Macromolecular Rapid Communications

Communication

Chiral Monolithic Absorbent Constructed by Optically Active Helical-Substituted Polyacetylene and Graphene Oxide: Preparation and Chiral Absorption Capacity Weifei Li, Bo Wang, Wantai Yang, Jianping Deng*

Chiral monolithic absorbent is successfully constructed for the first time by using optically active helical-substituted polyacetylene and graphene oxide (GO). The preparative strategy is facile and straightforward, in which chiral-substituted acetylene monomer (Ma), crosslinker (Mb), and alkynylated GO (Mc) undergo copolymerization to form the desired monolithic absorbent in quantitative yield. The resulting monoliths are characterized by circular dichroism, UV–vis absorption, scanning electron microscopy (SEM), FT-IR, Raman, energydispersive spectrometer (EDS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), XPS, and thermogravimetric analysis (TGA) techniques. The polymer chains derived from Ma form chiral helical structures and thus provide optical activity to the monoliths, while GO sheets contribute to the formation of porous structures. The porous structure enables the monolithic absorbents to demonstrate a large swelling ratio in organic solvents, and more remarkably, the helical polymer chains provide optical activity and further enantio-differentiating absorption ability. The present study establishes an efficient and versatile methodology for preparing novel functional materials, in particular monolithic chiral materials based on substituted polyacetylene and GO.

1. Introduction Monolithic materials have been in the focus of scientific interest and industrial applications in the last decades. The distinctive characteristics especially porous structure

W. Li, B. Wang, Prof. W. Yang, Prof. J. Deng State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China E-mail: [email protected] W. Li, B. Wang, Prof. W. Yang, Prof. J. Deng College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

make this unique type of materials remarkably attractive particularly in separation processes.[1–3] As an important subgroup, chiral monolithic materials also have been attracting wide attention.[4–6] Chiral monolithic materials fall into two major groups according to the primary framework: inorganic monoliths and organic polymer monoliths. In the first group, the most widely used framework material is silica.[7,8] Recently, other inorganic materials have also been utilized, e.g., zirconia-based monolith.[9] The second group is well exemplified by polystyrene (PS)-[6] and polyacrylate-based[10,11] monoliths. More recently, inorganic–organic hybrid monolith began to draw attention.[12] For both groups (inorganic and polymer monoliths), chiral sources may originate in naturally

wileyonlinelibrary.com

DOI: 10.1002/marc.201400546

319

Macromolecular Rapid Communications

W. Li et al.

www.mrc-journal.de

occurring small molecular organics[13–15] and macromolecules (e.g., proteins).[16–18] Reportedly, chiral monolithic materials have found significant applications in chiral separations,[19,20] asymmetric catalyses,[21,22] etc. Unfortunately, synthetic helical polymers,[23–30] even though they have been intensively investigated and elegantly used as chiral catalysts[31–34] and chiral selectors,[35] have not been employed to establish monolithic materials. Accordingly, the present article will report an unprecedented type of chiral monolith constructed by optically active helical polyacetylene and graphene oxide (GO). Graphene oxide has been used to prepare advanced monolithic materials due to the superior strength, large specific area, among other intriguing properties.[36,37] The obtained materials are expected to be used as absorbents towards organics, metal ions, etc.[38–42] Nonetheless, chiral monolithic materials composed of GO have not been reported yet in literature. Our previous studies demonstrate that a judicious combination of GO and chiral helical-substituted polyacetylenes can provide interesting functional hybrid materials via covalent[43,44] and noncovalent[45,46] bonds. The helical polymers were attached on GO[44] and reduced GO[45] sheets in the form of macromolecular chains and even nanoparticles

thereof.[43] Based on the preceding studies, we further envision that interesting monolithic materials will be fabricated by taking advantage of GO and helical polyacetylene, in which GO offers strength and contributes to the formation of porous channels inside the monolith, while helical polyacetylene chains provide the desired optical activity. To confirm our hypothesis, in the present study, we not only prepared a novel type of chiral monolithic materials, but established a versatile strategy (as illustratively presented in Figure 1) for preparing advanced functional materials, in particular chiral materials combining the advantages of helical polymers and GO.

