Article pubs.acs.org/cm
Hollow Carbon Nanoparticles of Tunable Size and Wall Thickness by Hydrothermal Treatment of α‑Cyclodextrin Templated by F127 Block Copolymers Zheng-Chun Yang,† Yu Zhang,† Jun-Hua Kong,‡ Siew Yee Wong,§ Xu Li,*,§ and John Wang*,† †
Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, BLK EA, #03-09, 117576, Singapore ‡ School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, 639798, Singapore § Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 3 Research Link, 117602, Singapore S Supporting Information *
ABSTRACT: On the basis of the strategy of forming supermolecular structure between αcyclodextrin and poly(ethylene oxide), a facile synthesis process has been successfully developed for producing hollow carbon nanoparticles of controllable size and morphology by hydrothermal treatment of α-cyclodextrin in the presence of Pluronic F127 as a soft template. The hollow carbon nanoparticles thus derived are demonstrated to exhibit excellent hydrophilic behavior. Their sizes and wall thicknesses can be tuned by adjusting the ratio of α-cyclodextrin to F127. After pyrolysis at 900 °C in argon gas, the hollow carbon nanoparticles exhibit a meso-/ microporous carbon wall with specific surface area of >400 m2/g and a high specific charge capacity of >450 mAh/g when employed as an anode in a lithium ion battery. KEYWORDS: hollow carbon nanoparticles, α-cyclodextrin, F127, hydrothermal treatment, soft template
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zinc oxide,15 aluminosilicates,16 SnO2,17 and zeolites,18 which are commonly available and can be made variable in morphology and size. Carbon precursors, such as glucose,19,20 sucrose,21 furfuryl alcohol,22 resorcinol formaldehyde,23 and dopamine,24 are assembled on the surface of these hard templates by either physical adsorption or chemical impregnation. The resultant carbon precursor/hard template hybrids are then thermally treated at a high enough temperature under an inert gas atmosphere to convert the precursor into carbon.25 Finally, the hard template is removed by chemical etching, for example, by HF or NaOH.1,14,26 Undoubtedly, the hard template approach is successful in producing HCNPs. The procedure involved is however a typical multiple step process, as it inevitably requires use and subsequent removal of hard template, often by a rather aggressive process, such as chemical etching. To avoid the complex synthesis route of the hard template method, soft template synthesis routes have been reported.27 With the soft template synthesis approach, pyrolysis of certain hollow polymeric spheres has recently been demonstrated as an interesting approach for producing HCNPs.28 In this soft template strategy, hollow polymeric spheres, such as resorcinol formaldehyde28 and polystyrene,29 are played as both template and carbon sources. These
INTRODUCTION For the past two decades, various porous carbon materials have been developed, as they exhibit excellent chemical and physical behavior, such as high chemical stability, strong mechanical integrity, and desirable electric conductivity and thermal conductivity, which are inevitably required by a number of technologically valuable applications.1−3 Among these porous carbon materials, hollow carbon nanoparticles (HCNPs) have received considerable attention recently for applications in energy storage, water treatment, and biomedicine, owing to their unique structure and functional behavior, such as very high specific surface area, low specific density, large controllable inner pore volume, and good mechanical strength.4 Indeed, they have been considered as an essential class of candidate materials for energy storage devices, such as supercapacitors,5,6 lithium−ion batteries,7−9 fuel cells,10,11 and hydrogen storage device.12 Since the