An amorphous/crystalline g-C3N4 homojunction for visible light photocatalysis reactions with superior activity

Article abstract of DOI:10.1039/c8cc01824c

An amorphous/crystalline g-C₃N₄ homojunction was prepared for the first time at high temperature, in which the ratio of crystalline g-C₃N₄ in the homojunction was optimized. The homogenous junction with a matche

Full text of DOI:10.1039/c8cc01824c

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
first methanofullerene derivatives of Sc N@D5h-C80
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Amorphous/crystalline g-C3N4homojunctionfor visiblelight
photocatalysisreaction with superior activity
Zhiguo Liu,a Gang Wang,a Hsueh-Shih Chen,b and Ping Yanga*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Amorphous/crystalline g-C3N4 homojunctionwas prepared for the temperature. For example, He et al.7prepared crystallineg-C3N4
first timeat high temperature,in which the ratio of crystalline g- through the addition of dopamine, which improved hydrogen
C3N4 in the homojunction was optimized.The homogenous production performance under visible light. However, increase
junction with
a matchedenergy level structureresulted in of crystallinity of g-C3N4 requires the introduction of admixture.
superiorphotocatalytic performance for the degradation oforganic Other efforts have been made to fabricate surface
pollutants and H2 evolution from splitting waterundervisible light heterojunction construction, such as MoS2/mpg-C3N4,8
irradiation.
Co3O4/CNS,9
g-C3N4/ZnGaNO,10
g-C3N4/BiOBr,11
g-
C3N4/AgX(X=Br, I),12 but, these junctions are mainly composed
of g-C3N4/inorganic semiconductors. Organic g-C3N4polymer is
generally not easy to bond to the inorganic semiconductor
surface and thus not conducive to the charge transfer at the
organic-inorganic interfaces.13
Graphitic carbon nitride (g-C3N4) as a metal-free visible light
photocatalyst has been widely investigated due to its unique
semiconductor band structure and excellent chemical
stability.1The suitable band edge of g-C3N4is possible to
photocatalytic degradation of organic pollutants and hydrogen
production via water splitting under visible light irradiation.2
However, bulk g-C3N4fabricated by conventional calcination
method at high temperature has small specific surface area
and low crystallinity.3 The quick recombination of photo-
generated electrons and holes in bulk g-C3N4limited the
applications.4Efforts have been made to modify the bulk g-
C3N4, such as nano-modification, special morphology control,
ion doping and surface heterojunction construction.5 It is
common to produce ultrathin g-C3N4through heat-treatment
at high temperature using a hot gas flow to delaminate g-C3N4
from layer to layer.6However, main attention focused on the
change of morphology, ignoring the influence of temperature
on the crystallinity and energy level of g-C3N4.
Crystalline g-C3N4 (CGCN) and amorphous g-C3N4 (AGCN) as
polymers are fabricated at different temperature with a similar
composition. CGCN and AGCN have different energy level
structure, which is conducive to the formation of close-
coupled copolymers. In this paper, CGCN was used as seeds to
optimize the morphology of AGCN, produce ultra-thin
nanosheets,
and
form
amorphous/crystalline
g-
C3N4homojunction (A-CGCN) via polymerization of melemon
the surface of CGCN. The homojunction results in the
orientation transfer of electron and hole in the different
crystal plane and displays superior photocatalytic performance.
Namely, A-CGCN was prepared without any pretreatment and
admixture for the first time.
The A-CGCN composites were obtained via polymerization
of melemon the surface of CGCN (as seeds). The synthesis
process of A-CGCN composites is shown in Scheme 1 (also in
Experimental section, ESI†). The samples was prepared by
controlling the calcination procedures and parameters (Table
S1, ESI†). A two-step process was used to produce thin g-
C3N4nanosheets with high crystallinity. Amorphous GCN
In fact, it is found that the g-C3N4 calcined at high
temperature not only has an ultra-thin layered structure but
also high degree of polymerization, in which g-C3N4 has higher
crystallinity and fewer crystal defects and is beneficial to the
internal charge transfer. It has been found that theg-
C3N4calcinedat high temperature has different band gap and
edge position compared with the one obtained at low
(
A600GCN) was fabricated at 600 °C. Crystalline GCN (CGCN)
was obtained after heating A600GCNat 750 °C. A further high
temperature treatment could delaminate A600GCN and
increase the crystallinity. Afterwards, CGCN was calcined in the
presence of melamine at 650 °C to obtain an amorphous-
crystalline GCN (A-CGCN)ultra-thin layer using CGCN as seeds.
