A nitrogen-doped porous carbon derived from copper phthalocyanines on/in ZIF-8 as an efficient photocatalyst for the degradation of dyes and the C[sbnd]H activation of formamides

Article abstract of DOI:10.1016/j.jphotochem.2017.10.026

A novel nitrogen doped carbon photocatalyst was successfully prepared from the carbonization of copper phthalocyanine (CuPc) on/in zeolitic imidazolate framework-8 (ZIF-8) hybrid. Carbonized catalysts derived from either ZIF-8 or CuPc exhibit poor activity towards the degradation of dyes (such as methyl orange (MO) and Rhodamine B (Rh B)), whereas carbonized CuPc complex supported on ZIF-8 exhibits extremely high performance. The weight ratios 1:2 and 1:8 of CuPc/ZIF-8 showed the high dye absorption activity, while the weight ratio 1:4 demonstrated the high photocatalytic activity in the presence of H₂O₂ as an oxidant. For the first time, the photocatalyst (Cu/N-PC) was used in C[sbnd]H activation of formamides in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant. The reaction proceeded within 30 min, in the presence 0.02 mol% of Cu.

Full text of DOI:10.1016/j.jphotochem.2017.10.026

Accepted Manuscript
Title: A nitrogen-doped porous carbon derived from copper
phthalocyanines on/in ZIF-8 as an efficient photocatalyst for
the degradation of dyes and the C-H activation of formamides
Authors: Siyavash Kazemi Movahed, Zeinab Piraman, Minoo
Dabiri
PII:
S1010-6030(17)30833-X
DOI:
Reference:
https://doi.org/10.1016/j.jphotochem.2017.10.026
JPC 10951
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
14-6-2017
13-10-2017
14-10-2017
Please cite this article as: Siyavash Kazemi Movahed, Zeinab Piraman, Minoo
Dabiri, A nitrogen-doped porous carbon derived from copper phthalocyanines
on/in ZIF-8 as an efficient photocatalyst for the degradation of dyes and the
C-H activation of formamides, Journal of Photochemistry and Photobiology A:
Chemistry https://doi.org/10.1016/j.jphotochem.2017.10.026
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A nitrogen-doped porous carbon derived from copper phthalocyanines on/in
ZIF-8 as an efficient photocatalyst for the degradation of dyes and the C-H
activation of formamides
Siyavash Kazemi Movahed, Zeinab Piraman, and Minoo Dabiri*
Shahid Beheshti University, Tehran, Islamic Republic of Iran. Fax: +98 21 22431661; Tel: +98
21 29903255; E-mail: m-dabiri@sbu.ac.ir
Graphical abstract
Highlights
1. A novel doped carbon from the carbonization of the CuPc on/in ZIF-8 hybrid.
2. The weight ratio of CuPc / ZIF-8 in the catalyst was studied in the behavior catalyst
1

3. The weight ratios 1:2 and 1:8 of CuPc / ZIF-8 showed the high dye absorption activity
4. The weight ratio 1:4 demonstrated the high photocatalytic activity
5. The C-H activation of formamides within 30 min under the solar-simulated light, in the
presence 0.02 mol% of Cu.
Abstract
A novel nitrogen doped carbon photocatalyst was successfully prepared from the carbonization of
copper phthalocyanine (CuPc) on/in zeolitic imidazolate framework-8 (ZIF-8) hybrid. Carbonized
catalysts derived from either ZIF-8 or CuPc exhibit poor activity towards the degradation of dyes
(such as methyl orange (MO) and Rhodamine B (Rh B)), whereas carbonized CuPc complex
supported on ZIF-8 exhibits extremely high performance. The weight ratios 1:2 and 1:8 of
CuPc/ZIF-8 showed the high dye absorption activity, while the weight ratio 1:4 demonstrated the
high photocatalytic activity in the presence of H2O2 as an oxidant. For the first time, the
photocatalyst (Cu/N-PC) was used in C-H activation of formamides in the presence of tert-butyl
hydroperoxide (TBHP) as an oxidant. The reaction proceeded within 30 min, in the presence 0.02
mol% of Cu.
Keywords: Heterogeneous catalysis; Photocatalysis; Degradation; C-H bond activation;
Nanostructure.
1. Introduction
Porous carbon, a class of non-oxide porous materials, provide unique characteristics such
as chemical inertness, easy availability, excellent mechanical and thermal stability, high
specific surface area, low density, large pore volumes, and surface hydrophobicity [1-3].
2

Porous carbon exhibit broad application including batteries [4], catalyst supports [5],
chromatography columns [6], gas separation [7], fuel cells [8], and water purification [9].
It has been proved that heteroatom doping (e.g., boron, nitrogen, phosphorus, sulfur, etc.)
inside the frame of porous carbons is robust access to tuning electronic properties or/and
electrical conductivity, as well as electron-donor tendency of the porous carbons [10-13].
Metal–organic frameworks (MOFs) are a class of porous crystalline materials that
consist of coordination bonds between transition-metal cations (nodes) and multitopic
organic ligands (linkers). In the last decade, MOFs have attracted worldwide attention due
to their topology, high surface area, high porosity, and low density. These materials have
potential applications in catalysis, sensing, clean energy, chemical separations, gas storage,
drug delivery, biomedical imaging, electron, ion, proton conduction and so on [14-16].
Recently, MOFs have been shown as new templates and reactive precursors to make porous
carbons by direct calcination in an inert atmosphere [17]. Zeolitic imidazolate frameworks
(ZIFs), a subclass of MOFs, are constructed from tetrahedral units, in which each metal
atom like Zn2+ or Co2+ connects four imidazolates (im−) ligands [18]. Different from their
MOF analogs with carboxyl-ligands, ZIFs not only exhibit exceptional thermal and
chemical stability but also contain a rich nitrogen source in the imidazolate ligands. All
these properties make ZIFs an excellent candidate for the construction of N-doped porous
carbons with superior performances [19,20].
Metal Phthalocyanines (MPcs) as important industrial pigments have been attracted
considerably remarkable due to excellent catalytic capability, low cost, negligible toxicity,
high chemical, photo and thermal stability, facile preparation on a large scale,
semiconducting properties, and most importantly intensive absorption in the red/near-
3

