Facile route fabrication of nickel based mesoporous carbons with high catalytic performance towards 4-nitrophenol reduction

Article abstract of DOI:10.1039/c3gc42121j

Novel nickel based mesoporous carbons are firstly in situ fabricated via pyrolysis of CTAB-chitosan-nickel supramolecular aggregates, which are pre-constructed by CTAB-directed self-assembly of 8-quinolinol modified chitosan and nickel acetate under basic conditions. This facile route fabrication method renders smart and homogeneously dispersed Ni nanoparticles (NPs) on the mesoporous carbonaceous framework without using any stabilizer and additional reductant, verified by high-energy X-ray diffraction, TEM, X-ray absorption fine structure, N₂ adsorption/desorption and Raman spectroscopy. Moreover, it is found that the morphology of Ni NPs, the textural property of carbonaceous supports, and the corresponding catalytic performance towards 4-nitrophenol reduction vary with the pyrolysis temperature. It is suggested that the nickel based mesoporous carbon pyrolyzed at 750 °C (Ni/MC-750) simultaneously possessing uniform spherical Ni NPs (24.5 nm) and bottle-neck mesopores exhibits the largest activity factor of 20.9 s^-1 g ^-1 of any nickel catalysts. the Partner Organisations 2014.

Full text of DOI:10.1039/c3gc42121j

Green Chemistry
View Article Online
View Journal | View Issue
PAPER
Facile route fabrication of nickel based
mesoporous carbons with high catalytic
performance towards 4-nitrophenol reduction†
Cite this: Green Chem., 2014, 16,
2273
Ying Yang,*a Yang Ren,b Chengjun Sunb and Shijie Haoa
Novel nickel based mesoporous carbons are firstly in situ fabricated via pyrolysis of CTAB-chitosan-nickel
supramolecular aggregates, which are pre-constructed by CTAB-directed self-assembly of 8-quinolinol
modified chitosan and nickel acetate under basic conditions. This facile route fabrication method renders
smart and homogeneously dispersed Ni nanoparticles (NPs) on the mesoporous carbonaceous frame-
work without using any stabilizer and additional reductant, verified by high-energy X-ray diffraction, TEM,
X-ray absorption fine structure, N2 adsorption/desorption and Raman spectroscopy. Moreover, it is found
that the morphology of Ni NPs, the textural property of carbonaceous supports, and the corresponding
catalytic performance towards 4-nitrophenol reduction vary with the pyrolysis temperature. It is
suggested that the nickel based mesoporous carbon pyrolyzed at 750 °C (Ni/MC-750) simultaneously
possessing uniform spherical Ni NPs (24.5 nm) and bottle-neck mesopores exhibits the largest activity
factor of 20.9 s−1 g−1 of any nickel catalysts.
Received 13th October 2013,
Accepted 8th January 2014
DOI: 10.1039/c3gc42121j
www.rsc.org/greenchem
by wetness impregnation of nickel ions and reduction under
an inert atmosphere.16 This tedious post-synthetic method
1. Introduction
Nickel nanoparticles (Ni NPs) have received considerable atten- renders instable catalysts with unevenly dispersed Ni NPs on
tion recently because of their low cost and remarkable catalytic the external surface or near pore mouths, resulting in a signifi-
performances in hydrogenation of nitrobenzene and nitro- cant loss of reactivity during recycling because of the weak
phenol, reduction of oxygen, and oxidation of olefins.1–8 To interaction between Ni NPs and the MC support.17 To replace
facilitate catalyst recovery, Ni NPs are commonly dispersed such conventional “low efficient” preparations, pyrolysis of
onto solid matrices to prepare heterogeneous nickel catalysts. metal coordination polymers or metal organic frameworks
Thus various materials have been used as supporting matrices, under an inert atmosphere is proved to be step-economic to
including silica, alumina, titania, zirconia, magnesia, carbon, in situ construct homogeneously dispersed metal NPs firmly
etc.9–14 Amongst them, porous carbonaceous supports are the attached inside the carbonaceous matrix,18,19 since the metal
most frequently used, and proved to be superior to oxide car- NPs are in situ reduced and deposited onto the carbonaceous
riers, due to their chemical inertness and excellent stability matrix formed almost simultaneously during pyrolysis.
under both acid and basic conditions. Mesoporous carbons However, the resulting carbonaceous frameworks are always
(MC) are much favored since they offer great advantages over disordered and lack in uniform pore size distributions, thus
conventional activated carbons (AC) owing to their well- blocking mass transportation. Despite continuous efforts, to
controlled mesopore structures which are favorable to transpor- fabricate the homogeneously dispersed Ni NPs firmly attached
tation of large molecules.15 Recent advances in the fabrication on MC via a step-economic method remains a challenge.
