Ag doped Bi2O2.33 microrods: Photocatalytic activity investigation

Article abstract of DOI:10.1039/c5ra24503f

Ag doped Bi₂O_2.33 was successfully synthesized via a facile and chemical strategy, and the photocatalytic activity of the products was investigated. The crystal structure and morphology of the products were characterized by XRD, FT-IR, FESEM and HRTEM. The products show good crystallinity of the body-centered tetragonal phase of Bi₂O_2.33. Results of UV-vis DRS show that Ag doped Bi₂O_2.33 exhibits stronger and broader spectral absorption than bare Bi₂O_2.33. The Ag-6% Bi₂O_2.33 was found to exhibit the highest photocatalytic activity in the rhodamine B degradation experiments, and achieved a degradation efficiency of 93.54%; while bare Bi₂O_2.33, Ag-3%, and Ag-9% achieved degradation efficiencies of 61.93%, 73.62%, and 82.32%, respectively. The stability and reusability of Ag doped Bi₂O_2.33 was also tested. The results showed that Ag-6% Bi₂O_2.33 could obtain good degradation efficiency during five cycles of reusing, 93.54%, 92.50%, 92.25%, 92.20% and 92.20%, respectively. The active species of O₂^.- and ^.OH during the photodegradation process were detected by EPR technology. Ag-doped Bi₂O_2.33 is a promising photocatalyst with high photocatalytic activity and stability, showing a great potential in the field of environmental remediation.

Full text of DOI:10.1039/c5ra24503f

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Ag doped Bi2O2.33 Microrods: Photocatalytic Activity Investigation
Xiaojuan Wang,a Alei Zhu,a Zhiyi Li a and Zhijun Liua*
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a R&D Institute of Fluid and Powder Engineering, Dalian University of Technology, Dalian 116024, China
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Ag doped Bi2O2.33 were successfully synthesized via a facile and chemical strategy, and the photocatalytic activity of the
products was investigated. The crystal structure and morphology of the products were characterized by XRD, FT-IR, FESEM and
HRTEM. The products show good crystallinity of body-centered tetragonal phase of Bi2O2.33. Results of UV-vis DRS show that Ag
doped Bi2O2.33 exhibits stronger and broader spectral absorption than bare Bi2O2.33. The Ag-6% Bi2O2.33 was found to exhibit the
highest photocatalytic activity in the Rhodamine B degradation experiments, and achieved a degradation efficiency of 93.54%;
while bare Bi2O2.33, Ag-3%, and Ag-9% achieved degradation efficiencies of 61.93%, 73.62%, and 82.32%, respectively. The
stability and reusability of Ag doped Bi2O2.33 was also tested. The results showed that Ag-6% Bi2O2.33 could obtain good
degradation efficiency in five cycles reusing, 93.54%, 92.50%, 92.25%, 92.20% and 92.20%, respectively. The active species of
·-
O2 and ·OH during the photodegradation process were detected by EPR technology. Ag-doped Bi2O2.33 is a promising
photocatalyst with high photocatalytic activity and stability, showing a great potential in the field of environmental
remediation.
Keywords: Ag doped Bi2O2.33, microrods, simulated sunlight, photocatalytic activity, Rhodamine B
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1. Introduction
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Bismuth oxide as multi-functional semiconductor materials has wide applications in photocatalysis,1-4
electrochemical electrode materials,5 optical coatings,6 and metal/insulator/semiconductor (MIS) capacitors.7
Bismuth oxide primarily displays four crystalline phases: monoclinic α-Bi2O3, tetragonal β-Bi2O3, body-centered
cubic γ-Bi2O3, and face-centered cubic δ-Bi2O3.8-10 Bi2O3 and its modifications have been investigated extensively
as they are promising photocatalysts with relatively narrow band gap and higher oxidation power of the valence
holes properties.11 Also, Bi2O3 is used as catalysts for degradation of various organic pollutants.12-16
Recently, more interests are focused on the nonstoichiometric phase Bi2O2.33 that usually exists as impurity in
the bismuth oxide thin films, bismuth oxides, and bismuth-oxide-based materials.17-19 Bi2O2.33 nanosheets were
synthesized by electrolytic corrosion of metal Bi, and detected one strong UV emission at room temperature; the
results indicated that Bi2O2.33 nanosheets had a great potential to be used for UV light emitters.20 Huang et al.
prepared 3D orange-like Bi2O2.33 microspheres by the conventional chemical precipitation technique, and the
products display super capacitive performance, suggesting the potential application in energy storage.21 Bi2O2.33
nanoflowers synthesized by Guan et al. via a one-step solvothermal method, and the products display
ferromagnetic signal at room temperature.22 Although the studies of Bi2O2.33 some properties, such as
photoluminescence, capacity and magnetism, have been conducted, to the best of our knowledge, there is no
report of the photocatalytic capability of nonstoichiometric phase Bi2O2.33 and its modifications.
