Dicationic ionic liquid grafted with silica-coated nano-Fe3O4 as a novel and efficient catalyst for the preparation of uracil-containing heterocycles

Article abstract of DOI:10.1007/s11164-020-04171-2

Abstract: Bisulfate-functionalized dicationic ionic liquid grafted with silica-coated nano-Fe₃O₄ (nano-[Fe₃O₄@SiO₂@BDIL] or NFSBDI) was synthesized as a novel nanomagnetic material, and its structure

Full text of DOI:10.1007/s11164-020-04171-2

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04171-2
Dicationic ionic liquid grafted with silica‑coated
nano‑Fe3O4 as a novel and efcient catalyst
for the preparation of uracil‑containing heterocycles
Abdolkarim Zare1 · Marziyeh Barzegar1
Received: 22 February 2020 / Accepted: 29 April 2020
© Springer Nature B.V. 2020
Abstract
Bisulfate-functionalized dicationic ionic liquid grafted with silica-coated nano-
Fe3O4 (nano-[Fe3O4@SiO2@BDIL] or NFSBDI) was synthesized as a novel nano-
magnetic material, and its structure was confrmed by EDS, FE-SEM, FT-IR, VSM,
XRD and TGA. Afterward, it was utilized as an efcient, magnetically recyclable
and dual-functional catalyst for the preparation of an important class of uracil-con-
taining heterocycles, namely pyrimido[4,5-b]quinolines. The one-pot multicompo-
nent reaction of dimedone, arylaldehydes and 6-amino-1,3-dimethyluracil in the
presence of NFSBDI under solvent-free conditions aforded pyrimido[4,5-b]quino-
lines in high yields and short times.
Graphical abstract
SiO2
O
Cl
O
O
N
NHMe2
O
O
Ar
O
N
Fe3O4
O
Si
N
HSO4
O
Me
Me
N
N
+
Solvent-free, 120°C
O
H2N
N
H
O
H
Ar
The reaction times = 15-30 min
Yields: 81-96%
O
Keywords Bisulfate-functionalized dicationic ionic liquid grafted with silica-coated
nano-Fe3O4 · Nano-[Fe3O4@SiO2@BDIL] (NFSBDI) · Nanomagnetic catalyst ·
Uracil-containing heterocycle · Pyrimido[4,5-b]quinoline
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04171-2) contains supplementary material, which is available to authorized users.
*
Abdolkarim Zare
abdolkarimzare@pnu.ac.ir; abdolkarimzare@yahoo.com
1
Department of Chemistry, Payame Noor University, PO Box 19395-3697, Tehran, Iran
Vol.:(0123456789)
1 3

A. Zare, M. Barzegar
Introduction
Ionic liquids (ILs) are of great signifcance in diferent scientifc and industrial felds
[1–8]; the benefts of these salts have been mentioned in the literature [1–8]. They
have been especially utilized as efcient homogeneous catalysts in organic synthesis
[5–8]. Heterogenization of ionic liquids through grafting with solid supports (nano
or bulk materials) can convert them to catalysts which have simultaneously the
advantages of ILs and heterogeneous catalysts. Handling, isolating, recycling and
reusing heterogeneous catalysts are easier than homogeneous ones [9–16].
Currently, preparation and application of nanomagnetic materials in scien-
tifc, medicinal and industrial felds are the theme of growing interest [17–27].
Nano-Fe3O4 is the best candidate to use as core for preparation of nanomagnetic
materials, since it has several unique characteristics, consisting of thermal and
chemical stability, non-toxicity, low cost, simple isolating and recycling, super-
paramagnetic property, large specifc surface area and capacity to graft with vari-
ous functional groups (for diferent uses) [21–27]. Nanomagnetic materials have
been applied as efcacious catalysts to promote organic transformations [21–27].
Solvent-free conditions and multicomponent reactions are practical, useful,
efcient and well-known techniques which have been used for production of a
wide range of organic, medical and complex materials; the advantages of these
techniques have been mentioned in the literature [28–33].
Nitrogen-bearing heterocycles have been found in the structures of many bioac-
tive and pharmaceutical compounds. Uracil, pyrimidine, quinoline and pyrimido-
quinoline are nitrogen-containing heterocycles which are present in the structures of
numerous biological compounds, e.g., anticancer [34, 35], antimicrobial [36], anti-
folate [37], anti-allergic [38], anti-infammatory [39], analgesic [39], DNA interca-
lating carrier [40], antiviral [41], antifungal [42] and antagonists [43] agents.
An important class of uracil-containing heterocycles is pyrimido[4,5-b]quinolines
which could synthesized through the one-pot multicomponent reaction of dimedone,
arylaldehydes and 6-amino-1,3-dimethyluracil. Some catalysts have been reported
for this transformation [44–52]; nevertheless, it has not been comprehensively stud-
ied in the literature. Hence, there is still an increasing interest to introduce new cata-
lysts for the reaction of dimedone, arylaldehydes and 6-amino-1,3-dimethyluracil.
Considering the benefts of grafting ILs with solid supports, nanomagnetic
materials, solvent-free conditions, multicomponent reactions and pyrimido[4,5-
b]quinolines, we have reported here synthesis of a novel nanomagnetic material,
namely bisulfate-functionalized dicationic ionic liquid grafted with silica-coated
nano-Fe3O4 (nano-[Fe3O4@SiO2@BDIL] or NFSBDI), and its characteriza-
tion using EDS (energy-dispersive X-ray spectroscopy), FE-SEM (feld emis-
sion scanning electron microscopy), FT-IR, VSM (vibrating sample magnetom-
etry), XRD (X-ray difraction), TG (thermal gravimetric) and DTG (diferential
thermal gravimetric). Then, we have reported the solvent-free preparation of
pyrimido[4,5-b]quinolines through the one-pot multicomponent reaction of dime-
done, arylaldehydes and 6-amino-1,3-dimethyluracil using NFSBDI as an ef-
cient, magnetically recyclable and dual-functional catalyst.
1 3

Dicationic ionic liquid grafted with silica-coated…
Experimental
Materials and instruments
The utilized starting materials and solvents were bought from Merck or Fluka
Chemical Companies. Observation of the reactions progress was done by thin-layer
chromatography (TLC) using silica gel SIL G/UV 254. For measurement of melt-
ing points, a Buchi B-545 instrument was utilized. FT-IR spectra were run using
1
a Shimadzu IR-60 apparatus. H and 13C NMR spectra were recorded by a Bruker
Avance DPX FT-NMR spectrometer. EDS was performed by a SAMx-EDS (France
system) device. A feld emission scanning electron microscope (model MIRA3TES-
CAN-XMU) was used to determine sizes and morphologies of the particles. VSM
analysis was carried out by a MDK (Meghnatis Daghigh Kavir) apparatus (Iran) at
room temperature. XRD analysis was performed using Cu Kα radiation (λ=1.5408,
model: X’Pert PRO MPD, PANalytical, the Netherlands). TGA was performed by
Bahr STA 504 (Germany) apparatus, at 25–600 °C, with temperature increase rate
of 10 °C min−1 in an argon atmosphere.
Preparation of nano‑[Fe3O4@SiO2@BDIL] (NFSBDI) (Scheme 1)
Nano-Fe3O4 was synthesized using the reported procedure [53, 54]. A mixture of
nano-Fe3O4 (0.75 g), Si(OEt)4 (2.25 mL), EtOH (60 ml), H2O (15 mL) and ammo-
nia (2.4 mL) was stirred and refuxed for 12 h to furnish intermediate I (which was
isolated from the reaction mixture by centrifuging and decanting). Afterward, a mix-
ture of (3-chloropropyl)trimethoxysilane (1.38 mL, 7.5 mmol) and intermediate I
in dry toluene (60 mL) was stirred under fowing nitrogen gas and refux conditions
for 12 h; the resulting mixture was centrifuged, decanted, washed by dry toluene
(twice) and Et2O and dried under vacuum at 90 ºC to give II [54, 55]. N,N,N′,N′-
tetramethylethylenediamine (1.12 mL, 7.5 mmol) was added to intermediate II in
toluene (45 mL), and the resulting mixture was stirred in refux conditions for 12 h.
1) HCl
2) NH3
H2O
SiO2
OH
OH
OH
(MeO)3Si
Toluene, reflux,12 h
Si(OEt)4
EtOH, H2O, NH3
Reflux,12 h
Cl
FeCl3.6H2O
Fe3O4
Na2SO3
+
Fe3O4
(I)
SiO2
Fe3O4
SiO2
O
Cl
N
O
NMe2
NMe2
Me2N
O
Si
Fe3O4
O
Si
Cl
Toluene, reflux, 12h
O
Me
Me
O
(III)
(II)
SiO2
O
O
O
Cl
N
H2SO4
Neat, 6h
NHMe2
HSO4
Fe3O4
Si
Me
Me
(NFSBDI)
Scheme 1 The synthesis of NFSBDI
1 3

A. Zare, M. Barzegar
The solid was separated from the solution by centrifuging and decanting, washed by
toluene and dried under vacuum at 90 °C to produce III. Finally, H2SO4 (0.42 mL,
7.5 mmol) was added gradually to III at room temperature and stirred for 5 h at the
same temperature and 1 h at 60 ºC; the residue was washed by distilled water and
dried under vacuum at 90 ºC to aford NFSBDI.
General procedure for the synthesis of pyrimido[4,5‑b]quinolines
A mixture of dimedone (0.140 g, 1 mmol), aldehyde (1 mmol), 6-amino-1,3-di-
methyluracil (0.155 g, 1 mmol) and NFSBDI (0.048 g) was stirred vigorously by a
small rod at 120 °C. When the reactants were consumed (as observed by TLC), the
reaction mixture was cooled to room temperature, ethyl acetate (40 mL) was added,
stirred and refuxed for 2 min, and the catalyst was isolated magnetically (washed by
ethyl acetate and dried). Ethyl acetate of the remained solution was evaporated, and
the residue was recrystallized from EtOH (95%) to give the pure product.
Note: Selected spectral data and original spectra of the synthesized pyrimido[4,5-
b]quinolines have been given in supplementary material.
Results and discussion
Characterization of the nanomagnetic material
The structure of nano-[Fe3O4@SiO2@BDIL] (NFSBDI) was verifed by EDS, FE-
SEM, FT-IR, VSM, XRD and TGA.
Iron, silicon, oxygen, carbon, nitrogen, sulfur and chlorine elements are present
in the structure of NFSBDI; the peaks pertaining to these elements were observed
in the EDS spectrum (Fig. 1), and no extra peak related to impurity was seen. Mor-
phologies and sizes of the particles were determined by FE-SEM (Fig. 1). As it can
be seen in Fig. 1, the particles had diferent crystalline and amorphous forms, and
their sizes were below 100 nm (i.e., NFSBDI is a nanomaterial); the interpretations
are in agreement with the literature [10].
The FT-IR spectrum of the novel bisulfate-functionalized dicationic ionic liquid
grafted with silica-coated nano-Fe3O4 is shown in Fig. 2, and the respective data
are summarized in Table 1. All expected peaks relevant to the bonds and functional
groups of NFSBDI were seen in the spectrum (Fig. 2 and Table 1); the obtained
data are in accordance with the literature [12, 54]. In another study to prove suc-
cessful functionalization of the ionic liquid on Fe3O4@SiO2, the FT-IR data of
nano-[Fe3O4@SiO2@BDIL] were compared with those reported for Fe3O4@SiO2
[56]. Two additional peaks (2925 and 2700–3734 cm−1) were observed in the FT-IR
spectrum of NFSBDI when compared with the Fe3O4@SiO2 spectrum; these addi-
tional peaks are related to the grafted ionic liquid. It should be mentioned that in the
FT-IR spectrum of Fe3O4@SiO2, there was a peak at about 3100–3680 cm−1 (cor-
responded to the OH groups on silica surface); however, in the NFSBDI spectrum, a
1 3

Dicationic ionic liquid grafted with silica-coated…
Fig. 1 The EDS spectrum and FE-SEM micrographs of NFSBDI
Fig. 2 The FT-IR spectrum of nano-[Fe3O4@SiO2@BDIL]
1 3

A. Zare, M. Barzegar
Table 1 The FT-IR results of
Peak (cm−1
)
Bond or functional group
NFSBDI
466
~648
590
Rocking of Si–O
Stretching of S–O
Fe–O
805
1089
1633
Symmetric stretching vibrations of Si–O–Si
Asymmetric stretching vibrations of Si–O–Si
Bending of O–H groups of H2O
adsorbed on silica surface
2925
Stretching vibration of C–H
2700–3734
Stretching of OH group of bisulfate
and OH groups on silica surface
peak at 2700–3734 cm−1 was observed (corresponded to the OH group of bisulfate
and the OH groups on silica surface).
VSM experiment was utilized for magnetic measurement of the nanomagnetic
catalyst (Fig. 3). Considering the VSM results, saturation magnetization of NFS-
BDI was 13.5 emu g−1. Saturation magnetization of the used nano-Fe3O4 for the
synthesis of NFSBDI has been reported 52 emu g−1 in the literature [54]. (We pre-
pared nano-Fe3O4 according to the reported procedure in the paper cited in reference
[54].) The silica layer coated on Fe3O4 nanoparticles and bisulfate-functionalized
dicationic ionic liquid grafted with the silica surface have caused the decreasing in
saturation magnetization of Fe3O4 nanoparticles. Nevertheless, proper magnetiza-
tion was observed for NFSBDI, and it could be readily separated from the reaction
mixture by an external magnet; Fig. 4 shows this subject.
The XRD diagram of NFSBDI showed two broad peaks (at 2θ ≈ 16.6°–32.0°
and 41.9°–45.9°) and some sharp difraction lines (at 2θ ≈ 9.9°, 11.4°, 18.9°,
21.3°, 22.0°, 25.2°, 26.5°, 28.8°, 30.5°, 32.2°, 35.9°, 37.6°, 38.6°, 39.4°, 46.4°,
Fig. 3 The VSM diagram of NFSBDI
1 3

Dicationic ionic liquid grafted with silica-coated…
Fig. 4 The images of an aque-
ous solution of NFSBDI before
(a) and after (b) applying
magnetic feld
47.9°, 52.5°, 54.2°, 57.5°, 59.5°, 61.1°, 63.2°, 67.6°, 71.9° and 74.8°) (Fig. 5).
The observed peak at 16.6°–32.0° belongs to SiO2 [10, 12], and the peaks
appeared at 30.5°, 35.9°, 46.4°, 57.5°, 63.2°, 71.9° and 74.8° are related to Fe3O4
[54]. The other peaks can be attributed to the grafted ionic liquid with silica-
coated nano-Fe3O4. According to the XRD diagram, the nanoparticles were in
amorphous and crystalline forms (the literature verifed this conclusion [10, 12]);
this topic was also observed in the FE-SEM micrographs (Fig. 1).
Fig. 5 The XRD diagram of the catalyst
1 3

A. Zare, M. Barzegar
For studying thermal stability of the nanomaterial, TG and DTG were used
(Fig. 6). According to the obtained curves, weight losses of NFSBDI have occurred
in two stages. The weight loss below 180 °C can be relevant to vaporization
of the absorbed solvents (or water) on the silica surface. The second weight loss
(180–600 °C) can be pertinent to decomposing the bisulfate-functionalized dica-
tionic ionic liquid grafted with silica-coated nano-Fe3O4 (organic part of the cata-
lyst) and the condensation of the silanol groups. These discussions were verifed by
the literature [10].
Catalytic performance of NFSBDI for the preparation of pyrimido[4,5‑b]quinolines
Catalytic performance of the novel bisulfate-functionalized dicationic ionic liquid
grafted with silica-coated nano-Fe3O4 (nano-[Fe3O4@SiO2@BDIL] or NFSBDI)
was examined for the synthesis of an important kind of uracil-containing het-
erocycles, i.e., pyrimido[4,5-b]quinolines. For this purpose, the reaction of dime-
done (1 mmol), 4-chlorobenzaldehyde (1 mmol) and 6-amino-1,3-dimethyluracil
(1 mmol) was chosen as a model (Scheme 2), and infuence of the nanocatalyst
amount and temperature on it was studied; the results are summed up in Table 2.
As Table 2 illustrates, the best catalyst amount and temperature were 0.048 g and
120 °C, correspondingly (Table 2, entry 2). Increasing the amount of NFSBDI and
the temperature did not improve the results (Table 2, entries 3 and 5).
After successful application of NFSBDI to promote the model reaction, to assess
its efectiveness and scope for the production of diverse derivatives of pyrimido[4,5-
b]quinolines, dimedone was reacted with miscellaneous arylaldehydes and 6-amino-
1,3-dimethyluracil; the attained reaction times and yields are shown in Table 3.
As Table 3 indicates, all aldehydes, consisting of benzaldehyde and arylaldehydes
Fig. 6 The TG and DTG curves of NFSBDI
1 3

Dicationic ionic liquid grafted with silica-coated…
Cl
CHO
O
O
N
O
O
O
N
N
N
NFSBDI
Different conditions
+
+
O
N
H
O
H2N
Cl
Scheme 2 The model reaction to obtain optimal conditions
Table 2 Infuence of the catalyst
Entry
The catalyst
amount (g)
Temp. (ºC)
Time (min)
Yield (%)
amount and temperature on the
reaction of dimedone (1 mmol)
with 4-chlorobenzaldehyde
(1 mmol) and 6-amino-1,3-
dimethyluracil (1 mmol)
1
2
3
4
5
0.040
0.048
0.060
0.048
0.048
120
120
120
110
125
40
15
15
30
15
91
96a
96a
85
96a
aThe reaction was completed
Table 3 The preparation of pyrimido[4,5-b]quinolines using NFSBDI
O
Ar
O
N
O
O
O
N
N
N
NFSBDI
Solvent-free, 120 °C
+
+
O
Ar
H
N
H
O
H2N
O
Compd. No
Ar
Time (min)
Yielda (%)
M.p. (°C), Found (reported)
1
C6H5
15
15
15
15
15
15
15
30
15
15
30
94
92
90
88
96
85
91
87
94
93
81
271–273 (267–270) [52]
280–282 (281–283) [50]
234–236 (227–230) [50]
324–326 (>300) [50]
293–295 (292–294) [47]
319–321 (>300) [47]
296–297 (this work)
289–291 (287–290) [50]
304–306 (>300) [45]
307–309 (>300) [47]
310–312 (307–310) [46]
2
3-BrC6H4
4-BrC6H4
2-ClC6H4
4-ClC6H4
3
4
5
6
2,4-Cl2C6H3
7
4-Cl,3-O2NC6H3
3-O2NC6H4
4-MeOC6H4
4-MeC6H4
8
9
10
11
4-HOC6H4
aIsolated yield
1 3

A. Zare, M. Barzegar
having halogen, electron-attracting and electron-releasing substituents on ortho-,
meta- or para-positions, aforded the corresponding pyrimido[4,5-b]quinolines
in high yields and short times. Having the acquired results in mind, NFSBDI
was a highly efcacious and general catalyst for the synthesis of pyrimido[4,5-b]
quinolines.
NFSBDI can be a dual-functional catalyst, because its anion (bisulfate) pos-
sess one acidic (hydrogen) and one weak basic (negative oxygen) sites; so, it can
be particularly applied for performing reactions which need acidic and basic cata-
lysts simultaneously, e.g., the synthesis of pyrimido[4,5-b]quinolines. These roles of
NFSBDI are obviously displayed in the mechanism (Scheme 3). As it can be seen in
Scheme 3, the acidic hydrogen of bisulfate has activated the carbonyl groups in steps
1, 3 and 5 (for accepting nucleophilic attacks) and catalyzed these steps; further-
more, it has catalyzed steps 2 and 6 through assisting removal of H2O molecule. In
the other hand, the basic site of bisulfate has activated the nucleophiles to catalyze
steps 1, 3 and 5; it also helps remove H2O in step 6. NFSBDI has also catalyzed tau-
tomerization (steps 4 and 7). The proposed mechanism is in accordance with the lit-
erature [46, 49]. Dual functionality of the catalysts containing acidic and basic sites
and the roles of the sites have been mentioned in the literature [8, 57].
To study recyclability of NFSBDI, the reaction of dimedone, 4-chlorobenzalde-
hyde and 6-amino-1,3-dimethyluracil was carried out, and the catalyst was recycled
according to the mentioned procedure in the experimental section. NFSBDI was suc-
cessfully reused for three times; nonetheless, the reaction times slightly increased,
and the yields slightly decreased during reusing (Fig. 7). The slight deactivation can
be attributed to wasting the catalyst during the recycling.
In another study, the reaction conditions and the results of NFSBDI for the syn-
thesis of products 1, 5 and 9 were compared with those of some reported catalysts
(Table 4). As the data of Table 3 illustrate, NFSBDI was superior than the other cat-
alysts in terms of the reaction time and yield. Besides, our synthesis was performed
in solvent-free conditions.
Conclusions
In summary, we have introduced a novel bisulfate-functionalized dicationic ionic
liquid grafted with silica-coated nano-Fe3O4 as a nanomagnetic catalyst for the
production of pyrimido[4,5-b]quinoline derivatives. The advantages of this work
include efcacy and wide scope of the catalyst, the preparation of the products in
high yields and short times, utilization of a few amount of the catalyst in the reac-
tion, application of solvent-free and multicomponent reaction techniques, magnetic
recyclability of the catalyst, no need to column chromatography for purifying the
products, easy purifcation of the products by recrystallization and good agreement
with green chemistry principles.
1 3

Dicationic ionic liquid grafted with silica-coated…
O
NHMe2
H
HO
S
O
O
O
O
NFSBDI
O
OH
O
O
Ar
O
O
O
NFSBDI
Ar
NFSBDI
H
Step 1
Ar
H
H
O
S
Me2HN
O
O
O
H
O
O
H
O
O
O
O
H
S
Me2HN
O
Ar
Ar
NFSBDI
_
H2O
O
O
Step 2
NHMe2
HO
O
O
H
S
N
N
O
O
O
H
O
O
O
O
O
Ar
Ar
N
N
N
Ar
NFSBDI
Tautomerization
Step 4
O
O
Step 3
H
N
N
O
O
S
H2N
HN
O
OH
N
O
O
NHMe2
O
O
O
O
Ar
O
Ar
N
NFSBDI
NFSBDI
O
Step 5
N
N
H
N
O
HN
O
O
O
O
H
O
H
S
H
O
O
NHMe2
O
NHMe2
S
HO
O
O
Ar
O
N
O
Ar
O
N
N
O
O
N
NFSBDI
_
H2O
Step 6
Tautomerization
Step 7
N
H
N
O
O
H
H
O
NHMe2
O
S
H
S
Me2HN
O
O
HO
O
O
O
Ar
O
N
SiO2
Fe3O4
O
O
O
Cl
N
NHMe2
HSO4
NFSBDI
=
NHMe2
=
Si
N
N
H
O
Me
Me
Pyrimido[4,5-b]quinoline
Scheme 3 The proposed reaction mechanism
1 3

A. Zare, M. Barzegar
Fig. 7 The results of recyclability of NFSBDI
Table 4 Comparing the reaction conditions and the results of NFSBDI with those of the reported cata-
lysts for the synthesis of products 1, 5 and 9
Catalyst
Conditions
Time (min) of
Yield (%) of
References
product 1/5/9
product 1/5/9
NFSBDI
p-Toluenesulfonic acid
InCl3
SBA-15/PrN(CH2PO3H2)2
Catalyst-free
Nano-Fe3O4@SiO2–SO3H
Solvent-free, 120 °C
H2O, 90 °C
H2O, refux
Solvent-free, 100 °C
[bmim]Brb, 95 °C
H2O, 70 °C
H2O, 75 °C
EtOH, 70 °C
Solvent-free, 125 °C
H2O, refux
15/15/15
180/150/180
–a/60/60
94/96/94
85/89/84
–a/91/89
89/85/–a
–a/90/95
92/92/86
90/95/93
–a/91/85
93/92/95
89/91/87
This work
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
20/15/–a
–a/210/210
30/25/40
30/25/45
–a/15/25
40/40/30
120/120/120
c
[H2-DABCO][ClO4]2
d
[dsim]HSO4
[TSSECM]e
Fe3O4 NPs-cellf
[52]
aIn the work, this product has not been synthesized
b1-n-Butyl-3-methylimidazolium bromide
c1,4-Diazabicyclo[2.2.2]octane-1,4-diium perchlorate
d1,3-Disulfonic acid imidazolium hydrogen sulfate
eN,N,N’,N’-tetramethyl-N-(silica-n-propyl)-N’-sulfonic acid-ethylenediaminium chloride/mesylate
fFe3O4 nanoparticles supported on cellulose
Acknowledgements The authors acknowledge Research Council of Payame Noor University for the sup-
port of this work.
1 3

Dicationic ionic liquid grafted with silica-coated…
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