Excellent degradation performance of 3D hierarchical nanoporous structures of copper towards organic pollutants

Article abstract of DOI:10.1039/C8TA07973K

Advanced oxidation processes provide a promising way to the degradation of organic pollutants in wastewater, wherein developing highly efficient catalysts is of paramount importance. Herein, three-dimensional (3D) hierarchical nanoporous structures of Cu catalysts with desirable geometries were synthesized by laser 3D printing combined with chemical dealloying. The resulting 3D nanoporous Cu (3D NP-Cu) exhibited a 660-fold larger specific surface area than conventional 2D ribbons or powder catalysts. The 3D NP-Cu catalysts exhibited high degradation efficiency towards azo dyes with a kinetic reaction constant of 0.147 min^?1, which is 14 times higher than that of the commercial catalyst of Cu²⁺ and 4 times higher than that of Cu⁰ powder. Impressively, the 3D NP-Cu exhibited fairly good reusability and excellent versatility, as indicated by the fast degradation of the mixture of complex dyes and reduction of the chemical oxygen demand (COD). The extraordinary catalytic activities of the 3D NP-Cu catalysts originated from their unique 3D hierarchical mill/nano-porous structures with large surface areas and numerous active atomic steps on Cu ligaments, which generate abundant active species and accelerate the transport of reactants. In addition, the presence of a small amount of Cu⁺ active species in the as-prepared 3D NP-Cu catalyst also played a critical role in promoting the degradation process, leading to the decomposition of azo dyes even in the absence of H₂O₂. Moreover, two possible pathways of degradation towards azo dyes were proposed based on liquid chromatograph-mass spectrometry analysis, i.e. reduction of azo bonds and demethylation of MO. The current work may inspire the development of new types of 3D nanostructured metal catalysts for remediation of wastewater.

Full text of DOI:10.1039/C8TA07973K

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
PAPER
Excellent degradation performance of 3D
hierarchical nanoporous structures of copper
towards organic pollutants †
Cite this: J. Mater. Chem. A, 2018, 6,
0992
2
Chong Yang,‡ Cheng Zhang ‡ and Lin Liu*
Advanced oxidation processes provide a promising way to the degradation of organic pollutants in
wastewater, wherein developing highly efficient catalysts is of paramount importance. Herein, three-
dimensional (3D) hierarchical nanoporous structures of Cu catalysts with desirable geometries were
synthesized by laser 3D printing combined with chemical dealloying. The resulting 3D nanoporous Cu
(3D NP-Cu) exhibited a 660-fold larger specific surface area than conventional 2D ribbons or powder
catalysts. The 3D NP-Cu catalysts exhibited high degradation efficiency towards azo dyes with a kinetic
ꢀ1
2+
reaction constant of 0.147 min , which is 14 times higher than that of the commercial catalyst of Cu
0
and 4 times higher than that of Cu powder. Impressively, the 3D NP-Cu exhibited fairly good reusability
and excellent versatility, as indicated by the fast degradation of the mixture of complex dyes and
reduction of the chemical oxygen demand (COD). The extraordinary catalytic activities of the 3D NP-Cu
catalysts originated from their unique 3D hierarchical mill/nano-porous structures with large surface
areas and numerous active atomic steps on Cu ligaments, which generate abundant active species and
+
accelerate the transport of reactants. In addition, the presence of a small amount of Cu active species
in the as-prepared 3D NP-Cu catalyst also played a critical role in promoting the degradation process,
Received 16th August 2018
Accepted 1st October 2018
2 2
leading to the decomposition of azo dyes even in the absence of H O . Moreover, two possible
pathways of degradation towards azo dyes were proposed based on liquid chromatograph-mass
spectrometry analysis, i.e. reduction of azo bonds and demethylation of MO. The current work may
inspire the development of new types of 3D nanostructured metal catalysts for remediation of wastewater.
DOI: 10.1039/c8ta07973k
rsc.li/materials-a
generation of free hydroxyl radicals ($OH) with strong oxidation
Introduction
0
potentials [E ($OH)/H
H O , which can react rapidly and non-selectively with almost
2 2
generated in various industries, have caused serious environ- all electron-rich organic compounds. Currently, the commer-
mental and water-security problems due to their non- cially available catalysts used in AOPs are Fenton reagents,
2
O ¼ +2.8 VNHE] by the decomposition of
Persistent organic pollutants (e.g., phenol and azo dyes),
16
1
–6
biodegradability, high carcinogenicity and toxicity.
Exploring new catalysts and efficient techniques to remove following limitations:
organic pollutants from wastewater has been an important ¼ 2–3), making degradation impossible outside acid environ-
subject worldwide in both catalytic materials and environ- ments; (2) low efficiency in utilizing H ; (3) generation of
Compared to the conventional iron-containing sludge which requires further disposal; (4)
which are mainly based on iron salts, but they have the
17–19
(1) a narrow pH working window (pH
2 2
O
7–13
mental science communities.
water treatment technologies, such as adsorption, biological difficulty in removal of the catalysts from the post-treated water
12
13
treatment, etc., advanced oxidation processes (AOPs) based on and poor reusability. Thus, development of new Fenton-like
the Fenton or Fenton-like reactions have attracted much solid catalysts with improved catalytic efficiency and dura-
attention and have already been devoted to practical applica- bility becomes a critical issue in wastewater treatment.
tions due to their capability in decomposing organic pollut-
ants.
Recently, metallic glasses (MGs) with unique disordering
14,15
The main mechanism of Fenton reactions is the atomic structures have emerged as promising catalysts for
20–27
degradation of organic pollutants from wastewater.
It was
reported that MGs exhibit higher efficiency and better reus-
State Key Laboratory of Material Processing and Die & Mould Technology, School of
Materials Science and Engineering, Huazhong University of Science and Technology,
ability in degrading dyeing wastewater than their crystallized
0
counterparts and conventional zero-valent metals (e.g. Fe ) due
4
†
1
‡
30074 Wuhan, China. E-mail: lliu2000@mail.hust.edu.cn; Tel: +86 27 87556894
Electronic supplementary information (ESI) available. See DOI:
0.1039/c8ta07973k
to their atomically disordering structures, high electron transfer
2
1,22,25
capability and chemical stability.
generation rate of $OH using Fe78Si
It was observed that the
Cu Nb
3
B
3
and Fe73.5Si13.5
B
9
1
These authors contributed equally.
9
20992 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
Journal of Materials Chemistry A
MG ribbons is one order of magnitude higher than that of the
Experimental
Preparation of 3D NP-Cu
2
+
currently used Fe-based catalysts (such as Fe , a-Fe O , a-
2
3
25
FeOOH, FeOCl) for wastewater treatment. As a result, the
degradation efficiency of Fe–B MG ribbons is 89 times higher The amorphous powders with a nominal composition of Zr -
5
5
than that of the commercial Fe powder in the degradation of Cu Ni Al (at%) were prepared by gas atomization technique,
3
0
5
10
28
direct blue 6. The Fe-based MG catalysts also showed excellent and the powders with a size less than 30 mm were sieved out for
versatility for rapid degradation of a mixture of various the SLM 3D printing of the MG networks. The 3D printing
hazardous azo dyes, including methyl orange, methyl blue, experiments were performed using a commercial SLM 3D
21,22,29
phenol, direct blue 6, etc.
In addition, Al-based and Mg- printing machine (Forwedo LM-120) equipped with a YAG ber
based MGs were recently explored as efficient Fenton-like laser device with a maximum power output of 500 W and typical
30
catalysts. Wang et al. reported that the Al–Ni–Y MG ribbons laser spot diameter of 80 mm. The forming chamber was vac-
could directly decolorize blue 2B in both alkaline and acidic uumed rst and then protected with argon gas (kept the oxygen
environments due to the low activation energy for the reactions content below 100 ppm). The principle of SLM 3D printing is
and the formation of nanoporous structures on the surface of sketched in Fig. 1 (see upper-le inset), wherein the network
the MGs. Instead of MG ribbons, MG powders were also used as components were manufactured by laser selective melting
a new form of catalyst, because powders could bear larger according to the CAD designed data of the components. The
21
specic surface areas as compared to ribbons. Wang et al.
reported that the ball-milled MG powders with rough surfaces observed in our previous works.
detailed processes and parameters of 3D printing can be
35,36
To obtain the nanoporous
exhibited nearly 1000 times higher degradation efficiency than structure of Cu, chemical dealloying was applied to the pre-
0
the commercial Fe powders for methyl orange degradation. To printed MG specimens with lattice geometries in a mixing
further enhance the specic surface area and degradation effi- aqueous solution containing hydrouoric acid (HF, 0.008 M)
ciency, construction of nanoporous (NP) structures on the MG and sulphuric acid (H SO , 1.0 M) under a free corrosion
2
4
ribbons or powders by means of chemical dealloying has been condition for 60 h. The as-dealloyed specimens were subse-
3
1,32
ꢂ
intensively studied in recent years.
In our previous studies, quently annealed at 400 C for 2 h to stabilize the nanoporous
33
Deng et al. developed a NP Cu catalyst with a controllable pore structure and to enhance the adhesion of the porous layer with
size (from 20–50 nm) by chemical dealloying of the MgCuGd the substrate.
MG ribbons, which exhibited superior degradation capability
toward phenol as compared to the normal MG ribbons and pure
34
Cu plates. Lately, Wang et al. observed that the catalyst of NP- Structural characterization
Cu powders fabricated by dealloying of ZrCuNiAl MG powders
The microstructure and composition of the as-prepared three-
in a diluted HF solution showed the versatility for degradation
of methyl orange in both acidic and neutral environments.
However, the challenge for nanoporous powder catalysts is the
dimensional nanoporous specimens (hereaer denoted as 3D
NP-Cu) were examined by X-ray diffraction (XRD, X'Pert PRO)
with Cu Ka radiation, scanning electron microscopy (FESEM,
Sirion 200) and transmission electron microscopy (TEM, Tecnai
G2 F20) coupled with energy dispersive X-ray spectroscopy
18,27
irretrievability in practical applications.
In this work, we present a novel bulk Cu catalyst with three-
dimensional hierarchically porous structures fabricated by the
combination of laser 3D printing and chemical dealloying
techniques, in which the 3D printing technique (based on
selective laser melting-SLM) was used to fabricate MG lattice
precursors with milli-porous network structures; subsequently
chemical dealloying was applied to produce nanoporous
structures on the surface of the 3D-printed MG frameworks. It
is found that these 3D nanoporous structures exhibit
(EDX). The specic surface area of the 3D NP-Cu sample was
measured by the Brunauer–Emmett–Teller (BET, ASAP2020)
ꢁ
660-fold larger specic surface areas than the conventional
MG ribbons and powders, thus showing high degradation
efficiency of towards organic pollutants. The resulting 3D
nanoporous structures of Cu (3D NP-Cu) exhibit superior
degradation efficiency towards azo dyes than the conventional
2
+
0
0
2 2
Fenton-like catalysts (such as Cu /H O , Cu and Fe powders
and 2D Cu nanoporous ribbon). Moreover, the 3D NP-Cu
shows good versatility to degrade complex azo dyes (i.e., the
mixture of different dyes) and to remove chemical oxygen
demand (COD) with high efficiency. It is revealed that the
excellent catalytic properties of 3D NP-Cu are attributed to the
Fig. 1 A schematic diagram showing various geometries of the 3D-
printed bulk metallic glasses (BMGs) in the order of specific surface
area. The insets illustrate the principles of selective laser melting (SLM)
3
D hierarchically porous conguration and unique micro-
structural features.
(upper-left) and dealloying (lower-right) techniques.
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. A, 2018, 6, 20992–21002 | 20993

View Article Online
Journal of Materials Chemistry A
Paper
technique. The structure and composition of the samples aer created on the surface of the 3D-printed frameworks by means
the degradation treatment were analyzed with SEM, TEM and of chemical dealloying in diluted HF solution (the details can be
XPS (X-ray photoelectron spectrometer VG MultiLab-2000) with seen in experimental section). Fig. 1 shows the 3D-printed
Al Ka excitation. All the binding energies were referenced to ZrCuNiAl MG frameworks with various geometries, including
the C 1s peak at 284.6 eV of surface adventitious carbon for XPS cube, 1D hollow, sandwich, 3D hollow and lattice structures,
measurements.
presented in the order of specic surface areas. Of all geome-
tries, the lattice structure has the largest specic surface area of
ꢀ
3
2
ꢀ1
2
.3 ꢃ 10 m g , and therefore was selected for the chemical
Degradation experiments
dealloying treatment in this study. The red-like appearance of
the sample shown in Fig. 1 indicates the formation of nano-
porous Cu on the surface of the latticed MGs aer the deal-
loying treatment.
Dye(s) degradation experiments were conducted in a 50 mL
conical ask under magnetic stirring and a uorescent lamp
ꢀ
2
(
with a light intensity of 0.960 mW cm ). The organic pollut-
ants, such as methyl orange (MO, C14 SO Na), Congo red
CR, C32 Na ), rhodamine B (RhB, C28 31ClN ),
methyl blue (MB, C37 Na ) and acid orange II (AO II,
C H N NaO S) were provided by Sinopharm Chemical
H
14
N
3
3
The surface and cross-sectional morphologies of the fabri-
cated 3D NP-Cu are shown in Fig. 2a and b, respectively, which
(
H
22
N
6
2
O
6
S
H
2
H
2 3
O
27
N
3
2 9 3
O S
indicate that
a homogeneous bi-continuous nanoporous
1
6
11
2
4
conguration with an average pore size of ꢁ90 nm (the pore size
distribution is shown in Fig. S1†) and thickness of ꢁ7.5 mm was
successfully prepared by dealloying and subsequently anneal-
ing treatment. The XRD pattern in Fig. 2c indicates the forma-
tion of a layer of Cu crystallites on the 3D-printed MG network
surface with a trace amount of the Cu O phase. The surface
2
composition and electronic structure of the 3D NP-Cu were
further examined by XPS. The binding energies at 932.2 eV and
ꢀ
1
Reagent Co., Ltd (Shanghai, China). A xed dosage of 27.2 g L
3
of the 3D NP-Cu samples (10 ꢃ 10 ꢃ 10 mm ) was used as the
catalyst for each of the following degradation experiments.
ꢀ
1
50 mL of the MO solution (containing 20 mg L of MO) and
ꢀ
1
a mixing solution with ve different dyes (containing 4 mg L
each) were taken as the simulated wastewaters. Aer the pH
value was xed at 2 by adjustment with H SO solution (1 M),
various amounts of H O (0–12 mM) were added into the solu-
tions using a pipette. Water specimens were sampled at pre-
determined time intervals, and methanol was employed
immediately to quench the reaction for further analysis. The
UV-vis spectrometer (Lambda 25, PerkinElmer) was used for
measuring the dye concentration. The maximum absorbance of
the ve dyes was recorded as 510 nm for MO, 495 nm for CR,
2
4
2
2
9
34.7 eV in a high-resolution XPS spectrum of Cu 2p3/2 corre-
0
+
spond to Cu and Cu , respectively, verifying the existence of
metallic Cu and a minor fraction of Cu O (ꢁ10 vol%) in the 3D
2
3
7
NP-Cu layer. The formation of Cu O could probably result from
2
the oxidation of nanoscale Cu ligaments using the dissolved
oxygen in dilute HF solution during the dealloying process.
Actually, a metastable Cu
stable CuO in nanostructures,
2
O phase is oen formed prior to
554 nm for RB, 664 nm for MB and 482 nm for AO II, respec-
40,41
such as nanopores and
tively. Chemical oxygen demand (COD) in the post-treated
solutions was measured with a COD reactor (HACH DRB200)
and HACH DR 3900 spectrophotometer. For quantitative anal-
ysis of the hydroxyl radical ($OH), the generation rate of $OH
was calculated according to a method reported in the litera-
nanoparticles, because the former has a higher symmetry,
leading to easy formation and high stability in the dealloying
process. The specic surface area of the nanoporous layer was
determined by BET measurements, yielding a specic surface
2
ꢀ1
area of approximately 6.0 m g , which is more than 660 times
38,39
ture,
in which benzoic acid was used as a probe. For analysis
of reusability, the identical 3D NP-Cu samples were reused
throughout dye degradation 5 times. Aer each time, the
samples were taken out from the breaker and then washed
using distilled water followed by ultrasonic cleaning before the
samples were used as catalysts again. To better understand the
degradation pathway, the degradation intermediates were
examined by liquid chromatography-mass spectrometry
(LC-MS, 1100 LC/MSD Trap, Agilent) with a C18 column of
2
3
50 mm ꢃ 4.6 mm. The column temperature was maintained at
ꢂ
0 C and the injected sample volume was 20 mL. LC-MS accu-
rate mass spectra were recorded across the range 50–500 m/z.
Results
Fabrication and microstructure characterization of the 3D
NP-Cu
The fabrication of 3D nanoporous structures involves two steps:
Fig. 2 SEM images of (a) top-surface and (b) cross-section of the as-
prepared three-dimensional nanoporous Cu (NP-Cu). (c) XRD pattern
and (d) XPS spectra of Cu 2p3/2 of the 3D NP-Cu prepared on the
(i) macroscale porous frameworks of Zr-based MG precursors
were rst prepared by SLM 3D printing of the amorphous
powders, and (ii) the nanoporous structure was subsequently lattice-BMG.
20994 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
Journal of Materials Chemistry A
larger than that of MG ribbons or powders (around concentration of methyl orange (MO). As the AOPs are normally
2
ꢀ1
0
.009 m g ).
The detailed microstructures of the 3D NP-Cu are further dation performance, therefore, we rst carried out an individual
examined by high resolution TEM coupled with EDX mapping, study of the effect of pH value, H O dosage and temperature,
parameter-dependent and many factors may affect the degra-
2
2
as shown in Fig. 3. Fig. 3a veries again that the nanoporous respectively, on the degradation of MO to understand the
structures of the dealloyed products were composed of nano- degradation mechanism and which factor plays a more
pores and nano-ligaments. The selected area electron diffrac- important role. Fig. 4a presents the UV-vis spectra of MO
tion (SAED) pattern ts well with the pattern of fcc poly- degradation using the 3D NP-Cu catalyst at various time inter-
ꢂ
crystalline Cu, and is in line with the XRD results shown in vals at 65 C, while keeping the pH ¼ 2 and H
2
O
2
¼ 6 mM
Fig. 2c. Note that the diffraction rings of Cu O were not constant. The characteristic absorption peak at 510 nm corre-
2
observed in the SAED pattern which is most likely due to the sponds to the azo chromophore (–N]N–), whose intensity is
small amount of the phase, and the peeling-off of Cu O during proportional to the concentration of MO. It can be see that the
2
2
the preparation of the TEM samples, as the Cu O phase is only peak intensity rapidly decreased aer 5 min and became
distributed on the most-exterior of the 3D NP-Cu samples. The invisible aer 10 min, signifying a fast degradation process
high-resolution TEM images in Fig. 3b clearly reveal a number using the 3D NP-Cu catalyst. Fig. 4b shows the effect of pH
of atomic steps on the Cu (111) planes, which plays an impor- values on the degradation rate (in terms of C
tant role in the enhancement of the catalytic properties of 3D are the dye concentration at time t and the original state,
and will be discussed in later sections. In addition, respectively). It is noted that the degradation rate was much
t 0 t
/C , where C and
C
0
42–45
NP-Cu,
the Cu O nanocrystals were also observed adjacent to the Cu faster at pH ¼ 2 (referring to an acidic environment) than at pH
2
ligaments as shown in Fig. 3c. The inverse fast Fourier trans- ¼ 7 (corresponding to an neutral environment). For example,
form (IFFT) pattern from the boxed region in Fig. 3c indicates the degradation of MO was nearly completed within 30 min at
that the Cu
Cu O (200)//Cu (111). The STEM image and compositional interval, demonstrating that the 3D NP-Cu catalyst works more
mappings of a representative ligament are shown in Fig. 3e–g, effectively in acidic environments. Regarding the effect of H
suggesting a homogenous distribution of Cu and O in the dosage, one can see in Fig. 4c, with the increase of H dosage
2
O phase has coherent relations with Cu in terms of pH ¼ 2, but only degraded by 40% at pH ¼ 7 in the same time
46
2
2 2
O
2 2
O
ligament, which implies that the Cu O phase, although in from 0 to 6 mM, the degradation efficiency is continuously
2
a trace amount, was homogeneously distributed on the 3D enhanced. However, further increasing the H O dosage up to
2
2
NP-Cu surface.
12 mM could inversely decrease the degradation efficiency,
suggesting that there exists a critical concentration of H
2 2
O
dosage for the degradation, which is roughly around 6 mM or
more. This phenomenon is due to the fact that, an excess
Catalytic performance of 3D NP-Cu towards dye degradation
Degradation tests of azo dyes were carried out by immersing the
amount of H
2
O
2
promotes the generation of less-active hydro-
$) by consuming the active radicals of
OH. Similar results were also reported in other Fenton-like
3D NP-Cu catalyst in water solution containing a certain
peroxyl radicals (HO
2
47
$
3
3,34
Cu-based catalysts.
As far as the temperature effect was
Fig. 3 TEM characterization of the 3D NP-Cu. (a) Bright-field TEM
image and the corresponding SAED pattern of the nanoporous Cu. (b)
High-resolution TEM micrograph showing the atomic steps on the
surface of a Cu ligament. (c) HRTEM image of Cu
2
O nanoparticles and Fig. 4 (a) UV absorption spectrum of MO solutions degraded using 3D
ꢂ
(
d) an inverse fast Fourier transform (IFFT) from the interface of Cu and NP-Cu for different time intervals at 65 C. (b) Effect of pH values, (c)
Cu
2
O. (e–g) HAADF-STEM image and element mappings of a repre- effect of H
2
O
2
dosage and (d) effect of reaction temperature on the
sentative ligament in NP-Cu.
MO degradation efficiency using of 3D NP-Cu.
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. A, 2018, 6, 20992–21002 | 20995

View Article Online
Journal of Materials Chemistry A
Paper
concerned, it was found that the degradation efficiency of 3D
NP-Cu increased continuously with increasing temperature
ꢂ
ꢂ
from 35 C to 65 C (see Fig. 4d) under the same H O dosage
2
2
(
6 mM) and pH value (pH ¼ 2). For example, the degradation
ꢂ
process was completed within 10 min at 65 C, which is only 1/3
of the time required for a complete degradation at 35 C.
ꢂ
As the degradation reaction is a thermal activation process,
the activation energy for the degradation of MO could be
calculated by the following Arrhenius-type equation:
ln k ¼ ꢀDE/RT + ln A
(1)
T
where k
T), A is a time pre-factor and R is the gas constant, and DE is the
activation energy for degradation. Based on the results shown in
T
is the reaction rate constant at different temperatures
(
ꢀ1
Fig. 4d, eqn (1) yields an activation energy (DE) of 30.6 kJ mol
for the degradation of MO using the 3D NP-Cu catalyst. This
value is much lower than that of Fe73Si
7
B
3
17Nb glassy powder
ꢀ
1
21
(78–114 kJ mol ) for similar treatment, indicating that
the degradation reaction is much easier to trigger by using 3D
NP-Cu than using MG ribbons and powders.
Fig. 5a shows the comparison of the MO degradation effi-
ciency by using 3D NP-Cu and other catalysts including homo-
2
+
geneous Fenton reagent Cu (in the form of cupric salt),
0
zero-value metal Cu , Fe-based MG ribbons and the controls
(
2
without adding any catalyst or H
% of MO was degraded, if solely applying H
any catalysts, implying that the decomposition of H
2
O
2
). It can be seen that only
(6 mM) without
itself to
2 2
O
2 2
O
generate $OH radicals is quite sluggish. However, the degra-
dation efficiency was highly enhanced by using 3D NP-Cu, as
indicated by the fact that complete degradation was achieved
within 10 min, which is much faster than in the cases of using
2
+
0
Cu and Cu powders (which are only about 10% and 30% of
degradation in the same time period, respectively). Interest-
2 2
ingly, even in the absence of H O , the degradation efficiency of
the 3D NP-Cu remains high enough, e.g., almost 99% of MO was
degraded within 30 min, probably due to the catalytic effect of
pre-existing Cu O, and this will be discussed in the later section.
2
Fig. 5 (a–c) Comparisons of the degradation efficiency and reaction
rate constant of the 3D NP-Cu with other commonly used catalysts.
ꢂ
Fig. 5b shows that the MO degradation curves followed the Experimental conditions: pH ¼ 2, [H O ] ¼ 6 mM, and temp ¼ 45 C.
2
2
pseudo-rst-order reaction kinetic model, from which the
reaction rate constant (k) can be calculated from the slopes of
results are shown in Table 1, which indicates that the rate
t 0
ln(C /C )–t plots and the results using different catalysts are
ꢀ
5
ꢀ1
constant of $OH using 3D NP-Cu is about 7.21 ꢃ 10
s , three-
shown in Fig. 5c. It can be seen that the reaction rate constant
times higher than that of the commercial Fenton-like reagent of
ꢀ1
for the 3D NP-Cu is 0.147 min , which is almost 14 times and 4
times higher than that of the homogeneous Fenton reagent
2
+
ꢀ5 ꢀ1
Cu (2.40 ꢃ 10
s ), demonstrating that the 3D NP-Cu cata-
lyst developed in this work exhibits a high degradation
efficiency.
2
+
0
(

Cu ) and Cu powders, respectively. The more interesting
nding is that the k value of 3D NP-Cu without H is also high
i.e., k ¼ 0.112 min ), compared to other well-known Fe-based
2 2
O
To examine the versatility of the 3D NP-Cu catalyst for the
degradation of different azo dye compounds, a mixture of ve
ꢀ
1
(
0
48
Fenton reagents, such as Fe powder, and Fe B Si Y (ref. 22)
and Fe73.5Si13.5B Nb Cu MG ribbons. Note that the degrada-
9 1 3
7
6
12
9 3
18
Table 1 Comparison of generation rate constant of $OH (k$OH) and
TOF value of 3D NP-Cu with the other various Cu-based Fenton-like
catalysts
tion efficiency and reaction rate constant are closely related to
the generation rate of $OH in Fenton-like reactions; the high
degradation efficiency and rate constant of 3D NP-Cu implies
that this porous catalyst could itself generate $OH in the Materials
degradation processes. In order to quantify the generation rate
ꢀ1
ꢀ1
k
$OH (s
)
TOF (s )
2
+
ꢀ5
ꢀ6
ꢀ3
ꢀ3
Cu
2
3
2.40 ꢃ 10
5.65 ꢃ 10
7.21 ꢃ 10
2.2 ꢃ 10
2.7 ꢃ 10
3.5 ꢃ 10
of $OH by using 3D NP-Cu, benzoic acid (BA) which can freeze
ꢀ5
D NP-Cu
D NP-Cu
49
$
OH radicals was used as a probe for the measurements. The
ꢀ5
20996 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
Journal of Materials Chemistry A
typical emerging contaminants, including methyl orange, acid
orange II, Congo red, rhodamine B and methyl blue, were used
as pollutants. When the ve different dyes were mixed together
in the solution, the characteristic peaks of each dye overlapped
with each other, yielding only three main characteristic peaks
located at 515, 554 and 629 nm respectively (Fig. S2(a)†). Here,
we choose the strongest peak at 554 nm for determining the
decolorization ability of the 3D NP-Cu. Actually, the analyses
using the other two characteristic peaks at 515 and 629 nm also
gave rise to similar results (Fig. S2(b)†). The decolorization of
the mixed dyeing solution is shown in Fig. 6. It can be seen that
degradation is almost completed within 30 min, demonstrating
again that the 3D NP-Cu exhibits a very high degradation effi-
ciency for complex pollutants. In addition, the COD value,
which is an important parameter to evaluate the quality of
puried water, was also examined in the mixed pollutants.
Similar to the degradation process of azo dyes, the 3D NP-Cu
catalyst also exhibited an excellent catalytic properties in
reducing the COD. For example, the COD of the mixed pollut-
ants was decreased by 92% aer 30 min of degradation (see
Fig. 6).
Fig. 7 Degradation of MO solution with the 3D NP-Cu at different
cycles.
Reusability
The reusability of the 3D NP-Cu catalyst was evaluated by recy-
cling experiments. Fig. 7 shows the change in degradation
efficiency aer 5 cycles (20 min for each cycle). Although the
degradation efficiency reduced slightly with increasing cycle
numbers, the degradation efficiency remained about 90% aer
5
cycles, demonstrating that the 3D NP-Cu catalyst has fairly
good stability and reusability. To clarify if there are any changes
in the microstructure of the 3D NP-Cu catalyst aer the degra-
dation treatment, the sample aer the rst cycle was further
investigated by SEM, XPS and TEM. SEM showed that two
typical regions with different surface morphologies could be
identied (see Fig. 8a and b), the rst one, which was the
majority, still kept the nanoporous structure unchanged
Fig. 8 (a and b) SEM morphologies and EDX analysis; (c) XPS spectra
and (d) dark-field TEM image of the 3D NP-Cu after the first cycle.
(
Fig. 8a), while the second one exhibited a nanoower-like
(
Fig. 8b), indicating the occurrence of oxidation of nanoporous
morphology enriched with a high content of O (45.52%)
Cu during the degradation process.
To identify the products of the oxidized regions, XPS
measurements were conducted and the results are shown in
Fig. 8c, which correspond to the Cu 2p XPS spectra. The peaks
0
located at 932.2 eV and 952.2 eV correspond to Cu , peaks at
9
34.7 eV and 954.0 eV correspond to Cu(I), and the two addi-
7,40
tional peaks at 943.0 eV and 963.0 eV correspond to Cu(II).
Based on the area of each peak, the relative content of Cu0, Cu(I)
and Cu(II) on the 3D NP-Cu surface was calculated to be around
35%, 37% and 28%, respectively, implying that the oxidation
led to the formation of both Cu O and CuO (Cu O was the
2
2
majority). Fig. 8d shows the dark-eld (DF) TEM image and
corresponding SAED pattern of the 3D NP-Cu aer the rst cycle
of degradation. The SAED pattern (inset in Fig. 8d) indicates the
2
existence of Cu and Cu O. The absence of any diffraction signals
Fig. 6 The degradation rate and COD removal of the mixture solution
consisting of five different dyes, including methyl orange, acid orange
of CuO in the SAED pattern may be due to the small amount of
the phase formed and relatively weak diffraction of CuO with
respect to metal Cu. The dark-eld TEM image taken from the
diffraction of Cu O (200) indicates that the Cu O nanoparticles
II, Congo red, rhodamine B and methyl blue (pH ¼ 2, [H
2
2
O ] ¼ 6 mM).
The inset showing a photograph of the solution mixture before and
after degradation.
2
2
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. A, 2018, 6, 20992–21002 | 20997

View Article Online
Journal of Materials Chemistry A
Paper
(the bright contrast) distributed homogeneously on the surfaces Cu, as conrmed by the subsequent XRD examination (see
of the Cu ligaments. It will be demonstrated that the formation Fig. S4†). Fig. 9b shows the comparison of the degradation
of the Cu O phase in the degradation process played a crucial efficiency between H -reduced 3D NP-Cu and the original 3D
2
2
role in obtaining high degradation efficiency and good NP-Cu samples. It is clearly shown that the H -reduced sample
2
reusability.
exhibited a remarkably slower degradation efficiency than the
un-treated one. This result indicates that Cu O nanoparticles in
D NP-Cu played a positive role in the degradation of MO. Since
the existence of Cu O nanoparticles has been readily veried on
2
both the as-prepared and post-degraded 3D NP-Cu samples (see
2
3
Discussion
Origins of high catalytic performance of 3D NP-Cu
The aforementioned results demonstrate that the 3D NP-Cu the results above), the good reusability and high degradation
developed in this work is a promising catalyst for the degrada- efficiency of the 3D NP-Cu catalyst even without adding H
tion of azo dyes with high degradation efficiency. The degra- can be reasonably understood.
O
2 2
dation may also involve the adsorption of MO due to the fact
Based on the above analyses and microstructure character-
that the 3D NP-Cu has a large specic surface area. To clarify ization, the catalysis mechanism for the degradation of azo dyes
this issue, we also measured the decolorization performance of using 3D NP-Cu is proposed in Fig. 10. Initially, the dyes and
the 3D NP-Cu sample without adding H
2
O
2
(Ar gas purge and
2 2
H O molecules were adsorbed on the surface of the 3D NP-Cu
under dark condition). The results (Fig. S3†) demonstrated that catalyst, especially at those active sites, such as atomic steps of
41,46
the adsorption using 3D NP-Cu indeed has some effects on the Cu ligaments and Cu
removal of MO, but the degradation process plays a more reactions were triggered. The degradation mechanisms could
important role in the fast decolorization of MO. For example, be described as follows:
O nanocrystals,
where the degradation
2
34,50
within the reaction time of 10 min, only 35% MO was removed
by the adsorption process, but 80% of MO was removed by
degradation. As matter of a fact, the adsorption process is the
+
Cu + H
2+
ꢀ
4
ꢀ1 ꢀ1
s
2
O
2
/ Cu + OH + $OH (k ¼ 1.0 ꢃ 10 M
)
(
2)

rst step of degradation of MO molecules. To understand the
+
+
2+
Surface-Cu + H O / H O + Cu (aq.) + $OH
(3)
2
2
3
physical origin of the high catalytic activity of 3D NP-Cu, we
need to determine the role of the specic active species and
their contributions to the degradation performance. In classic
Cu-based Fenton-like reactions, the $OH and Cu(I) are regarded
2+
Cu + H
+
+
2
ꢀ1 ꢀ1
s )
2
O
2
/ Cu + H + $HO
2
(k ¼ 4.6 ꢃ 10 M
(4)
7,34
to be the active species in degradation of azo dyes.
Accord-
ingly, to understand the individual role of $OH and Cu(I) on the
degradation of MO, we herein employed isopropyl alcohol (IPA,
Clearly, the generation of highly active $OH mainly results
+
from eqn (2) and (3) through decomposition of H
indicating that the existence of the Cu O phase plays a crucial
role in the degradation of azo dyes. The generated Cu can be
2 2
O using Cu ,
20 mM) and 2,9-dimethyl-1,10-phenanthroline (DMP, 10 mM)
2
as the scavengers of $OH and Cu(I), respectively, in the degra-
dation process. As shown in Fig. 9a, the degradation efficiency
of 3D NP-Cu decreased dramatically with the addition of DMP
2+
+
2 2
reduced back to Cu using H O according to eqn (4), but this
reaction is relatively sluggish as the generation rate constant of
[the Cu(I) scavenger], while only slightly decreased with the
2
ꢀ1 ꢀ1
$
HO (k ¼ 4.6 ꢃ 10 M
s ) is two orders of magnitude smaller
2
addition of IPA (the $OH scavenger). This indicates that the $OH
and Cu(I) in the solution are both active species, but Cu(I) plays
a more important role in the degradation of MO.
4
ꢀ1 ꢀ1
than eqn (2) (k ¼ 1.0 ꢃ 10 M
s ). Therefore, the overall
degradation efficiency could be controlled by eqn (4). The high
catalytic activity of 3D NP-Cu is mainly due to the existence of
To clarify the role of Cu
2
O nanoparticles in the degradation
+
abundant active species of Cu stemming from the pre-
efficiency, the 3D NP-Cu sample was rst reduced using H
2
at
2+
2
existence of Cu O and reduction of Cu , which results in the
ꢂ
300 C for 3 h and then subjected to degradation experiments.
generation of a large amount of $OH and the continuity of the
degradation process until completion. Note that the reaction in
2
Aer such treatment, Cu O was completely reduced to metal
Fig. 9 (a) MO degradation efficiency with the 3D NP-Cu in the pres-
ence of DMP as the Cu(I) scavenger and IPA as the $OH scavenger, as
compared with the case without a scavenger. (b) Comparison of
degradation efficiency between 3D NP Cu and H
2
reduced 3D NP-Cu. Fig. 10 The mechanism of MO degradation using 3D NP-Cu.
20998 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
Journal of Materials Chemistry A
eqn (3) is pH dependent and $OH can only form at the pH values
50
of less than 3.4 (i.e., in acidic environments). As such, the
effectiveness of Cu O would be declined at the neutral
2
environment, which is responsible for the low degradation
efficiency of 3D NP-Cu at pH ¼ 7 (see Fig. 4b).
However, the question then arises as to why the 3D NP-Cu
retains a high MO degradation efficiency in the absence of
2 2
H O . This phenomenon could be attributed to the following
+
two factors. First, Cu is capable of directly decomposing MO by
51
the following Sandmeyer reaction (5):
+
2+
Surface-Cu + –N]N– / R$ + Cu
(5)
Fig. 11 Comparison of the degradation efficiency of 3D NP-Cu and
+
O(h + e )
ꢀ
Cu
2
O + hv(vis) / Cu
2
(6) 2D NP-Cu towards degradation of MO. The 2D NP-Cu sample was
prepared by chemically dealloying a Zr55Cu30Ni
ribbon.
5
Al10 metallic glass
+
+
Cu O(h ) + H O / $OH(Cu O) + H
(7)
2
2
2
+
ꢀ
Cu
2
O(h ) + OH / $OH(Cu
2
O)
(8)
(9)
into $OH per second on one active site, was further calculated
ꢀ
ꢀ
38
Cu O(e ) + O / $O (Cu O)
2
2
2
2
according to the following equation:
V
ꢄ
OH
V
where R$ is the carbon center radicals. Second, Cu
semiconductor with a band gap of 2.0–2.2 eV (ref. 40) can be
activated by the visible light of the uorescent lamp used in the
2
O, as a p-type
TOF ¼
(10)
n
Cu;surf
where V$OH is the generation rate of the $OH radical and nCu,surf
is the number of active sites on the surface of the catalyst and V
is the volume of solution. Typically, the unsaturated Cu atoms
exposed on the surface are considered as the active sites.
Based on the TEM observations, the density of unsaturated
degradation experiments and generate valence band holes
ꢀ
through eqn (6), which subsequently react with H
2
ꢀ
O, OH or O
2
to produce active free radicals ($OH and/or $O ) through eqn
2
52
(
7–9). Ultimately, these free radicals oxidize pollutants into
1
9
2
inorganic or nontoxic materials. Especially, the nano-sized Cu
ligaments are benecial in transferring photo-induced elec-
trons and enhancing the separation efficiency of electron–hole
Cu atom was calculated to be 1.77 ꢃ 10 atom per m for Cu
1
9
2
(
111) plane and 1.91 ꢃ 10 atom per m and Cu
respectively. The Cu O nanoparticle takes around 10% of the
surface in the 3D NP structure. As such, the nCu,surf could be
estimated by using the following equation: nCu,surf ¼ ACu
densityCu,uc + ACu2O ꢃ density and the calculated TOF
2
O (111) plane,
2
40,53
pairs.
Indeed, the effect of visible light was conrmed by
comparing the degradation efficiency under a uorescent lamp
and in darkness (see Fig. S5†). Therefore, the excellent degra-
dation performance of 3D NP-Cu is attributed not only to the
larger surface area, but also to the catalytic reactions driven by
ꢃ
2
Cu O,uc
value of 3D NP-Cu is summarized in Table 1. It is seen that the
ꢀ3
ꢀ1
TOF value of the 3D NP-Cu reaches as high as 3.5 ꢃ 10
s ,
the unique Cu/Cu O structures.
2
which is signicantly higher than that of 2D NP-Cu (2.7 ꢃ
ꢀ3 ꢀ1 2+
Secondly, the unique 3D mill/nano hierarchically porous
congurations should also display signicant advantages
over the conventional ribbon, powder and 2D nanoporous
catalysts in terms of utilization of active sites and adsorption
of dye molecules as well as transport of by-products. To
conrm this hypothesis, we compared the degradation effi-
ciency and reaction rate constant of 3D NP-Cu and 2D NP-Cu
1
(
0
s ) and classic homogeneous Fenton-like catalyst of Cu
ꢀ
6
ꢀ1
2.2 ꢃ 10
s
). Thus, 3D NP-Cu indeed manifests the highest
intrinsic activity over other Cu-based Fenton-like catalysts,
owing to the better utilization of active sites resulting from the
unique 3D porous structure.
Degradation pathways
(
which was fabricated by chemical dealloying of a Zr-based
MG ribbon) with almost the same apparent surface area To clarify the decomposition processes of MO by using the 3D
2
(
ca. 484 mm ). The results (Fig. 11) demonstrate that the rate NP-Cu/H O system, the by-products generated in the degra-
2 2
constant of 3D NP-Cu is 3 times higher than that for the 2D dation process were examined by liquid chromatograph-mass
NP-Cu, respectively, conrming that the macroscale network spectrometry. Several intermediates were observed, including
structures played a positive role in the degradation of azo N,N-dimethylbenzene-1,4-diamine (m/z
dyes.
benzenesulfonate (m/z ¼ 172), 4-((4-aminophenyl)diazenyl)
Additionally, the higher generation rate constant of the benzenesulfonate (m/z ¼ 276), and 4-((4-(methylamino)phenyl)
¼
137), 4-amino-
ꢀ
5
ꢀ1
active $OH radical (k$OH) for 3D NP-Cu (k ¼ 7.21 ꢃ 10
s
) over diazenyl) benzenesulfonate (m/z ¼ 290). Based on the data, two
) and for Cu species (k ¼ possible degradation pathways were proposed, as illustrated in
) suggests that the 3D NP-Cu exhibits higher Fig. 12. In the rst pathway (le in Fig. 12), the –N]N– bond
efficiency in decomposition of H . To compare the intrinsic was rst reduced by zero valent Cu to form amino-group
catalytic activity between different catalysts, the turnover enriched components, which were gradually oxidized to
ꢀ5
ꢀ1
2+
that for 2D NP-Cu (k ¼ 5.65 ꢃ 10
s
ꢀ
5
ꢀ1
2.40 ꢃ 10
s
2 2
O
frequency (TOF), dened as the conversion number of H
2
O
2
phenol and N,N-dimethylhydroxylamine etc., and ultimately
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. A, 2018, 6, 20992–21002 | 20999

View Article Online
Journal of Materials Chemistry A
Paper
we tested its dynamic degradation performance towards MO
ꢀ1
(
MO concentration: 20 mg L ) by rotating the 3D nano-
structured fan. It is shown that the MO solution (red-like dyeing
solution) was completely decolorized within 8 min (Fig. 13c),
demonstrating the excellent catalytic performance of the 3D
printed fan-like component. The video of the whole dynamic
degradation processes can be seen in the ESI.†
To further demonstrate that the MO dye was completely
puried, we cultivated a few bean seeds in the post-treated
water for a few days to see if the post-treated water is innoc-
uous. As expected, the seeds could not be cultivated in the un-
treated MO solution (Fig. 13e). In contrast, the seeds success-
fully germinated and grew healthy in the degraded MO solution
Fig. 12 The possible degradation pathways of MO using 3D NP-Cu.
(Fig. 13f), demonstrating that the degradation performance of
2 2
degraded to CO and H O using $OH. In this regard, destruction
MO dye using 3D NP Cu is really excellent and shows good
potential for practical applications. The present work indicates
that the integration of nanotechnology with 3D printed parts is
promising for manufacturing high-performance catalysts by
combination of 3D printing and chemical dealloying tech-
niques, wherein, the rst builds up frameworks with desirable
geometries, and the latter produces nanostructures (e.g.,
nanoporous structures in this work). Although the total dosage
of the catalysts used might be higher than the conventional
nanoparticle AOP catalysts, but the 3D NP-Cu prepared in this
of chromophores occurred at the rst step of MO degradation.
Meanwhile, in an alternative degradation pathway (right in
Fig. 12), the MO molecule was decomposed through the
demethylation mechanism (that is the methyl group was
substituted by hydrogen atoms), followed by destruction of
chromophores, ring opening and nally mineralization to CO2
and H O.
2
Applications and implications
To demonstrate the applicability of the 3D NP-Cu catalysts for work could be recyclable by repeatedly dealloying treatment,
large-scale applications for wastewater treatment, we designed which is economical for practical applications. Furthermore,
and fabricated a large-size BMG fan-like component by SLM 3D although the present 3D NP-Cu catalysts exhibits low efficiency
printing (Fig. 13a) and then obtained a nanoporous Cu layer on of degradation at low pH values (i.e., strong acidic environ-
the component surface by chemical dealloying (Fig. 13b). Then, ments), it is expected that with further surface modication of
the nanoporous structures by, for example, thermal oxidation or
electrochemical treatment, degradation performance and
durability of the 3D NP-Cu catalysts could be further enhanced,
and this work is under progress and will be published in
a separated paper.
Conclusions
We have fabricated a novel 3D nanoporous Cu catalyst by the
combination of laser 3D printing and chemical dealloying
techniques. The as-prepared 3D NP-Cu catalysts demonstrated
excellent degradation efficiency towards azo dyes. For example,
nearly 100% degradation towards methyl orange, over 90%
degradation of the complex azo dyes and over 90% removal of
chemical oxygen demand, could be achieved within 30 min. In
addition, the 3D NP-Cu catalysts also exhibited good reusability
that can be used at least 5 times without signicant decay of the
degradation efficiency. The excellent catalytic properties of the
3D NP-Cu are attributed to the unique 3D hierarchically porous
structures that provide better accessibility to active sites and
accelerate the transport of reactants. In addition, the presence
of numerous active atomic steps on Cu ligaments and Cu O
2
Fig. 13 (a and b) Photographs of the 3D-printed BMG fan before and nanocrystals aer dealloying also played an important role in
after chemical dealloying treatment. (c) Pictures of the MO solution
with an interval of 1 min taken from a video recording the degradation
process using a dealloyed BMG-fan; (d) a photograph of the MO
solution after complete degradation with the dealloyed fan; (e and f)
degradation performance. The combination of 3D printing and
chemical dealloying techniques provides a good opportunity for
fabrication of three dimensional complex frameworks with
nanoporous structures. The successful fabrication of the
complex MG fan and nanoporous Cu on the surface with
images of Vigna radiata seeds grown in the as-treated solution by the
dealloyed fan and untreated MO solution (20 mg L , pH ¼ 2).
ꢀ1
21000 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018

View Article Online
Paper
Journal of Materials Chemistry A
excellent catalytic properties demonstrate the possibility of 19 M. Y. Xing, W. J. Xu, C. C. Dong, Y. C. Bai, J. B. Zeng, Y. Zhou,
large-scale applications of 3D NP-Cu catalysts in wastewater
treatment.
J. L. Zhang and Y. D. Yin, Chem, 2018, 4, 1.
20 J. Q. Wang, Y. H. Liu, M. W. Chen, D. V. Louzguine-Luzgin,
A. Inoue and J. H. Perepezko, Sci. Rep., 2012, 2, 418.
2
1 J. Q. Wang, Y. H. Liu, M. W. Chen, G. Q. Xie, D. V. Louzguine-
Luzgin, A. Inoue and J. H. Perepezko, Adv. Funct. Mater.,
2012, 22, 2567.
Conflicts of interest
There are no conicts to declare.
22 S. H. Xie, P. Huang, J. J. Kruzic, X. R. Zeng and H. X. Qian,
Sci. Rep., 2016, 6, 21947.
Acknowledgements
23 X. D. Qin, Z. W. Zhu, G. Liu, H. M. Fu, H. W. Zhang,
A. M. Wang, H. Li and H. F. Zhang, Sci. Rep., 2015, 5, 18226.
This work was nancially supported by the National Natural
Science Foundation of China under grant No. 51531003, 24 Z. Jia, W. C. Zhang, W. M. Wang, D. Habibi and L. C. Zhang,
1471074, 51771077, 51871102 and 51601065; the National Appl. Catal., B, 2016, 192, 46.
Program on Key Basic Research Project (973 Program) (Grant 25 Z. Jia, X. G. Duan, P. Qin, W. C. Zhang, W. M. Wang, C. Yang,
5
No. 2015C856801) and National Key Research and Development
Plan (Grant No. 2016YFB1100101). The authors are also grateful
H. Q. Sun, S. B. Wang and L. C. Zhang, Adv. Funct. Mater.,
2017, 27, 1702258.
to the Analytical and Testing Center, Huazhong University of 26 S. Q. Chen, G. N. Yang, S. T. Luo, S. J. Yin, J. L. Jia, Z. Li,
Science and Technology for technical assistance.
S. H. Gao, Y. Shao and K. F. Yao, J. Mater. Chem. A, 2017,
, 14230.
5
2
7 S. X. Liang, Z. Jia, W. C. Zhang, X. F. Li, W. M. Wang,
H. C. Lin and L. C. Zhang, Appl. Catal., B, 2018, 221, 108.
Notes and references
1
R. Q. Yang, S. J. Zhang, A. Li, G. B. Jiang and C. Y. Jing, 28 Y. Tang, Y. Shao, N. Chen and K. F. Yao, RSC Adv., 2015, 5,
Environ. Sci. Technol., 2013, 47, 12736. 6215.
K. Konstantinou and T. A. Albanis, Appl. Catal., B, 2004, 49, 1. 29 Z. Jia, X. Duan, W. C. Zhang, W. M. Wang, H. Q. Sun,
2
3
Y. X. Qin, L. Z. Zhang and T. C. An, ACS Appl. Mater.
Interfaces, 2017, 9, 17115.
S. B. Wang and L. C. Zhang, Sci. Rep., 2016, 6, 38520.
30 P. P. Wang, J. Q. Wang, H. Li, H. Yang, J. T. Huo, J. G. Wang,
C. T. Chang, X. M. Wang, R. W. Li and G. Wang, J. Alloys
Compd., 2017, 701, 759.
4
5
S. Lo and H. E. Poulsen, J. Mol. Med., 1996, 74, 297.
L. S. Silva, L. C. B. Lima, F. C. Silva, J. M. E. Matos,
M. R. M. C. Santos, L. S. Santos J u´ nior, K. S. Sousa and 31 J. S. Yu, Y. Ding, C. X. Xu, A. Inoue, T. Sakurai and
E. C. da Silva Filho, Chem. Eng. J., 2013, 218, 89. M. W. Chen, Chem. Mater., 2008, 20, 4548.
Q. Q. Wang, M. X. Chen, P. H. Lin, Z. Q. Cui, C. L. Chu and 32 G. Doubek, R. C. Sekol, J. Y. Li, W. H. Ryu, F. S. Gittleson,
6
B. L. Shen, J. Mater. Chem. A, 2018, 6, 10686.
G. Dong, Z. H. Ai and L. Z. Zhang, Water Res., 2014, 66, 22.
L. Ge, C. C. Han and J. Liu, Appl. Catal., B, 2011, 108–109,
S. Nejati, E. Moy, C. Reid, M. Carmo, M. Linardi,
P. Bordeenithikasem, E. Kinser, Y. Liu, X. Tong,
C. O. Osuji, J. Schroers, S. Mukherjee and A. D. Taylor,
Adv. Mater., 2016, 28, 1940.
7
8
100.
9
K. He, G. Chen, G. Zeng, A. Chen, Z. Huang, J. Shi, T. Huang, 33 Z. Deng, C. Zhang and L. Liu, Intermetallics, 2014, 52, 9.
M. Peng and L. Hu, Appl. Catal., B, 2018, 228, 19. 34 S. S. Wang and L. Liu, J. Hazard. Mater., 2017, 340, 445.
0 X. F. Qian, M. Ren, M. Y. Fang, M. Kan, D. T. Yue, Z. F. Bian, 35 D. Ouyang, N. Li, W. Xing, J. J. Zhang and L. Liu,
1
1
1
H. X. Li, J. P. Jia and Y. X. Zhao, Appl. Catal., B, 2018, 231,
08.
1 F. L. Wang, P. Chen, Y. P. Feng, Z. J. Xie, Y. Liu, Y. H. Su,
Intermetallics, 2017, 90, 128.
36 C. Yang, C. Zhang, W. Xing and L. Liu, Intermetallics, 2018,
94, 22.
1
Q. X. Zhang, Y. F. Wang, K. Yao, W. Y. Lv and G. G. Liu, 37 C. C. Jiang, S. Y. Pang, F. Ouyang, J. Ma and J. Jiang,
Appl. Catal., B, 2017, 207, 103.
J. Hazard. Mater., 2010, 174, 813.
2 Y. X. Li, Z. X. Yang, Y. L. Wang, Z. L. Bai, T. Zheng, X. Dai, 38 X. J. Yang, X. M. Xu, J. Xu and Y. F. Han, J. Am. Chem. Soc.,
S. T. Liu, D. X. Gui, W. Liu, M. Chen, L. H. Chen, J. Diwu, 2013, 135, 16058.
L. Zhu, R. H. Zhou, Z. F. Chai, T. E. Albrecht-Schmitt and 39 X. J. Hou, X. P. Huang, Z. H. Ai, J. C. Zhao and L. Z. Zhang,
S. Wang, Nat. Commun., 2017, 8, 1354. J. Hazard. Mater., 2016, 310, 170.
3 M. B. Ahmed, J. L. Zhou, H. H. Ngo, W. S. Guo, 40 C. S. Dong, M. L. Zhong, T. Huang, M. X. Ma, D. Wortmann,
1
N. S. Thomaidis and J. Xu, J. Hazard. Mater., 2017, 323, 274.
4 A. S. Stasinakis, Global NEST J., 2008, 10, 376.
5 E. Neyens and J. Baeyens, J. Hazard. Mater., 2003, 98, 33.
6 N. N. Tu ˇs ar, D. Mau ˇc ec, M. Rangus, I. Ar ˇc on, M. Mazaj,
M. Brajdic and I. Kelbassa, ACS Appl. Mater. Interfaces, 2011,
3, 4332.
41 V. R. Palkar, P. Ayyub, S. Chattopadhyay and M. Multani,
Phys. Rev. B: Condens. Matter Mater. Phys., 1996, 53, 2167.
1
1
1
M. Cotman, A. Pintar and V. Kau ˇc i ˇc , Adv. Funct. Mater., 42 T. Fujita, P. F. Guan, K. Mckenna, X. Y. Lang, A. Hirata,
2
012, 22, 820.
L. Zhang, T. Tokunaga, S. Arai, Y. Yamamoto, N. Tanaka,
Y. Ishikawa, N. Asao, Y. Yamamoto, J. Erlebacher and
M. W. Chen, Nat. Mater., 2012, 11, 775.
1
1
7 L. J. Xu and J. L. Wang, J. Hazard. Mater., 2011, 186, 256.
8 Z. Jia, J. Kang, W. C. Zhang, W. M. Wang, C. Yang, H. Sun,
D. Habibi and L. C. Zhang, Appl. Catal., B, 2017, 204, 537.
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. A, 2018, 6, 20992–21002 | 21001

View Article Online
Journal of Materials Chemistry A
Paper
43 W. Q. Zhang, J. He, S. Y. Liu, W. X. Niu, P. Liu, Y. Zhao, 48 L. G. Devi, S. G. Kumar, K. M. Reddy and C. Munikrishnappa,
F. J. Pang, W. Xi, M. W. Chen, W. Zhang, S. S. Pang and
J. Hazard. Mater., 2009, 164, 459.
Y. Ding, Nanoscale, 2018, 10, 8372.
49 M. E. Lindsey and M. A. Tarr, Chemosphere, 2000, 41, 409.
44 C. X. Xu, J. X. Su, X. Xu, P. P. Liu, H. J. Zhao, F. Tian and 50 D. Meyerstein, Inorg. Chem., 1971, 10, 638.
Y. Ding, J. Am. Chem. Soc., 2007, 129, 42.
5 N. Lopez, T. V. W. Janssens, B. S. Clausen, Y. Xu,
51 O. Nayken, L. Dyckerhoff, H. Schuster and R. Kerber,
Macromol. Chem. Phys., 1983, 184, 2251.
4
M. Mavrikakis, T. Bligaard and J. K. Nørskov, J. Catal., 52 L. X. Yang, S. L. Luo, Y. Li, Y. Xiao, Q. Kang and Q. Y. Cai,
004, 223, 232. Environ. Sci. Technol., 2010, 44, 7641.
6 L. F. Zou, J. Li, D. Zakharov, E. A. Stach and G. W. Zhou, Nat. 53 W. Zhai, F. Q. Sun, W. Chen, Z. Z. Pan, L. H. Zhang, S. H. Li,
2
4
4
Commun., 2017, 8, 307.
S. L. Feng, Y. Y. Liao and W. S. Li, Appl. Catal., A, 2013, 454,
7 J. D. Laat and H. Gallard, Environ. Sci. Technol., 1999, 33,
59.
2726.
21002 | J. Mater. Chem. A, 2018, 6, 20992–21002
This journal is © The Royal Society of Chemistry 2018