infrared region [21,22]. MPc as an organometallic semiconductor is the widely used
photosensitizer for the generation of singlet oxygen (1O2) because they can collect up to
50% of the energy available in the solar spectrum [23]. The catalytic performance of MPc
catalyst is limited by the aggregation tendency from large intrinsic π-conjugation, which
would self-association or negatively produce inactive dimers. Additionally, the catalyst
may also be deactivated via self-photodecomposition of MPc during the catalytic oxidation
[24]. To solve these issues, supports like the carbon nanotube, chitosan, graphene and
fibrous materials, including cellulose and silk have been used to immobilize MPc [25].
Herein, we report the novel protocol for the photocatalytic degradation of dyes and
the C-H activation of formamides by Cu/N-PC composite under the solar-simulated light.
The synthetic procedure of Cu/N-PC composite is illustrated in Scheme 1. Initially, the
CuPc@ZIF-8 composite was synthesized through a solvent-impregnation together with
milling. The CuPc was dispersed over the surface or/and filled the micropores of ZIF-8.
Finally, the CuPc@ZIF-8 was vacuum dried and carbonized at 900ºC under the inert
atmosphere. The weight ratio of CuPc/ZIF-8 may be one of the key parameters affecting
the impregnated/covered of copper species in/on the ZIF-8 as well as the catalytic activity.
In this study, different weights of CuPc were added into a fixed amount of ZIF-8 to
investigate CuPc/ZIF-8 weight ratio in the formation of CuPc@ZIF-8 and subsequently,
final carbonized catalyst.
2. 2.Experimental
2.1. Synthesis of copper phthalocyanine
4

The mixtures of phthalonitrile (10 mmol), ammonium heptamolybdate (0.01 mmol),
anhydrous copper(I) chloride (2.6 mmol) and nitrobenzene (15 mL) in a Schlenk flask was
degassed several times and refluxed under the nitrogen atmosphere (190 °C) for 4h. After
cooling to room temperature, the resulting mixture was dispersed in 80 mL toluene and
washed with 100 mL deionized water, 300 mL sodium hydroxide 5%, 300 mL hydrochloric
acid 10%, 400 mL deionized water and 100 mL acetone, respectively. The greenish blue
powder was dissolved in sulfuric acid 98% and precipitated in H2O. The resulting
precipitate was dried at 70
℃ [26].
2.2. Synthesis of ZIF-8
2-Methylimidazole (2-MeIm) (56 mmol, 100 mL of methanol solution) was
dropping added to zinc nitrate hexahydrate (7 mmol, 100 mL of methanol solution) and
stirred for 5 minutes, then stand for 1h at room temperature. The resulting milky solution
was centrifuged and washed with methanol for 3 times and dried under vacuum [27].
2.3. Synthesis of CuX/N-PC
To prepare the CuX/N-PC in different mass ratio, ZIF-8 (100 mg) was added to X (=
50, 25, and 12.5) mg of CuPc (in methanol (10 mL)) and homogenized by sonication for 1
h, and then milled in a mortar for 1h. After drying under vacuum, the resulting composite
(CuPcX@ZIF-8) was transferred into a quartz tube and carbonized at 900
℃ for 3 h with a
heating rate of 5 for 2h under Ar flow (yield = ~20%). The
℃
min-1 and kept at 900
℃
carbonized composite was sonicated in H2SO4 (1M) for 2h and continuously stirred at room
temperature for 20 h to remove unstable species (yield = ~ 90%). The resulting mixture was
washed with deionized water and dried at 70
℃. Finally, the sample was carbonized at the
5

same heating rate and kept at 900
yield = ~ 7%).
℃ for 0.5h under Ar flow (yield = ~ 40% and overall
2.4. Dye photodegradation reaction
The solution of dye (MO (64 mg/L, 18.5 mL) or Rh B (16 mg/L, 18.5 mL)) and
composite (0.002 g) were added in a beaker under a constant stirring condition at 500
rmp.min-1 at room temperature under dark conditions for 0.5 h to obtain a good adsorption–
desorption equilibrium between the dye molecules and the catalyst surface. After adding
H2O2 (1.5 mL) and exposing to a Xe lamp, 4 mL of solution separated and the concentration
of dye was determined and recorded with a UV-Vis spectrophotometer (at
or Rh B = 554 nm), every 5 minutes.
2.5. Dye absorption test in the dark
This experiment was performed to indicate that the dye was adsorbed in the dark
lMO = 465 nm
l
even in the presence of the catalyst, also the light was essential for efficient degradation:
the solution of dye (MO (64 mg/L, 18.5 mL) or Rh B (16 mg/L, 18.5 mL)) was added in a
beaker contain composite (0.002 g) and magnetically stirred at 500 rmp.min-1 at room
temperature in the dark, every 5 minutes 4 mL of solution separated and the concentration
of dye was determined and recorded with a UV-Vis spectrophotometer(at lMO = 465 nm or
lRh B = 554 nm).
2.6. General Procedure for the synthesized of enol carbamates
β-ketoester derivative (2 mmol), formamide (54 mmol), TBHP (12 mmol) and
composite (0.02 mol% of Cu) were mixed in a round-bottom flask (10 mL). The resulting
mixture stirred at 70 , exposed a Xe lamp, and the reaction monitored by thin layer
℃
chromatography (TLC). After the compilation of reaction, the reaction mixture was cooled
6

