formed simultaneously without the need for a second carbon precursor, external nitrogen supplier, or pore-forming agent. The resulting mesoporous N-doped carbons bear a low N content but a high proportion of graphitic N species and exhibit superior catalytic performance toward the reduction of 4-nitrophenol relative to that shown by previously reported metal catalysts and N-doped graphene. The ensemble effect of the mesostructured framework and effective N doping is responsible for the excellent performance, as better diffusion, adsorption, and activation of 4-nitrophenol in wastewaters are achieved through the elaborately fabricated mesoporous N-doped carbons.

Full text of DOI:10.1002/cctc.201500807

DOI: 10.1002/cctc.201500807
Communications
Facile Construction of Mesoporous N-Doped Carbons as
Highly Efficient 4-Nitrophenol Reduction Catalysts
Ying Yang,* Wen Zhang, Xiaohui Ma, Hairui Zhao, and Xin Zhang*[a]
Herein we propose a novel in situ N-doping method to devel-
op a new type of mesoporous N-doped carbons constructed
by direct pyrolysis of properly rigid strut N-rich metal–organic
frameworks at 9508C. This facile fabrication method creates
doped N that is evenly dispersed on mesoporous carbons
(ꢀ4.0 nm) formed simultaneously without the need for
a second carbon precursor, external nitrogen supplier, or pore-
forming agent. The resulting mesoporous N-doped carbons
bear a low N content but a high proportion of graphitic N spe-
cies and exhibit superior catalytic performance toward the re-
duction of 4-nitrophenol relative to that shown by previously
reported metal catalysts and N-doped graphene. The ensemble
effect of the mesostructured framework and effective N
doping is responsible for the excellent performance, as better
diffusion, adsorption, and activation of 4-nitrophenol in waste-
waters are achieved through the elaborately fabricated meso-
porous N-doped carbons.
erodes substrate diffusion and mass transfer. On the other
hand, mesoporous N-doped carbons (MNCs) with large surface
areas and regularly arranged mesopores were first developed
by a hard-templating approach, which involves filling the mes-
oporous silicate pores with nitrogen and carbon suppliers fol-
lowed by carbonization and final silicate template removal.[11]
Alternatively, by using an extra N supplier, the soft-templating
method can be made more step economical for the construc-
tion of MNCs simply by direct pyrolysis of well-defined C,N-
containing supramolecular aggregates.[12] However, the gener-
ality of this methodology is doubtful, because the harmonious
interaction between precursors and surfactant is crucial to
mesostructure formation, which decides the final porosity, and
thereby the available N suppliers are quite limited. Despite
continuous efforts, the facile and large-scale fabrication of
MNCs still remains a challenge.
Currently, metal–organic frameworks (MOFs) as a novel class
of nanoporous crystalline materials built from transition-metal
clusters as nodes and organic ligands as struts act as both
templates and precursors for the preparation of porous carbon
materials.[13] Owing to the large carbon content in MOFs, nano-
porous carbons (NPCs) also can be achieved by direct carboni-
zation of MOFs without the need for any additional carbon
source. Thus, several Zn-containing MOFs, such as ZIF-8,
ZnBTC, and the isoreticular metal–organic framework series,
IRMOF-x (x=1, 3, and 8), are used as the sole carbon precur-
sors to yield highly porous nanocarbons with ultrahigh surface
areas that show excellent properties in gas adsorption, electro-
chemical capacitance, sensing, and catalysis.[14] However, these
NPCs always possess a broad pore-size distribution, probably
because pyrolysis at low temperature (ꢁ8008C) followed by
acid washing erodes the pore arrangement upon ZnO removal.
Subsequently, the one-pot conversion of zinc–dicarboxylic acid
containing MOFs at high temperature (9508C) was recently
proven by us to be effective in obtaining narrowly distributed
mesopores by vaporizing away Zn metal (b.p. 9088C) during
pyrolysis.[15] Inspired by this, the incorporation of nitrogen into
a similar zinc–dicarboxylic acid constructed MOF precursor
could facilitate the one-pot synthesis of MNCs after pyrolysis at
9508C.
The design and application of N-doped carbons has become
a hot topic, as N doping has proven to be a powerful method
to modify the properties of carbon materials and thus provides
a promising way to extend the applications of such materials
from adsorption, energy conversion, and storage to catalysis.
