CHEMSUSCHEM FULL PAPERS DOI: 10.1002/cssc.201402593
Facile and Scalable Synthesis of Nanoporous Materials Based on Poly(ionic liquid)s Itxaso Azcune,*[a] Ignacio Garca,[a] Pedro M. Carrasco,[a] Aratz Genua,[a] Marek Tanczyk,[b] Manfred Jaschik,[b] Krzysztof Warmuzinski,[b] Germn CabaÇero,[a] and Ibon Odriozola*[a] A simple, fast, sustainable, and scalable strategy to prepare nanoporous materials based on poly(ionic liquid)s (PILs) is presented. The synthetic strategy relies on the radical polymerization of crosslinker-type ionic liquid (IL) monomers in the presence of an analogous IL, which acts as a porogenic solvent. This IL can be extracted easily after polymerization and
recycled for further use. The great advantages of this synthetic approach are the atom-efficiency and lack of waste. The effects of different monomer/porogen ratios on the specific surface area, porosity, and pore size have been investigated. Finally, the potential of the materials as CO2 sorbents has been evaluated.
Introduction Poly(ionic liquid)s (PILs) have emerged as a new class of functional polymers with multiple applications in materials science, such as solid ionic conductors, dispersants/stabilizers, CO2 absorbents, and carbonaceous materials precursors.[1] PILs derive from IL monomers, and therefore, they combine the chemical versatility of ILs with the spatial architecture and mechanical properties inherent to polymers. The porosity in polymers is a highly valued structural feature for certain applications (gas storage and separation, catalysts, packaging materials in chromatography, etc).[2] CO2 adsorbents and absorbents with large surface areas have been investigated extensively because of their large CO2 sorption capacity and high sorption and desorption rates.[3] Tang et al. showed that PILs that have a porous structure presented a higher surface area and faster CO2 sorption/desorption rates than those with nonporous structures.[4] Nanoporous materials are classified according to their pore size by IUPAC as microporous (< 2 nm), mesoporous (2–50 nm), and macroporous (50– 1000 nm). The synthesis of microporous PILs by the seed-swelling method has been reported recently.[5] However, the majority of published studies have focused on the synthesis of macroporous PILs.[6] Following the colloidal crystal templating strategy, Wilke et al. showed that mesoporous PILs with an enlarged specific surface area (150–220 m2 g 1) showed enhanced [a] Dr. I. Azcune, Dr. I. Garca, Dr. P. M. Carrasco, Dr. A. Genua, G. CabaÇero, Dr. I. Odriozola Materials Division IK4-CIDETEC Research Centre Paseo Miramn 196, 20009 Donostia-San Sebastin (Spain) E-mail: [email protected] [email protected] [b] Dr. M. Tanczyk, Dr. M. Jaschik, Prof. K. Warmuzinski Institute of Chemical Engineering Polish Academy of Sciences ul. Baltycka 5, 44-100 Gliwice (Poland) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402593.
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
CO2 transfer through the polymer matrix.[7] However, this synthetic strategy was time and energy consuming, and sacrificial components were needed to generate the pores, which resulted in a low utilization efficiency of the starting materials. This is not ideal, and modern synthetic chemists and materials scientists are in pursuit of environmentally friendly processes that are able to decrease resource and energy consumption as well as to provide scalability. Recently, an alternative strategy was reported for the preparation of mesoporous PILs through electrostatic complexation between PILs and polyacids.[8] However, this approach was only useful to provide materials with pendant carboxylate anions and could not be tailored with any desired anions. Consequently, scalable, straightforward, and versatile synthetic strategies that provide mesoporous PILs are still required. The use of porogenic solvents to create porous polymers has been documented widely. ILs exhibit unique properties that include negligible vapor pressure, nonflammability, high ionic conductivity, a wide electrochemical window, and good chemical and thermal stability.[9] These distinct properties make them ideal candidates to replace harmful volatile organic solvents to be used as reaction media in polymerization processes.[10] ILs have become particularly useful for the synthesis of molecularly imprinted polymers (MIPs)[11] and for the creation of porosity in the fabrication of sorbent phases for capillary microextraction[12] and monolithic stationary phases.[13] The use of ILs as solvents for the synthesis of (hyper-)crosslinked polymers, both neutral[14] and ionic,[15] has also been reported. Pavlova et al. prepared porous hyper-crosslinked hydrophilic networks by the simultaneous alkylation and polymerization of 4vinylpyridine in 1-butyl-3-methylimidazolium tetrafluoroborate.[15] The anion of the resulting porous PIL was the leaving group of the corresponding alkylation reagent. Further structural modification of such polymers by standard anion-exchange procedures is troublesome and difficult. For example, if the incorporation of fluorinated anions such as bis(triflurosulfoChemSusChem 2014, 7, 3407 – 3412
3407
CHEMSUSCHEM FULL PAPERS nyl)imide (TFSI) is desired to confer hydrophobicity to the material. This anion might be of interest for certain applications, such as postcombustion CO2 capture, in which water might compete in the absorption process. As acknowledged recently, the impact of water coadsorption with CO2 in microporous organic polymer (MOP) sorbents is dramatic.[16] The performance of hydrophobic MOPs in terms of CO2 uptake is less affected by moisture than that of their hydrophilic analogues, which show decreases of 5 and 50 %, respectively. In this paper we describe a simple, scalable, and universal approach for the synthesis of nanoporous materials based on PILs. To this end, we have explored the radical polymerization of bisvinyl-ended ILs in the presence of analogous nonpolymerizable ILs, which act as porogenic solvents and can be extracted easily after polymerization for reuse. It is known that porogenic solvents control the porous properties of the monolith through the solvation of the polymer chains in the reaction medium.[17] Small pores are created if the monomers and porogenic solvents are miscible, whereas macropores result from systems that present poor miscibility. In this sense, ILs that have the same chemical nature as PILs might be regarded as ideal solvents to obtain materials with small pores. The principal advantages of this synthetic approach are the atom-efficiency and lack of waste, as all the reagents and solvents can be recycled. In addition, we have investigated the effect of the percentage of the porogenic solvent on the properties of the porous PIL. The chemical and thermal properties of the PILs were analyzed by FTIR spectroscopy and thermogravimetric analysis (TGA). The surface morphologies of the products were determined by field-emission scanning electron microscopy (FE-SEM), and N2 adsorption–desorption measurements were performed to determine the specific surface area, average pore size, and porosity of the materials. Finally, the CO2 uptake of the samples was measured.
www.chemsuschem.org
Scheme 1. Synthetic pathway for nanoporous PILs.