to room temperature; the organic phase was dried over anhydrous Na2SO4 and filtered. The
crude reaction was concentrated under vacuum. The residue was purified by silica-gel thin
layer chromatography using n-hexane/ethyl acetate (10:1) as eluent to afford the pure
product.
3. Results and discussion
3.1. Characterization
Raman spectroscopy is a powerful technique to investigate the local structure of
carbonaceous materials [28]. The Raman spectra of N-PC, Cu0.125/N-PC, Cu0.25/N-PC, and
Cu0.5/N-PC composites are shown in Fig. 1. All composites exhibited G and D bands in the
Raman spectra. The G band at around 1570 cm-1 correspond to sp2-carbon in graphite
structures and the graphitization. The D band at around 1340 cm-1 correspond to sp3-carbon
in disordered carbon structures or doped heteroatoms [29]. The ID/IG ratio increases from
1.13 to 1.19, 1.21, and 1.23 by increasing the weight ratio of CuPcX/ZIF-8 from X= 0,
0.125, 0.25 to 0.5, which suggested a high concentration of defects, which possibly caused
by the heteroatom copper [27]. Additionally, the D band enhancement indicates the
interaction between the metal nanoparticles and graphite layer that occurs due to the
preferential growth of nanoparticles at graphite layer vacancies [30].
XRD measurement was done to study the crystal structure of the ZIF-8, (Fig. 2). The
sample exhibited pure crystal with the cubic I43m group, which matched with the well-
known ZIF-8 crystal structure. After the carbonization of ZIF-8 at 900 °C, the broad
diffraction peak centered at 2θ = 25° appeared and assigned to (0 0 2) lattice plane of the
7

graphitic carbon. Additionally, the absence of the diffraction peaks of Zn and ZnO
impurities indicates that Zn species vaporized away along with the Ar flow during the
thermal treatment process [31]. The XRD pattern of the carbonized CuPc (C Cu) includes
two sets of peaks. The first one is constituted by three peaks, situated at 2θ = 43.22°, 50.37°
and 73.99° can be assigned to the (1 1 1), (2 0 0) and (2 2 0) lattice planes of Cu (0). The
second set of peaks located at 2θ = 36.16° and 42.14°, could be assigned to the (1 1 1) and
(2 0 0) lattice planes of Cu2O. The appearance of the lattice planes of Cu (0) must arise
from reduction to Cu (0) due to decomposition/deligandation during high-temperature
treatment which was consistent with previous reports [32,33]. An apparent broad peak at
2θ = 25° has been recorded, which assigned to the (0 0 2) facet of the graphitic carbon. The
XRD patterns of Cu0.125/N-PC, Cu0.25/N-PC, and Cu0.5/N-PC composites showed a broad
peak for graphitic carbon at 2θ = 25° and a set peaks for Cu2O at 2θ = 36.22°, 42.18
,
61.32 , and 73.26 , which could be assigned to the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) lattice


planes of Cu2O. The absence of the diffraction peaks of metallic Cu showed that it was
readily oxidized in air to form Cu2O. Notably, the set peaks for Cu2O in the XRD pattern
of Cu0.25/N-PC was strong and sharp, while those in Cu0.125/N-PC and Cu0.5/N-PC appeared
to be weak, which suggested Cu2O in Cu0.25/N-PC has a high crystalline degree.
Additionally, the peaks at 2θ= 44° and 64° correspond to stainless steel sample holder of
powder diffractometer.
The isotherm of all composites exhibits a type-IV curve according to the IUPAC
classification, which suggests the existence of mesopores (Fig. 3). After Cu doping in N-
PC, the type of hysteresis loop was changed from type-I to type-III that indicated altering
the shape of the pores and increasing the non-uniformity size and shape the pores [34]. BET
8

surface area decreased dramatically from 1613.61 in N-PC to 868.89, 585.75 and 256.08
m2g-1 in Cu0.125/N-PC, Cu0.25/N-PC, and Cu0.5/N-PC composites, respectively. Additionally,
the pore volume dropped from 1.23 to 1.05, 0.58 and 0.33 m3g-1 in Cu0.125/N-PC, Cu0.25/N-
PC, and Cu0.5/N-PC composites, respectively (Table 1). These results indicate that the most
pores of N-PC were impregnated with the Cu, or the Cu was well distributed on/in the N-
PC composite.
The morphologies of all composites were characterized by the field emission
scanning electron microscopy (FESEM). ZIF-8 owns a typical rhombic structure with an
average size of 70 nm (Fig. 4a). After carbonization, the obtained N-PC retained the parent
ZIF-8 morphology, but the some shrinking and deforming were observed as well (Fig. 4b).
The impregnation/covering of Cu in/on the N-PC did not affect the morphology of
Cu0.125/N-PC and Cu0.25/N-PC composites (Figs. 4c-d). The agglomeration in the
morphology of carbonized catalyst was observed by the increasing of amount CuPc into
the ZIF-8 (Cu0.5/N-PC) (Fig. 4e).
The TEM images of N-PC and CuX/N-PC composites showed in Fig. 5 and Figs. S5
and S7. The TEM image of N-PC revealed partially destroyed ZIF-8 morphologies, with
distorted graphite structures and only a few oriented multilayer graphene domains were
observed (Figs 5a-b), which was consistent with the previous reports [35]. CuX/N-PC
composites exhibit a hollow bowl-like morphology (Fig. 5 c-j).
The photoelectrochemical properties and the electronic band structure of all
composites were further investigated through diffuse reflectance spectroscopy (DRS) (Fig.
9

