Design and Synthesis of Sm, Y, La and Nd-doped CeO2 with a broom-like hierarchical structure: a photocatalyst with enhanced oxidation performance

Article abstract of DOI:10.1002/cctc.201902309

CeO₂ doped with various rare earth (RE) ions (Sm, Y, La and Nd) having a broom-like hierarchical structure was successfully prepared by a template-free hydrothermal method. The photooxidation performance of RE-doped products was significantly better than that of pure CeO₂, and comparative experiments showed that Sm-doped CeO₂ (SC) has superior photooxidation activity, resulting about 3.0-times and 8.5-times higher activities of bisphenol A (BPA) degradation and of acetaldehyde (CH₃CHO) decomposition, respectively, than those of pure CeO₂. Due to the incorporation of RE ions, the surface exposed cerium ions are partly substituted by those cations, resulting in a higher concentration of oxygen vacancies (O_v) in RE-doped CeO₂. The increased O_v can act as a trapping center for photo-generated electrons to form a doping transition state between the conduction band (CB) and valence band (VB), which can restrict the recombination rate of electrons and holes effectively and lead to an outstanding enhancement of photooxidation performance. Furthermore, abundant highly reactive hydroxyl radicals (^.OH) and superoxide radicals (^.O₂ ^?), which are efficient intermediates with vivid oxidation ability, can further enhance the photocatalytic activity of RE-doped CeO₂. A cost-effective strategy for designing CeO₂-based semiconductor photocatalysts doped with multitudinous RE ions that have enhanced photooxidation performance is presented in this paper.

Full text of DOI:10.1002/cctc.201902309

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Design and Synthesis of Sm, Y, La and Nd-doped CeO2 with
a broom-like hierarchical structure: a photocatalyst with
enhanced oxidation performance
Bin Xu,*[a] Hui Yang,[a] Qitao Zhang,*[b] Saisai Yuan,[c] An Xie,[a] Ming Zhang,[a] and
Teruhisa Ohno*[d]
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CeO2 doped with various rare earth (RE) ions (Sm, Y, La and Nd)
having a broom-like hierarchical structure was successfully
prepared by a template-free hydrothermal method. The photo-
oxidation performance of RE-doped products was significantly
better than that of pure CeO2, and comparative experiments
showed that Sm-doped CeO2 (SC) has superior photooxidation
activity, resulting about 3.0-times and 8.5-times higher activities
CeO2. The increased Ov can act as a trapping center for photo-
generated electrons to form a doping transition state between
the conduction band (CB) and valence band (VB), which can
restrict the recombination rate of electrons and holes effectively
and lead to an outstanding enhancement of photooxidation
performance. Furthermore, abundant highly reactive hydroxyl
radicals ( OH) and superoxide radicals ( O2 ), which are efficient
intermediates with vivid oxidation ability, can further enhance
the photocatalytic activity of RE-doped CeO2. A cost-effective
strategy for designing CeO2-based semiconductor photocata-
lysts doped with multitudinous RE ions that have enhanced
photooxidation performance is presented in this paper.
*
*
À
of bisphenol
A (BPA) degradation and of acetaldehyde
(CH3CHO) decomposition, respectively, than those of pure CeO2.
Due to the incorporation of RE ions, the surface exposed cerium
ions are partly substituted by those cations, resulting in a
higher concentration of oxygen vacancies (Ov) in RE-doped
Introduction
stability and weak visible light absorption, which greatly hinder
their popularization and application as cost-efficient semi-
conductor photocatalysts.[2,3]
Recently, human health and ecosystems have been threatened
by a serious threat to environmental pollution mainly due to
organic pollutants and toxic gas wastes generated in industrial-
ization process.[1–3] Novel photocatalytic materials for elimina-
tion of multi-species pollutants from industrial streams have
been developed.[2–4] However, newly developed materials have
some problems such as a high rate of recombination of
photogenerated electrons and holes, poor photo-chemical
Cerium dioxide (CeO2) is one of the most important rare
earth metal oxides, and it has attracted much attention due to
its excellent properties such as low toxicity, high degree of
chemical stability, safety and resistance to photocorrosion
primarily.[4] It has various applications including applications as
UV blockers, polishing materials, photocatalysts, electrolytes,
sensors and fuel cells.[5] In addition, the photocatalytic proper-
ties of CeO2 are similar with those of TiO2-based materials
including a wide band gap (2.90 eV) and strong absorption in
the UV region. It is therefore a promising candidate material for
photocatalytic degradation of deleterious organic pollutants.
Previous studies have shown that morphology and size control,
doping of various metal ions, and heterojunction coupling are
three common strategies for enhancing the photocatalytic
performance of CeO2-based materials.[5,6] The morphology of
CeO2 plays a major role in its photocatalytic performance, and
our research group has successfully fabricated a series of high-
performance CeO2 photocatalysts with different morphologies
and superior performances including porous broom-like, hedge-
hog-like, confeito-like and hollow octahedral structures.[7–9]
Difference in morphology and size can determine the specific
surface area, active sites and separation of redox crystal facets,
which are related to improvement of photocatalytic perform-
ance. Choudhury has studied the effect of [Ce3+] and oxygen
vacancies on the photocatalytic activity of CeO2.[10] The large
deviated stoichiometry of CeO2 makes it easier for cerium ions
to be reduced from tetravalent cerium to trivalent cerium and
enhance the formation of active oxygen vacancies (OV).[11–13] The
[a] Assoc. Prof. B. Xu, H. Yang, Assoc. Prof. A. Xie, Prof. M. Zhang
School of Chemistry and Chemical Engineering
Yangzhou University
Yangzhou, 225009 (P. R. China)
E-mail: twt@yzu.edu.cn
[b] Assoc. Prof. Q. Zhang
International Collaborative Laboratory of 2D Materials for Optoelectronics
Science and Technology of Ministry of Education
Institute of Microscale Optoelectronics
Shenzhen University
Shenzhen, 518060 (P. R. China)
E-mail: qitao-zhang@szu.edu.cn
[c] S. Yuan
Department of Chemical and Biochemical for Energy Materials
Xiamen University
Xiamen, 361005 (P. R. China)
E-mail: yuansaisai66666@163.com
[d] Prof. T. Ohno
Department of Applied Chemistry
Faculty of Engineering
Kyushu Institute of Technology
Kitakyushu, 804-8550 (Japan)
E-mail: tohno@che.kyutech.ac.jp
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/cctc.201902309
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effectiveness of pure CeO2 also can be improved by introducing
foreign metal ions to promote the formation of expanded
crystal-structured CeO2-based products, which are more con-
venient for electronic transmission.[14] Some studies have
indicated that the introduction of various metal dopant such as
Fe, Eu and Mn can change the structure and optical properties
of CeO2.[15–17] Studies have also shown that the presence of
metal ions in the ceria lattice induced more trivalent ceria ions
and oxygen vacancies, which are more important for photo-
catalytic pollution degradation.[11] The key point of these
methods is the change in the oxygen vacancies concentration
of the products, which can serve as electron-capture centers.[10]
Thus, the as-formed oxygen vacancies can also effectively
suppress the recombination of electron-hole pairs, thereby
improving the final photocatalytic activity.[16–22] Therefore,
doping of foreign ions a cost-effective way to enhance the
activity of a CeO2-based photocatalyst. To the best of our
knowledge, it is very difficult to introduce different ions into the
lattice of ceria, and there has been no report about a summary
of CeO2 with doping a series of different RE ions and elucidation
of the effects on photocatalytic performance systematically.
In this paper, CeO2 materials doped with several rare earth
ions (Sm, Y, La and Nd) that have a broom-like hierarchical
structure were prepared by a template-less hydrothermal
method. The photooxidation efficiency of the samples were
evaluated by experiments on aqueous BPA degradation and on
CO2 evolution from CH3CHO decomposition. Furthermore, the
morphology, structure and photoelectrochemical properties
were examined to determine the effect of RE ions doping. Due
to an increasing concentration of oxygen vacancies, photo-
oxidation performance of RE-doped products was significantly
better than that of pure CeO2, and the results of comparative
experiments showed that Sm-doped CeO2 has the best photo-
oxidation activity. Thus, doping with appropriate ions is
effective for enhancing the photocatalytic activity of a bulk
photocatalyst.
assigned to the CeO2 (111) crystal plane, can be seen in
Figure 1A. After doping with different RE ions, the products still
maintain the broom-like hierarchical structure (Figure 1b–e).
However, there are distinct changes in the degree of surface
smoothness and average diameter and length of the nanorods.
It is notable that the lattice fringes in the RE-doped products
have interplanar spacing: SC (0.320 nm), YC (0.314 nm), LC
(0.328 nm) and NC (0.325 nm) (Figure 1B–E). The alteration in
lattice spacing indicates that those RE ions have been
successfully introduced into the interior lattice of CeO2, but the
crystal structure of ceria’s cubic fluorite is in fact preserved.
EDS mapping results (Figure 2) indicate that only cerium
and oxygen elements are clearly detected in pure CeO2 and are
evenly distributed among the nanorods. After the introduction
of RE ions, doping elements except for Ce and O also have a
good distribution on the surface (Figure 2b–e). In view of the
above results, it can be further inferred that photocatalysts
doped with different RE ions can be successfully prepared by a
hydrothermal treatment.
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XRD patterns of as-fabricated samples are shown in Fig-
ure 3a. The characteristic diffraction peaks of CeO2 are located
°
°
°
°
at 28.60 , 33.27 , 47.71 and 56.51 , corresponding to the crystal
planes of (111), (200), (220) and (311), respectively.[22,23] All of
the diffraction lines can be attributed to the phase of ceria with
a cubic fluorite structure (space group: Fm-3 m (225)), which is
in accordance with the standard data reported in the JCPDS
card (No. 65-5923).[23–24] The sharp diffraction peaks of products
suggest a high degree of crystallinity, and no appearance of
impurity peaks manifests that doping has a negligible effect on
crystal growth. Compared with pure CeO2, the elaborated XRD
patterns (Figure 3b) of the highest (111) peak exhibit an
obvious shift to a lower angle after doping. This phenomenon
can be conspicuously attributed to the introduction of rare
earth ions into the crystal structure.[24] And these results are
Results and Discussion
The morphology of as-prepared products was investigated by
FEÀ SEM and HRÀ TEM. As exhibited in Figure 1a, pure CeO2
shows a broom-like hierarchical morphology with a single root
length of 5 μm and diameter of 200 nm approximately. Clear
lattice fringes with interplanar spacing of 0.313 nm, which are
Figure 1. FEÀ SEM and HRÀ TEM images: (a, A) CeO2, (b, B) SC, (c, C) YC, (d, D)
Figure 2. HAADF image and distribution of element mapping images: (a)
CeO2, (b) SC, (c) YC, (d) LC and (e) NC.
LC and (e, E) NC.
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relativity intensity of a Raman shift of F2g, Rdopant and RCeÀ O can
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be calculated from Equation (1):[30,31]
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4
5
AeraR þ AeraR
O
F2g
V % ¼
%
CeÀ O
dopant
(1)
AeraF
2g
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7
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9
The calculated values are outlined in Table S2. Compared
with pure CeO2, the values of Ov clearly increase after RE ion
doping. And the value of Ov reaches a maximum of 12.50%
after Sm doping, being consistent with the result of XPS analysis
shown below.
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The surface chemical composition and the interactions
before and after doping were analyzed by XPS spectroscopy
(Figure S1 & Figure S2). The Ce3d electron core level and two
group peaks obtained (denoted as v and u) after deconvolution
treatment are displayed in Figure 4a. According to previous
studies,[31,32] the labels of (U, V), (U2, V2) and (U3, V3) can be
classified as Ce 3d5/2 and Ce 3d3/2 related to Ce4+, originating
from the final states of Ce (3d94f0) O (2p6), Ce (3d94f1) O (2p5)
and Ce (3d94f2) O (2p4), respectively. Two pairs of doublets, (U0,
V0) and (U1, V1), for the Ce 3d bond energy peak can be ascribed
to Ce3+, and the double lines correspond to Ce (3d94f1) O (2p6)
and Ce (3d94f1) O (2p5), respectively.[31,32] In order to estimate
the concentration of [Ce3+] of samples, these peaks were
deconvoluted and the calculated concentration value of as-
prepared samples are shown in Table S2. The [Ce3+] ratio is
obviously increased after RE ions doping, which is much higher
than the product without doping. Meanwhile, the concentration
of [Ce3+] of SC is 17.69%, which is the highest among the
products of doping. In addition, these peaks significantly shift
to a lower binding energy and it manifests that Sm ions indeed
dope into the lattice of CeO2 (Figure 4b). Therefore, it can be
understood that the introduction of dopants greatly influences
Figure 3. Structure characterization: (a) XRD patterns, (b) detailed view of
the highest (111) peak patterns, (c) Raman spectra and (d) enlarged view of
Raman spectra.
consistent with the changes in lattice fringes observed in
HRÀ TEM.
Rietveld refinement was further carried out to determine
the actual doping location of incorporated ions and the results
are summarized in Table S1. It can be clearly seen that the
lattice parameter values of RE-doped samples become larger
than that of pure CeO2 (5.4114 Å). The values are 5.4182 Å,
5.4290 Å, 5.4219 Å and 5.4211 Å for SC, YC, LC, and NC,
respectively. In comparation to Ce4+ (0.970 Å), the enlarged
lattice parameters can be attributed to the larger ionic radius of
various rare earth element ions such as Sm3+ (1.079 Å), Y3+
(1.019 Å), La3+ (1.160 Å), Nd3+ (1.109 Å). In the MO8 crystal
structure of ceria, the substitution reaction is more likely to
occur on cerium atoms located on the top and edge than in the
body center. When the rare earth ions have been introduced
into the crystal structure of CeO2, its crystal lattice would be
greatly expanded. It is well known that an expanded crystal
structure is more beneficial than normal MO8 crystal structure
for electronic transmission.[25]
the chemical environment of CeÀ O by the reduction of Ce4+
!
Ce3+, which is a foremost reason for the increased concen-
tration in oxygen vacancies, which are beneficial for enhancing
photocatalytic efficiency when compared with pure CeO2.[10]
Raman technology is an effective and non-destructive
technique for characterizing structural defects.[26] The distinct
peak at 460 cmÀ 1 is assigned to F2g vibration of the cubic
fluorite structure as illustrated in Figure 3c. Two weak Raman
peaks located at 540 cmÀ 1 and 600 cmÀ 1 were also detected,
and they are ascribed to extrinsic defects caused by doping
(Rdopant
)
and instinctive defect vibration of CeÀ O (RCe-O),
respectively.[27–29] An enlarged view of Raman peaks is shown in
Figure 3d. According to the results of previous studies,[30] cerium
ions show a trivalent state instead of tetravalent chemical
valence in the defect lattice partly. In order to maintain the
particles in an electrically neutral state, surface oxygen would
escape from the structure, eventually resulting in the formation
of inherent oxygen vacancies (Ov).[31] Later, more oxygen
vacancies would promote the separation of charge carriers and
limit the recombination rate of photo-generated carriers. The
relative photocatalytic performance would be enhanced. The
Figure 4. Separated peak curves of (a) Ce 3d, (c) O 1s, high-solution XPS
spectra of (b) Ce 3d, and (d) O 1s of all samples.
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Three different types of oxygen species, assigned to lattice
4.31À , and 5.30-times higher than those of YC, LC, NC and pure
CeO2, respectively. Besides, the tendency of À Ln (Ct/C0) as a
function of irradiation time is displayed in Table S3. It can be
concluded that the linear relationship between À Ln (Ct/C0) and
irradiation time follows the pseudo-first order kinetic equation,
where C0 is the initial concentration of BPA and Ct is the
concentration at a particular time. After numerical calculation,
the rate constant indicates that BPA degradation obeys the
Langmuir-Hinshelwood rate. For investigating the BPA photo-
catalytic degradation process, HPLC was used to analyze the
products of each stage. The peak of retention time of 7.74 min
is mainly attributed to BPA, and the intensity of the peak
decreases gradually during the reaction process, indicating that
BPA is degraded continuously (Figure S3). A new peak located
at a retention time of 4.04 min appears after photodegradation
for two hours, corresponding to p-hydroxyacetophenone, and
the intensity gradually increases. Therefore, it should be a major
degradation product. In addition, a weak peak at 5.09 min
belongs to phenol, and its intensity increases with increase in
reaction time. The results of HPLC show that p-hydroxyaceto-
phenone and phenol are the main intermediate products
during BPA degradation. These inter-mediate products may be
further oxidized and decomposed, and the final products are
non-toxic CO2 and H2O. Hence, the following reaction processes
are proposed in Equations (2–4):
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oxygen (Olat), oxygen vacancies (OV) and active surface oxygen
(OSur), can be clearly detected after deconvolution of the O1s
electron core level located binding energy of 528.76, 531.08,
and 532.95 eV, respectively (Figure 4c).[33] The binding energy of
these oxygen species significantly shifts towards lower binding
energy after doping of RE ions. However, the effects on Olat, Ov
and OSur are quite different. Compared with pure CeO2, the
binding energy value of Ov shows a change of 0.33 eV after Sm
doping. The binding energy value of the Olat and OSur shows
changes of only 0.12 eV and 0.20 eV, respectively. (Figure 4d).
Therefore, RE ions doping mainly affects the binding energy of
Ov. The Ov ratio after deconvolution and multimodal separation
is obtained in Table S2. It can be observed that the concen-
tration of [Ov] in doped-CeO2 is much higher than that in pure
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CeO2, while
a
similar phenomenon exists for [Ce3+]. In
particular, the concentrations of [Ce3+] and [Ov] in SC are
17.69% and 15.25%, respectively, which are significantly higher
than other products. It may due to the substitution process can
compensate for the charge generated by doping and promote
the formation of oxygen vacancies in defective structured CeO2.
And these vivacious Ov, acting as a trapping center for photo-
generated electrons, formed a doping transition state between
the conduction band (CB) and valence band (VB), and limited
the recombination rate of electrons and holes significantly,
leading to an outstanding improvement of photooxidation
performance effectively.[7] Therefore, it provides a forceful
evidence to speculate that RE-doped CeO2 should have higher
photocatalytic activity.[33,34]
CeO2 þ hn ! CeO2 ðhþÞ þ CeO2 ðeÀ Þ
(2)
.
OHÀ þ hþ ! OH
(3)
Firstly, photooxidation activity of as-prepared products was
evaluated by degradation of aqueous bisphenol A (BPA). The
BPA removal rate of SC reaches 98.76% under light irradiation
for 6 h (Figure 5a), which is significantly better than that of
other samples. The lowest rate constant for photocatalytic
degradation activity obtained for the pure CeO2 is only 34.07%.
According to the kinetic equation (Figure 5b), the rate constant
k value of SC is 0.5145 hÀ 1, and SC possesses 1.32À , 3.31À ,
ð4Þ
The BPA degradation pathways have already been estab-
lished, and it is also necessary to identify the main active
substance in the degradation process by trapping
experiments.[35,36] As demonstrated in Figure 5c, the photo-
degradation efficiency of BPA decreases rapidly from 98.76% to
*
12.83% after adding TBA, indicating that OH is one of the main
active species in the BPA photodegradation process. When
EDTA was added, the degradation efficiency was also reduced
to 17.87%, indicating that h+ also plays an important role in
the photocatalytic oxidation reaction. However, the degradation
efficiency of BPA is slightly reduced after the addition of KPS
(88.92%) and BQ (84.47%). Generally, obvious reduction of
photocatalytic efficiency indicates that the corresponding
substance owns an important effect.[34–36] Consequently, the
results of the active substance capture experiments indicate
*
*
that OH and h+ are the main active substances, while O2À and
eÀ have minor effects on the degradation of BPA in this RE-
doped CeO2 system. Besides, SC has no significant attenuation
after four cycles of BPA photooxidation degradation (Figure 5d),
Figure 5. (a) BPA photooxidation degradation curves, (b) degradation
kinetics constants, (c) degradation efficiency with the addition of scavengers
and (d) stability test.
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indicating the as-fabricated SC photocatalyst retains excellent
photocatalytic stability. Meanwhile, YC, LC, NC and pure CeO2
also maintain a good reusability.
The photooxidation activity of products was further eval-
uated from the photocatalytic decomposition of gaseous
acetaldehyde (CH3CHO). And the following reactions can be
considered in Equations (5–9):
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9
.
O2 þ eÀ ! O2
À
(5)
.
.
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À
À
CH3CHO þ O2 ! CH3CO þ HO2
(6)
(7)
(8)
(9)
CH3CHO þ HO2 ! CH3COÀ þ H2O2
À
.
CH3COÀ þ OH ! CH3COOH þ eÀ
Figure 7. Photoelctrochemical characterization: (a) UV-vis diffuse reflectance
spectra, (b) PL spectra, (c) transient photocurrent response curves, and (d)
EPR spectra.
2CH3COOH þ 4O2 ! 4CO2 þ 4H2O
Compared with pure CeO2, the photocatalytic activity is
clearly enhanced after RE ions doping (Figure 6a). In the case of
Sm doping, the amount of CO2 liberation reaches a maximum
of about 304.05 ppm, which is 8.50-times higher than that of
pure CeO2 (35.76 ppm). The excellent photocatalytic activity is
attributed to the concentration of Ov reaching a maximum
value in SC, and the results are consistent with results of Raman
and XPS analyses. The process of CH3CHO decomposition
follows the first-order kinetic equation obviously (Figure 6b).
According to the kinetic equation, the rate constant value of SC
reaches 0.3041 hÀ 1 and is clearly higher than other values (YC
(0.2762 hÀ 1), LC (0.1525 hÀ 1), NC (0.1128 hÀ 1), CeO2 (0.0364 hÀ 1)).
The SC photocatalyst as-fabricated in this paper shows much
higher activity for CH3CHO (340 ppm) oxidation than the
activities of commercial metal oxide photocatalysts such as TiO2
(21 ppm), S-doped TiO2 (150 ppm) and WO3 (200 ppm).[37,38] It
also shows much higher activity than the other CeO2 photo-
catalysts with different morphologies including nanoparticles
(200 ppm), hedgehog-like (140 ppm), confeito-like (100 ppm)
and octahedral structures (80 ppm).[7–9]
where α is the absorption coefficient, B is the material-related
constant, hν is the discrete photon energy, Eg is the absorption
bandgap, and n is the number of different types of electronic
transitions.[39] It has been shown the electronic transition
between the valence band and conduction band of CeO2 is a
direct transition, resulting in the value of n being 2.[40,41] The
Schuster-Kubelka-Munk equation is considered to be reliable for
determining a semiconductor bandgap. The band gap values of
CeO2, SC, YC, LC and NC were calculated to be 2.87, 2.59, 2.65,
2.74 and 2.79 eV, respectively (Figure S4). The results indicate
that rare earth ions doping can induce narrowing of the band
gap of CeO2. A smaller band gap energy (Eg) is considered to be
one of the crucial parameters for determining the final photo-
catalytic performance.[42] The doping of cations can favor the
formation of trivalent cerium (Ce3+) and create more oxygen
vacancies (Ov). An increasing concentration of Ov can also result
in the formation of a doping-related transition state which is
closer to the conduction band (CB) and reduce the band gap
energy.43 The potential of the valence band (VB) was
determined from a VB-XPS spectrum (Figure S5). The results
clearly revealed that the rare earth dopant was indeed
incorporated into the crystal lattice of CeO2, resulting in
alteration in the electronic properties of the RE ions doping
products.[39–41,43]
Photoluminescence (PL) analysis has also been frequently
used to determine the recombination rate of electrons and
holes (eÀ and h+). 44 Pure CeO2 shows a strong characteristic PL
peak with a value of about 423.54 nm and a weaker peak of
about 441.62 nm (Figure 7b). The two peaks are both attributed
to surface defects, which are usually accommodated between
the O2p valence band and the Ce4f conduction band. It is well
known that the major surface defects in CeO2 are oxygen
vacancies.[45] The doped CeO2 samples showed emission spectra
with the same number of peaks. However, the intensity of the
emission band was reduced for CeO2 doped with different RE
ions. SC showed the lowest PL intensity among all the RE-
doped CeO2 samples. This indicates an excellent efficiency of
The optical effect of dopant ion substitution into the CeO2
lattice was further confirmed using UV-vis absorption spectra
(Figure 7a). For semiconductors, the absorption edge of the
band follows Equation (10):
À
�
n
ðahuÞ ¼ B hu À Eg
(10)
Figure 6. (a) Time course of CO2 liberation from acetaldehyde decomposition
and (b) kinetics curves of all samples.
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promoting separation of holes and electron pairs, which can
efficaciously enhance the photocatalytic performance.[45]
same time, doping will regulate the energy band structure and
extend the absorption edge of CeO2 towards a wider light
region effectively.[46] Plots of the energy band structures for
fluorite-type CeO2 and RE-doped CeO2 are outlined in Figure S6.
The energy band structures of YC and LC are similar with that
of pure CeO2, and similar values of the band gap are consistent
with UV-vis results. Interestingly, it was found that new features
appear in the band gaps of SC and NC (Figure S6 (b) and (e)),
which are contributed to the overlap of energy levels between
the states of dopants (Sm and Nd) and the O, resulting in the
dopants-O binding. The exist of impurity energy levels signifi-
cantly change the band structures and narrow the band gap,
bringing higher light yield.
Based on all observed characterization results and the
results of photocatalytic evaluation experiments, a reasonable
reaction mechanism of RE ion-doped CeO2 is proposed (Fig-
ure 9). The introduction of RE ions into the cubic fluorite
structure of CeO2 can affect its crystal structure evidently. After
an incorporation of RE ions, the surface exposed cerium ions
are partly substituted by those cations, resulting in a higher
concentration of oxygen vacancies (Ov), which leads to a
formation of doping transition states. Then more Ov can
efficiently capture electrons in the conduction band (CB) and
limit the recombination rate of photo-generated electrons and
holes in doped-CeO2. These transition states caused by doping
can extend lifetime of photo-generated carriers during the
migration process and further lead to an effective separation
efficiency of photo-generated carriers. Additionally, abundant
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A photocurrent-time response test was carried out to
examine the interface charge separation kinetics, and the
results are shown in Figure 7c. The photocurrent response
curves show that the photocurrent intensity of all samples
suddenly increases and decreases when the light source is
turned on and off respectively, indicating their intrinsic proper-
ties of the semiconductor.[37,46] The photocurrent intensities of
RE ion-doped samples (SC (142.83 μA/cm2), YC (124.58 μA/cm2),
LC (104.68 μA/cm2), NC (109.08 μA/cm2)) are all higher than that
of pure CeO2 (61.21 μA/cm2). Interestingly, the photocurrent
intensity of SC reaches a maximum value that is 2.33-times
greater than that of pure CeO2. The increasing photocurrent
intensity indicates that the photogenerated charge carriers in
SC are much more effectively separated than those in other
samples. In general, a greater intensity of the photocurrent
means higher transfer efficiency of photogenerated electrons
and holes, which is beneficial for the photocatalytic reactions
and affords better photocatalytic performance.[16]
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The EPR results (Figure 7d) further revealed the main active
species. It can be clearly observed that the intensity of hydroxyl
*
*
À
radicals ( OH) and superoxide radicals ( O2 ) is stronger than
that of pure CeO2 after Sm doping, being in good agreement
with the results of the active species trapping experiments.
Actually, the formation of OH and O2 is important for
photocatalytic reactions due to both of them are highly efficient
intermediates to further promote the photocatalytic activity.
Hence, SC can achieve a significant improvement in photo-
oxidation performance.
*
*
À
*
*
À
hydroxyl radicals ( OH) and superoxide radical ( O2 ) can be
generated in the VB and CB, respectively. The higher concen-
*
*
À
Stoichiometric CeO2 is known to be an insulator, and the
features of the electronic density of states (DOS) calculated in
Figure 8 are in agreement with previous DFT+U results. And it
can be further used to revealing the modifications in electronic
structure and the mechanism of light absorption. Compared
with pure CeO2, it is evident that conduction bands of RE-doped
structures are shifted from a higher energy level to a lower
energy level. Meanwhile, the doping energy level of SC and NC
appeared obviously. This indicates a narrowed band gap may
cause a reduction of photo-electron transition energy. At the
tration of OH and O2 are both highly efficient intermediates
with vivid oxidation ability to further react with organic
compounds, leading to an outstanding enhancement of photo-
oxidation performance. Based on the experiments of BPA
degradation and of CH3CHO decomposition, we can draw
conclusions that the photocatalytic performance is apparently
enhanced after different RE ions doping and SC possesses the
Figure 9. A proposed mechanism for photocatalytic performance
enhancement.
Figure 8. Density of states (DOS) of all samples.
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and 0.144 g rare-earth salts (Sm(NO3)3 ·6H2O, La(NO3)3 ·6H2O Nd
(NO3)3 ·6H2O and (Y(NO3)3 ·6H2O) were dissolved in 20 ml deionized
water with vigorous magnetic stirring at a room temperature for
30 min. Then aqueous solution of ceric and other rare-earth salts
aqueous solution was dropped into the above mixture and stirred
for 30 min until the solution changed to faint yellow color. The
mixed solutions were then transferred into a 200 ml Teflon-lined
highest photooxidation activity among them. The reasons
maybe attribute to the following two factors, one is that the
ionic radius of Sm3+ is closer to Ce4+, leading to the entry of
ions into the interior of the lattice much more easily and readily.
The introduction of Sm ions leads to an expansion of the crystal
lattice in CeO2, which is more convenient for the transmission
of electrons. And those migrated electrons can hasten the
diffusion rate of oxygen and boost reactive oxygen species
(ROS) effectively. The other reason is that Sm has two variable
valence states and those two states will provide much more
oxygen vacancies, which represents that they can further
restrict the recombination rate of photogenerated carriers, then
lead to an efficient promotion of the photocatalytic activity.
Thus, RE ions doping is a feasible strategy to enhance the
photocatalytic efficiency of traditional semiconductors.
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°
autoclave and kept at 120 C for 36 h. After cooling to room
temperature naturally,
a
white precipitate was collected by
centrifugation and washed with deionized water and ethanol at
least three times each. Then RE-doped ceria was obtained by
°
calcination of the as-prepared precursor in air at 500 C for 4 h to
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collect the final faint yellow product. For simplification, samples of
Sm-doped CeO2, Y-doped CeO2, La-doped CeO2 and Nd-doped
CeO2 samples are denoted as SC, YC, LC and NC, respectively.
Characterization
X-ray diffraction (XRD) was performed on a Bruker-AXS X-ray focus
using a Cu Ka radiation source (40 kV/40 mA). Raman spectra was
obtained by an In Via Laser Confocal Raman Spectrometer.
Morphology and elemental mapping of the products were
observed by FE-SEM (Hitachi, S-4800) and HR-TEM (FEI, Tecnai G2
F30S-TWIN, 300 KV). UV-vis diffuse reflectance spectra (DRS) was
measured by a Varian Cary 5000 UV-vis spectrophotometer. The X-
ray photoelectron spectroscopy (XPS) experiment was carried out
on a Shimadzu KRATOS AXIS-NOVA system at room temperature
under 10À 9 Pa using Al Kα radiation and C 1s peak (284.6 eV)
reference. Electron paramagnetic resonance (EPR) radical signal was
recorded by a Brucker EPR A200 spectrometer. Photoluminescence
(PL) spectroscopy measurements were performed at an excitation
wavelength of 310 nm on a fluoro-spectrophotometer (Hitachi F-
4500) at room temperature.
Conclusion
In summary, CeO2 photocatalysts doped with different RE ions
were successfully prepared by a template-free hydrothermal
treatment. This method for design and synthesis is cost-
effective and can be easily extended to the manufacture of
other RE ion-doped inorganic semiconductor materials. FE-SEM
and HR-TEM images show that doped CeO2 with a broom-like
hierarchical structure is composed of numerous nanorods.
Raman and XPS analyses also reveal the doped-CeO2 has the
advantage of having much more oxygen vacancies. It is found
that SC exhibits superior photooxidation performance com-
pared with that of other doped products, resulting about 3.0-
times and 8.5-times higher activities than pure CeO2 for BPA
degradation and CH3CHO decomposition, respectively. There-
fore, rare earth ion-doped CeO2 established in this paper can
pave the way to fabricate other different RE ion-doped photo-
catalysts for energy-related and environmental remediation
applications.
Bisphenol A degradation experiments
Photooxidation of aqueous bisphenol A (BPA) was carried out with
a 300 W UV lamp (light intensity=100 mW/cm2) and temperature
°
was controlled at 25 C. Before the experiment, 120 mg photo-
catalyst and 120.0 ml BPA solution (20 mg/L) were added to the
reaction flask, and then an adsorption-desorption equilibrium was
achieved by stirring for 1 h in a dark place. Next, the UV lamp was
turned on and 4.0 mL of the suspension reaction liquid was
withdrawn from the reaction flask at regular intervals. The BPA
solution was separated from the photocatalyst by filtration with
double layers of a cellulose acetate membrane (pore size of
0.22 μm). The concentration of BPA was measured by a UV-Vis
spectrophotometer (λmax=277 nm). The degradation products
were determined by a high-performance liquid chromatograph
(HPLC) equipped with a JASCO UVIDEC-100-VI optical detector and
a chromatographic column of an Agilent eclipse XDB-C18 column
Experimental Section
Materials
Urea, cerium nitrate hexahydrate (Ce(NO3)3 ·6H2O), sodium citrate
dihydrate (C6H5O7Na3 ·2H2O), yttrium nitrate hexahydrate (Y
(NO3)3 ·6H2O), lanthanum nitrate hexahydrate (À La(NO3)3 ·6H2O),
samarium nitrate hexahydrate (Sm(NO3)3 ·6H2O) and neodymium
nitrate hexahydrate (Nd(NO3)3 ·6H2O) were used in this study. All
the chemical reagents used in the experiments were of analytical
grade, were commercially available with 99.9% purity and were
used without further purification. Deionized water was used
throughout the experiments.
°
(4.6×150 mm) with a column temperature of 25 C. The eluent
used was a mixed solvent of acetonitrile and water (1/1, v/v). The
flow rate of the mobile phase was 1 ml/min. The elution was
monitored at 277 nm.
Active species trapping experiments
In order to detect active species in the photodegradation process,
potassium persulphate (KPS) was used as electron (eÀ ) scavenger,
ethylenediaminetetraacetatic acid disodium (EDTA) was selected as
Preparation
First, 5.88 g C6H5O7Na3 ·2H2O was dissolved in 140 ml deionized
water and the solution was stirred vigorously at room temperature
for 10 min. Then 2.40 g urea was added to the solution and the
solution was stirred for 30 min. The homogeneous mixture was
prepared for further use. At the same time, 1.63 g Ce(NO3)3 ·6H2O
hole (h+) scavenger, tert-butanol (TBA) was employed as hydroxyl
*
radical ( OH) scavenger and 1, 4-benzoquinone (BQ) was chosen as
*
superoxide radical ( O2À ) scavenger. For comparison, an experiment
without
a
scavenger was also carried out under the same
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conditions. The photocatalyst with different a scavenger (1 mM)
was dispersed in BPA solution (120.0 ml, 20 mg/L). The following
process was same as the BPA photodegradation experiment
described in experimental section 4.
Acknowledgements
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This work was supported by the Natural Science Foundation of
Guangdong Province (Grant No. 2020 A151501982), the Major
Projects of Nature Science Research in Universities and Colleges in
Jiangsu Province, China (Grant No. 16KJA150008), the Natural
Science Foundation of China (Grant No. 21805191) and the JST
ACTÀ C program of Japan.
Acetaldehyde decomposition experiments
Photooxidation activity for decomposition of acetaldehyde
(CH3CHO) was also assessed. One hundred mg of photocatalyst
powder was spread on the bottom of a glass dish, and the glass
dish was placed in a Tedlar bag (AS ONE Co., Ltd.). Then 500 ppm
of CH3CHO was injected into the bag together with 125 cm3 of
artificial air. Then the bag fabricated above was put in a dark place
at room temperature for 2 h for a purpose of reaching an
adsorption-desorption equilibrium. A light-emitting diode lamp
(LED; Epitex, L365) was used as a light source and its intensity was
controlled at 1.0 mW/cm2, which emitted light with a central
wavelength of ca. 365 nm. The concentration of generated CO2 as a
function of irradiation time was monitored by an online gas
chromatograph (Agilent Technologies, 3000 A Micro-GC, TCD
detector) equipped with OV1 and PLOT-Q columns.
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Conflict of Interest
The authors declare no conflict of interest.
Keywords: Doped Ceria · Hierarchical structure · Oxygen
vacancies · Photooxidation
[1] N. Patel, R. Jaiswal, T. Warang, G. Scarduelli, Appl. Catal. B 2014, 150, 74–
81.
[2] Y. Wang, H. Arandiyan, J. Scott, A. Bagheri, H. Dai, J. Mater. Chem. A
2017, 5, 8825–8846.
[3] H. Xu, Z. Qu, C. Zong, W. Huang, F. Quan, N. Yan, Environ. Sci. Technol.
2015, 49, 6823–6830.
[4] H. J. Kim, G. Lee, M. G. Jang, K. J. Noh, J. W. Han, ChemCatChem 2019,
11, 2288–2296.
[5] M. K. Gnanamani, G. Jacobs, W. D. Shafer, B. H. Davis, ChemCatChem
2017, 9, 492–498.
[6] B. Chen, X. Li, R. Zheng, R. Chen, X. Sun, J. Mater. Chem. A 2017, 5,
13382–13391.
Photoelectrochemical measurement experiments
A typical working electrode was prepared as follows: 30 mg of the
photocatalyst was dispersed in 30 mL of acetone and subjected to
1-h ultrasonic treatment. Then single iodine (10 mg) was added to
enhance its ionic strength and sonicated for 30 min. Next, the
product was electroplated onto a 6×1 cm conductive glass (ITO)
using an electrophoresis method with 15 V DC power supplied for
°
5 min. Finally, the ITO glass was dried at 60 C for 10 h to obtain the
film electrode. Na2SO4 (0.1 M) aqueous solution was used as the
electrolyte. The working electrode was irradiated by a Xe arc lamp
and its intensity was controlled at 100 mW/cm2. Photoelectrochem-
ical measurements were performed on an electrochemical analyzer
[7] S. Yuán, S. Liu, Q. Zhang, M. Zhang, B. Xu, T. Ohno, ChemCatChem 2018,
10, 1–6.
[8] S. Yuan, Q. Zhang, B. Xu, Z. Jin, M. Zhang, T. Ohno, RSC Adv. 2014, 4,
62255–62261.
[9] B. Xu, Q. Zhang, S. Yuan, M. Zhang, T. Ohno, Chem. Eng. J. 2015, 260,
(CHI660D, Shanghai, Chenhua) in
a standard three-electrode
configuration with Pt as the counter electrode and Ag/AgCl as a
reference electrode.
126–132.
[10] B. Choudhury, P. Chetri, A. Choudhury, RSC Adv. 2014, 4, 4663–4671.
[11] Y. Huang, Y. Lu, Y. Lin, Y. Mao, G. Ouyang, H. Liu, J. Mater. Chem. A 2018,
6, 24740–24747.
Model and computational details
[12] B. Mandal, A. Mondal, S. S. Ray, A. Kundu, Dalton Trans. 2016, 45, 1679–
1692.
Density functional theory (DFT) computations were performed by
using the CASTEP module as implemented in Materials Studio 8.0
(Accelrys Inc.-San Diego, USA). Both the bulk crystalline cells and
the atom positions of the pristine and doped CeO2 were optimized
within the generalized gradient approximation (GGA) and the
exchange-correlation functional of Perdew-Burke-Ernzerhof (PBE).
The kinetic cut-off energy for the plane-wave basis set was chosen
to be 470 eV, the Monkhorst-Pack k-point meshes were set as 2×
2×5, and the ion-electron interactions were modeled by the
ultrasoft pseudo-potential. The convergence criteria of the geome-
try optimization for the energy change, maximum force, maximum
stress, and maximum displacement tolerances were set to 2.0×
10À 5 eV/atom, 0.03 eV/Å, 0.05 GPa, and 0.001 Å, respectively. Accu-
rate description of the electronic structure of rare elements is a
well-known issue for regular DFT approaches due to the localized
nature of the 4f electron. Hence, a tunable Hubbard type correction
term should be included into the DFT framework: DFT+U. The
value of U for Ce, Sm, Y, La, Nd was 6 eV. The super-cells used are
the fluorite cubic 2×2×1 cell with 48 atoms. Replacing a single Ce
atom with Sm, Y, La and Nd elements results in dopant
concentrations of 6.25%.
[13] F. Dvořák, O. Stetsovych, M. Steger, E. Cherradi, I. Matolínová, J. Phys.
Chem. C 2011, 115, 7496–7503.
[14] L.-W. Qian, X. Wang, H.-G. Zheng, Cryst. Growth Des. 2011, 12, 271–280.
[15] D. Channei, B. Inceesungvorn, N. Wetchakun, S. Phanichphant, Sci. Rep.
2014, 4, 5757.
[16] Y. Huang, B. Long, M. Tang, Z. Rui, M.-S. Balogun, Y. Tong, H. Ji, Appl.
Catal. B 2016, 181, 779–787.
[17] X. Zhou, J. Ling, W. Sun, Z. Shen, J. Mater. Chem. A 2017, 5, 9717–9722.
[18] L. Truffault, M.-T. Ta, T. Devers, K. Konstantinov, Mater. Res. Bull. 2010,
45, 527–535.
[19] J. Saranya, K. S. Ranjith, P. Saravanan, D. Mangalaraj, R. T. Rajendra Ku-
mar, Mater. Sci. Semicond. Process. 2014, 26, 218–224.
[20] C. Siriwong, N. Wetchakun, B. Inceesungvorn, Prog. Cryst. Growth
Charact. Mater. 2012, 58, 145–163.
[21] D. Jampaiah, K. M. Tur, S. J. Ippolito, Y. M. Sabri, RSC Adv. 2013, 3, 12963.
[22] E. Sasmaz, C. Wang, M. J. Lance, J. Lauterbach, J. Mater. Chem. A 2017, 5,
12998–13008.
[23] W. L. Wang, W. Y. Liu, X. L. Weng, Y. Shang, J. J. Chen, Z. G. Chen, Z. B.
Wu, J. Mater. Chem. A 2018, 6, 866–870.
[24] X. Zhang, X. Xie, H. Wang, J. Zhang, B. Pan, J. Am. Chem. Soc. 2013, 135,
18–21.
[25] Y. Lee, G. He, A. J. Akey, R. Si, M. Flytzani-Stephanopoulos, I. P. Herman,
J. Am. Chem. Soc. 2011, 133, 12952–12955.
[26] S. Chang, M. Li, Q. Hua, L. Zhang, Y. Ma, B. Ye, W. Huang, J. Catal. 2012,
293, 195–204.
[27] Z. D. Dohčević-Mitrovi, M. Grujić-Brojčin, M. Šćepanović, J. Phys.
Condens. Matter 2006, 18, S2061–S2068.
ChemCatChem 2020, 12, 1–10
www.chemcatchem.org
8
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
��
These are not the final page numbers!

Full Papers
doi.org/10.1002/cctc.201902309
ChemCatChem
[28] A. Tovt, L. Bagolini, F. Dvořák, N.-D. Tran, J. Mater. Chem. A 2019, 7,
[40] D. Jampaiah, S. J. Ippolito, Y. M. Sabri, B. M. Reddy, Catal. Sci. Technol.
2015, 5, 2913–2924.
[41] S. Hu, F. Zhou, L. Wang, J. Zhang, Catal. Commun. 2011, 12, 794–797.
[42] H. Yang, B. Xu, S. Yuan, Q. Zhang, M. Zhang, T. Ohno, Appl. Catal. B
2019, 243, 513–521.
[43] W. Liu, L. Cao, W. Cheng, Y. Cao, X. Liu, W. Zhang, X. Mou, L. Jin, X.
Zheng, W. Che, Q. Liu, T. Yao, S. Wei, Angew. Chem. Int. Ed. 2017, 56,
9312–9317; Angew. Chem. 2017, 129, 9440–9445.
[44] N. Tian, H. Huang, C. Liu, F. Dong, T. Zhang, X. Du, S. Yu, Y. Zhang, J.
Mater. Chem. A 2015, 3, 17120–17129.
1
2
3
4
5
13019–13028.
[29] L. Ma, D. Wang, J. Li, B. Bai, L. Fu, Y. Li, Appl. Catal. B 2014, 148, 36–43.
[30] M. S. M. Yoon, C. Jeong, J. H. Jang, K. S. Jeon, Chem. Mater. 2005, 17,
6069–6079.
[31] R. Ma, M. Jahurul Islam, D. Amaranatha Reddy, T. K. Kim, Ceram. Int.
2016, 42, 18495–18502.
[32] S. Hu, F. Zhou, L. Wang, J. Zhang, Catal. Commun. 2011, 12, 794–797.
6
7
[33] M. J. Islam, D. A. Reddy, J. Choi, T. K. Kim, RSC Adv. 2016, 6, 19341–
19350.
[34] Z. a Huang, Q. Sun, K. Lv, Z. Zhang, M. Li, B. Li, Appl. Catal. B 2015, 164,
[45] P. Ji, J. Zhang, F. Chen, M. Anpo, Appl. Catal. B 2009, 85, 148–154.
[46] Y. Xue, D. Tian, D. Zhang, C. Zeng, Comput. Mater. Sci. 2019, 158, 197–
208.
8
9
420–427.
[35] P. Dumrongrojthanath, T. Thongtem, A. Phuruangrat, Superlattices
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Microstruct. 2013, 54, 71–77.
[36] F. Deng, Y. Liu, X. Luo, D. Chen, S. Wu, Sep. Purif. Technol. 2013, 120,
156–161.
[37] K. Kondo, N. Murakami, T. Tsubota, T. Ohno, Appl. Catal. B 2013, 142,
362–367.
[38] Z. Jin, N. Murakami, T. Tsubota, T. Ohno, Appl. Catal. B 2014, 150, 479–
Manuscript received: December 18, 2019
Revised manuscript received: March 8, 2020
Accepted manuscript online: March 9, 2020
Version of record online: ■■■, ■■■■
485.
[39] P. Patsalas, S. Logothetidis, L. Sygellou, S. Kennou, Phys. Rev. B 2003, 68,
035104.
ChemCatChem 2020, 12, 1–10
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Photocatalysis: CeO2 doped with Sm,
Y, La and Nd having a broom-like hi-
erarchical structure was successfully
synthesized. The enhanced photoca-
talytic activity can be attributed to a
higher concentration of oxygen
Assoc. Prof. B. Xu*, H. Yang, As-
soc. Prof. Q. Zhang*, S. Yuan, As-
soc. Prof. A. Xie, Prof. M. Zhang, Prof. T.
Ohno*
1 – 10
Design and Synthesis of Sm, Y, La
and Nd-doped CeO2 with a broom-
like hierarchical structure: a photo-
catalyst with enhanced oxidation
performance
vacancies caused by doping. During
the process of photocatalytic degra-
dation, abundant highly reactive
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*
hydroxyl radicals ( OH) and superox-
*
À
ide radicals ( O2 ) are efficient inter-
mediates with vivid oxidation ability.