of nickel based mesoporous carbons focus on the synthesis of
From the latest research on the synthesis of MC, we know
MC by a conventional hard-templating approach first, followed that MC can be facilely fabricated via direct pyrolysis of supra-
molecular aggregates constructed by self-assembly of block
copolymer templates and polymerizable precursors.20–23
aState Key Laboratory of Heavy Oil Processing, China University of Petroleum,
Changping, Beijing 102249, China. E-mail: catalyticscience@163.com;
Tel: +86-10-89734979
Inspired by this methodology, we hypothesize that if the poly-
merizable precursors were substituted by nickel coordination
polymers, homogeneously dispersed Ni NPs may be in situ fab-
ricated into the MC matrix. However, the present polymeriz-
able precursors, like widely studied phenolic resin and its
derivatives, are hard to chelate metal ions to form metal
bX-ray Science Division, Argonne National Laboratory, 9700 S. Cass Ave., Argonne,
Illinois 60439, USA
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c3gc42121j
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 2273–2280 | 2273

View Article Online
Paper
Green Chemistry
coordination polymers due to the absence of chelating sites. It
is known that chitosan is a very abundant biodegradable and
biocompatible polysaccharide obtained by the alkaline de-
2. Experimental
2.1. Chemicals
acetylation of chitin,24 and possesses rich hydroxyl and amine All chemicals were of analytical grade and used as received
moieties with strong affinity for metal ions.25 Therefore, it is without any further purification. Cetyltrimethylammonium
speculated that chitosan may be a suitable chelating agent for (CTAB), chitosan, 8-quinolinol, nickel acetate tetrahydrate
constructing chitosan-nickel coordination polymers.
(Ni(CH3COO)2·4H2O), concentrated hydrochloric acid, 37% for-
We herein report novel nickel based mesoporous carbons maldehyde, 4-nitrophenol, sodium borohydride, triethylamine,
in situ fabricated by direct pyrolysis of CTAB-chitosan-nickel acetic acid (CH3COOH), ether, aqua ammonia (25 wt%), zinc
supramolecular aggregates, constructed via CTAB-directed self- chloride hexahydrate (ZnCl2·6H2O), acetone and ethanol were
assembly of 8-quinolinol modified chitosan (CTS-HQ) and commercially available.
nickel acetate under basic conditions. In this study, chitosan
was firstly modified by 5-chloromethyl-8-quinolinol to enhance
2.2. Preparation
its chelation with nickel ions and interaction with surfactant The synthetic procedures for nickel based mesoporous
CTAB via electronic attraction, facilitating the formation of carbons are depicted in Scheme 1. Chitosan was first modified
CTAB-chitosan-nickel supramolecular aggregates (or precursor by 5-chloromethyl-8-quinolinol to afford 8-quinolinol modified
composites). Owing to the difference in chemical and thermal chitosan, CTS-HQ, involving a two-step chemical transform-
stability between the chitosan and surfactant CTAB, as well as ation from 8-quinolinol (see ESI and Fig. S1–5, ESI†). Then the
the reducibility of carbons, the following pyrolysis is a unique precursor composite, Ni/CTS-P, was prepared by CTAB-directed
“one stone, three birds” strategy to remove CTAB, carbonize self-assembly of CTS-HQ and Ni(CH3COO)2·4H2O under basic
CTS-HQ and reduce nickel ions in a single step. The resulting medium. The molar ratio of the precursor gels used in the pre-
nickel based mesoporous carbons with homogeneously dis- ferred preparation is 1CTS-HQ : 0.5Ni(CH3COO)2·4H2O : 0.12
persed Ni NPs on the mesoporous carbonaceous framework CTAB : 8.0NH3 (25 wt%) : 114 H2O : 10 EtOH. In a typical syn-
are confirmed by various characterization techniques, and thesis, 0.5 g CTAB was dissolved in 18.5 ml of water, and
screened as catalysts with a large activity factor of 20.9 s−1 g−1 7.2 ml EtOH combined with 6.8 ml NH3·H2O were added and
towards 4-nitrophenol reduction.
stirred for 10 min. Then 1.6 g of CTS-HQ combined with 0.6 g
Scheme 1 Schematic illustration of nickel based mesoporous carbon preparation. (a) 5-Chloromethyl-8-quinolinol hydrochloride (1C·HCl) and
8-quinolinol modified chitosan (CTS-HQ) preparation. (b) Precursor composite Ni/CTS-P synthesized via CTAB-directed self-assembly was
pyrolyzed to yield Ni/MC-t.
2274 | Green Chem., 2014, 16, 2273–2280
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
of Ni(CH3COO)2·4H2O was added and the resulting green were injected from a calibrated on-line sampling valve. H2
mixture was stirred at room temperature for another 2 h, and adsorption was assumed to be complete after three successive
then transferred into a polypropylene bottle and reacted at peaks showed the same peak areas.