Various metal-free gas sensors,[1] supercapacitors,[2] electro-
chemical oxygen reduction reaction catalysts,[3] and metal-free
oxidative[4] and basic[5] catalysts have been developed by
doping N into carbons either directly during synthesis or by
postsynthetic treatment. Postsynthetic treatment of carbon
materials often leads to less-efficient surface functionalization;
in contrast, doping of carbons during synthesis by using N-
containing precursors (in situ N doping) can realize the homo-
geneous incorporation of nitrogen into the entire carbon ma-
terials, which facilitates control of the nitrogen dosage and
dopant state.[6] Indeed, N-doped carbon nanotubes and carbon
nanofibers have been synthesized by methods similar to those
used to prepare bulk carbon nanotubes by using precursors
such as melamine,[7] acetonitrile,[8] nitrogen heterocycles,[9] and
phthalocyanines.[10] Notably, such N-doped carbons often bear
low accessible surface areas and microporosities owing to the
absence of a well-defined precursor structure, which inevitably
To realize efficient N doping into the mesoporous carbons
by direct pyrolysis of zinc–dicarboxylic acid containing MOFs,
we hypothesized that such MOF precursors should be properly
rigid and bear a large amount of evenly distributed N moieties
as the component of the organic struts on the basis of the fol-
lowing considerations:
[a] Dr. Y. Yang, Dr. W. Zhang, Dr. X. Ma, Dr. H. Zhao, Prof. X. Zhang
China University of Petroleum
State Key Laboratory of Heavy Oil Processing
No.18, Fuxue Road, Changping District, Beijing 102249 (P.R. China)
E-mail: catalyticscience@163.com
zhangxin@cup.edu.cn
1) A MOF precursor having a properly rigid crystalline struc-
ture can afford regular mesostructures after pyrolysis. Oth-
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500807.
ChemCatChem 2015, 7, 3454 – 3459
3454
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
erwise, only randomly distrib-
uted pores are derived from
flexible MOFs, or mere regular
micropores are produced
from rigid MOFs.
2) Carbonization at high temper-
ature requires sufficient and
stable N species to be intro-
duced to guarantee the
proper N dosage in the final
state. Though the component
N species from the organic
struts is in excess, they could
be mostly converted into vol-
atile species during pyrolysis,
let alone the loosely attached
N moieties, which could va-
porize away completely upon
heating at 9508C. In this
sense, MNCs could be facilely
constructed by direct pyroly-
sis of properly rigid strut N-
rich MOFs.
Figure 1. Characterization of the NZnMOF precursor and MNC: a) SEM image of NZnMOF; b–e) C, N, O, and Zn el-
emental maps of NZnMOF; f) SEM image of MNC; g–j) C, N, O, and Zn elemental maps of MNC; k) N2 adsorption/
desorption isotherm and the corresponding pore-size distribution curve of MNC (inset); and l) high-resolution
TEM image of MNC.
To verify this hypothesis, we de-
signed a properly rigid MOF pre-
cursor constructed with zinc clus-
ters and inexpensive acidic a-dii-
mine struts, 1,4-bis(4-CO2HC6H4)-
2,3-dimethyl-1,4-diazabutadiene, which was facilely synthesized
by the condensation of 4-aminobenzoic acid with 2,3-butane-
dione by using formic acid as the catalyst (Scheme 1a; see also
Figures S1 and S2, Supporting Information).[16] The resulting N-
rich zinc–dicarboxylic acid containing MOF (NZnMOF, see Fig-
ure S3a) is well crystalline (Figure S4a) and has a stone-like
morphology (Figure 1a); furthermore, it displays a uniform dis-
tribution of the C, N, O, and Zn elements, as determined by X-
ray diffraction (XRD), scanning electron microscopy (SEM),
energy-dispersive X-ray spectroscopy (EDX) (Figure S5a), and
SEM mapping results (Figure 1b–e). The MNC was subsequent-
ly obtained by direct pyrolysis of NZnMOF under a N2 atmos-
phere at 9508C for 2 h (Scheme 1b), which yielded fluffy and
highly porous carbons (Figure 1 f) with an even distribution of
inserted N upon Zn removal (Figure 1 g–j and Figure S5b) and
bearing a mesoporous structure and a narrow mesopore size
distribution centered at approximately 4.0 nm (Figure 1k). The
high-resolution transmission electron microscopy (TEM) image
shows that the interplane spacing of the (002) crystal lattice is
approximately 0.34 nm (Figure 1 l), in agreement with the in-
terlayer distance of graphite.[17] The XRD pattern displays (002)
and (10 1) diffraction peaks at 2q=26 and 438, respectively
(Figure S4b), which is suggestive of a well-defined graphitic
structure.[17] These results demonstrate that the MNCs can be
facilely fabricated by one-pot conversion of properly rigid strut
N-rich MOFs at high temperature.