surface characteristics, dispersibility, average size, and morphology of the HCNPs strongly affect their chemical and physical behaviors, there have been several approaches developed for synthesizing HCNPs of varying sizes and morphologies. The first major class of the synthesis approaches is the hard template method, which has been demonstrated to produce monodispersed HCNPs with controllable morphology and inner pore structure in micrometer and submicrometer ranges.8,13 The typical hard templates are the monodispersed solid spheres, such as those made of mesoporous silica,8,13,14 © XXXX American Chemical Society
Received: October 31, 2012 Revised: February 6, 2013
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redispersed in DI water and centrifuged at 500 rpm for 30 min to remove the large agglomerated particles. Finally, the suspension was collected and freeze-dried for two days to obtain the narrowly dispersed powder of HCNPs for further study. The overall yield is 97.5%. The as-prepared and dried HCNPs were pyrolyzed in a tube furnace at 900 °C for 6 h under argon gas protection, leading to HCNPs with meso-/microporous carbon wall. Characterization. The size, morphology, and microstructure of the HCNPs were studied by using a scanning electron microscope (SEM) (XL 30 FEG-SEM Philips) and transmission electron microscop (TEM) (CM 300 FEG-Philips). Their hydrodynamic sizes and size distributions when dispersed in DI water were measured by using dynamic light scattering (DLS) (Malvern Zetasizer Nanosizer with a 633 nm HeNe laser). The carbon structure of HCNPs in powder form was studied by using a RENISHAW Raman Microscope with 514 nm laser radiation source. The functional groups of HCNPs were characterized by using a Fourier transform infrared (FTIR) spectroscope (Perkin-Elmer FT-IR 2000), where the FTIR sample was prepared by pressing the mixture of HCNPs powder and potassium bromide into a thin pellet. The amount of oxygen on the surface of the HCNPs was investigated using X-ray photoelectron spectroscopy (XPS) (AXIS Ultra). Bruker D8 X-ray diffraction (XRD) equipped with Cu Kα radiation (λ = 0.15418 nm) was used to study the crystal structure of the supramolecular inclusion complexes formed by F127 and α-CD. The samples were derived by freeze-drying the F127/α-CD mixed solution. N2 adsorption/desorption isotherms at −196 °C and CO2 adsorption isotherms at room temperature were measured using a Micromeritics ASAP 2020 system. The Brunauer−Emmett−Teller (BET) surface area was evaluated using N2 adsorption data in the relative pressure (P/P0) range of 0.06−0.2. The Barrett−Joyner− Halenda (BJH) and Dubinin-Astakhov pore size distributions were calculated by analyzing the adsorption branch of the N2 isotherms and the CO2 adsorption isotherms, respectively. Electrochemical Measurement. Electrochemical behavior of the pyrolyzed HCNPs as the anode in lithium (Li) ion batteries were investigated. The working electrode was fabricated by coating the slurry of HCNPs (80 wt %), carbon black (10 wt %), and polyvinylidene fluoride (PVDF) (10 wt %) in n-methyl pyrrolidinone (NMP) onto a copper foil. The coated copper foil was then dried in a vacuum oven at 120 °C for 12 h. Furthermore, Li foil with thickness and diameter of 0.4 and 14 mm, respectively, was used as the counter electrode, while Celgard 2325 membrane was utilized as the separator and 1 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume) was used as electrolyte. They were assembled into a 2032 button cell in argon-filled glovebox, in which both the moisture and oxygen level were controlled to be less than 1 ppm. The cells were charged and discharged on MACCOR 4200 battery and cell test equipment within the voltage range of 3−0.005 V (vs Li/Li+) at a current density of 50 mA/g at room temperature.
