Synthesis of Multicomponent Nanoparticles for Immobilization of Heavy Metals in Aqueous Phase

Abstract

This study is focused on the preparation of multicomponent nanoparticles (MCNPs) used to remediate artificial and real mine tailings. The nanoparticles were synthesized with 0.035 M or 0.007 M of sodium sulfate, 0.5 M of iron chloride and 0.8 M of sodium borohydride. Characterization of nanoparticles performed with a Transmission Electron Microscope (TEM), X-ray diffractometer (XRD), Fourier Transform Infrared Spectrometer (FTIR), and X-ray Photoelectron Spectrometer (XPS) demonstrated, these materials are in the nanoscale range, contain zero valent iron Fe (0) and iron sulfide (FeS) and are structurally modified after treatment. Simultaneous removal of heavy metals was carried out under oxidizing and reducing conditions using MCNPs reaching an efficiency of more than 98% for all of them. Kinetics conducted under oxidizing condition, pH 3 and 0.035M sodium sulfate shows that the highest removal of heavy metals from artificial mine tailings was achieved after 160 min of treatment although steady state was reached in 240 mins. Results of kinetic tests fit very well to a pseudo-second- order model, while the isothermal equilibrium adsorption tests were adjusted to a Freundlich isotherm. Also, nanoparticles showed a high adsorption capacity (~140 mg/g) when they were in contact with 200 mg Cu2+/L. Finally, multicomponent nanoparticles tested with real mine tailings in the presence of other competing chemicals results in heavy metals removal over 90%.

Full text

Cumbal et al.
103
Synthesis of Multicomponent Nanoparticles for
Immobilization of Heavy Metals in Aqueous Phase
NanoWorld Journal
Research Article Open Access
http://dx.doi.org/10.17756/nwj.2015-014
Luis Heriberto Cumbal Flores1,2, Alexis Debut1,2 and Carina Stael1
1Centro de Nanociencia y Nanotecnología, Universidad de las Fuerzas Armadas-ESPE, P.O. Box: 1715 231B, Sangolquí, Ecuador
2Departamento de Ciencias de la Vida, Universidad de las Fuerzas Armadas-ESPE, P.O. Box: 1715 231B, Sangolquí, Ecuador
*Correspondence to:
Luis Heriberto Cumbal Flores, PhD
Centro de Nanociencia y Nanotecnología
Universidad de las Fuerzas Armadas-ESPE
P.O. Box: 1715 231B, Sangolquí, Ecuador
Tel: 593 2 3989492
E-mail: lhcumbal@espe.edu.ec
Received: October 15, 2015
Accepted: December 26, 2015
Published: December 28, 2015
Citation: Cumbal LH, Debut A, Stael C. 2015.
Synthesis of Multicomponent Nanoparticles for
Immobilization of Heavy Metals in Aqueous
Phase. NanoWorld J 1(4): 103-109.
Copyright: © 2015 Cumbal et al. is is an Open
Access article distributed under the terms of the
Creative Commons Attribution 4.0 International
License (CC-BY) (http://creativecommons.
org/licenses/by/4.0/) which permits commercial
use, including reproduction, adaptation, and
distribution of the article provided the original
author and source are credited.
Published by United Scientic Group
Abstract
is study is focused on the preparation of multicomponent nanoparticles
(MCNPs) used to remediate articial and real mine tailings. e nanoparticles
were synthesized with 0.035 M or 0.007 M of sodium sulfate, 0.5 M of iron
chloride and 0.8 M of sodium borohydride. Characterization of nanoparticles
performed with a Transmission Electron Microscope (TEM), X-ray
diractometer (XRD), Fourier Transform Infrared Spectrometer (FTIR), and
X-ray Photoelectron Spectrometer (XPS) demonstrated, these materials are in
the nanoscale range, contain zero valent iron Fe (0) and iron sulde (FeS) and are
structurally modied after treatment. Simultaneous removal of heavy metals was
carried out under oxidizing and reducing conditions using MCNPs reaching an
eciency of more than 98% for all of them. Kinetics conducted under oxidizing
condition, pH 3 and 0.035 M sodium sulfate shows that the highest removal of
heavy metals from articial mine tailings was achieved after 160 min of treatment
although steady state was reached in 240 mins. Results of kinetic tests t very well
to a pseudo-second- order model, while the isothermal equilibrium adsorption
tests were adjusted to a Freundlich isotherm. Also, nanoparticles showed a high
adsorption capacity (~140 mg/g) when they were in contact with 200 mg Cu2+/L.