6a). The distinct absorption ability was observed in the visible light region. All CuX/N-PC
composites showed the enhanced visible light absorption in contrast to the N-PC and C Cu.
The Cu0.5/N-PC composite exhibit the strongest visible light absorption among all samples.
The band gap energy (Eg) was estimated from the intercept of the tangents to the plots of
(a
hv)2 vs. photon energy (Fig. 6b), and the calculated Eg value of C Cu, N-PC, Cu0.125/N-
PC, Cu0.25/N-PC, and Cu0.5/N-PC composites are around 2.91, 2.83, 2.79, 2.58, and 2.49,
respectively.
3.1. The photocatalytic activity of CuX/
MO and Rh B
N-PC composites on the degradation of
The photocatalytic activity of the composites on the degradation of MO dye under
the solar-simulated light was investigated (Fig. 7). First, the reaction mixture was stirred in
the dark for 30 min to complete the adsorption/desorption equilibration of the organic dye
by the composites. The C Cu, N-PC, Cu0.125/N-PC, Cu0.25/N-PC, and Cu0.5/N-PC composites
absorbed around 3.65%, 88.25%, 72.98%, 3.14%, and 65.72% of MO, respectively, in 30
min dark. The N-PC, Cu0.125/N-PC, and Cu0.5/N-PC composites showed the strong dark
absorption. Finally, after 30 min by switching on the lamp, about 75.44% in 50 mintotal(= 30
min dark+ under solar-simulated light), 70.99% in 50 mintotal, and 72.35% in 45 mintotal of MO removed
on C Cu, Cu0.25/N-PC, and Cu0.5/N-PC composites, respectively. Removing MO from C
Cu, Cu0.25/N-PC and Cu0.5/N-PC mainly attributed to the photocatalytic activity. For
determining photo-degradation rate, the absorption of MO in the dark over the composites
was tested (Fig. 7b). The first-order kinetic photocatalytic reaction rate constants of C Cu,
Cu0.25/N-PC, and Cu0.5/N-PC were calculated as 0.0496, 0.0627, and 0.0551 min-1,
10

respectively (Table 2). These results indicated that the order of the rate of the photocatalytic
activity was Cu0.25/N-PC Cu0.5/N-PC C Cu.


Some controlled experiments were designed to clarify the nature of photocatalytic
reaction over the Cu0.25/N-PC. The rate of the removal of MO was alerted to 0.0020, 0.0006,
and 0.0186 min-1 in the absence of light (Cu0.25/N-PC and H2O2), oxidant (Cu0.25/N-PC and
hv), and photocatalyst (H2O2 and hv), respectively (Fig. 7a). The rate of the removal of the
MO in the absence of light was very low. Accordingly, the Cu0.25/N-PC could not catalytic

decompose H2O2 and produced OH radicals. The removal of the MO in the absence of
photocatalyst condition (0.0186 min-1) indicates the direct photolysis of H2O2. By adding
Cu0.25/N-PC composite into the reaction medium, the rate increased around three times
(0.0628 min-1) rather than the reaction without the catalyst. This result indicated that H2O2

promotes the photocatalysis process by generating OH radicals via the capturing of the
photoinduced electrons in the excited Cu0.25/N-PC [36].
The rate of MO removal decreased to 0.0223 min-1 when the amount of H2O2 was
reduced to 0.5 mL (Fig. 7c). An excess amount of H2O2 (1.5 mL) retards the rate to 0.0536
-1

min . In higher concentration, H2O2 acts as the scavenger of OH radicals to generated
perhyroxy radicals (OOH) with lower oxidation potential [37].
The photocatalytic activity of the composites on the degradation of Rh B dye was
investigated as well (Fig. 8). The C Cu, N-PC, Cu0.125/N-PC, Cu0.25/N-PC, and Cu0.5/N-PC
composites absorbed around 2.40%, 91.22%, 75.64%, 1.20%, and 39.00% of Rh B,
respectively, in 30 min dark. The N-PC and Cu0.125/N-PC composites showed the strong
dark absorption. After 30 min by switching on the lamp, about 99.04% in 70 mintotal,
11

93.95% in 50 mintotal, 94.73% in 55 mintotal, and 95.04% in 60 mintotal of Rh B removed on
C Cu, Cu0.125/N-PC, Cu0.25/N-PC, and Cu0.5/N-PC composites, respectively. The removal
of Rh B in C Cu, Cu0.25/N-PC and Cu0.5/N-PC mainly attributed to the photocatalytic
activity. For determining photo-degradation rate, the absorption of Rh B in the dark over
composites was investigated (Fig. 8b). The first-order kinetic photocatalytic reaction rate
constants of C Cu, Cu0.25/N-PC, and Cu0.5/N-PC were calculated to 0.1243, 0.1308, and
0.0723 min-1, respectively (Table 3). The rate of the removal of Rh B was alerted in
different reaction conditions from 0.0012, 0.0008, and 0.0354 min-1 in the absence of light
(Cu0.25/N-PC and H2O2), oxidant (Cu0.25/N-PC and hv), and photocatalyst (H2O2 and hv),
respectively (Fig. 8a). The rate decreased to 0.062 and 0.1155 min-1 in 0.5 and 1.5 mL of
H2O2 (Fig. 8c).
The best photocatalytic activity of Cu0.25/N-PC could be attributed to the following
reasons: (i) Cu2O in Cu0.25/N-PC was well-crystallized, (ii) BET surface area was higher
than Cu0.5/N-PC, (iii) the absence of the agglomeration in Cu0.25/N-PC toward Cu0.5/N-PC
(iv) the possible synergetic effects between hollow carbon (from ZIF-8) and Cu2O (from
CuPc) which could be enhanced the intrinsic properties of each component.
The effect of radical scavenger was studied in the degradation of MO dye (Fig. 9a).
Hydroxyl radicals play a significant role in the degradation of dye. To investigate the role
of hydroxyl radicals, the degradation process was carried out in the presence of hydroxyl
radical scavenger like methanol (MeOH) [38]. The photocatalytic activity greatly decreased
by adding MeOH (0.01 Maq). The rate constant decreases more than three times from
0.0628 min−1 to 0.0200 min−1.The result showed that the •OH radicals played a significant
role in the MO degradation. Iodide ion (I-) was reported to be a scavenger of positive holes
12

