spectroscopic studies on covalent functionalization of single-walled carbon nanotubes with glycine

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journal homepage: www.elsevier .com/locate /saa

Spectroscopic studies on covalent functionalization of single-walledcarbon nanotubes with glycine

http://dx.doi.org/10.1016/j.saa.2014.09.0651386-1425/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author at: Department of Physics, NMSSVN College, Nagamalai,Madurai 625 019, Tamil Nadu, India. Tel.: +91 9486468945.

E-mail address: [email protected] (A. Milton Franklin Benial).

Please cite this article in press as: M. Deborah et al., Spectroscopic studies on covalent functionalization of single-walled carbon nanotubes with gSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), http://dx.doi.org/10.1016/j.saa.2014.09.065

M. Deborah a, A. Jawahar a, T. Mathavan b, M. Kumara Dhas b, A. Milton Franklin Benial b,⇑a Department of Chemistry, NMSSVN College, Madurai 625 019, Tamil Nadu, Indiab Department of Physics, NMSSVN College, Madurai 625 019, Tamil Nadu, India

h i g h l i g h t s

� The convenient and simple methodfor sidewall functionalization ofSWCNTs with glycine wasdemonstrated.� The red shift was observed in the

UV–Vis spectra of glycinefunctionalized SWCNTs.� The EPR absorption spectral data

found to be best fit for the Gaussianlineshape.� SEM images show that the increase in

the diameter of the SWCNTs wasobserved for glycine functionalizedSWCNTs.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 5 August 2014Received in revised form 8 September 2014Accepted 18 September 2014Available online xxxx

Keywords:CharacterizationElectron paramagnetic resonanceFunctionalizationSingle-walled carbon nanotubesGlycine

a b s t r a c t

Single-walled carbon nanotubes (SWCNTs) have a great potential in a wide range of applications, butfaces limitation in terms of dispersion feasibility. The functionalization process of SWCNTs with theamino acid, glycine involves oxidation reaction using a mild aqueous acid mixture of HNO3 and H2SO4

(1:3), via ultrasonication technique and the resulted oxidized SWCNTs were again treated with the aminoacid glycine suspension. The resulted glycine functionalized carbon nanotubes have been characterizedby XRD, UV–Vis, FTIR, EPR, SEM, and EDX, spectroscopic techniques. The enhanced XRD peak (002) inten-sity was observed for glycine functionalized SWCNTs compared with oxidized SWCNTs, which is likelydue to sample purification by acid washing. The red shift was observed in the UV–Vis spectra of glycinefunctionalized SWCNTs, which reveals that the covalent bond formation between glycine molecule andSWCNTs. The functional groups of oxidized SWCNTs and glycine functionalized SWCNTs were identifiedand assigned. EPR results indicate that the unpaired electron undergoes reduction process in glycinefunctionalized SWCNTs. SEM images show that the increase in the diameter of the SWCNTs was observedfor glycine functionalized SWCNTs, which indicates that the adsorption of glycine molecule on the side-walls of oxidized SWCNTs. EDX elemental micro analysis confirms that the nitrogen element exists in gly-cine functionalized SWCNTs. The functionalization has been chosen due to CONH bioactive sites inglycine functionalized SWCNTs for future applications.

� 2014 Elsevier B.V. All rights reserved.

Introduction

There is currently great interest in the potential use of carbonnanotubes (CNTs) and other carbon nanomaterials for biomedicalapplications [1]. Among them SWCNTs are molecular wires, have

lycine,

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2 M. Deborah et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx

become one of the most widely studied nanomaterials, primarilybecause of their unique physicochemical properties and have awide range of applications in molecular electronics, optoelectron-ics, drug delivery, and as biological sensors and imaging [2–8].However, the potential applications of SWCNTs are hindered bythe difficulties in processing. The chemical functionalization ofSWCNTs plays a key role in the realization of the promise of thismaterial [9]. The various chemical functionalization methodsinclude oxidation, hydrogenation, fluorination, and the additionof free radicals, carbenes, nitrenes, 1, 3 dipolar intermediates,and other reactive molecules to pristine nanotubes [1]. The processof functionalization involves the selective breaking of C@C bondsin the CNTs and is often done through oxidation [10]. The treat-ment of nanotubes in an oxidizing environment, for example, ina mixture of concentrated nitric and sulfuric acids, the oxygen-containing groups are introduced to the ends and sidewalls ofthe tubes. These groups, which are chemically attached to thetubes, are mostly represented by ACOOH groups, less by AC@O,and AOH groups. These groups can serve as starting points forfurther functionalization of the CNTs, since the acid groups canreact readily with alcohols or amines to give rise to ester or amidebonds respectively [11–13].

The chemical functionalization of SWCNTs has been shown toincrease their solubility in organic solvents, facilitate their process-ing and it affects the SWCNTs rope size and the results in exfoliationinto smaller bundles and individual CNTs [9]. Furthermore chemi-cally functionalized CNTs have the ability to cross the cell mem-brane and successfully transport bioactive molecules like DNA,RNA, drugs and proteins into the targeted cells [14]. Recently, theresearchers have found that the functionalized CNTs penetratefollowing a passive diffusion across the lipid bilayer similar to a‘‘nanoneedle’’ able to perforate the cell membrane without causingcell death. So, it is mandatory to understand the interaction mech-anism between SWCNTs and biological molecules for the safe use ofSWCNTs in biological applications [15–17]. A recent study foundthat the water soluble SWCNTs could be translocated easily intothe cytoplasm or the nucleus of a cell through its cell membrane,without producing any toxic effect. Feazell et al. demonstrated thatby combining the ability of platinum (IV) complexes which resistligand substitution with the proven capacity of SWCNTs to act asa longboat, shuttling smaller molecules across cell membranes[18]. Yu et al. reported the combination of electrochemical immu-nosensors using SWCNTs with multilabel secondary antibody-nanotube bioconjugates for the sensitive detection of a cancerbiomarker in serum and tissue lysates. The various anticancer drugssuch as platinum (IV), amino acid and paclitaxtol have been trans-ported into different types of cells via appropriately functionalizedSWCNTs have also been reported. The Ammonium functionalizedSWCNTs was applied in Bioimaging since it shows much brightervisible photoluminescence extending to near-infrared region(NIR) [19,20]. Zheng et al. have reported wrapping of DNA ontoSWCNTs through relatively weak p-stacking. Wang et al. havereported the functionalization of SWCNTs with an enzyme via theformation of a covalent bond. Dai et al. used SWCNTs as nonviralmolecular transporters for the delivery of short interfering RNA(siRNA) into human T cells and primary cells. Kotov et al. havereported biomodified SWCNTs as a biocompatible platform forpotential neuroprosthetic implants [21–23].

One of the most important applications of SWCNTs is the com-bination with different biomolecules such as amino acids, proteins,to form specific materials that benefit the electrical and mechani-cal properties of CNTs and the particular interactions of biologicalmacromolecules.

Huang et al. reported that bovine serum albumin (BSA) proteincould be covalently attached to CNTs via diimide-activated amida-tion under ambient conditions [24]. Biological macromolecules can

Please cite this article in press as: M. Deborah et al., Spectroscopic studies on cSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014),

be combined with SWCNTs either by direct adsorption onto theCNTs or via a specific linker molecule. Amino acids and their deriv-atives are important examples of carboxylic acids and are key pre-cursors for synthesis of hormones and low-molecular weightnitrogenous substances with each having enormous biologicalimportance. The functionalization of CNTs with amino acids is ofsignificant importance, since it not only improves the nanotubesolubility, but also opens a broad prospect for their biomedicalapplications [25–27].