100 °C under static conditions for 1 d. The precursor compo-
2.4. Catalytic reduction of 4-nitrophenol
site was recovered by filtration, dried overnight, and pyrolyzed
in a tubular furnace under a N2 atmosphere for 2 h. The The reduction of 4-nitrophenol (4-NP) was carried out in a
heating rate was 2 °C min−1 below 250 °C and 5 °C min−1 quartz cuvette and monitored using UV-vis spectroscopy
above 250 °C. Samples pyrolyzed at 550, 750 and 950 °C corres-
pond to Ni/MC-550, Ni/MC-750 and Ni/MC-950, respectively.
(Lambda 650s) at room temperature. For comparison, the
aqueous 4-NP solution (0.01 M) was prepared and measured
prior to monitoring the change of absorption. Then a total of
25 μl of aqueous 4-NP solution was mixed with 2.5 ml of a
2.3. Characterization
N2 adsorption/desorption isotherms were recorded at 77 K fresh NaBH4 (0.01 M) solution. Subsequently, a given amount
with a Micromeritics Tristar II 3020. Before measurements, the of nickel catalyst was added to start the reaction, and the UV
samples were outgassed at 300 °C for 3 h. The specific surface
spectrometry was employed to in situ monitor the reduction by
area was calculated by the Brunauer–Emmett–Teller (BET) measuring the absorbance of the solution at 400 nm as a func-
method and the pore size distributions were measured by tion of time at intervals of 1.25 min. After the reaction was fin-
Barrett–Joyner–Halenda (BJH) analysis from the desorption
ished, the mixture was centrifuged, and washed with ethanol
branch of the isotherms. Morphology and microstructure were and water three times. The resulting catalyst was re-dispersed
analyzed using a FEI Tecnai G2 F20 transmission electron in 25 μl of aqueous 4-NP solution and 2.5 ml of fresh NaBH4
microscope equipped with an energy dispersive X-ray spectro-
scopic analyzer operated at a voltage of 200 kV. Samples were
sonicated for 5 min in EtOH, one drop of the suspended
sample was dripped on a holey carbon film supported on a
300 mesh copper grid. Synchrotron X-ray diffraction measure-
ments were performed at the 11-ID-C beamline of the
Advanced Photon Source at Argonne National Laboratory.
High-energy X-rays of 115 keV energy and 0.6 mm × 0.6 mm
beam size were used to obtain two-dimensional (2D) diffrac-
tion patterns in the transmission geometry using a Perkin-
Elmer large area detector placed at 1.6 m from the sample.
Small-angle X-ray scattering (SAXS) measurements were per-
formed at the 12-ID-C station at the Advanced Photon Source
(APS, Argonne National Laboratory, Argonne, IL). The X-ray
energy was 12 keV, which corresponds to a wavelength of
1.0332 Å. The sample-to-detector distance was about 2 m.
X-ray absorption fine structure (XAFS) was carried out on a
beamline at the 20-ID and 20-BM at Advanced Photo
Source (APS) at Argonne National Laboratory. The XAFS data
were obtained in the transmission mode at the Ni K-edge
(8333.0 eV). For the Ni K-edge scan, a Ni foil was placed
between the transmission and reference ion chambers.
The XAFS data were processed using the Athena software for
background removal, post-edge normalization, and XANES
analysis. The extended X-ray absorption fine structure (EXAFS)
data were analyzed using the Artemis software, which
implemented FEFF (ESI†). Raman spectra were recorded with
a HORIBA Jobin Yvon HR800 with a microscope attachment.
The laser wavelength of 633 nm was focused using a diffrac-
tion limited spot, and the scan time was 2 s for each sample.
Metal content was estimated by inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analysis conducted on
a Perkin Elmer emission spectrometer. The dispersion of Ni
was checked by H2 chemisorption and carried out on a Micro-
meritics AutoChem II 2920 instrument. The sample (0.2 g) was
firstly pretreated in argon (30 ml min−1) at 250 °C for 1 h and
solution, and the test was repeated to probe the stability.
3. Results and discussion
3.1. Characterization
Fig. 1 shows the high-energy X-ray diffraction patterns of
various Ni-containing samples. As expected, the precursor
composite Ni/CTS-P exhibits no diffractions as compared to
nickel acetate, indicating the coordination of nickel ions with
CTS-HQ.26,27 Upon pyrolysis, all Ni/MC-t (t, pyrolysis tempera-
ture) samples display characteristics of fcc-structured Ni
(JCPDS file 04-0805) at (111), (200), (220), (311) and (222) diffr-
actions, indicating the formation of Ni nanocrystallites.28,29
However, the Ni/MC-750 catalyst exhibits the strongest diffrac-
tion intensity, suggesting most Ni nanocrystals formed when
pyrolyzed at 750 °C. The small angle X-ray scattering pattern
for Ni/MC-750 shows three weak peaks at q values of 0.212,
0.324 and 0.440 with a ratio of 1 : 31/2 : 2 (Fig. S6, ESI†), associ-
ated with 10, 11 and 20 reflections of low 2D hexagonal sym-
metry with p6m space group.30 A TEM image of Ni/MC-550
Fig. 1 High-energy X-ray diffraction patterns of (a) Ni(CH3COO)·4H2O,
the catalyst was cooled to room temperature and H2 pulses (b) Ni/CTS-P, (c) Ni/MC-550, (d) Ni/MC-750 and (e) Ni/MC-950.
