Optically Active Biobased Hollow Polymer Particles: Preparation

Feb 20, 2019 - Subsequently removing the cores provided hollow particles, which were then chiralized with chiral agents (R- and S-1-phenylethylamine) ...
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Optically Active Biobased Hollow Polymer Particles: Preparation, Chiralization, and Adsorption toward Chiral Amines Saleem Raza, Xueyong Yong, and Jianping Deng* State Key Laboratory of Chemical Resource Engineering; College of Materials Science and Engineering, Beijing University of Chemical Technology, Beisanhuan East Road 15#, Beijing 100029, China

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S Supporting Information *

ABSTRACT: The present work reports a new type of optically active biobased hollow polymer particles (OABHPs) starting from a commonly available biophenylpropene transanethole (ANE). To prepare the OABHPs, ANE and maleic anhydride (MAH) underwent precipitation copolymerization in the presence of particulate template as cores, thereby forming core/shell particles. Subsequently removing the cores provided hollow particles, which were then chiralized with chiral agents (R- and S-1-phenylethylamine) and (R- and Scyclohexyalethylamine) to fabricate the designed OABHPs. The as-prepared particles were characterized by SEM, TEM, elemental analysis, CD, and FT−IR measurements. The chiral particles’ enantioselectivity was further explored by using them as chiral adsorbent toward D- and L-alanine and (−)-cinchonidine and (+)-cinchonine. The optically active hollow particles showed good enantiomeric excess (e.e.) toward racemic alanine. The study not only opens up a new approach for preparing chiral polymer materials, but also provides a versatile platform for making a full use of biomass to develop advanced functional materials.

1. INTRODUCTION Chiral polymer particles have been drawing much interest due to their interesting optical activity and significant applications in chiral-related areas.1−7 In the last decades, synthetic chiral polymers have achieved remarkable progress.8−13 More recently, chiral polymer particles and chiral hybrid particles also have demonstrated substantial applications as chiral catalysts for asymmetric catalysis,4,14−16 chiral recognition/ adsorption,17−19 enantioselective crystallization20 and chiral drug release.21,22 However, up to date most of the chiral polymer particles were constructed by chiral monomers.23,24 It has been well recognized that chiral monomers are expensive and in particular highly limited in both varieties and number.25,26 To solve the limitations, chiral additives,27 chiral solvents,28 and chiral co-monomers29,30 were used to generate chiral polymers derived from achiral monomers via chiral induction and/or chirality transfer strategies. The present work reports a new approach for preparing chiral polymer particles starting from achiral biomass, rationally combining an idea of post-chiralization. Herein, trans-anethole (ANE) was taken as a model for biomass, as it abundantly exists in Chinese star anise,31 fennel,32 and anise,33 and has been broadly used as a seasoning. Using biomass to develop chiral particles provides a significant approach toward new, green materials to use in future perspectives.34,35 We hypothesize that hollow particles integrated with chiral moieties can be employed as high-performance adsorbents © XXXX American Chemical Society

toward chiral compounds, together with other pronounced advantages.36 In this regard, a judicious combination of biobased hollow polymer particles and chiral structures is expected to provide more promising optically active hollow particles which hopefully demonstrate both high adsorption ability and recyclability.37,38 In our previous work, biobased hollow polymer particles (BHPs)39 and biobased magnetic hollow particles40 originated in trans-anethole (ANE) were prepared and used as novel bioadsorbents. Based on our earlier studies concerning chiral polymer particles16,22,29,37 and biobased polymer particles,39,40 we in the present work established a novel strategy for constructing optically active hollow polymer particles. Specifically, the earlier hollow particles were chiralized by a “post-chiralization” concept (Scheme 1). A new type of optically active biobased hollow particles (abbreviated as OABHPs, herein including R-PEAHPs, S-PEA-HPs, R-CHEA-HPs, and S-CHEA-HPs), were prepared thereby. To explore their adsorption applications, the OABHPs were used as chiral adsorbent. The particles demonstrate the desired adsorption ability and enantioselectivity. The strategy established in the present work is expected Received: Revised: Accepted: Published: A

