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Study on novel modified large mesoporous silica FDU-12/polymer matrix nanocomposites for adsorption of Pb(II)

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In this study, porous methacrylate-modified FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6 nanocomposites were synthesized via a facile solution casting protocol. The physicochemical properties of the prepared materials were studied using various characterization techniques including Fourier transform-infrared spectroscopy, field emission-scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption/desorption. After characterization of the materials, the prepared nanocomposites were applied as novel adsorbents for the removal of Pb(II) from aqueous media. In this regard, the effect of various parameters including solution pH, adsorbent amount, contact time, and initial concentration of Pb(II) on the adsorption process was investigated. To study the mechanism of adsorption, kinetic studies were conducted. The kinetic models of pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion were employed. The results revealed that the adsorption of Pb(II) onto methacrylate-modified FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6 adsorbents followed the pseudo-second-order kinetic model. Also, different isotherms including Langmuir, Freundlich, and Dubinin-Radushkevich were applied to evaluate the equilibrium adsorption data. Langmuir isotherm provided the best fit with the equilibrium data of both adsorbents with maximum adsorption capacities of 99.0 and 94.3 mg g ⁻¹ for methacrylate-modified FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6, respectively, for the removal of Pb(II).
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RESEARCH ARTICLE
Study on novel modified large mesoporous
silica FDU-12/polymer matrix
nanocomposites for adsorption of Pb(II)
Hamed Ghaforinejad
1
, Hossein Mazaheri
1
, Ali Hassani Joshaghani
1
, Azam MarjaniID
2,3
*
1Department of Chemical Engineering, Arak Branch, Islamic Azad University, Arak, Iran, 2Department for
Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Viet
Nam, 3Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Viet Nam
*azam.marjani@tdtu.edu.vn
Abstract
In this study, porous methacrylate-modified FDU-12/poly(methyl methacrylate) and amine-
modified FDU-12/Nylon 6 nanocomposites were synthesized via a facile solution casting
protocol. The physicochemical properties of the prepared materials were studied using vari-
ous characterization techniques including Fourier transform-infrared spectroscopy, field
emission-scanning electron microscopy, transmission electron microscopy, and nitrogen
adsorption/desorption. After characterization of the materials, the prepared nanocomposites
were applied as novel adsorbents for the removal of Pb(II) from aqueous media. In this
regard, the effect of various parameters including solution pH, adsorbent amount, contact
time, and initial concentration of Pb(II) on the adsorption process was investigated. To study
the mechanism of adsorption, kinetic studies were conducted. The kinetic models of
pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion were
employed. The results revealed that the adsorption of Pb(II) onto methacrylate-modified
FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6 adsorbents fol-
lowed the pseudo-second-order kinetic model. Also, different isotherms including Langmuir,
Freundlich, and Dubinin-Radushkevich were applied to evaluate the equilibrium adsorption
data. Langmuir isotherm provided the best fit with the equilibrium data of both adsorbents
with maximum adsorption capacities of 99.0 and 94.3 mg g
-1
for methacrylate-modified
FDU-12/poly(methyl methacrylate) and amine-modified FDU-12/Nylon 6, respectively, for
the removal of Pb(II).
1. Introduction
Today, the discharge of environmental contaminants especially heavy metals (Pb(II), Cd(II),
Hg(II), Cr(VI), etc.) in the environment caused drastic concerns about the health of individu-
als exposed to them. Heavy metals are an important class of environmental contaminants due
to their high toxicity, carcinogenicity, nonbiodegradability, and bioaccumulative nature [1].
As an extremely toxic member of heavy metals, Pb(II) has bad effects on the kidney, liver,
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OPEN ACCESS
Citation: Ghaforinejad H, Mazaheri H, Hassani
Joshaghani A, Marjani A (2021) Study on novel
modified large mesoporous silica FDU-12/polymer
matrix nanocomposites for adsorption of Pb(II).
PLoS ONE 16(1): e0245583. https://doi.org/
10.1371/journal.pone.0245583
Editor: Yogendra Kumar Mishra, University of
Southern Denmark, DENMARK
Received: June 25, 2020
Accepted: January 5, 2021
Published: January 22, 2021
Copyright: ©2021 Ghaforinejad et al. This is an
open access article distributed under the terms of
the Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
reproductive system, brain functions, and basic cellular processes. It can cause mental retarda-
tion, insomnia, irritability, seizures, and renal damages. The major sources of Pb(II) in the
environment are ore and metals processing, production of fertilizers, pigments, batteries, and
leaded aviation fuels. Every day, health-related organizations and environmentalists express
their deep concern about these contaminants. Because of these concerns, especially about
human health, the US Environmental Protection Agency has announced a limit on the amount
of heavy metals in soil and water. Thus, contaminant uptake, especially from aquatic media is
urgent. Widespread researches have been conducted to introduce and develop decontamina-
tion methods. They are included chemical precipitation, electrochemical remediation, mem-
brane filtration, ion exchange, solvent extraction, coagulation, adsorption, etc. Among them,
the adsorption strategy is popular for effective water treatment owing to its several advantages.
This technique provided a simple, relatively fast, and low-cost methodology with high effi-
ciency and flexibility [2]. The method is also eco-friendly in large-scale manufacturing and can
combine with other conventional remediation methods.
Considering intensive developments in nanotechnology especially in the fields of catalysis
[39], extraction [1014], carrier materials [15], and adsorption [1621], polymer matrix
nanocomposites have attracted a great deal of attention in the field of adsorption. The use of
nanosized particles in the polymer matrixes provides high-performance hybrid nanocompo-
site materials with widespread applications. These materials combine ductility and flexibility
of organic polymer matrix with the benefits of inorganic nanofiller such as high thermal and
mechanical stability, and high surface area. On the other hand, the abundant functional groups
(hydroxyl, carbonyl, phenyl, amine, etc.) on the surface of polymer matrix nanocomposites
results in adsorbents with a good affinity toward adsorption of heavy metals [1,22,23].
Recently, mesoporous silica materials have attracted much attention to use as adsorbent or a
part of adsorbent in polymer matrix nanocomposites due to their unique properties. They pro-
vide high surface area, functionalizable surface, and tailorable pore dimensions which make
them a good candidate for adsorption processes. Over the past years, a plethora of mesoporous
silica materials (examples include MCMs, SBAs, KCC-1, KITs, FDUs) with a wide range of
pore geometries and particle morphologies have been introduced and used for widespread
applications, especially for adsorption [24,25]. Generally, they can be classified as 2D (e.g.
SBA-15, MCM-41) and 3D (e.g. MCM-48, SBA-16, KIT-6, FDU-12) architecture based on the
pore symmetry [26,27].
As a three-dimensional large mesoporous silica, FDU-12 possesses a highly ordered struc-
ture with a superior 3D channel which makes it ideal for mass transfer and diffusion of guest
molecules. It has unique properties of well-ordered pore structure, high specific surface area,
ultra-large pore diameter (10–26 nm), and adjustable pore size [28,29]. FDU-12 can be syn-
thesized with different pore size distributions as reported in recent studies [30,31]. To expand
the application of mesoporous silica materials (e.g. FDU-12), changing hydrophobicity, and
tailoring surface characteristics, the incorporation of organic functional groups onto the
ordered structure of the material with uniform distribution is a widely used choice. In the case
of nanocomposites, functionalization of the inorganic filler with a suitable functional group
could help linking up the filler with the polymer matrix through functional groups and also
more effective dispersion and penetration of the polymer chains in the porous structure of the
filler. Since the surface of mesoporous silica materials is densely populated with hydroxyl
groups, surface functionalization with a variety of organic moieties seems to be relatively easy
[32]. In this context, several studies reported surface functionalization of mesoporous silica
materials such as SBA-15, MCM-41, and KCC-1 with various organic groups [1,2,21,23,33,
34]. In comparison, there are few reports regarding the functionalization of mesoporous silica
FDU-12 [3539].