At high temperature, melem could form amorphous GCN on
a.School of Material Science & Engineering, University of Jinan, No. 336,
Nanxinzhuangxi Rd, Jinan, 250022, PR China, E-mail: mse_yangp@ujn.edu.cn.
b.Department of Materials Science & Engineering, National Tsing Hua University,
No. 101, Sec. 2, Guangfu Rd., Hsinchu City 300, Taiwan.
†Electronic
Supplementary Information (ESI) available: Experimental section, Photocatalytic
performance test, nitrogen adsorption-desorption, XPS, PL spectra, TEM images,
UV-vis spectra for AGCN, CGCN and A-CGCN. See DOI: 10.1039/x0xx00000x
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Scheme 1 Preparation illustration of A-CGCN composites.
the surface of CGCN to generate a A-CGCN junction. The
amorphous-crystalline g-C3N4homo-junction (A-CGCN), which
is composed of AGCN and CGCN with a similar composition but
different crystal structure, has different energy band structure
was finally created.
Fig. 1a, b, and c show the transmission electron microscopy
(TEM) images of samples AGCN, CGCN and A-CGCN,
respectively. All of samples revealed thin nanosheet
morphology. Compared with sample AGCN, the size of sample
CGCN is small because of treatment at much high temperature.
As expected, ultra-thin AGCN nanosheets (Fig. 1c) were
formed after the thermal polymerization. The specific surface
area of sample CGCN was found to be the largest (119.1 m2/g)
due to the treatment at much high temperature (750 °C). The
specific surface area of sample A-CGCN (87.6 m2/g) was
significantly increased compared with sample AGCN (57.7 m2/g)
from the Brunauer Emmett Teller (BET) analysis (Fig. S1 and
Table S2, ESI†). CGCN has a larger specific surface area than A-
CGCN but its performance is worse, so the improvement of A-
CGCN performance is mainly due to the formation of
homojunctions. That is, the effect of the specific surface area is
secondary in the experiment, and the main effect is due to the
proper homojunction and good crystallinity.
Fig. 1TEM images and XRD patterns of samples. TEM images of
samples AGCN (a), CGCN (b), A-CGCN(c). (d) XRD patterns. (e) HRTEM
image of A-CGCN. SAED patterns of AGCN(f), CGCN (g), A-CGCN (h).
surface of the sample. The C 1s spectrum (Fig.S2b, ESI†)
indicates that the two peaks at 284.3 and 287.5eV correspond
to the standard reference carbon (C-C) and sp2 hybridization at
C in N=C-(N)2, respectively (the spectrum of N 1s in Fig. S2c,
ESI†). The four peak posiꢀons corresponding to C-N=C
(398.1eV, Pyridinie-C), N-(C)3 (399.6eV, Pyrrole-C), N-H group
(400.6 eV, Graphitic-C) and π-excitation (403.8 eV).14 The XPS
analysis indicates sample CGCN and AGCN revealed similar
elemental composition and existence state with sample A-
CGCN.
The X-ray diffraction (XRD) patterns of samples AGCN, CGCN
and A-CGCN are presented in Fig. 1d. It is noteworthy that two
characteristic peaks at 12.8° and 27.9° for samples AGCN,
CGCN and A-CGCN corresponded to the (100) and (002) planes,
respectively. The former is the characteristic peak caused by
the periodic arrangement of the triazine in g-C3N4, the latter is
the stacking of the conjugated aromatic system of carbon
nitride, suggesting that samples AGCN, CGCN and A-CGCN
maintain g-C3N4 phase. The XRD peak intensity of sample
CGCN (10506) is high compared with sample AGCN (6646). This
demonstrates that calcination at high temperature improved
the crystallinity of g-C3N4. Sample A-CGCN (8637) revealed
higher peak intensity than that of sample AGCN because of
addition of CGCN. X-ray photoelectron spectroscopy (XPS)
analysis further indicates the elemental composition and
existence state of samples. The full XPS spectra of samples A-
CGCN, AGCN, and CGCN were tested (Fig. S2, S3 and S4,
ESI†).The result indicates that these samples contain only three
elements of C, N and O. No other extra peak was observed.
