Magnetic Nanoparticles of Fe3O4 Biosynthesized by Cnicus benedictus Extract: Photocatalytic Study of Organic Dye Degradation and Antibacterial Behavior

Full text

processes
Article
Magnetic Nanoparticles of Fe3O4Biosynthesized by
Cnicus benedictus Extract: Photocatalytic Study of
Organic Dye Degradation and Antibacterial Behavior
Álvaro de Jesús Ruíz-Baltazar 1, *, Nestor Méndez-Lozano 2, Daniel Larrañaga-Ordáz2,3,
Simón Yobanny Reyes-López 4, Marco Antonio Zamora Antuñano 2and
Ramiro Pérez Campos 5
1
CONACYT-Centro de F
í
sica Aplicada y Tecnolog
í
a Avanzada, Universidad Nacional Aut
ó
noma de M
é
xico,
Boulevard Juriquilla 3001, Santiago de Querétaro 76230, Mexico
2Universidad del Valle de México, Campus Querétaro, Naranjos Punta Juriquilla 1000, Santa Rosa Jáuregui,
Santiago de Querétaro 76230, Mexico; nestor.mendez@uvmnet.edu (N.M.-L.);
daniel.larranaga@fata.unam.mx (D.L.-O.); marco.zamora@uvmnet.edu (M.A.Z.A.)
3Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México,
Boulevard Juriquilla 3001, Santiago de Querétaro 76230, Mexico
4Instituto de Ciencias Biomédicas, Universidad Autónoma de Ciudad Juárez, Envolvente del PRONAF
y Estocolmo s/n, Ciudad Juárez, CHIC., México CP 32300, Mexico; simon.reyes@uacj.mx
5Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Av Universidad s/n,
Col. Chamilpa, Cuernavaca 62210, Mexico; ramirop21@gmail.com
*Correspondence: aruizbaltaza@fata.unam.mx
Received: 10 July 2020; Accepted: 1 August 2020; Published: 6 August 2020


Abstract:
Currently, the use of sustainable chemistry as an ecological alternative for the generation
of products or processes that are free of a polluting substance has assumed a preponderant role.
The aim of this work is to propose a bioinspired, facile, low cost, non-toxic, and environmentally
friendly alternative to obtaining magnetic nanoparticles with a majority phase of magnetite (Fe
3
O
4
).
It is important to emphasize that the synthesis was based on the chemical reduction through the
Cnicus benedictus extract, whose use as reducing agent has not been reported in the synthesis of iron
oxides nanoparticles. In addition, the Cnicus benedictus is an abundant endemic plant in Mexico with
several medicinal properties and a large number of natural antioxidants. The obtained nanoparticles
exhibited significant magnetic and antibacterial properties and an enhanced photocatalytic activity.
The crystallite size of the Fe
3
O
4
nanoparticles (Fe
3
O
4
NP’s) was calculated by the Williamson-Hall
method. The photocatalytic properties of the Fe
3
O
4
NP’s were studied by kinetics absorptions
models in the Congo red (CR) degradation. Finally, the antibacterial effects of the Fe
3
O
4
NPs were
evaluated mediated the Kirby–Bauer method against Escherichia coli and Staphylococcus aureus bacteria.
This route offers a green alternative to obtain Fe
3
O
4
NPs with remarkable magnetic, photocatalytic,
and antibacterial properties.
Keywords:
iron oxides; nanoparticles; organic dye degradation; photocatalytic effect
antibacterial behavior
1. Introduction
In recent years, the development of new nanomaterials and nanoscience study has cobranded
a preponderant place due to the wide number of researchers in those fields. This is due to the notables
physical, chemical, magnetic, optical, electronic, and catalytic properties exhibited by the materials at the
nanometric scale [
1
–
3
]. The quantic confinement of the atoms on the nanoparticles favors the reactivity
Processes 2020,8, 946; doi:10.3390/pr8080946 www.mdpi.com/journal/processes

Processes 2020,8, 946 2 of 17
of the nanoparticles, which results in better properties associated with the nanoparticles in comparison
to the bulk materials. Specifically, the Fe
3
O
4
nanoparticles have been employed in several applications
including magnetic resonance imaging (MRI), hyperthermia, drug delivery, heterogeneous catalysis,
photocatalysis, magnetic carriers, and wastewater treatment [
4
–
10
]. Some synthesis methodologies for
obtaining Fe
3
O
4
such as co-precipitations and thermal decomposition have been reported as more
common [
11
,
12
]. However, in many cases, the mentioned methods involve the use of surfactants,
reducing agents, and organic solvents, which are toxic, expensive, and have a negative environmental
impact [
13
–
15
]. In this sense, the new directrix for the synthesis of Fe
3
O
4
nanoparticles is focused
on the green chemical. Organic and biocompatible molecules such as vitamin B12, glucose cellulose,
amino acids, and even plant extracts have been employed as stabilizing and/or reducing agents [
16
–
20
].
It is important to emphasize that the search for new alternatives that promote sustainable chemistry
has become a priority issue. In this sense, endemic plants offer a sustainable and functional alternative
to obtain nanomaterials [
21
–
23
]. On the other hand, it is well known that, in recent years, the use of
plants as reducing agents (Myzus persicae, Ceratonia silique, Calotropis gigantean, Thymus kotschyanus leaf
extract, and Pisum sativum peels) during the chemical synthesis of Fe
3
O
4
nanoparticles has been widely
reported [
24
–
31
]. However, the diversity of plants, properties, and compounds present in each species
is very wide, and interaction in the synthesis process is reflected in the properties of the nanomaterials
obtained. Therefore, it is important to study, propose, and promote the use of endemic plants in
nanomaterial synthesis processes. On the other hand, the applications of the Fe
3
O
4
nanoparticles in the
field of degradation of organic pollutants and environmental remediation has been extensively studied
due to their photocatalytic properties and the emerging need for environmental remediation [
32
–
35
].
In this work, we report an environmentally friendly alternative synthesis route of Fe
3
O
4
nanoparticles
with significant antibacterial and photocatalytic activity evaluated in Congo red (CR) degradation.
A kinetic absorption model was conducted to describe in detail the CR degradation process.
2. Materials and Methods
2.1. Bio-Synthesis of Fe3O4 Nanoparticles
The synthesis of the particles was carried out from a precursor solution consisting of ferric
chloride (FeCl
3·
6H
2
O) and ferrous chloride (FeCl
2·
4H
2
O) in a 2:1 molar ratio. The Fe
2+
and the Fe
3+
ions were reduced using Cnicus benedictus extract. Briefly, the Cnicus benedictus extract was obtained,
dried, and milled with 3.87 g of Cnicus benedictus leaves, then it was mixed with 80 mL of deionized
water. The mixture was heated to 150
◦
C for 15 min. After this time, the infusion obtained was filtered
and transferred to the precursor solution of [Fe (III)/Fe (II)]. The pH of the mixture was adjusted to 12
by an NaOH solution. After 20 min of magnetically stirring, the reduction of Fe ions was carried out.
A color change of the post-reaction solution from dark reddish color into black color was observed.
This coloration change suggested the formation of the Fe3O4nanoparticles (Figure 1).
2.2. Materials CHARACTERIZATION
The size distribution and the morphology were identified using high-resolution scanning electron
microscope (HR-SEM) brand Hitachi SU8230 cold field emission at 3.0 keV. The elemental mapping by
energy dispersive X-ray spectroscopy (EDS) was performed by a Bruker XFlash 6/60 system coupled to
the microscope. The X-ray diffraction (XRD) analysis was carried out through an X-ray diffractometer
(Rigaku Ultima IV), with Cu K
α
radiation (
λ
=1.5406 Å) at a scan rate of 0.05
◦
/step with a speed of 2
◦
/min
in a diffraction range of 30–80
◦
at room temperature using parallel-beam geometry. Raman spectroscopy
of the sample was performed in solid state using a dispersive Raman spectrometer (Bruker-Senterra)
equipped with a microscope and a laser with λ=785 nm in a range from 200 to 800 cm−1.

