Sunlight-assisted decomposition of cephalexin by novel synthesized NiS-PPY-Fe3O4 nanophotocatalyst

Article abstract of DOI:10.1016/j.jphotochem.2017.02.003

In this research, the catalytic performance of NiS and NiS immobilized into the matrix of magnetite polypyrrole core/shell (Fe₃O₄@PPY) for degradation of cephalexin was investigated. After characterization, by FTIR, TG, XRD, VSM, DRS, PL, Brunauer–Emmett–Teller (BET), TEM and SEM techniques, the photocatalysts were used for degradation of a pharmaceutical pollutant; cephalexin under UV and sunlight irradiations. The results indicated that application of PPY-Fe₃O₄ as the catalyst supports significantly enhanced the photocatalytic activity of NiS. The degradation efficiency obtained by NiS-PPY-Fe₃O₄ was higher than the value obtained by NiS alone. Moreover, by use of the support, a significant red shift was occurred on the band gap energy of NiS resulting higher degradation of the pollutant under sunlight irradiation. Paramagnetic nature of the NiS-PPY-Fe₃O₄ photocatlyst enabled effective separation of the used catalysts from the reaction solution with the aid of an external magnetic field and avoiding the tedious filtration or centrifugation. Upon regeneration, the photocatalyst retained most of its initial efficiency. Addition of H₂O₂ to the photocatalyst mixture had an enhancing effect on the cephalexin degradation. The photodegradation products were identified by GC–MS technique.

Full text of DOI:10.1016/j.jphotochem.2017.02.003

Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Sunlight-assisted decomposition of cephalexin by novel synthesized
NiS-PPY-Fe O nanophotocatalyst
3
4
F. Torki, H. Faghihian*
Department of Chemistry, Islamic Azad University, Shahreza branch, Shahreza, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 8 December 2016
Received in revised form 17 January 2017
Accepted 4 February 2017
Available online 7 February 2017
In this research, the catalytic performance of NiS and NiS immobilized into the matrix of magnetite
polypyrrole core/shell (Fe O @PPY) for degradation of cephalexin was investigated. After characteriza-
tion, by FTIR, TG, XRD, VSM, DRS, PL, Brunauer–Emmett–Teller (BET), TEM and SEM techniques, the
3
4
photocatalysts were used for degradation of a pharmaceutical pollutant; cephalexin under UV and
sunlight irradiations. The results indicated that application of PPY-Fe
significantly enhanced the photocatalytic activity of NiS. The degradation efficiency obtained by NiS-PPY-
Fe was higher than the value obtained by NiS alone. Moreover, by use of the support, a significant red
shift was occurred on the band gap energy of NiS resulting higher degradation of the pollutant under
sunlight irradiation. Paramagnetic nature of the NiS-PPY-Fe photocatlyst enabled effective separation
3 4
O as the catalyst supports
Keywords:
Cephalexin
Magnetic nanophotocatalyst
3 4
Fe O @PPY-NiS
Sunlight
Photodegradation
3 4
O
3 4
O
of the used catalysts from the reaction solution with the aid of an external magnetic field and avoiding the
tedious filtration or centrifugation. Upon regeneration, the photocatalyst retained most of its initial
2 2
efficiency. Addition of H O to the photocatalyst mixture had an enhancing effect on the cephalexin
degradation. The photodegradation products were identified by GC–MS technique.
©
2017 Published by Elsevier B.V.
1
. Introduction
[9]. Among the environmental protection technologies, the
semiconductor based photocatalysis using solar energy has
attracted considerable attention in the field of environmental
remediation and solar energy utilization [10]. Advance oxidation
processes (AOPs) are capable to destroy environmentally persis-
tent pollutants by using photocatalysts activated by photons with
energy higher or equal to the band gap energy of the photocatalyst.
When the photon is absorbed by photocatalyst particle, an electron
The wide application of antibiotics in human and veterinary
medicine has led to large-scale dissemination of toxic pollutants in
the environment [1]. Pharmaceutical compounds, particularly
ꢀ
1
antibiotics, have been detected at concentrations up to the ng.L
level in wastewater and surface water [2]. Cephalexin, (6R,7R)-7-
[(2R)-2-amino-2-phenylacetyl]amino}-3-methyl-8-oxo-5-thia-1-
{
ꢀ
azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid (Fig. S1) is a broad-
spectrum antibiotic that kills a wide variety of bacteria that cause a
wide range of commonly-occurring infections, including: pneu-
monia, laryngitis, tonsillitis, acute bronchitis, middle ear infection;
urinary tract infections; infections of the skin and soft tissue [3].
Cephalexin is absorbed in the bloodstream via the intestines and
deposited in the infected tissue and works by killing the
pathogenic bacteria [4]. Common side effects of cephalexin
include upset stomach, diarrhea, and vomiting. Taking over dosage
of cephalexin, causes poison in body and need to medical care [4].
The most commonly used methods for removal of cephalexin from
aqueous solution are sono degradation [5], Fenton oxidation [6],
nanofiltration [7], adsorption [8] and advance oxidation processes
(e ) from the valence band (VB) is transferred to the conduction
band (CB), generating a hole (h ) in the VB. The e and h+ can
recombine on the surface or in the bulk of the particles releasing
the energy as heat, or migrate to the photocatalyst surface where
they can react with pollutant molecules absorbed on the surface of
the particle. In the presence of water molecules, electrons are
transferred from water molecule to the positive holes to produce
+
ꢀ
ꢁ
OH radicals which are powerful oxidants and react with organic
ꢁ
and toxic compounds. OH radicals play an important role in
initiating oxidation reactions, especially for substances that are
weakly absorbed on the photocatlyst surface [11]. Nickel sulfide is
utilized as photocatalyst because of high photocatalytic activity,
photochemical stability, non-toxicity and low cost. However, the
efficiency of NiS is limited by its relatively band gap energy
matching to the wavelength of incident UV photons [12]. Nano size
photocatalyts holds many advantages over the photocatalysts with
*
Corresponding author.
