Preparation of Silver Carbonate and its Application as Visible Light-driven Photocatalyst Without Sacrificial Reagent

Article abstract of DOI:10.1111/php.12495

Visible light-driven photocatalyst is the current research focus and silver oxyacid salts with p-block elements are the promising candidates. In this research, Ag₂CO₃ was prepared by a facile precipitation method and used to degrade the pollutants from waters. The results revealed that the silver carbonate with monoclinic structure quickly decomposed methyl orange and rhodamine B in less than 15 min under visible light irradiation. When it was recycled six times, the degradation of methyl orange still can reach 87% after 30 min. The calculated band gap of Ag₂CO₃ was 2.312 eV with Valence band edge potential of 2.685 eV and Conduction band 0.373 eV vs NHE, which endowed the excellent photo-oxidation ability of silver carbonate. Photogenerated holes and ozone anion radicals were the primary active species in the photo-oxidization degradation of dye. The generation of metallic silver resulted from photocorrosion and the consequent reduction in the ozone anion radical amount led to the performance degradation of Ag₂CO₃. The simple preparation method and high photocatalytic performance of Ag₂CO₃ increases its prospect of application in future.

Full text of DOI:10.1111/php.12495

Photochemistry and Photobiology, 2015, 91: 1315–1323
Preparation of Silver Carbonate and its Application as Visible Light-driven
Photocatalyst Without Sacrificial Reagent
Wei Jiang*, Ya Zeng, Xiaoyan Wang, Xiaoning Yue, Shaojun Yuan, Houfang Lu and Bin Liang
Multi-phase Mass Transfer and Reaction Engineering Laboratory, College of Chemical Engineering, Sichuan University,
Chengdu, China
Received 7 April 2015, accepted 27 June 2015, DOI: 10.1111/php.12495
ABSTRACT
Especially, Ag3PO4 (31–35) exhibited an outstanding photocat-
alytic performance in photodegradation process of dye, attracting
the attentions because of the adding of nonmetallic p-block ele-
ments. Such noticeable photocatalytic capacity was attributed to
the higher valence band and narrower band gap caused by the
hybrid of Ag4d orbitals with the O2p orbitals (36). Introducing
unoccupied s, p states of p-block elements can effectively tune
the potentials of conduction band of the Ag-based oxides. This
advisable strategy to achieve better Ag-based photocatalyst to
degrade persistent pollutants inspired more attempt by adding
different p-block elements into Ag-based oxides.
Carbon element is a nonmetallic p-block element. Ag2CO3
synthesized by Xu et al. (37) was used to photodegrade methy-
lene blue and phenol under visible light irradiation. The pho-
todegradation time was more than 40 and 120 min, respectively.
The Ag2CO3 prepared by this method possessed lower decompo-
sition rate and accompanied with serious performance degrada-
tion, and Na2CO3 was used as an anticorrosion reagent to retard
such undesired performance loss. Another approach was adding
AgNO3 to inhibit the photocorrosion effect of Ag2CO3, which
was attempted by Dai et al. (38). However, the performance and
stability of Ag2CO3 were not satisfactory yet, and the employ-
ment of AgNO3 as sacrificial reagent increased the cost, and
introduced the new pollution.
Visible light-driven photocatalyst is the current research
focus and silver oxyacid salts with p-block elements are the
promising candidates. In this research, Ag2CO3 was prepared
by a facile precipitation method and used to degrade the pol-
lutants from waters. The results revealed that the silver car-
bonate with monoclinic structure quickly decomposed methyl
orange and rhodamine B in less than 15 min under visible
light irradiation. When it was recycled six times, the degra-
dation of methyl orange still can reach 87% after 30 min.
The calculated band gap of Ag2CO3 was 2.312 eV with
Valence band edge potential of 2.685 eV and Conduction
band 0.373 eV vs NHE, which endowed the excellent photo-
oxidation ability of silver carbonate. Photogenerated holes
and ozone anion radicals were the primary active species in
the photo-oxidization degradation of dye. The generation of
metallic silver resulted from photocorrosion and the conse-
quent reduction in the ozone anion radical amount led to the
performance degradation of Ag2CO3. The simple preparation
method and high photocatalytic performance of Ag2CO3
increases its prospect of application in future.