In this work, glycine, the simplest a-amino acids that consti-tute proteins, having only hydrogen in its R side group is used.Glycine has attracted much attention due to its small size, whichallows comprehensive investigation on its interaction with CNTs.The glycine functionalized SWCNTs has been researched because,glycine has various active sites that may give some insight to fur-ther study of interaction between complicated biomolecules andCNTs. Glycine has the ability to act as an important inhibitorytransmitter in the brainstem and spinal cord and also acts as anovel antioxidant. Recently, a glycine gated chloride channelhas been identified in neutrophils, which can attenuate increasesin intracellular calcium ions and diminish oxidant damage med-iated by the white blood cells. To emphasize on the objectives ofthis study, glycine adsorption has been previously investigatedon several surfaces such as CNTs, graphite, Cu, TiO2, Si, Au, andPt for corrosion prevention, biocompatibility and biosensor[28–31]. The purpose of this work is to pave a new way for effec-tive functionalization of SWCNTs with amino acids. Here, wereport the preparation and characterization of glycine function-alized SWCNTs. The characterization work has been extensivelycarried out by using X-ray diffraction (XRD), ultraviolet–visible(UV–Vis), fourier transform infrared (FT-IR), electron paramag-netic resonance (EPR), scanning electron microscopy (SEM), andenergy dispersive X-ray (EDX) techniques. This fundamentalmodel provides a starting point for studies geared at understand-ing the interactions of CNTs with the more complex proteinsystems.

Materials and methods

The SWCNTs were purchased from Aldrich Chemical Co, St.Louis, MO, USA. Glycine, H2SO4, and HNO3 were purchased fromMerck, Germany.

Sample preparation

Oxidized SWCNTsPristine SWCNTs were mixed with a mixture of 3:1 concen-

trated sulfuric and nitric acid and sonicated for 3 h at 40 �C in anultrasonic bath to introduce carboxylic acid groups on the surfaceof SWCNTs. After sonication the mixture was added dropwise tocold distilled water and the resulting samples, oxidized SWCNTswere filtered and dried in vacuum at 80 �C for 4 h [32].

Glycine functionalized SWCNTsThe oxidized SWCNTs samples were mixed with 0.3 M glycine

suspension and sonicated for about 1 h at room temperature.After sonication the oxidized SWCNTs/glycine suspension wasdirectly filtered and the solid sample was dried in a vacuumfor about 16 h at room temperature [17]. In the similar way,glycine functionalized SWCNTs (0.6 and 0.9 M concentration ofglycine) were also prepared. Fig. 1 shows the scheme for thesynthesis of oxidized SWCNTs and glycine functionalizedSWCNTs.

ovalent functionalization of single-walled carbon nanotubes with glycine,http://dx.doi.org/10.1016/j.saa.2014.09.065


Fig. 1. Scheme for the synthesis of glycine functionalized SWCNTs. (a) Pristine SWCNTs was mixed with (H2SO4/HNO3 (3:1)), sonicated for 3 h and the mixture was added tocold distilled water. The samples were filtered and dried in vacuum at 80 �C for 4 h. (b) The oxidized SWCNTs was mixed with glycine suspension, sonicated for 1 h at roomtemperature. The samples were filtered and dried in vacuum at room temperature for 16 h.

Fig. 2. XRD spectra of (a) oxidized SWCNTs and (b) glycine functionalized SWCNTs.

M. Deborah et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2014) xxx–xxx 3

Spectral measurements

XRD analysisThe X-ray diffraction technique was used to characterize the

crystalline structure of the samples. XRD patterns were collectedusing a PANalytical (Eindhoven, The Netherlands) diffractometerwith a copper target at the wave length of k Cu Ka = 1.54 Å, a tubevoltage of 40 kV, and tube current of 30 mA. The scanning rangewas selected between 10� and 90� of 2h. For XRD studies, rectangu-lar pellets prepared by compression molding were used.