polymeric colloids are directly pyrolyzed at an appropriate combination of temperature and atmosphere, leading to the designed hollow carbon morphology. Apparently, the pyrolysis is a one-step process, which is simpler than the hard template strategy. There is however a challenge in order to precisely control the size, size distribution, and morphology of HCNPs derived from the direct pyrolysis of polymeric precursors. Thus, it would be of considerable interest to develop a facile approach to synthesize monodispersed HCNPs with controllable size. Amphiphilic molecules, such as block copolymers and surfactants, could form vesicle structures through selfassembling by hydrogen bonding and hydrophobic/hydrophilic interactions in aqueous environments.27 These vesicles could be used as soft templates for synthesizing HCNPs. On the basis of this strategy, we make use of the vesicle structure formed by block copolymer poly(ethylene oxide)-poly (propylene oxide)poly(ethylene oxide) (PEO-PPO-PEO) and α-cyclodextrin (αCD), which is the carbon precursor threaded onto PEO chains dangling on the vesicle surface. This unique approach, which is illustrated by Scheme 1, is on the basis of the understanding Scheme 1. Designed Synthesis Strategy for Narrowly Dispersed HCNPs, Where the Large Vesicle Structures Were Formed by Block Copolymer F127 When Used As Soft Templates and α-CD Threaded on the PEO Chains Dangling on the Surface of PEO-PPO-PEO Vesicles
that PEO chains in PEO-PPO-PEO can penetrate into the inner cavity of α-CD, which is a series of cyclic oligosaccharides, forming an inclusion type of supramolecular complexes.30,31 In addition, an important consideration is the strong hydrogen bonding between α-CD molecules which are threaded onto the PEO chains. It has been demonstrated that a stronger bonding between the carbon precursors would lead to a more orderly structure.1,27 Moreover, the commercially available block copolymer PEO106-PPO70-PEO106 (F127) is a desired choice of soft template. Indeed, it has been widely used as template for synthesizing mesoporous carbon materials, due to its well established chemical behaviors.1 Upon establishing the vesicle structure, where α-CD is threaded on the PEO chains, α-CD will then be converted to carbon structure by hydrothermal treatment.32,33 As detailed in Results and Discussion below, the uniquely new approach leads to narrowly dispersed HCNPs of controllable size and morphology.
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RESULTS AND DISCUSSION Preparation and Characterizations of HCNPs. SEM and TEM were employed to study the size, morphology, and texture of the as-synthesized HCNPs. Figure 1a,d,g shows the SEM images of HCNPs derived from 40 mL of aqueous solution of 60 mg of α-CD in the presence of 7.5, 15, and 30 mg of F127 by hydrothermal treatment, which are denoted as HCNPs-1, HCNPs-2, and HCNPs-3, respectively. From these SEM images, the as-synthesized particles are seen to exhibit a spherical morphology. In addition, as shown in Figure 1b,e,h, which are the respective TEM images of HCNPs-1, HCNPs-2, and HCNPs-3, these HCNPs exhibit a well-established hollow structure. Moreover, the average size of HCNPs measured by TEM and SEM increases when the amount of F127 in the solution is increased. The increase in the average size of HCNPs-1, HCNPs-2, and HCNPs-3 is shown in the distribution histograms in Figure 1c,f,i, respectively. As shown in the size distribution histograms, the averaged particle
EXPERIMENTAL SECTION
Materials. F127 is purchased from Sigma-Aldrich Company. α-CD is purchased from Tokyo Chemical Industry Company. Preparation of HCNPs. Various amounts of F127, namely, 7.5, 15, and 30 mg, respectively, were dissolved in 20 mL of deionized (DI) water and stirred at room temperature overnight. A total of 60 mg of α-CD in 20 mL of DI water was injected into the solution of F127 under stirring at 700 rpm. The mixed solution was stirred overnight and then transferred into a Teflon sealed autoclave chamber. Upon hydrothermal treatment at 200 °C for 6 h, the as-prepared HCNPs were collected and washed by DI water three times by centrifuging at 9000 rpm for 30 min. After washing, the black HCNPs were B
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Figure 2. DLS size distribution of the HCNPs in DI water formed from α-CD in the presence of various amounts of F127.
Figure 1. SEM and TEM images of the as-synthesized HCNPs. (a−c) SEM image, TEM image, and size distribution histograms of HCNPs1, respectively. (d−f) SEM image, TEM image, and size distribution histograms of HCNPs-2, respectively. (g−i) SEM image, TEM image, and size distribution histograms of HCNPs-3, respectively.
