Synthesis, modification and antimicrobial activity of carbon nanotube matrix.
Carbon nanotubes introduced by Iijma  are tubular structures with nanoscale diameter and micrometer length. CNT-based materials have been synthesized in various forms and potentially used in variety of areas such as catalysis , super-capacitors , and in mechanical applications .
Three-dimensional networks of multi-walled carbon nanotubes (MWNT) synthesized consist of a porous hydrophobic matrix with a good sorption capacity. This is a light-weight matrix with good structural flexibility and chemical stability.
Macroscopic porous matrix  synthesized by modified chemical vapor deposition (CVD) method and the morphology of the material was studied using SEM, Fe-SEM, TEM-EDXA and FT-IR. Matrix synthesized consists of nano-sized pores as is evident from porosity measurements. Membranes made of these matrices can be effectively used as filtering oil, bacterial contaminants, nano-size viruses, and other pollutants from water. Modification of CNT matrix can be done by nitric acid treatment  followed by linker attachments .
2. MATERIALS AND METHODS
Three-dimensional network of CNT was prepared by chemical vapor deposition  (CVD) method with slight modifications. Furnace for synthesis of CNT matrix was well designed and fabricated. Thermal Mass Flow Controllers (FM1V01-FAA-22-V-S) were purchased from Bronkhorst Hitec B.V., Netherlands. Ferrocene (powder), 1,2dichlorobenzene, and Quartz plate (2-inch) were purchased from Alfa-Aesar England. Ferrocene powders were dissolved in 1,2-dichlorobenzene (0.06 g/mL).
Synthesis of CNT matrix
The solution of ferrocene (0.06 g/mL) with 1,2-dichlorobenzene was continuously injected (0.13 mL/min, using syringe pump) into a quartz plate (washed with acetone) placed in a silica tube housed inside the CVD furnace(diagrammatic representation is shown in Fig.1.). The reaction temperature was kept at 860[degrees]C. Ar and [H.sub.2] were passed at a flowing rate of 2000 mL/min and 300 mL/min, respectively. After 5 hours, sponge-like CNT matrix was collected from quartz plate.
Modification of CNT
Carboxyl group was introduced into the purified carbon nanotube support by refluxing it in 60 mL of 3 M HN[O.sub.3] overnight ; during the process, carboxyl groups are formed at the ends of tubes as well as the defects on the sidewalls. The resulting mixture was cooled to room temperature, diluted with water, and filtered through polycarbonate membrane (0.2 [micro]m). The oxidized CNT sponge thus produced was sonicated with ethylene diamine and DCC for 1 hour. It was washed with methanol (3 x 20 mL) and dried in vacuum. Schematic representations of surface functionalization of carbon nanotubes are given in figures 2 and 3.
Test for absorption capacity of pristine CNT matrix
CNT matrix is cut into small pieces and an initially weighed sample is put into a syringe with Teflon sealing in one end and 1 mL of required solvent is added and a residence time of 20 minutes is allowed. Excess solvent is removed and the weight of the full material is noted. It is found that functionalization decreases the Q value considerably. Test results are summarized in tables 1 and 2.
Testing of antimicrobial activity of CNT Matrix
Water filtered through CNT sponge and the following parameters are tested before and after filtration. Experimental values are provided in Table 3.
3. RESULTS AND DISCUSSION
Surface characterization using SEM and FE-SEM
Microstructure characterization of CNT matrix was done by transmission electron microscope (TEM) analysis using Tecnai G220 S-TWIN instrument at an accelerating voltage 200 kV. The solution was dropcasted on to the grid and was dried under vacuum. SEM analysis was performed using Hitachi model S3000-H and TESCAN model VEGA3. The CNT Matrix samples were cut into required size and viewed with respect to various magnifications without any surface treatment. Field Emission-Scanning Electron Microscopy (FE-SEM) analysis was performed by using SUPRA 40VP model of Carl Zeiss make having EDX attachment of OXFORD make. The same sample as used for SEM analysis was taken for FE-SEM analysis (Fig.4).
Texture and elemental analysis by EDXA
The relative abundance of various elements in the deposited sample was analyzed by energy-dispersive X-ray analysis (EDX) using OXFORD make (Table 4). EDX analysis of CNT matrix is shown in Fig. 5.
TEM analysis of the CNT was performed to know the side-wall functionalization and the modification in the tube morphology. TEM analysis shows that the outer walls of CNT were functionalized and there was no destruction to the tube morphology. Although there occurs tube breakage due to agitation or sonication employed during the preparation of the bath. The layers of CNT were not thinned as shown in Figure 6B. The overlapping of CNT walls was clear from TEM analysis. CNT tube structure was not damaged and the agglomeration of CNT was controlled through functionalization.
FT-IR measurements of functionalized CNT Matrix were done. The extent of carboxylation affected to the surface of CNT can be assigned to these type peaks. A noticeable peak in the range from 2800-2950 [cm.sup.-1] and 2850 [cm.sup.-1] corresponds to v(C-H) stretching. It implies to the stability of CNT suspension in the aqueous medium. The peak at around 3400 [cm.sup.-1] corresponds to v(-OH) stretching. This peak can be assigned to the hydroxyl group from moisture, alcohol or carboxylic groups. From FT-IR analysis it is clear that functionalization of CNT was effective (Fig. 7).
