Super-hydrophobic ordered mesoporous carbon monolith

Super-hydrophobic ordered mesoporous carbon monolith

1336 Letters to the Editor / Carbon 44 (2006) 1298–1352 References Fig. 5. Plots of discharge capacity of the composite cathode of LiNi0.7Co0.3O2 w...

472KB Sizes 0 Downloads 9 Views

1336

Letters to the Editor / Carbon 44 (2006) 1298–1352

References

Fig. 5. Plots of discharge capacity of the composite cathode of LiNi0.7Co0.3O2 with MWCNTs wiring at different content as a function of the cycle number in 50 cycles.

efficiency. The research is of potential interest to application of MWCNTs as a conductive additive in cathode active materials for high-power lithium-ion batteries.

[1] Dominko R, Gaberscek M, Drofenik J, Bele M, Jamnik J. Influence of acetylene black distribution on performance of oxide cathodes for Li ion batteries. Electrochim Acta 2003;48:3709–16. [2] Tran N, Croguennec L, Jordy C, Biensan P, Delmas C. Influence of the synthesis route on the electrochemical properties of LiNi0.425Mn0.425Co0.15O2. Solid State Ionics 2005;176:1539–47. [3] Jiang J, Eberman KW, Krause LJ, Dahn JR. Reactivity of Liy[NixCo1  2xMnx]O2 (x = 0.1, 0.2, 0.35, 0.45, and 0.5; y = 0.3, 0.5) with nonaqueous solvents and electrolytes studied by ARC. J Electrochem Soc 2005;152:A566–9. [4] Suresh P, Shukla AK, Munichandraiah N. Synthesis and characterization of novel, high-capacity, layered LiMn0.9Ni0.05Fe0.05O2 as a cathode material for Li-ion cells. Electrochem Solid State Lett 2005;8:A263–6. [5] Dominko R, Gaberscek M, Drofenik J, Bele M, Pejovnik S, Jamnik J. The role of acetylene black distribution in cathodes for Li ion batteries. J Power Sources 2003;119–121:770–3. [6] Huang SH, Wen ZY, Yang XL, Gu ZH, Xu XH. Improvement of the high-rate discharge properties of LiCoO2 with the Ag additives. J Power Sources 2005;148:72–7. [7] Mukai SR, Hasegawa T, Takagi M, Tamon H. Reduction of irreversible capacities of amorphous carbon materials for lithium ion battery anodes by Li2CO3 addition. Carbon 2004;42:837–42.

Super-hydrophobic ordered mesoporous carbon monolith Lifeng Wang a, Yong Zhao b, Kaifeng Lin a, Xiaojun Zhao a, Zhichao Shan a, Yan Di a, Zhenhua Sun a, Xuejing Cao a, Yongcun Zou a, Dazhen Jiang a, Lei Jiang b,*, Feng-Shou Xiao a,* a

College of Chemistry & State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012, PR China b Key Laboratory of Organic Solids Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China Received 1 September 2005; accepted 5 December 2005 Available online 6 January 2006

Keywords: Porous carbon; Chemical treatment; Electron microscopy; Surface properties

Since the successful synthesis of cubic mesoporous carbon of CMK-1 by Ryoo et al. using mesoporous silica of MCM-48 as a template [1], the ordered mesoporous carbon materials have attracted much attention [1–3]. These mesoporous carbon materials with controllable pore sizes, high surface areas, and large pore volumes have been potentially applied in many fields of science and technology, such as battery electrodes, super-capacitor, adsorbents, and catalyst supports [1–3]. Research on mesoporous carbon materials has concentrated on its adsorption, electronic, and * Corresponding authors. Fax: +86 431 5168624 (F.-S. Xiao), Fax: +86 10 82627566 (L. Jiang). E-mail addresses: [email protected] (L. Jiang), [email protected] edu.cn (F.-S. Xiao).

0008-6223/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.12.007

structural properties, and the wettability of mesoporous carbon has not yet been investigated. Wettability is a very important property governed by both chemical composition and geometrical structure of solid surface [4–8]. Researchers have a great interest in fabrication of super-hydrophobic surface with a water contact angle larger than 150 for its fascinating properties and potential applications [4–8]. Recently, Jiang and coworkers have investigated botanic self-cleaning lotus leaves, biologic water-repellent legs of water striders, and artificial super-hydrophobic carbon nanofibers and carbon nanotubes, revealing the wide combinations of natural or artificial materials and super-hydrophobicity [6–8]. However, there is no successful combination of ordered mesostructured materials and super-hydrophobicity, especially for

Letters to the Editor / Carbon 44 (2006) 1298–1352

TEM images of the treated CM (Fig. 2) exhibit ordered hexagonal arrays of mesopores with one-dimensional channels. The chemical composition for the surface of treated CM was measured by X-ray photoelectron spectroscopy (XPS). The C, F, O concentrations are 50.3, 37.9, 11.8 at.%, respectively. These results confirm that the surface of treated CM is fully fluorinated and mainly consists of carbon and fluorine. Fig. 3 shows typical scanning electron microscopy (SEM) images of the top view of CM and the treated CM. Both CM (Fig. 3a) and the treated CM (Fig. 3c) show rough surface. The image in higher magnification (Fig. 3b) further shows that CM consists of rope-like particles and most of them align parallel to the plate of CM. In addition, there are micron-sized intervoids between the particles, where air can be occupied. Therefore, the rough surface of CM can be regarded as a composite surface of rope-like particles and air.

100

100

110

110 200

b a

1

2

3

4

5

1337

6

2 theta Fig. 1. XRD patterns of mesoporous carbon monolith (CM) before (a), after modification with FAS-17 (b).

ordered mesoporous carbon materials. In this letter, we report for the first time a super-hydrophobic mesoporous carbon monolith modified by fluoroalkylsilane of CF3(CF2)7CH2CH2Si(OCH3)3 (FAS-17), which combines highly ordered mesostructure and super-hydrophobicity, and extends the potential applications of mesoporous carbon materials in fabrication of novel chemical engineering materials, nonwetting liquid transfer, and liquid microchannels [4–6]. Ordered mesoporous carbon monolith (CM) was templated from SBA-15 [9]. Super-hydrophobic mesoporous carbon monolith was prepared by modifying the carbon monolith with fluorinated compounds. Carbon monolith was first oxidized by a hot mixture of concentrated sulfuric and nitric acids and then mixed with methanol solution of hydrolyzed fluoroalkylsilane of FAS-17 (1.0 wt.%). The resulting mixture was stirred for 3 h and subsequently heated at 140 C for 1 h. Fig. 1 shows X-ray diffraction (XRD) patterns of CM before and after treatment with FAS-17. CM exhibits three well-resolved peaks that can be indexed as (1 0 0), (1 1 0), and (2 0 0) reflections associated with p6mm hexagonal symmetry, indicating the highly ordered structure of original sample. After treatment with FAS-17, the modified CM still shows two peaks (Fig. 1b), indicating that CM retains its ordered mesostructure after the rigorous treatment. Nitrogen sorption isotherms of CM and the treated CM are both type-IV isotherms, indicating their characteristic of ordered mesostructures. It is worthy noting that, the treated CM has relatively low surface area, pore volume, and pore size as compared with CM, suggesting the introduction of FAS-17 into the inner pores (Table 1).

Fig. 2. TEM images of the treated CM taken in the [1 1 0] direction (a) and [1 0 0] direction (b).

1338

Letters to the Editor / Carbon 44 (2006) 1298–1352

Table 1 Textural properties of CM and treated CM samples Sample

Pore sizea (nm)

SBETb (m2 g1)

VPc (cm3 g1)

VPd (cm3 g1)

CM Treated CM

4.3 3.7

1100 512

1.32 0.57

0.06 0

a b c d

Calculated from adsorption branches of N2 adsorption/desorption isotherms based on BJH model. BET specific surface area. Primary mesopore volume. Micropore volume.

The wettability of CM has been investigated by measurement of the water contact angle (CA). Fig. 4a shows a water droplet on CM without modification. The contact angle for water is 79.1 ± 1.5, indicating that CM is rela-

Fig. 3. SEM top-images of CM (a, b) and the treated CM (c).

tively hydrophilic. The hydrophilic property may be related to the parallel orientation of rope-like particles, which is favorable for water spreading. Similar results were previously observed by Jiang and coworkers and they found that aligned carbon nanotube (ACNT) arrays of horizontal orientation could improve the hydrophilic properties [6]. Fig. 4b shows the shape of a water droplet on the surface of CM treated by FSA-17. Interestingly, the contact angle for water on the treated CM is 150.2 ± 1.5. This result indicates that the treated CM is super-hydrophobic. Obviously, the great enhancement in hydrophobicity is mainly caused by the successful coating of FAS-17 with relatively low surface free energy. The rough surface of treated CM is also essential for the hydrophobicity. For a smooth surface, even modified by n-perfluoroeicosane with

Fig. 4. Photographs of water droplet shape on the mesoporous carbon monolith (a) before and (b) after modification of FAS-17.

Letters to the Editor / Carbon 44 (2006) 1298–1352

the lowest surface free energy, the contact angle of water is only 119. Accordingly, both the lower surface free energy and the surface roughness contribute to the super-hydrophobicity of the treated CM [4–8]. Furthermore, the water adsorption experiments show that CM has an obvious adsorption for water (>92.0 mg g1), while the treated CM adsorbs little water (<9.2 mg g1). These results confirm that the pore surface in CM becomes hydrophobic during the treatment. In summary, super-hydrophobic ordered mesoporous carbon monolith (CM) has been successfully obtained through surface modification by FAS-17. The combination of dewetting properties and ordered mesostructure allows the controlled manipulation of the surface behavior of ordered mesoporous carbon materials and further extends their applications. The design of new type of mesostructured materials, such as novel chemical engineering materials, nonwetting liquid transfer, and liquid microchannels is also expected. Acknowledgements This work is supported by NSFC (20373018, 20233030, and 20121103), BASF, CNPC, the National High Technology Research and Development Program of China (863

1339

Program), State Basic Research Project (973 Program), and Ministry of Education of China. References [1] Ryoo R, Joo SH, Jun SJ. Synthesis of highly ordered carbon molecular sieves via template-mediated structural transformation. J Phys Chem B 1999;103:7743–6. [2] Lee J, Yoon S, Hyeon T, Oh SM, Kim KB. Synthesis of a new mesoporous carbon and its application to electrochemical double-layer capacitors. Chem Commun 1999:2177–8. [3] Yu J-S, Kang S, Yoon SB, Chai G. Fabrication of ordered uniform porous carbon networks and their application to a catalyst supporter. J Am Chem Soc 2002;124:9382–3. [4] Aussillous P, Que´re´ D. Liquid marbles. Nature 2001;411:924–7. [5] Gau H, Herminghaus S, Lenz P, Lipowsky R. Liquid morphologies on structured surfaces: from microchannels to microchips. Science 1999;283:46–9. [6] Sun T, Wang G, Liu H, Feng L, Jiang L, Zhu D. Control over the wettability of an aligned carbon nanotube film. J Am Chem Soc 2004;125:14996–7. [7] Gao X, Jiang L. Biophysics: water-repellent legs of water striders. Nature 2004;432:36. [8] Sun T, Feng L, Gao X, Jiang L. Bioinspired surfaces with special wettability. Acc Chem Res 2005;38:644–52. [9] Wang L, Lin S, Lin K, Yin C, Liang D, Di Y, et al. A facile synthesis of highly ordered mesoporous carbon monolith with mechanically stable mesostructure and superior conductivity from SBA-15 powder. Micropor Mesopor Mater 2005;85:136–42.

Synthesis of carbon nanotubes from solid carbon sources by direct microwave irradiation Dong-Myung Yoon a, Beom-Jin Yoon a, Kun-Hong Lee Hyung Seok Kim b, Chan Gyung Park b a

b

a,*

,

Department of Chemical Engineering, Electrical and Computer Division, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, Nam-Gu, Pohang, Kyungbuk 790-784, Republic of Korea Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, Nam-Gu, Pohang, Kyungbuk 790-784, Republic of Korea Received 20 September 2005; accepted 2 December 2005 Available online 19 January 2006

Keywords: Carbon nanotubes; Carbon composites; Microstructure

Carbon nanotubes (CNTs) have been synthesized from different carbon sources. Hydrocarbon vapors have been the dominant choice of carbon source, mainly because of the powerful synthesis technique of chemical vapor deposition (CVD) [1]. The hydrogen in the hydrocarbon sources

*

Corresponding author. Fax: +82 54 279 8298. E-mail address: [email protected] (K.-H. Lee).

0008-6223/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.12.008

inhibits the formation of amorphous carbons, resulting in clean CNTs which do not require post cleaning treatments. Liquid hydrocarbons could also be converted to CNTs through catalytic decomposition [2], arc discharge [3], and sonochemical method. Solid carbons—mainly graphite—were initially used to synthesize CNTs in arcdischarge or in laser ablation. Non-violent techniques to transform solid carbon sources into CNTs have also been investigated. Thermal heating