The peak of O element is ascribed to the H2O adsorbed on the
Fig. 1e shows the high resolution transmission electron
microscopy (HRTEM) image of sample A-CGCN. Phase AGCN and
CGCN have different crystallinity due to different calcination
temperatures. The HRTEM image of phase CGCN displays that
the lattice distance ofg-C3N4 layer is 0.324 nm, corresponding
to the (002) inter planes. Phase CGCN exhibited clear lattice
fringes compared with AGCN, exhibiting that CGCN has better
crystallinity. To further study the crystallinity of samples, the
selected area electron diffraction images of samples AGCN,
CGCN and A-CGCN are shown in Fig. 1f, g and h. As expected,
sample AGCN is relatively more amorphous shown by absence
of diffraction spots or rings (Fig. 1f). The presence of some
clear diffraction rings in Fig. 1g indicates sample CGCN is with
high crystallinity. Because sample A-CGCN contains a small
amount of CGCN, a weak diffraction ring was observed in Fig.
1h. This result suggests that A-CGCN forms in the CGCN after
the thermal polymerization process.
The energy band structure of samples determined by UV-vis
diffuse reflectance test (UV-vis DRS) and the XPS valence band
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Fig. 2 (a) UV-vis DRS and (b) plots of (αhν)1/2 vs photon energy of AGCN,
CGCN and A-CGCN. (c) XPS valence band spectra of samples AGCN and CGCN.
(d) Schematic illustration of electron-hole separation and transport at A-
CGCN heterojunction interface and in AGCN and CGCN.
(VB) spectroscopy shown in Fig. 2 are investigated for the
discussion of photocatalytic mechanism. The band edge of A-
CGCN is located between AGCN and CGCN, which further
confirmed the electronic coupling of these two components in
the A-CGCN homojunction via polymerization. The tangents to
the cross section of plots of (αhν)1/2 vs photon energy
generally show the band gap width are 2.59, 2.76 and 2.7 eV
for samples AGCN, CGCN and A-CGCN (Fig. 2b), respectively.
The different band gaps of AGCN and CGCN make it possible to
prepare a homogenous junction with a matched energy level
structure.
Fig. 3 (a) Photocatalytic degradation of RhB renderings and (b) fitting
histogram of photocatalytic degradation of RhB; (c) effect of capture
agent on the photocatalytic activity of A-CGCN;(d) H2 production
curves and (e) apparent rate constants for H2 evolution of AGCN and
A-CX%GCN(X = 0.5, 4, 6, 10) samples under visible light (λ > 420 nm);
(f)stability test of A-C6%GCN for four cycling H2 evolution.
photoluminescence (PL) spectra (Fig. S5, ESI†).Namely, the
weakening of the luminescence peak of sample CGCN is
ascribed to the better crystallinity, which facilitates electron
transfer to the sample surface. The weakening of the emission
peak of A-CGCN is mainly due to the accumulation of holes and
electrons on CGCN and AGCN, respectively, resulting in the
separation of space.
The energy band structures of samples AGCN and CGCN are
further characterized by XPS valence band analysis (Fig. 2c).15 It
shows that the valence band positions of AGCN and CGCN
differ by 0.5 eV. According to the band gaps of AGCN and
CGCN obtained from Fig. 2b, the difference between AGCN
and CGCN in the conduction band position is 0.33 eV.
Photocatalytic mechanism is proposed in Fig. 2d based on the
band gap data.
The visual evaluation of photocatalytic performance
improvement is characterized by photocatalytic degradation of
organic pollutants and H2 evolution from splitting water under
In the case of visible light irradiation, the electrons in the
valence band are excited and transferred to the conduction
band while holes are left in the valence band. Because the
different conduction band and valence band of AGCN and
CGCN are 0.33 and 0.5 eV, respectively (Fig. 2d), the transfer of
electrons on the AGCN conduction band to the conduction
band of CGCN occurred while the holes on the valence band of
CGCN was transferred to the valence band of AGCN. The
driving force of this charge transfer is the potential difference
between AGCN and CGCN. This directional transfer of
electrons and holes results in the major accumulation of
electrons on the CGCN and the concentration of holes mainly
on the AGCN. The spatial separation of these charges would be
beneficial to reduce the recombination rate of electron-hole
pairs. In addition, CGCN has high crystallinity and few internal
defects, making it easier for electrons to migrate to the CGCN
surface in the reduction reaction, which is consistent to
visible light irradiation (λ
≥420 nm). Fig. 3a and b show the
results of RhB degradation under visible light. A-CGCN has the
best degradation effect and degrades 100% within 10 min. In
contrast, AGCN and CGCN degrade 30 and 70%, respectively.
