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Hydrophobic deep eutectic solvents for purification of water contaminated with Bisphenol-A
Journal Pre-proof Hydrophobic deep eutectic solvents for purification of water contaminated with Bisphenol-A C. Florindo, Nathalie V. Monteiro, Bernardo D. Ribeiro, L.C. Branco, I.M. Marrucho PII:
S0167-7322(19)33526-3
DOI:
https://doi.org/10.1016/j.molliq.2019.111841
Reference:
MOLLIQ 111841
To appear in:
Journal of Molecular Liquids
Received Date: 23 June 2019 Revised Date:
26 September 2019
Accepted Date: 27 September 2019
Please cite this article as: C. Florindo, N.V. Monteiro, B.D. Ribeiro, L.C. Branco, I.M. Marrucho, Hydrophobic deep eutectic solvents for purification of water contaminated with Bisphenol-A, Journal of Molecular Liquids (2019), doi: https://doi.org/10.1016/j.molliq.2019.111841. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
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Hydrophobic deep eutectic solvents for
3
purification of water contaminated with
4
Bisphenol-A
5
C. Florindo,1,2 Nathalie V. Monteiro,1 Bernardo D. Ribeiro,3 L. C. Branco4 and I. M. Marrucho1,2*
6 7 8 9 10 11
1
12
Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
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2
14
Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal
15
3
16
de Janeiro, Brazil
17
4
18
Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de
Instituto de Tecnologia Química e Biológica António Xavier, www.itqb.unl.pt,
Escola de Química, Universidade Federal Do Rio de Janeiro, 21941-598 Rio
REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de
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20
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*Corresponding author. Tel.: +351 218413385; fax: +351 218499242. E-mail address:
22
[email protected] (I. M. Marrucho). 1
23
Abstract
24
The occurrence of micropollutants in aquatic ecosystems poses a serious public
25
health and environmental problem. For that purpose, the main goal of this work
26
is the removal of an endocrine disruptor micropollutant compound, Bisphenol-A
27
(BPA), from aqueous environments using hydrophobic deep eutectic solvents
28
(DES). In particular, DES composed of DL-Menthol or quaternary ammonium
29
salts as hydrogen bond acceptors (HBA) and natural fatty acids as hydrogen
30
bond donors (HBD) were prepared. Extraction efficiencies were maximized by
31
optimizing the experimental parameters in the extraction BPA from water using
32
a central composite design combined with a response surface methodology.
33
Thus, the effect of several parameters, such as stirring speed, contact time,
34
DES/water ratio and initial BPA concentration on the extraction efficiencies were
35
evaluated.
36 37
Keywords: Hydrophobic Deep Eutectic Solvents; Wastewater Treatment;
38
Bisphenol-A; Liquid-liquid extraction; Central Composite Design
39
2
40
1. Introduction
41
Currently, one of the major societal challenges is to provide good quality
42
water to everyone, by dramatically reducing or completely eliminating the
43
current hazardous micropollutants present in the water resources around the
44
globe.1, 2 In the coming decades, water scarcity, even in regions considered to
45
be currently rich in water, puts on the 2030 agenda for the sustainable
46
development the urgent development of innovative and sustainable water
47
solutions so that clean water and sanitation can be provided to everyone.3
48
Micropollutants have been emerging as a new class of pollutants since,
49
despite their very small concentration in water streams, their presence can be
50
related to numerous harmful effects on the health of animals and humans, such
51
as carcinogenic and endocrine disrupting effects, antibiotic resistance of
52
microorganisms, etc.4-6 Heavy metals, pharmaceuticals, personal care products,
53
dyes, waterproofing treatments, plasticizers, pesticides, and others, are all
54
classified as micropollutants.7 Among these, Bisphenol-A (BPA) is an emerging
55
micropollutant of special importance since it has been detected in increasing
56
concentrations globally in water sources, as conventional water treatment plants
57
are incapable of removing it completely. BPA has been largely used as a
58
plasticizer from food and drink plastic packaging to plastic medical devices.
59
However, BPA is a also well-known endocrine disruptor compound, that mimics
60
the estrogen hormone, thus affecting the normal development and function of
61
human and wildlife reproductive system.8 Although the European Union and
62
Canada have recognized its harmful effects and banned its use in baby bottles
63
since 2011,
64
consequent removal from water sources.
9,6
there is a long way to go until its full legislative control and
3
65
The development of effective and sustainable innovative water cleaning
66
technologies, typically to complement the existing ones, is a crucial step to
67
achieve the targeted goal of sustainable development. Different extraction
68
techniques, such as aqueous biphasic systems,10,
69
adsorption15, 16 and liquid-liquid extraction17-19, have been tested for removal of
70
BPA from water, with good extraction efficiencies. However, most of these
71
techniques are not sustainable, since they are based on high cost solvents or
72
materials of difficult recycle and reuse, not to mention their hazardousness and
73
consequent water contamination. As a result, benign and recyclable solvents
74
have been searched and developed, so that a truly circular technology can be
75
achieved. Deep eutectic solvents (DES) have been highlighted as sustainable
76
solvents and showed to provide sustainable solutions in numerous scientific and
77
technological fields.20,
78
solvents for numerous applications.20 The ease of preparation, the possibility to
79
use natural and biodegradable components makes DES versatile alternative
80
green solvents.22 DES can be defined as mixtures of two or more compounds
81
composed by hydrogen bond donors (HBD) and acceptors (HBA), which can
82
form liquids at room temperature.23 DES emerged as green, sustainable and
83
more advantageous solvents compared to ionic liquids and traditional organic
84
solvents, especially considering their environmentally friendly character,
85
biodegradability, low price and straightforward preparation. This class of
86
solvents showed great potential for a diversity of applications, such as in
87
electrochemistry,24
88
extraction and separation,27, 28 catalysis,29 organic synthesis,30 among others.
21
11
liquid membranes,12-14
In recent years, DES have emerged as alternative
nanotechnology,25
stabilization
of
DNA
and
RNA,26
89
Since most DES reported in the literature are water soluble, limiting their
90
application in several processes, the development of hydrophobic DES has 4
91
been attracting the attention of researchers. The preparation and application of
92
several hydrophobic DES in extraction processes, such as removal of metal
93
ions from water, indium extraction from hydrochloric and oxalic acids, removal
94
of pesticides and endocrine disruptor compounds from water, among others 4, 17,
95
31, 32
, has already been reported.
96
The main goal of this work is to evaluate the removal of BPA, from aqueous
97
environments using hydrophobic DES. For that purpose, two different families of
98
hydrophobic DES, namely ionic and neutral, were developed and their ability to
99
extract BPA was evaluated through liquid-liquid extraction. In particular, DES
100
using natural components, as DL-Menthol which can be used as hydrogen bond
101
acceptor (HBA) and hydrogen bond donor (HBD), and different quaternary
102
ammonium salts with long alkyl chain, such as [N7777]Br, [N8888]Br and [N8881]Br,
103
as HBA combining several natural carboxylic acids as HBD, such as octanoic
104
and decanoic acid, were prepared. Chemical structures of hydrophobic DES
105
and the micropollutant used in this work, and their respective acronyms are
106
depicted in Figure 1 as well as in Table A1 in Appendices.
5
[N8888]Br
DL-Menthol Octanoic acid
Decanoic acid [N8881]Br
POLLUTANT
Bisphenol - A
107 108
Figure 1. Chemical structures and respective acronyms of DES and
109
micropollutant studied in this work.
110
Moreover, the most influential experimental parameters on the extraction of
111
BPA from water were identified and optimized using a central composite design
112
(CCD). The optimization of extraction conditions is of utmost importance, since
113
it is crucial to reduce the energy and operation associated cost, leading to
114
environmentally friendly process.
115 116
2. Experimental section
117 118
2.1. Materials
119
DL-Menthol (purity ≥ 95%), tetraheptylammonium bromide ([N7777]Br)
120
(purity ≥ 99%), tetraoctylammonium bromide ([N8888]Br) (purity ≥ 98%),
121
methyltrioctylammonium bromide ([N8881]Br) (purity ≥ 97%), octanoic acid (C8)
122
(purity ≥ 98%) and decanoic acid (C10) (purity ≥ 98%) were purchased from
6
123
Sigma-Aldrich and used as received. The micropollutant Bisphenol-A (mass
124
fraction purity ≥ 99 %) was purchased from Sigma Aldrich and used with no
125
further purification. All aqueous solutions were prepared using high purity water
126
(Milli-Q water) with a specific conductance <0.1 mS/cm.
127
2.2. Methodologies
128
2.2.1. Preparation of DES
129
Hydrophobic DES were prepared according to the methodology proposed
130
in our previous work.33 All DES were prepared by mixing the two components in
131
previously established proportions in a glass vial with a mechanical stirrer) at
132
500 rpm and 333.15 K, until a homogeneous liquid was formed. In the
133
preparation of DES, an analytical high-precision balance with an uncertainty of
134
± 10-5 g, was used to weigh the known masses of the individual compounds into
135
bottles with caps. The HBAs (DL-Menthol, tetraoctylammonium bromide
136
([N8888]Br), tetraheptylammonium bromide ([N7777]Br), methyltrioctylammonium
137
bromide ([N8881]Br) were first dried in a high vacuum pump at 40 °C for at least
138
four days, while the carboxylic acids were used without any further purification,
139
since they usually have very low amount of water. Their water contents were
140
determined by Karl Fischer titration (< 500 ppm). All prepared hydrophobic DES
141
were completely characterized by 1H and13C NMR and FTIR spectroscopy, in
142
order to confirm their expected structures and final purities.
143
2.2.2. Liquid-liquid extraction procedure
144
Liquid-liquid extractions were carried out at (25.0±0.1)oC using the
145
prepared hydrophobic DES as extractants. BPA can be found in water
146
environments at very low concentrations, usually ranging from ng/L to mg/L. In
147
this work, in order to use a simple and fast screening technique, UV-vis 7
148
spectroscopy, slightly greater concentrations were prepared using stock
149
aqueous solutions of BPA of 100 mg/L, 50 mg/L and 25 mg/L.