The use of N-doped carbons for sewage treatment is highly
desirable, as highly efficient catalysts with a low cost and high
stability are urgently required for the large-scale degradation
of organic pollutants generated from agricultural and industrial
sources. Among which, the catalytic reduction of 4-nitropheol
(4-NP) is of great importance, because it makes waste profita-
ble owing to the production of industrially related 4-amino-
phenol (4-AP) as a source for the production of aniline and
paracetamol.[18] For this process, various supported metal cata-
lysts, such as Au, Pd, Ag, and Ni, and bimetallic catalysts, such
as PtNi, AuCu, and PdCu,[19] have been proven to be highly
active for the conversion of 4-NP. Metal-free catalysts have re-
cently emerged as new and promising candidates for the re-
duction of 4-NP. Gazi and Ananthakrishnan reported the metal-
free-photocatalytic reduction of 4-NP by using a resin-support-
ed dye under visible-light irradiation.[20] More recently, N-
doped graphene (NG) was found to be active toward the re-
duction of 4-NP and exhibited activity comparable to that of
Scheme 1. Schematic illustration of a) the synthesis of 1,4-bis(4-CO2HC6H4)-
2,3-dimethyl-1,4-diazabutadiene (L) and b) the synthesis of mesoporous N-
doped carbons through pyrolysis of N-rich MOF precursors.
ChemCatChem 2015, 7, 3454 – 3459
www.chemcatchem.org
3455
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
metal catalysts.[21] In our experiment, NaBH4 was not able to
reduce 4-NP even after 2 days without a catalyst. However,
with an ultrasmall amount of added MNC, the color of the re-
action mixture changed from yellow to entirely colorless after
10 min (Figure 2a). Considering the possibility that there could
be a decrease in the concentration of 4-NP caused by the ad-
sorption of 4-NP on the large surface area of the MNC, a control
experiment was undertaken. 4-NP and the MNC were mixed in
the presence of water, and the resultant mixture was analyzed
by UV/Vis spectroscopy (Figure S6). The adsorption of 4-NP on
the MNC was found to be insignificant. A significant decrease
in the absorbance at l=400 nm associated with concomitant
evolution of a peak at l=298 nm (Figure 2b) is further indica-
tive of the reduction of 4-NP to 4-AP.[19b] The conversion of 4-
NP was calculated from Equation (1):
catalyzed reaction (Figure S8 and Figure 2c), and this is indica-
tive of pseudo-zero-order kinetics (k=5.8”10À8 molLÀ1 À1), in
s
accordance with the reaction kinetics reported for NG. The
nonlinear relationship between ln(Ct/C0) and t (Figure 2d) fur-
ther demonstrates the completely different reaction kinetics
from a metal-catalyzed first-order reaction,[19] whereas the MNC
shows activity that is comparable to that of previously report-
ed metal catalysts.[23] To compare the activities of the different
N-doped carbons, the specific rate constant (K) [Eq. (2)] was
then calculated:
k
m
ð2Þ
K ¼
in which k is the rate constant and m is the mass of the cata-
lyst in grams.
Ct
ð1Þ
Conversion ½%Š ¼
It is clear that the MNC exhibits a much larger specific
C0
rate constant (11.6”10À4 molLÀ1 À1 gÀ1) than NG (5.3”
s
10À4 molLÀ1 À1 gÀ1) (Table S1), and this suggests that the MNC
s
has a higher activity than NG. Furthermore, the MNC can be
easily recycled up to 11 times and displays high activity
(ꢀ98%) after 7 cycles if the reaction is allowed to proceed for
10 min, and this is indicative of its superior recyclability (Fig-
ure 2e).
in which C0 and Ct are the concentrations of 4-NP at time t and
0, respectively, measured from the relative intensity of absorb-
ance (At/A0) at l=400 nm. The four marked isosbestic points
at l=224, 245, 281, and 313 nm are clear, which is demonstra-
tive of a clean conversion process without the formation of
any byproducts.[22] GC–MS analysis also demonstrated the con-
version of 4-NP into 4-AP (Figure S7).
