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Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/graphene thin films Mohd Omaish Ansari, Mohammad Mansoob Khan, Sajid Ali Ansari, Ikhlasul Amal, Jintae Lee, Moo Hwan Cho
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(13)01342-6 http://dx.doi.org/10.1016/j.matlet.2013.09.098 MLBLUE15866
To appear in:
Materials Letters
Received date: 6 July 2013 Accepted date: 25 September 2013 Cite this article as: Mohd Omaish Ansari, Mohammad Mansoob Khan, Sajid Ali Ansari, Ikhlasul Amal, Jintae Lee, Moo Hwan Cho, Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/ graphene thin films, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2013.09.098 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/graphene thin films Mohd Omaish Ansaria, Mohammad Mansoob Khana, Sajid Ali Ansaria, Ikhlasul Amalb, Jintae Leea and Moo Hwan Choa* a
School of Chemical Engineering, bDepartment of Materials Science and Engineering,Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, South Korea. *Email: [email protected], Phone: 82-53-810-2517; Fax: 82-53- 810-4631
Abstract Highly conducting nanocomposite film of polyaniline (Pani) with graphene (GN) was prepared by incorporating GN nanoplatelets in Pani matrix, followed by sulfonating it with fuming sulfuric acid. Sheet-like GN nanoplatelets were distributed uniformly in a Pani matrix, leading to high electrical conductivity due to - interaction between sulfonated Pani (s-Pani) and GN. Studies of the thermoelectrical behavior and ammonia-sensing behavior on GN@s-Pani showed high DC electrical conductivity retention under ageing conditions as well as excellent reproducible sensing response towards ammonia vapor in contrast to acid-protonated Pani. Keywords: Polyaniline; GN@s-Pani; Conductivity; Isothermal
1
Introduction Recently, composites of polyaniline (Pani) with carbonaceous materials, such as CNT and graphene (GN), have attracted considerable attention for their potential applications in future technologies [1]. Among the different derivatives of Pani, sulfonated-Pani (s-Pani) has attracted considerable interest because they possess distinct properties, such as high stability, good electrochemical properties, etc., which makes them suitable for applications in sensors, fuel cells, etc. [2,3]. s-Pani contains an ionizable sulfonic group that plays the role of an inner dopant ion. Therefore, no anion exchange occurs during the redox process and the material is considerably more stable than acid doped Pani [4]. On the other hand, due to the electron withdrawing nature of sulfonic group, the conductivity of s-Pani is lower than acid-protonated Pani. To achieve the beneficial properties of s-Pani, suitable fillers can be incorporated, which bestows electrical conductivity and can also give rise to Pani with hitherto unreported properties. Among the different allotropes of carbon, GN is a rising star owing to its good combination of mechanical strength and conductivity, which is in contrast to the insulating properties of diamond, charcoal etc. [5]. Owing to the exceptional properties of both s-Pani and GN, it is expected that composite of s-Pani and GN will give materials with unique properties. A large number of reports on the synthesis of s-Pani by different routes have been published [6,7], but there are few reports on the sulfonation of as-prepared Pani film by a solution casting method, and its electrical/electrochemical properties. In this study, GN@s-Pani film was prepared, and their gas sensing properties and electrical stability under ageing conditions were examined. Experimental Section
2
The synthesis of an emeraldine base (EB) of GN@s-Pani film is reported elsewhere [8]. The EB film was sulfonated by stirring in 200 mL of 30% H2SO4 for 2 hours, followed by washing with water and methanol, and drying at 80 ºC [9]. For isothermal and cyclic ageing studies, the film was annealed at 150 ºC in order to remove moisture and other volatile impurities. The sulfonated film (GN@s-Pani) was checked for electro-neutrality and ammonia vapor sensing. The detail of the experimental setup is reported elsewhere [10]. The stability of GN@s-Pani was examined in terms of DC electrical conductivity retention under isothermal and cyclic ageing conditions using a standard 4-in-line probe device. In isothermal ageing, the film was heated to 50, 70, 90, 110 and 130 °C, and the electrical conductivity was measured at 10 minute intervals. In cyclic ageing experiments, the DC electrical conductivity was measured five times from 40-150 °C. Results and Discussion Scanning electron microscopy (SEM) of the Pani films revealed a uniform morphology without morphological defects on the surface (Fig. 1a), whereas in the case of GN@Pani, the GN sheets were imbedded and distributed on the surface (Fig. 1b). The cross sectional SEM image of the fractured films showed a significant difference in the morphological features. Pani showed a compact structure (Fig. 1c), whereas in GN@Pani, the GN sheets can be observed clearly from the fractured view side (Fig. 1d). A uniform distribution on the surface and inside the matrix may contribute to a better translation of the nano-physical properties of both Pani and GN into the resulting GN@Pani film. X-ray diffraction (XRD) of emeraldine base GN@s-Pani film (Fig. 1e) showed a single broad amorphous peak for Pani at 2 = 19.5°, due to the periodicity parallel to the polymer chain
3
[11], as well as a sharp peak at 2 = 26.5° that was assigned to graphite, which is indicative of the presence of GN in the composite with a typical d-spacing of 0.33 nm [11]. The XRD pattern of GN@s-Pani showed an increase in the intensity of Pani peak, which might be due to the sulfonic group entering the Pani lattice and filling the vacant side leading to a more ordered arrangement [12]. The broadening and slight shift in the peak of Pani after sulfonation was related to steric hindrance induced after the incorporation of a sulfonic group in the Pani lattice. The diffused reflectance spectra (DRS) of GN@Pani revealed three absorption peaks at 280 nm, 326 nm and 550 nm, which were assigned to the excitation of nitrogen in the benzenoid segments (–*, polaron-* and n–* transition respectively) (Fig. 1f). In the case of GN@sPani composite, the absorption peaks shifted to 287 nm 383 nm and 633 nm, indicating the delocalization of charge through the GN@s-Pani chain. (Fig.1) The initial electrical conductivity at room temperature of as-prepared GN@s-Pani was 1.42 S/cm, which was much higher than s-Pani (0.2x10-2 S/cm). The incorporation of a sulfonic group decreases the conductivity of Pani due to the –M effect but GN@s-Pani exhibited high electrical conductivity due to the very high electron mobility of GN. The increase in electrical conductivity was attributed to the additional synergistic effect of s-Pani and GN because both are conducting, and to the - interaction between s-Pani and GN, which provides more efficient network for the transfer of charge carriers (Fig. 2a) [11]. After annealing the film at 150 °C, the conductivity decreased to 0.35 S/cm and remained stable, which might be due to the loss of moisture, degradation of low molecular weight oligomers, impurities, etc. The electrical conductivity increased with increasing temperature, and showed remarkable stability, even
4
beyond 170 °C compared to mineral acid doped Pani (Fig. 2b) [4]. The DC electrical conductivity retention examined under cyclic ageing conditions showed that the GN@s-Pani film was quite stable for multiple cycles (Fig. 2c). The conductivity increased from 40 °C to 150 °C in each cycle, and subsequent cycles revealed little loss (~14%, ~17%, ~25% and ~30% in 2nd, 3rd, 4th and 5th cycle respectively) compared to Pani nanocomposites reported with different fillers [8,10,11]. In the case of DC electrical conductivity retention under isothermal ageing conditions, the initial conductivity at 50, 70, 90, 110 and 130 °C was 0.35, 0.46, 0.57, 0.65 and 0.79 S/cm respectively. The increase in electrical conductivity with increasing temperature was attributed to the thermal effect, increasing the mobility of charge carriers. The change in the relative electrical conductivity during each experiment was divided by the duration of the experiment (30 min) to obtain the relative electrical conductivity loss/gain per minute of heating according to the following equation:
Fig. 2d shows that at 50 °C, there was a gain in electrical conductivity, whereas loss was observed at higher temperatures. On the other hand, the loss was negligible as compared to the HCl-doped Pani, which is the typical behavior of semiconducting materials [8,11]. These results suggest that sulfonic groups have a major effect on DC electrical conductivity stabilization because loss of dopant is minimized at higher temperatures. Reports on acid-doped Pani composite with TiO2, GN, Ag and ZnO showed stability until ~130 °C, after which a loss of electrical conductivity was observed at higher temperature [8,11,13-15]. In the present case, GN@s-Pani showed high conductivity at room temperature (1.42 S/cm) as well as remarkable stability up to 170 °C. Therefore, the presence of GN increases the electrical
5
