- Email: [email protected]
xanthan gum nanocomposite: Conductivity and thermal properties
Synthetic Metals 162 (2012) 171–175
Contents lists available at SciVerse ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Fabrication and characterization of polyaniline/xanthan gum nanocomposite: Conductivity and thermal properties Saeedeh Gilani Larimi, Hamid Heydarzadeh Darzi ∗ , Ghasem Najafpour Darzi Babol University of Technology, P.O. Box 484 Babol, Iran
a r t i c l e
i n f o
Article history: Received 3 October 2011 Received in revised form 16 November 2011 Accepted 26 November 2011 Available online 15 December 2011 Keywords: Nanocomposite Polyaniline Xanthan gum Conductivity Thermal stability
a b s t r a c t A novel conductive and thermally stable nanocomposite was synthesized by oxidative polymerization of aniline in the presence of xanthan gum. The fabricated nanocomposite morphology and structure were examined by atomic forced microscopy (AFM) and FT-IR measurement. The conductivity investigation of novel polyaniline (PANI) based nanocomposite exhibited that xanthan gum (XG) can improve the electrical conductivity up to 2.48 × 10−1 with 2 g xanthan gum in 0.2 mol l−1 aniline solution. Thermogravimetric analyzer (TGA) was used to study the thermal behavior of nanocomposite. The TGA curves indicated that xanthan gum enhanced the thermal stability of nanocomposite at less than 270 ◦ C and over 350 ◦ C. A problem limiting the application of polyaniline is its hydrophobic property that was solved approximately by the presence of xanthan gum in its nanocomposite. The swelling tests revealed that xanthan gum promoted the hydrophilic property of polyaniline extremely. © 2011 Elsevier B.V. All rights reserved.
1. Introduction By developing new technologies, the demand for novel materials with desirable properties is increasing gradually. One of the methods to develop such materials is the fabrication of nanocomposites from compatible materials. Among many of materials, research about conducting polymers has increased in recent years due to their number of industrial and scientific applications [1–4]. Most of these applications are based on physical characteristics that exhibit electrical and thermal properties like metals or semiconductors [5–8]. One of the most noted conducting polymers that has attracted much attention owing to its very simple preparation and good environmental stability is polyaniline (PANI), which can be doped by protonic acids to attain high electrical conductivities [3,5,9–11]. On the other hand, two facts that restrict the application of polyaniline are its insolubility among common solvents and its non-biodegradablility [2,4]. It is known that compatibility of conducting polymers and carbohydrates can exhibit molecular interactions that may affect the specific properties associated with solubility and biodegradability of them. Xanthan gum is a natural sourced water soluble carbohydrate that is mainly prepared by biological process. Its biodegradability and easy solubility in both hot and cold water make it suitable material for a large number of applications. Xanthan gum has several advantages that make it
∗ Corresponding author. Tel.: +98 9111535048; fax: +98 1113234204. E-mail address: [email protected] (H.H. Darzi). 0379-6779/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.11.027
appropriate choice to use it as a composer which distinguishes it among other bio-sourced materials. Some its advantages are easy and inexpensive production, well biocompatible property, nontoxic and high water solubility. Besides, the lone pair electrons at oxygen atoms in carboxylic groups of xanthan gum can be effective in electrical conductivity [12–15]. Many applications have been reported in the literature concerning nanocomposite of polyaniline and natural or synthetic carbohydrates but the electrical and thermal properties of polyaniline/xanthan gum nanocomposite, which is the object of this work, have not been studied yet [1,3,8]. In this study, polyaniline/xanthan gum nanocomposite was prepared in the aqueous solution using APS (ammonium persulfate) as an oxidant [16,17]. The morphology and structure of synthesized nanocomposite were examined by atomic force microscopy (AFM) and Fourier transform infrared (FTIR) respectively. In addition, the tea bag method for showing the improvement of polyaniline hydrophilic behavior associated with its water-soluble property using xanthan gum were carried out.
2. Experimental 2.1. Materials In this work aniline, ammonium peroxy disulfate (APS, (NH4 )2 S2 O8 ), sodium hydroxide, hydrochloric acid (Merck, Germany) and xanthan gum (Mw = 2 × 106 ) were used. Deionized water was used during this work. Aniline monomer was purified
172
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
Fig. 1. AFM images of XG (a), PANI (b) and PANI/XG nanocomposite No. 2 (c) (image size = 10 m × 10 m).
by simple distillation. All reagents were used without further purification.
and NaOH (pH 13.0) solutions were added to distilled water to attain the favorite pH.
