Highly efficient removal of paraquat pesticide from aqueous solutions using a novel nano Kaolin modified with sulfuric acid via host–guest interactions

Article abstract of DOI:10.1007/s10847-019-00973-z

Contamination of wastewaters with pesticides has significant risk for environmental water. In spite of the rule of Europ, paraquat is used extensively as an herbicide in the all around the world and it is likely to be released into drinking water. Therefore the elimination of it from water is very important. In this paper a new sulfuric acid modified nano kaolin sorbent was synthesized with a simple and low cost method. Thereafter it was applied for removing of paraquat and the experimental conditions such as concentration of herbicide, dose of sorbent and pH of solution were optimized. The results showed the unmodified Kaolin wasn’t able to remove the paraquat efficiently. But with the proposed modified nano Kaolin removal percent reach to 98% in a short time 60 min. Also the results showed this system obeys from Frendluich adsorption isotherm.

Full text of DOI:10.1007/s10847-019-00973-z

Journal of Inclusion Phenomena and Macrocyclic Chemistry
https://doi.org/10.1007/s10847-019-00973-z
ORIGINAL ARTICLE
Highly efcient removal oꢀ paraquat pesticide ꢀrom aqueous solutions
using a novel nano Kaolin modiꢁed with sulꢀuric acid via host–guest
interactions
Roya Mohammadzadeh Kakhki1 · Azam Karimian · Masoud Saadati Rad
1
1
Received: 3 August 2019 / Accepted: 31 December 2019
©
Springer Nature B.V. 2020
Abstract
Contamination of wastewaters with pesticides has signiꢀcant risk for environmental water. In spite of the rule of Europ,
paraquat is used extensively as an herbicide in the all around the world and it is likely to be released into drinking water.
Therefore the elimination of it from water is very important. In this paper a new sulfuric acid modiꢀed nano kaolin sorbent
was synthesized with a simple and low cost method. Thereafter it was applied for removing of paraquat and the experimen-
tal conditions such as concentration of herbicide, dose of sorbent and pH of solution were optimized. The results showed
the unmodiꢀed Kaolin wasn’t able to remove the paraquat eꢁciently. But with the proposed modiꢀed nano Kaolin removal
percent reach to 98% in a short time 60 min. Also the results showed this system obeys from Frendluich adsorption isotherm.
Keywords Sulfuric acid modiꢀed nano Kaolin · Adsorption · Paraquat · Adsorption isotherm
Introduction
Among the various methods that can be used in removal
of organic pollutaants, physical adsorption is a simple and
effective method for removal of wastewater pollutants
[8–10]. To date some sorbents such as activated carbon [11],
polymeric materials [12], silica [13], graphitic carbon nitride
[14] have been used for removing of paraquat from waters.
Natural based sorbents due to environmental friendly
and cost eꢂective materials are very interesting for this pur-
pose. One of the restrictions of the natural sorbents is the
blockage of micropores and diꢁculty of adsorbing of bulky
molecules on the surface of the sorbent [15–17]. Therefore,
some modiꢀcations can improve their performance. With
decreasing the size of sorbent due to higher eꢂective sur-
face the adsorbing, its sorption capability will be improved.
Nanosized materials due to their unique properties such as
high surface area, narrow pore size are suitable for removal
of pollutants [18, 19]. Also surface functional groups have
critical role in removal eꢁciency. To date various groups
have been grafted on the surface of sorbents [20].
Environmental pollutants is a big problem that aꢂects the
whole world. Therefore, it is important to manage the waste
waters of large-scale wastewater plants. Paraquat (1,1-dime-
thyl-4,4-bipyridyl dichloride), also known as methyl violo-
gen, is one type of herbicides that is usually used for grass
and wood. Furthermore, it is used in nonagricultural ꢀelds
due to its interesting properties [1]. But this herbicide is
toxic (WHO Class II, moderately hazardous) and due to its
mobility can enter to the soil or ground waters. The permis-
sible amount of it is about 0.1 ppm with regard to eꢃuent
standards. Therefore, the ꢀnding an eꢁcient way for removal
of this pesticide is very necessary. The half-life of paraquat
in in the environment is from 16 months to 13 years [2].
Therefore, with regard of its concentration, it can aꢂect on
the life of animals and plants [3]. Moreover, it can have dan-
gerous eꢂects on the human health and cause some illnesses
[
4–7].
Kaolin with a 3-dimensional structure with cages of SiO
4
and AlO tetrahedral bounds and therefore, ring pores and
4
lots of binding sites can have some host–guest interactions
with various molecules. Intermolecular forces of host–guest
systems are strong interactions such as hydrogen bonding,
π interactions and etc. The positive guest molecules can fall
in to rings and make strong interactions with the guest [8].
*
Roya Mohammadzadeh Kakhki
Romohammadzadeh@gonabad.ac.ir
1
Department of Chemistry, Faculty of Sciences, University
of Gonabad, Gonabad, Iran
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1
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
With modiꢀcation the surface of Kaolin pores with sulfuric
acid, the hydrogen bonding interactions between host and
special guest molecules lead to more eꢂective interactions
and therefore encapsulated molecule keeps stronger in the
guest cages. To date, the investigations on the removal and
adsorption models of paraquat are very limited. Therefore, in
this work a nano Kaolin modiꢀed with sulfuric acid was syn-
thesized and characterized and was used as a new and high
eꢁcient natural based sorbent for elimination of paraquat
pesticide from water and the experimental conditions were
optimized. Results showed this new adsorbent is eꢁcient
and applicable for removal of paraquat pesticide from water.
OSO H
3
ClSO H, CH Cl
2
3
2
Kaolin
Kaolin
OSO H
3
rt, 90 min
OSO H
3
Scheme 1 Preparation of Kaolin-sulfuric acid
Results and discussion
Characterization of nano Kaolin–SO3H
Kaolin-sulfuric acid composite was prepared by a simple,
low cost and convenient method. Functionalization on the
surface of the nano Kaolin particles with sulfuric acid group
was achieved by chlorosulfonic acid in CH2Cl2 (Scheme 1).
The synthesized nano Kaolin-sulfuric acid composite was
characterized by FT-IR, pH test, FESEM and EDS analysis.
Experimental
Preparation of nano Kaolin–OSO3H
The nano Kaolin–OSO H particles were synthesized as fol-
3
lowing; ꢀrstly, 0.5 g of Kaolin was dispersed in dry CH Cl
2
2
(30 ml) by ultrasonic bath for 0.5 h. Subsequently, chlorosul-
FT‑IR analysis
fonic acid (0.3 ml) was added drop wise to solution of Kao-
lin over a period of 20 min at room temperature under stir-
ring. The mixture was further stirred for 2 h. The obtained
products were collected with centrifuge and washed, with
CH Cl and water and then dried under vacuum at 70 °C for
The FT-IR analysis of the Kaolin-sulfuric acid exhibits basic
−
1
characteristic peak at approximately 1217 and 1124 cm
which was attributed to the presence of S–O vibration that
were covered by a stronger absorbance of Si–O bond at 1087
2
2
−
1
−1
4
h to give nano Kaolin–OSO H as a light yellow powder
cm [21]. In addition, the Si–OH group peak at 900 cm
3
[
20].
was disappeared for Kaolin modiꢀed sulfuric acid nano-
particles [21]. The FT-IR spectrum of Kaolin-sulfuric acid
also shows a broad stretching absorption around 2800–3600
Sorption experiments
−
1
cm corresponding to OH group of sulfuric acid while
the stretching vibrations of the OH bonds of Kaolin was
In order to investigate on the sorption ability of Kaolin and
modiꢀed Kaolin, various doses of nanosorbent were added
to 40 ml of paraquat solution with diꢂerent concentrations.
After stirring, in distinct times some samples were taken
out and were centrifuged for removing the residual sorbent.
Then after they were determined at 268 nm with UV–Vis
spectrophotometry. Also the eꢂect on pH of solution and
doses the sorbent and concentration of paraquat were evalu-
ated with this procedure. Removal percent in each stage was
obtained by the following Eq:
−
1
appeared at 2450–2690 cm (Fig. 1).
pH test
For investigation on the grafting of sulfonyl group on the
surface of nano Kaolin, also a pH test was performed. For
this purpose about 0.5 g nano Kaolin modiꢀed sulfuric acid
was dispersed in 50 ml H O with an initial pH 6.6 and was
2
stirred for 24 h. Then the pH measured by pH meter and
showed due to acidic groups the pH of water was shifted to
acidic media about 2.35.
ꢀ
ꢁ
ꢂ × 100
%
Adsorption = C − C C
t
0
0
Furthermore, the adsorption isotherms were plotted and
Morphology and elemental analysis and oꢀ nano Kaolin
modiꢁed sulꢀuric acid
investigated. The paraquat loading on the sorbent at equilib-
rium (q ) was calculated by this equation:
e
ꢀ
ꢁ
FESEM images are shown in Fig. 2. As can be observed
in this Figure, the structure of the synthesized materials is
in nanoscale. Also EDS analysis shows that S atoms can
be loaded on the surface of the nano Kaolin (Fig. 3 and
Table 1).
q (mg∕g) = C (mg∕L) − C (mg∕L) × V(L)∕W(g)
e
0
e
where C and C is the initial and equilibrium concentrations
0
e
(
ppm) of paraquat and W (g) and V (L) are the weight of
sorbent and the volume of the solution respectively.