conductivity, whereas due to the sulfonic group, the loss of dopant is minimized, providing a highly stable nanocomposite. (Fig. 2) When the film was dipped in a 0.1 M ammonia solution, there was the formation of ammonium salt (SO3-……NH4+) of GN@s-Pani, which is similar to the EB form of Pani, hence an increase in resistivity was observed. On the other hand, upon heating the film, the ammonium salt decomposed with the release of NH3 and the resistivity decreased [16]. Upon successive doping, however, the resistivity was always higher than the previous value, which might be due to the incomplete decomposition of the salt, leading to partial neutralization of the conducting backbone. (Fig. 3) The film showed an excellent reproducible sensing response towards exposure to low concentration (0.01 M) of ammonia, the resistivity increased on exposing the film to ammonia vapor, and decreased to the initial value under ambient atmosphere. Even after several cycles, the conductivity decreased from 0.40 to 0.28 S/cm due to the reasons mentioned above. Complete de-doping does not occur and the film remained conducting, even after several cycles, which is in contrast to acid-doped Pani, where acid-base neutralization occurs, leading to insulating state of Pani [16]. This suggests that ammonia interacts with imine nitrogen through its lone pair of electrons, decreasing the intensity of positive charge on nitrogen (Fig. 3). This leads to the decrease in the mobility of solitons, polarons and bipolarons, hence an increase in resistivity. However this interaction is electrostatic and due to small magnitude of positive charge on imine nitrogen it is reversible under ambient atmosphere where desorption of ammonia occurs and
6
resistivity is restored. This indicates that no anion exchange takes place due to the inner sulfonic group, hence no redox reaction occurs. Therefore, the conducting state is maintained. Conclusions GN@s-Pani film was prepared successfully by solvent casting technique, later sulfonating it with fuming sulfuric acid. The film showed high electrical conductivity (1.42 S/cm) compared to s-Pani (0.2x10-2 S/cm) due to the high mobility of charge carriers via - interaction between s-Pani and GN. Electrical conductivity studies revealed high conductivity retention, after repeated use, whereas ammonia sensing was reproducible with little neutralization of s-Pani backbone. On account of their better thermoelectric and sensing performance, such a material should be a suitable replacement for Pani in a range of electrical and electronic devices. Acknowledgements This study was supported by Basic Science Research Program through National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No:2012R1A1A4A01005951). References [1] Fan H, Zhao N, Wang H, Li X, Xu J. Matter Lett 2013;92:157-60. [2] Wei XL, Wang YZ, Long SM , Bobeczko C, Epstein AJ. J Am Chem Soc 1996;118:2545-55. [3] Yadav SK, Cho JW. Appl Surf Sci 2013;266:360-67. [4] Bai H, Xu Y, Zhao L, Li C, Shi G. Chem Commun 2009;1667-79. [5] LiuJ, TangJ, GoodingJJ. J Mater Chem 2012;22:12435-52.
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[6] KeWJ, Lin GH, Hsu CP, Chen CM, Cheng YS, Jen TH, Chen SA. J Mater Chem 2011;21:13483-89. [7] Deore BA, Yu I, Freund MS. J Am Chem Soc 2004;126:52-3. [8] Ansari MO, Mohammad F. J Appl Polym Sci 2012;124:4433-42. [9] Yue J, Epstein AJ. J Am Chem Soc 1990;112:2800-01 [10] Ansari MO, Mohammad F. Sensors and Actuat B-Chem 2011;157:122-29. [11] Ansari MO, Yadav SK, Cho JW, Mohammad F. Compos Part B-Eng 2013;47:155-61. [12] Koul S, Dhawan SK, Chandra R. Synth Met 2001;124:295-99 [13] Ansari MO, Mohammad F. Compos Part B-Eng 2012;43:3541-48. [14] Ansari SP, Mohammad F. ISRN Mater Sci 2012;2012:1-7. [15] Xiang J, Drzal LT. Polymer 2012;53:4202-10 [16] Khan AA, Khalid M. J Appl Polym Sci 2010;117:1601-07. Figure captions: Fig. 1. (a) SEM image of Pani, (b) GN@Pani, (c) side view of fractured Pani film, (d) side view of fractured GN@Pani film, (e) XRD patterns of GN@Pani and GN@s-Pani and (f) DRS of GN@Pani and GN@s-Pani. Fig. 2. (a) Schematic representation of interaction between s-Pani and GN, (b) electrical conductivity with increasing temperature, (c) electrical conductivity during cycling ageing and (d) change in the relative electrical conductivity during isothermal ageing. Fig. 3. Mechanism of reversible interaction of GN@s-Pani with ammonia.
8
GN@s-Pani prepared by incorporating GN into Pani, later sulfonated by fuming H2SO4. ¾ GN@s-Pani film showed enhanced thermoelectric behavior under ageing experiments. ¾ GN@s-Pani showed better ammonia sensing behavior than acid protonated Pani.
9
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Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/graphene thin films Mohd Omaish Ansari, Mohammad Mansoob Khan, Sajid Ali Ansari, Ikhlasul Amal, Jintae Lee, Moo Hwan Cho
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(13)01342-6 http://dx.doi.org/10.1016/j.matlet.2013.09.098 MLBLUE15866
To appear in:
Materials Letters
Received date: 6 July 2013 Accepted date: 25 September 2013 Cite this article as: Mohd Omaish Ansari, Mohammad Mansoob Khan, Sajid Ali Ansari, Ikhlasul Amal, Jintae Lee, Moo Hwan Cho, Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/ graphene thin films, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2013.09.098 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Enhanced thermoelectric performance and ammonia sensing properties of sulfonated polyaniline/graphene thin films Mohd Omaish Ansaria, Mohammad Mansoob Khana, Sajid Ali Ansaria, Ikhlasul Amalb, Jintae Leea and Moo Hwan Choa* a
School of Chemical Engineering, bDepartment of Materials Science and Engineering,Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, South Korea. *Email: [email protected], Phone: 82-53-810-2517; Fax: 82-53- 810-4631
Abstract Highly conducting nanocomposite film of polyaniline (Pani) with graphene (GN) was prepared by incorporating GN nanoplatelets in Pani matrix, followed by sulfonating it with fuming sulfuric acid. Sheet-like GN nanoplatelets were distributed uniformly in a Pani matrix, leading to high electrical conductivity due to - interaction between sulfonated Pani (s-Pani) and GN. Studies of the thermoelectrical behavior and ammonia-sensing behavior on GN@s-Pani showed high DC electrical conductivity retention under ageing conditions as well as excellent reproducible sensing response towards ammonia vapor in contrast to acid-protonated Pani. Keywords: Polyaniline; GN@s-Pani; Conductivity; Isothermal
1
Introduction Recently, composites of polyaniline (Pani) with carbonaceous materials, such as CNT and graphene (GN), have attracted considerable attention for their potential applications in future technologies [1]. Among the different derivatives of Pani, sulfonated-Pani (s-Pani) has attracted considerable interest because they possess distinct properties, such as high stability, good electrochemical properties, etc., which makes them suitable for applications in sensors, fuel cells, etc. [2,3]. s-Pani contains an ionizable sulfonic group that plays the role of an inner dopant ion. Therefore, no anion exchange occurs during the redox process and the material is considerably more stable than acid doped Pani [4]. On the other hand, due to the electron withdrawing nature of sulfonic group, the conductivity of s-Pani is lower than acid-protonated Pani. To achieve the beneficial properties of s-Pani, suitable fillers can be incorporated, which bestows electrical conductivity and can also give rise to Pani with hitherto unreported properties. Among the different allotropes of carbon, GN is a rising star owing to its good combination of mechanical strength and conductivity, which is in contrast to the insulating properties of diamond, charcoal etc. [5]. Owing to the exceptional properties of both s-Pani and GN, it is expected that composite of s-Pani and GN will give materials with unique properties. A large number of reports on the synthesis of s-Pani by different routes have been published [6,7], but there are few reports on the sulfonation of as-prepared Pani film by a solution casting method, and its electrical/electrochemical properties. In this study, GN@s-Pani film was prepared, and their gas sensing properties and electrical stability under ageing conditions were examined. Experimental Section
2
The synthesis of an emeraldine base (EB) of GN@s-Pani film is reported elsewhere [8]. The EB film was sulfonated by stirring in 200 mL of 30% H2SO4 for 2 hours, followed by washing with water and methanol, and drying at 80 ºC [9]. For isothermal and cyclic ageing studies, the film was annealed at 150 ºC in order to remove moisture and other volatile impurities. The sulfonated film (GN@s-Pani) was checked for electro-neutrality and ammonia vapor sensing. The detail of the experimental setup is reported elsewhere [10]. The stability of GN@s-Pani was examined in terms of DC electrical conductivity retention under isothermal and cyclic ageing conditions using a standard 4-in-line probe device. In isothermal ageing, the film was heated to 50, 70, 90, 110 and 130 °C, and the electrical conductivity was measured at 10 minute intervals. In cyclic ageing experiments, the DC electrical conductivity was measured five times from 40-150 °C. Results and Discussion Scanning electron microscopy (SEM) of the Pani films revealed a uniform morphology without morphological defects on the surface (Fig. 1a), whereas in the case of GN@Pani, the GN sheets were imbedded and distributed on the surface (Fig. 1b). The cross sectional SEM image of the fractured films showed a significant difference in the morphological features. Pani showed a compact structure (Fig. 1c), whereas in GN@Pani, the GN sheets can be observed clearly from the fractured view side (Fig. 1d). A uniform distribution on the surface and inside the matrix may contribute to a better translation of the nano-physical properties of both Pani and GN into the resulting GN@Pani film. X-ray diffraction (XRD) of emeraldine base GN@s-Pani film (Fig. 1e) showed a single broad amorphous peak for Pani at 2 = 19.5°, due to the periodicity parallel to the polymer chain
3
[11], as well as a sharp peak at 2 = 26.5° that was assigned to graphite, which is indicative of the presence of GN in the composite with a typical d-spacing of 0.33 nm [11]. The XRD pattern of GN@s-Pani showed an increase in the intensity of Pani peak, which might be due to the sulfonic group entering the Pani lattice and filling the vacant side leading to a more ordered arrangement [12]. The broadening and slight shift in the peak of Pani after sulfonation was related to steric hindrance induced after the incorporation of a sulfonic group in the Pani lattice. The diffused reflectance spectra (DRS) of GN@Pani revealed three absorption peaks at 280 nm, 326 nm and 550 nm, which were assigned to the excitation of nitrogen in the benzenoid segments (–*, polaron-* and n–* transition respectively) (Fig. 1f). In the case of GN@sPani composite, the absorption peaks shifted to 287 nm 383 nm and 633 nm, indicating the delocalization of charge through the GN@s-Pani chain. (Fig.1) The initial electrical conductivity at room temperature of as-prepared GN@s-Pani was 1.42 S/cm, which was much higher than s-Pani (0.2x10-2 S/cm). The incorporation of a sulfonic group decreases the conductivity of Pani due to the –M effect but GN@s-Pani exhibited high electrical conductivity due to the very high electron mobility of GN. The increase in electrical conductivity was attributed to the additional synergistic effect of s-Pani and GN because both are conducting, and to the - interaction between s-Pani and GN, which provides more efficient network for the transfer of charge carriers (Fig. 2a) [11]. After annealing the film at 150 °C, the conductivity decreased to 0.35 S/cm and remained stable, which might be due to the loss of moisture, degradation of low molecular weight oligomers, impurities, etc. The electrical conductivity increased with increasing temperature, and showed remarkable stability, even
4
beyond 170 °C compared to mineral acid doped Pani (Fig. 2b) [4]. The DC electrical conductivity retention examined under cyclic ageing conditions showed that the GN@s-Pani film was quite stable for multiple cycles (Fig. 2c). The conductivity increased from 40 °C to 150 °C in each cycle, and subsequent cycles revealed little loss (~14%, ~17%, ~25% and ~30% in 2nd, 3rd, 4th and 5th cycle respectively) compared to Pani nanocomposites reported with different fillers [8,10,11]. In the case of DC electrical conductivity retention under isothermal ageing conditions, the initial conductivity at 50, 70, 90, 110 and 130 °C was 0.35, 0.46, 0.57, 0.65 and 0.79 S/cm respectively. The increase in electrical conductivity with increasing temperature was attributed to the thermal effect, increasing the mobility of charge carriers. The change in the relative electrical conductivity during each experiment was divided by the duration of the experiment (30 min) to obtain the relative electrical conductivity loss/gain per minute of heating according to the following equation:
Fig. 2d shows that at 50 °C, there was a gain in electrical conductivity, whereas loss was observed at higher temperatures. On the other hand, the loss was negligible as compared to the HCl-doped Pani, which is the typical behavior of semiconducting materials [8,11]. These results suggest that sulfonic groups have a major effect on DC electrical conductivity stabilization because loss of dopant is minimized at higher temperatures. Reports on acid-doped Pani composite with TiO2, GN, Ag and ZnO showed stability until ~130 °C, after which a loss of electrical conductivity was observed at higher temperature [8,11,13-15]. In the present case, GN@s-Pani showed high conductivity at room temperature (1.42 S/cm) as well as remarkable stability up to 170 °C. Therefore, the presence of GN increases the electrical
