Nonaqueous lyotropic ionic liquid crystals: Preparation, characterization, and application in extraction

Article abstract of DOI:10.1002/chem.201500306

A class of new ionic liquid (IL)-based nonaqueous lyotropic liquid crystals (LLCs) and the development of an efficient IL extraction process based on LC chemistry are reported. The nonaqueous LLCs feature extraordinarily high extraction capacity, excellent separation selectivity, easy recovery, and biocompatibility. This work also demonstrates that the introduction of self-assembled anisotropic nanostructures into an IL system is an efficient way to overcome the intrinsically strong polarity of ILs and enhances the molecular recognition ability of ILs. The distribution coefficients of IL-based LLCs for organic compounds with H-bond donors reached unprecedented values of 50-60 at very high feed concentrations (>100 mg mL^-1), which are 800-1000 times greater than those of common ILs as well as traditional organic and polymer extractants. The IL-based nonaqueous LLCs combining the unique properties of ILs and LCs open a new avenue for the development of high-performance extraction methods. Putting order into ionic liquids: Ionic liquid (IL)-based nonaqueous lyotropic liquid crystals (LLCs) exhibit extraordinarily high extraction capacity, excellent separation selectivity, and easy recycling. The introduction of self-assembled nanostructures into IL systems is an efficient way to enhance the recognition ability for H-bond donor molecules. The IL-based LLCs successfully combine the unique properties of ILs and LCs and provide a new platform for high-performance separation.

Full text of DOI:10.1002/chem.201500306

DOI: 10.1002/chem.201500306
Full Paper
&
Ionic Liquids
Nonaqueous Lyotropic Ionic Liquid Crystals: Preparation,
Characterization, and Application in Extraction
Xianxian Liu, Qiwei Yang, Zongbi Bao, Baogen Su, Zhiguo Zhang, Qilong Ren, Yiwen Yang,
[a]
and Huabin Xing*
Abstract: A class of new ionic liquid (IL)-based nonaqueous
lyotropic liquid crystals (LLCs) and the development of an ef-
ficient IL extraction process based on LC chemistry are re-
ported. The nonaqueous LLCs feature extraordinarily high
extraction capacity, excellent separation selectivity, easy re-
covery, and biocompatibility. This work also demonstrates
that the introduction of self-assembled anisotropic nano-
structures into an IL system is an efficient way to overcome
the intrinsically strong polarity of ILs and enhances the mo-
lecular recognition ability of ILs. The distribution coefficients
of IL-based LLCs for organic compounds with H-bond
donors reached unprecedented values of 50–60 at very high
À1
feed concentrations (>100 mgmL ), which are 800–1000
times greater than those of common ILs as well as tradition-
al organic and polymer extractants. The IL-based nonaqu-
eous LLCs combining the unique properties of ILs and LCs
open a new avenue for the development of high-per-
formance extraction methods.
[
8]
Introduction
have investigated functional ILs with tailored structures, IL
[
9]
mixtures with tunable physicochemical properties, deep eu-
[
5c,10]
[11]
The development of environmentally benign and energy-effi-
cient separation methods is vitally important for a sustainable
society. Recently, considerable attention has been paid to ionic
liquid (IL)-mediated extractive separation methods, including
tectic solvents,
and IL-based hybrid materials to enhance
the affinity of IL extractants for organic compounds. Some
progress has been made, but it is still a great challenge to
design industrially attractive IL-based extractants with high ca-
pacity for H-bond donor solutes, which is vitally important for
the production of clean energy and high-purity chemicals.
Herein, we report a class of new nonaqueous lyotropic
liquid crystals (LLCs) with anionic surfactant carboxylate ILs
(ASC-ILs) and the development of an IL-based LLC extraction
process. The IL-based nonaqueous LLCs form self-assembled
anisotropic nanostructures consisting of an ordered H-bond ac-
ceptor interface and a nonpolar domain (Figure 1c), which
overcome the strong isotropic polarity of common ILs, signifi-
cantly enhance the molecular recognition ability of ILs for H-
bond donor solutes, and thus result in extraordinarily high ex-
traction capacity and excellent separation selectivity. The distri-
bution coefficients of specific H-bond solutes reached unprece-
dented values of 50–60 at very high feed concentrations of
[
1]
[2]
liquid–liquid extraction, microextraction, and membrane ex-
[
3]
traction, because of their lower environmental impact. IL ex-
traction has been widely used in the separation and purifica-
tion of H-bond donor compounds, for example, the deacidifi-
[
4]
cation, desulfurization, and denitrification of fuel oils and the
[
5]
enrichment of bioactive compounds and biomacromole-
[
6]
cules from biodiesels and other biomass. ILs generally show
improved selectivity compared with traditional organic extrac-
tants because of their multiple solvation interactions and en-
[
7]
hanced H-bond basicity and H-bonding interactions.
However, a key drawback to IL-mediated extraction process-
es is the relatively low extraction capacity for organic com-
[
1d,4c,5,8b]
[7a,d]
pounds,
due to the intrinsically strong polarity of ILs
resulting from their charged structures, which seriously limits
their application. This problem is made even worse by the fact
that, in some cases, the polarity of ILs must be high enough to
form low-miscibility biphasic extraction systems with nonpolar
À1
more than 100 mgmL , which are 800–1000 times greater
than those of common IL, traditional organic, and polymer ex-
tractants. In addition, this LLC extraction also has the merit of
easy recovery of solutes through breaking the self-organized
LLC nanostructures. To our knowledge, this is the first example
of an IL-based nonaqueous LLC extraction process.