Results and Discussion The studied crosslinkable IL monomer was prepared by the reaction of 1-vinylimidazole with 1,4-dibromobutane followed by a standard anion-exchange procedure with a hydrophobic LiTFSI salt (Scheme 1). 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was selected as the porogen IL as it is chemically similar to the monomer, which thus ensures compatibility and good miscibility. Different monomer/porogen weight ratios (M/P = 1:0, 1:0.5, 1:1, 1:2, 1:3, 1:5, and 1:10) were used to investigate the effect of concentration on the formation of the porous PIL. The polymerization reactions were performed upon addition of a radical initiator, azobisisobutyronitrile (AIBN; 2 wt %), by heating at 100 8C for 24 h. The solidified porous material was then washed repeatedly with acetone in a centrifugal vessel and dried under vacuum (95–98 % yield). Interestingly, the IL was recovered quantitatively (100 % yield) by evaporation of the acetone with high purity as shown by 1H NMR analysis (Figures S2 and S3). FTIR spectroscopy was performed to investigate the presence of unreacted vinyl groups. Both the monomer and the 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 1. a) FTIR spectra of the M and P. b) Magnification of the 1750– 1400 cm 1 region of the FTIR spectra of M, P, and PIL samples.
porogen presented the characteristic bands of the TFSI anion at n˜ = 1347, 1328, 1179, 1132, and 1050 cm 1 (Figure 1 a). The bands between n˜ 2879 and 2965 cm 1 were attributed to the C H stretch of the butyl side-chain of the porogen, whereas the signals above n˜ 3000 cm 1 belonged to the imidazole ring and C H stretch of the vinyl group. In addition, the monomer presented characteristic bands at n˜ 1675–1650 and 1600 cm 1, which correspond to the C=C stretch of the vinyl group, which ChemSusChem 2014, 7, 3407 – 3412
3408
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org
the application of the BrunauerEmmett-Teller (BET) theory are depicted in Figure 4 a. The largest surface area was exhibited by PIL1:1 (86.2 m2 g 1) followed by PIL1:2 (20.10 m2 g 1). The values for the other samples were close to that of PIL1:0, synthesized in bulk. According to these results, there should be an optimum M/P ratio that would provide the required degree of crosslinking to ensure a permanent nanoporous structure. Beyond that dilution, the formation of a stable nanostructure Figure 2. Swelling test in water and acetone. PIL samples from left to right: PIL1:0, PIL1:0.5, PIL1:1, PIL1:2, PIL1:3, PIL1:5, was not detected by the analytiand PIL1:10. a) Dry PIL samples. b) PIL samples in water. c) PIL samples in acetone. d) Percentage of swelling of PIL cal techniques used. The hystesamples in acetone. resis of the isotherm of PIL1:1, classified as type IV, indicated can be used to ascertain the degree of polymerization. This set the presence of capillary condensation (Figure 4 b). Barret– of signals did not arise in the FTIR spectra of the PILs, which Joyner–Halenda (BJH) theory predicts an adsorption average proves that the polymerization occurred quantitatively pore diameter of 8.5 nm and a desorption average pore diame(Figure 1). All polymers showed similar absorption spectra as they had the same chemical composition. In addition, all the PILs prepared in the presence of the porogen showed the same FTIR spectra as PIL1:0, which confirms the complete elimination of the porogen in the washing step. Once the porous PILs from different M/P ratios were prepared, their swelling behavior was studied. Dry samples arranged in order of the increasing amount of porogen from PIL1:0 to PIL1:10 are shown in Figure 2 a. The samples presented very limited swelling in water, probably because of the presence of hydrophobic TFSI anions (Figure 2 b). In contrast, the samples showed a nonlinear degree of swelling in acetone (Figure 2 c). Here, the degree of swelling showed a linear increase (correlated to the porogen quantity) until a maximum of 500 vol % was reached for PIL1:5. If the amount of porogen was doubled (PIL1:10), a decrease of the swelling volume was observed clearly (Figure 2 d). This could be explained by the dilution of the monomer in the mixture, which avoids the formation of a highly cross-linked network. The porous morphology of the PILs was analyzed by FE-SEM under the same experimental conditions to enable a direct comparison (Figure 3). All the PILs synthesized in the presence of porogen exhibited a nanoporous sponge-like surface morphology, in contrast to the smooth surface of PIL1:0, synthesized in bulk in the absence of the porogenic solvent. Following the IUPAC criteria for nanoporous materials, the vast majority of the detected pores fell into the mesoporous type. In the case of PIL1:1 and PIL1:2, the presence of macropores was also observed. However, the existence of micropores could not be determined by this technique because of the insufficient resolution of the FE-SEM microscope. N2 adsorption isotherms were measured at 77 K to determine the specific surface area, average pore size, and porosity Figure 3. FE-SEM micrographs of PIL1:0, PIL1:0.5, PIL1:1, PIL1:2, PIL1:3, PIL1:5, and of the materials. The specific surface area values obtained by PIL1:10. Scale bar corresponds to 200 nm in all cases. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2014, 7, 3407 – 3412
3409
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org gen) may disintegrate and thus, the surface area may not increase with an increase in the porogen mass fraction. The porosity of PIL1:1 was calculated to be roughly 22 %. Although the obtained surface area values were lower than those reported for materials obtained through the hard-templating pathway, for which specific surface areas of 150– 220 m2 g 1 were reported,[7] the present methodology still remains valuable from the point of view of preparation efficiency and practical convenience. The values of the surface area, pore diameter, adsorption kinetics, and CO2 uptake are listed in Table 1. Table 1. List of the synthesized PILs and their surface area, pore diameter, adsorption kinetics, and CO2 uptake. PILM/P
P/M BET surface area Pore diameter[a] Time constant [CO2][c] [nm] (t)[b] [s] [mol kg 1] [m2 g 1]
PIL1:0 0 0.00 PIL1:0.5 0.5 0.08 1 86.21 PIL1:1 2 20.10 PIL1:2 3 0.00 PIL1:3 5 0.06 PIL1:5 0.11 PIL1:10 10
– – 8.5–6.8 7.3–4.0 – – –
2877.22 323.67 32.82 69.67 1545.25 1920.26 564.05
0.057 0.083 0.098 0.100 0.095 0.081 0.074
[a] In the case of negligible surface area, the values of pore diameters were not considered. [b] Time constant at 400–600 mbar and 20 8C. [c] CO2 concentration at 1 bar and 20 8C.
Figure 4. a) BET surface area versus porogen proportion. b) N2 adsorption– desorption isotherms of mesoporous PIL1:1 measured at 77 K. c) Pore size distribution and cumulative pore volume.
ter 6.8 nm (4 VA 1; Figure 4 c). Although these values are smaller than those achieved for materials obtained by hard-templating pathways,[7] they are still within the mesoporous range. According to Wilke et al.,[7] the pore size depends on the template size and stability of the porous structure obtained, among other factors. Unstable structures obtained with a higher mass fraction of the template (or, in our case, poro 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
The CO2 uptake and adsorption kinetics of the seven PILs were then investigated. Before the measurements the samples were degassed for 24 h under high vacuum (10 6 mbar) at 90 8C. Only a minor decrease in mass during degassing was observed (0.9 to 1.7 %). The CO2 adsorption isotherms measured at 293 K are shown in Figure 5 a. The largest uptake was achieved by the polymers with the largest surface areas, PIL1:1 and PIL1:2 (0.1 mol kg 1), but an almost identical value was reached by PIL1:3, which showed a negligible surface area. The uptake decreased for PIL1:5 and PIL1:10, and the lowest value was observed for PIL1:0 (0.06 mol kg 1). The results showed that the uptake of CO2 was not related solely to the surface area, which suggests that the CO2 uptake is not an adsorption phenomenon but rather absorption in the polymer matrix. These observations are in accordance with the results of Tang et al.[4a] and Wilke et al.[7] for a variety of nonporous and mesoporous PILs. Tang et al. stated plainly that the CO2 sorption capacity depends mainly on the chemical structure of PILs, whereas the rate of CO2 sorption is affected by the surface area of the polymers. The larger the surface area, the shorter the time required to reach the absorption equilibrium. The absorption kinetics of each PIL are depicted in Figure 5 b. It was observed clearly that the equilibrium was reached 80 times faster by PIL1:1 than by the PILs with negligible surface areas, such as PIL1:0. These results are consistent with the hypothesis that the sorption into the highly crosslinked PIL1:0 was much slower than into the mesostructured PILs. However, by increasing the surface area by four times, PIL1:2 and PIL1:1, the kinetics was only twice faster. Clearly, the experiments showed that, for the materials studied, even a small surface area such as 20 m2 g 1 was sufficient from the standpoint of the rate of CO2 transport and the ChemSusChem 2014, 7, 3407 – 3412
3410
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org within the values reported in the literature, with enhanced kinetics for the porous materials. The sorption capacity of the materials could be further enhanced by modifying the chemical structure of the IL monomers by selecting cation, anion, and core structure with higher affinity towards CO2 , for example, by increasing the ion polarity.[19]
Conclusions A simple and rapid synthetic procedure to prepare nanoporous poly(ionic liquid)s using ionic liquids (ILs) as porogens is described. The proposed strategy is robust and scalable (batches of 30 g have been prepared). In addition, no waste material is generated, and the porogen is recovered and recycled. Likewise, the synthetic advantages overcome some difficulties that other approaches might face in terms of scalability, energy consumption (e.g., sintering of hard templates), and safety (e.g., the use of harmful volatile solvents). Moreover, the tailorable structure of an IL makes it possible to design the most compatible IL porogen for each IL monomer. Therefore, this approach could be extended easily to the synthesis of poly(ionic liquid)s with other chemical structures with higher a affinity towards CO2 uptake. Further investigation in this sense is in progress.
Experimental Section Materials and methods Figure 5. a) CO2 adsorption isotherm of the PILM/P samples at 293 K. b) 1/t (t, time constant) vs. P/M ratio.
sorption capacity of these materials. Thus, it is not always advisable to maximize the surface area at all cost. In this study, polymers based on imidazolium and TFSI anions were synthesized as a proof-of-concept of a new preparation method for nanoporous PILs. The CO2 sorption capacities of these PILs were comparable to literature values, and we were mindful that the CO2 loading capacity of a given PIL depends on temperature and pressure. Therefore, measurement conditions must be taken into account if literature values are compared directly. CO2 loading capacities of imidazoliumbased nonporous PILs have been reported in the range of 1.53–3.31 mgCO2 gPIL 1 for TFSI and PF6 anions, respectively, and up to 12.46 mgCO2 gPIL 1 for the PIL with acetate anions at 25 8C and atmospheric pressure.[18] In addition, Wilke et al. reported nonporous, highly cross-linked, imidazolium TFSI-based PILs with a loading capacity of 5.2 mgCO2 gPIL 1 at 0 8C and atmospheric pressure.[7] For nonporous PIL1:0, CO2 loading capacities of 2.64 mgCO2 gPIL 1 (0.06 mol kg 1) and 4.18 mgCO2 gPIL 1 (0.095 mol kg 1) were measured at 20 and 0 8C, respectively, under the same pressure (Supporting Information). The CO2 uptake of a given PIL is decreased by increasing the temperature. In our experiments, the sorption capacity of PIL1:0 at 20 8C was reduced by 60 % compared to that at 1 bar and 0 8C. In any case, the CO2 uptake values reported in this paper fall 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1,4-Dibromobutane (99 %) and 1-vinylimidazole (99 %) were purchased from Sigma–Aldrich. AIBN (98 %) was purchased from Acros Organics. Acetone (99.5 %), acetonitrile, and ethyl acetate were purchased from Scharlab. 1-Butyl-1-methylimidazolium chloride and bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) were purchased from IoLiTec. IR spectra were recorded by using an ATRFTIR Jasco 4100 spectrometer. NMR spectra were recorded by using a Bruker Avance III NMR spectrometer in appropriate deuterated solvents. TGA was performed by using a Q500 TG-DTA analyzer manufactured by TA Instruments in the temperature range between 25 and 600 8C under N2 at a heating rate of 10 8C min 1 (Supporting Information). A Carl Zeiss Ultra Plus field-emission scanning electron microscope was used to compare the morphology of the obtained polymers. The N2 adsorption isotherms measurements were performed at 77 K by using a Micromeritics ASAP 2020 analyzer. The CO2 adsorption isotherm measurements at were performed at 298 K by using a Hiden Isochema IGA-003 gravimetric analyzer (Supporting Information).
Preparation of 1,4-di(N,N’-vinylimidazolium)butane di[bis(trifluoromethanesulfonyl)imide] (M) To a solution of 1-vinylimidazole (420 mmol, 39.9 g) in acetonitrile (150 mL) at 60 8C was added 1,4-dibromobutane (200 mmol, 43.6 g) dropwise. After 24 h, the product was precipitated, washed in ethyl acetate, and dried under reduced pressure. The reaction yielded 77.8 g (96 %) of white powder. The resulting dibromide salt (91.55 mmol, 37.0 g) was dissolved in deionized water (400 mL), and a solution of LiTFSI (201.0 mmol, 57.7 g) in deionized water (50 mL) was added. After 1 h, the solid was collected by filtration and washed thoroughly with deionized water. The reaction yielded ChemSusChem 2014, 7, 3407 – 3412
3411
CHEMSUSCHEM FULL PAPERS 70 g (98 %) of white powder. M.p. 83.19 8C; 1H NMR (500 MHz, CDCl3, 25 8C, Me4Si): d = 9.43 (s, 2 H, CH), 8.20 (s, 2 H, CH), 7.90 (s, 2 H, CH), 7.29 (dd, 3J(H,H) = 15.6 Hz, 8.7 Hz, 2 H, CH), 5.94 (dd, 3 J(H,H) = 2.4 Hz, 15.6 Hz, 2 H, CH2), 5.44 (dd, 3J(H,H) = 8.7 Hz, 2.4 Hz, 2 H, CH2), 4.23 (m, 4 H, CH2), 1.84 ppm (m, 4 H, CH2).
Synthesis of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (P) To solution of 1-butyl-3-methylimidazolium chloride (0.1 mol, 17.47 g) in deionized water (100 mL) was added a solution of LiTFSI (0.11 mol, 31.58 g) in deionized water (50 mL). After stirring for 1 h, the suspension was centrifuged, washed with copious water, and dried to yield 32.62 g (80 % yield) of the product as an oil. 1H NMR (500 MHz, CDCl3, 25 8C, Me4Si): d = 8.73 (s, 1 H, CH), 7.30 (s, 1 H, CH), 7.29 (s, 1 H, CH), 4.16 (t, 3J(H,H) = 7.5 Hz, 2 H, CH2), 3.93 (s, 3 H, CH3), 1.84 (m, 2 H, CH2), 1.36 (m, 2 H, CH2), 0.95 ppm (t, 3 J(H,H) = 7.4 Hz, 3 H, CH3).
General procedure for the synthesis of PILs M, P, and AIBN were blended together. The homogenous mixture was degassed and kept under a N2 atmosphere. The mixture was then heated to 100 8C for 24 h. The resulting composite material was then transferred to a centrifuge vessel and washed with acetone until the total weight of IL porogen (100 %) was recovered. The solid was dried under vacuum. Synthesis of PIL1:0 : The general procedure was followed starting from M (35 g) and AIBN (0.70 g) to give 33.5 g of PIL1:0 (96 % yield). Synthesis of PIL1:0.5 : The general procedure was followed starting from M (7 g), P (3.5 g), and AIBN (0.14 g) to give 6.65 g of PIL1:0.5 (95 % yield). Synthesis of PIL1:1: The general procedure was followed starting from M (37 g), P (37 g), and AIBN (0.74 g) to give 35.6 g of PIL1:1 (96 % yield). Synthesis of PIL1:2 : The general procedure was followed starting from M (7 g), P (14 g), and AIBN (0.14 g) to give 6.74 g of PIL1:2 (96 % yield). Synthesis of PIL1:3 : The general procedure was followed starting from M (7 g), P (21 g), and AIBN (0.14 g) to give 6.79 g of PIL1:3 (97 % yield). Synthesis of PIL1:5 : The general procedure was followed starting from M (7 g), P (35 g), and AIBN (0.14 g) to give 6.86 g of PIL1:5 (98 % yield). Synthesis of PIL1:10 : The general procedure was followed starting from M (20 g), P (200 g), and AIBN (0.40 g) to give 19.6 g of PIL1:10 (98 % yield).
Acknowledgements The authors acknowledge financial support from the European Commission through the INTERACT project funded by the European Union’s Seventh Framework Program for Research, Technological Development and Demonstration under grant agreement number 608535. The authors acknowledge the collaboration of SOLVIONIC in the framework of the PIL-TO-MARKET project (FP7PEOPLE-IAPP-2008-230747).
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org Keywords: absorption · ionic liquids · materials science · mesoporous materials · polymers
[1] a) J. Lu, F. Yan, J. Texter, Prog. Polym. Sci. 2009, 34, 431 – 448; b) O. Green, S. Grubjesic, S. Lee, M. A. Firestone, Polym. Rev. 2009, 49, 339 – 360; c) M. D. Green, T. E. Long, Polym. Rev. 2009, 49, 291 – 314; d) J. Yuan, D. Mecerreyes, M. Antonietti, Prog. Polym. Sci. 2013, 38, 1009 – 1039; e) J. Yuan, M. Antonietti, Polymer 2011, 52, 1469 – 1483; f) D. Mecerreyes, Prog. Polym. Sci. 2011, 36, 1629 – 1648. [2] D. Wu, F. Xu, B. Sun, R. Fu, H. He, K. Matyjaszewski, Chem. Rev. 2012, 112, 3959 – 4015. [3] C.-H. Yu, C.-H. Huang, C.-S. Tan, Aerosol Air Qual. Res. 2012, 12, 745 – 769. [4] a) J. Tang, H. Tang, W. Sun, M. Radosz, Y. Shen, Polymer 2005, 46, 12460 – 12467; b) J. Tang, H. Tang, W. Sun, H. Plancher, M. Radosz, Y. Shen, Chem. Commun. 2005, 3325 – 3327; c) S. Supasitmongkola, P. Styring, Energy Environ. Sci. 2010, 3, 1961 – 1972; d) E. I. Privalova, P. MkiArvela, D. Y. Murzin, J. P. Mikkhola, Russ. Chem. Rev. 2012, 81, 435 – 457. [5] J. Zhu, J. Zhou, H. Zhang, R. Chu, J. Polym. Res. 2011, 18, 2011 – 2015. [6] a) F. Yan, J. Texter, Chem. Commun. 2006, 2696 – 2698; b) J. Huang, C.-A. Tao, Q. An, W. Zhang, Y. Wu, X. Li, D. Shena, G. Li, Chem. Commun. 2010, 46, 967 – 969; c) X. Hu, J. Huang, W. Zhang, M. Li, C. Tao, G. Li, Adv. Mater. 2008, 20, 4074 – 4078; d) F. Yan, J. Texter, Angew. Chem. Int. Ed. 2007, 46, 2440 – 2443; Angew. Chem. 2007, 119, 2492 – 2495; e) D. England, N. Tambe, J. Texter, ACS Macro Lett. 2012, 1, 310 – 314. [7] A. Wilke, J. Yuan, M. Antonietti, J. Weber, ACS Macro Lett. 2012, 1, 1028 – 1031. [8] a) Q. Zhao, M. Yin, A. P. Zhang, S. Prescher, M. Antonietti, J. Yuan, J. Am. Chem. Soc. 2013, 135, 5549 – 5552; b) Q. Zhao, S. Soll, M. Antonietti, J. Yuan, Polym. Chem. 2013, 4, 2432 – 2435; c) Q. Zhao, P. Zhang, M. Antonietti, J. Yuan, J. Am. Chem. Soc. 2012, 134, 11852 – 11855. [9] N. V. Plechkova, K. R. Seddon, Chem. Soc. Rev. 2008, 37, 123 – 150. [10] P. Kubisa, Prog. Polym. Sci. 2004, 29, 3 – 12. [11] a) K. Booker, M. C. Bowyer, C. I. Holdsworth, A. McCluskey, Chem. Commun. 2006, 1730 – 1732; b) H. Wang, Y. Zhu, J. Lin, X. Yan, Electrophoresis 2008, 29, 952 – 959; c) K. Booker, M. C. Bowyer, C. J. Lennard, C. I. Holdsworth, A. McCluskey, Aust. J. Chem. 2007, 60, 51 – 56; d) C. He, Y. Long, J. Pan, K. Li, F. Liu, Talanta 2008, 74, 1126 – 1131; e) H.-F. Wang, Y.-Z. Zhu, X.-P. Yan, R.-Y. Gao, J.-Y. Zheng, Adv. Mater. 2006, 18, 3266 – 3270. [12] a) A. Shearrow, S. Bhansali, A. Malik, J. Chromatogr. A 2009, 1216, 6349 – 6355; b) A. M. Shearrow, G. A. Harris, L. Fang, P. K. Sekhar, L. T. Nguyen, E. B. Turner, S. Bhansali, A. Malik, J. Chromatogr. A 2009, 1216, 5449 – 5458. [13] B. Singco, C. Lin, Y. Cheng, Y. S. Yh, H. Huang, Anal. Chim. Acta 2012, 746, 123 – 133. [14] a) P. Snedden, A. I. Cooper, K. Scott, N. Winterton, Macromolecules 2003, 36, 4549 – 4556; b) A. I. Cooper, K. Scott, P. Sneddon, N. Winterton, Polym. Prepr. 2004, 45, 291 – 292; c) L. Peng, J. Zhang, J. Li, B. Han, Z. Xue, G. Yang, Angew. Chem. Int. Ed. 2013, 52, 1792 – 1795; Angew. Chem. 2013, 125, 1836 – 1839; d) Y.-H. Shih, B. Singco, W.-L. Liu, C.-H. Hsu, H.-Y. Huang, Green Chem. 2011, 13, 296 – 299; e) L. Zhu, C.-Y. Huang, Y. H. Patel, J. Wu, S. V. Malhotra, Macromol. Rapid Commun. 2006, 27, 1306 – 1311. [15] L. A. Pavlova, M. V. Pavlov, V. A. Davankov, Dokl. Chem. 2006, 406, 6 – 8. [16] R. Dawson, L. A. Stevens, T. C. Drage, C. E. Snape, M. W. Smith, D. J. Adams, A. I. Cooper, J. Am. Chem. Soc. 2012, 134, 10741 – 10744. [17] C. Viklund, F. Svec, J. M. J. Frchet, Chem. Mater. 1996, 8, 744 – 750. [18] E. I. Privalova, E. Karjalainen, M. Nurmi, P. Mki-Arvela, K. Ernen, H. Tenhu, D. Y. Murzin, J.-P. Mikkola, ChemSusChem 2013, 6, 1500 – 1509. [19] R. S. Bhavsar, S. C. Kumbharkar, U. K. Kharul, J. Membr. Sci. 2012, 389, 305 – 315. Received: June 26, 2014 Revised: July 30, 2014 Published online on September 12, 2014
ChemSusChem 2014, 7, 3407 – 3412
3412
Facile and Scalable Synthesis of Nanoporous Materials Based on Poly(ionic liquid)s Itxaso Azcune,*[a] Ignacio Garca,[a] Pedro M. Carrasco,[a] Aratz Genua,[a] Marek Tanczyk,[b] Manfred Jaschik,[b] Krzysztof Warmuzinski,[b] Germn CabaÇero,[a] and Ibon Odriozola*[a] A simple, fast, sustainable, and scalable strategy to prepare nanoporous materials based on poly(ionic liquid)s (PILs) is presented. The synthetic strategy relies on the radical polymerization of crosslinker-type ionic liquid (IL) monomers in the presence of an analogous IL, which acts as a porogenic solvent. This IL can be extracted easily after polymerization and
recycled for further use. The great advantages of this synthetic approach are the atom-efficiency and lack of waste. The effects of different monomer/porogen ratios on the specific surface area, porosity, and pore size have been investigated. Finally, the potential of the materials as CO2 sorbents has been evaluated.