The Raman spectra showed G and D band features characteristic for carbon as CNT incorporated within the matrix as shown in Figure 6. The peak at ~1480 [cm.sup.-1] shows the disorder-induced D band and that for the tangential G band the peak is at ~1670 [cm.sup.-1]. Absence of prominent radial breathing modes in the Raman spectra was noted for all scans. The ratio of G and D band is a good indicator of quality of CNT. In the present case the peak intensity of D and G band are comparable revealing that the structural defects within the CNT were less after functionalization. The Raman spectroscopy results thus confirm the presence of multi-walled carbon nanotubes in the CNT matrix (Fig. 8).
To conclude, we have successfully synthesized the CNT matrix and modified by functionalization, and tested for efficiency as water filter and as solid support, as it can adsorb organic solvents better than the commonly used polymer resin-based solid support. The CNT matrix formed and functionalized is characterized SEM, FE-SEM, TEM, FT-IR, RAMAN spectra and EDX analysis.
This work was supported by Department of Science and Technology, Govt. of India under WOSA Scheme. The authors acknowledge Dr. R. M. Panicker (CSIR-Central Electrochemical Research Institute, Karaikudi), Dr. C. Arunan (KSCSTE, Kerala), Dr. R. Micheal (Carlsberg University, Copenhagen), and Dr. C. P Vinod (NCL, Pune) for their support and guidance.
6. REFERENCES AND NOTES
 Iijima, S. Nature 1991, 354, 56. [CrossRef]
 Planeix, J. M.,;Coustel, N.; Coq, B.; Brotons, V.; Kumbhar, P. S.; Dutartre, R. J Am ChemSoc, 1994, 116, 7935. [CrossRef]
 Che, G. L.; Lakshmi, B. B.; Fisher, E. R.; Martin, C. R. Nature 1998, 393, 346. [CrossRef]
 Calvert, P. Nature 1999, 399, 210. [CrossRef]
 Gui, X.; Wei, J.; Wang, K.; Cao, A.; Zhu, H.; Jia, Y.; Shu, Q.; Wu, D. Adv. Mater. 2009, 22, 617.
 Bianco, A.; Kostarelos, K.; Partidos, C.; Prato, M. Chemical Communications 2004, 130, 571. [CrossRef]
 Koshio, A.; Yudasaka, M.; Zhang, M.; Iijima, S. NanoLett. 2001, 1, 361. [CrossRef]
 Hoebeke, J.; Graff, R.; Briand, J. P. J. Am. Chem. Soc. 2003, 125, 6160. [CrossRef]
 Rosca, I. D.; Watari, F.; Uo, M.; Akaska, T. Carbon 2005, 43, 3124. [CrossRef] E. Sudha (a) *, R. Selvam (b), P. Sivaswaroop (c), and K. P. Subhash Chandran (b) *
(a) JNTU Hyderabad, India.
(b) Research & P. G. Department of chemistry, SriVyasaNSS College, Thrissur, Kerala, India-680623.
(c) IGNOURegional Center, Nagpur, India-440033.
Article history: Received: 21 April 2014; revised: 06 June 2014; accepted: 18 June 2014. Available online: 03 October 2014.
* Corresponding authors. E-mail: email@example.com, firstname.lastname@example.org
Table 1. Observed Q value of pristine sample in different solvents. S.I No. solvent density Initial wt.(w1) g/[cm.sup.3] 1 Ethanol 0.790 0.0005 2 Methanol 0.790 0.0612 3 Toluene 0.864 0.0017 4 Ethyl acetate 0.899 0.0129 5 Water 0.997 0.0075 6 DMF 0.984 0.0610 S.I No. Wt. after full Q value ([w.sub.2]) ([w.sub.2]/[w.sub.1]) 1 0.0678 135.60 2 0.1518 102.60 3 0.0751 44.18 4 0.1907 14.78 5 0.1578 21.04 6 0.0964 1.58 Table 2. Observed Q value of -COOH functionalized sample. S.I No. Solvent Initial wt (g) Final wt (g) Q value 1 Ethanol 0.0731 0.2945 27.745 2 Methanol 0.0747 1.4920 19.990 3 Toluene 0.0864 0.7554 8.743 4 Ethyl acetate 0.0899 0.2507 2.789 5 Water 0.0821 0.2845 3.465 6 DMF 0.0984 0.0235 0.238 Table 3. Testing of water filter potential andantimicrobial activity of CNT Matrix. Parameters tested Before filtration After filtration pH 4.78 6.3 Conductivity 0.791 S/m 0.680 S/m Turbidity 4.7 ntu 0.2 ntu Iron content 0.32 mg 0.175 mg E. Coli bacteria 20/100 mL N/A Table 4. Relative abundance of various elements in the deposited sample. Element Weight% Atomic% Compd % Formula C K 27.26 33.31 99.88 CO2 Si K 0.05 0.03 0.10 SiO2 Cl K 0.02 0.01 0.00 O 72.67 66.66 Totals 100.00
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|Author:||Sudha, E.; Selvam, R.; Sivaswaroop, P.; Chandran, K.P. Subhash|
|Publication:||Orbital: The Electronic Journal of Chemistry|
|Date:||Jul 1, 2014|
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