A question that needs addressing is what makes the MNC
more efficient than NG? Thus, we conducted a series of charac-
terizations and comparative experiments in an attempt to un-
Interestingly, the absorbance intensity at l=400 nm and the
conversion of 4-NP change linearly with time (t) for the MNC-
derstand the relationship between textural properties,
status, and catalytic performance of the MNC.
N
In a control experiment, a similar N-doped carbon (NC) was
synthesized by direct pyrolysis of N-rich zeolitic imidazolate
frameworks (ZIF-8) and was comparatively studied (Supporting
Information). It is surprising that the NC was completely inac-
tive (Figure S9), even though the amount of catalyst used was
increased or the reaction time was prolonged. The N2 adsorp-
tion reveals that the NC shows a type I isotherm (Figure S10)
and a high specific surface area of 1043 m2gÀ1 (Table 1); these
are indicative of its microporous nature.[24] Moreover, the MNC
exhibits a type IV isotherm with a narrow pore-size distribution
centered at approximately 4.0 nm (Figure 1k and Table 1).
During the pseudo-zero-order reaction, the adsorption of 4-NP
ions is much faster than desorption, so the number of 4-NP
ions adsorbed on the MNC is not determined by their concen-
tration but by the number of active sites on the MNC. In this
perspective, the mesopore structure in the MNC undoubtedly
facilitates diffusion of the 4-NP ions and accelerates their ad-
sorption onto the active sites, which is linked to the superior
performance. Likewise, the MNC also shows an advantage over
microporous NG in terms of mass transportation, and thereby
the MNC exhibits a higher reaction rate. Therefore, the pore
size plays a vital role in catalytic activity by affecting mass
transportation, which is in accordance with the reported role
of the pore size on mass transport in proton-exchange-mem-
brane fuel cells.[25]
Figure 2. a) Optical photos of the color change during the reaction, b) the
reduction of 4-NP in aqueous solution recorded every 2.5 min by using
0.05 mg MNC, c) time-dependent conversion of 4-NP, d) the relationship be-
tween ln(Ct/C0) and reaction time (t), e) catalytic conversion of 4-NP at differ-
ent cycles, and f) the XPS spectrum of the N1s region for MNC.
In a comparative experiment, a pure mesoporous carbon
(MC) was prepared by direct pyrolysis of MOF-5 (Supporting In-
formation); it was proven to be inactive (Figure S11), though it
ChemCatChem 2015, 7, 3454 – 3459
www.chemcatchem.org
3456
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
ly 3.1 wt%, and the surface
Table 1. Textual properties and surface N content from XPS analysis.
N
content is approximately
[a]
[b]
[c]
Material
SBET
Vp
Dp
Elemental
XPS
Different N content [at%]
2.4 wt% (corresponding to
N content N content
2.1 at%), as estimated by XPS
analysis (Table 1), which is less
than the corresponding N con-
tent in the MNC. The N1s spec-
trum could also be deconvolut-
ed into three kinds of doped
N: graphitic (401.2 eV), pyrrodic
[m2gÀ1
]
[cm3gÀ1
]
[nm] [wt%]
[wt%/at%] Graphitic Pyridinic Pyrrodic Amine
MNC
NC
2269
1043
–
2817
615
2.813
0.536
–
2.097
0.540
4.0
nd
–
4.2
4.0
3.6
–
(3.2/2.8)
–
50.1
–
11.1
0
23.1
–
44.4
0
26.8
–
22.2
0
–
–
22.2
0
NG[d]
MC
14.7
–
(13.0/11.1)
(0/0)
MNC-p
3.1
(2.4/2.1)
57.3
21.1
21.6
–
[a] The BET surface area was obtained from the adsorption branches in the relative pressure range of 0.05 to
0.20. [b] The single-point adsorption total pore volume was taken at a relative pressure of 0.99. [c] The pore-
size distribution was calculated from the desorption branches by the Barret–Joyner–Halenda (BJH) method;
nd=not detected. [d] Data taken from Ref. [21].
