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method. Although this technique is still in its initial stages of development, it holds promise for increasing the applications of amorphous carbon ﬁlms. Acknowledgements The authors are thankful to Profs. Y. Gogotsi and K. Byrappa for their helpful discussion, and to Drs. T. Fujiwara, R. Teranishi and T. Fujino for their help in this work. Financial support from Kagawa Science and Technology Forum is acknowledged very much. References
Fig. 3. Micro-Raman spectrum of the patterned carbon ﬁlms on a silicon wafer.
advantages include (a) single-step fabrication without the need for masking and etching, (b) operation at room temperature and under atmospheric pressure without any complicated vacuum systems, and (c) a high production rate of about several hundred micrometers per minute. Our method oﬀers these remarkable features for the conventional photolithographic method; however, it has the disadvantage of low resolution. Therefore, it is still diﬃcult for this method to replace the lithograph method immediately. On the other hand, this method also has the potential to enable the production of new types of adhesives with high thermal stability, chemical stability, and suﬃcient strength to adhere hard particles, such as diamond particles, onto conductive substrates. This feature can be observed by applying this method to ethanol/diamond particle suspensions. These new applications do not require a high resolution; thus, this method is more realistic in terms of actual application. In the future, these results will be reported as one of the applications of this direct patterning
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Ordered mesoporous carbon particles covered with carbon nanotubes Fabing Su a, Xu Li b, Lu Lv a, X.S. Zhao a
Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore b Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore Received 26 September 2005; accepted 31 October 2005 Available online 1 December 2005
Keywords: Porous carbon; Carbon nanotubes; Chemical vapor deposition; Microstructure
Corresponding author. Tel.: +65 6874 4727; fax: +65 6779 1936. E-mail address: [email protected]
0008-6223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.10.056
The discovery of a variety of carbon nanostructures has signiﬁcantly advanced the science and engineering of
Letters to the Editor / Carbon 44 (2006) 799–823
carbon materials. Carbon nanotubes (CNTs) exhibit unique electronic, mechanical, and chemical properties, which make them attractive for a wide range of novel applications . With the rapidly growing demands of applications in energy storage, such as fuel cells, lithium-ion batteries, and capacitors, nanostructured carbons used as electrodes with tailorable structural, morphological, and surface properties are highly desirable. Recently, template synthesis has been widely employed to prepare various porous carbons. In particular, ordered mesoporous carbons (OMC) replicated from ordered mesoporous silicas have been studied extensively in developing novel nanostructured carbons with unique properties, such as controllable pore size, high surface area, and tailorable surface properties . Herein, we describe the preparation of an interesting carbon nanostructure, namely ordered OMC covered with CNTs (designed as OMC/CNT). One of the most prominent advantages of such hybrid carbon is the improvement of electronic conductivity compared with ordered OMCs without carbon nanobutes (CNTs) covered. The CNTs on the external surface of the OMC were found to form an interconnected network, which facilitates electron transport between the OMC particles. The hybrid materials are thus potentially useful for application as electrode materials. The idea is to use ordered mesoporous silica SBA-15 as the template to create OMC and a catalyst supported on the template particle surface to grow CNTs. First, 0.5 g of solid SBA-15, which was prepared following the method as described previously , was mixed with 0.2 g of nickel nitrate hexahydrate dissolved in 3 ml deionized water. The mixture was sonicated for 30 min, dried in air at 120 C for 3 h followed by calcination at 500 C for 3 h to obtain a SBA-15-supported nickel catalyst. Carbon deposition was carried out using the chemical vapor deposition (CVD) method with benzene as the carbon precursor at 900 C for 2 h . The black sample thus obtained was
treated with 20% HF solution, followed by 6 M HNO3 solution. Finally, the solid was washed with water and dried in air at 150 C for 5 h to obtain the resultant carbon sample OMC/CNT. Fig. 1(a) shows the SEM image of the SBA-15 template, which is built up with bundles of bamboo-shaped primary particles with diameters in the range of 300–500 nm. The carbon sample prepared from the template (see Fig. 1(b)) is not only composed of bamboo-shaped primary particles  but also a large number of CNTs covering the surfaces of the primary carbon particles. Some white dots (residual nickel particles) on the tips of nanotubes are also seen, indicating the tip-growth model of the CNTs . TEM image shown in Fig. 1(c) shows the presence of many curved CNTs with diﬀerent diameters grown on the external surface of templated carbon. The TEM image of the carbon sample shown in Fig. 1(d) exhibits highly ordered arrays of pore channels constructed from carbon nanorods replicated from the channels of SBA-15. The interplanar distance of the arrays was estimated to be around 10 nm. Fig. 1(d) also reveals the presence of nickel particles with several tens of nanometers in size on the external surface of the carbon while some less than the channel size of SBA-15 are embedded into the carbon nanorods presumably due to the conﬁnement of pore space of template SBA-15 [6,7], suggesting the presence of nickel residue after acid washing. The content of nickel in OMC/CNT was estimated to be about 3.6 wt.% according to energy dispersion X-ray spectroscope (EDX) analysis. Fig. 1(e) clearly shows that the CNTs have an external diameter of around 20– 50 nm and an inner diameter of about several nanometers, which is closely related to the particle size of the nickel catalyst . Importantly, these CNTs interconnect the ordered mesoporous carbon particles, thus facilitating electron transport in electrochemical applications. Fig. 1(f) shows the fringe-lattice of a CNT with multi-walls and an inner diameter of about 7 nm. The graphene layers are parallel to the axis of the CNTs, which is diﬀerent from the amor-
Fig. 1. SEM images of (a) SBA-15 and (b) OMC/CNT and (c)–(f) TEM images of OMC/CNT observed at diﬀerent magniﬁcations.
10 100 Pore size (nm)
1.0 1.5 2.0 2.5 2Theta (Degree) +o
(**) C (+) Ni (o) Ni3C Intensity
Volume ads. (cm3/g, STP)
Letters to the Editor / Carbon 44 (2006) 799–823
0.2 0.4 0.6 0.8 Relative pressure (P/P0)
+ OMC/CNT +
40 50 60 70 2Theta (Degree)
Fig. 2. (a) N2 adsorption–desorption isotherms and BJH–PSD curves (inset) of SBA-15 and OMC/CNT (for clarity, the isotherm of SBA-15 was vertically shifted for 100 cm3/g); (b) XRD pattern of OMC/CNT, together with SAXS patterns (inset) of SBA-15 and OMC/CNT.
phous CNTs prepared with an iron catalyst supported on SBA-15 as template . Fig. 2(a) shows the N2 adsorption–desorption isotherms of the SBA-15 and OMC/CNT samples, showing the mesoporous structure of the SBA-15 template and the OMC/ CNT sample because of their type IV isotherms with an H1 and H2 hysteresis loops, respectively. The pore size distribution (PSD) curves derived from the Barrett–Joyner– Halenda (BJH) method using the adsorption branches are shown in the inset of Fig. 2(a). The pore sizes of template SBA-15 and carbon OMC/CNT estimated from the maximum positions of the BJH–PSD curves are 7.9 and 3.9 nm, respectively. The speciﬁc surface areas of the template and carbon OMC/CNT determined according to the Brunauer–Emmett–Teller (BET) method are 720 and 462 m2/g, respectively, while the total pore volumes obtained from the volume of nitrogen adsorbed at the relative pressure of 0.99 are 1.0 and 0.67 cm3/g, respectively. The XRD pattern of carbon OMC/CNT depicted in Fig. 2(b) shows a strong diﬀraction peak at about 26.0 and a small peak at 42.6 two theta, corresponding to (0 0 2) and (1 0 0) diﬀractions of graphitic carbon, respectively . The three peaks at 44.5, 51.9 and 76.5 two theta, corresponding to (1 1 1), (2 0 0) and (2 2 0) reﬂections respectively, can be indexed to a face-centered cubic (fcc) structure of nickel (JCPDS ﬁle No. 4-485), further demonstrating the presence of residual nickel in OMC/CNT. The small peak at 39.8 two theta ((1 0 0) reﬂection) together with the (1 0 1) reﬂection peak at 44.6 two theta implies the presence of Ni3C phase . It is noted that the peak at about 44.5 is due to diﬀerent diﬀractions of the (1 0 1) reﬂection of graphitic carbon, the (1 1 1) reﬂection of Ni metal and the (1 0 1) reﬂection of Ni3C phase. The smallangle X-ray scattering (SAXS) patterns of the template and OMC/CNT presented as the inset of Fig. 2(b) display three well-resolved (1 0 0), (1 1 0), and (2 0 0) peaks, demonstrating the presence of ordered two-dimensional hexagonal pore arrays in the SBA-15 template and the OMC/ CNT sample . The interplanar distance d100 of sample OMC/CNT was estimated to be 10.0 nm, consistent with the TEM observations (see Fig. 1(d)).
In summary, the synthesis of nanocarbon materials consisted of ordered mesoporous carbon covered with carbon nanotubes using nickel supported on SBA-15 as template is demonstrated. The presence of carbon nanotubes on the external surface of ordered mesoporous carbon can improve the electronic conductivity of the carbon materials because of the formation of interconnected network of CNTs, which facilities electron transport between the ordered mesoporous carbon particles. The nanostructured carbon material described in this work may ﬁnd applications in electrochemical energy conversion and storage. Acknowledgement We thank NUS for ﬁnancial support (Grant Number R279000183112). References  Baughman RH, Zakhidov AA, de Heer WA. Carbon nanotubes—the route toward applications. Science 2002;297:787–92.  Ryoo R, Joo SH, Kruk M, Jaroniec M. Ordered mesoporous carbons. Adv Mater 2001;13:677–81.  Zhao D, Huo Q, Feng J, Chmelka BF, Stucky GD. Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures. J Am Chem Soc 1998;120:6024–36.  Su F, Zeng J, Bao XY, Yu Y, Lee JY, Zhao XS. Synthesis and characterization of highly ordered graphitic mesoporous carbon as a Pt catalyst support for direct methanol fuel cells. Chem Mater 2005;17:3960–7.  Otsuka K, Abe Y, Kanai N, Kobayashi Y, Takenaka S, Tanabe E. Synthesis of carbon nanotubes on Ni/carbon-ﬁber catalysts under mild conditions. Carbon 2004;42:727–36.  Lu A-H, Schmidt W, Tatar S-D, Spliethoﬀ B, Popp J, Kiefer W, et al. Formation of amorphous carbon nanotubes on ordered mesoporous silica support. Carbon 2005;43:1811–4.  Lee J, Jin S, Hwang Y, Park J-G, Park HM, Hyeon T. Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods. Carbon 2005;43:2536–43.  Bououdina M, Grant D, Walker G. Eﬀect of processing conditions on unsupported Ni-based catalysts for graphitic-nanoﬁbre formation. Carbon 2005;43:1286–92.