Ice-Templating Synthesis of Polyaniline Microflakes Stacked by One

May 4, 2009 - Jonathan Spender , Alexander L. Demers , Xinfeng Xie , Amos E. Cline , M. Alden Earle , Lucas D. Ellis , and David J. Neivandt. Nano Let...
0 downloads 0 Views 8MB Size
Download PDF
J. Phys. Chem. C 2009, 113, 9047–9052

9047

Ice-Templating Synthesis of Polyaniline Microflakes Stacked by One-Dimensional Nanofibers Hui-yan Ma,† Yu Gao,† Yin-hua Li,‡ Jian Gong,*,† Xia Li,† Bin Fan,† and Yu-lin Deng*,‡ Key Laboratory of Polyoxometalates Science of Ministry of Education, Northeast Normal UniVersity, Changchun, Jilin, 130024, China, and School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0620 ReceiVed: December 20, 2008; ReVised Manuscript ReceiVed: March 17, 2009

In this paper, a facile and environmentally friendly route, an ice-templating method, has been developed to prepare polyaniline (PANI) microflakes stacked by one-dimensional (1D) uniform nanofibers with diameters in the range 22-32 nm. Although the ice-templating method has been used for preparing ultrapure materials with unique structures in recent years, to our knowledge, this is the first report on using the ice-templating method to direct the polymerization of aniline. Platelet-shaped ice crystals with high aspect ratios provide a particularly novel template to microscopically confine PANI microflakes. The concentration of reagents (aniline, H4SiW12O40 doping acid, and ferric chloride oxidant) and the growth mechanism of PANI flakes are investigated in our experiment. The structure and morphology of the PANI microflakes are characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) patterns, energy-dispersive X-ray analysis (EDX), and scanning electron microscopy (SEM). The conductivity of the doped PANI microflakes is 0.120 S/cm. The PANI microflakes piled up with nanofibers have super performance in sensitivity, time response, and reversibility to NH3. 1. Introduction As a unique conducting polymer, polyaniline (PANI) has captivated much attention from chemists owing to its straightforward polymerization, chemical stability, relatively high conductivity, and great potential applications in molecular electronic devices, batteries, nonlinear optics, antistatic coatings, etc.1-5 More importantly, its simple nonredox doping/dedoping chemistry based on acid/base reaction provides wide application prospects for future nanodevices.6,7 In the past few decades, much excellent research on the shape-controlled synthesis of PANI nanostructures such as nanofibers, rods, noodles, spheres, wires, and tubes has been reported.8-10 Among these nanostructures, PANI nanofibers which combine the properties of high surface area with one-dimensional organic conductors have carved a niche for themselves in material chemistry along the years. “Soft and hard” templates have been frequently introduced to direct the growth of PANI nanofibers.11-18 For these strategies, however, low yield, complex template fabrication, tedious template removal, and dilapidated structure caused by the template removal process still limit their applications.19 In order to avoid these disadvantages of “soft” or “hard” templates, new methods have been explored including “nanofiber seeding”20 and “interfacial polymerization”.21,22 High-quality PANI nanofibers can be synthesized in large quantity by these methods. However, synthesis of the nanofiber seeds with nanodiameter (∼100 nm) and complex purification process are required, and noxious organic reagents (e.g., CCl4, CS2, benzene, and toluene) are unavoidable. Therefore, a green and facile chemical route to synthesize uniform, high-quality PANI nanofibers in bulk quantities is appealing. * Corresponding authors. E-mail: [email protected] or Jian.Gong@ ipst.gatech.edu (J.G.); [email protected] (Y.D.). † Northeast Normal University. ‡ Georgia Institute of Technology.

Since Mahler23 and Deville24 adopted ice crystals with different shapes as new templates to synthesize silica fibers and flakes, and a layered-hybrid complex composite, the directional and undirectional freezing methods have attracted more and more attention. Using the ice-templating methods, scientists have obtained some novel microstructures, such as microgel fibers,25 microhoneycombs,26 and porous structures.27-32 In the icetemplating methods, ice template piled up with a large quantity of hexagonal ice crystals grown in situ can be easily removed by thawing followed by drying. Ultrapure materials with porous structure can be easily prepared by using this method. However, to the best of our knowledge, the synthesis of PANI using an ice-templating method has not been reported to date. Hence, in our paper, we introduced this green and facile chemical way to synthesize uniform and high-quality PANI nanofibers in the form of a microflake structure. The method avoids not only tedious template fabrication, complex process control, and taxing template removal, but also additional noxious organic reagents. 2. Experimental Section 2.1. Materials. Aniline (Beijing Chemical Co.) was distilled twice under vacuum before use. Iron(III) chloride hexahydrate (ferric chloride; FeCl3 · 6H2O) was purchased from a Beijing chemical factory without further purification. In our experiment, FeCl3 was used as a milder polymerization initiator. A much lower reaction rate than that by (NH4)2S2O8 (APS) used in most polymerizations could guarantee that the polymerization of aniline completely takes place in the frozen ice phase and yields textured plates stacked with uniform and finer nanofibers.33-35 H4SiW12O40 (SiW12) was prepared and characterized according to the literature.36a 2.2. Polymerization. In a typical experiment, 0.1 mL of aniline was added to 40 mL of SiW12 (0.5 g) solution. Then 0.3530 g of ferric chloride (FeCl3 · 6H2O) (molar ratio aniline: oxidant:acid ) 6:7:1) as a mild oxidant was dissolved in the

10.1021/jp8112683 CCC: $40.75  2009 American Chemical Society Published on Web 05/04/2009

9048

J. Phys. Chem. C, Vol. 113, No. 21, 2009

Ma et al.

Figure 1. SEM images of PANI microflakes synthesized using ice-templating method. Aniline ) 0.1 mL; aniline:oxidant:acid ) 6:7:1. Lamellar flakes at low magnification (A) and at higher magnification (B).

Figure 2. (left) Diameter size distribution and (right) EDX spectrum of PANI nanofiber. Synthetic conditions: aniline ) 0.1 mL; aniline:oxidant: acid ) 6:7:1; aging 20 days.

above solution, and the resulting solution was stirred another 1 min at room temperature to ensure complete mixing. After that, the amber solution was allowed to stand in a freezer at -10 °C for 20 days. Finally, after the frozen ice thawed, the products remained. The green precipitate was filtered and washed with distilled water and ethanol several times, in order to remove excess ions and monomers thoroughly, and then dried in a vacuum at 50 °C for 24 h. Pure PANI was obtained through a nonredox base doping process. SiW12-doped PANI powder was dipped for 4 h in 50 mL of aqueous ammonia (0.5 mol/L) and then filtered; the powder was washed with distilled water several times until the solution was neutral. Finally, the PANI base was dried in a vacuum at 50 °C for 24 h. 2.3. Characterization. The morphology of the resulting PANI was observed with an XL-30 ESEM FEG scanning electron microscope (SEM) operated at 20 kV. Fourier transform infrared (FT-IR) spectra were obtained by using an Alpha Centauri 560 Fourier transform infrared spectrophotometer (frequency range 4000-400 cm-1) with a KBr pellet. X-ray diffraction (XRD) was performed on a D/Max III C X-ray diffractometer by using a Cu KR radiation source. Scans were made from 3 to 60° (2θ) at a speed of 2 °C min-1. The conductivity of PANI was measured with a standard four-probe technique (China). Disk-shaped samples were prepared from powders using 20 MPa pressure at room temperature. 3. Results and Discussion 3.1. Characterization of the PANI Structure. Figure 1 shows SEM images of PANI samples synthesized using the icetemplating method under the condition of the molar ratio of aniline:oxidant:acid ) 6:7:1 (aniline ) 0.1 mL). The low

magnification SEM image in Figure 1A shows that the products are lamellar and textured microflakes, which are aslant inserted along an axis and form a dendrite-like morphology. Higher magnification SEM image reveals that the resulting products consist of one-dimensional (1D) nanofibers (Figure 1B). The diameters of the fibers in the microflakes are in the range 22-32 nm with an average diameter of 26.2 nm (Figure 2 (left)). The data of energy-dispersive X-ray analysis (EDX) reveal the presence of carbon, nitrogen, oxygen, and tungsten and the absence of iron and chlorine (Figure 2 (right)). The amounts of C, N, and W are considerably large by counting. All the results proved that PANI nanofibers are doped with SiW12. The molecular structure of the PANI microflakes is characterized by FT-IR spectroscopy. As shown in Figure 3 (left), the peaks in the frequency range of 2900-3500 cm-1 are due to the N-H stretching vibrations of the leucoemeraldine component. The characteristic absorption peaks appearing at 1572.93 and 1483.07 cm-1 correspond to the CdC stretching vibration of quinoid and benzenoid rings, respectively. The peak at 1299.33 cm-1 attributes to the C-N stretching vibration with aromatic conjugation. The peak at 1141.37 cm-1 assigned to the characteristic of QdNH+sB (where Q and B denote quinoid ring and benzene ring, respectively) is also observed. SiW12 with a Keggin structure consists of one {SiO4} tetrahedron surrounded by four {W3O13} sets formed by three edge-sharing octahedra. There are four kinds of oxygen atoms in the SiW12, which are Oa (oxygen in {SiO4} tetrahedron), Ob (cornersharing oxygen between different {W3O13} sets), Oc (edgesharing oxygen bridge within {W3O13} sets), and Od (terminal oxygen atom) [see inset in Figure 3 (left)]. Four characteristic peaks of SiW12 (783.01 cm-1 ascribed to W-Oc-W, 879.41

Ice-Templating Synthesis of PANI Microflakes

J. Phys. Chem. C, Vol. 113, No. 21, 2009 9049

Figure 3. (left) FT-IR spectrum and (right) XRD pattern of PANI microflakes stacked by nanofibers using ice-templating method. Synthetic conditions: aniline ) 0.1 mL; aniline:oxidant:acid ) 6:7:1; aging 20 days.

Figure 4. SEM images of PANI synthesized with different concentrations of solution ([aniline]/[oxidant]/[doping acid] ) 6:7:1): (A) aniline ) 0.05 mL; (B) aniline ) 0.1 mL; (C) aniline ) 0.2 mL. Other synthetic conditions: VH2O ) 40 mL; -10 °C; 20 days.

cm-1 ascribed to W-Ob-W, 916.19 cm-1 ascribed to Si-Oa, and 964.39 cm-1 ascribed to WdOd) attest to the presence of SiW12 in the PANI.36a These results demonstrate the successful polymerization of PANI doped with SiW12. In Figure 3 (right), the XRD pattern of the doped PANI obtained using the ice-templating method shows a sharp peak at 2θ ) 7.51°, which is close to the PANI repetition unit. This result suggests that doping with SiW12 leads to a more ordered structure with relatively distinct Bragg reflections.36b Meanwhile, one broad band centered at 2θ ) 26.75° is observed, which indicates that the PANI microflakes are still amorphous, although the PANI is ordered with a short interlayer distance. 3.2. Morphology. It is important to note that the concentrations of the reagents affect the morphology of the resulting products. The SEM images in Figure 4 show the dependence of the delicate structures of products on the reaction agent concentrations at the molar ratio of [aniline]/[oxidant]/[acid] of 6:7:1. It is obvious that the size of the flakes obtained from high concentration is bigger than those obtained from low concentration. The thickness of the flakes also increases, such as ca. 420, 900, and 4000 nm with increasing concentration of aniline from 0.05, 0.1, and 0.2 mL, respectively. We speculate the possible reason of these phenomena as follows. On one hand, increasing the concentration of reactants can improve reaction kinetics and speed up the reaction rate. On the other hand, different freezing points of the solution also affect the size of ice crystals. At the same temperature, high particle concentration (including all ions and molecules) can slow down the freezing rate and prolong the time for crystallization, and yield larger ice crystals, compared with low particle concentration. Hence, we conclude that low freezing rate in company with the faster reaction rate leads to the creation of a bigger and thicker microstructure of products.27,32

For substantially studying the effect of the doping acid concentration on the morphology of PANI, herein, parallel experiments were carried out with the concentration of SiW12 ranging from 0 to 8.685 mM and the molar ratio of [aniline]/ [oxidant] remaining at constant value, e.g., 1:1.2. From Figure 5A to 5D, we can see that there is an obvious evolution of the product morphology. In the absence of doping acid, as shown in Figure 5A, a membrane rather than microflakes is obtained. In Figure 5B, by using a small quantity of SiW12 (0.1 g), the membrane begins to transfer into a textured sheet. Upon further increasing the amount of SiW12 to 0.5 g (Figure 5C), microflakes are observed. When the quantity of doping acid reaches 1.0 g, some ribbed flakes with compact texture form as shown in Figure 5D. All the results mentioned above show that SiW12 also has an important effect on the morphology of PANI. We speculate that the addition of SiW12 not only can be beneficial for aniline to form anilinium cations,37 but also can enhance interfacial adhesion between aniline and ice template through hydrogen bonding interactions between SiW12 anions and water molecules (ice)38 to form microflakes with a smooth surface as the results of experiment reveal. 3.3. Growth Mechanism of PANI Microflakes. At the conditions reported in this paper, the PANI products are mainly in the form of lamellar and textured microflakes, which are aslant inserted along an axis and form a dendrite-like morphology, although the size and the thickness of those flakes formed at different reaction conditions are various. These lamellar and textured PANI structures are derived from the morphologies of ice templates. In the course of freezing, ice crystals expel the solutes, which are dispersed homogeneously in water from the forming ice phase and entrap them within the directed channels between the ice crystals. Therefore, ice crystals piled here offer a lamellar and textured template to define microscopically the

9050

J. Phys. Chem. C, Vol. 113, No. 21, 2009

Ma et al.

Figure 5. SEM images of PANI synthesized with different doping acid (SiW12) concentrations: (A) 0 mM; (B) 0.8685 mM (0.1 g); (C) 4.343 mM (0.5 g); (D) 8.685 mM (1.0 g). Other synthetic conditions: aniline ) 0.1 mL; [aniline]/[FeCl3 · 6H2O] ) 6:7; VH2O ) 40 mL; -10 °C; 20 days.

Figure 6. Schematic representation of polymerization process of PANI microflakes stacked by 1D nanofibers using ice-templating method. (A) Dispersal of solutes; (B) primary nanofiber growth; (C) further template-directed growth; (D) dendrite-like product leaving after removal of ice templates.

growth of PANI and further direct the formation of lamellar PANI microflakes. Deville, Walter, and Mukai have reported a similar growth model of hierarchical SiO2 ribbed or lamellar flakes.23,24,26 Interestingly, in our experiment, these lamellar and textured PANI microflakes are aslant inserted along an axis and form a dendrite-like morphology. The formation of such structures is reasonable since there are various morphologies of ice templates used as the structure-directing template during the whole synthetic process. Since 1997, Emoto has performed several water crystal experiments. His results reveal the fact that it is difficult to get a highly uniform shape and structure of ice crystals because its physical shape easily adapts to whatever environment is present.39 Also, a video, which is available free of charge via the Internet, offers powerful evidence that there are plenty of dendrite-like ice crystals accompanying aslant or ribbed ice flakes when water freezes.40 Here, we further suggest the formation mechanism of PANI dendrite-like microflakes as shown in Figure 6. First, under freezing condition, ice crystals exclude the oxidant and polymer molecules at the freezing front. Selectively, reactant molecules are encapsulated in the dendritic ice scaffolds owing to a fast freezing rate (Figure 6A). Second, the primary PANI nanofibers form among the ice scaffolds (Figure 6B) under the action of oxidant. Third, to a certain extent, the closely packed ice crystals slow the polymerization rate of reactants compared with the liquid system. However, we deduce the largo growth process is more beneficial for the primary nanofibers growing along the dendritic morphology of ice template because of enough time and space (Figure 6C).

Last, dendrite-like PANI can be obtained (Figure 6D) after the ice template is removed by thawing followed by drying. Based on the above factors, dendrite-like PANI microflakes can be obtained. Although the size and thickness are different at different conditions in our paper, these products are all made up of nanofibers. This may be due to the low reaction rate at low temperature and without disturbance, which is favorable for the formation of 1D nanofibers.33 On the other hand, the structure of ice crystals packed closely leads to effective prevention of the “secondary growth” of primary PANI nanofibers to a certain extent.41 By this strategy, dendrite-like PANI microflakes stacked by 1D nanofibers rather than other morphologies are obtained. 3.4. Sensor’s Gas Sensitivity to NH3 Vapor and Reversibility. The details of the sensor construction used in our experiments have been reported in our previous publication.42 First, PANI nanofiber films were fabricated by using a dropcoating technique. The films were deposited onto a porcelain tube that consisted of a 1 mm × 1 mm Pt electrode. The substrates were equipped with integrated electrodes to the sensitive film. The films were prepared from pastes that were obtained by adding an organic vehicle for improving the adhesion of the layers to the substrates to the above powders. Second, the films were dried for 1 h under vacuum at 40 °C. The PANI device was finally put into an air-proof test box (about 27 L). Six-volt dc voltages were applied. The box and the device were flushed with N2 continuously until the electrical resistance reached a steady value. Then, a certain amount of volatile

Ice-Templating Synthesis of PANI Microflakes

J. Phys. Chem. C, Vol. 113, No. 21, 2009 9051 indicates that the PANI nanofibers doped with SiW12 have excellent performance as a chemical sensor, which supports the results of gas sensitivity to NH3. 4. Conclusions

Figure 7. (left) Resistance changes of PANI nanofiber microflakes upon exposure to different concentrations of NH3 vapor ((A) 100, (B) 50, and (C) 10 ppm). (right) Reversible circulation response changes of PANI nanofiber microflakes upon exposure to NH3 (100 ppm). The x-axis is the response time; the y-axis R/R0 is resistance (R) normalized to the initial resistance (R0) prior to gas exposure. Synthetic conditions: aniline ) 0.1 mL; aniline:oxidant:acid ) 6:7:1.

solvent was injected into the test box with a syringe. The changes in electrical resistance were monitored and recorded automatically with a computer. The gas sensitivity of the PANI nanofibers was defined as the ratio of R/R0, in which R0 is the initial resistance of the PANI nanofibers before exposure to the test gas and R is the time-dependent resistance of the PANI nanofibers exposed to the test gas. In Figure 7 (left), we show the response of the PANI nanofiber microflakes upon exposure to different concentrations of NH3. The microflakes show a significant increase in resistance when exposed to 100 ppm NH3 (the resistance average value R/R0 of the gas is NH3 ∼ 26.2). Compared with previous PANI nanotubes (the resistance average value R/R0 of the gas is NH3 ∼ 3.2 or 1.74), the PANI nanofiber microflakes have better gas sensitivity to NH3 gas.42 The results indicate that the PANI microflakes synthesized by using the ice-templating method show excellent performance as a chemical sensor. This is consistent with their porous nature, as well as the thin and strongly adherent structure of the nanofiber microflakes, which makes gas molecules easily diffuse into and out of the nanofibers. Another important property of the PANI device is its reversibility at room temperature. It can also be seen in Figure 7 (right) that the resistance almost returns to the original baseline for all cycles tested in this study, indicating that the PANI device has a reasonable reproducibility. Therefore, the PANI nanofiber microflakes not only bear diaphanous morphology but also show better performance in both sensitivity and time response in comparison with PANI reported previously.42 Although the mechanism of gas sensitivity to vapor is complex, here it is probably due to the fact that the PANI nanofibers have high surface area to allow for easy adsorption of gas molecules. Another important reason is due to the difference of the conductivity of doped and dedoped PANI. PANI is a conjugated polymer in that it can be tailored for specific applications through a nonredox acid/base doping process, and most sensors made of PANI are based on the reversible reaction of acid/alkali.43 As a result, the conductivity of PANI decreases with increasing amount of alkali and increases with increasing amount of acid. In order to investigate the effect of SiW12 on the conductivity of PANI, the conductivities of SiW12-doped PANI and pure PANI were measured with a standard four-probe technique, respectively. The results indicate that the conductivity of SiW12-doped PANI is 0.120 S/cm and that of pure PANI is less than 10-6 S/cm. Obviously, the presence and the absence of SiW12 have great influence on the conductivity of PANI, although both doped PANI and dedoped PANI have similar nanofiber structures. This property

In summary, a facile and green route is demonstrated for the construction of PANI microflakes staked by 1D nanofibers using an ice-templating method in one step, which has unprecedented merits as follows: (1) Both the fabrication and purification are quite simple, green, and in one step. The use of an ice template gets rid of conventional templates, surfactants, or organic solvent. (2) Concentration of solution (particularly to doping acid) has an effect on the morphology of PANI. (3) The closely piled ice crystals effectively prevent the “secondary growth” of primary nanofibers and lead to the formation of lamellar or ribbed microflakes staked by pure, uniform nanofibers. (4) The small-diameter, strongly adherent structure and porous nature of the PANI nanofiber microflakes appear to have super performance in both sensitivity and time response of NH3, and have excellent reversible property, which could be used for the fabrication of highly sensitive chemical sensors. In addition, this approach may also be extended to a variety of technology applications requiring the use of substrate-supported flakes, for example, displays and sensors. Acknowledgment. This work was supported by the Program for Changjiang Scholars and Innovative Research Team in University and the Science Foundation of Jilin Province (20070505). References and Notes (1) Skoheim, T. A.; Elsenbaumer, R. L.; Reynolds, J. R. Handbook of Conducting Polymers, 2nd ed.; Marcel Dekker: New York, 1997. (2) Heeger, A. J. J. Phys. Chem. B 2001, 105, 8475. (3) Lei, J.; Menon, V. P.; Martin, C. R. Polym. AdV. Technol. 1992, 4, 124. (4) Wohlgenannt, M.; Tandon, K.; Mazumdar, S.; Ramsesha, S.; Vardeny, Z. V. Nature 2001, 409, 494. (5) Lahav, M.; Durkan, C.; Gabai, R.; Katz, E.; Willner, I.; Welland, M. E. Angew. Chem., Int. Ed. 2001, 40, 4095. (6) Virji, S.; Huang, J. X.; Kaner, R. B.; Weiller, B. H. Nano Lett. 2004, 4, 491. (7) Huang, J. X.; Kaner, R. B. Angew. Chem., Int. Ed. 2004, 43, 5817. (8) Meng, L. H.; Lu, Y.; Wang, X.; Zhang, J.; Duan, Y.; Li, C. Macromolecules 2007, 40, 2981. (9) (a) Armes, S. P.; Aldissi, M.; Agnew, S.; Gottesfeld, S. Langmuir 1990, 6, 1745. (b) Vincent, B.; Waterson, J. J. Chem. Soc., Chem. Commun. 1990, 683. (c) Stejskal, J.; Kratochvil, P.; Armes, S. P.; Lascelles, S. F.; Riede, A.; Helmstedt, M.; Prokes, J.; Krivka, I. Macromolecules 1996, 29, 6814. (d) Wei, Z.; Wan, M. AdV. Mater. 2002, 14, 1314. (10) (a) Martin, C. R. Science 1994, 266, 1961. (b) Martin, C. R. Chem. Mater. 1996, 8, 1739. (c) Wu, C. G.; Bein, T. Science 1994, 264, 1757. (d) Liu, J.; Lin, Y.; Liang, L.; Voigt, J. A.; Huber, D. L.; Tian, Z. R.; Coker, E.; Mckenzie, B.; Mcdermott, M. J. Chem.sEur. J. 2003, 9, 604. (11) Nascimento, G. M.; Silva, C. H. B.; Temperini, M. L. A. Macromol. Rapid Commun. 2006, 27, 255. (12) Wei, Z.; Zhang, Z.; Wan, M. Langmuir 2002, 18, 917. (13) Zhang, L.; Wan, M. Nanotechnology 2002, 13, 750. (14) Zhang, L.; Wan, M. J. Phys. Chem. B 2003, 107, 6748. (15) Duchet, J.; Legras, R.; Demoustier-Champagne, S. Synth. Met. 1998, 98, 113. (16) Cepak, V. M.; Martin, C. R. Chem. Mater. 1999, 11, 1363. (17) Martin, C. R. Science 1994, 266, 1961. (18) Misoska, V.; Price, W.; Ralph, S.; Wallace, G. Synth. Met. 2001, 121, 1501. (19) Ma, M.; Li, G.; Wang, M.; Cheng, Y.; Bai, R.; Chen, H. Chem.sEur. J. 2006, 12, 3254. (20) Zhang, X.; Goux, W. J.; Manohar, S. K. J. Am. Chem. Soc. 2004, 126, 4502. (21) Huang, J. X.; Virji, S.; Weiller, B. H.; Kaner, R. B. J. Am. Chem. Soc. 2003, 125, 314. (22) Huang, J. X.; Kaner, R. B. J. Am. Chem. Soc. 2004, 126, 851. (23) Mahler, W.; Bechtold, M. F. Nature 1980, 285, 27.

9052

J. Phys. Chem. C, Vol. 113, No. 21, 2009

(24) Deville, S.; Saiz, E.; Nalla, R. K.; Tomsia, A. P. Science 2006, 311, 515. (25) (a) Shi, Q.; An, Z.; Tsung, C. K.; Liang, H.; Zheng, N.; Hawker, C. J.; Stucky, G. D. AdV. Mater. 2007, 19, 4539. (b) Ishiguro, H.; Rubinsky, B. Cryobiology 1994, 31, 483. (c) Li, D.; Xia, Y. AdV. Mater. 2004, 16, 1151. (d) Sun, X. Y.; Shankar, R.; Bo¨rner, H. G.; Ghosh, T. K.; Spontak, R. J. AdV. Mater. 2007, 19, 87. (26) Mukai, S. R.; Nishihara, H.; Tamon, H. Chem. Commun. 2004, 7, 874. (27) Zhang, H.; Cooper, A. I. AdV. Mater. 2007, 19, 1529. (28) Zhang, H.; Edgar, D.; Murray, P.; Rak-Raszewska, A.; GlennonAlty, L.; Cooper, A. I. AdV. Funct. Mater. 2008, 18, 222. (29) Mukai, S. R.; Nishihara, H.; Shichi, S.; Tamon, H. Chem. Mater. 2004, 16, 4987. (30) Mukai, S. R.; Nishihara, H.; Shichi, S.; Tamon, H. Microporous Mesoporous Mater. 2003, 63, 43. (31) Madihally, S. V.; Matthew, H. W. T. Biomaterials 1999, 20, 1133. (32) Gutie´rrez, M. C.; Garcı´a-Carvajal, Z. Y.; Jobba´gy, M.; Rubio, F.; Yuste, L.; Rojo, F.; Ferrer, M. L.; Monte, F. D. AdV. Funct. Mater. 2007, 17, 3505. (33) (a) Pan, L.; Pu, L.; Shi, Y.; Sun, T.; Zhang, R.; Zheng, Y. AdV. Funct. Mater. 2006, 16, 1279. (b) Li, D.; Kaner, R. B. J. Am. Chem. Soc. 2006, 128, 968. (34) Zhang, Z.; Deng, J.; Shen, J.; Wan, M.; Chen, Z. Macromol. Rapid Commun. 2007, 28, 585. (35) Zhang, L.; Wan, M.; Wei, Y. Macromol. Rapid Commun. 2006, 27, 366.

Ma et al. (36) (a) Ander, T.; Gilbert, H. Inorg. Synth. 1990, 27, 457. (b) Pouget, J. P.; Jozefowicz, M. E.; Epstein, A. J.; Tang, X.; MacDiarmid, A. G. Macromolecules 1991, 24, 779. (37) (a) Zhang, Z.; Wei, Z.; Wan, M. Macromolecules 2002, 35, 5937. (b) Wei, Z.; Wan, M.; Lin, T.; Dai, L. AdV. Mater. 2003, 15, 136. (38) (a) Shi, Z. Y.; Gu, X.; Peng, J.; Wan, E. J. Mol. Struct. 2005, 737, 147. (b) Pope, M. T. Heteropoly and Isopoly Oxometalates; Springer: Berlin, 1983. (39) (a) Emoto, M. Messages from Water; Sunmark: Hado, Japan, 1999; Vol. 1. (b) Emoto, M. Messages from Water; Sunmark: Hado, Japan, 2001; Vol. 2. (40) http://v.youku.com/v_show/id_XMjgxODA1MzY)_rss.html. (41) (a) Wang, Y.; Jing, X. L. J. Phys. Chem. B 2008, 112, 1157. (b) Zhang, X.; Kolla, H. S.; Wang, X. H.; Raja, K.; Manohar, S. K. AdV. Funct. Mater. 2006, 16, 1145. (c) Chiou, N. R.; Epstein, A. J. Synth. Met. 2005, 153, 69. (42) (a) Gao, Y.; Yao, S.; Gong, J.; Qu, L. Macromol. Rapid Commun. 2007, 28, 286. (b) Gao, Y.; Gong, J.; Li, X.; Fan, B.; Su, Z.; Qu, L. J. Phys. Chem. C 2008, 112, 8215. (c) Xue, B.; Qi, S.; Gong, J.; Gao, Y.; Yao, S.; Yin, R.; Qu, L. J. Nanosci. Nanotechnol. 2007, 7, 4515. (d) Gao, Y.; Wang, F. C.; Gong, J.; Su, Z.; Qu, L. J. Nanosci. Nanotechnol. 2008, 8, 5972. (43) (a) Zhang, Z.; Deng, J.; Sui, J.; Yu, L.; Wan, M.; Wei, Y. Macromol. Chem. Phys. 2006, 207, 763. (b) Huang, W. S.; Humphrey, B. D.; MacDiarmid, A. G. J. Chem. Soc., Faraday Trans. 1986, 82, 2385.

JP8112683