2.2. Analyses and characterizations 2.3. Synthesis of polyaniline The morphologies and structural studies were investigated by atomic force microscopy (AFM) (Nanosurf scanning probe-optical microscope, EasyScan II, Swiss) and Fourier transform infrared (FTIR) spectrometer spectra in the range 500–2000 cm−1 (Shimadzu model 4100, Japan) respectively. A standard four-probe method using a Keithley 196 System DMM Digital Multi-meter and an Advantest R1642 programmable dc voltage/current generator as the current Source for detecting the room temperature conductivity was used. Thermal properties were examined by thermogravimetric analyzer (TGA) (Perkin Elmer model 4000, USA). In order to consider the hydrophilic property of polyaniline based nanocomposite the swelling tests were carried out by tea bag method in various pHs. Based on this method as reported in literatures [18,19] a small bag made of nylon (50 mm × 90 mm; 200 mesh) was filled with 100 mg of fabricated nanocomposite as initial sample. Afterward the filled bag was soaked in 200 ml distillated water at room temperature. After 24 h when the swelling reach to equilibrium amount filled bag was removed from the medium and let the excess water to remove by hanging during 15 min. The swelling amount (S) was explained as follows: S(g/g) =
Ws − Wi . Wi
where Ws and Wi are the swollen and initial samples weight respectively. For preparing the pH media, standard aqueous HCl (pH 1.0)
Polyaniline was fabricated using oxidative polymerization of aniline which reported in other literature. Based on this procedure aniline monomers were dissolved in aqueous HCl (1 M) in the presence of ammonium peroxydisulfate (APS) as the oxidant at ice temperature. The fabricated polyaniline was undoped using aqueous ammonia (1 M), dried at 60 ◦ C in an air oven for 48 h and stored in a dessicator for further experimentation [1–3].
2.4. Synthesis of polyaniline/xanthan gum nanocomposite The nanocomposite of polyaniline and xanthan gum was synthesized by adding the slightly viscous solution of xanthan gum to the aniline solution. For producing the polyaniline based nanocomposite 5 experiments with various amounts of xanthan gum were conducted. Aniline was dissolved in 1000 ml of aqueous solution of HCl and ammonium peroxydisulfate together with xanthan gum was dissolved in 1000 ml HCl (1 M) separately. The prepared mixture of xanthan gum and oxidant was added slowly to the aniline solution at ice temperature and was stirred for an hour to reaction was accomplished. The fabricated nanocomposite was separated and purified as mentioned for polymerization of aniline. The information about production of nanocomposites is given in Table 3.
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
173
Table 1 Surface roughness parameters of pure XG, pure PANI and PANI/XG nanocomposite No. 2. Roughness parameters
Pure XG Pure PANI Nanocomposite No. 2
Fig. 2. FT-IR spectra of PANI (a), XG (b), nanocomposite No. 1 (c), No. 2 (d) and No. 3 (f).
3. Results and discussion Atomic force microscopy was used to analyze the surface morphology and roughness of the prepared nanocomposite. The PANI, XG and synthesized nanocomposite surfaces were imaged in a scan size of 10 m × 10 m and are shown in Fig. 1. The surface roughness parameters of the materials which are expressed in terms of the mean roughness (Sa), the root mean square of the Z data (Sq) and the mean difference between the five highest peaks and lowest valleys (Sz) were calculated from AFM images using tapping mode method via Nanosurf EasyScan software at a scan area of 10 m × 10 m given in Table 1. The film of pure XG shows homogeneity, as it could be predicted. A different morphology with more
Sa
Sq
Sz
1716.8 pm 2456.6 pm 1913.2 pm
2.15 nm 8.3 nm 5.79 nm
55.24 nm 94.3 nm 64.71 nm
roughness than that of XG film is observed for a pure PANI based film. As can be seen from the AFM image of synthesized nanocomposite and reported parameters in Table 1 the surface roughness of nanocomposite is more than XG and less than pure PANI that it is probably due to the effect of XG on the structure of PANI. Also the average particle sizes of substances obtained from AFM images were reported in Table 3. The average particle size of pure PANI and XG is 73 and 43 nm respectively. Particle size of synthesized nanocomposites reported in Table 3 shows that xanthan gum by molecular interaction with PANI can affect the particle size and reduce it from 73 to 50 nm. FTIR spectra of pure polyaniline (a) and xanthan gum (b) are shown in Fig. 2. The x-axis represents wavelength (cm−1 ) and yaxis shows the light transmittance through the samples. Polyaniline has representative peaks at 1586, 1490, 1307, 1130 and 816 cm−1 . The bands at 1586, 1490 cm−1 were attributed to C C and C N in the quinoid ( N Q N where Q = quinoid ring) and benzoid units, while the band at 1130 cm−1 is due to the quinoid unit of polyaniline ( N Q N where Q = quinoid ring). The band at 1307 cm−1 is allocated to the C N of benzoid unit. The band at 816 cm−1 may be assigned to C C and C H for benzoid unit of polyaniline. These results indicate that the fabrication of polyaniline was promising [20–23]. In the case of xanthan gum FT-IR analysis two characteristic peaks were observed. One of them appears at 1615 cm−1 and the other at 1476 cm−1 which are attributed to COO− groups. Additional bands of xanthan gum appear at 1417, 1023 cm−1 and 1568 cm−1 due to C H, O H and C O bonds respectively. As can be expected the synthesized nanomopsites have a composed structure of two polymers: polyaniline and xanthan gum. The FT-IR spectra of nanocomposites show the all of representative peaks of both xanthan gum and polyaniline which is mentioned above. Polyaniline–xanthan gum nanocomposite No. 2 has characteristic band at 1610, 1590, 1495, 1570, 1311, 1135, 1020, 1420 and 810 which are attributed to COO− group of xanthan gum, C C of benzonoid rings of PANI, C C of quinonoid rings of PANI, C O bond of xanthan gum, C N of benzonoid rings of PANI, quinonoid rings of PANI, hydroxyl group of xanthan gum, C H bond of xanthan gum
Table 2 FT-IR spectra of pure PANI, pure XG, nanocomposite No. 1, No. 2 and No. 3. Nanocomposite No.
