The enhanced properties in photocatalytic wastewater treatment: Sulfanilamide (SAM) photodegradation and Cr6+ photoreduction on magnetic Ag/ZnFe2O4 nanoarchitectures

Article abstract of DOI:10.1016/j.jallcom.2021.159085

Ag/ZnFe₂O₄ nanoarchitectures composed of ZnFe₂O₄ nanoparticles loading onto Ag nanowires were fabricated by hydrothermal method. The Ag/ZnFe₂O₄ nanocomposites possessed excellent performanc

Full text of DOI:10.1016/j.jallcom.2021.159085

Journal of Alloys and Compounds 867 (2021) 159085
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
The enhanced properties in photocatalytic wastewater treatment:
6
+
Sulfanilamide (SAM) photodegradation and Cr photoreduction on
magnetic Ag/ZnFe O nanoarchitectures
2
4
⁎
Tianyu Liu, Chongxi Wang, Wei Wang , Guojiang Yang, Zhiying Lu, Peng Xu, Xiaonan Sun,
⁎
Jintao Zhang
School of Chemical Engineering and Materials, Changzhou Institute of Technology, Changzhou, Jiangsu 213032, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Ag/ZnFe O nanoarchitectures composed of ZnFe O4 nanoparticles loading onto Ag nanowires were fabri-
2
4
2
Received 6 December 2020
Received in revised form 19 January 2021
Accepted 4 February 2021
Available online 6 February 2021
cated by hydrothermal method. The Ag/ZnFe
mulated photocatalytic wastewater treatment like sulfanilamide (SAM) photodegradation and Cr
photoreduction. The improvement of photoactivity could be ascribed to the successful formation of
Schottky interface between ZnFe nanoparticles and Ag nanowires and the enhanced light absorption
2 4
O nanocomposites possessed excellent performance in si-
6+
2 4
O
ability in visible light region with modified energy band structures, which make further efforts to the
ameliorate separation and improved mobility of photo-induced charge carriers with enhanced performance
Keywords:
ZnFe O nanoparticles decorated Ag
2 4
nanowires
in photocatalysis. The Ag/ZnFe
ponent and more importantly, the unique magnetic properties enabled the Ag/ZnFe O
2
O
4
nanocomposites exhibited outstanding photoactivity than single com-
photocatalysts to be
Schottky interface
Visible-light photocatalysis
SAM photodegradation
2 4
recycled easily with the aid of external magnetic field, which make it possible for practical applications.
© 2021 Elsevier B.V. All rights reserved.
6+
Cr photoreduction
1. Introduction
photo-excited carriers with prolonged lifetime when composing
with other semiconductors to form Schottky barrier [10,11].
ZnFe , as a magnetic semiconductor material, has been widely
2
O
4
In the previous studies, noble metal nanoparticles were always
loaded, reduced, or deposited onto the semiconductors by various
investigated due to the special magnetic behavior with excellent
stability and photo response capability. Ascribe to the theoretical
band position (EVB = 0.38 eV, ECB = −1.54 eV), a relatively more ne-
gative conduction band (CB) position makes it possible to realize the
photocatalytic or photoelectrochemical water splitting to generate
methods. Zhang et al. prepared Ag activated ZnFe
with Ag loading onto ZnFe hollow spheres with excellent acetone gas
sensing properties [12]. Huerta-Aguilar et al. reduced HAuCl onto
ZnFe to form Au/ZnFe nanocomposites and applied it in the de-
2 4
O nanocomposites
2 4
O
4
2
O
4
2 4
O
hydrogen on ZnFe
2
O
4
, which could be utilized to develop new en-
gradation of paracetamol [13]. Zhu et al. fabricated Ag/ferrite nano-
composites via wet impregnation method and exhibited good properties
in 4-chlorophenol photodegradation [14]. These nanocomposites
showed excellent separation efficiency during photocatalysis process.
The loading of noble metal could effectively improve the light adsorp-
tion, and the Schottky barrier formed between metal and semiconductor
can also promote the charge migration and separation, which was also
conducive to the enhanced performance in photocatalysis [15]. Ac-
cording to our previous study, noble metal nanostructures with rela-
tively larger size were also suitable for light adsorption according to the
ergy resources and alleviate energy crisis [1–3]. However, the poor
photocatalytic efficiency resulted by the short hole transport length
limited the application without further modification. In recent years,
many strategies have been made such as coupling with other
semiconductors [4–7], noble metal loading [8,9] to conquer these
limitations. These methods facilitated the generation, separation,
and migration of photo-excited charge carriers after light irradiation
accompanied with the improvement of photocatalytic performance.
Among various strategies, noble metal was considered as a thriving
way to broaden the light absorption, inhibit the recombination of
Mie’s theory, and the obtained “reversed” nanostructures like Au/TiO
and Au/ZnO nanoarchitectures exhibited good properties in photo-
catalysis such as H -generation, dye degradation and methanol oxida-
tion [16,17]. Based on the above analysis, we fabricate the magnetically
separable Ag/ZnFe nanostructures through hydrothermal method
with different amount of ZnFe loading and Ag nanowires acted as
2
2
⁎
2 4
O
Corresponding authors.
E-mail addresses: wangwei2017@czu.cn (W. Wang), zhangjt@czu.cn (J. Zhang).
2 4
O
https://doi.org/10.1016/j.jallcom.2021.159085
0925-8388/© 2021 Elsevier B.V. All rights reserved.

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
supporter in this study. The as-prepared Ag/ZnFe
2
O
4
nanocomposites
2.4. Photocatalytic wastewater treatment: SAM degradation and Cr6+
reduction
showed significantly enhanced photocatalytic activity in sulfanilamide
6+
(
2 4
SAM) degradation and Cr photoreduction. In addition, the Ag/ZnFe O
nanocomposites retained the magnetic separable properties, which was
necessary for practical application. Furthermore, the possible me-
The catalytic activity through Ag/ZnFe
conducted by SAM photodegradation and Cr reduction. Typically,
2
O
4
6
nanocomposites was
+
6+
chanism of charge separation in Ag/ZnFe
cess were also discussed. The Ag/ZnFe
2
O
O
4
4
during photocatalysis pro-
nanocomposites could be
20 mg sample was dispersed in 50 mL 20 mg/L SAM or Cr aqueous
solution. The pH of Cr6+ solution was adjusted to 2 with H
SO (1 M).
2
2
4
considered potentially for water purification due to the outstanding
performance in simulated wastewater treatment process.
Before light irradiation, the adsorption-desorption equilibrium was
established after the mixture was stirred in dark for 1 h. Then a
300 W Xe lamp with 400 nm cut-off was used to illuminate the
2
. Experimental section
photodegradation system. About 4 mL solution was withdrawn at a
given time interval and then centrifuged to separate solid catalyst for
further analysis. The photocatalytic activity was estimated according
to the maximum absorption wavelength (λmax = 258 nm) of SAM [18]
and the colored Cr(VI)-diphenylcarbazide method (λmax = 540 nm)
[19] monitored on UV–Vis spectrometer (UV-1201).
2.1. Preparation of Ag nanowires
Ag nanowires were prepared via a hydrothermal method according
3
to the following steps: 0.5 g AgNO and 1.0 g polyvinylpyrrolidone (PVP)
were dissolved into 40 mL mixed solution containing 37 mL ethylene
glycol (EG) and 3 mL glycerol. After 500 µL 0.5 mg/mL NaCl/EG solution
was added into the mixture, the whole reaction system was transferred
into the 50 mL Teflon-lined stainless-steel autoclave and reacted at
3
. Results and discussion
3
.1. XRD analysis
120 °C for 3 h. The gray mixture after the reaction was washed and
centrifuged with absolute ethanol for several times. The Ag nanowires
were obtained after drying at 60 °C overnight.
The crystallographic structure of as-obtained Ag/ZnFe
composites were studied by XRD (Fig. 1). Pure ZnFe exhibited dif-
fraction peaks at 31.8°, 35.5°, 42.7°, 47.5°, 56.6°, 62.8° and 68.1°, which
confirmed the cubic structure of ZnFe (JCPDS No. 22-1012). After
sample were loaded onto Ag nanorods, the diffraction peaks of
remained the same except for four additional peaks positioned
2 4
O nano-
2 4
O
2 4
2.2. Preparation of Ag/ZnFe O nanoarchitectures
2 4
O
ZnFe
ZnFe
2
O
4
2 4 2 4
Ag/ZnFe O nanoarchitectures with ZnFe O nanoparticles de-
2
O
4
corated Ag nanowires were fabricated as described below: 1 mmol
at 38°, 44°, 66° and 77° corresponding to the metallic Ag (JCPDS No.
5–2871). The purity of Ag/ZnFe nanocomposites were evident be-
.
3 2 2 2
Zn(CH COO) 2H O, 2 mmol FeCl and certain amount of Ag nano-
6
2 4
O
wires were dispersed in 30 mL deionized water with continuous
stirring for 2 h. After 1 mL ethylenediamine was added into the
solution, the whole mixture was stirred for another 1 h and trans-
ferred into 50 mL Teflon-lined stainless-steel autoclave and reacted
cause no other peaks were observed apart from the above-mentioned
3+
peaks. As is known to all, Ag element could react with Fe to generate
+
Ag ions, but in our fabrication process, ZnFe
2
O
4
was obtained from zinc
.
acetate {Zn(CH
3
COO)
2
2H
2
O} and ferrous chloride (FeCl ), which could
2
at 160 °C for 6 h. The Ag/ZnFe
after the products washed, centrifuged, and dried at 60 °C. Pure
ZnFe nanoparticles were synthesized under identical conditions
except for the addition of Ag nanowires. For simplicity, we denote
Ag/ZnFe samples with 5%, 10%, 15%, 20% and 25% Ag content as
AgZFO5, AgZFO10, AgZFO15, AgZFO20 and AgZFO25. The pure
ZnFe sample was denoted as ZFO.
2 4
O nanocomposites were obtained
+
prevent the formation of Ag ions and destroy the structure of Ag na-
nowires. Moreover, the existence of metallic Ag also suggested the
stability of Ag during the preparation procedure and the feasible route
2 4
O
2 4
to prepare Ag/ZnFe O nanocomposites.
2 4
O
O
2 4
3.2. Morphological analysis
2
.3. Characterizations
The Ag/ZnFe
nanowires were fabricated through continuous hydrothermal stra-
tegies and the morphology of obtained Ag/ZnFe samples were
2 4 2 4
O nanocomposites with ZnFe O loading onto Ag
X-ray diffraction patterns (XRD) was acquired to investigate the
2 4
O
crystal structure of Ag/ZnFe
O
2 4
samples on D8 Bruker advanced X-ray
viewed by SEM and TEM. From Fig. 2A we could find that uniform
diffractometer. Scanning electron microscope (SEM, Hitachi S-4800)
and Transmission electron microscope (TEM, JEOL, JEM-2100) were
employed to observe the microstructure and morphology of the
samples. X-ray photoelectron spectrum (XPS) was carried out on
Thermo Fischer ESCALAB 250Xi X-ray photoelectron spectrometer
under an Al K
spectra were achieved from Shimadzu UV-2500 spectrophotometer
with BaSO as reference. The magnetism properties of pure ZnFe
and Ag/ZnFe nanocomposites were analyzed on VSM-7407 vi-
brating sample magnetometer (Lake Shore, USA). The electron spin
α
radiation (hv = 1486.6 eV). UV–Vis diffuse reflectance
4
2 4
O
2 4
O
-
resonance (ESR) signals of spin-trapped·O
2
radicals were acquired
from Bruker model ESR JES-FA300 spectrometer. The electrochemical
measurements were investigated by CHI-760E electrochemical work-
station with 0.5 M Na SO solution as electrolyte. The as-prepared
2 4
samples were regarded as working electrode. Ag/AgCl and platinum
were selected as reference electrode and counter electrode, respec-
tively. The PL spectra and time-resolved photoluminescence (TRPL)
spectra of samples were recorded on an FL3-TCSPC fluorescence
spectrophotometer and time-resolved fluorescence spectrum
(Edinburgh FLS9800) with an excitation wavelength of 280 nm,
respectively.
Fig. 1. XRD patterns of as-obtained samples.
2

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
Fig. 2. SEM images of Ag nanowires (A); AgZFO5 (B); AgZFO10 (C); AgZFO15 (D); AgZFO20 (E) and AgZFO25 (F).
Ag nanowires accompanied with clean surface were prepared via
hydrothermal method. After Ag nanowires were composed with
bonds, respectively [25,26]. It should be noted that the binding en-
ergy of O 1s was slightly shifted to higher values compared to that of
ZnFe
2
O
4
, the small nanoparticles were clearly observed and an-
pure ZnFe
which could attribute to the interactions between Ag and ZnFe
Moreover, the existence of Ag0 species in Ag/ZnFe
nanocompo-
sites was proved according to the Ag 3d fine spectra (Fig. S2). The
photoelectron peaks situated at 374.2 eV and 368.2 eV were
observed to be the evidence of metallic Ag with no other oxidation
state of Ag due to the slitting energy of Ag 3d doublet was 6.0 eV
[27–29], also represented the stability of Ag during the fabrication
2 4 2 4
O (530.9 and 529.7 eV for 5% Ag/ZnFe O , respectively)
chored on the surface of Ag nanowires with high dispersion as
indicated in Fig. 2B–F. With the increase of Ag content, it can be seen
clearly on the SEM pictures that the amounts of nanoparticles at-
tached to the Ag nanowires were also decreased, indicating the
feasibility of the experimental procedure. In addition, when the
loading amount of ZnFe
the exceeded ZnFe particles will also agglomerate itself rather
than forming a composite to generate Ag/ZnFe interface (Fig. 2B
and C). It can be seen from the photocatalytic experiments that the
photocatalytic performance of the Ag/ZnFe composite decreases
when the optimal amount of ZnFe particles is exceeded. This may
2 4
O .
2 4
O
2 4
O particles exceeded the optimal amount,
2 4
O
2
O
4
2 4
process of Ag/ZnFe O nanocomposites.
2 4
O
3.4. UV–Vis analysis
2 4
O
be discussed in the following photocatalytic experiment sections.
Otherwise, the HRTEM of AgZFO15 sample depicted in Fig. S1C re-
vealed the successful construction of interfacial attachment between
UV–Vis measurement was conducted to analyze the optical
properties of Ag/ZnFe nanocomposites. Due to the smaller band
gap energy (E = 2.00 eV) measured by Kubelka-Munk formalism,
pure ZnFe exhibited a certain absorption capacity in the whole
spectral region (200–800 nm). As depicted in Fig. 4A, Ag nanowire
exhibited relative lower light absorption ability from 200 nm to
2 4
O
g
Ag nanowires and ZnFe
adjacent lattice fringes was 0.254 nm, which belonged to the (331)
crystalline planes of ZnFe (JCPDS No. 65-3111). Meanwhile, the
HRTEM analysis could also suggested the fabrication of Ag/ZnFe
nanocomposites instead of physical mixture. Moreover, the intimate
hybrid structure of Ag/ZnFe was conducive to the charge se-
2
4
O . The lattice spacing distance between the
2 4
O
2 4
O
O
2 4
800 nm than that of ZnFe
2
4 2 4
O . So, after Ag and ZnFe O were com-
bined, the absorption spectrum of Ag/ZnFe
2 4
O
could shift due to the
2
O
4
change of the ratio of the two components, which would further
affect the band gap energy [30]. Despite all this, the obtained
Ag/ZnFe O nanoarchitectures showed enhanced light absorption
2 4
paration during the photocatalytic procedure, thus improving the
photocatalytic efficiency.
ability in visible light region (400–600 nm). The band gap energy of
different samples was also calculated and listed in Table 1. The
3.3. XPS analysis
2 4
UV–Vis analysis suggested that the Ag/ZnFe O nanocomposites
The surface elemental composition of Ag/ZnFe
2
O
4
nanocompo-
displayed better performance in light absorption ability, which could
contribute to the efficient use of solar energy and benefit to the
improvement of photocatalytic performance.
sites were employed by XPS technique as shown in Fig. 3. The full
scan of pure ZnFe and Ag/ZnFe were similarity except for
2
O
4
2 4
O
some cases. Simultaneously, the fine scan of Zn 2p, Fe 2p, O 1 s and
Ag 3d were recorded to confirm the chemical states of different
elements. In fine scan of Zn 2p, two obvious peaks centered at
binding energies of 1020.9 eV and 1044.0 eV could be identified to Zn
3.5. Photocatalytic wastewater treatment
As an antibiotic which was usually used for human and veter-
inary science and difficult to be disposed of, sulfanilamide (SAM)
was chemically stable due to the aromatic ring with heteroatoms,
amino group, and sulfonic group [31,32]. So, in this study, SAM was
first opted as a simulated pollutant to measure the photoactivity of
2+
2
p3/2 and Zn 2p1/2, respectively, indicating the existence of Zn in
Ag/ZnFe nanocomposites [20–22]. Four bands shown in Fig. 3(c)
2 4
O
located at 710.6, 724.7, 718.8 and 732.8 eV, which could be indexed
to Fe 2p3/2, Fe 2p1/2 and their satellite peaks, indicating the presence
3
+
of Fe oxidation state in Ag/ZnFe
O
2 4
samples [23,24]. For O 1s fine
2 4
Ag/ZnFe O nanocomposites, which was photo-stable under visible
spectrum, the divided peaks situated at 530.8 and 529.5 eV could
ascribed to the absorbed oxygen and lattice oxygen of Fe‒O and Zn‒O
light illumination on account of the negligible change in UV–Vis
absorbance (< 5%). A comparison of different photocatalysts for SAM
3

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
Fig. 3. XPS spectra of ZFO and AgZFO15 samples: (A) full scan; (B) Zn 2p; (C) Fe 2p and (D) O 1s.
photodegradation was presented in Fig. 5A. Pristine ZnFe
2
O
4
nano-
order reaction, and the corresponding reaction rate constants (k)
with different sacrificial agents were calculated and listed in Fig. 5B.
As we mentioned above, Ag could trap electrons due to the Schottky
particles exhibited lower performance during SAM photodegrada-
tion process, indicating the suppressed carrier separation rate and
efficiency. However, after coupling with Ag nanowires, the
barriers formed in the Ag/ZnFe
electrons on ZnFe surface could transferred to Ag, which accel-
erate the charge separation on ZnFe and help the carriers to
participate in photocatalytic reactions [33–35]. Besides, the effective
Ag/ZnFe interface was also affected by excessive loadings, the
2 4
O interfaces and the photo-excited
Ag/ZnFe
2
O
4
nanocomposites showed enhanced photoactivity during
2 4
O
SAM photocatalytic degradation, especially for AgZFO15 sample,
which could increase the degradation efficiency from 48.4% to 98.4%
in 2 h. The photocatalytic degradation kinetics of SAM followed first-
2 4
O
2 4
O
Fig. 4. UV–Vis spectrum of as-fabricated Ag/ZnFe
2
O
4
samples (A) and the Kubelka-Munk transformed function of different samples (B).
4

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
Table 1
on the traditionally SPR effect theory, the electrons could transfer
2 4
Band gap energy of as-prepared Ag/ZnFe O samples.
from noble metal (Ag) to semiconductors (ZnFe
electrons would transfer from lower work function one (ZnFe
= ~2.07 eV) to the higher one (Ag, Φ = 4.26 eV). The band gap
energy of ZnFe was estimated as 2.00 eV according to the UV–Vis
analysis and shown in Table 1. When the above two materials (Ag
and ZnFe ) form a composite and illuminated by visible light, the
photogenerated electrons will transfer from the conduction band
CB) of ZnFe to Ag due to the Schottky barriers in order to achieve
Fermi level equilibration when ZnFe and Ag get into contact
2 4
O ). However,
Sample
Band gap energy (eV)
2 4
O ,
Φ
s
m
ZFO
2.00
2.01
2.01
2.02
2.02
2.03
2 4
O
AgZFO5
AgZFO10
AgZFO15
AgZFO20
AgZFO25
2 4
O
(
2 4
O
2 4
O
charge separation efficiency could decrease due to the photo-excited
electrons had the tendency to recombine with holes on agglomer-
[13,36–38]. Therefore, the surface plasmon resonance (SPR) effect of
nano Ag in this composite system is very weak to realize the transfer
of photogenerated electrons from Ag to ZnFe O due to the existence
ated ZnFe
excess amount of ZnFe
amount of Ag in Ag/ZnFe
photocatalytic performance. To further confirm the photoactivity of
as-fabricated Ag/ZnFe
nanoarchitecture, Cr6+ photoreduction re-
O
2 4
nanoparticles rather than transferring to Ag due to the
onto Ag nanowires. Therefore, the optimal
was necessary to obtain the best
2
4
O
2 4
of Schottky barrier formed between ZnFe O4 and Ag [39], and the
2
O
2 4
proposed schematic illustration of electron-hole transfer during the
photocatalysis process on Ag/ZnFe O4 system under the visible light
2
2
O
4
irradiation was illustrate in Fig. 7. Therefore, the as-fabricated
action was also conducted according to the colored Cr(VI)-diphe-
nylcarbazide (DPC) method. From Fig. S4A we could find the
Ag/ZnFe O4 nanocomposites could be primarily considered as an
2
effective catalyst for wastewater treatment due to the excellent
6
+
6+
concentration of Cr ions were decreased dramatically after light
illumination according to the peaks centered at around 540 nm. The
performance in SAM photodegradation and Cr photoreduction.
During the photodegradation process, the photo-excited charge
carriers could generate and separated to react with the adsorbed
2 4
O
for Cr6+ photoreduction was also im-
poor efficiency of ZnFe
proved after combining with Ag nanowires. The reaction rate con-
stant (k) of Ag/ZnFe
sample in Cr6+ photoreduction were 0.0095,
H O or O2 to form active species contributing to the catalysis pro-
2
2
O
4
gress. The active species during photocatalysis process was in-
−1
0
4
.0132, 0.0146, 0.0119 and 0.0081 min , which was 3.96, 5.5, 6.08,
.96, and 3.38 times higher than that of pure ZnFe )
vestigated by capturing experiment with the addition of sacrificial
agent. In this study, TEOA, t-BuOH and BQ were selected to realize
O
4
(0.0024 min−1
2
+
-
(
Fig. 6A and B). As is known to all, Ag could exhibit the surface
h ,·OH and ·O2 quenching, respectively [40,41]. Because of the ad-
dition of quenching agents, the photocatalytic activity of AgZFO15
plasmonic resonance (SPR) effect due to its intrinsic property. Based
Fig. 5. Photocatalytic SAM degradation performance (A, B) over different samples and photocatalytic performance with different sacrificial agent on AgZFO15 (C, D).
5

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
6
+
Fig. 6. Photocatalytic Cr reduction performance (A, B) over different samples and photocatalytic performance with different sacrificial agent on AgZFO15 (C, D).
of ·OH and h+ were also evidenced by the photodegradation effi-
ciency were reduced to 34.0% and 67.9% in the presence of t-BuOH
and TEOA (Fig. 5C and D). It should be noted that, the active species
during Cr6+ photoreduction was also·O
-
due to the degrade
2
efficiency was decreased from 82.7% to 23.6%, which also suggested
-
6+
the importance of ·O
2
during Cr photoreduction process (Fig. 6C
-
and D). Moreover, the high-intensity of DMPO- ·O
2
signals obtained
from ESR spectra exhibited in Fig. S5 could also demonstrate the
-
generation of ·O
successful formation of Ag/ZnFe
Schottky barriers in Ag/ZnFe
2
during the photocatalytic process, indicating the
nanoarchitectures and effective
system.
2 4
O
2 4
O
The reusability and stability were all crucial factors in practical
use during photocatalysis process [42,43]. The cycling test of SAM
photodegradation and Cr6+ photoreduction with AgZFO15 sample
were displayed in Fig. S3 and Fig. S4B. The photocatalytic perfor-
mance exhibited no obvious decrease after 3 cycles with photo-
catalytic efficiency from 98.4% to 95.2% for SAM photodegradation
and 82.7–80.1% for Cr6+ reduction, respectively, which could indicate
the stability and the possibility during a longer operation time.
Fig. 7. Schematic illustration of electron-hole transfer during the photocatalysis
process on Ag/ZnFe system under the visible light irradiation (E : energy in
vacuum; Φ : work function of Ag; Φ : work function of ZnFe ; F : Fermi level of
Ag; F : Fermi level of ZnFe ; Fms: Fermi level of equilibrium position; VB: valance
band of ZnFe ; CB: conduction band of ZnFe ).
2 4
Besides, pure ZnFe O sample exhibited a magnetic saturation (Ms)
2
O
4
v
value of 70.26 emu/g. Because of the content of Ag nanowires existed
in AgZFO15 nanocomposites was as high as 15%, the Ms value of
AgZFO15 nanocomposites was decreased to 58.65 emu/g. The hys-
teresis loop of AgZFO15 sample illustrated in Fig. S6 also proved that
the AgZFO15 sample could be separated magnetically. Thus, it was
m
s
2
O
4
m
s
2 4
O
2
O
4
2 4
O
sample exhibited a decreasing trend. We could clearly find that the
degradation performance of SAM evidently reduced from 98.4% to
2 4
convinced that the Ag/ZnFe O nanocomposites could be a separable
1
1.6% due to the addition of BQ, which suggested the importance of
and effective photocatalyst for contaminants treatment based on the
results of photocatalytic reaction.
-
2
·O during SAM photodegradation. Comparatively, the lower effect
6

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
2 4
Fig. 8. Photocurrent response under visible light irradiation (A) and EIS plots of different Ag/ZnFe O samples (B).
Fig. 9. PL (A) and TRPL (B) spectra of ZFO and AgZFO15 samples.
3.6. Photoelectrochemical properties
2 4
lower resistance of Ag/ZnFe O samples and photo-excited carriers
could be separated effectively and speedy transferred during the
photocatalysis process. Overall, the existence of metallic Ag could
promote the charge separation and transformation and made it
The photoelectrochemical measurements were performed to
gain deep understanding into the separation and migration of photo-
excited carriers during photocatalysis [44–46]. Fig. 8A displayed the
2 4
possible for Ag/ZnFe O nanocomposites to achieve a higher rate of
transient on-off photocurrent response of ZnFe
nanocomposites after deposited onto FTO electrodes. Bulk ZnFe
2
O
4
and Ag/ZnFe
2
O
O
4
photocatalysis.
2
4
was responsive to visible light illumination with average photo-
3.6.1. PL and TRPL analysis
current density of 0.11 µA cm−2. Obviously, affected by the formation
Solid-state photoluminescence (PL) and time-resolved photo-
luminescence (TRPL) spectra were conducted to further evaluate the
lifetime of photo-induced charge carriers. From Fig. 9A we could find
that AgZFO15 exhibited lower PL emission peak compared to the ZFO
sample, indicating the improved separation of photo-excited charge
carriers. Furthermore, TRPL decay curve of ZFO and AgZFO15 sample
were also collected. As shown in Fig. 9B, the fluorescence lifetime of
AgZFO15 was longer than that of ZFO sample, which could also re-
veal the higher separation ability of photogenerated electron-hole
2 4
of Schottky barriers between Ag/ZnFe O interface, the AgZFO
serious samples exhibited good sensitivity to the visible light irra-
diation, suggesting the effective charge generation and separation
after being a composite. The AgZFO15 sample exhibited average
photocurrent density of 2.45 times higher compared to that of pure
−
2
2 4
ZnFe O (0.27 µA cm ). This result was also corresponding to the
6+
SAM photodegradation and Cr photoreduction experiment, in-
dicating the enhanced mobility and longer lifetime of photoinduced
charge carriers were accountable for the improvement of
photoactivity. Moreover, the conclusion of photocurrent tests could
also contribute to the existence of the interface between two com-
ponents.
2 4
pairs on Ag/ZnFe O nanoarchitectures.
3.7. Possible mechanism
To explore the interfacial charge transfer of Ag/ZnFe
the electrochemical impedance spectroscopy (EIS) study was also
carried out and depicted in Fig. 8B [47,48]. The results indicated that
2
O
4
samples,
According to the former analysis, the possible mechanism during
photocatalytic progress was illustrated in Fig. 10. Under the light
irradiation, ZnFe
charge carriers. Due to the Schottky barriers between ZnFe
Ag, the photo-induced electrons could migrate from CB of ZnFe
O
2 4
could adsorb photo irradiation to generate
and
to
compared to pure ZnFe
2
O ,
4
the Ag/ZnFe O
2 4
nanocomposites
2 4
O
exhibited a smaller semicircle in the Nyquist plots, representing the
2 4
O
7

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
2 4
Fig. 10. Schematic illustrations of charge transfer-separation for waste water treatment during photocatalysis process on Ag/ZnFe O nanoarchitecture under visible light
irradiation.
Ag, which could contribute to the separation of charge carriers, fa-
cilitate the prolonged lifetime to take part in the photocatalytic
Declaration of Competing Interest
procedures. The holes and electrons could react with adsorbed H
2
O
The authors declare that they have no known competing fi-
nancial interests or personal relationships that could have appeared
to influence the work reported in this paper.
-
2 2
and O to form active species such as·OH and·O , which will further
take part in photocatalytic process and both displayed decisive roles.
Acknowledgement
4. Conclusions
This work was financially sponsored by National Natural Science
Foundation of China (Grant no. 52071283), Natural Science Foundation
of Jiangsu Province (BK20170661), National Science Foundation of
Changzhou Institute of Technology (No. E3-6701-18-075) and 2019
Support Program for Young Scholars of Changzhou Institute of
Technology (No. A3-3008-19-008).
2 4
Herein, we reported the fabrication of Ag/ZnFe O nanocompo-
sites with ZnFe
as-synthesis Ag/ZnFe
2
O
4
nanoparticles decorated onto Ag nanowires. The
nanocomposites showed enhanced
2 4
O
properties in simulated wastewater treatment process like SAM
photodegradation and Cr6+ photoreduction. The best performance
was reflected in AgZFO15, with
a
SAM photodegradation rate
−
1
6+
constant of 0.0330 min and a Cr photoreduction rate constant of
Appendix A. Supporting information
−
1
0
.0146 min . The enhanced separation efficiency of photo-induced
carriers caused by Schottky interface generated between Ag and
ZnFe and the appropriate content of two components were
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.jallcom.2021.159085.
2 4
O
responsible for the enhanced photoactivity. This work offered a new
strategy into the energy conversion of magnetic nanocomposites and
unusual fabrication procedures to prepare composite nanostructures
References
[
1] A. Behera, D. Kandi, S. Mansingh, S. Martha, K. Parida, Facile synthesis of
ZnFe @RGO nanocomposites towards photocatalytic ciprofloxacin degrada-
tion and H energy production, J. Colloid Interface Sci. 556 (2019) 667–679.
[2] J.Y. Long, W.Z. Wang, S.Y. Fu, L.M. Liu, Hierarchical architectures of wrinkle-like
ZnFe nanosheet-enwrapped ZnO nanotube arrays for remarkably photo-
electrochemical water splitting to produce hydrogen, J. Colloid Interface Sci.
36 (2019) 408–413.
2 4
containing noble metals. Likewise, the Ag/ZnFe O nanocomposites
2 4
O
could be utilized in wastewater treatment and energy fields due to
the high photoactivity, high stability and magnetic separable prop-
erties.
2
2 4
O
5
[3] X.D. Zhu, N. Guijarro, Y.P. Liu, P. Schouwink, R.A. Wells, F.L. Formal, S. Sun, C. Gao,
K. Sivula, Spinel structural disorder influences solar-water-splitting performance
CRediT authorship contribution statement
of ZnFe
4] M.X. Chen, Y.Z. Dai, J. Guo, H.T. Yang, D.N. Liu, Y.L. Zhai, Solvothermal synthesis of
biochar@ZnFe /BiOBr Z-scheme heterojunction for efficient phohocatalytic
ciprofloxacin degradation under visible light, Appl. Surf. Sci. 493 (2019)
361–1367.
5] Y. Li, Y.Z. Li, Y.D. Yin, D.H. Xia, H.R. Ding, C. Ding, J. Wu, Y.H. Yan, Y. Liu, N. Chen,
P.K. Wong, A.H. Lu, Facile synthesis of highly efficient ZnO/ZnFe photocatalyst
2 4
O nanorod photoanodes, Adv. Mater. 30 (2018) 1801612.
[
Tianyu Liu: Methodology, Formal analysis, Investigation, Data
curation, Writing - original draft, Writing - review & editing.
Chongxi Wang: Experimental, Validation. Wei Wang: Formal ana-
lysis, Funding acquisition. Guojiang Yang: Validation. Zhiying Lu:
Validation. Peng Xu: Formal analysis. Xiaonan Sun: Formal analysis.
Jintao Zhang: Resources, Supervision, Funding acquisition.
2 4
O
1
[
2 4
O
using earth-abundant sphalerite and its visible light photocatalytic activity,
Appl. Catal. B-Environ. 226 (2018) 324–336.
8

T. Liu, C. Wang, W. Wang et al.
Journal of Alloys and Compounds 867 (2021) 159085
[
6] F.J. Sun, Q.H. Zeng, W. Tian, Y.M. Zhu, W. Jiang, Magnetic MFe
Co, & Ni) composite photocatalysts and their application for dye wastewater
treatment, J. Environ. Chem. Eng. 7 (2019) 103011.
2
O
4
-Ag
2
O (M = Zn,
highly efficient photocatalytic water pollutants removal, Ceram. Int. 45 (2019)
23522–23527.
[28] L.Q. Jing, Y.G. Xu, C.C. Qin, J. Liu, S.Q. Huang, M.Q. He, H. Xu, H.M. Li, Visible-light-
[
7] N.K. Veldurthi, N.K.R. Wswar, S.A. Singh, G. Madras, Heterojunction ZnWO
ZnFe composites with concerted effects and integrated properties for en-
hanced photocatalytic hydrogen evolution, Catal. Sci. Technol. (2018)
083–1093.
4
/
2 4 3 4
driven ZnFe O /Ag/Ag VO photocatalysts with enhanced photocatalytic activity
under visible light irradiation, Mater. Res. Bull. 95 (2017) 607–615.
[29] Y.Y. Lan, Z.F. Liu, G. Liu, Z.G. Guo, M.N. Ruan, H. Rong, X.F. Li, 1D ZnFe O na-
2 4
2
O
4
8
1
2
norods coupled with plasmonic Ag, Ag S nanoparticles and Co-Pi cocatalysts for
[
[
8] O. Sacco, V. Vaiano, D. Sannino, R.A. Picca, N. Cioffi, Ag modified ZnS for pho-
tocatalytic water pollutants degradation: influence of metal loading and pre-
paration method, J. Colloid Interface Sci. 537 (2019) 671–681.
9] V. Vaiano, C.A. Jaramillo-Paez, M. Matarangolo, J.A. Navio, M.D. Hidalgo, UV and
visible-light driven photocatalytic removal of caffeine using ZnO modified with
different noble metals (Pt, Ag and Au), Mater. Res. Bull. 112 (2019) (2019)
efficient photoelectrochemical water splitting, Int. J. Hydrog. Energy 44 (2019)
19841–19854.
[30] T.S. Wu, K.X. Wang, G.D. Li, S.Y. Sun, J. Sun, J.S. Chen, Montmorillonite-supported
Ag/TiO nanoparticles: an efficient visible-light bacteria photodegradation ma-
2
terial, ACS Appl. Mater. Interfaces 2 (2010) 544–550.
3
[31] W.Y. Zhu, J.C. Liu, S.Y. Yu, Y. Zhou, X.L. Yan, Ag loaded WO nanoplates for effi-
2
51–260.
10] A. Furube, L.C. Du, K. Hara, R. Katoh, M. Tachiya, Ultrafast plasmon-induced
electron transfer from gold nanodots into TiO nanoparticles, J. Am. Chem. Soc.
29 (2007) 14852–14853.
cient photocatalytic degradation of sulfanilamide and their bactericidal effect
under visible light irradiation, J. Hazard. Mater. 318 (2016) 407–416.
[
[
[
[
2
[32] G.W. Wang, S.Y. Li, X. Ma, J. Qiao, G.S. Li, H.B. Zhang, J. Wang, Y.T. Song, A novel
3
+
1
3 5 2 4 4
Z-scheme sonocatalyst system, Er : Y Al O12@Ni(Fe0.05Ga0.95) O -Au-BiVO ,
11] N. Shin-ichi, I. Aimi, T. Hiroaki, Self-assembled heterosupramolecular visible
light photocatalyst consisting of gold nanoparticle-loaded titanium (IV) dioxide
and surfactant, J. Am. Chem. Soc. 132 (2010) 6292–6293.
and application in sonocatalytic degradation of sulfanilamide, Ultrason.
Sonochem. 45 (2018) 150–156.
[33] J. Cao, B.D. Luo, H.L. Lin, B.Y. Xu, S.F. Che, Visible light photocatalytic activity
12] C. Zhang, Q.D. Wu, B.B. Zheng, J.J. You, Y.F. Luo, Synthesis and acetone gas sensing
enhancement and mechanism of AgBr/Ag
orange, J. Hazard. Mater. 217 (2012) 107–115.
[34] N. Khadgi, A.R. Upreti, Photocatalytic degradation of Microcystin-LR by visible
light active and magnetic, ZnFe -Ag/rGO nanocomposite and toxicity assess-
3 4
PO hybrids for degradation of methyl
2 4
properties of Ag activated hollow sphere structured ZnFe O , Ceram. Int.
4
4 (2018) 20700–20707.
13] C.A. Huerta-Aguilar, A.A. Ramírez-Alejandre, P. Thangarasu, J.A. Arenas-Alatorre,
I.A. Reyes-Dominguez, M.L. Corea, Crystal phase induced band gap energy en-
2 4
O
ment of the intermediates, Chemosphere 221 (2019) 441–451.
hancing the photo-catalytic properties of Zn-Fe
2
O
4
/Au NPs: experimental and
[35] A.H. Mady, M.L. Baynosa, D.T.J.J. Shim, Facile microwave-assisted green synthesis
theoretical studies, Catal. Sci. Technol. 9 (2019) 3066–3080.
2 4
of Ag-ZnFe O @rGO nanocomposites for efficient removal of organic dyes under
[
[
[
14] Z.R. Zhu, F.Y. Liu, H.B. Zhang, J.F. Zhang, L. Han, Photocatalytic degradation of
UV- and visible-light irradiation, Appl. Catal. B-Environ. 203 (2017) 416–427.
4
-chlorophenol over Ag/MFe
chemical co-precipitation method: a comparative study, RSC Adv. 5 (2015)
5499–55512.
15] L.M. Liu, W.Z. Wang, J.Y. Long, S.Y. Fu, Y.J. Liang, J.L. Fu, Three-dimensional
plasmonic photoanode of Au nanoparticles/ZnFe nanosheets coated onto ZnO
2
O
4
(M = Co, Zn, Cu, and Ni) prepared by a modified
[36] D.J. Singh, M. Gupta, R. Gupta, Density-functional description of spinel ZnFe
2 4
O ,
Phys. Rev. B 63 (2001) 205102.
[37] J. Takaobushi, M. Ishikawa, S. Ueda, E. Ikenaga, J.J. Kim, M. Kobata, Y. Takeda,
Y. Saitoh, M. Yabashi, Y. Nishino, D. Miwa, K. Tamasaku, T. Ishikawa, I. Satoh,
5
O
2 4
4
H. Tanaka, K. Kobayshi, T. Kawai, Electronic structures of Fe3−xMxO (M=Mn,Zn)
spinel oxide thin films investigated by x-ray photoemission spectroscopy and
x-ray magnetic circular dichroism, Phys. Rev. B 76 (2007) (2007) 205108.
nanotube arrays for photoelectrochemical production of hydrogen, Sol. Energy
Mater. Sol. Cells 195 (2019) 330–338.
16] T.Y. Liu, W. Chen, T. Huang, G.R. Duan, X.J. Yang, X.H. Liu, Titania-on-gold na-
noarchitectures for visible-light-driven hydrogen evolution from water splitting,
J. Mater. Sci. 51 (2016) 6987–6997.
[38] S.H. Wei, S.B. Zhang, First-principles study of cation distribution in eighteen
II III
IV II
closed-shell A B
2 4 2 4
O and A B O spinel oxides, Phys. Rev. B 63 (2001) 045112.
[39] L.L. Ma, J.X. Jiang, C.L. Tan, Z.H. Wang, S.H. Li, Calculation and experimental re-
search of electronic structure and magnetic properties of Mn-Zn spinel-ferrite, J.
Chin. Ceram. Soc. 38 (2010) 1577–1581.
[
[
17] T.Y. Liu, W. Chen, Y.X. Hua, X.H. Liu, Au/ZnO nanoarchitectures with Au as both
supporter and antenna of visible light, Appl. Surf. Sci. 392 (2017) 616–623.
18] R.X. Wang, J.H. Tang, X.Y. Zhang, D. Wang, X. Wang, S. Xue, Z.H. Zhang,
[40] T.Y. Liu, G.J. Yang, W. Wang, C.X. Wang, M. Wang, X.N. Sun, P. Xu, J.T. Zhang,
D.D. Dionysiou, Construction of novel Z-scheme Ag/ZnFe
2
O
4
/Ag/BiTa1−x
V
x
O
4
3 5
Preparation of C N nanosheets with enhanced performance in photocatalytic
system with enhanced electron transfer capacity for visible light photocatalytic
degradation of sulfanilamede, J. Hazard. Mater. 375 (2019) 161–173.
methylene blue (MB) degradation and
Environ. Res. 188 (2020) 109741.
2
H -evolution from water splitting,
[
[
[
[
19] X.D. Du, X.H. Yi, P. Wang, W.W. Zheng, J.G. Deng, C.C. Wang, Robust photo-
[41] W.L. Shi, F. Guo, S.L. Yuan, In situ synthesis of Z-scheme Ag
3
PO /CuBi pho-
4
2 4
O
catalytic reduction of Cr(VI) on UiO-66-NH
2
(Zr/Hf) metal-organic framework
tocatalysts and enhanced photocatalytic performance for the degradation of
tetracycline under visible light irradiation, Appl. Catal. B-Environ. 209 (2017)
720–728.
membrane under sunlight irradiation, Chem. Eur. J. 356 (2019) 393–399.
20] Y. Qu, D. Zhang, X. Wang, H.L. Qiu, T. Zhang, M. Zhang, G. Tian, H.J. Yue, S.H. Feng,
G. Chen, Porous ZnFe
2
O
4
nanospheres as anode materials for Li-ion battery with
[42] P.F. Tan, Y. Liu, A.Q. Zhu, W.X. Zeng, H. Cui, J. Pan, Rational design of Z-scheme
high performance, J. Alloy. Compd. 721 (2017) 697–704.
system based on 3D hierarchical CdS supported 0D Co
S
9 8
nanoparticles for su-
21] P.S. Yoo, D.A. Reddy, Y.F. Jia, S.E. Bae, S. Huh, C.L. Li, Magnetic core-shell ZnFe
2
O
4
/
perior photocatalytic
10385–10394.
H
2
generation, ACS Sustain. Chem. Eng. (2018)
6
ZnS nanocomposites for photocatalytic application under visible light, J. Colloid
Interface Sci. 486 (2017) 136–143.
22] P.F. Tan, A.Q. Zhu, L.L. Qiao, W.X. Zeng, Y.J. Ma, H.G. Dong, J.P. Xie, J. Pan,
[43] Y.J. Ma, J. Jiang, A.Q. Zhu, P.F. Tan, Y. Bian, W.X. Zeng, H. Cui, J. Pan, Enhanced
visible-light photocatalytic degradation by Mn /CeO heterojunction:
Z-scheme system photocatalyst, Inorg. Chem. Front. 5 (2018) 2579–2586.
[44] X.L. Hu, Y.W. Yong, Y. Xu, X.K. Hong, Y.Q. Weng, X.H. Wang, X.X. Yao, Enhanced
photocatalytic nitrogen fixation of AgI modified g-C with nitrogen vacancy
3
O
4
2
a
Constructing a direct Z-scheme photocatalytic system based on 2D/2D WO
ZnIn nanocomposite for efficient hydrogen evolution under visible light,
Inorg. Chem. Front. 6 (2019) 929–939.
23] C.W. Li, A.C. Zhang, L.X. Zhang, J. Song, S. Su, Z.J. Sun, J. Xiang, Enhanced pho-
tocatalytic activity and characterization of magnetic Ag/BiOI/ZnFe compo-
sites for Hg removal under fluorescent light irradiation, Appl. Surf. Sci.
33 (2018) 914–926.
24] Z.Y. Lu, Z.H. Yu, J.B. Dong, M.S. Song, Y. Liu, X.L. Liu, Z.F. Ma, H. Su, Y.S. Yan,
P.W. Huo, Facile microwave synthesis of a Z-scheme imprinted ZnFe /Ag/
3
/
2 4
S
3 4
N
[
[
[
synthesized by an in-situ decomposition-thermal polymerization method, Appl.
Surf. Sci. 531 (2020) 147348.
[45] Y.J. Ma, P.F. Ou, Z.Y. Wang, A.Q. Zhu, L.L. Lu, Y.H. Zhang, W.X. Zeng, J. Song, J. Pan,
Interface engineering in CeO (111) facets decorated with CdSe quantum dots for
2
photocatalytic hydrogen evolution, J. Colloid Interface Sci. 579 (2020) 707–713.
[46] Y.J. Ma, Y. Bian, Y. Liu, A.Q. Zhu, H. Wu, H. Cui, D.W. Chu, J. Pan, Construction of
2 4
O
0
4
2 4
O
PEDOT with the specific recognition ability towards photocatalytic activity and
selectivity for tetracycline, Chem. Eng. J. 337 (2018) 228–241.
Z-scheme system for enhanced photocatalytic
H
2
evolution based on CdS
quantum dots/CeO
2552–2562.
2
nanorods heterojunction, ACS Sustain. Chem. Eng. 6 (2018)
2 4
25] P. Dai, M.Z. Wu, T.T. Jiang, H.B. Hu, X.X. Yu, Z.M. Bai, Silver-loaded ZnO/ZnFe O
mesoporous hollow spheres with enhanced photocatalytic activity for 2, 4-di-
chlophenol degradation under visible light irradiation, Mater. Res. Bull.
[47] Q.Q. Liu, Y.G. Xu, J. Wang, M. Xie, W. Wei, L.Y. Huang, H. Xu, Y.H. Song, H.M. Li,
Fabrication of Ag/AgCl/ZnFe composites with enhanced photocatalytic ac-
2 4
O
1
07 (2018) 339–346.
tivity for pollutant degradation and E. coli disinfection, Colloid Surf. A 553 (2018)
114–124.
[
[
26] Y.S. Fu, P. Xiong, H.Q. Chen, X.Q. Sun, X. Wang, Magnetically separable ZnFe O -
2 4
graphene catalyst and its high photocatalytic performance under visible light
irradiation, Ind. Eng. Chem. Res. 50 (2011) 7210–7218.
27] F. Cao, Y.N. Wang, J.M. Wang, X. Yang, Y. Chen, X.C. Xv, J. Zhou, S. Li, G.W. Qin,
[48] W.X. Zeng, Y. Bian, S. Cao, Y.J. Ma, Y. Liu, A.Q. Zhu, P.F. Tan, J. Pan, Phase trans-
formation synthesis of strontium tantalum oxynitride-based heterojunction for
improved visible light-driven hydrogen evolution, ACS Appl. Mater. Interfaces
10 (2018) 21328–21334.
2 4
ZnO/ZnFe O /Ag hollow nanofibers with multicomponent heterojunctions for
9