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In the case of polymer matrix nanocomposites, various organic polymers have been applied
for the preparation of polymer-based nanocomposites containing mesoporous materials. As a
low density, transparent, thermoplastic, and rigid polymer, poly(methyl methacrylate)
(PMMA) provided good flexibility and low cost. This versatile amorphous polymer has also
excellent electrical and mechanical properties, and good resistance to non-polar solvents,
acidic and alkaline solutions, and inorganic reagents [40,41]. Another versatile polymer used
in polymer matrix nanocomposites is Nylon. Nylon polymer is an electron-rich and polar syn-
thetic polyamide composed of microfibrils that are interconnected forming a three-dimen-
sional network with a porous structure [22,42]. Among various types of commercial Nylons,
Nylon 6 and Nylon 6,6 continue to be the most popular types. Nylon 6 fibers have high tensile
strength and provided highly abrasion resistance. This polymer is also resistant to various
types of chemicals such as acids and alkalis.
Herein, we present the synthesis and characterization of two novel modified mesoporous
silica FDU-12 materials using silane coupling agents of 3-(triethoxysilyl)propyl methacrylate
and N
1
-(3-trimethoxysilylpropyl)diethylenetriamine. The prepared materials were then used
as nanofiller for the preparation of poly(methyl methacrylate)- and Nylon 6-based nanocom-
posites. The nanocomposites were synthesized via a facile and fast method and characterized
by various characterization techniques. To study the applicability of the prepared nanocompo-
sites for adsorption purposes, the nanocomposites were used as novel adsorbents for removal
of Pb(II) ions from aqueous solutions. Kinetic studies were also conducted for the two pre-
pared materials. Our results showed the potential of methacrylate- and amine-functionalized
FDU-12 for the adsorption of Pb(II) ions as a model of heavy metals from aqueous media.
2. Experimental
2.1. Materials and reagents
In this study, toluene (99%), absolute ethanol (99.5%), formic acid (99%), hydrochloric acid
(37%), acetic acid (99.5%), ortho-phosphoric acid (85%), tetraethyl orthosilicate (TEOS), boric
acid (99.5%), potassium chloride (99.5%), sodium hydroxide (97%), and lead(II) nitrate
(99.5%) were obtained from Merck (Darmstadt, Germany). Poly(methyl methacrylate)
(PMMA, average M
w
~120,000), Nylon 6 (NY6), Pluronic F-127 (Mw ~ 12600 Da), 1,3,5-tri-
methylbenzene (TMB, 98%), and N
1
-(3-trimethoxysilylpropyl)diethylenetriamine were pur-
chased from Sigma-Aldrich (St. Louis, MO, USA). 3-(triethoxysilyl)propyl methacrylate (98%)
was obtained from TCI (Europe). Deionized water was prepared using a water purification sys-
tem (Oklahoma, USA). The stock standard solution of Pb(II) (1000 mg L
1
) was prepared in
water. Working standard solutions were prepared by diluting the stock solution. The Brigh-
ton-Robinson buffer system was used for the preparation of aqueous solutions with different
pHs.
2.2. Instruments
The Fourier transform-infrared (FT-IR) spectra were recorded using a Thermo Nicolet Avatar
330 FT-IR spectrometer (USA) between 4000 and 400 cm
-1
with a resolution of 4 cm
-1
. The
surface morphology of the samples was examined using a MIRA3 TESCAN-XMU field emis-
sion-scanning electron microscope (FE-SEM, Czech Republic). Transmission electron micros-
copy (TEM) analysis was performed on a Philips CM 120 microscope (Philips Electronics,
Eindhoven, The Netherlands). For the analysis, the samples were dispersed in 2-propanol and
a drop of the suspension was put on a carbon-coated nickel grid. Nitrogen adsorption/desorp-
tion analysis was performed on a Belsorp-mini II (BEL Japan Inc., Osaka, Japan) at 77 K. A
flame atomic absorption spectroscopy (FAAS, Agilent, Model 240FS AA, USA) was used for
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Pb quantification in the samples. In the case of samples with a low level of Pb, an inductively
coupled plasma-optical emission spectrometer (ICP-OES, PerkinElmer, Optima 7300 DV,
USA) was applied. A 100 W ultrasonic liquid processor (MISONIX XL-2000 Series, Raleigh,
North Carolina, USA) was used for sonochemical reactions.
2.3. Synthesis and surface modification of large mesoporous silica FDU-12
The large mesoporous silica FDU-12 was synthesized according to the previous reports [29,
43] with some modifications. Briefly, 3.0 g of Pluronic F-127 was dissolved in 120 mL of 2.0
mol L
-1
hydrochloric acid. After 15 min, 7.5 g of potassium chloride was added to the solution.
Then, 3.0 g of TMB was added and the mixture was stirred at 288 K for 2 h. Afterward, 12.5 g
of TEOS was added to the solution and the mixture was heated to 383 K in an autoclave and
remained at this temperature for 72 h. The white solid product was collected and washed with
water and ethanol and oven-dried at 343 K for 24 h. The calcination of the material was per-
formed at 823 K for 5 h.
Two silane coupling agents including 3-(triethoxysilyl)propyl methacrylate and N
1
-(3-tri-
methoxysilylpropyl)diethylenetriamine were used to surface modification of the prepared
FDU-12 through the post-synthesis modification technique. Typically, 0.5 g of the synthesized
FDU-12 and 0.5 mL of silane coupling agent were added to 40 mL of dried toluene. The mix-
ture was refluxed at 383 K for 24 h. The resultant product was then isolated through a Bu¨chner
funnel and washed with toluene and ethanol, and oven-dried at 343 K for 24 h. The FDU-12
samples modified with 3-(triethoxysilyl)propyl methacrylate and N
1
-(3-trimethoxysilylpropyl)
diethylenetriamine were denoted as FDU-12-MA and FDU-12-TA, respectively.
2.4. Preparation of FDU-12-MA/PMMA and FDU-12-TA/NY6
For the preparation of FDU-12-MA/PMMA nanocomposite with FDU-12-MA content of 3.0
wt%, 4.85 g of PMMA was dissolved in 40 mL of dry toluene (with the help of heating at 80˚C
under nitrogen atmosphere) and the mixture was sonicated for 15 min. Afterward, 0.15 g (3.0
wt%) of the prepared FDU-12-MA was added to 10 mL of dry toluene and the mixture was
sonicated for 15 min. Then, the FDU-12-MA mixture was added to the polymer solution with
mechanical stirring, sonicated for 15 min, and refluxed for 24 h. After cooling down to room
temperature, the resultant mixture was sonicated for another 15 min, poured into a clean glass
Petri dish, and dried at room temperature for 5 h. The FDU-12-MA/PMMA nanocomposite
was washed with pure water, dried, and used for adsorption experiments.