Processes 2020,8, 946 3 of 17
Processes 2020, 8, x FOR PEER REVIEW 3 of 19
Figure 1. Schematic representation of the green procedure to obtaining Fe
3
O
4
NPs by Cnicus benedictus
as reducing agent.
2.2. Materials CHARACTERIZATION
The size distribution and the morphology were identified using high-resolution scanning
electron microscope (HR-SEM) brand Hitachi SU8230 cold field emission at 3.0 keV. The elemental
mapping by energy dispersive X-ray spectroscopy (EDS) was performed by a Bruker XFlash 6/60
system coupled to the microscope. The X-ray diffraction (XRD) analysis was carried out through an
X-ray diffractometer (Rigaku Ultima IV), with Cu Kα radiation (λ = 1.5406 Å) at a scan rate of
0.05°/step with a speed of 2°/min in a diffraction range of 30–80° at room temperature using parallel-
beam geometry. Raman spectroscopy of the sample was performed in solid state using a dispersive
Raman spectrometer (Bruker-Senterra) equipped with a microscope and a laser with λ = 785 nm in a
range from 200 to 800 cm
−1
.
2.3. Congo Red Photo Degradation
The photocatalytic activity assay of Fe
3
O
4
nanoparticles was carried out through the degradation
of CR. The experiments were performed using 1 mL of organic dye (CR) employed at 4 ppm.
Posteriorly, Fe
3
O
4
NPs synthesized by Cnicus benedictus were added to the CR solution. The
concentration of Fe
3
O
4
NPs was 20 µg/mL. The CR photodegradation process was monitored by Uv-
vis equipment (Metash UV6000) in a range of 200–800 nm and a step of 2 nm with a bandwidth of 1.8
nm, ±0.5 nm of wavelength accuracy, and 0.3 nm of wavelength repeatability in intervals of 3 min
until the SPR of the CR disappeared. In order to discard an intrinsic photobleaching associated with
Congo red, a control experiment with CR and in the absence Fe
3
O
4
NPs was carried out. The
photodegradation of the CR was evaluated for a period of 40 min, and no variations were observed
in the characteristic absorbance of the Congo red.
2.4. Antibacterial Activity
The antibacterial effect was tested with the Kirby-Bauer method. The Gram-positive
Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria were employed
to determine the antimicrobial behavior of the Fe
3
O
4
NPs. The microbial cultures were incubated at
36 °C for 24 h. Solutions of Fe
3
O
4
NPs were put in contact with studied bacteria. Six filter paper discs
of 5 mm of diameter were impregnated with 5 mL of Fe
3
O
4
NPs. Solutions of iron nanoparticles at
different concentrations were performed and labeled. Specifically, C1 was associated with the disk
control, and the samples labeled as C2 (5 mM), C3 (10 mM), C4 (15 mM), C5 (20 mM), and C6 (25
mM) corresponded to the different Fe
3
O
4
NPs concentrations. Finally, the measurements of the
inhibition zone were collected. Statistically, an ANOVA analysis was employed to validate the
Figure 1.
Schematic representation of the green procedure to obtaining Fe
3
O
4
NPs by Cnicus benedictus
as reducing agent.
2.3. Congo Red Photo Degradation
The photocatalytic activity assay of Fe
3
O
4
nanoparticles was carried out through the degradation
of CR. The experiments were performed using 1 mL of organic dye (CR) employed at 4 ppm. Posteriorly,
Fe
3
O
4
NPs synthesized by Cnicus benedictus were added to the CR solution. The concentration of
Fe
3
O
4
NPs was 20
µ
g/mL. The CR photodegradation process was monitored by Uv-vis equipment
(Metash UV6000) in a range of 200–800 nm and a step of 2 nm with a bandwidth of 1.8 nm,
±
0.5 nm of
wavelength accuracy, and 0.3 nm of wavelength repeatability in intervals of 3 min until the SPR of the
CR disappeared. In order to discard an intrinsic photobleaching associated with Congo red, a control
experiment with CR and in the absence Fe
3
O
4
NPs was carried out. The photodegradation of the CR
was evaluated for a period of 40 min, and no variations were observed in the characteristic absorbance
of the Congo red.
2.4. Antibacterial Activity
The antibacterial effect was tested with the Kirby-Bauer method. The Gram-positive Staphylococcus
aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria were employed to determine the
antimicrobial behavior of the Fe
3
O
4
NPs. The microbial cultures were incubated at 36
◦
C for 24 h.
Solutions of Fe
3
O
4
NPs were put in contact with studied bacteria. Six filter paper discs of 5 mm of
diameter were impregnated with 5 mL of Fe
3
O
4
NPs. Solutions of iron nanoparticles at different
concentrations were performed and labeled. Specifically, C1 was associated with the disk control,
and the samples labeled as C2 (5 mM), C3 (10 mM), C4 (15 mM), C5 (20 mM), and C6 (25 mM)
corresponded to the different Fe
3
O
4
NPs concentrations. Finally, the measurements of the inhibition
zone were collected. Statistically, an ANOVA analysis was employed to validate the measurement
of the inhibition zone and, consequently, the antibacterial effect of the Fe
3
O
4
NPs. The comparison
between the antibacterial behavior of E. coli and S. aureus was modeled mathematically by curve
fit models.
3. Results and Discussion
3.1. Scanning Electron Microscopy
The Fe
3
O
4
NPs were characterized by scanning electron microscopy (SEM). Figure 2a shows
a secondary electrons image obtained at 15 kV; in this image, it is possible to identify the morphology
and the distribution size of the Fe
3
O
4
NPs synthesized by Cnicus benedictus. The Fe
3
O
4
NPs show
agglomeration due to the steric effect of the nanoparticles [
20
]. However, in Figure 2b, the individual

Processes 2020,8, 946 4 of 17
nanoparticles confined in a cluster were observed. The average distribution size of the nanoparticles
was 20 nm approximately. This value could be considered as a first approximation. Subsequent analysis
by XRD supported this fact. Additionally, an EDS mapping of the sample is presented in Figure 2c,
which displays the Fe and the O as constitutive elements of the sample. In this sense, it was possible to
affirm that the Fe
3
O
4
NPs could be synthesized by Cnicus benedictus as the reducing agent, thus offering
a new alternative in the green chemical in the field of synthesis of iron oxides nanoparticles Fe
3
O
4
NPs. Nevertheless, a more precise characterization of the iron oxides obtained was necessary and is
presented below.
Processes 2020, 8, x FOR PEER REVIEW 4 of 19
measurement of the inhibition zone and, consequently, the antibacterial effect of the Fe
3
O
4
NPs. The
comparison between the antibacterial behavior of E. coli and S. aureus was modeled mathematically
by curve fit models.
3. Results and Discussion
3.1. Scanning Electron Microscopy
The Fe
3
O
4
NPs were characterized by scanning electron microscopy (SEM). Figure 2a shows a
secondary electrons image obtained at 15 kV; in this image, it is possible to identify the morphology
and the distribution size of the Fe
3
O
4
NPs synthesized by Cnicus benedictus. The Fe
3
O
4
NPs show
agglomeration due to the steric effect of the nanoparticles [20]. However, in Figure 2b, the individual
nanoparticles confined in a cluster were observed. The average distribution size of the nanoparticles
was 20 nm approximately. This value could be considered as a first approximation. Subsequent
analysis by XRD supported this fact. Additionally, an EDS mapping of the sample is presented in
Figure 2c, which displays the Fe and the O as constitutive elements of the sample. In this sense, it was
possible to affirm that the Fe
3
O
4
NPs could be synthesized by Cnicus benedictus as the reducing agent,
thus offering a new alternative in the green chemical in the field of synthesis of iron oxides
nanoparticles Fe
3
O
4
NPs. Nevertheless, a more precise characterization of the iron oxides obtained
was necessary and is presented below.
Figure 2. SEM image obtained by secondary electrons at (a) 130, (b) 80 kx, and (c) EDS mapping of
Fe
3
O
4
NPs obtained by Cnicus benedictus.
3.2. X-Ray Analysis of the Nano-Crystalline Fe
3
O
4
Figure 3a shows the experimental X-Ray diffraction pattern associated with the sample
synthesized by the green route using Cnicus benedictus. Based on the diffraction peaks observed in
the experimental XRD pattern, it was possible to correlate this XRD pattern with the cubic structure
(Fm3m-325) of the magnetite (JCPDF# 96-900-5813). In order to support the structural
characterization of the sample, Table 1 indicates the location of the diffraction peaks (2θ), the
interplanar distance (d-spacing), and the hkl index typical of the magnetite structure.
On the other hand, the crystallite size and strain could be calculated from the experimental XRD
pattern according to the Williamson-Hall method. However, in the first part of the Williamson-Hall
analysis, it was necessary to obtain parameters derivate to the fit of the peaks profile.
Figure 2.
SEM image obtained by secondary electrons at (
a
) 130, (
b
) 80 kx, and (
c
) EDS mapping of
Fe3O4NPs obtained by Cnicus benedictus.
3.2. X-Ray Analysis of the Nano-Crystalline Fe3O4
Figure 3a shows the experimental X-Ray diffraction pattern associated with the sample synthesized
by the green route using Cnicus benedictus. Based on the diffraction peaks observed in the experimental
XRD pattern, it was possible to correlate this XRD pattern with the cubic structure (Fm3m-325) of the
magnetite (JCPDF# 96-900-5813). In order to support the structural characterization of the sample,
Table 1indicates the location of the diffraction peaks (2
θ
), the interplanar distance (d-spacing), and the
hkl index typical of the magnetite structure.
Table 1.
Parameters obtained from the XRD patterns of the Fe
3
O
4
NPs and involved in the Williamson-Hall
analysis. FWHM: full width at half maximum.
2θd-spacing hkl FWHM
(Corrected) Asymmetry Areal
Asymmetry
Integral
Breadth
Shape
Factor
Size
Uncorrected
Size
Corrected
30.24 2.9571 220 0.5069 1.0005 1.6403 0.588 0.861
18.03811703
18.3
35.62 2.5185 311 0.6984 0.7643 0.7378 0.893 0.782
13.27506532
13.4
38.1 2.4213 222 0.4058 0.6814 0.8878 0.242 1.68
23.01235689
24.1
43.2 2.0925 400 0.8135 1.4181 1.2442 0.277 2.936
11.67014924
11.8
53.62 1.7061 422 0.46792 1.1632 1.0717 0.3921 1.052
21.13618779
21.1
57.08 1.6102 511 0.7651 1.7009 1.1468 0.486 1.576
13.13289818
13.5
62.84 1.4802 440 0.6574 0.8412 0.994 0.646 1.017
15.73424925
16.6