Finally, multicomponent nanoparticles tested with real mine tailings in the
presence of other competing chemicals results in heavy metals removal over 90%.
Keywords
Multicomponent, Nanoparticles, Removal, Heavy metals, Mine tailing
Introduction
Mining is an important economic activity worldwide, but it has generated a
huge pollution in the environment, mainly because of poor exploitation processes
and wrong disposal of mine tailings [1-3]. Actually, the delivery of hazardous
contaminants to the ecosystem, especially heavy metals into the water streams is a
great concern (EPA, 2012). Chemical characterization of mine tailings has found
the presence of heavy metals such as Hg2+, As5+, Pb2+, Cu2+, Zn2+, Ag+, Ni2+, Mn2+,
and others [4]. Due to the recognized toxicity of heavy metals, the exposure to
these elements, even in trace concentrations, is considered to be harmful to living
beings [5, 6]. ese pollutants can be assimilated through inhalation, ingestion
and skin adsorption, bringing about serious illnesses, like cancer, neurological,
endocrinological and immunological dysfunction, Alzheimer, among others [7].
e toxicity of heavy metals is attributed to their physicochemical properties.
Generally, these pollutants are highly soluble in water, especially at low pH,
spreading out more easily in water streams [8]. Additionally, heavy metals are
persistent and cannot be rapidly degraded in nature [9], accumulating in living

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Aqueous Phase Cumbal et al.
studies on thin lms of the nanoparticle were carried out using
a diractometer (EMPYREAN, PANalytical) with a θ–2θ
conguration (generator–detector), wherein a copper X-ray
tube emitted a wavelength of λ =1.54 Ao. FTIR attenuated
total reection spectra were recorded on a Spectrum Two IR
spectrometer (Perkin Elmer, USA) to detect the dierent
functional groups involved in the capture of heavy metals by
the multicomponent nanoparticles. XPS spectra were recorded
on an AXIS ULTRA equipped with Magnetic Immersion
Lens and Charge Neutralization System with a new Spherical
Mirror Analyzer and monochromatic source (Al Kα) operated
at 150 W (15 kV, 10 mA).
Removal of heavy metals
Batch kinetic tests for heavy metals removal by nanoparticles
were carried out using 100 mL Boeco bottles under oxidant
environment and pH 3±0.2. e removal was initiated by
mixing 5 or 9 mL of MCNPs with 50 mL of articial aqueous
mine tailings, which resulted in concentrations of 5.3 mg/L
Cu2+, 4.99 mg/L Zn2+, 4.24 mg/L Mn2+, 2.48 mg/L Ni2+, 2.98
mg/L Pb2+, 4.1 mg/L Ag+, and 0.99 mg/L As5+. ese initial
concentration values are within the range of reported heavy
metal levels in aqueous mine tailings [23, 24]. Bottles were
placed in a water bath and agitated for 4 hours at 25 °C. During
the test, 10 samples of 2 mL of treated aqueous phase were
ltered with a 0.2 μm PVDF lter for heavy metals analyses.
In addition, kinetic tests for each heavy metal in the presence
of high concentration of other metals were performed under
otherwise same experimental conditions. To test pH eects,
the removal experiments were performed at an initial pH of 3,
5, 7, and 9, adjusted with 0.1 N NaOH and/or 0.1 N HCl and
by adding 0.2 M of sodium acetate buer to the glass bottles.