(h+). The photocatalytic effect slightly increased (rate constant = 0.0700 min-1) by adding
KI (0.01 Maq). Thereby, photo-excited holes acted slightly on dye degradation [39].
−


Dissolved oxygen can act as a photo-generated electron scavenger to give O2 and OH
active species [40]; the latter has been proven to be the major oxidation species in this
−
−


process. To examine the role of O2 , benzoquinone (BQ) (0.01 Maq) was used as an O2
quencher. Adding BQ could decrease the photocatalytic efficiency of composite (rate
−
constant = 0.0416 min-1), which showed that the MO photo-degradation is caused by O2

to a low degree. The same results were observed in quenching experiments for Rh B. The
addition of radical scavenger leads to the change of rate constant from 0.1313 min-1 to
0.1418, 0.0399, and 0.0653 min-1 for KI, MeOH, and BQ (as radical scavengers),
respectively (Fig. 9b). In conclusion, the dye degradation on Cu0.25/N-PC was attributed to
hydroxyl and superoxide radicals.
Based on the above experiments, a possible photocatalytic mechanism for dye degradation was
proposed in Fig. 10. In principle, the electrons may transit from valance band (vb) to conduction
band (cb) in Cu2O semiconductor under simulated light irradiation, leading to the generation of
e-/h+ pairs, which will be separated rapidly and transferred to the surface of Cu2O (Fig. 10). The
•-
•
electrons reduced O2 to O2 and H2O2 to OH. The experimental results above illustrate that
Cu0.25/N-PC composite exhibits the higher photocatalytic activity than C Cu. The hollow carbon
structure can strongly enhance the adsorption capacity of Cu0.25/N-PC composite. The adsorbed
dye molecules are aggregated on the surface of hollow carbon structure. Due to the small size of
the dye molecule, it is easy to penetrate the carbon layer [41] and be captured by the reactive
•-
•
species O2 and OH radicals, which has a strong oxidizability and can completely degrade dye
molecules in the desired efficiency.
13

The Photoluminescence (PL) emission spectra have been widely used to investigate
the efficiency of charge carrier trapping, immigration and transfer, and to understand the
fate of e-/h+ pairs in semiconductor particles [42]. Furthermore, the better separation of
photogenerated e-/h+ pairs in the CuX/N-PC composite was confirmed by PL emission
spectra of C Cu and CuX/N-PC composites. In Fig. 11, it was indicated that the CuX/N-PC
composite exhibited much lower emission intensity than C Cu, indicating that the
recombination of the photogenerated charge carrier was inhibited greatly in the Cu/N-PC
composite. The e
ffi
cient charge separation could increase the lifetime of the charge carriers
ciency of the interfacial charge transfer to adsorbed substrates, and then
and enhance the e
ffi
account for the higher activity of the Cu/N-PC composite photocatalyst. This result similar
to other reports in carbon doped or composites semiconductor metal oxide photocatalyst
(such as TiO2 and ZnO) [41-45].
3.2. The photocatalytic activity of CuX/
of formamides
N-PC composites on the C-H activation
The catalytic activity of CuX/N-PC composites was examined in the synthesis of
carbamates by C-H activation of formamides. Carbamates have frequently been found in
many biologically active products, pharmaceutical drugs, agricultural chemicals as well as
foams. They also play a unique role in organic chemistry as valuable intermediates and
protecting groups [46]. Traditional methods for the synthesis of these compounds include
the reaction of amines with phosgene and its derivatives or the reaction of alcohols with
isocyanates. Two main drawbacks of these procedures are toxic and harmful reagents and
the generation of by-products. Recently, Kumar et al. reported that the CuBr2 catalyzed the
14

oxidative C-O coupling by C-H activation of formamides to give enol carbamates [47]. The
main problem of this reaction is the inability to recycling all catalyst at the end of the
reaction. Therefore, we used Cu/N-PC composite as a reusable photocatalyst in the
synthesis of carbamates by C-H activation of formamides.
We initialized the optimization process using ethyl acetoacetate 1a (1.0 eq.) and N, N-
dimethylformamide (DMF) 2a (27.0 eq.) as coupling partner, and the reaction was
performed with Cu0.25/N-PC composite (0.02 mol% of Cu) and tert-butyl hydroperoxide
(TBHP) as oxidant (6 eq.) under the solar-simulated light (Table 4, entry 1). Low yield
(15%) was obtained after 4h. The yield increased to 97% by increasing the reaction
temperature to 70 °C (Table 4, entry 2). To examine the photocatalyst activity of Cu0.25/N-
PC, the reaction designed without solar-simulated light and under the thermal condition.
The yield decreased to 59% (Table 4, entry 3). Different types of oxidants such as meta-
chloroperoxybenzoic acid (m-CPBA), hydrogen peroxide (H2O2), urea hydrogen peroxide
(UHP), and cerium ammonium nitrate (CAN) were tested. The results show that none of
them have any obvious influence to improve the reaction (Table 4, entries 4-7). Decreasing
the amount of the catalyst (0.01 mol% of Cu) leads to the lower yield (Table 4, entry 8).
We also used N-PC, Cu0.125/N-PC, and Cu0.5/N-PC composites, in the model reaction. The
observed yields of enol carbamate in all cases were surprisingly inferior (Table 4, entries
9-11).
After obtaining the optimum reaction conditions, we evaluated the generality and
the scope of substrates for the C-H activation of formamides (Table 5). Various β-ketoesters
were used as substrates for the formation of enol carbamates. The nature of the β-ketoesters
and formamides did not have any profound influence on the reactivity.
15