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 2273–2280 | 2275

View Article Online
Paper
Green Chemistry
Fig. 2 TEM images and the corresponding particle size distributions of (a, d) Ni/MC-550, (b, e) Ni/MC-750 and (c, f) Ni/MC-950, and the selected
area electron diffraction (g), single electron microdiffraction (h) and high-resolution TEM (i, with its FFT pattern, inset) images of Ni/MC-750.
shows some mesoporous carbon nanotubes with homo-
geneously dispersed spherical NPs centered at ca. 23.6 nm
(Fig. 2a and d). Ni/MC-750 exhibits slightly larger NPs
embedded into the mesoporous carbons with an average dia-
meter of 24.5 nm (Fig. 2b and e). However, Ni/MC-950 does
not inherit the spherical shapes of pure Ni NPs, but rather dis-
plays irregularly congregated NPs with increased average dia-
meter (Fig. 2c and f). Selected area electron diffraction (SAED)
pattern of Ni/MC-750 exhibits diffraction rings with fcc poly-
Fig. 3 (A) Ni K-edge XANES and (B) the corresponding Fourier trans-
crystalline (Fig. 2g), and the electron microdiffraction of single
formed EXAFS spectra for (a) Ni/CTS-P, (b) Ni/MC-550, (c) Ni/MC-750,
(d) Ni/MC-950 and (e) Ni foil.
ˉ
Ni NP demonstrates the fm3m symmetrical structure (Fig. 2h).
The HRTEM image combined with the FFT pattern for Ni/
MC-750 displays clear lattice fringes throughout the whole par-
ticle, and the fringes in the (111) direction are 0.203 nm
(Fig. 2i), confirming XRD findings.
Nickel specific XAFS was carried out to explore the elec-
tronic structure and the local structure ranged from 1 to 3 Å.
As illustrated in Fig. 3, compared to Ni/CTS-P, the Ni/MC-t
series show decreased white line intensity along with the
newly present pre-edge peak at ca. 8320 eV, suggesting that the
Ni(+2) species are mostly reduced.31,32 In the corresponding k
space, Ni/MC-t series show clear oscillations at a higher k
region of k > 8 Å−1 as compared to Ni/CTS-P (Fig. S7, ESI†),
indicating the dominance of high Z backscatters, which would
be Ni in our system. Correspondingly, the Fourier transformed
EXAFS data (r space) exhibit one prominent peak at ca. 2.2 Å
from the Ni–Ni contributions for Ni/MC-t series, different from
2276 | Green Chem., 2014, 16, 2273–2280
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
Table 1 Best fit parameters obtained from the analysis of the Ni K-edge EXAFS spectraa
Materials
Shell
Fitting range Δr [Å]
CN
4.8
7.4
7.7
R [Å]
σ2 [Å2]
ΔE [eV]
R factor (%)
Ni/MC-550
Ni/MC-750
Ni/MC-950
Ni foil
Ni–Ni
Ni–Ni
Ni–Ni
Ni–Ni
1.25–2.95
1.00–2.94
1.18–2.95
—
2.49
2.48
2.48
2.48
0.00560
0.00584
0.00586
—
5.64
5.22
4.94
—
1.841
0.014
0.295
—
12
a CN = coordination number, R = coordination distance, σ2 = Debye–Waller factor, and ΔE0 = inner potential correction.
the dominated Ni–O/C pairs at ca. 1.6 Å for Ni/CTS-P. On the
N2 adsorption reveals that all Ni/MC-t samples exhibit a
other hand, the Ni–Ni peak intensity, proportional to the type IV isotherm with a sharp inflection step at P/P0 ranging
coordination number, varies with the pyrolysis temperature. from 0.25 to 0.35 (Fig. 4A), characteristic of mesoporous
Owing to the disordering in the higher shells, only the first materials.36,37 However, different from the H4-type hysteresis
shell ranging from 1.0 to 3.2 Å was curve-fitted. As illustrated loop in Ni/MC-550, Ni/MC-750 and Ni/MC-950 exhibit H2-type
in Table 1, the Ni–Ni coordination number increases from 4.8 hysteresis loops in the medium P/P0 range, corresponding to
to 7.7 as the pyrolysis temperature was elevated from 550 to bottle-neck pores.38 It is observed that the surface area and the
950 °C, indicating larger Ni NPs formed. However, all Ni/MC-t pore volume decrease with an increase of the pyrolysis temp-
samples possess smaller coordination numbers than that of a erature (Table 2). The Smeso/Smicro and Vmeso/Vmicro ratios
Ni foil (CN = 12), suggesting that most Ni NPs are coordina- increase gradually from 0.27 to 0.47 and from 1.62 to 2.24,
tively unsaturated.
respectively, suggesting that more mesoporous structures are
The FT-IR spectrum of Ni/CTS-P shows CH2 stretches at created when elevating the pyrolysis temperature from 550 to
2925 and 2855 cm−1 from the surfactant CTAB, and character- 950 °C. All Ni/MC-t samples show pore sizes around 4.30 nm
istic phenyl and pyridyl vibrations between 1600 and (Fig. 4B), suggesting that Ni NPs are mainly distributed on the
1300 cm−1 (Fig. S8, ESI†), suggesting that CTS-HQ has been carbonaceous framework.
incorporated into the precursor composite via CTAB-directed
The local structure of carbonaceous supports was investi-
self-assembly.33–35 However, these peaks disappear for Ni/ gated by Raman spectroscopy. As illustrated in Fig. 5, Ni/MC-t
MC-750 and Ni/MC-950 after the simultaneous CTAB removal samples exhibit D and G bands centered at ca. 1355 and
and CTS-HQ carbonization, though there is some residue for 1585 cm−1, respectively, arising from the disordered carbon
Ni/MC-550.
and ordered graphene sheet.39 The Ni/MC-750 shows the
largest IG/ID (relative ratio of the G band to the D band) value
of 1.08 among the Ni/MC-t series (0.71 for Ni/MC-550 and 0.88
for Ni/MC-550), owing to the most developed graphene sheet
formed when pyrolyzed at 750 °C.
The physical properties of the catalysts such as Ni content,
dispersion and crystallite size for different Ni/MC-t catalysts
calculated from ICP-AES and H2 irreversible adsorption are
shown in Table 3. It is clear that the H2 uptake (Fig. S9, ESI†)
amount decreases sharply from 48.3 to 11.7 μmol g−1 cat with
a decline in Ni loading from 1.49 to 0.33 wt%. However, the Ni
dispersion does not follow this trend, and the Ni/MC-750 cata-
lyst shows the highest dispersion of 4.7% of any Ni/MC-t cata-
lysts. On the other hand, the average Ni crystallite diameter
Fig. 4 (A) N2 adsorption/desorption isotherms and (B) BJH pore size
distributions of (a) Ni/MC-550, (b) Ni/MC-750 and (c) Ni/MC-950.
Table 2 Characteristics of Ni/MC-t series, BET surface area, SBET (m2 g−1); external surface area, Sext (m2 g−1); micropore surface area, Smicro
(m2 g−1); pore volume, Vp (cm3 g−1); micropore volume, Vmicro (cm3 g−1) and pore diameter, Dp (nm)
SBET a (m2 g−1
)
Sext (m2 g−1
)
Smicro (m2 g−1
)
Smeso/Smicro
Vp (cm3 g−1
)
Vmicro c (cm3 g−1
)
Vmeso/Vmicro
Dp e (nm)
b
d
Materials
Ni/MC-550
Ni/MC-750
Ni/MC-950
307.3
221.9
177.2
66.0
60.4
57.0
241.3
161.5
120.2
0.27
0.37
0.47
0.294
0.203
0.165
0.112
0.070
0.051
1.62
1.90
2.24
4.30
4.27
4.40
a The BET surface areas are obtained from the adsorption branches in the relative pressure range of 0.05–0.20. b Mesopore surface areas are
determined by subtracting the micropore surface areas from the BET surface areas. c Microporous volumes are calculated by the t-plot method.
d Mesopore volumes are determined by subtracting the micropore volume from the total pore volume. e The pore size distributions are calculated
from the desorption branches by the Barrett–Joyner–Halenda (BJH) method.
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 2273–2280 | 2277

View Article Online
Paper
Green Chemistry
estimated by H2 chemisorption shows a slight deviation from
the TEM results.
3.2. Catalytic properties
It is known that 4-aminophenol (4-AP) is very useful and
important in many applications including analgesic and anti-
pyretic drugs, photographic developer, corrosion inhibitor and
anticorrosion-lubricant, etc.41 The reduction of 4-NP to 4-AP
has been extensively used as a benchmark system to evaluate
the catalytic activity of metal NPs. Metal NPs can effectively
catalyze the reduction of nitro compounds by acting as an elec-
tronic relay system, wherein the electron transfer takes place
−
from donor BH4 to acceptor nitro groups.42,43 As shown in
Fig. 6a, the adsorption peak of 4-NP was red-shifted from 317
to 400 nm immediately upon the addition of NaBH4 solution
which corresponds to a color change from light yellow to
yellow green, due to the formation of the 4-nitrophenolate ion
under alkaline conditions.44 In the absence of catalyst, the
adsorption peak at 400 nm remained unaltered even for a
couple of days. By contrast, addition of a suitable amount of
catalyst into the solution caused a decolorization of the
4-nitrophenolate solution, and meanwhile the peak intensity
at 400 nm successively decreased with two new adsorption
peaks appeared at 235 and 295 nm, suggesting the formation
of 4-AP.45 The UV-vis spectra show an isosbestic point at
313 nm (Fig. 6b–d), suggesting that the catalytic reduction of
4-NP gives only 4-AP without a by-product.46 Fig. 6b–d illus-
trates the absorbance vs. reaction time plots towards 4-NP
reduction using different Ni/MC-t catalysts. We found that a
delay time of 1.25 min at the beginning of the catalytic
reduction exists. The short induction period may correlate to
Fig. 5 Raman spectra and their fitted patterns for (a) Ni/MC-550,
(b) Ni/MC-750 and (c) Ni/MC-950.
