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Enhanced electromagnetic shielding behaviour of multilayer graphene anchored luminescent TiO2 in PPY matrix
Materials Letters 158 (2015) 167–169
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electromagnetic shielding behaviour of multilayer graphene anchored luminescent TiO2 in PPY matrix Ankit Gupta a,b, Swati Varshney b, Abhishake Goyal c, Pradeep Sambyal a, Bipin Kumar Gupta a, S.K. Dhawan a,n a
CSIR-National Physical Laboratory, Dr K. S. Krishnan Road, New Delhi 110012, India Delhi Institute of Tool Engineering, New Delhi 110020, India c Delhi Technological University, New Delhi 110042, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 8 February 2015 Received in revised form 30 April 2015 Accepted 30 May 2015 Available online 3 June 2015
Present research is focussed on the development of a novel composite material for highly-efficient absorption of electromagnetic interference (EMI) pollution. Herein, we report synthesis and characterization of polypyrrole (PPY) composite containing multi-layered graphene (MLG) anchored with titanium dioxide (TiO2) via in-situ oxidative polymerization of pyrrole. The tuning of the microwave signals has achieved via composites with different weight ratios of MLG and TiO2. The maximum Total shielding effectiveness (SET), 53 dB was observed for PPY/MLG/TiO2 (5% composite) in the frequency range of 12.4– 18 GHz. The observed results suggest that the composite material could be a new alternative for building block of electromagnetic shielding applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: Polymers Nanocomposites Luminescence Multilayer structure Dielectrics
1. Introduction Recent innovations in the field of electronic devices and our increased dependency on these products have amplified the need of error free electronic systems. These issues have encouraged scientists to develop materials that can shield the electronic devices against EM radiation [1,2]. Metal coated/plated polymers are the most widely used materials for EMI shielding because of their high conductivity. However, metal shields have poor flexibility, high weight, tendency to corrode, and limited tuning of the SE [3,4]. Literature survey shows that the conducting polymer composites offer various advantageous properties in the use of EMI shielding applications. PPY is a nitrogen based cyclic conducting polymer which offers good conductivity, environmental stability, and ease of synthesis [5,6]. However, conducting polymers lack in mechanical strength, it restricts their fabrication as an EMI shield for commercial applications. To overcome this, in the present work, dielectrics like TiO2 are incorporated in the polymer matrix to enhance the absorption properties and thermal stability of these polymers (see Supporting information) [3,7] and multi layered graphene (MLG) is incorporated as a conductive reinforcing material. Therefore, PPY composite incorporated with MLG decorated n
Corresponding author. PRFx: þ91 11 25726938 E-mail address: [email protected] (S.K. Dhawan).
http://dx.doi.org/10.1016/j.matlet.2015.05.154 0167-577X/& 2015 Elsevier B.V. All rights reserved.
with TiO2 constitutes a new generation material with great potential for EMI shielding applications.
2. Experimental MLG was synthesized using chemical exfoliation graphite in the acidic medium [8]. The TiO2 nano particles were synthesized by sol–gel method [9]. In-situ polymerization of pyrrole was carried out for the synthesis of the composite. Initially, The MLG and TiO2 nanoparticles were ultra-homogenized in a 0.3 M aqueous solution of Sodium Lauryl Sulphate with distilled pyrrole (0.1 M) for 2 h. The solution was polymerized using FeCl3 (0.2 M). The solution is then filtered and the residue is dried at 60 °C. Several compositions of PPY:MLG:TiO2 having weight ratios 1:0.01:0.01, 1:0.05:0.05, 1:0:0.05 and 1:0.05:0 were prepared. The schematic of the synthesis of the composite is shown in Fig. 1a.
3. Results and discussions Fig. 1b shows the XRD pattern of PPY, MLG, TiO2 and PPY/TiO2/MLG. TiO2 nanoparticles show the characteristic peaks at 2θ 25.36°, 36.24°, 37.84°, 39.41°, 48.12°, 54.08°, which correspond to the (1 0 1), (1 0 3), (0 0 4), (1 1 2), (2 0 0) and (1 0 5) crystal
168
A. Gupta et al. / Materials Letters 158 (2015) 167–169
Fig. 1. a) Schematic representation of the synthesis of composite b) X-Ray Diffraction (XRD) of different constituent materials.
planes, respectively confirming the anatase phase of TiO2 [10]. The XRD spectrum of MLG, shows sharp peak at 26.22° and 54.51°. The peak at 26.22° is significantly broader than the corresponding peak of graphite, which verifies the good exfoliation of the graphite [11]. The neat PPY shows the characteristics broad hump from 17° to 27°, with two low intensity peaks at 22.94° and 26.62° [7]. The composite (PPY/0.05TiO2/0.05MLG), shows the characteristic peaks of TiO2 and MLG. Additionally, the presence of broad diffraction pattern in the range of 11.8°–25.34° is due to the polymer matrix. A slight shifting in the characteristic peaks was observed, which could be due to the synergistic interaction among the PPY, TiO2 and MLG. The TEM image of TiO2 nanoparticles (Fig. 2a) reveals the presence of fine particles (9–12 nm) having uniform morphology [12]. Fig. 2b shows the TEM image of the MLG sheets of few micrometers. The TEM and SEM images of the PPY/MLG/TiO2 composite are shown in Fig. 2c and d, respectively. The TEM image of the composite reveals the presence of MLG sheets decorated with TiO2 nanoparticles and polyprrole. The SEM micrograph of the composite exhibits a MLG flakes are uniformly covered with polypyrrole and TiO2 particles. The SEM & TEM interpretations are in accordance with the XRD results. The shielding measurement has been done using scattering parameters by Nicolson Ross Weir method (see Supporting information). Fig. 3b, c and d shows the variation of SET (Total Shielding Effectiveness), SER (Shielding Effectiveness due to Reflection) and SEA (Shielding Effectiveness Due To Absorption) with frequency in the 12.4–18 GHz range, respectively. SET of PPY, PPY/TiO2, PPY/MLG, PPY/0.01MLG/0.01TiO2 and PPY/0.05MLG/0.05TiO2 is 7, 13, 19, 28 and 53 dB, respectively. It is very evident from the mentioned data that with the addition of even small weight percentage of TiO2 and MLG, the value of SET increases significantly. This is attributed to the combined effect of TiO2 and MLG. Moreover, the SEA of both the composites is more than 80% of the SET, which manifests the great microwave absorption properties of the synthesized composite. SER can be expressed as.
(
SER (dB) ≈ 10 log σ AC /μ R f
σ AC ≈ ωεo ε´´
)
(1)
(2)
where sAC is conductivity; μR is relative permeability; ω is angular frequency and f is frequency. It can be inferred from the Eq. 1, that SER is directly proportion to the conductivity of the sample. Thus, high conductivity of MLG leads to higher value of PPY/MLG than PPY/TiO2. Fig. 3c also shows the gradual decrease in SER with the increase in frequency. The disturbance in the orientation of dipoles in a system due to increased frequency could be a possible reason for the retardation of SER. The validity of the above equations could be verified from the Fig. 3c and h. SEA can be expressed as [13]
SE A (dB) ≈ kd (пfμσ )1/2
(3)
where K is constant; d is the thickness of the shield and other symbols describe the same variables which is described earlier. Fig. 3d and g verifies the above equation. A view of good measure of microwave absorption can also be indicated by the loss tangent, tan δ E ε´´/ε´. If tan δ is greater than 1, then the materials are considered to be “lossy” materials. This indicates strong absorption at a given frequency [14]. Fig. 3f, clearly shows that the ratio of ε´´/ε´ being more than 1 for all the composites. Further, the imminent increase in the microwave absorption properties of the PPY/0.05 M/ 0.05/T can be related to the both complex and real part of permittivity of nano size of TiO2 particles. Due to the small size, the anisotropic energy of the particles will be high and the increased anisotropy energy contributes to the enhancement of microwave absorption [15]. Besides the small size of TiO2 particles, the efficient decoration of TiO2 particles on MLG sheets lead to the increased polarization charges on the surface. The interaction of EM waves with the charges on these surfaces leads to the interfacial polarization and lags of polarization, which helps in the increase of high dielectric loss in the composite and high absorption effectiveness.
Fig. 2. Transmission electron microscope (TEM) image of a) TiO2 b) MLG c) PPY/0.05MLG/0.05TiO2 & d) Scanning Electron Microscope (SEM) image of PPY/0.05MLG/0.05TiO2.
A. Gupta et al. / Materials Letters 158 (2015) 167–169
169
Fig. 3. a) Dielectric loss of different composites b) SET versus frequency c) SER versus frequency d) SEA versus Frequency e) PL emission spectra (excited at 254 nm) f) Tangent loss g) SEA versus (sAC)1/2 h) SER versus log sAC.
Photoluminescence study is carried out to evaluate the effect of the presence of TiO2 in the PL properties of the polymer matrix. Fig. 3e shows the typical PL spectra of TiO2 nanoparticles, with a strong peak at 398 nm and other peaks observed within the wavelength range of 450–470 nm, which are attributed to the excitonic PL. This mainly results from the surface oxygen vacancies and defects [16,17]. As compared to TiO2 particles, the PL intensity of the PPY composites containing TiO2 and MLG is significantly decreased. This is due to the fact that the PPY is a p-type narrowbandgap semiconductor polymer and PPY has a quenching effect, which decreases the PL intensity with the increase of its concentration [17,18]. It is interesting to note that the PL intensity of PPY/0.05MLG/0.05TiO2 composite is more than the PPY/0.05TiO2 composite. The probable reason behind this result can be the higher interfacial area provided by Multi Layer Graphene sheets to TiO2 particles. The remarkable increase in the PL intensity of PPY/0.05MLG/0.05TiO2 composite in comparison to the PPY/0.01MLG/0.01TiO2 reveals the potential use of the composite for the photoluminescence based device applications.
4. Conclusions A facile method has been proposed to design a novel composite for EMI shielding effectiveness at 12.4–18 Hz frequency range. The XRD and morphological analysis of the composite justify the compatibility of MLG and TiO2 particles with PPY matrix. The shielding effectiveness of the synthesized composite (MLG/PPY/TiO2) is nearly 53 dB with 46 dB, the shielding effectiveness due to absorption. This intriguing effectiveness, high absorption properties and encouraging PL intensity results provide a platform for a multifunctional nanocomposite for both shielding and photoluminescence based applications in next generation electronic devices.
Acknowledgments The authors wish to thank Dr. Amitava Sen Gupta, Director, N.P.L., for his keen interest in the work. The authors also thank Dr. N. Vijayan, Dr. Vidyanand and K. N. Sood for recording XRD
pattern, TEM micrograph and SEM micrograph, respectively. We would also like to thank Dr. Gazala Ruhi for her guidance throughout this project.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.05.154
References [1] T. Pardoen, C. Bailly, J. Thomassin, C. Je, I. Huynen, C. Detrembleur, Mater. Sci. Eng.: R: Rep. 74 (2013) 211 21232. [2] C.-S. Zhang, Q.-Q. Ni, S.-Y. Fu, K. Kurashiki, Compos. Sci. Technol. 67 (14) (2007) 2973–2980. [3] S. Varshney, A. Ohlan, V.K. Jain, V.P. Dutta, S.K. Dhawan, Mater. Chem. Phys. 143 (2) (2014) 806 80813. [4] J.J. Kuldeep Singh, Anil Ohlan, Viet Hung Pham, R Balasubramaniyan, Swati Varshney, Nanoscale 5 (6) (2013) 2411 242420. [5] X. Li, J. Sun, G. He, G. Jiang, Y. Tan, B. Xue, J. Colloid Interface Sci. 411 (2013) 34–40. [6] K. Shi, I. Zhitomirsky, J. Colloid Interface Sci. 407 (2013) 474–81. [7] S.K. Singh, R.K. Shukla, Mater. Sci. Semicond. Process. 31 (2015) 245–250. [8] W.-L. Song, M.-S. Cao, M.-M. Lu, S. Bi, C.-Y. Wang, J. Liu, J. Yuan, L.-Z. Fan, Carbon N. Y 66 (2014) 67–76. [9] R. Sharmiladevi, R. Venckatesh, Int. J. Innov. Res. Sci. Eng. Technol. 3 (8) (2014) 15206–15211. [10] W. Wang, I.W. Lenggoro, Y. Terashi, T.Oh. Kim, K. Okuyama, Mater. Sci. Eng. B. 123 (2005) 194–202. [11] L. C, Y.-P.S. Wei-Li Song, Gregory E. LeCroy, J. Mater. Chem. 22 (2012) 17133–17139. [12] K. Singh, A. Ohlan, A.K. Bakshi, S.K. Dhawan, Mater. Chem. Phys. 119 (2010) 201–207. [13] Y. Jia, P. Xiao, H. He, J. Yao, F. Liu, Z. Wang, Y. Li, Appl. Surf. Sci. 258 (17) (2012) 6627–6631. [14] D. a Makeiff, T. Huber, Synth. Met. 156 (2006) 497–505. [15] Ankit Gupta, Avinash Pratap Singh, S.K. Dhawan, RSC Adv. 4 (2014) 62413–62422. [16] Bipin Kumar Gupta, Garima Kedawat, S.K. Dhawana, RSC Adv. 5 (2015) 10623. [17] Y. Yang, J. Wen, J. Wei, R. Xiong, J. Shi, C. Pan, ACS Appl. Mater. Inter. 5 (2013) 6201–6207. [18] B.K. Gupta, V. Grover, G. Gupta, V. Shanker, Nanotechnology vol. 21 (47) (2010) 475701.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electromagnetic shielding behaviour of multilayer graphene anchored luminescent TiO2 in PPY matrix Ankit Gupta a,b, Swati Varshney b, Abhishake Goyal c, Pradeep Sambyal a, Bipin Kumar Gupta a, S.K. Dhawan a,n a
CSIR-National Physical Laboratory, Dr K. S. Krishnan Road, New Delhi 110012, India Delhi Institute of Tool Engineering, New Delhi 110020, India c Delhi Technological University, New Delhi 110042, India b
art ic l e i nf o
a b s t r a c t
Article history: Received 8 February 2015 Received in revised form 30 April 2015 Accepted 30 May 2015 Available online 3 June 2015
Present research is focussed on the development of a novel composite material for highly-efficient absorption of electromagnetic interference (EMI) pollution. Herein, we report synthesis and characterization of polypyrrole (PPY) composite containing multi-layered graphene (MLG) anchored with titanium dioxide (TiO2) via in-situ oxidative polymerization of pyrrole. The tuning of the microwave signals has achieved via composites with different weight ratios of MLG and TiO2. The maximum Total shielding effectiveness (SET), 53 dB was observed for PPY/MLG/TiO2 (5% composite) in the frequency range of 12.4– 18 GHz. The observed results suggest that the composite material could be a new alternative for building block of electromagnetic shielding applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: Polymers Nanocomposites Luminescence Multilayer structure Dielectrics
1. Introduction Recent innovations in the field of electronic devices and our increased dependency on these products have amplified the need of error free electronic systems. These issues have encouraged scientists to develop materials that can shield the electronic devices against EM radiation [1,2]. Metal coated/plated polymers are the most widely used materials for EMI shielding because of their high conductivity. However, metal shields have poor flexibility, high weight, tendency to corrode, and limited tuning of the SE [3,4]. Literature survey shows that the conducting polymer composites offer various advantageous properties in the use of EMI shielding applications. PPY is a nitrogen based cyclic conducting polymer which offers good conductivity, environmental stability, and ease of synthesis [5,6]. However, conducting polymers lack in mechanical strength, it restricts their fabrication as an EMI shield for commercial applications. To overcome this, in the present work, dielectrics like TiO2 are incorporated in the polymer matrix to enhance the absorption properties and thermal stability of these polymers (see Supporting information) [3,7] and multi layered graphene (MLG) is incorporated as a conductive reinforcing material. Therefore, PPY composite incorporated with MLG decorated n
Corresponding author. PRFx: þ91 11 25726938 E-mail address: [email protected] (S.K. Dhawan).
http://dx.doi.org/10.1016/j.matlet.2015.05.154 0167-577X/& 2015 Elsevier B.V. All rights reserved.
with TiO2 constitutes a new generation material with great potential for EMI shielding applications.
2. Experimental MLG was synthesized using chemical exfoliation graphite in the acidic medium [8]. The TiO2 nano particles were synthesized by sol–gel method [9]. In-situ polymerization of pyrrole was carried out for the synthesis of the composite. Initially, The MLG and TiO2 nanoparticles were ultra-homogenized in a 0.3 M aqueous solution of Sodium Lauryl Sulphate with distilled pyrrole (0.1 M) for 2 h. The solution was polymerized using FeCl3 (0.2 M). The solution is then filtered and the residue is dried at 60 °C. Several compositions of PPY:MLG:TiO2 having weight ratios 1:0.01:0.01, 1:0.05:0.05, 1:0:0.05 and 1:0.05:0 were prepared. The schematic of the synthesis of the composite is shown in Fig. 1a.
3. Results and discussions Fig. 1b shows the XRD pattern of PPY, MLG, TiO2 and PPY/TiO2/MLG. TiO2 nanoparticles show the characteristic peaks at 2θ 25.36°, 36.24°, 37.84°, 39.41°, 48.12°, 54.08°, which correspond to the (1 0 1), (1 0 3), (0 0 4), (1 1 2), (2 0 0) and (1 0 5) crystal
168
A. Gupta et al. / Materials Letters 158 (2015) 167–169
Fig. 1. a) Schematic representation of the synthesis of composite b) X-Ray Diffraction (XRD) of different constituent materials.
planes, respectively confirming the anatase phase of TiO2 [10]. The XRD spectrum of MLG, shows sharp peak at 26.22° and 54.51°. The peak at 26.22° is significantly broader than the corresponding peak of graphite, which verifies the good exfoliation of the graphite [11]. The neat PPY shows the characteristics broad hump from 17° to 27°, with two low intensity peaks at 22.94° and 26.62° [7]. The composite (PPY/0.05TiO2/0.05MLG), shows the characteristic peaks of TiO2 and MLG. Additionally, the presence of broad diffraction pattern in the range of 11.8°–25.34° is due to the polymer matrix. A slight shifting in the characteristic peaks was observed, which could be due to the synergistic interaction among the PPY, TiO2 and MLG. The TEM image of TiO2 nanoparticles (Fig. 2a) reveals the presence of fine particles (9–12 nm) having uniform morphology [12]. Fig. 2b shows the TEM image of the MLG sheets of few micrometers. The TEM and SEM images of the PPY/MLG/TiO2 composite are shown in Fig. 2c and d, respectively. The TEM image of the composite reveals the presence of MLG sheets decorated with TiO2 nanoparticles and polyprrole. The SEM micrograph of the composite exhibits a MLG flakes are uniformly covered with polypyrrole and TiO2 particles. The SEM & TEM interpretations are in accordance with the XRD results. The shielding measurement has been done using scattering parameters by Nicolson Ross Weir method (see Supporting information). Fig. 3b, c and d shows the variation of SET (Total Shielding Effectiveness), SER (Shielding Effectiveness due to Reflection) and SEA (Shielding Effectiveness Due To Absorption) with frequency in the 12.4–18 GHz range, respectively. SET of PPY, PPY/TiO2, PPY/MLG, PPY/0.01MLG/0.01TiO2 and PPY/0.05MLG/0.05TiO2 is 7, 13, 19, 28 and 53 dB, respectively. It is very evident from the mentioned data that with the addition of even small weight percentage of TiO2 and MLG, the value of SET increases significantly. This is attributed to the combined effect of TiO2 and MLG. Moreover, the SEA of both the composites is more than 80% of the SET, which manifests the great microwave absorption properties of the synthesized composite. SER can be expressed as.
(
SER (dB) ≈ 10 log σ AC /μ R f
σ AC ≈ ωεo ε´´
)
(1)
(2)
where sAC is conductivity; μR is relative permeability; ω is angular frequency and f is frequency. It can be inferred from the Eq. 1, that SER is directly proportion to the conductivity of the sample. Thus, high conductivity of MLG leads to higher value of PPY/MLG than PPY/TiO2. Fig. 3c also shows the gradual decrease in SER with the increase in frequency. The disturbance in the orientation of dipoles in a system due to increased frequency could be a possible reason for the retardation of SER. The validity of the above equations could be verified from the Fig. 3c and h. SEA can be expressed as [13]
SE A (dB) ≈ kd (пfμσ )1/2
(3)
where K is constant; d is the thickness of the shield and other symbols describe the same variables which is described earlier. Fig. 3d and g verifies the above equation. A view of good measure of microwave absorption can also be indicated by the loss tangent, tan δ E ε´´/ε´. If tan δ is greater than 1, then the materials are considered to be “lossy” materials. This indicates strong absorption at a given frequency [14]. Fig. 3f, clearly shows that the ratio of ε´´/ε´ being more than 1 for all the composites. Further, the imminent increase in the microwave absorption properties of the PPY/0.05 M/ 0.05/T can be related to the both complex and real part of permittivity of nano size of TiO2 particles. Due to the small size, the anisotropic energy of the particles will be high and the increased anisotropy energy contributes to the enhancement of microwave absorption [15]. Besides the small size of TiO2 particles, the efficient decoration of TiO2 particles on MLG sheets lead to the increased polarization charges on the surface. The interaction of EM waves with the charges on these surfaces leads to the interfacial polarization and lags of polarization, which helps in the increase of high dielectric loss in the composite and high absorption effectiveness.
Fig. 2. Transmission electron microscope (TEM) image of a) TiO2 b) MLG c) PPY/0.05MLG/0.05TiO2 & d) Scanning Electron Microscope (SEM) image of PPY/0.05MLG/0.05TiO2.
A. Gupta et al. / Materials Letters 158 (2015) 167–169
169
Fig. 3. a) Dielectric loss of different composites b) SET versus frequency c) SER versus frequency d) SEA versus Frequency e) PL emission spectra (excited at 254 nm) f) Tangent loss g) SEA versus (sAC)1/2 h) SER versus log sAC.
Photoluminescence study is carried out to evaluate the effect of the presence of TiO2 in the PL properties of the polymer matrix. Fig. 3e shows the typical PL spectra of TiO2 nanoparticles, with a strong peak at 398 nm and other peaks observed within the wavelength range of 450–470 nm, which are attributed to the excitonic PL. This mainly results from the surface oxygen vacancies and defects [16,17]. As compared to TiO2 particles, the PL intensity of the PPY composites containing TiO2 and MLG is significantly decreased. This is due to the fact that the PPY is a p-type narrowbandgap semiconductor polymer and PPY has a quenching effect, which decreases the PL intensity with the increase of its concentration [17,18]. It is interesting to note that the PL intensity of PPY/0.05MLG/0.05TiO2 composite is more than the PPY/0.05TiO2 composite. The probable reason behind this result can be the higher interfacial area provided by Multi Layer Graphene sheets to TiO2 particles. The remarkable increase in the PL intensity of PPY/0.05MLG/0.05TiO2 composite in comparison to the PPY/0.01MLG/0.01TiO2 reveals the potential use of the composite for the photoluminescence based device applications.
