Enhanced ethylene photodegradation performance of g-C3N4-Ag3PO4 composites with direct Z-scheme configuration

Article abstract of DOI:10.1002/chem.201404284

Photocatalytic oxidation of ethylene continues to be a challenge at the frontier of chemistry. In a previous report, a simple Ag₃PO₄ semiconductor material was shown to have strong photooxidative properties and efficiently oxidised water and decomposed organics in aqueous solution under visible-light illumination. Herein, its effects on the photo-oxidation of gaseous C₂H₄ were investigated by fabricating graphitic C₃N₄-Ag₃PO₄ composite semiconductors with direct Z-scheme configuration. It was found that both the ethylene photo-oxidative activity and the stability of Ag₃PO₄ are considerably improved by fabrication of Z-scheme composites. Moreover, stable C₂H₄ photo-oxidation activity could be obtained by treating the composite at 450°C for 3 h after long-term operation. From the point of view of environmental pollutant cleanup, the present technique avoids the side reaction of oxidising water and will be valuable for further investigations on both Ag₃PO₄ and CH degradation.

Full text of DOI:10.1002/chem.201404284

DOI: 10.1002/chem.201404284
Full Paper
&
Green Chemistry
Enhanced Ethylene Photodegradation Performance of g-C N –
3
4
Ag PO Composites with Direct Z-Scheme Configuration
3
4
[a, b]
[a]
[b]
Xuxing Chen,
Xintang Huang, and Zhiguo Yi*
Abstract: Photocatalytic oxidation of ethylene continues to
be a challenge at the frontier of chemistry. In a previous
report, a simple Ag PO semiconductor material was shown
the ethylene photo-oxidative activity and the stability of
Ag PO4 are considerably improved by fabrication of Z-
3
scheme composites. Moreover, stable C H photo-oxidation
3
4
2
4
to have strong photooxidative properties and efficiently oxi-
dised water and decomposed organics in aqueous solution
under visible-light illumination. Herein, its effects on the
photo-oxidation of gaseous C H were investigated by fabri-
activity could be obtained by treating the composite at
4508C for 3 h after long-term operation. From the point of
view of environmental pollutant cleanup, the present tech-
nique avoids the side reaction of oxidising water and will be
valuable for further investigations on both Ag PO and CH
2
4
cating graphitic C N –Ag PO composite semiconductors
3
4
3
4
3
4
with direct Z-scheme configuration. It was found that both
degradation.
Introduction
which can efficiently oxidise water and decompose organics in
aqueous solution when illuminated under sunlight. The strong
photo-oxidative capability of Ag PO triggered us to investi-
Ethylene (C H ) is a gaseous volatile organic compound (VOC)
2
4
3
4
that acts as a plant hormone having great influence on plant
gate its effects on the oxidation of gaseous C H . In compari-
2 4
[
1–2]
growth.
Ethylene released from fruits, vegetables, and flow-
son with liquid-phase photodegradation, isolating Ag PO
3 4
ers can accelerate aging and spoiling of plants. Even small
amounts of C H gas in the atmosphere in a storage facility
from aqueous solution is helpful to avoid the side reaction of
oxidising water and thus prolong its stability.
2
4
can induce undesirable reactions in most fresh products, such
as development of senescence, bitter flavours, chlorophyll loss,
disease susceptibility, and physiological disorders. Consequent-
It is well known that plant photosynthesis involves a Z-
scheme system with two photochemical processes: photosys-
tems PS I and PS II. In plants, the two processes take place si-
multaneously in time but separately in space, and this inspired
scientists to design effective artificial solar photocatalytic sys-
tems by mimicking the Z-scheme configuration of plants.
Some artificial Z-scheme photocatalysts consisting of two semi-
conductors that can catalyse H and O generation, respective-
[3]
ly, the removal of trace amounts of ethylene is imperative.
Previously, biotechnological materials, such as soil bacteria,
dry biobeds, and biofilters, were applied for the removal of
[
4–7]
ethylene.
However, high production costs and inefficiency
in removing trace amounts of ethylene are drawbacks of these
methods. Semiconductor photocatalysts have received great
attention due to their applications in environmental pollution
2
2
ly, along with an electron mediator, have been developed for
splitting water into H and O . The electron mediator plays
2
2
[
8–16]
remediation as well as solar energy conversion.