FTIR spectra COO− a
Pure XG Pure PANI 1 2 3 a b c d e f g h i j
1615 – 1600 1610 1617
1476 – 1465 1470 1477
C Cb
C Cc
C Od
C Oe
C Nf
N Q Ng
O Hh
C Hi
C Hj
– 1586 1582 1590 1595
– 1490 1488 1495 1500
1568 – 1560 1570 1565
1406 – 1400 1403 1408
– 1307 1305 1311 1300
– 1130 1128 1135 1120
1023 – 1030 1020 1024
1417 – 1425 1420 1416
– 816 814 810 800
COO− of xanthan gum. Stretching deformation of benzonoid rings. Stretching deformation of quinonoid rings. Asymmetric stretching carboxylate anion. Symmetric stretching carboxylate anion. Stretching of the benzenoid ring. Vibration mode of N Q N (Q refers to the quinonic-type rings). Bending vibrations of xanthan gum. Bending vibrations of xanthan gum. Out-of-plane deformation of C H in the p-disubstituted benzene ring.
174
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
100
Table 3 Effect of preparation conditions and amount of xanthan gum on the conductivity and particle size of synthesized nanocomposites.
Pure PANI
Weight loos ( %)
Pure XG 80
Composite No.1 Composite No.2
60
Nanocomposite No.
XG (g)
Aniline (mol)
Oxidant (APS) (mol)
Average particle size (nm)
Conductivity
Pure PANI 1 2 3 4 5 Pure XG
– 1 2 3 4 5 –
0.2 0.2 0.2 0.2 0.2 0.2 –
0.25 0.25 0.25 0.25 0.25 0.25 –
71 68 59 57 52 50 43
1.63 × 10−1 1.91 × 10−1 2.48 × 10−1 1.52 × 10−1 0.92 × 10−1 0.65 × 10−1 0.08 × 10−1
Composite No.3
40 20 0 0
100
200
300
400
500
600
700
800
Temperature (°C)
and C H bond of PANI respectively. All results are given in Table 2; as can be seen from these spectra the intensity of peaks grows by increasing in amount of each composer. The FTIR spectra suggest that the synthesized nanocomposites have the complex structure of both polyaniline and xanthan gum. For considering the thermal properties of initial substances and the products, TGA of pure polyaniline, xanthan gum and their nanocomposites (Nos. 1, 2 and 3) is done in the temperature range 0–800 ◦ C and the thermograms are presented in Fig. 3. The thermal behavior of pure polyaniline shows the three-step weight loss process that the initial weight loss of approximately 10% up to 110 ◦ C is due to the removal of moisture present in the polymer. The small weight loss of nearly 8% up to 280 ◦ C is owing to loss of oligomer and doping agent as volatile material. A massive weight loss of 80% up to 800 ◦ C is attributed to the degradation of the polymer chain indicating polymer was degraded completely. In addition, the thermogravimetric study of xanthan gum shows single step decomposition that starts at 230 ◦ C following the extremely small initial weight loss due to the removal of moisture. As can be concluded from the xanthan gum thermogram, the xanthan gum decomposition temperature was found to be 280 ◦ C. The rate of weight loss continues to 50% and then decreases insofar as a char yield of 32% was achieved at 800 ◦ C. In case of polyaniline/xanthan gum nanocomposite, the threestep weight loss was observed. The initial weight loss is approximately 6% up to 100 ◦ C due to the moisture removal. This quantity of weight loss indicates that presence of xanthan gum in nanocomposite may form a regular lattice which it can trap moisture in itself. This thermal stability in this range was improved with increasing the amount of xanthan gum in composites. Also, these effects were observed in the second step up to 270 ◦ C that nearly 7% weight loss occurs. As can be seen from the last step of nanocomposites and pure polyaniline thermograms, a char yield is improved from zero to variable amount from 7 to 22% which is the main effect of xanthan gum on thermal stability of nanocomposites. These results proved the fact that presence of xanthan gum enhances the thermal stability of synthesized nanocomposite less than 270 ◦ C and over 350 ◦ C. The conductive property of PANI/XG nanocomposites for realizing the effect of xanthan gum on it was considered. As mentioned above, several proportions of xanthan gum in nanocomposites were synthesized and the consequences are given in Table 3. These results reveal that conductivity of synthesized nanocomposites was improved by increasing the amount of xanthan gum. The maximum value of conductivity was achieved 2.48 × 10−1 by 2 g of xanthan gum. The increasing of polyaniline based nanocomposite conductivity could be explained with the presence of COO− groups in
xanthan gum. Xanthan gum has a side chain in each monomer unit containing a d-glucuronic acid unit between two d-mannose that each of them has a carboxyl groups in it. Based on literatures, presence of lone pair electrons at oxygen atoms in carboxylic group play host to proton conduction that probably can improve the electron mobility. However, by increasing the amount of xanthan gum more than 2 g, conductivity of nanocomposites was decreased compared with what was obtained for pure polyaniline. Descended in conductivity by increasing in amount of xanthan gum might be due to the fact that in higher concentration of xanthan gum in nanocomposite it acts as impurity. Fig. 4 shows the hydrophilic property of polyaniline based nanocomposite in various pH values 4, 7 and 10 at room temperature. The swelling amount was found to enlarge with increasing of xanthan gum ratio in nanocomposites. Also, swelling studies revealed that environmental pH value can affect the nanocomposites property. It is known that a high concentration of charged ionic groups in the hydro-gel increases the swelling due to osmosis and charge repulsion. As can be seen from Fig. 4 the maximum swelling amount was achieved by neutral pH. Owing to inclusion of xanthan gum, synthesized nanocomposite has a carboxyl anion in its side chain such that repulsive forces between these anions make swelling. Due to the absence of other ions in neutral pH anion–anion repulsive forces become stronger. In acidic pH values, most of the carboxylate anions are protonated; therefore the main anion–anion repulsive forces are neutralized and consequently swelling amount declined. Likewise, a charge screening effects of the cations limit the swelling at basic pH values.