Here in, Ag doped Bi2O2.33 microrods are prepared by a facile method, and the optical property and
photocatalytic performance of the products are also investigated. Our results show that Ag doped Bi2O2.33
demonstrate significantly enhanced photocatalytic activity, and has a promising application in the degradation of
organic pollutants.
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2 Experimental
2.1 Materials and methods
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Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and Rhodamine B (RhB) were purchased from Sinopharm Chemical
Reagent Co., Ltd. Silver nitrate (AgNO3) and sodium hydroxide (NaOH) were purchased from Tianjin Kermel
Chemical Reagent Co., Ltd. Nitric acid (HNO3) and sodium dodecyl benzene sulfonate (SDBS) were purchased from
Tianjin Damao Chemical Reagent Co., Ltd. All chemical reagents were of analytical grade and used without further
purification.
Ag doped Bi2O2.33 as photocatalyst was prepared by the co-precipitation method using Bi(NO3)3·5H2O and
AgNO3 as starting materials. In a typical synthesis procedure: 6 mmol Bi(NO3)3·5H2O and 0.18 mmol AgNO3
powder were completely dissolved in 20 mL 2 mol·L-1 nitric acid under vigorous stirring at room temperature to
obtain transparent Bi3+ and Ag+ aqueous solution, with 0.05g SDBS as surfactant. 4 mol·L-1 NaOH was added
dropwise into the above solution with the help of agitation until pH reaches to 12. After stirring for 3 h at 40 °C,
the resulting mixture was then left still 4 h at room temperature. Then the slurry was centrifuged and washed
* Corresponding author: Eꢀmail: liuzj@dlut.edu.cn, Tel.&Fax: ++86ꢀ411ꢀ84986285
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several times with distilled water and absolute ethanol, and the solids were oven-dried at 60 °C for 12 h. Finally,
the products were calcined at 500 °C for 4 h in air. Samples synthesized with Bi3+: Ag+ at mole ratio of 1:0.03,
1:0.06, 1:0.09 were denoted as Ag-3%, Ag-6% and Ag-9%, respectively. For comparison, bare Bi2O2.33 was
synthesized under same conditions without adding Ag source.
2.2 Catalyst characterization
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The crystalline structures and compositions of as-prepared samples were determined by a Shimadzu XD-3A X-ray
diffractometer with Cu Kα irradiation at 30 kV and 30 mA. The surface morphology and microstructures of the
samples were characterized by field-emission scanning electron microscopy (FE-SEM, Nova Nano SEM 450) and
field emission (high-resolution) transmission electron microscopy (HRTEM, TF30), respectively. Fourier transform
infrared spectrometer (FT-IR, EQUINOX55) spectra were recorded in the range of 400-4000 cm-1. UV−vis
diffuse-reflectance spectra (JASCO, UV-550) were collected in the wavelength range of 200-̶800 nm. Electron
paramagnanetic resonance spectra (Bruker, EPR-300E) were recorded at room temperature in dark or under
simulated sunlight irradiation using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the radical trap to detect the
active species during the photodegradation process.
2.3 Photocatalytic Measurement
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The photocatalytic activity of the products was tested by the degradation of RhB. It was performed in a quartz
reactor with a 500 W Xe lamp as the light source to simulated sunlight irradiation with wavelength range of
200-̶800 nm. In each experiment, 0.05 g of the as-prepared photocatalysts was added to a 50 mL RhB solution
with a concentration of 20 mg·L-1. Before irradiation, the suspensions were magnetically stirred for 60 min in the
dark to ensure the system to reach absorption-desorption equilibrium. All photocatalytic experiments were
accompanied with magnetic stirring and performed under the same simulated sunlight irradiation. Upon
illumination for every 30 min, 3 mL of the suspension was extracted and centrifuged (9000 rpm) for 10 min,
analyzed by recording UV-vis spectra on a UV 1100 spectrophotometer. The concentration of RhB was determined
at its characteristic absorption wavelength of 554 nm. Photodegradation efficiency can be calculated by the
following formula:
Photodegradation rate % = C -C ×100
（1）
0
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C0
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where C0 is the concentration of RhB before irradiation (t=0) and C is the concentration of RhB after a certain
irradiation time.