Photocata-
a role in shuttling the photogenerated electrons between the
[23]
lytic oxidation of ethylene is a promising alternative and has
attracted considerable attention over the last ten or more
H and O photocatalysts. Since the energy level of the con-
2 2
duction-band (CB) bottom of Ag PO is more positive than the
3
4
[
17–21]
ꢀ
*
ꢀ
[24]
years.
The development of highly active photocatalysts re-
reduction potential of O (O +e ! O , ꢀ0.33 V vs. NHE),
2
2
2
[
22]
mains a challenging task. Previously, we reported the strong
photo-oxidation properties of silver orthophosphate (Ag PO ),
making a Z-scheme system by introducing another semicon-
ductor will be of benefit not only for C H removal, but also for
3
4
2
4
prolonging the lifetime of Ag PO if the photoexcited electrons
3
4
[
a] X. X. Chen, Prof. X. T. Huang
in the CB of Ag PO can be transferred to the newly introduced
3
4
Institute of Nanoscience and Nanotechnology
Department of Physics, Central China Normal University
Wuhan 430079 (P. R. China)
semiconductor. Graphitic carbon nitride (g-C N ) was intro-
3
4
duced herein on the basis of the facts that 1) a large specific
surface area is good for adsorption of gas molecule; 2) a
highly negative conduction band minimum (ꢀ1.12 V vs. NHE)
[b] X. X. Chen, Prof. Z. G Yi
Key Laboratory of Optoelectronic Materials Chemistry and Physics
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences, Fuzhou 350002 (P. R. China)
Fax: (+86)0591-83714946
is beneficial to the reduction of O and a not too low valence
2
band (VB, +1.57 V vs NHE) makes the transfer of photoexcited
electrons from the CB of Ag PO to the VB of g-C N possible;
E-mail: zhiguo@fjirsm.ac.cn
3
4
3
4
3
) the cheap and simple synthetic route favours large-scale
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404284.
[25–30]
manufacture and modifications.
Moreover, such a Z-
Chem. Eur. J. 2014, 20, 1 – 8
1
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
scheme system is beneficial to g-C N in photodecomposition
3
4
of gaseous organic contaminants, because the potential of its
valence-band (VB) top is more negative than the oxidation po-
ꢀ
ꢀ
+
*
[31–33]
tential of OH (OH +h ! OH, +2.59 V vs. NHE),
as men-
tioned above. Based on the aforementioned considerations,
a direct g-C N –Ag PO Z-scheme photocatalyst without an
3
4
3
4
electron mediator was prepared for the first time by a facile
route utilising affordable AgNO , Na HPO , and urea as the
3
2
4
[
34–35]
feedstocks,
and its effects on photodegradation of ethyl-
ene were examined.
Results and Discussion
X-ray diffraction patterns of g-C N , Ag PO , and g-C N –
3
4
3
4
3
4
Ag PO4 composites before and after C H photodegradation
3
2
4
are shown in Figure 1. Diffraction peaks for a well-crystallised
Figure 2. Typical SEM images of as-prepared samples of a) Ag
c) 50% g-C –50% Ag PO , and d) 30% g-C –70% Ag PO . e) TEM and
f) HRTEM images of 70% g-C –30% Ag PO
3 4 3 4
PO , b) g-C N ,
3
N
4
3
4
3
N
4
3
4
3
N
4
3
4
.
Figure 1. XRD patterns. a) Ag
3
PO
PO
PO
PO
4
before and b) after photodegradation of
before and d) after photodegradation of
before and f) after photodegradation of
4
before and h) after photodegradation of
dimensional lamellar g-C N (Figure 2c and d). With increasing
3 4
C
C
C
C
2
2
2
2
H
4
H
4
H
4
H
4
. c) 30% g-C
. e) 50% g-C
. g) 70% g-C
. i) g-C
3
N
4
–70% Ag
–50% Ag
–30% Ag
3
4
Ag PO4 content, irregular sphere-like Ag PO4 becomes more
3 3
3
N
4
3
4
evident. TEM observations further confirmed a well-connected
interface between g-C N and Ag PO (Figure 2e and f).
3
N
4
3
3
4
3
4
3
N
4
before and j) after photodegradation of C
2
H
4
.