The developed protocol was also applicable to forming different carbamates from 2-
carbonyl-substituted phenol (similar to the enol tautomer of β-diketo moiety) (Table 5,
entries 16-18). Several formamides reacted smoothly with ortho-hydroxyacetophenone in
good yields.
Based on the above studies, a plausible mechanism was proved is proposed for the
synthesis of enol carbamates using formamide and β-ketoester outlined in Fig. 12. The
Cu0.25/N-PC composite was subjected to light irradiation, and Cu2O can be excited and
produce photogenerated electron-hole pairs. Then, t-BuOOH reduced to t-BuO• and OH-
by the photogenerated electron in CB. The β-ketoester (
1) deprotonated by hydroxyl anion
and generated copper complex (
i
) with Cu0.25/N-PC composite. The t-BuO• radical can
abstracted hydrogen from the reacting formamide (
radical (ii). The radical (ii) reacted with the copper complex (
enol carbamate ( ).
2
) and generated the corresponding
i
) and afforded the desired
3
Reusability is an important characteristic of the heterogeneous catalysis which
should be examined in the catalytic reaction. Therefore, we performed a reusability test for
the Cu0.25/N-PC composite in the C-H activation of DMF and ethyl acetoacetate under the
optimized conditions. After the reaction completion, the catalyst was collected by
centrifuge. By adding a new batch of ethyl acetoacetate and DMF, the recovered composite
can be used directly for the next run. This recycling protocol enabled the Cu0.25/N-PC to be
used for seven runs, furnishing quantitative conversion of substrates without loss of activity
and selectivity. Fig. 13a depicted the recovery and reusability of Cu0.25/N-PC composite.
16

Furthermore, no significant change was observed in the morphology of Cu0.25/N-PC after
the seven runs, which was concluded by the TEM image given in Fig. 13b.
The table 6 provides a comparison of the present method with other reported copper
catalytic systems in the C-H bond activation of DMF and ethyl acetoacetate. Clearly, the present
catalyst exhibited a simple, high effective, and less time-consuming method for the C-H bond
activation.
4. Conclusions
In conclusion, we have successfully demonstrated that the CuX/N-PC composite is a novel,
simple, effective and reusable heterogeneous photocatalyst for the degradation of dyes (MO
and Rh B) and the C-H activation of formamides. To study the effect of the weight ratio,
the array of carbon composites was prepared. We also used C Cu, N-PC, Cu0.125/N-PC,
Cu0.25/N-PC, and Cu0.5/N-PC in the photocatalytic degradation of dyes such as MO and Rh
B. While the N-PC, Cu0.125/N-PC, and Cu0.5/N-PC composites exhibited high to medium
the absorption activity of dyes, the Cu0.25/N-PC composite revealed the high photocatalytic
activity in the presence of H2O2 as the oxidant. The best photocatalytic activity of Cu0.25/N-
PC could be attributed to the high crystallinity of Cu2O, high BET surface area, the absence
agglomeration, and possible synergetic effects between hollow carbon and Cu2O. The
catalyst showed the high reusability, and can be recycled for several times without
considerable loss of activity.
17

Acknowledgements
We gratefully acknowledge financial support from the Research Council of Shahid
Beheshti University and the Iranian National Science Foundation (Proposal No: 94028845).
References
[1] S. De, A. M. Balu, J. C. van der Waal, R. Luque, Biomass-derived porous carbon
materials: synthesis and catalytic applications. ChemCatChem 7 (2015) 1608-1629.
[2] Y. Xia, Z. Yang, R. Mokaya, Templated nanoscale porous carbons. Nanoscale 2 (2010)
639-659.
[3] B. Sakintuna, Y. Yurum, Templated porous carbons: a review article. Ind. Eng. Chem.
Res. 44 (2005) 2893-2902.
[4] K. Zhang, Z. Hu, J. Chen, Functional porous carbon-based composite electrode
materials for lithium secondary batteries. J. Energy Chem. 22 (2013) 214-225.
[5] J. L. Figueiredo, Functionalization of porous carbons for catalytic applications. J.
Mater. Chem. A 1 (2013) 9351-9364.
[6] C. West, C. Elfakir, M. Lafosse, Porous graphitic carbon: A versatile stationary phase
for liquid chromatography. J. Chromatogr. A 1217 (2010) 3201-3216.
[7] S. M. Saufi, A. F. Ismail, Fabrication of carbon membranes for gas separation–a
review. Carbon 42 (2004) 241-259.
[8] Y. Zheng, J. Liu, J. Liang, M. Jaroniec, S. Z. Qiao, Graphitic carbon nitride materials:
controllable synthesis and applications in fuel cells and photocatalysis. Energy
Environ. Sci. 5 (2012) 6717-6731.
18

[9] H. Li, Application of porous carbon macrostructures for water purification. Prog.
Chem. 28 (2016) 1462-1473.
[10]
Y.-Z. Chen, C. Wang, Z.-Y. Wu, Y. Xiong, Q. Xu, S.-H. Yu, H.-L. Jiang, From
bimetallic metal-organic framework to porous carbon: high surface area and
multicomponent active dopants for excellent electrocatalysis. Adv. Mater. 27 (2015)
5010-5016.
[11]
Y. Zheng, Y. Jiao, M. Jaroniec, Y. Jin, S. Z. Qiao, Nanostructured metal-free
electrochemical catalysts for highly efficient oxygen reduction. Small 8 (2012) 3550-
3566.
[12]
L. Yang, S. Jiang, Y. Zhao, L. Zhu, S. Chen, X. Wang, Q. Wu, J. Ma, Y. Ma,
Z. Hu, Boron-doped carbon nanotubes as metal-free electrocatalysts for the oxygen
reduction reaction. Angew. Chem. Int. Ed. 50 (2011) 7132-7135.
[13]
L. He, F. Weniger, H. Neumann, M. Beller, Synthesis, characterization, and
application of metal nanoparticles supported on nitrogen-doped carbon: catalysis
beyond electrochemistry. Angew. Chem. Int. Ed. 55 (2016) 12582-12594.
[14]
H.-C. Zhou, J. R. Long, O. M. Yaghi, Introduction to metal–organic
frameworks. Chem. Rev. 112 (2012) 673-674.
[15]
J. L. C. Rowsell, O. M. Yaghi, Metal–organic frameworks: a new class of
porous materials. Micropor. Mesopor. Mat. 73 (2004) 3-14.
[16]
H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi, The chemistry and
applications of metal-organic frameworks. Science 341 (2013) 1230444.
19

[17]
Y. Deng, Y. Xie, K. Zou, X. Ji, J. Review on recent advances in nitrogen-doped
carbons: preparations and applications in supercapacitors. Mater. Chem. A 4 (2016)
1144-1173.
[18]
A. Schejn, A. Aboulaich, L. Balan, V. Falk, J. Lalevée, G. Medjahdi, L. Aranda,
K. Mozet, R. Schneider, Cu2+-doped zeolitic imidazolate frameworks (ZIF-8): efficient
and stable catalysts for cycloadditions and condensation reactions. Catal. Sci. Technol.
5 (2015) 1829-1839.
[19]
P. Zhang, F. Sun, Z. Xiang, Z. Shen, J. Yun, D. Cao, ZIF-derived in situ
nitrogen-doped porous carbons as efficient metal-free electrocatalysts for oxygen
reduction reaction. Energy Environ. Sci. 7 (2014) 442-450.
[20]
Z. Wang, T. Yan, J. Fang, L. Shi, D. Zhang, Nitrogen-doped porous carbon
derived from a bimetallic metal–organic framework as highly efficient electrodes for
flow-through deionization capacitors. J. Mater. Chem. A 4 (2016) 10858-10868.
[21]
S. Ge, D. Li, S. Huang, W. Chen, G. Tu, S. Yu, Q. He, J. Gong, Y. Li, C. Hong,
C. Wu, Z. Zheng, A magnetically recyclable Fe3O4@C@TNCuPc composite catalyst
for chromogenic identification of phenolic pollutants. J. Mol. Catal. A: Chem. 410
(2015) 193-201.
[22]
Z. Zhang, W. Wang, D. Jiang, J. Xu, CuPc sensitized Bi2MoO6 with remarkable
photo-response and enhanced photocatalytic activity. Catal. Commun. 55 (2014) 15-
18.
[23]
Z. Zhang, W. Wang, L. Zhang, Large improvement of photo-response of CuPc
sensitized Bi2WO6 with enhanced photocatalytic activity. Dalton Trans. 42 (2013)
4579-4585.
20

[24]
Z. Wang, H. Chen, P. Tang, W. Mao, F. Zhang, G. Qian, X. Fan, Hydrothermal
in situ preparation of the copper phthalocyanine tetrasulfonate modified titanium
dioxide photocatalyst. Colloids Surf. A 289 (2006) 207-211.
[25]
Z. Han, X. Han, X. Zhao, J. Yu, H. Xu, Iron phthalocyanine supported on
amidoximated PAN fiber as effective catalyst for controllable hydrogen peroxide
activation in oxidizing organic dyes. J. Hazard. Mater. 2016, 320, 27-35.
[26]
1968.
[27]
G. Schulz, R. Polster, Production of copper phthalocyanines. US3412102 (A),
R. Zheng, S. Liao, S. Hou, X. Qiao, G. Wang, L. Liu, T. Shu, L. Du, A hollow
spherical doped carbon catalyst derived from zeolitic imidazolate framework
nanocrystals impregnated/covered with iron phthalocyanines. J. Mater. Chem. A 4
(2016) 7859-7868.
[28]
M. Wang, X. Xu, Y. Liu, Y. Li, T. Lu, L. Pan, From metal-organic frameworks
to porous carbons: A promising strategy to prepare high-performance electrode
materials for capacitive deionization. Carbon 108 (2016) 433-439.
[29]
B. Chen, R. Li, G. Ma, X. Gou, Y. Zhu, Y. Xia, Cobalt sulfide/N,S codoped
porous carbon core–shell nanocomposites as superior bifunctional electrocatalysts for
oxygen reduction and evolution reactions. Nanoscale 7 (2015) 20674-20684.
[30]
S. K. Movahed, M. Dabiri, A. Bazgir, A one-step method for preparation of
Cu@Cu2O nanoparticles on reduced graphene oxide and their catalytic activities in N-
arylation of N-heterocycles. Appl. Catal. A: General 481 (2014) 79-88.
[31]
T. Toyao, M. Fujiwaki, K. Miyahara, T.-H. Kim, Y. Horiuchi, M. Matsuoka,
Design of zeolitic imidazolate framework derived nitrogen-doped nanoporous carbons
21

