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.
1
3