Processes 2020,8, 946 5 of 17
Processes 2020, 8, x FOR PEER REVIEW 5 of 19
Figure 3. (a) XRD pattern profile fitting and pseudo-Voigt analysis of broadening. (b) Cumulative
residual fitting peak (c) Fitting intensity of the (311) plane of the magnetite and (d) convolution of
the instrumental resolution function (IRF)
The diffraction profile from the Fe
3
O
4
nanoparticles was fitted with pseudo-Voigt (pV) function
[36–38]. The pseudo-Voigt function is the convolution of Gauss and Lorentz functions. In general
form, pV function is given by [39]:
𝑝𝑉(𝑥)=𝜂𝐺(𝑥)+(1−𝜂)𝐿(𝑥)
(1)
where G(x) and L(x) are defined as the sum of the Gaussian peak and the Lorentzian peak,
respectively. In both functions, parameters such as height (height of the peak at the maximum) peak
center (position of the maximum) and FWHM (full width at half maximum of the peak) are involved.
In this sense, it is necessary to obtain the normalized peaks of Gauss (G´(x)) and Lorentz (L´(x)),
consequently, the pV(x) can be expressed as:
𝑝𝑉(𝑥)=𝐼[𝜂𝐺
,
(𝑥,𝛤)+(1−𝜂)𝐿
,
(𝑥)
(2)
where I is the intensity of the peak normalized by Gauss and Lorentz. Γ is the FWHM for Gaussian
and Lorentzian peaks, 𝑥 is the peak position, and ƞ is the Gaussian ratio. The Lorentzian part is
described by:
𝐿´(𝑥)=1
𝜋𝛤2
⁄
(𝑥−𝑥

)

+(𝛤/2)

(3)
and the Gaussian part is:
Figure 3.
(
a
) XRD pattern profile fitting and pseudo-Voigt analysis of broadening. (
b
) Cumulative
residual fitting peak (
c
) Fitting intensity of the (311) plane of the magnetite and (
d
) convolution of the
instrumental resolution function (IRF)
On the other hand, the crystallite size and strain could be calculated from the experimental XRD
pattern according to the Williamson-Hall method. However, in the first part of the Williamson-Hall
analysis, it was necessary to obtain parameters derivate to the fit of the peaks profile.
The diffraction profile from the Fe
3
O
4
nanoparticles was fitted with pseudo-Voigt (pV)
function
[36–38]
. The pseudo-Voigt function is the convolution of Gauss and Lorentz functions.
In general form, pV function is given by [39]:
pV(x)=ηG(x)+(1−η)L(x)(1)
where G(x) and L(x) are defined as the sum of the Gaussian peak and the Lorentzian peak, respectively.
In both functions, parameters such as height (height of the peak at the maximum) peak center
(position of the maximum) and FWHM (full width at half maximum of the peak) are involved.
In this sense, it is necessary to obtain the normalized peaks of Gauss (G
´
(x)) and Lorentz (L
´
(x)),
consequently, the pV(x) can be expressed as:
pV(x)=I[ηG,(x,Γ)+(1−η)L,(x)(2)
where Iis the intensity of the peak normalized by Gauss and Lorentz.
Γ
is the FWHM for Gaussian
and Lorentzian peaks,
x0
is the peak position, and
η
is the Gaussian ratio. The Lorentzian part is
described by:
L(x)=1
π
Γ/2
(x−x0)2+(Γ/2)2(3)
and the Gaussian part is:
G(x)=1
σ√2πe−(x−x0)2
2σ2(4)

Processes 2020,8, 946 6 of 17
Finally, the pseudo-Voigt expression was employed for the fit profile peaks in the XRD analysis of
the Fe3O4nanoparticles and can be written as follows [40]:
pV(x)=h∗[η∗exp




−(x−x0)2
−2σ2




+(1−η)(Γ/2)2
(x−x0)2+(Γ/2)2](5)
where:
h=2I
πΓh1+√ln2−1i (6)
σ=Γ
2√2ln2(7)
In this sense, Figure 3a,b, show the multipeaks fitting analysis and the cumulative residual fitting
peak associated with the residual fit in the analysis, respectively.
In representative form of the fitting peaks, Figure 2c illustrates the fitting intensity associated with
the (311) plane of the magnetite; in this plot, it is possible to observe the Gaussian and the Lorentzian
parts corresponding to the Pseudo-Voigt fit process. In this case, a correlation factor (R
2
) of 0.9945 was
observed. Consequently, this result indicated that the FWHM values were consistent for the subsequent
analysis. In order to support the pseudo-Voigt profile peak fitting, the instrumental resolution function
(IRF) of the equipment is described in Figure 3d. The IRF was plotted from the modified Caglioti
equation, which is described as follows [38]:
FWHM2=Utan2θ+Vtanθ+W+Z
cosθ(8)
Additionally, the IRF was calculated by the pseudo-Voigt method. In this procedure, the Gaussian
(HG) and the Lorentzian (HL) parts were calculated started from the following expressions [39]:
H2
G=Utan2θ+Vtanθ+W(9)
HL=Xtanθ+Y
cosθ+Z(10)
The HG and the HL parts of the IRF are shown in graph 3(d). The convolution of the HG and the
HL is presented in the IRF pseudo-Voigt (HpV) graph (Figure 3d). It is important to note that the HpV
and the Caglioti curve are very similar due to the refinement of U, V, and W parameters.
3.3. Williamson-Hall Analysis
Based on the results obtained from the pseudo-Voigt analysis, the FWHM values were employed
to calculate the crystallite size and strain, which could be obtained by the Williamson-Hall plot
method. This method presupposes that the peaks observed from the X-ray diffraction pattern are the
convolution of the Gaussian part (broadening due to the strain) and the Lorentzian part (influence of the
crystallite size) [6,39,41] Mathematically, this relationship can be expressed in the reciprocal space as:
βcosθ
λ=1
DV
+2ε2sinθ
λ(11)
In this sense, from the graph of the (
βcosθ)
versus (2
sinθ/λ)
, it is possible to obtain the microstrain
and the domain size with the values of slope and intercepts, respectively.
The Williamson-Hall plot is described in Figure 4a. In this case, the crystallite size obtained by the
pseudo-Voigt method was 17.47 nm. In order to corroborate this value, Table 1describes the parameter
involved in the Williamson-Hall plot analysis. The profile function employed in the calculations was
the pseudo-Voigt model. However, the values of the Gauss and the Lorentz parts were compared and

Processes 2020,8, 946 7 of 17
are shown in Figure 4b,c, respectively. In all cases of the profile-fitting analysis of XRD peaks, similar
values of crystallite size were obtained.
Processes 2020, 8, x FOR PEER REVIEW 8 of 19
Figure 4. Williamson-Hall plot of the Fe
3
O
4
NPs synthesized by Cnicus benedictus calculated by the (a)
Pseudo-Voigt, (b) Lorentz and (c) Gauss functions.
Table 2 shows the values of the crystallite size and strain calculated for the sample. The
calculations performed based on the FWHM of each intensity show a stable size and strain associated
with the sample. In this case, the crystallite size was 14 nm according to the size observed by SEM. It
is important to note that the pseudo-Voigt method is a functional and highly accurate method for
calculating the crystallite size from the XRD patterns; due to this method, it is a combination of the
Lorentz and the Gauss method for fit peak profiles, which makes it an excellent tool for XRD pattern
processing [38].
Table 2. Crystallite size and strain calculated from pseudo-Voigt, Lorentz, and Gauss methods.
Profile function Profile broadening
S
ize (nm)
S
train (%)
Pseudo-Voigt FWHM 14.45±6.27 0.289±0.145
Integral breadth 18.10±4.32 0.1624±0.192
Lorentzian FWHM 18.04±2.11 0.0640±0.017
Integral breadth 22.11±4.98 0.032±0.016
Gaussian FWHM 13.89±3.32 0.09±0.181
Integral breadth 17.70±5.78 0.012±0.154
3.4. Raman Spectroscopy
In order to elucidate the oxidative phases obtained from the green synthesis of the nanoparticles,
a Raman analysis is presented in Figure 5. In this figure, it is possible to identify three phases
associated with the iron oxide. The main phase identified was magnetite with an approximate value
of 45.5%, and the second phase was hematite (39.81%), and the minority phase was maghemite (Table
3). These results can be attributed to the facile oxidation of the NPs due to the interaction with the
medium. However, it is important to mention that the XRD analysis supported the formation of Fe
3
O
4
(a) (b)
(c)
Figure 4.
Williamson-Hall plot of the Fe
3
O
4
NPs synthesized by Cnicus benedictus calculated by the (
a
)
Pseudo-Voigt, (b)Lorentz and (c)Gauss functions.
Table 2shows the values of the crystallite size and strain calculated for the sample. The calculations
performed based on the FWHM of each intensity show a stable size and strain associated with the
sample. In this case, the crystallite size was 14 nm according to the size observed by SEM. It is important
to note that the pseudo-Voigt method is a functional and highly accurate method for calculating the
crystallite size from the XRD patterns; due to this method, it is a combination of the Lorentz and the
Gauss method for fit peak profiles, which makes it an excellent tool for XRD pattern processing [38].
Table 2. Crystallite size and strain calculated from pseudo-Voigt, Lorentz, and Gauss methods.
Profile Function Profile Broadening Size (nm) Strain (%)
Pseudo-Voigt FWHM 14.45 ±6.27 0.289 ±0.145
Integral breadth 18.10 ±4.32 0.1624 ±0.192
Lorentzian FWHM 18.04 ±2.11 0.0640 ±0.017
Integral breadth 22.11 ±4.98 0.032 ±0.016
Gaussian FWHM 13.89 ±3.32 0.09 ±0.181
Integral breadth 17.70 ±5.78 0.012 ±0.154
3.4. Raman Spectroscopy
In order to elucidate the oxidative phases obtained from the green synthesis of the nanoparticles,
a Raman analysis is presented in Figure 5. In this figure, it is possible to identify three phases associated
with the iron oxide. The main phase identified was magnetite with an approximate value of 45.5%,
and the second phase was hematite (39.81%), and the minority phase was maghemite (Table 3).
These results can be attributed to the facile oxidation of the NPs due to the interaction with the medium.

Processes 2020,8, 946 8 of 17
However, it is important to mention that the XRD analysis supported the formation of Fe
3
O
4
as the
main phase. However, the reduction of the Fe ions by Cnicus benedictus was carried out as a result of
the synthesis of Fe
3
O
4
. It has been reported that the presence of antioxidants in some organic extracts
promotes Fe ions reduction [
42
]. Specifically, the Cnicus benedictus extract offers a green alternative to
obtain Fe3O4NPs.
Processes 2020, 8, x FOR PEER REVIEW 9 of 19
as the main phase. However, the reduction of the Fe ions by Cnicus benedictus was carried out as a
result of the synthesis of Fe
3
O
4
. It has been reported that the presence of antioxidants in some organic
extracts promotes Fe ions reduction [42]. Specifically, the Cnicus benedictus extract offers a green
alternative to obtain Fe
3
O
4
NPs.
Figure 5. Deconvolution analysis of the Raman spectra of Fe
3
O
4
NPs.
Table 3 describes the location of the main intensities observed in the Raman spectra of the Fe
3
O
4
NPs synthesized by environmentally friendly methodology. Moreover, the phonon modes attributed
to each intensity are shown in Table 3. These values are supported by previous studies reported in
the literature [43–45]. This result is conclusive in respect to the iron oxide obtained by the green
synthesis method, although with Cnicus benedictus, we can affirm that it is possible to obtain Fe
3
O
4
NPs in the majority phase and consequently evaluate the magnetic and the catalytic properties of the
magnetite.
Table 3. Deconvolution of Raman spectra for the quantification of iron oxide phases obtained by
green synthesis route.
Phase Center Max Phonon modes Max Height FWHM Area % Phase
Magnetite
337.223 T2g 205.855 454.371 1145.410 8.82417337
467.565 T2g 649.779 100.823 470.199 3.6223863
490.854 T2g 169.265 389.238 845.322 6.51231252
561.327 T2g 868.329 127.992 818.774 6.30778824
665.161 A1g 350.471 524.393 2627.970 20.2457311
45.5123916
Hematite
224.171 A1g 193.966 615.686 908.971 7.00266079
287.060 Eg 434.132 275.124 1047.700 8.0714211
392.236 Eg 266.167 444.447 1656.890 12.7645861
617.429 Eg 169.405 38.060 1554.730 11.9775513
39.8162194
Maghemite 715.584 A1g 285.457 43.956 1904.400 14.6713891
3.5. Analysis of Magnetic Properties of the Fe
3
O
4
Obtained by Green Route
Figure 6 shows the hysteresis curve or the magnetization curve of the Fe
3
O
4
NPs. In this figure,
we can observe an approximately superparamagnetic behavior [38,46,47] The saturation
magnetization (Ms) value was 43.85 emu/g, while the coercivity field (Hc) of the sample was 143.75
Figure 5. Deconvolution analysis of the Raman spectra of Fe3O4NPs.
Table 3.
Deconvolution of Raman spectra for the quantification of iron oxide phases obtained by green
synthesis route.
Phase Center Max Phonon Modes Max Height FWHM Area % Phase
Magnetite
337.223 T2g 205.855 454.371 1145.410 8.82417337
467.565 T2g 649.779 100.823 470.199 3.6223863
490.854 T2g 169.265 389.238 845.322 6.51231252
561.327 T2g 868.329 127.992 818.774 6.30778824
665.161 A1g 350.471 524.393 2627.970 20.2457311
45.5123916
Hematite
224.171 A1g 193.966 615.686 908.971 7.00266079
287.060 Eg434.132 275.124 1047.700 8.0714211
392.236 Eg266.167 444.447 1656.890 12.7645861
617.429 Eg169.405 38.060 1554.730 11.9775513
39.8162194
Maghemite 715.584 A1g 285.457 43.956 1904.400 14.6713891
Table 3describes the location of the main intensities observed in the Raman spectra of the Fe
3
O
4
NPs synthesized by environmentally friendly methodology. Moreover, the phonon modes attributed
to each intensity are shown in Table 3. These values are supported by previous studies reported in the
literature [
43
–
45
]. This result is conclusive in respect to the iron oxide obtained by the green synthesis
method, although with Cnicus benedictus, we can affirm that it is possible to obtain Fe
3
O
4
NPs in the
majority phase and consequently evaluate the magnetic and the catalytic properties of the magnetite.
3.5. Analysis of Magnetic Properties of the Fe3O4Obtained by Green Route
Figure 6shows the hysteresis curve or the magnetization curve of the Fe
3
O
4
NPs. In this figure,
we can observe an approximately superparamagnetic behavior [
38
,
46
,
47
] The saturation magnetization
(Ms) value was 43.85 emu/g, while the coercivity field (Hc) of the sample was 143.75 Oe. Both values

Processes 2020,8, 946 9 of 17
were consistent with the typical values reported in the literature for superparamagnetic materials [
48
,
49
].
In this sense, it was possible to affirm that the sample of Fe
3
O
4
NPs effectively had a superparamagnetic
behavior and, consequently, their potentials application in optoelectronics or biomedicine, among
others, is notable. In other words, the green synthesis of Fe
3
O
4
NPs by Cnicus benedictus offers an
environmentally friendly alternative for obtaining magnetic nanoparticles.
Processes 2020, 8, x FOR PEER REVIEW 10 of 19
Oe. Both values were consistent with the typical values reported in the literature for
superparamagnetic materials [48,49]. In this sense, it was possible to affirm that the sample of Fe
3
O
4
NPs effectively had a superparamagnetic behavior and, consequently, their potentials application in
optoelectronics or biomedicine, among others, is notable. In other words, the green synthesis of Fe
3
O
4
NPs by Cnicus benedictus offers an environmentally friendly alternative for obtaining magnetic
nanoparticles.
Figure 6. Magnetic hysteresis loop of the Fe
3
O
4
NPs at room temperature.
3.6. Photocatalytic Effect: Congo Red (CR) Degradation
In order to evaluate the photocatalytic behavior of the Fe
3
O
4
NPs, a CR degradation process was
conducted. Figure 7a shows the Uv-vis spectra associated with the CR Fe
3
O
4
NPs and the CR Fe
3
O
4
samples at an initial time (t = 0). In this figure, the characteristic peak associated with the CR was
observed at 500 nm in the samples of CR and Fe
3
O
4
/CR. Figure 7b illustrates the CR degradation
process, in which it was possible to observe the CR degradation in a reaction time of 36 min. This fact
indicated that the CR degradation by Fe
3
O
4
NPs was possible due to the reactivity of the nanoparticles
obtained by green synthesis route.
(a) (b)
Figure 6. Magnetic hysteresis loop of the Fe3O4NPs at room temperature.
3.6. Photocatalytic Effect: Congo Red (CR) Degradation
In order to evaluate the photocatalytic behavior of the Fe
3
O
4
NPs, a CR degradation process was
conducted. Figure 7a shows the Uv-vis spectra associated with the CR Fe
3
O
4
NPs and the CR Fe
3
O
4
samples at an initial time (t =0). In this figure, the characteristic peak associated with the CR was
observed at 500 nm in the samples of CR and Fe
3
O
4
/CR. Figure 7b illustrates the CR degradation
process, in which it was possible to observe the CR degradation in a reaction time of 36 min. This fact
indicated that the CR degradation by Fe
3
O
4
NPs was possible due to the reactivity of the nanoparticles
obtained by green synthesis route.
Processes 2020, 8, x FOR PEER REVIEW 10 of 19
Oe. Both values were consistent with the typical values reported in the literature for
superparamagnetic materials [48,49]. In this sense, it was possible to affirm that the sample of Fe
3
O
4
NPs effectively had a superparamagnetic behavior and, consequently, their potentials application in
optoelectronics or biomedicine, among others, is notable. In other words, the green synthesis of Fe
3
O
4
NPs by Cnicus benedictus offers an environmentally friendly alternative for obtaining magnetic
nanoparticles.
Figure 6. Magnetic hysteresis loop of the Fe
3
O
4
NPs at room temperature.
3.6. Photocatalytic Effect: Congo Red (CR) Degradation
In order to evaluate the photocatalytic behavior of the Fe
3
O
4
NPs, a CR degradation process was
conducted. Figure 7a shows the Uv-vis spectra associated with the CR Fe
3
O
4
NPs and the CR Fe
3
O
4
samples at an initial time (t = 0). In this figure, the characteristic peak associated with the CR was
observed at 500 nm in the samples of CR and Fe
3
O
4
/CR. Figure 7b illustrates the CR degradation
process, in which it was possible to observe the CR degradation in a reaction time of 36 min. This fact
indicated that the CR degradation by Fe
3
O
4
NPs was possible due to the reactivity of the nanoparticles
obtained by green synthesis route.
(a) (b)
Figure 7.
Uv-vis spectra of the (
a
) Fe
3
O
4
NPs, the Fe
3
O
4
NPs-CR, and the CR (40 mgL
−1
) and (
b
) Congo
red photodegradation by Fe3O4NPs synthesized using Cnicus benedictus.

Processes 2020,8, 946 10 of 17
In general form, this behavior can be explained as a combination of oxidation and reduction
processes in which the surface of the Fe
3
O
4
NPs is a substrate where the CR molecules are absorbed.
Subsequently, the nanoparticles act as active sites for the electron interactions between the organic
dyes and the Fe
3
O
4
NPs. The photocatalytic mechanism for organic dyes degradation involves the dye
excitation under visible light with wavelength (
λ
>400nm) from the ground state (Dye0) to the triplet
excited state (Dye *). During this procedure, the excited state dye species generates a semi-oxidized
radial cation (Dye
•
+) by an electron injection into the conduction band of Fe
3
O
4
. A derivate to the
reaction between the trapped electrons and the dissolved oxygen in the system with superoxide radical
anions (O2
•−
) are generated [
50
,
51
]. Consequently, this superoxide radicals anion results in hydroxyl
radicals (OH
•
) formation [
52
–
54
], which are responsible for the oxidation and the degradation of the
organic dye compound present in the CR (Figure 8).
Processes 2020, 8, x FOR PEER REVIEW 11 of 19
Figure 7. Uv-vis spectra of the (a) Fe
3
O
4
NPs, the Fe
3
O
4
NPs-CR, and the CR (40 mgL
−1
) and (b) Congo
red photodegradation by Fe
3
O
4
NPs synthesized using Cnicus benedictus.
In general form, this behavior can be explained as a combination of oxidation and reduction
processes in which the surface of the Fe
3
O
4
NPs is a substrate where the CR molecules are absorbed.
Subsequently, the nanoparticles act as active sites for the electron interactions between the organic
dyes and the Fe
3
O
4
NPs. The photocatalytic mechanism for organic dyes degradation involves the
dye excitation under visible light with wavelength (λ > 400nm) from the ground state (Dye0) to the
triplet excited state (Dye *). During this procedure, the excited state dye species generates a semi-
oxidized radial cation (Dye•+) by an electron injection into the conduction band of Fe
3
O
4
. A derivate
to the reaction between the trapped electrons and the dissolved oxygen in the system with superoxide
radical anions (O2 •−) are generated [50,51]. Consequently, this superoxide radicals anion results in
hydroxyl radicals (OH•) formation [52–54], which are responsible for the oxidation and the
degradation of the organic dye compound present in the CR (Figure 8).
Figure 8. Schematic representation of dye photodegradation process.
On the other hand, the adsorption rate and the equilibrium concentration at which CR is
degraded can be described in detail by theoretical adsorption models.
3.7. Theoretical Adsorption Kinetic Models
In order to describe the adsorption kinetic behavior of the Fe
3
O
4
NPs, four theoretical models
were analyzed with respect to the experimental data obtained from the photodegradation of the CR
by Fe
3
O
4
NPs. Pseudo-first order, Pseudo-second order, Elovich, and Intraparticle diffusion models
were employed to describe and calculate the kinetics adsorption parameters of the organic dye. The
equations that govern these models are described in Table 4, and which have been described in
several reports [6,35,42,55].
Table 4. Theoretical adsorption models employed for the photodegradation of the CR by Fe
3
O
4
NPs.
Theoretical model Equation
Pseudo first order 
 =
(−) (11)
Pseudo second order 

=
(−) (12)
Figure 8. Schematic representation of dye photodegradation process.
On the other hand, the adsorption rate and the equilibrium concentration at which CR is degraded
can be described in detail by theoretical adsorption models.
3.7. Theoretical Adsorption Kinetic Models
In order to describe the adsorption kinetic behavior of the Fe
3
O
4
NPs, four theoretical models
were analyzed with respect to the experimental data obtained from the photodegradation of the
CR by Fe
3
O
4
NPs. Pseudo-first order, Pseudo-second order, Elovich, and Intraparticle diffusion
models were employed to describe and calculate the kinetics adsorption parameters of the organic dye.
The equations that govern these models are described in Table 4, and which have been described in
several reports [6,35,42,55].
Table 4. Theoretical adsorption models employed for the photodegradation of the CR by Fe3O4NPs.
Theoretical Model Equation
Pseudo first order dq
dt =K1(qe−qt)
Pseudo second order dq
dt =K2(qe−qt)2
Elovich dqt
dt =αe−βqt
Intraparticle diffusion qt=ki√t+Ci

Processes 2020,8, 946 11 of 17
Figure 9a–d show the graphs associated with theoretical kinetic adsorption models. The correlation
values existent between the experimental data and the theoretical model are described in Table 3.
In this table, it is possible to observe that the intraparticle diffusion model exhibited the highest
correlation value R2, (0.9557). Based on this result, we could affirm that the CR degradation process
was carried out in addition to the intraparticle diffusion process. From the physic-chemical point
of view, the intraparticle diffusion model was described by tree steps. Firstly, an instantaneous
adsorption was detected because the concentration in the external solution was sufficiently high.
Then, a gradual adoption was observed during the CR degradation process. The time associated with
this step depended on the system variables such as temperature, absorbent particle size, and solute
concentration [
56
–
59
]. Finally, the organic molecules that degraded exhibited a slow adsorption rate
until the final equilibrium. Therefore, the intraparticle diffusion model can describe the CR degradation
process and the solute concentration, and the particle size of the Fe
3
O
4
NPs takes a preponderant role
in the CR degradation rate.
Processes 2020, 8, x FOR PEER REVIEW 12 of 19
Elovich 

=𝛼𝑒 (13)
Intraparticle diffusion 𝑞=𝑘
√
𝑡+𝐶 (14)
Figure 9a–d show the graphs associated with theoretical kinetic adsorption models. The
correlation values existent between the experimental data and the theoretical model are described in
Table 3. In this table, it is possible to observe that the intraparticle diffusion model exhibited the
highest correlation value R2, (0.9557). Based on this result, we could affirm that the CR degradation
process was carried out in addition to the intraparticle diffusion process. From the physic-chemical
point of view, the intraparticle diffusion model was described by tree steps. Firstly, an instantaneous
adsorption was detected because the concentration in the external solution was sufficiently high.
Then, a gradual adoption was observed during the CR degradation process. The time associated with
this step depended on the system variables such as temperature, absorbent particle size, and solute
concentration [56–59]. Finally, the organic molecules that degraded exhibited a slow adsorption rate
until the final equilibrium. Therefore, the intraparticle diffusion model can describe the CR
degradation process and the solute concentration, and the particle size of the Fe
3
O
4
NPs takes a
preponderant role in the CR degradation rate.
Figure 9. Experimental and theoretical kinetic adsorption models: (a) Pseudo-first order, (b) Pseudo-
second order, (c) Elovich, and (d) Intraparticle diffusion models.
3.8. Antibacterial Effect
In order to evaluate the antibacterial effect of the Fe
3
O
4
NPs obtained by green route, the
inhibition zones in E. coli and S. aureus bacteria strains were measured. Figure 10a displays the
inhibition zones presented by the Fe
3
O
4
NPs at different Fe
3
O
4
NPs concentrations. In this plot, the
antibacterial effect was major in the case of the E. Coli bacteria in comparison to the S. aureus strain.
(a)
(
d
)
(c)
(
b
)
Figure 9.
Experimental and theoretical kinetic adsorption models: (
a
) Pseudo-first order, (
b
) Pseudo-second
order, (c) Elovich, and (d) Intraparticle diffusion models.
3.8. Antibacterial Effect
In order to evaluate the antibacterial effect of the Fe
3
O
4
NPs obtained by green route, the inhibition
zones in E. coli and S. aureus bacteria strains were measured. Figure 10a displays the inhibition zones
presented by the Fe
3
O
4
NPs at different Fe
3
O
4
NPs concentrations. In this plot, the antibacterial effect
was major in the case of the E. Coli bacteria in comparison to the S. aureus strain. Moreover, the differences
between the variances of inhibition zones were determined by an ANOVA analysis. In this process,
the p-value corresponding to the F-statistic was lower than 0.05 (p <0.05), this value suggesting that
one or more treatment was significantly different. It was possible to affirm that the Fe
3
O
4
NPs obtained
by Cnicus Bendictus had an antibacterial effect due to the box-plot of the ANOVA analysis (Figure 10b)

Processes 2020,8, 946 12 of 17
showing significant differences in relation to the control sample. In this case, C1 was associated
with the disk control, and the samples labeled as C2 (5 mM), C3 (10 mM), C4 (15 mM), C5 (20 mM),
and C6 (25 mM) corresponded to the Fe
3
O
4
NPs concentrations. On the other hand, post hoc Tukey HSD
test could be employed to identify which pairs of treatments were significantly different from each other.
Figure 10c illustrates graphically the Tukey test and the pairs of treatments with significant differences
(inset Figure 10c). Through these results, the bactericidal effect of nanoparticles could be statistically
corroborated. It was verified that this effect is related to the capacity of the particles to interact with
the bacterial membrane, generating structural and physiological changes in the microorganism and
generating its elimination. It has been reported that the Fe
3
O
4
NPs exhibit remarkable reactivity
with phosphorus and sulfur compounds, which are present in the proteins of the cell membrane in
the bacteria [
60
,
61
]. In others words, the electronegative groups of polysaccharides on the bacterial
membrane can act as sites of attraction for Fe
3
O
4
NPs and iron cations. This fact generates alterations
in the structure and the permeability of the cell membrane due to the excess of metals or metallic
ions that promote a disorder in metabolic functions [
62
] In this sense, the difference between the
antibacterial effects presented by E. coli and S. aureus can be attributed to the structural differences
associated with Gram-positive and Gram-negative bacteria and their cell membranes. In the case of
the S. Aureus, the cell membrane was smooth and single-layered and the thickness of the cell wall was
20–80 nanometers, while the E. Coli bacteria had a wavy and double-layered cell wall, but the thickness
of the cell wall was minor in comparison with the Gram-positive bacteria. In this sense, the major
antibacterial effect observed in the E. coli bacteria could be explained as a function of their cellular
structure and cell wall morphology [25].
Processes 2020, 8, x FOR PEER REVIEW 13 of 19
Moreover, the differences between the variances of inhibition zones were determined by an ANOVA
analysis. In this process, the p-value corresponding to the F-statistic was lower than 0.05 (p < 0.05),
this value suggesting that one or more treatment was significantly different. It was possible to affirm
that the Fe
3
O
4
NPs obtained by Cnicus Bendictus had an antibacterial effect due to the box-plot of the
ANOVA analysis (Figure 10b) showing significant differences in relation to the control sample. In
this case, C1 was associated with the disk control, and the samples labeled as C2 (5 mM), C3 (10 mM),
C4 (15 mM), C5 (20 mM), and C6 (25 mM) corresponded to the Fe
3
O
4
NPs concentrations. On the
other hand, post hoc Tukey HSD test could be employed to identify which pairs of treatments were
significantly different from each other. Figure 10c illustrates graphically the Tukey test and the pairs
of treatments with significant differences (inset Figure 10c). Through these results, the bactericidal
effect of nanoparticles could be statistically corroborated. It was verified that this effect is related to
the capacity of the particles to interact with the bacterial membrane, generating structural and
physiological changes in the microorganism and generating its elimination. It has been reported that
the Fe
3
O
4
NPs exhibit remarkable reactivity with phosphorus and sulfur compounds, which are
present in the proteins of the cell membrane in the bacteria [60,61]. In others words, the
electronegative groups of polysaccharides on the bacterial membrane can act as sites of attraction for
Fe
3
O
4
NPs and iron cations. This fact generates alterations in the structure and the permeability of
the cell membrane due to the excess of metals or metallic ions that promote a disorder in metabolic
functions [62] In this sense, the difference between the antibacterial effects presented by E. coli and S.
aureus can be attributed to the structural differences associated with Gram-positive and Gram-
negative bacteria and their cell membranes. In the case of the S. Aureus, the cell membrane was
smooth and single-layered and the thickness of the cell wall was 20–80 nanometers, while the E. Coli
bacteria had a wavy and double-layered cell wall, but the thickness of the cell wall was minor in
comparison with the Gram-positive bacteria. In this sense, the major antibacterial effect observed in
the E. coli bacteria could be explained as a function of their cellular structure and cell wall
morphology [25].
Figure 10. (a) Bar graphs of the diameter of the inhibition zone measured from the bacterial
susceptibility, (b) box-plot of antibacterial activity of Fe
3
O
4
against S. aureus and E. coli bacteria. (c)
Scatter plot of Tukey comparison by pairs.
Figure 10.
(
a
) Bar graphs of the diameter of the inhibition zone measured from the bacterial susceptibility,
(
b
) box-plot of antibacterial activity of Fe
3
O
4
against S. aureus and E. coli bacteria. (
c
) Scatter plot of
Tukey comparison by pairs.

Processes 2020,8, 946 13 of 17
Finally, based on the experimental data corresponding to antibacterial behavior of the Fe
3
O
4
NPs,
it could be modeled mathematically. Starting with graph 11(a), which describes the antibacterial
response of E. Coli and S. Aureus bacteria to the Fe
3
O
4
NPs, it was possible to associate this behavior
with the sigmoid dose-response curve model fit, which is described by the following equation:
y=A1+A1−A2
1+10(logx0−x)p(12)
Figure 11b models graphically the antibacterial response of the S. aureus bacteria to the Fe
3
O
4
NPs synthesized by Cnicus benedictus and their corresponding parameters. It is important to note that
the correlation factor R
2
was 0.98, Thus, the dose response fitting could describe, with high precision,
the experimental bactericidal behavior of the S. aureus.
Processes 2020, 8, x FOR PEER REVIEW 15 of 19
Figure 11. Antibacterial curve fitting (a) comparison between E. coli and S. aureus. (b) S. aureus
behavior (dose response model) and (c) E. Coli behavior (two sites competition model).
In conclusive form, it was possible to affirm that the Gram-negative bacteria (E. Coli) was more
susceptible to the interaction with the Fe
3
O
4
NPs, which exhibited high specific surface area,
promoting better contact with the microorganisms; consequently, the Fe
3
O
4
NPs could be attached to
the cell membrane and penetrate inside the bacteria.
4. Conclusions
The green synthesis by Cnicus benedictus as a reducing agent offers an environmental friendly
alternative to obtaining Fe
3
O
4
NPs. The organic compounds present in the Cnicus benedictus extract
have the capacity to carry out the iron ions reduction and, consequently, the Fe
3
O
4
NPs formation in
the majority phase. Iron oxides such as hematite and maghemite were also observed in our study.
However, the mentioned iron oxide appeared in the minor phase due to the great reactivity of the
iron oxides with the aqueous media promoting the facile oxidation of the iron oxide species. On the
other hand, the obtained Fe
3
O
4
NPs showed a very similar behavior to the superparamagnetic
materials. This fact indicated that the nanoparticles synthesized can be evaluated for potential
application in the magnetism materials field, among others. Additionally, this research was focused
on environmental remediation applications, specifically in the Congo red photodegradation.
Conclusively, it was observed that the Fe
3
O
4
NPs are capable of carrying out the photodegradation
of the organic dye (CR). Finally, it was possible to affirm that the Fe
3
O
4
NPs synthesized by green
route offer a facile, low cost, non-toxic, and environmental friendly alternative to obtaining functional
Figure 11.
Antibacterial curve fitting (
a
) comparison between E. coli and S. aureus. (
b
)S. aureus behavior
(dose response model) and (c)E. Coli behavior (two sites competition model).
On the other hand, the bactericidal effect of the Fe
3
O
4
NPs against E. coli also was modeled
mathematically. However, the best fit of the experimental data associated with the Gram-negative
bacteria (E. coli) was fit to the two sites competition model, which is described by:
y=A2+A1−A2
1+10(x−logx01 )+A1−A2(1−f)
1+10(x−logx02 )(13)

Processes 2020,8, 946 14 of 17
In this case, the R2 value was 0.998, and the associated parameters are inset in the Figure 11c.
Consequently, by the two sites, the competition model could describe the bactericidal behavior of the
Fe
3
O
4
NPs against E. Coli bacteria. This fact indicated that the two site competition models attributed
to the antibacterial effect against E. coli were more complex in comparison to the S. aureus behavior.
However, this effect was significantly notable. This fact supports the discussion in regard to the
characteristics of the Gram-positive and the Gram-negative bacteria described previously; the thickness
of the cell wall of the bacteria has a preponderant role in the antibacterial behavior.
In conclusive form, it was possible to affirm that the Gram-negative bacteria (E. Coli) was more
susceptible to the interaction with the Fe
3
O
4
NPs, which exhibited high specific surface area, promoting
better contact with the microorganisms; consequently, the Fe
3
O
4
NPs could be attached to the cell
membrane and penetrate inside the bacteria.
4. Conclusions
The green synthesis by Cnicus benedictus as a reducing agent offers an environmental friendly
alternative to obtaining Fe
3
O
4
NPs. The organic compounds present in the Cnicus benedictus extract
have the capacity to carry out the iron ions reduction and, consequently, the Fe
3
O
4
NPs formation in the
majority phase. Iron oxides such as hematite and maghemite were also observed in our study. However,
the mentioned iron oxide appeared in the minor phase due to the great reactivity of the iron oxides
with the aqueous media promoting the facile oxidation of the iron oxide species. On the other hand,
the obtained Fe
3
O
4
NPs showed a very similar behavior to the superparamagnetic materials. This fact
indicated that the nanoparticles synthesized can be evaluated for potential application in the magnetism
materials field, among others. Additionally, this research was focused on environmental remediation
applications, specifically in the Congo red photodegradation. Conclusively, it was observed that
the Fe
3
O
4
NPs are capable of carrying out the photodegradation of the organic dye (CR). Finally,
it was possible to affirm that the Fe
3
O
4
NPs synthesized by green route offer a facile, low cost,
non-toxic, and environmental friendly alternative to obtaining functional Fe
3
O
4
NPs with proven
magnetic and catalytic properties. Additionally, it was possible to affirm that the Fe
3
O
4
NPs exhibited
an antibacterial effect. However, the Gram-negative bacteria (S. aureus) was more susceptible to the
interaction with the Fe
3
O
4
NPs, which exhibited high specific surface area, promoting better contact
with the microorganisms and, consequently, the Fe
3
O
4
NPs could be attached to the cell membrane
and penetrate inside the bacteria.
Author Contributions:
Conceptualization, formal analysis, investigation, writing—original draft preparation
and project administration,
Á
.d.J.R.-B.; Investigation and review and editing, S.Y.R.-L.; methodology, D.L.-O.;
investigation, data curation, N.M.-L.; investigation, review and editing, M.A.Z.A.; R.P.C., review and editing.
All authors have read and agreed to the published version of the manuscript.
Funding:
This research was funded by National Council for Science and Technology (CONACYT, M
é
xico) in
collaboration with the Center of Applied Physics and Advanced Technology (CFATA-UNAM) through “Cathedras
CONACYT program”. Project number: 155.
Acknowledgments: Á
lvaro de Jes
ú
s Ru
í
z-Baltazar appreciates the support provided by the National Council for
Science and Technology (CONACYT, M
é
xico) in collaboration with the Center of Applied Physics and Advanced
Technology (CFATA-UNAM) through “Cathedra CONACYT” program. Likewise, to the national materials
characterization laboratory (LaNCaM) belonging to CFATA-UNAM.
Conflicts of Interest: The authors declare no conflict of interest for the publication of this work.
References
1.
Ahmed, M.A.; Abou-Gamra, Z.M.; ALshakhanbeh, M.A.; Medien, H. Control synthesis of metallic gold
nanoparticles homogeneously distributed on hexagonal ZnO nanoparticles for photocatalytic degradation of
methylene blue dye. Environ. Nanotechnol. Monit. Manag. 2019,12, 100217. [CrossRef]
2.
Patwardhan, S.V.; Manning, J.R.H.; Chiacchia, M. Bioinspired synthesis as a potential green method for the
preparation of nanomaterials: Opportunities and challenges. Curr. Opin. Green Sustain. Chem.
2018
,12,
110–116. [CrossRef]

Processes 2020,8, 946 15 of 17
3.
Carabineiro, S.A.C. Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes.
Front. Chem. 2019,7, 702. [CrossRef] [PubMed]
4.
Argurio, P.; Fontananova, E.; Molinari, R.; Drioli, E. Photocatalytic membranes in photocatalytic membrane
reactors. Processes 2018,6, 162. [CrossRef]
5.
Meramo-hurtado, S.I.; Zuorro, A. Environmental Assessment of Large Scale Production of Magnetite (Fe3O4)
Nanoparticles via Coprecipitation. Appl. Sci. 2019,9, 1682.
6. Jain, B.; Hashmi, A.; Sanwaria, S.; Singh, A.K.; Susan, M.A.B.H.; Carabineiro, S.A.C. Catalytic Properties of
Graphene Oxide Synthesized by a “Green” Process for Efficient Abatement of Auramine-O Cationic Dye.
Anal. Chem. Lett. 2020,10, 21–32. [CrossRef]
7.
Aghazadeh, M.; Karimzadeh, I.; Ganjali, M.R.; Mohebi Morad, M. A novel preparation method for surface
coated superparamagnetic Fe3O4 nanoparticles with vitamin C and sucrose. Mater. Lett.
2017
,196, 392–395.
[CrossRef]
8.
Zhang, H.; Zhao, J.; Ou, X. Facile synthesis of Fe3O4 nanowires at low temperature (80
◦
C) without autoclaves
and their electromagnetic performance. Mater. Lett. 2017,209, 48–51. [CrossRef]
9.
Hoseinpour, V.; Ghaemi, N. Green synthesis of manganese nanoparticles: Applications and future
perspective–A review. J. Photochem. Photobiol. B Biol. 2018,189, 234–243. [CrossRef]
10.
Polo, A.M.S.; Lopez-Peñalver, J.J.; S
á
nchez-Polo, M.; Rivera-Utrilla, J.; L
ó
pez-Ram
ó
n, M.V.; Rozal
é
n, M. Halide
removal from water using silver doped magnetic-microparticles. J. Environ. Manag. 2020,253. [CrossRef]
11.
Mi, S.; Liu, R.; Li, Y.; Xie, Y.; Chen, Z. Large low-field magnetoresistance of Fe3O4 nanocrystal at room
temperature. J. Magn. Magn. Mater. 2017,428, 235–238. [CrossRef]
12.
Xu, J.; Li, Q.; Zong, W.; Zhang, Y.; Li, S. Ultra-wide detectable concentration range of GMR biosensors using
Fe3O4 microspheres. J. Magn. Magn. Mater. 2016,417, 25–29. [CrossRef]
13.
Betancourt-Buitrago, L.A.; Hernandez-Ramirez, A.; Colina-Marquez, J.A.; Bustillo-Lecompte, C.F.;
Rehmann, L.; Machuca-Martinez, F. Recent developments in the photocatalytic treatment of cyanide
wastewater: An approach to remediation and recovery of metals. Processes 2019,7, 225. [CrossRef]
14.
Aguas, Y.; Hincapi
é
, M.; S
á
nchez, C.; Botero, L.; Fern
á
ndez-Ibañez, P. Photocatalytic inactivation of
Enterobacter cloacae and Escherichia coli using titanium dioxide supported on two substrates. Processes
2018,6, 137. [CrossRef]
15.
Hern
á
ndez-Abreu, A.B.;
Á
lvarez-Torrellas, S.;
Á
gueda, V.I.; Larriba, M.; Delgado, J.A.; Calvo, P.A.; Garc
í
a, J.
Enhanced removal of the endocrine disruptor compound Bisphenol A by adsorption onto green-carbon
materials. Effect of real effluents on the adsorption process. J. Environ. Manag. 2020,266. [CrossRef]
16.
David, L.; Moldovan, B. Green synthesis of biogenic silver nanoparticles for efficient catalytic removal of
harmful organic dyes. Nanomaterials 2020,10, 202. [CrossRef] [PubMed]
17.
Ali, E.M.; Abdallah, B.M. Effective inhibition of candidiasis using an eco-friendly leaf extract of
calotropis-gigantean-mediated silver nanoparticles. Nanomaterials 2020,10, 422. [CrossRef] [PubMed]
18.
Sharifi-Rad, M.; Pohl, P. Synthesis of biogenic silver nanoparticles (Agcl-nps) using a pulicaria vulgaris gaertn.
aerial part extract and their application as antibacterial, antifungal and antioxidant agents. Nanomaterials
2020,10, 638. [CrossRef]
19.
Wu, Z.; Ferreira, D.F.; Crudo, D.; Bosco, V.; Stevanato, L.; Costale, A.; Cravotto, G. Plant and biomass
extraction and valorisation under hydrodynamic cavitation. Processes 2019,7, 965. [CrossRef]
20.
Ribeiro, R.P.P.L.; Barreto, J.; Xavier, M.D.G.; Martins, D.; Esteves, A.A.C.; Branco, M.; Tirolien, T.; Mota, J.P.B.;
Bonfait, G. Cryogenic Neon Adsorption on Co3(ndc)3(dabco) Metal-Organic Framework. Microporous
Mesoporous Mater. 2020,3, 110055. [CrossRef]
21.
Gene, M. Enhanced Silver Nanoparticle Synthesis by Escherichia Coli Transformed with Candida Albicans.
Materials 2019,12, 4180.
22.
Catalysis, R.; Yu, C.; Tang, J.; Liu, X.; Ren, X.; Zhen, M. Green Biosynthesis of Silver Nanoparticles Using
Eriobotrya japonica (Thunb) Leaf Extract for reductive catalysis. Materials 2019,12, 189. [CrossRef]
23.
Chemat, F.; Abert Vian, M.; Fabiano-Tixier, A.S.; Nutrizio, M.; Režek Jambrak, A.; Munekata, P.E.S.;
Lorenzo, J.M.; Barba, F.J.; Binello, A.; Cravotto, G. A review of sustainable and intensified techniques for
extraction of food and natural products. Green Chem. 2020,22, 2325–2353. [CrossRef]
24.
Fakhri, A.; Tahami, S.; Nejad, P.A. Preparation and characterization of Fe3O4-Ag2O quantum dots decorated
cellulose nanofibers as a carrier of anticancer drugs for skin cancer. J. Photochem. Photobiol. B Biol.
2017
,
175, 83–88. [CrossRef] [PubMed]