containing metal species for carbon dioxide fixation reactions. ChemSusChem 8
(2015) 3905-3912.
[32]
Q. He, X. Yang, R. He, A. Bueno-López, H. Miller, X. Ren, W. Yang, B. E.
Koel, Electrochemical and spectroscopic study of novel Cu and Fe-based catalysts for
oxygen reduction in alkaline media. J. Power Sources 213 (2012)169-179.
[33]
L. Ding, J. Qiao, X. Dai, J. Zhang, J. Zhang, B. Tian, Highly active
electrocatalysts for oxygen reduction from carbon-supported copper-phthalocyanine
synthesized by high temperature treatment. Int. J. Hydrogen Energy 37 (2012) 14103-
14113.
[34]
G. Leofanti, M. Padovan, G. Tozzola, B. Venturelli, Surface area and pore
texture of catalysts. Catal. Today 41 (1998) 207-219.
[35]
A. Aijaz, N. Fujiwara, Q. Xu, From Metal−organic framework to nitrogen-
decorated nanoporous carbons: high CO2 uptake and efficient catalytic oxygen
reduction. J. Am. Chem. Soc. 136 (2014) 6790-6793.
[36]
Q. Xia, X. Yu, H. Zhao, S. Wang, H. Wang, Z. Guo, H. Xing, Syntheses of
novel lanthanide metal–organic frameworks for highly efficient visible-light-driven
dye degradation. Cryst. Growth Des. 17 (2107) 4189–4195
[37]
L. Ai, C. Zhang, L. Li, J. Jiang, Iron terephthalate metal–organic framework:
revealing the effective activation of hydrogen peroxide for the degradation of organic
dye under visible light irradiation. Appl. Catal. B 148-149 (2014) 191-200.
[38]
L. G. Devi, S. G. Kumar, K. M. Reddy, C. Munikrishnappa, Photo degradation
of methyl orange an azo dye by advanced fenton process using zero valent metallic
22

iron: influence of various reaction parameters and its degradation mechanism. J.
Hazard. Mater. 164 (2009) 459-467.
[39]
P. Liang, C. Zhang, H. Sun, S. Liu, M. Tadé, S. Wang, Photocatalysis of C, N-
doped ZnO derived from ZIF-8 for dye degradation and water oxidation. RSC Adv. 6
(2016) 95903-95909.
[40]
Y. Li, J. Wang, H. Yao, L. Dang, Z. Li, Efficient decomposition of organic
compounds and reaction mechanism with BiOI photocatalyst under visible light
irradiation. J. Mol. Catal. A: Chem. 334 (2011) 116-122.
[41]
T. Chen, S. Yu, X. Fang, H. Huang, L. Li, X. Wang, H. Wang, Enhanced
photocatalytic activity of C@ZnO core-shell nanostructures and its
photoluminescence property. Apple. Surf. Sci. 389 (2106) 303-310.
[42]
Y. Yu, J. C. Yu, J.-G. Yu, Y.-C. Kwok, Y.-K. Che, J.-C. Zhao, L. Ding., W.-K.
Ge, P.-K. Wong, Enhancement of photocatalytic activity of mesoporous TiO2 by using
carbon nanotubes. Appl. Catal. A: General 289 (2005) 186–196.
[43]
J. Mu, C. Shao, Z. Guo, Z. Zhang, M. Zhang, P. Zhang, B. Chen, Y. Liu, High
photocatalytic activity of ZnO-Carbon nanofiber heteroarchitectures. ACS Appl.
Mater. Interfaces 3 (2011) 590–596
[44]
J. Yu, T. Ma, S. Liu, Enhanced photocatalytic activity of mesoporous TiO2
aggregates by embedding carbon nanotubes as electron-transfer channel. Phys. Chem.
Chem. Phys., 13 (2011) 3491–3501
[45]
W. Ren, Z. Ai, F. Jia, L. Zhang, X. Fan, Z. Zou, Low temperature preparation
and visible light photocatalytic activity of mesoporous carbon-doped crystalline TiO2.
Appl. Catal. B: Environmental 69 (2007) 138–144.
23

[46]
D. Saberi, A. Heydari, CuO nanoparticles supported on α-Fe2O3-modified
CNTs: a magnetically separable catalyst for oxidative C–O coupling of formamides
with 1,3-dicarbonyl compounds. Tetrahedron Lett. 54 (2013) 4178-4180.
[47]
G. S. Kumar, C. U. Maheswari, R. A. Kumar, M. L. Kantam, K. R. Reddy,
Copper-catalyzed oxidative C-O coupling by direct C-H bond activation of formamides:
synthesis of enol carbamates and 2-carbonyl-substituted phenol carbamates. Angew.
Chem. Int. Ed. 50 (2011) 11748-11751.
[48]
D. Saberi, S. Mansoori, E. Ghaderi, K. Niknam, Copper nanoparticles on
charcoal: an effective nanocatalyst for the synthesis of enol carbamates and amides via
an oxidative coupling route. Tetrahedron Lett. 57 (2016) 95–99
[49]
B. D. Barve, Y. C. Wu, M. El‐ Shazly, D. W. Chuang, Y. M. Chung, Y. H.
Tsai, S. F. Wu, M. Korinek, Y. C. Du, C. T. Hsieh, J. J. Wang, Synthesis of carbamates
by direct c–h bond activation of formamides. Eur. J. Org. Chem. (2012) 6760–6766.
24

Scheme 1. Schematic diagram illustrating the synthesis of Cu/N-PC composite
25

Fig. 1 Raman spectra of N-PC, Cu0.125/N-PC, Cu0.25/N-PC and Cu0.5/N-PC
composites
26

Fig. 2 XRD patterns of ZIF-8, N-PC, C Cu, Cu0.125/N-PC, Cu0.25/N-PC and Cu0.5/N-PC
composites.
27

Fig. 3 Nitrogen adsorption–desorption isotherms of N-PC, Cu0.125/N-PC, Cu0.25/N-PC and
Cu0.5/N-PC composites.
28

Fig. 4 FESEM images of a) ZIF-8 (scale bar = 100 nm), b) N-PC(scale bar = 200 nm), c)
Cu0.125/N-PC (scale bar = 200 nm), d) Cu0.25/N-PC(scale bar = 200 nm), and e) Cu0.5/N-PC
(scale bar = 200 nm) composites.
29