UV–Vis measurementsA Shimadzu UV-3600 UV–Vis-NIR spectrophotometer (Shima-

dzu Scientific Instruments, Columbia, MD) was used for absorptionspectra measurements in the wavelength range of 200–600 nm.

FT-IR measurementsThe FT-IR spectra of the samples dispersed in the potassium

bromide matrix were recorded in the wave number range of400–4000 cm�1 at 64 scans per spectrum at 4 cm�1 resolutionusing a computerized Bruker Optik GmbH FT-IR spectrophotome-ter. Spectra were corrected for the moisture and carbon dioxidein the optical path.

EPR measurementsEPR spectra of the samples were recorded at room temperature

using a Bruker EMX plus spectrometer with 100 kHz field modula-tion frequency and phase sensitive detection. The ESR spectra wererecorded by varying the magnetic field in the range of 50–650 mTwith the following spectrometer settings: field modulation ampli-tude 0.4 mT; conversion time, 40 ms; radio-frequency power,5.0 mW; receiver gain, 2000; sweep width, 600 mT; sweep time,81 s; number of scans, 40; 2048 k resolution and radio frequency,9.78 GHz. The temperature was controlled using a controller withwater as a coolant.

SEM imagingThe surface morphological studies of the samples were carried

out by scanning electron microscopy (SEM–VEGA3 TESCAN, USA).

EDX measurementsThe chemical composition of oxidized SWCNTs and glycine

functionalized SWCNTs were characterized by energy dispersivespectrometer (Bruker Nano, Germany).


Results and discussion

XRD analysis

The structure of the oxidized SWCNTs and glycine functional-ized SWCNTs were characterized by XRD technique. Fig. 2 showsthe X-ray diffraction patterns of oxidized SWCNTs and glycinefunctionalized SWCNTs. For oxidized SWCNTs, two peaks appearedat 2h = 25.87�, 42.67� and for glycine functionalized SWCNTs, twopeaks appeared at 2h = 26.48� and 42.91� which were assigned to(002), (110) diffraction plane of SWCNTs. These two diffractionpeaks are attributed to the graphitic structure of SWCNTs (JCPDS41-1487) [33]. It could be seen that the XRD pattern of glycinefunctionalized SWCNTs was very similar to the oxidized SWCNTs,which indicates that the glycine functionalized SWCNTs still hadthe same cylinder wall structure as oxidized SWCNTs. It can beconcluded that the functionalization process would not changethe general structure of SWCNTs. However, the enhanced XRDpeak (002) intensity was observed for glycine functionalizedSWCNTs compared with oxidized SWCNTs, which is likely due tosample purification by acid washing. This is an indication of themore ordered CNTs floss in the glycine functionalized SWCNTs.

UV–Vis analysis

The UV–Vis spectra of oxidized SWCNTs and glycine functional-ized SWCNTs were shown in Fig. 3 and their corresponding spec-tral data were given in Table 1. The characteristic peak appeared



Fig. 3. UV–Vis spectra of (a) oxidized SWCNTs, (b) 0.3, (c) 0.6, and (d) 0.9 M glycinefunctionalized SWCNTs.

Table 1UV–Vis spectral data for oxidized SWCNTs and glycine functionalized SWCNTs.

Sample Absorbancek1 (nm)

Absorbancek2 (nm)

Oxidized SWCNT 265 –

Glycine functionalizedSWCNTs

Concentration ofglycine

278 371

0.3 M0.6 M 289 3710.9 M 294 373


at 265 nm for oxidized SWCNTs, which is in good agreement withthe reported value [34]. The red shift was observed for glycinefunctionalized SWCNTs around �278 nm, �289 nm and �294 nm(0.3, 0.6 and 0.9 M concentration of glycine) respectively, whichindicates that the covalent bond formation between glycine mole-cule and SWCNTs. The appearance of another peak around�371 nm (0.3, 0.6 and 0.9 M concentration of glycine), which isattributed to the formation of charge transfer complex, glycinefunctionalized SWCNTs.