November 26, 2018 February 14, 2019 February 20, 2019 February 20, 2019 DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research Scheme 1. Schematic Illustration for Synthesis of BHPs, R-PEA-HPs, S-PEA-HPs, R-CHEA-HPs, and S-CHEA-HPs

2.4. Synthesis of R-/S-PEA and R-/S-CHEA Chiralized Hollow Particles (OABHPs). Two groups of hollow particles obtained above (each 0.2 g) were respectively put in two small bottles and 10 mL ethanol was added in each one, and then (0.2 mL) R- and S-PEA was added separately. Chiralization process lasted for 6 h with constant stirring at 40 °C. Subsequently, the chiralized hollow particles were obtained by centrifugation, washed thoroughly with ethanol and dried in oven. The same procedure was applied to R-/S-CHEA. Finally, we obtained totally four types of OABHPs (R-PEA-HPs, SPEA-HPs, R-CHEA-HPs, and S-CHEA-HPs). 2.5. Adsorption Study of Chiral Hollow Particles. The adsorption ability of OABHPs, R-PEA-HPs, S-PEA-HPs, RCHEA-HPs, and S-CHEA-HPs, were studied toward different chiral compounds (D-alanine, L-alanine, rac-alanine, (+)-cinchonine, (−)-cinchonidine). The experimental procedure is as follows. 10 mg of chiral hollow particles was dispersed in a small bottle containing 10 mL of chiral amine aqueous solution; the concentration of the solutions was 100 mg/L. The mixture was stirred for a predetermined time. Then the solution was subjected to UV−vis spectroscopy measurement to determine the chiral amine concentration. The adsorbed amount of chiral amine compounds was calculated by the following eq 1:

to provide a variety of sustainable polymeric materials derived from biomass.

2. EXPERIMENTAL SECTION 2.1. Materials. The hollow particles were synthesized according to our earlier work,39,40 using monomers maleic anhydride (MAH) and trans-anethole (ANE) purchased from Tokyo Chemical Industry (TCI). Divinylbenzene (DVB) was obtained from Alfa Aesar and used without further purification. We purchased 2,2′-azobis(isobutyronitrile) (AIBN) from Aldrich and recrystallized with methanol. R-/S-1-phenylethylamine and R-/S-cyclohexylethylamine were purchased from TCI. D-alanine, L-alanine, rac-alanine, (+)-cinchonine, and (−)-cinchonidine were bought from Acros Organics and used without purification. All the solvents were distilled by standard methods. 2.2. Characterizations. The morphology of the hollow particles (BHPs) and optically active particles (OABHPS: RPEA-HPs, S-PEA-HPs, R-CHEA-HPs, and S-CHEA-HPs) were observed with scanning electron microscopy (SEM, Hitachi S-4800) and transmission electron microscope (TEM, Hitachi H-800). For the measurement of CD and UV−vis absorption spectra, Jasco810 spectropolarimeter was used. FT−IR spectra measurement was carried out with Nicolet NEXUS 870 infrared spectrometer (KBr pellet). Elemental analysis was measured on an Elementar vario EL cube elemental analyzer machine. The adsorption performance of all the four OABHPs was carried out by UV−vis spectrophotometer (Shanghai Jinghua756MC). 2.3. Formation of Hollow Particles. The PMV template particles and core/shell particles (Scheme 1) were prepared according to literature.39,40 After polymerization, the core/shell particles were taken from the vacuum oven and added in a beaker with 20 mL of acetone. Then, the beaker was ultrasonicated for 30 min to remove the template and centrifuged to isolate the particles. The hollow particles were collected and thoroughly washed with ethanol.

ji A − A t zyz ijj Ci × V yzz Q = jjj i zzz × j z j A i k { k M {

(1)

Taking alanine as example, herein, Q is the adsorption amount (mg/g), Ai is the initial UV−vis absorbance of the alanine solution, and At is the absorbance at certain time t. Ci is the initial concentration of solution (mg/mL), V is the volume of the solution (mL), and M is the amount of chiral hollow particles (mg). To investigate the enantio-differentiating adsorption of the 4 types of chiral hollow particles toward racemic alanine, we conducted the following chiral adsorption tests. The procedure is as follows. D-Alanine and L-alanine enantiomers were mixed B

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

Figure 1. SEM images of (a) biobased hollow particles, (b) R-PEA-HPs, and (c) S-PEA-HPs. The insets in images a, b, and c indicates the TEM images of the corresponding particles; scale bar: 500 nm.

were first prepared by precipitation polymerization, as reported earlier.39,40 Subsequently, the PMV particles, together with comonomers (ANE and MAH) and cross-linking agent DVB, were mixed together to prepare the core/shell particles. The core/shell particles were treated with acetone, thus removing PMV template cores to lead to biobased hollow particles (BHPs).39,40 Afterward, the hollow particles were chiralized with R-/S-PEA and R-/S-CHEA, and four types of optically active biobased hollow particles, named as R-PEA-HPs, S-PEAHPs, R-CHEA-HPs and S-CHEA-HPs, were prepared accordingly. The advantages of the resulting chiral hollow particles include easy preparation, hollow structure, a large amount of voids in the shells and intriguing optical activity. The as-prepared BHPs, R-/S-PEA-HPs, and R-/S-CHEA-HPs were characterized by SEM, TEM, CD, FT−IR, and elemental analysis techniques, as to be discussed below. 3.2. Characterizations of the Particles. The morphology of BHPs, R-/S-PEA-HPs, and R-/S-CHEA-HPs was observed by SEM and TEM. As presented in Figure 1, BHPs with average-diameter of 800−1000 nm were successfully prepared through precipitation polymerization, as shown in Figure 1a. After modification with R-PEA and S-PEA, the obtained optically active hollow particles (Figures 1b and 1c) still showed smooth surface. The chiralized particles kept unchanged in size and surface morphology, and the shell also showed no observable change. The insets in Figure 1a, b, and c present TEM images showing spherical form and hollow structure. The same observations were obtained in the cases of R- and S-CHEA-HPs in Supporting Information (SI) Figure S1. FT−IR spectra and elemental analysis techniques were also employed to investigate the chemical composition of the particles. In the FT−IR spectra (Figure 2), the peaks at 1510 and 1253 cm−1 (spectrum a) respectively reflect the benzene ring and methoxyl group in the hollow particles. The signals at 1853 and 1780 cm−1 represent the anhydride groups in (spectrum a) of hollow particles. All the peaks can be observed in R-PEA-HPs (spectrum b) and S-PEA-HPs (spectrum c), but with obviously weakened intensity in the peaks at 1855 and 1780 cm−1. However, the characteristic peaks of newly formed amide band (formed by the reaction between amino groups of chiral compounds and carboxyl groups in BHPs) merged with other peaks at the range of 1733−1510 cm−1. Besides, we can also find characteristic peaks of hydrogen bonding, appearing at the range of 3000−3500 cm−1 in the spectra of R-PEA-HPs and S-PEA-HPs, indicating the successful formation of R-/SPEA-HPs. For R-/S-CHEA-HPs, the same conclusion can be drawn according to SI Figure S2. Elemental analysis technique was further taken to determine the elemental percentage in the

together in equal amount (D- and L-alanine in deionized water) to form the racemate solution, in which the optical rotation was almost zero. A predetermined amount of chiral hollow particles (10 mg) was immersed in the racemate solution. At regular intervals, the supernatant was isolated and subjected to HPLC measurement. The chiral adsorption capacity of the 4 types (R-PEA-HPs, S-PEA-HPs, R-CHEA-HPs, and S-CHEAHPs) was measured by enantiomer excess (e.e.) which was determined according to eq 2:42 enantiomericexcess(e.e.)(%) =

