Efficient Fe2O3/C-g-C3N4 Z-scheme heterojunction photocatalyst prepared by facile one-step carbonizing process

Article abstract of DOI:10.1016/j.jpcs.2019.02.017

Photocatalytic water purification has emerged as new effective ways for an environment preserve and purification in few decades. As a part of studies on photocatalytic water purification, constructing heterojunction structured compounds with different photocatalysts for efficient organic pollutant degradation is regarded as key-strategy. Herein, facile one-step carbonizing process was introduced for synthesizing Fe₂O₃/C-g-C₃N₄ based Z-scheme heterojunction photocatalyst. The two times of photocatalytic organic pollutant degradation rate of Fe₂O₃/C-g-C₃N₄ based Z-scheme heterojunction photocatalyst was enhanced comparing with pristine Fe₂O₃/g-C₃N₄ heterojunction photocatalyst through rhodamine B (RhB) degradation under AM 1.5G (100 mWcm^?2, 1 sun) illumination. The reasons for enhanced photocatalytic RhB degradation efficiency of Fe₂O₃/C-g-C₃N₄ based Z-scheme heterojunction photocatalyst were revealed to efficient charge transfer during light induced RhB degradation reaction by constructing junction structures among Fe₂O₃, amorphous carbon layer and g-C₃N₄, which proved by fluorescence spectroscopy, XPS, SEM, TEM and UV–Vis analysis.

Full text of DOI:10.1016/j.jpcs.2019.02.017

Accepted Manuscript
Efficient Fe O /C-g-C N Z-scheme heterojunction photocatalyst prepared by facile
3 4
2
3
one-step carbonizing process
Myung Jong Kang, Hyejin Yu, Wonjoo Lee, Hyun Gil Cha
PII:
S0022-3697(18)32759-8
https://doi.org/10.1016/j.jpcs.2019.02.017
PCS 8915
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 12 October 2018
Revised Date: 28 January 2019
Accepted Date: 17 February 2019
Please cite this article as: M.J. Kang, H. Yu, W. Lee, H.G. Cha, Efficient Fe O /C-g-C N Z-scheme
3 4
2
3
heterojunction photocatalyst prepared by facile one-step carbonizing process, Journal of Physics and
Chemistry of Solids (2019), doi: https://doi.org/10.1016/j.jpcs.2019.02.017.
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ACCEPTED MANUSCRIPT
Graphical abstract
1

ACCEPTED MANUSCRIPT
Efficient Fe O /C-g-C N Z-scheme heterojunction photocatalyst prepared by facile
2
3
3
4
one-step carbonizing process
a
a
b
a,
Myung Jong Kang, Hyejin Yu, Wonjoo Lee, Hyun Gil Cha *
a
Bio-based Chemistry Research Center, Korea Research Institute of Chemical Technology
KRICT), 406-30, Jongga-ro, Jung-gu, Ulsan 44429, Republic of Korea
(
b
Chemical Industry Development Research Center, Korea Research Institute of Chemical
Technology (KRICT), 45, Jongga-ro, Jung-gu, Ulsan 681-802, Republic Korea
*
Corresponding author;
Email address: hgcha@krict.re.kr. (H. G. Cha)
1

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Abstract
Photocatalytic water purification has emerged as new effective ways for an environment
preserve and purification in few decades. As a part of studies on photocatalytic water
purification, constructing heterojunction structured compounds with different photocatalysts
for efficient organic pollutant degradation is regarded as key-strategy. Herein, facile one-step
carbonizing process was introduced for synthesizing Fe O /C-g-C N based Z-scheme
2
3
3
4
heterojunction photocatalyst. The two times of photocatalytic organic pollutant degradation
rate of Fe O /C-g-C N based Z-scheme heterojunction photocatalyst was enhanced
2
3
3
4
comparing with pristine Fe O /g-C N heterojunction photocatalyst through rhodamine B
2
3
3
4
-2
(
RhB) degradation under AM 1.5G (100 mWcm , 1 sun) illumination. The reasons for
enhanced photocatalytic RhB degradation efficiency of Fe O /C-g-C N based Z-scheme
2
3
3
4
heterojunction photocatalyst were revealed to efficient charge transfer during light induced
RhB degradation reaction by constructing junction structures among Fe O , amorphous
2
3
carbon layer and g-C N , which proved by fluorescence spectroscopy, XPS, SEM, TEM and
3
4
UV-Vis analysis.
Keywords: Photocatalysis; Iron oxide; g-C N ; Z-scheme heterojunction; Photodegradation.
3
4
2