In the case of FDU-12-TA/NY6, 4.85 g of NY6 was dissolved in 40 mL of formic acid (with
the help of heating at 80˚C under nitrogen atmosphere) and the mixture was refluxed under
nitrogen atmosphere for 6 h to obtain a clear solution. Afterward, 0.15 g (3.0 wt%) of the pre-
pared FDU-12-TA was added to 10 mL of formic acid and the mixture was sonicated for 15
min. Then, the FDU-12-TA mixture was added dropwise to the NY6 solution, sonicated for 15
min, and refluxed for 12 h. After refluxing, the mixture was sonicated for another 15 min, cast
to a clean glass Petri dish, and dried at room temperature. The FDU-12-TA/NY6 nanocompo-
site was washed with pure water, dried, and used for adsorption experiments.
2.5. Adsorption experiments
Batch adsorption experiments were carried out to study the adsorption behavior of Pb(II) ions
onto the FDU-12-MA/PMMA and FDU-12-TA/NY6. For each experiment, 10 mL of an aque-
ous standard solution of Pb(II) with the desired concentration was exposed to the accurately
weighed amount of adsorbent in 20 mL polyethylene containers. The adsorption process was
performed at 180 rpm and 298 K for 24 h. After that, the adsorbent was separated from the
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solution and the concentration of Pb(II) in the solution was quantified by the means of FAAS
or ICP-OES. The removal efficiency (RE) was computed using the following equation (Eq 1):
RE %ð Þ ¼ CiCe
Ci100 ð1Þ
where C
i
and C
e
are the initial and equilibrium concentration of the metal ion in the solution
(mg L
-1
), respectively. The adsorption capacity (q
e
, mg g
-1
) was calculated according to the fol-
lowing equation (Eq 2):
qe¼CiCe
W
 Vð2Þ
Where Vis the solution volume (mL) and Wrefers to the adsorbent amount (mg).
3. Results and discussion
3.1. Synthesis and characterization
Considering the relatively inert and hydrophobic nature of the pristine FDU-12, and also the
tendency of nanoparticles to agglomerate, the surface functionalization is necessary to provide
a homogenous dispersion of prepared mesoporous silica in the polymer matrix for the prepa-
ration of polymer nanocomposites. In the present study, the surface of the prepared pristine
FDU-12 was treated with two different silane coupling agents of 3-(triethoxysilyl)propyl meth-
acrylate and N
1
-(3-trimethoxysilylpropyl)diethylenetriamine. These coupling agents improve
the interfacial interaction of inorganic filler and organic polymer matrix. The methacrylate-
and amine-functionalized FDU-12 materials were then applied as nanofiller for the prepara-
tion of two nanocomposites using PMMA and NY6 as organic polymers.
The chemical structure and morphology of the prepared materials were examined by
FT-IR, FE-SEM, TEM, and N
2
adsorption/desorption techniques. The FT-IR spectra of pris-
tine FDU-12, FDU-12-MA, FDU-12-TA, pristine PMMA, FDU-12-MA/PMMA, pristine
NY6, and FDU-12-TA/NY6 are shown in Fig 1. In the case of pristine FDU-12, the bands at
463 and 810 cm
1
are attributed to the bending and symmetric stretching vibration of Si–O–
Si. Also, the band at 1078 cm
1
corresponds to the asymmetric stretching vibration of the Si–
O–Si bond [28,43]. The broadband around 3435 cm
1
corresponds to O–H stretching of the
surface silanol groups and the physically adsorbed water molecules. The band centered at 1633
cm
1
is attributed to the bending vibration of H–O–H. For FDU-12-MA and FDU-12-TA, in
addition to the bands observed for pure FDU-12, new bands related to the organic part of the
silane coupling agent are appeared. The bands located at 2957 and 2849 cm
1
are assigned to
the C–H stretching vibrations of CH
2
and the band at 1471 cm
1
is corresponding to the bend-
ing vibration of the C–H. In the case of FDU-12-MA, the new band at 1733 cm
1
is character-
istic of the C = O bond of the silane coupling agent. For FDU-12-TA, the broadband at 3200–
3500 cm
1
indicated the presence of–OH and–NH
2
groups on the surface of FDU-12-TA.
These data indicated successful modification of pure FDU-12 with 3-(triethoxysilyl)propyl
methacrylate and N
1
-(3-trimethoxysilylpropyl)diethylenetriamine. The FT-IR spectrum of
FDU-12-MA/PMMA composite shows absorption bands at 2994 and 2944 cm
1
which corre-
spond to C–H asymmetric stretching in CH
3
and CH
2
groups, respectively. Also, the peak
located at 2842 cm
1
is related to the C–H symmetric stretching in CH
3
. The characteristic
band at 1722 cm
1
which corresponds to the C = O bond is also observed. These bands in addi-
tion to the new bands observed in the spectrum of FDU-12-MA/PMMA correspond to differ-
ent modes of CH
2
and CH
3
vibrational modes indicated the presence of PMMA in the
structure of the prepared nanocomposite which is in accordance with other reports [23,44].
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Also, the similarities between the spectra of pristine PMMA and FDU-12-MA/PMMA are
quite obvious. In the case of the C = O bond, the stretching vibration was observed at 1715 and
1722 cm
1
for pristine PMMA and FDU-12-MA/PMMA, respectively. The shifts of C = O
stretching vibrations may be due to the interaction of modified nanofiller with polymer matrix
(hydrogen bonding interactions) which decreases the strength of the C = O bond in the poly-
mer [4547]. For FDU-12-TA/NY6, the characteristic peaks at 3284, 2856 & 2929 cm
1
corre-
spond to the stretching vibration of N-H bond and C-H stretching vibrations of the NY6.
Also, the peaks located at 1631 and 1532 cm
1
are attributed to the stretching vibration of car-
bonyl groups and N-H bending vibration which all are related to NY6 [1]. The similarities
between the spectra of pristine NY6 and FDU-12-TA/NY6 are observable. In the case of C = O
bond, the stretching vibration observed at 1628 and 1631 cm
1
for pristine NY6 and FDU-
12-TA/NY6, respectively. This shift also may be due to the hydrogen bonding interactions
between nanofiller and polymer matrix which decreases the strength of the C = O bond in the
polymer.
The morphology of the prepared materials was studied via FE-SEM and TEM techniques.
The FE-SEM images of pristine FDU-12, FDU-12-MA, FDU-12-TA, FDU-12-MA/PMMA,
and FDU-12-TA/NY6 are shown in Fig 2. The FE-SEM image of the pristine FDU-12 and
modified samples (FDU-12-MA, FDU-12-TA) showed a relatively regular hexagonal prism
morphology which is a typical characteristic morphology of FDU-12 [43,48]. This indicates
that the morphology of the FDU-12 was retained after modification with the used silane cou-
pling agents. At higher magnifications, the growing crystals are visible. In the case of polymer
composites, the modified FDU-12 particles are visible on the surface of nanocomposites sug-
gesting that the mesoporous material is incorporated in the polymer matrix. The TEM images
of pristine FDU-12 are shown in Fig 3. A well-ordered structure is seen. As reported in the lit-
erature [4850], the FDU-12 exhibited ordered mesopore arrangement characteristics. In the
images, the large cage units with regular alignment in the highly ordered lattice are obvious.
Fig 1. FT-IR spectra of pristine FDU-12, FDU-12-MA, FDU-12-TA, pristine PMMA, FDU-12-MA/PMMA, pristine NY6,
and FDU-12-TA/NY6.
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The nitrogen adsorption/desorption isotherms of the pure FDU-12, FDU-12-MA, and
FDU-12-TA materials are shown in Fig 4A–4C. As shown in the figure, according to the
IUPAC classification, all three samples exhibited type IV isotherms with H2-type hysteresis
loops. The pristine FDU-12, FDU-12-MA, and FDU-12-TA samples showed a BET surface
area of 376, 29, and 115 m
2
g
-1
, respectively. According to the BJH model (Fig 4D), mean pore
diameters of 9.2, 1.2, and 6.9 nm were found for pristine FDU-12, FDU-12-MA, and FDU-
12-TA samples, respectively. In comparison, the textural parameters of pristine FDU-12 have
reduced upon surface modification with silane coupling agents, as it was anticipatable. The
obtained textural parameters of the materials are shown in Table 1.
Fig 2. FE-SEM images of pristine FDU-12, FDU-12-MA, FDU-12-TA, FDU-12-MA/PMMA, and FDU-12-TA/NY6 at three
magnifications.
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Fig 3. TEM images of pristine FDU-12.
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Fig 4. N
2
adsorption/desorption isotherms of (a) pristine FDU-12, (b) FDU-12-MA, (c) FDU-12-TA, and (d) the BJH pore size distribution
curves of the samples.
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Table 1. Textural properties of the synthesized pristine FDU-12, FDU-12-MA, and FDU-12-TA.
Sample BET BJH
SA
a
PV
b
PD
c
SA PV PD
(m
2
g
-1
) (cm
3
g
-1
) (nm) (m
2
g
-1
) (cm
3
g
-1
) (nm)
Pristine FDU-12 376 0.8387 8.9 326 0.8004 9.2
FDU-12-MA 29 0.0787 10.9 38 0.0812 1.2
FDU-12-TA 115 0.3831 13.4 135 0.3896 6.9
a
Surface area
b
Total pore volume
c
Mean pore diameter
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3.2. Adsorption studies
3.2.1. The effect of pH on adsorption. As an important factor affecting the adsorption
process, the effect of pH on the adsorption of Pb(II) ions onto the FDU-12-MA/PMMA and
FDU-12-TA/NY6 adsorbents was investigated in the range of 2.0–12.0. The experiments were
performed using 10 mL of an aqueous standard solution of Pb(II) at the concentration level of
50 mg L
-1
with an adsorbent dosage of 10.0 mg. The adsorption was performed at 298 K for 24
h. As can be seen in Fig 5A, for both adsorbents, the removal efficiency was increased with
increasing solution pH up to 9.0 and then no significant enhancement occurred. The low
removal efficiency in acidic mediums could be related to the competition of H
+
ions with Pb
(II). In other words, the H
+
ions in the solution occupy the attainable active sites on the adsor-
bent and compete with Pb(II) ions due to the electrostatic forces. This results in fewer accessi-
ble sites for Pb(II) leads to less adsorption of Pb(II) in acidic mediums. Accordingly, pH = 9.0
was selected for further experiments.
3.2.2. The effect of adsorbent dosage. To study the effect of adsorbent dosage on the
adsorption of Pb(II) from aqueous solution, various dosages between 2.0 and 50.0 mg were
tested. In these experiments, 10 mL of an aqueous standard solution of Pb(II) at the concentra-
tion level of 50 mg L
-1
(pH = 9.0) was used. The adsorption was performed at 298 K for 24 h.
The obtained results are shown in Fig 5B. As seen in the figure, the removal efficiency for two
adsorbents was enhanced with increasing adsorbent dosage from 2.0 to 5.0 mg. No surprising
enhancement in removal efficiency was observed for higher amounts. With enhancing adsor-
bent dosage, more accessible adsorption sites are available which increases removal efficiency.
So, 5.0 mg of each of the adsorbents were used for further experiments.
3.2.3. The effect of contact time. The effect of contact time on the adsorption process
was investigated for the two adsorbents. In this step, 10 mL of an aqueous standard solution of
Pb(II) at the concentration level of 50 mg L
-1
(pH = 9.0) with an adsorbent dosage of 5.0 mg
was used. The adsorption was performed at 298 K. Fig 5C shows the effect of contact time (20
to 600 min) on Pb(II) removal by FDU-12-MA/PMMA and FDU-12-TA/NY6 adsorbents.
Considerable enhancement in removal efficiency was observed when contact time was
increased up to 220 and 240 min for FDU-12-MA/PMMA and FDU-12-TA/NY6, respectively.
No further adsorption occurred for longer times. The obtained results showed a relatively fast
adsorption process. This was mainly due to the high accessible sites on the surface of FDU-
12-MA/PMMA and FDU-12-TA/NY6 adsorbents. Based on the results, contact times of 220
and 240 min (for FDU-12-MA/PMMA and FDU-12-TA/NY6, respectively) were selected for
further experiments to ensure that equilibrium is reached.
3.2.4. The adsorption kinetic studies. To study the mechanism of adsorption, kinetic
studies were conducted. Four kinetic models including pseudo-first-order (PFO), pseudo-sec-
ond-order (PSO), Elovich, and intraparticle diffusion (IPD) were employed. The applied
Fig 5. The effect of (a) pH, (b) adsorbent amount, and (c) contact time on adsorption of Pb(II) by the prepared adsorbents.
https://doi.org/10.1371/journal.pone.0245583.g005
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equations are expressed in the following forms:
logðqeqtÞ ¼ logqek1
2:303 tð3Þ
t
qt¼1
hþ1
qe
tð4Þ
h¼k2q2
eð5Þ
qt¼lnðabÞ
bþlnt
bð6Þ
qt¼kdif ðtÞ0:5þCð7Þ
Where q
e
(mg g
-1
), q
t
(mg g
-1
), k
1
(min
-1
), h(mg g
-1
min
-1
), k
2
(g mg
-1
min
-1
), α(mg g
-1
min
-1
) & β(g mg
-1
), k
dif
(mg g
-1
min
-0.5
), and C(mg g
-1
) are the adsorption capacity at equilib-
rium, the adsorption capacity at time t, PFO rate constant, the initial sorption rate in PSO
model, PSO rate constant, Elovich constants, IPD rate constant, and a constant, respectively.
The results of the fitting are illustrated in Fig 6A–6D and Table 2. As shown in Table 2, in the
case of both adsorbents, the PSO kinetic model provided better R
2
than those obtained by
other models, which suggests that the chemical adsorption process can be well described with
the PSO model. The presence of hydroxyl, amine, and carbonyl groups on the surface of adsor-
bents might be involved in the process.
3.2.5. The effect of Pb(II) concentration and adsorption isotherm. To study the effect
of the initial concentration of Pb(II) on the adsorption behavior, a concentration range
between 2.0 and 70.0 mg L
-1
(pH = 9.0) was investigated. The adsorbent dosage of 5.0 mg of
each adsorbent was used for the experiments. The adsorption time was set to 220 and 240 min
for FDU-12-MA/PMMA and FDU-12-TA/NY6, respectively. The obtained data are shown in
Fig 6. The kinetic adsorption models of (a) pseudo-first-order, (b) pseudo-second-order, (c) Elovich, (d) intra-particle diffusion; (e) the
equilibrium isotherm and the isotherm models of (f) Langmuir, (g) Freundlich, and (h) Dubinin–Radushkevich for the adsorption of Pb(II)
onto FDU-12-MA/PMMA and FDU-12-TA/NY6.
https://doi.org/10.1371/journal.pone.0245583.g006
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Fig 6E. The equilibrium adsorption studies were investigated by Langmuir, Freundlich, and
Dubinin-Radushkevich (D-R) isotherm models. The linear forms of the applied isotherm
models are expressed as follows:
Ce
qe¼1
qmax kLþCe
qmax ð8Þ
logqe¼1
nlogCeþlogkFð9Þ
lnqe¼lnqmax BðRT lnð1þ1
CeÞÞ2ð10Þ
Where C
e
(mg L
-1
), q
e
(mg g
-1
), q
max
(mg g
-1
), k
L
(L mg
-1
), n&k
F
((mg g
-1
) (L mg
-1
)
1/n
), B
(mol
2
kJ
-2
), R(j mol
-1
K
-1
), and T(K) are the concentration of Pb(II) at equilibrium, the
adsorption capacity at equilibrium, the maximum adsorption capacity of adsorbent, the Lang-
muir constant, the Freundlich isotherm constants for adsorption capacity and adsorption
intensity, Dubinin–Radushkevich isotherm constant, the universal gas constant, and tempera-
ture, respectively. The adsorption isotherms and the calculated parameters from the isotherms
models are shown in Fig 6F–6H and Table 3, respectively. As can be seen, considering the R
2
value, the Langmuir model fitted the experimental data (for both adsorbent) better than the
other models. The R
2
values of the Langmuir model were obtained 0.9970 and 0.9978 for
FDU-12-MA/PMMA and FDU-12-TA/NY6 adsorbents, respectively. On the other hand, the
maximum adsorption capacities of FDU-12-MA/PMMA and FDU-12-TA/NY6 obtained by
Table 2. The parameters obtained by kinetic models for the adsorption of Pb(II) onto FDU-12-MA/PMMA and FDU-12-TA/NY6.
Model Adsorbent R
2
Parameters
a
PFO FDU-12-MA/PMMA 0.9846 k
1
= 0.0214 q
e
= 51.1
FDU-12-TA/NY6 0.9469 k
1
= 0.0184 q
e
= 74.1
PSO FDU-12-MA/PMMA 0.9999 k
2
= 0.0008 q
e
= 99.0 h= 7.6511
FDU-12-TA/NY6 0.9983 k
2
= 0.0004 q
e
= 98.0 h= 4.0371
Elovich FDU-12-MA/PMMA 0.9149 α= 75.5465 Β= 0.0741
FDU-12-TA/NY6 0.9884 α= 25.0980 β= 0.0665
IPD FDU-12-MA/PMMA 0.7883 k
dif
= 2.7262 C= 56.3580
FDU-12-TA/NY6 0.9596 k
dif
= 3.1103 C= 43.6304
a
The units are as same as mentioned in Section 3.2.4.
https://doi.org/10.1371/journal.pone.0245583.t002
Table 3. The parameters obtained by isotherm models for the adsorption of Pb(II) onto FDU-12-MA/PMMA and FDU-12-TA/NY6.
Model Adsorbent R
2
Parameters
a
Langmuir FDU-12-MA/PMMA 0.9970 k
L
= 1.5781 q
max
= 99.0
FDU-12-TA/NY6 0.9978 k
L
= 1.6308 q
max
= 94.3
Freundlich FDU-12-MA/PMMA 0.8289 k
F
= 42.2474 n= 2.0640
FDU-12-TA/NY6 0.8378 k
F
= 39.4094 n= 2.1529
D-R FDU-12-MA/PMMA 0.7366 B= 2.59 ×10
7
q
max
= 56.7
FDU-12-TA/NY6 0.7429 B= 2.57 ×10
7
q
max
= 55.7
a
The units are as same as mentioned in Section 3.2.5.
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the Langmuir model were found 99.0 and 94.3 mg g
1
, respectively. The obtained theoretical
maximum adsorption capacities were in good agreement with those obtained in experiments
(93.3 and 90.2 mg g
1
for FDU-12-MA/PMMA and FDU-12-TA/NY6 adsorbents, respec-
tively). Table 4 shows data from the previous reports for the removal of Pb(II). It can be
observed that the FDU-12-MA/PMMA and FDU-12-TA/NY6 adsorbents exhibited promising
Pb(II) adsorption capacity when compared to other adsorbents.
Based on the Langmuir adsorption isotherm model assumption, there are a fixed number
of identical adsorption sites on the saturated monolayer surface of the adsorbent and the
energy of adsorption is constant. To predict the adsorption performance, the equilibrium
parameter of R
L
was calculated for the Langmuir model. It can be defined as follows:
RL¼1
1þ ðCekLÞð11Þ
The R
L
value represents the performance of the adsorption process. In this regard, R
L
=0,
0<R
L
<1, R
L
= 1, and R
L
>1 suggests irreversible, favorable, linear, and unfavorable adsorp-
tion process. The calculated R
L
values are shown in Fig 7. All the values were obtained in the
range of 0 and 1 which represented favorable adsorption of Pb(II) onto the FDU-12-MA/
PMMA and FDU-12-TA/NY6 adsorbents.
Table 4. Comparison of the adsorption capacity of FDU-12-MA/PMMA and FDU-12-TA/NY6 toward Pb(II) ions
with other adsorbents.
Adsorbent q
max
(mg g
-1
) pH Reference
Oxidized multiwalled carbon nanotubes/polypyrrole composite 26.32 6.0 [51]
SBA-15-supported Pb(II) imprinted polymer 42.55 6.0 [52]
Oil palm bio-waste/multiwalled carbon nanotubes reinforced PVA hydrogel 30.03 7.0 [53]
Triamino-functionalized KCC-1/chitosan-oleic acid nanocomposites 168 9.0 [24]
Fe
3
O
4
/cyclodextrin polymer nanocomposite 64.5 5.5 [54]
FDU-12-MA/PMMA 99.0 9.0 This work
FDU-12-TA/NY6 94.3 9.0 This work
https://doi.org/10.1371/journal.pone.0245583.t004
Fig 7. The calculated values of R
L
.
https://doi.org/10.1371/journal.pone.0245583.g007
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4. Conclusions
In conclusion, two types of nanocomposites including FDU-12-MA/PMMA and FDU-12-TA/
NY6 were fabricated via the simple and fast solution polymerization technique. The three-
dimensional large mesoporous silica FDU-12 was synthesized and modified with methacrylate
and triamine moieties and incorporated into the organic polymers. Due to the relatively large
surface area and abundant active sites of the prepared nanofillers, the newly prepared meso-
porous silica-based nanocomposites showed good performance toward Pb(II) removal from
aqueous solutions. After investigation of the affecting experimental parameters including sam-
ple solution pH, adsorbent dosage, contact time, and initial concentration of the metal ion,
several kinetic models were studied and the best fit achieved with the pseudo-second-order
model for adsorption of Pb(II) using FDU-12-MA/PMMA and FDU-12-TA/NY6. On the
other hand, four isotherm models were applied to investigate the equilibrium adsorption stud-
ies. Among them, the Langmuir model showed the best fit (R
2
values of 0.9970 and 0.9978 for
FDU-12-MA/PMMA and FDU-12-TA/NY6, respectively). The maximum adsorption capaci-
ties of 99.0 and 94.3 mg g
1
(by the Langmuir model) were obtained using FDU-12-MA/
PMMA and FDU-12-TA/NY6, respectively. In conclusion, the prepared porous nanocompo-
sites showed acceptable characteristics to be considered as effective adsorbents for heavy met-
als (e.g. Pb(II)) uptake from aqueous media.
Supporting information
S1 Graphical abstract.
(TIF)
Author Contributions
Conceptualization: Hamed Ghaforinejad, Azam Marjani.
Data curation: Hamed Ghaforinejad.
Formal analysis: Ali Hassani Joshaghani.
Investigation: Hossein Mazaheri.
Methodology: Hamed Ghaforinejad.
Project administration: Hossein Mazaheri, Ali Hassani Joshaghani, Azam Marjani.
Resources: Hossein Mazaheri.
Supervision: Hossein Mazaheri, Ali Hassani Joshaghani, Azam Marjani.
Validation: Hamed Ghaforinejad.
Writing – original draft: Hamed Ghaforinejad.
Writing – review & editing: Azam Marjani.
References
1. Mohammadnezhad G, Soltani R, Abad S, Dinari M. A novel porous nanocomposite of aminated silica
MCM-41 and nylon-6: Isotherm, kinetic, and thermodynamic studies on adsorption of Cu (II) and Cd (II).
Journal of Applied Polymer Science. 2017; 134(40):45383.
2. Soltani R, Marjani A, Hosseini M, Shirazian S. Synthesis and characterization of novel N-methylimida-
zolium-functionalized KCC-1: A highly efficient anion exchanger of hexavalent chromium. Chemo-
sphere. 2020; 239:124735. https://doi.org/10.1016/j.chemosphere.2019.124735 PMID: 31499306
PLOS ONE
Synthesis of nanoporous materials for adsorption
PLOS ONE | https://doi.org/10.1371/journal.pone.0245583 January 22, 2021 13 / 16
3. Rezaei M, Chermahini AN, Dabbagh HA, Saraji M, Shahvar A. Furfural oxidation to maleic acid with
H2O2 by using vanadyl pyrophosphate and zirconium pyrophosphate supported on well-ordered meso-
porous KIT-6. Journal of Environmental Chemical Engineering. 2019; 7(1):102855.
4. Hosseini SM, Ghiaci M, Kulinich SA, Wunderlich W, Farrokhpour H, Saraji M, et al. Au-Pd@ g-C3N4 as
an efficient photocatalyst for visible-light oxidation of benzene to phenol: experimental and mechanistic
study. The Journal of Physical Chemistry C. 2018; 122(48):27477–85.
5. Saini D, Kaushik J, Garg AK, Dalal C, Sonkar SK. N, S-codoped Carbon Dots for Nontoxic Cell Imaging
and As a Sunlight-Active Photocatalytic Material for the Removal of Chromium. ACS Applied Bio Materi-
als. 2020.
6. Shahzeydi A, Ghiaci M, Farrokhpour H, Shahvar A, Sun M, Saraji M. Facile and green synthesis of cop-
per nanoparticles loaded on the amorphous carbon nitride for the oxidation of cyclohexane. Chemical
Engineering Journal. 2019; 370:1310–21.
7. Babaei Z, Chermahini AN, Dinari M, Saraji M, Shahvar A. Cleaner production of 5-hydroxymethylfurfural
from fructose using ultrasonic propagation. Journal of cleaner production. 2018; 198:381–8.
8. Chermahini AN, Hafizi H, Andisheh N, Saraji M, Shahvar A. The catalytic effect of Al-KIT-5 and KIT-5-
SO 3 H on the conversion of fructose to 5-hydroxymethylfurfural. Research on Chemical Intermediates.
2017; 43(10):5507–21.
9. Babaei Z, Chermahini AN, Dinari M, Saraji M, Shahvar A. A sulfonated triazine-based covalent organic
polymer supported on a mesoporous material: a new and robust material for the production of 5-hydro-
xymethylfurfural. Sustainable Energy & Fuels. 2019; 3(4):1024–32.
10. Dastkhoon M, Ghaedi M, Asfaram A, Arabi M, Ostovan A, Goudarzi A. Cu@ SnS/SnO2 nanoparticles
as novel sorbent for dispersive micro solid phase extraction of atorvastatin in human plasma and urine
samples by high-performance liquid chromatography with UV detection: application of central compos-
ite design (CCD). Ultrasonics sonochemistry. 2017; 36:42–9. https://doi.org/10.1016/j.ultsonch.2016.
10.030 PMID: 28069228
11. Soltani R, Shahvar A, Dinari M, Saraji M. Environmentally-friendly and ultrasonic-assisted preparation
of two-dimensional ultrathin Ni/Co-NO3 layered double hydroxide nanosheet for micro solid-phase
extraction of phenolic acids from fruit juices. Ultrasonics sonochemistry. 2018; 40:395–401. https://doi.
org/10.1016/j.ultsonch.2017.07.031 PMID: 28946438
12. Saraji M, Shahvar A. Selective micro solid-phase extraction of epinephrine, norepinephrine and dopa-
mine from human urine and plasma using aminophenylboronic acid covalently immobilized on magnetic
nanoparticles followed by high-performance liquid chromatography-fluorescence detection. Analytical
Methods. 2016; 8(4):830–9.
13. Shahvar A, Soltani R, Saraji M, Dinari M, Alijani S. Covalent triazine-based framework for micro solid-
phase extraction of parabens. Journal of Chromatography A. 2018; 1565:48–56. https://doi.org/10.
1016/j.chroma.2018.06.033 PMID: 29921466
14. Saraji M, Shahvar A. Metal-organic aerogel as a coating for solid-phase microextraction. Analytica Chi-
mica Acta. 2017; 973:51–8. https://doi.org/10.1016/j.aca.2017.04.029 PMID: 28502427
15. Hubbell JA, Chilkoti A. Nanomaterials for drug delivery. Science. 2012; 337(6092):303–5. https://doi.
org/10.1126/science.1219657 PMID: 22822138
16. Awad AM, Jalab R, Benamor A, Naser MS, Ba-Abbad MM, El-Naas M, et al. Adsorption of organic pol-
lutants by nanomaterial-based adsorbents: An overview. Journal of Molecular Liquids. 2020:112335.
17. Kegl T, Kos
ˇak A, Lobnik A, Novak Z, Kralj AK, Ban I. Adsorption of rare earth metals from wastewater
by nanomaterials: A review. Journal of hazardous materials. 2020; 386:121632. https://doi.org/10.1016/
j.jhazmat.2019.121632 PMID: 31753662
18. Soltani R, Marjani A, Shirazian S. A hierarchical LDH/MOF nanocomposite: single, simultaneous and
consecutive adsorption of a reactive dye and Cr(vi). Dalton Transactions. 2020; 49(16):5323–35.
https://doi.org/10.1039/d0dt00680g PMID: 32248208
19. Abu-Danso E, Pera
¨niemi S, Leiviska
¨T, Kim T, Tripathi KM, Bhatnagar A. Synthesis of clay-cellulose
biocomposite for the removal of toxic metal ions from aqueous medium. Journal of hazardousmaterials.
2020; 381:120871. https://doi.org/10.1016/j.jhazmat.2019.120871 PMID: 31374372
20. Bajpai VK, Shukla S, Khan I, Kang S-M, Haldorai Y, Tripathi KM, et al. A sustainable graphene aerogel
capable of the adsorptive elimination of biogenic amines and bacteria from soy sauce and highly effi-
cient cell proliferation. ACS Applied Materials & Interfaces. 2019; 11(47):43949–63. https://doi.org/10.
1021/acsami.9b16989 PMID: 31684721
21. Soltani R, Shahvar A, Gordan H, Dinari M, Saraji M. Covalent triazine framework-decorated phenyl-
functionalised SBA-15: its synthesis and application as a novel nanoporous adsorbent. New Journal of
Chemistry. 2019; 43(33):13058–67.
PLOS ONE
Synthesis of nanoporous materials for adsorption
PLOS ONE | https://doi.org/10.1371/journal.pone.0245583 January 22, 2021 14 / 16
22. Morales-Luckie RA, Sa
´nchez-Mendieta V, Olea-Mejia O, Vilchis-Nestor AR, Lo
´pez-Te
´llez G, Varela-
Guerrero V, et al. Facile solventless synthesis of a nylon-6, 6/silver nanoparticles composite and its
XPS study. International Journal of Polymer Science. 2013; 2013.
23. Mohammadnezhad G, Abad S, Soltani R, Dinari M. Study on thermal, mechanical and adsorption prop-
erties of amine-functionalized MCM-41/PMMA and MCM-41/PS nanocomposites prepared by ultra-
sonic irradiation. Ultrasonics sonochemistry. 2017; 39:765–73. https://doi.org/10.1016/j.ultsonch.2017.
06.001 PMID: 28733004
24. Zarei F, Marjani A, Soltani R. Novel and green nanocomposite-based adsorbents from functionalised
mesoporous KCC-1 and chitosan-oleic acid for adsorption of Pb (II). European Polymer Journal. 2019;
119:400–9.
25. Soltani R, Marjani A, Moguei MRS, Rostami B, Shirazian S. Novel diamino-functionalized fibrous silica
submicro-spheres with a bimodal-micro-mesoporous network: Ultrasonic-assisted fabrication, charac-
terization, and their application for superior uptake of Congo red. Journal of Molecular Liquids. 2019;
294:111617.
26. Soltani R, Marjani A, Hosseini M, Shirazian S. Meso-architectured siliceous hollow quasi-capsule. Jour-
nal of Colloid and Interface Science. 2020. https://doi.org/10.1016/j.jcis.2020.03.003 PMID: 32182479
27. Soltani R, Marjani A, Hosseini M, Shirazian S. Mesostructured Hollow Siliceous Spheres for Adsorption
of Dyes. Chemical Engineering & Technology. 2020; 43(3):392–402.
28. Wu Q, Li Y, Hou Z, Xin J, Meng Q, Han L, et al. Synthesis and characterization of Beta-FDU-12 and the
hydrodesulfurization performance of FCC gasoline and diesel. Fuel processing technology. 2018;
172:55–64.
29. Fan J, Yu C, Gao F, Lei J, Tian B, Wang L, et al. Cubic mesoporous silica with large controllable
entrance sizes and advanced adsorption properties. Angewandte Chemie International Edition. 2003;
42(27):3146–50. https://doi.org/10.1002/anie.200351027 PMID: 12866103
30. Fan J, Yu C, Lei J, Zhang Q, Li T, Tu B, et al. Low-temperature strategy to synthesize highly ordered
mesoporous silicas with very large pores. Journal of the American Chemical Society. 2005; 127
(31):10794–5. https://doi.org/10.1021/ja052619c PMID: 16076161
31. Yu T, Zhang H, Yan X, Chen Z, Zou X, Oleynikov P, et al. Pore structures of ordered large cage-type
mesoporous silica FDU-12s. The Journal of Physical Chemistry B. 2006; 110(43):21467–72. https://doi.
org/10.1021/jp064534j PMID: 17064096
32. Carmona D, Balas F, Santamaria J. Pore ordering and surface properties of FDU-12 and SBA-15 meso-
porous materials and their relation to drug loading and release in aqueous environments. Materials
Research Bulletin. 2014; 59:311–22.
33. Wei Q, Nie Z, Hao Y, Chen Z, Zou J, Wang W. Direct synthesis of thiol-ligands-functionalized SBA-15:
Effect of 3-mercaptopropyltrimethoxysilane concentration on pore structure. Materials Letters. 2005; 59
(28):3611–5.
34. Zou B, Hu Y, Jiang L, Jia R, Huang H. Mesoporous material SBA-15 modified by amino acid ionic liquid
to immobilize lipase via ionic bonding and cross-linking method. Industrial & Engineering Chemistry
Research. 2013; 52(8):2844–51.
35. Kao H-M, Chang P-C, Wu J-D, Chiang AS, Lee C-H. Direct synthesis, characterization and solid-state
NMR spectroscopy of large-pore vinyl-functionalized cubic mesoporous silica FDU-12. Microporous
and mesoporous materials. 2006; 97(1–3):9–20.
36. Sarvi MN, Bee TB, Gooi CK, Woonton BW, Gee ML, O’Connor AJ. Development of functionalized
mesoporous silica for adsorption and separation of dairy proteins. Chemical Engineering Journal. 2014;
235:244–51.
37. Deka JR, Saikia D, Lai Y-S, Tsai C-H, Chang W-C, Kao H-M. Roles of nanostructures and carboxylic
acid functionalization of ordered cubic mesoporous silicas in lysozyme immobilization. Microporousand
Mesoporous Materials. 2015; 213:150–60.
38. Hodgkins RP, Garcia-Bennett AE, Wright PA. Structure and morphology of propylthiol-functionalised
mesoporous silicas templated by non-ionic triblock copolymers. Microporous and mesoporous materi-
als. 2005; 79(1–3):241–52.
39. Cui H-Z, Li Y-L, Liu S, Zhang J-F, Zhou Q, Zhong R, et al. Novel Pb (II) ion-imprinted materials based
on bis-pyrazolyl functionalized mesoporous silica for the selective removal of Pb (II) in water samples.
Microporous and Mesoporous Materials. 2017; 241:165–77.
40. Molla-Abbasi P, Ghaffarian SR, Danesh E. Porous carbon nanotube/PMMA conductive composites as
a sensitive layer in vapor sensors. Smart materials and structures. 2011; 20(10):105012.
41. Moller K, Bein T, Fischer RX. Entrapment of PMMA polymer strands in micro-and mesoporous materi-
als. Chemistry of materials. 1998; 10(7):1841–52.
PLOS ONE
Synthesis of nanoporous materials for adsorption
PLOS ONE | https://doi.org/10.1371/journal.pone.0245583 January 22, 2021 15 / 16
42. Beecroft LL, Ober CK. Nanocomposite materials for optical applications. Chemistry of materials. 1997;
9(6):1302–17.
43. Meng Q, Du P, Wang B, Duan A, Xu C, Zhao Z, et al. Synthesis of zirconium modified FDU-12 by differ-
ent methods and its application in dibenzothiophene hydrodesulfurization. RSC advances. 2018; 8
(48):27565–73.
44. Dinari M, Mohammadnezhad G, Soltani R. Fabrication of poly (methyl methacrylate)/silica KIT-6 nano-
composites via in situ polymerization approach and their application for removal of Cu 2+ from aqueous
solution. RSC advances. 2016; 6(14):11419–29.
45. Patel JP, Xiang ZG, Hsu SL, Schoch AB, Carleen SA, Matsumoto D. Path to achieving molecular dis-
persion in a dense reactive mixture. Journal of Polymer Science Part B: Polymer Physics. 2015; 53
(21):1519–26.
46. Patel JP, Deshmukh S, Zhao C, Wamuo O, Hsu SL, Schoch AB, et al. An analysis of the role of nonre-
active plasticizers in the crosslinking reactions of a rigid resin. Journal of Polymer Science Part B: Poly-
mer Physics. 2017; 55(2):206–13.
47. Patel JP, Xiang ZG, Hsu SL, Schoch AB, Carleen SA, Matsumoto D. Characterization of the crosslink-
ing reaction in high performance adhesives. International Journal of Adhesion and Adhesives. 2017;
78:256–62.
48. Liu Q, Dong H. In-situ Immobilizing Ni Nanoparticles to FDU-12 via Trehalose with Fine Size and Loca-
tion Control for CO2 Methanation. ACS Sustainable Chemistry & Engineering. 2020.
49. Huang L, Yan X, Kruk M. Synthesis of ultralarge-pore FDU-12 silica with face-centered cubic structure.
Langmuir. 2010; 26(18):14871–8. https://doi.org/10.1021/la102228u PMID: 20726611
50. Lawrence G, Anand C, Strounina E, Vinu A. Biomolecule Encapsulation Over Mesoporous Silica with
Ultra-Large Tuneable Porous Structure Prepared by High Temperature Microwave Process. Science of
Advanced Materials. 2014; 6(7):1481–8.
51. Nyairo WN, Eker YR, Kowenje C, Akin I, Bingol H, Tor A, et al. Efficient adsorption of lead (II) and cop-
per (II) from aqueous phase using oxidized multiwalled carbon nanotubes/polypyrrole composite. Sepa-
ration Science and Technology. 2018; 53(10):1498–510.
52. Liu Y, Liu Z, Gao J, Dai J, Han J, Wang Y, et al. Selective adsorption behavior of Pb (II) by mesoporous
silica SBA-15-supported Pb (II)-imprinted polymer based on surface molecularly imprinting technique.
Journal of hazardous materials. 2011; 186(1):197–205. https://doi.org/10.1016/j.jhazmat.2010.10.105
PMID: 21109351
53. Zulfiqar M, Lee SY, Mafize AA, Kahar NAMA, Johari K, Rabat NE. Efficient Removal of Pb (II) from
Aqueous Solutions by Using Oil Palm Bio-Waste/MWCNTs Reinforced PVA Hydrogel Composites:
Kinetic, Isotherm and Thermodynamic Modeling. Polymers. 2020; 12(2):430. https://doi.org/10.3390/
polym12020430 PMID: 32059376
54. Badruddoza AZM, Shawon ZBZ, Tay WJD, Hidajat K, Uddin MS. Fe3O4/cyclodextrin polymer nano-
composites for selective heavy metals removal from industrial wastewater. Carbohydrate polymers.
2013; 91(1):322–32. https://doi.org/10.1016/j.carbpol.2012.08.030 PMID: 23044139
PLOS ONE
Synthesis of nanoporous materials for adsorption
PLOS ONE | https://doi.org/10.1371/journal.pone.0245583 January 22, 2021 16 / 16
... Silica gel also shows good selectivity, swelling resistance and can be reused [16]. Thus, silica was modified with chelating agents to enhance adsorption performance for azo dyes [17], heavy metals [18,19], pesticides [20], and polycyclic aromatic hydrocarbons [21]. An extensive literature search found no work related to mono-amine modified silica adsorbent (MAMS) at different particle sizes in removing sulfonated aromatic amines from their aqueous solutions. ...
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Polyvinyl alcohol (PVA) hydrogel are still restricted for some applications because their lower mechanical strength and thermal stability. The PVA-based composites are drawing attention for the removal of heavy metals based on their specific functionality in adsorption process. The main objective of this work is to synthesize oil palm bio-waste (OPB)/multiwalled carbon nanotubes (MWCNTs) reinforced PVA hydrogels in the presence of N,N'-methylenebisacrylamide (NMBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator via simple in-situ polymerization technique. The as-prepared reinforced nanocomposites were characterized by FESEM, BET surface area, differential scanning calorimetry (DSC), TGA and FTIR analysis. The possible influence of OPB and MWCNTs on the tensile strength, elongation at break and elastic modulus of the samples were investigated. It was found that reinforced nanocomposites exhibited enhanced mechanical properties as compared to non-reinforced material. The evaluation of reinforced nanocomposites was tested by the removal of Pb(II) aqueous solutions in a batch adsorption system. The pseudo-second-order kinetic model was used to illustrate the adsorption kinetic results and Langmuir isotherm was more suitable to fit the equilibrium results providing maximum adsorption capacities. The evaluation of thermodynamic parameters describes the spontaneous, endothermic and chemisorption adsorption process while activation energy reveals the physical adsorption mechanism. Therefore, the coordination effects among OPB, MWCNTs and PVA polymer hydrogels can produce a promising adsorbent material for wastewater treatment applications.
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A facile and one‐pot strategy for the preparation of novel diamino‐functionalized hollow siliceous spheres (DAF‐HSS) is suggested. FE‐SEM images of DAF‐HSS showed a monodispersed hollow sphere morphology. Also, TEM images revealed that the DAF‐HSS has a porous structure with parallel semi‐long‐range channels. DAF‐HSS material was used as an adsorbent for the removal of hazardous monocationic dyes in aqueous solution. Neutral red (NR) and crystal violet (CV) were selected as model compounds. Isotherm and kinetic studies were carried out and their different linear forms were used and compared. The equilibrium data fitted better with the Langmuir model and the maximum adsorption capacity of the DAF‐HSS at 298 K was calculated to be ~222 and ~185 mg g–1 toward NR and CV, respectively.
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Rare earth elements are widely used in chemical engineering, the nuclear industry, metallurgy, medicine, electronics, and computer technology because of their unique properties. To fulfil ever increasing demands for these elements, recycling of rare-earth-element-containing products as well as their recovery from wastewater is quite important. In order to recover rare earth elements from wastewater, their adsorption from low-concentration aqueous solutions, by using nanomaterials, is investigated due to technological simplicity and high efficiency. This paper is a review of the state-of-the-art adsorption technologies of rare earth elements from diluted aqueous solutions by using various nanomaterials. Furthermore, desorption and reusability of rare earth metals and nanomaterials are discussed. On the basis of this review it can be concluded that laboratory testing indicates promising adsorption capacities, which depend significantly on nanomaterial type and adsorption conditions. The adsorption process, which mostly follows the Langmuir, Freundlich, Sips, and Temkin isotherms, is typically endothermic and spontaneous. Furthermore, pseudo-second order, pseudo-first order, and intra-particle diffusion models are the best models to describe the kinetics of adsorption. The dominant adsorption mechanisms are surface complexation and ion exchange. More investigation, however, will be required in order to synthesize appropriate, environmentally friendly, and efficient nanomaterials for adsorption of rare earth elements from real wastewater.
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A key challenge in adsorption process of toxic organic and inorganic species is the design and development of adsorbent materials bearing an abundance of accessible adsorption sites with high affinity to achieve both fast adsorption kinetics and elevated adsorption capacity for toxic contaminants. Herein, a novel anion-exchange adsorbent based on fibrous silica nanospheres KCC-1 was synthesized by a facile hydrothermal-assisted post-grafting modification of KCC-1 with 1-methyl-3- (triethoxysilylpropyl)imidazolium chloride for the first time. Silica fibers with micro-mesoporous structure display the proper combination of features to serve as a potential scaffold for decorating adsorption sites to create desired ion-exchange adsorbent. The obtained N-methylimidazolium-functionalized KCC-1 (MI-Cl-KCC-1) with fibrous nanosphere morphology showed a high surface area (∼241 m2 g-1) and high pore volume (0.81 m2 g-1). The adsorption behaviors of toxic hexavalent chromium from aqueous media by the MI-Cl-KCC-1 were systematically studied using the batch method. The adsorption rate was relatively fast, and MI-Cl-KCC-1 possesses a high capacity for the adsorption of Cr(VI). The maximum Cr(VI) adsorption was obtained at pH 3.0-4.0. Different non-linear isotherm equations were tested for choosing an appropriate adorption isotherm behavior, and the adsorption data for MI-Cl-KCC-1 were consistent with the Langmuir model with a maximum adsorption capacity of 428 ± 8 mg g-1.