Processes 2020,8, 946 16 of 17
25.
Naeimi, H.; Nazifi, Z.S.; Amininezhad, S.M. Preparation of Fe3O4 encapsulated-silica sulfonic acid
nanoparticles and study of their
in vitro
antimicrobial activity. J. Photochem. Photobiol. B Biol.
2015
,149, 180–188.
[CrossRef] [PubMed]
26.
Marim
ó
n-Bol
í
var, W.; Gonz
á
lez, E.E. Green synthesis with enhanced magnetization and life cycle assessment
of Fe3O4 nanoparticles. Environ. Nanotechnol. Monit. Manag. 2018,9, 58–66. [CrossRef]
27.
Prasad, C.; Krishna Murthy, P.; Hari Krishna, R.H.; Sreenivasa Rao, R.; Suneetha, V.; Venkateswarlu, P.
Bio-inspired green synthesis of RGO/Fe3O4 magnetic nanoparticles using Murrayakoenigii leaves extract
and its application for removal of Pb(II) from aqueous solution. J. Environ. Chem. Eng.
2017
,5, 4374–4380.
[CrossRef]
28.
Beyene, H.D.; Werkneh, A.A.; Bezabh, H.K.; Ambaye, T.G. Synthesis paradigm and applications of silver
nanoparticles (AgNPs), a review. Sustain. Mater. Technol. 2017,13, 18–23. [CrossRef]
29.
Li, W.H.; Yang, N. Green and facile synthesis of Ag-Fe3O4 nanocomposites using the aqueous extract of
Crataegus pinnatifida leaves and their antibacterial performance. Mater. Lett.
2016
,162, 157–160. [CrossRef]
30.
Patra, J.K.; Baek, K.H. Green biosynthesis of magnetic iron oxide (Fe3O4) nanoparticles using the aqueous
extracts of food processing wastes under photo-catalyzed condition and investigation of their antimicrobial
and antioxidant activity. J. Photochem. Photobiol. B Biol. 2017,173, 291–300. [CrossRef]
31.
Dominguez, J.R.; Gonzalez, T.; Cuerda-Correa, E.M.; Muñoz-Peña, M.J. Combating paraben pollution
in surface waters with a variety of photocatalyzed systems: Looking for the most efficient technology.
Open Chem. 2019,17, 1317–1327. [CrossRef]
32.
Gonz
á
lez, T.; Dominguez, J.R.; Cuerda-Correa, E.M.; Correia, S.E.; Donoso, G. Selecting and improving
activated homogeneous catalytic processes for pollutant removal. Kinetics, mineralization and optimization.
J. Environ. Manag. 2020,256. [CrossRef] [PubMed]
33.
Fern
á
ndez-perales, M.; Rozalen, M.; S
á
nchez-polo, M.; Rivera-utrilla, J.; L
ó
pez-ram
ó
n, M.V.;
Á
lvarez, M.A.
Solar degradation of sulfamethazine using RGO/Bi composite photocatalysts. Catalysts
2020
,10, 573.
[CrossRef]
34.
Moreno-Castilla, C.; L
ó
pez-Ram
ó
n, M.V.; Fontecha-C
á
mara, M.
Á
.;
Á
lvarez, M.A.; Mateus, L. Removal of
phenolic compounds fromwater using copper ferrite nanosphere composites as fenton catalysts. Nanomaterials
2019,9, 901. [CrossRef]
35.
Peluso, A.; Gargiulo, N.; Aprea, P.; Pepe, F.; Peluso, A.; Gargiulo, N.; Aprea, P.; Pepe, F.; Peluso, A.;
Gargiulo, N.; et al. Nanoporous Materials as H
2
S Adsorbents for Biogas Purification: A Review. Sep. Purif. Rev.
2018,00, 1–12. [CrossRef]
36.
Tabatabai Yazdi, S.; Iranmanesh, P.; Saeednia, S.; Mehran, M. Structural, optical and magnetic properties of
MnxFe3
−
xO4 nanoferrites synthesized by a simple capping agent-free coprecipitation route. Mater. Sci. Eng.
B Solid-State Mater. Adv. Technol. 2019,245, 55–62. [CrossRef]
37.
Andrzejewski, B.; Bednarski, W.; Ka´zmierczak, M.; Łapi´nski, A.; Pogorzelec-Glaser, K.; Hilczer, B.; Jurga, S.;
Nowaczyk, G.; Zał
e¸
ski, K.; Matczak, M.; et al. Magnetization enhancement in magnetite nanoparticles
capped with alginic acid. Compos. Part B Eng. 2014,64, 147–154. [CrossRef]
38.
Scardi, P.; Ermrich, M.; Fitch, A.; Huang, E.W.; Jardin, R.; Kuzel, R.; Leineweber, A.; Mendoza Cuevas, A.;
Misture, S.T.; Rebuffi, L.; et al. Size–strain separation in diffraction line profile analysis. J. Appl. Crystallogr.
2018,51, 831–843. [CrossRef] [PubMed]
39.
Sen, R.; Das, G.C.; Mukherjee, S. X-ray diffraction line profile analysis of nano-sized cobalt in silica matrix
synthesized by sol-gel method. J. Alloys Compd. 2010,490, 515–523. [CrossRef]
40.
Mittal, M.; Gupta, A.; Pandey, O.P. Role of oxygen vacancies in Ag/Au doped CeO 2 nanoparticles for fast
photocatalysis. Sol. Energy 2018,165, 206–216. [CrossRef]
41.
Yadav, S.; Asthana, A.; Chakraborty, R.; Jain, B.; Singh, A.K.; Carabineiro, S.A.C.; Susan, M.A.B.H. Cationic
dye removal using novel magnetic/activated charcoal/
β
-cyclodextrin/alginate polymer nanocomposite.
Nanomaterials 2020,10, 170. [CrossRef]
42.
De Jesus Ru
í
z-Baltazar,
Á
. Green Composite Based on Silver Nanoparticles Supported on Diatomaceous
Earth: Kinetic Adsorption Models and Antibacterial Effect. J. Clust. Sci. 2018,29, 509–519. [CrossRef]
43.
Shebanova, O.N.; Lazor, P. Raman spectroscopic study of magnetite (FeFe2O4): A new assignment for the
vibrational spectrum. J. Solid State Chem. 2003,174, 424–430. [CrossRef]
44.
Jubb, A.M.; Allen, H.C. Vibrational spectroscopic characterization of hematite, maghemite, and magnetite
thin films produced by vapor deposition. ACS Appl. Mater. Interfaces 2010,2, 2804–2812. [CrossRef]

Processes 2020,8, 946 17 of 17
45.
Vanhecke, D.; Crippa, F.; Lattuada, M.; Balog, S.; Rothen-Rutishauser, B.; Petri-Fink, A. Characterization
of the shape anisotropy of superparamagnetic iron oxide nanoparticles during thermal decomposition.
Materials (Basel). 2020,13, 2018. [CrossRef] [PubMed]
46.
Huaccallo, Y.;
Á
lvarez-Torrellas, S.; Mar
í
n, M.P.; Gil, M.V.; Larriba, M.;
Á
gueda, V.I.; Ovejero, G.; Garc
í
a, J.
Magnetic Fe3O4/multi-walled carbon nanotubes materials for a highly efficient depletion of diclofenac by
catalytic wet peroxideoxidation. Environ. Sci. Pollut. Res. 2019,26, 22372–22388. [CrossRef] [PubMed]
47.
Hekmatara, H.; Seifi, M.; Forooraghi, K. Microwave absorption property of aligned MWCNT/Fe3O4. J. Magn.
Magn. Mater. 2013,346, 186–191. [CrossRef]
48.
Zhou, X.; Shi, Y.; Ren, L.; Bao, S.; Han, Y.; Wu, S.; Zhang, H.; Zhong, L.; Zhang, Q. Controllable synthesis,
magnetic and biocompatible properties of Fe 3 O 4 and
α
-Fe 2 O 3 nanocrystals. J. Solid State Chem.
2012
,196,
138–144. [CrossRef]
49.
Qin, Y.; Zhang, H.; Tong, Z.; Song, Z.; Chen, N. A facile synthesis of Fe3O4@SiO2@ZnO with superior
photocatalytic performance of 4-nitrophenol. J. Environ. Chem. Eng. 2017,5, 2207–2213. [CrossRef]
50.
Ajmal, A.; Majeed, I.; Malik, R.N.; Idriss, H.; Nadeem, M.A. Principles and mechanisms of photocatalytic
dye degradation on TiO 2 based photocatalysts: A comparative overview. RSC Adv.
2014
,4, 37003–37026.
[CrossRef]
51.
Patel, J.; Singh, A.K.; Carabineiro, S.A.C. Assessing the photocatalytic degradation of fluoroquinolone
norfloxacin by Mn:ZnS quantum dots: Kinetic study, degradation pathway and influencing factors.
Nanomaterials 2020,10, 964. [CrossRef]
52.
Wang, N.; Zheng, T.; Zhang, G.; Wang, P. A review on Fenton-like processes for organic wastewater treatment.
J. Environ. Chem. Eng. 2016,4, 762–787. [CrossRef]
53.
Zazouli, M.A.; Ghanbari, F.; Yousefi, M.; Madihi-Bidgoli, S. Photocatalytic degradation of food dye by
Fe3O4-TiO2 nanoparticles in presence of peroxymonosulfate: The effect of UV sources. J. Environ. Chem. Eng.
2017,5, 2459–2468. [CrossRef]
54.
Montañez, J.P.; Heredia, C.L.; Sham, E.L.; Farf
á
n Torres, E.M. Photodegradation of herbicide Metsulfuron-
methyl with TiO2 supported on magnetite particles coated with SiO2. J. Environ. Chem. Eng.
2018
,6,
7402–7410. [CrossRef]
55.
Chakraborty, R.; Asthana, A.; Singh, A.K.; Yadav, S.; Susan, M.A.B.H.; Carabineiro, S.A.C. Intensified
elimination of aqueous heavy metal ions using chicken feathers chemically modified by a batch method.
J. Mol. Liq. 2020,312, 113475. [CrossRef]
56.
Du, T.; Zhou, L.F.; Zhang, Q.; Liu, L.Y.; Li, G.; Luo, W.B.; Liu, H.K. Mesoporous structured aluminaosilicate
with excellent adsorption performances for water purification. Sustain. Mater. Technol.
2018
,18, e00080.
[CrossRef]
57.
Wen, T.; Wang, J.; Li, X.; Huang, S.; Chen, Z.; Wang, S.; Hayat, T.; Alsaedi, A.; Wang, X. Production of
a generic magnetic Fe3O4 nanoparticles decorated tea waste composites for highly efficient sorption of Cu(II)
and Zn(II). J. Environ. Chem. Eng. 2017,5, 3656–3666. [CrossRef]
58.
Singh, K.K.; Senapati, K.K.; Sarma, K.C. Synthesis of superparamagnetic Fe3O4 nanoparticles coated with
green tea polyphenols and their use for removal of dye pollutant from aqueous solution. J. Environ. Chem. Eng.
2017,5, 2214–2221. [CrossRef]
59.
Ou, J.; Mei, M.; Xu, X. Magnetic adsorbent constructed from the loading of amino functionalized Fe3O4
on coordination complex modified polyoxometalates nanoparticle and its tetracycline adsorption removal
property study. J. Solid State Chem. 2016,238, 182–188. [CrossRef]
60.
Atta, A.M. Antimicrobial Activity of Hybrids Terpolymers Based on Magnetite Hydrogel Nanocomposites.
Materials 2019,12, 3604.
61.
Xia, Q.H.; Ma, Y.J.; Wang, J.W. Biosynthesis of silver nanoparticles using Taxus yunnanensis callus and their
antibacterial activity and cytotoxicity in human cancer cells. Nanomaterials
2016
,6, 160. [CrossRef] [PubMed]
62.
V
á
zquez Olmos, A.R.; Vega Jim
é
nez, A.L.; Paz D
í
az, B. Mecanos
í
ntesis y efecto antimicrobiano de
ó
xidos
metálicos nanoestructurados. Mundo Nano Rev. Interdiscip. Nanocienc. Nanotecnol. 2018,11, 29. [CrossRef]
©
2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).