E-mail address: faghihian@iaush.ac.ir (H. Faghihian).
http://dx.doi.org/10.1016/j.jphotochem.2017.02.003
010-6030/© 2017 Published by Elsevier B.V.
1

5
0
F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
average size more than nano, including high surface-to-volume
ratio, promising optical behaviors, higher activity, solar utilization
and complete mineralization. In the meantime, the nano size
photocatalysts have some hindrance and limitations. First, it is
difficult to separate nano sized particles from solution for reusing.
Second, due to their high surface energy, nanoparticles easily
aggregate to large clusters which make them deactivated and
unsuitable for application. Immobilization of photocatalyst on
catalyst supports can removed this problems and enhanced
degradation efficiency. Many materials are explored as catalyst
supports including porous organic and inorganic compounds [13].
Among the catalyst supports, magnetic materials show obvious
priority, due to their super paramagnetic nature which enable
easily and effectively separation of catalyst from the reaction
solution with the help of an external magnetic field [14,15].
adsorption-desorption experiments were conducted by a BET,
Belsorp max instrument, BEL Company, Japan. The concentration
of cephalexin was determined by HPLC, Agilent 1200 Series
Degradation products were identified by GC-Mass instrument,
5975C Agilent with a Bpx 30 m ꢃ 0.25 mm ꢃ 0.25
mm capillary
column.
2.2. Preparation of magnetite nanoparticles (Fe
3 4
O )
Typically, 10.8 g of FeCl 6H O and 3.98 g of FeCl 4H O (molar
3
ꢂ
2
2 2
ꢂ
ratio of 1:2) were dissolved in 50 mL hydrochloric acid (0.5 M) in a
tree-necked erlen meyer flask equipped with a condenser and
nitrogen inlet. The pH of the solution was adjusted to 11 by slow
addition of sodium hydroxide solution (1.5 M) and the mixture was
ꢁ
stirred under N
2
atmosphere at 80 C for 3 h. The reaction mixture
Moreover, Fe
3
O
4
has large surface area, which increases absorp-
was cooled to room temperature; the solid was magnetically
collected and rinsed by deionized water until the filtrate was
neutral. Finally the black precipitate was washed with ethanol and
tivity and promote the photocatalytic degradation. Some isolators
such as carbon nanotube, silica and polymers also can exclude
ꢀ
+
ꢁ
recombination of e /h . Polymers are innoxious materials being
chemically inert and mechanically stable with high durability,
inexpensive and readily available and used as support of the
photocatalysts [16]. Polypyrrole (PPY) is one of the promising
conducting polymers due to its high conductivity, ease of
preparation, good environmental stability and high surface area
dried at 60 C for 8 h [18].
3 4
2.3. Synthesis of Fe O @PPY Core/Shell
The magnetite polypyrrole core/shell (Fe
in-situ chemical oxidative polymerization of pyrrole in aqueous
solution of amuminum persulphate (APS). 1.0 g of Fe nano-
3 4
O @PPY) prepared by
[17]. PPY prevent the aggregation of magnetic nanoparticles and
3 4
O
stabilize them in acidic and basic media and also as insulator
prevent the recombination of electron/hole pair.
particles dispersed into 0.5 g of APS solution was ultrasonicated for
1 h. The mixture transferred into a 250 mL, two-neck flask followed
by addition of 0.5 mL of pyrrole and shaken at room temperature
In this research, we combined the advantages of Fe
3 4
O and PPY
to make a PPY@Fe core/shell as the support for NiS photo-
3
O
4
2 3 4
for 8 h under N atmosphere. The black product (Fe O @PPY) was
catalyst. The magnetic photocatalyst impregnated with NiS was
used as a high performance nanocomposite material for degrada-
tion of cephalexin under UV and sunlight irradiations.
magnetically separated and sequentially washed with deionized
water and methanol and dried at 60 C for 24 h [19]. Scheme of
ꢁ
3 4
Fe O @PPY preparation shown in Fig. S2. The experimental
conditions for core/shell preparation is given in Table S1.
2. Experimental
2
.4. Synthesis of NiS nanoparticles
2.1. Materials and methods
Preparation of NiS nanoparticles was conducted by hydrother-
All chemicals, iron (lll) chloride (FeCl
3
ꢂ
6H
2
O), pyrrole (C
4
H
5
N),
4
mal method; a homogeneous mixture of NiSO (10 mmol), NaOH
iron (ll) chloride (FeCl
chloric acid (HCl), amonium persulphate (APS), m-cresole, hydro-
gen peroxide (H ), nickel sulfate (Ni SO ) and thioacetamide,
2
ꢂ4H
2
O), sodium hydroxide (NaOH), hydro-
(15 mmol), thioacetamide (12 mmol), and deionized water (60 mL)
was prepared under vigorous stirring. The reaction mixture was
then transferred into a 100-mL Teflon-lined reactor and heated at
2
O
2
2
4
ꢁ
were purchased from Merck Company. Cephalexin pharmaceutical
capsule (500 mg) were prepared from Farabi Pharmaceutical
Company, Isfahan, Iran.
The synthesized photocatalysts were characterized by X-ray
diffraction method (XRD, JEOL100CX) with CoK
160 C for 24 h. The mixture was slowly cooled to room
temperature and the solid product was collected by filtration
and was washed with water and ethanol several times to ensure
elimination of the impurities adsorbed on the surface of the
ꢁ
a
radiation
product. Finally, the NiS nanoparticles were dried at 70 C for 2 h
(
l=1.788 A) operated at 40 kV and 30 mA. Transmission electron
[20].
microscopy (TEM) images were prepared by a Phillips (Netherland)
CM10 instrument. Energy dispersive analysis of X-rays (EDAX),
field emission electron microscopy (FESEM) was studied by use of
JSM-6701F instrument, Japan. Fourier transformation infrared
spectroscopy (FTIR) spectra were prepared in the region of 4000–
3 4
2.5. Synthesis of Fe O @PPY-NiS nanophotocatalysts
The Fe
content were prepared by adding NiS nanoparticles (10–80%) to
appropriate amount of Fe @PPY dispersed in m-cresol solution.