70 pH=7
60
pH=10 Swelling (g/g)
Fig. 3. TGA thermograms of pure PANI, pure XG, nanocomposite Nos. 1, 2 and 3.
50
pH=4
40 30 20 10 0 10
20
30
40
50
60
70
80
90
% XG/composite (w/w) Fig. 4. Influence of pH values and amount of XG on equilibrium swelling of synthesized nanocomposites at 25 ◦ C.
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
4. Conclusions In this work polyaniline/xanthan gum nanocomposite was synthesized by oxidative polymerization of aniline in the presence of xanthan gum. The (AFM) and FT-IR measurements confirm the morphology and structure of synthesized nanocomposite. The TGA curves revealed that xanthan gum can decrease the weight loss of nanocomposite that a char yield is improved from zero for pure polyaniline to 22% for nanocomposite. Besides, xanthan gum enhanced the electrical conductivity up to 2.48 × 10−1 with 2 g xanthan gum in 0.2 mol l−1 aniline solution that by increasing in amount of it more than 2 g in nanocomposite decreased the electrical conductivity. Because of xanthan gum is a water soluble biopolymer it can affect the hydrophilic property of polyaniline. The tea bag method was used for determining the swelling amount of nanocomposite in aqueous solution and showed that the swelling amount of nanocomposite was extremely increased by the addition of xanthan gum. References [1] M. Lukasiewic, A. Ptaszek, L. Koziel, B. Achremowicz, M. Grzesik, Polym. Bull. 58 (2007) 281–288. [2] B. Naskar, A. Dan, S. Ghosh, S.P. Moulik, Carbohydr. Polym. 81 (2010) 700–706. [3] A. Ahmed, F. Mohammad, M.Z. Rahman, Synth. Met. 144 (2004) 29–49.
175
[4] J. Nizioia, J. Laska, Synth. Met. 101 (1999) 720–721. [5] H. Mirhosseini, Ch P. Tan, N. Hamid, S. Yusof, Colloids Surf. A 315 (2008) 47–56. [6] J. Kamonsawas, A. Sirivat, S. Niamlang, P. Hormnirun, W. Prissanaroon-Ouajai, J. Sensors 10 (2010) 5590–5603. [7] A. Pron, M. Zagorska, Y. Nicolauc, F. Genoud, M. Nechtschein, Synth. Met. 84 (1997) 89–90. [8] L.D. Acqua, C. Tonin, R. Peila, F. Ferrero, M. Catellani, Synth. Met. 146 (2004) 213–221. [9] B. Davodi, M.S. Lashkenari, H. Eisazadeh, Synth. Met. 161 (2011) 1207–1210. [10] M. Yavuz, T. Tilki, C. Karabacak, O. Erol, H. Unal, M. Uluturk, M. Cabuk, Carbohydr. Polym. 79 (2010) 318–324. [11] A. Ptaszek, W. Berski, P. Ptaszek, T. Witczak, U. Repelewicz, M. Grzesik, Carbohydr. Polym. 76 (2009) 567–577. [12] C. Sasso, D. Beneventi, E. Zeno, M. Petit-Conil, D. Chaussy, M.N. Belgacem, Synth. Met. 161 (2011) 397–403. [13] J. Laska, A. Prince, Synth. Met. 84 (1997) 117–118. [14] M. Nedjhioui, N. Moulai-Mostefa, A. Morsli, A. Bensmaili, Desalination 185 (2005) 543–550. [15] N.E.A. Shuhaimi, L.P. Teo, S.R. Majid, A.K. Arof, Synth. Met. 160 (2010) 1040–1044. [16] M.A. Ayadi, J.C. Leuliet, F. Chopard, M. Berthou, M. Lebouche, Food Bioprod. Process. 82 (2004) 320–325. [17] M. Aleahmad, H. Gh Taleghani, H. Eisazadeh, Synth. Met. 161 (2011) 990–995. [18] P.S. Gils, D. Ray, P.K. Sahoo, Int. J. Biol. Macromol. 45 (2009) 364–371. [19] F. Hua, M. Qian, J. Mater. Sci. 36 (2001) 731–738. [20] K. Gupta, P.C. Jana, A.K. Meikap, Synth. Met. 160 (2010) 1566–1573. [21] Sh. Wang, Z. Tan, Y. Li, L. Sun, T. Zhang, Thermochim. Acta 441 (2006) 191–194. [22] P. Liu, Curr. Opin. Solid State Mater. Sci. 12 (2008) 9–13. [23] G. Ramya, C. Renugadevi, Ch. Rao, D.C. Trivedi, React. Funct. Polym. 68 (2008) 701–709.