Table 3 H2 adsorption properties and reaction data over Ni/MC-t
catalysts
Ni loadinga H2 uptake
(wt%)
Dispersionb
TOFd
(s−1
c
Materials
(μmol g−1 cat) (%)
ds
)
Ni/MC-550 1.49
Ni/MC-750 0.37
Ni/MC-950 0.33
48.3
14.9
11.7
3.8
4.7
4.2
25.6 0.01
20.8 1.44
23.2 0.39
a Estimated by ICP-AES. b The Ni dispersion was calculated based on
%D = 1.17X/Wf (literature40). c The average Ni crystallite diameter was
calculated by ds = 971/%D (literature40). d Reaction conditions: 0.01 M
4-NP, 25 μl; 0.01 M NaBH4, 2.5 ml and duration, 1.25 min. TOF, s−1
:
(turnover frequency) moles of 4-NP converted per mole surface Ni per
second.
Fig. 6 (a) UV-vis spectra of 4-nitrophenol before and after adding NaBH4 solution, (b) the reduction of 4-nitrophenol in aqueous solution recorded
every 1.25 min using 3.0 mg Ni/MC-550, (b) the reduction of 4-nitrophenol in aqueous solution recorded every 1.25 min using 0.3 mg Ni/MC-750,
(c) the reduction of 4-nitrophenol in aqueous solution recorded every 1.25 min using 0.7 mg Ni/MC-950, (e) the relationship between ln(Ct/C0) and
reaction time (t) and (f) the recyclability of the Ni/MC-750.
2278 | Green Chem., 2014, 16, 2273–2280
This journal is © The Royal Society of Chemistry 2014

View Article Online
Green Chemistry
Paper
the coordinatively unsaturated surface Ni atoms, which promote dispersed nickel complex in the precursor composite Ni/CTS-P
the chemisorption of 4-nitrophenolate ions and thereby is the key to realize the homogeneously distributed Ni NPs on
accelerate the reaction. The reduction was completely finished the mesoporous carbonaceous framework after pyrolysis, con-
within ca. 10 min over 3 mg Ni/MC-550, 0.3 mg Ni/MC-750 and firmed by various characterization techniques. All nickel based
0.7 mg Ni/MC-950. Considering that the reductant concen- mesoporous carbons are active for the catalytic reduction of 4-
tration is much higher than that of 4-NP (CNaBN /C4-NP = 100) NP, but their catalytic performances vary with the morphology
4
in the reaction mixture, the pseudo-first-order rate kinetics of Ni NPs and the textural property of carbonaceous supports
with respect to 4-NP concentration could be used to evaluate created under different pyrolysis temperatures. It is revealed
the catalytic rate. The reaction kinetics can be described as that the Ni/MC-750 catalyst simultaneously possessing
−ln(Ct/C0) = kt, where k is the rate constant at a given tempera- uniform spherical Ni NPs (24.5 nm) and bottle-neck meso-
ture and t is the reaction time. C0 and Ct are the 4-NP concen- pores exhibits the largest activity factor of 20.9 s−1 g−1 and out-
tration at the beginning and at time t, respectively. As performs any nickel catalysts reported. Recyclability test
expected, a good linear correlation of ln(Ct/C0) vs. reaction demonstrates that Ni/MC-750 is stable and can be recycled.
time t was obtained (Fig. 6e), whereby the kinetic rate constant Therefore, it should be noted that the methodology demon-
k was estimated to be 1.51 × 10−3, 6.26 × 10−3 and 2.40 × 10−3 strated in this study may be extended to the preparation of
s−1 for Ni/MC-550, Ni/MC-750 and Ni/MC-950. To compare other metal based mesoporous carbons, since CTS-HQ can
different catalysts, we calculated the ratio of rate constant K chelate with many other metal species, such as Fe, Co, Cu, Ru
over total weight of nickel catalyst, where K = k/m. Thus the and Pt.
activity factor K was calculated to be 0.5, 20.9 and 3.4 s−1 g−1
for Ni/MC-550, Ni/MC-750 and Ni/MC-950, respectively. It is
clear that Ni/MC-750 shows the largest activity factor (in agree-
ment with the comparison of TOF values listed in Table 3),
Acknowledgements
which is about 22 times larger than the previously reported
PNC/XSD facilities at the Advanced Photon Source, and
ratio for NiCo2 alloys (0.95 s−1 g−1),47 and ca. 9 times more
research at these facilities, are supported by the U.S. Depart-
than that for the reported Ni NPs (7 nm) in a spherical poly-
ment of Energy – Basic Energy Sciences, the Canadian Light
electrolyte brush nanoreactor (2.38 s−1 g−1).48 The best per-
Source and its funding partners, the University of Washington,
formance of Ni/MC-750 arises from the combined uniform
and the Advanced Photon Source. Use of the Advanced Photon
spherical Ni NPs and bottle-neck mesopores with enhanced
Source, an Office of Science User Facility operated for the
graphene structure facilitating mass transformation. To
U.S. Department of Energy (DOE) Office of Science by Argonne
explore whether there is leaching during reactions, we per-
National Laboratory, was supported by the U.S. DOE under
formed a filtration to remove the Ni/MC-750 catalyst from the
Contract No. DE-AC02-06CH11357. Financial support for this
4-NP solution when the reaction proceeded for 3 min. Follow-
research work from the National Natural Science Foundation
ing that, the filtrate was continuatively stirred and monitored
of China (21303229) and the Science Foundation of China
by UV-vis spectroscopy at regular intervals. It is found that the
University of Petroleum, Beijing (2462013YJRC018) is also
peak height at 400 nm remains nearly unchanged, suggesting
acknowledged.
that no leaching occurred. To check the reusability of nickel
catalysts, and to avoid any possible saturation effect, when
ca. 40% 4-NP was converted, the representative Ni/MC-750 was
recovered from the reaction mixture by simple filtration and
washing with water, and reused under the same conditions as
Notes and references
for the initial cycle. As shown in Fig. 6f, Ni/MC-750 can be
successfully recycled and reused in 6 successive reactions with
a conversion of 37.0–42.0%. Moreover, TEM analysis of the
spent Ni/MC-750 catalyst revealed that the dispersion and size
distribution of Ni NPs did not show any obvious change after
six runs (Fig. S10, ESI†) compared with the fresh catalyst
(Fig. 2b), suggesting the high stability of the Ni/MC-750
catalyst.
1 P. Lu, T. Teranishi, K. Asakura, M. Miyake and N. Toshima,
J. Phys. Chem. B, 1999, 103, 9673.
2 Y. Du, H. Chen, R. Chen and N. Xu, Appl. Catal., A, 2004,
277, 259.
3 A. Wang, H. Yin, H. Lu, J. Xue, M. Ren and T. Jiang, Lang-
muir, 2009, 25, 12736.
4 H. Liu, J. Deng and W. Li, Catal. Lett., 2010, 137, 261.
5 Y. Du and R. Chen, Chem. Biochem. Eng. Q., 2007, 21, 251.
6 H. Lu, H. Yin, Y. Liu, T. Jiang and L. Yu, Catal. Commun.,
2008, 10, 313.
7 W. M. Millán and M. A. Smit, J. Appl. Polym. Sci., 2009, 112,
2959.
4. Conclusions
In summary, novel nickel based mesoporous carbons have
been facilely fabricated via direct pyrolysis of surfactant-
directed CTAB-chitosan-nickel supramolecular aggregates
under different temperatures. Construction of an evenly
8 M. Islam, D. Hossain, P. Mondal, A. S. Roy, S. Mondal and
M. Mobarak, Bull. Korean Chem. Soc., 2010, 31, 3765.
9 X. C. Wang, L. Q. Meng, F. Wu, Y. J. Jiang, L. Wang and
X. D. Mu, Green Chem., 2012, 14, 758.
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 2273–2280 | 2279

View Article Online
Paper
Green Chemistry
10 J. F. Pang, A. Q. Wang, M. Y. Zheng, Y. H. Zhang, 28 C. D. Liang, Z. J. Li and S. Dai, Angew. Chem., Int. Ed., 2008,
Y. Q. Huang, X. W. Chen and T. Zhang, Green Chem., 2012,
14, 614.
47, 3696.
29 Y. Wan and D. Y. Zhao, Chem. Rev., 2007, 107, 2821.
11 S. Schimpf, C. Louis and P. Claus, Appl. Catal., A, 2007, 30 Y. R. Liu, J. Mater. Sci., 2009, 44, 3600.
318, 45.
31 L. S. Sarma, C.-H. Chen, S. M. S. Kumar, G.-R. Wang,
12 A. Shrotri, A. Kanksale, J. N. Beltramini, H. Gurav and
S. V. Chilukuri, Catal. Sci. Technol., 2012, 2, 1852.
13 E. van Ryneveld, A. S. Mahomed, P. S. van Heerden,
S.-C. Yen, D.-G. Liu, H.-S. Sheu, K.-L. Yu, M.-T. Tang,
J.-F. Lee, C. Bock, K.-H. Chen and B.-J. Hwang, Langmuir,
2007, 23, 5802.
M. J. Green and H. B. Friedrich, Green Chem., 2011, 13, 32 O. M. Daniel, A. DeLaRiva, E. L. Kunkes, A. K. Datye,
1819. J. A. Dumesic and R. J. Davis, ChemCatChem, 2010, 2, 1107.
14 M. Banu, S. Sivasanker, T. M. Sankaranarayanan and 33 J. M. R. Gallo, H. O. Pastore and U. Schuchardt, J. Catal.,
P. Venuvanalingam, Catal. Commun., 2011, 12, 673. 2006, 243, 57.
15 J. F. Pang, A. Q. Wang, M. Y. Zheng, Y. H. Zhang, 34 M. R. Maurya and S. Sikarwar, J. Mol. Catal. A: Chem., 2007,
Y. Q. Huang, X. W. Chen and T. Zhang, Green Chem., 2012,
14, 614.
16 P. F. Fulvio, C. D. Liang, S. Dai and M. Jaroniec,
Eur. J. Inorg. Chem., 2009, 605.
263, 175.
35 M. R. Maurya, A. K. Chandrakar and S. Chand, J. Mol.
Catal. A: Chem., 2007, 270, 225.
36 A. Corma, Chem. Rev., 1997, 97, 2373.
17 X. Y. Li, X. Wang, S. Y. Song, D. P. Liu and H. J. Zhang, 37 P. A. Robles-Dutenhefner, K. A. D. Rocha, E. M. B. Sousa
Chem.–Eur. J., 2012, 18, 7601. and E. V. Gusevskaya, J. Catal., 2009, 265, 72.
18 Z. L. Li, J. H. Liu, Z. W. Huang, Y. Yang, C. G. Xia and 38 M. Kruk and M. Jaroniec, Chem. Mater., 2001, 13, 3169.
F. W. Li, ACS Catal., 2013, 3, 839.
19 S. Q. Ma, G. A. Goenaga, A. V. Call and D.-J. Liu, Chem.–
Eur. J., 2011, 17, 2063.
39 W. Chaikittisilp, M. Hu, H. J. Wang, H.-S. Huang, T. Fujita,
K. C.-W. Wu, L.-C. Chen, Y. Yamauchi and K. Ariga, Chem.
Commun., 2012, 48, 7259.
20 T.-Y. Ma, L. Liu and Z.-Y. Yuan, Chem. Soc. Rev., 2013, 42, 40 D. G. Mustard and C. H. Bartholomew, J. Catal., 1981, 67,
3977. 186.
21 Y. Wan, Y. F. Shi and D. Y. Zhao, Chem. Mater., 2008, 20, 41 G. H. Chang, Y. L. Luo, W. B. Lu, X. Y. Qin, A. M. Asiri,
932.
A. O. Al-Youbibc and X. P. Sun, Catal. Sci. Technol., 2012, 2,
22 Y. H. Deng, T. Yu, Y. Wan, Y. F. Shi, Y. Meng, D. Gu,
800.
L. J. Zhang, Y. Huang, C. Liu, X. J. Wu and D. Y. Zhao, J. 42 H. Wu, X. Huang, M. M. Gao, X. P. Liao and B. Shi, Green.
Am. Chem. Soc., 2007, 129, 1690. Chem., 2011, 13, 651.
23 R. L. Liu, Y. F. Shi, Y. Meng, F. Q. Zhang, D. Gu, Z. X. Chen, 43 J. Li, C.-Y. Liu and Y. Liu, J. Mater. Chem., 2012, 22, 8426.
B. Tu and D. Y. Zhao, J. Am. Chem. Soc., 2006, 128, 44 A. Gangula, R. Podila, R. M. L. Karanam, C. Janardhana
11652.
and A. M. Rao, Langmuir, 2011, 27, 15268.
24 F. Y. Liu, L. D. Carlos, R. A. S. Ferreira, J. Rocha, 45 X. Huang, X. P. Liao and B. Shi, Green. Chem., 2011, 13, 2801.
M. C. Ferro, A. Tourrette, F. Quignard and M. Robitzer, J. 46 Y. H. Deng, Y. Cai, Z. K. Sun, J. Liu, C. Liu, J. Wei, W. Li,
Phys. Chem. B, 2010, 114, 77.
25 E. Guibal, Prog. Polym. Sci., 2005, 30, 71.
C. Liu, Y. Wang and D. Y. Zhao, J. Am. Chem. Soc., 2010,
132, 8466.
26 S. Shylesh, P. P. Samuel, S. Sisodiya and A. P. Singh, Catal. 47 K.-L. Wu, X.-W. Wei, X.-M. Zhou, D.-H. Wu, X.-W. Liu, Y. Ye
Surv. Asia, 2008, 12, 266. and Q. Wang, J. Phys. Chem. C, 2011, 115, 16268.
27 M. Salavati-Niasari and A. Amiri, Appl. Catal., A, 2005, 48 Z. M. Zhu, X. H. Guo, S. Wu, R. Zhang, J. Wang and L. Li,
290, 46.
Ind. Eng. Chem. Res., 2011, 50, 13848.
2280 | Green Chem., 2014, 16, 2273–2280
This journal is © The Royal Society of Chemistry 2014