Authors:
Waseem Khan1, Rahul Sharma2, PK Chaudhury3, AM Siddiqui1, Parveen Saini2*
1Department of Physics, Jamia Millia Islamia, New Delhi-110 025, India
2CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110 012, India
3Solid State Physics Laboratory, Timarpur, Delhi- 110 054, India
Received: 05 December, 2016; Accepted: 16 December, 2016; Published: 17 December, 2016
Parveen Saini, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110 012, India. E-mail:
Khan W, Sharma R, Chaudhury PK, Siddiqui AM, Saini P (2016) Synthesis of Carboxylic Functionalized Multi Wall Carbon Nanotubes and Their Application for Static Charge Dissipative Fibers. Int J Nanomater Nanotechnol Nanomed 2(1): 025-028. DOI: 10.17352/2455-3492.000011
© 2016 Khan W, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Carbon nanotubes (CNTs); Functionalization; Electron microscopy; Raman spectroscopy; Infrared spectroscopy; Electrostatic dissipation (ESD)
In the present study, multi wall carbon nanotubes (CNTs) were chemically functionalized by concentrated nitric acid refluxing for 8 hours to form acid functionalized CNTs (FCNTs). Fourier transformed infrared spectra reveal the formation of carboxylic acid (-COOH) functional groups on the surface of chemically treated CNTs. The increase in intensity of Raman spectra D band relative to G band and enhancement of oxygen to carbon ratio confirm the functionalization and formation of –COOH groups, which in turn increase the dispersibility of CNTs in water, thus rendering them solution processable. The X-ray diffraction pattern and scanning electron microscopy images confirm the structure retention of CNTs even after harsh acid treatment. These functionalized CNTs show good affinity towards cotton fibers and the surface resistivity of FCNTs coated fiber has been found to be ~ 1010 Ω/square making them suitable for use as an anti-static material.
Introduction
The use of electronic gadgets has become widespread and indispensable in the present technological era. This has given birth to an undesirable effect known as electrostatic dissipation (ESD) effect [1] . The accumulation of static charge in electronic goods packaging (which are primarily insulating polymeric materials) causes unnecessary damage to their electronics. Therefore, the importance of development of the ESD free materials has been realized for ultimate utility in electronic packaging. As the electrical conductivity is identified as prerequisite for static charge buildup control, several efforts have been made in the past to develop conducting materials based static safe compositions [2–8]. In particular, CNTs with excellent electrical conductivity, low density, high corrosion resistance, outstanding mechanical properties along with high thermal, chemical and environmental stability [6,9–12] is considered as most promising candidate for ESD control applications. However, their hydrophobicity and the inherent inertness of graphitic skeleton pose major challenges for their direct utilization via formation of CNTs filled composites or surface coatings. To solve these issues CNTs are often modified by covalent and non-covalent schemes (known as functionalization) which enhance their hydrophilicity, processability and compatibility [13–16] . The grafting of oxygen containing functional groups at the open ends and sidewalls of CNTs is a useful approach towards the covalent functionalization of CNTs. Particularly, the carboxylic acid group (i.e. –COOH functionality) happens to be the most common functional groups which open up the possibility of further modification of CNTs via suitable solution based chemical routes. It is worth mentioning that functionalized CNTs contain polar groups which enable their dispersion inside solvents, enhances compatibility with polymeric matrices and improves their ability to surface coat the polymeric substrate based packaging materials [16–20].
Here, we have reported the synthesis of covalently functionalized MWCNTs which can be easily coated over cotton fibers and demonstrated the application of these functionalized CNTs coated fibers for anti- static application.
Experimental
Materials
The MWCNTs used in the experiment was purchased from Nanoshel with diameter 10-20 nm, length 3-8 µm and (>99 %) purity. The 70% nitric acid of analytical grade was procured from Merck Specialties Pvt. Ltd. Cellulose nitrate membrane filters with 0.45 μm pore size produced by Millipore were used in this experiment.
Functionalization
About 250 mg of pristine MWCNTs was mixed with 200 mL concentrated nitric acid and the mixture was refluxed for 8 hours followed by its ultracentrifugation at 10000 rpm. The FCNT pulp was dispersed in 500 mL distilled water followed by filtration through a cellulose nitrate membrane filter (0.45 μm pore size) using a vacuum filtration assembly. The sample was repeatedly washed with distilled water till neutral pH of filtrate. The filtered FCNTs bedding was dried in a vacuum oven at 80ºC for 24h and obtained FCNTs powder was characterized using different techniques. Figure 1a,b, show the schematics of pristine CNTs and functionalized CNTs (FCNTs) respectively whereas Figure 1c shows the actual refluxing setup used to carry out the reaction.