Contents lists available at SciVerse ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Fabrication and characterization of polyaniline/xanthan gum nanocomposite: Conductivity and thermal properties Saeedeh Gilani Larimi, Hamid Heydarzadeh Darzi ∗ , Ghasem Najafpour Darzi Babol University of Technology, P.O. Box 484 Babol, Iran
a r t i c l e
i n f o
Article history: Received 3 October 2011 Received in revised form 16 November 2011 Accepted 26 November 2011 Available online 15 December 2011 Keywords: Nanocomposite Polyaniline Xanthan gum Conductivity Thermal stability
a b s t r a c t A novel conductive and thermally stable nanocomposite was synthesized by oxidative polymerization of aniline in the presence of xanthan gum. The fabricated nanocomposite morphology and structure were examined by atomic forced microscopy (AFM) and FT-IR measurement. The conductivity investigation of novel polyaniline (PANI) based nanocomposite exhibited that xanthan gum (XG) can improve the electrical conductivity up to 2.48 × 10−1 with 2 g xanthan gum in 0.2 mol l−1 aniline solution. Thermogravimetric analyzer (TGA) was used to study the thermal behavior of nanocomposite. The TGA curves indicated that xanthan gum enhanced the thermal stability of nanocomposite at less than 270 ◦ C and over 350 ◦ C. A problem limiting the application of polyaniline is its hydrophobic property that was solved approximately by the presence of xanthan gum in its nanocomposite. The swelling tests revealed that xanthan gum promoted the hydrophilic property of polyaniline extremely. © 2011 Elsevier B.V. All rights reserved.
1. Introduction By developing new technologies, the demand for novel materials with desirable properties is increasing gradually. One of the methods to develop such materials is the fabrication of nanocomposites from compatible materials. Among many of materials, research about conducting polymers has increased in recent years due to their number of industrial and scientific applications [1–4]. Most of these applications are based on physical characteristics that exhibit electrical and thermal properties like metals or semiconductors [5–8]. One of the most noted conducting polymers that has attracted much attention owing to its very simple preparation and good environmental stability is polyaniline (PANI), which can be doped by protonic acids to attain high electrical conductivities [3,5,9–11]. On the other hand, two facts that restrict the application of polyaniline are its insolubility among common solvents and its non-biodegradablility [2,4]. It is known that compatibility of conducting polymers and carbohydrates can exhibit molecular interactions that may affect the specific properties associated with solubility and biodegradability of them. Xanthan gum is a natural sourced water soluble carbohydrate that is mainly prepared by biological process. Its biodegradability and easy solubility in both hot and cold water make it suitable material for a large number of applications. Xanthan gum has several advantages that make it
∗ Corresponding author. Tel.: +98 9111535048; fax: +98 1113234204. E-mail address: [email protected] (H.H. Darzi). 0379-6779/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.11.027
appropriate choice to use it as a composer which distinguishes it among other bio-sourced materials. Some its advantages are easy and inexpensive production, well biocompatible property, nontoxic and high water solubility. Besides, the lone pair electrons at oxygen atoms in carboxylic groups of xanthan gum can be effective in electrical conductivity [12–15]. Many applications have been reported in the literature concerning nanocomposite of polyaniline and natural or synthetic carbohydrates but the electrical and thermal properties of polyaniline/xanthan gum nanocomposite, which is the object of this work, have not been studied yet [1,3,8]. In this study, polyaniline/xanthan gum nanocomposite was prepared in the aqueous solution using APS (ammonium persulfate) as an oxidant [16,17]. The morphology and structure of synthesized nanocomposite were examined by atomic force microscopy (AFM) and Fourier transform infrared (FTIR) respectively. In addition, the tea bag method for showing the improvement of polyaniline hydrophilic behavior associated with its water-soluble property using xanthan gum were carried out.
2. Experimental 2.1. Materials In this work aniline, ammonium peroxy disulfate (APS, (NH4 )2 S2 O8 ), sodium hydroxide, hydrochloric acid (Merck, Germany) and xanthan gum (Mw = 2 × 106 ) were used. Deionized water was used during this work. Aniline monomer was purified
172
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
Fig. 1. AFM images of XG (a), PANI (b) and PANI/XG nanocomposite No. 2 (c) (image size = 10 m × 10 m).
by simple distillation. All reagents were used without further purification.
and NaOH (pH 13.0) solutions were added to distilled water to attain the favorite pH.
2.2. Analyses and characterizations 2.3. Synthesis of polyaniline The morphologies and structural studies were investigated by atomic force microscopy (AFM) (Nanosurf scanning probe-optical microscope, EasyScan II, Swiss) and Fourier transform infrared (FTIR) spectrometer spectra in the range 500–2000 cm−1 (Shimadzu model 4100, Japan) respectively. A standard four-probe method using a Keithley 196 System DMM Digital Multi-meter and an Advantest R1642 programmable dc voltage/current generator as the current Source for detecting the room temperature conductivity was used. Thermal properties were examined by thermogravimetric analyzer (TGA) (Perkin Elmer model 4000, USA). In order to consider the hydrophilic property of polyaniline based nanocomposite the swelling tests were carried out by tea bag method in various pHs. Based on this method as reported in literatures [18,19] a small bag made of nylon (50 mm × 90 mm; 200 mesh) was filled with 100 mg of fabricated nanocomposite as initial sample. Afterward the filled bag was soaked in 200 ml distillated water at room temperature. After 24 h when the swelling reach to equilibrium amount filled bag was removed from the medium and let the excess water to remove by hanging during 15 min. The swelling amount (S) was explained as follows: S(g/g) =
Ws − Wi . Wi
where Ws and Wi are the swollen and initial samples weight respectively. For preparing the pH media, standard aqueous HCl (pH 1.0)
Polyaniline was fabricated using oxidative polymerization of aniline which reported in other literature. Based on this procedure aniline monomers were dissolved in aqueous HCl (1 M) in the presence of ammonium peroxydisulfate (APS) as the oxidant at ice temperature. The fabricated polyaniline was undoped using aqueous ammonia (1 M), dried at 60 ◦ C in an air oven for 48 h and stored in a dessicator for further experimentation [1–3].