diameter of HCNPs-1, HCNPs-2, and HCNPs-3 is 200, 300, and 400 nm, respectively. In addition, the averaged inner pore diameter of HCNPs also increases with increasing concentration of F127 in the solution. For HCNPs-1, HCNPs-2, and HCNPs-3, the average pore diameter is 100, 140, and 220 nm, respectively. The average wall thickness of HCNPs-1, HCNPs2, and HCNPs-3 is measured to be 50, 60, and 80 nm, respectively. These particle and pore size distribution results show that the particle diameter, size of the inner pore, and wall thickness of HCNPs are tunable by just varying the concentration of F127. Since the as-synthesized HCNPs are well dispersed in DI water without any further surface modification, their hydrodynamic size and size distribution in water were measured by using DLS. As shown in Figure 2, the hydrodynamic size of HCNPs-1, HCNPs-2, and HCNPs-3 increases as the amount of F127 increases, which agrees well with what is observed in SEM and TEM. The average hydrodynamic size measured by using DLS for HCNPs-1, HCNPs-2, and HCNPs-3 is 214, 341, and 441 nm with polydispersity index (PDI) of 0.107, 0.125, and 0.068, respectively, which is larger than the average size measured by SEM and TEM. This indicates the existence of certain hydrophilic functional groups on the surface of HCNPs, which make the hydrodynamic diameter larger. When the HCNPs were dispersed in DI water, these hydrophilic functional groups on the surface extended and were counted by the DLS measurement. To study the chemical structure of HCNPs, FTIR spectroscopy was used to exam the functional groups of HCNPs. As shown by the similar FTIR spectra in Figure 3, HCNPs-1, HCNPs-2, and HCNPs-3 demonstrate similar chemical structure. By comparing the FTIR spectra of the as-synthesized HCNPs with α-CD, the carbonization of α-CD during the hydrothermal process is verified by the appearance of CC vibration bands at 1635 cm−1.34 In addition, after hydrothermal
Figure 3. FTIR spectra of α-CD, F127, and HCNPs formed in the presence of various amounts of F127.
treatment, the HCNPs exhibit hydroxyl and carboxyl functional groups, which are demonstrated by the vibration bands at 3440 and 1704 cm−1, respectively.34 Interestingly, by comparing between the FTIR spectra of the as-prepared HCNPs and F127 in Figure 3, the molecular structure of F127 is largely retained under the hydrothermal condition, as demonstrated by the observation of the characteristic bands (2890, 1465, 1343, and 1109 cm−1) of F127 block copolymer in the FTIR spectra of HCNPs, which are marked by * in Figure 3.35 To further confirm the structure of the as-synthesized HCNPs, a Raman spectrometer was used to study the carbon structure. The Raman spectra of HCNPs-1, HCNPs-2, and HCNPs-3 as shown in Figure 4 all demonstrate a typical spectrum of carbonized materials, which is characterized by the peak at 1346 (D band) and 1556 cm−1 (G band) and labeled by * in Figure 4.34 In addition, the G band in Figure 4 is broader than the normal G band of a typical disordered graphite, indicating that there are aromatic and olefinic molecules coexisting in HCNPs because of the in-plane bond-stretching motion of the C sp2 atom pairs.34 Moreover, there is a broad band in the range of 2500−3000 cm−1, which could be assigned to the stretching mode of sp3 C−Hx groups.32 The Raman results agree well with the FTIR results, which demonstrate not C
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inclusion complex formed between α-CD and F127, arising from the penetration of PEO into the inner cavity of α-CD.36 As shown in Figure 5, there is no such peak observed in the XRD trace of α-CD alone, where there is no guest molecule in the α-CD inner cavity, which exhibits a less symmetrical conformation.37 Under the hydrothermal condition, which is carried out at high temperature and pressure, the as-formed F127/α-CD supermolecular complexes will be self-assembled into a kind of vesicle structure due to the hydrophobic/ hydrophilic balances between PPO block in F127 and PEO/αCD segment.38,39 α-CD is carbonized at such a temperature and pressure, simultaneously.33 However, F127 is retained under the hydrothermal condition, as demonstrated by the FTIR result. As a result, the PEO block chains are present within the carbon wall of the as-synthesized HCNPs, giving rise to a hybrid structure which exhibits hydrophilic stability. Since the vesicle size of F127 could be varied by tuning the concentration of F127,38 the corresponding size of the asformed HCNPs is tunable. Pyrolysis of HCNPs. As discussed above, the monodispersed HCNPs exhibit a hybrid structure, which is that the carbon hollow nanoparticles are surface-decorated by PEO chains. F127 molecules are expected to disintegrate upon an appropriate pyrolysis in an inert atmosphere. In our study, the as-prepared HCNPs were pyrolyzed at 900 °C for 6 h in argon gas. SEM and TEM images of HCNPs-1, -2, and -3 after pyrolysis, which are coded as HCNPs-1a, HCNPs-2a, and HCNPs-3a, are shown in Figure 6. It is seen that the hollow spherical structure of HCNPs is well retained after the pyrolysis. The average particle diameters of the pyrolyzed HCNPs-1a, HCNPs-2a, and HCNPs-3a are measured as 122, 162, and 260 nm, respectively. In addition, the wall thicknesses of HCNPs-1a, HCNPs-2a, and HCNPs-3a are measured to be
Figure 4. Raman spectra of the HCNPs derived from hydrothermal process.