(400.2 eV),
and
pyridinic
(398.3 eV) configurations (Fig-
ure S15) with compositions of
21.1, 21.6, and 57.3 at%, respec-
tively. It is clear that the propor-
does have a high surface area of 2817 m2gÀ1 and a mesopore
size of 4.2 nm (Figure S12 and Table 1). This result is indicative
of the critical role of N doping in this reaction. The MNC is
active because high positive spin and asymmetric charge den-
sity are introduced by N doping, which confers quasimetallic
properties onto the N-doped carbons. The total amount of N
in the MNC is 3.6 wt%, and the surface N content is approxi-
mately 3.2 wt% (corresponding to 2.8 at%) estimated by X-ray
photoelectron spectroscopy (XPS) analysis (Table 1), which is
much lower than the corresponding N content in NG. It is clear
that excessively doped N species cannot bring about high ac-
tivity, which is similar to oxidative catalysis[4b] but contrary to
N-doped electrochemical[3a] and basic catalysis.[5] To gain
deeper insight into the doped N status, the N1s binding ener-
gies of the MNC were investigated, and the corresponding
spectra were composed (Figure 2 f) and integrated (Table 1).
The N1s narrow scan spectrum was deconvoluted into three
types of doped N: graphitic (401.0 eV), pyrrodic (400.2 eV), and
pyridinic (398.8 eV) configurations[26] in proportions of 23.1,
26.8, and 50.1 at%, respectively. NG also shows four types of
tion of graphitic N was improved by 7.2% in the MNC-p rela-
tive to the graphitic N content in the MNC. It is speculated
that the parent NH2 moieties in IRMOF-3 can be facilely con-
verted into graphitic N species; whereas the C=N groups in
NZnMOF may undergo transformation from imine groups into
amine groups before their conversion into graphitic N, which
thus leaves fewer graphitic N species. Accordingly, the MNC-p
shows a larger rate constant (6.4”10À8 molLÀ1 sÀ1, see Fig-
ure S16 and Table S1) and a larger specific rate constant (12.7”
10À4 molLÀ1 À1 gÀ1) than the MNC and can be recycled many
s
times (Figure S17). On the basis of these results, it is clear that
the activity decreases with an increase in the elemental and
XPS N content over the three N-doped carbons (Figure 3a),
which suggests that only a small amount of graphitic N is
needed for this reaction. On the other hand, the activity in-
creases with an increase in the proportion of graphitic N spe-
cies (Figure 3b), which play a significant role in the adsorption
and activation of 4-NP. Therefore, the proportion of graphitic N
incorporated proves to be decisive to catalytic performance,
whereas a small amount of active sites are satisfied.
doped
N with different proportions: graphitic (401.4 eV,
11.1 at%), pyrrodic (400.2 eV, 22.2 at%), amine (399.5 eV,
22.2 at%), and pyridinic (398.6 eV, 44.4 at%) configurations.[21]
It is suggested that the activity is not dependent on the
amount of doped N but on the total amount of graphitic N
species that supply proper adsorption sites for the activation
of 4-NP during the reaction[21] and that are considered to be
the active sites. In this study, the higher active N content
(50.1 at%) can be attributed to the enhanced activity of the
MNC, and it is probable that pyrolysis at a high temperature
(9508C) facilitates the conversion of amine N species into
graphitic N species. If this is true, further improvement in the
graphitic N content in the N-doped mesoporous carbon could
bring about better activity. To verify this speculation, IRMOF-3
was chosen as a model, because it contains rich and easily
converted amine N species. In our experiment, as-synthesized
IRMOF-3 was directly pyrolyzed at 9508C to yield another mes-
oporous N-doped carbon, that is, MNC-p (Supporting Informa-
tion). XRD and N2 adsorption studies demonstrate that its
graphitic structure (Figure S13) and pore size are similar to
those of the MNC (Figure S14 and Table 1). Elemental analysis
revealed that the total N content in the MNC-p is approximate-
Figure 3. The relationship of specific rate constant versus a) elemental and
XPS N content and b) the proportion of graphitic N species.
In summary, a new type of mesoporous N-doped carbon
(MNC) was successfully developed in situ by a facile synthetic
methodology: direct pyrolysis of a properly rigid strut N-rich
metal–organic framework (MOF) at 9508C. High-temperature
treatment facilely created a low content of N but simultane-
ously formed a sufficient number of active N sites evenly dis-
persed on the mesoporous carbons. The resulting mesoporous
ChemCatChem 2015, 7, 3454 – 3459
www.chemcatchem.org
3457
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
N-doped carbons exhibited pseudo-zero-order kinetics toward
the reduction of 4-nitrophenol and show catalytic performance
that is superior to that of previously reported metal catalysts
and N-doped graphene. The excellent catalytic performance
can be ascribed to the ensemble effect of the elaborately de-
signed mesostructures and the doped N sites, which facilitate
diffusion of 4-nitrophenol and accelerate its adsorption and ac-
tivation on the active N sites. The successful design of highly
active MNCs gives a strong indication of the generality of this
method for the facile construction of various mesoporous N-
doped carbons through such a unique “one stone, three birds”
strategy to carbonize MOFs, to convert N species, and to va-
porize Zn metal in a single step. This unprecedented approach
not only opens another gateway for applications of N-contain-
ing MOF but also provides new insight for N-doping strategies.