FT-IR analysis

FT-IR spectroscopy was used to identify the chemical groupsthat were attached to SWCNTs [35]. The FT-IR Spectra of oxidizedSWCNTs and glycine functionalized SWCNTs were shown in Fig. 4and their corresponding FT-IR assignments were listed in Table 2.The peaks at 1746 cm�1 and 1084 cm�1 were in correspondence

Fig. 4. FT-IR spectra of (a) oxidized SWCNTs, (b) 0.3, (c) 0.6, and (d) 0.9 M glycinefunctionalized SWCNTs.


to C@O, CAO stretching, respectively, which indicates the exis-tence of carboxyl groups on the surface of oxidized SWCNTs. Thesame peaks in the glycine functionalized SWCNTs were observed,which indicates the existence of carboxyl groups remaining afterthe reaction with glycine [36,37]. The amino acid treated SWCNTssamples provided good evidence for the desired functionalities incontrast with the oxidized SWCNTs. Another peak in the regionaround �1596 cm�1 is due to the carbonyl stretching mode of qui-none type units along the side walls of the carbon nanotube [38].Functionalization of glycine on the oxidized SWCNTs, whichresulted in the formation of secondary amide on the SWCNTs isconfirmed by the characteristic peak around �1288 cm�1 whichis assigned to CAN stretching and another peak in the regionaround �858 cm�1 is assigned to the NAH stretching mode, whichconfirms that glycine molecules have been bonded to SWCNTs[17,32]. The NAH groups observed on the glycine functionalizedsamples indicates that the amidation reactions occurred betweenthe amino groups of glycine and the carboxyl groups on the sur-faces of the SWCNTs [35]. The OAH bending and CAOH stretchingmodes in carboxylic acid were observed around �1345 cm�1 and�642 cm�1 respectively [39,40]. The CAH bending mode appearedaround �1453 cm�1 [41]. Thus FT-IR spectra confirms that oxi-dized SWCNTs has been successfully functionalized by glycine.

EPR analysis

Electron paramagnetic resonance (EPR) spectroscopy is an idealmethod for providing insights into the spin properties of SWCNTsas it can probe conduction electrons and unpaired spins [42]. Theeffect of defects and the presence metal content in the CNTs wereassessed with EPR studies. EPR measurements are sensitive tometallic impurities and dangling bond defects [43]. Fig. 5 showsthe EPR spectra of oxidized SWCNTs and glycine functionalizedSWCNTs (0.3, 0.6 and 0.9 M concentration of glycine). Fig. 6 showsthe EPR absorption spectra and Gaussian fit of oxidized SWCNTsand glycine functionalized SWCNTs (0.3, 0.6 and 0.9 M concentra-tion of glycine). The EPR parameters such as line width, g-factor,spin concentration and R2 from Gaussian fit were obtained for oxi-dized SWCNTs and glycine functionalized SWCNTs and listed inTable 3.

Line shapeThe line shape was analyzed for the EPR absorption spectral

data using the Origin 8 software package. The EPR line shape isusually described by Lorentzian and Gaussian line shapes. TheEPR absorption spectral data were found to be the best fit (correla-tion coefficient value [R2] > 0.98) for the Gaussian function,f(x) = a ⁄ exp � ((x � b)2/2c2), where a, b and c are real constants[44]. The EPR absorption spectra for the oxidized SWCNTs and gly-cine functionalized SWCNTs have a Gaussian lineshape. The dipolarbroadening generally produces Gaussian-shaped lines.

Line width and g-factorThe full width at half maximum (FWHM) line width values for

the EPR spectra of oxidized SWCNTs and glycine functionalizedSWCNTs were obtained from the Gaussian fit. The line widthreduction was observed with increasing concentration of glycine,which indicates the effect of dipolar interaction decreases in gly-cine functionalized SWCNTs. The line shape and g-factor are sensi-tive to metallic impurities and dangling bond defects. The defectsthat are present in the nanotubes significantly contribute to thebroad line shape of EPR spectra and modify the ‘g’ values depend-ing on the type of defects. The broad line shape in the EPR spectraof CNTs has usually been correlated to the presence of metal cata-lysts [43]. The broaden line width values (Table 3) were obtainedfor oxidized SWCNTs and glycine functionalized SWCNTs, which



Table 2FT-IR spectral assignments of oxidized SWCNTs and glycine functionalized SWCNTs.

Assignment Oxidized SWCNTs wavenumber (cm�1) Glycine concentration

0.3 M wavenumber (cm�1) 0.6 M wavenumber (cm�1) 0.9 M wavenumber (cm�1)

C@O stretching 1743 1745 1746 1751C@O stretching 1596 1598 1598 1600CAH bending 1454 1458 1452 1458OAH bending 1352 1345 1349 1345CAN stretching – 1289 1292 1288CAO stretching 1079 1085 1084 1086NAH stretching – 861 859 858CAOH stretching 646 647 642 646

Fig. 5. EPR of (a) oxidized SWCNTs and (b) 0.3, (c) 0.6 and (d) 0.9 M glycine functionalized SWCNTs.


indicates the presence of metal catalyst iron in the samples. Theg-value of �2.04–2.23, which is assigned to the interactionbetween the localized electrons and delocalized electrons in thenanotubes trapped at defects or magnetic ions site. The more thedeviation from the free electron ‘g’ value, the more is the localiza-tion by defects. The g-value was calculated using the magnetic fieldB0, which is obtained from the central position of the EPR spectralline. If the observed g value is close to the free electron g value(2.0023), which reveals that the system is isotropic in nature. Theg-value is independent of the magnetic field direction only in isotro-pic systems. In the present study, EPR lines are seen with the g-valueof 2.083–2.100, which is assigned to the interaction between thelocalized electrons and delocalized electrons in the nanotubestrapped at defects or magnetic ions site. The g-factor value also con-firms the presence of impurities, defects or magnetic ion site.

Signal intensity and spin concentrationThe EPR signal intensity decreases with increasing concentra-

tion of glycine, which were shown in Fig. 5, which reveals thatthe SWCNTs successfully reacted with glycine. The spin concentra-tion values were obtained for oxidized SWCNTs and glycine func-tionalized SWCNTs from the Gaussian fitting of EPR absorptionspectral data, which were shown in Table 3. The spin concentrationvalue decreases with increasing concentration of glycine, which


shows that the unpaired electron undergoes reduction process inglycine functionalized SWCNTs.

SEM and EDX analysis

SEM is a powerful tool used for the evaluation of CNTs morphol-ogy. SEM is probably the only technique that can provide informa-tion on both CNT morphology and the metallic impurity content[45]. In order to observe changes in the morphology of the glycinefunctionalized SWCNTs, SEM imaging of the samples was carriedout and compared with those of the oxidized SWCNTs. A represen-tative image of glycine functionalized SWCNTs, along with animage of oxidized SWCNTs, were shown in Fig. 7. The SEM imageof oxidized SWCNTs was observed with an average diameter of�35 nm. After the functionalization of a glycine molecule on theoxidized SWCNTs, which resulted in an increase of the averagediameter of �55 nm due to the adsorption of glycine on thesidewalls of oxidized SWCNTs [17]. After functionalization withglycine, the SWCNTs are less isolated and distinct as compared tooxidized SWCNTs due to weak tube-tube interaction among theCNTs. The glycine molecules were adsorbed on the surface ofoxidized SWCNTs by polar interactions, p–p stacking, hydrogenbonding and covalent bonding [17]. Agglomeration of the SWCNTswas not observed by SEM images, which indicates the higher



Fig. 6. EPR absorption spectra and Gaussian fit (---) of (a) oxidized SWCNTs and (b) 0.3, (c) 0.6 and (d) 0.9 M glycine functionalized SWCNTs.

Table 3EPR parameters of oxidized SWCNTs and glycine functionalized SWCNTs.

Samples R2 from Gaussian fit Spin concentration from Gaussian fit (a.u) FWHM (mT) g-Factor

Oxidized SWCNTs 0.996 2.00 � 1013 258.4 2.093

Glycine functionalized SWCNTs Glycine concentration 0.996 8.92 � 1012 265.1 2.0830.3 M0.6 M 0.954 5.46 � 1012 255.9 2.1000.9 M 0.989 2.32 � 1012 241.4 2.096

Fig. 7. SEM images of (a) oxidized SWCNTs and (b) glycine functionalized SWCNTs.


dispersing ability of SWCNTs in solvents [25]. Fig. 8 shows the EDXspectra of (a) oxidized SWCNTs and (b) glycine functionalizedSWCNTs. The EDX elemental micro analysis (wt.%) of oxidizedSWCNTs and glycine functionalized SWCNTs were listed in Table 4.The EDX elemental micro analysis confirms that the element


nitrogen exists in glycine functionalized SWCNTs along with car-bon, oxygen and transition metal catalyst iron. The spectral linecorresponds to element nitrogen was not appearing in the EDXspectra (Fig 8a) of oxidized SWCNTs, which is also evident thatthe adsorption of glycine molecules on oxidized SWCNTs [35].



Fig. 8. EDX spectra of (a) oxidized SWCNTs and (b) glycine functionalized SWCNTs.

Table 4EDX elemental micro analysis (wt.%) of oxidized SWCNTs and glycine functionalizedSWCNTs.

Samples Normalized wt.%

C O Fe N

Oxidized SWCNTs 95.18 4.80 0.02 –Glycine functionalized SWCNTs 93.21 3.73 0.07 2.99


Conclusion

The convenient and simple method for sidewall functionaliza-tion of SWCNTs with glycine was demonstrated. The spectroscopicstudies on oxidized SWCNTs and glycine functionalized SWCNTswere carried out using XRD, UV–Vis, FT-IR, EPR, SEM and EDX spec-troscopic techniques. XRD study concluded that the functionaliza-tion process would not change the general structure of SWCNTs.From the UV–Vis study, the characteristic peak was observed at265 nm for oxidized SWCNTs and the same peak was red shiftedfor glycine functionalized SWCNTs. The appearance of anotherpeak is attributed to the formation of charge transfer complex, gly-cine functionalized SWCNTs. FT-IR study confirms the presence offunctional groups of oxidized SWCNTs and glycine functionalizedSWCNTs. The EPR line shape analysis shows that the EPR absorp-tion spectral data found to be best fit for the Gaussian lineshape,which confirms the dipolar broadening of the spectral line. EPRstudy also reveals that the spin concentration value decreases withincreasing concentration of glycine, which implies that theunpaired electron undergoes reduction process in glycine function-alized SWCNTs. The SEM image of glycine functionalized SWCNTswas observed with an average diameter of �55 nm, which is dueto the adsorption of glycine molecule on the sidewalls of oxidizedSWCNTs The EDX analysis confirms that the glycine moleculeswere functionalized on the oxidized SWCNTs. The applications ofamino acid functionalized SWCNTs derivatives prepared in thepresent work will be based on hydrogen bonding ability and chem-ical reactivity of terminal carboxyl groups in the side chain. Theglycine functionalized SWCNTs, prepared in this work by a simplemethod, which have CONH group and it can be a valuable precur-sor for peptide synthesis, targeted drug delivery, design and fabri-cation of covalently integrated nanotube composites, biomaterials,and other biomedical and engineering applications.


Acknowledgement

The authors thank their college management for encourage-ment and permission to carry out this work. This work was sup-ported by the UGC Research Award Scheme, New Delhi (F. No.30-35/2011 (SA-II)).

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