Functionalization of CarboxylatedMulti-Wall Nanotubes with Derivatives of N 1-( 11 H-Indeno [ 1 , 2-b ] quinoxalin-11-ylidene ) benzene-1 , 4-diamine

Quinoxaline derivatives are compounds with pharmaceutical applications. In this study, derivatives of N1-(11H-indeno[1,2b]quinoxalin-11-ylidene)benzene-1,4-diamine were synthesized and attached to carboxylated multi-wall nanotubes (MWNT–COOH). Functionalized carbon nanotubes were characterized by scanning electron microscopy (SEM) to study the shape of structures, transmission electron microscopy (TEM), fast Fourier transform infrared (FT-IR), Raman spectroscopy, and elemental analysis.


Introduction
Carbon nanotubes (CNTs) have unique properties that make them attractive for different engineering applications and many other �elds [1].Recently exploration of the biological and medical applications of CNTs has become a rapidly expanding �eld of research.In particular, the uses of CNTs as carriers of biologically active molecules are studied, such as drug delivery [2].Multi-walled carbon nanotubes are more attractive than single-walled carbon nanotubes because of their relatively low production costs and availability in large quantities.However, because of their chemical inertness, carbon nanotubes have to be functionalized in order to acquire additional physicochemical properties [3].ese groups, which are chemically attached to the tubes, are mostly represented by -COOH groups, less by -C=O, and -OH groups [4][5][6].Amidation of CNTs, can be done on the already carboxyl-functionalized nanotubes via treatment in octadecylamine (ODA).Amidation also can be done by �rst substituting a hydroxyl (-OH) group in a carboxylic (-COOH) group on chlorine by treatment in oxalyl chloride or SOCl 2 with the following addition of a long-chain molecule of octadecyl amine [7,8].Compounds such as quinoxaline derivatives are an important class of benzoheterocycles which has received much attention in recent years owing to their both biological properties and pharmaceutical applications.ese derivatives are particularly well known to antimicrobial [9], anticancer [10], antimalarial [11], anti-in�ammatory [12], antinociceptive [13], antitubercular [14], anthelmintic [15], antidiabetic [16], and antiepileptic [17] properties.Carbon nanotubes can be used to deliver their cargoes to cells and organs.In this paper, we investigated, synthesis of MWNT-indenoquinoxalines, on the MWNT in addition to developing the amidation of MWNT with aromatic amine.e products were characterized by FT-IR, SEM, TGA, TEM, and elemental analysis.Synthesis route of modi�ed MWNT-COOH is shown in Figure 1.

Preparation of MWNT-COCl
. 60 mg of the MWNT-COOH were sonicated in 90 mL of DMF for 40 min to give a suspension.Oxalyl chloride (2.5 mL) was added dropwise to the MWNT suspension at 0 ∘ C under N 2 .e mixture was stirred at 0 ∘ C for 2 h and then at room temperature for another 2 h.Finally the temperature was raised to 70 ∘ C and the mixture was stirred overnight to remove excess oxalyl chloride.Aer cooling to room temperature, the mixture was �ltered and washed thoroughly with EtOH [19] (Figure 3).150 mg of 5 dissolved in DMF was added to the 50 mg MWNT-COCl, and the mixture was stirred at 100 ∘ C for 48 h.en the mixture was cooling to   room temperature and �ltered and washed to �MF and ethyl alcohol.Subsequently, the black solid was vacuum-dried at room temperature (Figure 4).
Figure 5 shows the FT-I� spectrum of the modi�ed MWNTs.In spectrum A, the band at around 1527 cm −1 corresponds to the stretching mode of the C=C double bond that forms the framework of the carbon nano tube sidewall [20].e peaks at 1704, 3304 cm −1 , and 1071 cm −1 apparently corresponds to the stretching modes of the carboxylic acid groups [21,22].In spectrum B, the new strong peak at 3439-3500 cm −1 can be assigned to the N-H stretching  A uniform tubular layer due to amide group on the surface of the MWNT (the rough part) is observable.It seems that the diameters of B, C are slightly increased in comparison to A.
e TEM images of the MWNT-COOH (A) and the MWNT-indenoquinoxaline derivatives (B, C) are compared in Figure 7. e MWNT-COOH seemed to be a bundle or a rope of MWNT.However, the dissociation of the bundles was observed in the MWNT-indenoquinoxaline derivatives.Functionalization prevented MWNT to aggregate in the form of bundles and enhanced their dispersibility.So, the MWNT-indenoquinoxaline derivatives showed a high and facile dispersion in solvents than the MWNT-COOH did.e TEM images revealed that the functionalization of MWNT-COOH with indenoquinoxaline derivatives retained the nature of MWNT-COOH even aer the functionalization, without destroying their original electronic structure and behavior.It can be concluded that the amount of functional groups introduced on MWNT-COOH was not large enough to destroy the structure of MWNT-COOH.
Raman spectroscopy is a powerful tool used to provide structural information about MWNT-COOH before and aer functionalization.As shown in Figure 8 e increase in intensity of the defect mode at 1339 cm was related to sp3 hybridization of carbon and is used as an evidence of the disruption of the aromatic system of  electrons by the attached molecules [23][24][25][26].
As a result of this functionalization, the solubility of MWNT-indenoquinoxaline derivatives was improved sig-ni�cantly, and they were easily dispersed in DMF.A dispersion test gives a fair idea whether the modi�cation on the carbon nanotubes has been achieved or not. Figure 9 presents a photograph of three vials containing MWNT-COOH and MWNT-indenoquinoxaline derivatives dispersed in DMF.As can be seen from Figure 8, MWNT-COOH are insoluble in DMF, while the modi�ed CNTs can be directly dispersed in DMF (without sonication) homogeneously and no precipitation was found even aer it was sealed for 1 month at room temperature.

Conclusions
e chemistry of MWNTs offers considerable scope for development of functional materials, structures, and devices based on MWNTs.A detailed methodology for the modi-�cation and functionalization of multi-walled carbon nanotube (MWNT) via amidation has been presented.We have introduced indenoquinoxaline derivatives onto the surface of nanotubes.e functionalized MWNTs were demonstrated by SEM images, FT-IR, Raman spectroscopy, and elemental analysis.e results show successful functional groups.

F 4 :
Preparation of

T 1 :
Elemental analysis of A carboxylated multiwalled carbon nanotubes and B (11H-indeno[1,2-b]quinoxalin-11-ylidene) benzene-1,4-diamine multiwalled, C (8-nitro-11H-indeno[1,2-b] quinoxalin-11-ylidene)benzene-1,4-diamine.carbonyl peak in the spectrum B shi to 1657 cm −1 (as compared with 1704 cm −1 in spectrum A) is a result of amide (C=O)NH linkage formation.In the spectrum C, strong peak at 1647 cm −1 is a result of amide group (C=O)NH and two peak in the range of 1393 and 1517 cm −1 are for (NO 2 ) group.e morphology of the resulting MWNT-5 was observed with SEM.In Figure 6, SEM images of A, B, C are shown.It indicates that the MWNT-COOH (A) has a smooth surface.e changes in the morphology for B and C are remarkable.