Copper and cerium co-doped cobalt ferrite nanoparticles: structural, morphological, optical, magnetic, and photocatalytic properties

Abstract

A rapid synthetic technique is investigated for magnetic nanoparticles (Co1−yCuyFe2−xCexO4 (x = 0, y = 0), (x = 0.05, y = 0), (x = 0, y = 0.5), and (x = 0.05, y = 0.5)). The structure, morphology, optical and magnetic performance of prepared nanoparticles are analyzed by powder XRD, XPS, FT-IR, SEM-EDAX, TEM, DRS, and VSM. The photocatalytic activity of the synthesized nanoparticles for the removal of the Congo red (CR) dye and bisphenol A (BPA) from aqueous solution is examined by UV–visible spectrometer. Research indicates that the co-doping of Cu²⁺ and Ce³⁺ showed marked effect on the structural, optical, magnetic, and photocatalytic properties of the CoFe2O4 nanoparticles. DRS showed that the Co0.5Cu0.5Fe1.95Ce0.05O4 nanoparticles have lower band gap energy (0.78 eV) than other synthesized compounds. High removal percentage of CR and BPA (99.09% and 99.33%) was observed within 30 min and 180 min under visible and UV–light illumination respectively using Co0.5Cu0.5Fe1.95Ce0.05O4. The corresponding photocatalytic degradation kinetics and mechanism are analyzed.

Full text

RESEARCH ARTICLE
Copper and cerium co-doped cobalt ferrite nanoparticles: structural,
morphological, optical, magnetic, and photocatalytic properties
Venkat Savunthari Kirankumar
1
&Shanmugam Sumathi
1
Received: 26 December 2018 /Revised: 18 March 2019 /Accepted: 25 April 2019
#Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
A rapid synthetic technique is investigated for magnetic nanoparticles (Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),(x=0.05,y=0),(x=
0, y=0.5),and(x=0.05,y= 0.5)). The structure, morphology, optical and magnetic performance of prepared nanoparticles are
analyzed by powder XRD, XPS, FT-IR, SEM-EDAX, TEM, DRS, and VSM. The photocatalytic activity of the synthesized
nanoparticles for the removal of the Congo red (CR) dye and bisphenol A (BPA) from aqueous solution is examined by UV–
visible spectrometer. Research indicates that the co-doping of Cu
2+
and Ce
3+
showed marked effect on the structural, optical,
magnetic, and photocatalytic properties of the CoFe
2
O
4
nanoparticles. DRS showed that the Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanopar-
ticles have lower band gap energy (0.78 eV) than other synthesized compounds. High removal percentage of CR and BPA
(99.09% and 99.33%) was observed within 30 min and 180 min under visible and UV–light illumination respectively using
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
. The corresponding photocatalytic degradation kinetics and mechanism are analyzed.
Keywords Cobalt ferrite .Combustion .Photocatalytic activity .Congo red .Bisphenol A
Introduction
Metal and mixed metal oxides play a crucial role in different
fields such as material science, physics, chemistry, and biolo-
gy (Ravikumar et al. 2017; Suganthi and Rajan 2017;Ren
et al. 2018; Ghosh et al. 2016). The study of characteristics
of metal oxide enables to understand the applications in fuel
cell (Tucker 2017), LEDs (light-emitting devices) (Yeh et al.
2017), lithium ion batteries (Wenelska et al. 2016), solar cell
(Tsai et al. 2017), catalysis (Singh et al. 2017), transistors/
FETs (Guan-Hung et al. 2016), H
2
OandCO
2
(air) purification
(Davó-Quinonero et al. 2017; Singh and Shang-Lien 2017),
UV screening (Chen-Yu et al. 2017), humidity and gas sensors
(Falsafi et al. 2017), and photodetectors (Shaikh et al. 2017).
They also have important applications in medical science and
biology such as cancer treatment, bio labeling, drug delivery,
fluorescent imaging,efficient antimicrobial agent, and bio tag-
ging (Ruthradevi et al. 2017; Sanpo et al. 2013).
Among the metal oxides, ferrite materials have a wide
range of applications in catalysis, sensors, drug delivery,
and wastewater treatment (Falsafi et al. 2017;Ruthradevi
et al. 2017; Sanpo et al. 2013; Yadav et al. 2018a,2018b;
Sundararajan et al. 2017). Cobalt ferrite (CoFe
2
O
4
)isan
inverse spinel oxide having a cation distribution of [Fe
3+
]
A
[Co
2+
Fe
3+
]
B
(Yadav et al. 2018a,2018b). Recently, many
researchers have investigated the effect of doping and co-
doping in cobalt ferrite nanoparticles Co
1−x
Zn
x
Fe
2
O
4
(Yadav et al. 2018a,2018b), Co
1−x
Mg
x
Fe
2
O
4
(Sundararajan et al. 2017), Co
1−x
Nd
x
Fe
2
O
4
(Mounkachi
et al. 2017), Co
1−x
Cu
x
Fe
2
O
4
(Sundararajan and Kennedy
2017), Co
1−x
Ce
x
Fe
2
O
4
(Tong et al. 2016), CoFe
2−x
Bi
x
O
4
(Kiran and Sumathi 2017), Co
1−x
Cu
x
Fe
2
O
4
(Kirankumar
et al. 2017), CoFe
2−x
Gd
x
O
4
(Yadav et al. 2018a,2018b),
CoFe
2−x
Sm
x
O
4
(Falsafi et al. 2017), Co
1−x
Ni
x
FeO
4
(He
2013), Co
1−y
Cu
y
Fe
2−x
Bi
x
O
4
(Sumathi and Lakshmipriya
2017), and RGO-CoFe
2
O
4
(He and Lu 2017). Copper-
and cerium-based materials have various applications in
catalysis, photoluminescence, sensors, laser, LED, and bi-
ology (Sundararajan et al. 2017;Tongetal.2016;
Charbgoo et al. 2017;Rajeshetal.2018). Earlier, many
synthetic techniques were reported for the synthesis of
Responsible editor: Suresh Pillai
*Shanmugam Sumathi
sumathishanmugam2003@gmail.com
1
Department of Chemistry, School of Advanced Science, VIT,
Vellore, Tamil Nadu 632014, India
Environmental Science and Pollution Research
https://doi.org/10.1007/s11356-019-05286-9