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3. Results and discussion
3.1 Crystal structure analysis
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The typical XRD patterns of Bi2O2.33 prepared with different content of Ag are shown in Fig. 1a, suggesting the
nonstoichiometric phase of Bi2O2.33. The characteristic peaks at 2θ of 10.06°, 20.18°, 26.38°, 29.20°, 30.42°, 32.90°,
35.68°, 45.44° and 47.22° correspond to the (004), (008), (105), (107), (00 12), (110), (00 14), (1 1 12), (200)
crystalline planes of the body-centered tetragonal phase of Bi2O2.33 (JCPDS No.27-0051), respectively. And no
impurities or other phases were observed in the as the synthesized samples. After doping with Ag, the intensity
and the shape of diffraction peaks of samples have no obvious changes. A little different shift trend of (107)
diffraction peak was detected in the XRD patterns for Ag-doped samples, as shown in Fig. 1b. (107) peak showed
a shift to lower angle with the increase in Ag doping content. The main reason is that the doped ion radius of Ag+
(0.126 nm) is bigger than that of Bi3+ (0.096 nm). Besides, a typical pattern of the FCC (face-center cubic)
structure of metallic Ag (JCPDS No.04-0783) was observed in the XRD patterns of Ag doped samples as shown in
Fig. 1(d). The presence of separate Ag2O phases was not observed due to the low dopant concentration or the
substitution of Bi3+ lattice sites by the doped Ag+. The sharp peaks indicate a good crystallinity of Bi2O2.33
.
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Fig. 1 XRD patterns of samples: (1) bare sample, (2) Ag-3%, (3) Ag-6%, (4) Ag-9%
The typical FTIR spectra of bare Bi2O2.33 and Ag-6% measured in the range of 400-4000 cm-1 are shown in Fig.
2. According to the study of Fruth et al. 23,24, each absorption band in the range of 200-800 cm-1 was attributed to
the stretching vibration mode of Bi-O, taking into account the mean wavenumber and the intensity of the bands.
Such phenomenon was also reported by Carrazan et al.,25 showing that in the 400~600 cm-1 range, the stretching
and deformation modes involving Bi-O could be observed. The absorption bands at 541 cm-1, 503 cm-1 and 430
cm-1 confirm the existence of Bi-O. In addition, the appearance of sharp bands centered at ~3440 cm-1 and 1400
cm-1 indicated the existence of O-H stretching of the absorbed H2O molecules and the carbonate moieties which
are generally observed when FTIR samples were measured in air.26,27 It was found that the FTIR spectra of Ag-6%
sample, were quite similar to the bare Bi2O2.33 (Fig. 2), suggesting that the addition of Ag has little effect on the
FTIR adsorption bands.
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Fig. 2. FT-IR spectra of bare sample and Ag-6% doped sample
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3.2 Morphological analysis
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Figure 3 shows the local SEM and TEM images of Bi2O2.33. As presented in Fig. 3a, the Ag-6% sample appeared as
microrods with a length of 4 μm and an aspect ratio of 10. Sample of Ag-6% displayed a rod shape decorated with
a few nanoparticles (Fig. 3b). The prepared Bi2O2.33 was body-centered tetragonal phase (with lattice parameters
of a=3.85 Å，b=3.85 Å, c=35.10 Å, α=90°, β=90° and γ=90°). The lattice fringe image shown in Fig. 3d clearly
revealed high crystallinity of Bi2O2.33 rods. An HRTEM image taken from the edge in Fig. 3c showed the
interplanar distances of 0.278 nm, a typical (110) plane of Bi2O2.33. In addition, the SAED pattern in Fig. 3c inset
exhibited a body-centered tetragonal symmetric diffraction pattern that could be ascribed to single-crystalline
nature of Bi2O2.33. However, due to the low content and well dispersion of Ag over Bi2O2.33 rods, no significant
fringe lattices associated with Ag were detected in the HRTEM image.
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Fig. 3 SEM images of Ag-6% (a), TEM photos of Ag-6% (b-d)
3.3 Optical absorption property
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The optical properties of synthesized Bi2O2.33 photocatalysts were studied by UV-vis DRS spectroscopy. As shown
in Fig. 4a, prepared samples demonstrate good absorption performance of ultraviolet and visible light. There is a
strong absorption at approximately 456 nm for all samples, which is assigned to the intrinsic band-gap absorption
of Bi2O2.33. After Ag doped, doping samples show an additional remarkable strong and broad absorption bands in
the range of 500~700 nm in visible light region. Samples doped with Ag-3%, Ag-6% and Ag-9% exhibit absorption
bands centered at ~562 nm, ~574 nm and ~598 nm, respectively. There are similar results found in precious work,
and the explanation might be that: the additional broad prominent absorption observed for doping samples
should be attributed to the surface plasmon resonance effect of Ag; and the surface plasmon absorption on the
surface of Ag derives from a collective oscillation of free electrons excited by the matching photon energy.28–32
The absorption bands of Ag doped samples extend significantly toward visible light and the absorption intensity
also increases. The doping of Ag leads to the red shift that seems more apparent in the sample with a higher Ag
ratio. Therefore, the prepared samples have greater absorption efficiency at the visible light region and improved
utilization of sunlight.
The band-gap energy, which represents the energy change of an electron transition from oxygen valence band
(VB) to bismuth conduction band (CB), is of great significance in photocatalytic activity.33 The band-gap energy of
synthesized photocatalysts can be estimated from Tauc’s plots by the following formula: 34
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αhν=A(hν-Eg)n/2
（2）
where α is the absorption coefficient near the absorption edge, hν is the photon energy, A is a constant, Eg is the
absorption band-gap energy, and n has different values depending on the absorption process. Here n=1 for the
direct transition semiconductor material of bismuth oxide.35,36 The plots of (αhν)2 versus hν of the samples are
shown in Fig. 4b. Eg is estimated by the straight portion of the (αhν)2 versus hν plot to α = 0. Then, the band-gap
energy of bare sample, Ag-3%, Ag-6% and Ag-9% is 2.70, 2.26, 2.20 and 2.14 eV, respectively.
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Fig. 4 (a) UV–vis DRS of synthesized samples, (b) Tauc’s plots to estimate the band-gap energy (Eg).
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3.4 Photocatalytic activity
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The photocatalytic activity of the synthesized photocatalysts was evaluated by the photodegradation of RhB
under simulated sunlight irradiation and compared with the direct photolysis (Blank). Figure 5a displays UV-vis
absorbance spectra of RhB solution at different time intervals in the presence of bare Bi2O2.33 under simulated
sunlight irradiation. Clearly, the absorption peaks at 554 nm gradually decreased with increasing irradiation time.
The absorption intensity of RhB at 554 nm steadily decreased upon increasing irradiation times, in accordance
with the gradual color change of the reaction solution from rich-red color to pale pink at different times (Fig. 5a,
inset). Figure 5b displays the change in concentration of RhB upon irradiation time in the absence and presence
of undoped and Ag-doped Bi2O2.33. For all the adsorption processed in dark, little difference was found on the
degradation of RhB. Under the same reaction condition for 180 min, only 9.87% degradation occurred relative to
the direct photolysis (Blank), whereas bare Bi2O2.33, Ag-3%, Ag-6% and Ag-9% achieved degradation efficiencies of
61.93%, 73.62%, 93.54% and 82.32%, respectively (Table 1). Under simulated sunlight and in the same
illumination time, Ag-doped samples exhibited enhanced photocatalytic activity because of their lower band-gap
energy and higher optical absorption in wider visible light region.37
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Fig. 5 (a) UV−vis spectra of an RhB solution by 6% Ag doped Bi2O2.33 under simulated sunlight irradiation (I0 = 140 mW cm−2). The inset
shows photographs of the color change of the RhB solution during different reaction times. (b) RhB concentration varying with time over
different samples.
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The photodegradation of RhB by direct photolysis or photocatalysts was examined by fitting the experimental
data to the following pseudo-first-order decay kinetics equation. Based on the Langmuir-Hinshelwood model,38
the reaction rate constant can be estimated as:
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k = - 1 ln(CC
)
（3）
t
0
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where C0 and C are the initial concentration of RhB (C0 = 20 mg·L-1) and the RhB concentration at time t, and k is
the first-order kinetic constant. Figure 6 shows the five fitted lines according to our photocatalysis experiments.
The kinetic constants and regression coefficients (R2) were also listed in Table 1. It was found that Ag-6% sample
exhibits a photocatalytic activity of 26.5, 2.7, 2.0 and 1.5 times higher than that of direct photolysis, bare sample,
Ag-3% and Ag-9%, respectively.
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Fig. 6 linear plots of ln(C0/C ) versus time.
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Table 1 Band-gap energy, photodegradation efficiency, Kinetic constants and regression coefficients of prepared samples in RhB
degradation simulated sunlight irradiation
Samples
blank
Eg (eV)
/
Photodegradation
9.87%
Kinetic constant (min-1)
R2
5.54E-4
0.9704
0.9815
0.9861
0.9874
0.9946
bare
2.70
2.26
2.20
2.14
61.93%
5.40E-3
Ag-3%
Ag-6%
Ag-9%
73.62%
7.40E-3
93.54%
1.47E-2
82.32%
9.89E-3
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According to former study39, RhB has visible-light screening effect. As seen in Fig 5a, RhB aqueous solution has
a strong absorbance at the wavelength from 450 nm to 600 nm. When the concentration of the dye is high, a
significant amount of visible light would be absorbed by the dye molecules rather than by the catalysts, and thus
the efficiency of the catalytic reaction is reduced. As shown in Fig. 5b, the blank sample has much lower
degradation efficiency than those with catalysts added; and it meant that in RhB degradation, the effect of
self-sensitization is much less than that of photocatalysis. To get a further confirmation of no self-sensitization,
four 3 W monochromatic lights (λ = 420 nm) instead of the 500 W Xe lamp were used as the light source for the
photodegradation of RhB over the bare Bi2O2.33 and Ag-6% Bi2O2.33. This is due to RhB has no absorbance at the
wavelength of 420 nm (Fig. 5a). As shown in Fig. 7, the RhB photodegradation efficiencies over the bare Bi2O2.33
and Ag-6% Bi2O2.33 were 68.98% and 97.36%, respectively; while no self-degradation of RhB occurred under the
same condition. The results confirmed that the photocatalytic activity enhancement of the prepared catalysts is
not induced by the self-sensitization effect.
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blank
bare sample
Agꢀ6%
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Irradiation Time (min)
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Fig. 7 Photocatalytic degradations of RhB over bare Bi2O2.33 and Ag-6% Bi2O2.33 under irradiation of monochromatic light (λ = 420 nm)
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Further photocatalytic degradation experiments were carried out using Ag-6% to test the stability and
reusability of the as-synthesized photocatalysts. The catalyst (Ag-6%) was reused for five times under the same
conditions (Fig.8). The photodegradation efficiencies of RhB for the five cycles are 93.54%, 92.50%, 92.25%, 92.20%
and 92.20%, respectively. Ag-6% demonstrates a relatively good stability in five cycles, which is of great
importance for promising and practical application of such photocatalyst.
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Fig. 8 The photodegradation of RhB by Ag-6% for five cycles.
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Furthermore, reactive species trapping experiments were performed to investigate the reactive oxidizing
·-
·-
species in the photocatalytic process. ·OH and O2 were detected by EPR technology (with DMPO). As O2 was
very unstable in water and slow reaction with DMPO, the involvement of O2·- was examined in methanol.40 Figure
9 shows EPR trap signals (with DMPO) of Ag-6% Bi2O2.33 in two different dispersions. Figure 9a shows that four
characteristic peaks of DMPO-·OH in the range of 3330-3400 nm were observed in aqueous dispersions of Ag-6%
Bi2O2.33 under simulated sunlight irradiation but no such signals were detected in dark. The intensity ratio of the
four characteristic peaks is nearly 1: 2: 2: 1, and it can be inferred the existence of ·OH during the photocatalytic
·-
process.41,42 Furthermore, Figure 9b shows that six characteristic peaks of DMPO-O2 species were also detected
in methanol dispersions of Ag-6% Bi2O2.33 under simulated sunlight irradiation but very weak nearly none signals
were detected in dark. The intensity of the six characteristic peaks is nearly the same, and it can be inferred the
existence of O2·- during the photocatalytic process.41,42 EPR results indicated that certain light irradiation is crucial
·-
·-
to the generation of ·OH and O2 species and directly confirmed that both ·OH and O2 are produced on the
surface of Ag-6% Bi2O2.33 under simulated sunlight irradiation.
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Fig. 9 EPR spectra of the reactive oxidizing species trapped by DMPO in Ag-6% Bi2O2.33 aqueous dispersions (a) and methanol dispersions
(b)
3.5 Mechanism of photocatalytic activity
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The photocatalysis principle of semiconductor is usually elucidated by photogenerated electrons and holes
together. A probable mechanism of photocatalytic reaction occurring in the surface of Bi2O2.33 with 6% Ag content
under simulated sunlight illumination is illustrated in Scheme 1. When photons with an energy ≥2.20 eV are
absorbed by Bi2O2.33, photogenerated electrons (e-) are aroused and transferred from valence band (VB) to
conduction band (CB) across the band gap, resulting in holes and electrons in VB and CB, respectively. Electrons
was then transferred to the surface of photocatalyst and react with adsorbed O2 to generate superoxide radical
anions (O2·-), which combines with H2O to form H2O2 afterwards; and H2O2 combines with electrons on the
surface of photocatalysts to form ·OH. Holes react with OH- or H2O to generate hydroxyl radicals (·OH). The active
·-
oxidizing species (O2 and ·OH) play significant roles in degrading adsorbed RhB molecules nearby, driving the
photodegradation of RhB molecule. The RhB degradation occurs in two competitive processes: one is stepwise
N-de-ethylation, and the other is the destruction of conjugated structure43. In the photodegradation process,
these two degradation processes both took place, and the destruction of conjugated structure was the main way.
After the conjugated structure of RhB was destructed, two other processes, opening-ring and mineralization
followed, and some organic acidic molecules appeared in the system, which were finally mineralized to water and
carbon dioxide44
.
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Scheme 1 Digram of light excited electron-hole separation and the photogradation process.
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Accordingly, the enhanced photocatalytic activity for Ag-doped Bi2O2.33 could be attributed to the improved
capacity of generation of electron-hole pair efficiently. Doping appropriate Ag can induce defects on the shallow
surface of photocatalyst, which could become the center of electron or hole traps, or act as the center of charge
carrier recombination which in turn captures the photogenerated electrons in the bulk phase45. However,
excessive Ag in the bulk phase can also work as the recombination centers of electron-hole pairs which have
negative effect on photo catalysis reaction46. This may be the explanation for the result that 6% Ag-doped Bi2O2.33
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was observed to exhibit the highest activity other than 9% Ag-doped Bi2O2.33 in RhB degradation experiments.
Moreover, the structure of Ag-doped Bi2O2.33 affords an attachment for RhB molecules and shortens the distance
of electron transition from the inner to the surface, which ensures high flux and rapid RhB diffusion. Such
structure also has positive effect on the separation of photoelectrons from holes and the degradation efficiency
of RhB. On the other hand, the recombination of photogenerated electrons and holes was efficiently suppressed,
improving the quantum efficiency. As a consequence, more oxidative species are generated and result in higher
photocatalytic performance.
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4 Conclusions
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Bi2O2.33 and Ag-doped Bi2O2.33 were successfully synthesized via a facile and chemical strategy, and their optical
property and photocatalytic performance were examined for the first time. It is found that Ag-doped Bi2O2.33
exhibit enhanced photocatalytic activity than bare Bi2O2.33. The Ag-6% sample yields the highest RhB removal
ratio of 93.54%. Also, the modified Bi2O2.33 also exhibits a favorable stability and reusability; after five cycles, Ag-6%
sample could still maintain a degradation yield of 92.20%. As such, the prepared Ag-doped Bi2O2.33 seems a
promising photocatalyst with high photocatalytic activity and stability, showing a great potential in the field of
environmental remediation.
261
Acknowledgement
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This work was financially supported by the Fundamental Research Funds for Central Universities (Grant No.
DUT852018).
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References
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
[1] Y. Sun, W. Wang, L. Zhang and Z. Zhang, Chem. Eng. J., 2012, 211-212, 161-167.
[2] A. K. Chakraborty, S. B. Rawal, S. Y. Han, S. Y. Chai and W. I. Lee, Appl. Catal. A-Gen., 2011,407, 217-223.
[3] H. Y. Jiang, G. G. Liu, M. Li, J. J. Liu, W. B. Sun, J. H. Ye and J. Lin, Appl. Catal. B-Environ., 2015, 163, 267-276.
[4] W. J. Wang, X. Q. Chen, G. Liu, Z. R. Shen, D. H. Xia, P. K. Wong and J. C. Yu, Appl. Catal. B-Environ., 2015,
176-177, 444-453.
[5] F. L. Zheng, G. R. Li, Y. N. Ou, Z. L. Wang, C. Y. Su and Y. X. Tong, Chem. Commun., 2010, 46, 5021-5023.
[6] L. Zhou, W. Z. Wang, H. L. Xu, S. M. Sun and M. Shang, Chem.-Eur. J., 2009, 15, 1776-1782.
[7] P. Marija, K. Aleksandar, B. Biljana, R. Milena, M. Branko, R.-M. Ana and R. Marko, Mater. Lett., 2010, 64,
2247-2250.
[8] S. Anandan, G.-J. Lee, P.-K. Chen, C. Fan and J. J. Wu, Ind. Eng. Chem. Res., 2010, 49, 9729-9737.
[9] H. Y. Jiang, K. Cheng and J. Lin, Phys. Chem. Chem. Phys., 2012, 14, 12114-12121.
[10] H. Y. Jiang, G. G. Liu, T. Wang, P. Li, J. Lin and J. H. Ye, RSC Adv., 2015, 5, 92963.
[11] K. Brezesinski, R. Ostermann, P. Hartmann, J. Perlich and T. Brezesinski, Chem. Mater., 2010, 22, 3079-3085.
[12] G. P. He, C. L. Xing, X. Xiao, R. P. Hu, X. X Zuo and J. M. Nan, Appl. Catal. B-Environ., 2015, 170-171, 1-9.
[13] M. M. Mohamed and A. A. Saleh, Micropor. Mesopor. Mater., 2015, 204, 62-72.
[14] S. Swati, U. Ahmad, K. M. Surinder and K. K. Sushil, Ceram. Int., 2015, 41, 3355-3364.
[15] J. M. Zhang, Z. F. Zhang, Y. Y. Zhang, C. M. Li, X. G. Sun, H. Y. Si, Z. Peng and Y. T. Li, Mater. Express, 2015, 5,
336-342.
[16] M. Faisala, A. A. Ibrahima, H. Bouzid, S. A. Al-Sayari, M. S. Al-Assiri and A. A. Ismail, J. Mol. Catal. A: Chem.,
2014, 387, 69-75.
[17] T. P. Gujar, V. R. Shinde, C. D. Lokhande, R. S. Mane and S. H. Han, J. Power Sources, 2006, 161, 1479-1485.
[18] L. Leontiea, M. Caraman, M. Delibas and G. I. Rusua, Mater. Res. Bull., 2001, 36, 1629-1637.
[19] X. L. Gou, R. Li, G. X. Wang, Z. X. Chen and D. Wexler, Nanotechnology, 2009, 20, 495-501.
[20] G. L. Fang, G. Chen, J. Q. Liu and X. Wang, J. Phys. Chem. C, 2010, 114, 864-867.
9

RSC Advances
Page 10 of 11
View Article Online
DOI: 10.1039/C5RA24503F
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
[21] X. J. Huang, J. Yan, F. L. Zeng, X. L. Yuan, W. J. Zou and D. S. Yuan, Mater. Lett., 2013, 90, 90-92.
[22] H. M. Guan, X. D. Zhang and Y. Xie, J. Phys. Chem. C, 2014, 118, 27170-27174.
[23] V. Frutha, M. Popab, D. Bergerc, C. M. Ionicaa and M. Jitianua, J. Eur. Ceram. Soc., 2004, 24, 1295-1299.
[24] R. Irmawati, M. N. Noorfarizan Nasriah, Y. H. Taufiq-Yap and S. B. Abdul Hamid, Catal. Today, 2004, 93-95,
701-709.
[25] S. R. G. Carrazan, C. Martin, V. Rives and R. Vidal, Spectrochim Acta A, 1996, 52, 1107-1118.
[26] M. Faisal, S. B. Khan, M. M. Rahman, A. Jamal and M. M. Abdullah, Appl. Surf. Sci., 2012, 258, 7515-7522.
[27] S. B. Khan, M. Faisal, M. M. Rahman and A. Jamal, Talanta, 2011, 85, 943-949.
[28] H. Zhang, G. Wang, D. Chen, X. J. Lv and J. H. Li, Chem. Mater., 2008, 20, 6543-6549.
[29] J. He, I. Ichinose, T. Kunitake, and A. Nakao, Langmuir, 2002, 18, 10005-10010.
[30] B. Wiley, Y.G. Sun, B. Mayers and Y.N. Xia, Chem. Eur., 2005, 11, 454–463.
[31] Y. X. Tang, P. X. Wee, Y. K. Lai, X. P. Wang, D. G. Gong, P. D. Kanhere, T. T. Lim, Z. L. Dong and Z. Chen, J. Phys.
Chem. C , 2012, 116, 2772–2780.
[32] M. R. Elahifard, S. Rahimnejad, S. Haghighi and M. R. Gholami, J. Am. Chem. Soc., 2007, 129(31), 9552–
9553.
[33] M. Ge, Y. Li, L. Liu, Z. Zhou and W. Chen, J. Phys. Chem. C, 2011, 115, 5220-5225.
[34] N. T. Hahn, S. Hoang, J. L. Self and C. B. Mullins, ACS Nano, 2012, 6, 7712-7722.
[35] S. Iyyapushpam, S. T. Nishanthi and D. P. Padiyan, J. Alloy Compd., 2013, 563, 104-107.
[36] L. Shan, G. Wang, D. Li, X. San, L. Liu, L. Dong and Z. Wu, Dalton Trans., 2015, 44, 7835-7843.
[37] Q. Huang, S. Zhang, C. Cai and B. Zhou, Mater. Lett., 2011, 65, 988-990.
[38] J. Xu, W. Meng, Y. Zhang, L. Li and C. Guo, Appl. Catal. B-Environ., 2011, 107, 355-362.
[39] H. Wang, S. Li, L. Zhang, Z. Chen, J. Hu, R. Zou, K. Xu, G. Song, H. Zhao, J. Yang and J. Liu, RSC Adv., 2013, 15,
9011.
[40] L. S. Zhang, K. H. Wong, H. Y. YIP, C. Hu, J. C. Yu, C. Y. Chan and P. K. Wong. Environ. Sci. Technol., 2010, 44,
1392−1398.
[41] W. W. Wang , T. W. Ng, W. K. Ho, J. H. Huang, S. Liang, T. C. An, G. Y. Li, J. C. Yu and P. K. Wong, Appl. Catal.
B-Environ., 2013, 129, 482−490
[42] X. F. Yang, H. Cui, Y. Li, J. L. Qin, R. Zhang and H. Tang, ACS Catalysis, 2013, 3, 363−369
[43] J. Li, X. Zhang, Z. Ai, F. Jia, L. Zhang and J. Lin, J. Phys. Chem. C, 2007, 111, 6832-6836.
[44] Z. He, S. Yang, Y. Ju and C. Sun, J. Environ. Sci., 2009, 21, 268-272.
[45] Y. Li, S. Peng, F. Jiang, G. Lu and S. Li, J. Serb. Chem. Soc., 2007, 72, 393-402.
[46] K. Zhang, D. Jing, Q. Chen and L. Guo, Int. J. Hydrogen Energy, 2010, 35, 2048-2057.
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DOI: 10.1039/C5RA24503F
Ag doped Bi2O2.33 Microrods: Photocatalytic Activity Investigation
Xiaojuan Wang,a Alei Zhu,a Zhiyi Lia and Zhijun Liua*
a R&D Institute of Fluid and Powder Engineering, Dalian University of Technology, Dalian 116024, China
This paper presents the research of synthesized Ag doped Bi2O2.33 sheets by a facile method, and the investigation of the
products photocatalytic ability.
* Corresponding author: E-mail: liuzj@dlut.edu.cn, Tel.&Fax: ++86-411-84986285