The histogram of sample A-CGN (Fig. 3b) shows that the
degradation rate of sample A-CGN is 5.7 times high compared
with sample AGCN. Furthermore, the photocatalytic testing of
samples AGCN and CGCN were carried out after physically
mixing, the effect is much worse than the effect of A-CGCN. It
is confirmed that the formation of type II homogeneous
junctions by AGCN and CGCN can obviously improve its
performance.
In order to further study the photocatalytic reaction
mechanism and active species, the active species capture
experiment was performed (Fig.3c). AgNO3, triethanol amine
(TEOA), para-benzoquinone (BQ), tertiary butanol (TBA) were
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used as capture agents for e-, h+, O2 and ·OH, respectively. degradation of organic pollutants such as RhB. The hydrogen
When AgNO3 and BQ were added to the photocatalytic system, generation efficiency of sample A-CGCN with 6% CGCN is 57
there is no significant effect in the photocatalysis. On the times high compared with that of AGCN nanosheets under
contrary, the photocatalytic effect decreased apparently when visible light irradiation. The result is expected to be utilizable
TEOA and TBA were added to the solution. However, the for improvement of the construction and property of g-C3N4
inhibition of photocatalytic performance after addition of TBA composites.
is not as effective as TEOA. In the photocatalytic system of A- This work was supported in part by the projects from the
C0.5%GCN, the main active substances are h+ and the secondary National Natural Science Foundation of China (no. 51572109
active substance is ·OH. The electron-hole separation and and 51772130)
transport at A-CGCN heterojunction interface and in AGCN and
CGCN was indicated in Fig. 2d. The electrons and holes are
Conflicts of interest
spatially and directionally separated, resulting in an increase in
the concentration of holes and electrons. Most of the holes
are directly used to degrade RhB, and the remaining holes
There are no conflicts to declare.
react with H2O to form ·OH and then oxidative decompose
RhB. Meanwhile, electrons do not combine with surface-
Notes and references
-
adsorbed O2 to form O2 , but rather exists in the form of an
1
2
3
(a) X. Wang, K. Maeda and A. Thomas, Nature, 2009,
(b) G. Liu, P. Niu and C. Sun, J. Am. Chem. Soc., 2010, 132
11642;(c) T. Xiong, W. Cen and Y. Zhang, ACS Catal., 2016,
2462;(d) Y. Chen, Q. Zhou and G. Zhao, Adv. Funct. Mater.,
2017; (e) W. J. Ong, L. L. Tan and Y. H. Ng, Chem. Rev, 2016,
116,7159.
(a) K. Dai, L. Lu and C. Liang, Appl. Catal. B-Environ., 2014,
156, 331; (b) X. Chen, W. Lu and T. Xu, Chem. Eng. J., 2017,
328, 853; (c) S. Cao and J. Yu, J. Phys. Chem. Lett., 2014,
2101; (d) Q. Tay, P. Kanhere, C. F. Ng, J. Mater. Chem. A,
8, 76;
excited state, which is more advantageous to the reaction of e-
with H2O to produce H2, improving the performance of
photocatalytic hydrogen production. To eliminate the effect of
heat on the degradation efficiency during photocatalysis,
sample ACGN* is kept at 60 °C under the dark (Fig. S6, ESI†).
To investigate the effect of amount of CGCN on the
photocatalysis activity, the ratio of CGCN in A-CGCN junctions
was adjusted (Table S1, ESI†). In addition, Pt was loaded on A-
CGCN for H2 generation from splitting water. The results
indicate that the ideal loading of Pt is 2 wt% and the optimized
weight ratio of CGCN in A-CGCN was 6% (Figs. S7 and S8, ESI†).