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 1 The FT-IR spectra of
a modiꢀed and b unmodiꢀed
nano Kaolin
Fig. 2 FESEM images of sulfu-
ric acid modiꢀed nano Kaolin
Adsorption study
Eꢂect oꢀ pH on the removal efciency
While with nano Kaolin the adsorption eꢁciency was
negligible, with modiꢀcation of the surface of nano Kao-
lin with sulfuric acid the removal percent was increased
signiꢀcantly. Therefore, the modiꢀed nano Kaolin was
selected for more investigations.
The solution pH has an important role in removing of
organic pollutants. Because this factor has signiꢀcant eꢂects
on the surface charge of the sorbent and the structure of the
sorbate molecules and therefore, interactions between sorb-
ent and sorbate change in various pHs. For evaluation of the
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 3 EDS analysis of modiꢀed nano Kaolin
Table 1 EDS data for unmodiꢀed and modiꢀed nano Kaolin
It is known that paraquat is stable in acidic media, but
unstable in alkaline solutions (Fig. 5). In our experiments,
due to instability of this compound in higher pHs [22], the
initial absorbance of paraquat was very low and therefore
the whole removal in basic media was obtained lower than
acidic conditions. In lower pHs due to interaction of hydro-
gen of sulfonyl group and paraquat the adsorption eꢁciency
is enhanced.
EDS
Kaolin
Modiꢀed nano Kaolin
Element
%Weight
%Atomic
%Weight
%Atomic
O
60.3
15.9
19.3
4.5
73.9
11.6
13.5
1.0
59.7
15.1
18.1
4.6
73.7
11.1
12.7
1.0
Al
Si
Zr
S
–
–
2.5
1.5
Inꢃuence oꢀ the dose oꢀ sorbent on removal efciency
For investigating the eꢂect of sorbent amount, some experi-
ments were done at room temperature with varying the sorb-
ent amount from 0.01 to 0.03 g. The obtained results show
that adsorption eꢁciency is increased with increasing of
the sorbent (Fig. 6). In higher doses the surface area of the
sorbent is increased that lead to enhance active adsorption
sites [8–10].
Eꢂect oꢀ initial dye concentration
As is shown in Fig. 7 with increasing the concentration of
dye, due to higher diꢂusion of dye molecules from bulk to
the surface of sorbent, the adsorption percent is increased.
But in much higher concentrations, the available sites are
saturated leading to decrease the removal percent [19].
Fig. 4 Eꢂect of pH on the removal eꢁciency of paraquat
inꢄuence of pH on the removal eꢁciency, paraquat solutions
with pH 2–10 were investigated (Fig. 4). Adjustment of pH
was performed by HCl and NaOH solutions.
Adsorption isotherms
In plotting of adsorption isotherms the relationship between
the loaded sorbate per mass unit of adsorbent, q (mg/g)
e
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 5 Degradation rout of para-
OH-
CH OH
3
quat in alkaline solutions
H C N
N CH3
3
N
N CH3
OH-
CH OH
3
N
N
and concentration of sorbate in equilibrium C (mg/L) was
e
investigated.
In this work, the adsorption system was analyzed by Fre-
undlich and Langmuir isotherm models. The data in Fig. 8
show this phenomenon obeys from Freundlich model. There-
fore, the adsorption is in a non-uniform distribution in a
heterogeneous surface [23].
The equations of Fig. 8a and b are as follow:
2
a
Freundlich equation Y=2.5052x+0.9778 (R =0.99)
2
b
Langmuir equation Y=0.2636x+0.0138 (R =0.043)
Fig. 6 Eꢂect of amount of sorbent on the removal eꢁciency
Therefore, with regard to Freundlich equation (ln q =
e
ln K + 1/n ln C ), the amount of n and K was obtained
F
e
f
0
.92 and 11.5 mg/g.
Conclusion
A nanoscale modiꢀed natural adsorbent as nano Kaolin
modiꢀed sulfuric acid was prepared and its performance
as an adsorbent was evaluated for removing of paraquat
as an herbicide. The conditions for reaching to high
eꢁciency were optimized. Under these conditions the
removal percent reached to approximately 98% in 60 min.
Furthermore, some investigations on the adsorption mod-
els showed this system obeys from Freundlich adsorption
isotherm.
Fig. 7 Eꢂect of concentration on the removal eꢁciency
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Journal of Inclusion Phenomena and Macrocyclic Chemistry
Fig. 8 a Freundlich and b Lang-
muir isotherms
new Cu modiꢀed nanoclinoptilolite. J. Incl. Phenom. Macrocycl.
Chem. 91, 133–139 (2018)
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