INTRODUCTION
In this research, Ag2CO3 was prepared by a facile ion-ex-
change method, and used as visible light-driven photocatalyst to
decompose MO and RhB without any additives under Xenon
lamp and solar light. The effect of different carbonate precursors
on the performance of Ag2CO3 was investigated and the stability
of as-prepared Ag2CO3 samples was studied.
Recently, with the development in the field of photocatalysis, the
new photocatalysts driven by visible light have attracted more
and more attention for production of clean energy and remedia-
tion of environmental pollution due to the high solar light utiliza-
tion rate (1,2). Generally, two main strategies are employed to
achieve the visible light-driven photocatalyst: modification of
UV light-driven photocatalyst, especially TiO2 with N (3–5), C
(6–8), S (9–11), P (12) and F (13), and design of novel semicon-
ductor materials with narrower band gap energy, such as CdS
(14), ZnS (15) and BiVO4(16,17). Among them, the semiconduc-
tors containing silver are focused specially owing to their inter-
esting and high-efficient photocatalytic performance. The typical
examples include Ag2O (18) and its derivative Ag-based oxides
with p-block elements such as AgVO3 (19–22), AgSbO3 (23–
25), AgGaO2 (26–28), Ag3AsO4 (29) and AgAlO2 (30), which
were reported to decompose persistent organic pollutants such as
phenol, methylene blue (MB), rhodamine B (RhB), methyl
orange (MO) under visible light with eye-catching reaction rate.
MATERIALS AND METHODS
Materials. Silver nitrate, sodium carbonate, methyl orange (MO), metha-
nol, rhodamine B (RhB) and indigo carmine, all were purchased from
Chengdu Kelong Chemical Reagent Company (Chengdu, China), and
were used directly as received. Deionized water was used throughout this
study.
Preparation of Ag2CO3. Ag2CO3 nanoparticles were synthesized by a
simple ion-exchange precipitation reaction between AgNO3 (0.2 M) and
Na2CO3 (0.1 M) in liquid phase at room temperature. In a typical proce-
dure, under magnetically stirring, 25 mL of AgNO3 (0.2 M) was added
into a 100 mL homemade light-tight beaker, which was encapsulated
with tinfoil paper to block light. Subsequently, 55 mL of carbonate
(0.1 M) was dropped into the AgNO3 solution by (ZDJ-3D) automatic
titrator with dropping speed of 3.2 mL minꢀ1. After dropping finished,
keep stirring more than 2.5 h. The admixture was filtered and washed
with DI water to remove the unreacted components and by-products.
*Corresponding author email: weijiang@scu.edu.cn (Wei Jiang)
© 2015 The American Society of Photobiology
1315

1316 Wei Jiang et al.
Finally, the yellowish powders were vacuum-dried at 40°C for 24 h. All
the above steps were conducted in darkroom with red dark room lamp.
Sample characterization. The morphology of the specimens was
detected by a JSM-7500F field emission scanning electron microscopy
(FESEM, Japan). The structural features were determined using glancing
angle X-ray diffraction (GA-XRD, X’Pert proMPD, the Netherlands) with
a Cu Ka radiation (wavelength k = 0.15406 nm). UVꢀVis spectropho-
tometer (TU-1901, Ge Beijing spectrometer, China) with barium sulfate
as the reference was used to acquire the UVꢀVis diffusion reflection
spectra of Ag2CO3 specimens. Fourier transform infrared spectroscopy
(FT-IR) of sample was determined with a NEXUS 670. A VG ESCA-
LAB MKII XPS system with Al Ka source and a charge neutralizer was
employed to conduct the X-ray photoelectron spectroscopy (XPS) mea-
surements. The specific surface area of samples was determined by a
laser particle sizer (JL-6000, Chengdu Jinxin Powder Analyse Instrument
Co., Ltd.). An FLsp920 instantaneous spectrometer was utilized to carry
out the photoluminescence spectrum (PL) analysis of Ag2CO3. The active
species in the photocatalytic process of Ag2CO3 was probed by electron
spin resonance (ESR) with an ER200-SRC.
