Interfacially bonded CuCo2O4/TiO2 nanosheet heterostructures for boosting photocatalytic H2 production

Article abstract of DOI:10.1039/c9cy01209e

Constructing high-performance, economical and environmentally friendly photocatalysts remains a challenge for the efficient conversion of solar energy. In this work, CuCo₂O₄ nanoparticles modified on TiO₂ nanosheets have b

Full text of DOI:10.1039/c9cy01209e

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ISSN 2044-4761
PAPER
Chaoqiu Chen, Yong Qin et al.
Highly dispersed Pt nanoparticles supported on carbon
nanotubes produced by atomic layer deposition for hydrogen
generation from hydrolysis of ammonia borane
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Interfacial bonded CuCo O /TiO nanosheets heterostructures
2
4
2
for boosting photocatalytic H production
2
a
a
a
b
c
a*
a*
Chenhui Xu , Chenyang Jin , Wenxi Chang , Xiaoyun Hu , Hui Deng , Enzhou Liu , Jun Fan
aSchool of Chemical Engineering, Northwest University, Xi’an 710069, P. R. China.
bSchool of Physics, Northwest University, Xi’an 710069, P. R. China.
cCollege of Life Sciences, Northwest University, Xi’an 710069, P. R. China.
*e-mail address: liuenzhou@nwu.edu.cn and fanjun@nwu.edu.cn

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Abstract
Constructing high-performance, economical and environmentally friendly photocatalysts remains a
2 4
challenge for the efficient conversion of solar energy. In this work, CuCo O nanoparticles modified on
2
TiO nanosheets has been designed and fabricated via a facile hydrothermal method followed by an in
2 4 2
situ calcination process. The resultant 10%-CuCo O /TiO heterostructure exhibited superior
-1
-1
2
photocatalytic activity under full spectra. The H generation rate can reach 4830 μmol g h under 300
2
W Xe lamp irradiation, which is 32 times higher than that of pristine TiO and the highest increase fold
2
of binary TiO -based non-noble system reported so far. Its apparent quantum yield (AQY) value can
reach 11.5% at 365 nm. Furthermore, we demonstrate that there are chemical bonds formed at the
2 4 2
interface between well-dispersed CuCo O and TiO by XPS spectra and electronegativity theory, and
the efficient separation of charge carriers due to the p-n junction adopting the interfacial Ti-O-Cu/Co
bonds is crucial for the improved performance and photostability. This work develops possibilities to
2 4
prepare feasible CuCo O -based heterostructures for energy conversion.
2 4 2
Keywords: CuCo O ; TiO nanosheets; Hydrogen evolution; Interfacial chemical bonds

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Introduction
Unsustainable fossil fuels and global environmental pollution caused by burning fossil fuels trigger
2
an upsurge to develop new sources of energy. Hydrogen (H ) is an ideal alternative for traditional fossil
fuels due to its renewable, pollution-free and high-energy intensity features.1-6 At present, H
2
production mainly depends on the reforming of coal and natural gas, which will inevitably aggravate
the consumption of non-renewable energy and bring environmental pollution. How to produce H
2
rationally has become a research hotspot. Economical, efficient and pollution-free photocatalytic
technology based on semiconductors has attracted significant attention. Photocatalytic technology can
be used to degrade organic pollutants, reduce heavy metal ions and produce H
2
from water splitting.7-11
2
Titanium dioxide (TiO ) possesses many merits of stability, non-toxicity and abundant reserves,
which is the most extensive investigated material in the field of photocatalysis. However, wide
band-gap and fast recombination of photoinduced carriers still limit the practical application in solar
conversion.12-17 Among many strategies, the morphology control has been commonly employed to
2
enhance the activities of TiO , such as nanoparticle, nanowire, nanosheet and nanorod etc. Due to
2
unique microstructures and peculiar physicochemical properties, two-dimensional TiO exhibits great
2
potential in photocatalysis. Compared with bulk structures, TiO nanosheets possess larger specific
surface areas and highly active surface atoms, which are conducive to the surface adsorption and
reaction.18-23 Nevertheless, poor separation of charge carriers is still the bottleneck restricting its
practical application.
Modification of noble metal cocatalysts (e.g. Pt, Au, Ag etc.) as electron donor and acceptor is favor
for improving H
2 2
production due to the formation of Schottky barrier and the decrease of H evolution
overpotential.24-27 However, the scarcity severely retards their practical application. Compared with

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noble metal, the space electron orbital of transition metals are easy to accept electron pairs and require
relatively little energy. Besides, they have strong redox and coordination ability, and the excellent
photoelectric properties make them the most promising materials in multiple fields.28-30 More recently,
transition metal phosphides (TMPs) become an effective resolution to improve the phtotocatalytic
2 2
activity of semiconductors. Song et al. used Ni P, NiCoP and FeP to improve the performance of TiO
nanoparticles.31 The H production rates reached 1410, 1540 and 770 μmol h−1 g−1 under optimum
2
2
condition, which was 12.5, 13.6 and 6.8 times higher than that of bare TiO . Yue et al. demonstrated
3 2
that the efficient separation of photoinduced hole-electron between Cu P and TiO can significantly
3
2
2 2
enhances H generation rate. Unfortunately, the efficiency of TMP for TiO is still hard to achieve the
level of that of noble metals. Therefore, it is necessary to explore novel and more efficient co-catalysts.
2 4
P-type semiconductor CuCo O has attracted considerable attention in high performance electrode
materials owing to high conductivity, corrosion resistance, nontoxicity, and low cost. Compared with
3 4 2 4
single metal oxides CuO or Co O , ternary compounds CuCo O possesses higher electrochemical
activity and conductivity due to the lower activation energy of charge transfer in multivalent transition
metal cations.33-36 Moreover, ternary compounds still reserve excellent properties of monometallic
oxides.37 Currently, CuCo
O is gradually emerging in the field of photocatalysis, such as degradation
2 4
2
of methyl orange, reduction of hexavalent chromium and CO , but rarely reported in hydrogen
evolution.38-41
2 4
Based on the above understanding, a novel heterojunction of ternary CuCo O nanoparticles
2
modified 2D TiO nanosheets was successfully fabricated using a facile hydrothermal method followed
2 4
by an in situ calcination process. CuCo O with an average size about 10 nm were well dispersed onto
2 2 4 2
the TiO nanosheets. Under 300 W Xe lamp irradiation, the 10%-CuCo O /TiO sample exhibited

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superior photocatalytic activity in H
2
production (4830 μmol g-1 h ). The excellent activities of
-1
2 2
CuCo O4/TiO mainly belongs to the formation of interfacial chemical bonding, lower overpotential
2 4 2
and efficient separation of electron-hole pairs across the p-n junction between CuCo O and TiO
nanosheets. Finally, the possible mechanism of charge transfer over CuCo
and discussed in detail.
2 4 2
O and TiO was proposed

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Experimental section
Fabrication of TiO Photocatalysts
2
2
TiO nanosheets were fabricated via a hydrothermal method. Typically, 3 mL of HF (40%) was
slowly added into 27 mL of tetrabutyltitanate (TBT) under vigorous stirring. Then, the mixed solution
o
was heated at 180 C for 24 h in Teflon-lined stainless steel vessel. After cooling down, the white
suspensions were washed with NaOH solution (1 M) to remove the fluoride ion, and then washed with
o
ethanol and water. Finally, the obtained TiO
2
nanosheets were dried at 60 C for 12 h.
Fabrication of CuCo O /TiO Nanosheets
2
4
2
2 4 2
CuCo O /TiO hybrids were synthesized through an in situ calcination reaction. In detail, a certain
amount of Cu(NO
3
)
2
·3H
2
O, Co(NO
3
)
2
·6H
2
O and (NH
4
)
2
3
CO aqueous solution (1 M) were dissolved in
o
1
00 mL water in a three-neck flask and refluxed at 100 C for 1.5 h after adding TiO
2
powder. Then,
o
the precipitates were washed by ethanol and dried at 60 C for 10 h. Finally, the CuCo
2
O
4
/TiO
2
o
composites were obtained after calcination at 300 C for 3 h and denoted as х%- CuCo
2
O
4
/TiO
2
(x
2 4
represents the mass fraction of CuCo O
in the composite calculated by the input amount of Cu2+ and
2
+
2 4 2
Co ). Besides, CuCo O was prepared under the same conditions without adding TiO nanosheets.
2 4 2
The preparation processes of CuCo O /TiO and the detailed conditions are illustrated in Fig. 1.
2 4 2
Figure 1. Synthesis route of CuCo O /TiO nanosheets.

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Characterization
The crystalline phases, morphologies and textural characteristics of the obtained samples were
analyzed by X-ray powder diffraction (SmartLAB SE, Rigaku), transmission electron microscopy
2
(Tecnai G2 F30) and N adsorption/desorption isotherm (Quantachrome NOVA 2000e). The elemental
composition and chemical state of the samples were measured by X-ray photoelectron spectroscopy
(Kratos AXIS NOVA). The UV/vis spectrophotometer (Shimadzu UV-3600) was employed to analyze
the photoresponse properties of the catalysts. Photoluminescence spectra and fluorescence decay
spectra were acquired on Hitachi F-7000 and Edinburgh FLS-1000.
A series of photoelectrochemical performances consisting of I–t curves (0.5 V bias potential),
5
electrochemical impedance spectroscopy (frequency ranging from 0.01 to 10 Hz) and Linear sweep
−
1
voltammetry (scan rate of 10 mV s ) were measured using a CHI660E electrochemical workstation in
0
2 4
.5 M Na SO electrolyte. The as-synthesized 4 mg samples on the ITO glass, the Pt wire and Ag/AgCl
(saturated with KCl solution) electrode were functioned as working electrode, counter electrode and
reference electrode, respectively.
Photocatalytic Activity Measurements
An on-line detection system (Lab Solar-IIIAG, Beijing Perfect Light Technology Co. Ltd, China)
was employed to evaluate the activity of samples. A 300 W Xe lamp was used as the full spectrum
light source (350- 780 nm). 20 mg sample was placed in a Pyrex top-irradiation vessel containing 100
mL of mixture solution (20% TEOA) as sacrificial agent. The distance from lamp to reactor is about 20
-2
cm and the light intensity at this position is about 382 mW cm . Before irradiation, the system was
2
evacuated completely until the vacuum gauge reached in a stable state. The generated H was detected
2 2
by a gas chromatography (Tianmei, GC7900) with N as carrier. In addition, Pt/TiO catalysts obtained

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by photo-deposition H
2
PtCl
6
·6H
2
2
O (1 g/L) were also tested for photocatalytic H evolution under same
conditions.
The apparent quantum yield (AQY) was investigated with 365 nm band-pass filter under 300 W Xe
2
2
lamp. The average irradiation intensity was 20.38 mW/cm and the irradiation area was 24 cm . The
QE is calculated based on the eqn. (1) below.
Number of evolved H molecules2
2
QE 
100%
Number of incident photons
2
tNA

100%
1
ISt
(1)
hc
-2
A
I, t, λ, N , ν, S, c and h are corresponding to incident light density (W·cm ), illumination time (s),
-1
2
incident light wavelength (nm), Avogadro constant, H generation rate (mol·s ), illumination area
2
(
cm ), velocity of light and Planck constant.
Hydroxyl Radical Trapping Experiment
Detection of the surface hydroxyl radical groups (•OH) by probe molecule terephthalic acid (TA)
was performed under 300 W Xe lamp irradiation. The reaction (eqn. (2)) product 2-hydroxyterephthalic
acid (TA-OH) could be measured at 425 nm by PL spectroscopy. First, the 20 mg different samples
were immersed in 50 mL mixed solution (0.05 M TA and 0.02 M NaOH) and the dark adsorption
process was carried out for 30 min. Then, under light irradiation, about 3 mL solution was withdrawn
from the mixture every 10 min intervals and detected by Hitachi-F7000 florescence spectrophotometer
with excitation at 315 nm.

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+
·OH
(2)

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Results and discussion
Structures and Compositions of Photocatalysts
(311)
CuCo2O4
20%-CuCo2O4/TiO2
10%-CuCo2O4/TiO2
8%-CuCo2O4/TiO2
6%-CuCo2O4/TiO2
TiO2
1
0
20
30
40
50
60
70
80 35
40
2θ (degree)
Figure 2. XRD patterns of samples.
o
o
o
o
o
o
As shown in Fig. 2, the signals centered at 19.1 , 31.3 , 36.9 , 44.9 , 59.2 , and 65.2 match to (111),
(
220), (311), (222), (400), (511), and (440) plane of the cubic spinel CuCo O
2 4
(JCPDF No. 01-1155),42
o
o
o
o
respectively. All binary composites exhibit the similar diffraction peaks at 25.2 , 37.9 , 48.0 , 53.9 ,
o
o
o
6
2.7 , 70.3 , and 75.2 , corresponding to (101), (004), (200), (105), (204), (116), (215) crystal planes of
anatase TiO
2
(JCPDF No. 21-1272).43 Via partial enlarged detail, it can be found that the peak at 37.9o
2 4
broadens gradually with the increase content of CuCo O , and when loading content reaches 20%, the
2 4 2 4 2
diffraction peak of CuCo O can be obviously observed, indicating that the binary CuCo O /TiO
composite has been successfully fabricated.

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Figure 3. (a-e): TEM images of samples (TiO
2
, and 6%, 8%, 10%, 20%- CuCo
2
O
4
/TiO
2
), (f) and (g):
2 4 2
magnification TEM image and size distribution histograms of 10%- CuCo O /TiO , (h-l) and (m): the
2 4 2
corresponding EDX mapping images and EDS spectrum of 10%-CuCo O /TiO .
2
The SEM images (Fig. S1) show that the surface of TiO becomes rough and aggregated with the
2 4
increase of CuCo O loading content, which could be clearly seen in TEM images. It can be seen from
2
Fig. 3 that the pristine TiO has ultrathin rectangular nanosheets structure with thickness approximately
1
0 nm and 40-60 nm side length. The clear lattice fringes of 0.35 nm matches well with (101) plane
of anatase TiO . For 10%-CuCo O /TiO (Figure 3d and i), the CuCo O nanoparticles with
2
2
4
2
2
4
average size about 8 nm are homogenously anchored on the surface of TiO , but almost
2
completely covers the surface of TiO nanosheets in 20%-CuCo O /TiO composite. This
2
2
4
2
shielding effect severely inhibits the photocatalytic activity of the binary catalyst. The lattice

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spacing of 0.26 nm corresponds to (311) planes of cubic CuCo O . It can be seen Cu and Co
2
4
elements are evenly dispersed on the surface of TiO based on the EDX mapping (Fig. 3h–i).
2
Moreover, from EDS analysis (Fig. 3m), the atomic ratio of Cu : Co is about 1 : 2, which is
accordance with the stoichiometric ratio of CuCo O .
2
4
4
3
3
2
2
1
1
00
50
00
50
00
50
00
2.5
2.0
1.5
1.0
0.5
0.0
CuCo2O4
0%-CuCo2O4/TiO2
TiO2
1
0
20
40
60
80
100
Pore Diameter (P/Po)
5
0
0
0
.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
2
Figure 4. N adsorption-desorption isotherm plots and pore diameter distributions (insert) of samples.
The nitrogen adsorption-desorption test was performed to investigated the specific surface areas
of the samples. As shown in Fig. 4, it can be categorized as type IV isotherms with H3 hysteresis
2
2 4 2
loop for TiO and 10%-CuCo O /TiO , indicating the presence of slit-like mesopores due to
stacking of nanosheets.44 The BET surface area (Table S1) of 10%-CuCo
O /TiO (102.04 m g ) is
2
−1
2 4 2
2
−1
2
greatly improved compared with that of TiO (46.53 m g ), which may be caused by more slit like
2
pores produced in gas (CO ) insitu pyrolysis process. This improvement of specific surface area
provides more active sites and facilitates interfacial mass transfer in photocatalytic reaction.

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5
30.53
10%-CuCo2O4/TiO2
(
a) Ti 2p
(b) O 1s
1
0%-CuCo2O4/TiO2
4
59.22
5
28.53
532.63
CuCo2O4
4
64.92
4
57.67
463.16
5
29.07
530.87
5
32.66
4
59.03
TiO2
5
30.09
TiO2
4
64.76
5
32.00
4
56
458
460
462
464
466
468
526
528
530
532
534
Binding Energy (eV)
Binding Energy (eV)
(
c) Co 2p
10%-CuCo2O4/TiO2
(d) Cu 2p
10%-CuCo2O4/TiO2
9
35.13
7
82.74
955.15
Sat.
781.47
Sat.
796.57 798.41
Sat.
Sat.
CuCo2O4
CuCo2O4
9
34.45
Sat.
7
81.01
954.46
779.68
794.82
Sat.
7
96.49
Sat.
9
51.80
Sat.
9
31.97
7
75 780 785 790 795 800 805 810
930 935 940 945 950 955 960 965
Binding Energy (eV)
Binding Energy (eV)
Figure 5. High-resolution XPS spectra of samples (a) Ti 2p, (b) O 1s, (c) Co 2p and (d) Cu 2p.
2 4 2
The survey spectra (Fig. S2) exhibits the presence of Ti, Cu, Co and O elements in CuCo O /TiO .
High-resolution Ti 2p XPS spectrum (Fig. 5a) shows two major peaks at 459.22 and 464.92 eV,
attributed to the formation of Ti4+ state. Meanwhile, two tiny Ti3+ signals at 457.67 and 463.16 eV
2 4 2 4 2
appears after loading CuCo O O /TiO in Fig. 5b displays three
.45 The O 1s XPS spectra of CuCo
characteristic peaks centered at 528.53, 530.53 eV and 532.63 eV, which are indexed to the lattice
and the oxygen of adsorbed hydroxide ions, respectively.46,47 The
2 4 2
oxygen in CuCo O and TiO
high-resolution Co 2p spectrum (Fig. 5c) can be deconvoluted into two major characteristic peaks with
spin-energy separation value about 15 eV, indicating Co2+ (782.74 and 798.41 eV) and Co3+ (781.47
and 796.57 eV) exist in composites, which are characteristic of spinel cobalt oxides.38 The peaks at
7
85.97, 789.51 and 803.64 eV belong to the shake-up satellites, further confirming the presence of

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multivalent cobalt. As shown in Fig. 5d, Cu 2p peak can be fitted into two prominent peaks located at
9
35.13 and 955.15 eV, which is attributed to Cu2+ in composites.48
For comparison, the single catalysts (TiO
2
and CuCo
2
O
4
) were also investigated by XPS analysis.
2
+
3+
+
Interestingly, the ratio of Co /Co is obtained as 1.7, and Cu (931.97 and 951.80 eV) could be
2 4
observed in CuCo O
.49 However, the ratio of Co /Co becomes 0.8 and only Cu2+ exists in
2+
3+
2 4 2 2 4
CuCo O /TiO O ,
hybrid. Meanwhile, part of the Ti4+ shows the conversion to Ti3+ after loading CuCo
implying the following redox reaction (eqn. (3)) occurs on surface based chemical bonding during the
annealing process.
Ti4+ + Co /Cu = Ti + Co /Cu
2+
+
3+
3+
2+
(3)
Therefore, the theoretical calculation of electronegativity and comparative experiments were carried
5
0
out to explain this phenomenon. Electronegativity (EN) is the scale of the ability of an atom to attract
electrons in compounds. According to eqn. (4), the EN of given elements with different oxidation state
and coordination number can be calculated. χ푖, 푛 * , 퐼푚, 푅 and 푟푖 are EN, effective principal
quantum numbers, ultimate ionization energy, Rydberg constant and ionic crystal radius, respectively.
The specific values are shown in Table. 1.
*
1/ 2
i  0.105n (I / R) / r  0.863
(4)
m
i
Table 1. Electronegativity Values Calculated by the eqn (4).
χ
i
Element
n*
m
I /eV
R/eV
i
r /Å
Ti4+
Ti3+
Co2+
Co3+
Cu+
3.45
3.45
3.45
3.45
3.45
3.45
43.267
27.4917
17.083
33.5
13.6
13.6
13.6
13.6
13.6
13.6
0.745
0.81
0.79
0.685
0.74
0.71
1.73028345
1.498850064
1.376918106
1.69298601
1.231973565
1.48622849
7.72638
20.2924
Cu2+

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4
+
2+
+
4+
EN values of Ti , Co and Cu are calculated as 1.73, 1.38 and 1.23, indicating Ti has stronger
electronic affinity than Co2+ and Cu when forming chemical bonds. Hence, it can be inferred the
+
2 4 2
formation process of CuCo O /TiO as follows in Fig. 6. During calcination reaction, CuCo(OH)₂CO₃
2 2 4
attached to TiO could be decomposed and gradually produce CuCo O , accompanied by the
2
formation of many oxygen vacancies, which react with lattice oxygen on the surface of TiO to form
chemical bonds. The different electronegativity leads to electron migration from Co/Cu to Ti across
Ti-O-Co/Cu. Hence, it produced Ti3+ and high valence state Cu /Co . Meanwhile, the binding
2+
3+
energy of lattice oxygen in TiO
respectively.
2 2 4
(530.09 eV) and CuCo O (529.07 eV) shows red and blue shifts,
2 4 2
Figure 6. The synthesis mechanism of CuCo O /TiO composite.
2 4 2
In order to prove the existence of interfacial chemical bond, the 10%-CuCo O /TiO composite
prepared by mechanical mixing were also characterized by XPS spectrum. As shown in Fig. S3, the
univalent copper ion is not oxidized and the ratio of Co /Co remains at 1.8, and there is no Ti3+ in
hybrid via mechanical fabrication, further indicating the interfacial bonding due to unsaturated
coordination atoms occurs during annealing process like Zheng et al.’s work.51 In addition, according
2
+
3+
to XPS valence band spectra (Fig. 7), the valance band position (EVB) of TiO
2 2 4
and CuCo O are
obtained as 2.27 and 0.41 eV, respectively.

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(a)
(b)
CuCo2O4
TiO2
0
.41
1
2.27
-2
-1
0
2
3
4
0
1
2
3
4
5
Binding energy(eV)
Binding energy(eV)
2 4 2
Figure 7. XPS valence band spectra of (a) CuCo O and (b) TiO .
Photocatalytic Activities and Stabilities
3
50
300
50
200
1
2%-CuCo2O4/TiO2
1
1
2%-CuCo2O4/TiO2
0%-CuCo2O4/TiO2
(a)
(b)
(c)
4
3
3
2
2
1
1
00
50
00
50
00
50
00
10%-CuCo2O4/TiO2
8%-CuCo2O4/TiO2
6%-CuCo2O4/TiO2
5000
4000
3000
2000
3
65 nm
8%-CuCo2O4/TiO2
4%-CuCo2O4/TiO2
6%-CuCo2O4/TiO2
4%-CuCo2O4/TiO2
2%-CuCo2O4/TiO2
2%-CuCo2O4/TiO2
TiO2
CuCo2O4
2
TiO2
CuCo2O4
1
1
50
00
1
000
0
5
0
0
5
0
0
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
Irradiation time (h)
Irradiation time (h)
Irradiation time (h)
6
000
(d)
(e)
5246
(f)
5
4
3
2
1
000
000
000
000
000
0
Pt/TiO2
Before
5000
4
3
2
1
000
000
000
000
0
3719
2
739
2653
After
1593
0
5
10
15
20
10
20
30
40
50
60
70
80
1%
3%
5%
7%
10%
Irradiation time (h)
2θ (degree)
Figure 8. (a) Photocatalytic H
2
evolution amounts and (b) H evolution rates of the samples, (c)
2
AQY under 300 W Xe lamp irradiation with 365 nm band-pass filter, (d) cycling tests on
1
2 4 2 2 4 2
0%-CuCo O /TiO composite, (e) XRD patterns of 10%-CuCo O /TiO before and after use and (f)
2 2
H generation of different content Pt/TiO .
2
The photocatalytic H evolution for all samples was evaluated with triethanolamine (TEOA) as the

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DOI: 10.1039/C9CY01209E
2
trapping agent under irradiation of 300 W Xe lamp. Fig. 8a and Fig. 8b display the H evolution yield
2
and the photocatalytic H evolution rate (PHER) of all samples after 5 h irradiation, respectively. It can
be seen that the PHER increases to the maximum after 4 h’s irradiation and keeps the balance, which
2
may be related to the activation of reaction sites and the dissolution of produced H in water at the
2 2 4
initial stage. Due to the fast recombination of photoinduced carriers, the TiO and CuCo O exhibit
relatively low PHER of 151 and 42 μmol g-1 h-1, respectively. In contrast, the PHER increases
-1
-1
2 4 2
significantly with modification of CuCo O . The optimum H production activity of 4830 μmol g h
2 4 2
is obtained at 10% of CuCo O , which is about 32 times than single TiO and the highest increase fold
2
of binary TiO -based non-noble system reported so far (summarized in Table. 2). Its apparent quantum
yield (AQY) value was calculated to be 11.5% at 365 nm (Fig. 8c). However, the shielding effect
2 4
caused by excessive CuCo O inhibits the photocatalytic activity of the binary catalyst. Additionally,
2 4 2
the PHER of 10%-CuCo O /TiO shows negligible decrease after four consecutive cycles (Fig. 8d),
and there are no significant changes before and after in the XRD patterns (Fig. 8e), confirming
excellent stability.
Table 2. Summary of Reported TiO
2
–Based Photocatalytic.
increase
Photocatalyst
Cu P/TiO
Ni P/TiO
NiCoP/TiO
FeP/TiO
CuO /TiO
Cu/TiO
-TiO
/TiO
Light source
Scavenger
H
2
yield
AQY
References
multiple
-
1
-1
-1
-1
3
2
300 Xe
300 Xe
300 Xe
300 Xe
300 Xe
300 Xe
350 Xe
300 Xe
10%TEOA
20%Methanol
20%Methanol
20%Methanol
20%Methanol
10% methanol
20% methanol
20%TEOA
7940 µmol h g
11
4.6%
33
-1
2
2
1410 µmol h g
12.5
13.6
6.8
-
32
-1
2
1540 µmol h g
-
32
-
1
-1
2
770 µmol h g
-
32
49
-
1
-1
x
2
1523.2 µmol h g
18.2
6.6
7.05%
-
-1
-1
2
12779 µmol h g
62
-1
-1
Co
3
O
4
2
(B)
6359µmol h g
9.2
10.9%
11.5%
63
-1
-1
CuCo
2
O
4
2
4830 µmol h g
32
This work

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For comparison, the photocatalytic activity of Pt/TiO
2
catalysts fabricated by photo-deposition
reaction was measured under the same conditions. The highest PHER (Fig. 8f) achieves 5246 μmol g-1
-1
2 2 4 2
h over 3%-Pt/TiO , which is slightly higher than that of 10%-CuCo O /TiO . What's more, the PHER
-1
-1
2 4 2
of 10%-CuCo O /TiO prepared by mechanical mixing is 1190 μmol g h (Fig. S4), which is far less
than that of the composite prepared by insitu calcination process. Based on the above results, it can be
explained that this heterojunction and surface chemical bonding can significantly enhance
photocatalytic activity. Considering application economy, it is obviously that CuCo
alternative to Pt for its high practical potential in photocatalysis.
Optical Properties of Photocatalysts
2 4
O is a suitable
(a)
CuCo2O4
(b)
TiO2
0%-CuCo2O4/TiO2
1
1
2%-CuCo2O4/TiO2
1
0%-CuCo2O4/TiO2
%-CuCo2O4/TiO2
%-CuCo2O4/TiO2
8
6
4
%-CuCo2O4/TiO2
%-CuCo2O4/TiO2
2
TiO2
2
00
300
400
500
600
700
800
200
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Figure 9. (a) UV–vis diffuse reflectance spectra of prepared samples inset is the photographs of
2
samples under daylight (inset is the photographs of samples under daylight: (I) TiO , (II) 4% (III) 8%
2 4 2 2 4 2 2 4 2
(IV) 10%-CuCo O /TiO , (Ⅴ) CuCo O ) and (b) PL spectra of TiO and 10%-CuCo O /TiO .
2
As shown in Fig. 9a, TiO nanosheets exhibit excellent photoresponse to ultraviolet region but have
2 4
little absorption above 400 nm. CuCo O shows superior absorption to the full spectrum, possibly due
to its own black color and narrow band gap. Therefore, the absorption of visible light of the hybrid
2 4
catalysts increases with the addition of CuCo O , which is consistent with the color change of samples.
Interestingly, a broad absorption peak appeared between 600 and 800 nm, attributed to the d-d

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transition of Co and Cu ions species.52,53 As depicted in Kubelka-Munk plots (Fig. S5), the band gap
g 2 2 4
energy (E ) of TiO and CuCo O are calculated as 2.97 and 1.56 eV, respectively, which is in line with
previous reports.41,54
The separation efficiency of photogenerated carriers were analyzed by steady-state and
time-resolved photoluminescence (PL) spectra. Fig. 9b shows the steady-state PL spectra under
2
excitation with 220 nm. The high PL intensity of pristine TiO indicates the high recombination of
2 4 2
charge carriers. The 10%-CuCo O /TiO composite displays lower PL intensity, revealing that the
2 4
coupled CuCo O could effectively promotes the separation of electrons and holes through Ti-O-Cu/Co
bonds, which increases useful carriers in photocatalysis. Furthermore, time-resolved PL study based on
bi-exponential kinetic fitting exhibits the decay data in Fig. 10. The resulting emission lifetimes are
1
1
1 2 2 4 2 2 1
.78 (τ ) and 8.66 (τ ) ns for 10%-CuCo O /TiO hybrids, shorter than those of TiO 1.87 (τ ) and
2 2 2 4 2
0.04 (τ ) ns. The average radiative lifetime <τ> for bare TiO nanosheets and 10%-CuCo O /TiO
hybrids is obtained to be 7.83 and 6.83 ns, respectively. The decreased fluorescent lifetime suggests a
charge transfer nonradiative pathway across chemical bonding and efficient charge separation between
2 2 4
TiO and CuCo O
.55
(a)
TiO2
(b)
1
0%-CuCo2O4/TiO2
τ1 1.87 (66.56% )
τ2 10.04 (33.44% )
τ1 1.78 (63.74% )
τ2 8.66 (36.26% )
<τ> 7.83
<τ> 6.83
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Time (ns)
Time (ns)
Figure 10. Time-resolved transient PL decay of (a) TiO
2
and (b) 10%-CuCo O /TiO .
2 4 2

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Photoelectrochemical Measurements
4
3
2
0
0
0
1
2
9
6
3
0
(a)
10%-CuCo2O4/TiO2
TiO2
(b)
10
0
TiO2
10%-CuCo2O4/TiO2
0
20
40
60
80
100
0
2
4
6
8
10
4
Time (s)
Z' (10 Ω)
-
100
0.0
0.5
1.0
1.5
2.0
(
c)
(d)
1
6.31 Hz
-80
-60
-40
-20
0
-
-
-
-
28.50 Hz
TiO2
0%-CuCo2O4/TiO2
1
TiO2
0%-CuCo2O4/TiO2
1
0
.01 0.1
1
10
100 1000 10000100000
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
Frequency (Hz)
Potential (V vs. RHE)
Figure 11. (a) I-t curves, (b) Nyquist plots, (c) bode phase spectra and (d) linear sweep voltammetry
curves of the samples.
2 4 2
To further investigate the modification effects of CuCo O on TiO in promoting the photocatalytic
activity, charge separation and migration during the photocatalytic process, the photoelectric
characteristics were performed in 0.5 M Na
2
SO
4
solution. As shown in Fig. 11a, the
1
2 4 2
0%-CuCo O /TiO exhibits higher photocurrent density of 3.91 μA at 0.5 V bias potential, which is
2
2
.73 folds than that of pristine TiO (1.43 μA), indicating improved separation efficiency of charge
carriers. According to the smaller arc radius in EIS analysis (Fig. 11b), the interfacial charge transfer
2 4 2
resistance of CuCo O /TiO decreases significantly, which is due to intimate electronic interaction
5
6
2 2 4
between TiO and CuCo O . There are two time constants (two semicircle) in the Bode diagram (Fig.
1
1c), corresponding to double layer at low frequency and the space charge region at high frequency.
The charge transfer in space charge region plays a key role in photocatalysis. Hence, according to eqn.

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(
5), the electron lifetime of TiO
2
and CuCo
2
O
4
are obtained 5.58 ms and 9.76 ms, further indicating
effective charge carrier separation in CuCo
2
O
4
/TiO
2
heterojunction.57
(5)
τ푛 = 1/2휋푓푛
As shown in LSV curve (Fig. 11d), CuCo
(−1.54 V vs SCE) at -1 mA cm−2 current density, suggesting hydrogen reduction
surface.58 Based on the above results, the CuCo
O with
2 4
2 4 2
O /TiO presents a lower overpotential (-1.40 vs SCE) than
that of bare TiO
2
process is easier to react on CuCo
2
O
4
/TiO
2
2
superior conductivity significantly improves the photoelectric properties of TiO , which could be
attributed to p-n junction with chemical bonding at the interface and the lower overpotential for H
2
production.
Proposed Photocatalytic Mechanism
1
1
1
4000
2000
0000
1
4000
70 min
(
a) TA
60 min
50 min
(b) TA and TiO
2
60 min
50 min
40 min
30 min
20 min
10 min
40 min
12000
10000
8000
30 min
2
1
0 min
0 min
8
6
4
2
000
000
000
000
0
0
min
0
min
6
4
000
000
2000
0
3
50
400
450
500
550
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
1
1
1
4000
2000
0000
14000
12000
10000
8000
6000
4000
2000
0
(
c) TA and CuCo
2
O
4
70 min
60 min
(d) TA and 10% -CuCo O /TiO
2
4
2
70 min
6
5
0 min
0 min
50 min
40 min
30 min
20 min
10 min
40 min
0 min
20 min
0 min
min
3
8
6
4
2
000
000
000
000
0
1
0
min
0
3
50
400
450
500
550
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
Figure 12. PL intensity of TA-OH generated by different samples under illumination.
For sake of clearly analyzing the charge transfer route, the hydroxyl radical (·OH) trapping

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experiment was carried out for an hour. From Fig. 12a, blank experiment shows that only
negligible ·OH is produced in the absence of catalyst. Fig. 12b exhibits an intense emission signals at
4
2
25 nm, revealing pristine TiO produces a large number of ·OH under solar irradiation. That is
because EVB position (2.27 eV vs NHE) is more positive than +1.99 eV (E·OH/OH-), implying holes in
-
59
2 2 4
the VB of TiO can oxidize OH to ·OH. In Fig. 12c, CuCo O with negative EVB potential (0.41 eV
2 4 2
vs NHE) is difficult to generate ·OH. Interestingly, the ·OH produced by binary CuCo O /TiO (Fig.
1
2
2d) are much lower than those produced by TiO , implying the oxidizability of holes reduces due to
the transfer to negative energy band, which is similar to type II heterojunction.
-
2
1
H+
e-
H2
-
-
-
-
-
-
-
e-
CuCo O
+
+
+
+
+
+
+
-
2
4
CuCo O
Ef
2
4
0
1
2
E
f
Ef
h+
TEOA
TEOA+
TiO2
TiO2
h+
Before contact
After contact
2 4 2
Figure 13. Photocatalytic water splitting mechanism of CuCo O /TiO .
According to the above analysis, a proposed mechanism for the improved photoactivity of the
2 4 2 2
CuCo O /TiO hybrids towards H evolution under light illumination is displayed in Fig. 13. Ultrathin
lamellar and nanoparticle favor interphase transport of charge carriers. The coordinatively unsaturated
nanosheets.60 The
2 4 2
metal atoms promote the hybridization between CuCo O nanoparticles and TiO
2 2 4 2 2 4
EVB of TiO and CuCo O are 2.27 and 0.41 eV, respectively. The EVB of TiO and CuCo O are -0.70
2 2 4
and -1.15 eV, respectively. The intimate contact between n-type TiO and p-type CuCo O establishes

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a p-n junction with staggered band alignment.33,61 Moreover, the equilibrium Fermi level (E
) produces
f
2 2 4
an inner electric field directed from TiO to CuCo O . First, light irradiation urges the simultaneous
2 4 2
generation of electron-hole pairs both in CuCo O and TiO . Then, due to the staggered band edge
2 4 2
positions, the photoinduced electrons in CuCo O are rapidly transferred to the CB of TiO to achieve
2 2
photocatalytic H evolution. Meanwhile, the photoexcited holes migrated from the VB of TiO to
2 4 2 4 2
CuCo O are consumed by the sacrificial agent TEOA. This CuCo O /TiO p-n junction with
interfacial bonding of Ti-O-Cu/Co inhibits the recombination of photogenerated hole-electron pairs and
accelerates the charge carrier migration, thus significantly improving the photocatalytic activity.
Conclusions
2 4 2
In summary, the CuCo O nanoparticles modified on TiO nanosheets have been successfully
fabricated via a facile hydrothermal method followed by an in situ calcination reaction. The
generation (4830 μmol g-1
1
2 4 2 2
0%-CuCo O /TiO sample exhibits superior photocatalytic activity in H
-1
2
h ), which is 32 folds than that of pristine TiO . This typical p-n junction material possesses unique
properties of abundant surface reactive sites, improved current density, reduced charge transfer
2 2 4
impedance, and lower overpotential for H production. Moreover, the well dispersion of CuCo O onto
2
the surface of TiO nanosheets adopting interfacial chemical bonding is beneficial to charger transfer
and photostability in photocatalytic process. Finally, this work develops a new horizon for exploring
2 4
non-noble metal CuCo O -based photocatalysts.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China
Nos.21676213, 21476183, and 51372201), the China Postdoctoral Science Foundation
No.2016M600809) and the Natural Science Basic Research Plan in Shaanxi Province of China
(
(

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(No.2017JM2026).

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References
1
2
3
J. Low, J. Yu, M. Jaroniec, S. Wageh and A. A. Al-Ghamdi, Adv. Mater., 2017, 29, 160194.
J. Fu, Q. Xu, J. Low, C. Jiang and J. Yu, Appl. Catal. B, 2019, 243, 556-565.
N. C. Zheng, T. Ouyang, Y. Chen, Z. Wang and Z. Q. Liu, Catal. Sci. Technol., 2019, 9,
1
357-1364.
4
H. Han, W. Wang, L. Yao, C. Hao, Y. Liang, J. Fu and P. Zeng, Catal. Sci. Technol., 2019, 9,
989-1997.
1
5
6
Z. Guan, J. Pan, Q. Li, G. Li and J. Yang, ACS Sustain. Chem. Eng., 2019, 7, 7736-7742.
X. Ren, P. Gao, X. Kong, R. Jiang, P. Yang, Y. Chen, Q. Chi and B. Li, J. Colloid Interface
Sci., 2018, 530, 1-8.
7
J. Lin, J. Hu, C. Qiu, H. Huang, L. Chen, Y. Xie, Z. Zhang, H. Lin and X. Wang, Catal. Sci.
Technol., 2019, 9, 336-346.
8
9
1
Q. Li, T. Shi, X. Li, K. Lv, M. Li, F. Liu, H. Li and M. Lei, Appl. Catal. B, 2018, 229, 8-14
P. Kuang, L. Zhang, B. Cheng and J. Yu, Appl. Catal., B, 2017, 218, 570-580.
W. Qi, S. Liu, F. Li, H. Jiang, Z. Cheng, S. Zhao and M. Yang, Catal. Sci. Technol., 2019, 9,
0
2
571-2577.
1
1
1
2
Q. Yu, X. Meng, T. Wang, P. Li and J. Ye, Chem. Commun., 2015, 51, 3630-3633.
R. Shwetharani, M. Sakar, C. A. N. Fernando, V. Binas and R. G. Balakrishna, Catal. Sci.
Technol., 2019, 9, 12-46.
13
14
15
L. Nie, B. Duan, A. Lu and L. Zhang, ACS Sustain. Chem. Eng., 2018, 7, 1658-1666.
E. Liu, C. Xu, C. Jin, J. Fan and X. Hu, J. Taiwan. Inst. Chem. Eng., 2019, 97, 316-325.
Y. Yang, Q. Deng and Y. Zhang, Chem. Eng. J., 2019, 360, 1247-1254.

Catalysis Science & Technology
Page 26 of 29
View Article Online
DOI: 10.1039/C9CY01209E
1
1
1
6
7
8
R. Zhong, Z. Zhang, S. Luo, Z. C. Zhang, L. Huang and M. Gu, Catal. Sci. Technol., 2019, 9,
5-85.
S. Sun, Q. Chi, H. Zhou, W. Ye, G. Zhu and P. Gao, Int. J. Hydrogen Energy., 2019, 44,
553-3559.
X. Hu, S. Lu, J. Tian, N. Wei, X. Song, X. Wang and H. Cui, Appl. Catal., B, 2019, 241,
29-337.
7
3
3
1
2
9
0
X. Wang, R. Xia, E. Muhire, S. Jiang, X. Huo and M. Gao, Appl. Surf. Sci., 2018, 459, 9-15.
R. Zhong, Z. Zhang, H. Yi, L. Zeng, C. Tang, L. Huang and M. Gu, Appl. Catal., B, 2018,
2
37, 1130-1138.
2
2
2
1
2
3
Y. Li, Z. Liu, Y. Wu, J. Chen, J. Zhao, F. Jin and P. Na, Appl. Catal., B, 2018, 224, 508-517.
X. Li, J. Xiong, J. Huang, Z. Feng and J. Luo, J. Alloy. and Compd., 2019, 774, 768-778.
T. Wang, X. Meng, G. Liu, K. Chang, P. Li, Q. Kang, L. Liu, M. Li, S. Ouyang and J. Ye, J.
Mater. Chem. A., 2015, 3, 9491-9501.
2
2
4
5
B. Liu, J. Wang, J. Yang and X. Zhao, Appl. Surf. Sci., 2019, 464, 367-375..
L. Ling, Y. Feng, H. Li, Y. Chen, J. Wen, J. Zhu and Z. Bian, Appl. Surf. Sci., 2019, 483,
7
72-778.
2
2
6
7
F. Fina, H. Menard and J. T. Irvine, Phys. Chem. Chem. Phys., 2015, 17, 13929-13936.
R. Shi, Y. Cao, Y. Bao, Y. Zhao, G. I. N. Waterhouse, Z. Fang, L. Z. Wu, C. H. Tung, Y. Yin
and T. Zhang, Adv. Mater., 2017, 29, 1700803.
2
2
3
8
9
0
Y. Zhang, G. Wang and Z. Jin, Int. J. Hydrogen Energy., 2019, 44, 10316-10327.
H. Yang, R. Cao, P. Sun, X. Deng, S. Zhang and X. Xu, Appl. Surf. Sci., 2018, 458, 893-902.
P. Sun, M. Qiu, M. Li, W. Mai, G. Cui and Y. Tong, Nano Energy., 2019, 55, 506-515.

Page 27 of 29
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY01209E
3
3
3
3
3
1
2
3
4
5
R. Song, W. Zhou, B. Luo and D. Jing, Appl. Surf. Sci., 2017, 416, 957-964.
X. Yue, S. Yi, R. Wang, Z. Zhang and S. Qiu, Nanoscale., 2016, 8, 17516-17523.
P. Liang, F. Wang and Z.-A. Hu, Chem. Eng. J., 2018, 350, 627-636.
S. K. Bikkarolla and P. Papakonstantinou, J. Power Sources., 2015, 281, 243-251.
X. Chen, J. Zhang, Y. Huang, Z. Tong and M. Huang, J. Environ. Sci-China., 2009, 21,
296-1301.
Y. Feng, J. Liu, D. Wu, Z. Zhou, Y. Deng, T. Zhang and K. Shih, Chem. Eng. J., 2015, 280,
14-524.
1
3
6
5
3
3
3
7
8
9
W. Chang, W. Xue, E. Liu, J. Fan and B. Zhao, Chem. Eng. J., 2019, 362, 392-401.
S. M. N. Jeghan and M. Kang, Mater. Res. Bull., 2017, 91, 108-113.
M. Kebir, M. Trari, R. Maachi, N. Nasrallah, B. Bellal and A. Amrane, J. Environ. Chem.
Eng., 2015, 3, 548-559.
4
4
4
0
1
2
M. Jiang, Y. Gao, Z. Wang and Z. Ding, Appl. Catal., B., 2016, 198, 180-188.
S. M. N. Jeghan, J. Y. Do and M. Kang, J. Ind. Eng. Chem., 2018, 57, 405-415.
A. Pendashteh, S. E. Moosavifard, M. S. Rahmanifar, Y. Wang, M. F. El-Kady, R. B. Kaner
and M. F. Mousavi, Chem. Mater., 2015, 27, 3919-3926.
4
4
3
4
Y. Li, X. Feng, Z. Lu, H. Yin, F. Liu and Q. Xiang, J. Colloid Interface Sci., 2018, 513,
8
66-876.
X. Lu, J. Xie, S.-y. Liu, A. Adamski, X. Chen and X. Li, ACS Sustain. Chem. Eng., 2018, 6,
3140-13150.
1
4
4
5
6
K. Liu, Y. Song and S. Chen, Nanoscale., 2015, 7, 1224-1232.
X. Du, X. Zhang, Z. Xu, Z. Yang and Y. Gong, Int. J. Hydrogen Energy., 2018, 43,

Catalysis Science & Technology
Page 28 of 29
View Article Online
DOI: 10.1039/C9CY01209E
5
012-5018.
4
7
S. K. Md Saad, A. Ali Umar, M. I. Ali Umar, M. Tomitori, M. Y. Abd. Rahman, M. Mat
Salleh and M. Oyama, ACS Omega., 2018, 3, 2579-2587.
4
4
8
9
S. Vijayakumar, S.-H. Lee and K.-S. Ryu, Electrochim. Acta., 2015, 182, 979-986.
Y. Liu, B. Zhang, L. Luo, X. Chen, Z. Wang, E. Wu, D. Su and W. Huang, Angew. Chem.
Int. Ed. Engl., 2015, 54, 15260-15265.
5
5
0
1
L. Keyan and X. Dongfeng, J. Phys. Chem. A., 2006, 110, 11332-11337.
Z. Zheng, B. Huang, X. Meng, J. Wang, S. Wang, Z. Lou, Z. Wang, X. Qin, X. Zhang and Y.
Dai, Chem. Commun. (Camb)., 2013, 49, 868-70.
5
2
X. Qiu, M. Miyauchi, K. Sunada, M. Minoshima, L. Min, L. Yue, L. Ding, Y. Shimodaira, Y.
Hosogi and Y. Kuroda, Acs Nano., 2012, 6, 1609-1618.
5
5
3
4
G. Dai, S. Liu, Y. Liang and T. Luo, Appl. Surf. Sci., 2013, 264, 157-161.
S. Hu, P. Qiao, L. Zhang, B. Jiang, Y. Gao, F. Hou, B. Wu, Q. Li, Y. Jiang, C. Tian, W.
Zhou, G. Tian and H. Fu, Appl. Catal., B, 2018, 239, 317-323.
5
5
5
6
J. Fu, C. Bie, C. Bei, C. Jiang and J. Yu, ACS Sustain. Chem. Eng., 2018, 6, 2767-2779.
J. Zhang, M. Vasei, Y. Sang, H. Liu and J. P. Claverie, ACS Appl Mater Inter., 2016, 8,
1
903-1912.
5
5
7
8
J. Jia, Q. Zhang, Z. Li, X. Hu, E. Liu and J. Fan, J. Mater. Chem. A., 2019, 7, 3828-3841.
S. Hua, D. Qu, L. An, W. Jiang, Y. Wen, X. Wang and Z. Sun, Appl. Catal., B, 2019, 240,
2
53-261.
5
6
9
0
B. Zhu, P. Xia, Y. Li, W. Ho and J. Yu, Appl. Surf. Sci., 2017, 291, 175-183.
W. Lei, Y. Mi, R. Feng, P. Liu, S. Hu, J. Yu, X. Liu, J. A. Rodriguez, J.-o. Wang, L. Zheng,

Page 29 of 29
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C9CY01209E
K. Tang, S. Zhu, G. Liu and M. Liu, Nano Energy., 2018, 50, 552-561.
61
62
63
R. Shen, J. Xie, X. Lu, X. Chen and X. Li, ACS Sustain. Chem. Eng., 2018, 6, 4026-4036.
W. J. Foo, C. Zhang and G. W. Ho, Nanoscale., 2013, 5, 759-764.
J. Si, S. Xiao, Y. Wang, L. Zhu, X. Xia, Z. Huang and Y. Gao, Nanoscale., 2018, 10,
2
596-2602.