FeII/FeIII Doped Bi/BiOBr Hierarchical Microspheres as a Highly Efficient Catalyst for Degradation of Organic Contaminants at Neutral pH: The Role of Visible Light and H2O2

Article abstract of DOI:10.1002/cctc.201700549

A novel Fe^II/Fe^III doped Bi/BiOBr (FBB) visible-light, Fenton-like catalyst was successfully synthesized by using the solvothermal method. The morphological and structural features of FBB were analyzed by XRD, field emission (FE)-SEM, TEM, Brunauer–Emmett–Teller (BET), and X-ray photoelectron spectroscopy (XPS) techniques. The results revealed that the presence of Fe could promote the growth of Bi metal nanoparticles, and increase the specific surface areas of FBB. Rhodamine B (RhB) photodegradation experiments indicated that FBB with the Fe/Bi molar ratio (0.2–0.3) exhibited higher photocatalytic activities. In the photo-Fenton-like reaction, the degradation efficiency of bisphenol A (BPA) over FBB-25 was increased to 100 % within 30 min whereas it was 3 % and 12 % in the Fenton-like and photocatalytic reactions. Moreover, 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) were completely degraded within 30 min over FBB-25. The presence of visible light can promote the rapid reaction rate between Fe^II and Fe^III over FBB with H₂O₂, producing more hydroxyl radicals (^.OH) and more holes. The radical scavenger experiments demonstrated that holes and hydroxyl radicals (^.OH) were the main active species. FBB-25 is still stable after five cycles. Therefore, FBB-25 has great potential in wastewater treatment.

Full text of DOI:10.1002/cctc.201700549

Accepted Article
Title: Fe(II)/Fe(III) Doped Bi/BiOBr Hierarchical Microspheres as a
Highly Efficient Catalyst for Degradation of Organic Contaminants
at Neutral pH: The Role of Visible Light and H2O2
Authors: Wentao Li, Xin Geng, Feng Xiao, Guangyu An, and
Dongsheng Wang
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ChemCatChem
10.1002/cctc.201700549
FULL PAPER
Fe(II)/Fe(III) Doped Bi/BiOBr Hierarchical Microspheres as a
Highly Efficient Catalyst for Degradation of Organic
Contaminants at Neutral pH: The Role of Visible Light and H
Wentao Li,[a,b] Xin Geng, [a,b] Feng Xiao,*[a] Guangyu An, [a] and Dongsheng Wang[a]
2
O
2
Abstract: A novel Fe(II)/Fe(III) doped Bi/BiOBr (FBB) visible-light-
Fenton-like catalyst was successfully synthesized by using the
solvothermal method. The morphological and structural features of
FBB were analyzed by XRD, FESEM, TEM, BET, and XPS. The
results revealed that the presence of Fe could promote the growth of
Bi metal nanoparticles, and increase the specific surface areas of
like and photocatalytic reaction. Moreover, 2-chlorophenol (2-CP), 4-
chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-
trichlorophenol (2,4,6-TCP) were completely degraded within 30min
over FBB-25. The presence of visible light can promote the rapid
propagating reaction rate between Fe(II) and Fe(III) over FBB with
H2O2, producing more hydroxyl radicals (•OH) and more holes. The
radical scavenger experiments demonstrated that holes and
hydroxyl radicals (•OH) were mainly active species. FBB-25 is still
stable after five cycles. Therefore, FBB-25 has a great potential in
the wastewater treatment.
FBB. The rhodamine
b (RhB) photodegradation experiments
indicated that FBB with the Fe/Bi molar ratio (0.2-0.3) exhibited the
higher photocatalytic activities. In the photo-Fenton-like reaction, the
degradation efficiency of bisphenol a (BPA) over FBB-25 was
increased to 100% within 30min while 3% and 12% in the Fenton-
Introduction
For several decades, chlorophenols (CPs) and bisphenol A
hydrogen peroxide (H
2 2
O ), where ≡Fe(II) and ≡Fe(III) mean the
(
BPA), known as ubiquitous environmental contaminants, are
Fe(II)/Fe(III) species in solid or solution phase. In general, the
widely existed in nature. CPs has been widely used as usual raw
materials or intermediates in chemical industries,[1-3] including
the production of pesticides, synthetic resins, and
pharmaceuticals. BPA is mainly used to manufacture
polycarbonate plastic and epoxy resins. [4-5] Due to their potential
carcinogenic and mutagenic activities, they can negatively affect
the environment and damage livers’ physiological processes.