Samples of 5 mL were collected after completing the treatment
(4 hours), ltered, and analyzed for heavy metals. Tests under
reductive conditions were carried out in 80 mL glass vials
lled with 64 mL of articial mine tailing containing MCNPs
and sealed with Teon-lined caps. Additionally, we have also
performed adsorption isotherm measurements using dierent
concentrations of Cu (2, 4, 6, 8, 10, 15, 20, 50, 100 and 200
mg/L) and 9 mL of MCNPs. e amount of Cu2+ adsorbed
per unit mass of wet nanoparticles was calculated through the
Equation 1:
()
ot
t
c cv
q
m
−
=------------------------------(1)
where qt (mg/g) corresponds to the amount of Cu2+
adsorbed per gram of wet nanoparticles at time t (min), C0
(mg/L) is the initial concentration of Cu2+ in the solution,
Ct(mg/L) refers to the concentration of Cu2+ at a time t, m (g)
is the mass of the multicomponent nanoparticles used in tests
and V (L) refers to the initial volume of the stock solution
[25].
Chemical and physical analyses
Heavy metals such as Pb2+, Ag+, Ni2+, Mn2+, Zn2+ and Cu2+
were analyzed with an atomic absorption spectrometer, Perkin
Elmer AA 800, using standardized methods [26]. Arsenic was
quantied using a Flow Injection Analysis System (FIAS)
coupled to AA800 and a discharge lamp. For the operation
of FIAS system, it was used a solution of 10% v/v of HCl as
carrier and a solution of 0.2% w/v NaBH4 + 0.05 % NaOH
tissues until getting hazardous concentrations [7, 10, 11].
Similarly, because of its persistence in the environment, heavy
metals are likely to sediment at the bottom of lakes, rivers,
lagoons, and oceans, causing adverse eects on ecosystems,
altering their normal conditions. us, provoking death of
aquatic species, and even passing through the trophic chain
[12, 13]. Owing to the environmental and health concerns,
many conventional techniques have been developed to
remediate media contaminated with heavy metals; even
though with limited performance in terms of eectiveness and
removal eciency. For example, microbial cells have been used
as bioaccumulators of soluble and particulate heavy metals
from industrial wastes with high eciency [14-17]; however,
these metals could be released back into the liquid phase when
the biomass is degraded. Current techniques make use of
nanoparticles or composite materials for remediation of heavy
metals in water. Nevertheless, almost all approaches rely on
the functionalization of nanoparticles with dierent reactive
groups or loading nanostructures on supporting materials to
provide them, with the capability of capturing the heavy metals
[18-21]. Besides all these preparation techniques are complex.
Multicomponent nanoparticles, prepared and characterized
by Kim et al. (2011) [22] have shown good performance for
TCE and pesticides degradation. However, from the best of
our knowledge, there is no study related to the application
of these nanoparticles in the simultaneous removal of heavy
metals from the aqueous phase.
Materials and Methods
Materials
Chemicals were purchased from Fisher Scientic: Ferric
chloride (FeCl3.6H2O, 99,8%), sodium sulfate (Na2SO4,
99,9%), sodium borohydride (NaBH4, >98%) ascorbic acid
(USP/FCC), hydrochloric acid (HCl, 37,3%), nitric acid
(HNO3, 69,5%), sodium hydroxide (NaOH, 98%), 55 buer
solution (0.2 M Sodium acetate, 96%), and potassium iodide
(KIO3, 99%) from Himedia.
General procedure for preparation of the multicomponent
nanoparticles
e MCNPs were prepared using a modied method
developed by Kim et al. [22]. In a typical procedure, solutions
of 0.5 M FeCl3.6H20 and 0.8 M NaBH4 + 0.035 M or 0.007
M Na2SO4 were prepared using DI water purged with nitrogen
for 15 min. en, 5 mL of the latter solution was added drop
wise to the mixture of 50 mL of FeCl3 contained in a ask
attached to a vacuum line. is mixture was placed under
vigorous stirring using an orbital shaker for 15 min at ambient
temperature. During this process, the color of the iron solution
changes from yellowish to blackish color, indicating the
formation of MCNPs. e resulting product, multicomponent
nanoparticles, was centrifuged at 7000 rpm for 2 min and
washed several times with nitrogenized deionized water. e
puried nanoparticles were lyophilized for 16 h and stored in
an air-free bottle for further characterization.