Figure 3 shows UV/Vis diffusive-reflectance spectra (DRS) of
g-C N , Ag PO , and g-C N -Ag PO composites before and
3
4
3
4
3
4
3
4
cubic structure type were identified for all of the Ag PO -con-
after the photocatalytic reaction. A sharp basal absorption
edge located at about 460 nm is in good consistency with the
3
4
taining samples (Figure 1a–h). For the g-C N4 samples (Fig-
3
[25]
ure 1i, j), only a characteristic peak around 27.48 can be identi-
bandgap of pristine g-C N (2.7 eV). Ag PO shows a sharp
3 4 3 4
fied. With decreasing volume ratio of g-C N , the intensity of
basal absorption edge at about 530 nm, in agreement with our
3
4
[22]
the characteristic peak of g-C N decreases gradually. Peaks re-
previous report. The g-C N –Ag PO composites with differ-
3 4 3 4
3
4
lated to other impurities were not observed in the as-synthes-
ised samples. After photodegradation of C H , some diffraction
ent mass ratios show two-stage absorption edges that are dis-
tinct from that of either g-C N or Ag PO and, with increasing
2
4
3
4
3
4
peaks of Ag were detected in the XRD pattern of Ag PO . How-
content of Ag PO , the two-stage absorption edges of the g-
3 4
3
4
ever, there were fewer Ag diffraction peaks in the XRD patterns
of the composite materials (see also Figure S1 in the Support-
ing Information). These results show that the stability of
Ag PO was indeed improved by coupling with g-C N .
C N -Ag PO composites moves to longer wavelength. The
3 4 3 4
changes of the absorption spectra with Ag PO content imply
3
4
different electronic structures of the g-C N –Ag PO compo-
3
4
3
4
sites, whereas the absorption spectral changes before and
after the photodegradation experiments (see also Supporting
Information, Figure S2) indicate that silver reduction reaction
in Ag PO still cannot be avoided completely, although the sta-
3
4
3
4
Morphologies of the as-prepared samples were characterised
by SEM (Figure 2a–d). Pristine Ag PO4 consists of irregular
3
sphere-like particles with a diameters ranging from 500 nm to
3
4
2
mm (Figure 2a). Bare g-C N (Figure 2b) clearly shows a crisp-
bility of Ag PO4 apparently can be improved by fabricating
3
4
3
ate two-dimensional lamellar structure with a broader size dis-
tribution varying from hundreds of nanometres to several mi-
crometres. The g-C N –Ag PO composites consists of irregular
composites.
The specific surface areas of the samples are summarised in
2
ꢀ1
Table 1. The Ag PO sample shows the smallest (1.64 m g ),
3
4
3
4
3
4
2
ꢀ1
sphere-like Ag PO particles interconnected with crispate two-
the g-C N sample shows a larger (16.93 m g ) and the 50%
3 4
3
4
&
&
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
2
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Figure 4. Time courses of a) C
-Ag PO composites.
2 4 2
H degradation and b) CO evolution on g-
Figure 3. UV/Vis diffuse-reflectance spectra of g-C
3 4 3 4 3 4
N , Ag PO , and g-C N –
C
3
N
4
3
4
Ag PO composites before (a) and after (b) the photo-oxidation reaction.
3
4
lnðC =CÞ ¼ kt
ð1Þ
0
Table 1. Surface areas S and kinetic rate constants k of Ag
3
PO
4
, g-C
3
N
4
,
and g-C
3 4 3 4
N –Ag PO composites.
2
ꢀ1
ꢀ1
Sample
S [m g
]
k [h
]
where C is the initial concentration of C H , C the concentra-
0 2 4
tion of C H at certain instant during the reaction, and k the
Ag
3
PO
4
1.64
10.56
25.32
21.79
16.93
0.30
0.92
0.53
1.05
0.08
2
4
30% g-C
50% g-C
70% g-C
3
N
3
N
3
N
4
4
4
–70% Ag
–50% Ag
–30% Ag
3
PO
3
PO
3
PO
4
4
4
pseudo-first-order rate constant. The plots of ln(C /C) versus il-
0
lumination time were found to be linear (Figure 5). This sug-
gests that the photodegradation reactions follow pseudo-first-
order kinetics. The apparent reaction rate constants k for the
photodegradation of C H were calculated by linear fitting of
3 4
g-C N
2
4
the experimental data. The k values of g-C N –Ag PO compo-
3
4
3
4
g-C N –50% Ag PO4 composite shows the largest
3
4
3
sites were much higher than those of g-C N and Ag PO . In
3
4
3
4
2
ꢀ1
(25.32 m g ) specific surface area.