Fig. 3d and e show the H2 evolution from splitting water,
displaying a significant performance difference between AGCN
and A-CGCN, in which the efficiency of sample A-CGCN (1179
µmolh-1g-1) is 57 times of that of sample CGCN (20.5 µmolh-1g-
1). This is ascribed to the formation of A-CGCN junctions
because the hydrogen generation efficiency of sample
AGCN+CGCN obtained by physically mixing AGCN and CGCN is
similar to sample AGCN (Fig. S8, ESI†). The photocatalytic
performance improvement of sample A-CGCN is ascribed to
the following reasons, AGCN and CGCN are polymers with the
same crystal structure, through polymerization reaction to
form A-CGCN is more closely linked, II) the potential difference
between AGCN and CGCN promotes the spatial separation of
electrons and holes, reducing the recombination rate, III)
CGCN reveals fine crystallinity and few internal defects,
resulting in efficient electron transfer to the surface.
Furthermore, after four cycles, the hydrogen generation
efficiency of sample A-CGCN was not degraded obviously as
shown in Fig. 3f and their morphology was not changed(Fig. S9,
ESI†), indicating sample A-CGCN is with high stability.
,
6
,
5,
2015, 27, 4930; (e) J. Zhang, Y. Wang and J. Jin, ACS Appl.
Mater. Inter., 2013, , 10317.
(a) D. Feng, Y. Cheng and J. He, Carbon, 2017, 125, 454; (b) H.
Shi, G. Chen and C. Zhang, ACS Catal., 2014, , 3637; (c) M.
5
4
Bellardita, E. I. García-López, G. Marcì, Appl. Catal. B-Environ.,
2018, 220, 222.
H. Shi, G. Chen and C. Zhang, ACS Catal., 2014, 4, 3637-3643.
(a) X. Chen, Y. Jun, K. Takanabe, K. Maeda, K. Domen, X. Z. Fu
，
4
5
M. Antonietti and X. Wang, Chem. Mater., 2009, 21,4093; (b)
J. Zhang, F, Guo and X. Wang, Adv. Funct. Mater., 2013, 23,
3008; (c) X. Li, J. Zhang, X. Chen, A. Fischer, A. Thomas, M.
Antonietti and X. Wang, Chem. Mater., 2011,23, 4344; (d) J.
Sun, J. Zhang, M. Zhang, M. Antonietti, X. Fu and X. Wang,
Nat. Commun., 2012,3, 1139; (e)G. Jiang, C. Zhou, X. Xia, F.
Yang, D. Tong, W. Yu and S. Liu, Mater. Lett., 2010, 64, 2718.
S. W. Cao, Y. P. Yuan, J. Fang, Int. J. Hydrogen Energ, 2013, 38
1258.
6
,
7
8
F. He, G. Chen and Y. Yu, Chem .Commun., 2015, 51, 6824.
Y. Hou, A. Laursen, J. Zhang, G. Zhang, Y. Zhu, X. Wang，S.
Dahl and I. Chorkendorff, Angew. Chem. Int. Ed., 2013, 52
3621.
,
9
J. Zhang, M. Grzelczak, Y. Hou, K. Maeda, K. Domen, X. Fu, M.
Antonietti and X. Wang, Chem. Sci., 2012, , 443.
3
10 M. Yang, Q. Huang and X. Jing, Mater. Sci. Eng. B, 2012, 177
600.
,
11 J. Fu, Y. Tian, B. Chang, F. Xi and X. Dong, J. Mater. Chem.,
2012, 22, 21159.
12 H. Xu, J. Yan, Y. Xu, Y. Song, H. Li, J. Xia, C. Huang and H. Wan,
Appl. Catal. B: Environ., 2013,129, 182.
13 F. He, ACS Appl. Mater. Inter., 2014, 6, 7171.
In conclusion, an optimized calcination condition at high
temperature delaminated g-C3N4 and improved the
crystallinity, which leads to a different energy band structure
without changing crystal structure. A two-step calcination
process made superior thin g-C3N4 with fine crystallinity and
large surface area. A-CGCN homojunctions with a compatible
phase ratio were created by a two-step polymerization of
melem using crystalline g-C3N4nanosheets as seeds. The A-
CGCN revealed a superior photocatalytic performance for the
14 J. Meng, J. Pei and Z. He, RSC Advances, 2017, 7, 24097-
24104.
15 F. Dong, Z. Zhao and T. Xiong, ACS Appl. Mater. Inter., 2013,
, 11392.
5
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