通讯作者地址: Sun, YP (通讯作者), Clemson Univ, Dept Chem, Clemson, SC 29634 USA  
地址: 
1. Clemson Univ, Dept Chem, Clemson, SC 29634 USA 
2. Clemson Univ, Lab Emerging Mat & Technol, Clemson, SC 29634 USA  
电子邮件地址: syaping@clemson.eduA successful attempt in the functionalization and solubilization of boron nitride nanotubes is reported, and a functionalization mechanism based on interactions of amino functional groups with nanotube surface borons is proposed

K. A. Shiral Fernando ( Clemson University,USA)

Su-Yuan Xie

Wei Wang ( Clemson University,USA)

Xin Wang ( Clemson University,USA)

Ya-Ping Sun ( Clemson University,USA)

Yi Lin ( Clemson University,USA)

谢素原

Chemical Communications

Xiamen University Institutional Repository

Solubilization of boron nitride nanotubesSu-Yuan Xie, Wei Wang, K. A. Shiral Fernando, Xin Wang, Yi Lin and Ya-Ping Sun*Received (in Cambridge, UK) 15th April 2005, Accepted 20th May 2005First published as an Advance Article on the web 15th June 2005DOI: 10.1039/b505330gA successful attempt in the functionalization and solubilizationof boron nitride nanotubes is reported, and a functionalizationmechanism based on interactions of amino functional groupswith nanotube surface borons is proposed.There has been much recent interest in boron nitride nanotubes(BNNTs) for their electronic,1–3 thermal,4–6 and mechanicalproperties,7,8 which are in many cases different from and/orsuperior to those of carbon nanotubes.9 For example, BNNTs aresemiconductors with a wide band-gap (4–5 eV) independent of thenanotube chirality or morphology.1–3 The thermal conductivity,oxidation resistivity, thermal and chemical stability, and yieldresistance of BNNTs are higher than those of their carbon analogs.Among widely discussed unique applications of BNNTs are theiruse as nanoscale semiconductors operating in oxidative environ-ments at high temperatures5,6 and as insulating nanocomposites ofhigh thermal conductivity.6,10Most investigations in the literature were focused on BNNTs inthe solid state, because these nanotubes, like their carboncounterparts, are generally insoluble in common organic andaqueous media.11 For carbon nanotubes, the research efforts ontheir functionalization and solubilization have stimulated andenabled the exploitation of the properties and applications that arenot accessible in the solid state, such as the dispersion of carbonnanotubes in polymeric nanocomposites and the compatibilizationwith biological systems.12,13 Similarly significant effects on theresearch of BNNTs may be expected from the introduction of thenanotubes into homogeneous solution. We report here a successfulattempt in the solubilization of BNNTs.14 The solubilization wasbased on interactions of amino groups in oligomeric diamine-terminated poly(ethyleneglycol) (PEG) with the BNNT surface,conceptually similar to those proposed in the solubilization ofcarbon nanotubes.15,16 The solubilization procedure and resultsfrom the characterization of BNNTs before and after thesolubilization are presented and discussed.BNNTs were synthesized by the carbon nanotube substitutionreaction,17–19 in which purified multiple-walled carbon nanotubes(MWNTs, Nanostructure & Amorphous Materials, Inc.) wereused as a template to react with boron oxide (powder, 99.8%, AlfaAesar) and anhydrous ammonia (National Welders SupplyCompany) in a quartz chamber at high temperature (1200 uC),followed by thermal treatment (780 uC) in low-pressure air toremove the residual carbon from the sample.4 The X-rayphotoelectron spectroscopy (XPS, Kratos AXIS 165) analysis ofthe sample yielded a B:N ratio of 1.05:1, with the slight excess ofboron due to residual boron oxide. Upon further purification byrepeated washing with hot water to remove boron oxide, thecontent of BNNTs in the sample was at least 75% by weight,comparable with those reported in the literature.17–20The thermogravimetric analysis (TGA, Mettler-Toledo TGA/SDAT851e) result of the sample in air is shown in Fig. 1. Theweight increase at high temperatures was due to the oxidation ofboron in the BNNTs,4 and the amount of increase (y25%) wasconsistent with the estimated BNNT content in the sample.The presence of BNNTs in the sample was confirmed byscanning (SEM, Hitachi S-4700) and transmission electronmicroscopy (TEM, Hitachi HD-2000) characterization. TheSEM image in Fig. 2 (top) shows abundant nanotubes. TheTEM results suggest that the BNNTs are mostly long tubes ofaround 20 nm in diameter (Fig. 2, bottom), with generally thinnerwalls than those in the starting MWNTs and also with a distortedlayer structure in the wall.The BNNTs were solubilized via functionalization{ with amine-terminated oligomeric poly(ethyleneglycol) (PEG1500N, Scheme 1).In a typical experiment, a sample of BNNTs (42 mg) was mixedwith PEG1500N (800 mg), and the mixture was heated to 100 uCand kept at that temperature for 3 days under nitrogen protection.Upon cooling to ambient temperature, the reaction mixture wasextracted repeatedly with deionized water, coupled with centri-fuging at 3000 g. According to the weight of the solid residue, themajority (more than 55%) of the starting BNNTs were solubilizedin water as a result of the functionalization with PEG1500N(Scheme 1).The functionalized BNNTs are soluble in water and organicmedia compatible with PEG1500N. While BNNTs are colorless, theattachment of PEG1500N in the functionalized BNNTs changedthe sample color to brown (Fig. 3). Both the functionalization andDepartment of Chemistry and Laboratory for Emerging Materials andTechnology, Clemson University, Clemson, SC 29634-0973, USA.E-mail: syaping@clemson.edu; Fax: +1-864-656-5007;Tel: +1-864-656-5026Fig. 1 A TGA trace of the BNNT sample (air, 10 uC min21), where theweight increase is due to the addition of oxygen.COMMUNICATION www.rsc.org/chemcomm | ChemComm3670 | Chem. Commun., 2005, 3670–3672 This journal is  The Royal Society of Chemistry 2005the solution color are likely due to interactions of the PEG1500Namino groups with nanotubes, as proposed in Scheme 1.According to results from control experiments, the amino moietyin the functionalization agent is necessary for the functionalizationand solubilization of BNNTs. In fact, there was no solubilizationat all when the nanotube sample was simply heated in neatdeionized water under the same experimental conditions. Similarly,no meaningful solubilization was found with the use of alcohol-terminated or methoxy-terminated PEG (PEG1500OH andPEG1500OCH3, respectively) as the functionalization agent.The functionalization of BNNTs with PEG1500N was reversible.The brown-colored solution of PEG1500N-functionalized BNNTswas placed in a membrane tubing (molecular weight cutoffy12000) for dialysis against fresh deionized water. In less than3 days, the color disappeared and the solution turned into asuspension (Fig. 3), from which colorless BNNTs were recoveredalmost quantitatively via simple low-speed centrifuging. As shownin Fig. 4, the FT-IR (Thermal-Nicolet Nexus 670) spectral featuresof the recovered BNNTs are generally the same as those of thestarting BNNTs (except for several small peaks due to residualPEG1500N), with the characteristic peaks at 1380 cm21 and800 cm21 due to B–N vibrations parallel and perpendicular to thenanotube axis, respectively.21Additional experiments were performed to confirm that thesolution color was indeed associated with the PEG1500N–BNNTinteractions. One was to precipitate the PEG1500N-functionalizedBNNTs from the brown-colored solution via high-speed centri-fuging. At 25000 g for 30 min, brownish precipitates wereobserved, and the solution became only slightly yellowish,suggesting that the color was attached to the nanotubes. InFig. 2 SEM (top) and TEM (bottom) images of the purified BNNTs.Scheme 1Fig. 3 (a) An aqueous solution of the PEG1500N-functionalized BNNTs.(b) The suspension from the dialysis of the solution in (a) against water. (c)The supernatant from the low-speed centrifuging of the suspension in (b).Fig. 4 The FT-IR spectra of the starting (a) and recovered (b) BNNTsamples in a KBr matrix.This journal is  The Royal Society of Chemistry 2005 Chem. Commun., 2005, 3670–3672 | 3671another experiment, the PEG1500N-functionalized BNNTs weredialyzed against an aqueous solution of the PEG1500N withmatching concentration. No meaningful precipitation or change insolution color were observed after the dialysis. Thus, the colormust be a part of the functionalization, as proposed in Scheme 1.The dispersion of the PEG1500N-functionalized BNNTs wasexamined by both TEM and AFM (Molecular Imaging PicoPlus).For the TEM specimen, a small drop of an aqueous solution of thefunctionalized BNNTs was placed on a holey-carbon-coatedcopper grid, followed by solvent evaporation. As shown in theTEM image in Fig. 5, the nanotubes are well-dispersed. Thesample for AFM measurement was deposited on a mica substrate.However, the presence of abundant functional group PEG1500Nmade the imaging somewhat difficult. Thus, the specimen wastreated at 400 uC in air for 1 h to remove some of the attachedPEG1500N molecules from the sample. The subsequent AFMimage of the thermally treated specimen exhibits island-likestructures on the nanotube surface (Fig. 5), which may beattributed to the remaining PEG1500N functional groups.In summary, BNNTs could be introduced into homogeneousaqueous and organic solutions via the functionalization witholigomeric PEG molecules bearing amino moieties. The colorchange of the sample from colorless to brown upon thefunctionalization was identified as being associated with interac-tions between the PEG amino groups and the nanotube surface.Both the solubilization and the color change were found to bereversible, which could be interpreted mechanistically as being dueto the formation and dissociation of amine–boron ionic bonds.The solubilization via functionalization may add a new dimensionin applications of BNNTs, such as their homogeneous dispersionin nanocomposite materials for unique thermal and opticalproperties.Financial support from NSF, NASA, and the Center forAdvanced Engineering Fibers and Films (NSF-ERC at ClemsonUniversity) is gratefully acknowledged.Notes and references{ The largely ionic interactions in the solubilization, as discussed later in themanuscript, are more chemical (acid–base reactions) than physical, thusmay still be classified as ‘‘functionalization’’.1 A. Rubio, J. L. Corkill and M. L. Cohen, Phys. Rev. B: Condens.Matter, 1994, 49, 5081.2 M. Radosavljevi, J. Appenzeller, V. Derycke, R. Martel, Ph. Avouris,A. Loiseau, J.-L. Cochon and D. Pigache, Appl. Phys. Lett., 2003, 82,4131; J. S. Lauret, R. Arenal, F. Ducastelle, A. Loiseau, M. Cau,B. Attal-Tretout, E. Rosencher and L. Goux-Capes, Phys. Rev. Lett.,2005, 94, 37405.3 J. Cumings and A. Zettl, Solid State Commun., 2004, 129, 661;M. Ishigami, J. D. Sau, S. Aloni, M. L. Cohen and A. Zettl, Phys. Rev.Lett., 2005, 94, 56804.4 W. Q. Han, W. Mickelson, J. Cumings and A. Zettl, Appl. Phys. Lett.,2002, 81, 1110.5 C. C. Tang and Y. Bando, Appl. Phys. Lett., 2003, 83, 659.6 Y. Xiao, X. H. Yan, J. Xiang, Y. L. Mao, Y. Zhang, J. X. Cao andJ. W. Ding, Appl. Phys. Lett., 2004, 84, 4626.7 N. G. Chopra and A. Zettl, Solid State Commun., 1998, 105, 297.8 H. F. Bettinger, T. Dumitrica, G. E. Scuseria and B. I. Yakobson, Phys.Rev. B: Condens. Matter, 2002, 65, 41406.9 M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, Science ofFullerenes and Carbon Nanotubes, Academic Press, New York, 1996.10 M. Jacoby, Chem. Eng. News, 2004, 82, 35, 34.11 R. Z. Ma, D. Golberg, Y. Bando and T. Sasaki, Philos. Trans. R. Soc.London, Ser. A, 2004, 362, 2161.12 J. Chen, M. A. Hamon, H. Hu, Y. S. Chen, A. M. Rao, P. C. Eklundand R. C. Haddon, Science, 1998, 282, 95.13 Y.-P. Sun, K. Fu, Y. Lin and W. Huang, Acc. Chem. Res., 2002, 35,1096; S. Niyogi, M. A. Hamon, H. Hu, B. Zhao, P. Bhowmik, R. Sen,M. E. Itkis and R. C. Haddon, Acc. Chem. Res., 2002, 35, 1105;J. L. Bahr and J. M. Tour, J. Mater. Chem., 2002, 12, 1952; A. Hirsch,Angew. Chem. Int. Ed., 2002, 41, 1853; V. N. Khabashesku,W. E. Billups and J. L. Margrave, Acc. Chem. Res., 2002, 35, 1087;S. Banerjee, M. G. C. Kahn and S. S. Wong, Chem. Eur. J., 2003, 9,1898; D. Tasis, N. Tagmatarchis, V. Georgakilas and M. Prato, Chem.Eur. J., 2003, 9, 4000.14 The functionalization of BNNTs with stannic oxide nanoparticles hasbeen reported (W. Q. Han and A. Zettl, J. Am. Chem. Soc., 2003, 125,2062), but no solubilization.15 J. Chen, A. M. Rao, S. Lyuksyutov, M. E. Itkis, M. A. Hamon, H. Hu,R. W. Cohn, P. C. Eklund, D. T. Colbert, R. E. Smalley andR. C. Haddon, J. Phys. Chem. B, 2001, 105, 2525.16 (a) W. Huang, S. Fernando, L. F. Allard and Y.-P. Sun, Nano Lett.,2003, 3, 565; (b) W. Huang, S. Fernando, Y. Lin, B. Zhou, L. F. Allardand Y.-P. Sun, Langmuir, 2003, 19, 7084; (c) K. A. S. Fernando, Y. Linand Y.-P. Sun, Langmuir, 2004, 20, 4777.17 W. Q. Han, Y. Bando, K. Kurashima and T. Sato, Appl. Phys. Lett.,1998, 73, 3085.18 W. Q. Han, J. Cumings, X. S. Huang, K. Bradley and A. Zettl, Chem.Phys. Lett., 2001, 346, 368.19 J. Wu, W. Q. Han, W. Walukiewicz, J. W. Ager, III, W. Shan,E. E. Haller and A. Zettl, Nano Lett., 2004, 4, 647.20 F. F. Xu, Y. Bando, R. Z. Ma, D. Golberg, Y. B. Li and M. Mitome,J. Am. Chem. Soc., 2003, 125, 8032.21 E. Borowiak-Palen, T. Pichler, G. C. Fuentes, B. Bendjemil, X. Liu,A. Graff, G. Behr, R. J. Kalenczuk, M. Knupfer and J. Fink, Chem.Commun., 2003, 82.Fig. 5 TEM (left) and AFM (right) images of the PEG1500N-functiona-lized BNNTs.3672 | Chem. Commun., 2005, 3670–3672 This journal is  The Royal Society of Chemistry 2005

Solubilization of boron nitride nanotubes

https://dspace.xmu.edu.cn/bitstream/2288/3137/1/b505330g.pdf

Solubilization of boron nitride nanotubes

Abstract

Similar works

Full text

Available Versions

Xiamen University Institutional Repository