21173269, 91127040), Beijing Natural Science Foundation
(2152025), the Science Foundation of China University of Petrole-
um, Beijing (2462013YJRC018), Ministry of Science and Technolo-
gy of China (2011BAK15B05), and Specialized Research Fund for
the Doctoral Program of Higher Education (20130007110003).
Keywords: doping · mesoporous materials · metal–organic
frameworks · pyrolysis · reduction
[1] a) M. Hamadanian, B. Khoshnevisan, F. K. Fotooh, Struct. Chem. 2011, 22,
1205–1211; b) L. Bai, Z. Zhou, Carbon 2007, 45, 2105–2110.
[2] a) Y. S. Yun, H. H. Park, H. J. Jin, Materials 2012, 5, 1258–1266; b) K. S.
Kim, S. J. Park, J. Electroanal. Chem. 2012, 673, 58–64; c) F. W. Ma, H.
Zhao, L. P. Sun, Q. Li, L. H. Huo, T. Xia, S. Gao, G. S. Pang, Z. Shi, S. H.
Feng, J. Mater. Chem. 2012, 22, 13464–13468.
[3] a) T. C. Nagaiah, A. Bordoloi, M. D. Sµnchez, M. Muhler, W. Schuhmann,
ChemSusChem 2012, 5, 637–641; b) Z. Y. Lin, M. K. Song, Y. Ding, Y. Liu,
M. L. Liu, C. P. Wong, Phys. Chem. Chem. Phys. 2012, 14, 3381–3387.
[4] a) K. Chizari, A. Deneuve, O. Ersen, I. Florea, Y. Liu, D. Edouard, I. Janow-
ska, D. Begin, C. Pham-Huu, ChemSusChem 2012, 5, 102–108; b) Y. J.
Gao, G. Hu, J. Zhong, Z. J. Shi, Y. Zhu, D. S. Su, J. G. Wang, X. H. Bao, D.
Ma, Angew. Chem. Int. Ed. 2013, 52, 2109–2113; Angew. Chem. 2013,
125, 2163–2167.
Experimental Section
Sample preparation
4-Aminobenzoic acid (57.6 g, 420 mmol) was dissolved in MeOH
(200 mL) containing formic acid (80 drops) as the catalyst. Then,
2,3-butanedione (17.6 mL, 200 mmol) was added dropwise, and
the resulting mixture was stirred at ambient temperature for 24 h.
The resulting pale-yellow precipitate was isolated by filtration and
was washed with cold methanol to afford acidic a-diimine ligand
L. Then, zinc nitrate hexahydrate (9.0 g, 30 mmol) and L (3.2 g,
10 mmol) were dissolved in DMF (50 mL) under constant agitation
under atmospheric conditions. Upon the formation of a clear solu-
tion, triethylamine (11 mL) was added dropwise, and the mixture
was stirred for another 1 h. The resulting dark-yellow solid was fil-
tered off, washed with DMF, and dried under vacuum to yield the
nonporous NZnMOF precursor. As-made NZnMOF was placed in
a quartz boat, flushing with N2 flow, and was further heated in
a horizontal tube furnace up to 9508C at a rate of 58CminÀ1 and
was maintained at this temperature for 2 h under N2 flow to yield
the mesoporous N-doped carbon (MNC).
[5] X. Jin, V. V. Balasubramanian, S. T. Selvan, D. P. Sawant, M. A. Chari, G. Q.
Lu, A. Vinu, Angew. Chem. Int. Ed. 2009, 48, 7884–7887; Angew. Chem.
2009, 121, 8024–8027.
[6] a) D. S. Su, J. Zhang, B. Frank, A. Thomas, X. C. Wang, J. Paraknowitsch,
R. Schlçgl, ChemSusChem 2010, 3, 169–180; b) C. H. Zhang, L. Fu, N.
Liu, M. H. Liu, Y. Y. Wang, Z. F. Liu, Adv. Mater. 2011, 23, 1020–1024.