particular, the 70% g-C N –30% Ag PO composite exhibited
3
4
3
4
Figure 4a and b show the time course of C H photodegra-
ꢀ1
2
4
the highest k value (1.0464 h ), which was about 3.47 times
dation and CO evolution on the Ag PO , g-C N and g-C N -
2
3
4
3
4
3
4
higher than that of Ag PO and 12.38 times higher than that of
3
4
Ag PO composites, respectively. To confirm the photocatalytic
3
4
activity of the samples, self-degradation of C H was measured
2
4
as well. This indicated that the introduction of g-C N improves
3
4
the adsorption of gases, and the Z-scheme composites help to
promote C H photodegradation. The highest activity for C H
4
2
4
2
photodegradation was obtained on the g-C N –Ag PO compo-
3
4
3
4
site with a g-C N :Ag PO mass ratio of 7:3. C H was complete-
3
4
3
4
2
4
ly decomposed within only 3 h. During the photo-oxidation of
C H , no other products except CO were detected. The fact
2
4
2
that the CO2 yields for all g-C N -containing samples were
3
4
greater than that which can be generated from C H reveals an
2
4
obvious adsorption effect of g-C N (see Supporting Informa-
3
4
tion, Figure S3).
The kinetics of C H degradation on all the semiconductors
2
4
Figure 5. Pseudo-first-order kinetics of a) Ag
3
PO
4
, b) 30% g-C
–30% Ag
3
N
4
–70%
was investigated by applying the Langmuir–Hinshelwood
Ag PO , c) 50% g-C –50% Ag PO , d) 70% g-C
3
4
3
N
4
3
4
3
N
4
3
PO , and e) g-
4
[
36]
model [Eq. (1)]
3 4
C N .
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
3
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
g-C N . The k values are listed in Table 1 and are consistent
3
4
with the photodegradation data presented in Figure 4.
Photoluminescence (PL) originates from the migration, trans-
fer, and recombination of photogenerated charge carriers in
a semiconductor. There is a strong correlation between PL in-
tensity and photodegradation performance. Higher PL intensity
indicates greater recombination of charge carriers, which re-
sults in lower photodegradation activity. The PL spectra of g-
C N , Ag PO and 70% g-C N –30% Ag PO under excitation at
3
4
3
4
3
4
3
4
325 nm are shown in Figure 6. The main emission peak centred
Figure 7. In situ IR spectra of ethylene photo-oxidation on 30% Ag
0% g-C composite collected at different illumination times with simulat-
ed sunlight.
3 4
PO –
7
3 4
N
Figure 6. Room-temperature PL spectra of g-C
0% Ag PO under excitation at 325 nm.
3 4 3 4 3 4
N , Ag PO , and 70% g-C N –
3
3
4
at about 460 nm for the pure g-C N sample and a broad PL
3
4
peak in the range of 420–620 nm for pure Ag PO are ascribed
3
4
[
37–38]
to bandgap recombination of electron–hole pairs.
In com-
parison with pure g-C N and Ag PO , addition of Ag PO or g-
3
4
3
4
3
4
C3N4 does not alter the spectral position of the peaks, but
clearly reduces the relative intensity of PL spectra. These re-
sults indicate that the heterojunction structure formed in the
g-C N –Ag PO composite promotes effective electron–hole
3
4
3
4
pair separation, which could be a reason for the superior pho-
todegradation activity of the g-C N -Ag PO composites.
3
4
3
4
Figure 7 shows in situ IR spectra of ethylene photo-oxidation
on the 30% Ag PO –70% g-C N composite collected at differ-
3
4
3
4
ent times of simulated sunlight illumination. The broad band
ꢀ
1
ꢀ1
at 2900–3200 cm and the band at 1889 cm correspond to
ꢀ
1
adsorbed C H , and the band at 2360 cm corresponds to ad-
2
4
sorbed CO . With increasing illumination time, the broad band
2
ꢀ
1
ꢀ1
at 2900–3200 cm and the band at 1889 cm gradually de-
cayed and disappeared after 90 min of illumination, while the
Figure 8. Stability test of C
2
H
4
photodegradation on the 70% g-C
degradation. b) CO evolution.
3 4
N –30%
Ag PO composite (0.2 g). a) C
3
4
2
H
4
2
ꢀ
1
band at 2360 cm became stronger. A broad peak at 3300–
ꢀ
1
3
600 cm , which corresponds to adsorbed water, emerged
after 5 min of illumination and gradually increased in intensity
with increasing illumination time. During the experiment, no
other intermediate product was detected. These results indi-
cate that C H reacted with O under simulated sunlight illumi-
cycles, the activity decreased slowly, and the calculated turn-
over number (for calculation, see Supporting Information S4)
was 1.68 under the assumption that CO is the only product
2
and is generated only on Ag PO . Stability of a photocatalyst is
2
4
2
3
4
nation and produced H O and CO2 (C H +3O !2CO +
one of the most important parameters for its application in
practice. Although the stability of Ag PO was improved by
2
2
4
2
2
2
H O).