BPA and CPs (i.e., 2,4-dichlorophenol (2,4-DCP), 2,4,6-
trichlorophenol (2,4,6-TCP)) have been listed as priority toxic
pollutants by the US Environmental Protection Agency (EPA).[6-7]
Traditional wastewater treatment methods for CPs and BPA,
including biodegradation, [ physical adsorption, [9] and chemical
reaction rate of ≡Fe(II) with H
magnitude higher than that reaction rate (Eq.(2)),
the reduction of ≡Fe(III) to ≡Fe(II) (Eq. (2)) becomes the rate-
limiting step, leading to a lower activity.
2
O
2
(Eq. (1)) is several orders of
[13]
and thus
≡Fe(II)+H
2
O
2
→ ≡Fe(III)+•OH+OH-
→ ≡Fe(II)+•O
+H+
→ HO •+H
• → ≡Fe(II)+O
• → ≡Fe(III)+H
(1)
(2)
(3)
(4)
(5)
(6)
≡Fe(III)+H
•OH+ H
2
O
2
2
2
O
2
2
2
O
≡Fe(III)+ •O
2
/HO
/HO
2 2
H O +e → •OH +OH
2
2
≡Fe(II)+ •O
2
2
2
O
-1
In the aid of light irradiation, some heterogeneous Fenton
catalysts can show higher catalytic activities. [14-16] The electron
is excited by light from the semiconductor, remaining more holes
in the valence band. And then the photo-induced electrons react
with H O to generate more radical ∙OH (Eq. (6)) or promote the
2 2
reduction of ≡Fe(III) to≡Fe(II). These active species can further
oxidize organic contaminants. [
8]
[
10]
treatment processes,
are difficult to satisfy human’s
requirement for water quality. As emerging alternative
technologies, advanced oxidation processes (AOPs) are efficient
enough to remove organic wastewater pollutants. Because
strong oxidizing radical species generated by AOPs can
completely degrade organic pollutants into non-toxic products
17-19]
Many semiconductors have
been reported to remove contaminants under light radiation,
such as TiO
, [20-21] CdS, [22-23] ZnO [24] and BiOX(X=Cl, Br, I).[25-26]
such as CO
2
, H
2
O and inorganic salts. Among the AOPs, the
2
hydroxyl radical (∙OH) is a friendly-environmentally active specie
from Fenton-like process (Eq. (1-5)). [11,12] In the ∙OH formation
process, Fe(II) is a vital factor to join in the activation of
However, BiOBr has been most extensively investigated
because it can capture solar energy from the visible light region.
Zhang et al prepared the 3-D microspherical BiOBr via an
ethylene glycol-assisted solvothermal method, and investigated
the effect of morphology on the photocatalytic performance. [
Cheng et al reported that Ag/AgBr /BiOBr hybrid exhibited
superior driven-visible-light photocatalytic performance in the
degradation of organic dye compared to N-doped P25. [28] Xiong
et al showed that more exposed {010} facets could enhance the
photocatalytic activity of BiOBr under visible light. [ Although
many methods are adopted to improve the photocatalytic activity
of BiOBr, these improvements are not efficient for CPs and BPA
degradation.
27]
[
[
a]
b]
W.T. Li, X. Geng, F. Xiao, G.Y. An, D.S. Wang
Key Laboratory of Drinking Water Science and Technology,
Research Center for Eco-Environmental Sciences
Beijing 100085 (P.R. China)
E-mail: fengxiao@rcees.ac.cn
W.T. Li, X. Geng
29]
University Chinese Academy of Sciences
Beijing 100049 (P.R. China)
To degrade better CPs and BPA, H
2 2
O is introduced to
enhance the photocatalytic performance. In this work,
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Fe(II)/Fe(III) doped Bi/BiOBr (FBB) visible-light-Fenton-like
catalyst was prepared by the ethylene glycol-assisted
solvothermal method. X-ray diffraction (XRD), X-ray
photoelectron spectroscopy (XPS), field emission scanning
electron microscopy (FESEM), UV-Vis diffuse reflectance
spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) specific
surface area were carried out to characterize the structure
properties of FBB. BPA and CPs were selected to evaluate the
photo-Fenton-like catalytic activity of Fe(II)/Fe(III) doped
Bi/BiOBr hierarchical microspheres. The results showed that
FBB exhibited excellent catalytic performance in the visible-light-
2 2
Fenton-like reaction. It was attributed that the presence of H O
increased the multiple transformation rate of Fe(II) and Fe(III)
over FBB under visible light irradiation.