5
conductivity, whereas due to the sulfonic group, the loss of dopant is minimized, providing a highly stable nanocomposite. (Fig. 2) When the film was dipped in a 0.1 M ammonia solution, there was the formation of ammonium salt (SO3-……NH4+) of GN@s-Pani, which is similar to the EB form of Pani, hence an increase in resistivity was observed. On the other hand, upon heating the film, the ammonium salt decomposed with the release of NH3 and the resistivity decreased [16]. Upon successive doping, however, the resistivity was always higher than the previous value, which might be due to the incomplete decomposition of the salt, leading to partial neutralization of the conducting backbone. (Fig. 3) The film showed an excellent reproducible sensing response towards exposure to low concentration (0.01 M) of ammonia, the resistivity increased on exposing the film to ammonia vapor, and decreased to the initial value under ambient atmosphere. Even after several cycles, the conductivity decreased from 0.40 to 0.28 S/cm due to the reasons mentioned above. Complete de-doping does not occur and the film remained conducting, even after several cycles, which is in contrast to acid-doped Pani, where acid-base neutralization occurs, leading to insulating state of Pani [16]. This suggests that ammonia interacts with imine nitrogen through its lone pair of electrons, decreasing the intensity of positive charge on nitrogen (Fig. 3). This leads to the decrease in the mobility of solitons, polarons and bipolarons, hence an increase in resistivity. However this interaction is electrostatic and due to small magnitude of positive charge on imine nitrogen it is reversible under ambient atmosphere where desorption of ammonia occurs and
6
resistivity is restored. This indicates that no anion exchange takes place due to the inner sulfonic group, hence no redox reaction occurs. Therefore, the conducting state is maintained. Conclusions GN@s-Pani film was prepared successfully by solvent casting technique, later sulfonating it with fuming sulfuric acid. The film showed high electrical conductivity (1.42 S/cm) compared to s-Pani (0.2x10-2 S/cm) due to the high mobility of charge carriers via - interaction between s-Pani and GN. Electrical conductivity studies revealed high conductivity retention, after repeated use, whereas ammonia sensing was reproducible with little neutralization of s-Pani backbone. On account of their better thermoelectric and sensing performance, such a material should be a suitable replacement for Pani in a range of electrical and electronic devices. Acknowledgements This study was supported by Basic Science Research Program through National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No:2012R1A1A4A01005951). References [1] Fan H, Zhao N, Wang H, Li X, Xu J. Matter Lett 2013;92:157-60. [2] Wei XL, Wang YZ, Long SM , Bobeczko C, Epstein AJ. J Am Chem Soc 1996;118:2545-55. [3] Yadav SK, Cho JW. Appl Surf Sci 2013;266:360-67. [4] Bai H, Xu Y, Zhao L, Li C, Shi G. Chem Commun 2009;1667-79. [5] LiuJ, TangJ, GoodingJJ. J Mater Chem 2012;22:12435-52.
7
[6] KeWJ, Lin GH, Hsu CP, Chen CM, Cheng YS, Jen TH, Chen SA. J Mater Chem 2011;21:13483-89. [7] Deore BA, Yu I, Freund MS. J Am Chem Soc 2004;126:52-3. [8] Ansari MO, Mohammad F. J Appl Polym Sci 2012;124:4433-42. [9] Yue J, Epstein AJ. J Am Chem Soc 1990;112:2800-01 [10] Ansari MO, Mohammad F. Sensors and Actuat B-Chem 2011;157:122-29. [11] Ansari MO, Yadav SK, Cho JW, Mohammad F. Compos Part B-Eng 2013;47:155-61. [12] Koul S, Dhawan SK, Chandra R. Synth Met 2001;124:295-99 [13] Ansari MO, Mohammad F. Compos Part B-Eng 2012;43:3541-48. [14] Ansari SP, Mohammad F. ISRN Mater Sci 2012;2012:1-7. [15] Xiang J, Drzal LT. Polymer 2012;53:4202-10 [16] Khan AA, Khalid M. J Appl Polym Sci 2010;117:1601-07. Figure captions: Fig. 1. (a) SEM image of Pani, (b) GN@Pani, (c) side view of fractured Pani film, (d) side view of fractured GN@Pani film, (e) XRD patterns of GN@Pani and GN@s-Pani and (f) DRS of GN@Pani and GN@s-Pani. Fig. 2. (a) Schematic representation of interaction between s-Pani and GN, (b) electrical conductivity with increasing temperature, (c) electrical conductivity during cycling ageing and (d) change in the relative electrical conductivity during isothermal ageing. Fig. 3. Mechanism of reversible interaction of GN@s-Pani with ammonia.
8
GN@s-Pani prepared by incorporating GN into Pani, later sulfonated by fuming H2SO4. ¾ GN@s-Pani film showed enhanced thermoelectric behavior under ageing experiments. ¾ GN@s-Pani showed better ammonia sensing behavior than acid protonated Pani.
9
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