Evaluation of photocatalytic activity. The photocatalytic activity of the
as-prepared samples for decolorization of MO and RhB aqueous solution
was examined at ambient temperature in an OCRS-IV photoreactor sys-
tem with a 500 W Xenon lamp and a UV cut-off filter (Ultraviolet
ZJB380 glass, k > 380 nm) as the visible light source. The typical
detailed experimental procedure is conducted as following: Four 10 mL
test tubes filled with 10 mL MO (16 mg Lꢀ1) or RhB (16 mg Lꢀ1) aque-
ous solution were used to conduct the parallel testing in dark. Ag2CO3
powder (0.1000 g) was dispersed into each tube. The dye solution mixed
with Ag2CO3 powder was placed in the dark with stirring for 30 min to
reach the adsorption equilibrium. The lights were then turned on. At each
given time interval, 5 mL suspension was sampled from each tube and
centrifuged to remove the Ag2CO3 powder. The concentration of MO or
RhB during the degradation was monitored via colorimetry by using an
UVꢀVis spectrophotometer (TU-1810, Beijing). At last the results of
four tubes were averaged to determine the decomposition rate of the dye.
In order to research the possibility of applying Ag2CO3 for actual sys-
tem, the photocatalytic performance of Ag2CO3 under solar light was car-
ried out according to the above procedure except that the artificial light
resource for irradiation was replaced by the natural sunlight in different
weather conditions.
samples were in good agreement with those of the monoclinic
structure of Ag2CO3 (No. 26-0339), with space group of P21/m,
ꢀ
ꢀ
ꢀ
a = 4.852(4) A, b = 9.553(8) A, c = 9.553(8) A and b = 91.96°
(39). No peak belonging to metallic silver was observed. How-
ever, XPS measurements results shown in Fig. 1D revealed that
as-prepared sample was a mixture of 36% metallic Ag and 64%
monovalent silver ion. XPS and XRD results suggested that the
sample is the hybrid of Ag2CO3 and Ag. Such structure could be
expected to improve the performance and stability of silver salts
under light irradiation due to the plasmon resonance (40–42).
UV–Vis DRS. The ultraviolet–visible diffuse reflectance spectrum
(UV–Vis DRS) in Fig. 1E indicated that the yellowish Ag2CO3
could absorb solar energy with a wavelength shorter than 480 nm,
and the band gap energy estimated from the intercept of the
tangent to the plot is 2.30 eV. It should be noticed that the visible
edge is steep, sufficiently indicating that the transition from
valence band to conduction band is the intrinsic absorption band of
Ag2CO3, rather than from the impurity to the conduction band.
Further simulation with DFT in Fig. 1F confirmed that the
indirect band gap and direct band gap of Ag2CO3 was 2.312 eV
and 2.812 eV, respectively. The indirect band gap and the direct
band gap at the Q point are energetically close, and steep rise
occurs in photocurrent. The corresponding partial DOS (PDOS)
presented in Supporting Information Fig. S2 confirmed that
the root of the main difference of the valence band (VB)
should ascribe to the difference of the Ag 4d PDOS calculated
by Ud,Ag = 7.2 eV and Ud,Ag = 10.2 eV. Due to the small band
gap, Ag2CO3 should harvest visible light. The value of valence
band and conduction band of Ag2CO3 can be obtained based on
the experimental value of band gap and the following equation
(40):
EVB ¼ X ꢀ Ee þ 0:5Eg;
DFT simulation conditions. Electronic structure of Ag2CO3 was ana-
lyzed by the plane wave pseudopotential approach based on the density
functional theory (DFT). After geometry optimization, the electronic struc-
ture was calculated by using CASTEP code. The GGA was used to describe
the exchange and correlation energy of the electrons. The ultrasoft pseu-
dopotential in the Vanderbilt form was used for the ion–electron interaction.