L−D × 100 L+D

(2)

In the above equation, L and D are the content of D- and Lalanine, according to the corresponding peak areas in HPLC spectra. Therefore, with the help of above equation we can easily calculate (e.e.) value and analyze the different absorption capacity of chiral hollow particles toward racemic alanine. For the other pair of chiral compound, (+)-cinchonine and (−)-cinchonidine, the same methods described above were taken to perform the adsorption test. 2.6. Regeneration and Recycling Use Ability. For regeneration study, only R-PEA-HPs and R-CHEA-HPs were selected because the four types of hollow particles had nearly the same ability toward the adsorbate. The detailed regeneration process is presented as follows. 10 mL of Lalanine solution with initial concentration 100 mg/L was charged in a small bottle, in which 10 mg of R-PEA-HPs was added. The adsorption was carried out under stirring for 9 h at room temperature to achieve a maximum adsorption amount. Then the R-PEA-HPs were separated by filtration and washed thoroughly by 2 mL HCl and THF mixed solution with a ratio of (1:1 in mL). Then the recovered R-PEA-HPs were further washed with ethanol three times, stored in oven at 60 °C for overnight, and reused for the next adsorption−desorption cycle. The same procedure was applied for R-CHEA-HPs regeneration and recycling use.

3. RESULTS AND DISCUSSION 3.1. Synthesis of Chiral Hollow Particles. Attaching chiral functionality to biobased hollow polymer particles is a novel method to prepare multifunctional materials. In this study, R-PEA, S-PEA, R-CHEA, and S-CHEA were introduced as chiral modifiers to prepare optically active biobased hollow particles. As presented in Scheme 1, BHPs were prepared first via a precipitation copolymerization process. The BHPs were further modified with chiral compounds (R-/S-PEA) and (R-/ S-CHEA) to prepare OABHPs, including totally four groups, namely, R-PEA-HPs, S-PEA-HPs, R-CHEA-HPs, and SCHEA-HPs. To synthesize the BHPs, PMV template particles C

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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nm, while in R-/S-PEA modified particles, relatively stronger CD signals appeared in 200−250 nm because of the benzene rings in R-/S-PEA. 3.3. Adsorption Study toward Chiral Compounds. The prepared chiral hollow particles have two attractive advantages when used as chiral adsorbent. One is the hollow structure, and the other one is the grafted chiral moieties on the shells. The former endowed the chiral hollow particles with potentially high adsorption capacity, while the latter one played key roles in enantioselectively adsorbing chiral compounds. The adsorption study of the four types of chiral hollow particles (R- and S-PEA-HPs, R- and S-CHEA-HPs) toward chiral compounds including D-alanine, L-alanine, racalanine, (+)-cinchonine and (−)-cinchonidine was systemically investigated. The results are shown in Figure 4. Figure 4a presents the adsorption study of R-PEA-HPs toward D- and Lalanine. The R-PEA-HPs showed a preferential adsorption toward L-alanine. In the contrast, S-PEA-HPs preferentially adsorbed D-alanine, as presented in Figure 4b. The maximum adsorption ability of S-PEA-HPs toward D- and L-alanine are 20.1 and 14 mg/g, respectively. The results demonstrate that the chiral particles have enantioselective adsorption functionality toward alanine. Furthermore, the adsorption ability of both R-PEA-HPs and S-PEA-HPs toward rac-alanine was also investigated; the results are presented in Figure 4c. In this case, the maximum adsorption of R-PEA-HPs was 16.2 mg/g; for S-PEA-HPs, it was 15.2 mg/g. That is, the two types of particles behaved similarly toward racemic alanine. The enantioselectivity will be discussed in more detail later. To elucidate the adsorption ability of the original hollow particles (BHPs), we further carried out a series of batch adsorption experiments toward D-alanine, L-alanine and racalanine with the same initial concentration as above. The adsorption ability of BHPs as a function of adsorption time is shown in Figure 4d. The results indicate that both adsorption capacity and enantioselectivity of BHPs were not remarkable. Therefore, the introduced chiral moieties made primary contribution to the observed adsorption of the chiral hollow particles. To further explore the adsorption behaviors of R- and SPEA-HPs toward other chiral compounds, (+)-cinchonine and (−)-cinchonidine were also taken as examples. The adsorption results are shown in Figure 5. The R-PEA-HPs showed a better adsorption toward (−)-cinchonidine, as illustrated in Figure 5a. On the contrary, the adsorption of R-PEA-HPs toward

Figure 2. FT−IR spectra of (a) hollow particles (HPs), (b) R-PEAHPs, and (c) S-PEA-HPs (KBr tablet).

R-PEA-HPs, S-PEA-HPs, R-CHEA-HPs, and S-CHEA-HPs, as presented in Table 1. The changes in element percentage offer further supports for the formation of chiral particles. Table 1. Element Percentage in Chiral Hollow Particles and Original Hollow Particles element

C (%)

N (%)

H (%)

BHPs R-PEA-HPs S-PEA-HPs R-CHEA-HPs S-CHEA-HPs

65.12 67.85 67.77 66.67 66.21

3.01 2.90 3.18 3.05

5.855 7.036 7.004 8.192 8.074

To acquire more information about the grafting of chiral moieties in the hollow particles, R-/S-PEA-HPs and R-/SCHEA-HPs were dispersed in ethanol and then subjected to CD measurement, as presented in Figure 3. In Figure 3a Rand S-PEA-HPs respectively demonstrate positive and negative strong CD signals in the wavelength range of 200−250 nm, demonstrating the successful chiralization of the hollow particles. The measurement further indicates the introduction of chirality in the originally achiral biomass-based polymers. Similar phenomena have been previously observed and discussed in literature.41 Meanwhile, the R-CHEA and SCHEA modified hollow particles were also characterized by CD analysis, for which the results are illustrated in Figure 3b. Unfortunately, the particles show weak CD signals around 200 nm. In this case, R-CHEA and S-CHEA have no benzene rings, and as a consequence, weak CD signals appeared around 200

Figure 3. CD spectra of (a) R-PEA-HPs and S-PEA-HPs; (b) R-CHEA-HPs and S-CHEA-HPs. The spectra were measured using methanol solution, homogeneously dispersed by ultrasonic. D

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 4. Adsorption of (a) R-PEA-HPs toward D- and L-alanine; (b) S-PEA-HPs toward D- and L-alanine; (c) R- and S-PEA-HPs toward racalanine; (d) Control test: pure hollow particles’ adsorption toward alanines. (c = 100 mg/L).

Figure 5. Adsorption of (a) R-PEA-HPs toward (+)-cinchonine and (−)-cinchonidine; (b) S-PEA-HPs toward (+)-cinchonine and (−)-cinchonidine. (c = 100 mg/L)

(+)-cinchonine was not very noticeable because of relatively weaker binding force. Moreover, the maximum adsorption of R-PEA-HPs toward (−)-cinchonidine and (+)-cinchonine are 21.1 and 17.2 mg/g, respectively. The results show that RPEA-HPs have a better binding ability toward (−)-cinchonidine as compared with (+)-cinchonine. The adsorption of SPEA-HPs toward (−)-cinchonidine and (+)-cinchonine was also conducted, as illustrated in Figure 5b. S-PEA-HPs showed remarkable adsorption ability toward (+)-cinchonine, and the maximum adsorption amount at 9 h was 23.5 mg/g. In addition, the adsorption of S-PEA-HPs toward (−)-cinchonidine at the first 60 min was the same as toward the opposite one, but from then on the adsorption amount increased only slightly. This is due to the weak interaction between S-PEAHPs and (−)-cinchonidine. To explore the potential applications of the chiral hollow particles, we chose another pair of chiral compounds named as R-/S-cyclohexyalethylamine to chirally modify the hollow particles, thus providing R-CHEA-HPs and S-CHEA-HPs

(Scheme 1). The chiral particles were characterized as discussed above. R- and S-CHEA-HPs were also applied to check the adsorption ability toward D-alanine, L-alanine and rac-alanine. The results are shown in Figure 6. Figure 6a demonstrates the adsorption ability of R-CHEA-HPs toward D- and L-alanine. Within the first 30 min the adsorption toward both D- and L-alanine kept the same, but after 30 min the adsorption of R-CHEA-HPs toward L-alanine became larger gradually, and the maximum adsorption was observed at 9 h, with an adsorption amount of 18.1 mg/g. In the contrast, the maximum adsorption amount toward D-alanine was 14 mg/g. The adsorption behavior of S-CHEA-HPs toward Dand L-alanine was also studied, and the results are illustrated in Figure. 6b. S-CHEA-HPs adsorbed more D-alanine than the other enantiomer. In addition, the maximum adsorption amount of S-CHEA-HPs toward D- and L-alanine was 16.8 and 14.8 mg/g, respectively. The adsorption ability of R- and S-CHEA-HPs were also investigated toward rac-alanine, as presented in Figure 6c. In E

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 6. Adsorption of (a) R-CHEA-HPs toward D- and L-alanine; (b) S-CHEA-HPs toward D- and L-alanine; (c) R- and S-CHEA-HPs toward rac-alanine. (c = 100 mg/L).

Figure 7. Adsorption of (a) R-CHEA-HPs toward (+)-cinchonine and (−)-cinchonidine; (b) S-CHEA-HPs toward (+)-cinchonine and (−)-cinchonidine. (c = 100 mg/L).

Figure 8. Time−e.e. profiles of residual racemic alanine solution after being absorbed by (a) R- and S-PEA-HPs and (b) R- and S-CHEA-HPs.

this case, enantioselective adsorption was accomplished, however, we found that the R- and S-CHEA-HPs had equal binding ability toward rac-alanine. This is obviously different from R- and S-PEA-HPs, possibly due to the R- and S-PEAHPs containing benzene ring. Nonetheless, the exact driving force for the difference needs to be deeply explored.

The adsorption capacity of R- and S-CHEA-HPs toward (+)-cinchonine and (−)-cinchonidine was also investigated, and the results are presented in Figure 7. R-CHEA-HPs showed significant adsorption ability toward (−)-cinchonidine. At the first 90 min, rapid uptake occurred and then gradually decreased. The maximum adsorption amount at 9 h was 19 mg/g. However, the maximum adsorption amount of RF

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 9. Recycling use of (a) R-PEA-HPs toward L-alanine; (b) R-CHEA-HPs toward L-alanine.

THF mixed solution. The relevant results are shown in Figure 9. The recovered R-PEA-HPs and R-CHEA-HPs showed good adsorption ability toward L-alanine in the second cycle. Figure 9a shows the adsorption capability of R-PEA-HPs toward Lalanine in three adsorption/desorption cycles. Figure 9b presents adsorption/desorption ability of R-CHEA-HPs toward L-alanine. Briefly, only slight decreases occurred in the two groups of chiral particles, indicating that the R-PEAHPs and R-CHEA-HPs have good regeneration and recycling use ability. This is another great advantage of chiral hollow particles, together with the other attractive advantages as mentioned above. The decrease in adsorption amount is possibly due to the change in the porous structure in the shells of the chiral hollow particles. This will be hopefully overcome through optimization of the hollow particles in terms of composition, microstructure, morphology, etc. Studies are currently ongoing along these directions.

CHEA-HPs toward (+)-cinchonine was only 15.1 mg/g, less than (−)-cinchonidine. Moreover, the adsorption of S-CHEAHPs toward (+)-cinchonine and (−)-cinchonidine was further studied, as illustrated in Figure 7b. The S-CHEA-HPs showed higher adsorption ability toward (+)-cinchonine than (−)-cinchonidine. The maximum adsorption amounts toward (+)-cinchonine and (−)-cinchonidine are 21.5 and 17 mg/g, respectively. 3.4. Enantio-Selective Adsorption Using Racemic Adsorbate. To examine the practical applicability of the prepared chiral particles in chiral resolution, enantioselectivity test was conducted next. R-PEA-HPs, S-PEA-HPs, R-CHEAHPs, and S-CHEA-HPs were utilized to perform adsorption in a racemic-alanine solution (Figure 4c and 6c). Figure 4c presented above shows the corresponding adsorption of R- and S-PEA-HPs toward racemic alanine. R-PEA-HPs showed a higher adsorption toward racemic alanine, as compared with SPEA-HPs. Furthermore, the enantiomeric excess (e.e.) was measured to examine the particles’ chiral recognition ability. The adsorption amount of R- and S-PEA-HPs at 9 h was 16.2 and 15.2 mg/g, respectively. However, the final e.e. was 12.7% for R-PEA-HPs and −12% for S-PEA-HPs, as shown in Figure 8a. Moreover, e.e. of R- and S-CHEA-HPs was also measured, as shown in Figure 6c and Figure 8b. Figure 6C shows that the maximum adsorption of R-CHEA-HPs was 16.3 mg/g; for SCHEA-HPs, it was 16 mg/g. Corresponding e.e. values for the two sets of particles are both approximately 10.5% (+ for RCHEA-HPs, − for S-CHEA-HPs). To summarize, the chiral hollow particles possess promising potential applications as novel chiral adsorbent. The present work established a new strategy to prepare novel chiral hollow polymer particles from achiral monomer, demonstrating remarkable importance both in industrial point of view and for practical applications. In addition, various chiral compounds can provide different chiral recognition capacity to the chiralized particles thereof. The enantioselectivity demonstrated by the chiral hollow particles should be due to the enantioselective interactions between them to the adsorbates. Namely, in the course of adsorption, one of a pair of enantiomers preferentially undergoes interactions with the chiral moieties, especially hydrogen bonding. This results in the enantioselective adsorption as discussed above.43 3.5. Recycling Use Study. Considering that all the four types of chiral hollow particles have similar adsorption ability toward chiral amines as discussed above, we selected R-PEAHPs and R-CHEA-HPs as representatives for performing recycling use test. After adsorption of L-alanine, the adsorbed L-alanine can be easily desorbed with the help of HCl and

4. CONCLUSIONS We synthesized four types of chiral hollow particles, which were prepared from biomass trans-anethole (ANE) through copolymerization with maleic anhydride (MAH) in the presence of particulate templates to form core/shell particles first. Subsequently removing the cores provided biobased hollow particles (BHPs) and then they were chiralized with four types of chiral compounds. The resulting four types of chiral hollow particles, R-PEA-HPs, S-PEA-HPs, R-CHEAHPs, and S-CHEA-HPs, were obtained in regular morphology and hollow structure. The chiral hollow particles were subjected to adsorption and enantioselective adsorption studies, demonstrating good adsorption and enantioselectivity. They also showed good regeneration and recycling use abilities.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.8b05884. SEM images of R-CHEA-HPs and S-CHEA-HPs, FT− IR spectra of R-CHEA-HPs and S-CHEA-HPs and preparation of core/shell particles (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. G

DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Jianping Deng: 0000-0002-1442-5881 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21474007, 21774009). S.R. thanks China Scholarship Council (CSC, 2016420010).

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DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.8b05884 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX