carbons

carbons

Letters to the Editor / Carbon 44 (2006) 1581–1616 Acknowledgment The work is financially supported by the Natural Science Foundation of China (202760...

346KB Sizes 3 Downloads 20 Views

Letters to the Editor / Carbon 44 (2006) 1581–1616

Acknowledgment The work is financially supported by the Natural Science Foundation of China (20276078, 90210034, 20503038), the Shanxi Natural Science and Chinese Academy of Sciences. References [1] Vergunst Th, Linders MJG, Kapteijn F, Moulijn JA. Carbon-based monolithic structures. Catal Rev-Sci Eng 2001;43(3):291–314. [2] Alcanˇiz-Monge J, Blanco C, Linares-Solano A, Brydson R, Rand B. Development of new carbon honeycomb structures from cellulose and pitch. Carbon 2002;40:541–50. [3] Garcı´a-Bordeje´ E, Kapteijn F, Moulijn JA. Preparation and characterization of carbon-coated monoliths for catalyst supports. Carbon 2002;40:1079–88. [4] Yates M, Blanco J, Martin-Luengo MA, Martin MP. Vapor adsorption capacity of controlled porosity honeycomb monoliths. Micropor Mesopor Mater 2003;65:219–31. [5] Wang Y, Huang Z, Liu Z, Liu Q. A novel activated carbon honeycomb catalyst for simultaneous SO2 and NO removal at low temperatures. Carbon 2004;42:423–60.

1601

[6] Lozano-Castello´ D, Cazorla-Amoro´s D, Linares-Solano A, Quinn DF. Activated carbon monoliths for methane storage: influence of binder. Carbon 2002;40:2817–25. [7] Tennison SR. Phenolic resin-derived activated carbons. Appl Catal A Gen 1998;173:289–311. [8] Gadkaree KP, Jaroniec M. Pore structure development in activated carbon honeycombs. Carbon 2000;38:983–93. [9] Mochida I, Korai Y, Ku C, Watanabe F, Sakai Y. Chemistry of synthesis, structure, preparation and application of aromatic-derived mesophase pitch. Carbon 2000;38:305–28. [10] Yamada I, Imamura T, Kakiyama H, Honda H, Oi S, Fukuda K. Characteristics of meso-carbon microbeads separated from pitch. Carbon 1974;12:307–19. [11] Liu Z, Liu L, Liu P, Liu Z, Niu H. A method of activated carbon honeycombs made from coal. CN patent 200410092429, 2004. [12] Yates M, Blanco J, Avila P, Martin MP. Honeycomb monoliths of activated carbons for effuent gas purification. Micropor Mesopor Mater 2000;37:201–8. [13] Valde´s-Solı´s T, Marba´n G, Fuertes AB. Preparation of microporous carbon-ceramic cellular monoliths. Micropor Mesopor Mater 2001;43:113–26. [14] Gadkaree KP. Carbon honeycomb structures for adsorption applications. Carbon 1998;36:981–9.

Easy synthesis and supercapacities of highly ordered mesoporous polyacenes/carbons Liang Zhou, Huiqiao Li, Chengzhong Yu *, Xufeng Zhou, Jiawei Tang, Yan Meng, Yongyao Xia, Dongyuan Zhao Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Han Dan Road 220, Shanghai 200433, PR China Received 7 June 2005; accepted 15 February 2006 Available online 15 March 2006

Keywords: Porous carbon; Pyrolysis; Electrochemical property

Ordered mesoporous carbons with high surface area and large pore volume have attracted much attention for their potential applications in catalyst supporters [1], absorbents [2], electrode materials [3], and templates [4]. Polyacenes [5] are usually prepared by the pyrolysis of phenol formaldehyde (PF) resin at relatively low temperatures. At higher pyrolysis temperatures, the composition and the property of final compounds are similar to those of normal carbon materials. Here, we report the synthesis of highly ordered mesoporous polyacenes/carbons via a facile one-step nanocasting process by using KIT-6 [6] as the hard template and a commercially available PF resin (Mw = 4500) as the pre-

*

Corresponding author. Tel.: +86 21 6564 2065; fax: +86 21 65641740. E-mail address: [email protected] (C. Yu).

0008-6223/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.02.025

cursor without any catalysts. The synthesis procedures include impregnation, solidification (130 C for one day), pyrolysis at different temperatures for 5 h in N2 atmosphere and the template removal process using HF. The resultant mesoporous polyacenes/carbons are designated as P-X-Y, where P represents polyacenes/carbons, X is the loading amount of PF resin per gram of silica template, and Y is the pyrolysis temperature. The X-ray diffraction (XRD) patterns of KIT-6, polyacene/silica composite and the corresponding mesoporous material P-1.0-580 are shown in Fig. 1A. P-1.0-580 shows an XRD pattern similar to KIT-6 and five well resolved peaks are observed, indicating that the product is a faithful replica of KIT-6. The XRD patterns of the products prepared at different conditions are shown in Fig. 1B–D for comparison. Interestingly, samples prepared at 580 C

1602

Letters to the Editor / Carbon 44 (2006) 1581–1616

with different loading amounts (X = 0.5, 1.0, 1.5, 2.0) show similar XRD patterns (Fig. 1B), suggesting that highly ordered mesoporous polyacenes/carbons with an Ia-3d mesostructure can be obtained in a wide region of loading amounts. For a constant loading amount (X = 1), the pyrolysis temperature was varied from 580 to 950 C. P1.0-580 and P-1.0-780 are faithful replicas of KIT-6 with the symmetry of Ia-3d. However, for P-1.0-950, an additional peak at 2h = 0.64 is observed, which can be indexed to the 1 1 0 peak of an I41/a space group [7]. At the same high pyrolysis temperature of 950 C, lowing the loading amount (X = 0.5) may also lead to mesoporous polyacenes with an I41/a symmetry, however, when X P 1.5, the product P-1.5-950 show the XRD pattern with a typical Ia-3d mesostructure (Fig. 1D). It can be concluded that the samples prepared at relatively high pyrolysis temperature (950 C) with a relatively low loading amount (X 6 1.0) may undergo an obvious structural transformation from Ia-3d to I41/a symmetry. The highly ordered mesostructure can be confirmed in transmission electron microscopy (TEM) studies. Interestingly, ordered mesoporous polyacenes/carbons with both Ia-3d (Fig. 2(A)) and I41/a symmetry (Fig. 2(B)) can be observed in the TEM images for sample P-1.5-580; however, the latter is the minor phase compared to the Ia-3d symmetry. This is also in accordance with the XRD results: no evidence of symmetry transformation is reflected in the XRD pattern of sample P-1.5-580 (Fig. 1B(c)).

N2 sorption analysis is also conducted and the results are summarized in Table 1. Generally, the BET surface area and the total pore volume increases slightly as the decreases of the loading amount. As the pyrolysis temperature varies, the BET surface area and the total pore volume shows only small differences. The sorption isotherms and pore size distribution for P-2.0-580, P-1.0-580 and P-1.0950 are shown in Fig. 3. P-2.0-580 has a typical monomodal pore system centered at 3.9 nm. However, P-1.0-580 and P-1.0-950 show quite different sorption isotherms with two hysteresis loops, which indicate the existence of a bimodal pore system. Moreover, P-1.0-950 showed a more pronounced bimodal pore size distribution. It can be concluded that high pyrolysis temperature and low loading amount may favor the formation of the bimodal pore system. The polymer nature of PF resin precursor is very important for the structure transformation and the formation of the bimodal pore system. The PF resin macromolecules may enter large pores preferentially (referred to as macromolecular effect). Additionally, the PF resin macromolecules have very strong interactions with each other. When they are incorporated into the pores of the hard template, a partial-filling effect may generate: a fraction of the silica porosity is completely filled with PF resin; while the other remains empty. A proposed mechanism is schematically shown in Fig. 4. When the loading amount is low, the macromolecular effect may lead to preferential loading of the resin precursor into

Fig. 1. XRD patterns of A: (a) the KIT-6 hard template, (b) polyacene/silica composite and (c) P-1.0-580; B: (a) P-0.5-580, (b) P-1.0-580, (c) P-1.5-580 and (d) P-2.0-580; C: (a) P-1.0-580, (b) P-1.0-780 and (c) P-1.0-950; and D:(a) P-0.5-950, (b) P-1.0-950 and (c) P-1.5-950.

Letters to the Editor / Carbon 44 (2006) 1581–1616

1603

Fig. 2. TEM images of ordered mesoporous material P-1.5-580 recorded along the (1 1 1) directions of an (A) Ia-3d space group; (B) I41/a space group.

Table 1 The surface area (S), total pore volume (V) and pore size (D) for all mesoporous products Sample

S (m2/g)

V (cm3/g)

D (nm)

P-0.5-580 P-1.0-580 P-1.5-580 P-2.0-580 P-1.0-780 P-0.5-950 P-1.0-950 P-1.5-950

1100 1000 950 770 1050 1150 1000 900

1.22 1.28 0.96 0.83 1.07 1.21 1.18 1.09

3.4 3.4 3.9 3.9 3.7 3.3 3.4 3.9

the primary pores rather than the complementary pores [8]. Since a majority of the complementary pores of KIT-6 are not filled (Fig. 4(a)), subsequent removing of silica may result in symmetry transformation due to the elimination of the linkers between two enantiomeric rods. Moreover, the partial-filling effect may result in discontinuous filling of the channels (Fig. 4(a)), leading to the bimodal pore distribution. With the increasing of the loading amount, the complementary pores are gradually fully filled and the partial-filling effect also becomes less distinct (Fig. 4(c)). Finally, faithful replications with the symmetry of Ia-3d and monomodal pore system are obtained (Fig. 4(d)). The

Fig. 4. Schematically drawing of the proposed mechanism for the structural transformation and formation of a bimodal pore system in ordered mesoporous polyacenes/carbons. For mesoporous silica KIT-6 with both primary and complementary pores, a low resin/silica ratio may lead to preferential and discontinuous loading of PF macromolecules into primary pores (a); removing of silica may give rise to a structural transformation and a bimodal pore size distribution (b). At high loading ratio, both the primary and the complementary pores are filled fully (c), leading to faithfully replicated mesoporous polyacenes with a monomodal pore system (d).

Fig. 3. (A) N2 sorption isotherms and (B) pore size distribution curves for (a) P-2.0-580, (b) P-1.0-580, and (c) P-1.0-950, respectively.

1604

Letters to the Editor / Carbon 44 (2006) 1581–1616

above mechanism may also explain the influence of pyrolysis temperature. Increasing the pyrolysis temperature may destroy more complementary linkers and favor the partial-filling effect since the condensation and aggregation of PF resin may be more pronounced at high temperatures. Therefore, when compared P-K-1.0-950 with P-K-1.0-580, the former material shows more apparent bimodal pore size distribution and a deformed symmetry of I41/a. Cycle voltammetry (CV) measurements have been conducted to investigate the electrochemical properties of the products. For samples prepared at different temperatures with the same loading amount (X = 1), P-1.0-780 exhibits the highest capacitance of 127 F/g, while P-1.0-580 and P-1.0-950 has a lower capacitance of 87 and 93 F/g, respectively. For P-1.0-780, the CV curves remain the rectangular shape even when the scan rate is increased to 40 mV/s. It is also important to note that at such a fast scan rate, the capacity has a loss less than 5% of that obtained at a scan rate of 5 mV/s, indicating a good rate capability and power ability. In summary, highly ordered mesoporous polyacenes/ carbons have been synthesized successfully via a simple nanocasting process. The influences of the loading amount and the pyrolysis temperature on the structure and the capacitance of the products have been studied. CV measurements show that the products have good capacitive behaviors and high specific capacitances (up to 127 F/g). Such materials are good candidates for the fabrication of electrochemical double-layer capacitors.

Acknowledgements This work was financially supported by the National Science Foundations of China (20301004 and 20421303), State key research program (2004CB217800) and Shanghai Science Committee (0352nm108, 04JC1408F and 03QF14002). References [1] Joo SH, Choi SJ, Oh I, Kwak J, Liu Z, Terasaki O, et al. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001;412:169–72. [2] Hartmann M, Vinu A, Chandrasekar G. Adsorption of vitamin E on mesoporous carbon molecular sieves. Chem Mater 2005;17:829–33. [3] Zhou HS, Zhu SM, Hibino M, Honma I, Ichihara M. Lithium storage in ordered mesoporous carbon (CMK-3) with high reversible specific energy capacity and good cycling performance. Adv Mater 2003;15: 2107–11. [4] Lu AH, Schmidt W, Taguchi A, Spliethoff B, Tesche B, Schuth F. Taking nanocasting one step further: replicating CMK-3 as a silica material. Angew Chem Int Ed 2002;41:3489–92. [5] Yata S, Okamoto E, Satake H, Kubota H, Fujii M, Taguchi T, et al. Polyacene capacitors. J Power Sources 1996;60:207–12. [6] Kleitz F, Choi SH, Ryoo R. Cubic Ia3d large mesoporous silica: synthesis and replication to platinum nanowires, carbon nanorods and carbon nanotubes. Chem Commun 2003:2136–46. [7] Ryoo R, Joo SH, Jun S. Synthesis of highly ordered carbon molecular sieves via template-mediated structural transformation. J Phys Chem B 1999;103:7743–6. [8] Sakamoto Y, Kim TW, Ryoo R, Terasaki O. Three-dimensional structure of large-pore mesoporous cubic Ia3d silica with complementary pores and its carbon replica by electron crystallography. Angew Chem Int Ed 2004;43:5231–4.

Novel catalyst particle production method for CVD growth of single- and double-walled carbon nanotubes Paula Queipo a, Albert G. Nasibulin a, David Gonzalez a, Unto Tapper b, Hua Jiang b, Taku Tsuneta c, Kestas Grigoras d, Jose A. Duen˜as e, Esko I. Kauppinen a,b,* a

d

NanoMaterials Group, Laboratory of Physics and Center for New Materials Helsinki University of Technology, P.O. Box 1000, FIN-02044 VTT Espoo, Finland b VTT Processes P.O. Box 1000, FIN-02044 VTT Espoo, Finland c Low Temperature Laboratory, Helsinki University of Technology P.O. Box 2200, FIN-02015 HUT Espoo, Finland Microelectronics Centre, Micronova, Helsinki University of Technology, P.O. Box 3500, FIN-02015 HUT Espoo, Finland e Department of Physics and Astronomy, The Queen’s University of Belfast, BT7 1NN Belfast, UK Received 24 October 2005; accepted 20 February 2006 Available online 15 March 2006

Keywords: Carbon nanotubes; Chemical vapor deposition; Transmission electron microscopy; Scanning electron microscopy; Particle size

*

Corresponding author. Address: NanoMaterials Group, Laboratory of Physics and Center for New Materials Helsinki University of Technology, P.O. Box 1000, FIN-02044 VTT Espoo, Finland. Tel.: +358 20 722 6165; fax: +358 20 722 7021. E-mail address: [email protected]fi (E.I. Kauppinen). 0008-6223/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.02.027