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1
. Introduction
As the potential ramifications of environmental damage become clear, efforts on protecting
environment and improving global environmental standards for environmental pollution
control have become an important issue. In recent decades, the development of environmental
purification methods and materials, which are economically efficient, have been studied
intensively. To that end, the degradation of organic pollutants during water purification by
various catalytic methods have been investigated for the purification of industrial and
municipal effluents. In this manner, various photocatalysts based on metal oxides such as
TiO , [1-3] ZnO, [4] and NaBiO [5] have been applied for organic pollutant degradation,
2
3
mineralization of dyes and indoor volatile organic compounds (VOCs) [6, 7]. For enhanced
photocatalytic degradation efficiency for azo dyes, like rhodamine B (RhB), methyl orange
(MO), and methylene blue (MB), construction of heterojunction photocatalysts within a
composite structure of photocatalytic metal oxides with dopants, [8-10] nanocomposites with
double species metal oxide photocatalysts, [11-13] and carbon-based materials with metal
oxide photocatalysts [14-17] have been widely investigated.
However, it remains challenging to develop metal-oxide-based photocatalysts with high
chemical stability at various pH ranges, while maintaining high photocatalytic properties. For
this, α-phase Fe O (hematite) is an attractive photocatalytic material which has optimum
2
3
band position for efficient solar light absorption in the region where the sun emits maximum
energy [18]. In addition, hematite is an abundant material in nature, which means that is has
high economic efficiency and corrosion resistivity in alkaline and acidic media [19].
Graphitic carbon nitride (g-C N ), a triazine-structured metal-free semiconductor, has high
3
4
reducibility and visible light absorption while being economically efficient [20]. However,
applying g-C N for solar fuel generation and efficient organic pollutant degradation is limited
3
4
3

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by the rapid charge recombination of g-C N . As a result, multi-component photocatalysts
3
4
which construct heterojunction photocatalysts from semiconductors and g-C N have been
3
4
studied widely. These composite photocatalysts exhibit much higher photoactivity than pure
g-C N due to a double charge transfer mechanism in which the photo-generated electrons in
3
4
the conduction band of g-C N are injected into the other semiconductor [21-23]. By
3
4
constructing Z-scheme catalysts, which the photo-generated electrons in the conduction band
of the semiconductor are injected into the valance band and annihilate the hole of g-C N , the
3
4
photocatalytic activity of heterojunction photocatalysts can be improved [24, 25].
In this study, highly photoactive heterojunction photocatalysts containing Fe O and g-C N
2
3
3
4
4
are reported. Heterojunction structure for both double charge transfer (Fe O /g-C N
2
3
3
heterojunction photocatalyst, Fg) and Z-scheme (Fe O /C-g-C N
4
heterojunction
2
3
3
photocatalyst, FCg) heterojunction catalyst were constructed, and their photocatalytic
characteristics were measured by investigating their RhB degradation properties.
2
. Experimental procedures
2
-1. Synthesis of the Fe O /g-C N (Fg) heterojunction photocatalyst
2
3
3
4
To synthesize Fe O nanoparticles, 10 ml of a 0.17 M FeCl (Sigma-Aldrich) solution
2
3
3
and 10 ml of 0.085 M NaNO (Sigma-Aldrich) were mixed. After 30 min, a 0.09 M
3
concentration of HCl (Dajeong Chemical) was added to the mixture and stirred. After
an additional 30 min, 1.5 g of oxalic acid (Sigma-Aldrich) was added to the solution
and stirred. The resulted green-yellow solution was transferred to a Teflon-lined
autoclave reactor and reacted at 393 K for 2 h. The autoclave reactor was cooled
naturally, and the bright yellow precipitate was collected and washed several times
with water and ethanol. The collected particles were annealed at 853 K for 4 h under
4

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an air atmosphere. A g-C N was synthesized by annealing 0.5 g of melamine (Sigma-
3
4
Aldrich) at 833 K for 2 h at a heating rate of 20 K/min under a N flow. The Fg was
2
synthesized by annealing a mixture of Fe O and g-C N (1:1 wt.%) at 853 K over 4 h
2
3
3
4
at a heating rate of 20 K/min under a N flow.
2
2
-2. Synthesis of the Fe O /C-g-C N (FCg) heterojunction photocatalyst
2 3 3 4
FCg was synthesized using one-step facile methods with a solid-state carbonizing
reaction by modification of previously reported method [26]. The FCg was
synthesized by annealing a mixture of the bright yellow precipitate (FeOOH, produced
by the same synthesis reactions with Fe O nanoparticles as above, but excluding the
2
3
post-annealing step in air) with g-C N (1:1 wt.%) at 853 K for 4 h at a heating rate of
3
4
2
0 K/min under a N flow.
2
2
-3. Characterization
The surface morphology of the Fg and FCg heterojunction photocatalysts were
investigated using scanning electron microscopy (SEM, Hitachi Horiba S-4300)
operated with a 5 kV incident electron beam. Energy-dispersive X-ray spectroscopy
(
EDS) and high-resolution transmission electron microscopy (HR-TEM) analyzes were
performed with transmission electron microscopy (TEM, JEOL 2100F) operated with a
00 kV incident electron beam. The crystal structure was investigated by X-ray
2
-1
diffraction (XRD, Rigaku Ultima 2000) with scan speed of 1 deg.min over the range
of 20-80 deg. in 2θ mode using Cu K radiation. UV-Vis measurements were
α
performed with diffuse reflectance spectroscopy (Varian 7000) for the Fg and FCg
heterojunction photocatalysts mixed with BaSO (Sigma-Aldrich) in the range of 800-
4
5

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4
00 nm. The chemical binding states of the Fg and FCg heterojunction photocatalysts
were investigated using X-ray photoelectron spectroscopy (XPS, Kratos Ultra DLD)
with Al K radiation. To obtain emission spectra of g-C N , Fg and FCg, fluorescence
α
3
4
spectrometer (Hitach-F700) was used under excitation light of 375 nm.
2
-4. Photocatalytic evolution
Photocatalytic decomposition of RhB was carried out in a home-made reaction
apparatus under an illumination of 1 sun. RhB was selected as a standard dye for
investigation of photocatalytic activity. The samples were illuminated with simulated
sunlight from a 300 W xenon lamp (Asahi Spectra HAL-320, ozone free) using a HAL
2
AM 1.5G filter with a measured intensity of 1 sun (100 mW/cm , spectrally corrected)
fixed at 15 cm above the solution surface for the photodegradation experiments. The
experimental set up was designed according to the following scheme 1. To study the
effect of different band structures on the photodegradation of RhB, experiments were
carried out with Fe O powder, Fg and FCg. Each 0.05 g of photocatalysts was mixed
2
3
-5
individually with 60 ml of RhB solution (10 M) in water. The dye degradation rate
was monitored using a UV-Vis spectrophotometer. The photocatalytic efficiency (η)
was calculated according to Eq. (1) as follows:
η = (C – C) / Co× 100%
(1)
o
where C and C are the concentration of RhB at time t = 0 (initial RhB concentration)
o
and t = t (final RhB concentration) after photoirradiation, respectively. The
concentration of the target dye is calculated using a calibration curve. The maximum
absorption of RhB occurred at 552 nm.
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3
. Results and Discussion
-1. Structure of the Fg and FCg heterojunction photocatalysts
3
The morphology of the synthesized Fg and FCg heterojunction photocatalysts were
investigated by SEM. In the Fg heterojunction photocatalyst shown in Fig. 1a, which
the g-C N particles are attached on the Fe O surface, and the surface is covered by a
3
4
2
3
thin g-C N layer on the Fe O particles (Fig. 1b). The morphology of FCg is shown in
3
4
2
3
Fig. 1c. The g-C N attached to the Fe O surface, which is covered by a carbon layer
3
4
2
3
and g-C N layer on the Fe O particles (Fig. 1d). The existence of thin layers of
3
4
2
3
carbon and g-C N on the Fe O in FCg and a thin layer of g-C N on the Fe O in Fg
3
4
2
3
3
4
2
3
were also revealed by TEM images, as shown in Fig. 2a and 2c, respectively. In the
HR-TEM image of Fg (Fig. 2b), the g-C N particles attached directly on the surface of
3
4
Fe O . However, in case of FCg (Fig. 2d), the thin carbon layer covered the surface of
2
3
the Fe O particles within a thickness of 1-2 nm, while the thin-layered g-C N
4
2
3
3
particles attached on carbon layer coated Fe O particles.
2
3
The carbon layer coated on the surface of FCg was also confirmed by TEM-EDS
analysis. According to the TEM-EDS component analysis, Fg was 38% Fe, 57% O, 4%
C, and 1% N as atomic ratios (Fig. S1) and the composition of FCg contained atomic
ratios of 32% Fe, 53% O, 14% C, and 1% N (Fig. S2). In both Fg and FCg, the atomic
ratio between Fe and O were in good agreement with the equivalent atomic ratio
between Fe and O for Fe O . Additionally, the high carbon atomic ratio in FCg (14%)
2
3
compared to that of Fg (4%) confirmed that FCg has a layer structure with thin layers
of carbon and g-C N particles are attached on the carbon coated Fe O surface, which
3
4
2
3
are consistent with HR-TEM images.
7

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The thin carbon layer between Fe O nanoparticles and g-C N was derived from
2
3
3
4
annealing process of FeOOH- g-C N . During the thermal decomposition process,
3
4
water vapor from FeOOH intercalated on layer stacking structure of g-C N , reducing
3
4
the Van der Waals’ forces between g-C N layers. Because of reduced Van der Waals’
3
4
forces between g-C N layers, g-C N is exfoliated and some of exfoliated g-C N
3
4
3
4
3
4
layer being carbonized during thermal carbonizing process. The formed Fe O
2
3
nanoparticles from FeOOH attached on this g-C N /carbon particle, finally,
3
4
constructing Fe O /carbon/g-C N Z-scheme heterojunction structure.[26]
2
3
3
4
As shown in Fig. 3, Fg and FCg exhibited an amorphous phase, which appeared as a
wide bump in the range of approximately 10 to 30 deg. in the XRD patterns, instead of
sharp peaks for carbon and g-C N (Fig. 3). It means that amorphous carbon layer is
3
4
exist in Fg and FCg. Based on TEM study, the g-C N nanoparticles are attached on
3
4
the Fe O in Fg and both g-C N particle and thin carbon layer are attached on the
2
3
3
4
Fe O in FCg. In addition, Fg and FCg showed clear peaks which are well matched
2
3
with the previously reported XRD peaks of Fe O [19] and g-C N [20].
2
3
3
4
The chemical binding state of each atom in Fg and FCg was confirmed by XPS
analysis. The XPS survey scan spectra of Fg and FCg are shown in Fig. S3. As shown
in Fig. 4a, the high-resolution C 1s spectra display a peak at 284.8 eV, which is
2
assigned to the surface carbon on Fe O in FCg and the sp hybridized carbon in the
2
3
aromatic ring attached to the (-NH ) group in the g-C N in both Fg and FCg [27, 28].
2
3
4
The Fe 2p spectra shown in Fig. 4b were deconvoluted into two peaks at 724.1 eV and
10.8 eV in both Fg and FCg. These two peaks at 724.1 eV and 710.7 eV are
7
3+
correspond to Fe 2p and 2p of typical Fe O , respectively [29]. For the N 1s XPS
3/2
1/2
2
3
spectra, the signal was deconvoluted into two peaks at 401.2 eV and 398.9 eV for FCg,
8

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and at 401 eV and 398.6 eV for Fg (Fig. 4c). The main peak at 398.9 eV for FCg and
2
3
98.6 eV for Fg are attributed to the sp N involved in the triazine ring [27]. The other
N 1s peaks at 401.2 eV for FCg and 401 eV for Fg, which are correspond to the
bridging of nitrogen atoms with carbon (N-(C) ) [30, 31]. The slightly higher binding
3
energy for FCg than Fg indicates that the existence of the thin carbon layer between
Fe O and g-C N . The O 1s spectra are shown in Fig. 4d; the peak at 530.2 eV is
2
3
3
4
corresponds to the Fe-O binding energy of Fe O ,[32] while the peak at 531.9 eV is
2
3
corresponds to the carbon-oxygen binding energy, and the peak at 533.5 eV is
corresponds to the hydroxyl group of FeOOH formed by water adsorption onto Fe O
2
3
[
33].
The results of the structural analysis with SEM, TEM, XRD, and XPS suggest that
FCg has a Z-scheme heterojunction between Fe O particle, carbon layer and g-C N
2
3
3
4
nanoparticles, while Fg has a heterojunction structure between the Fe O and g-C N
2
3
3
4
nanoparticles.
3
-2. Optical properties of the Fg and FCg heterojunction photocatalysts
The optical images of Fg and FCg are shown in Fig. 5a. Fg maintains the original red-
brown color of the Fe O , while the color of FCg has changed to gray. To
2
3
investigation optical absorption, UV-Vis diffuse reflectance spectrum (DRS) of Fg and
FCg are obtained and presented on Fig. 5b. Interestingly, both Fg and FCg showed
absorption on visible light region and FCg have higher absorption efficiency than Fg.
Two absorbance edges were observed in both Fg and FCg: one occurs at ca. 430 nm,
which is corresponds to the band gap energy of bulk g-C N , [27, 28] and the other
3
4
9

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occurs at ca. 560 nm, which is corresponding to the intrinsic narrow band gap of Fe O3
2
[
34].
The photoluminescence (PL) emission spectra was investigated to figure out
recombination rate of photogenerated electron-hole pairs and lifetime of charge
carriers. The typical fluorescence spectra of g-C N , Fg and FCg are displayed on Fig.
3
4
5
6
c. A g-C N showed a wide emission peak at around 468 nm with tails expanding to
3 4
50 nm, which is ascribed to the band-gap recombination of photo-excited electron-
hole pairs. After combining Fe O , Fg and FCg showed significantly reduced PL
2
3
intensity, relatively to g-C N , which indicates more efficient electron-hole separation
3
4
on the interface between F O and g-C N due to the formation of heterojunction
2
3
3
4
structures. In addition, carbon on the surface of semiconductors could afford
outstanding electron mobility. It is generally believed that the formation of
heterojunction structures in photocatalysts lead to the fast separation of electrons and
holes and thus, results in the high photodegradation activity. The recombination rate of
photo-induced electron-hole pairs is greatly suppressed, which lengthens the
lifetime of photo-generated carriers and subsequently favors the enhancement of
photocatalytic performance [35].
3
-3. RhB degradation properties of the Fg and FCg heterojunction photocatalysts
To evaluate the photocatalytic activity of the product, Fe O powder, Fg and FCg were
2
3
used to dye degradation experiments. RhB was selected as the model organic
pollutant. The mineralization mechanism of RhB by photocatalytic reaction in water is
like below equations (Eq (2)-(8)):
-
+
Fe O + hv
→
Fe O (e + h )
(2)
2
3
2
3
1
0

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-
+
-
+
e (Fe O ) + h (g-C N ) + hv
→
g-C N (e + h ) (3)
2
3
3
4
3
4
+
+
h (Fe O ) + H O
→
H +
•
OH
(4)
2
3
2
+
-
h (Fe O ) + OH
→
•
OH
(5)
2
3
-
-
-
O + e (g-C N )
→ •O2 (6)
2
3
4
•
OH + RhB (Colored)
→ CO + H O + degraded products (Decolored) (7)
2 2
-
•
O + RhB (Colored)
→ CO + H O + degraded products (Decolored) (8)
2 2
2
The absorbance spectrum for RhB (Fig. 6a), and UV-Vis absorption spectroscopy was
used to record the adsorption behavior of the solution after degradation experiment.
The evolution of the RhB absorbance spectra in the presence of Fe O powder, Fg and
2
3
FCg were investigated. The photocatalytic degradation process is divided into two
stages: in the first stage, RhB is immediately adsorbed, and in the second stage, the
RhB molecules are decomposed through the photocatalytic reaction. The concentration
of dye molecules was recorded as the RhB adsorption curve vs. time in the presence of
Fe O powder, Fg, and FCg under light irradiation (Fig. 6b). The results show that the
2
3
FCg heterojunction photocatalyst exhibited the highest rate of photodegradation
compared to that of the Fg heterojunction photocatalyst and the Fe O powder. This
2
3
indicates that the rate of photodegradation of the RhB dye is critically affected by the
heterojunction with an amorphous carbon layer between the g-C N and Fe O .
3
4
2
3
Considering that the photocatalytic reaction occurs on the surface of the photocatalyst,
the energetics on the surface depend on the photo-generated carrier separation and
migration. When the junction structure between Fe O and g-C N is formed, in case
2
3
3
4
of Fg, both Fe O and g-C N generates separated electron-hole pairs with light
2
3
3
4
irradiation. The generated holes flow from valance band of Fe O to valance band of g-
2
3
C N , meanwhile the generated electrons flow from conduction band of g-C N to
3
4
3
4
1
1

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conduction band of Fe O .[36, 37] However, when Z-scheme structure of Fe O and g-
2
3
2
3
C N is formed with carbon inter-layer, in case of FCg, only photo-generated electrons
3
4
in Fe O move from conduction band of Fe O to valance band of g-C3N4,
2
3
2
3
recombining with photo-generated holes in valance band of g-C N , supplying
3
4
electrons for electron-hole charge separation from valance band of g-C N to
3
4
conduction band of g-C N through internal carbon layer.[34, 38, 39] Considering the
3
4
organic pollutant degradation by photocatalysts are mainly occurred by light-generated
holes rather than light-generated electrons, because of converting oxygen to oxygen
radical for organic pollutant degradation is competitive reaction with hydrogen
evolution reaction in aqueous media,[40, 41] results in Z-scheme structured catalysts
can induce higher hole mobility for organic pollutant degradation rather than direct-
junction of heterojunction photocatalysts. Thus, the rate of photodegradation of RhB is
highest for FCg, while the rates of photodegradation with the Fe O and the Fg
2
3
heterojunction are lower.
photodegradation on the catalyst surface can be described as a first-order equation (Eq.
9)):
As shown in Fig. 6c, the kinetics of RhB dye
(
ln (C /C) = kt
(9)
o
-1
where k is the rate constant (min ), C is the initial concentration of RhB, and C is the
o
actual concentration of RhB at irradiation time t. The rate constant, k, is determined
from the slope of the linear relationship between ln (C /C) and the irradiation time.
o
The value of k gives an indication of the activity of the photocatalyst. It clearly reveals
that the decrease in dye concentration follows a linear pattern with the exposure time
for different heterojunctions. This indicates that the photodegradation of RhB obeys
the rules for a pseudo-first-order kinetic reaction. The RhB photodegradation with
1
2