The corresponding valence atomic configurations of O, C and Ag were
2s22p4, 2s22p2 and 4d105s1, respectively. The set value of energy cutoff for
a plane wave basis was 400 eV, and a 6 9 696 Monkhorst-Pack k-mesh is
used. The other parameters employed in calculation were as following:
1 9 10ꢀ6 eV/atom of the self-consistent convergence accuracy; 0.01 eV of
the convergence criterion for the maximal force between atoms; 5 9 10ꢀ4
where EVB, Ee and Eg are the valence band, free electron energy
on the hydrogen scale (ca. 4.5 eV) and the band gap of Ag2CO3,
respectively. X is the calculated Pearson absolute electronegativ-
ity of the Ag2CO3.
The calculated value of valence band EVB of Ag2CO3 was
2.685 eV, and consequently the bottom of conduction band ECB
was 0.373 eV vs NHE.
6
ꢀ
A of the maximum displacement; 0.02 GPa of the stress; 1 9 10 eV/atom
Photodegradation of MO and RhB with Ag2CO3 and its
stability
of the SCF tolerance; 5 eV of the Up parameter for O and C and 10.2 eV of
the Ud parameter for Ag. The Fermi level was as the zero of energy. In addi-
tion, only the spin-up results were shown in this paper because of the com-
plete symmetry between spin-up and spin-down states.
Photodegradation of two typical organic dyes, methyl orange (MO)
and rhodamine B (RhB), were conducted to exhibit the photo-ox-
idative ability of Ag2CO3, without any additives as electron accep-
tor. The corresponding standard absorption curves of MO and RhB
solution are shown in Supporting Information Fig. S3.
RESULTS
The characteristics of the as-prepared Ag2CO3 samples
The adsorption of two dyes on the Ag2CO3 powder was taken
into account and determined, which only 5% initial concentration
of MO, and 9% of RhB was adsorbed when equilibrium was
reached in the dark after half an hour with sufficient stirring (See
Supporting Information Fig. S4). The pH value of the solution
was kept at the value of deionized water during the reaction. In
order to exclude the interference of the self photodegradation
effect of dye under visible light irradiation, photodegradation of
MO and RhB under the same conditions without photocatalyst
was carried out (See Supporting Information Fig. S5), and the
Appearance and morphology. As-prepared yellow fine powders
possess a smooth trapezoid single crystal without obvious frac-
ture and an average diameter of 1.5 lm as is shown in Fig. 1A,
B. The main particle size distribution ranged from 0.8 to 2 lm
(See Supporting Information Fig. S1). Moreover, measured speci-
fic surface area of Ag2CO3 was about 0.437 m2 gꢀ1
.
Crystal structure. X-ray diffraction (XRD) results in Fig. 1C
confirmed that all the diffraction peaks of the as-prepared

Photochemistry and Photobiology, 2015, 91 1317
Figure 1. The characterization of as-prepared fresh Ag2CO3: (A) SEM 9 3000; (B) SEM 9 20 000; (C) XRD pattern; (D) XPS results of Ag 3d5/2
peak; (E) UV–Vis DRS from 200 nm to 800 nm; (F) Energy-band diagram of Ag2CO3 calculated by a density functional method.
results showed that the self photodegradation of dye can be neg-
ligible.
Figure 2 showed the fast decreasing tendency of MO and
RhB against light illumination time over Ag2CO3. The profile
displayed the high photo-oxidation activity of Ag2CO3. When
the Ag2CO3 was used at the first time, the degradation of MO
could reach 98% after 14 min. After Ag2CO3 was recycled six
times, the degradation of MO can also reach 87% after 30 min
in Fig. 2A. Furthermore, the performances and stability of
Ag2CO3 in photodegradation of RhB was in accordance with the

1318 Wei Jiang et al.
Figure 2. The photoactivity and stability of Ag2CO3 by degradation of (A) MO and (B) RhB.