only that carbonization happened but also the appearance of surface functionalization. From the experimental results discussed above, it could be concluded that, by hydrothermal treatment of α-CD in the presence of various concentrations of F127, hydrophilic and monodispersed HCNPs could be generated with tunable size and morphology. As detailed in Scheme 1, F127 plays as the soft template while α-CD is the carbon precursor. According to the phase diagram of F127, F127 dissolved in DI water at the designed mass concentration, which is 0.019, 0.037, and 0.075 wt %, respectively, adapts a single macromolecule.35 Upon injection of the α-CD solution, the PEO block chain of F127 could penetrate into the inner cavity of α-CD molecules to form an inclusion type of supramolecular complexes.30,31 To demonstrate the as-formed supramolecular inclusion complexes, XRD studies on the freeze-dried starting materials before hydrothermal treatment are carried out. As shown in Figure 5, the supramolecular inclusion complexes formed by threading α-CD onto the PEO blocks of F127 are confirmed by the appearance of the characteristic XRD peak of the channeltype crystal structure of the α-CD,30,31 which is observed at 19.4° with F127/α-CD complexes. Such channel-type ordered structure represents a type of the necklace-like supramolecular
Figure 6. SEM and TEM images of the HCNPs after pyrolysis at 900 °C in argon. (a−c) SEM image, TEM image, and size distribution histograms of HCNPs-1a, respectively. (d−f) SEM image, TEM image, and size distribution histograms of HCNPs-2a, respectively. (g−i) SEM image, TEM image, and size distribution histograms of HCNPs3a, respectively.
Figure 5. XRD results of pure F127, α-CD, and the supramolecular inclusion complexes formed from α-CD (60 mg) and F127 at various contents (7.5, 15, 30 mg) before hydrothermal treatment. D
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Figure 7. N2 adsorption/desorption isotherm curves of HCNPs-1 (a), HCNPs-2 (b), and HCNPs-3 (c) and those for the pyrolyzed HCNPs, which are donated HCNPs-1a (a), HCNPs-2a (b), and HCNPs-3a (c), respectively.
14, 19, and 34 nm, respectively. Both the average diameter and wall thickness increase with the increase in the concentration of F127. Comparing the dimension of HCNPs before and after pyrolysis, it is noted that the overall carbon particle size and the average wall thickness are expectedly decreased after pyrolysis. Such a decrease is apparently due to the decomposition of F127 and the functional groups in HCNPs, which leads to a shrinkage in the carbon particle size and wall thickness. The decomposition of F127 through pyrolysis is confirmed by the studies of FTIR and XPS, which are shown in Figures S1 and S2 (see Supporting Information), respectively. As shown in Supporting Information Figure S1, similar FTIR spectra are observed with HCNPs-1a, HCNPs-2a, and HCNPs-3a, which suggests that the pyrolyzed HCNPs exhibit similar chemical structure. By comparing the FTIR spectrum of the pyrolyzed HCNPs with that of F127 in Supporting Information Figure S1, the characteristic bands of F127 block copolymers, which are 2890, 1465, 1343, and 1109 cm−1,40 are not present in the FTIR spectra of HCNPs after pyrolysis. Furthermore, the decreases in intensity of oxygen peaks (531 eV, Supporting Information Figure S2) in the XPS spectra of the pyrolyzed HCNPs also demonstrates the decomposition of F127 and surface functional groups of HCNPs. Both the 1346 (D band) and 1556 cm−1 (G band)34 in the Raman spectra of HCNPs-1a, HCNPs-2a, and HCNPs-3a (Supporting Information Figure S3) are narrower than those in Figure 4, indicating the decomposition of F127 and further condensation of carbon shell under the high temperature treatment in argon, which agrees well with the TEM, FTIR, and XPS results. The N2 adsorption/desorption isotherms of both the assynthesized HCNPs and the pyrolyzed sample are shown in Figure 7. For the as-synthesized HCNPs, negligible N2 adsorption occurs in a P/P0 range of 0−0.9 indicating nonporous character of the wall before pyrolysis. A sharp increase in N2 uptake at P/P0 = 0.9−1.0 corresponds to the interparticle voids, which becomes less significant as the particle size increases for the samples from HCNPs-1 to HCNPs-2 to HCNPs-3. The BET specific surface areas of HCNPs-1, HCNPs-2, and HCNPs-3 before pyrolysis are thus quite small with the values of 30.5, 22.7, and 12.9 m2/g, respectively. For HCNPs-1a after pyrolysis (Figure 7a), there is a linear increase in gas uptake occurring at low P/P0 = 0.06−0.2 due to the monolayer adsorption of N2 molecules inside pores, which gives rise to a BET specific surface area of 317.5 m2/g. It is followed by a long plateau at P/P0 = 0.2−0.9 indicating the full filling of the pores. This is supported by the BJH pore size distribution (Supporting Information Figure S4a) that only small pores (450 mAh/g when employed as an anode in a lithium ion battery.
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ASSOCIATED CONTENT
S Supporting Information *
FTIR spectra of the pyrolyzed HCNPs at 900 °C in argon and that of F127. XPS spectra of the HCNPs before and after pyrolysis at 900 °C in argon. Raman spectra of the pyrolyzed HCNPs at 900 °C in argon. BJH pore size distributions of the pyrolyzed HCNPs measured by N2. CO2 adsorption isotherm curves of HCNPs-1a, HCNPs-2a, and HCNPs-3a. DubininAstakhov pore size distributions of the pyrolyzed HCNPs measured by CO2. Li discharge/charge (Li insertion/extraction) curves. This material is available free of charge via the Internet at http://pubs.acs.org.
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Figure 8. Lithium ion battery cycling performance of HCNPs pyrolyzed at 900 °C in argon.
AUTHOR INFORMATION
Corresponding Author
*Phone: +65 6516 3325. Fax: +65 6776 3604. E-mail:
[email protected] (J.W.). Phone: +65 6874 8421. E-mail:
[email protected] (X.L.).
pyrolyzed HCNPs electrode measured under long-term cycling up to 75 cycles at the rate of 50 mA/g, revealing a good reversibility and cyclic performance. Even after 75 cycles, the specific capacity of the HCNPs electrode maintains a value of 443, 266, and 265 mAh/g for HCNPs-1a, HCNPs-2a, and HCNPs-3a, respectively. Such an electrochemical performance could well be attributed to the microporous structure of the pyrolyzed HCNPs. It has been reported that the microporous structure plays a key role in determining the thermodynamic and kinetic behavior of Li-ion insertion and extraction process.42,43 As shown in Supporting Information Figure S4, HCNPs-1a exhibits the highest level of microporosity among the three samples. In addition, as shown in Figure 6, HCNPs-1a also has the thinnest carbon wall, which would lead to a better utilization of both the external and internal surfaces of the hollow carbons for Li storage. As a result, a higher capacity is expected for HCNPs-1a, as compared with the other two samples, which are demonstrated to be the case. The reversible capacity of HCNPs-1a is higher than the theoretical capacity calculated for graphite, which is 372 mAh/g.8,41 This indicates that the HCNPs prepared in this work could be promising candidates for Li ion battery materials.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This work is supported by the Agency for Science, Technology and Research (A*Star, Singapore), Grant 1121202013, conducted at the National University of Singapore.
(1) Liang, C.; Li, Z.; Dai, S. Angew. Chem., Int. Ed. 2008, 47, 3696. (2) Lee, J.; Kim, J.; Hyeon, T. Adv. Mater. 2006, 18, 2073. (3) Stein, A.; Wang, Z. Y.; Fierke, M. A. Adv. Mater. 2009, 21, 265. (4) Jin, Q.; Zheng, M.; Wu, Y.; Xie, C.; Xiao, Y.; Liu, Y. J. Mater. Sci. 2012, 47, 711. (5) You, B.; Yang, J.; Sun, Y.; Su, Q. Chem. Commun. 2011, 47, 12364. (6) Han, Y.; Dong, X.; Zhang, C.; Liu, S. J. Power Sources 2012, 211, 92. (7) Lee, K. T.; Jung, Y. S.; Oh, S. M. J. Am. Chem. Soc. 2003, 125, 5652. (8) Yang, S.; Feng, X.; Zhi, L.; Cao, Q.; Maier, J.; Mullen, K. Adv. Mater. 2010, 22, 838. (9) Zhang, H.; Xu, H.; Zhao, C. Mater. Chem. Phys. 2012, 133, 429. (10) Chai, G. S.; Yoon, S. B.; Kim, J. H.; Yu, J. Chem. Commun. 2004, 2766. (11) Han, S. J.; Yun, Y. K.; Park, K. W.; Sung, Y. E.; Hyeon, T. Adv. Mater. 2003, 15, 1922. (12) Fang, B.; Kim, M.; Kim, J. H.; Yu, J. S. Langmuir 2008, 24, 12068. (13) Chen, X. C.; Kierzek, K.; Jiang, Z. W.; Chen, H. M.; Tang, T.; Wojtoniszak, M.; Kalenczuk, R. J.; Chu, P. K.; Borowiak-Palen, E. J. Phys. Chem. C 2011, 115, 17717. (14) Yoon, S. B.; Sohn, K.; Kim, J. Y.; Shin, C. H.; Yu, J. S.; Hyeon, T. Adv. Mater. 2002, 14, 19. (15) Zheng, M.; Liu, Y.; Zhao, S.; He, W.; Xiao, Y.; Yuan, D. Inorg. Chem. 2010, 49, 8674. (16) Joo, J. B.; Kim, P.; Kim, W.; Kim, J.; Kim, N. D.; Yi, J. Curr. Appl. Phys. 2008, 8, 814. (17) Zhang, C.; Wu, H. B.; Yuan, C.; Guo, Z.; Lou Angew, X. W. Chem. Int. Ed. 2012, 51, 9592. (18) Kyotani, T.; Nagai, T.; Inoue, S.; Tomita, A. Chem. Mater. 1997, 9, 609.
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CONCLUSIONS A facile synthesis strategy has been successfully developed for preparing HCNPs, by hydrothermal treatment of α-CD in the presence of F127 as template. This new strategy makes use of the vesicle structures formed by block copolymer of PEO-PPOPEO, threaded with α-CD onto PEO chains, dangling on the vesicle surface. The as-prepared HCNPs from hydrothermal treatment are narrowly dispersed and hydrophilically stable in an aqueous environment, due to the surface decoration by PEO chain and other hydrophilic functional groups, such as carboxyl and hydroxyl groups. Upon pyrolysis at 900 °C in argon, an allcarbon hollow spherical structure is developed. The size and carbon wall thickness of the HCNPs thus derived could well be controlled by adjusting the initial concentration of F127 in the aqueous phase. The meso-/microporous wall structure of the pyrolyzed HCNPs was demonstrated by their N2 adsorption/ desorption and CO2 adsorption isotherms. The pyrolyzed HCNPs exhibit a specific surface area of >400 m2/g. In addition, the HCNPs perform a high specific charge capacity of F
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Chemistry of Materials
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(19) Wang, F.; Pang, L.; Jiang, Y.; Chen, B.; Lin, D.; Lun, N.; Zhu, H.; Liu, R.; Meng, X.; Wang, Y.; Bai, Y.; Yin, L. Mater. Lett. 2009, 63, 2564. (20) Ikeda, S.; Tachi, K.; Ng, Y. H.; Ikoma, Y.; Sakata, T.; Mori, H.; Harada, T.; Matsumura, M. Chem. Mater. 2007, 19, 4335. (21) Oda, Y.; Fukuyama, F.; Nishikawa, K.; Namba, S.; Yoshitake, H.; Tatsumi, T. Chem. Mater. 2004, 16, 3860. (22) Almeida, C.; Zarbin, A. J. G. Carbon 2006, 44, 2869. (23) Fuertes, A. B.; Valle-Vigon, P.; Sevilla, M. Chem. Commun. 2012, 48, 6124. (24) Xiao, C.; Chu, X.; Yang, Y.; Li, X.; Zhang, X.; Chen, J. Biosens. Bioelectron. 2011, 26, 2934. (25) Xia, Y. D.; Mokaya, R. Adv. Mater. 2004, 16, 886. (26) Zhi, L.; Wang, J. J.; Cui, G. L.; Kastler, M.; Schmaltz, B.; Kolb, U.; Jonas, U.; Mullen, K. Adv. Mater. 2007, 19, 1849. (27) Lai, L.; Huang, G.; Wang, X.; Weng, J. Carbon 2010, 48, 3145. (28) Yang, M.; Wang, G. Colloids Surf., A 2009, 345, 121. (29) Lu, A.; Sun, T.; Li, W.; Sun, Q.; Han, F.; Liu, D.; Guo, Y. Angew. Chem., Int. Ed. 2011, 50, 11765. (30) Li, J.; Li, X.; Zhou, Z.; Ni, X.; Leong, K. W. Macromolecules 2001, 34, 7236. (31) Li, J.; Ni, X.; Leong, K. Angew. Chem., Int. Ed. 2003, 42, 69. (32) Sevilla, M.; Fuertes, A. B. Chem.Eur. J. 2009, 15, 4195. (33) Shin, Y.; Wang, L. Q.; Bae, I. T.; Arey, B. W.; Exarhos, G. J. J. Phys. Chem. C 2008, 112, 14236. (34) Yang, Z.; Li, X.; Wang, J. Carbon 2011, 49, 5207. (35) Ulanski, P.; Pawlowska, W.; Kadlubowski, S.; Henke, A.; Gottlieb, R.; Arndt, K. F.; Bromberg, L.; Hatton, T. A.; Rosiak, J. M. Polym. Adv. Technol. 2006, 17, 804. (36) Harada, A.; Li, J.; Kamachi, M. Macromolecules 1993, 26, 5698. (37) McMullan, R. K.; Saenger, W.; Fayos, J.; Mootz, D. Carbohydr. Res. 1973, 31, 37. (38) Prudhomme, R. K.; Wu, G. W.; Schneider, D. K. Langmuir 1996, 12, 4651. (39) Xiong, X. Y.; Tam, K. C.; Gan, L. H. Macromolecules 2003, 36, 9979. (40) Su, Y.; Liu, H.; Wang, J.; Chen, J. Langmuir 2002, 18, 865. (41) Han, F.; Bai, Y.; Liu, R.; Yao, B.; Qi, Y.; Lun, N.; Zhang, J. Adv. Energy Mater. 2011, 1, 798. (42) Hu, J.; Li, H.; Huang, X. Solid State Ionics 2005, 176, 1151. (43) Xing, W.; Xue, J.; Zheng, T.; Gibaud, A.; Dahn, J. R. J. Electrochem. Soc. 1996, 143, 3482.
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dx.doi.org/10.1021/cm303513y | Chem. Mater. XXXX, XXX, XXX−XXX