2
3
4
To study the stability of the g-C N –Ag PO composite semi-
fabricating a g-C N –Ag PO Z-scheme structure, the photode-
3 4 3 4
3
4
3
4
conductors, the g-C N -Ag PO composite with
a
g-
gradation activity for C H still decreased slowly in long-term
2 4
3
4
3
4
C N :Ag PO mass ratio of 7:3 was further employed to carry
operation. We then heat-treated g-C N -Ag PO composites
3
4
3
4
3
4
3
4
out a cycling C H photodegradation test (Figure 8). After five
that had endured five cycles of C H4 photodegradation at
2
4
2
&
&
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
4
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Figure 9. Stability study of C
2 4 3 4
H photodegradation on a 70% g-C N –30%
Ag PO composite that was subjected to five cycles of photoreaction and
3
4
2 4 2
then heat-treated at 4508C for 3 h (0.2 g). a) C H degradation. b) CO evolu-
tion.
4508C for 3 h and found that the heat-treated samples
showed stable functionality in a further five cycles (Figure 9).
From the XRD patterns, UV/Vis spectra and SEM and TEM
images (see Supporting Information, Figures S5 and S6) we
suggest that nanosilver generated during heat treatment plays
an important role in the stable C H photo-oxidation activity.
2
4
As previously reported, COH and O Cꢀ are the most strongly
2
[39]
oxidising agents in the photodegradation of ethylene. How-
ever, for pure Ag PO , as shown in Figure 10a, the potential of
3
4
its CB minimum is about +0.5 V versus NHE and the potential
[
24]
of its VB maximum is about +2.85 V versus NHE. Under light
+
illumination, the photogenerated electrons will reduce Ag to
produce Ag, and only COH can be generated. As a consequence,
Ag PO can photo-oxidise ethylene via the generated COH in
3
4
the initial stage and is deactivated as silver reduction reactions
proceed. For g-C N , the potential of its CB minimum is about
3
4
ꢀ
1.1 V versus NHE and the potential of its VB maximum is
[
26]
Figure 10. a) Band-edge positions of g-C
3
N
4
and Ag
redox potentials. Charge transfer b) in the convention-
al g-C N -Ag PO heterojunction and c) in the g-C N –Ag PO Z-Scheme
3 4
PO in conjunction with
about +1.6 V versus NHE. Under light illumination, the pho-
ꢀ
ꢀ
OH /COH and O C
/O
ꢀ
2 2
togenerated electrons can reduce O2 to produce O C , but
holes in the valence band cannot oxidise OH to generate COH.
2
3
4
3
4
3
4
3
4
ꢀ
mode under sunlight illumination.
Thus, it is easy to understand why g-C N exhibits weak or
3
4
negligible ethylene photodegradation activity, although the
large specific surface area of g-C N shows good adsorption of
tion, the photoexcited holes tend to transfer from the VB of
Ag PO to the VB of g-C N , and the electrons from the CB of
3
4
ethylene molecules. Only by fabricating g-C N –Ag PO compo-
3
4
3
4
3
4
3
4
sites was the activity for ethylene photodegradation signifi-
g-C N to the CB of Ag PO . This will result in a lower photode-
3 4 3 4
cantly improved, whatever the mass ratio of g-C N4 and
gradation activity than those of pure Ag PO and pure g-C N ,
3 4 3 4
3
Ag PO .
or complete deactivation by acceleration of Ag PO photocor-
3 4
3
4
If g-C N4 and Ag PO4 form a conventional g-C N –Ag PO
4
rosion. Therefore, we can conclude that the transfer of photo-
excited electrons and holes in the g-C N -Ag PO composites
3
3
3
4
3
heterojunction (see Figure 10b), then, under sunlight illumina-
3
4
3
4
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
did not follow the conventional heterojunction mode (Fig-
ure 10b) according to our experimental results. A direct g-
C N –Ag PO Z-scheme system without an electron mediator is
periments indicated that the Z-scheme composites exhibited
considerably improved efficiency in ethylene photodegrada-
tion in comparison with pure Ag PO and g-C N . The highest
3
4
3
4
3
4
3
4
therefore suggested (see Figure 10c). Under sunlight illumina-
activity was observed in the g-C N –Ag PO Z-scheme compo-
3 4 3 4
tion, most of the photoexcited electrons in the CB of Ag PO4
site with a g-C N :Ag PO mass ratio of 7:3. Moreover, the sta-
3 4 3 4
3
transfer to the VB of g-C N , and they either recombine with
bility of Ag PO was obviously improved by fabrication of the
3 4
3
4
the holes therein or are further excited to the CB of g-C N .
Z-scheme composite, and the material treated at 4508C for 3 h
showed stable functionality after long-term operation. The
present study will be valuable for further investigations on
both Ag PO and CH degradation.
3
4
This results in efficient space separation of the photoinduced
charge carriers without sacrificing Ag PO . Then, the photoex-
3
4
cited electrons in the CB of g-C N are trapped by atmospheric
3
4
3
4
O near the surface of g-C N to form reactive superoxide radi-
2
3
4
ꢀ
cal anions (O C ), while the holes in the VB of Ag PO react
2
3
4
Experimental Section
with adsorbed water molecules (or surface hydroxyl groups)
near the surface of Ag PO to form hydroxyl radicals (COH). Fi-
3
4
Synthesis of g-C N4
3
ꢀ
2
nally, C H is oxidised by the highly reactive COH and O C radi-
2
4
g-C N was synthesised by thermal treatment of 5 g of urea (AR, Si-
3
4
cals into carbon dioxide and water, and the stability of Ag PO4
3
nopharm Chemical Reagent Co. Ltd) in an alumina crucible with
a cover. After drying at 708C, the precursor was heated to 5508C
for 3 h at a heating rate of 58Cmin . The light yellow product was
washed with nitric acid (0.1m) and distilled water to remove any
residual alkaline species (e.g., ammonia) adsorbed on the sample
surfaces and then dried at 808C for 12 h.
is thus improved.
The activity differences between the composites can be ex-
plained as follows: the photoexcitation processes of the semi-
conductors are affected by the light illumination conditions,
while electron transfer is determined by the interface state be-
tween the g-C N and Ag PO semiconductors. Too much or
ꢀ1
3
4
3
4
too little of either of the two semiconductors (Figure 11) will
Synthesis of Ag
PO powder
3 4
Ag PO powder was synthesised by the ion-exchange method as
3
4
[24]
described in our former report. Appropriate amounts of AgNO3
and Na HPO4 were mixed and milled thoroughly until the initial
2
colour changed to yellow. The product was washed with distilled
water several times and dried at room temperature overnight.
Synthesis of g-C N -Ag PO Z-scheme composites
3
4
3
4
The g-C N –Ag PO Z-scheme composites with different mass
3
4
3
4
ratios were prepared by dispersing g-C N and Ag PO with differ-
3
4
3
4
ent mass ratio in distilled water at room temperature under mag-
netic stirring for 24 h. After filtration, the mixtures were dried at
8
08C for 12 h.
Materials characterisation
The crystal phases of the samples were analysed with a Rigaku
Miniflex II X-ray diffractometer with CuKa radiation (l=
ꢀ
1
0
.154178 nm). A scan rate of 58min was used to record powder
XRD patterns in the 2q range of 20–808. SEM (JSM-6700F) as well
2
as TEM and HRTEM (JEM-2010 and FEI, Tecnai G F20 FEG TEM)
were used to characterise the morphology and microstructure of
the products. As Ag PO is very unstable under electron irradiation,
3
4
during the TEM experiment we took the images very quickly and
never at the same spot. The UV/Vis diffuse-reflection spectra (DRS)
were collected on a UV/Vis/NIR spectrophotometer (PerkinElmer
Lambda 900) equipped with an integrating sphere assembly with
Figure 11. Schematic illustration of unmatched light absorption and charge
transfer in g-C N -Ag PO composites with various volume ratios.
3 4 3 4
BaSO as reflectance standard. The spectra were recorded at room
4
result in unmatched photoexcitation and electron transfer. A Z-
scheme structure composed of 70% g-C N and 30% Ag PO
4
temperature in air in the range from 300 to 800 nm. The surface
areas of the samples were measured with a TriStar II 3020-BET/BJH
surface area analyser. The PL spectra of the photocatalysts were
obtained by a Varian Cary Eclipse spectrometer at an excitation
wavelength of 325 nm. In situ FTIR studies were performed on
a Nexus FTIR (Thermo Nicolet) spectrometer by using a diffuse-re-
flectance attachment equipped with a reaction chamber. 128
3
4
3
was the best composition that we obtained.