[7] a) M. Terrones, P. Redlich, N. Grobert, S. Trasobares, W. K. Hsu, H. Ter-
rones, Y. Q. Zhu, J. P. Hare, C. L. Reeves, A. K. Cheetham, M. Ruhle, H. W.
Kroto, D. R. M. Walton, Adv. Mater. 1999, 11, 655–658; b) M. Terrones, H.
Terrones, N. Grobert, W. K. Hsu, Y. Q. Zhu, J. P. Hare, H. W. Kroto, D. R. M.
Walton, P. Kohler-Redlich, M. Ruhle, J. P. Zhang, A. K. Cheetham, Appl.
Phys. Lett. 1999, 75, 3932–3934.
[8] a) M. Glerup, M. Castignolles, M. Holzinger, G. Hug, A. Loiseau, P. Bernier,
Chem. Commun. 2003, 2542–2543; b) A. G. Kudashov, A. V. Okotrub,
L. G. Bulusheva, L. P. Asanov, Y. V. Shubin, N. F. Yudanov, L. I. Yudanova,
V. S. Danilovich, O. G. Abrosimov, J. Phys. Chem. B 2004, 108, 9048–
9053.
[9] a) R. Sen, B. C. Satishkumar, S. Govindaraj, K. R. Harikumar, M. K. Renga-
nathan, C. N. Rao, J. Mater. Chem. 1997, 7, 2335–2337; b) D. P. Kim, C. L.
Lin, T. Mihalisin, P. Heiney, M. M. Labes, Chem. Mater. 1991, 3, 686–692;
c) J. Liu, R. Czerw, D. L. Carroll, J. Mater. Res. 2005, 20, 538–543.
[10] L. J. Zhi, T. Gorelik, R. Friedlein, J. S. Wu, U. Kolb, W. R. Salaneck, K.
Mullen, Small 2005, 1, 798–801.
[11] a) T. P. Fellinger, F. HaschØ, P. Strasser, M. Antonietti, J. Am. Chem. Soc.
2012, 134, 4072–4075; b) Y. D. Xia, R. Mokaya, Chem. Mater. 2005, 17,
1553–1560; c) Y. D. Xia, R. Mokaya, Adv. Mater. 2004, 16, 1553–1558;
d) A. Vinu, K. Ariga, T. Mori, T. Nakanishi, S. Hishita, D. Golberg, Y. Bando,
Adv. Mater. 2005, 17, 1648–1652.
Catalytic test
The reduction of 4-nitrophenol (4-NP) was performed in a quartz
cuvette and was monitored by UV/Vis spectroscopy (754PC) at
room temperature. A solution of 4-NP in water (0.01m, 25 mL) was
mixed with certain content of the catalyst in sodium borohydride
aqueous solution (2.5 mL), and UV spectroscopy was employed to
in situ monitor the reduction by measuring the absorbance of the
solution at l=400 nm as a function of time at an interval of
2.5 min. After the reaction was finished, the mixture was centri-
fuged and washed with ethanol (3”) and water (3”). The resulting
catalyst was redispersed in aqueous 4-NP solution (0.01m, 25 mL)
and fresh NaBH4 solution (2.5 mL), and the test was repeated to
probe the stability. In this study, the linear relationships between
the conversion of 4-NP and the reaction time and between the ab-
sorbance of 4-NP and the reaction time were observed, and the fit-
ting showed R2 >0.99800 and a standard error smaller than 0.06.
[12] J. Wei, D. D. Zhou, Z. K. Sun, Y. H. Deng, Y. Y. Xia, D. Y. Zhao, Adv. Funct.
Mater. 2013, 23, 2322–2328.
[13] a) W. Chaikittisilp, K. Ariga, Y. Yamauchi, J. Mater. Chem. A 2013, 1, 14–
19; b) B. Liu, H. Shioyama, T. Akit, Q. Xu, J. Am. Chem. Soc. 2008, 130,
5390–5391; c) H. L. Jiang, B. Liu, Y. Q. Lan, K. Kuratani, T. Akita, H.
Shioyama, F. Q. Zong, Q. Xu, J. Am. Chem. Soc. 2011, 133, 11854–11857.
[14] a) S. J. Yang, T. Kim, J. H. Im, Y. S. Kim, K. Lee, H. Jung, C. R. Park, Chem.
Mater. 2012, 24, 464–470; b) N. L. Torad, M. Hu, Y. Kamachi, K. Takai, M.
Imura, M. Naitoa, Y. Yamauchi, Chem. Commun. 2013, 49, 2521–2523;
c) W. Chaikittisilp, M. Hu, H. J. Wang, H. S. Huang, T. Fujita, K. C. W. Wu,
L. C. Chen, Y. Yamauchi, K. Ariga, Chem. Commun. 2012, 48, 7259–7261;
d) S. Lim, K. Suh, Y. Kim, M. Y. Yoon, H. Park, D. N. Dybtsev, K. Kim, Chem.
Commun. 2012, 48, 7447–7449; e) H. B. Aiyappa, P. Pachfule, R. Bane-
rjee, S. Kurungot, Cryst. Growth Des. 2013, 13, 4195–4199; f) N. L. Torad,
M. Hu, S. Ishihara, H. Sukegawa, A. A. Belik, M. Imura, K. Ariga, Y. Sakka,
Y. Yamauchi, Small 2014, 10, 2096–2107; g) N. L. Torad, R. R. Salunkhe,
Acknowledgements
The authors gratefully acknowledge financial support from the
National Natural Science Foundation of China (21303229,
ChemCatChem 2015, 7, 3454 – 3459
www.chemcatchem.org
3458
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
Y. Li, H. Hamoudi, M. Imura, Y. Sakka, C. C. Hu, Y. Yamauchi, Chem. Eur. J.
2014, 20, 7895–7900.
[22] Y. H. Deng, Y. Cai, Z. K. Sun, J. Liu, C. Liu, J. Wei, W. Li, C. Liu, Y. Wang,
D. Y. Zhao, J. Am. Chem. Soc. 2010, 132, 8466–8473.
[23] a) S. Panigrahi, S. Basu, S. Praharaj, S. Pande, S. Jana, A. Pal, S. K. Ghosh,
T. Pal, J. Phys. Chem. C 2007, 111, 4596–4605; b) P. Veerakumar, M. Ve-
layudham, K. L. Lu, S. Rajagopal, Appl. Catal. A 2012, 439–440, 197–
205; c) S. Wunder, F. Polzer, Y. Lu, Y. Mei, M. Ballauff, J. Phys. Chem. C
2010, 114, 8814–8820; d) H. Li, J. Liao, Y. Du, T. You, W. Liao, L. Wen,
Chem. Commun. 2013, 49, 1768–1770.
[24] A. Corma, Chem. Rev. 1997, 97, 2373–2420.
[25] C. S. Kong, D. Y. Kim, H. K. Lee, Y. G. Shul, T. H. Lee, J. Power Sources
2002, 108, 185–191.
[15] Y. Yang, Y. Zhang, C. J. Sun, X. S. Li, W. Zhang, X. H. Ma, Y. Ren, X. Zhang,
ChemCatChem 2014, 6, 3084–3090.
[16] B. P. Buffin, A. Kundu, Inorg. Chem. Commun. 2003, 6, 680–684.
[17] P. P. Su, H. Xiao, J. Zhao, Y. Yao, Z. G. Shao, C. Li, Q. H. Yang, Chem. Sci.
2013, 4, 2941–2946.
[18] X. Huang, X. P. Liao, B. Shi, Green Chem. 2011, 13, 2801–2805.
[19] a) Z. D. Pozun, S. E. Rodenbusch, E. Keller, K. Tran, W. J. Tang, K. J. Ste-
venson, G. Henkelman, J. Phys. Chem. A J. Phys. Chem. B J. Phy. Chem. C
2013, 117, 7598–7604; b) Y. Y. Lin, Y. Qiao, Y. J. Wang, Y. Yan, J. B. Huang,
J. Mater. Chem. 2012, 22, 18314–18320; c) Y. Yang, Y. Ren, C. J. Sun, S. J.
Hao, Green Chem. 2014, 16, 2273–2280.
[26] H. L. Peng, Z. Y. Mo, S. J. Liao, H. G. Liang, L. J. Yang, F. Luo, H. Y. Song,
Y. L. Zhong, B. Q. Zhang, Sci. Rep. 2013, 1765.
[20] S. Gazi, R. Ananthakrishnan, Appl. Catal. B 2011, 105, 317–325.
[21] X. K. Kong, Z. Y. Sun, M. Chen, C. L. Chen, Q. W. Chen, Energy Environ.
Sci. 2013, 6, 3260–3266.
Received: July 21, 2015
Published online on September 23, 2015
ChemCatChem 2015, 7, 3454 – 3459
www.chemcatchem.org
3459
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim