Optically Active Particles with Tunable Morphology: Prepared by

Jun 10, 2016 - Optically Active Particles with Tunable Morphology: Prepared by Embedding Graphene Oxide/Fe3O4 in Helical Polyacetylene. Weifei Li and ...
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Optically Active Particles with Tunable Morphology: Prepared by Embedding Graphene Oxide/Fe3O4 in Helical Polyacetylene Weifei Li and Jianping Deng* State Key Laboratory of Chemical Resource Engineering and College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China S Supporting Information *

ABSTRACT: We report a novel and straightforward methodology for constructing hybrid particles with tunable morphology (spherical vs nonspherical) by embedding inorganic components (graphene oxide and/or Fe3O4 nanoparticles) inside chiral helical polyacetylene. Scanning electron microscopic images ascertain the spherical or nonspherical morphology of the particles. The intense circular dichroism effects demonstrate that the hybrid particles (spherical, ellipsoid-like, and cake-like) possess remarkable optical activity. The use of the chiral magnetic hybrid particles in enantioselective crystallization of racemic phenylalanine demonstrates the kind of particles’ significant potential applications in chiral technologies and chiral processes. The study not only creates an unprecedented type of chiral hybrid particles, but also provides a versatile strategy for preparing advanced functional hybrid particles with tunable morphology from polymers and even from inorganic and metallic materials. KEYWORDS: nonspherical particles, tunable morphology, optical activity, helical polymers, graphene oxide, Fe3O4, enantioselective crystallization Optically active polymeric particles26 have gathered everincreasing interest due to the judicious combination of the advantages of chiral polymers and particles. Apart from usual chiral (nonhelical) polymers, chirally helical polymers27−30 have also been used for forming optically active polymer particles. 31 So far optically active particles have been successfully employed in diverse chiral-related research areas.32 Especially noteworthy is the work from Freire, Riguera, et al.,33 in which optically active particles were constructed by helical polymer and metal ions. Nonetheless, all the optically active particles already reported in the literature possess routine spherical morphology. We previously created a unique type of optically active helical polymer particles based on chirally helical polymers.34−36 We also prepared optically active hybrid materials consisting of helical polymer and graphene oxide (GO)37,38 or Fe3O4 nanoparticles (Fe3O4 NPs).39 We further hypothesize that if we embed relatively rigid components inside polymer particles, the rigid components may prevent the particles from forming spherical morphology. Excitingly, we experimentally justified our hypothesis and successfully prepared ellipsoid-like and cake-like hybrid particles by using chirally helical polymer and graphene oxide (GO) and/or Fe3O4 NPs. The resulting particles not only showed interesting optical activity, but also demonstrated the desirable controllability in shape. Despite a number of studies dealing with

1. INTRODUCTION Particles with tunable morphology promote scientific and technological advances due to their distinctive properties and uses. This can be clearly exemplified by the numerous nonspherical particles (NSPs)1,2 which have constituted a unique research area because of their significant applications as carriers,3 biological sensors,4 crystals,5 and functional coatings.6 Among the NSPs, polymer-based ones7,8 are especially drawing rapidly increasing attention. Up to now, various polymeric NSPs have been developed, such as Janus,9,10 yolk-like,11 mushroom-like,12 dumbbell-like,13 acorn-like,14 and spindlelike15 architectures. Meanwhile, these NSPs have been explored in diverse applications as emulsifiers16 and in functional interfaces.17 They also can be used as novel biohybrids.18 For preparing polymer-derived NSPs, a variety of elegant methods have been established including (seed) emulsion polymerization,19 self-assembly,20 multistep polymerization,21 pressing,22 templating,23 and micromolding polymerization24 processes. More recently, NSPs containing multicavity structures were also reported.25 Remarkably different from the preparation techniques established in the literature, in this contribution we report a novel strategy for constructing nonspherical polymer hybrid particlesthrough embedding inorganic components inside polymer particles, by which we efficiently adjusted the morphology of the particles and provided a distinctive class of optically active hybrid NSPs. We further experimentally demonstrated their potential applications as chiral materials by accomplishing enantioselective crystallization. © 2016 American Chemical Society

Received: March 2, 2016 Accepted: June 10, 2016 Published: June 10, 2016 16273

DOI: 10.1021/acsami.6b02654 ACS Appl. Mater. Interfaces 2016, 8, 16273−16279

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ACS Applied Materials & Interfaces polymer/GO hybrid particles in the literature,40,41 the present work is the first one to use GO for adjusting the shape of hybrid particles.