Conclusion
g-C N –Ag PO Z-scheme composite semiconductors were pre-
ꢀ1
3
4
3
4
single-beam spectra were co-added at a resolution of 4 cm and
pared by
a
simple method utilising affordable AgNO3,
the spectra were presented as Kubelka–Munk function referred to
adequate background spectra. The background and sample spec-
Na HPO , and urea as feedstocks. Ethylene photooxidation ex-
2
4
&
&
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
tra were taken (the average of accumulated 32 scans) over the fre-
[12] a) J. Tang, Z. Zou, J. Ye, Angew. Chem. Int. Ed. 2004, 43, 4463–4466;
Angew. Chem. 2004, 116, 4563–4566; b) J. Tang, J. R. Durrant, D. R. Klug,
J. Am. Chem. Soc. 2008, 130, 13885–13891.
ꢀ1
quency range 4000–600 cm
.
[
[
[
[
13] S. Kumar, T. Surendar, A. Baruah, V. Shanker, J. Mater. Chem. A 2013, 1,
Photodegradation activity test
5333–5340.
14] F. J. Zhang, F. Z. Xie, S. F. Zhu, J. Liu, J. Zhang, S. F. Mei, W. Zhao, Chem.
Eng. J. 2013, 228, 435–441.
15] D. Jiang, J. Zhu, M. Chen, J. J. Xie, J. Colloid Interface Sci. 2014, 417,
The photo-oxidation of C H was carried out in a sealed Pyrex reac-
2
4
tor of 450 mL capacity. In a typical reaction, 0.2 g of sample was
dispersed uniformly on the bottom of the reactor, and the reactor
was illuminated by using a 300 W Xe lamp from the top. 90 mL of
C H was injected into the reactor by microsyringe. Prior to illumi-
115–120.
16] J. Martin, N. Umezawa, X. W. Chen, J. H. Ye, J. W. Tang, Energy Environ.
Sci. 2013, 6, 3380–3386.
2
4
nation, the reaction system was protected from light for 2 h to
reach adsorption/desorption equilibrium of C H on the sample. At
[17] S. Y. Ye, Y. C. Fang, X. L. Song, S. C. Luo, Chem. Eng. J. 2013, 225, 499–
508.
2
4
[
[
[
[
[
18] D. R. Park, J. L. Zhang, K. Ikeue, H. Yamashita, M. Anpo, J. Catal. 1999,
a certain time intervals, 4 mL of gas was sampled from the reactor
and the amounts and types of gases were analysed on a gas chro-
matograph (GC9720 Fuli) equipped with a six-way-valve gas sam-
pler, a flame ionisation detector, a HP-Plot/U capillary column,
a thermal conductivity detector, and a molecular sieve 13X
column.
1
85, 114–119.
19] B. Hauchecorne, T. Tytgat, S. W. Verbruggen, D. Hauchecorne, D. Terren-
sa, M. Smits, K. Vinken, S. Lenaerts, Appl. Catal. B 2011, 105, 111 – 116.
20] S. Kim, Y. Watabe, T. Aida, H. Niiyama, J. Chem. Eng. Jpn. 2005, 38, 828–
8
34.
21] H. G. Ahn, B. M. Choi, D. J. Lee, J. Nanosci. Nanotechnol. 2006, 6, 3599–
603.
22] Z. G. Yi, J. H. Ye, K. Naoki, K. Tetsuya, Nat. Mater. 2010, 9, 559–564.
3
Acknowledgements
[23] a) N. Fu, Z. L. Jin, Y. Q. Wu, G. X. Lu, D. Y. Li, J. Phys. Chem. C 2011, 115,
8
1
586–8593; b) Y. Sasaki, A. Iwase, H. Kato, A. Kudo, J. Catal. 2008, 259,
33–137; c) K. Sekizawa, K. Maeda, K. Domen, K. Koike, O. Ishitani, J.
This work was financially supported by the National Key Proj-
ect on Basic Research (Grant No. 2013CB933203), the Natural
Science Foundation of China (Grant No. 21373224), the Natural
Science Foundation of Fujian Province (Grant No. 2012J01242),
the open project program of the State Key Laboratory of High
Performance Ceramics and Microstructures (Grant No.
SKL201202SIC), and the One Hundred Talents Program of the
Chinese Academy of Sciences.
Am. Chem. Soc. 2013, 135, 4596–4599.
24] P. M. Wood, Biochem. J. 1988, 253, 287–289.
[25] X. C. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson,
[
Nat. Mater. 2009, 8, 76–80.
[
[
[
26] D. Mitoraj, H. Kisch, Chem. Eur. J. 2010, 16, 261–269.
27] S. C. Yan, Z. S. Li, Z. G. Zou, Langmuir 2010, 26, 3894–3901.
28] Q. Y. Li, B. Yue, H. Iwai, T. Kako, J. H. Ye, J. Phys. Chem. C 2010, 114,
4100–4105.
29] S. C. Yan, S. B. Lv, Z. S. Li, Z. G. Zou, Dalton Trans. 2010, 39, 1488–1491.
30] H. J. Yan, H. X. Yang, J. Alloys Compd. 2011, 509, L26–L29.
31] W. H. Koppenol, J. F. Liebman, J. Phys. Chem. 1984, 88, 99–101.
[
[
[
Keywords: ethylene · green chemistry · photochemistry ·
photodegradation · semiconductors
[32] J. P. Hoare, in Encyclopedia of Electrochemistry, Vol. 2 (Ed: A. J. Bard),
Marcel Dekker, New York, 1974, pp. 191.
[
[
[
33] D. M. Blake, J. Webb, C. Turchi, K. Magrini, Sol. Energy Mater. 1991, 24,
84–593.
34] H. Tada, T. Mitsui, T. Kiyonaga, T. Akita, K. Tanaka, Nat. Mater. 2006, 5,
82–786.
35] Y. Sasaki, H. Nemoto, K. Saito, A. Kudo, J. Phys. Chem. C 2009, 113,
7536–17542.
5
[
1] N. Keller, M. N. Ducamp, D. Robert, V. Keller, Chem. Rev. 2013, 113,
029–5070.
2] M. R. Hoffmann, S. T. Martin, W. Choi, D. W. Bahnmann, Chem. Rev. 1995,
5, 69–96.
5
7
[
9
1
[
[
3] C. X. Jiang, K. Hara, A. Fukuoka, Angew. Chem. 2013, 52, 6265–6268.
4] J. A. M. de Bont, Antonie van Leeuwenhoek Anton. Leeuw. Int. J. G. 1976,
[
[
36] J. Hou, Z. Wang, S. Jiao, H. Zhu, CrystEngComm 2012, 14, 5923–5928.
37] D. L. Jiang, L. L. Chen, J. J. Zhu, M. Chen, W. D. Shi, J. M. Xie, Dalton
Trans. 2013, 42, 15726–15734.
42, 59–71.
[
[
5] L. Elsgaard, Appl. Environ. Microbiol. 1998, 64, 4168–4173.
6] B. De Heyder, A. Overmeire, H. V. Langenhove, W. Verstraete, Biotechnol.
Bioeng. 1994, 44, 642–648.
[
38] Q. Liang, Y. Shi, W. Ma, Z. Li, X. Yang, Phys. Chem. Chem. Phys. 2012, 14,
1
5657–15665.
39] S. Yamazaki, S. Tanaka, H. Tsukamoto, J. Photochem. Photobiol. A 1999,
21, 55–61.
[
[7] L. Elsgaard, Appl. Environ. Microbiol. 2000, 66, 3878–3882.
[8] T. Inoue, A. Fujishima, S. Konishi, K. Honda, Nature 1979, 277, 637–638.
[9] X. Chen, S. Shen, L. Guo, S. S. Mao, Chem. Rev. 2010, 110, 6503–6570.
1
[
[
10] I. K. Konstantinou, T. A. Albanis, Appl. Catal. B 2004, 49, 1–14.
11] A. L. Linsebigler, G. Lu, J. T. Yates, Chem. Rev. 1995, 95, 735–758.
Received: July 7, 2014
Published online on && &&, 0000
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Great for degradation: Graphitic C N –
&
Green Chemistry
3
4
Ag PO composites with a direct Z-
3
4
X. X. Chen, X. T. Huang, Z. G Yi*
& – &&
scheme configuration (see figure) show
both significantly improved ethylene
photodegradation activity and increased
stability of Ag PO .
&
Enhanced Ethylene Photodegradation
Performance of g-C N –Ag PO
3
4
3
4
3
4
Composites with Direct Z-Scheme
Configuration
&
&
Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
8
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!