[4,5b,9b]
solvents.
To overcome this drawback, numerous groups
[a] X. Liu, Dr. Q. Yang, Dr. Z. Bao, Dr. B. Su, Dr. Z. Zhang, Prof. Q. Ren,
IL-based liquid crystals (LCs) can be regarded as materials
that combine the unique properties of ILs and LCs. They have
self-assembled anisotropic nanostructures, wide electrochemi-
Prof. Y. Yang, Prof. H. Xing
Key Laboratory of Biomass Chemical Engineering of Ministry of Education
College of Chemical and Biological Engineering
Zhejiang University
Hangzhou 310027 (P. R. China)
E-mail: xinghb@zju.edu.cn
[12]
cal windows, and tunable structures and properties. Due to
these attributes, a number of IL-based LC systems including
[13]
thermotropic LCs, aqueous LLCs, and LLCs consisting of two
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500306.
[14]
different ILs were prepared and utilized as novel materials
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Figure 1. POM texture of a) [Ch][Lau]–DMSO LLC and b) [Ch][Lau]–DMF LLC.
The fraction of IL is 10 mol%; c) schematic illustration of IL-based nonaqu-
eous LLCs; d) hydrogen-bond basicity parameter b and e) dipolar/polarity
parameter p* of the mixture of IL and DMSO.
[
13a,b,14a]
for ion conductors with nano ion channels,
organized
and electrochemi-
However, nonaqueous LLCs with strong H-
[
12a]
[12,14e]
reaction media,
materials synthesis,
[
14d]
cal capacitors.
bond acceptor interfaces and their application in extraction
have not been explored. The absence of water in LLCs is cru-
cial for many extraction processes, because the extraction effi-
ciency of organic solutes can often be significantly reduced by
water due to their limited hydrophilicity. In this work, we pre-
pared a class of new nonaqueous LLCs and investigated their
separation performance for typical H-bond donor compounds.
Figure 2. Structures of ACS-ILs and the optical textures of different ASC-ILs
in the penetration experiments with different polar solvents at 303 K. A, B,
and C represent [Ch][Lau], [N2222][Lau], and [Emim][Lau], respectively. The
corresponding information for [P4444][Lau] is in Figure S1 in the Supporting
Information. 1, 2, 3, 4 represent methanol, DMSO, DMF and acetonitrile, re-
spectively. The scale bars represent 50 mm. The arrows indicate the direction
of IL concentration gradient from low concentration to high concentration.
dissolved in acetonitrile, DMSO, DMF, or methanol. Cross-
streaks (lamellar LC, Figures 2 and S1) were detected in [Ch]
[Lau]–DMF, [Ch][Lau]–acetonitrile and [OHemim][Lau]–metha-
nol mixtures. Nevertheless, no optical defects were detected
when the cations were changed to tetrabutylphosphonium
([P4444][Lau]; Figure S1) Thus, ASC-ILs with smaller organic cat-
ionic moieties are more likely to bring out LLC properties be-
cause smaller cations enhance the interaction between anion
and cation and weaken the electrostatic repulsion among
Results and Discussion
The ASC-ILs (Figure 2 and Scheme S1 in the Supporting Infor-
mation) were designed to form LLC nanostructures in a wide
range of polar solvents. Long-chain carboxylates were selected
as anions because of their high H-bond basicity, low polarity,
[
15]
and good biocompatibility.
The ASC-ILs were prepared by acid–base neutralization be-
[
15b]
tween fatty acids and ILs with hydroxide as anion in water.
The formation of nonaqueous LLCs was investigated through
[17]
anions, which stabilizes the aggregates.
In contrast, tradi-
[
14d,16]
solvent-penetration experiments:
the pure ASC-IL was set
tional anionic surfactants with metal cations, such as sodium
laurate and potassium laurate, did not easily form nonaqueous
LLCs due to their low solubility in polar organic solvents.
This type of new nonaqueous LLCs has strong H-bond ac-
ceptor interfaces provided by the ordered arrangement of car-
boxylate anions (Figure 1c). The Kamlet–Taft H-bond basicity
between a microscope slide and a coverslip, a drop of a sol-
vent, such as DMSO, DMF, acetonitrile, or methanol, was added
at the edge of the coverslip, and then the solvent penetrated
the IL and established a concentration gradient (Figure 2 and
Figure S1 in the Supporting Information). Carboxylate ILs with
anion carbon numbers greater than eight have self-aggrega-
tion properties and could form various nanostructures, such as
LCs and micelles, in polar solvents. The cationic species of the
ASC-ILs have crucial effects on the formation and types of LLC
phase. With laurate as anion, a fanlike texture indicating a typi-
cal hexagonal LC was found by polarized optical microscopy
[7a]
parameter b exceeded 1.0 when the molar concentration of
[Ch][Lau] was greater than 0.15 (Figure 1d). On the other hand,
the dipolar/polarity parameter p* of the mixture of ASC-IL and
polar solvent decreased quickly with increasing concentration
of IL due to formation of the nonpolar domain and the hydro-
phobic character of long-chain carboxylate anions (Figure 1e).
Furthermore, the choline-based ASC-ILs are more biocompat-
ible and have low toxicity compared with common imidazoli-
(
[
POM) when 2-hydroxyethyltrimethylammonium laurate ([Ch]
Lau]), 1-ethyl-3-methylimidazolium laurate ([Emim][Lau]), tet-
[15]
raethyl quaternary ammonium laurate ([N2222][Lau]), and 1-hy-
droxyethyl-3-methylimidazolium laurate ([OHemim][Lau]) were
um ILs, which is essential for the development of environ-
mentally benign separation methods.
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The separation performance of nonaqueous LLCs was inves-
tigated by batch extraction experiments with tocopherols as
typical solutes, which are the most important fat-soluble anti-
oxidants in biological systems. As shown in Figure 1a, the LLC
extractant [Ch][Lau]–DMSO showed extraordinary extraction ef-
ficiency for tocopherol compared to other extractants, includ-
with LLC extractant, whereas less than 6.6% d-tocopherol was
extracted with [Emim][OAc]–DMSO as extractant under the
same conditions. Other nonaqueous LLCs containing different
ASC-ILs and polar solvents also showed excellent extraction ca-
pacities for tocopherol (Figure 3c; Figure S2 and Table S1 in
the Supporting Information). Therefore, this class of novel non-
aqueous LLC extractants has made tremendous progress
toward better extraction capacity compared with existing ex-
tractants, as was highlighted by the unparalleled distribution
ing common ILs, organic solvents, and polymer extractants. At
À1
a feed concentration C of 5 mgmL , the distribution coeffi-
f
cient for d-tocopherol Dd-toc of [Ch][Lau]–DMSO was up to
49.52, which is 26 and 99 times larger than those of organic
coefficients obtained at very high C . This is of crucial signifi-
f
extractants DMF (1.88) and DMSO (0.50), and also significantly
larger than those of common IL-containing extractants without
LC structure, such as 1-ethyl-3-methylimidazolium acetate
cance for the development of industrially attractive extraction
technology, because the consumption of relatively expensive
ILs required for a certain task can be dramatically decreased by
the high capacity of LLCs.
(
[Emim][OAc])–DMSO (3.01) and [P4444][Lau]–DMSO (10.00). For
comparison, we also tested the separation performance of IL–
The new nonaqueous LLC extractants also showed excellent
extraction capacities for other H-bond donor compounds, such
as oleic acid (see the Supporting Information, Figure S3) and
naphthenic acid (see the Supporting Information, Figure S4),
which are typical solutes in the deacidification of fuel oils and
phenol (see the Supporting Information, Figure S5). The distri-
water mixtures. The Dd-toc values of [Ch][Lau]–water, [Bmim]
[
N(CN) ]–water, and [Emim][Ala]–water were all less than 0.02
2
À1
at a C value of 10 mgmL . We observed that D
increased
f
d-toc
with increasing alkyl chain length of the cation, but the value
was still less 0.5, which indicates that the absence of water in
extractants is crucial for d-tocopherol extraction.
bution coefficient of oleic acid in [Ch][Lau]–DMSO reached
À1
Furthermore, with increasing C , the D
with organic sol-
367.29 at a C value of 50 mgmL , which is much larger than
f
d-toc
f
vents or common ILs as extractants declined drastically (Fig-
values reported in the literature for ILs and polymer extractants
ure 3a), indicating poor capacities of these traditional extrac-
(see the Supporting Information, Table S2). The D
value
oleicacid
À1
À1
tants. For example, when C increased from 5 mgmL to
was as high as 136.20 at a C value of 200 mgmL , which is
f
f
À1
1
25 mgmL , the D
for [Emim][OAc]–DMSO and [P4444][Lau]–
thousands of times greater than those of [Bmim][N(CN)2],
poly(ethylene glycol) with an average molar mass of 200 (PEG
200), and [P4444][Lau]–DMSO (see the Supporting Information,
Figure S2 and Table S3). In the case of phenol, [Ch][Lau]–DMSO
showed superior extraction capacity (>2000) to the organic
extractant DMSO.
d-toc
DMSO dropped to 0.10 and 0.27, respectively. In contrast, no
decrease in Dd-toc was observed for the LLC extractant with in-
creasing C , and the D
values gradually increased and
f
d-toc
reached an unprecedented value of 58.89 at a very high C of
f
À1
1
25 mgmL , which is 841 times larger than that of [Emim]
[
OAc]–DMSO (0.07) and 981 times larger than that of [P4444
]
The excellent extraction capacity mainly depended on the
formation of self-organized anisotropic nanostructures and the
nature of the ASC-ILs. As shown in Figure 3b, a striking differ-
ence of the trend in the distribution coefficient with the in-
creasing IL concentration was found between common IL ex-
tractants and LLC extractants. In the common IL system [Ch]
[
Lau]–DMSO (0.06). These results indicate that 98.3% d-toco-
pherol could be separated from oil by a one-stage extraction
[
OAc]–DMSO, the Dd-toc value increases at first and then de-
creases sharply after passing through a maximum with increas-
ing concentration of IL, because the polarity of the extractant
increases with increasing concentration of IL, which disfavors
the extraction of organic solutes. In the [Ch][Lau]–DMSO LLC
system, Dd-toc steadily increases with increasing concentration
of IL. Furthermore, compared with Dd-toc of the [Ch][Lau]–
DMSO LLC system, Dd-toc for [P4444][Lau]–DMSO in the absence
of LLC is very low, although it has the same laurate anion and
higher lipophilicity, and this indicates that the LLC structure
plays a crucial role in the capacity. The Dd-toc value with [Ch]
[
Lau]–DMSO as extractant was also larger than that of [C mim]
12
[
Br]–DMSO (Figure 3a), which has a dodecyl chain in the cation
and a LLC structure (see the Supporting Information, Fig-
ure S6), and this indicates that anionic surfactivity is also a key
to the excellent performance of LLC extractants. Nonaqueous
Figure 3. a) Distribution coefficient of d-tocopherol Dd-toc in extractant–
hexane biphasic systems at different feed concentrations C . The molar frac-
f
tion of IL in the extractant was 0.1; b) Effect of the molar ratio of IL on Dd-toc
À1
at a C
tants at C
f
of 100 mgmL ; c) Dd-toc values for different IL-based LLCs as extrac-
[18]
LLCs also could be induced with nonionic surfactants, such
À1
f
=100 mgmL . LLC1: [Ch][Lau]–acetonitrile (10:90, molar), LLC2:
as polyoxyethylene alkyl ether, but these LLCs are not applica-
ble for extraction due to their high miscibility with nonpolar
solvents.
[
[
Ch][Myr]–DMSO (10:90, molar), LLC3: [Ch][Pal]–DMSO (10:90, molar), LLC4:
2222][Lau]–DMSO (50:50, molar), and LLC5: [Emim][Lau]–DMSO (40:60,
N
molar).
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The ASC-IL-based nonaqueous LLC extractants not only have
extraordinary capacity but also excellent selectivity for H-bond
solutes, which is a key parameter for practical applications. The
selectivity of d-tocopherol over methyl linoleate, a main com-
ponent of edible oils, reaches a very high value of 358.76 with
and microstructure of extraction phase. Figure 5a shows the IR
spectra of the [Ch][Lau]–DMSO–tocopherol system; the peak at
À1
3507 cm , which is assigned to the hydroxyl stretching of H-
bonded d-tocopherol, increases with increasing amount of
[Ch][Lau]–DMSO as extractant (Figure 4a). More importantly, al-
Figure 4. a) Selectivities of a) d-tocopherol versus methyl linoleate and b) d-
tocopherol versus a-tocopherol with [Ch][Lau]–DMSO (10:90, molar) LLC as
extractant; c) Structures of tocopherol homologues.
though the selectivity decreases with increasing C , its value
f
À1
still exceeds 131.15 at a C value of 125 mgmL , which is clear-
f
ly superior to the results with common ILs (e.g., the selectivity
À1
is 0.96 at a C value of 125 mgmL with [Emim][OAc]). For the
f
oil-deacidification process, surprisingly high selectivity for oleic
acid over triolein was obtained with [Ch][Lau]–DMSO as extrac-
tant (see the Supporting Information, Figure S7), and the distri-
bution coefficient reached 6350.66 at
a Cf value of
À1
100 mgmL . Similarly, the LLC extractant also showed excel-
lent selectivity for naphthenic acid (>1500) over octane, a typi-
cal component of gasoline (see the Supporting Information,
Figure S8). Therefore, the molecular recognition of these H-
bond donor solutes by the LLC extractant is highly specific and
exclusive, because their selectivities are greater than 250.
Interestingly, ASC-IL-based LLC extractants also show good
selectivity for the separation of bioactive homologues, which is
an important process for the production of high-purity drugs
but is very challenging because of their high structural similari-
ty. As shown in Figure 4b, the selectivity of d-tocopherol
Figure 5. a) IR spectra of the mixture of a-tocopherol and [Ch][Lau]–DMSO
extractant (XIL =0, 1, 10, 20, 40 mol%); the concentration of d-tocopherol
was 15 mm; b) XRD patterns of the [Ch][Lau]–DMSO extractants equilibrated
À1
with different feed concentrations of tocopherols; pink: 0 mgmL , green:
À1
À1
1
0 mgmL , blue: 100 mgmL ; c)–e) Transition of LC texture on addition of
tocopherol. f) Schematic illustration of the extraction mechanism of
nonaqueous LLCs.
[Ch][Lau], and thus indicates the presence of an H-bond inter-
action between tocopherol and [Ch][Lau]. Figure 5b–5e show
the XRD patterns and POM spectra of the [Ch][Lau]–DMSO
phase with and without tocopherol. After dissolution of toco-
pherol, the optical-defect texture of the [Ch][Lau]–DMSO phase
transformed from fanlike (Figure 5c) to a cross-shaped texture
(Figure 5e), which indicates that the LC structure partially
changed from the hexagonal phase to the lamellar phase. The
transition of the LC structures of the other four LLC extractants
are shown in Figure S9 in the Supporting Information. The
pink curve in Figure 5b corresponds to the XRD pattern of the
pristine [Ch][Lau]–DMSO phase. Four peaks appeared in the
versus a-tocopherol S
reached 6.34 at a Cf value of
d/a
À1
10 mgmL and barely decreased with increasing C . Therefore,
f
slight differences in the structures of homologues could be
recognized, and one homologue could be selectively separated
from the mixture of homologues by the LLC extractants with
H-bonds as the selection guide. Conventional micelles and mi-
croemulsion can dissolve some sparingly soluble compounds
in an aqueous phase, but these systems generally show poor
[
19]
selectivity to target molecules. The excellent molecular rec-
ognition of H-bond donor solutes and even their homologues
by LLCs further highlights the advantage of IL-based non-
aqueous LLCs for high-performance extraction.
1
/2
spectrum, peaks 2, 3, and 4 with relative positions of 1:3 :2
1/2 1/2
For a better understanding of the extraction mechanism of
ASC-IL-based LLCs and to determine the microinteraction be-
tween the ASC-ILs and the target solutes, POM, IR spectrosco-
py, and XRD were employed to investigate the interactions
and peaks 1 and 2 with relative positions of 3 :4 , which in-
dicate that both hexagonal and cubic phases existed in the
pristine [Ch][Lau]–DMSO sample. After dissolving tocopherol,
the cubic phase could still be observed in the tested samples
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(
blue and green curves in Figure 5b, peaks 1 and 2 with rela-
formed into [Emim][OH] by passing the aqueous solution through
a strongly basic anion-exchange resin. An aqueous solution of
1/2 1/2
tive positions of 3 :4 ); however, the original peaks 2, 3, and
of the pink curve changed significantly, and only two peaks
peaks 2 and 4) with relative positions of 1:2 were observed,
AgNO was used to confirm whether or not anion exchange was
4
3
complete. The concentration of [Emim][OH] was determined by
acid–base titration. Then an equimolar amount of fatty acid was
added to the solution of [Emim][OH]. The mixture was then stirred
at room temperature for 12 h. Subsequently, water was distilled off
at 333 K under reduced pressure. The obtained ASC-ILs were fur-
ther dried under high vacuum at the same temperature for at least
24 h to remove traces of water. The ASC-ILs with choline ([Ch]), tet-
raethylammonium ([N2222]), and tetrabutylphosphonium ([P4444]) as
cations were prepared by acid–base neutralization between fatty
acids and quaternary ammonium hydroxide or tetrabutylphospho-
nium hydroxide in water.
(
which suggests that the hexagonal phase gradually changed
into the lamellar phase, which is consistent with the phenom-
enon observed in the POM spectra. On the basis of the POM
and XRD results, we propose that the tocopherols mainly pen-
etrate into the position between two IL molecules, which indu-
ces the transformation of the LC structure. According to the
aforementioned analysis, for the LLC extraction process, strong
H-bond acceptor interfaces in the LLC recognize the targeted
solutes through selective H-bond interaction and then hold
these solutes through the nanostructure of the LC phase (Fig-
ure 5 f). In other words, the unique nanostructure in IL-based
LLC extractants provides outstanding cooperative effects be-
tween H-bonds and the van der Waals interactions, which
overcome the strong isotropic polarity of common ILs and sig-
nificantly enhance their molecular recognition ability for H-
bond donor solutes. Therefore, the IL-based nonaqueous LLCs
show extraordinarily high extraction capacity and excellent se-
lectivity for H-bond donor solutes compared with traditional IL
extractants.
Solvatochromism studies
The Kamlet–Taft dipolarity and polarizability p* and hydrogen-
bond basicity b were determined by solvatochromic experiments
[21]
with N,N-diethyl-4-nitroaniline and 4-nitroaniline as probes. Ali-
quots of probe/dichloromethane solutions of a certain concentra-
tion were added to a small vessel and, after evaporating all the di-
chloromethane, the IL–cosolvent mixture was added to the vessel,
which was shaken thoroughly to ensure complete mixing. Then
the UV/Vis spectrum of the sample was measured with a Shimadzu
UV-2550 spectrophotometer. An external circular water bath was
used to maintain the temperature of the cell. Scanning was repeat-
ed seven times for each measurement to record the maximum ab-
sorption wavelength of samples. The uncertainty in the maximum
absorption wavelength was Æ0.5 nm. The values of p* and b were
calculated through Equations (1) and (2)
The solutes captured in the LLC phase could be recovered
by simply adding a certain amount of water and acetonitrile to
break the self-organized nanostructures of the LLCs (see the
Supporting Information, Figure S10). The Dd-toc value of the
[
Ch][Lau]–DMSO system drastically decreased from 57.85 to
0
.04 after adding solvents, which indicates that 96.1% toco-
pherol was separated from the IL phase. Systematic investiga-
tions of the recycling of the ILs are under way.
Ã
p ¼ 8:649 À 0:314~n
ð1Þ
ð2Þ
DENA
Ã
b ¼ À0:357 ~n NA À 1:176p þ 11:12
Conclusion
where ~n DENA and ~n NA are the maximum absorption wavenumbers of
N,N-diethyl-4-nitroaniline and 4-nitroaniline in the samples,
respectively.
We designed a new class of nonaqueous LLCs and developed
an efficient IL-based LLC extraction process. The IL-based non-
aqueous LLCs show extraordinarily high extraction capacity for
H-bond donor solutes, excellent separation selectivity for struc-
ture-related compounds and even homologues, as well as easy
recycling. Our work shows that the introduction of self-assem-
bled nanostructures into IL systems is an efficient way to en-
hance their molecular recognition ability. As new soft materials,
IL-based LLCs successfully combine the unique properties of
ILs and LCs, which not only opens a new avenue for the devel-
opment of high-performance separation technologies, but also
is valuable for the development of advanced sensors, drug-de-
livery systems, and materials synthesis.
IR measurements
The samples were prepared by mixing the DMSO solutions of d-to-
copherol (15 mm) with the [Ch][Lau]–DMSO solution. The volume
ratio of d-tocopherol solution to [Ch][Lau]–DMSO was 1:20. Then
the FTIR spectra of the mixtures were recorded with a Nicolet 6700
À1
FTIR spectrometer at a resolution of 4 cm and 32 scans per
[22]
sample in a liquid sampling cell (optical path length: 0.5 mm).
HPLC Analysis
The HPLC system included an autosampler, a Waters 1525 binary
pump, and a Waters 2487 Dual l absorbance detector. A Sunfire
C18 column (5 mm, 4.6”250 mm) was used for the separation of
solutes. The composition of mobile phase and the detection l de-
pended on the kind of solute. A mixture of methanol and water
Experimental Section
Preparation of ASC-ILs
(95/5, v/v) was used as mobile phase in the analysis of tocopherols
The ASC-ILs (for structures see Figure 2 and Scheme S1 in the Sup-
porting Information) with 1-ethyl-3-methylimidazolium ([Emim])
and 1-hydroxyethyl-3-methylimidazolium ([OHemim]) as cations
were synthesized by a similar method to that described in the liter-
and methyl linoleate with detection wavelengths of 292 and
[22]
205 nm, respectively.
In the case of oleic acid and olein, the
mobile phase consisted of solution A (methanol/water/aqueous so-
lution of H SO (pH 3)=90/10/0.2, v/v) and solution B (isopropyl al-
2
4
[15b,20]
ature.
Firstly, [Emim][Br] was dissolved in water and trans-
cohol/acetonitrile 45/55 v/v) with gradient elution as follows: 0!
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1
5 min, 100% solution A; 15!37 min, 100% solution B. The flow
in University of China (NCET-13-0524) and the Fundamental Re-
search Funds for the Central Universities of China
À1
rate was 1.5 mLmin .
(
2014XZZX003-17).
GC analysis
The analysis of octane was carried out on a gas chromatograph
equipped with a flame-ionization detector (Shimadzu GC2010) and
Keywords: extraction · ionic liquids · liquid crystals · molecular
recognition · surfactants
HP-5 capillary column (30 m”0.25 mm I.D.”0.25 mm d ). Nitrogen
f
was used as carrier gas. All samples were diluted with ethanol
before analysis. The chromatographic conditions for analysis were
as follows: the temperatures of injector and detector were set to
[
1] a) J. G. Huddleston, H. D. Willauer, R. P. Swatloski, A. E. Visser, R. D.
Rogers, Chem. Commun. 1998, 1765–1766; b) K. E. Gutowski, G. A.
Broker, H. D. Willauer, J. G. Huddleston, R. P. Swatloski, J. D. Holbrey,
R. D. Rogers, J. Am. Chem. Soc. 2003, 125, 6632–6633; c) X. Q. Sun,
H. M. Luo, S. Dai, Chem. Rev. 2012, 112, 2100–2128; d) M. G. Freire,
A. M. Claudio, J. M. M. Araujo, J. A. P. Coutinho, I. M. Marrucho, J. N. Can-
ongia Lopes, L. P. N. Rebelo, Chem. Soc. Rev. 2012, 41, 4966–4995;
e) M. G. Freire, J. F. B. Pereira, M. Francisco, H. Rodriguez, L. P. N. Rebelo,
R. D. Rogers, J. A. P. Coutinho, Chem. Eur. J. 2012, 18, 1831–1839; f) P. K.
Mohapatra, A. Sengupta, M. Iqbal, J. Huskens, W. Verboom, Chem. Eur. J.
5
23 and 553 K respectively. A temperature-gradient procedure was
used as the column temperature program: held at 333 K for 2 min,
À1
and then increased to 368 K at a rate of 5 Kmin ; after holding for
2
2
min, the temperature was increased to 523 K at a rate of
0 Kmin and maintained for 5 min. The analyses were repeated
À1
at least three times to ensure accuracy.
2
013, 19, 3230–3238.
[
[
[
2] a) F. Loe-Mie, G. Marchand, J. Berthier, N. Sarrut, M. Pucheault, M. Blan-
chard-Desce, F. Vinet, M. Vaultier, Angew. Chem. Int. Ed. 2010, 49, 424–
427; Angew. Chem. 2010, 122, 434–437; b) P. Sun, D. W. Armstrong,
Anal. Chim. Acta 2010, 661, 1–16; c) X. X. Han, D. W. Armstrong, Acc.
Chem. Res. 2007, 40, 1079–1086.
POM measurements
The optical defect textures of liquid crystals were investigated by
using a polarizing optical microscope (Olympus BX51) equipped
with a temperature-control unit. The samples were observed as
films on a slide at a certain temperature.
3] a) L. C. Branco, J. G. Crespo, C. A. M. Afonso, Angew. Chem. Int. Ed. 2002,
4
1, 2771–2773; Angew. Chem. 2002, 114, 2895–2897; b) E. Miyako, T.
Maruyama, N. Kamiya, M. Goto, Chem. Commun. 2003, 2926–2927;
c) L. C. Branco, J. G. Crespo, C. A. M. Afonso, Chem. Eur. J. 2002, 8,
XRD measurements
3865–3871.
X-ray diffraction data were collected on a Rigaku X-ray diffractome-
ter (Ultima IV) with CuKa (l=1.5418 Š) radiation operating at 40 kV
and 40 mA. The samples were scanned from 1.4 to 10.0 in 2q with
a scan step of 0.026 at constant temperature.
4] a) E. Kuhlmann, M. Haumann, A. Jess, A. Seeberger, P. Wasserscheid,
ChemSusChem 2009, 2, 969–977; b) P. S. Kulkarni, C. A. M. Afonso, Green
Chem. 2010, 12, 1139–1149; c) M. S. Manic, V. Najdanovic-Visak, M. N. da
Ponte, AIChE J. 2011, 57, 1344–1355; d) Y. Sun, L. Shi, Fuel 2012, 99,
83–87; e) J. H. Xu, S. Zhao, W. Chen, M. Wang, Y. F. Song, Chem. Eur. J.
2
012, 18, 4775–4781.
Batch extraction experiments
[
5] a) A. A. Lapkin, M. Peters, L. Greiner, S. Chemat, K. Leonhard, M. A.
Liauw, W. Leitner, Green Chem. 2010, 12, 241–251; b) A. Arce, A. March-
iaro, O. Rodríguez, A. Soto, AIChE J. 2006, 52, 2089–2097; c) A. P.
Abbott, P. M. Cullis, M. J. Gibson, R. C. Harris, E. Raven, Green Chem.
The batch extraction experiments were performed as follows. Cer-
tain amount of solutes were dissolved in hexane to prepare the
feed solutions. The nonaqueous LLC extractants were prepared by
dissolving ASC-ILs in polar solvents such as dimethyl sulfoxide, di-
methylformamide, acetonitrile, and methanol. Then the feed solu-
tion was mixed with equal volume of extractant in a flask. After
being vigorously shaken in a thermostatic rotary shaker at 303 K
2
007, 9, 868–872; d) L. Y. Kong, Q. W. Yang, H. B. Xing, B. G. Su, Z. B.
Bao, Z. G. Zhang, Y. W. Yang, Q. L. Ren, Green Chem. 2014, 16, 102–107;
e) M. G. Freire, C. M. S. S. Neves, I. M. Marrucho, J. N. Canongia Lopes,
L. P. N. Rebelo, J. A. P. Coutinho, Green Chem. 2010, 12, 1715–1718.
[6] a) D. M. Phillips, L. F. Drummy, D. G. Conrady, D. M. Fox, R. R. Naik, M. O.
(
Æ0.1 K), the flask was allowed to stand for a certain time to reach
Stone, P. C. Trulove, H. C. D. Long, R. A. Mantz, J. Am. Chem. Soc. 2004,
1
26, 14350–14351; b) S. G. Cull, J. D. Holbrey, V. Vargas-Mora, K. R.
phase splitting. Samples were taken from each of the two phases
and diluted with mobile phase for HPLC or GC analysis. The con-
centration of naphthenic acid was determined by acid–base titra-
tion. The distribution coefficient D and the selectivity of solute
i versus j Si/j were calculated with Equations (3) and (4).
Seddon, G. J. Lye, Biotechnol. Bioeng. 2000, 69, 227–233; c) S. S. Y. Tan,
D. R. MacFarlane, J. Upfal, L. A. Edye, W. O. S. Doherty, A. F. Patti, J. M.
Pringlea, J. L. Scotta, Green Chem. 2009, 11, 339–345; d) P. S. Barber,
C. S. Griggs, G. Gurau, Z. Liu, S. Li, Z. X. Li, X. M. Lu, S. J. Zhang, R. D.
Rogers, Angew. Chem. Int. Ed. 2013, 52, 12350–12353; Angew. Chem.
i
2
2
013, 125, 12576–12579; e) Z. Du, Y. L. Yu, J. H. Wang, Chem. Eur. J.
007, 13, 2130–2137.
D ¼ C =C
ð3Þ
ð4Þ
[7] a) J. L. Anderson, J. Ding, T. Welton, D. W. J. Armstrong, J. Am. Chem.
Soc. 2002, 124, 14247–14254; b) K. Dong, S. J. Zhang, Chem. Eur. J.
2012, 18, 2748; c) Q. W. Yang, H. B. Xing, Z. B. Bao, B. G. Su, Z. G. Zhang,
Y. W. Yang, S. Dai, Q. L. Ren, J. Phys. Chem. B 2014, 118, 3682–3688;
d) P. G. Jessop, D. A. Jessop, D. B. Fu, L. Phan, Green Chem. 2012, 14,
i
ei
ri
ꢀ
Si=j ¼ D D
i
j
where Cei and C are the mass fractions of solute in the extraction
ri
1245–1259; e) K. Dong, S. J. Zhang, D. X. Wang, X. Q. Yao, J. Phys. Chem.
phase and the raffinate phase, respectively. The extraction equilibri-
um procedures were repeated at least three times.
A 2006, 110, 9775–9782.
[
8] a) S. M. Murray, R. A. O’Brien, K. M. Mattson, C. Ceccarelli, R. E. Sykora,
K. N. West, J. H. Davis, Angew. Chem. Int. Ed. 2010, 49, 2755–2758;
Angew. Chem. 2010, 122, 2815–2818; b) X. L. Ni, H. B. Xing, Q. W. Yang,
J. Wang, B. G. Su, Z. B. Bao, Y. W. Yang, Q. L. Ren, Ind. Eng. Chem. Res.
Acknowledgements
2
012, 51, 6480–6488; c) L. Y. Garcia-Chavez, A. J. Hermans, B. Schuur,
A. B. de Haan, Sep. Purif. Technol. 2012, 97, 2–10.
The research was supported by the National Natural Science
Foundation of China (21222601, 21476192, and 21436010), the
Zhejiang Provincial Natural Science Foundation of China
[
9] a) H. Niedermeyer, J. P. Hallett, I. J. Villar-Garcia, P. A. Hunt, T. Welton,
Chem. Soc. Rev. 2012, 41, 7780–7802; b) Q. W. Yang, H. B. Xing, B. G. Su,
K. Yu, Z. B. Bao, Y. W. Yang, Q. L. Ren, Chem. Eng. J. 2012, 181–182, 334–
342; c) G. Chatel, J. F. B. Pereira, V. Debbeti, H. Wang, R. D. Rogers, Green
(
LR13B060001), the Program for New Century Excellent Talents
Chem. Eur. J. 2015, 21, 9150 – 9156
www.chemeurj.org
9155
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Chem. 2014, 16, 2051–2083; d) S. Taguchi, T. Ichikawa, T. Katoc, H.
Ohno, RSC Adv. 2013, 3, 23222–23227.
10] a) A. P. Abbott, D. Boothby, G. Capper, D. L. Davies, R. K. Rasheed, J. Am.
Chem. Soc. 2004, 126, 9142–9147; b) W. J. Guo, Y. C. Hou, W. Z. Wu, S. H.
Ren, S. D. Tian, K. N. Marsh, Green Chem. 2013, 15, 226–229; c) M. Fran-
cisco, A. Bruinhorst, M. C. Kroon, Angew. Chem. Int. Ed. 2013, 52, 3074–
I. Grillo, H. Lee, D. Parker, D. Plana, R. M. Richardson, Langmuir 2012, 28,
2502–2509; e) J. L. Zhang, B. X. Han, Acc. Chem. Res. 2013, 46, 425–
433.
[
[15] a) D. Coleman, N. Gathergood, Chem. Soc. Rev. 2010, 39, 600–637; b) M.
Petkovic, J. L. Ferguson, H. Q. Nimal Gunaratne, R. Ferreira, M. C. Leitao,
K. R. Seddon, L. P. N. Rebelo, C. S. Pereira, Green Chem. 2010, 12, 643–
649; c) R. Klein, D. Touraud, W. Kunz, Green Chem. 2008, 10, 433–435.
[16] P. Brown, C. Butts, R. Dyer, J. Eastoe, I. Grillo, F. Guittard, S. Rogers, R.
Heenan, Langmuir 2011, 27, 4563–4571.
[17] T. L. Greaves, A. Weerawardena, C. Fong, C. J. Drummond, J. Phys. Chem.
B 2007, 111, 4082–4088.
[18] M. U. Araos, G. G. Warr, J. Phys. Chem. B 2005, 109, 14275–14277.
[19] N. Rapoport, Prog. Polym. Sci. 2007, 32, 962–990.
[20] Y. Fukaya, Y. Iizuka, K. Sekikawa, H. Ohno, Green Chem. 2007, 9, 1155–
1157.
[21] a) Y. F. Cao, H. B. Xing, Q. W. Yang, B. G. Su, Z. B. Bao, R. H. Zhang, Y. W.
Yang, Q. L. Ren, Green Chem. 2012, 14, 2617–2625; b) M. J. Kamlet, J. L.
Abboud, R. W. Taft, J. Am. Chem. Soc. 1977, 99, 6027–6038.
[22] T. Chen, G. F. Payne, Ind. Eng. Chem. Res. 2001, 40, 3413–3417.
3085; Angew. Chem. 2013, 125, 3152–3163.
[
[
[
11] a) Z. B. Zhang, Q. Zhao, J. Y. Yuan, M. Antonietti, F. H. Huang, Chem.
Commun. 2014, 50, 2595–2597; b) H. D. Qiu, A. K. Mallik, M. Takafuji, H.
Ihara, Chem. Eur. J. 2011, 17, 7288–7297.
12] a) K. Binnemans, Chem. Rev. 2005, 105, 4148–4204; b) C. Fong, T. Le,
C. J. Drummond, Chem. Soc. Rev. 2012, 41, 1297–1322; c) P. H. J.
Kouwer, T. M. Swager, J. Am. Chem. Soc. 2007, 129, 14042–14052.
13] a) B. Soberats, E. Uchida, M. Yoshio, J. Kagimoto, H. Ohno, T. Kato, J. Am.
Chem. Soc. 2014, 136, 9552–9555; b) B. Soberats, M. Yoshio, T. Ichikawa,
S. Taguchi, H. Ohno, T. Kato, J. Am. Chem. Soc. 2013, 135, 15286–15289;
c) J. D. Holbrey, K. R. J. Seddon, Chem. Soc. Dalton Trans. 1999, 2133–
2
140; d) W. Dobbs, J. Suisse, L. Douce, R. Welter, Angew. Chem. Int. Ed.
006, 45, 4179–4182; Angew. Chem. 2006, 118, 4285–4288.
14] a) T. Ichikawa, T. Kato, H. Ohno, J. Am. Chem. Soc. 2012, 134, 11354–
1357; b) M. A. Reppy, D. H. Gray, B. A. Pindzola, J. L. Smithers, D. L. Gin,
2
[
1
J. Am. Chem. Soc. 2001, 123, 363–371; c) B. A. Pindzola, D. L. Gin, Lang-
muir 2000, 16, 6750–6753; d) P. Brown, C. P. Butts, J. Eastoe, D. Fermin,
Received: January 23, 2015
Published online on May 8, 2015
Chem. Eur. J. 2015, 21, 9150 – 9156
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9156
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim