Mesoporous Carbon Composite

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J. Phys. Chem. C 2007, 111, 18073-18077

18073

Poly(3,4-ethylenedioxythiophene)/Mesoporous Carbon Composite Jiacheng Wang,†,‡ Xiaofeng Yu,†,‡ Yongxiang Li,† and Qian Liu*,† State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, 1295 Dingxi Road, Shanghai 200050, P. R. China, and Graduate School of the Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100039, P. R. China ReceiVed: June 25, 2007; In Final Form: August 27, 2007

A new type of organic-inorganic poly(3,4-ethylenedioxythiophene) PEDOT/mesoporous carbon composite was first synthesized by a simple in situ polymerization of 3,4-ethylenedioxythiophene monomer within the mesopores and on the particle surface of CMK-3. The composition, morphology, and structure of the composite were investigated by thermal analysis, X-ray photoelectron spectroscopy (XPS), electron microscopy, X-ray diffraction, and FT-IR. The composite contained 67.3 wt % of PEDOT and 32.2 wt % of CMK-3 carbon after the mass of the physically adsorbed water was subtracted. Electron microscopy (SEM and TEM) images clearly showed that PEDOT polymer was equally deposited on the surface of CMK-3 nanoparticles. SEM images also displayed the morphological similarity to the support CMK-3 carbon except for the bigger size of the nanoparticles in the composite due to the coverage of polymer PEDOT on the support CMK-3 carbon. FT-IR and XPS analysis showed that PEDOT had been prepared in the resultant composite. The performance of this interesting composite is being investigated.

Introduction Since the discovery of ordered mesoporous carbons,1 growing attention has been focused on their potential applications in catalysts supports, electrode materials, adsorption, fuel cells, gas storage, electromagnetic shielding material, and hard templates for other ordered mesoporous inorganic materials. Mesoporous carbons are of particular interest because of their remarkable properties, such as good mechanical stability, high specific surface area, large pore volume, and adjustable pore size contribution. Joo et al. synthesized ordered mesoporous carbon CMK-5 and Pt nanoparticle-loaded mesoporous catalysts.2 A Ä lvarez and his co-workers reported the electrochemical capacitor performance of CMK-3 carbon.3 A new kind of composite nanostructure between polyaniline and CMK-3 templated from SBA-15 was prepared for use as highperformance electrochemical capacitors.4 Zhou carefully investigated the adsorption capacity of CMK-3 carbon for different gases.5 Furthermore, CMK-3 was also used as solid template to prepare other inorganic mesoporous materials, such as CuO, SiO2, CNX, MgO, etc.6 CMK-3 carbon has particular nanostructure and good electronic conductivity. Thus, it can be used as the additives to fabricate various CMK-3 carbon-containing composite. Till now, research studies on CMK-3 carbon-filled composites have been few. A novel ordered mesoporous carbon (CMK-3)/fused silica composite ceramic has been prepared by us, and it displayed excellent electromagnetic interference shielding efficiency in the X-band.7 In this paper, a kind of novel organic-inorganic poly(3,4-ethylenedioxythiophene)/mesoporous carbon composite, was prepared via a simple in situ polymerization process. Poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives * Author to whom correspondence should be addressed. E-mail: [email protected]; fax: (+86) 21 5241 3122; tel (+86) 21 5241 2612. † Shanghai Institute of Ceramics. ‡ Graduate School of the Chinese Academy of Sciences.

Figure 1. The schematic synthesis process of the PEPOT/mesoporous carbon composite.

have been at the forefront of field-conducting polymers for more than 10 years.8 Peng et al. synthesized PEDOT/carbon nanotube composites via an electrochemical polymerization method.9 A new organic-inorganic poly(3,4-ethylenedioxythiophene)/V2O5 nanocomposite was prepared by Vadivel Murugan.10a Arbizzani made the Li1.03Mn1.97O4/PEDOT composite via a chemical polymerization method and investigated its electrochemical property.10b However, the composite of conductive CMK-3 carbon with a specific nanostructure and PEDOT has not been found. Thus, there is need for developing a new-style composite based on CMK-3 mesoporous carbon and PEDOT. At present, we combined CMK-3 carbon with the polymer PEDOT via in situ polymerization to first form a kind of novel PEDOT/mesoporous carbon composite. The synthetic process is illustrated in Figure 1. The carbon nanowires composed of CMK-3 carbon are uniformly dispersed in the organic polymer PEDOT. CMK-3 is also a mesoporous support to load PEDOT during the synthetic process of the composite. When CMK-3 with high specific surface area was added into the solution mixture of EDOT monomer and H2SO4, EDOT monomer can be adsorbed inside the pores and around the particles of CMK3. After ammonium persulfate solution was added slowly to the above solution, EDOT gradually polymerized and deposited on the particle surface or within the mesopores of CMK-3 carbon as shown in Figure 1. The composition, morphology, and structure of the composite were investigated by thermal analysis, electron microscopy, X-ray diffraction, and FT-IR.

10.1021/jp0749468 CCC: $37.00 © 2007 American Chemical Society Published on Web 11/20/2007

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Figure 2. N2 sorption isotherms of CMK-3 and PEDOT/mesoporous carbon composite.

Figure 3. TG-DTA-DTG curves of PEDOT/mesoporous carbon composite in the air flow.

TABLE 1: TG Results from the PEDOT/Mesoporous Carbon Composite

200 °C for 4 h. The surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The pore size distribution curves were calculated from the analysis of the desorption branch of the isotherm using the Barrett-JoynerHalenda (BJH) algorithm. Scanning electron microscopy (SEM) images were recorded using a JEOL JXA-8100 scanning electron microanalyzer. Samples were mounted using a conductive carbon double-sided sticky tape. A thin (ca. 10 nm) coating of gold sputter was deposited onto the samples to reduce the effects of charging. Transmission electron microscopy (TEM) images were recorded on a JEOL 2010 CX electron microscope operating at 200 kV. Samples for analysis were prepared by spreading them on a holey carbon film supported on a grid. Thermogravimetry (TG) and differential thermal analysis (DTA) of the sample was carried out on a thermal analyzer (STA 449/ C, Netzsch) in an air flow. The sample was placed in the cell and then heated at a rate of 10 °C/min. Infrared spectroscopic investigation was carried out on a Bruker Vector 22 spectrometer using the KBr pellet method.

composite

40-180 °C (wt %)

180-470 °C (wt %)

470-650 °C (wt %)

residual mass (wt %)

8.6

61.5

29.4

0.5

Experimental Section Materials Synthesis. Ordered mesoporous carbon CMK-3 was synthesized as reported previously, and SBA-15 silica was used as the solid template.1b Specifically, 1 g of SBA-1511 was mixed with 5 mL of aqueous solution containing 1.25 g of sucrose and 0.14 g of H2SO4. The resulting slurry was placed in an oven at 80 °C for 6 h and then 160 °C for another 6 h. In order to obtain fully polymerized and carbonized sucrose inside the pores of the silica SBA-15 template, 0.8 g of sucrose, 0.09 g of H2SO4, and 5 g of water were again added to the pretreated sample, and the mixture was again subjected to the thermal treatment described above. Then the carbonization was completed by pyrolysis at 900 °C under N2 flow. Ordered mesoporous carbon CMK-3 was obtained by removing the silica template using 5 wt % hydrofluoric acid solution at room temperature. The chemical polymerization of 3, 4-ethylenedioxythiophene (EDOT) on the surface of mesoporous carbon was performed with ammonium persulfate as an oxidant. A typical synthesis procedure was as follows. Ordered mesoporous carbon was thermally treated at 100 °C in a vacuum oven to remove the physically adsorbed water, and then 0.5 g of ordered mesoporous carbon was finely quantified. Subsequently, it was immersed in methanol/water solution (200 mL, 50%) containing 1.2 g of 3, 4-ethylenedioxythiophene (EDOT monomer) and 10 g of H2SO4 while being stirred for 1 h. Then, 50 mL of solution containing 0.4 g of ammonium persulfate was slowly added dropwise into the above solution with magnetically stirring at a reaction temperature of 0-5 °C. The reaction mixture was stirred for an additional 4 h at 0-5 °C, after which the black product of the reaction was filtered and washed repeatedly with deionized water and methanol. The resulting polymer/mesoporous carbon composite was dried under vacuum at 80 °C for 12 h to absolutely remove the physically adsorbed water. Materials Characterization. Powder X-ray diffraction (XRD) analysis was performed using a Rigaku D/MAX-λ B instrument with Cu KR radiation (40 kV, 60 mA). Nitrogen sorption characterization of the materials was measured on a Micromeritics ASAP2010 surface area and pore size analyzer at liquid nitrogen temperature (-196 °C). Prior to measurement, the sample was dehydrated at 100 °C for 1 h and then degassed at

Results and Discussion It is well-known that CMK-3 carbon derived from SBA-15 is composed of hexagonally ordered carbon nanowire arrays, and the nitrogen sorption analysis in Figure 2 indicates that CMK-3 carbon we prepared here exhibits a type IV isotherm, implying a very narrow pore size distribution with uniform mesopores.1b The synthesized mesoporous carbon CMK-3 had a high surface area of 1105 m2/g. After PEDOT grew on the surface of mesoporous carbon CMK-3 to form the PEDOT/ mesoporous carbon composite, this composite hardly absorbed N2 under the entire pressure (P/P0) range 0-1.0 as shown in Figure 2. The surface area of the PEDOT/mesoporous carbon calculated from the isotherm is only 5 m2/g which is extremely lower than that of the pure mesoporous carbon CMK-3. The sharp reduction of the surface area obviously indicates that some PEDOT completely filled the mesopores of CMK-3. Thus, the synthesized PEDOT/mesoporous carbon composite has a kind of special nanostructure, i.e., the carbon nanowire arrays dispersed uniformly into the particles of PEDOT as shown in Figure 1. This largely increases the contact area between CMK-3 carbon and PEDOT, and according the calculated surface areas from the nitrogen sorption analysis of CMK-3 and the PEDOT/ mesoporous carbon composite, it appears that the contact area of CMK-3 carbon and PEDOT is about 1100 m2/g, which will be in favor of electrochemical capacitance performance of the PEDOT/mesoporous carbon composite. At the same time, such an interesting PEDOT/mesoporous composite with ordered

PEDOT/Mesoporous Carbon Composite

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Figure 4. SEM images of (a) mesoporous carbon and (b) PEDOT/mesoporous carbon composite.

nanostructure can facilitate ionic motion compared with conventional mesoporous materials, in which the mesopores are randomly connected.12 In order to confirm the PEDOT content in the composite, the thermal analysis of the PEDOT/mesoporous carbon composite in air flow was investigated with TG-DTA measurements. Figure 3 shows the TG-DTA curves of the PEDOT/mesoporous carbon composite. There are three major stages of weight loss in the TG curve. However, it is difficult to finely distinguish the three weight losses, so the DTG curve is conducted according to the TG curve by differential. The results of three weight losses derived from the DTG curve are summarized in Table 1. The first weight loss is ∼8.6 wt % occurring below 180 °C, which results from the physical loss of water. It indicates a hydrophilic surface property of the PEDOT/mesoporous carbon composite. At the same time, the DTA curve shows an evident endothermic peak with a maximum located at ∼95 °C. The temperature range fits well with that of the first stage of weight loss in the TG curve. The second huge weight loss of ∼61.5 wt % with an exothermic peak at ∼337 °C in the DTA curve is between 180 and 470 °C, which is mainly due to the thermal decomposition of PEDOT in air. The third stage between 470 and 650 °C with a weight loss of about 29.4 wt % is ascribed to the combustion of CMK-3 carbon in air.13 Accordingly, there is a clear exothermic peak with a maximum at ∼597 °C in the TG curve. At 650 °C, the residual mass is ∼0.5 wt %, which is mainly attributed to the possible SiO2 residue from SBA-15 template for CMK-3 carbon. It also implies that the template SBA-15 for CMK-3 mesoporous carbon was almost completely removed by HF solution. So, according to the results of TG-DTA analysis, it is clear that the synthesized PEDOT/mesoporous carbon composite contains 61.5 wt % of the PEDOT, 29.4 wt % of the CMK-3 carbon, 8.6 wt % of the physically adsorbed water, and 0.5 wt % of the residual mass from SBA-15 template shown in Table 1. However, the mass of the physically adsorbed water can change and is not constant with the storage period of the PEDOT/ mesoporous carbon composite. Thus, we must recalculate the composition of the solid components after the weight of the physically adsorbed water is subtracted from the total weight of the PEDOT/mesoporous composite. After recalculation, the PEDOT/mesoporous composite contains 67.3 wt % of the PEDOT, 32.2 wt % of the CMK-3 carbon, and 0.5 wt % of the residual mass from SBA-15 template. The particle morphologies and microstructures of CMK-3 carbon and the PEDOT/mesoporous carbon composite were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 4 shows the typical SEM images of the mesoporous carbon CMK-3 (a) and PEDOT/

Figure 5. TEM images of mesoporous carbon (a, b) seen from the [100] and [001] directions and (c, d) PEDOT/mesoporous carbon composite at different magnifications.

mesoporous carbon composite (b). It can be clearly seen that the pure CMK-3 carbon is mainly made up of big rodlike particles with a diameter of several micrometers, and every big particle is composed of many sub-micrometer-sized aggregated rodlike particles with a diameter of ∼0.3 µm. After PEDOT developed on the surface of CMK-3 to form such a special PEDOT/mesoporous carbon composite, the morphology evidently changed greatly as shown in Figure 4b, though it displayed the morphological similarity to the support CMK-3 carbon (Figure 4a). On the surface of the composite, there seems to be a thick outer coating compared to the pure CMK-3 carbon, indicating that there is a strong self-interaction between the CMK-3 carbon nanowires and polymer PEDOT. It can also be illustrated in Figure 1. So the diameter of the small nanoparticles constituting the PEDOT/mesoporous carbon composite increased to ∼0.5 µm, which is clearly bigger than that of the small particles of CMK-3 carbon. At the same time, we could not observe the single PEDOT particles existing in the composites from the SEM images, and thus all PEDOT polymer molecules were deposited within the mesopores of CMK-3 and on the surface of CMK-3 particles. It can be calculated that the thickness of the PEDOT deposited on the mesoporous carbon particles is about 100 nm according to the SEM observation.

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Figure 6. Wide-angle XRD patterns of mesoporous carbon CMK-3 (a) and PEDOT/mesoporous carbon composite (b). The signals “/” represent the PEDOT.

Hence, the PEDOT/mesoporous carbon composite was successfully prepared as observed with SEM. The morphology of CMK-3 carbon is the reverse hexagonal structure of ordered SBA-15. TEM images of CMK-3 carbon shown in Figure 3a and 3b confirmed highly ordered mesoporous nanowires viewed from the [100] and [001] directions,1b and these wires are in the same perfect hexagonally mesostuctured arrays. The particle morphology of the PEDOT/mesoporous carbon composite in Figure 5c is rodlike, which is very in good agreement with the observation result from SEM (Figure 4a). On the edge of the particle, the thin part is the freshly deposited PEDOT on the surface of CMK-3 particle. A highermagnification TEM image (Figure 5d) does not illustrate the ordered mesoporous carbon nanowires, which implies that the surface of CMK-3 carbon is certain to be covered with a layer of PEDOT. This result is very consistent with the SEM images. Figure 6 illustrates the wide-angle XRD patterns of the mesoporous carbon (a) and PEDOT/mesoporous carbon composite (b). In Figure 6a, there are two broad diffraction peaks are at about 2θ ) 21.5° and 43°. These signals correspond to the (002) and (101) diffractions of graphite. However, several small but acute peaks (*) appear in the wide-angle XRD pattern of the PEDOT/mesoporous carbon composite, which is ascribed to the layered ordered structure of PEDOT molecules. At the same time, X-ray photoelectron spectroscopy (XPS) indicated that the surfaced atomic composition of the organic-inorganic composite was C (64.5%), O (30.0%), and S (4.5%), which is consistent with theoretical values of PEDOT. It clearly showed that CMK-3 particles were certain to be coated with the polymer PEDOT. Figure 7 shows the FTIR spectra for the mesoporous carbon CMK-3 (a) and PEDOT/mesoporous carbon composite (b). Characteristics peaks at 3500 cm-1 and 1096 cm-1 are observed in the IR spectrum of mesoporous carbon (Figure 7a). These peaks can be attributed to -OH (3500 cm-1) and C-C-O (1096 cm-1), respectively. For the PEDOT/mesoporous carbon composite as shown in Figure 7b, spectrum b, we can summarize the observed bands as follows: ν(C-C)ring stretching at 1389 cm-1 and 1348 cm-1; ν(CdC)ring at 1187 cm-1; ν(CO-CH2CH2-OC) at 1186 cm-1 and 1085 cm-1; ν(C-S)ring and σ(CS-C) stretching at 834 cm-1 and 688 cm-1, respectively.14 These results indicate that PEDOT has been prepared in our experiment.

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Figure 7. FT-IR spectra of CMK-3 mesoporous carbon (a) and PEDOT/mesoporous carbon composite (b).

Conclusion A kind of novel organic-inorganic PEDOT/mesoporous carbon composite has been successfully prepared by a simple in situ polymerization method. Electron microscopy (SEM and TEM) images clearly showed that PEDOT polymer was equably deposited on the surface of CMK-3 nanoparticles, and no additional PEDOT particles appeared in the final PEDOT/ mesoporous carbon composite. It also implies that there is a strong self-interaction between the CMK-3 carbon nanowires and the polymer PEDOT. At the same time, the SEM images displayed the morphological similarity to the support CMK-3 carbon except for the bigger size of the nanoparticles in the composite due to the coverage of polymer PEDOT on the support CMK-3 carbon. The thermal analysis indicated that the organic-inorganic composite we prepared contained 67.3 wt % of PEDOT and 32.2 wt % of CMK-3 carbon after the mass of the physically adsorbed water was subtracted. FT-IR and XPS analysis showed that PEDOT had been prepared in the resultant composite. Moreover, other polymer (PPy, PS, polyaniline, etc.)/ mesoporous carbon composites can also be synthesized to obtain novel organic-inorganic composites. The properties such as electronic conductivity and electrochemical performance of this novel and interesting PEDOT/mesoporous carbon composite were investigated. References and Notes (1) (a) Ryoo, R.; Joo, S. H.; Jun, S. J. Phys. Chem. B 1999, 103, 7743. (b) Jun, S.; Joo, S. H.; Ryoo, R.; Kruk, M.; Jaroniec, M.; Liu, Z.; Ohsuna, T.; Terasaki, O. J. Am. Chem. Soc. 2000, 122, 10712. (2) Joo, S. H.; Choi, S. J.; Oh, I.; Kwak, J.; Liu, Z.; Terasaki, O.; Ryoo, R. Nature 2001, 412, 169. (3) A Ä lvarez, S.; Blanco-Lo´pez, M. C.; Miranda-Ordieres, A. J.; Fuertes, A. B.; Centeno, T. A. Carbon 2005, 43, 866. (4) Wang, Y. G.; Li, H. Q.; Xia, Y. Y. AdV. Mater. 2006, 18, 2619. (5) Zhou, L.; Liu, X.; Li, J.; Wang, N.; Wang, Z.; Zhou, Y. Chem. Phys. Lett. 2005, 413, 6. (6) (a) Lai, X.; Li, X.; Geng, W.; Tu, J.; Li, J.; Qiu, S. Angew. Chem., Int. Ed. 2007, 46, 738. (b) Lu, A. H.; Schmidt, W.; Taguchi, A.; Spliethoff, B.; Tesche, B.; Schu¨th, F. Angew. Chem., Int. Ed. 2002, 41, 3489. (c) Vinu, A.; Ariga, K.; Mori, T.; Nakanishi, T.; Hishita, S.; Golberg, D.; Bando, Y. AdV. Mater. 2005, 17, 1648. (d) Roggenbuck, J.; Tiemann, M. J. Am. Chem. Soc. 2005, 127, 1096. (e) Roggenbuck, J.; Koch, G.; Tiemann, M. Chem. Mater. 2006, 18, 4151. (7) Wang, J.; Xiang, C.; Liu, Q.; Pan, Y.; Guo, J. Submitted. (8) Groenendaal, L. B.; Jonas, F.; Freitag, D.; Pielartzik, H.; Reynolds, J. R. AdV. Mater. 2000, 12, 481. (9) Peng, C.; Snook, G. A.; Fray, D. J.; Shaffer, M. S. P.; Chen, G. Z. Chem. Commun. 2006, 4629.

PEDOT/Mesoporous Carbon Composite (10) (a) Vadivel Murugan, A.; Kale, B. B.; Kwon, C.-W.; Campet, G.; Vijaymohanan, K. J. Mater. Chem. 2001, 11, 2470. (b) Arbizzani, C.; Mastragostino, M.; Rossi, M. Electrochem. Commun. 2002, 4, 545. (11) (a) Zhao, D.; Huo, Q.; Feng, J.; Chmelka, B. F.; Stucky, G. D. J. Am. Chem. Soc. 1998, 120, 6024. (b) Zhao, D.; Feng, J.; Huo, Q.; Melosh, N.; Fredrickson, G. H.; Chmelka, B. F.; Stucky, G. D. Science 1998, 279, 548.

J. Phys. Chem. C, Vol. 111, No. 49, 2007 18077 (12) Yoon, S.; Lee, J.; Hyeon, T.; Oh, S. M. J. Electrochem. Soc. 2000, 147, 2507. (13) Wang, J.; Liu, Q. J. Phys. Chem C 2007, 111, 7266. (14) (a) Choi, J. W.; Han, M. G.; Oh, S. G.; Im, S. S. Synth. Met. 2004, 141, 293. (b) Kvarnstro¨m, C.; Neugebauer, H.; Blomquist, S.; Ahonen, H. J.; Kankare, J.; Ivaska, A. Electrochim. Acta 1999, 44, 2739.