2. Experimental Section 2.1. Materials (nbd)Rh+B−(C6H5)4 was synthesized according to the method reported earlier.[47] Monomer a (abbreviated as Ma) and monomer b (Mb, as structurally presented in Figure 1) were prepared according to literature.[48,49] Propargylamine, isobutyl chloroformate, N-methylmorpholine, dicyclohexylcarbodiimide (DCC), and 4-dimethylaminopyridine (DMAP) were purchased

Figure 1. Schematic illustration of the strategy for preparing chiral monoliths (top). Bottom: The photographs of monolith-1 (without Mc) and monolith-4 (with 15% Mc) before A,C) and after swelling B,D) in THF for 3 weeks at room temperature.

320

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.MaterialsViews.com

Chiral Monolithic Absorbent Constructed by Optically Active Helical-Substituted Polyacetylene . . .

Macromolecular Rapid Communications www.mrc-journal.de

from Aldrich and used as received. Graphite powder (300 mesh, 75%–82% C, 18%–25% ash) was bought from Alfa Aesar. Potassium permanganate (KMnO4), hydrogen peroxide solution (H2O2, 30%), hydrochloric acid (HCl), 96% sulfuric acid (H2SO4), and NaOH were commercially obtained. All the amino acids (D and L isomers), and R- and S-phenethylamine were bought from Aladdin Company (Shanghai, China) and directly used.

2.2. Measurements Circular dichroism (CD) and UV–vis absorption spectra were conducted on a Jasco-810 spectropolarimeter. Specific rotations were measured on a Jasco P-1020 digital polarimeter with a sodium lamp as a light source at room temperature. FT-IR spectra were recorded with a Nicolet NEXUS 670 spectrophotometer (KBr tablet). X-ray diffraction (XRD) analyses were performed with Shimadzu XRD-6000. Scanning electron microscopy (SEM) was observed on JEOL J-800 and Hitachi S-4700 electron microscope. Thermogravimetric analysis (TGA) was carried out with a Q50 TGA at a scanning rate of 10 °C min−1 under N2. Raman spectra were recorded on a Renishaw inVia-Reflex confocal Raman microscope with an excitation wavelength of 532 nm. Pore analysis was carried out on a BK122W sorption analyzer.

2.3. Preparation of Graphene Oxide and Alkynylated GO GO was prepared with the method reported by Hummers and Offeman with slight modification.[50] We detailed the preparing processes in an earlier report.[43] A dialysis method was utilized to purify GO, for which more details are described below. GO was dispersed in a large amount of deionized water, and then the dispersion solution was put into a dialysis bag and immersed in deionized water. The external water was renewed each day. This process lasted for 3 weeks. The residue was centrifugated (17 000 rpm, 20 min) and then filtered under reduced pressure through a 0.2-μm PTFE. The product was dried up under vacuum at 30 °C for 72 h. The alkynylated GO, i.e., Mc (Figure 1) was prepared by referring to previous studies.[43,44]

2.4. Preparation of Chiral Polymer/GO Monoliths The preparative processes are schematically illustrated in Figure 1. The whole procedure was conducted under N2 atmosphere. First, alkynylated GO (Mc) (0.08 g) was dispersed in THF (3.5 mL) under ultrasonication at room temperature for 5 h. Then, Ma (0.4 g) and Mb (0.02 g)/THF (1 mL) was charged into the GO dispersion by ultrasonication for 3 h. Rh catalyst [(nbd) Rh+B−(C6H5)4], 0.01 g)/THF (0.5 mL) solution was added dropwise in the system above, which initiated the polymerization of Ma and Mb. The C C moieties pregrafted on the alkynylated GO (Mc) sheets also took part in polymerization. After polymerization, the product was immersed in excessive THF (20 mL) to remove the uncross-linked polymers and the other impurities. THF was renewed once every 3 d, which lasted for 2 weeks. The product was then dried up under vacuum at 30 °C. Monoliths were obtained in quantitative (yield, 98.3% –99.6%).

www.MaterialsViews.com

2.5. Swelling Ratio of Monoliths The resultant monoliths possessed excellent swelling property in usual solvents. Swelling ratios were measured as follows,[39] by taking THF as example. A monolith (Wd) was put into a dialysis bag and immersed in excessive THF at room temperature. After immersion for a given time, the monolith was taken out and a filter paper was utilized to remove the excess THF on the surface, and then the monolith was weighed again. The above immersion and weighing process was repeated until the weight of the monolith reached a constant value (Ws). The swelling ratio of the monolith was determined by the equation, swelling ratio = (Ws−Wd)/Wd.

2.6. Enantioselective Absorption by Chiral Monoliths We investigated the enantioselective absorption property of the chiral monolith towards phenylalanine, phenethylamine, alanine, BOC-alanine, and leucine enantiomers. A typical enantioselective absorption procedure was performed as follows (taking phenylalanine as example).[51] First, D- and L-phenylalanine (100 mg) were separately dissolved in THF (100 mL). Approximately 0.05 g monolith was put into dialysis bag, and then soaked it in the D-phenylalanine (or L-phenylalanine) solution for about 30 h under room temperature. After every certain period of time, the outer THF solution was subjected to optical rotation measurement. The chiral compound concentration can be determined according to optical rotation and specific rotation data.

3. Results and Discussion As shown in Figure 1, the chiral monolithic absorbents were synthesized by a one-step approach. Copolymerization of Ma (monomer), Mb (cross-linker), and Mc (alkynylated GO) in the presence of catalyst (nbd)Rh+B−(C6H5)4 was performed in THF at 30 °C for 4 h. It should be pointed out that regular monoliths could not be obtained in the absence of cross-linker (Mb). When Mb was added, the desired monolith could be obtained quantitatively. Totally five monoliths were prepared, for which the specific preparing parameters are listed in Table S1 (Supporting Information, the same below). The difference in them lies in the varied alkynylated GO (Mc) concentration, namely 0, 5, 10, 15, and 20 wt% for monolith-1, -2, -3, -4, and -5, respectively. All the five monoliths could be obtained in a bulk form, and maintained the bulk shape even after a remarkable swelling, as shown in Figure S1 (Supporting Information). Before and after swelling, the color of the monoliths changed little, as evidenced by monolith-1 (without alkynylated GO) and monolith-4 (alkynylated GO, 15 wt%) as displayed in Figure 1. Monolith-1 shows a brown color, while for the other four monoliths with GO, they all exhibit a dark black color because of the presence of GO sheets. To further verify the formation of chiral monolithic absorbent as expected, the products were characterized

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

321

Macromolecular Rapid Communications

W. Li et al.

www.mrc-journal.de

by FT-IR spectroscopy, as presented in Figure S2 (Supporting Information). The FT-IR spectra for GO, Ma, Mb, alkynylated GO (Mc), monolith-1, and monolith-4 are illustrated, with monolith-4 as representative for the four monoliths containing GO. Detailed analysis of the spectra is presented in Figure S2 (Supporting information). A comparison among the spectra provides important information. After the copolymerization, several new peaks disappeared or appeared in the FT-IR spectrum of monolith-4 (spectrum B) compared to the spectrum of Mc (spectrum C). The peak at 2115 cm−1 (indicating the C C moieties attached on the surface of GO, spectrum C) disappeared after polymerization, and indicated that C C groups took part in polymerization. In spectrum B, the new peaks at 1734 and 1797 cm−1 are attributed to C O structures in carboxylic acid moieties contained on GO sheets and ester carbonyl groups in Ma and Mb, as structurally displayed in Figure 1. Additionally, the peak at 1387 cm−1 ( OH on the surface of GO) in monolith-4 cannot be observed in monolith-1. The FT-IR spectra preliminarily confirm the successful formation of chiral helical polymer/GO monoliths. Figure 2 shows the SEM images of the chiral polymer/ GO monoliths. Compared to the SEM images in Figure 2A,B (monolith-1, without adding Mc), the SEM images in Figure 2C (5 wt% Mc), 2D (10 wt% Mc), 2E,F (15 wt% Mc), and Figure 2G,H (20 wt% Mc) demonstrated that the monoliths with GO sheets (monoliths-1–4) had unidirectional porous channel structures. From the SEM images, we can also clearly observe that the pores decreased in width at first and then increased as GO concentration increased (0–20 wt% Mc), but the corresponding number of pores showed the opposite tendency. The uniform lamellar structures cannot be observed when adding low mass fraction of GO (5 wt% Mc, Figure 2C); however, layerby-layer structures can be clearly observed when more GO was added Figure 2D, 2E). Compared with Figure 2E,F, the SEM images in Figure 2G,H show that the width of the pore channel increased while number of the pore channels decreased. This observation can be understood as below. When further more alkynylated GO was added, the amount of polymers inserted between GO sheets decreased. This led to decreased interaction among polymer chains inside two GO sheets when the monolith swelled, and finally the distance between GO sheets widened, as observed in Figure 2G,H. To acquire more insights into the pore structures, the composition of pore ridges and valleys was separately characterized by energy-dispersive spectrometer (EDS), for which the results are described in Figure S3 (Supporting Information, with monolith-4 as representative). The data definitely indicate that no N element was detected in the pore ridges, clearly confirming that the ridges were predominantly composed of GO sheets. On the other hand,

322

Figure 2. Typical SEM images of monolith-1 (A,B; without Mc), monolith-2 (C, with 5% Mc), monolith-3 (D, with 10% Mc), monolith-4 (E, F; with 15% Mc), monolith 5 (G,H; with 20% Mc). All the monoliths were swelled in THF at room temperature for 3 weeks; freeze-drying for 72 h before SEM observation.

the relatively high content of N element in the valleys means that they were predominantly constructed by the substituted polyacetylene chains. N2 absorption measurements were conducted to investigate the Brunauer–Emmett–Teller (BET) specific surface area and porous structure of the chiral polymer/GO monoliths. Figure S4 (Supporting Information) shows the nitrogen absorption–desorption isotherms and pore size distribution of monolith-1 and monolith-4, respectively. We can see clearly that the adsorption and desorption profiles were nearly overlapped. It is indicated that the BET curves belong to the IV-type according to IUPAC rules. Additionally, the type of hysteresis loop indicated the pores in the monoliths are homogeneous.[52] The pores parameters of monolith-1 and monolith-4 are: BET specific area, 2.415 and 4.329 m2 g−1; pore diameter, 10.277 and 18.801 nm, respectively. The data show that the chiral polymer/GO hybrid monoliths possessed mesopores (2–50 nm) structure. Furthermore, the addition of GO

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.MaterialsViews.com

Chiral Monolithic Absorbent Constructed by Optically Active Helical-Substituted Polyacetylene . . .

Macromolecular Rapid Communications www.mrc-journal.de

sheets helped enlarge the pores and meanwhile increase the specific area of monolith-4 relative to monolith-1. The porous structures rendered the monoliths with significant swelling property, as will be reported later on. Alkynylated GO (Mc) and monolith-4 were further subjected to X-ray diffraction (XRD) analysis. The XRD patterns are shown in Figure S5 (Supporting Information). In the case of alkynylated GO, there is a sharp reflection peak at 2θ = 9.7° in the XRD pattern, reflecting an interlayer spacing (d) of 1.044 nm.[53] However, the peak at 9.7° disappeared in the XRD pattern of monolith-4, but a wide peak appeared instead. It shows that the GO crystal structure was destroyed since a large amount of copolymer chains inserted into the interlayer of graphene sheets, for this consideration the SEM images in Figure 2 offered directed evidence. Moreover, we can determine ID/IG ratio of Mc according to Raman spectroscopy.[54] ID means the peak intensity at ≈1347 cm−1 while IG indicates the peak intensity at 1586 cm−1. They, respectively, correspond to the number of sp3 and sp2 C atoms. The recorded Raman spectra are presented in Figure S6 (Supporting Information). In the present study, the ratio of ID/IG reduced from 0.83 (for Mc) to 0.31 (for monolith-4) by calculating the corresponding peaks area. The decrease in ID/IG shows a significant increase in the average amount of sp2 C. Raman spectra analyses also provide a further support for our conclusion that a large amount of helical copolymer was inserted between GO sheets in monolith-4. The thermal stability of the prepared chiral polymer/ GO hybrid monoliths was examined by TGA technique. The analyses were performed from room temperature to 1000 °C at a heating rate of 10 °C min−1 under a nitrogen atmosphere. The results are presented in Figure S7 (Supporting Information). The oxygen-containing functional

groups on the surface of GO sheets began to burn at a temperature of about 190 °C. The remaining fraction of nonvolatile materials remained at a temperature up to 1000 °C. The helical polymers began to burn at approximately 250 °C, indicating that the polymer chains decomposed around this temperature. For monoliths-1–5, they, respectively, left ca. 13.2%, 18.5%, 23.7%, 28.6%, and 34.3% at 1000 °C. It further demonstrates that approximately 5.3%, 10.5%, 15.4%, and 21.1% Mc was contained in the corresponding monolith, which are in accordance with the corresponding theoretical values (5%, 10%, 15%, and 20%). Furthermore, we can clearly see that curve a (without Mc) consumed at a rate faster than curves b (5% Mc), c (10% Mc), d (15% Mc), and e (20% Mc). It further shows that the monoliths became more stable in the same order, due to the gradually increased GO (Mc). The optical activity of the five monoliths (monoliths-1–5) was characterized by measuring their CD and UV–vis absorption spectra (Figure 3). In the previous study,[43] the homopolymer of Ma possessed an intensive CD signal around 350 nm due to the formation of onehanded helical structures. The monolith derived from the cross-linker Mb (i.e., without Ma and Mc) failed to show CD signal around the same wavelength, as can be seen in Figure 3A. Our previous studies show that for helical-substituted polyacetylenes but without pendent chiral moieties, they could not show optical activity.[48] Moreover, the chirality derived from helical structures and the side-chain chirality tend to cooperate in chiral processes, e.g., asymmetric catalysis.[55] Monoliths-1–5 showed intensive CD signals and UV–vis absorptions at a wavelength between 400 and 450 nm. Here, it should be pointed out that the spectra were recorded on swelled monolith samples by clicking them between two pieces

Figure 3. CD and UV–vis absorption spectra of monoliths-1–5 swollen in THF at 25 °C for 2 weeks. Pure cross-linker indicates the homopolymer purely derived from the cross-linker (Mb) in Figure 1. The spectra were recorded by firstly swelling the monoliths in THF; for details, see the Experimental section.

www.MaterialsViews.com

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

323

Macromolecular Rapid Communications

W. Li et al.

www.mrc-journal.de

of quartz glass (for more details, see the Experimental section), and the thickness of the monoliths cannot keep uniform in all the tests. This measurement led to the complexity of the spectra. Nonetheless, intense CD signals can be observed clearly. According to our earlier studies,[43–45,51] the intense CD effects and UV– vis absorptions indicate that the monoliths possessed optical activity originating in the helical polymer chains. Nevertheless, when compared to the CD and UV–vis spectra of the corresponding homopolymer (the polymer derived from Ma) measured in solutions,[43] the CD and UV–vis absorption spectra in Figure 3A,B showed considerable red shifts. This phenomenon also appeared in optically active hydrogels and particles ever reported by us.[56,57] It can be understood by the fact that the effective conjugation length of helical polymer segments was elongated by cross-linking. The porous structures are favorable for the monoliths to absorb oils. Figure S8 (Supporting Information) describes the swelling ratios of monoliths-1–5 as a function of time in THF at room temperature. We can see clearly the swelling ratio of the monoliths gradually increased with the elongation of immersion time. Moreover, an increase of Mc content resulted in the equilibrium swelling ratio of the monoliths increasing from 10 (monolith-1, without Mc) to 17 times (monolith-4, with 15% Mc). But for monolith-5, the swelling ratio decreased unexpectedly. It could be explained as follows. When the content of Mc was lower (≤15 wt%), Mc efficiently increased the number of the pore channels inside the monolith, which is favorable for the equilibrium swelling ratio to be increased. However, the pore numbers decreased when excessive Mc was added (20 wt%), which became not favorable for further increasing the swelling of monolith. In addition, the time for reaching equilibrium swelling decreased with increasing the amount of Mc, as demonstrated in Figure S8 (Supporting Information).

Figure S8 (Supporting Information) shows that the composition of the monoliths affected largely their oil absorbency (the oils: CHCl3, C7H8, THF, CH3COCH3, C2H5OH, and CH3OH). Even for a same monolith, it performed differently toward different oils in swelling. Taking monolith-4 as example, the oil absorbency of it for different oils is shown in Figure 4A. The equilibrium absorbency for the examined oils ranged from 9 to 17 times. Among the oils, the maximum absorbency appeared in the case of THF. Nonetheless, the swelling of the monoliths is indeed a much complex process, depending on molecular weight and polarity of oils.[38] Thus, regular tendency could not be observed among the oils in Figure 4A. To explore the chiral recognition performance of the monoliths, we utilized monolith-4 as a model chiral monolith and D- and L-phenylalanine, alanine, BOC-alanine, leucine, and R-, and S-phenethylamine as model chiral compounds to be recognized. The relevant results are presented in Figure S9 (Supporting Information) and Figure 4B. Taking phenylalanine as example, THF solution (100 mL) of D- and L-phenylalanine (c = 1 mg mL−1) was separately prepared and absorbed by monolith-4 for 30 h. Optical rotation of the solutions was measured at given intervals. Figure S9 (Supporting Information) describes the absorption profiles and demonstrates the chiral absorption feature of the monolithic absorbent. Taking Figure S9A (Supporting Information) as example, monolith-4 preferentially absorbed L-phenylalanine. It absorbed 75% of L-phenylalanine, but only 26% of L-phenylalanine (Figure S9A, Supporting Information) was absorbed. For other enantiomers examined, monolith-4 also exhibited chiral absorption capacity to varied degrees. The chiral absorption results were presented in Figure 4B. The most pronounced enantioselective absorption feature (up to 49%) appeared in D- and L-phenylalanine. Based on the investigations, we conclude that the monoliths showed remarkable chiral recognition capacity.

Figure 4. A) Swelling ratio of monolith-4 toward achiral oils; B) chiral absorption of monolith-4 toward enantiomers. The experiments were conducted in THF at room temperature.

324

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.MaterialsViews.com

Chiral Monolithic Absorbent Constructed by Optically Active Helical-Substituted Polyacetylene . . .

Macromolecular Rapid Communications www.mrc-journal.de

For investigating the function of Mc in the chiral recognition process, we subsequently took monolith-1 (without Mc) to carry out chiral absorption experiments. The data were described in Figure S9F (Supporting Information). In the contrast test, 37% of L-phenylalanine and 10% of D-phenylalanine were absorbed; the difference between them is only 27%. The reason for the remarkable difference in chiral absorption between Figure S9A (Supporting Information) (monolith-4) and Figure S9F (Supporting Information) (monolith-1) may be explained as below, referring to our earlier study.[58] Inside the monoliths, the helical polymer chains forming helices of predominant one-handed screw sense, which enantioselectively interacted with chiral molecules through interactions of hydrogen bonds. When GO sheets (Mc) are present inside the monoliths (monolith-4), the pore size and specific area increased, so small molecules can easily penetrate inside the monolith. As a result, more chiral molecules were absorbed and correspondingly more pronounced chiral absorption feature was observed in the case of monolith with Mc (monolith-4) than the one without Mc (monolith-1). To obtain more insights into the chiral adsorption of the monoliths, we especially extended the adsorption time and the results are presented in Figure S10A (Supporting Information). It demonstrates that the monoliths kept the chiral adsorption feature for up to 50 h. In addition, we conducted chiral adsorption tests by using racemic alanine solution (c = 1 mg mL−1) composed of equal amount of D- (−) and L- (±) alanine) with monolith-4. Optical rotation of the solution was plotted against the adsorption time, as described in Figure S10B (Supporting Information). It also shows that the monolith preferably adsorbed L-alanine, similar to Figure S9C (Supporting Information). Next, we will continue our work to optimize the chiral monoliths in composition and pore structures, to further improve their chiral absorption ability. Additionally, the novel chiral monoliths are also expected to find significant applications in asymmetric catalysis, chiral resolution, enantioselective release, and so on.

4. Conclusion In the present study, we prepared a novel type of chiral monolithic absorbents starting from optically active helical polyacetylene and GO. The resultant monoliths possessed remarkable optical activity derived from chiral helical-substituted polyacetylene. The GO sheets led to the formation of layered structures and mesopores inside the monoliths. The porous structure facilitated the monolithic absorbents to show large swelling ability in general organic solvents. The optically active helical polymer chains allowed the monolith to show enantio-differentiating absorption

www.MaterialsViews.com

ability towards the examined enantiomers. The most exciting chiral absorption effect appeared in phenylalanine, in which the maximum difference in absorbing the two enantiomers was up to 49%. The present methodology hopefully extends to other helical and nonhelical polymers for functionalizing graphene (oxide), which will lead to a large number of novel graphene-based materials, especially chiral materials. These findings encourage us to further design and develop new graphene-derived materials with chiral recognition, chiral resolution, wave-absorbing abilities, etc. Acknowledgements: This work was supported by the National Natural Science Foundation of China (21474007, 21274008, and 21174010), the Funds for Creative Research Groups of China (51221002), and the “Specialized Research Fund for the Doctoral Program of Higher Education” (SRFDP 20120010130002). Received: September 26, 2014; Revised: November 2, 2014; Published online: December 9, 2014; DOI: 10.1002/marc.201400546 Keywords: chiral absorbent; chiral absorption; graphene oxide; helical polymers

[1] A. Inayat, B. Reinhardt, H. Uhlig, W.-D. Einicke, D. Enke, Chem. Soc. Rev. 2013, 42, 3753. [2] T. Zhou, K. H. Row, J. Sep. Sci. 2012, 35, 1294. [3] A. Ghanem, T. Ikegami, J. Sep. Sci. 2011, 34, 1945. [4] R. Healey, A. Ghanem, Chirality 2013, 25, 314. [5] D. Wistuba, J. Chromatogr. A 2010, 1217, 941. [6] M. Teraguchi, M. Ohtake, H. Inoue, A. Yoshida, T. Aoki, T. Kaneko, K. Yamanada, J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 2348. [7] A. Mesina, M. Flieger, F. Bachechi, M. Sinibaldi, J. Chromatogr. A 2006, 1120, 69. [8] H.-F. Wang, Y.-Z. Zhou, X.-P. Yan, R.-Y. Gao, J.-Y. Zheng, Adv. Mater. 2006, 18, 3266. [9] J.-M. Park, J. H. Park, J. Chromatogr. A 2014, 1339, 229. [10] M. Guerrouache, M. Millot, B. Carbonnier, Macromol. Rapid Commun. 2009, 30, 109. [11] W. Bragg, S. A. Shamsi, J. Chromatogr. A 2012, 1267, 144. [12] H. Lin, J. Ou, S. Tang, Z. Zhang, J. Dong, Z. Liu, H. Zou, J. Chromatogr. A 2013, 1301, 131. [13] J. He, X. Wang, M. Morill, S. A. Shamsi, Anal. Chem. 2012, 84, 5236. [14] M. Ahmed, A. Ghanem, J. Chromatogr. A 2014, 1345, 115. [15] M.-L. Hsieh, L.-K. Chau, Y.-S. Hon, J. Chromatogr. A 2014, 1358, 208. [16] Y. Zheng, X. Wang, Y. Ji, Talanta 2012, 91, 7. [17] T. Hong, Y. Zheng, W. Hu, Y. Ji, Anal. Biochem. 2014, 464, 43. [18] R. Gotti, J. Fiori, E. Calleri, C. Temporini, D. Lubda, G. Massolini, J. Chromatogr. A 2012, 1234, 45. [19] L. N. Tran, S. Dixit, J. H. Part, J. Chromatogr. A 2014, 1356, 289. [20] E. L. Pfaunmiller, M. Hartmann, C. M. Dupper, S. Soman, D. S. Hage, J. Chromatogr. A 2012, 1269, 198. [21] Y.-S. Kim, X.-F. Guo, G.-J. Kim, Catal. Today 2010, 150, 91. [22] V. Chiroli, M. Benaglia, A. Puglisi, R. Porta, R. P. Jumde, A. Mandoli, Green Chem. 2014, 16, 2798.

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

325

Macromolecular Rapid Communications

W. Li et al.

www.mrc-journal.de

[23] J. Z. Liu, J. W. Y. Lam, B. Z. Tang, Chem. Rev. 2009, 109, 5799. [24] V. Jain, K. S. Cheon, K. Tang, S. Jha, M. M. Green, Isr. J. Chem. 2011, 51, 1067. [25] E. Yashima, K. Maeda, H. Iika, Y. Furusho, K. Nagai, Chem. Rev. 2009, 109, 6102. [26] J. G. Rudick, V. Percec, Acc. Chem. Res. 2008, 41, 1641. [27] Y. Yoshida, Y. Mawatari, A. Motoshige, R. Motoshige, T. Hiraoki, M. Wagner, K. Müllen, M. Tabata, J. Am. Chem. Soc. 2013, 135, 4110. [28] F. Freire, J. M. Seco, E. Quiñoá, R. Riguera, Angew. Chem. Int. Ed. 2011, 50, 11692. [29] F. Helmich, C. C. Lee, A. P. H. J. Schenning, E. W. Meijer, J. Am. Chem. Soc. 2010, 132, 16753. [30] H. Jia, M. Teraguchi, T. Aoki, Y. Abe, T. Kaneko, S. Hadano, T. Namikoshi, T. Ohishi, Macromolecules 2010, 4, 8353. [31] K. Maeda, K. Tanaka, K. Morino, E. Yashima, Macromolecules 2007, 40, 6783. [32] T. Yamamoto, T. Yamada, Y. Nagata, M. Suginome, J. Am. Chem. Soc. 2010, 132, 7899. [33] K. Terada, T. Masuda, F. Sanda, J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4971. [34] R. P. Megens, G. Roelfes, Chem. Eur. J. 2011, 17, 8514. [35] C. Zhang, H. Wang, Q. Geng, T. Yang, L. Liu, R. Sakai, T. Satoh, T. Kakuchi, Y. Okamoto, Macromolecules 2013, 46, 8406. [36] W. Wan, L. Li, Z. Zhao, H. Hu, X. Hao, D. A. Winkler, L. Xi, T. C. Hughes, J. Qiu, Adv. Funct. Mater. 2014, 24, 4915. [37] S. Wang, F. Tristan, D. Minami, T. Fujimori, R. Cruz-Silva, M. Terrones, K. Takeuchi, K. Teshima, F. Rodríguez-Reinoso, M. Endo, K. Kaneko, Carbon 2014, 76, 220. [38] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, F. Xu, F. Banhart, L. Sun, R. S. Ruoff, Adv. Funct. Mater. 2012, 22, 4421. [39] Y. Li, L. Qi, H. Ma, Analyst 2013, 138, 5470. [40] S. Tong, X. Zhou, C. Zhou, Y. Li, W. Li, W. Zhou, Q. Jia, Analyst 2013, 138, 1549. [41] Y. Li, J. Chen, L. Huang, C. Li, J.-D. Hong, G. Shi, Adv. Mater. 2014, 26, 4789.

326

[42] M. A. Worsley, T. Y. Olson, J. R. I. Lee, T. M. Willey, M. H. Nielsen, S. K. Roberts, P. J. Pauzauskie, J. Biener, J. H. Satcher Jr., T. F. Baumann, J. Phys. Chem. Lett. 2011, 2, 921. [43] W. Li, X. Liu, G. Qian, J. P. Deng, Chem. Mater. 2014, 26, 1948. [44] W. Li, J. Liang, W. Yang, J. P. Deng, ACS Appl. Mater. Interfaces 2014, 6, 9790. [45] C. Ren, Y. Chen, H. Zhang, J. P. Deng, Macromol. Rapid Commun. 2013, 34, 1368. [46] J. W. Yi, J. Park, K. S. Kim, B. H. Kim, Org. Biomol. Chem. 2011, 9, 7434. [47] R. R. Schrock, J. A. Osborn, Inorg. Chem. 1970, 9, 2339. [48] J. P. Deng, J. Tabei, M. Shiotsuki, F. Sanda, T. Masuda, Macromolecules 2004, 37, 1891. [49] R. Liu, F. Sand, T. Masuda, J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 4175. [50] W. S. Hummers, R. E. Offeman Jr., J. Am. Chem. Soc. 1958, 80, 1339. [51] C. Song, C. Zhang, F. Wang, W. Yang, J. P. Deng, Polym. Chem. 2013, 4, 645. [52] K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti, J. Rouquerol, T. Siemieniewska, Pure Appl. Chem. 1985, 57, 603. [53] Y. Guo, S. Guo, J. Ren, Y. Zhai, S. Dong, E. Wang, ACS Nano 2010, 4, 4001. [54] Q. Yang, X. J. Pan, F. Huang, K. C. Li, J. Phys. Chem. C 2010, 114, 3811. [55] D. Zhang, C. Ren, W. Yang, J. P. Deng, Macromol. Rapid Commun. 2012, 33, 652. [56] H. Zhang, J. Song, J. P. Deng, Macromol. Rapid Commun. 2014, 35, 1216. [57] L. Ding, Y. Huang, Y. Zhang, J. P. Deng, W. T. Yang, Macromolecules 2011, 44, 736. [58] K. Zhou, L , Tong, J. Deng, W. Yang, J. Mater. Chem. 2010, 20, 781.

Macromol. Rapid Commun. 2015, 36, 319−326 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.MaterialsViews.com

Chiral monolithic absorbent constructed by optically active helical-substituted polyacetylene and graphene oxide: preparation and chiral absorption capacity.

Chiral monolithic absorbent is successfully constructed for the first time by using optically active helical-substituted polyacetylene and graphene ox...
1MB Sizes 0 Downloads 8 Views