Introduction Poly(ionic liquid)s (PILs) have emerged as a new class of functional polymers with multiple applications in materials science, such as solid ionic conductors, dispersants/stabilizers, CO2 absorbents, and carbonaceous materials precursors.[1] PILs derive from IL monomers, and therefore, they combine the chemical versatility of ILs with the spatial architecture and mechanical properties inherent to polymers. The porosity in polymers is a highly valued structural feature for certain applications (gas storage and separation, catalysts, packaging materials in chromatography, etc).[2] CO2 adsorbents and absorbents with large surface areas have been investigated extensively because of their large CO2 sorption capacity and high sorption and desorption rates.[3] Tang et al. showed that PILs that have a porous structure presented a higher surface area and faster CO2 sorption/desorption rates than those with nonporous structures.[4] Nanoporous materials are classified according to their pore size by IUPAC as microporous (< 2 nm), mesoporous (2–50 nm), and macroporous (50– 1000 nm). The synthesis of microporous PILs by the seed-swelling method has been reported recently.[5] However, the majority of published studies have focused on the synthesis of macroporous PILs.[6] Following the colloidal crystal templating strategy, Wilke et al. showed that mesoporous PILs with an enlarged specific surface area (150–220 m2 g 1) showed enhanced [a] Dr. I. Azcune, Dr. I. Garca, Dr. P. M. Carrasco, Dr. A. Genua, G. CabaÇero, Dr. I. Odriozola Materials Division IK4-CIDETEC Research Centre Paseo Miramn 196, 20009 Donostia-San Sebastin (Spain) E-mail: [email protected] [email protected] [b] Dr. M. Tanczyk, Dr. M. Jaschik, Prof. K. Warmuzinski Institute of Chemical Engineering Polish Academy of Sciences ul. Baltycka 5, 44-100 Gliwice (Poland) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402593.
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
CO2 transfer through the polymer matrix.[7] However, this synthetic strategy was time and energy consuming, and sacrificial components were needed to generate the pores, which resulted in a low utilization efficiency of the starting materials. This is not ideal, and modern synthetic chemists and materials scientists are in pursuit of environmentally friendly processes that are able to decrease resource and energy consumption as well as to provide scalability. Recently, an alternative strategy was reported for the preparation of mesoporous PILs through electrostatic complexation between PILs and polyacids.[8] However, this approach was only useful to provide materials with pendant carboxylate anions and could not be tailored with any desired anions. Consequently, scalable, straightforward, and versatile synthetic strategies that provide mesoporous PILs are still required. The use of porogenic solvents to create porous polymers has been documented widely. ILs exhibit unique properties that include negligible vapor pressure, nonflammability, high ionic conductivity, a wide electrochemical window, and good chemical and thermal stability.[9] These distinct properties make them ideal candidates to replace harmful volatile organic solvents to be used as reaction media in polymerization processes.[10] ILs have become particularly useful for the synthesis of molecularly imprinted polymers (MIPs)[11] and for the creation of porosity in the fabrication of sorbent phases for capillary microextraction[12] and monolithic stationary phases.[13] The use of ILs as solvents for the synthesis of (hyper-)crosslinked polymers, both neutral[14] and ionic,[15] has also been reported. Pavlova et al. prepared porous hyper-crosslinked hydrophilic networks by the simultaneous alkylation and polymerization of 4vinylpyridine in 1-butyl-3-methylimidazolium tetrafluoroborate.[15] The anion of the resulting porous PIL was the leaving group of the corresponding alkylation reagent. Further structural modification of such polymers by standard anion-exchange procedures is troublesome and difficult. For example, if the incorporation of fluorinated anions such as bis(triflurosulfoChemSusChem 2014, 7, 3407 – 3412
3407
CHEMSUSCHEM FULL PAPERS nyl)imide (TFSI) is desired to confer hydrophobicity to the material. This anion might be of interest for certain applications, such as postcombustion CO2 capture, in which water might compete in the absorption process. As acknowledged recently, the impact of water coadsorption with CO2 in microporous organic polymer (MOP) sorbents is dramatic.[16] The performance of hydrophobic MOPs in terms of CO2 uptake is less affected by moisture than that of their hydrophilic analogues, which show decreases of 5 and 50 %, respectively. In this paper we describe a simple, scalable, and universal approach for the synthesis of nanoporous materials based on PILs. To this end, we have explored the radical polymerization of bisvinyl-ended ILs in the presence of analogous nonpolymerizable ILs, which act as porogenic solvents and can be extracted easily after polymerization for reuse. It is known that porogenic solvents control the porous properties of the monolith through the solvation of the polymer chains in the reaction medium.[17] Small pores are created if the monomers and porogenic solvents are miscible, whereas macropores result from systems that present poor miscibility. In this sense, ILs that have the same chemical nature as PILs might be regarded as ideal solvents to obtain materials with small pores. The principal advantages of this synthetic approach are the atom-efficiency and lack of waste, as all the reagents and solvents can be recycled. In addition, we have investigated the effect of the percentage of the porogenic solvent on the properties of the porous PIL. The chemical and thermal properties of the PILs were analyzed by FTIR spectroscopy and thermogravimetric analysis (TGA). The surface morphologies of the products were determined by field-emission scanning electron microscopy (FE-SEM), and N2 adsorption–desorption measurements were performed to determine the specific surface area, average pore size, and porosity of the materials. Finally, the CO2 uptake of the samples was measured.
www.chemsuschem.org
Scheme 1. Synthetic pathway for nanoporous PILs.
Results and Discussion The studied crosslinkable IL monomer was prepared by the reaction of 1-vinylimidazole with 1,4-dibromobutane followed by a standard anion-exchange procedure with a hydrophobic LiTFSI salt (Scheme 1). 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was selected as the porogen IL as it is chemically similar to the monomer, which thus ensures compatibility and good miscibility. Different monomer/porogen weight ratios (M/P = 1:0, 1:0.5, 1:1, 1:2, 1:3, 1:5, and 1:10) were used to investigate the effect of concentration on the formation of the porous PIL. The polymerization reactions were performed upon addition of a radical initiator, azobisisobutyronitrile (AIBN; 2 wt %), by heating at 100 8C for 24 h. The solidified porous material was then washed repeatedly with acetone in a centrifugal vessel and dried under vacuum (95–98 % yield). Interestingly, the IL was recovered quantitatively (100 % yield) by evaporation of the acetone with high purity as shown by 1H NMR analysis (Figures S2 and S3). FTIR spectroscopy was performed to investigate the presence of unreacted vinyl groups. Both the monomer and the 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 1. a) FTIR spectra of the M and P. b) Magnification of the 1750– 1400 cm 1 region of the FTIR spectra of M, P, and PIL samples.
porogen presented the characteristic bands of the TFSI anion at n˜ = 1347, 1328, 1179, 1132, and 1050 cm 1 (Figure 1 a). The bands between n˜ 2879 and 2965 cm 1 were attributed to the C H stretch of the butyl side-chain of the porogen, whereas the signals above n˜ 3000 cm 1 belonged to the imidazole ring and C H stretch of the vinyl group. In addition, the monomer presented characteristic bands at n˜ 1675–1650 and 1600 cm 1, which correspond to the C=C stretch of the vinyl group, which ChemSusChem 2014, 7, 3407 – 3412
3408
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org
the application of the BrunauerEmmett-Teller (BET) theory are depicted in Figure 4 a. The largest surface area was exhibited by PIL1:1 (86.2 m2 g 1) followed by PIL1:2 (20.10 m2 g 1). The values for the other samples were close to that of PIL1:0, synthesized in bulk. According to these results, there should be an optimum M/P ratio that would provide the required degree of crosslinking to ensure a permanent nanoporous structure. Beyond that dilution, the formation of a stable nanostructure Figure 2. Swelling test in water and acetone. PIL samples from left to right: PIL1:0, PIL1:0.5, PIL1:1, PIL1:2, PIL1:3, PIL1:5, was not detected by the analytiand PIL1:10. a) Dry PIL samples. b) PIL samples in water. c) PIL samples in acetone. d) Percentage of swelling of PIL cal techniques used. The hystesamples in acetone. resis of the isotherm of PIL1:1, classified as type IV, indicated can be used to ascertain the degree of polymerization. This set the presence of capillary condensation (Figure 4 b). Barret– of signals did not arise in the FTIR spectra of the PILs, which Joyner–Halenda (BJH) theory predicts an adsorption average proves that the polymerization occurred quantitatively pore diameter of 8.5 nm and a desorption average pore diame(Figure 1). All polymers showed similar absorption spectra as they had the same chemical composition. In addition, all the PILs prepared in the presence of the porogen showed the same FTIR spectra as PIL1:0, which confirms the complete elimination of the porogen in the washing step. Once the porous PILs from different M/P ratios were prepared, their swelling behavior was studied. Dry samples arranged in order of the increasing amount of porogen from PIL1:0 to PIL1:10 are shown in Figure 2 a. The samples presented very limited swelling in water, probably because of the presence of hydrophobic TFSI anions (Figure 2 b). In contrast, the samples showed a nonlinear degree of swelling in acetone (Figure 2 c). Here, the degree of swelling showed a linear increase (correlated to the porogen quantity) until a maximum of 500 vol % was reached for PIL1:5. If the amount of porogen was doubled (PIL1:10), a decrease of the swelling volume was observed clearly (Figure 2 d). This could be explained by the dilution of the monomer in the mixture, which avoids the formation of a highly cross-linked network. The porous morphology of the PILs was analyzed by FE-SEM under the same experimental conditions to enable a direct comparison (Figure 3). All the PILs synthesized in the presence of porogen exhibited a nanoporous sponge-like surface morphology, in contrast to the smooth surface of PIL1:0, synthesized in bulk in the absence of the porogenic solvent. Following the IUPAC criteria for nanoporous materials, the vast majority of the detected pores fell into the mesoporous type. In the case of PIL1:1 and PIL1:2, the presence of macropores was also observed. However, the existence of micropores could not be determined by this technique because of the insufficient resolution of the FE-SEM microscope. N2 adsorption isotherms were measured at 77 K to determine the specific surface area, average pore size, and porosity Figure 3. FE-SEM micrographs of PIL1:0, PIL1:0.5, PIL1:1, PIL1:2, PIL1:3, PIL1:5, and of the materials. The specific surface area values obtained by PIL1:10. Scale bar corresponds to 200 nm in all cases. 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2014, 7, 3407 – 3412
3409
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org gen) may disintegrate and thus, the surface area may not increase with an increase in the porogen mass fraction. The porosity of PIL1:1 was calculated to be roughly 22 %. Although the obtained surface area values were lower than those reported for materials obtained through the hard-templating pathway, for which specific surface areas of 150– 220 m2 g 1 were reported,[7] the present methodology still remains valuable from the point of view of preparation efficiency and practical convenience. The values of the surface area, pore diameter, adsorption kinetics, and CO2 uptake are listed in Table 1. Table 1. List of the synthesized PILs and their surface area, pore diameter, adsorption kinetics, and CO2 uptake. PILM/P
P/M BET surface area Pore diameter[a] Time constant [CO2][c] [nm] (t)[b] [s] [mol kg 1] [m2 g 1]
PIL1:0 0 0.00 PIL1:0.5 0.5 0.08 1 86.21 PIL1:1 2 20.10 PIL1:2 3 0.00 PIL1:3 5 0.06 PIL1:5 0.11 PIL1:10 10
– – 8.5–6.8 7.3–4.0 – – –
2877.22 323.67 32.82 69.67 1545.25 1920.26 564.05
0.057 0.083 0.098 0.100 0.095 0.081 0.074
[a] In the case of negligible surface area, the values of pore diameters were not considered. [b] Time constant at 400–600 mbar and 20 8C. [c] CO2 concentration at 1 bar and 20 8C.
Figure 4. a) BET surface area versus porogen proportion. b) N2 adsorption– desorption isotherms of mesoporous PIL1:1 measured at 77 K. c) Pore size distribution and cumulative pore volume.
ter 6.8 nm (4 VA 1; Figure 4 c). Although these values are smaller than those achieved for materials obtained by hard-templating pathways,[7] they are still within the mesoporous range. According to Wilke et al.,[7] the pore size depends on the template size and stability of the porous structure obtained, among other factors. Unstable structures obtained with a higher mass fraction of the template (or, in our case, poro 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
The CO2 uptake and adsorption kinetics of the seven PILs were then investigated. Before the measurements the samples were degassed for 24 h under high vacuum (10 6 mbar) at 90 8C. Only a minor decrease in mass during degassing was observed (0.9 to 1.7 %). The CO2 adsorption isotherms measured at 293 K are shown in Figure 5 a. The largest uptake was achieved by the polymers with the largest surface areas, PIL1:1 and PIL1:2 (0.1 mol kg 1), but an almost identical value was reached by PIL1:3, which showed a negligible surface area. The uptake decreased for PIL1:5 and PIL1:10, and the lowest value was observed for PIL1:0 (0.06 mol kg 1). The results showed that the uptake of CO2 was not related solely to the surface area, which suggests that the CO2 uptake is not an adsorption phenomenon but rather absorption in the polymer matrix. These observations are in accordance with the results of Tang et al.[4a] and Wilke et al.[7] for a variety of nonporous and mesoporous PILs. Tang et al. stated plainly that the CO2 sorption capacity depends mainly on the chemical structure of PILs, whereas the rate of CO2 sorption is affected by the surface area of the polymers. The larger the surface area, the shorter the time required to reach the absorption equilibrium. The absorption kinetics of each PIL are depicted in Figure 5 b. It was observed clearly that the equilibrium was reached 80 times faster by PIL1:1 than by the PILs with negligible surface areas, such as PIL1:0. These results are consistent with the hypothesis that the sorption into the highly crosslinked PIL1:0 was much slower than into the mesostructured PILs. However, by increasing the surface area by four times, PIL1:2 and PIL1:1, the kinetics was only twice faster. Clearly, the experiments showed that, for the materials studied, even a small surface area such as 20 m2 g 1 was sufficient from the standpoint of the rate of CO2 transport and the ChemSusChem 2014, 7, 3407 – 3412
3410
CHEMSUSCHEM FULL PAPERS
www.chemsuschem.org within the values reported in the literature, with enhanced kinetics for the porous materials. The sorption capacity of the materials could be further enhanced by modifying the chemical structure of the IL monomers by selecting cation, anion, and core structure with higher affinity towards CO2 , for example, by increasing the ion polarity.[19]
Conclusions A simple and rapid synthetic procedure to prepare nanoporous poly(ionic liquid)s using ionic liquids (ILs) as porogens is described. The proposed strategy is robust and scalable (batches of 30 g have been prepared). In addition, no waste material is generated, and the porogen is recovered and recycled. Likewise, the synthetic advantages overcome some difficulties that other approaches might face in terms of scalability, energy consumption (e.g., sintering of hard templates), and safety (e.g., the use of harmful volatile solvents). Moreover, the tailorable structure of an IL makes it possible to design the most compatible IL porogen for each IL monomer. Therefore, this approach could be extended easily to the synthesis of poly(ionic liquid)s with other chemical structures with higher a affinity towards CO2 uptake. Further investigation in this sense is in progress.
Experimental Section Materials and methods Figure 5. a) CO2 adsorption isotherm of the PILM/P samples at 293 K. b) 1/t (t, time constant) vs. P/M ratio.
sorption capacity of these materials. Thus, it is not always advisable to maximize the surface area at all cost. In this study, polymers based on imidazolium and TFSI anions were synthesized as a proof-of-concept of a new preparation method for nanoporous PILs. The CO2 sorption capacities of these PILs were comparable to literature values, and we were mindful that the CO2 loading capacity of a given PIL depends on temperature and pressure. Therefore, measurement conditions must be taken into account if literature values are compared directly. CO2 loading capacities of imidazoliumbased nonporous PILs have been reported in the range of 1.53–3.31 mgCO2 gPIL 1 for TFSI and PF6 anions, respectively, and up to 12.46 mgCO2 gPIL 1 for the PIL with acetate anions at 25 8C and atmospheric pressure.[18] In addition, Wilke et al. reported nonporous, highly cross-linked, imidazolium TFSI-based PILs with a loading capacity of 5.2 mgCO2 gPIL 1 at 0 8C and atmospheric pressure.[7] For nonporous PIL1:0, CO2 loading capacities of 2.64 mgCO2 gPIL 1 (0.06 mol kg 1) and 4.18 mgCO2 gPIL 1 (0.095 mol kg 1) were measured at 20 and 0 8C, respectively, under the same pressure (Supporting Information). The CO2 uptake of a given PIL is decreased by increasing the temperature. In our experiments, the sorption capacity of PIL1:0 at 20 8C was reduced by 60 % compared to that at 1 bar and 0 8C. In any case, the CO2 uptake values reported in this paper fall 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1,4-Dibromobutane (99 %) and 1-vinylimidazole (99 %) were purchased from Sigma–Aldrich. AIBN (98 %) was purchased from Acros Organics. Acetone (99.5 %), acetonitrile, and ethyl acetate were purchased from Scharlab. 1-Butyl-1-methylimidazolium chloride and bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) were purchased from IoLiTec. IR spectra were recorded by using an ATRFTIR Jasco 4100 spectrometer. NMR spectra were recorded by using a Bruker Avance III NMR spectrometer in appropriate deuterated solvents. TGA was performed by using a Q500 TG-DTA analyzer manufactured by TA Instruments in the temperature range between 25 and 600 8C under N2 at a heating rate of 10 8C min 1 (Supporting Information). A Carl Zeiss Ultra Plus field-emission scanning electron microscope was used to compare the morphology of the obtained polymers. The N2 adsorption isotherms measurements were performed at 77 K by using a Micromeritics ASAP 2020 analyzer. The CO2 adsorption isotherm measurements at were performed at 298 K by using a Hiden Isochema IGA-003 gravimetric analyzer (Supporting Information).
Preparation of 1,4-di(N,N’-vinylimidazolium)butane di[bis(trifluoromethanesulfonyl)imide] (M) To a solution of 1-vinylimidazole (420 mmol, 39.9 g) in acetonitrile (150 mL) at 60 8C was added 1,4-dibromobutane (200 mmol, 43.6 g) dropwise. After 24 h, the product was precipitated, washed in ethyl acetate, and dried under reduced pressure. The reaction yielded 77.8 g (96 %) of white powder. The resulting dibromide salt (91.55 mmol, 37.0 g) was dissolved in deionized water (400 mL), and a solution of LiTFSI (201.0 mmol, 57.7 g) in deionized water (50 mL) was added. After 1 h, the solid was collected by filtration and washed thoroughly with deionized water. The reaction yielded ChemSusChem 2014, 7, 3407 – 3412
3411
CHEMSUSCHEM FULL PAPERS 70 g (98 %) of white powder. M.p. 83.19 8C; 1H NMR (500 MHz, CDCl3, 25 8C, Me4Si): d = 9.43 (s, 2 H, CH), 8.20 (s, 2 H, CH), 7.90 (s, 2 H, CH), 7.29 (dd, 3J(H,H) = 15.6 Hz, 8.7 Hz, 2 H, CH), 5.94 (dd, 3 J(H,H) = 2.4 Hz, 15.6 Hz, 2 H, CH2), 5.44 (dd, 3J(H,H) = 8.7 Hz, 2.4 Hz, 2 H, CH2), 4.23 (m, 4 H, CH2), 1.84 ppm (m, 4 H, CH2).
Synthesis of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (P) To solution of 1-butyl-3-methylimidazolium chloride (0.1 mol, 17.47 g) in deionized water (100 mL) was added a solution of LiTFSI (0.11 mol, 31.58 g) in deionized water (50 mL). After stirring for 1 h, the suspension was centrifuged, washed with copious water, and dried to yield 32.62 g (80 % yield) of the product as an oil. 1H NMR (500 MHz, CDCl3, 25 8C, Me4Si): d = 8.73 (s, 1 H, CH), 7.30 (s, 1 H, CH), 7.29 (s, 1 H, CH), 4.16 (t, 3J(H,H) = 7.5 Hz, 2 H, CH2), 3.93 (s, 3 H, CH3), 1.84 (m, 2 H, CH2), 1.36 (m, 2 H, CH2), 0.95 ppm (t, 3 J(H,H) = 7.4 Hz, 3 H, CH3).
General procedure for the synthesis of PILs M, P, and AIBN were blended together. The homogenous mixture was degassed and kept under a N2 atmosphere. The mixture was then heated to 100 8C for 24 h. The resulting composite material was then transferred to a centrifuge vessel and washed with acetone until the total weight of IL porogen (100 %) was recovered. The solid was dried under vacuum. Synthesis of PIL1:0 : The general procedure was followed starting from M (35 g) and AIBN (0.70 g) to give 33.5 g of PIL1:0 (96 % yield). Synthesis of PIL1:0.5 : The general procedure was followed starting from M (7 g), P (3.5 g), and AIBN (0.14 g) to give 6.65 g of PIL1:0.5 (95 % yield). Synthesis of PIL1:1: The general procedure was followed starting from M (37 g), P (37 g), and AIBN (0.74 g) to give 35.6 g of PIL1:1 (96 % yield). Synthesis of PIL1:2 : The general procedure was followed starting from M (7 g), P (14 g), and AIBN (0.14 g) to give 6.74 g of PIL1:2 (96 % yield). Synthesis of PIL1:3 : The general procedure was followed starting from M (7 g), P (21 g), and AIBN (0.14 g) to give 6.79 g of PIL1:3 (97 % yield). Synthesis of PIL1:5 : The general procedure was followed starting from M (7 g), P (35 g), and AIBN (0.14 g) to give 6.86 g of PIL1:5 (98 % yield). Synthesis of PIL1:10 : The general procedure was followed starting from M (20 g), P (200 g), and AIBN (0.40 g) to give 19.6 g of PIL1:10 (98 % yield).
Acknowledgements The authors acknowledge financial support from the European Commission through the INTERACT project funded by the European Union’s Seventh Framework Program for Research, Technological Development and Demonstration under grant agreement number 608535. The authors acknowledge the collaboration of SOLVIONIC in the framework of the PIL-TO-MARKET project (FP7PEOPLE-IAPP-2008-230747).
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org Keywords: absorption · ionic liquids · materials science · mesoporous materials · polymers
[1] a) J. Lu, F. Yan, J. Texter, Prog. Polym. Sci. 2009, 34, 431 – 448; b) O. Green, S. Grubjesic, S. Lee, M. A. Firestone, Polym. Rev. 2009, 49, 339 – 360; c) M. D. Green, T. E. Long, Polym. Rev. 2009, 49, 291 – 314; d) J. Yuan, D. Mecerreyes, M. Antonietti, Prog. Polym. Sci. 2013, 38, 1009 – 1039; e) J. Yuan, M. Antonietti, Polymer 2011, 52, 1469 – 1483; f) D. Mecerreyes, Prog. Polym. Sci. 2011, 36, 1629 – 1648. [2] D. Wu, F. Xu, B. Sun, R. Fu, H. He, K. Matyjaszewski, Chem. Rev. 2012, 112, 3959 – 4015. [3] C.-H. Yu, C.-H. Huang, C.-S. Tan, Aerosol Air Qual. Res. 2012, 12, 745 – 769. [4] a) J. Tang, H. Tang, W. Sun, M. Radosz, Y. Shen, Polymer 2005, 46, 12460 – 12467; b) J. Tang, H. Tang, W. Sun, H. Plancher, M. Radosz, Y. Shen, Chem. Commun. 2005, 3325 – 3327; c) S. Supasitmongkola, P. Styring, Energy Environ. Sci. 2010, 3, 1961 – 1972; d) E. I. Privalova, P. MkiArvela, D. Y. Murzin, J. P. Mikkhola, Russ. Chem. Rev. 2012, 81, 435 – 457. [5] J. Zhu, J. Zhou, H. Zhang, R. Chu, J. Polym. Res. 2011, 18, 2011 – 2015. [6] a) F. Yan, J. Texter, Chem. Commun. 2006, 2696 – 2698; b) J. Huang, C.-A. Tao, Q. An, W. Zhang, Y. Wu, X. Li, D. Shena, G. Li, Chem. Commun. 2010, 46, 967 – 969; c) X. Hu, J. Huang, W. Zhang, M. Li, C. Tao, G. Li, Adv. Mater. 2008, 20, 4074 – 4078; d) F. Yan, J. Texter, Angew. Chem. Int. Ed. 2007, 46, 2440 – 2443; Angew. Chem. 2007, 119, 2492 – 2495; e) D. England, N. Tambe, J. Texter, ACS Macro Lett. 2012, 1, 310 – 314. [7] A. Wilke, J. Yuan, M. Antonietti, J. Weber, ACS Macro Lett. 2012, 1, 1028 – 1031. [8] a) Q. Zhao, M. Yin, A. P. Zhang, S. Prescher, M. Antonietti, J. Yuan, J. Am. Chem. Soc. 2013, 135, 5549 – 5552; b) Q. Zhao, S. Soll, M. Antonietti, J. Yuan, Polym. Chem. 2013, 4, 2432 – 2435; c) Q. Zhao, P. Zhang, M. Antonietti, J. Yuan, J. Am. Chem. Soc. 2012, 134, 11852 – 11855. [9] N. V. Plechkova, K. R. Seddon, Chem. Soc. Rev. 2008, 37, 123 – 150. [10] P. Kubisa, Prog. Polym. Sci. 2004, 29, 3 – 12. [11] a) K. Booker, M. C. Bowyer, C. I. Holdsworth, A. McCluskey, Chem. Commun. 2006, 1730 – 1732; b) H. Wang, Y. Zhu, J. Lin, X. Yan, Electrophoresis 2008, 29, 952 – 959; c) K. Booker, M. C. Bowyer, C. J. Lennard, C. I. Holdsworth, A. McCluskey, Aust. J. Chem. 2007, 60, 51 – 56; d) C. He, Y. Long, J. Pan, K. Li, F. Liu, Talanta 2008, 74, 1126 – 1131; e) H.-F. Wang, Y.-Z. Zhu, X.-P. Yan, R.-Y. Gao, J.-Y. Zheng, Adv. Mater. 2006, 18, 3266 – 3270. [12] a) A. Shearrow, S. Bhansali, A. Malik, J. Chromatogr. A 2009, 1216, 6349 – 6355; b) A. M. Shearrow, G. A. Harris, L. Fang, P. K. Sekhar, L. T. Nguyen, E. B. Turner, S. Bhansali, A. Malik, J. Chromatogr. A 2009, 1216, 5449 – 5458. [13] B. Singco, C. Lin, Y. Cheng, Y. S. Yh, H. Huang, Anal. Chim. Acta 2012, 746, 123 – 133. [14] a) P. Snedden, A. I. Cooper, K. Scott, N. Winterton, Macromolecules 2003, 36, 4549 – 4556; b) A. I. Cooper, K. Scott, P. Sneddon, N. Winterton, Polym. Prepr. 2004, 45, 291 – 292; c) L. Peng, J. Zhang, J. Li, B. Han, Z. Xue, G. Yang, Angew. Chem. Int. Ed. 2013, 52, 1792 – 1795; Angew. Chem. 2013, 125, 1836 – 1839; d) Y.-H. Shih, B. Singco, W.-L. Liu, C.-H. Hsu, H.-Y. Huang, Green Chem. 2011, 13, 296 – 299; e) L. Zhu, C.-Y. Huang, Y. H. Patel, J. Wu, S. V. Malhotra, Macromol. Rapid Commun. 2006, 27, 1306 – 1311. [15] L. A. Pavlova, M. V. Pavlov, V. A. Davankov, Dokl. Chem. 2006, 406, 6 – 8. [16] R. Dawson, L. A. Stevens, T. C. Drage, C. E. Snape, M. W. Smith, D. J. Adams, A. I. Cooper, J. Am. Chem. Soc. 2012, 134, 10741 – 10744. [17] C. Viklund, F. Svec, J. M. J. Frchet, Chem. Mater. 1996, 8, 744 – 750. [18] E. I. Privalova, E. Karjalainen, M. Nurmi, P. Mki-Arvela, K. Ernen, H. Tenhu, D. Y. Murzin, J.-P. Mikkola, ChemSusChem 2013, 6, 1500 – 1509. [19] R. S. Bhavsar, S. C. Kumbharkar, U. K. Kharul, J. Membr. Sci. 2012, 389, 305 – 315. Received: June 26, 2014 Revised: July 30, 2014 Published online on September 12, 2014
ChemSusChem 2014, 7, 3407 – 3412
3412