4. Conclusions A facile method has been proposed to design a novel composite for EMI shielding effectiveness at 12.4–18 Hz frequency range. The XRD and morphological analysis of the composite justify the compatibility of MLG and TiO2 particles with PPY matrix. The shielding effectiveness of the synthesized composite (MLG/PPY/TiO2) is nearly 53 dB with 46 dB, the shielding effectiveness due to absorption. This intriguing effectiveness, high absorption properties and encouraging PL intensity results provide a platform for a multifunctional nanocomposite for both shielding and photoluminescence based applications in next generation electronic devices.
Acknowledgments The authors wish to thank Dr. Amitava Sen Gupta, Director, N.P.L., for his keen interest in the work. The authors also thank Dr. N. Vijayan, Dr. Vidyanand and K. N. Sood for recording XRD
pattern, TEM micrograph and SEM micrograph, respectively. We would also like to thank Dr. Gazala Ruhi for her guidance throughout this project.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.05.154
References [1] T. Pardoen, C. Bailly, J. Thomassin, C. Je, I. Huynen, C. Detrembleur, Mater. Sci. Eng.: R: Rep. 74 (2013) 211 21232. [2] C.-S. Zhang, Q.-Q. Ni, S.-Y. Fu, K. Kurashiki, Compos. Sci. Technol. 67 (14) (2007) 2973–2980. [3] S. Varshney, A. Ohlan, V.K. Jain, V.P. Dutta, S.K. Dhawan, Mater. Chem. Phys. 143 (2) (2014) 806 80813. [4] J.J. Kuldeep Singh, Anil Ohlan, Viet Hung Pham, R Balasubramaniyan, Swati Varshney, Nanoscale 5 (6) (2013) 2411 242420. [5] X. Li, J. Sun, G. He, G. Jiang, Y. Tan, B. Xue, J. Colloid Interface Sci. 411 (2013) 34–40. [6] K. Shi, I. Zhitomirsky, J. Colloid Interface Sci. 407 (2013) 474–81. [7] S.K. Singh, R.K. Shukla, Mater. Sci. Semicond. Process. 31 (2015) 245–250. [8] W.-L. Song, M.-S. Cao, M.-M. Lu, S. Bi, C.-Y. Wang, J. Liu, J. Yuan, L.-Z. Fan, Carbon N. Y 66 (2014) 67–76. [9] R. Sharmiladevi, R. Venckatesh, Int. J. Innov. Res. Sci. Eng. Technol. 3 (8) (2014) 15206–15211. [10] W. Wang, I.W. Lenggoro, Y. Terashi, T.Oh. Kim, K. Okuyama, Mater. Sci. Eng. B. 123 (2005) 194–202. [11] L. C, Y.-P.S. Wei-Li Song, Gregory E. LeCroy, J. Mater. Chem. 22 (2012) 17133–17139. [12] K. Singh, A. Ohlan, A.K. Bakshi, S.K. Dhawan, Mater. Chem. Phys. 119 (2010) 201–207. [13] Y. Jia, P. Xiao, H. He, J. Yao, F. Liu, Z. Wang, Y. Li, Appl. Surf. Sci. 258 (17) (2012) 6627–6631. [14] D. a Makeiff, T. Huber, Synth. Met. 156 (2006) 497–505. [15] Ankit Gupta, Avinash Pratap Singh, S.K. Dhawan, RSC Adv. 4 (2014) 62413–62422. [16] Bipin Kumar Gupta, Garima Kedawat, S.K. Dhawana, RSC Adv. 5 (2015) 10623. [17] Y. Yang, J. Wen, J. Wei, R. Xiong, J. Shi, C. Pan, ACS Appl. Mater. Inter. 5 (2013) 6201–6207. [18] B.K. Gupta, V. Grover, G. Gupta, V. Shanker, Nanotechnology vol. 21 (47) (2010) 475701.