Figure 3. Degradation of MO with Ag2CO3 under solar light irradiation: (A) sunny day; (B) cloudy day.
MO in Fig. 2B. The degradation of RhB was about 98% first
tive slow degradation of MO in cloudy day should ascribe to the
and 62% after Ag2CO3 was recycled six times. When the
Ag2CO3 was used at the first time, the full UV–Vis absorption
spectra of MO and RhB solution in photocatalytic degradation
process against time were shown in Supporting Information
Fig. S6. The corresponding time consumed increased from 14 to
32 min because of recycling. Other researchers’ results, by con-
trast, spent more than 18 min to degrade 90% RhB (38), which
used a simple facile precipitation reaction between NaHCO3 and
AgNO3. Obviously, the performance and stability of the silver
carbonate were better than that reported in literature (37,38). The
oxidative performance and stability of self-made Ag3PO4 was
tested under the same conditions and provided as a comparison
(See Supporting Information Fig. S7). It can be found that the
photocatalytic performance of Ag2CO3 is roughly equivalent to
Ag3PO4 when used at the first time; however, the performance
stability of the former is significantly better than the latter. It is
worth noting that the excellent performance of Ag2CO3 was
achieved without adding any sacrificial reagents.
relatively weak light irradiation.
Characterization of used catalyst
The photocatalytic performance of used Ag2CO3 could be inves-
tigated with SEM, XPS and XRD analysis. SEM picture of
Ag2CO3 catalyst after six cycles in Fig. 4A,B exhibited the
unsmooth outward appearance with many fissures and holes on
the surface of crystal, which can be regarded as the consequence
of photocorrosion. The XPS result in Fig. 4C clearly showed that
the shoulder peak of metallic Ag at 367.9 eV was enlarged com-
paring with the Ag+ peak at 367.6 eV after six cycle, and the
calculated ratio of metallic Ag to monovalent silver ion increased
to 58.3:41.7, which suggested that it was the generation of metal-
lic silver that resulted in the performance degradation of
Ag2CO3. The peak of generated Ag simple substance was also
easily observed in the results of XRD in Fig. 4D. Such tendency
meant that the stability of Ag2CO3 depended significantly on
the decomposing rate of salts to metallic silver. However, this
performance decaying rate of Ag2CO3 after repeated using was
slower than that of Ag3PO4 since its ratio of Ag to Ag+
increased from 37.7:62.3 to 77.5:22.5 after reusing. The detailed
comparison was shown in Supporting Information Fig. S8. It
could be summarized that the stability of Ag2CO3 under light
irradiation was relatively excellent.
Herein, in order to investigate the possibility of applying
Ag2CO3 for actual system (43), the experiments of photodegra-
dation of MO with Ag2CO3 under solar light in sunny or cloudy
day was proceeded, and the results were demonstrated in
Fig. 3A,B, respectively. The dye was decomposed completely in
4.5 min in sunny day with average light illumination of 22 Klux,
and in 14 min in cloudy day with 2.3 Klux. Apparently, the rela-

Photochemistry and Photobiology, 2015, 91 1319
Figure 4. The characterization of used Ag2CO3 after six cycles: (A) SEM 9 10 000; (B) SEM 9 20 000; (C) XPS results of Ag 3d5/2 peak; (D) XRD
pattern.
(42,45,46). Furthermore, no any signals judged as superoxide
Photodegradation mechanism of Ag2CO3
anion radicals or hydroxyl radical ware observed. At starting
Generally three possible active species were considered in a typi-
cal photodegradation mechanism analysis: photogenerated holes,
hydroxyl radicals and superoxide anion radicals. In this research,
it is reasonable to exclude the possibility of the two latters partic-
ipating in the photodegradation reaction because the electrode
potential of OH radicals is 2.80 eV, and Oꢀ2 radicals is
ꢀ0.046 eV, which is beyond the calculated redox potential range
of Ag2CO3 under visible light irradiation. The photogenerated
hole of Ag2CO3 is the latent active specie, but the other possible
candidates cannot be eliminated directly since multiple oxygen-
derived free radicals could be generated in a photochemical pro-
cess. Thus, ESR analysis and radical-trapping experiment (44)
were carried out to determine the possible active species, con-
structing the photodegradation mechanism of Ag2CO3.
time, 0 min, almost no observable peaks were found, but with
the lighting time expansion, the ESR signal of ozone anion radi-
cals increased sharply, which confirmed that such signal was
induced by the light. After light irradiation, the seven line spec-
trums signal intensity was significantly strengthened. Therefore,
the ozone anion radicals can be considered as the probable active
specie in the photocatalytic process of Ag2CO3.
˙
˙
It is worth mentioning that the signal strength of fresh
Ag2CO3 is higher than that of reused sample after light irradia-
tion. Such result confirms the conclusion surmised from results
of XRD and XPS, and is a complement to the deduction that
performance degradation of Ag2CO3 is because of the decreasing
of the Oꢀ3 radicals amount resulted by the decrease of Ag+ ion
˙
amount. As the electrode potential of ozone in neutral solution is
1.24 eV, the ozone should generate from the dissolved oxygen
in solution after light irradiation, and obtain the photogenerated
electron to form ozone anion radical. At same time, because the
CB potential of Ag2CO3 is lower than the electrode potential of
Ag/AgNO3 (0.80 eV), Ag+ ion should also attract the photogen-
ESR analysis. The ESR analysis results of fresh and used
Ag2CO3 in dark and with light at different time were shown in
Fig. 5. The plots confirmed that only ozone anion radicals, O3ꢀ
˙
were observed since the seven line spectrums have been detected

1320 Wei Jiang et al.
process with Ag2CO3 as photocatalyst under visible light irradia-
tion. Same termination effect of photoreaction was observed in
photodegradation process of RhB with Ag2CO3, which was
shown in Fig. 6B.
The indigo carmine solution with different concentration was
used to determine the ozone generation rate of Ag2CO3 in solu-
tion under visible light irradiation. The results in Fig. 7 con-
firmed that ozone was generated continuously with silver
carbonate under light illumination. The generation speed of
ozone almost kept constant, and consequently, the eliminating
speed of indigo carmine was proportional to the initial concentra-
tion of dye. The calculated generation speed of ozone radicals
was 0.034 mmol per catalyst weight (g) per minute.
PL analysis. The PL spectra of the Ag2CO3 was measured and
compared with Ag3PO4 in Fig. 8. Weaker emission intensity of
Ag2CO3 than Ag3PO4 demonstrated the less recombination rate
of photogenerated hole and electron and consequently higher
quantum efficiency, which means stronger photo-oxidability. The
fact further confirmed the importance of the more separated pho-
togenerated carriers of Ag2CO3 in enhancing their photocatalytic
activity. This is another important reason for the excellent photo-
catalytic performance of Ag2CO3.
Figure 5. ESR signals of Ag2CO3 without light irradiation and with
light irradiation.
erated electron to be reduced to metallic Ag. Besides, it is worth
noted that the performance degradation tendency of Ag2CO3 also
weakens, which indicates that the reduction of Ag+ ion and the
generation of Oꢀ3 are competitive under visible light irradiation.
˙
This is one of the reasons why Ag2CO3 is efficient in degrada-
Proposed photocatalytic process mechanism
tion of organic pollutant.
Considering the above facts, the measured and calculated redox
potentials of Ag2CO3 and other possible related substances in
the photodegradation process were marked in Fig. 9A, and the
proposed photoreaction process of dye on the surface of
Ag2CO3 under visible light irradiation was described in
Fig. 9B. After photogenerating under visible light irradiation,
the hole and electron pair of Ag2CO3 could separate, mineraliz-
ing the organic pollutants, or recombine, releasing fluorescent
light. The strong photo-oxidative capacity of Ag2CO3 under vis-
ible light irradiation should originate from its unrecombined
holes themselves, and the ozone anion radicals derived from the
reaction between transmitted energetic electrons and the
dissolved oxygen. Another undesired side reaction was the
Radical-trapping experiments. For further determining the exis-
tence of ˙Oꢀ3 radicals and investigating its function in pho-
todegradation process of Ag2CO3, a radical-trapping experiment
was conducted, and indigo carmine and methanol were used as
trapping agent for generated ozone and hole, respectively. The
possible masking effect of the scavengers for MO detection in
spectrophotometry analysis was excluded based on the results in
Supporting Information Fig. S9.
The results shown in Fig. 6A confirmed that the respective
addition of methanol or indigo carmine retarded the photocat-
alytic activity of Ag2CO3 significantly. The simultaneous adding
of two trapping agents terminated the MO photodegradation
Figure 6. (A) MO and (B) RhB degradation rate with different scavengers by Ag2CO3 under light irradiation.

Photochemistry and Photobiology, 2015, 91 1321
The photoreactions of Ag2CO3 were explained in detail as the
following steps:
Ag2CO3 þ hv ! eꢀ þ hþ
3O2 ! 2O3
O3 þ eꢀ ! ꢁOꢀ3
dye þ hþ ! . . . ! CO2 þ H2O
dye þ ꢁO3ꢀ ! . . . ! CO2 þ H2O
Agþ þ eꢀ ! Ag
Figure 7. The eliminating speed of indigo carmine with Ag2CO3 under
visible light illumination.
CONCLUSION
In summary, a novel visible light-responsive photocatalyst,
Ag2CO3, was successfully prepared by facile precipitation. Its
band gap is 2.312 eV, and VB and CB edge potentials were cal-
culated to be 2.685 and 0.373 eV, respectively. Excellent photo-
oxidation performance and stability of as-prepared Ag2CO3 with-
out any sacrificial reagents were shown by photodegradation of
MO and RhB. When it was used for the first time, 98% of MO
was decomposed no more than 15 min, and after recycled six
times, the degradation of MO also can reach 87% after 30 min.
In addition as-prepared sample is proved to be practical in actual
situations. Based on these demonstrations, the performance
decreased gradually due to the decomposition of Ag2CO3 to
form metallic Ag. In the photocatalytic process of Ag2CO3, the
photogenerated holes and ozone anion radicals were the decisive
active species for the degradation of dye. This work not only
uses a simple method to synthesize a novel efficient photocata-
lyst that can be used for degradation of organic pollutants, but
also confirms the important role of ozone played in the photo-ox-
idative process when the band gap of photocatalyst does not
cover the electrode potential range of hydroxyl radicals. This
interesting theory deepens insight into the mechanism of photo-
catalytic degradation of organic pollutants with narrow band gap
photocatalyst, and provides a possible approach to enhance the
performance and stability of photocatalyst in future.
Figure 8. Photoluminescence spectra from 300 nm to 650 nm of as-pre-
pared Ag2CO3 sample with Ag3PO4 powder as contrast.
reduction of lattice Ag+ with transmitted electron, resulting in
the generation of metallic Ag and lowering the photocatalytic
performance of Ag2CO3.
Figure 9. The diagram of photocatalysis mechanism of Ag2CO3 under light irradiation: (A) schematic of redox potentials; (B) reaction process.

1322 Wei Jiang et al.
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Additional Supporting Information may be found in the online
version of this article:
Figure S1. The particle size distribution of Ag2CO3 samples.
Figure S2. Density of states (DOS) simulation of Ag2CO3.
Figure S3. Standard curve of MO solution and RhB solution.
Figure S4. The adsorption of MO and RhB on the surface of
Ag2CO3 without light illumination.
Figure S5. Self-degradation of MO and RhB solution under
light irradiation without Ag2CO3.
Figure S6. UV–Vis absorption spectra of MO and RhB solu-
tion during photodegradation process by Ag2CO3 at the first
cycle.
Figure S7. The photocatalytic performance comparison of
fresh Ag2CO3 and Ag3PO4; the consuming time for reaching the
90% degradation rate of MO with Ag2CO3 and Ag3PO4 as pho-
tocatalysts in recycling.
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