3 4
O @PPY-NiS nanophotocatalysts; with different NiS
ꢀ
1
4
00 cm on Nicolet single beam FT-IR, Impact 400D using KBr
pellet. The surface morphology, purity and crystallinity of
Fe @PPY-NiS were studied by EDAX spectra, TEM and SEM
3 4
O
The mixture was shaken for 15 h at room temperature. The product
was collected magnetically, washed respectively with deionized
3 4
O
ꢁ
images. The average size of nanocomposite determined by image
processing software (Image J. software). The band gap energy of
nanophotocatalyst determined by use of diffuse reflectance
spectroscopy (DRS) by a UV–vis model V-670, Japan, and the
thermal curves of the nanocomposites (TG-DTG) were prepared by
a Perkin-Elmer thermal analyzer model SSC-5200) from 25 to
water and methanol and dried at 70 C for 6 h [21]. Synthesis
3 4
scheme of Fe O @PPY-NiS is shown in Fig. S3.
2.6. Photodegradation of cephalexin
A photocatalytic reactor comprising of a cylindrical Pyrex-glass
cell and a medium pressure Hg lamp (75 W, Philips, I-line,
maximum emission at 365.4 nm, UV), located 10 cm above the
reactor was used for photodegradation experiments. Pre-deter-
mined amount of photocatalyst was added into cephalexin
ꢁ
ꢁ
ꢀ1
8
00 C with heating rate of 10 C.min and in air atmosphere. The
magnetic property of the samples was measured by a commercial
SQUID magnetometer from Quantum Design, Vibrating Sample
Magnetometer (VSM). Photoluminescence (PL) spectra were
prepared by a Cary Eclipse (FL0906M003) instrument. Nitrogen
solution and the mixture was properly shaken until
a

F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
51
homogeneous suspension was obtained. The suspension was
shaken for 0.5 h at dark till adsorption/desorption process was
at equilibration. After equilibration, the mixture was irradiated for
known period while it was agitated to ensure homogeneity. The
photocatalyst was then separated from the solution by applying an
external magnetic field and the concentration of cephalexin in the
remaining solutions was measured by HPLC-UV at
l 254 nm. The
degradation efficiency was calculated by the following equation:
%
C
D = [(C
o
ꢀ C)/C
o
] ꢃ 100
(1)
o
and C are cephalexin concentration before and after irradiation
respectively.
3. Results and discussion
3.1. Characterization of the synthesized photocatalysts
3
.1.1. TEM, SEM and BET analysis
The TEM images of Fe @PPY and SEM image of Fe
NiS shown in (Fig. 1a and b). On the TEM image of Fe
presence of globular particles, with irregular shape and core/shell
structure was observed. The SEM image of Fe @PPY-NiS
indicated that the spherical nano particles were uniformly
aggregated. The particle size of Fe @PPY and Fe @PPY-NiS
calculated by Image J software was respectively 40 and 50 nm. The
increase in the particle size of Fe @PPY-NiS compare to
Fe @PPY is attributed to the coordination bond formed between
3
O
4
3
O
4
@PPY-
3 4
O @PPY the
3
O
4
3 4 3 4
Fig. 2. XRD Pattern of Fe O (a), NiS (b) and syntheszied Fe O @PPY-NiS (c).
3
O
4
3 4
O
ꢁ
diffraction lines observed at 2u of 18, 30, 32, 48, 50, 57 and 60
3
O
4
belonged to NiS and was in good agreement with the standard data
(JCPDS 12-0041) [20]. No diffraction line observed for PPY because
of the amorphous nature of this compound [21]. The average
3 4
O
lone-pair electrons of N atoms of PPY and NiS atoms [21]. The
elementary analysis of the sample obtained from EDX spectra and
maps given in Fig. S4 and data shown in Table S2.
3 4
particle sizes of Fe O and NiS calculated by Scherrer’s equation:(2)
D = 0.94 /ßCos Where D is the average size and ß stands for the
l
u
The surface area of the samples obtained by Brunauer–
full-width at half-height of the peaks. The average particle size
obtained by Scherrer’s equation was close to the values obtained by
TEM and SEM analysis.
2
ꢀ1
Emmett–Teller (BET) technique was 62.2, 48.7 and 29.9 m .g
respectively for Fe @PPY, NiS and Fe @PPY-NiS sample. As
expected, after introduction of NiS into Fe
surface area of the new photocatalyst (Fe
3
O
4
3 4
O
3
O
4
@PPY sample, the
@PPY-NiS) was
3
O
4
3.1.3. Ft ir
significantly decreased. But the surface area still was sufficient
to adsorb enough pollutant molecules for degradation process. The
higher catalytic performance of this sample compared to bulk NiS
was attributed to the fact that the incorporation of NiS on the
catalyst support reduced the recombination of electron/hole pair
In the spectrum of Fe
3
O
4
, the absorption band appeared at
ꢀ1
470 cm was attributed to the characteristic Fe-O band and the
ꢀ1
peak at 1400 cm belonged to OH in-plane (O ꢀꢀ H)in and peaks
ꢀ1
appeared at 1600 and 3400 cm
related to water molecules
@PPY
absorbed on the surface of the sample (Fig. 3a). In the Fe
3 4
O
spectrum, besides the characteristic peaks belonged to polypyr-
role, the Fe-O band slightly shifted from 470 to lower wave number
(Fig. 3b). This reflected the effect of coordination interaction
3
.1.2. XRD analysis
In the XRD patterns of nanocomposite (Fig. 2), the diffraction
ꢁ
lines of Fe
3
O
4
appeared around 2
u
of 41.5, 50.7, 63, 67, 74.5 which
between Fe
3 4
O nanoparticle and polypyrrole chain [23]. The
ꢀ1
was in accordance with the JCPDS card 65–3107 [22]. The
absorption bands at 1000 and 1100 cm
3 4
in Fe O @PPY and
3 4 3 4
Fig 1. TEM images of Fe O @PPY (a), SEM images of Fe O @PPY-NiS (b).

5
2
F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
ꢁ
started from 300 C caused by decomposition of PPY of the sample.
ꢁ
The maximal weight loss in this step appeared at 500 C and
ꢁ
gradually continued till 800 C. Gao et al. studied the thermal
stability of pure PPY and Fe
that pure PPY decomposed properly at 650 C, but in the composite
3
O
4
-PPY nanocomposite. They reported
ꢁ
according to Fe
Similar observation was occurred in this work. The higher thermal
stability attributed to the interaction between Fe and
3 4
O loading, its thermal stability was improved [27].
3 4
O
polypyrrole chain and also interaction of nitrogen atom of PPY
and NiS [21].
3
.1.5. VSM analysis
Magnetization is a phenomenon that describes the response of
magnetic materials to an applied external magnetic field.
Application of a magnetic field can make the direction of magnetic
moment of the nanoparticles the same as the field direction, and
the magnetization increases with increasing magnetic field until it
reaches the saturation magnetization. In the magnetization curves
of Fe
saturation magnetization value obtained for Fe
Fe @PPY-NiS was respectively 80.2, 58.3 and 47.3 emu.g .
3
O
4
, Fe
3
O
4
@PPY and Fe
3
O
4
@PPY-NiS shown in Fig. 5, the
Fig. 3. FT-IR specta of Fe
3
O
4
(a), Fe
3
O
4
@PPY (b) and Fe
3
O
4
@PPY-NiS (c).
O
4
, Fe @PPYand
3 4
O
3
ꢀ
1
3
O
4
Fe
3
O
4
@PPY–NiS spectra are respectively assigned to the CH in-
Although a significant decrease on saturation magnetization of
plane (C ꢀꢀ H)in and CH out-of-plane (C ꢀꢀ H)out vibration (Fig. 3b and
Fe O happened after coating by PPY and hybridizing with NiS, but
3
4
ꢀ1
c) [24]. The peaks around 1500 and 1474 cm are respectively
the remaining magnetic properties of the final photocatalysts was
sufficient to separate the used photocatalyst by placing a magnet
bar outside of the vessels containing the dispersed nanophotoca-
talyst in aqueous solution (Fig. 5d). Habibi-Yongjeh et al. synthe-
sized magnetically nanocomposites; ZnO/AgBr/Fe O /Ag VO and
attributed to C ꢀꢀ N and C ꢀꢀ C asymmetric and symmetric ring-
ꢀ1
stretching of PPY [23]. The peak at 1400 cm is stretching band
related to C
¼
C of PPY ring. The weak absorption bands of NH and
CH stretching vibration of polypyrrole appeared respectively at
3
4
3
4
ꢀ1
ꢀ1
3404 and 2358 cm
and the band at 3404 cm
related to
3 4 3 4 3 4
g-C N /Fe O /AgI and reported that by combination of Fe O with
symmetrical stretch vibration of NH group has been buried under
board OH peak of water molecules at 3400 cm [25]. From the
results, it inferred that in- situ polymerization in the present of
the studied compounds, the magnetic properties of nanocompo-
sites was considerably decreased [28,29].
ꢀ
1
Fe
3
O
4
was successfully occurred and Fe
3
O
4
@PPY nanoparticles
3.1.6. DRS analysis
were obtained. In Fig. 3c the NiS stretching (Ni-S)s shoulder band
The photo-absorption ability of the samples was studied by the
UV–VIS diffuse reflectance spectrum (Fig. 6). The absorption edges
of Fe O @PPY-NiS, NiS and Fe O @PPY obtained from curves. The
ꢀ1
at 626 cm and broad band belonged to Fe-O appeared around
ꢀ
1
ꢀ1
4
70 cm . The peak at 562 cm
corresponds to the bending
3
4
3 4
vibration of metal sulfur bond (Ni-S)v [26]. It is interesting to note
optical band gap energy can be obtained according to Eq. (4), which
ꢀ
1
that the main absorption band at 1600 cm of water molecules
became more intense due to adsorption of water molecules by NiS
is based on the onset of UVꢀVIS DRS of the powdered materials:
opt
ꢀ1
E
g
(ev) = 1240/
l
edge (nm)
(3)
nanoparticles. The peak at 3400 cm
3 4
related to Fe O was
Where Egopt is the optical band gap that can be used to analyze the
optical absorption and the number 1240 is obtained from the
disappeared because of moist adsorption by NiS nanocopmposite.
3.1.4. Thermal analysis
TG-DTG curves of Fe
3
O
4
@PPY-NiS showed a continuous weight
ꢁ
loss between 25ꢀ800 C. The first part of the weight loss appeared
ꢁ
around 100 C attributed to the elimination of the moisture and
unreacted monomers [21] (Fig. 4). The second major weight loss
Fig. 4. Thermal curves (TG-DTG) of Fe
3
O
4
@PPY-NiS.
3 4 3 4 3 4
Fig. 5. Magnetization curves of Fe O (a), Fe O @PPY (b), Fe O @PPY-NiS (c).

F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
53
3 4 3 4
Fig. 7. PL spectra of NiS (a), Fe O @PPY (b), Fe O @PPY-NiS (c).
Fig. 6. DRS curves of Fe
3
O
4
@PPY-NiS (a), NiS (b) and Fe
3
O
4
@PPY (c).
3.2. Performance of the photocatalysts
relationship between frequency and wavelength as described by
Eq. (4)
For preparation of stock solution of cephalexin, a 500 mg tablet
was powdered and transferred to a 100 mL volumetric flask. The
mixture was shaken well until proper dissolving of the drug and
was diluted up to the mark with deionized water. The cephalexin
solutions (50 mg. L ) irradiated in the presence of known amount
3 4
of NiS or Fe O @PPY-NiS nanophotocatalysts under UV or sunlight
E (eV) = h
y
= hc/el
(4)
8
ꢀ1
ꢀ1
Where h is Planck’s constant, c is about 3 ꢃ10 m s , the speed of
light in the vacuum, e is the electron charge, the unit of is meter
l
(
m), then 1240 can be obtained from hc/e, g is the wavelength
l
radiation. After equilibration, the photocatalyst was separated and
the concentration of cephalexin was measured in the solution. The
isocratic HPLC method used for measurement of concentration of
the remaining pollutant. Method development was carried out on
corresponding to the intersection point of the vertical and
horizontal parts of the spectrum [27].
3 4
The wavelength of the absorption edge of the Fe O @PPY, NiS
and Fe @PPY-NiS were respectively 442, 555 and 568 nm and
the band gap energy of the samples calculated by Eq. (4) were
respectively 2.8, 2.3 and 2.1 ev. (Fig. 6). According the results, when
NiS immobilized on the Fe O @PPY support, a red shift was
3 4
occurred in its band gap energy. The shift facilitated the sun-light
assisted degradation of the pollutant. Therefore by using of
3
O
4
ODS Hypersil C18, 250 mm ꢃ 4.7 mm, 5
m (Particle Size) column.
The mobile phase was a mixture of TBAHS (0.01 M,) and methanol
ꢀ
1
in the ratio of 50:50 v/v. The flow rate was set at 1.0 mL min and
UV detection at 254 nm. The retention time of cephalexin found to
be 2.5 min [32]. The chromatograms of the irradiated samples
showed that, peak intensity at 254 nm was significantly decreased
during degradation process indicating that the pollutant was
efficiently degraded (Fig. 8) The calibration curve was plotted over
the concentration range of 30–700 mg L by plotting peak areas
vs. cephalexin concentration. The correlation coefficient was
0.9902 and regression equation obtained Y = 16.066X + 1940.6.
Fe
the phtocatalyst by solar radiation was close to the efficiency
obtained by UV irradiation and make the Fe @PPY-NiS as a
3 4
O @PPY-NiS with lower band gap, the degradation efficiency of
ꢀ1
3
O
4
suitable novel candidate for degradation of pollutant under
sunlight as well as UV irradiations. Guo et al. reported synthesis
of NiS by hydrothermal method and DRS study showed that the
absorption edge of the synthesized NiS was 2.23 ev and similar to
the result of this work [20]. Singh et al. studied effect of support on
degradation efficiency photocatalyst. Their results shown that
2 2
immobilized TiO on polymer (TiO /Polyaniline) degradation of
brilliant blue KN-R dye increased clearly [16].
3.1.7. Photoluminescence analysis
Photoluminescence spectra were recorded to determine the
charge separation efficiency of the prepared photocatalysts and are
given in (Fig. 7). The excitation wavelength was 227 nm and the
emission peaks were appeared at 305 and 390 nm for NiS and at
5
3
49 nm for PPY-Fe
05, 390 belonged to NiS were observed with lower intensity and
was also appeared at the original
wavelength at 549 nm. These observations indicated that the
immobilization of NiS on the PPY-Fe support decreased
3 3 4
O4. In the NiS-PPY-Fe O sample the peaks at
3 4
the peak attributed to PPY-Fe O
3 4
O
recombination of electron/hole charges and quenched the
emission intensity. Similar observation was made by Habibi-
Yongjeh who studied photoluminescence of nanocomposites and
reported that by incorporation of g-C
AgI/Ag CrO nanocomposites, the photoluminescence intensity of
g-C was significantly decreased [30,31].
3 4 2 4 3 4
N into Ag SO and Fe O /
2
4
3 4
N
Fig. 8. Chromatographs of cephalexin degradation.

5
4
F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
The statistical parameters of the measurement are given in
Table S3.
(
a)
0
0
.6
.5
S1
S2
S3
S4
3
.2.1. Influence of different parameters on degradation efficiency
.2.1.1. Effect of initial concentration. The effect of initial
3
0.4
0.3
concentration on the degradation of the pollutant studied in
ꢀ
1
various concentration (30–700 mg L
)
(Fig. 9) by using
Fe @PPY-NiS and NiS under UV and sunlight radiations. At
3 4
O
0
0
.2
.1
0
lower concentration, the number of the available active sites of the
photocatalyst is more than the pollutant molecules; therefore, the
pollutant molecules mostly adsorbed on the catalyst surface where
the OH radicals are produced and readily interact with the
ꢀ
1
pollutant molecules. With pollutant concentration of 50 mg L
,
0.2
1
2
4
proper degradation was occurred. At higher concentration, the
adsorption sites fully engaged and unabsorbed cephalexin caused
lower penetration of photons through the solution [33]. However,
Catalyst concentration (g.L-1)
(
b)
1
1
20
ꢀ1
at 700 mg L , the degradation efficiency of 68, and 62% was
respectively obtained by Fe @PPY-NiS and NiS under UV, and the
values of 53 and 45% obtained by Fe @PPY-NiS and NiS under
sunlight irradiation. To study the kinetic of reactions, the rate
constants were obtained from the slopes of lnC/C vs ‘t' plots. The
3 4
O
00
80
60
3 4
O
o
ꢀ3
2
ꢀ3
2
rate constants of 9.3 ꢃ10 (R = 0.9572), 1.7 ꢃ10 (R = 0.9119),
ꢀ
3
2
ꢀ3
2
4
.0 ꢃ10 (R = 0.9482) and 1.4 ꢃ10 (R = 0.9020) were obtained
for Fe @PPY-NiS (S1) and NiS (S3) under UV and Fe @PPY-NiS
S2) and NiS (S4) under sunlight irradiation respectively (Fig. S5).
4
2
0
0
0
3
O
4
3 4
O
(
S1
S2
The photocatalysts used in this research listed in Table S4. The
degradation percentages at the above-mentioned photocatlysts
was respectively 100, 69, 90 and 57%. These results confirmed that
0
10
20
30
40
50
60
70
80
90
3 4
for NiS catalyst immobilized on the Fe O @PPY support, the
%
Loading NiS
efficiency was significantly improved. Additionally, by use of
support the band gap energy of photocatalyst shifted to lower
energy and sunlight degradation became more pronounced.
Fig. 10. Effect of photocatalyst dosage on cephlexin degradation iradiation (a),
Effect of NiS loading (b).
optimized efficiency observed with the photocatalyst containing
3
.2.1.2. Effect of photocatalyst dosage and NiS loading. Degradation
ꢀ1
5
3 4
0% of semiconductors (Fe O @PPY-NiS (50%)). When the photo-
of cephalexin with different photocatalysts dose (0.2–4 g L
studied for Fe O @PPY-NiS and NiS under UV and sunlight
3 4
)
catalyst loading was small, lower incident photons absorbed, lower
ꢁ
OH generated and consequently degradation become negligible.
irradiations. The degradation percentage increased with
increasing photocatalyst dose and then remained constant or
slightly decreased (Fig. 10a). By increasing of photocatalyst dosage,
the whole number of available adsorption sites increased, more
pollutant molecules absorbed and hence the interaction between
OH radicals and the pollutant molecules facilitated. At higher dose,
aggregation of the photocatalysts particles lowered the surface
area, and increased incoming light scattering [34].
On the other hand when the NiS content exceeded to 50%,
aggregation of the nanoparticles caused lower surface area and
lower degradation efficiency. In a research conducted by A.
Nezamzadeh. Ejhieh et al. cefixim was degraded by a photocatalyst
prepared by immobilization of NiO on clinoptilolite support. The
ꢀ1
efficiency of 72% in 20 mg L pollutant solution was reported. The
reported photocatalyst contained maximally 13.3% of NiO [35]. But
in the present work we prepared photocatalyst with 50% of NiS
content. This significantly enhanced the degradation up to 90 and
The influence of NiS loading was studied by the catalyst
containing different amount of NiS (10–80%) (Fig. 10b). The
3 4
100% for Fe O @PPY-NiS respectively under sunlight and UV
irradiations. This indicated the enhancing effect of insulator and
support on the efficiency of photocatalyst.
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
S1
S2
S3
S4
3
.2.1.3. Effect of irradiation time. The drug degradation studied for
irradiation time between 1 and 6 h (Fig. 11). The reaction was
kinetically very fast and most of degradation percentage obtained
within 30 min and then became slower until after 360 min the
equilibration was established. The slower degradation efficiency
observed after the first step is caused by adsorption of
intermediate degradation products by catalyst surface which
limited the number of pollutant molecules absorbed by the
photocatalyst [33]. However, Fe
degradation efficiency respectively under UV and sunlight within
0 min. The time required for such a degradation amount is much
3 4
O @PPY-NiS showed 82 and 65%
3
30
50
100
200
300
500
700
lower than the values reported by the other researchers. Elmolla
et al. report degradation of amoxicillin, ampicillin and cloxacillin in
aqueous solution by use of ZnO under UV radiation. Their optimal
degradation was obtained after 180 min [36]. Kemary et al. reports
*
N.D: Not Detect
Cephalexin Concentration (mg.L-1)
3 4
Fig. 9. Effect of the initial concentration on cephalexin degradation by Fe O @PPY-
NiS under UV and sunlight iradiations.

F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
55
Waals forces between unionized cephalexin molecules and the
absorbent cannot be ignored [8]. The measured pHpzc of
photocatalysts was 7.0. Cephalexin at pH lowers than 2.6 is
positive charge because amine group is protonated and the surface
charge of the photocatalyst is also positive and hence adsorption of
cephalexin molecules limited. At pH in range of 2.6-6.9 cephalexin
is zwitterionic form and surface of photocatalyst is positive.
Therefore repulsion force between positive part of cephalexin and
catalyst prevent of cephalexin adsorption. Maximum interaction
between nonionized cephalexin molecules and neutral surface
catalyst caused wan der walls force at pH 7.0 and follow it the
highest degradation. At pH higher than 7.0, the catalyst surface
charge is negative and the cephalexin molecules carried negative
charge, and a repulsion force again limited the of cephalexin
1
.8
.6
.4
.2
0
S1
S2
S3
S4
0
0
0
0
-
30
20
70
120
170
220
270
320
370
420
Time (min)
adsorption by the catalyst. Additionally at alkalia media reaction
ꢀ
Fig. 11. Effect of iraddiation time on cephalexin degradation by Fe
3
O
4
@PPY-NiS and
between hydroxyl radicals and HO
low reactivity:
produced new radicals with
2
NiS.
ꢁ
2ꢀ
ꢁ
2 2
O + O
ꢀ
OH + HO ! H
(5)
5
0% degradation of ciprofloxacin (4 mg Lꢀ1) under UV radiation
after 60 min by using ZnO nanophotocatalyst [37]. Kosslick et al.
ꢀ
1
reported that 85% of ibuprofen (10 mg L ) was degraded after
80 min by UV–vis irradiation at the presence of TiO [38]. Saadati
ꢁ
ꢁ
1
2
1
OH + H
2
O
2
! H
2
O + O
2
H
(6)
ꢀ
et al. reported degradation of tetracycline (15 mg L ) by using Cl-
TiO under UV irradiation and reported up to 73% degradation after
0 min [39]. Sayed et al. studied degradation of metronidazole
At high pH the concentration of scavenger radicals such as
2
2ꢀ
ꢀ
3
CO
3
, HCO
may increase and results in the decrease of hydroxyl
radical concentration. This also limited the degradation rate of
cephalexin at higher pH value [1].
6
ꢀ
1
(
1
1 mg L ) by use of CuO and up to 97% degradation reported after
20 min of UV radiation [40].
3
.2.1.5. Effect of temperature. The photodegradation of cephalexin
3
.2.1.4. Effect of pH. The pH dependency of the photodegradation
was investigated at three different temperature of 30, 40, 50 and
6
degradation efficiency was obtained. This could be attributed to
the lower concentration of dissolved oxygen at higher
process was examined in pH range 3 to 9. (Fig. 12). Degradation
efficiency increased with increasing pH from 3 to 7 and then
decreased. The catalyst was highly active at neutral pH. Cephalexin
ꢁ
0 C (Fig. 13). In general, by increasing of temperature lower
has pK
a
= 2.6 for the carboxyl group and pK
a
= 6.9 for the amine
ꢁ
temperatures. Dissolved oxygen produced extra OH radicals
group. At lower pH of 2.6 cephalexin is in cationic form. In the pH
range 2.6–6.9 cephalexin mainly exists in zwitterionic form and at
pH higher than 6.9 is in anionic form [8]. But isoelectric pH (PI) of
cephalexin is about 5.5. In this point total charge of molecules
become neutral. It seems that the main mechanism of adsorption is
electrostatic attraction between active sites of the absorbent and
the functional groups of the cephalexin. Furthermore, van der
which improved degradation process via the following reactions
[41].
ꢀ
ꢁ
ꢀ
2
O
2
2
+ e ! O
(7)
(8)
ꢁ
ꢀ
+
O
+ h ! H
2 2 2
O + O
1
1
1
1
30
20
10
00
1
1
2
0
8
6
4
2
9
8
7
6
5
4
3
0
0
0
0
0
0
0
2
4
6
8
10
12
pH initial
S1
S2
S3
S4
0
1
2
3
4
5
pH
6
7
8
9
10
3 4
Fig. 12. Effect of pH on cephalexin degradation by Fe O @PPY-NiS and NiS.

5
6
F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
2ꢀ
ꢀ
2
S1
S2
S3
S4
ꢁ
ꢁ
H
2
2
O
2
+ O
! OH + OH + O
(12)
(13)
(14)
ꢁ
ꢁ
H
O
2
+ OH ! H
2 2
O + OH
ꢁ
ꢁ
HO
2
+ OH ! H
2 2
O + O
2 2
The effect of H O on the degradation of pollutants was studied
by Tseng et al. They studied the effect of hydrogen peroxide on the
photocatalytic degradation of monochlorobenzene in the presence
2
5
30
35
40
45
50
55
60
65
of TiO
with the results of this research [43]. Saadati et al. report
degradation of tetracycline by using TiO under UV irradiation.
concentration in
2
and obtained the results which are in good agreements
o
Temperature ( C)
2
Fig. 13. Effect of temperature on cephalexin degradation by Fe
3
O
4
@PPY-NiS and
Their results showed that by increasing of H
2
O
2
NiS.
ꢀ1
the range of 50 to 100 mg L , the rate constant of degradation
increased. Higher concentration of
decreased of degradation [39].
2 2
H O caused significant
ꢁ
ꢀ
ꢀ
+ H+
O
2
+ e ! H
2
O
2
(9)
3
.2.2.2. Addition of organic scavenger. By adding 0.1 M isopropanol
and benzoquinone solution to the cephalexin solution, the
degradation efficiency significantly decreased (Fig. 15). It is
suggested that isopropanol reacts more rapidly than cephalexin
ꢀ
ꢀ
ꢁ
H
2
O
2
+ e ! OH + OH
(10)
Benacherine et al. effect of oxygen on photodegradation of
ꢁ
ꢀ
with OH and e aq according to reaction 15 and 16 causing a
amoxicillin by Goethite (ᾲ-FeOOH) was investigated. One of the
most limitation in photodegradation process electron acceptor
molecules such as oxygen. Oxygen trapped photo induced electron
Eqs. (7) and (8)). But illustrated degradation of amoxicillin slightly
inhibited deoxygenated solution. According to (Eqs. (7) and (8))
oxygen trapped e /h but in another reactions (Eqs. (9) and (10))
OH radical was produced and enhanced oxidation pollutant [41].
The confirmation of significant improvement of O
reported by Cavicchioli et al. in aeration solutions of heavy metals
42].
ꢁ
ꢀ
significant decrease on OH and e aq concentration. It should be
ꢁ
noticed that in reaction 15 stable iso-prOH radical is produced.
ꢁ
ꢁ
ꢁ
(
OH + i-PrOH ! H O + i-prOH + i-prO
(15)
(16)
2
ꢀ
+
ꢀ
+ i-prOH ! H + i-prOꢀ
ꢁ
e
aq
2
has been
Uresti et al. studied effect of radical scavengers on degradation
of pharmaceutical pollutant and reported in presence of 2-
propanol degradation of pollutant decreased clearly [44].
Mohamed et al. reported by using tert-butyl alcohol as a radical
hydroxyl scavenger for degradation process of organic pollutant by
manganese ferrite-graphene hybrid, photocatalytic degradation
efficiency decreased [45].
[
3
.2.2. Effect of additive compounds
.2.2.1. Addition of H The effect of H
cephalexin studied by adding different aliquots of H O
2 2
5 mL of cephalexin solution (50 mg L ) (Fig. 14). Addition of H
3
2
O
2
.
2
O
2
on the degradation of
solution to
ꢀ
1
As indicated in Fig. 14, addition of benzoquinone to cephalexin
solution decreased the degradation efficiency of the photo-
2
2
O
2
ꢁ
first yielded additional OH radicals via reaction between H
2
O
2
and
ꢀ
ꢁ
ꢁ
catalysts. Benzoquinone is a super oxide radical (O2 ) quencher
ꢀ
ꢀ
e
or O
2
(Eqs. (11) and (12)) which increased degradation
ꢁ
ꢁ
and according to Eqs. (7)–(10), reduced the generation of OH
efficiency. The excess H
radicals and restrained the degradation of cephalexin [43].
The optimized efficiency obtained by addition of H
2
O
2
trapped OH radicals to form weaker
ꢁ
radicals. Pelaez et al. also studied the effect of benzoquinone on the
HO
2
2
degradation of microcystin-LR by NF-TiO under visible light
2
O
2
(0.1 M) in to
irradiation and similar to our result, they reported that benzoqui-
none acting as an organic scavenger [46].
aqueous solution.
ꢀ
ꢁ
ꢀ
H
2
O
2
+ e ! OH + OH
(11)
0
.6
.5
.4
.3
.2
.1
0
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
S1
S2
S3
S4
S1
S2
S3
S4
0
0
0
0
0
0
0.01
0.1
0.2
0
Isopropanole
Benzoquinone
H O Concentration (M)
Organic Scavenger
2
2
Fig. 14. Effect of H
2
O
2
addition on cephalexin degradation.
Fig. 15. Effect of organic scavengers on cephalexin degradation.

F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
57
ꢁ
ꢀ
O ! OH ꢁ + OHꢀ
O
+ H
2
(21)
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
S1
S2
S3
S4
ꢁ
ꢁ
ꢁ
ꢀ
ꢁ
ꢁ
ꢀ
NO
2
2
+ O ! NO
2
+ OH + OH
(22)
(23)
(24)
ꢁ
NO
+ OH ! HOONO
HOONO ! NO ꢀ
+ H+
3
3ꢀ
The present of NO
in degradable medium could increase
degradation efficiency. This anion helps the generation of OH
radical thought Eqs. (19)–(24). In the presence of scavengers such
as isopropyl that decreased photo degradation, OH radical
0
Nitrate
Oxalate
Inorganic Scavenger
Fig. 16. Effect of inorganic scavengers on cephalexin degradation.
Bicarbonate
EDTA
Cloride
3ꢀ
generated by photolysis of NO compensate the scavenger effect
(
Eqs. (19)–(24)) [52].
3
.2.2.3. Addition of inorganic scavenger. The effect of addition of
inorganic salts including Na EDTA, Na , NaCl, NaHCO and
NaNO on the degradation efficiency was studied (Fig. 16). By
3.3. Regeneration of photocatalysts
2
C
2 2
O
4
3
3
addition 0.1 M of salts solution into cephalexin solution have
different effect on degradation of cephalexin. It is believed that
One of the most important advantages of magnetic heteroge-
neous photocatalys is the ease of separation of catalysts from the
reactants or products, which results in the possibility to reuse or
ꢁ
ꢁ
ꢁ
some anions including HCO
3
, CO
3
, and Cl impose a scavenging
+
effect on the photodegradation of cephalexin by scavenging h and
3 4
recycle them without additional steps. In this work, Fe O @PPY-
ꢁ
OH to form ionic radicals which have lower potential for
NiS and NiS were regenerated. The magnetically photocatalyst
separated from the solution by applying appropriate external
+
ꢁ
degradation than h and OH [47,48].
ꢁ
magnetic field and then regenerated by heat treatment at 150 C
3ꢀ
3ꢀ
ꢀ
+
3
ꢁ
3
ꢁ
ꢁ
(
HCO + CO + Cl ) + h ! (HCO
+ CO
+ Cl )
(17)
(18)
ꢁ
and 400 C for 4 h. NiS was filtered from the solution and
ꢁ
ꢁ
regenerated by heat treatment at 300 C and 600 C because NiS
based on the results of TG-DTG has higher thermal stability than
the magnetic catalyst. Heat treatment caused the removal of
degradation products from the surface of the photocatlysts. The
regenerated photocatalyst was reused for degradation of cepha-
lexin for five cycles. The photocatalyst retained most of their initial
activity after regeneration. However after each regeneration a
significant decrease was observed. The decrease was more
pronounce with increasing the number of reusing cycles. The
decrease explained by the fact that part of degradation products
are not removed during regeneration steps and remained on the
catalyst surface. In addition, during the recycling, some nano-
photocatalysts particles may be leach out to the solution.
Moreover, during the repeated heat treatments, the catalysts
particles aggregated which results in the decrease of the catalyst
active surface area. This is more pronounced for NiS which was
heated at higher temperatures. (Fig. 17).
3ꢀ
3ꢀ
ꢀ
ꢁ
3
ꢁ
3
ꢁ
ꢁ
(
HCO + CO + Cl ) + OH ! (HCO
+ CO
+ Cl )
ꢁ
ꢀ
2ꢀ
ꢁ
Cl + Cl ! Cl
At the concentration used in this work (0.1 M), the influence of
sodium oxalate on the degradation of cephalexin was insignificant
and small reduction on degradation efficiency was occurred
+
(
Fig. 16). Habibi-Yongjeh reported that oxalate is an h scavenger
+
and inhibited the positive h role in photocatalytic process and
decreased degradation of the studied pollutant [13].
By addition of EDTA to reaction solution lower degradation of
+
the pollutant was observed (Fig.16). EDTA as an h quencher had an
inhibition effect on the degradation process. Similar effect has been
reported by Mohamed et al. who used manganese ferrite-graphene
hybrid photocatalyst for elimination of water organic pollutants
[
45].
3ꢀ
NO showed an adverse effect on cephalexin degradation. The
ꢀ
ꢀ1
ꢀ
absorption spectra of NO
2
and NO
3
contain weak n !
p
* bands
= 7.4 M cm ) respectively,
enable to absorb solar and UV irradiations ( > 295 nm). Therefore
ꢀ
1
ꢀ1
ꢀ1
at 360 nm (e= 22.5 M cm ) and (e
l
the incident ray is partially absorb by nitrate and the anion became
excited and produced reactive radicals leads to the formation of
120
S1(150)
S1(400)
S3(200)
S3(600)
ꢁ
ꢁ
OH and NO
2
according to the reactions 20–22 [49]. But when the
100
80
energy of the incident photons is not suitable to be absorbed by
nitrate, it acts as OH radical scavenger causing lower degradation.
Andreozzi et al. reported effect of nitrate addition at degradation
6
4
2
0
0
0
0
pollutant [50] for irradiation with
interaction nitrate with incident light shown at below [51].
l> 280 nm. The mechanism of
ꢀ
hv
ꢀ
NO !½NO ꢄꢅ
ð19Þ
3
3
NO3ꢀ]* ! NO
ꢁ
ꢁ
ꢀ
[
2
+ O
(20)
1
2
3
4
5
No.cycle
3 4
Fig. 17. Regenaration of Fe O @PPY-NiS and NiS photocatalysts.

5
8
F. Torki, H. Faghihian / Journal of Photochemistry and Photobiology A: Chemistry 338 (2017) 49–59
3.4. GC–MS analysis
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2.1 and 12.2 are belonge to degradation products of cephalexin are
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