150
Mixtures composed by each one of the prepared hydrophobic DES and the
151
aqueous solution of BPA were initially stirred vigorously during 10 min, which
152
was the minimum time to reach equilibrium, and then left to settle for 12h, to
153
ensure complete separation of phases. The extractions were carried out at
154
(25.0±0.1)oC. Thereafter, the two phases were carefully separated using a
155
needled syringe and the concentration of the remaining micropollutant in the
156
water-rich phase was measured using UV–vis spectroscopy with a Shimadzu
157
model UV-1800–Pharma-Spec spectrophotometer. Furthermore, to eliminate
158
possible interferences of DES and their interaction with micropollutant in the
159
quantification, only the concentration of BPA in the water phase was
160
experimentally determined. A calibration curve was previously established for
161
BPA in Milli-Q water (curves with R2 > 0.997). All the experiments were carried
162
out in triplicates so that standard deviations of the measurements could be
163
calculated.
164 165
3. Results and discussion 3.1. Performance of different DES as extractants
166
In this work, hydrophobic DES were prepared using ionic hydrophobic
167
compounds such as quaternary ammonium salts with long alkyl chains, namely
168
[N7777]Br, [N8888]Br and [N8881]Br and carboxylic acids, while neutral hydrophobic
169
DES were prepared combining a natural compound, DL-menthol, with
170
carboxylic acids. These DES were prepared at a molar ratio of 1:2, which was
171
determined to be liquid in previous works where phase diagrams of each
172
system were measured. The studied DES are listed in Table A1 in Appendices. 8
173
Terms like deep eutectic solvents, eutectic solvents, eutectic mixtures or low
174
transition temperature mixtures have been used in literature until now to
175
designate this class of compounds, which means that the acronym DES has
176
been used to designate eutectic mixtures that are liquid at room temperature
177
and thus can be used as solvents. In this work we have used deep eutectics
178
(those based on quaternary ammonium salts) and not deep eutectics (those
179
based on DL-Menthol). Although we acknowledge here this difference, we have
180
used the acronym DES for all the solvents used in this work, independently of
181
the fact of the depression in the melting point being deep or not.
182
Nine hydrophobic DES were initially screened for extraction of Bisphenol-A from
183
water environments. The extraction efficiencies, EE %, were calculated from the
184
Bisphenol-A (BPA) concentration in the water-rich phase before, , , and
185
after the extraction, , :
186
(%) =
, ,
,
x 100
(eq. 1)
187 188
The extraction efficiencies of BPA using several DES are displayed in Figure 2,
189
and listed in Table B1 in Appendices.
9
100
80
EE%
60
40
[N
88
81
[N
88
0
88 ]B ]B r: r[ : C ND 10 8 8L 8 1M ]Be n [N r:th [N 88 Col 88 8 81 81 ]B ]B r: r: C D 10 LM en D th Lol M en th D ol L:C M en 8 th ol :C 10
20
190 191
Figure 2. Extraction efficiencies (EE %) of Bisphenol-A obtained for all DES
192
used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, DES/water ratio =
193
1/1, temperature = 25 ºC, contact time = 10 min).
194
Good extraction efficiencies (> 85%) of BPA from contaminated water were
195
achieved using all the selected hydrophobic DES. These large extraction
196
efficiency values to remove BPA from water are essentially linked to the DES
197
hydrophobicity, since BPA possess a very low water solubility (~120mg/L at
198
25ºC) and a high octanol-water partition coefficient (Kow) of 3.40,34 leading to a
199
large affinity for the organic hydrophobic DES phase. However, some difference
200
in the extraction efficiencies between the studied DES can be observed.
201
Analysing the data in Figure 2, it is clear that the extraction efficiencies depend
202
on the choice of the components of DES, especially on the HBD. Moreover, the
10
203
extraction efficiencies increased with the increase of the alkyl chain length in
204
both the fatty acid and also in the quaternary ammonium salt, which
205
corroborates our previous remarks on the fact that the more hydrophobic the
206
DES are, the higher the extraction efficiencies.35 Thus, the extraction
207
efficiencies of BPA follow the HBA order: [N8888]Br: HBD (∼98% EE) > [N7777]Br:
208
HBD (∼95% EE) > [N8881]Br: HBD (∼91% EE) ≥ DL-Menthol: HBD (∼87% EE).
209
Regarding the HBD of DES, the trend of the extraction efficiencies can be
210
organized in the following order [N7777]Br > [N8888]Br > [N8881]Br > DL-Menthol
211
for C8 acid, and [N7777]Br ~ [N8888]Br > [N8881]Br > DL-Menthol for C10 acid,
212
where the latter is the DES with the lowest EE%.
213
For all the HBAs studied there is a small difference in the BPA extraction
214
between octanoic and decanoic acid, except for [N7777]Br where similar results
215
within the experimental error were obtained. Looking at [N8881]Br as HBA, it can
216
be seen that extraction efficiencies using DL-Menthol and decanoic acid as
217
HBDs are also comparable, probably due their similar hydrophilicity.
218
Consequently, it can be concluded that the extraction of BPA from water seems
219
to be directly related to water solubility of components of the hydrophobic DES.
220 221 222
3.2. Screening of experimental parameters influencing the extraction efficiency
223
The optimization of the experimental parameters of a process is perhaps the
224
most important aspect for its implementation at an industrial level, since it
225
largely influences the cost/efficiency ratio. Therefore, in this section, the
226
influence of several experimental variables, such as mass ratio of HBA/HBD of
227
DES, contact time, stirring speed of mixing, DES to water ratio and initial
11
228
concentration of micropollutant, in the extraction efficiencies is evaluated and
229
discussed in detail.
230 231
3.2.1. HBA/HBD molar ratio
232
As it has been recognized by several authors, the molar ratio between HBA and
233
HBD is one of the important factors influencing the physicochemical properties
234
of DES.36 In order to explore the impact of using different molar ratio of eutectic
235
mixtures, where they are still liquid at working temperature, on the extraction
236
efficiencies of BPA, four molar HBA: HBD ratios (1:2, 1:3, 1:4 and 1:5) were
237
selected and used to prepare DES belonging to the three quaternary
238
ammonium salts DES families ([N7777]Br, [N8888]Br and [N8881]Br) and DL-
239
Menthol DES family. The reason to select these specific molar ratios of HBA:
240
HBD is due to the fact that higher proportions of salt than acid would not lead to
241
liquid phase at room temperature. The extraction results of BPA from aqueous
242
solutions using different molar HBA:HBD proportions of different ionic and
243
neutral DES are presented in Figure 3 and also listed in Table B2 in
244
Appendices.
12
100 1:2 1:3 1:4 1:5
80
EE%
60
40
20
ho D
LM en
th
en t M r: D L-
[N
88 81
]B
[N
ol :C 8
l
8 B r: C 88 81 ]
r: C 7] B 77 7
[N
[N
88 88 ]
B r: C
10
8
0
245 246
Figure 3. Influence of HBA: HBD ratio of five DES families on the extraction
247
efficiencies (EE %) of BPA ([C0]BPA = 0.1 g/L, Stirring speed = 300 rpm,
248
DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
249 250
It can be seen that the molar ratios do not significantly influence the extraction
251
efficiencies for the studied DES, and [N8888]Br:C8 is the one where larger
252
differences in the BPA extraction efficiencies with the HBA:HBD molar ratios
253
were observed. Thus, in general, it can be concluded that the incorporation of
254
more acid (increasing from 1:2 to 1:5) does not favour the extraction efficiencies
255
of BPA for both ionic and neutral DES. Since the best performance for all the
256
studied systems was always achieved using the lowest HBA: HBD molar ratio
257
(1:2), this ratio was chosen to carry out further studies.
258
13
3.2.2. Effect of initial concentration of BPA in water
259 260
In order to explore the effect of initial concentration of micropollutant on the
261
extraction efficiency of BPA, the initial concentration was varied from 0.1 g/L to
262
0.025 g/L (100, 50 and 25 ppm) and the obtained results are presented in
263
Figure 4 and listed in Table B3 in Appendices. 100
80 0.1 g/L 0.05 g/L 0.025 g/L
EE %
60
40
ac
id
10
ac 8
:C
en
th
ol
ol th en
M LD
D
L-
M
]B 81
:C
M Lr:
D
81 88
[N 88 [N
ol en
C r: ]B
]B 81 88
th
10
8 C r:
C r: ]B [N
[N
77
77
77 77 [N
10
8 C r: ]B
r: ]B
88 88
[N
[N
88
88
]B
r:
C
C
8
10
0
id
20
264 265
Figure 4. Influence of initial concentration of Bisphenol-A in water on the
266
extraction efficiencies (EE %) for all DES used in this work (Stirring speed = 300
267
rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
268 269
It can be seen that the initial concentration of the BPA greatly influences the
270
EE% of BPA for the majority of the studied DES. Overall, extraction efficiencies
271
decrease as the concentration of BPA decreases as follows: 0.1 g/L > 0.05 g/L
272
> 0.025 g/L. However, for DES composed of decanoic acid as HBD, this
273
decrease in %EE is much smaller than for DES composed of more hydrophilic
274
HBD, such as octanoic acid or DL-Menthol. This fact is true for the all studied 14
275
DES, both ionic and neutral. This behavior of the EE% with BPA initial
276
concentration is linked to hydrophobic character of the HBD: the extraction
277
efficiencies of BPA carried out with DES composed of decanoic acid are less
278
affected by the initial concentration of micropollutant than those composed of
279
octanoic acid or DL-menthol as HBD. This gives the opportunity to tune the
280
DES chemical structure through the HBD in order to maintain the extraction
281
efficiency. In some cases, such as [N7777]Br: C10, the differences achieved in
282
the EE% at different initial concentrations of BPA are negligible. In conclusion,
283
the best DES to efficiently remove BPA at low concentrations are the ionic most
284
hydrophobic, [N7777]Br: C10 and [N8888]Br: C10, and therefore the less effective
285
are the most hydrophilic, [N8881]Br: C8 and DL-Menthol: C8.
286 287
3.2.3. Effect of contact time
288
Contact time is a crucial parameter that reflects the kinetics of the separation
289
process. A fast kinetics, as thus a short contact time, is usually desired. In order
290
to find the optimal time to carry out the extraction of BPA from aqueous
291
solutions, the best DES of each family, those with HBA: HBD ratio of (1:2), were
292
selected to perform these experiments. Figure 5 shows the extraction
293
efficiencies of BPA from water as a function of time at 25 ºC and also listed in
294
Table B4 in Appendices.
295 296 297 298
15
100
EE %
95
90
[N7777]Br: C10 [N8888]Br: C10 [N8881]Br: C10 [N8881]Br: DL-Menthol DL-Menthol: C10
85
80 5
10
20
30
Time (min)
299 300
Figure 5. Influence of contact time on the extraction efficiencies (EE %) for the
301
best DES used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm,
302
temperature = 25 ºC, DES/water ratio = 1/1).
303 304
It can be concluded that the extraction process of BPA using all the proposed
305
DES is quite fast, and the equilibrium can be reached after 5 to 10 min. Thus,
306
the contact time was set to 10 min to ensure that the equilibrium is attained for
307
all DES.
308 309
3.2.4. Effect of stirring speed
310
Stirring speed is another parameter that might influence the extraction efficiency
311
of BPA. The influence of stirring speed on the extraction efficiencies of BPA for
312
the most performing DES used in this work, which are [N7777]Br: C10, [N8888]Br:
313
C10, [N8881]Br: C10, [N8881]Br: DL-Menthol and DL-Menthol: C10, is shown in
314
Figure 6 and listed in Table B5 in Appendices.
16
100
EE %
95
90
[N7777]Br: C10 [N8888]Br: C10 [N8881]Br: C10 [N8881]Br: DL-Menthol DL-Menthol: C10
85
80 100
300
500
750
Stirring speed (rpm)
315 316
Figure 6. Influence of stirring speed on the extraction efficiencies (EE %) for the
317
best DES used in this work ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1,
318
temperature = 25 ºC, contact time = 10 min).
319 320
These results show that the increase of the stirring speed leads to a minor
321
decrease in the EE% for some DES, especially for the highest stirring speed,
322
750 rpm. This can probably be due to the different solubilities of water in DES35
323
and the fact that the stirring speed might affect the dispersion of water in the
324
studied DES. On the other hand, for [N8881]Br: C10
325
negligible, taking into account the error bars. In conclusion, not taking into
326
account the highest stirring speed, after 300 rpm, no significant increase in EE%
327
is obtained. Thus, 300 rpm was chosen as the optimal extraction stirring speed,
328
for energetic considerations.
this effect is almost
329 330
3.2.5. Effect of DES/water mass ratio
17
331
In terms of cost of an industrial extraction process, it is desirable to obtain
332
higher extraction efficiencies for a minimum amount of solvent. The effect of the
333
mass ratio of the DES/water phases in the BPA extraction efficiencies was
334
studied and the results are shown in Figure 7 and listed in Table B6 in
335
Appendices.
336 337 338 100
80 1/3 1/2 1/1 3/1
EE %
60
40
20
ac ]B 88 r id : 81 C 10 ]B r: ac D D id LLM M en en th D th Lol ol M :C en 8 th ac ol id :C 10 ac id
d
r: C 8
88 81
[N
[N
88 8
1] B
10
ac i
ac id r: C
]B
77 77 [N
[N
ac i
r: C 8
10 77 7
7] B
r: C
]B [N
88 88 [N
[N
88 8
8] B
r: C 8
ac id
d
0
339 340
Figure 7. Effect of DES/water ratio on the extraction efficiencies (EE %) for all
341
DES used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature
342
= 25 ºC, contact time = 10 min).
343
18
344
It can be observed that the increase of DES/water mass ratio does not have a
345
significant effect in the BPA extraction efficiencies. An exception is the case of
346
3/1 DES/water ratio, where a large decrease in the extraction efficiencies is
347
observed for DES based on octanoic acid as HBD. These results are probably
348
due to the lower hydrophobicity of these DES and higher solubility of water in
349
them.35
350
In general, these results show that only a small mass of DES is needed to treat
351
large volumes of contaminated water, which is probably due to high
352
hydrophobicity of the DES and the very low solubility of BPA in water. These
353
results are of particular importance when the DES starting materials are
354
expensive, such as in the case of hydrophobic quaternary ammonium salts with
355
long alkyl chains.
356 357 358
3.3. Optimization
of
the
extraction
efficiency
using
Experimental Design
359 360
The response surface methodology (RSM) is a useful and efficient statistical
361
tool which allows optimizing the response of a system to the change of a set of
362
independent variables. In this work, a Central Composite Design (CCD) was
363
used to determine a set of experimental conditions leading to an optimal
364
extraction efficiency of BPA. From the previously carried out studies, two
365
experimental parameters, initial concentration of micropollutant and the
366
DES/water mass ratio, could be identified as important for the extraction of
367
Bisphenol-A
368
experimental parameter that, generally, greatly influences the solubility and,
369
consequently, the extraction processes. Since [N8888]Br: C10 (1:2) DES
from
water
environments.
Temperature
is
also
another
19
370
presented the highest extraction efficiency values, it was selected to be used in
371
CCD, where the optimal temperature, DES/water ratio and initial concentration
372
of BPA parameter to achieve the highest extraction efficiencies.
373
The levels of the studied variables are shown in Table 1.
374 375
Table 1. Optimization of BPA extraction for [N8888]Br: C10 (1:2) using a
376
experimental central composite design.
377
Experimental Factors Temperature DES/water Ratio Initial Concentration (C0)
- 1.68
-1
0
+1
+ 1.68
19
26
35
45
50
0.24
0.96
2
3.05
3.76
0.03
0.04
0.06
0.08
0.09
of BPA 378 379 380
A fixed extraction time of 10 min and stirring speed of 300 rpm were used, since
381
these parameters do not influence the extraction efficiencies. The experimental
382
data obtained were analyzed by Pareto analysis of variance (ANOVA) and fitted
383
to
384
analysis. Detailed data are provided in Appendices.
385
The statistical design software STATISTICA 6.0 (Statsoft Inc., Tulsa, U.S.A.)
386
was used to analyze the data and graphically display the results. Central
387
composite design was implemented for the experimental design analysis, using
388
the response surface and the desirability approach, which converts each
389
response variable in an individual desirability function ranging from 0 to 1. This
a
second-order
polynomial
equation
using
multiple
regression
20
390
design allows the interpretation of the association between the response of the
391
percentage of extraction efficiencies and the independent variables that
392
influence the BPA extraction from water. The influence of each parameter in
393
BPA extraction efficiency using a CCD is illustrated in Figure 8 and listed in
394
Table C1 in Appendices.
395
396 397
i) ii) iii) Figure 8. Response surface (top) and desirability plots (bottom) of the
398
extraction efficiencies (EE %) of BPA from water using [N8888]Br:C10 DES with
399
the combined effects of: i) Temperature and DES/water ratio; ii) initial
400
concentration of BPA in water and DES/water ratio; and iii) initial concentration
401
of BPA in water and Temperature.
402 403
An F-test and p-value were applied to the obtained model to check the
404
significance of each coefficient. The low p-value (< 0.0001) and the high F-test
405
indicate the suitability of the model. The repeatability of the model was assured
21
406
through an average of three replicas of extraction efficiencies experiments with
407
95.77 ± 0.02 of EE%.
408
In Figure 8 b) a steep decrease of the extraction efficiencies of BPA with initial
409
concentration of BPA, independently of temperature and DES/water ratio, can
410
be observed. The response curve temperature versus DES/water mass ratio
411
are relatively flat, with a maximum at low temperatures and low DES/water
412
mass ratio, revealing that after all the small effect of these two parameters. It is
413
important to note that the most important factor is the initial concentration of
414
BPA as well as the interaction between temperature and DES/water ratio.
415
These results were consistent with ANOVA table and also showed that higher
416
temperatures are not beneficial or required for this extraction process, as much
417
lower temperatures or even room temperature. It means that in most cases,
418
higher extraction efficiencies were achieved at 25 °C or lower temperatures.
419
As shown in Figure 8, and as previously demonstrated in the experimental
420
work, by adjusting the different factors similar extraction efficiencies can be
421
obtained. This result is very attractive for industrial application, since the
422
process can be performed at low temperatures, lowering costs in terms of
423
energy.
424
4. Reuse of DES
425
From an economical point of view, it is very important to have a solvent that can
426
be used for multiple extractions, without losing its extraction capacity. In order to
427
evaluate the possibility of reuse the DES, sequential extraction cycles were
428
carried out, always using the same DES in contact with “fresh” contaminated
429
water phase. Since [N8888]Br: C10 allowed to achieve the highest extraction
430
efficiencies, this DES was chosen. The results for five consecutive DES reuse
431
cycles are shown in Figure 9 and listed in Table B7 in Appendices. 22
432 433
Figure 9. Extraction capability (EE %) of [N8888]Br: C10 DES during several
434
cycles ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, stirring speed = 300 rpm,
435
temperature = 25 ºC, contact time = 10 min).
436 437
From the analysis of Figure 9 it is obvious that [N8888]Br: C10 DES could be
438
reused up to five times without loss of its BPA extraction capability. This is
439
directly related to the solubility of BPA in DES which was verified that is around
440
five hundred times higher than in water. As mentioned before this is an
441
important property from the economic and the sustainable point of view.
442
5. Conclusions
443
Hydrophobic DES have attracted considerable attention as task specific
444
solvents for the extraction micropollutants, which typically are also hydrophobic,
445
without contamination of water streams. In the present work, several
446
hydrophobic DES, prepared using natural hydrophobic compounds such as DL-
447
Menthol and fatty acids and several quaternary ammonium salts, were prepared
448
and their efficiency in the extraction of an emerging micropollutant, Bisphenol-A, 23
449
from water environments, evaluated. The results showed that [N8888]Br: C10 can
450
extract almost 100% of BPA from water environments under the optimal
451
conditions. The recycling of DES is also possible due to its large capacity for
452
this micro pollutant.
453 454
Acknowledgements
455
C. Florindo and L. C. Branco, gratefully acknowledge the financial support of
456
FCT/MCTES (Portugal) for the PhD fellowship SFRH/BD/102313/2014 and for
457
the contract under Programa Investigador FCT 2013 (IF/0041/2013). This work
458
was financed by CQE project (UID/QUI/00100/2013) and Research Unit
459
GREEN-it "Bioresources for Sustainability" (UID/Multi/04551/2013).
460 461
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28
APPENDICES
Hydrophobic deep eutectic solvents for purification of water contaminated with bisphenol-A
C. Florindo,1,2 Nathalie V. Monteiro,1 Bernardo D. Ribeiro,3 L. C. Branco4 and I. M. Marrucho1,2*
1
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de
Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal 2
Instituto de Tecnologia Química e Biológica António Xavier, www.itqb.unl.pt,
Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal 3
Escola de Química, Universidade Federal Do Rio de Janeiro, 21941-598 Rio
de Janeiro, Brazil 4
REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de
Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
*Corresponding Author: Isabel M. Marrucho ([email protected])
A. Deep Eutectic Solvents Synthesis and characterization Table A1. List of the hydrophobic DESs prepared in this work.
HBA
Tetraheptylammonium bromide, [N7777]Br
HBD
Octanoic acid, C8 acid Decanoic acid, C10 acid
Tetraoctylammonium bromide, [N8888]Br
Octanoic acid, C8 acid Decanoic acid, C10 acid
Methyltrioctylammonium bromide, [N8881]Br
Octanoic acid, C8 acid Decanoic acid, C10 acid DL-Menthol
MW
Molar
(g/mol)
Ratio
[N7777]Br: C8
259.70
1:2
[N7777]Br: C10
278.40
1:2
[N8888]Br: C8
278.40
1:2
[N8888]Br: C10
297.10
1:2
[N8881]Br: C8
245.68
1:2
[N8881]Br: C10
264.38
1:2
253.71
1:2
DL-Menthol: C8
148.23
1:2
DL-Menthol: C10
166.93
1:2
Abbreviation
[N8881]Br: DLMenthol
DL-Menthol
Octanoic acid, C8 acid Decanoic acid, C10 acid
S2
Characterization of the best DES studied, [N8888]Br: C10
Decanoic acid, C10
[N8888]Br
0.00
[N8888]Br: C10 (1:2)
4000
3500
3000
2500 2000 Wavenumber cm-1
1500
1000
Figure A1. FTIR analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
S3
Figure A2. DSC analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
Figure A3. TGA analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
S4
B. Liquid-liquid extraction technique Table B1. Extraction efficiencies (EE %) of Bisphenol - A obtained for all DESs (1:2 molar ratio) used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, DES/water ratio = 1/1, temperature = 25 ºC, contact time = 10 min).
DESs
Extraction Efficiencies (EE%)
[N7777]Br: C8
94.91 ± 1.919
[N7777]Br: C10
97.10 ± 1.547
[N8888]Br: C8
90.48 ± 2.039
[N8888]Br: C10
97.61 ± 1.567
[N8881]Br: C8
84.24 ± 2.523
[N8881]Br: C10
91.99 ± 3.026
[N8881]Br: DL-Menthol
91.45 ± 3.026
DL-Menthol: C8
81.65 ± 1.938
DL-Menthol: C10
92.43 ± 1.231
S5
Table B2. Influence of ratio between HBA and HBD in some DESs on the extraction efficiencies (EE %) ([C0]BPA = 0.1 g/L, Stirring speed = 300 rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
Extraction Efficiencies (EE %) DESs 1:2
1:3
1:4
[N7777]Br: C10
97.10 ± 1.234
94.69 ± 0.971
93.89 ± 1.342
[N8888]Br: C8
92.80 ± 2.039
89.89 ± 2.322
87.36 ± 0.238
[N8881]Br: C8
84.24 ± 2.523
82.75 ± 1.609
81.75 ± 0.613
83.30 ± 1.478
73.63 ± 1.500
85.29 ± 1.483
81.01 ± 1.938
79.39 ± 1.655
78.45 ± 2.898
[N8881]Br: DLMenthol DL-Menthol: C8
1:5
86.77 ± 0.786 81.78 ± 0.274 84.02 ± 1.582 79.76 ± 2.696
S6
Table B3. Influence of initial concentration of Bisphenol-A on the extraction efficiencies (EE %) for all DESs used in this work (Stirring speed = 300 rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
Extraction Efficiencies (EE %) DESs 100ppm
50ppm
25ppm
[N7777]Br: C8
94.91 ± 1.938
81.63 ± 2.5034
64.31 ± 2.473
[N7777]Br: C10
97.10 ± 1.231
96.34 ± 0.442
93.20 ± 0.981
[N8888]Br: C8
87.79 ± 1.919
81.87 ± 1.058
67.47 ± 0.314
[N8888]Br: C10
97.31 ± 1.547
94.79 ± 0.216
86.35 ± 0.432
[N8881]Br: C8
79.57 ± 2.039
73.20 ± 0.583
47.46 ± 2.198
[N8881]Br: C10
86.54 ± 1.567
88.19 ± 0.615
78.30 ± 1.452
[N8881]Br: DL-Menthol
89.41 ± 2.523
84.88 ± 0.356
71.44 ± 0.648
DL-Menthol: C8
81.65 ± 3.026
73.22 ± 0.583
59.81 ± 0.255
DL-Menthol: C10
94.17 ± 2.892
91.12 ± 1.155
82.15 ± 3.219
Table B4. Influence of contact time on the extraction efficiencies (EE %) for the best deep eutectic solvents used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature = 25 ºC, DES/water ratio = 1/1).
Extraction Efficiencies (EE %) DESs 5 min
10 min
20 min
30 min
[N7777]Br: C10
97.70 ± 0.240
98.46 ± 0.343
97.63 ± 0.306
98.40 ± 1.456
[N8888]Br: C10
98.44 ± 0.279
99.14 ± 0.573
97.94 ± 0.762
98.47 ± 0.887
[N8881]Br: C10
93.84 ± 0.970
94.55 ± 0.133
93.85 ± 0.322
93.98 ± 0.457
92.21 ± 0.545
92.47 ± 0.259
92.06 ± 0.032
91.88 ± 0.234
95.16 ±1.633
94.97 ± 0.466
95.19 ± 1.139
95.09 ± 0.791
[N8881]Br: DLMenthol DL-Menthol: C10
S7
Table B5. Influence of stirring speed on the extraction efficiencies (EE %) for the best DESs used in this work ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, temperature = 25 ºC, contact time = 10 min).
Extraction Efficiencies (EE %) DESs 100 rpm
300 rpm
500 rpm
750 rpm
[N7777]Br: C10
97.31 ± 0.239
97.10 ± 0.343
96.84 ± 0.306
95.91 ± 1.456
[N8888]Br: C10
98.36 ± 0.852
99.14 ± 0.718
97.94 ± 0.643
96.47 ± 0.869
[N8881]Br: C10
92.60 ± 1.023
92.65 ± 0.733
92.08 ± 0.321
91.65 ± 0.467
91.99 ± 0.545
91.00 ± 0.259
91.45 ± 0.256
92.08 ± 0.234
95.60 ± 0.805
94.53 ± 0.272
95.65 ± 0.238
93.09 ± 0.713
[N8881]Br: DLMenthol DL-Menthol: C10
S8
Table B6. Effect of DES/water ratio on the extraction efficiencies (EE %) for all DESs used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature = 25 ºC, contact time = 10 min).
Extraction Efficiencies (EE %) DESs 1/3
1/2
1/1
3/1
[N7777]Br: C8
95.06 ± 0.230
94.03 ± 0.128
94.35±0.793
79.31 ± 0.928
[N7777]Br: C10
98.70 ± 0.300
98.94 ± 0.600
97.10±0.650
96.00 ± 0.380
[N8888]Br: C8
88.33 ± 0.960
91.07 ± 0.485
91.24±1.071
77.12 ± 1.938
[N8888]Br: C10
98.23 ± 0.671
98.68 ± 0.190
97.03±0.815
95.86 ± 0.707
[N8881]Br: C8
86.40 ± 2.340
85.03 ± 0.730
84.22±0.023
65.72 ± 1.624
[N8881]Br: C10
94.74 ± 0.196
92.97 ± 0.888
90.33±2.350
87.60 ± 1.120
[N8881]Br: DL-
92.21 ± 0.400
91.00 ± 0.600
87.89±5.022
84.55 ± 1.473
DL-Menthol: C8
83.75 ± 4.494
85.03 ± 0.730
84.22±0.023
61.13 ± 0.967
DL-Menthol: C10
94.88 ± 0.500
94.83 ± 0.600
93.91±0.400
89.82 ± 1.141
Menthol
S9
Table B7. Extraction capability (EE %) of [N8888]Br: C10 DES during several cycles ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, stirring speed = 300 rpm, temperature = 25 ºC, contact time = 10 min).
[N8888]Br: C10
Extraction Efficiencies (EE%)
1st cycle
98.5714
2nd cycle
98.7744
3rd cycle
98.3985
4th cycle
98.7068
5th cycle
98.8571
S10
C. Design Experimental Experiment Table C1. Extraction efficiencies obtained for removal of Bisphenol-A from water environments using a central composite design (CCD). Experimen
DES/wate
Temperat
C0 of BPA
EE
ts
r Ratio
ure
(%)
1
0.96
26.0
0.04
97.35
2
0.96
26.0
0.08
99.19
3
0.96
45.0
0.04
96.28
4
0.96
45.0
0.08
98.49
5
3.05
26.0
0.04
87.44
6
3.05
26.0
0.08
97.56
7
3.05
45.0
0.04
92.86
8
3.05
45.0
0.08
97.78
9
0.24
35.0
0.06
98.45
10
3.76
35.0
0.06
95.94
11
2.00
19.0
0.06
97.98
12
2.00
51.0
0.06
95.79
13
2.00
35.0
0.03
91.44
14
2.00
35.0
0.09
97.72
15 (C)
2.00
35.0
0.06
95.74
16 (C)
2.00
35.0
0.06
95.78
17 (C)
2.00
35.0
0.06
95.78
S11
Highlights
•
Hydrophobic DESs combining natural components were prepared.
•
An endocrine disruptor micropollutant is removed from aqueous environments.
•
All hydrophobic DESs showed promising abilities of extracting Bisphenol-A.
•
Hydrophobic DES can be reused for several cycles.
•
The process of extraction is feasible from an economical and time-consuming point of view.
No conflict of interests are declared.
S0167-7322(19)33526-3
DOI:
https://doi.org/10.1016/j.molliq.2019.111841
Reference:
MOLLIQ 111841
To appear in:
Journal of Molecular Liquids
Received Date: 23 June 2019 Revised Date:
26 September 2019
Accepted Date: 27 September 2019
Please cite this article as: C. Florindo, N.V. Monteiro, B.D. Ribeiro, L.C. Branco, I.M. Marrucho, Hydrophobic deep eutectic solvents for purification of water contaminated with Bisphenol-A, Journal of Molecular Liquids (2019), doi: https://doi.org/10.1016/j.molliq.2019.111841. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
1
2
Hydrophobic deep eutectic solvents for
3
purification of water contaminated with
4
Bisphenol-A
5
C. Florindo,1,2 Nathalie V. Monteiro,1 Bernardo D. Ribeiro,3 L. C. Branco4 and I. M. Marrucho1,2*
6 7 8 9 10 11
1
12
Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal
13
2
14
Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal
15
3
16
de Janeiro, Brazil
17
4
18
Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de
Instituto de Tecnologia Química e Biológica António Xavier, www.itqb.unl.pt,
Escola de Química, Universidade Federal Do Rio de Janeiro, 21941-598 Rio
REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de
19
20
21
*Corresponding author. Tel.: +351 218413385; fax: +351 218499242. E-mail address:
22
[email protected] (I. M. Marrucho). 1
23
Abstract
24
The occurrence of micropollutants in aquatic ecosystems poses a serious public
25
health and environmental problem. For that purpose, the main goal of this work
26
is the removal of an endocrine disruptor micropollutant compound, Bisphenol-A
27
(BPA), from aqueous environments using hydrophobic deep eutectic solvents
28
(DES). In particular, DES composed of DL-Menthol or quaternary ammonium
29
salts as hydrogen bond acceptors (HBA) and natural fatty acids as hydrogen
30
bond donors (HBD) were prepared. Extraction efficiencies were maximized by
31
optimizing the experimental parameters in the extraction BPA from water using
32
a central composite design combined with a response surface methodology.
33
Thus, the effect of several parameters, such as stirring speed, contact time,
34
DES/water ratio and initial BPA concentration on the extraction efficiencies were
35
evaluated.
36 37
Keywords: Hydrophobic Deep Eutectic Solvents; Wastewater Treatment;
38
Bisphenol-A; Liquid-liquid extraction; Central Composite Design
39
2
40
1. Introduction
41
Currently, one of the major societal challenges is to provide good quality
42
water to everyone, by dramatically reducing or completely eliminating the
43
current hazardous micropollutants present in the water resources around the
44
globe.1, 2 In the coming decades, water scarcity, even in regions considered to
45
be currently rich in water, puts on the 2030 agenda for the sustainable
46
development the urgent development of innovative and sustainable water
47
solutions so that clean water and sanitation can be provided to everyone.3
48
Micropollutants have been emerging as a new class of pollutants since,
49
despite their very small concentration in water streams, their presence can be
50
related to numerous harmful effects on the health of animals and humans, such
51
as carcinogenic and endocrine disrupting effects, antibiotic resistance of
52
microorganisms, etc.4-6 Heavy metals, pharmaceuticals, personal care products,
53
dyes, waterproofing treatments, plasticizers, pesticides, and others, are all
54
classified as micropollutants.7 Among these, Bisphenol-A (BPA) is an emerging
55
micropollutant of special importance since it has been detected in increasing
56
concentrations globally in water sources, as conventional water treatment plants
57
are incapable of removing it completely. BPA has been largely used as a
58
plasticizer from food and drink plastic packaging to plastic medical devices.
59
However, BPA is a also well-known endocrine disruptor compound, that mimics
60
the estrogen hormone, thus affecting the normal development and function of
61
human and wildlife reproductive system.8 Although the European Union and
62
Canada have recognized its harmful effects and banned its use in baby bottles
63
since 2011,
64
consequent removal from water sources.
9,6
there is a long way to go until its full legislative control and
3
65
The development of effective and sustainable innovative water cleaning
66
technologies, typically to complement the existing ones, is a crucial step to
67
achieve the targeted goal of sustainable development. Different extraction
68
techniques, such as aqueous biphasic systems,10,
69
adsorption15, 16 and liquid-liquid extraction17-19, have been tested for removal of
70
BPA from water, with good extraction efficiencies. However, most of these
71
techniques are not sustainable, since they are based on high cost solvents or
72
materials of difficult recycle and reuse, not to mention their hazardousness and
73
consequent water contamination. As a result, benign and recyclable solvents
74
have been searched and developed, so that a truly circular technology can be
75
achieved. Deep eutectic solvents (DES) have been highlighted as sustainable
76
solvents and showed to provide sustainable solutions in numerous scientific and
77
technological fields.20,
78
solvents for numerous applications.20 The ease of preparation, the possibility to
79
use natural and biodegradable components makes DES versatile alternative
80
green solvents.22 DES can be defined as mixtures of two or more compounds
81
composed by hydrogen bond donors (HBD) and acceptors (HBA), which can
82
form liquids at room temperature.23 DES emerged as green, sustainable and
83
more advantageous solvents compared to ionic liquids and traditional organic
84
solvents, especially considering their environmentally friendly character,
85
biodegradability, low price and straightforward preparation. This class of
86
solvents showed great potential for a diversity of applications, such as in
87
electrochemistry,24
88
extraction and separation,27, 28 catalysis,29 organic synthesis,30 among others.
21
11
liquid membranes,12-14
In recent years, DES have emerged as alternative
nanotechnology,25
stabilization
of
DNA
and
RNA,26
89
Since most DES reported in the literature are water soluble, limiting their
90
application in several processes, the development of hydrophobic DES has 4
91
been attracting the attention of researchers. The preparation and application of
92
several hydrophobic DES in extraction processes, such as removal of metal
93
ions from water, indium extraction from hydrochloric and oxalic acids, removal
94
of pesticides and endocrine disruptor compounds from water, among others 4, 17,
95
31, 32
, has already been reported.
96
The main goal of this work is to evaluate the removal of BPA, from aqueous
97
environments using hydrophobic DES. For that purpose, two different families of
98
hydrophobic DES, namely ionic and neutral, were developed and their ability to
99
extract BPA was evaluated through liquid-liquid extraction. In particular, DES
100
using natural components, as DL-Menthol which can be used as hydrogen bond
101
acceptor (HBA) and hydrogen bond donor (HBD), and different quaternary
102
ammonium salts with long alkyl chain, such as [N7777]Br, [N8888]Br and [N8881]Br,
103
as HBA combining several natural carboxylic acids as HBD, such as octanoic
104
and decanoic acid, were prepared. Chemical structures of hydrophobic DES
105
and the micropollutant used in this work, and their respective acronyms are
106
depicted in Figure 1 as well as in Table A1 in Appendices.
5
[N8888]Br
DL-Menthol Octanoic acid
Decanoic acid [N8881]Br
POLLUTANT
Bisphenol - A
107 108
Figure 1. Chemical structures and respective acronyms of DES and
109
micropollutant studied in this work.
110
Moreover, the most influential experimental parameters on the extraction of
111
BPA from water were identified and optimized using a central composite design
112
(CCD). The optimization of extraction conditions is of utmost importance, since
113
it is crucial to reduce the energy and operation associated cost, leading to
114
environmentally friendly process.
115 116
2. Experimental section
117 118
2.1. Materials
119
DL-Menthol (purity ≥ 95%), tetraheptylammonium bromide ([N7777]Br)
120
(purity ≥ 99%), tetraoctylammonium bromide ([N8888]Br) (purity ≥ 98%),
121
methyltrioctylammonium bromide ([N8881]Br) (purity ≥ 97%), octanoic acid (C8)
122
(purity ≥ 98%) and decanoic acid (C10) (purity ≥ 98%) were purchased from
6
123
Sigma-Aldrich and used as received. The micropollutant Bisphenol-A (mass
124
fraction purity ≥ 99 %) was purchased from Sigma Aldrich and used with no
125
further purification. All aqueous solutions were prepared using high purity water
126
(Milli-Q water) with a specific conductance <0.1 mS/cm.
127
2.2. Methodologies
128
2.2.1. Preparation of DES
129
Hydrophobic DES were prepared according to the methodology proposed
130
in our previous work.33 All DES were prepared by mixing the two components in
131
previously established proportions in a glass vial with a mechanical stirrer) at
132
500 rpm and 333.15 K, until a homogeneous liquid was formed. In the
133
preparation of DES, an analytical high-precision balance with an uncertainty of
134
± 10-5 g, was used to weigh the known masses of the individual compounds into
135
bottles with caps. The HBAs (DL-Menthol, tetraoctylammonium bromide
136
([N8888]Br), tetraheptylammonium bromide ([N7777]Br), methyltrioctylammonium
137
bromide ([N8881]Br) were first dried in a high vacuum pump at 40 °C for at least
138
four days, while the carboxylic acids were used without any further purification,
139
since they usually have very low amount of water. Their water contents were
140
determined by Karl Fischer titration (< 500 ppm). All prepared hydrophobic DES
141
were completely characterized by 1H and13C NMR and FTIR spectroscopy, in
142
order to confirm their expected structures and final purities.
143
2.2.2. Liquid-liquid extraction procedure
144
Liquid-liquid extractions were carried out at (25.0±0.1)oC using the
145
prepared hydrophobic DES as extractants. BPA can be found in water
146
environments at very low concentrations, usually ranging from ng/L to mg/L. In
147
this work, in order to use a simple and fast screening technique, UV-vis 7
148
spectroscopy, slightly greater concentrations were prepared using stock
149
aqueous solutions of BPA of 100 mg/L, 50 mg/L and 25 mg/L.
150
Mixtures composed by each one of the prepared hydrophobic DES and the
151
aqueous solution of BPA were initially stirred vigorously during 10 min, which
152
was the minimum time to reach equilibrium, and then left to settle for 12h, to
153
ensure complete separation of phases. The extractions were carried out at
154
(25.0±0.1)oC. Thereafter, the two phases were carefully separated using a
155
needled syringe and the concentration of the remaining micropollutant in the
156
water-rich phase was measured using UV–vis spectroscopy with a Shimadzu
157
model UV-1800–Pharma-Spec spectrophotometer. Furthermore, to eliminate
158
possible interferences of DES and their interaction with micropollutant in the
159
quantification, only the concentration of BPA in the water phase was
160
experimentally determined. A calibration curve was previously established for
161
BPA in Milli-Q water (curves with R2 > 0.997). All the experiments were carried
162
out in triplicates so that standard deviations of the measurements could be
163
calculated.
164 165
3. Results and discussion 3.1. Performance of different DES as extractants
166
In this work, hydrophobic DES were prepared using ionic hydrophobic
167
compounds such as quaternary ammonium salts with long alkyl chains, namely
168
[N7777]Br, [N8888]Br and [N8881]Br and carboxylic acids, while neutral hydrophobic
169
DES were prepared combining a natural compound, DL-menthol, with
170
carboxylic acids. These DES were prepared at a molar ratio of 1:2, which was
171
determined to be liquid in previous works where phase diagrams of each
172
system were measured. The studied DES are listed in Table A1 in Appendices. 8
173
Terms like deep eutectic solvents, eutectic solvents, eutectic mixtures or low
174
transition temperature mixtures have been used in literature until now to
175
designate this class of compounds, which means that the acronym DES has
176
been used to designate eutectic mixtures that are liquid at room temperature
177
and thus can be used as solvents. In this work we have used deep eutectics
178
(those based on quaternary ammonium salts) and not deep eutectics (those
179
based on DL-Menthol). Although we acknowledge here this difference, we have
180
used the acronym DES for all the solvents used in this work, independently of
181
the fact of the depression in the melting point being deep or not.
182
Nine hydrophobic DES were initially screened for extraction of Bisphenol-A from
183
water environments. The extraction efficiencies, EE %, were calculated from the
184
Bisphenol-A (BPA) concentration in the water-rich phase before, , , and
185
after the extraction, , :
186
(%) =
, ,
,
x 100
(eq. 1)
187 188
The extraction efficiencies of BPA using several DES are displayed in Figure 2,
189
and listed in Table B1 in Appendices.
9
100
80
EE%
60
40
[N
88
81
[N
88
0
88 ]B ]B r: r[ : C ND 10 8 8L 8 1M ]Be n [N r:th [N 88 Col 88 8 81 81 ]B ]B r: r: C D 10 LM en D th Lol M en th D ol L:C M en 8 th ol :C 10
20
190 191
Figure 2. Extraction efficiencies (EE %) of Bisphenol-A obtained for all DES
192
used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, DES/water ratio =
193
1/1, temperature = 25 ºC, contact time = 10 min).
194
Good extraction efficiencies (> 85%) of BPA from contaminated water were
195
achieved using all the selected hydrophobic DES. These large extraction
196
efficiency values to remove BPA from water are essentially linked to the DES
197
hydrophobicity, since BPA possess a very low water solubility (~120mg/L at
198
25ºC) and a high octanol-water partition coefficient (Kow) of 3.40,34 leading to a
199
large affinity for the organic hydrophobic DES phase. However, some difference
200
in the extraction efficiencies between the studied DES can be observed.
201
Analysing the data in Figure 2, it is clear that the extraction efficiencies depend
202
on the choice of the components of DES, especially on the HBD. Moreover, the
10
203
extraction efficiencies increased with the increase of the alkyl chain length in
204
both the fatty acid and also in the quaternary ammonium salt, which
205
corroborates our previous remarks on the fact that the more hydrophobic the
206
DES are, the higher the extraction efficiencies.35 Thus, the extraction
207
efficiencies of BPA follow the HBA order: [N8888]Br: HBD (∼98% EE) > [N7777]Br:
208
HBD (∼95% EE) > [N8881]Br: HBD (∼91% EE) ≥ DL-Menthol: HBD (∼87% EE).
209
Regarding the HBD of DES, the trend of the extraction efficiencies can be
210
organized in the following order [N7777]Br > [N8888]Br > [N8881]Br > DL-Menthol
211
for C8 acid, and [N7777]Br ~ [N8888]Br > [N8881]Br > DL-Menthol for C10 acid,
212
where the latter is the DES with the lowest EE%.
213
For all the HBAs studied there is a small difference in the BPA extraction
214
between octanoic and decanoic acid, except for [N7777]Br where similar results
215
within the experimental error were obtained. Looking at [N8881]Br as HBA, it can
216
be seen that extraction efficiencies using DL-Menthol and decanoic acid as
217
HBDs are also comparable, probably due their similar hydrophilicity.
218
Consequently, it can be concluded that the extraction of BPA from water seems
219
to be directly related to water solubility of components of the hydrophobic DES.
220 221 222
3.2. Screening of experimental parameters influencing the extraction efficiency
223
The optimization of the experimental parameters of a process is perhaps the
224
most important aspect for its implementation at an industrial level, since it
225
largely influences the cost/efficiency ratio. Therefore, in this section, the
226
influence of several experimental variables, such as mass ratio of HBA/HBD of
227
DES, contact time, stirring speed of mixing, DES to water ratio and initial
11
228
concentration of micropollutant, in the extraction efficiencies is evaluated and
229
discussed in detail.
230 231
3.2.1. HBA/HBD molar ratio
232
As it has been recognized by several authors, the molar ratio between HBA and
233
HBD is one of the important factors influencing the physicochemical properties
234
of DES.36 In order to explore the impact of using different molar ratio of eutectic
235
mixtures, where they are still liquid at working temperature, on the extraction
236
efficiencies of BPA, four molar HBA: HBD ratios (1:2, 1:3, 1:4 and 1:5) were
237
selected and used to prepare DES belonging to the three quaternary
238
ammonium salts DES families ([N7777]Br, [N8888]Br and [N8881]Br) and DL-
239
Menthol DES family. The reason to select these specific molar ratios of HBA:
240
HBD is due to the fact that higher proportions of salt than acid would not lead to
241
liquid phase at room temperature. The extraction results of BPA from aqueous
242
solutions using different molar HBA:HBD proportions of different ionic and
243
neutral DES are presented in Figure 3 and also listed in Table B2 in
244
Appendices.
12
100 1:2 1:3 1:4 1:5
80
EE%
60
40
20
ho D
LM en
th
en t M r: D L-
[N
88 81
]B
[N
ol :C 8
l
8 B r: C 88 81 ]
r: C 7] B 77 7
[N
[N
88 88 ]
B r: C
10
8
0
245 246
Figure 3. Influence of HBA: HBD ratio of five DES families on the extraction
247
efficiencies (EE %) of BPA ([C0]BPA = 0.1 g/L, Stirring speed = 300 rpm,
248
DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
249 250
It can be seen that the molar ratios do not significantly influence the extraction
251
efficiencies for the studied DES, and [N8888]Br:C8 is the one where larger
252
differences in the BPA extraction efficiencies with the HBA:HBD molar ratios
253
were observed. Thus, in general, it can be concluded that the incorporation of
254
more acid (increasing from 1:2 to 1:5) does not favour the extraction efficiencies
255
of BPA for both ionic and neutral DES. Since the best performance for all the
256
studied systems was always achieved using the lowest HBA: HBD molar ratio
257
(1:2), this ratio was chosen to carry out further studies.
258
13
3.2.2. Effect of initial concentration of BPA in water
259 260
In order to explore the effect of initial concentration of micropollutant on the
261
extraction efficiency of BPA, the initial concentration was varied from 0.1 g/L to
262
0.025 g/L (100, 50 and 25 ppm) and the obtained results are presented in
263
Figure 4 and listed in Table B3 in Appendices. 100
80 0.1 g/L 0.05 g/L 0.025 g/L
EE %
60
40
ac
id
10
ac 8
:C
en
th
ol
ol th en
M LD
D
L-
M
]B 81
:C
M Lr:
D
81 88
[N 88 [N
ol en
C r: ]B
]B 81 88
th
10
8 C r:
C r: ]B [N
[N
77
77
77 77 [N
10
8 C r: ]B
r: ]B
88 88
[N
[N
88
88
]B
r:
C
C
8
10
0
id
20
264 265
Figure 4. Influence of initial concentration of Bisphenol-A in water on the
266
extraction efficiencies (EE %) for all DES used in this work (Stirring speed = 300
267
rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
268 269
It can be seen that the initial concentration of the BPA greatly influences the
270
EE% of BPA for the majority of the studied DES. Overall, extraction efficiencies
271
decrease as the concentration of BPA decreases as follows: 0.1 g/L > 0.05 g/L
272
> 0.025 g/L. However, for DES composed of decanoic acid as HBD, this
273
decrease in %EE is much smaller than for DES composed of more hydrophilic
274
HBD, such as octanoic acid or DL-Menthol. This fact is true for the all studied 14
275
DES, both ionic and neutral. This behavior of the EE% with BPA initial
276
concentration is linked to hydrophobic character of the HBD: the extraction
277
efficiencies of BPA carried out with DES composed of decanoic acid are less
278
affected by the initial concentration of micropollutant than those composed of
279
octanoic acid or DL-menthol as HBD. This gives the opportunity to tune the
280
DES chemical structure through the HBD in order to maintain the extraction
281
efficiency. In some cases, such as [N7777]Br: C10, the differences achieved in
282
the EE% at different initial concentrations of BPA are negligible. In conclusion,
283
the best DES to efficiently remove BPA at low concentrations are the ionic most
284
hydrophobic, [N7777]Br: C10 and [N8888]Br: C10, and therefore the less effective
285
are the most hydrophilic, [N8881]Br: C8 and DL-Menthol: C8.
286 287
3.2.3. Effect of contact time
288
Contact time is a crucial parameter that reflects the kinetics of the separation
289
process. A fast kinetics, as thus a short contact time, is usually desired. In order
290
to find the optimal time to carry out the extraction of BPA from aqueous
291
solutions, the best DES of each family, those with HBA: HBD ratio of (1:2), were
292
selected to perform these experiments. Figure 5 shows the extraction
293
efficiencies of BPA from water as a function of time at 25 ºC and also listed in
294
Table B4 in Appendices.
295 296 297 298
15
100
EE %
95
90
[N7777]Br: C10 [N8888]Br: C10 [N8881]Br: C10 [N8881]Br: DL-Menthol DL-Menthol: C10
85
80 5
10
20
30
Time (min)
299 300
Figure 5. Influence of contact time on the extraction efficiencies (EE %) for the
301
best DES used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm,
302
temperature = 25 ºC, DES/water ratio = 1/1).
303 304
It can be concluded that the extraction process of BPA using all the proposed
305
DES is quite fast, and the equilibrium can be reached after 5 to 10 min. Thus,
306
the contact time was set to 10 min to ensure that the equilibrium is attained for
307
all DES.
308 309
3.2.4. Effect of stirring speed
310
Stirring speed is another parameter that might influence the extraction efficiency
311
of BPA. The influence of stirring speed on the extraction efficiencies of BPA for
312
the most performing DES used in this work, which are [N7777]Br: C10, [N8888]Br:
313
C10, [N8881]Br: C10, [N8881]Br: DL-Menthol and DL-Menthol: C10, is shown in
314
Figure 6 and listed in Table B5 in Appendices.
16
100
EE %
95
90
[N7777]Br: C10 [N8888]Br: C10 [N8881]Br: C10 [N8881]Br: DL-Menthol DL-Menthol: C10
85
80 100
300
500
750
Stirring speed (rpm)
315 316
Figure 6. Influence of stirring speed on the extraction efficiencies (EE %) for the
317
best DES used in this work ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1,
318
temperature = 25 ºC, contact time = 10 min).
319 320
These results show that the increase of the stirring speed leads to a minor
321
decrease in the EE% for some DES, especially for the highest stirring speed,
322
750 rpm. This can probably be due to the different solubilities of water in DES35
323
and the fact that the stirring speed might affect the dispersion of water in the
324
studied DES. On the other hand, for [N8881]Br: C10
325
negligible, taking into account the error bars. In conclusion, not taking into
326
account the highest stirring speed, after 300 rpm, no significant increase in EE%
327
is obtained. Thus, 300 rpm was chosen as the optimal extraction stirring speed,
328
for energetic considerations.
this effect is almost
329 330
3.2.5. Effect of DES/water mass ratio
17
331
In terms of cost of an industrial extraction process, it is desirable to obtain
332
higher extraction efficiencies for a minimum amount of solvent. The effect of the
333
mass ratio of the DES/water phases in the BPA extraction efficiencies was
334
studied and the results are shown in Figure 7 and listed in Table B6 in
335
Appendices.
336 337 338 100
80 1/3 1/2 1/1 3/1
EE %
60
40
20
ac ]B 88 r id : 81 C 10 ]B r: ac D D id LLM M en en th D th Lol ol M :C en 8 th ac ol id :C 10 ac id
d
r: C 8
88 81
[N
[N
88 8
1] B
10
ac i
ac id r: C
]B
77 77 [N
[N
ac i
r: C 8
10 77 7
7] B
r: C
]B [N
88 88 [N
[N
88 8
8] B
r: C 8
ac id
d
0
339 340
Figure 7. Effect of DES/water ratio on the extraction efficiencies (EE %) for all
341
DES used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature
342
= 25 ºC, contact time = 10 min).
343
18
344
It can be observed that the increase of DES/water mass ratio does not have a
345
significant effect in the BPA extraction efficiencies. An exception is the case of
346
3/1 DES/water ratio, where a large decrease in the extraction efficiencies is
347
observed for DES based on octanoic acid as HBD. These results are probably
348
due to the lower hydrophobicity of these DES and higher solubility of water in
349
them.35
350
In general, these results show that only a small mass of DES is needed to treat
351
large volumes of contaminated water, which is probably due to high
352
hydrophobicity of the DES and the very low solubility of BPA in water. These
353
results are of particular importance when the DES starting materials are
354
expensive, such as in the case of hydrophobic quaternary ammonium salts with
355
long alkyl chains.
356 357 358
3.3. Optimization
of
the
extraction
efficiency
using
Experimental Design
359 360
The response surface methodology (RSM) is a useful and efficient statistical
361
tool which allows optimizing the response of a system to the change of a set of
362
independent variables. In this work, a Central Composite Design (CCD) was
363
used to determine a set of experimental conditions leading to an optimal
364
extraction efficiency of BPA. From the previously carried out studies, two
365
experimental parameters, initial concentration of micropollutant and the
366
DES/water mass ratio, could be identified as important for the extraction of
367
Bisphenol-A
368
experimental parameter that, generally, greatly influences the solubility and,
369
consequently, the extraction processes. Since [N8888]Br: C10 (1:2) DES
from
water
environments.
Temperature
is
also
another
19
370
presented the highest extraction efficiency values, it was selected to be used in
371
CCD, where the optimal temperature, DES/water ratio and initial concentration
372
of BPA parameter to achieve the highest extraction efficiencies.
373
The levels of the studied variables are shown in Table 1.
374 375
Table 1. Optimization of BPA extraction for [N8888]Br: C10 (1:2) using a
376
experimental central composite design.
377
Experimental Factors Temperature DES/water Ratio Initial Concentration (C0)
- 1.68
-1
0
+1
+ 1.68
19
26
35
45
50
0.24
0.96
2
3.05
3.76
0.03
0.04
0.06
0.08
0.09
of BPA 378 379 380
A fixed extraction time of 10 min and stirring speed of 300 rpm were used, since
381
these parameters do not influence the extraction efficiencies. The experimental
382
data obtained were analyzed by Pareto analysis of variance (ANOVA) and fitted
383
to
384
analysis. Detailed data are provided in Appendices.
385
The statistical design software STATISTICA 6.0 (Statsoft Inc., Tulsa, U.S.A.)
386
was used to analyze the data and graphically display the results. Central
387
composite design was implemented for the experimental design analysis, using
388
the response surface and the desirability approach, which converts each
389
response variable in an individual desirability function ranging from 0 to 1. This
a
second-order
polynomial
equation
using
multiple
regression
20
390
design allows the interpretation of the association between the response of the
391
percentage of extraction efficiencies and the independent variables that
392
influence the BPA extraction from water. The influence of each parameter in
393
BPA extraction efficiency using a CCD is illustrated in Figure 8 and listed in
394
Table C1 in Appendices.
395
396 397
i) ii) iii) Figure 8. Response surface (top) and desirability plots (bottom) of the
398
extraction efficiencies (EE %) of BPA from water using [N8888]Br:C10 DES with
399
the combined effects of: i) Temperature and DES/water ratio; ii) initial
400
concentration of BPA in water and DES/water ratio; and iii) initial concentration
401
of BPA in water and Temperature.
402 403
An F-test and p-value were applied to the obtained model to check the
404
significance of each coefficient. The low p-value (< 0.0001) and the high F-test
405
indicate the suitability of the model. The repeatability of the model was assured
21
406
through an average of three replicas of extraction efficiencies experiments with
407
95.77 ± 0.02 of EE%.
408
In Figure 8 b) a steep decrease of the extraction efficiencies of BPA with initial
409
concentration of BPA, independently of temperature and DES/water ratio, can
410
be observed. The response curve temperature versus DES/water mass ratio
411
are relatively flat, with a maximum at low temperatures and low DES/water
412
mass ratio, revealing that after all the small effect of these two parameters. It is
413
important to note that the most important factor is the initial concentration of
414
BPA as well as the interaction between temperature and DES/water ratio.
415
These results were consistent with ANOVA table and also showed that higher
416
temperatures are not beneficial or required for this extraction process, as much
417
lower temperatures or even room temperature. It means that in most cases,
418
higher extraction efficiencies were achieved at 25 °C or lower temperatures.
419
As shown in Figure 8, and as previously demonstrated in the experimental
420
work, by adjusting the different factors similar extraction efficiencies can be
421
obtained. This result is very attractive for industrial application, since the
422
process can be performed at low temperatures, lowering costs in terms of
423
energy.
424
4. Reuse of DES
425
From an economical point of view, it is very important to have a solvent that can
426
be used for multiple extractions, without losing its extraction capacity. In order to
427
evaluate the possibility of reuse the DES, sequential extraction cycles were
428
carried out, always using the same DES in contact with “fresh” contaminated
429
water phase. Since [N8888]Br: C10 allowed to achieve the highest extraction
430
efficiencies, this DES was chosen. The results for five consecutive DES reuse
431
cycles are shown in Figure 9 and listed in Table B7 in Appendices. 22
432 433
Figure 9. Extraction capability (EE %) of [N8888]Br: C10 DES during several
434
cycles ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, stirring speed = 300 rpm,
435
temperature = 25 ºC, contact time = 10 min).
436 437
From the analysis of Figure 9 it is obvious that [N8888]Br: C10 DES could be
438
reused up to five times without loss of its BPA extraction capability. This is
439
directly related to the solubility of BPA in DES which was verified that is around
440
five hundred times higher than in water. As mentioned before this is an
441
important property from the economic and the sustainable point of view.
442
5. Conclusions
443
Hydrophobic DES have attracted considerable attention as task specific
444
solvents for the extraction micropollutants, which typically are also hydrophobic,
445
without contamination of water streams. In the present work, several
446
hydrophobic DES, prepared using natural hydrophobic compounds such as DL-
447
Menthol and fatty acids and several quaternary ammonium salts, were prepared
448
and their efficiency in the extraction of an emerging micropollutant, Bisphenol-A, 23
449
from water environments, evaluated. The results showed that [N8888]Br: C10 can
450
extract almost 100% of BPA from water environments under the optimal
451
conditions. The recycling of DES is also possible due to its large capacity for
452
this micro pollutant.
453 454
Acknowledgements
455
C. Florindo and L. C. Branco, gratefully acknowledge the financial support of
456
FCT/MCTES (Portugal) for the PhD fellowship SFRH/BD/102313/2014 and for
457
the contract under Programa Investigador FCT 2013 (IF/0041/2013). This work
458
was financed by CQE project (UID/QUI/00100/2013) and Research Unit
459
GREEN-it "Bioresources for Sustainability" (UID/Multi/04551/2013).
460 461
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28
APPENDICES
Hydrophobic deep eutectic solvents for purification of water contaminated with bisphenol-A
C. Florindo,1,2 Nathalie V. Monteiro,1 Bernardo D. Ribeiro,3 L. C. Branco4 and I. M. Marrucho1,2*
1
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de
Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal 2
Instituto de Tecnologia Química e Biológica António Xavier, www.itqb.unl.pt,
Universidade Nova de Lisboa, Apartado 127, 2780-901 Oeiras, Portugal 3
Escola de Química, Universidade Federal Do Rio de Janeiro, 21941-598 Rio
de Janeiro, Brazil 4
REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de
Lisboa, Campus da Caparica, 2829-516 Caparica, Portugal
*Corresponding Author: Isabel M. Marrucho ([email protected])
A. Deep Eutectic Solvents Synthesis and characterization Table A1. List of the hydrophobic DESs prepared in this work.
HBA
Tetraheptylammonium bromide, [N7777]Br
HBD
Octanoic acid, C8 acid Decanoic acid, C10 acid
Tetraoctylammonium bromide, [N8888]Br
Octanoic acid, C8 acid Decanoic acid, C10 acid
Methyltrioctylammonium bromide, [N8881]Br
Octanoic acid, C8 acid Decanoic acid, C10 acid DL-Menthol
MW
Molar
(g/mol)
Ratio
[N7777]Br: C8
259.70
1:2
[N7777]Br: C10
278.40
1:2
[N8888]Br: C8
278.40
1:2
[N8888]Br: C10
297.10
1:2
[N8881]Br: C8
245.68
1:2
[N8881]Br: C10
264.38
1:2
253.71
1:2
DL-Menthol: C8
148.23
1:2
DL-Menthol: C10
166.93
1:2
Abbreviation
[N8881]Br: DLMenthol
DL-Menthol
Octanoic acid, C8 acid Decanoic acid, C10 acid
S2
Characterization of the best DES studied, [N8888]Br: C10
Decanoic acid, C10
[N8888]Br
0.00
[N8888]Br: C10 (1:2)
4000
3500
3000
2500 2000 Wavenumber cm-1
1500
1000
Figure A1. FTIR analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
S3
Figure A2. DSC analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
Figure A3. TGA analysis of the hydrophobic DESs ([N8888]Br: C10) studied in this work.
S4
B. Liquid-liquid extraction technique Table B1. Extraction efficiencies (EE %) of Bisphenol - A obtained for all DESs (1:2 molar ratio) used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, DES/water ratio = 1/1, temperature = 25 ºC, contact time = 10 min).
DESs
Extraction Efficiencies (EE%)
[N7777]Br: C8
94.91 ± 1.919
[N7777]Br: C10
97.10 ± 1.547
[N8888]Br: C8
90.48 ± 2.039
[N8888]Br: C10
97.61 ± 1.567
[N8881]Br: C8
84.24 ± 2.523
[N8881]Br: C10
91.99 ± 3.026
[N8881]Br: DL-Menthol
91.45 ± 3.026
DL-Menthol: C8
81.65 ± 1.938
DL-Menthol: C10
92.43 ± 1.231
S5
Table B2. Influence of ratio between HBA and HBD in some DESs on the extraction efficiencies (EE %) ([C0]BPA = 0.1 g/L, Stirring speed = 300 rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
Extraction Efficiencies (EE %) DESs 1:2
1:3
1:4
[N7777]Br: C10
97.10 ± 1.234
94.69 ± 0.971
93.89 ± 1.342
[N8888]Br: C8
92.80 ± 2.039
89.89 ± 2.322
87.36 ± 0.238
[N8881]Br: C8
84.24 ± 2.523
82.75 ± 1.609
81.75 ± 0.613
83.30 ± 1.478
73.63 ± 1.500
85.29 ± 1.483
81.01 ± 1.938
79.39 ± 1.655
78.45 ± 2.898
[N8881]Br: DLMenthol DL-Menthol: C8
1:5
86.77 ± 0.786 81.78 ± 0.274 84.02 ± 1.582 79.76 ± 2.696
S6
Table B3. Influence of initial concentration of Bisphenol-A on the extraction efficiencies (EE %) for all DESs used in this work (Stirring speed = 300 rpm, DES/water ratio = 1/1, Temperature = 25 ºC, Contact time = 10 min).
Extraction Efficiencies (EE %) DESs 100ppm
50ppm
25ppm
[N7777]Br: C8
94.91 ± 1.938
81.63 ± 2.5034
64.31 ± 2.473
[N7777]Br: C10
97.10 ± 1.231
96.34 ± 0.442
93.20 ± 0.981
[N8888]Br: C8
87.79 ± 1.919
81.87 ± 1.058
67.47 ± 0.314
[N8888]Br: C10
97.31 ± 1.547
94.79 ± 0.216
86.35 ± 0.432
[N8881]Br: C8
79.57 ± 2.039
73.20 ± 0.583
47.46 ± 2.198
[N8881]Br: C10
86.54 ± 1.567
88.19 ± 0.615
78.30 ± 1.452
[N8881]Br: DL-Menthol
89.41 ± 2.523
84.88 ± 0.356
71.44 ± 0.648
DL-Menthol: C8
81.65 ± 3.026
73.22 ± 0.583
59.81 ± 0.255
DL-Menthol: C10
94.17 ± 2.892
91.12 ± 1.155
82.15 ± 3.219
Table B4. Influence of contact time on the extraction efficiencies (EE %) for the best deep eutectic solvents used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature = 25 ºC, DES/water ratio = 1/1).
Extraction Efficiencies (EE %) DESs 5 min
10 min
20 min
30 min
[N7777]Br: C10
97.70 ± 0.240
98.46 ± 0.343
97.63 ± 0.306
98.40 ± 1.456
[N8888]Br: C10
98.44 ± 0.279
99.14 ± 0.573
97.94 ± 0.762
98.47 ± 0.887
[N8881]Br: C10
93.84 ± 0.970
94.55 ± 0.133
93.85 ± 0.322
93.98 ± 0.457
92.21 ± 0.545
92.47 ± 0.259
92.06 ± 0.032
91.88 ± 0.234
95.16 ±1.633
94.97 ± 0.466
95.19 ± 1.139
95.09 ± 0.791
[N8881]Br: DLMenthol DL-Menthol: C10
S7
Table B5. Influence of stirring speed on the extraction efficiencies (EE %) for the best DESs used in this work ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, temperature = 25 ºC, contact time = 10 min).
Extraction Efficiencies (EE %) DESs 100 rpm
300 rpm
500 rpm
750 rpm
[N7777]Br: C10
97.31 ± 0.239
97.10 ± 0.343
96.84 ± 0.306
95.91 ± 1.456
[N8888]Br: C10
98.36 ± 0.852
99.14 ± 0.718
97.94 ± 0.643
96.47 ± 0.869
[N8881]Br: C10
92.60 ± 1.023
92.65 ± 0.733
92.08 ± 0.321
91.65 ± 0.467
91.99 ± 0.545
91.00 ± 0.259
91.45 ± 0.256
92.08 ± 0.234
95.60 ± 0.805
94.53 ± 0.272
95.65 ± 0.238
93.09 ± 0.713
[N8881]Br: DLMenthol DL-Menthol: C10
S8
Table B6. Effect of DES/water ratio on the extraction efficiencies (EE %) for all DESs used in this work ([C0]BPA = 0.1 g/L, stirring speed = 300 rpm, temperature = 25 ºC, contact time = 10 min).
Extraction Efficiencies (EE %) DESs 1/3
1/2
1/1
3/1
[N7777]Br: C8
95.06 ± 0.230
94.03 ± 0.128
94.35±0.793
79.31 ± 0.928
[N7777]Br: C10
98.70 ± 0.300
98.94 ± 0.600
97.10±0.650
96.00 ± 0.380
[N8888]Br: C8
88.33 ± 0.960
91.07 ± 0.485
91.24±1.071
77.12 ± 1.938
[N8888]Br: C10
98.23 ± 0.671
98.68 ± 0.190
97.03±0.815
95.86 ± 0.707
[N8881]Br: C8
86.40 ± 2.340
85.03 ± 0.730
84.22±0.023
65.72 ± 1.624
[N8881]Br: C10
94.74 ± 0.196
92.97 ± 0.888
90.33±2.350
87.60 ± 1.120
[N8881]Br: DL-
92.21 ± 0.400
91.00 ± 0.600
87.89±5.022
84.55 ± 1.473
DL-Menthol: C8
83.75 ± 4.494
85.03 ± 0.730
84.22±0.023
61.13 ± 0.967
DL-Menthol: C10
94.88 ± 0.500
94.83 ± 0.600
93.91±0.400
89.82 ± 1.141
Menthol
S9
Table B7. Extraction capability (EE %) of [N8888]Br: C10 DES during several cycles ([C0]BPA = 0.1 g/L, DES/water ratio = 1/1, stirring speed = 300 rpm, temperature = 25 ºC, contact time = 10 min).
[N8888]Br: C10
Extraction Efficiencies (EE%)
1st cycle
98.5714
2nd cycle
98.7744
3rd cycle
98.3985
4th cycle
98.7068
5th cycle
98.8571
S10
C. Design Experimental Experiment Table C1. Extraction efficiencies obtained for removal of Bisphenol-A from water environments using a central composite design (CCD). Experimen
DES/wate
Temperat
C0 of BPA
EE
ts
r Ratio
ure
(%)
1
0.96
26.0
0.04
97.35
2
0.96
26.0
0.08
99.19
3
0.96
45.0
0.04
96.28
4
0.96
45.0
0.08
98.49
5
3.05
26.0
0.04
87.44
6
3.05
26.0
0.08
97.56
7
3.05
45.0
0.04
92.86
8
3.05
45.0
0.08
97.78
9
0.24
35.0
0.06
98.45
10
3.76
35.0
0.06
95.94
11
2.00
19.0
0.06
97.98
12
2.00
51.0
0.06
95.79
13
2.00
35.0
0.03
91.44
14
2.00
35.0
0.09
97.72
15 (C)
2.00
35.0
0.06
95.74
16 (C)
2.00
35.0
0.06
95.78
17 (C)
2.00
35.0
0.06
95.78
S11
Highlights
•
Hydrophobic DESs combining natural components were prepared.
•
An endocrine disruptor micropollutant is removed from aqueous environments.
•
All hydrophobic DESs showed promising abilities of extracting Bisphenol-A.
•
Hydrophobic DES can be reused for several cycles.
•
The process of extraction is feasible from an economical and time-consuming point of view.
No conflict of interests are declared.