of helical polyacetylene and alkynyl-Fe3O4 NPs (D, MHPs); (4) nonspherical cake-like hybrid particles consisting of helical polyacetylene and micro-MGO (E, CHPs; micro-MGO, ca. 35 μm); and (5) nonspherical cake-like hybrid particles consisting of helical polyacetylene and micro-MGO together with alkynylFe3O4 NPs (F, CMHPs). The relevant parameters are listed as below (Table 1). The spherical particles were prepared via emulsion35 (NPs, Figure 1A) and suspension36 (MPs, Figure 1B) polymerization approaches, in which SDS (sodium dodecyl sulfonate) and PVA (poly(vinyl alcohol)) were respectively used as emulsifier and stabilizer. After initiation by Rh catalyst, the monomer underwent emulsion or suspension polymerizations, providing the designed optically active spherical particles consisting of chirally helical polymer. These particles have been studied in detail in our earlier work.35,36 To further prepare particles with tunable morphology, GO, which possesses a large specific area and mechanical strength, was taken as a rigid component and added in monomer latex particles. Such intentionally added rigid components are expected to play the role of hard frameworks, preventing the subsequently formed polymer particles from forming routine spherical architectures and thus resulting in nonspherical particles instead (Figure 1C,E,F). The as-prepared particles were directly characterized by SEM, as shown in Figure 2. In Figure 2, the diameters of A (NPs) and B (MPs) are 370 nm and 85 μm, respectively. Based on the spherical particles, ellipsoid-like hybrid particles D (EHPs-5%) and E (EHPs-10%) were synthesized by adding 5 and 10% nano-MGO (ca. 60 nm, Figure S1A, Supporting Information, the same as below) via emulsion polymerization, while cake-like hybrid particles F (F-1 and F-2, CHPs-10%) and G (G-1 and G-2, CHPs-15%) were respectively fabricated by adding 10 and 15% micro-MGO (ca. 35 μm, Figure S1B) via suspension polymerization. AR (aspect ratio, described in Table 1) was used to characterize the ratio of major axis/minor axis (D and E) and length/thickness (F, G, and H). The AR of the spherical NPs (A, 370 nm/370 nm) and MPs (B, 85 μm/85 μm) was 1. However, the ARs of the ellipsoid-like particles D (EHPs-5%) and E (EHPs-10%) are approximately 1.38 (290 nm/210 nm) and 1.62 (420 nm/260 nm), respectively. This clearly shows that the particles were successfully tuned from spherical to ellipsoid-like morphology. The values of AR also indicate that both the major axis and minor axis in E (EHPs10%) were higher than those in D (EHPs-5%), due to the increase of nano-MGO in quantity. When microscaled GO was used instead of nanoscaled GO, different results were obtained. A further comparison among

2. RESULTS AND DISCUSSION Figure 1 illustrates the overall strategy for preparing the hybrid particles with tunable morphology by embedding GO and (or)

Figure 1. Schematic strategy for preparing spherical nanoparticles (NPs, A), spherical microparticles (MPs, B), ellipsoid-like hybrid particles (EHPs, C), spherical magnetic hybrid particles (MHPs, D), cake-like hybrid particles (CHPs, E), and cake-like magnetic hybrid particles (CMHPs, F). Part G shows the scanning electron microscopic (SEM) image of L-phenylalanine induced by CMHPs. More SEM images are presented in the Supporting Information.

Fe3O4 NPs. The aims of the present work are (1) to create a straightforward, versatile methodology for constructing hybrid particles with tunable morphology and (2) to establish novel chiral particles constructed by synthetic chirally helical polymers. The prepared particles can be grouped into five categories (Figure 1A−F): (1) helical polyacetylene-derived, both nanoscaled (A, NPs) and microscaled (B, MPs) spherical particles containing no other component; (2) nonspherical ellipsoid-like hybrid particles consisting of helical polyacetylene and nanoMGO (C, EHPs; MGO, alkynylated GO; nano-MGO, ca. 60 nm in size); (3) spherical magnetic hybrid particles consisting Table 1. Parameters of Chiral Hybrid Particlesa particle

M1 (g)

M2 (g)

MGOb

Fe3O4c

routed

ARe

morphology

NPs EHPs-5% EHPs-10% MPs CHPs-10% CHPs-15% MHPs CMHPs

0.07 0.07 0.07 0.1 0.1 0.1 0.1 0.1

0.014 0.014 0.014 0.02 0.02 0.02 0.02 0.02

− 5 10 − 10 15 − 15

− − − − − 0 10 10

a-1 a-2 a-2 b-1 b-2 b-2 b-2′ b-3

370 nm/370 nm 290 nm/210 nm 420 nm/260 nm 85 μm/85 μm 110 μm/40 μm 115 μm/52 μm 92 μm/92 μm 121 μm/62 μm

sphere ellipsoid-like ellipsoid-like sphere cake-like cake-like sphere cake-like

a [Rh-cat]:[M1 + 2M2], 1/100 (mol/mol). bwt %: MGO:[M1 + M2] (nano-MGO for NPs and EHPs; micro-MGO for CHPs and CMHPs). cwt %: alkynyl-Fe3O4:[M1 + M2]. dPolymerization method: routes a and b are emulsion polymerization and suspension polymerization, respectively. e Aspect ratio: major axis/minor axis for NPs and EHPs; length/thickness for MPs, CHPs, and CMHPs.

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To further tune the thickness of CHPs-15% (G, Figure 2), micro-MGO was used together with alkynyl-Fe3O4 NPs (Figure S1C), thereby leading to cake-like magnetic hybrid particles (CMHPs, H) rather than the spherical magnetic microspheres (C, MHPs consisting of polymers and alkynyl-Fe3O4 NPs) studied by us earlier.36 By comparing B, C, and H (Figure 2), we conclude that the formation of cake-like CMHPs should be attributed to micro-MGO. Despite the noticeable increase in both length and thickness of the CMHPs (121 μm/62 μm), the value of AR decreased to 1.95. The phenomenon further demonstrates that, in such nonspherical particles, the increase in thickness was more appreciable than in length. The reason for this observation is the same as discussed above. The micrographs in Figure 2I show that MPs and MHPs formed porous structures; however, lamellar together with porous structures coexisted in the CMHPs. The lamellar structures were considered being derived from the micro-MGO layers. Moreover, the lamellar structures also provide evidence for the formation process of cake-like hybrid particles, i.e. through the packing of MGO layers. Based on the above investigations, we propose the mechanisms for forming the particles as presented in Figure 3 (see below).

Figure 2. SEM images of spherical nanoparticles (NPs, A), microspheres (MPs, B), magnetic hybrid microspheres (MHPs, C), ellipsoid-like hybrid particles (D, E, EHPs-5% and EHPs-10% with 5 and 10% nano-MGO, respectively), cake-like hybrid particles (CHPs10%, F-1 and F-2 with 10% micro-MGO; CHPs-15%, G-1 and G-2 with 15% micro-MGO), cake-like magnetic hybrid particles (CMHPs, H-1 and H-2 with 15% MGO and 5% Fe3O4), and the inner structure of MPs, MHPs, and CMHPs (I). The polymer emulsion and suspension samples were directly placed on a glass sheet for SEM observation.

Figure 3. Proposed mechanisms for forming spherical magnetic hybrid particles (I, MHPs), ellipsoid-like hybrid particles (II, EHPs), cake-like hybrid particles (III, CHPs), and cake-like magnetic hybrid particles (IV, CMHPs).

the SEM images in B, F, and G (Figure 2) shows that the spherical particles B (MPs) obviously changed to cake-like hybrid particles F (F-1 and F-2, CHPs-10%) and G (G-1 and G-2, CHPs-15%). The AR (length/thickness) was found to be 1 (MPs, 85 μm/85 μm, B), 2.75 (CHPs-10%, 110 μm/40 μm, F), and 2.21 (CHPs-15%, 115 μm/52 μm, G). Both the length and the thickness of the cake-like particles increased with increasing micro-MGO content. However, the increasing degree in thickness is more than that in length, thus causing the decrease in AR. This can be explained as follows. With the enhancement of micro-MGO concentration, the micro-MGO layers tended to stack rather than to disperse due to the poor dispersibility in water.

Without any additive (herein, it means GO and Fe3O4 NPs), routine spherical polymer particles (Figure 2A,B) are formed, according to our earlier studies.35,36 In Figure 3I, chiral magnetic particles (MHPs, Figure 2C) retained the spherical shape even in the presence of Fe3O4 NPs, since the Fe3O4 NPs (13 nm, Figure S1C) are far smaller than the microscaled particles thereof (MHPs, 92 μm). Therefore, the Fe3O4 NPs can be readily embedded inside the particles and have little influence on the morphology of the resulting MHPs. In Figure 3II, when nano-MGO (nanoscale alkynyl-GO, approximately 60 nm, Figure S1A) was dispersed in water and then SDS was 16275

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reflects that MGO and Fe3O4 were sufficiently embedded inside the particles. Thermal properties of the obtained particles were measured by TGA (thermal gravimetric analysis, Figure 5).42,43 Relative

added, the nano-MGO was wrapped by SDS due to the hydrophobicity of the nano-MGO sheets (alkynylated GO). After polymerization, ellipsoid-like particles (EHPs, Figure 2D,E) are formed, in which the nano-MGO layers are encapsulated. The −CC groups on the MGO participated in polymerization, also enabling the MGO layers to be retained inside the particles. Nonetheless, the sheet architecture of MGO prevented the resulting hybrid particles from forming spherical morphology. In Figure 3III, the micro-MGO layers with relatively larger size (ca. 35 μm, Figure S1B) stacked and worked as rigid components, also restraining the formation of spherical particles; so after polymerization, cake-like particles (CHPs, Figure 2F,G) are reasonably fabricated due to the higher packing tendency of the MGO layers, when compared to the case in Figure 3II. In Figure 3IV, the thickness of the CHPs could be further tuned by adding alkynyl-Fe3O4 NPs due to their rigidity and dispersion between MGO layers, resulting in cake-like magnetic hybrid particles (CMHPs, Figure 2H). Herein, apart from chiral monomer, achiral monomer was also used to successfully construct cake-like particles in the same way as reported above (Figure S2). To confirm the fabrication of the above particles, they were characterized by Fourier transform infrared (FT-IR) spectroscopy (Figure S3). The detailed analyses are presented in the Supporting Information. Referring to our previous studies,36,37 the FT-IR spectra show the successful formation of cake-like hybrid particles containing micro-MGO and Fe3O4 (CMHPs) and ellipsoid-like hybrid particles (EHPs) containing nanoMGO. The conclusion can be further supported by Raman spectra (Figure S4). The detailed analyses about Raman spectra are described in the Supporting Information. To further confirm the distribution of MGO inside the particles, the samples were subjected to XPS (X-ray photoelectron spectroscopy, Figure 4) and EDS (energy dispersive

Figure 5. TGA analysis of NPs (A-a, without additive), EHPs-5% (Ab, with 5% nano-MGO), EHPs-10% (A-c, with 10% nano-MGO), MPs (B-a, without additive), CHPs-10% (B-b, with 10% micro-MGO), CHPs-15% (B-c, with 15% micro-MGO), and CMHPs (B-d, with 15% micro-MGO and 10% Fe3O4).

to 87.3 and 90.3% weight loss in the NPs (Figure 5A-a) and MPs (Figure 5B-a), EHPs-5% (A-b) and EHPs-10% (A-c) showed weight losses of 82.7 and 77.6%, respectively (Figure 5A). This demonstrates that approximately 4.6 and 9.7% of nano-MGO was contained in the corresponding particles. In Figure 5B, the weight losses of CHPs-10% (B-b), CHPs-15% (B-c), and CMHPs (B-d) were respectively 80.7, 75.5, and 71.2%. This indicates that micro-MGO and/or Fe3O4 wrapped in the particles was approximately 9.6% (micro-MGO), 14.8% (micro-MGO), and 19.1% (micro-MGO and Fe3O4), respectively. For the CMHPs, the content of Fe3O4 was 4.7% as calculated from the VSM (vibrating sample magnetometer, see below, Figure 6) measurement. Taking the weight loss of 19.1%

Figure 6. Hysteresis loops of alkynyl-Fe3O4 (MNPs, a), magnetic microspheres (MHPs, b), and CMHPs (c). Magnetic responsivity of the CMHPs (inset).

Figure 4. XPS spectra of (a) MPs, (b) CMHPs, and (c) EHPs-10%.

into consideration, the content of micro-MGO contained in CMHPs could be determined as approximately 14.4%, in good accordance with the corresponding theoretical values. N2 absorption measurements (Figure S6) were conducted to investigate the BET pore size and specific surface area.44 The detailed analyses are described in the Supporting Information. The parameters of the NPs and EHPs-10% are as follows: BET specific area, 2.521 and 4.638 m2/g; pore diameter, 10.324 and 18.673 nm, respectively. For the MPs, CHPs-15%, and CMHPs, the corresponding BET specific area is 3.271, 6.632, and 7.583 m2/g, and the pore diameter is 34.388, 42.603, and 47.942 nm, respectively. The above data show that the BET specific area and pore diameter of the particles increased with the addition of MGO and Fe3O4.

spectroscopy, Figure S5) measurements. For XPS spectra measurement (Figure 4, tested depth 1−3 nm in surface), we took the MPs, EHPs-10% (containing 10% nano-MGO), and CMHPs as typical samples. In Figure 4, we can observe a peak at 405 eV, reflecting the presence of nitrogen element, which was determined to be 4.23, 4.31, and 4.28%, respectively. The results indicate a basically identical content of N in the surfaces of the three samples. Accordingly, we can conclude that the tested surfaces of the particles contained no MGO and Fe3O4. The conclusion is further supported by EDS spectra (Figure S5). The comparison of atomic (C and N) percent of MPs, EHPs-10%, and CMHPs indicates that the ratio of C:N varied little. This, in combination with XPS measurement, strongly 16276

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ACS Applied Materials & Interfaces The magnetic properties of alkynyl-Fe3O4 NPs, magnetic microspheres (MHPs), and CMHPs containing micro-MGO and alkylnyl-Fe3O4 NPs were characterized by using a VSM (Figure 6). The MSM (maximum saturation magnetization) of alkynylated Fe3O4 NPs was 57.9 emu/g (Figure 6a). For the MHPs and CMHPs, the MSM reduced to 2.81 emu/g (Figure 6b) and 2.76 emu/g (Figure 6c). The difference in MSM is mainly related to the amount of nonmagnetic materials (see Table 1). With the same proportion of nonmagnetic materials, the MHPs and CMHPs possessed nearly the same MSM value. The magnetic particles could be also quickly separated with an external magnetic field (Figure 6, inset). To explore the hybrid particles’ optical activity, the samples were characterized by circular dichroism (CD) and UV−vis absorption spectroscopies.28−30 All of the particles were crosslinked and could not dissolve in any solvent, so we could not quantitatively measure CD and UV−vis spectra. The measurement process is stated in Supporting Information. The CD and UV−vis spectra are recorded in Figure 7 and Figure S7. Just as

Figure 8. SEM images of phenylalanine crystals induced through enantioselective crystallization: (A) without additive; (B) with chiral CMHPs as additive.

below). The results indicate that optically active CMHPs can be employed as special chiral selectors for enantioselective crystallization. The phenylalanine crystals formed in the enantioselective crystallization processes were further characterized by CD spectroscopy (Figure S8). The detailed discussion is presented in the Supporting Information. The CD spectra (Figure S8), together with the SEM images (Figure 8), encourage us to conclude that the hollow needle-like phenylalanine crystals obtained by using CMHPs as additive were primarily formed by L-phenylalanine. The plot of enantiomeric excess (ee) against crystallization time was determined, as presented in Figure 9. The calculation

Figure 7. CD spectra of (A) NPs (A-a), EHPs-5% (A-b), EHPs-10% (A-c), and pure cross-linker (A-d). CD spectra of (B) MPs (B-a), CHPs-10% (B-b), CHPs-15% (B-c), and CMHPs (B-d).

expected, the spherical nanoparticles (NPs, A-a), ellipsoid-like hybrid particles (EHPs-5%, A-b; EHPs-10%, A-c), microspheres (MPs, B-a), cake-like hybrid particles (CHPs-10%, B-b; CHPs15%, B-c; CMHPs, B-d) all exhibited remarkable CD (Figure 7) and UV−vis absorptions (Figure S7) between 410 and 450 nm. This demonstrates that the substituted polyacetylenes constructing the particles adopted helical conformations with predominantly one-handed screw sense, according to our previous studies.28−30 Accordingly, we think that all the particles possessed the desirable optical activity. This property is desired for the particles to perform enantioselective crystallization, as to be reported next. To demonstrate the uses of the optically active particles, herein cake-like hybrid particles (CMHPs) were taken as representative to perform enantioselective crystallization. Interestingly, we found CMHPs preferentially induced Lphenylalanine to form beautiful hollow needle-like crystals (Figure 1G). In the enantioselective crystallization process, enantioselective recognition and adsorption by the CMHPs should be involved first. The particles containing the preferentially adsorbed L-phenylalanine acted as nucleation sites for the subsequent enantioselective crystallization. Figure 8 presents the SEM images for the phenylalanine crystals. In Figure 8B, the chiral CMHPs induced phenylalanine to form hollow needle-like crystals. Furthermore, the as-obtained crystals were demonstrated to be mainly constructed by Lphenylalanine (see below). However, in the cases without the addition of any additive, only irregular crystals were obtained (Figure 8A), which were verified to be constructed by racemic phenylalanine (no CD signal around 225 nm, Figure S8c, see

Figure 9. Enanatiomeric excess of the obtained crystals. L-Phenylalanine exceeds in the crystals.

method of ee is described in the Supporting Information. The result indicates that L-phenylalanine predominantly crystallized. A maximum ee, up to 48% was achieved after 85 h. Initially, Lphenylalanine was preferentially induced to crystallize by the CMHPs. After 85 h, the other enantiomer, D-phenylalanine, began to crystallize, leading to the decrease in ee. It is worth pointing out that the CMHPs not only efficiently induced Lphenylalanine to preferentially crystallize, but also could be easily recycled due to the presence of Fe3O4 NPs.

3. CONCLUSION We succeeded for the first time in creating a versatile strategy for achieving optically active polyacetylene-derived hybrid particles with tunable morphology by embedding GO and/or Fe3O4 NPs. The resulting hybrid particles (spherical, ellipsoidlike, and cake-like) showed remarkable optical activity. The cake-like hybrid particles (CMHPs) were taken as representative and successfully served as a chiral additive to induce enantioselective crystallization of phenylalanine racemate. The straightforward preparation methodology is also expected to extend to other types of polymers for fabricating novel hybrid particles with tunable morphology, thereby leading to many more polymer-based advanced functional particles. Another point is also worthy to be stressed. The hybrid particles 16277

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ACS Applied Materials & Interfaces containing graphene (oxide) may possess superior electrochemical and thermoconductive properties. The studies along these directions also deserve much attention.

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4. EXPERIMENTAL SECTION Detailed experimental materials and measurements are presented in the Supporting Information. 4.1. Fabrication of Graphene Oxide (GO) and Alkynyl-GO (MGO). Nano- and microscale graphene oxides (nano-GO and microGO) were prepared by referring to earlier reports.37,38,45 Detailed processes are stated in the Supporting Information. 4.2. Fabrication of Spherical Nanoparticles (NPs) and Microspheres (MPs). The spherical nanoparticles (NPs, described in Figure 1A) were prepared via catalytic emulsion polymerization (step a-1 in Figure 1). The typical synthetic procedure of NPs (diameter 370 nm) was stated in the previous article.35 The microspheres (MPs, diameter 85 μm, in Figure 1B) were synthesized by suspension polymerization (step b-1 in Figure 1) by referring to our earlier study.36 The products were subjected to SEM observation. 4.3. Synthesis of Ellipsoid-like Hybrid Particles (EHPs). The ellipsoid-like hybrid particles (EHPs, Figure 1C, step a-2) were synthesized according to a similar procedure for preparing spherical NPs via emulsion polymerization (step a-1). The detailed process can be found in the Supporting Information. 4.4. Preparation of Cake-like Hybrid Particles (CHPs). The cake-like hybrid particles (CHPs, Figure 1E, step b-2) were synthesized by suspension polymerization according to the preparation of MPs (Figure 1B, step b-1), referring to our earlier study.36 A typical preparation process is described in the Supporting Information. 4.5. Preparation of Magnetic Hybrid Microparticles (MHPs). First, oleic acid coated Fe3O4 NPs were prepared by a slightly modified coprecipitation method in the literature,46 and then OPNTU silane was utilized to attach −CC moieties on the particles, yielding alkynyl-Fe3O4 NPs (MNPs, Figure S1C). Then monomer M1, monomer M2, and MNPs were utilized to fabricate optically active magnetic microparticles according to our earlier study.30 The product derived from this route (step b-2′) showed spherical morphology (Figure 1D). The preparation of MHPs was concisely depicted as follows (Figure 1, step b-2′). A 0.01 g sample of MNPs was dispersed homogeneously under ultrasonification in 2 mL of chloroform, in which M1 (0.1 g) and M2 (0.02 g) were successively charged. The mixture was added into PVA aqueous solution, followed by slowly adding (nbd)Rh+B−(C6H5)4 (0.0032 g) into the system above under vigorously stirring. The system was kept for 4 h. When the polymerization ended, magnetic microspheres suspended in PVA aqueous solution were separated by the help of a magnet. The product was observed by SEM (Figure 1D). 4.6. Fabrication of Cake-like Magnetic Hybrid Particles (CMHPs). The cake-like magnetic hybrid particles (CMHPs) were synthesized via a suspension polymerization approach by using alkynyl-Fe3O4 NPs and micro-MGO simultaneously (Figure 1, step b-3). A certain amount of micro-MGO (0.018 g) and alkynyl-Fe3O4 NPs (0.006 g) were added into the chloroform−aqueous dispersion containing monomer M1 and cross-linked M2. The major procedure for suspension polymerization remained the same as stated above. 4.7. Enantioselective Crystallization of Phenylalanine Induced by Cake-like Magnetic Hybrid Particles (CMHPs). Enantioselective crystallization experiments were accomplished in a similar way according to our earlier studies.37,38 Specific processes are presented in the Supporting Information.

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(micro-MGO), TEM images of alkynyl-Fe3O4; SEM images of cake-like hybrid particles; FT-IR spectra, BET, EDS spectrum, UV−vis spectra, CD spectra; references (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 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, 21274008, 21174010) and the Funds for Creative Research Groups of China (51221002).

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REFERENCES

(1) Walther, A.; Müller, A. H. E. Janus Particles: Synthesis, SelfAssembly, Physical Properties, and Applications. Chem. Rev. 2013, 113, 5194−5261. (2) Hu, J.; Zhou, S. X.; Sun, Y. Y.; Fang, X. S.; Wu, L. M. Fabrication, Properties and Applications of Janus Particles. Chem. Soc. Rev. 2012, 41, 4356−4378. (3) Fish, M. B.; Thompson, A. J.; Fromen, C. A.; Eniola-Adefeso, O. Emergence and Utility of Nonspherical Particles in Biomedicine. Ind. Eng. Chem. Res. 2015, 54, 4043−4059. (4) Seiffert, S.; Thiele, J.; Abate, A. R.; Weitz, D. A. Smart Microgel Capsules from Macromolecular Precursors. J. Am. Chem. Soc. 2010, 132, 6606−6609. (5) Ding, T.; Song, K.; Clays, K.; Tung, C. H. Fabrication of 3D Photonic Crystals of Ellipsoids: Convective Self-Assembly in Magnetic Field. Adv. Mater. 2009, 21, 1936−1940. (6) Kim, S. H.; Lee, S. Y.; Yang, S. M. Janus Microspheres for a Highly Flexible and Impregnable Water-Repelling Interface. Angew. Chem., Int. Ed. 2010, 49, 2535−2538. (7) Visaveliya, N.; Köhler, J. M. Single-Step Microfluidic Synthesis of Various Nonspherical Polymer Nanoparticles via in Situ Assembling: Dominating Role of Polyelectrolytes Molecules. ACS Appl. Mater. Interfaces 2014, 6, 11254−11264. (8) Ge, J. P.; Hu, Y. X.; Zhang, T. R.; Yin, Y. D. Superparamagnetic Composite Colloids with Anisotropic Structures. J. Am. Chem. Soc. 2007, 129, 8974−8974. (9) Liang, F. X.; Shen, K.; Qu, X. Z.; Zhang, C. L.; Wang, Q.; Li, J. L.; Liu, J. G.; Yang, Z. Z. Inorganic Janus Nanosheets. Angew. Chem., Int. Ed. 2011, 50, 2379−2382. (10) Kaewsaneha, C.; Tangboriboonrat, P.; Polpanich, D.; Eissa, M.; Elaissari, A. Janus Colloidal Particles: Preparation, Properties, and Biomedical Applications. ACS Appl. Mater. Interfaces 2013, 5, 1857− 1869. (11) Zhao, L. L.; Liu, H. R.; Wang, F. W.; Zeng, L. Design of Yolk− Shell Fe3O4@PMAA Composite Microspheres for Adsorption of Metal Ions and pH-Controlled Drug Delivery. J. Mater. Chem. A 2014, 2, 7065−7074. (12) Yamagami, T.; Kitayama, Y.; Okubo, M. Preparation of StimuliResponsive “Mushroom-Like” Janus Polymer Particles as Particulate Surfactant by Site-Selective Surface-Initiated AGET ATRP in Aqueous Dispersed Systems. Langmuir 2014, 30, 7823−7832. (13) Park, J. G.; Forster, J. D.; Dufresne, E. R. High-Yield Synthesis of Monodisperse Dumbbell-Shaped Polymer Nanoparticles. J. Am. Chem. Soc. 2010, 132, 5960−5961. (14) Huang, X. P.; Qian, Q. P.; Wang, Y. P. Nisotropic Particles from a One-Pot Double Emulsion Induced by Partial Wetting and Their Triggered Release. Small 2014, 10, 1412−1420. (15) Wang, J.; Zhu, W.; Liu, L. X.; Chen, Y. M.; Wang, C. Synthesis and Cellular Internalization of Spindle Hematite/Polymer Hybrid Nanoparticles. ACS Appl. Mater. Interfaces 2015, 7, 5454−5461.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b02654. Experimental materials and measurements; preparation of GO, MGO, EHPs, and CHPs; enantioselective crystallization experiment; AFM (nano-MGO), SEM 16278

DOI: 10.1021/acsami.6b02654 ACS Appl. Mater. Interfaces 2016, 8, 16273−16279

Research Article

ACS Applied Materials & Interfaces

(36) Zhang, H. Y.; Song, J. X.; Deng, J. P. The First Suspension Polymerization for Preparing Optically Active Microparticles Purely Constructed from Chirally Helical Substituted Polyacetylenes. Macromol. Rapid Commun. 2014, 35, 1216−1223. (37) Li, W. F.; Liu, X.; Qian, G. Y.; Deng, J. P. Immobilization of Optically Active Helical Polyacetylene-Derived Nanoparticles on Graphene Oxide by Chemical Bonds and Their Use in Enantioselective Crystallization. Chem. Mater. 2014, 26, 1948−1956. (38) Li, W. F.; Liang, J. Y.; Yang, W. T.; Deng, J. P. Chiral Functionalization of Graphene Oxide by Optically Active HelicalSubstituted Polyacetylene Chains and Its Application in Enantioselective Crystallization. ACS Appl. Mater. Interfaces 2014, 6, 9790−9798. (39) Zhang, H. Y.; Qian, G. Y.; Song, J. X.; Deng, J. P. Optically Active, Magnetic Microparticles: Constructed by Chiral Helical Substituted Polyacetylene/Fe3O4 Nanoparticles and Recycled for Uses in Enantioselective Crystallization. Ind. Eng. Chem. Res. 2014, 53, 17394−17402. (40) Yin, P. T.; Shah, S.; Chhowalla, M.; Lee, K. B. Design, Synthesis, and Characterization of Graphene-Nanoparticle Hybrid Materials for Bioapplications. Chem. Rev. 2015, 115, 2483−2531. (41) Georgakilas, V.; Otyepka, M.; Bourlinos, A. B.; Chandra, V.; Kim, N.; Kemp, K. C.; Hobza, P.; Zboril, R.; Kim, K. S. Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications. Chem. Rev. 2012, 112, 6156− 6214. (42) Das, S.; Irin, F.; Ma, L.; Bhattacharia, S. K.; Hedden, R. C.; Green, M. J. Rheology and Morphology of Pristine Graphene/ Polyacrylamide Gels. ACS Appl. Mater. Interfaces 2013, 5, 8633−8640. (43) Qin, Y.; Yuan, J.; Li, J.; Chen, D. C.; Kong, Y.; Chu, F. Q.; Tao, Y. X.; Liu, M. L. Crosslinking Graphene Oxide into Robust 3D Porous N-Doped Graphene. Adv. Mater. 2015, 27, 5171−5175. (44) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Reporting Physisorption Data for Gas/Solid Systems with Special Reference to the Determination of Surface Area and Porosity. Pure Appl. Chem. 1985, 57, 603−619. (45) Hummers, W. S.; Offeman, R. E. Preparation of Graphitic Oxide. J. Am. Chem. Soc. 1958, 80, 1339−1339. (46) El-Boubbou, K.; Gruden, C.; Huang, X. F. Magnetic GlycoNanoparticles: A Unique Tool for Rapid Pathogen Detection, Decontamination, and Strain Differentiation. J. Am. Chem. Soc. 2007, 129, 13392−13393.

(16) Kim, J. W.; Lee, D.; Shum, H. C.; Weitz, D. A. Colloid Surfactants for Emulsion Stabilization. Adv. Mater. 2008, 20, 3239− 3243. (17) Huang, Y.; Liu, M. J.; Wang, J. X.; Zhou, J. M.; Wang, L. B.; Song, Y. L.; Jiang, L. Controllable Underwater Oil-Adhesion-Interface Films Assembled from Nonspherical Particles. Adv. Funct. Mater. 2011, 21, 4436−4441. (18) Yoshida, M.; Roh, K. H.; Mandal, S.; Bhaskar, S.; Lim, D.; Nandivada, H.; Deng, X. P.; Lahann, J. Structurally Controlled BioHybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells. Adv. Mater. 2009, 21, 4920−4925. (19) Takahashi, H.; Nagao, D.; Watanabe, K.; Ishii, H.; Konno, M. Magnetic Field Aligned Assembly of Nonmagnetic Composite Dumbbells in Nanoparticle-Based Aqueous Ferrofluid. Langmuir 2015, 31, 5590−5595. (20) Zhang, W. J.; D’Agosto, F.; Boyron, O.; Rieger, J.; Charleux, B. Toward a Better Understanding of the Parameters That Lead to the Formation of Nonspherical Polystyrene Particles via RAFT-Mediated One-Pot Aqueous Emulsion Polymerization. Macromolecules 2012, 45, 4075−4084. (21) Sacanna, S.; Irvine, W. T. M.; Chaikin, P. M.; Pine, D. J. Lock and Key Colloids. Nature 2010, 464, 575−578. (22) Kao, Y. H.; Chi, M. H.; Tsai, C. C.; Chen, J. T. Nanopressing: Toward Tailored Polymer Microstructures and Nanostructures. Macromol. Rapid Commun. 2014, 35, 84−90. (23) Uemura, T.; Kaseda, T.; Kitagawa, S. Controlled Synthesis of Anisotropic Polymer Particles Templated by Porous Coordination Polymers. Chem. Mater. 2013, 25, 3772−3776. (24) Namjoo, A.; Abdolbaghi, S.; Saadat, Y.; Hosseinzadeh, S. Micromolding-Polymerization as a Novel Method for Production of Nonspherical Polymer Particles: Formation Mechanism of Polystyrene Particles. Colloid Polym. Sci. 2015, 293, 1781−1789. (25) Huang, Y.; Wang, J. X.; Zhou, J. M.; Xu, L.; Li, Z. R.; Zhang, Y. Z.; Wang, J. J.; Song, Y. L.; Jiang, L. Controllable Synthesis of Latex Particles with Multicavity Structures. Macromolecules 2011, 44, 2404− 2409. (26) Preiss, L. C.; Werber, L.; Fischer, V.; Hanif, S.; Landfester, K.; Mastai, Y.; Muñoz-Espí, R. Amino-Acid-Based Chiral Nanoparticles for Enantioselective Crystallization. Adv. Mater. 2015, 27, 2728−2732. (27) Freire, F.; Quiñoá, E.; Riguera, R. Supramolecular Assemblies from Poly(phenylacetylene)s. Chem. Rev. 2016, 116, 1242−1271. (28) Liu, J. Z.; Lam, J. W. Y.; Tang, B. Z. Acetylenic Polymers: Syntheses, Structures, and Functions. Chem. Rev. 2009, 109, 5799− 5867. (29) Yashima, E.; Maeda, K.; Iida, H.; Furusho, Y.; Nagai, K. Helical Polymers: Synthesis, Structures, and Functions. Chem. Rev. 2009, 109, 6102−6211. (30) Palmans, A. R. A.; Meijer, E. W. Amplification of Chirality in Dynamic Supramolecular Aggregates. Angew. Chem., Int. Ed. 2007, 46, 8948−8968. (31) Kim, H.; Jin, Y. J.; Kim, B. S.; Aoki, T.; Kwak, G. Optically Active Conjugated Polymer Nanoparticles from Chiral Solvent Annealing and Nanoprecipitation. Macromolecules 2015, 48, 4754− 4757. (32) Dai, C. H.; Yang, D. L.; Zhang, W. J.; Bao, B. Q.; Cheng, Y. X.; Wang, L. H. Far-red/Near-Infrared Fluorescent Conjugated Polymer Nanoparticles with Size-Dependent Chirality and Cell Imaging Applications. Polym. Chem. 2015, 6, 3962−3969. (33) Arias, S.; Freire, F.; Quiñoá, E.; Riguera, R. Nanospheres, Nanotubes, Toroids, and Gels with Controlled Macroscopic Chirality. Angew. Chem., Int. Ed. 2014, 53, 13720−13724. (34) Luo, X. F.; Deng, J. P.; Yang, W. T. Helix-Sense-Selective Polymerization of Achiral Substituted Acetylenes in Chiral Micelles. Angew. Chem., Int. Ed. 2011, 50, 4909−4912. (35) Chen, B.; Deng, J. P.; Yang, W. T. Hollow Two-Layered Chiral Nanoparticles Consisting of Optically Active Helical Polymer/Silica: Preparation and Application for Enantioselective Crystallization. Adv. Funct. Mater. 2011, 21, 2345−2350. 16279

DOI: 10.1021/acsami.6b02654 ACS Appl. Mater. Interfaces 2016, 8, 16273−16279