ZnFe-LDH/GO nanocomposite coated on the glass support as a highly efficient catalyst for visible light photodegradation of an emerging pollutant

Article abstract of DOI:10.1016/j.molliq.2020.112532

This study reports the fabrication of ZnFe-layered double hydroxides with sulfate-intercalated anion (ZnFe-SO₄-LDH) modified with graphene oxide (GO) by chemical co-precipitation method. They were then coated on the glass substrates (denoted as ZnFe-LDH/GO/GS). The XRD, SEM, EDX, X-ray Dot-mapping, FTIR, AFM, UV–Vis DRS, and PL analyses were used for the characterization of the as-synthesized sample. The photocatalytic implementation of the as-prepared photocatalyst was scrutinized for the degradation of phenazopyridine hydrochloride (PhP) from the solution under visible light irradiation. The prepared photocatalyst showed photocatalytic performance of elimination PhP, the degraded rate of pollutant could reach 60.01% in 150 min of photocatalysis process under the optimum conditions: initial PhP concentration of 15 mg/L, pH of 8 (natural pH), and 3 photocatalysts plates. The addition of 1 mmol/L of potassium persulfate (k₂S₂O₈) caused the degradation efficiency of 93.95% within the 150 min of photocatalytic process. Trapping experiments indicated the influence order of O₂ ^?· > [rad]OH > h⁺ for the ROSs present in decomposition. The transformation of five intermediates of PhP produced in the photocatalytic degradation process was identified by the GC–MS technique. 60% COD removal efficiency was achieved after 300 min of photocatalytic reaction confirming mineralization of the PhP solution. Finally, a reusability test of ZnFe-LDH/GO/GS photocatalyst in the PhP degradation revealed that almost 12% drop occurred after five successive cycles.

Full text of DOI:10.1016/j.molliq.2020.112532

Journal of Molecular Liquids 302 (2020) 112532
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
ZnFe-LDH/GO nanocomposite coated on the glass support as a highly
efficient catalyst for visible light photodegradation of an
emerging pollutant
a
a,b,c,
d
a
Parisa Yekan Motlagh , Alireza Khataee
⁎, Aydin Hassani , Tannaz Sadeghi Rad
a
Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, 51666-16471 Tabriz, Iran
Department of Environmental Engineering, Gebze Technical University, 41400 Gebze, Turkey
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
Department of Materials Science and Nanotechnology Engineering, Faculty of Engineering, Near East University, 99138 Nicosia, TRNC, Mersin 10, Turkey
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
This study reports the fabrication of ZnFe-layered double hydroxides with sulfate-intercalated anion (ZnFe-SO4-
LDH) modified with graphene oxide (GO) by chemical co-precipitation method. They were then coated on the
glass substrates (denoted as ZnFe-LDH/GO/GS). The XRD, SEM, EDX, X-ray Dot-mapping, FTIR, AFM, UV–Vis
DRS, and PL analyses were used for the characterization of the as-synthesized sample. The photocatalytic imple-
mentation of the as-prepared photocatalyst was scrutinized for the degradation of phenazopyridine hydrochlo-
ride (PhP) from the solution under visible light irradiation. The prepared photocatalyst showed photocatalytic
performance of elimination PhP, the degraded rate of pollutant could reach 60.01% in 150 min of photocatalysis
process under the optimum conditions: initial PhP concentration of 15 mg/L, pH of 8 (natural pH), and 3
Received 2 November 2019
Received in revised form 4 January 2020
Accepted 18 January 2020
Available online 20 January 2020
Keywords:
Advanced oxidation process
Layered double hydroxides
Visible light photocatalyst
Modified graphene oxide
Nanocatalyst
2 2 8
photocatalysts plates. The addition of 1 mmol/L of potassium persulfate (k S O ) caused the degradation effi-
ciency of 93.95% within the 150 min of photocatalytic process. Trapping experiments indicated the influence
−
·
N •OH N h+ for the ROSs present in decomposition. The transformation of five intermediates of
order of O
2
Phenazopyridine
PhP produced in the photocatalytic degradation process was identified by the GC–MS technique. 60% COD re-
moval efficiency was achieved after 300 min of photocatalytic reaction confirming mineralization of the PhP so-
lution. Finally, a reusability test of ZnFe-LDH/GO/GS photocatalyst in the PhP degradation revealed that almost
12% drop occurred after five successive cycles.
©
2020 Elsevier B.V. All rights reserved.
1
. Introduction
Many chemical drugs as emerging contaminants (ECs) presents in
variety of organs. An in vivo study on mouse models reported carcino-
genicity following the long-term administration of the PhP [2,5].
Therefore, it is vital to treat the aqueous environments contaminated
by the PhP and its metabolites. Resistant compounds can be removed
or decomposed using advanced oxidation processes (AOPs) on the
basis of hydroxyl radical (•OH) formation [6]. Recently, the
photocatalysis has been of great interest because of cost-effectiveness,
eco-friendly and high-throughput properties [7,8]. Moreover, a variety
of photocatalysts have been used to eradicate PhP contaminants, includ-
the aqueous solutions are potent risk factors for a wide spectrum of dis-
eases because of photo-transformation, high toxicity and non-
biodegradability [1,2]. Some of the drugs and resulting metabolites
discharged from major pollution sources (domestic, industrial and hos-
pital wastewaters) into the surface and groundwater resources may not
be completely eliminated or transformed within the common water
treatment processes [3,4]. Among various pharmaceutical compounds,
phenazopyridine hydrochloride (PhP) is one of the analgesics in atten-
uating the pain caused by irritation or urinary tract infection [2,5]. The
discharge of PhP and corresponding metabolites, including alanine
and p-aminophenol, into the aquatic solutions can negatively threaten
the life of aquatic organisms through the involvement of liver and a
ing TiO
2
electrospun fibers [9], activated carbon-supported ZnO [10],
TiO /CdS [11], and many others. These catalysts have shown promising
2
degradation performance in aqueous solution. It is worth noting that
the recent studies focused on novel, effective, simple, and low-cost
approaches to control the discharge of analgesic pharmaceuticals. Re-
cently, layered double hydroxides (LDHs) are great of importance for
application as photocatalysts due to their high anion exchange capacity,
large specific surface area, and convenient synthesis method [12].
Hydrotalcite-like compounds (LDHs) are of ionic lamellar materials
from anionic clay category [13], which possess the lattice structure
⁎
Corresponding author.
E-mail addresses: a_khataee@tabrizu.ac.ir, alirezakhataee@duytan.edu.vn
(A. Khataee).
https://doi.org/10.1016/j.molliq.2020.112532
167-7322/© 2020 Elsevier B.V. All rights reserved.
0

2
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
with brucite-shaped layers with positive charges. They have a divalent
DPA as an electron acceptor can enhance the electron transfer, predis-
posing for reactions of photocatalysis [30].
Inspired by these pioneering works above, this study reports the fab-
4
rication of ZnFe-SO -LDH nanoplates modified with graphene oxide
2
+
2+
2+
2+
2+
metal ion of M (e.g., Ca , Zn , Mg , and Ni ), which have been
–
2+
covered octahedrally by 6 OH hydroxyl groups. The M metal substi-
tution with a trivalent cation of M3 causes positively charged lamellas
to be repeated periodically, which are alternated by charge-
+
(GO), coated them on the glass substrates (denoted as ZnFe-LDH/GO/
GS) and selected as a fixed photocatalyst for the heterogeneous photo-
catalytic system. The as-prepared sample was characterized by several
techniques and assessed in terms of its photocatalytic performance in
the photocatalytic degradation of PhP as a target pollutant. The main op-
erating factors such as the number of photocatalyst plates, PhP concen-
tration, initial pH, oxidant, the effect of scavengers and the durability of
the catalyst over frequentative trials were tested. Then, the kinetic of the
treatment process was perused. The transformation intermediates of
PhP produced in the photocatalytic degradation system were recog-
nized by the gas chromatography–mass spectrometry (GC–MS) tech-
nique. As far as the authors are aware, this type of LDH/GO coated on
glass substrates has not been reported for the photocatalytic degrada-
tion of target pharmaceuticals.
n−
counterbalancing of A ions [14]. The method of production and the
type of precursors determine the nanocompositescompensation of net
n−
positive charge by the intercalation of A anions, including carbonates,
hydroxyl groups, sulfates and nitrates, which are in hydrated interla-
mellar galleries [13]. Nonetheless, bare LDHs typically have lower quan-
tum yield under ultraviolet and visible light irradiation because of their
poor charge carrier mobility, rapid recombination of photo-induced
−
+
charges, and lower electron-hole (e − h ) transfer [15,16]. The per-
formance of LDHs as nanophotocatalysts can be efficiently enhanced
through various modifications, such as doping, coating, combination
with various semiconductors and immobilization on preferred sub-
strates. Nowadays, graphene oxide (GO) based materials have received
extensive attention along with their wide application in the environ-
mental remediation processes [17,18]. The reason behind this lies in
their outstanding charge carrier mobility; high electrical conductivity
accepts photogenerated electrons from the conduction bands of most
of the semiconductors and acting as an electron receiver and donor,
and interesting nanostructure [19]. The GO-based nanophotocatalyst
is able to enhance the physicochemical properties of graphene and
also provide a new photocatalyst that uses the advantages of GO along
with other nanomaterials [20]. A variety of LDH and modified LDH
have been applied as the heterogenous photocatalyst in the
photocatalysis reaction. For example, Shao et al. studied the photocata-
lytic activity of Zn-Ti LDH for the photodegradation of methylene blue
2. Experimental
2.1. Materials
Sodium nitrate (NaNO
zinc (II) sulfate (ZnSO .7H
formic acid (CH , 98–100%), 2-propanol (C
none (C , 99%), dopamine (C 11NO
(C 10O, 99%), potassium persulfate (K
Merck (Germany). Ethanol (C OH, 96%) and Tris-HCl buffer
(C 11NO .HCl, 99%) was supplied by Sigma Aldrich (USA). Hydrochlo-
3
, 99%), iron (II) sulfate (FeSO
O, 99.5%), sodium hydroxide (NaOH, 99%),
O, 99%), 1,4-benzoqui-
, 99%) and diethyl ether
, 99%), were provided by
4 2
.7H O, 99.5%),
4
2
O
2 2
3 8
H
6
H
4
O
2
8
H
2
4
H
2 2 8
S O
2
H
5
3 4
[21]. Sahoo et al. used an Ag@Ag VO /ZnCr LDH nanocomposite for pho-
4
H
3
tocatalytic degradation of phenol [22]. However, the heterogeneous
suspended photocatalysts within the slurry reactors are used to perform
the photocatalysis. Such photocatalysts are inappropriate for taking
light energy, and so lead to low efficacy of photocatalysis [23]. There is
a probability of leakage and subsequently secondary pollution for
suspended photocatalysts whose continuous use depends on recycling
with additional processes [23]. Two main problems are solved by
nanophotocatalyst immobilization on solid supports instead of its
suspended status: 1) photocatalyst recovering and filtering, 2) de-
creased intensity of visible light following dispersion and absorption
of the catalyst particles-induced radiation. The practical purposes can
efficiently benefit from the photocatalyst immobilization that can be
achieved by different approaches and supports for the photocatalyst
ric acid (HCl, 38%) was obtained from Royalex (India). GO nanoplates
(99 + %, 3.4–7 nm, 6–10 layers) were obtained from US Research
Nanomaterials (USA). Glass substrates were used as the support.
Phenazopyridine hydrochloride (PhP) was obtained from Shahre Daru
Laboratories, (Tehran, Iran). The PhP pharmaceutical used as a model
11 5 w
pollutant (Molecular formula C11H N .HCl, λmax 427 nm, M 249.7 g/
mol, solubility in water 15.9 g/L at 25 °C).
2.2. Synthesis of the samples
2.2.1. Synthesis of modified GO
GO (0.02 g) was dispersed in distilled water (DI, 150 mL) by
ultrasonication (ULTRA 8060 D-H, 36 kHz, 150 W, England), which re-
sulted in stable aqueous-dispersed GO. The GO was modified under a
continuous flow rate of ozone (30 L/h) in a cylindrical Pyrex reactor.
Ozone was generated in an ozone generator (BE-72, Iran) using oxygen
gas, which was supplied by an oxygen generator (Airsep, USA). The cy-
lindrical reactor was placed in a water bath, and the temperature was
adjusted to 75 °C for 15 min. The obtained solution was then dried in
an oven, and the precipitates were collected. The experimental condi-
tions of ozone modification of GO are reported in our previous research
[31].
[24]. Transparency to UV radiation, high specific surface area and chem-
ical inertness are mainly parameters required for satisfactory supports.
The use of surface engineering methods for photocatalyst immobiliza-
tion on glass supports is promisingly suitable for wastewater treatment
with the aid of photocatalytic-immobilized reactors. Nevertheless, these
glass supports are non-adhesive and inert for catalyst immobilization,
which can be improved by surface modification of support materials
[
25]. Dopamine hydrochloride (DPA), because of self-polymerizing
and depositing of DPA on the inorganic or organic surfaces via dopa-
mine, has attracted recently further attention for the functionalization
of various substrates [26]. The DPA also provides numerous active
sites for organic contaminant linking through π-π stacking interactions,
hydrogen bonding or electrostatic interactions. This occurs due to abun-
dant functional groups, including catechol groups, aromatic moieties
and amine groups, which are considered as an advantage for secondary
modification [26,27]. In addition, these interactions between DPA and
the carrier exist between DPA and water contaminants, thereby provid-
ing a method for removing water-containing pollutants. For instance,
Gao et al. [28] report dopamine functionalized tannic-acid-templated
mesoporous silica nanoparticles as a new sorbent for the efficient re-
2.2.2. Synthesis of ZnFe-SO
4
-LDH
2 4 2
.7H O (0.001 mol) and ZnSO .7H O
For ZnFe-SO -LDH, FeSO
4
4
(0.003 mol) were dissolved with a molar ratio of 3:1 in 40 mL of distilled
water. The solution was titrated slowly with NaOH solution (2 mol/L)
until the pH reached 8 at room temperature and under Ar atmosphere.
The solution was then kept stirring for 24 h. The precipitates were cen-
trifuged and dried in an oven at 60 °C.
2.2.3. Synthesis of ZnFe-SO
ZnFe-SO -LDH/GO was synthesized through the chemical co-
precipitation method. For the synthesis of ZnFe-SO -LDH/GO, a distinct
proportion of FeSO .7H O, ZnSO .7H O with a molar ratio of 3:1 and
0.04 g of modified GO was dissolved in 40 mL of distilled water, followed
4
-LDH/GO
4
2
+
moval of Cu
from aqueous solution. Guo et al. have obtained
4
polydopamine modified chitosan aerogels and it showed efficient re-
moval toward heavy metals and organic dyes [29]. On the other hand,
4
2
4
2
,

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
3
sonication for 15 min. The solution was titrated slowly with NaOH solu-
tion (2 mol/L) until the pH reached 8. Subsequently, the solution was
kept stirring for 12 h under Ar atmosphere, and the precipitates were
centrifuged and dried in an oven at 60 °C.
of the glass substrates (4.7 cm width × 5.4 cm high and 4 mm thickness)
was coated with ZnFe-LDH/GO nanocomposite. Typically, three glass
substrates (number of photocatalyst sheets) were placed in the PhP
aqueous solution (300 mL, 15 mg/L) with a glass vessel, and then the
mixed solution was stirred for 30 min in dark to achieve an
adsorption-desorption equilibrium. After that, the suspension was illu-
minated under a 10 W LED lamp (λ~400 nm) as a visible light source.
The pH of PhP solution was adjusted using NaOH and HCl solutions
(1 mol/L) and measured with a pH meter (Ohaus 3100, USA). Periodi-
cally, 3 mL of the suspension was taken out and the remnant PhP con-
centration was monitored using an ultraviolet-visible (UV–Vis)
spectrophotometer (SU-6100, Philler scientific, USA) at a maximum
wavelength of 427 nm.
2
4
.2.4. ZnFe-SO -LDH/GO coated on the glass substrate
A glass plate of 5.4 cm × 4.7 cm was sectioned and rinsed with dis-
tilled water for removing debris from the surface, followed by drying
in an oven. Then, the glass was immersed in NaOH 2 mol/L for 1 day
and then was dried. Dopamine hydrochloride (DPA) (2 mg/mL) and
ZnFe-SO -LDH/GO (1 mg/mL) were dissolved in 50 mmol/L Tris-HCl
4
buffer (pH = 8.5). Then the solution was coated on the glass at room
temperature. After that, the glass plates were dried in an oven at
1
00 °C for 4 h. The DPA and LDH/GO layer was coated on glass substrate
five times repeatedly. The fabrication process of the ZnFe-LDH/GO
nanocomposite on the glass substrate is schematically shown in
Scheme 1.
2.5. Detection of hydroxyl radicals
•
The detection of OH radicals was tested in the photocatalytic system
using a terephthalic acid (TA) photoluminescence method. For this pur-
−
4
−3
2
.3. Instrumentation
pose, 5 × 10 mol/L of TA was poured into 2 × 10 mol/L of NaOH and
the drug solution was replaced by TA solution. Next, three photocatalyst
plates were added to 300 mL of TA solution, followed by subjecting to
visible light illumination. After regular intervals, the samples were
taken out to be analyzed by a fluorescence spectrophotometer (Perkin
Elmer LS45, USA) at the wavelengths between 350 and 600 nm and ex-
citation wavelength of 315 nm.
The crystallographic characteristics of the samples were analyzed by
X-ray diffraction (XRD) (PANalytical X'Pert PRO, Germany, Cu Kα radi-
ation: 0.15406 nm; 45 kV, 40 mA). Scanning electron microscopic
(
SEM) micrographs of the samples were obtained using a Tescan
Mira3 microscope (Czech Republic). Energy-dispersive X-ray (EDX)
spectroscopy of the samples was performed using a Zeiss Sigma 300.
The surface topography of coated and bare glass plates was explored
by atomic force microscopy (AFM) using a nano-surf mobile scanning
probe-optical microscope (Switzerland) connected to version 1.8 soft-
ware. The parameters of surface roughness included average roughness
2.6. Toxicity assessment
2.6.1. Plant species, growth condition, and experiments
Lemna minors were provided from Mazandaran wetland in Northern
Iran and were rinsed by distilled water and cultivated in modified
(
S
a
), valley depth (S
v
), root mean square (S
).
q p
), peak height (S ) and
peak-valley height (S
y
Steinberg culture medium including 349 mg/L KNO
12.5 mg/L K HPO , 108 mg/L Ca(NO .4H O, 49 mg/L MgSO
0.04 mg/L Na MoO .2H O, 0.45 mg/L FeCl .6H O, 0.1 mg/L MnCl
1.1 mg/L H BO , 0.1 mg/L ZnSO .7H O, 1.5 mg/L EDTA, all were provided
3
, 90 mg/L KH
.7H
.2H
2
PO
O,
O,
4
,
Atomic absorption spectroscopy (AAS) (NovAA 400, Analytik Jena,
Germany) was used to study the leaching concentrations of zinc and
iron. The functional groups of samples were carried out by an FTIR
spectrometer (Tensor 27, Bruker, Germany) in the range of 400–4000
2
4
3
)
2
2
4
2
2
4
2
3
2
2
2
3
3
4
2
by Merck (Germany). The toxicity experiments were done in optimum
condition for 3 h. Samples were taken after different time spans of 60,
120, and 180 min to analyze their toxicity. In addition, grown plants in
pure distilled water were used as the control sample.
1
/cm by the KBr disk method. The chemical oxygen demand (COD) of
the PhP solution was determined before and after the treatment process
using standard method ASTM D6697-01 with a Palin test apparatus
(
United Kingdom) [32]. The photoluminescence (PL) spectra of the as-
synthesized samples were monitored by a spectrometer (Perkin Elmer
3. Results and discussion
LS45, USA). Ultraviolet-visible diffuse reflectance spectrophotometry
(
UV–Vis DRS) of the samples were recorded on an Analytik Jena spec-
3.1. Characterization
trophotometer (S 250, Germany). Gas chromatography-mass spectrom-
etry (GC–MS) analysis was performed with Agilent 6890 system
coupled with an Agilent 5973 mass instrument (Agilent Technologies,
Palo Alto, Canada). The characteristics of the GC–MS instrument can
be found in our previous report [31].
Fig. 1 shows the XRD pattern of pure ZnFe-LDH/GO and ZnFe-LDH/
GO coated on the glass substrate. For the ZnFe-LDH/GO sample
(Fig. 1a), the measured XRD pattern shows the characteristic diffraction
peaks of the LDH structure via a hexagonal phase. The detected diffrac-
tion peaks are corresponding to the crystallographic planes of (003),
(006), (110), (101), (009), (012), (015), (018), (110), and (113)
which can be indexed to typical LDH materials [14]. Moreover, the dif-
fraction peak of the (001) plane (2θ ~ 10°) corresponds to the GO.
These results indicate the integration of GO into the LDHs and confirm
the successful synthesis of ZnFe-LDH/GO. The high reflection intensity
2
.4. Photocatalytic performance experiments
Photocatalytic oxidation experiments were conducted in a 500 mL
capacity beaker glass photoreactor. The reactor was equipped with
glass substrates, which were located in the reactor. The outer surface
Scheme 1. Schematic illustration for the fabrication process of ZnFe-LDH/GO on DPA-coated glass substrates.

4
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
Fig. 1. XRD pattern of the (a) pure ZnFe-LDH/GO and (b) ZnFe-LDH/GO/GS samples.
of the observed peaks shows the high crystallinity of the LDH. The mea-
sured XRD pattern for ZnFe-LDH/GO/GS (Fig. 1b) shows the characteris-
tic diffraction peaks of the LDH structure via a hexagonal phase along
with the reflections intrinsic to the quartz glass. It is also worth pointing
out that the ZnFe-LDH/GO/GS shows an insignificance shift for the peaks
from their normal positions in the pattern of pure ZnFe-LDH/GO
that the impurity phase was formed by incorporation of Si into the coat-
ing [6].
SEM images were taken to explore the morphologies of the bare
glass and ZnFe-LDH/GO nanocomposite coated on glass substrates
(Fig. 2). As shown in Fig. 2a,b, the bare glass substrate showed an exces-
sively rough surface with disordered valleys. Fig. 3a–d shows the SEM
images of ZnFe-LDH/GO coated on the glass substrates. As can be seen
in these figs, the orientation of hexagonal patterned LDH nanorods is
in perpendicular and lateral sides to the glass support. Similar size and
shape can be seen for the nanorods grown along the c-axis on the
glass support. The average diameter size rods are about 70 nm. The
SEM cross-sectional view was used to measure the thickness of the
ZnFe-LDH/GO coated on glass substrates. According to Fig. 3e, f, no obvi-
ous gap exists between the DPA layer and glass support, suggesting the
binding of a thin DPA layer with the substrate. The thickness of the
(
3
(
Fig. 1a). The peaks at 14.36°, 22.81°, 27.61°, 31.96°, 34.41°, 35.51°,
8.06°, 41.41°, 46.86°, and 56.66° are ready to be indexed to the (003),
006), (110), (101), (009), (012), (015), (018), and (110) planes, re-
spectively, which correspond to the characteristic model of hydrotalcite
structure [14,33]. On the other hand, the peaks attributed to the quartz
phase of the glass substrate at 20.41° and 41.76° are indexed as planes
(
100), and (200). In addition, the extra peaks in the pattern show that
an impurity phase of zinc‑iron silicate is present, probably because of
the partial glass substrate dissolution in the alkaline condition and
Fig. 2. (a, b) SEM images of the bare glass substrate with different magnification.

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
5
Fig. 3. (a–d): top-view and (e, f) cross-sectional SEM images of glass substrate after coating of ZnFe-LDH/GO with different magnification.
fabricated ZnFe-LDH/GO nanocomposite was estimated at about
9.5 μm. It is also worth pointing out that the thickness of films might
also increase by repeating the coating process for better control of film
uniformity.
The elemental composition of the as-prepared photocatalyst was de-
termined by EDX microanalysis, and the results are shown in Fig. 4. The
EDX spectrum of photocatalyst confirmed the presence of C, N, O, Si, S,
Fe, and Zn elements in the sample. Fig. 5 displays EDX mapping images
of the ZnFe-LDH/GO coated on the glass substrates. The obtained results
reveal the homogeneous distribution of elements in the photocatalyst,
which implying the successful deposition of LDH on the glass substrate.
The topology and roughness properties of the bare glass, DPA, and
ZnFe-LDH/GO coated on the glass substrate were examined by AFM
analysis. Fig. 6 shows the results of two-dimensional and three-
dimensional AFM images from the samples, with the brightest region
as the highest point of the glass surface and the dark area as the valleys.
1

6
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
had a different structure. The change of topology was due to the ZnFe-
LDH/GO nanocomposite incorporation on the surface of the bare glass.
The AFM images were applied for achieving documents regarding
the quantitative measurement of surface roughness, whose parameters,
including bare, DPA, and ZnFe-LDH/GO nanocomposite coated on a
glass substrate, are given in Table 1, which are estimated in an AFM
scanning area of 6 μm × 6 μm. The surface of the bare glass has the
highest roughness with an average roughness value of 118.99 nm. A de-
crease in the S
ness surface displayed the uniform deposition of DPA film on the surface
of the glass substrate. The S and S values of the DPA/GS nanocompos-
a
value to 13.87 nm and the production of more smooth-
a
q
ite were increased when ZnFe-LDH/GO nanocomposite was coated on
the DPA/GS, which implies the more coarse surface after coating on
the DPA/GS.
Fig. 7 shows the FTIR spectrum of the ZnFe-LDH/GO/GS sample. The
band around 823 1/cm represents the stretching and vibration mode of
M-O in the hydrotalcite, and the bands at 400–500 1/cm are related to
2
+
the vibration mode of O\\M\\O, where M denotes the cations of Zn
and Fe3 [34]. The band located at 1064 1/cm is related to sulfate ions
+
Fig. 4. EDX analysis of the ZnFe-LDH/GO/GS sample.
[35]. The band at 1637 1/cm is associated with the bending mode of in-
terlayer water molecules [36]. The absorption band at 2509 1/cm is at-
tributed to the stretching vibration of C_O, which indicated that GO
is successfully intercalated in the LDH [36]. On the other hand, the
band appeared at 1242 1/cm ascribed to the C\\O bending vibration
[36]. In addition, the broad peak around 3222 1/cm corresponds to the
stretching vibrations of N\\H and O\\H groups in the DPA [37,38].
The band at 2960 1/cm is related to the asymmetric stretching mode
of C\\H. The weak band at around 3552 1/cm is observed due to the
stretching mode of COOH [36]. The broad and strong band at the
As can be seen in Fig. 6a the rough surface of the bare glass substrate
contains hills and valleys. In addition, the two-dimensional AFM
image (see Fig. 6a) shows the irregular structure. On the other hand,
the coating of DPA on the glass substrate decrease the roughness of its
surfaces and the DPA coated on glass showed the lowest surface
smoothness (Fig. 6b). In addition, the ZnFe-LDH/GO/GS nanocomposite
has higher roughness compared to DPA coated on glass (DPA/GS)
(Fig. 6c). As can be seen in Fig. 6c, the ZnFe-LDH/GO/GS nanocomposite
Fig. 5. X-ray Dot-mapping analysis of major elements for the ZnFe-LDH/GO/GS sample.

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
7
Fig. 6. AFM two-dimensional image and its corresponding three-dimensional image of the (a) bare glass substrate, (b) DPA coated on the glass substrate (DPA/GS), and (c) ZnFe-LDH/GO
film coated on DPA/GS.
range of 3701 1/cm is assigned to the stretching vibrations of –OH with
hydrogen bonding and surface water molecules [36].
Therefore, the GO incorporation into the LDH crystalline lattice could in-
crease harvesting light in the visible region.
The light-harvesting feature of photocatalysts is a key parameter for
a photocatalytic process. Therefore, UV–Vis diffuse reflectance spectra
were utilized to measure the optical characteristics of the as-
synthesized samples (Fig. 8). As can be seen, ZnFe-LDH/GO nanocom-
posite exhibits a redshift in comparison to the ZnFe-LDH sample.
The PL behavior shows the separation and recombination process of
−
+
electron-hole pairs (e − h ) in the synthesized catalysts [33]. The PL
spectra of the ZnFe-LDH/GO/GS sample were monitored at an excitation
wavelength of 315 nm to study the photocatalytic activities. Fig. 9 dis-
plays the PL spectra changes via the photocatalytic process with a TA so-
lution for the ZnFe-LDH/GO/GS photocatalyst at different time intervals.
•
As can be seen from the figure, the generation of OH radicals was in-
creased by enhancing the illumination time. Our findings are consistent
with the results reported in the other studies [39,40].
Table 1
Area roughness parameters of the bare, DPA, and ZnFe-LDH/GO coated on glass substrates
resulted from analyzing three randomly selected AFM analyses.
3
.2. Comparison of various processes for PhP degradation
Samples
Roughness parameters
(nm) (nm)
S
a
S
q
S
y
(nm)
S
p
(nm)
v
S (nm)
Fig. 10a displays the role of various processes on PhP elimination to
Bare glass
DPA coated on glass
LDH/GO coated on glass
118.99
13.87
22.93
152.34
17.62
29.57
1031.7
117.19
227.74
541.13
60.96
133.3
−490.61
−56.22
−94.44
find out the most effective system. The photolysis experiment revealed
that there was 14.96% of DE (%) after 180 min irradiation, confirming
that PhP itself is very hard to be decomposed under visible light

8
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
Fig. 9. PL spectra changes during the photocatalytic process with the terephthalic acid
Fig. 7. FTIR spectrum of the ZnFe-LDH/GO/GS sample.
solution for the ZnFe-LDH/GO/GS photocatalyst at different time intervals.
irradiation. However, the application of only ZnFe-LDH/GO/GS nano-
composite leads to 1.5 times higher decomposition rate in comparison
to photolysis via the adsorption process. However, visible light irradia-
tion could sharply increase the efficiency of the system causing ZnFe-
LDH/GO/GS nanocomposite in which 60.01% of PhP was degraded
after an additional 150 min of photocatalysis process. The synergistic
function of a visible light plus catalyst in PhP degradation was verified
by comparing evaluated systems and related elimination efficiency. In
addition to the involvement of photolysis and adsorption in the elimina-
tion process, the incident light provides considerable energy to the cat-
alyst to generate reactive oxygen species (ROSs), resulting in the
effective oxidation of PhP molecules. The synergistic index was evalu-
ated for photocatalytic system with the help of Eq. (1), so that the PhP
removal efficiency via only UV, ZnFe-LDH/GO/GS, and UV/ZnFe-LDH/
GO/GS systems and related rate constant (kapp) were explored by
systems on the apparent pseudo-first-order constant of PhP elimination
was given in Table 2.
kapp;Vis=ZnFe−LDH=GO=GS
Synergy index ¼
ð1Þ
kapp;Vis þ kapp;ZnFe−LDH=GO=GS
In this equation, kapp refers to the rate constant (1/min) of the as-
mentioned processes. The value of 2 was calculated for the synergy factor
of the photocatalytic system. This shows an efficient PhP degradation due
to a positive interaction between visible light irradiation and adsorption.
3.3. Factors affecting the photocatalytic process
3.3.1. Photocatalyst amount
The optimal photocatalyst amount should be detected due to its
major role in the efficiency of the robust degradation of photocatalysis.
Accordingly, the number of photocatalyst from 2 to 4 sheets were exam-
ined in a series of experiments for the decomposition of 15 mg/L of PhP
at pH 8 and 150 min of light exposure (Fig. 10b). It is clearly seen from
Fig. 10b that under the same experimental conditions, the DE (%) de-
pends on the number of the photocatalyst. The DE (%) was highest
with three photocatalyst sheets and dropped thereafter with the in-
creasing number of photocatalyst sheets. The increased photocatalytic
degradation efficiency from 2 to 3 photocatalyst sheets is principally
contributed to the elevated total surface area and active sites, which be-
came accessible on the surface of catalyst following an increase in the
concentration of catalyst. The number of photocatalyst sheets from 3
to 4 decreased the efficiency of degradation, probably due to reduced
penetration of light, and diminished available surface area of the
photocatalyst [41]. The obtained result implies that we cannot achieve
greater DE (%) by increasing the photocatalyst amount.
pseudo-first-order model by drawing a plot of ln (A
0 t
/A ) versus time,
where A and A are the highest peak intensity of the absorption spectra
0
t
determined at the beginning and at different time (t), respectively. The
obtained results indicated that for all studied systems, the correlation
2
2
coefficient (R ) values of the pseudo-first-order model (R ≥ 0.8057) re-
vealing that all the systems followed pseudo-first-order kinetics, which
is in accordance with the literature [18]. The influence of various
3.3.2. Initial PhP concentration
One of the main parameters studied in the present research is to eval-
uate the photocatalytic dissociation dependency on the aqueous pollutant
concentration [42]. The degradation of PhP was investigated and its initial
concentration was changed from 5 to 25 mg/L. As shown in Fig. 10c, the
process efficiency was reduced from 90.00% to 16.01% with increasing
PhP concentration from 5 mg/L to 25 mg/L. Decreased initial PhP concen-
tration elevated the possibility of the reaction of PhP with oxidizing spe-
cies, resulting in higher efficiency of degradation. Nevertheless, the
excess PhP concentration decreased the degradation efficiency. At lower
PhP concentration, the active sites are enough on the photocatalyst sur-
face to comparatively interact with low PhP molecules in the solution,
Fig. 8. UV–Vis diffuse reflectance spectra of ZnFe-LDH and ZnFe-LDH/GO samples.

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
9
Fig. 10. (a) Removal potential of PhP by various systems ([photocatalyst sheets] = 3, [PhP]
0
= 15 mg/L, and pH = 8); (b) Effect of number of photocatalyst sheets ([PhP]
0
= 15 mg/L, and
0
pH = 8); (c) Effect of PhP concentration ([photocatalyst sheets] = 3, and pH = 8); (d) Effect of initial pH of solution ([photocatalyst sheets] = 3, and [PhP] = 15 mg/L).
resulting in high PhP degradation efficiency. However, remaining concen-
trations can be seen by raising the concentration of PhP in the aqueous so-
lution. Thus, some of the PhP is able to interact only with insufficient
active sites on the photocatalyst surface, thereby increasing the PhP deg-
radation efficiency at higher initial concentrations [33,42].
Moreover, Martínez et al. [46] by evaluating the solution pH effect on
the ketoprofen photocatalytic degradation reported occurred photocat-
+
2
alytic reactions on the TiO surface by oxidation and reduction with h
−
or •OH and e . In addition, they showed the influence of solution pH on
the photocatalyst surface reactions and so •OH. The main oxidant spe-
cies are the holes at low or neutral values of pH, while •OH at high pH
value. Therefore, pH = 11.2 was chosen to be optimal to maximize
the ketoprofen photocatalytic removal.
3
.3.3. pH of solution
The pH of a solution can affect significantly the photocatalytic pro-
cess [43,44]. The effect of the initial pH on the degradation efficiency
of PhP was evaluated in the range of pH 3–11 (Fig. 10d). The results re-
vealed that the degradation performance increased with the solution
pH up to 8 and subsequently reduced, probably due to differences in
the interactions of the catalyst surface with PhP molecules. Based on
previous results, the pH value of the photocatalytic process can influ-
ence the photocatalyst surface charge properties as well as affect the ad-
sorption trend of the organic compound and the catalyst [45,46]. An
et al. [45] by evaluating the solution pH effect on the lamivudine photo-
catalytic elimination found the lamivudine elimination uncontrolled by
the catalyst surface charge properties.
Here, the surface properties of heterogeneous catalysts markedly in-
fluence the decomposition process, particularly the surface charge. Thus,
the pH at the point of zero charge (pHpzc) was determined for ZnFe-
LDH/GO to identify its surface charge. A pHpzc of 7.2 was detected for
ZnFe-LDH/GO, indicating positive charge (pH b 7.2) and negative charge
a
(pH N 7.2) at the surface of the sample. However, the PhP pK value is
equal to 5.12. A positive charge can be seen for PhP molecules in
pH b 5.12, but a negative charge in pH N 5.12. Therefore, acidic and alka-
line pH values are not advantageous for PhP to be adsorbed on the surface
of ZnFe-LDH/GO/GS. Weak adsorption at low pH values can be attributed
to the repulsing influence of two positive charges, whereas negative
charges can be found for either photocatalyst or PhP in the alkaline envi-
ronment, inducing their electrostatic repulsion and lower efficiency of
PhP photodegradation. The results show that the photodegradation pro-
cess is more favored under conditions close to neutral media (pH 8).
Table 2
Determination of the degradation efficiency, pseudo-first-order kapp (1/min) removal rate
2
constants and coefficient of determination (R ) within 180 min of reaction time.
Process
Degradation
efficiency (%) (1/min)
k
R2
Kinetic equation
3.4. Effect of scavengers
Only visible light
ZnFe-LDH/GO/GS
Vis/ZnFe-LDH/GO/GS 60.01
14.96
23.09
0.0009
0.0014
0.0046
0.9704 y = 0.0009x − 0.0158
0.9271 y = 0.0014x − 0.0266
0.8057 y = 0.0046x − 0.1377
The reactive oxygen species (ROSs) in the process of PhP degrada-
tion are very significant in photocatalytic reactions under visible light.
Experiments trapping ROSs were performed by augmentation of

10
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
various scavengers to discriminate their roles in the photocatalytic deg-
radation of PhP. For this aim, various scavengers agents, such as formic
acid (FA), isopropanol alcohol (IPA), and 1,4-benzoquinone (BQ) were
examined without the use of scavengers. The presence of all scavengers
reduced DE (%) of ZnFe-LDH/GO/GS, however, most noticeable out-
−
·
comes were obtained with the use of •OH and O
2
scavengers
+
•
used to capture photogenerated holes (h ), hydroxyl radicals ( OH),
(Fig. 11). Because of a two-fold increase in the amount of scavengers,
there was severe impairment in the performance (Fig. 11). Moreover,
−·
and superoxide radicals (O
2
), respectively [47]. To evaluate the photo-
•
catalytic activity inhibition of individual compounds, their impacts were
the PL analysis was used to confirm the production of OH species for
Fig. 11. Effect of different scavenger on the PhP degradation efficiency (a) [PhP]:[scavenger] = 1:0.5, and (b) [PhP]:[scavenger] = 1:1. Experimental condition: [photocatalyst sheets] = 3,
PhP] = 15 mg/L, and pH = 8.
[
0

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
11
Clearly, the addition of K
of PhP because of the enhanced generation of sulfate (SO
2
S
2
O
8
increased the photocatalytic degradation
·
−
4
) radicals
·
−
(
Eq. (2)). In addition, the photochemical generation of SO
4
radicals
by analogy to the Fenton and Fenton-like reactions, Eqs. (3) and (4)
could be proposed for persulfate activation by Fe2 and Fe ions, re-
+
3+
spectively [48]. Moreover, according to Eqs. (5) and (6), activation of
2
−
2+
·−
S O
2
8
with surface Zn ions resulted in the generation of more SO
4
radicals that could decompose PhP molecules [49].
2
− hv
ꢀ−
S2O → 2SO4
ð2Þ
ð3Þ
8
Fe2 þ S2O 82 −→Fe3þ þ SO4ꢀ− þ SO4
þ
2−
Fe3 þ S2O82−→Fe2þ þ S2O8ꢀ−
þ
ð4Þ
Zn2
þ
þ
þ
S2
O
2−
→Zn þ SOꢀ 4− þ SO4
3þ
2−
ð5Þ
ð6Þ
8
Zn2 þ SOꢀ 4− →Zn þ SO4
3þ
2−
3.6. Transformation intermediates of PhP
Fig. 12. Effect of K
2
S
2
O
8
on the degradation efficiency of PhP. Experimental condition:
= 15 mg/L, and pH = 8.
[photocatalyst sheets] = 3, [PhP]
0
To obtain the degradation intermediates of PhP, the
photodegradation of PhP was performed and intermediates were iden-
tified by GC–MS during the photocatalytic reaction. Table 3 lists five
compounds distinguished as intermediates. In the PhP molecules, the
double bond, phenolic group, and amine group are easily attached by
radicals through photocatalytic oxidation because they are functional
groups with relatively high electron density. Also, it was possible to as-
sume the cleavage of N_N, C\\N, and C\\C bonds to be the early reac-
tion stages leading to the destruction of some rings with the likely
production of compounds such as six-membered aromatic ring contain-
ing N heteroatom. There also might be other compounds resulting from
PhP dissociation, which were not recognized prior to the formation of
the detected compounds. Low-carbon-content aliphatics including
propan-1-amine, and N-methylacetamide are generated by additional
oxidation of these cyclic intermediates via cleavage of the rings by con-
secutive attacks of ROSs. Finally, partial mineralization of all these ali-
the ZnFe-LDH/GO/GS sample during the decomposition. As seen in
Fig. 9, the prolongation of irradiation time gradually elevates the inten-
sity of PL, suggesting the generation of OH species on the sample sur-
•
face within the pollutant degradation under visible light irradiation.
−
·-
The aforementioned observations confirmed the influence order of O
N •OH N h for all ROSs present in the reaction of decomposition.
2
+
3
.5. Effect of enhancer
The free radicals can be produced by oxidants, thereby speeding up
the degradation reaction [33]. To assess the influence of oxidant on DE
%) of PhP, potassium persulfate (K ) with an initial concentration
(
2 2 8
S O
of 0.5 mmol/L and 1 mmol/L was introduced to the solution under pho-
tocatalytic process at a concentration PhP of 15 mg/L. Fig. 12 shows that
the presence of K
2
S
2
O
8
drastically increased the reaction rate of PhP,
2 2
phatic compounds into H O, CO , and inorganic ions is plausible [50].
where 72.41% and 93.95% DE (%) were achieved within 150 min of pho-
tocatalytic process with 0.5 and 1 mmol/L, respectively. Moreover, the
PhP removal by the K S O (1 mmol/L) alone in the absence of catalyst
2 2 8
and light irradiation was 10.94%. It should be noted that the obtained re-
sult for evaluating catalytic activity in persulfate alone is independent of
the previous adsorption-desorption equilibrium in the dark condition.
Accordingly, rising concentrations of inorganic ions along with a drop
in COD concentration in the treated suspension can be regarded as ac-
ceptable indices of contaminant mineralization [51]. At a PhP concentra-
tion of 15 mg/L with optimized parameters, the photocatalytic process
efficiency was tested by COD analyses. The result was a COD degrada-
tion efficiency of 60% during 300 min of treatment.
Table 3
Identified intermediates during degradation of PhP through the photocatalytic process.
No.
Compound
t
R
(min)
Main fragments (m/z)(%)
Structure
1
2
Propan-1-amine
N-methylacetamide
3.117
3.357
59.00 (100.00%), 56.10 (4.92%), 60.00 (3.23%), 73.00 (2.23%), 61.00 (2.09%)
59.00 (100.00%), 60.00 (2.86%), 57.00 (1.29%), 56.10 (0.29%), 61.10 (0.22%)
3
4
5
Benzen,1,2-dimethyl
Benzen,1,3-dimethyl
2,6-diamino pyridine
3.938
4.237
91.00 (100.00%), 59.00 (80.50%), 106.10 (57.90%), 105.10 (24.31%), 77.00 (10.71%)
91.00 (100.00%), 106.10 (55.46%), 105.10 (22.30%), 77.00 (10.69%), 92.00 (7.56%)
213.10 (100.00%), 108.00 (58.28%), 81.10 (47.52%), 57.10 (27.54%), 55.10 (24.02%)
29.942

12
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
Fig. 13. (a) Reusability of ZnFe-LDH/GO/GS photocatalyst, (b) SEM image of ZnFe-LDH/GO/GS photocatalyst after five consecutive experimental runs. Experimental condition:
photocatalyst sheets] = 3, [PhP] = 15 mg/L, and pH = 8.
[
0
3
.7. Reusability and stability of the ZnFe-LDH/GO/GS photocatalyst
Reusability for a photocatalyst is one of the main parameters to ex-
significantly that could be attributed to the dissociation of hazardous in-
termediates due to the generation of ROSs through the photocatalytic
process using ZnFe-LDH/GO/GS photocatalyst. Consequently, the photo-
catalytic process was put forward as an outstanding elimination system,
which could remove pharmaceutical pollutants and decline the toxicity
of the treated solution.
plore its economic status and practical purposes [52]. Hence, a series
of recycling experiments were carried out using ZnFe-LDH/GO/GS as
photocatalyst toward the dissociation of PhP under visible light irradia-
tion, as shown in Fig. 13. The tests were consecutively repeated five
times to evaluate the reduced efficiency of PhP degradation after each
run. As shown in Fig. 13a, the decline in DE (%) of PhP was not significant
after five cycles. The five cycles of photocatalysis with ZnFe-LDH/GO/GS
photocatalyst yielded degradation efficiencies of 60.01%, 56.26%,
4. Conclusions
In conclusion, we have elaborately fabricated a novel ZnFe-LDH/GO/
GS photocatalyst. The photocatalytic implementation of the as-prepared
photocatalyst was scrutinized for the degradation of PhP, as a model
emerging contaminant, under visible light. The photocatalytic perfor-
mance could reach 60.01% during 150 min of the photocatalytic process
under the conditions of initial PhP concentration of 15 mg/L, pH of 8
(natural pH), and 3 sheets. Trapping experiments indicated the influ-
5
3.90%, 50.30%, and 48.10%, respectively, obviously indicating the
photocatalyst robustness to degrade the desired contaminant in the
aqueous environment. The iron and zinc released in the solution during
PhP degradation were assessed as well. The insignificant amount of iron
and zinc released indicate high physicochemical durability of the ZnFe-
LDH/GO/GS. The leached amounts of zinc and iron after 5 cycles
−
·
+
(
Table 4) were b1.249 mg/L and 0.2759 mg/L, which are lower than
ence order of O
2
N•OH N h for the ROSs present in decomposition.
the legal limit of iron (i.e., 0.3 mg/L) and zinc (i.e., 3 mg/L) concentra-
tions in drinking water according to World Health Organization recom-
mendations, revealing lack of secondary pollution by the ZnFe-LDH/GO/
GS [53,54]. Additional analysis was conducted in the nature of the re-
covered ZnFe-LDH/GO/GS photocatalyst. As depicted in Fig. 13b the
SEM image of the photocatalyst was approximately the same as that
of fresh photocatalyst (see Fig. 3) after the five cycles, indicating that
ZnFe-LDH/GO/GS had good stability throughout the photocatalytic
process.
Moreover, the addition of oxidant improved the performance of the sys-
tem. The reusability experiments showed that the reusable ZnFe-LDH/
GO/GS photocatalyst provides effective polluted water treatment with
low zinc and iron leaching. GC–MS result reveals that PhP molecules
can be dissociated into non-toxic intermediates. Five compounds were
identified as intermediates. Results have revealed that 60% of COD re-
moval efficiency was achieved after 300 min of photocatalytic reaction.
Finally, the toxicity of the as-prepared photocatalyst catalyzed photo-
catalytic process was assessed on an aquatic plant, L. minor. The ob-
tained result revealed a gradual decrement in the toxicity of the
treated solutions by the progress in the reaction time from 60 to
180 min. Therefore, the present study provides new insights into the
practical development of photocatalysts based on LDH for the decompo-
sition of pollutants under visible-light irradiation.
3
.8. Toxicity assessment
The literature review showed that various aquatic species have been
used to assess the influence of initial pollutants and their intermediate
compounds which were generated along with the photocatalytic pro-
cesses [38]. The advantages of using aquatic plants are their sensitivity
to a wide range of pollutants, simple structure, and high growth rate
Table 4
Leaching concentrations of zinc and iron from ZnFe-LDH/GO/GS into the solution for each
cycle.
[31]. Lemna minor is a rapidly spreading aquatic, small and wide range
Cycle
Zn (mg/L)
.050
a
Fe (mg/L)
0.2032
a
genome size plant, so it is a suitable species for the examination of pol-
lutant toxicity [55]. Fig. 14 shows the visual change in the frond color
and decomposition of Lemna minor fronds after exposure to the control
solution, control PhP solution and PhP solution exposed to various reac-
tion times. It was observed that the greatest toxicity occurred in the un-
treated PhP solution (15 mg/L). In the pollutant solutions treated by the
photocatalytic process, the toxicity decreased gradually by increasing
exposure time. It can be assumed that toxic by-products may be formed
at 60 and 120 min of photocatalytic process and were stacked in the so-
lution. By elevation of reaction time up to 180 min, the toxicity reduced
1
1
2
3
4
2.492
0.1615
0.1613
0.0477
0.2759
1
2
.903
.086
1.249
5
a
Legal limit of concentration: 3 mg/L (Zn) and 0.3 mg/L (Fe).

P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
13
Fig. 14. The visual changes of L. minor locate in (a) control solution, (b) PhP solution, and photocatalytic treated samples for (c) 60 min, (d) 120 min, and (e) 180 min.
synergistic effect for photocatalytic degradation of diclofenac: mechanisms, model-
ing and degradation pathway, J. Mol. Liq. 291 (2019), 111342.
Authors statement
[
9] S.M. Boyer, J. Liu, S. Zhang, M.I. Ehrlich, D.L. McCarthy, L. Tong, J.B. DeCoste, W.E.
Bernier, W.E. Jones, The role of ruthenium photosensitizers in the degradation of
We would like to confirm that there is no known conflict of interest
associated with this publication.
phenazopyridine with TiO
2
electrospun fibers, J. Photochem. Photobiol., A 329
(2016) 46–53.
[
[
[
10] H.S. Hilal, G.Y.M. Al-Nour, A. Zyoud, M.H. Helal, I. Saadeddin, Pristine and supported
ZnO-based catalysts for phenazopyridine degradation with direct solar light, Solid
State Sci. 12 (2010) 578–586.
Declaration of competing interest
11] A.H. Zyoud, N. Zaatar, I. Saadeddin, C. Ali, D. Park, G. Campet, H.S. Hilal, CdS-
2
sensitized TiO in phenazopyridine photo-degradation: catalyst efficiency, stability
and feasibility assessment, J. Hazard. Mater. 173 (2010) 318–325.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
12] H. Lu, Z. Zhu, H. Zhang, J. Zhu, Y. Qiu, L. Zhu, S. Küppers, Fenton-like catalysis and ox-
idation/adsorption performances of acetaminophen and arsenic pollutants in water
on a multimetal Cu–Zn–Fe-LDH, ACS Appl. Mater. Interfaces 8 (2016) 25343–25352.
13] X. Guo, F. Zhang, D.G. Evans, X. Duan, Layered double hydroxide films: synthesis,
properties and applications, Chem. Commun. 46 (2010) 5197–5210.
[
[
Acknowledgment
14] D. Polese, A. Mattoccia, F. Giorgi, L. Pazzini, L. Di Giamberardino, G. Fortunato, P.G.
Medaglia, A phenomenological investigation on chlorine intercalated layered dou-
ble hydroxides used as room temperature gas sensors, J. Alloys Compd. 692
The authors thank the University of Tabriz and Near East University
for the support provided.
(2017) 915–922.
[
15] G. Zhao, L. Liu, C. Li, T. Zhang, T. Yan, J. Yu, X. Jiang, F. Jiao, Construction of diatomite/
ZnFe layered double hydroxides hybrid composites for enhanced photocatalytic
degradation of organic pollutants, J. Photochem. Photobiol., A 367 (2018) 302–311.
References
[
16] D.P. Sahoo, S. Nayak, K.H. Reddy, S. Martha, K. Parida, Fabrication of a co(OH)
2
/ZnCr
[
1] A.L. Boreen, W.A. Arnold, K. McNeill, Photochemical fate of sulfa drugs in the aquatic
environment:sulfa drugs containing five-membered heterocyclic groups, Environ.
Sci. Technol. 38 (2004) 3933–3940.
LDH “p–n” heterojunction photocatalyst with enhanced separation of charge car-
2 2
riers for efficient visible-light-driven H and O evolution, Inorg. Chem. 57 (2018)
3840–3854.
[
2] A. Khataee, T.S. Rad, B. Vahid, S. Khorram, Preparation of zeolite nanorods by corona
discharge plasma for degradation of phenazopyridine by heterogeneous sono-
Fenton-like process, Ultrason. Sonochem. 33 (2016) 37–46.
[17] X. Li, R. Shen, S. Ma, X. Chen, J. Xie, Graphene-based heterojunction photocatalysts,
Appl. Surf. Sci. 430 (2018) 53–107.
[18] R. Hassandoost, S.R. Pouran, A. Khataee, Y. Orooji, S.W. Joo, Hierarchically structured
3
+
4+
[
3] S. Bae, D. Kim, W. Lee, Degradation of diclofenac by pyrite catalyzed Fenton oxida-
ternary heterojunctions based on Ce /Ce
3 4
modified Fe O nanoparticles an-
tion, Appl. Catal., B 134-135 (2013) 93–102.
4] F.J. Beltrán, A. Aguinaco, J.F. García-Araya, Kinetic modelling of TOC removal in the
photocatalytic ozonation of diclofenac aqueous solutions, Appl. Catal., B 100
chored onto graphene oxide sheets as magnetic visible-light-active photocatalysts
for decontamination of oxytetracycline, J. Hazard. Mater. 376 (2019) 200–211.
[19] Z. Xu, M. Yue, L. Chen, B. Zhou, M. Shan, J. Niu, B. Li, X. Qian, A facile preparation of
edge etching, porous and highly reactive graphene nanosheets via ozone treatment
at a moderate temperature, Chem. Eng. J. 240 (2014) 187–194.
[
(2010) 289–298.
[
5] E.D. Green, R.C. Zimmerman, W.H. Ghurabi, D.P. Colohan, Phenazopyridine hydro-
chloride toxicity: a cause of drug-induced methemoglobinemia, Ann. Emerg. Med.
[20] K. Chakraborty, T. Pal, S. Ghosh, RGO-ZnTe: a graphene based composite for tetracycline
degradation and their synergistic effect, ACS Appl. Nano Mater. 1 (2018) 3137–3144.
[21] M. Shao, J. Han, M. Wei, D.G. Evans, X. Duan, The synthesis of hierarchical Zn–Ti lay-
ered double hydroxide for efficient visible-light photocatalysis, Chem. Eng. J. 168
(2011) 519–524.
8
(1979) 426–431.
[
6] M. Alikarami, R. Darvishi Cheshmeh Soltani, A. Khataee, An innovative combination
of electrochemical and photocatalytic processes for decontamination of bisphenol a
endocrine disruptor form aquatic phase: insight into mechanism, enhancers and
bio-toxicity assay, Sep. Purif. Technol. 220 (2019) 42–51.
7] A. Ziarati, A. Badiei, R. Luque, Engineered bi-functional hydrophilic/hydrophobic
yolk@shell architectures: a rational strategy for non-time dependent ultra selective
photocatalytic oxidation, Appl. Catal., B 240 (2019) 72–78.
[22] D.P. Sahoo, S. Patnaik, D. Rath, K.M. Parida, Synergistic effects of plasmon induced
[
Ag@Ag
evolution and phenol oxidation reactions, Inorg. Chem. Front. 5 (2018) 879–896.
[23] C. Zhang, H.-C. Yang, L.-S. Wan, H.-Q. Liang, H. Li, Z.-K. Xu, Polydopamine-coated po-
rous substrates as platform for mineralized β-FeOOH nanorods with
photocatalysis under sunlight, ACS Appl. Mater. Interfaces 7 (2015) 11567–11574.
3 4
VO /ZnCr LDH ternary heterostructures towards visible light responsive
O
2
[
8] M. Irandost, R. Akbarzadeh, M. Pirsaheb, A. Asadi, P. Mohammadi, M. Sillanpää, Fab-
rication of highly visible active N, S co-doped TiO @MoS heterojunction with
2 2
a

14
P.Y. Motlagh et al. / Journal of Molecular Liquids 302 (2020) 112532
[
[
[
[
[
[
[
[
[
[
[
[
[
[
24] M. Mehrjouei, S. Müller, D. Möller, Removal of fuel oxygenates from water using ad-
and ultrafast sonophotocatalytic performance for degradation of antibiotics, Inorg.
Chem. 58 (2019) 1834–1849.
[41] A. Hassani, P. Eghbali, A. Ekicibil, Ö. Metin, Monodisperse cobalt ferrite nanoparticles
vanced oxidation technologies by means of falling film reactor, Chem. Eng. J. 211-
212 (2012) 353–359.
25] C.A. Hong, H.Y. Son, Y.S. Nam, Layer-by-layer siRNA/poly(L-lysine) multilayers on
polydopamine-coated surface for efficient cell adhesion and gene silencing, Sci.
Rep. 8 (2018) 7738.
26] S. Liu, Q. Hu, J. Qiu, F. Wang, W. Lin, F. Zhu, C. Wei, N. Zhou, G. Ouyang, Enhanced
photocatalytic degradation of environmental pollutants under visible irradiation
by a composite coating, Environ. Sci. Technol. 51 (2017) 5137–5145.
27] Y. Liu, K. Ai, L. Lu, Polydopamine and its derivative materials: synthesis and promis-
ing applications in energy, environmental, and biomedical fields, Chem. Rev. 114
2 4 3 4
assembled on mesoporous graphitic carbon nitride (CoFe O /mpg-C N ): a magnet-
ically recoverable nanocomposite for the photocatalytic degradation of organic dyes,
J. Magn. Magn. Mater. 456 (2018) 400–412.
[42] L. Yanyan, T.A. Kurniawan, Z. Ying, A.B. Albadarin, G. Walker, Enhanced photocata-
3 2 2
lytic degradation of acetaminophen from wastewater using WO /TiO /SiO compos-
ite under UV–VIS irradiation, J. Mol. Liq. 243 (2017) 761–770.
[43] A. Hassani, A. Khataee, S. Karaca, M. Fathinia, Heterogeneous photocatalytic ozona-
tion of ciprofloxacin using synthesized titanium dioxide nanoparticles on a mont-
morillonite support: parametric studies, mechanistic analysis and intermediates
identification, RSC Adv. 6 (2016) 87569–87583.
[44] M.S. Peres, M.G. Maniero, J.R. Guimarães, Photocatalytic degradation of ofloxacin
and evaluation of the residual antimicrobial activity, Photochem. Photobiol. Sci. 14
(2015) 556–562.
(2014) 5057–5115.
28] J. Gao, H. Lei, Z. Han, Q. Shi, Y. Chen, Y. Jiang, Dopamine functionalized tannic-acid-
templated mesoporous silica nanoparticles as a new sorbent for the efficient re-
2+
moval of Cu from aqueous solution, Sci. Rep. 7 (2017) 45215.
29] D.-M. Guo, Q.-D. An, Z.-Y. Xiao, S.-R. Zhai, D.-J. Yang, Efficient removal of Pb(II), Cr
(VI) and organic dyes by polydopamine modified chitosan aerogels, Carbohydr.
[45] T. An, J. An, H. Yang, G. Li, H. Feng, X. Nie, Photocatalytic degradation kinetics and
Polym. 202 (2018) 306–314.
2
mechanism of antivirus drug-lamivudine in TiO dispersion, J. Hazard. Mater. 197
30] S. Mondal, M. Chatti, A. Mallick, P. Purkayastha, pH triggered reversible photoin-
(2011) 229–236.
duced electron transfer to and from carbon nanoparticles, Chem. Commun. 50
[46] C. Martínez, S. Vilariño, M.I. Fernández, J. Faria, M.C. L, J.A. Santaballa, Mechanism of
degradation of ketoprofen by heterogeneous photocatalysis in aqueous solution,
Appl. Catal., B 142-143 (2013) 633–646.
(2014) 6890–6893.
31] L. Li, M. Sillanpää, M. Tuominen, K. Lounatmaa, E. Schultz, Behavior of titanium diox-
ide nanoparticles in Lemna minor growth test conditions, Ecotox. Environ. Safe. 88
[47] A. Hassani, P. Eghbali, Ö. Metin, Sonocatalytic removal of methylene blue from water
(2013) 89–94.
2 4 3 4
solution by cobalt ferrite/mesoporous graphitic carbon nitride (CoFe O /mpg-C N )
nanocomposites: response surface methodology approach, Environ. Sci. Pollut. Res.
25 (2018) 32140–32155.
32] ASTM D6697-01, Standard Test Method for Determination for Chemical Oxygen De-
mand (Manganese III Oxygen Demand) of Water (Withdrawn 2010), ASTM Interna-
tional, West Conshohocken, PA, 2001.
33] P. Yekan Motlagh, A. Khataee, T. Sadeghi Rad, A. Hassani, S.W. Joo, Fabrication of
ZnFe-layered double hydroxides with graphene oxide for efficient visible light pho-
tocatalytic performance, J. Taiwan Inst. Chem. Eng. 101 (2019) 186–203.
34] A. Khataee, S. Arefi-Oskoui, L. Samaei, ZnFe-Cl nanolayered double hydroxide as a
novel catalyst for sonocatalytic degradation of an organic dye, Ultrason. Sonochem.
[48] X. Shi, C. Zou, G. Pan, H. Gong, L. Xu, Y. Zhou, Atomically smooth gallium nitride sur-
2
−
2+
face prepared by chemical-mechanical polishing with S
2
O
8
-Fe based slurry,
Tribol. Int. 110 (2017) 441–450.
x
[49] C. Li, G. Zhao, L. Liu, J. Yu, X. Jiang, F. Jiao, Preparation of CuO @ZnFe-LDH composites
and photocatalytic degradation of 4-nitrophenol by activated persulfate, J. Mater.
Sci. Mater. Electron. 29 (2018) 19461–19471.
[50] N. Oturan, S.O. Ganiyu, S. Raffy, M.A. Oturan, Sub-stoichiometric titanium oxide as a
new anode material for electro-Fenton process: application to electrocatalytic de-
struction of antibiotic amoxicillin, Appl. Catal., B 217 (2017) 214–223.
40 ( (2018) 703–713.
35] H. Zhang, X. Wen, Y. Wang, Synthesis and characterization of sulfate and
dodecylbenzenesulfonate intercalated zinc–iron layered double hydroxides by
one-step coprecipitation route, J. Solid State Chem. 180 (2007) 1636–1647.
[51] H. Lin, J. Niu, J. Xu, Y. Li, Y. Pan, Electrochemical mineralization of sulfamethoxazole
36] J. Ni, J. Xue, L. Xie, J. Shen, G. He, H. Chen, Construction of magnetically separable
2 2
by Ti/SnO -Sb/Ce-PbO anode: kinetics, reaction pathways, and energy cost evolu-
tion, Electrochim. Acta 97 (2013) 167–174.
[52] J. Shao, W. Sheng, M. Wang, S. Li, J. Chen, Y. Zhang, S. Cao, In situ synthesis of carbon-
doped TiO single-crystal nanorods with a remarkably photocatalytic efficiency,
2
Appl. Catal., B 209 (2017) 311–319.
[53] S. Dehghan, B. Kakavandi, R.R. Kalantary, Heterogeneous sonocatalytic degradation
3 4
NiAl LDH/Fe O –RGO nanocomposites with enhanced photocatalytic performance
under visible light, Phys. Chem. Chem. Phys. 20 (2018) 414–421.
37] R. Pizzoferrato, E. Ciotta, I.V. Ferrari, M. Braglia, P.G. Medaglia, A. Mattoccia, L. Di
Giamberardino, M. Richetta, P. Knauth, M.L. Di Vona, Ionic conductivity of ZnAl lay-
ered double hydroxide films grown on aluminum substrate, Solid State Ionics 314
(2018) 30–35.
3 4
of amoxicillin using ZnO@Fe O magnetic nanocomposite: influential factors, reus-
[
38] J.-S. Park, M.T. Brown, T. Han, Phenol toxicity to the aquatic macrophyte Lemna
paucicostata, Aquat. Toxicol. 106-107 (2012) 182–188.
39] P. Eghbali, A. Hassani, B. Sündü, Ö. Metin, Strontium titanate nanocubes assembled
ability and mechanisms, J. Mol. Liq. 264 (2018) 98–109.
[54] World Health Organization, Guidelines for Drinking-Water Quality, 2nd edn1,
WHO, Geneva, 1993 Recommendations.
[
on mesoporous graphitic carbon nitride (SrTiO
ization and catalytic performance, J. Mol. Liq. 290 (2019), 111208.
40] R. Abazari, A.R. Mahjoub, S. Sanati, Z. Rezvani, Z. Hou, H. Dai, Ni–Ti layered double
3
/mpg-C
3
N
4
): preparation, character-
[55] W. Drost, M. Matzke, T. Backhaus, Heavy metal toxicity to Lemna minor: studies on
the time dependence of growth inhibition and the recovery after exposure,
Chemosphere 67 (2007) 36–43.
[
hydroxide@graphitic carbon nitride nanosheet: a novel nanocomposite with high