Results and Discussion
Phase Structure and Morphological Structure
Figure 1A shows that the XRD patterns of the as-prepared
samples. The diffraction peaks of BiOBr are perfectly indexed as
a tetragonal BiOBr phase (JCPDS-ICDD Card No.00-009-0393).
After the addition of Fe(II) to the precursors, the diffraction
position of {110} plane shifts slightly towards a higher 2θ value
with the increase of Fe/Bi ratio (see in the insert image in Figure
1A), and other peaks exhibit similar behaviors. This attributes
that the incorporation of Fe ion into BiOBr matrix by replacing
Bi3+ lattice sites results into the changes of the lattice
Figure 1. A: XRD patterns of BiOBr and Fe(II)/Fe(III) doped Bi/BiOBr with
parameters. [
30]
In addition, the rhombohedral phase of Bi
different Fe/Bi molar ratio (insert: diffraction peak position of {110} in the range
(
JCPDS-ICDD Card No.00-044-1246) is observed in the
of 28-35 degree);B: FESEM images (a
EDX-mapping (a , b ) and TEM images (a
adsorption-desorption isotherms of BiOBr and Fe(II)/Fe(III) doped Bi/BiOBr
1
1
, b ), Magnified-FESEM images (a
2 2
, b ),
samples. The intensity of diffraction peaks of Bi metal phase is
intensified with the addition of Fe(II), indicating that the addition
of Fe(II) improve the crystallinity of rhombohedral Bi phase in the
samples.
3
3
4
, b ) of BiOBr (a) and FBB-25(b);C:
4
N
2
samples
The morphological structures of the as-prepared samples
were examined by FESEM and TEM. Figure 1B displays the
magnified images of FESEM and TEM, as well as FESEM-
3
The EDX mapping of a microsphere in FBB-25 (Figure 2B-b )
suggests that the Fe, Br, O, and Bi elements are distributed
uniformly in FBB-25.
mapping. The pure BiOBr sample (Figure 1B-a
) consists of many flowerlike hierarchical microspheres (~5
um) self-assembled by nanosheets.The FBB-25 microspheres
Figure 1B-b and Figure 1B-b ) with a decreased diameter of
1
and Figure 1B-
Figure 1C-a shows that the
N
2
adsorption-desorption
a
2
isotherms of BiOBr and FBB. The distinct hysteresis loops are
observed at 0.5-1.0 p/p0 from the isotherms, which belong to
type IV, indicating a characteristic of mesoporous materials.
(
1
2
around 3μm are self-assembled by nanosheets and are looser.
Figure S1 (see in supporting information) shows that nanosheets
and pore diameters become bigger when the Fe/Bi molar ratio is
increased from 0.15 to 0.35, and this result was caused by the
incorporation of Fe into BiOBr matrix. The morphological
structure of the sample was further analyzed by TEM. As shown
in Figure 1B-b , the FBB-25 sample consists of hierarchical
4
microspheres that have solid centers, which presents much
thinner edge of a single nanosheet compared with BiOBr (Figure
[
31]
According to the IUPAC recommendations,
the above
hysteresis loops can be categorized as type H3 loops, which are
defined as materials made up of platelike particles. The
mesopore sizes and specific areas of products were determined
by using the Barrett-Joyner-Halenda (BJH) and Brunauer-
Emmett-Teller (BET) methods, respectively, as shown in
Figure1C-b. After the addition of Fe(II), the pore size, pore
volume and surface specific area of FBB sample are obviously
increased, which is listed at Table S2. For example, the BET
surface areas and pore sizes of BiOBr, FBB-15, FBB-20, FBB-
1
B-a
4
). Figure S2 exhibits the EDX of one point in a microsphere
), and the result indicates that the Bi /Br atomic
(
Figure 1B-b
2
2
5, FBB-30, and FBB-35 are determined to 20.37, 30.72, 44.82,
ratio in FBB-25 is 1.0, which is higher than that (0.76) of BiOBr.
This fact implies that elemental Bi particles are deposited on
FBB-25, consistent with XRD and XPS results (see at Table S1).
2
62.97, 55.64, 58.44 m /g and 6.57 nm, 7.39 nm, 8.89 nm, 8.24
3
+
nm, 8.62 nm, 8.36 nm, respectively. The replace of Bi lattice
sites by Fe ions results in increased physical parameter values.
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Chemical Composition by XPS and Light Adsorption
The surface chemical compositions of the BiOBr and FBB-25
sample were investigated by XPS (Figure 2A). Figure S3 shows
the survey of BiOBr and FBB-25, indicating that BiOBr and FBB-
25 consist of Bi, O, Br and Bi, O, Br, Fe, including trace C
element. Figure 2A-a shows the high-resolution XPS spectra for
Bi 4f. The two strong peaks at binding energy around 159 eV
and 165 eV can be ascribed to Bi4f3/2 and Bi4f1/2, respectively.
For FBB-25(or BiOBr), the peak at 159 eV can be fitted into two
peaks of 158.3 eV (158.0 eV) and 159.5 eV (159.6 eV) that are
assigned to metallic Bi and Bi3+ in BiOBr. [32] The concentrations
of Bi on the surface of BiOBr and FBB-25 are determined to be 5%
and 10%, respectively, as shown at Table S3. In Figure 2A-b,
the O1s peak centered at 531 eV can be assigned to three
peaks of 530.4 eV (530.4 eV), 531.8 eV (531.4 eV), and 533.2
eV (532.9 eV) that are attributed to Bi-O bonds in BiOBr,
hydroxyl groups on the surface and oxygen deficient regions,
respectively. [ The addition of Fe can increase the oxygen
deficient from 6% to 9% (see at Table S3). Figure 2A-c shows
the Br3d peaks at 68.7 eV (68.6 eV) and 69.7 eV (69.7 eV) that
correspond to Br3d5/2 andBr3d3/2. The Fe 2p peaks at 711 eV
and 723 eV are ascribed to Fe2p3/2 and Fe2p1/2 (Figure 2A-d).
The peak at 711 eV can be fitted into 710.3 eV and 712 eV that
0
33]
Figure 2. A:High resolution XPS spectra of FBB-25 and BiOBr: Fe 2p, Bi 4f,
O1s, Br 3d; B: UV-Vis diffuse reflectance spectra (a) and plots of the (ahv)1/2
versus hv (b) of the as-prepared samples.
ascribed to Fe2+ and Fe3+, [34] where the molar ratio of Fe /Fe
2+
3+
is 0.5:0.5. In Table S1, the Bi/O atomic ratio in FBB-25 is 0.54,
which is higher than that (0.69) of BiOBr. This indicates that Bi
particles are deposited on FBB-25, and the oxygen deficient
amount is increased.
The UV-Vis diffuse reflectance spectra of BiOBr and FBB
samples were further carried out in Figure 2B-a, finding the
adsorption edge of round 430 nm for BiOBr. However, the
adsorption edge of Fe(II)/Fe(III) doped Bi/BiOBr appears shifted
remarkably towards the higher wavelength with the addition of
Fe content. This suggests that the transition of impurity energy
levels can enhance the adsorption of visible light. According to
the classical formula (Eq. (7)), [35] the band gaps (Eg) of BiOBr
and 62.8% are achieved for BiOBr, FBB-15, FBB-20, FBB-25,
FBB-30, and FBB-35, respectively, indicating that the Fe/Bi
molar ratios of 0.2-0.3 exhibit higher photocatalytic activities for
RhB degradation. 73.4% and 62.8% are achieved for BiOBr,
FBB-15, FBB-20, FBB-25, FBB-30, and FBB-35, respectively,
indicating that the Fe/Bi molar ratios of 0.2-0.3 exhibit higher
photocatalytic activities for RhB degradation.
Considering the chemical composition in the FBB samples,
H
2
O
2
is introduced to activate the photocatalytic sites,
generating hydroxyl radicals to degrade efficiently organic
contaminants. The degradation efficiencies of BPA and CPs
were chosen to evaluate the photo-Fenton-like catalytic
performance of FBB-25.
and FBB can be calculated, shown in Table S2.
n/2
A(hv-E
In Eq.(7), A, h, a, v, and E
g
)
= ahv
(7)
g
present constant, Planck’s constant,
absorption coefficient, frequency of incident photon, and band
gap energy, respectively. The n value is directly determined by
the optical transition types of semiconductors, such as n value of
Catalytic oxidation of BPA in visible light/catalyst/H
2
O
2
system
) versus
4
for BiOBr. [36] The band gaps of BiOBr and FBB-25 are
Figure 3 shows the change of BPA concentration (C/C
o
calculated to be 2.52 eV and 1.61 eV, respectively (Figure 2B-b).
reaction time for FBB-25 under different conditions. In the dark
or visible light, there is almost no BPA degradation efficiency,
and around 15% of BPA degradation is achieved in the Fenton-
like reaction. However, 20 mg/L BPA is completely degraded
Catalytic activity
Photodegradation of RhB
within 30 min in the presence of 5 mM H
implying that the combination of visible light and H
significant role in the BPA degradation efficiency. The H
2
O
2
and visible light,
2
O
2
has
The photocatalytic activities of the obtained samples were
evaluated via RhB degradation with initial concentration of 20
mg/L (see in Figure S4). Obviously, RhB photodegradation
efficiency is negligible with the absence of photocatalysts. In the
adsorption-desorption equilibrium, FBB-25 exhibits the highest
adsorption capacity (around 21 mg/g). After 30min irradiation,
RhB degradation efficiencies of 71.8%, 53.6%, 71.4%, 78.7%,
2
O
2
degradation rate in the Fenton-like reaction is far lower than that
in the visible-light Fenton-like reaction (Figure S5). This is
because visible light can increase a propagating reaction
2 2
between Fe(II) and Fe(III) under H O .
(Eq.(1, 8-9)) [37]
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Catalytic degradation of chlorophenols in visible light/catalyst/
H O system
2 2
Visible light-Fenton-like catalytic oxidation of chlorophenols (2-
CP, 4-CP, 2, 4-DCP, and 2, 4, 6-TCP) degradation were carried
out over FBB-25. Figure 5a and Figure 5b show the results of
chlorophenols degradation and TOC removal. As seen from
Figure 5a and Figure 5b, the degradation efficiencies of 2-CP, 4-
CP, 2, 4-DCP, and 2, 4, 6-TCP at 30 min irradiation are almost
100%, when TOC removal efficiencies are 39.2%, 79.8%,73.3%
and 47.9%, respectively. The extent of chlorophenols
degradation and TOC removal follows the order of 4-CP > 2,4,6-
TCP ≈ 2-CP ≈2,4-DCP (Figure 5c), which has the distinct
difference from previous reports. Benitez suggested that the
order of oxidation rate was 4-CP > 2, 4-DCP > 2, 4, 6-TCP for
both UV radiation and Fenton’s reagent and 2, 4, 6-TCP > 2, 4-
DCP >4-CP for ozonation. [39] Tang also reported the same order
of 2-CP > 2, 4-DCP > 2, 4, 6-TCP by Fenton’s reagent. [40] In
general, the hydroxyl radicals react faster with chlorophenols
having lower number of chlorine atoms, [39, 41] which indicates
that the visible light-Fenton-like catalytic oxidation mechanism of
chlorophenols by FBB-25 is different from Fenton’s reagent
oxidation process.
Figure 3. BPA degradation as a function of irradiation time by FBB-25 with
H
H
2
O
2
or visible light (BPA concentration: 20mg/L; FBB-25 dosage: 0.5g/L;
concentration: 5mM)
O
2 2
Figure 5d exhibits the degradation of multiple chlorophenols
over FBB-25. The results show that the degradation efficiency of
every chlorophenol is almost the same (i.e. 100% at 30min).
Compared with single chlorophenol degradation, pseudo-first-
order reaction rate constants in the multiple chlorophenols
degradation were the same (Figure 5c and Figure 5d). This
implies that the reactive species are no selective.
Half-life times and pseudo-first kinetic constants on
degradation of CPs and BPA over various photocatalysts at
neutral conditions were tabulated in Table S4. The results show
that the degradation rate of CPs and BPA was slow using other
photocatalysts, slower by Fenton-like reaction. This is attributed
that few active species are produced in those catalytic reactions.
It implies that FBB-25 is quite comparable to other catalysts.
Figure 4. (a) BPA degradation and TOC removal efficiency (b) as a function of
irradiation time by FBB-25 with H under visible light; (c) pseudo-first-order
reaction rate constants(k) of BPA degradation and TOC removal (BPA
concentration:20mg/L; FBB-25:0.5g/L;H concentration: 0-20mM)
2
O
2
2 2
O
The H
2
O
2
initial concentration is a key parameter in the visible
2 2
Catalytic mechanism in visible light/catalyst/H O system
light-Fenton-like reaction. Hence, the degradation of 20 mg/L
BPA via FBB-25 was initially conducted to evaluate the effect of
The active species of FBB-25 were carried out via a series of
trapping experiments during the visible-light Fenton-like reaction.
H
2
O
2
concentration. Figure 4a and Figure 4b show the change
of BPA concentration or TOC removal efficiency versus
irradiation time under different H concentration. The results
show that BPA degradation rate and TOC removal efficiency are
increased with the increase of H concentration. TOC removal
efficiencies with 1 mM, 5 mM, 10 mM and 20 mM of H are
5.0%, 57.2%, 83.4%, and 77.5% at 120 min. After more than
0 mM of H initial concentration, BPA degradation rate
The degradation of BPA was repeated with 5 mM H O2 under
2
2
O
2
visible light by adding 1 mM of 1,4-benzoquinone (BQ), 1 mM of
isopropanol (IPA ) and 10 mM of ammonium oxalate (AO) as a
superoxide radical(·O2- scavenger,[42]
) a hydroxyl radical
2
O
2
scavenger (·OH) [ and a hole scavenger,
43]
[44]
respectively. As
2
O
2
3
1
shown in Fig.6a, the removal efficiencies of BPA are inhibited by
IPA (~30%) and AO (~30%) at 30min while BQ increase the
BPA degradation due to increasing the reduction rate of Fe(III)
to Fe(II). [ In addition, the pseudo-first-order rate constants with
2
O
2
constant and TOC removal rate constant almost keep stable
Figure 4c and Figure S6). This indicates that 10 mM H is the
optimized value for BPA degradation. In the oxidation of BPA,
most of TOC was removed in the formation of CO and H O, and
45]
(
2 2
O
-
1
-1
no scavengers, IPA, AO and BQ are 0.081 min ,0.013 min ,
-1
-1
2
2
0.012 min , and 0.12 min (Fig.6b), respectively. This indicates
that the active species of FBB-25 are mainly holes and ·OH
radicals for BPA degradation in the visible light-Fenton-like
reaction.
few was left, including including some low-molecular-weight
organic acids (i.e., acetic acid, oxalate, and propanedioic
acid),[ which agreed with the decrease of pH (from 7.0 to 5.5).
38]
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ChemCatChem
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.
Figure 5. Chlorophenols degradation as a function of irradiation time by FBB-25 with
H
2
O
2
under visible light: (a) chlorophenols degradation, (b)TOC removal
efficiencies,(c) pseudo-first-order reaction rate constants of chlorophenols degradation and TOC removal;(d) multiple chlorophenols degradation;(e) pseudo-first-
order reaction rate constants of multiple chlorophenols degradation.(single solution or multiple solution concentration of 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP
2 2
concentration: 20mg/L; FBB-25 dosage: 0.5g/L;H O concentration:10mM)
Figure 6. Effect of different scavengers on the degradation of BPA with FBB-
5 under visible light and 5mM H : (a) BPA degradation, (b) pseudo-first-
order reaction rate constants (BPA concentration: 20mg/L; FBB-25 dosage:
.5g/L; H concentration: 5mM)
2
2 2
O
0
2 2
O
Figure 8. Formation of hydroxyl radicals in photocatalytic, Fenton-like, and
photo-Fenton-like reactions (FBB-25 dosage: 0.5g/L; concentration:
mM).
2 2
H O
5
To further investigate how
photocatalytic active sites, H degradation and surface Fe(II)
concentration over FBB-25 were carried out. As shown in Figure
, Fe(II) concentration on the surface of FBB-25 was increased
in the photocatalytic reaction (Eq.(8-9))). In the photo-Fenton-
like reaction, Fe(II) concentration was increased when H was
completely consumed at 60min of reaction time. This implies
that surface Fe(III) over FBB-25 is reduced to Fe(II) in the
presence of visible light. The ·OH radicals change was observed
H
2
O
2
can activate the
2
O
2
7
Figure 7. The change of surface Fe(II) concentration and H
over FBB-25 with or without under visible light: (a) surface Fe(II)
2 2
concentration FBB-25 dosage:1.0g/L; H O
2 2
O concentration
2
O
2
2 2
H O
concentration, (b)
H
O
2 2
(
concentration:10mM)
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Figure 10. Cycle runs in the photo-Fenton-like catalytic degradation of BPA (A)
Figure 9. ESR signals of ∙OH produced by FBB-25 during the photo-Fenton-
and 4-CP (B) in the presence of FBB-25 under visible light irradiation within 30
like reaction (a1,a2) and Fenton-like reaction(b1,b2)
min(FBB-25 dosage: 0.5g/L; H
concentration: 20mg/L).
2 2
O concentration:10mM; BPA and 4-CP
in the reaction systems (Fig.8). The reaction rate constant
(
0.205 uM/min) of ·OH formation in the photo-Fenton-like
crystal face{101}, {110}, {200}and {203}. In addition, the Fe, Bi
and Br were almost no released into solution from FBB-25
reaction is higher 11-fold than that (0.019 uM/min) in the Fenton-
like reaction. This indicates that large amount of Fe (II) was
produced and then oxidized by H
reaction (Eq. (1,9)).
(
Table S5). It indicates that the FBB-25 is stable during the
2
O
2
in the photo-Fenton-like
photo-Fenton-like catalytic oxidation of the pollutant molecules,
and has a good potential in the application.
+
BiOBr + hv → h + e
Fe(III) + e → ≡Fe(II)
(8)
(9)
≡
To verify the above reaction mechanism, the ESR
spectroscopy was adopted to track the hydroxyl radical by using
Conclusions
5
, 5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trapping
In summary, Fe(II)/Fe(III) doped Bi/BiOBr hierarchical
photocatalyst was successfully synthesized by using one-step
solvothermal method. The presence of Fe(II)/Fe(III) can promote
the growth of Bi metal nanoparticles and increase the surface
areas of FBB samples. Compared with previous report catalysts,
FBB-25 shows higher catalytic performance for the degradation
of BPA and CPs during the visible light-Fenton-like reaction.
This is attributed to the rapid multiple transformation of Fe(III)
and Fe(II) over FBB under the visible light and the reaction of
reagent. The hydroxyl radical, ∙OH characterized by four
intensity peaks, was detected in the presence of FBB-25(Fig.12).
During the photo-Fenton-like catalytic reaction, the four peaks’
intensities at 30min were higher than those at 1min, while their
intensities at 30min were lower than those at 1min for Fenton-
like reaction. This indicates that more hydroxyl radicals were
produced in the photo-Fenton-like catalytic reaction and
confirms the above reaction mechanism.
Based on the above analysis, the mechanism of photo-
Fenton-like catalytic degradation of organic contaminants was
proposed, as following: Firstly, the oxidation of ≡Fe (II) to ≡Fe (III)
H
2
O
2
with Fe(II). The radical scavenger experiments
demonstrated that holes and hydroxyl radicals (·OH) were
mainly active species. After five cycles, the regenerated FBB-25
is still stable.
by H
oxidize contaminants; Secondly, the reduction of ≡Fe(III) to
Fe(II) by photogenerated electrons (Eq.(2,9) from FBB-25 in
2 2
O (Eq.(1)), producing more hydroxyl radicals (∙OH) to
≡
the presence of visible light; Thirdly, the increase of separation
efficiency of photogenerated electrons and holes, remaining
more holes to degrade organic contaminants.
Experimental Section
Materials
Stability of Catalyst
Bismuth nitrate pentahydrate (Bi(NO
tetrahydrate (FeCl ·4H O, >99%), potassium bromide(KBr, >98%),
rhodamine b (RhB, >95%), ethylene glycol (CH
acid (CH COOH,>99%), hydrogen peroxide (H
3 3 2
) ·5H O, >98%), ferrous chloride
2
2
To test the stability and reusability of FBB-25 in the photo-
Fenton-like catalytic reaction, the catalyst was reused to
2 2
OHCH OH,>98%), acetic
3
2 2
O , >99%), and 2-
degrade BPA and 4-CP for five times under the same conditions, thiobarbituric acid (TBA, >98.5%) were obtained from Sinopharm
and the result is shown in Fig.10. The catalytic efficiencies of
FBB-25 for BPA and 4-CP almost were up to 100% within 20-30
min after five cycles. And the phase structure of FBB-25 after
used in five cycle runs was further analyzed via XRD (Figure S7),
where the characteristic peaks of BiOBr still existed, such as the
Chemical Reagent Co., Ltd. 2,4,6-trichlorophenol (2,4,6-TCP, >99.9%),
-chlorophenol (2-CP, >99.9%), 2,4-dimethylphenol (2,4-DMP, >99.9%),
and bisphenol a (BPA, >99%) were purchased from Tokyo Kasei Kogyo
Co., Ltd. 2-deoxy-d-ribose(C , >99%), and trichloroacetic acid (TCP,
99%) were purchased from Alfa Aesar. The ultrapure water (Mill-Q
Biocel, 18MΩ) was used to prepare the aqueous solutions.
2
5 10 4
H O
>
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10.1002/cctc.201700549
FULL PAPER
Preparation of Fe(II)/Fe(III) Doped Bi/BiOBr
Surface Fe(II) generating amount over FBB-25 were measured in the
photocatalytic reaction, Fenton-like reaction and photo-Fenton-like
catalytic reaction. Analysis of Fe(II) concentration was carried out using
The Fe-doped Bi/BiOBr sample was obtained by a solvothermal method
1
,10-phenanthroline,[46] as following: 2 ml suspended solution drawn from
under Ar atmosphere, as following:
FeCl ·4H O with different Fe/Bi molar ratios (i.e.,0, 0.15, 0.2, 0.25, 0.3,
.35) were uniformly mixed into 30 ml of ethylene glycol containing 3 ml
3 3 2
3 mmol Bi(NO ) ·5H O and
the reactor was mixed uniformly with 2 ml 0.5% 1,10-phenanthroline
solution as well as 2 ml NaAc-HAc solution, and then centrifuged to
2
2
0
measure Fe(II) concentration. The H
by the spectrophotometric method. [47]
2 2
O concentration was determined
acetic acid under magnetic stirring for 30 min. The resultant solution was
added to 30 ml ethylene glycol with 3 mmol KBr under vigorous stirring
for 30min. Next, the mixture was transferred to a 100ml of Teflon
autoclave and kept for 12 h at 433 K. After being cooled to room
temperature, the fresh product was separated centrifugally and washed
with ethanol and ultrapure water. Finally, the sample was freeze-dried
under vacuum. The resultant products were denoted as FBB-x, where x
Hydroxyl Radical Measurement
The ·OH concentration was measured using the deoxyribose method [48,
49],
as following: 2.8 mM 2-deoxy-d-ribose solution was oxidized by ·OH
(
0
15, 20, 25, 30, 35) referred to the ratio of Fe to Bi as 0.15, 0.2, 0.25,
.30, 0.35, respectively. All the operations were done under Ar
generated from different systems (photocatalytic, Fenton-like and photo-
Fenton-like reaction). Subsequently, 5 ml reaction solution was stopped
by 1.25 ml of 28 g/L TCP, and then 1.25 ml of 10 g/L TBA was added,
subsequently heated at 368 K for 30 min. After centrifuged, the
absorbance of TBA-MDA reaction product was measured at 532 nm
using the ultraviolet-visible spectrophotometer (UV-2990, Shimadzu,
Japan). The ·OH concentration was calculated from the TBA-MDA
atmosphere.
Characterization
The XRD patterns of FBB samples were obtained using an X-ray
diffractometer (X’Pert PRO MPD, PANalytical) with the Cu Kα irradiation
source (λ=1.5406 A) at the scope of 5-90 . The morphological structure
reaction product with an extinction coefficient of 1.56 *10 M cm−1. [49]
5
−1
o
and chemical composition of the sample was measured by TEM (H-7500,
Hitachi Limited) and FESEM (SU-8020, Hitachi Limited) with the energy-
dispersive X-ray spectrometer. XPS was used to analyze the surface
chemical compositions and states with Al-K X-ray irradiation (ESCALAB
Acknowledgements
The authors appreciate financial supports from the National
Basic Research Program from Ministry of Science and
Technology (no.2011CB933700), and National Natural Science
Foundation of China (no. 51378014, 51578529, 51338010,
2
50Xi, Thermo Fisher Scientific, USA). The background of shirley and
linear was utilized for peak fitting with C 1s calibrated to 284.6 eV for all
the spectra. The UV-vis DRS were obtained by using UV-vis
spectrometer (UV-3600,Shimadzu, Japan) with an integrating sphere
using BaSO as the reference. The specific surface area was determined
a
4
21107125).
by using a full automatic analyzer (ASAP2020HD88, Micromeritics
Instrument Corp).
Keywords: Bi/BiOBr • Fe(II)/Fe(III) • photodegradation •
hydrogen peroxide • organic contaminants
Catalytic Activity
The photo-Fenton-like degradation tests of BPA via FBB-25 were
achieved to evaluate the catalytic activity of FBB-25, including the
Fenton-like and photocatalytic experiments. A 300 W Xe lamp with a 400
nm cut-off filter at 15 A of current and 14 V of voltage was used as a
visible light, and the vertical distance between lamp and liquid level was
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ChemCatChem
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FULL PAPER
Highly catalyst: FBB-25
is an excellent visible-
light-Fenton-like catalyst
for degradation of organic
contaminants in waste-
water. Visible light can
increase the multiple
transformation rate of ≡
Fe(III) to ≡ Fe(II) over
FBB in the presence of
Wentao Li, Xin Geng, Feng
Xiao*, Guangyu An,
Dong sheng Wang
Page No. – Page No.
Title
H
2
O
2
,
producing more
holes
radicals
and
to
hydroxyl
degrade
organic molecules.
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