2.4. Synthesis of polyaniline/xanthan gum nanocomposite The nanocomposite of polyaniline and xanthan gum was synthesized by adding the slightly viscous solution of xanthan gum to the aniline solution. For producing the polyaniline based nanocomposite 5 experiments with various amounts of xanthan gum were conducted. Aniline was dissolved in 1000 ml of aqueous solution of HCl and ammonium peroxydisulfate together with xanthan gum was dissolved in 1000 ml HCl (1 M) separately. The prepared mixture of xanthan gum and oxidant was added slowly to the aniline solution at ice temperature and was stirred for an hour to reaction was accomplished. The fabricated nanocomposite was separated and purified as mentioned for polymerization of aniline. The information about production of nanocomposites is given in Table 3.
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
173
Table 1 Surface roughness parameters of pure XG, pure PANI and PANI/XG nanocomposite No. 2. Roughness parameters
Pure XG Pure PANI Nanocomposite No. 2
Fig. 2. FT-IR spectra of PANI (a), XG (b), nanocomposite No. 1 (c), No. 2 (d) and No. 3 (f).
3. Results and discussion Atomic force microscopy was used to analyze the surface morphology and roughness of the prepared nanocomposite. The PANI, XG and synthesized nanocomposite surfaces were imaged in a scan size of 10 m × 10 m and are shown in Fig. 1. The surface roughness parameters of the materials which are expressed in terms of the mean roughness (Sa), the root mean square of the Z data (Sq) and the mean difference between the five highest peaks and lowest valleys (Sz) were calculated from AFM images using tapping mode method via Nanosurf EasyScan software at a scan area of 10 m × 10 m given in Table 1. The film of pure XG shows homogeneity, as it could be predicted. A different morphology with more
Sa
Sq
Sz
1716.8 pm 2456.6 pm 1913.2 pm
2.15 nm 8.3 nm 5.79 nm
55.24 nm 94.3 nm 64.71 nm
roughness than that of XG film is observed for a pure PANI based film. As can be seen from the AFM image of synthesized nanocomposite and reported parameters in Table 1 the surface roughness of nanocomposite is more than XG and less than pure PANI that it is probably due to the effect of XG on the structure of PANI. Also the average particle sizes of substances obtained from AFM images were reported in Table 3. The average particle size of pure PANI and XG is 73 and 43 nm respectively. Particle size of synthesized nanocomposites reported in Table 3 shows that xanthan gum by molecular interaction with PANI can affect the particle size and reduce it from 73 to 50 nm. FTIR spectra of pure polyaniline (a) and xanthan gum (b) are shown in Fig. 2. The x-axis represents wavelength (cm−1 ) and yaxis shows the light transmittance through the samples. Polyaniline has representative peaks at 1586, 1490, 1307, 1130 and 816 cm−1 . The bands at 1586, 1490 cm−1 were attributed to C C and C N in the quinoid ( N Q N where Q = quinoid ring) and benzoid units, while the band at 1130 cm−1 is due to the quinoid unit of polyaniline ( N Q N where Q = quinoid ring). The band at 1307 cm−1 is allocated to the C N of benzoid unit. The band at 816 cm−1 may be assigned to C C and C H for benzoid unit of polyaniline. These results indicate that the fabrication of polyaniline was promising [20–23]. In the case of xanthan gum FT-IR analysis two characteristic peaks were observed. One of them appears at 1615 cm−1 and the other at 1476 cm−1 which are attributed to COO− groups. Additional bands of xanthan gum appear at 1417, 1023 cm−1 and 1568 cm−1 due to C H, O H and C O bonds respectively. As can be expected the synthesized nanomopsites have a composed structure of two polymers: polyaniline and xanthan gum. The FT-IR spectra of nanocomposites show the all of representative peaks of both xanthan gum and polyaniline which is mentioned above. Polyaniline–xanthan gum nanocomposite No. 2 has characteristic band at 1610, 1590, 1495, 1570, 1311, 1135, 1020, 1420 and 810 which are attributed to COO− group of xanthan gum, C C of benzonoid rings of PANI, C C of quinonoid rings of PANI, C O bond of xanthan gum, C N of benzonoid rings of PANI, quinonoid rings of PANI, hydroxyl group of xanthan gum, C H bond of xanthan gum
Table 2 FT-IR spectra of pure PANI, pure XG, nanocomposite No. 1, No. 2 and No. 3. Nanocomposite No.
FTIR spectra COO− a
Pure XG Pure PANI 1 2 3 a b c d e f g h i j
1615 – 1600 1610 1617
1476 – 1465 1470 1477
C Cb
C Cc
C Od
C Oe
C Nf
N Q Ng
O Hh
C Hi
C Hj
– 1586 1582 1590 1595
– 1490 1488 1495 1500
1568 – 1560 1570 1565
1406 – 1400 1403 1408
– 1307 1305 1311 1300
– 1130 1128 1135 1120
1023 – 1030 1020 1024
1417 – 1425 1420 1416
– 816 814 810 800
COO− of xanthan gum. Stretching deformation of benzonoid rings. Stretching deformation of quinonoid rings. Asymmetric stretching carboxylate anion. Symmetric stretching carboxylate anion. Stretching of the benzenoid ring. Vibration mode of N Q N (Q refers to the quinonic-type rings). Bending vibrations of xanthan gum. Bending vibrations of xanthan gum. Out-of-plane deformation of C H in the p-disubstituted benzene ring.
174
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
100
Table 3 Effect of preparation conditions and amount of xanthan gum on the conductivity and particle size of synthesized nanocomposites.
Pure PANI
Weight loos ( %)
Pure XG 80
Composite No.1 Composite No.2
60
Nanocomposite No.
XG (g)
Aniline (mol)
Oxidant (APS) (mol)
Average particle size (nm)
Conductivity
Pure PANI 1 2 3 4 5 Pure XG
– 1 2 3 4 5 –
0.2 0.2 0.2 0.2 0.2 0.2 –
0.25 0.25 0.25 0.25 0.25 0.25 –
71 68 59 57 52 50 43
1.63 × 10−1 1.91 × 10−1 2.48 × 10−1 1.52 × 10−1 0.92 × 10−1 0.65 × 10−1 0.08 × 10−1
Composite No.3
40 20 0 0
100
200
300
400
500
600
700
800
Temperature (°C)
and C H bond of PANI respectively. All results are given in Table 2; as can be seen from these spectra the intensity of peaks grows by increasing in amount of each composer. The FTIR spectra suggest that the synthesized nanocomposites have the complex structure of both polyaniline and xanthan gum. For considering the thermal properties of initial substances and the products, TGA of pure polyaniline, xanthan gum and their nanocomposites (Nos. 1, 2 and 3) is done in the temperature range 0–800 ◦ C and the thermograms are presented in Fig. 3. The thermal behavior of pure polyaniline shows the three-step weight loss process that the initial weight loss of approximately 10% up to 110 ◦ C is due to the removal of moisture present in the polymer. The small weight loss of nearly 8% up to 280 ◦ C is owing to loss of oligomer and doping agent as volatile material. A massive weight loss of 80% up to 800 ◦ C is attributed to the degradation of the polymer chain indicating polymer was degraded completely. In addition, the thermogravimetric study of xanthan gum shows single step decomposition that starts at 230 ◦ C following the extremely small initial weight loss due to the removal of moisture. As can be concluded from the xanthan gum thermogram, the xanthan gum decomposition temperature was found to be 280 ◦ C. The rate of weight loss continues to 50% and then decreases insofar as a char yield of 32% was achieved at 800 ◦ C. In case of polyaniline/xanthan gum nanocomposite, the threestep weight loss was observed. The initial weight loss is approximately 6% up to 100 ◦ C due to the moisture removal. This quantity of weight loss indicates that presence of xanthan gum in nanocomposite may form a regular lattice which it can trap moisture in itself. This thermal stability in this range was improved with increasing the amount of xanthan gum in composites. Also, these effects were observed in the second step up to 270 ◦ C that nearly 7% weight loss occurs. As can be seen from the last step of nanocomposites and pure polyaniline thermograms, a char yield is improved from zero to variable amount from 7 to 22% which is the main effect of xanthan gum on thermal stability of nanocomposites. These results proved the fact that presence of xanthan gum enhances the thermal stability of synthesized nanocomposite less than 270 ◦ C and over 350 ◦ C. The conductive property of PANI/XG nanocomposites for realizing the effect of xanthan gum on it was considered. As mentioned above, several proportions of xanthan gum in nanocomposites were synthesized and the consequences are given in Table 3. These results reveal that conductivity of synthesized nanocomposites was improved by increasing the amount of xanthan gum. The maximum value of conductivity was achieved 2.48 × 10−1 by 2 g of xanthan gum. The increasing of polyaniline based nanocomposite conductivity could be explained with the presence of COO− groups in
xanthan gum. Xanthan gum has a side chain in each monomer unit containing a d-glucuronic acid unit between two d-mannose that each of them has a carboxyl groups in it. Based on literatures, presence of lone pair electrons at oxygen atoms in carboxylic group play host to proton conduction that probably can improve the electron mobility. However, by increasing the amount of xanthan gum more than 2 g, conductivity of nanocomposites was decreased compared with what was obtained for pure polyaniline. Descended in conductivity by increasing in amount of xanthan gum might be due to the fact that in higher concentration of xanthan gum in nanocomposite it acts as impurity. Fig. 4 shows the hydrophilic property of polyaniline based nanocomposite in various pH values 4, 7 and 10 at room temperature. The swelling amount was found to enlarge with increasing of xanthan gum ratio in nanocomposites. Also, swelling studies revealed that environmental pH value can affect the nanocomposites property. It is known that a high concentration of charged ionic groups in the hydro-gel increases the swelling due to osmosis and charge repulsion. As can be seen from Fig. 4 the maximum swelling amount was achieved by neutral pH. Owing to inclusion of xanthan gum, synthesized nanocomposite has a carboxyl anion in its side chain such that repulsive forces between these anions make swelling. Due to the absence of other ions in neutral pH anion–anion repulsive forces become stronger. In acidic pH values, most of the carboxylate anions are protonated; therefore the main anion–anion repulsive forces are neutralized and consequently swelling amount declined. Likewise, a charge screening effects of the cations limit the swelling at basic pH values.
70 pH=7
60
pH=10 Swelling (g/g)
Fig. 3. TGA thermograms of pure PANI, pure XG, nanocomposite Nos. 1, 2 and 3.
50
pH=4
40 30 20 10 0 10
20
30
40
50
60
70
80
90
% XG/composite (w/w) Fig. 4. Influence of pH values and amount of XG on equilibrium swelling of synthesized nanocomposites at 25 ◦ C.
S.G. Larimi et al. / Synthetic Metals 162 (2012) 171–175
4. Conclusions In this work polyaniline/xanthan gum nanocomposite was synthesized by oxidative polymerization of aniline in the presence of xanthan gum. The (AFM) and FT-IR measurements confirm the morphology and structure of synthesized nanocomposite. The TGA curves revealed that xanthan gum can decrease the weight loss of nanocomposite that a char yield is improved from zero for pure polyaniline to 22% for nanocomposite. Besides, xanthan gum enhanced the electrical conductivity up to 2.48 × 10−1 with 2 g xanthan gum in 0.2 mol l−1 aniline solution that by increasing in amount of it more than 2 g in nanocomposite decreased the electrical conductivity. Because of xanthan gum is a water soluble biopolymer it can affect the hydrophilic property of polyaniline. The tea bag method was used for determining the swelling amount of nanocomposite in aqueous solution and showed that the swelling amount of nanocomposite was extremely increased by the addition of xanthan gum. References [1] M. Lukasiewic, A. Ptaszek, L. Koziel, B. Achremowicz, M. Grzesik, Polym. Bull. 58 (2007) 281–288. [2] B. Naskar, A. Dan, S. Ghosh, S.P. Moulik, Carbohydr. Polym. 81 (2010) 700–706. [3] A. Ahmed, F. Mohammad, M.Z. Rahman, Synth. Met. 144 (2004) 29–49.
175
[4] J. Nizioia, J. Laska, Synth. Met. 101 (1999) 720–721. [5] H. Mirhosseini, Ch P. Tan, N. Hamid, S. Yusof, Colloids Surf. A 315 (2008) 47–56. [6] J. Kamonsawas, A. Sirivat, S. Niamlang, P. Hormnirun, W. Prissanaroon-Ouajai, J. Sensors 10 (2010) 5590–5603. [7] A. Pron, M. Zagorska, Y. Nicolauc, F. Genoud, M. Nechtschein, Synth. Met. 84 (1997) 89–90. [8] L.D. Acqua, C. Tonin, R. Peila, F. Ferrero, M. Catellani, Synth. Met. 146 (2004) 213–221. [9] B. Davodi, M.S. Lashkenari, H. Eisazadeh, Synth. Met. 161 (2011) 1207–1210. [10] M. Yavuz, T. Tilki, C. Karabacak, O. Erol, H. Unal, M. Uluturk, M. Cabuk, Carbohydr. Polym. 79 (2010) 318–324. [11] A. Ptaszek, W. Berski, P. Ptaszek, T. Witczak, U. Repelewicz, M. Grzesik, Carbohydr. Polym. 76 (2009) 567–577. [12] C. Sasso, D. Beneventi, E. Zeno, M. Petit-Conil, D. Chaussy, M.N. Belgacem, Synth. Met. 161 (2011) 397–403. [13] J. Laska, A. Prince, Synth. Met. 84 (1997) 117–118. [14] M. Nedjhioui, N. Moulai-Mostefa, A. Morsli, A. Bensmaili, Desalination 185 (2005) 543–550. [15] N.E.A. Shuhaimi, L.P. Teo, S.R. Majid, A.K. Arof, Synth. Met. 160 (2010) 1040–1044. [16] M.A. Ayadi, J.C. Leuliet, F. Chopard, M. Berthou, M. Lebouche, Food Bioprod. Process. 82 (2004) 320–325. [17] M. Aleahmad, H. Gh Taleghani, H. Eisazadeh, Synth. Met. 161 (2011) 990–995. [18] P.S. Gils, D. Ray, P.K. Sahoo, Int. J. Biol. Macromol. 45 (2009) 364–371. [19] F. Hua, M. Qian, J. Mater. Sci. 36 (2001) 731–738. [20] K. Gupta, P.C. Jana, A.K. Meikap, Synth. Met. 160 (2010) 1566–1573. [21] Sh. Wang, Z. Tan, Y. Li, L. Sun, T. Zhang, Thermochim. Acta 441 (2006) 191–194. [22] P. Liu, Curr. Opin. Solid State Mater. Sci. 12 (2008) 9–13. [23] G. Ramya, C. Renugadevi, Ch. Rao, D.C. Trivedi, React. Funct. Polym. 68 (2008) 701–709.