Characterization
Transmission electron microscope images were recorded
digitally (Tecnai G2 Spirit TWIN, FEI, Holland). XRD

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Synthesis of Multicomponent Nanoparticles for Immobilization of Heavy Metals in
Aqueous Phase Cumbal et al.
as reducing agent. For this analysis, samples of articial and
real mine tailings were pretreated with a solution of potassium
iodide and ascorbic acid 5% to reduce all the As species to As3+.
For FIAS-absorption spectrometer the calibration curve with
a correlation index, R ≥ 99%, was obtained before analyzing
the samples. For the analysis of anions, an ion chromatograph
Dionex ICS 1100 was used, equipped with a guard column
AG14 and an analytical column AS14, both of 4mm, and a
sample loop of 50 μL. A solution of 35 mM sodium hydroxide
was used as eluent. Physicochemical properties of real mine
tailings such as dissolved oxygen, conductivity and pH were
determined using a Mettler Toledo multiparameter.
Results and Discussion
Characterization of MNPs
Size characterization of MCNPs, demonstrated that there
is no signicant dierence when using 0.007 and 0.035 M
of sodium sulfate during preparation of nanoparticles. TEM
images of MCNPs have shown almost the same diameter
on average size of 24-42 nm [Figure 1]. Nevertheless,
the nanosized particles indeed inuence the physical and
chemical properties of the nanoparticles and therefore the
surface electronic structure [27, 28]. e high reactivity of
the atoms on the surface of nanoparticles due to a decrease
in size, confer to electrons more energy because of quantum
connement [29]. Also, reactivity depends on the amount of
Fe(0) and FeS formed during the preparation of MCNPs. In
this study, it was used approximately 27.9 g/L of Fe(III) and
1.12 or 0.224 g/L of sulfur in the preparation of the particles.
XRD spectrum of nanoparticles shows peaks corresponding
to Fe(0) and a small amount of FeS precipitates, as depicted in
Figure S1 (Supporting Information). In regard to the stability
of these nanoparticles, it can be implied they are greatly stable
in aqueous solutions. Results on pH measurements of the
nanoparticles solutions, exhibited a value of around 9.90. At
this pH there is an absence of hydrogen ions (H+) preventing
early oxidation of nanoparticles [30]. Lu et al. (2007) [29]
reported that nanoparticles were more stable at pH over 8.
In addition, when these nanoparticles are manufactured under
reducing conditions, dissolved oxygen is as low as 0.02 mg/L.
is, in turn, contributes to the stability of the nanoparticles
since FeS does not react with oxygen to produce oxidized
nanoparticles [31]. On the other hand, the high conductivity of
the nanoparticles solution (~36 mS/cm) may produce a strong
ow of electrons at the nanoparticles surface, suggesting an
increase of its roughness that contributes to a higher surface
area, and therefore, higher reactivity [22].
Kinetic study
Figure 2 shows the reaction kinetics of Pb2+ removal from
articial mine tailing using Fe/FeS nanoparticles prepared
with 0.035 M or 0.007 M Na2SO4. e highest removal of
this heavy metal occurred after approximately ve minutes
of reaction [Figure 2]. However, Pb2+ reached a complete
steady state after 160 mins. Most of the heavy metals utilized
in this study (Mn2+, Zn2+, Cu2+, Ag+, Ni2+) attained a steady
condition after approximately 40 min, only As5+ reached this
condition at 160 min (data not shown in Figure 2). Results of
kinetic tests of all heavy metals did not evidence a signicant
dierence on removals using multicomponent nanoparticles
with dierent concentrations of sodium sulfate (0.035 M and
0.007 M) (data not shown). ese experimental values t a
pseudo-second-order model [Equation 2].
2
2
11
t ee
t
t
q kq q
= +
where k2 (g/mg.h) is the pseudo-second-order rate
constant, qe is the amount of metal adsorbed (mg/g) at
equilibrium and qt is the amount of the adsorption (mg/g)
at any time t (h) [25]. Table S1 (Supporting Information)
summarizes the calculated qe values, pseudo-second-order rate
constants k2 and correlation coecient values. e qe and k2 are
calculated from de slope and the intercept of the plots of t/qt
versus t according to the Equation 2. All tting curves exhibit
Figure 1: TEM images of MCNPs prepared using 0.035 M Na2SO4, 0.035 M
FeCl3.6H2O and 0.8 M NaBH4.
Figure 2: Removal of Pb2+ using MCNPs prepared with 0.5 M FeCl3.6H2O,
0.035 M and 0.007 M Na2SO4 and 0.8 MNaBH4.
----------------------------(2)

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good linearity with a correlation coecient nearly equal to
unity (R2 ~ 1.0) as shown in Figure 3. is behavior suggests
that chemical adsorption is the main mechanism for removal
of heavy metals from articial mine tailing [32, 33].
Adsorption capacity study
e adsorption capacity of multicomponent nanoparticles,
using dierent concentrations of Cu2+, showed almost
instantaneous removals in the rst ve minutes with any
desorption throughout the test as shown in Figure S2
(Supporting Information). e removal eciency and
adsorption capacity of the multicomponent nanoparticles,
increased progressively from 98.59% and 1.51 mg/g to 99.91%
and 135.64 mg/g for 2 and 200 mg/L of Cu2+, respectively.
is behavior could be credited to an enhancement in the
Brownian motion, propitiating higher collisions among copper
ions dissolved in water and a better diusion of them towards
multicomponent nanoparticles [25, 34].
Adsorption isotherms study
Isotherm tests were conducted to describe the adsorption
behavior of the multicomponent nanoparticles when removing
Cu2+. Results of adsorption tests t well Freundlich isotherm
model (Equation 3), exhibiting a correlation coecient value
of 0.988 as shown in Figure S3 (Supporting Information).
1/
K
n
ee
qC
=--------------------------- (3)
where, qe (mg/g) and Ce (mg/L) are the amount of pollutant
adsorbed and the concentration in the aqueous phase and K
and n are constants for Cu adsorption on MCNPs at 25 °C.
e elevated correlation coecient obtained with Freundlich
model suggests that adsorption of heavy metals may occur on
a rough surface of nanoparticles as described above. In other
words, there is a heterogeneous distribution of the active sites
on the surface of the nanoparticles where the metals are bound
[25]. Furthermore, having adjusted the adsorption isotherm
data to a Freundlich model, it reinforces the fact that sodium
sulfate contacted with borohydride promotes the precipitation
of FeS on the surface Fe(0) core of nanoparticles, contributing
to their roughness [22].
Study of simultaneous removal of heavy metals from the
aqueous phase
Despite good removal of heavy metals achieved on tests
conducted with articial mine tailing samples under dierent
pH, redox potential, and concentrations of sodium sulfate,
certain values have shown to be better than the others. For
instance, using 0.035 M of sodium sulfate in the preparation
of MCNPs resulted on better removals than employing 0.007
M. Sodium sulfate concentration has been demonstrated to
be directly proportional to roughness as well as to the increase
of surface area of multicomponent nanoparticles [22]. Also,
under reducing conditions and 0.035 M Na2SO4, removal of
toxic metals (~99%) was slightly enhanced compared to the
under oxidized environment (~97%) [Figure 4]. Reduced
conditions provided a favorable setting for the removal of
heavy metals because oxygen was not present in solution [35];
thus nanoparticles were not easily oxidized and did not lose
their reactivity. Tests using MCNPs prepared with 0.035 M
of sodium sulfate applied to real mine tailings contaminated
with heavy metals showed also high eciency to immobilize
the metallic elements [Figure 5]. More than 99% of removal
was achieved for the majority of toxic metals from the liquid
phase. erefore, the property of the nanoparticles that causes
high removal of heavy metals from water is its chemical
composition: Fe(0) and FeS. It is obvious that the active groups
of the multicomponent nanoparticles chemically immobilize
the toxic metals [Figure 6]. Clearly, XPS spectra show peaks
related to the formation of CuO with binding energies of
953.8 and 934.1 eV for Cu2p1/2 and Cu2p3/2, respectively.
Chemical sorption of heavy metals on MCNPs is also
conrmed by FTIR tests performed on samples containing
fresh and after treatment multicomponent nanoparticles
[Figure 7]. As seen in Figure 7, the graphical representations
Figure 3: Pseudo-second-order kinetic studies of heavy metals removal using
MCNPs 0.35 M Na2SO4.
Figure 4: Removal of dierent heavy metals from articial water using MCNPs
prepared with 0.035 M Na2SO4 under reducing and oxidizing environments
at 20 °C.

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Aqueous Phase Cumbal et al.
of both samples reveal a decrease of frequency from 3308 to
3226 (-OH stretching), 1637 to 1626 (H-H bonding/bending
vibration of water). Changes on peaks from 1403 to 1120
may imply the existence of residual hydroxyl groups on the
surface of MCNPs. is can be assumed due to the formation
of complex of Sulfur-OH-Cu2+ and Sulfur-O-Cu2+ during the
adsorption of Cu2+. At 1349 cm-1 the intensity of the band is
increased after adsorption. It seems that adsorption induces
the increase of the amount of hydroxyl groups, which may arise
from the formation of surface precipitate of Cu(OH)2. e
other peaks shifted as compared with those of fresh MCNPs,
indicating a strong interaction between the multicomponent
nanoparticles and the copper cation. Also, scientic literature
describes the formation of metal suldes when metals are
contacted with the fraction of FeS [36]. e excellent removal
of arsenic from the aqueous phase (>98%) accomplished is this
study is essentially due to dierent reactions that arsenates
bear when contacted with elemental iron of nanoparticles.
According to Ramos et al. [37], Arsenic(V) in the presence of
elemental iron nanoparticles is reduced to As0 or As3+. Also, it
may form complex Fe-oxide-As3+ or develop complexes with
iron hydroxides. Moreover, Li & Zhang [38] reported that
redox mechanisms are dominant when elements such as Zn2+,
Pb2+, Cu2+, As5+ are brought into contact with zero valent iron
nanoparticles and reduced to Zn0 and Pb0, or are immobilized
by the hydroxides or oxides.
Eect of temperature
Tests conducted using MCNPs at dierent temperatures
demonstrated that there is no need to raise the temperature
in order to enhance heavy metals removal. On the contrary,
it produces a small decrease on their removal [Figure S4].
is could be related to the increase of nanoparticles size. It
has been demonstrated, as the size of nanoparticles increases
surface area and reactivity is reduced [28, 39]. However, a
rapid physical adsorption of heavy metals on the surface of
nanoparticles counterbalances the increase of particle size.
Besides, results of kinetic tests showed a rapid adsorption of
heavy metals, which is the main property of physisorption
[30]. On the other hand, raising the temperature during the
treatment could promote an increase of Brownian motion, that
enhances the pollutant diusion but it could also interfere with
intermolecular weak forces (Van der Waals forces) causing
the release of metallic ions from the surface of nanoparticles
[30]. Nonetheless, if physisorption were the only adsorption
mechanism in the treatment, there would be desorption of
pollutants in the aqueous media due to high temperatures.
Leakage of heavy metals was not observed on the removal
tests on both the articial and the real mine tailings. erefore,
chemical adsorption also plays an important role on the heavy
metals uptake as it was explained above.
Eect of pH
Hydrogen potential (pH) is also one of the factors
that, has great inuence not only on the nanoparticle
stability but also in the adsorption of heavy metals on solid
surfaces (nanoparticles). At acidic pH there exists a negative
interference with heavy metal uptake from water. Hydrogen
ions compete for the reactive sites on the multicomponent
nanoparticles [40]. Also, high concentration of H+ the surface
of nanoparticles is positively charged [41], inhibiting in
some extent, adsorption of metallic ions due to electrostatic
repulsion [42]. In this study the removal eciency of heavy
metals conducted under a pH of 3 is slightly lower compared to
the removal eciency at higher pH values as shown in Figure
S5 (Supporting Information). Nevertheless, the removal at
pH 3 is not signicantly lower compared to those at higher
Figure 6: XPS spectrum of MCNPs prepared with 0.035 M Na2SO4 under
reducing environment at 20 °C before(A)and after(B)treatmentof copper.
Figure 7: FTIR spectra of MCNPs prepared with 0.035M Na2SO4 under
reducing environment at 20 ºC before (A) and after (B) treatment of copper.
Figure 5: Removal of dierent heavy metals from liquid mine tailings using
MCNPs prepared with 0.035 M Na2SO4 under reducing environment at 20 °C.

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pH values of 5, 7, and 9. is can be attributed to the fact
that at acidic pH, heavy metals are more soluble, osetting
to a certain level, the negative eects of competition between
metallic cations and H+. Soluble metals are found as free ions
available for binding more easily to the reactive sites of the
multicomponent nanoparticles [43]. Besides, at pH values
greater than 5, ions H+ are almost at equilibrium with ions
OH-, so there is less competition between hydrogen ions and
heavy metals for binding the reactive sites of the nanoparticles
[44]. As a result, the removal eciency observed in these
tests, revealed a slight enhancement at pH values of 5, 7, and
9 [Figure S5]. Finally, at high pH values, namely 9, there are
no hydrogen ions to compete with the pollutants. Indeed,
high concentration of OH-, negatively charges surface of the
nanoparticles enhancing the attraction and adsorption of
metallic cations; thus, increasing the removal eciency [45].
Conclusion
• Novel multicomponent nanoparticles were successfully
synthesized using sodium sulfate (Na2SO4) and without
any stabilizing agent. e use of sodium sulfate in the
synthesis of the multicomponent nanoparticles, allowed
the manufacture of nanomaterials in an environmentally
friendly approach since there is a lower release of hydrogen
sulde, a noxious gas to the environment and to the human
health.
• e physicochemical characterization of multicomponent
nanoparticles demonstrated that they are stable for a short
time. Likewise, the size distribution reveals that they have
an appropriate size within a range previously reported,
as well as a great surface area, meaning they are suitable
for obtaining high removal eciency of heavy metals as
observed in this work.
• e multicomponent nanoparticles demonstrated both
rapid adsorption kinetics (within the rst ve minutes),
and no desorption of heavy metals along the testing
period, suggesting the occurrence of physical and chemical
adsorption mechanisms for uptake of metals. Data of
kinetic tests t well on a pseudo-second-order model, thus
conrming chemical adsorption for the removal of the
pollutants. On the other hand, the isothermal adsorption
of heavy metals onto the multicomponent nanoparticles
follows a Freundlich isotherm model, indicating the
presence of heterogeneous surface on the nanoparticles.
• Also, environmental conditions play a role in the removal
of heavy metals using multicomponent nanoparticles.
Tests conducted at dierent temperatures demonstrated
good removal eciencies between the toxic metals and
the nanoparticles; however, at higher temperature the
eciency dropped about 1.6% due to Brownian motion.
Hydrogen potential also inuences the removal eciency
of heavy metals when using multicomponent nanoparticles
for the uptake. Lower removal is achieved at acidic pH (pH
3) due to competition with hydrogen ions. While at basic
pH the removal is higher because surface of nanoparticles
is negatively charged, thus attracting heavy metals.
Acknowledgments
e authors thank to Dr. Jenny Gun and Dr. Ovadia
Lev from Hebrew University for the XPS spectra and to
Universidad de las Fuerzas Armadas for the nancial support
through the Grant PIC2013-T-012. We also appreciate the
help given by Daniel Delgado and Carla Bastidas in the
laboratory and Dr. Brajesh Kumar for his careful review of the
manuscript.
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