Peertechz is an international Open Access, peer-reviewed podium which aims to provide scientists, researchers, academicians...
Submit Manuscript
Figure 1:
Characterization
The surface morphology was observed using scanning electron microscope (SEM), Model; VT-EVO, MA-10, Carl–Zeiss, UK. Raman data was recorded on Horiba Jobin- Yvon Laser Spectrometer 6400 using 514.5 nm wavelength as excitation source. Fourier transform infrared (FTIR) transmittance data was obtained using Agilent Technologies Cary 630 system using pressed pellets of sample mixed with KBr. The surface resistivity of uncoated and FCNTs coated fiber was measured by surface resistivity meter.
Results and Discussion
FTIR Spectroscopy
Figure 2a shows the FTIR spectra of pristine CNTs and FCNTs where the noticeable peak at ~ 1636 cm-1 in both samples corresponds to the stretching vibrations of the carbon-carbon double bonds (i.e. -C=C- bond stretch) which constitute the CNTs backbone. The presence of this peak in both the samples shows that the basic skeleton of CNTs is preserved even after the acid treatment. However, the appearance of additional peak in FCNTs at ~1742 cm-1 (-C=O stretch) and reduction in relative intensity of –C=C- stretch peak confirms the successful oxidation and introduction of carboxylic acid (i.e. -COOH) groups over CNTs backbone. These results are complimented by the Raman spectra (Figure 2b which shows that the intensity of D-band relative to G-band (i.e. ID/IG ratio) is significantly higher for FCNTs as compared to pristine CNTs. This indicates that a sufficiently large number of defects have been created upon functionalization which can serve as functional handle and active surface sites for the dispersion of CNTs (Figure 2c) inside polar solvents (e.g. water in present case) & their interaction with other species. Further, the absence of any new band and only minor shift in the position of Raman bands (Figure 2b) and XRD peaks (Figure 2d) revealed that the basic structure of CNTs remained unaffected by functionalization.
Figure 2:
Field emission scanning electron microscopy (FESEM) & EDX
In harmony with earlier observations, the FESEM images of pristine CNTs (Figure 3a) and FCNTs (Figure 3b) provides the visual evidence of the preservation of structural features of CNTs in FCNTs even after encountering harsh acid treatment conditions.
Figure 3c,d show the EDX spectra of pristine CNTs and FCNTs respectively whereas corresponding inset shows their elemental composition. It is observed that the proportion of carbon and oxygen atoms (i.e. C/O ratio) decreases upon functionalization, which supports the formation of oxygen containing functional groups over CNTs’ surface. Interestingly, the attachment of -COOH groups makes the surface of CNTs hydrophilic which not only facilitates their dispersion in water (Figure 2d) but also allows adsorption over suitable substrates. As the CNTs are electrically conducting, their coating over insulating substrates is expected to reduce surface resistivity, which is considered an index to assess the suitability of a material for anti-static application [8,21,22].
Figure 3:
Figure 4a,b show the optical images of bare and FCNTs coated fiber respectively. It can be seen that the bare fiber is white in color whereas upon FCNTs coating, the fiber becomes blackish in color due to decoration of adsorbed FCNTs. The coated FCNTs networks are expected to improve the surface conductivity and hence charge dissipation characteristics. Indeed, the surface resistivity measurements have shown that bare cotton fiber is insulating in nature with resistivity value of >1012 Ω/square (Figure 4c). In contrast, FCNTs coated fiber displays several orders lower resistivity i.e. 1010 Ω/square (Figure 4d) and clearly passes the anti-static criteria [6,23,24]. These fibers are considered potential candidate for making woven fabrics with antistatic & static charge dissipation characteristics, with ultimate utility in ESD safe electronic packaging applications.
Figure 4:
Conclusion
The successful functionalization of MWCNTs was achieved in just 8 hours of refluxing in HNO3. The COOH group was successfully attached on CNTs which is confirmed by the appearance of corresponding peak in its FTIR spectrum. Raman spectroscopy further validates this by exhibiting an increase in D band intensity. The acid treatment is able to functionalize the CNTs without deteriorating their structure which is backed by FESEM images and XRD and patterns. The improved dispersion results as a consequence of functionalization. FCNTs also prove their worth as a possible anti-static material as their surface coating on insulating polymeric fiber brings its resistivity down to ~1010 Ω/square.
Acknowledgement
W. K. is thankful to Dr. A. M. Biradar for granting permission to carry out part of his work at NPL. One of the authors, W.K. is thankful to UGC for providing UGC-BSR Fellowship.