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-1
FCg exhibits a maximum rate constant of about 0.043 min , which is approximately
-1
twice as fast as the 0.024 min , which is maximum efficiency with the Fg catalyst that
does not have a carbon layer on its surface. Based on the above analyses and
discussions, the photo-induced hole-charge separation and migration of the FCg
heterojunction photocatalyst is demonstrated, and it is corresponds to a Z-scheme
catalyst [24, 25, 42, 43].
4
. Conclusion
In summary, Fe O /g-C N (Fg) and Fe O /C-g-C N (FCg) heterojunction
2
3
3
4
2
3
3
4
photocatalysts were synthesized via simple solid-state reactions.
The FCg
heterojunction photocatalyst had an amorphous carbon layer between the FeOOH and
g-C N . XPS, TEM, and EDS mapping results confirmed the presence of a thin carbon
3
4
layer between the Fe O and g-C N in the FCg catalyst. The FCg heterojunction
2
3
3
4
photocatalyst exhibited enhanced RhB photocatalytic degradation efficiency, which
was two times greater than that of the Fg heterojunction photocatalyst. This is due to
the high charge carrier mobility and transfer ability of FCg, which induced by Z-
scheme heterojunction structure, resulting in enhanced RhB photocatalytic
degradation. This study can provide new strategies for increasing RhB degradation
during photo-induced water purification with photocatalysts.
Acknowledgements
This work was supported by the Korea Research Institute of Chemical Technology
(
KRICT) core project (SI1941-20&KK1941-30).
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Figure captions
Scheme 1. Scheme of reaction system for photocatalytic Rhodamine B degradation by FCg or
Fg heterojunction photocatalysts.
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Fig. 1. SEM images of (a) and (b) Fe O /g-C N (Fg) heterojunction photocatalyst, (c) and (d)
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Fe O /C-g-C N (FCg) heterojunction photocatalyst.
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Fig. 2. (a) TEM image of the Fe O /g-C N (Fg) heterojunction photocatalyst, (b) HR-TEM
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image of the surface of Fg (inset: FFT pattern of Fe O and g-C N ), (c) TEM image of the
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Fe O /C-g-C N (FCg) heterojunction photocatalyst, (d) HR-TEM image of the surface of
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FCg (inset: FFT pattern of Fe O and g-C N ),; the scale bars correspond to 200 nm in (a) and
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(c), and 5 nm in (b) and (d).
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Fig. 3. XRD patterns for Fg and FCg.
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Fig. 4. XPS spectra for Fg and FCg: (a) C 1s, (b) Fe 2p, (c) N 1s, and (d) O 1s
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Fig. 5. (a) Optical images, (b) UV-Vis diffuse reflectance spectra (DRS) and Fluorescence
spectra of of Fg and FCg.
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Fig. 6. RhB degradation properties with Fe O , Fg, and FCg.
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Fig. 7. Schematic of the electron-hole separation and migration pathway in FCg
photocatalysts.
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Highlights
ò Fe O /g-C- N (Fg) and Fe O /C-g-C N (FCg) heterojunction photocatalysts synthesized
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via simple solid-state reaction.
ò Z-scheme heterojunction between Fe O and g-C N was constructed by insertion of
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amorphous carbon layer.
ò Photocatalytic activities of double charge transfer heterojunction and Z-scheme
heterojunction between Fe O and g-C N heterojunction was studied.
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