cobalt ferrite nanoparticles such as sol–gel (He 2012), mi-
crowave (Sundararajan et al. 2017), co-precipitation
(Mounkachi et al. 2017), combustion (Kiran and Sumathi
2017), hydrothermal (He et al. 2014), and sonochemical
(Yadav et al. 2018a,2018b) techniques. However, the com-
bustion technique offers numerous advantages than the
other techniques such as short preparation time, crystallin-
ity, high energy efficiency, homogeneity, and simplicity
(Kiran and Sumathi 2017; Sumathi and Lakshmipriya
2017).
Generally, water is continuously contaminated by heavy
metals, organic compounds, dyes, pesticides, surfactants
etc. Organic compounds and dyes have been widely used
in textile, paper and pulp, food, leather, synthetic rubber,
and pharmaceutical industries etc. Congo red (CR) is an
anionic dye, used from histology to stain tissues for micro-
scopic examination and to serve as an acid-base indicator
(Ilayaraja et al. 2013). Bisphenol A (BPA) is widely used
in plastics and epoxy resins (Li et al. 2016). CR and BPA
may cause various health problems including vomiting,
shortness of breath, nausea, diarrhea, cancer, and skin
and eye irritations (Chatterjee et al. 2007;Ahmadietal.
2015;Zhangetal.2014). Therefore, removal of CR and
BPA has been studied far and extensive by some tech-
niques such as physical, chemical, and biological tech-
niques. Among these techniques, advanced oxidation pro-
cesses (chemical method) are a very useful technique for
removal of CR and BPA (Ahmadi et al. 2015; Zhang et al.
2014). Recently, Zhu et al. (Zhu et al. 2017)andBhagwat
et al. (Bhagwat et al. 2017) reported 91.60% (210 min) and
80% (420 min) removal of CR using Fe
3
O
4
/Bi
2
S
3
and Mg–
TiO
2
nanoparticles under UV and visible light, respective-
ly. Ruey-an and Chun-Yi (2017) and Bechambi et al.
(2015) conveyed the degradation of BPA 55% (180 min)
and60%(5h)usingN–TiO
2
/TNT and C–ZnO under UV–
light irradiations. Recently, many reports are available on
the photocatalytic degradation using CoFe
2
O
4
nanoparti-
cles for the removal of organic compounds (Sundararajan
et al. 2017; Sundararajan et al. 2017; Tong et al. 2016;
Chen et al. 2018a,2018b). To the best of our knowledge,
copper and cerium co-doped cobalt ferrite nanoparticles
have not yet been studied for photocatalytic activity.
The aim of the current work is to synthesize un-doped,
doped, co-doped cobalt ferrite (Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=
0, y=0)), (x=0.05, y=0), (x=0, y=0.5), and (x=0.05,
y= 0.5)) nanoparticles using combustion technique
employing glycine as a fuel. The structural, morphological,
optical, and magnetic properties of copper and cerium co-
doped cobalt ferrite nanoparticles are studied using differ-
ent techniques. The synthesized nanoparticles are
employed for the photocatalytic performance of CR and
BPA, and a suitable degradation mechanism is proposed.
Experimental
Materials
All the chemicals employed in the current study were pur-
chased from S.D. fine chemicals, India, were of analytical
reagent grade and utilized without further treatment or
purification.
Synthesis of un-doped, doped, co-doped ferrite
nanoparticles
Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0, y= 0), (x= 0.05, y= 0), (x=0,
y=0.5),and(x=0.05,y= 0.5) nanoparticles were synthesized
via a combustion route. Typically, Co(NO
3
)
2
⋅6H
2
O,
Cu(NO
3
)
2
⋅3H
2
O, Fe(NO
3
)
3
⋅9H
2
O, and Ce(NO
3
)
3
⋅6H
2
Owere
dissolved in double distilled water followed by adding glycine
(C
2
H
5
NO
2
) and it was continuously stirred at 80 °C for 15–
20 min towards the formation of a homogeneous solution.
After that, the homogeneous solution was exposed to pre-
heated furnace at 350 °C for 5–7 min. Finally, the obtained
particles were ground well and sintered at 700 °C for 2 h (un-
doped). Doped and co-doped cobalt ferrite particles were
sintered at 700 and 900 °C for 2 h.
Characterization
The structure and crystal phase of the synthesized nanoparticles
were analyzed by powder X-ray diffraction (D8 advance
BRUKER Germany). The functional group and surface mor-
phology of the prepared nanoparticles were observed with
Fourier-transform infrared spectroscopy (SHIMADZU) and
scanning electron microscope (ZEISS EV018). The optical
and magnetic properties of the prepared nanoparticles were mea-
suredbyUV–diffuse reflectance spectroscopy (JASCO V670)
and vibrating sample magnetometer (LAKESHORE 7410).
Photocatalytic activity
Photocatalytic activity of the Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=
0), (x= 0.05, y= 0), (x=0, y= 0.5), and (x= 0.05, y=0.5)
nanoparticles was evaluated by degradation of CR and BPA
in an aqueous solution. A 250 W mercury lamp for UV–light
and 500 W tungsten lamp was used for visible light irradia-
tions. In this experiment, 25 mg of synthesized nanoparticles
were added into 50 ml of aqueous solution of CR (10 ppm).
For BPA (10 ppm), 50 mg of synthesized nanoparticles were
added into the 50 ml of aqueous solution. Then, the solution
was mechanically stirred in dark condition for 60 min to reach
the equilibrium between nanoparticles and CR or BPA. At a
given interval of time, 3 ml of sample was taken, and the
nanoparticles were centrifuged to analyze the absorbance of
Environ Sci Pollut Res

the degradation products using UV–visible spectrophotometer
(JASCO V-730).
Results and discussion
Structural analysis
Figure 1a demonstrates the powder X-ray diffraction pattern
of prepared Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),(x=0.05,y=
0), (x=0, y= 0.5), and (x= 0.05, y= 0.5) nanoparticles. As
shown in Fig. 1a, the diffraction peaks at 18.43°, 30.33°,
35.72°, 37.37°, 43.31°, 53.88°, 57.44°, and 62.91° corre-
sponds to (111), (202), (311), (222), (400), (422), (333), and
(404) planes of CoFe
2
O
4
(JCPDS No. 96-591-0064)
(Kirankumar and Sumathi 2018). In the case of doped nano-
particles, the diffraction peak (311) is shifted slightly to higher
angle (Fig. 1b). But no other secondary phase is observed; the
introduction of copperand ceriumdid not showany change in
the pure crystal phase structure of CoFe
2
O
4
. The particle size
of the synthesized nanoparticles was estimated by Scherrer
equation (Kiran and Sumathi 2017).Thecalculatedcrystalline
size and lattice parameter values are tabulated in Table 1.
According to Vegard’s law (Fig. 2), it is observed that the
lattice parameter increased when introducing the larger sized
ion cerium (1.034 Å) in the place of (0.645 Å) [22, 23] and
decreased when introducing smaller ion copper (0.73 Å) in the
place of cobalt (0.745 Å) (Table 1and Fig. 2). The decrease in
average crystalline size of doped and co-doped cobalt ferrite
nanoparticles is explored in Table 1. Similar results are ob-
served by Tong et al. (2016) and Sanpo et al. (2013) for the
cerium-doped cobalt ferrite and copper-doped cobalt ferrite
nanoparticle.
In order to study the chemical states and surface chem-
ical composition of elements in the Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0.05, y= 0.5) nanoparticles, X-ray photoelectron
Fig.1 aPowder XRD pattern of Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),(x=0.05,y=0),(x=0,y=0.5),and(x=0.05,y= 0.5) nanoparticles. bNarrow scan
diffraction pattern from 34.0 to 40.0°
Environ Sci Pollut Res

spectroscopy analysis was performed (Fig. 3). As given in
Fig. 3a, the survey scan of co-doped cobalt ferrite nanopar-
ticles contains elemental peaks of Co 2p, Cu 2p, Fe 2p, Ce
3d, and O 1s without other impurities. Figure 3bdisplays
the Co (2p) for the Co
2+
-containing samples: peaks at
778.20, 780.35 eV, 793.78, and 795.13 eV and 784.31,
788.88, 800.10, and 801.35 eV are corresponding to Co
2p
3/2
,Co2p
1/2
,andBshake-up^satellite (donated at Sat.),
respectively (Chen et al. 2018a,2018b; Lin et al. 1997).
TheCu2pshowninFig.3c consists of two spin-orbit
doublets Cu 2p
3/2
(931.77 and 932.91 eV) and Cu 2p
1/2
(951.27 and 953.06 eV) which indicates the presence of
Cu
2+
ions. In addition, two corresponding shake-up satel-
lites were noted at 938.85, 941.55, 959.28, and 960.65 eV
(Kirankumar and Sumathi 2018;Piumettietal.2017).
Figure 3dshowstheFe2p
3/2
(708.80 and 710.90 eV) and
Fe 2p
1/2
(722.85 and 725.08 eV) of Fe 2p species, and the
equivalent shake-up satellites (717.95 eV) confirmed the
presence of Fe
3+
ions (Chen et al. 2018a,2018b;Lin
et al. 1997). The XPS spectrum of Ce 3d is depicted in
Fig. 3e. Ce 3d peaks can be fitted into nine peaks due to
its variable oxidation states (Ce
3+
and Ce
4+
); 880.17 eV
(Ce
3+
), 887.04 eV (Ce
4+
), 890.26 eV (Ce
4+
), 894.38 eV
(Ce
4+
), and 898.21 eV (Ce
4+
) and 902.03 eV (Ce
4+
),
905.55 eV (Ce
3+
), 908.74 eV (Ce
4+
), and 914.10 eV
(Ce
4+
)areassignedtoCe3d
5/2
and Ce 3d
3/2
of Ce
3+
and
Ce
4+
ions present in the magnetic nanoparticles (Piumetti
et al. 2017; Good et al. 2017; Falsafi et al. 2017;Choietal.
2015). The O 1s spectrum (Fig. 3f) demonstrates the two
peaks at 528.11 and 529.65 eV that are assigned to oxygen
adsorbed in the lattice or metal oxygen (Srivastava et al.
1994 and Praline et al. 1980).
Functional group analysis
The FT-IR spectra of synthesized Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
[(x=0, y=0), (x= 0.05, y=0), (x=0, y=0.5), and (x=
0.05, y= 0.5)] is given in Fig. 4. For the cobalt ferrite
nanoparticles, the peaks found at 535.23 cm
−1
and
404.68 cm
−1
areassignedtotheFe–O stretching vibration
at octahedral sites and Co–O stretching vibration at tetra-
hedral sites, respectively (Sundararajan et al. 2017;Tong
et al. 2016; Kiran and Sumathi 2017; Yadav et al. 2018a,
2018b). For doping and co-doping of cobalt ferrite nano-
particles, it could be seen that the adsorption bands of
doped and co-doped cobalt ferrite nanoparticles are slight-
ly shifted to higher values compared to cobalt ferrite nano-
particles. From the above results, it is noted that the pure
structure of cobalt ferrite nanoparticles did not change with
introduction of the copper and cerium which co-exist with
the powder XRD patterns.
Morphological analysis
The morphology of the synthesized nanoparticles was an-
alyzed using scanning electron microscopy. Figure 5a–d
displays the high pores and agglomerated structure of
Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0, y=0), (x=0.05, y=0), (x=
0, y=0.5), and(x=0.05, y= 0.5) nanoparticles. This phe-
nomenon attributed to the combustion synthesis (Kiran and
Sumathi 2017; Sumathi and Lakshmipriya 2017). The
EDAX confirmed the presence of cobalt, iron, and oxygen
as given in Fig. 5a, and the elements copper and cerium
were observed in all the doped and co-doped cobalt ferrite
nanoparticles (Fig. 5b–d). Moreover, to confirm the com-
position of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles, ele-
ment mapping was carried out. As indicated in Fig. 6a–f,
the scanning electron microscope image and corresponding
mapping composition display the presence of cobalt, cop-
per, iron, cerium, and oxygen. Also, the mapping obvious-
ly explained that both copper and cerium elements are uni-
formly distributed in the cobalt ferrite nanoparticles.
TEM analysis was employed to measure its shape and
size of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles (Fig. 7a–d).
The nanoparticles were randomly distributed with the par-
ticlesizeof10–50 nm. From selected area electron diffrac-
tion (SAED) pattern of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
samples
(Fig. 6e), the calculated d-spacing from the patterns resem-
bles (111), (202), (311), (222), (400), (422), (333), and
(404) planes and it is in excellent agreement with the pow-
der XRD data (Fig. 1). Particle size analysis was carried
out from TEM images, and it was found to be 27.25 nm for
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles and found to be in
good agreement with the crystallite size (37.80 nm) obtain-
ed from the powder XRD data.
Table 1 Lattice parameter (a), average crystalline size (D), band gap energy (E
g
), saturation magnetization (M
S
), and coercivity (H
C
)ofCo
1−y
Cu
y
Fe
2
−x
Ce
x
O
4
(x=0,y=0),(x=0.05,y=0),(x=0,y=0.5),and(x=0.05,y=0.5)nanoparticles
Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
a(Å) D(nm) E
g
(eV) M
S
(emu/g) H
C
(Oe)
x=0,y=0 8.3425 48.20 ± 1.5 1.38 62.34 2071.9
x=0.05,y= 0 8.3645 41.50 ± 1.2 1.12 43.59 2169.4
x=0,y=0.5 8.3242 44.60 ± 1.7 1.24 27.11 1482.8
x=0.05,y= 0.5 8.3892 37.80 ± 1.4 0.78 52.11 1204.7
Environ Sci Pollut Res

Fig. 3 XPS spectra asurvey scan, bdeconvoluted Co 2p,cdeconvoluted Cu 2p, ddeconvoluted Fe 2p, edeconvoluted Ce 3d, and edeconvoluted O 1s
of Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0.05, y=0.5)nanoparticles
Fig. 2 Lattice parameter of Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),(x=0.05, y=0),(x=0, y=0.5),and(x=0.05, y=0.5)nanoparticles
Environ Sci Pollut Res

UV-DRS analysis
The optical properties of un-doped, doped, and co-doped
nanoparticles were studied by UV–diffuse reflectance spec-
troscopy. In general, Kubelka–Munk (KM) function F(R)giv-
en in the Eqs. (1)and(2) is applied to the diffuse reflectance
spectra to obtain the optical band gap (Sundararajan et al.
2017).
FRðÞ¼1−RðÞ
2
2Rð1Þ
where, R—reflectance, F(R)—Kubelka–Munk function,
and α—absorption coefficient. The modified Tauc relation
thus becomes,
FRðÞhv ¼Ahv−EgðÞ
nð2Þ
where n= 2 and 1/2 represent direct and indirect tran-
sitions that give direct and indirect band gap, respectively.
The optical band gap values are given in Fig. 8,which
were estimated from the intersection of the extrapolated
linear portion of the curve from Tauc plots of (F(R)hv)
2
against photon energy (hv) for synthesized samples. The
optical band gap values (Fig. 8and Table 1)ofCo
1
−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0, y=0), (x=0.05, y=0), (x=0,
y=0.5), and (x= 0.05, y= 0.5) nanoparticles are found to
be 1.38 eV, 1.12 eV, 1.24 eV, and 0.78 eV, respectively.
The doping and co-doping of copper and cerium lowered
the band gap energy from 1.38 eV (un-doped CoFe
2
O
4
)to
0.78 eV (co-doped CoFe
2
O
4
). The lowering of band gap
could be due to additional energy level which is created
due to doping. XPS spectrum confirmed the co-existence
of Ce
3+
and Ce
4+
in the synthesized compound. The elec-
tronic transition from Ce
3+
to Ce
4+
couldalsoleadtored
shift in the absorbance (Chen et al. 2018a,2018b). The
charge transfer between Ce 4f levels and cobalt ferrite
plays an important role in the generation of electron-
hole pair for enhanced photocatalytic activity.
Fig. 4 FT-IR spectra of Co
1
−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),
(x= 0.05, y=0), (x=0,y=0.5),
and (x=0.05,y=0.5)
nanoparticles
Environ Sci Pollut Res

Fig. 5 a–dSEM-EDAX analysis of Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),(x=0.05,y=0),(x=0,y=0.5),and(x=0.05, y=0.5)nanoparticles
Environ Sci Pollut Res

Fig. 7 a–dTEM images, eSAED patterns, and fparticle size analysis results of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles
Fig. 6 aSEM image and b–felemental mappings of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles
Environ Sci Pollut Res

VSM analysis
Magnetic properties of the Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=
0), (x=0.05, y=0), (x=0, y=0.5), and (x=0.05, y= 0.5)
nanoparticles were investigated at room temperature utiliz-
ing VSM instrument (Fig. 9). The values of saturation mag-
netization (M
S
) and coercivity (H
C
) are given in Table 1. All
the nanoparticles are ferro-magnetic in nature; CoFe
2
O
4
(62.34 emu/g) has highest magnetization than the
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
,CoFe
1.95
Ce
0.05
O
4
,and
Co
0.5
Cu
0.5
Fe
2
O
4
. The doping and co-doping of copper and
cerium ions in the cobalt ferrite nanoparticles reduce the
saturation magnetization and coercivity values. These phe-
nomena could be explained due to the magnetic dilution of
the ferrite system by the doping and co-doping of non-
magnetic ions (Kiran and Sumathi 2017). As per Neel’s
theory (Shoushtari et al. 2016 and Gu et al. 2017), the mag-
netism of ferrite nanoparticles is a sum of magnetic moment
of each sub-lattice. The amount of saturation magnetization
depends upon the dispersion of ions in the A and B location.
In the current work, the non-magnetic Cu
2+
and Co
2+
employed in the A location of sub-lattice, while Ce
3+
and
Fe
3+
were placed in the B location of sub-lattice. The mag-
netic moment of Co
2+
was 3.87 μwhile that of Cu
2+
was
1.73 μ(tetrahedral site), and Fe
3+
was 5 μwhile that of
Ce
3+
was 2.54 μ(octahedral site). It is thus not surprising
that doping and co-doping of Cu and Ce into CoFe
2
O
4
re-
duced the magnetization (Shoushtari et al. 2016 and Gu et al.
2017). Similar observation is noted by Balavijayalakshmi
et al. (2012) for the copper-doped cobalt ferrite, Ahmad
et al. (2018) for the CoFe
2−x
Ce
x
O
4
, and Sumathi and
Lakshmipriya (2017) for the Cu- and Bi-co-doped CoFe
2
O
4
.
Fig. 8 Optical band gap values of Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
.ax=0,y=0. bx=0.05,y=0.cx=0,y=0.5.dx= 0.05, y= 0.5 nanoparticles
Environ Sci Pollut Res

Photocatalytic degradation
The photocatalytic degradation of Congo red (CR) was inves-
tigated using Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0, y= 0), (x= 0.05,
y= 0), (x=0, y= 0.5), and (x= 0.05, y= 0.5) nanoparticles
under UVand visible light irradiation. The photocatalytic deg-
radation of bisphenol A (BPA) was studied using the synthe-
sized compounds under UV light alone. The parameters such
as effect of dopant, effect of dosage of catalyst, and concen-
tration of organic pollutants were studied for optimization.
Effect of Cu
2+
and Ce
3+
dopant on the degradation
of Congo red and bisphenol A
Fifty milliliters of CR (10 ppm) dye solution and 25 mg of Co
1
−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0, y= 0), (x= 0.05, y= 0), (x=0, y=
0.5), and (x=0.05, y= 0.5) nanoparticles were subjected to
UV and visible light illumination (Fig. 10a, b). The results in
Table 2state that the percentage removal efficiency increases
by doping and co-doping of copper and cerium in cobalt fer-
rite nanoparticles under UVand visible light. Both copper and
cerium ions played a crucial role in the photocatalytic degra-
dation of CR and BPA. Moreover, it was noticed that the
degradation of CR by CoFe
1.95
Ce
0.05
O
4
nanoparticles was
higher than the Co
0.5
Cu
0.5
Fe
2
O
4
nanoparticles. At the same
time, it was clearly seen that copper and cerium co-doped
cobalt ferrite (Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
) nanoparticles have
degraded CR higher than the un-doped cobalt ferrite and
CoFe
1.95
Ce
0.05
O
4
Co
0.5
Cu
0.5
Fe
2
O
4
nanoparticles. It could be
due to the small particle size and lower band gap energy of the
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles compared to the
CoFe
1.95
Ce
0.05
O
4
,Co
0.5
Cu
0.5
Fe
2
O
4
,andCoFe
2
O
4
nanoparti-
cles. Figure 10b, c and Table 2show the removal of CR using
CoFe
2
O
4
,CoFe
1.95
Ce
0.05
O
4
,Co
0.5
Cu
0.5
Fe
2
O
4
,and
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles under different condi-
tions. From the literature, we have noticed that the addition of
hydrogen peroxide creates Fenton type system and increases
the reactivity by producing large number of reactive species.
Hence, to improve the percentage removal of CR under visible
light, the reaction was carried out with 50 μof hydrogen
peroxide (H
2
O
2
)(Fig.10c). From Fig. 10c, it can be clearly
seen that the degradation of CR is almost completed in 30 min
using Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
. Hence, for additional studies,
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
was selected.
For the colorless compound BPA degradation, 50 ml of
BPA (10 ppm) solution and 50 mg of synthesized nanoparti-
cles were used and studied under UV–light irradiation
(Fig. 10d). The percentage removal of BPA is summarized
in Table 2. BPA photocatalytic degradation by CoFe
2
O
4
,
CoFe
1.95
Ce
0.05
O
4
,Co
0.5
Cu
0.5
Fe
2
O
4
,and
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles was 69.20%,
76.35%, 73.82%, and 94.43% within 180 min. Copper and
cerium co-doped cobalt ferrite nanoparticles exhibited much
higher degradation compared to other nanoparticles, which
was attributed to the small particle size and low band gap
energy of copper and cerium co-doped cobalt ferrite nanopar-
ticles. On comparison (Table 3) with earlier reports,
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles show higher photo-
catalytic activity for the degradation of CR and BPA
(Table 3). We observed the higher removal efficiency of CR
Fig. 9 Magnetization of Co
1
−y
Cu
y
Fe
2−x
Ce
x
O
4
(x=0,y=0),
(x= 0.05, y=0), (x=0,y=0.5),
and (x=0.05,y=0.5)
nanoparticles at room temperature
Environ Sci Pollut Res

Fig. 10 aCR degradation using synthesized nanoparticles under UV light. bCR degradation under visible light without H
2
O
2
.cCR degradation under
visible light with H
2
O
2
.dBPA degradation using Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
under UV light
Table 2 Percentage of photodegradation of CR and BPA using prepared nanoparticles
Co
1−y
Cu
y
Fe
2−x
Ce
x
O
4
x=0,y=0 x=0.05,y=0 x=0,y=0.5 x=0.05,y=0.5
(CR) 10 ppm, 25 mg
(15 min) UV light
75.56% 94.23% 85.43% 95.82%
(CR) 10 ppm, 25 mg
(180 min) visible light
73.85% 79.94% 78.87% 82.41%
(CR) 10 ppm, 25 mg
(90 min) visible light (H
2
O
2
)
88.46% 95.42% 94.89% 98.99%
(BPA)10ppm,50mg
(180 min) UV light
69.20% 76.35% 73.82% 94.43%
Environ Sci Pollut Res

(98.99) and BPA (94.43) using Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles by 90 min visible light and 180 min UV–light
irradiation, respectively. Hence, Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles were chosen for further processes (quantity of
catalyst and kinetic studies).
Effect of nanoparticle dosage
The photocatalytic degradation of CR and BPA was carried
out with various dosages of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nano-
particles (Table 4). It was noted that percentage of degradation
of the organic pollutants increased with increase in the dosage
of catalyst (Fig. 11 and Table 4). When the dosage of catalyst
is less, lower active sites are available for the absorption of
photons in the media, and hence, most of the light might be
transmitted through the CR and BPA solution and percentage
of degradation was less. With higher dosage of nanoparticles,
the absorption of photons was complete without any transmis-
sion, and hence, higher percentage of degradation of CR and
BPA was noted (Wang et al. 2013). The rise in the nanoparti-
cles dosage is useful for the creation of photogenerated e−–h+
(electron–hole) and reactive oxygen species responsible for
the degradation of molecule.
Effect CR and BPA concentration
In photocatalytic degradation process, the concentration of the
dye solution is the vital parameter to examine the photocata-
lytic activity. As the concentration of CR and BPA increases
from 5 to 15 ppm, the percentage ofthe degradation decreases
(Table 4and Fig. 11c, d). The reasons could be (1) CR and
BPA may cover a greater number of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
active sites which suppress generation of the oxidants and
results in lower degradation efficiency. (2) Higher CR and
BPA concentration absorbs more photons, and hence, an in-
sufficiency of photons to activate Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles surface which in turn retarded the degradation
of CR and BPA at a higher concentration (Kirankumar and
Sumathi 2018). (3) At higher concentration of dye solution,
another key factor may also hinder the photodegradation of
CR and BPA: more dye molecules required more photocata-
lytic active sites (photocatalysts).
Kinetic studies
Figure 12a, b demonstrates the kinetic studies of the
photodegradation of CR and BPA with
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles. It was noticed that
Table 3 Comparison of CR and BPA degradation using different catalysts
Catalyst Catalyst quantity Dye Light Time Removal efficiency References
Fe
3
O
4
/Bi
2
S
3
0.03 g CR (10 ppm) UV 210 min 91.60% (Zhu et al. 2017)
Mg–TiO
2
0.05 g CR (10 ppm) Visible 420 min 80.0% (Bhagwat et al. 2017)
CoFe
2
O
4
0.03 g CR (15 ppm) Visible 120 min 62.20% Iervolino et al. (2017)
BiOBr/CoFe
2
O
4
0.03 g CR (15 ppm) Visible 120 min 90.70% Iervolino et al. (2017)
CoFe
2
O
4
0.01 g CR (10 ppm) Visible 90 min 69.20% (Jiang et al. 2016)
Co
0.5
Cu
0.5
Fe
2
O
4
0.01 g CR (10 ppm) Visible 90 min 71.20% (Jiang et al. 2016)
Co
0.5
Cu
0.5
Fe
1.9
Bi
0.1
O
4
0.01 g CR (10 ppm) Visible 90 min 87.70% (Kirankumar and Sumathi 2018)
0.01 g CR (10 ppm) UV 90 min 93.30% (Kirankumar and Sumathi 2018)
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
0.025 g CR (10 ppm) UV 15 min 95.80% Present work
0.025 g CR (10 ppm) Visible 90 min 98.90% Present work
0.025 g CR (10 ppm) Visible 30 min 98.90% Present work
N–TiO
2
/TNT 1 g BPA (10 ppm) UV 180 min 55.0% (Bechambi et al. 2015)
C–ZnO 0.5 g BPA (50 ppm) UV 300 min 60.0% (Bechambi et al. 2015)
Bi
2
WO
6
/CoFe
2
O
4
0.5 g BPA (10 ppm) UV 120 min 92.0% (Wang et al. 2013)
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
0.05 g BPA (10 ppm) UV 180 min 94.40% Present work
0.075 g BPA (10 ppm) UV 180 min 99.30% Present work
Table 4 Percentage degradation of CR and BPA using
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles under different conditions
Effect of catalyst (CR)
10 ppm (30 min)
Visible–light (H
2
O
2
)
15 mg 25 mg 35 mg
94.80% 98.90% 99.00%
Effect of catalyst (BPA)
10 ppm, (180 min) UV light
25 mg 50 mg 75 mg
91.20% 94.40% 99.30%
Effect of dye concentration 5 ppm 10 ppm 15 ppm
(CR) 25 mg, (30 min)
Visible–light (H
2
O
2
)
98.90% 98.90% 82.70%
(BPA) 50 mg,
(180 min) UV light
99.00% 94.40% 81.00%
Environ Sci Pollut Res

the photodegradation of CR and BPA over
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles follows the
Langmuir–Hinshelwood kinetics as communicated with fol-
lowing equation (Zhang et al. 2014):
lnCt
=C0¼−kt
where C
0
—initial concentration of dye, C
t
—concentration
at different time t, and k—pseudo-first order rate constant
(min
−1
). The kvalues for CR and BPA photodegradation uti-
lizing Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles are
0.34781 min
−1
(CR; UV light), 0.3368 min
−1
(CR; visible–
light), and 0.0368 min
−1
(BPA; UV light), respectively.
Mechanism of photocatalytic activity
Detecting main active species in the photocatalytic reaction is
of crucial importance to elaborate the photocatalytic mecha-
nism of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
magnetic nanoparticles. In
order to identify the reactive species responsible for the reac-
tion, the scavengers such as ethylene diamine tetraacetic acid
(EDTA for h
+
), iso-propanol (IPA for
•
OH), and benzoquinone
Fig. 11 Impact of catalyst amount on the degradation of aCR and bBPA. Impact of dye concentration by the Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles c
CR and dBPA
Environ Sci Pollut Res

(BQ for
⋅
O
2
−
were added to the CR and BPA solution and the
similar photodegradation procedure was carried out in the
presence of scavengers (Fig. 12c, d). In the absence of scav-
engers (NS), the removal of CR and BPA were 98.96% and
94.43%. WhenEDTA and BQ were added, the removal of CR
and BPA reduced crucially to 56.24% (EDTA) and 29.87%
(BQ) and 41.98% (EDTA) and 12.58% (BQ), respectively.
However, there was slight change in removal of CR
(88.90%) and BPA (78.64%) was observed in the presence
of IPA compared to EDTA and BQ. It could be finalized that
the species
⋅
O
2
−
and h
+
play a crucial part in the removal of CR
and BPA than
•
OH.
The magnetic nanoparticles were irradiated using UV/
visible light and the electrons (e
−
) in the valence band (VB)
were excited to the conduction band (CB) with the gener-
ation of holes (h
+
)intheVBEq.(3). Commonly, these e
−
and h
+
recombine quickly which will reduce the
photocatalytic activity of the catalyst. In the case of
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles, the Ce 4f level
(intra-band impurity level) has crucial influence on the
photoexcited charge generation, interfacial electron trans-
fer,andalsoontheinhibitionofe
−
–h
+
recombination. It is
published that Ce
4+
can act as an effective electron scav-
enger to trap the CB electrons of the magnetic nanoparti-
cles. The Ce
4+
ion is superior in trapping electrons when
compared to molecular oxygen due to Lewis acidic in na-
ture Eq. (4). The electron transferred to the adsorbed O
2
Eq. (5) and produce a superoxide radical anion
⋅
O
2
−
(Zhang
et al. 2014). Meanwhile, the photo induced h
+
in magnetic
nanoparticle can be also readily scavenged by the H
2
O
molecules to yield
•
OH radicals Eq. (6). The highly reac-
tive
⋅
O
2
−
and h
+
areresponsibleforthephotodegradationof
CR and BPA. The plausible mechanism is proposed is as
follows (Nasir et al. 2015)
Fig. 12 First-order kinetics for aCR and bBPA. Effect of scavenger on the degradation of cCR and dBPA by the Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles under visible and UV light irradiation
Environ Sci Pollut Res

CoFe2O4þhυ→hþþe−ð3Þ
Ce4þþe−→Ce3þð4Þ
Ce3þþO2→O2−þCe4þð5Þ
hþþH2O→OH þHþð6Þ
CR and BPA þO2−→Mineral acid þCO2þH2Oð7Þ
CR and BPA þhþ→Mineral acid þCO2þH2Oð8Þ
Reusability of nanoparticles
Figure 13a shows the photographs of magnetically induced
separation of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles. In the
presence of the magnet, the solution becomes transparent
within 30 s, because of the rapid collection of the magnetic
nanoparticles. We have also studied the stability of the
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles. After each run, sam-
ples were recovered using an external magnet, dried at 100 °C
for 5 h, and reused. Although CR and BPA removal was
diminished continuously after 3 cycles, the decrease is
Fig. 13 aSeparation of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles using magnet. bReusability of Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles for CR and BPA
degradation. cPowder XRD pattern before and after three consecutive cycles (Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles)
Environ Sci Pollut Res

negligible, and it may be ascribed to loss of the nanoparticles
during recovery and residual photocatalytic products on the
surface of nanoparticles which reduced the contact area
among nanoparticles and CR and BPA pollutant (Pelaez
et al. 2009). After 3 cycles, the removal efficiencies of
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles for the
photodegradation of CR and BPA are 97.72% and 96.02%,
respectively. Additionally, to affirm the stability of the
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles, the utilized nanopar-
ticles after three cycles were analyzed by powder XRD
(Fig. 13c). The powder XRD pattern of
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles before and after
recycling is found to be similar. From the above outcomes, it
is noted that the nanoparticles are very stable and have an
excellent photocatalytic activity.
Conclusion
In summary, we have successfully prepared pure un-doped,
doped, and co-doped cobalt ferrite nanoparticles by combus-
tion technique and analyzed by different instruments.
Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
photocatalyst has shown small par-
ticle size, narrow bandgap energy with respect to pure
CoFe
2
O
4
, CoFe
1.95
Ce
0.05
O
4
,andCo
0.5
Cu
0.5
Fe
2
O
4
nanoparti-
cles, and the good removal efficiency of CR and BPA is
achieved. Co
0.5
Cu
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticles degraded
95.82% and 99.33% of CR and BPA in 15 min and
180 min, respectively, under UV light. In addition, the %
degradation CR is 99.09% within 30 min under visible light
with H
2
O
2
. Moreover, it is found that the
Cu
0.5
Co
0.5
Fe
1.95
Ce
0.05
O
4
nanoparticle is very stable and reus-
able for photocatalytic degradation of CR and BPA and it has
great possible application in water treatment.
Acknowledgments We would like to thank the VIT management for
giving all essential facilities and seed grant for research to complete the
analysis.
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