Addition of Some Primary and Secondary Amines to Graphene Oxide , and Studying Their Effect on Increasing its Electrical Properties

Previously many properties of graphene oxide in the field of medicine, biological environment and in the field of energy have been studied. This diversity in properties is due to the possibility of modification on the composition of this Nano compound, where the Graphene oxide is capable of more modification via addition other functional groups on its surface or at the edges of the sheet. The reason for this modification possibility is that the Sp3 hybridization (tetrahedral structure) of the carbon atoms in graphene oxide, and it contains many oxygenic functional groups that are able to reac with other groups. In this research the effect of addition of some amine compounds on electrical properties of graphene oxide has been studied by the preparation of graphene oxide amino containing compound, which could be classified under Nano carbon compounds containing nitrogen (N-doped carbon nanomaterials). These amines are used as expanders for the distance between the layers of graphene oxide (spacers), and thus prevent agglomeration of graphene oxide layers in addition to enhanced electric properties of graphene oxide. The following amines (thiocarbohydrazide(TCH),o-phenylenediamine(oPD) and poly aniline(PAni)) were used for the preparation of the corresponding amino graphene oxide (GO-TCH, GO-containing Benzoimidazol & benzoxazole, and GO-PAni), and characterized by X-RAY diffraction (XRD) ,infra red spectrum (FTIR) and atomic force microscope (AFM) , also the electrical properties of these materials were studied using inductance, capacitance, and resistance ( LCR) measurements.


Introduction:
The deficiency in the quantity of fossil fuel and increasing of pollution that is considered as a main problem of nowadays, as result many researchers rush up to a find superior materials in order to use them in renewable energy devices to promote their performance.Graphene oxide is one of the carbon allotropes with a Nano size that gives a high surface area and the ample of oxygenic functional groups that gives the ability to react and join with active or catalysis material [1].This modification on graphene oxide makes it able to save and generate energy; furthermore, these functional groups give it porous structure, so it could be used as current collector or doped Open Access material for electrodes in supercapacitor or lithium batteries [2].This distinctive nano structure of graphene oxide enables us to use it in various applications like electronics, fuel cells, supercapacitor and sensors.In principle, we can't use graphene oxide in applications that require electric conductivity.This is due to poverty of graphene oxide to electrical conductivity [3].In this research, the addition of amines on graphene oxide surface has been studied for increasing the property that graphene oxide lacks and to obtain a higher conductivity material that can improve the used renewable energy device properties.Graphene oxide has many vital features like high surface area, disperse in water and produce a homogenous colloidal suspension, prepared by a simple and low cost method [4], not toxic, good mechanical properties and the most important point is that GO has many different functional groups.According to Lerf-Klinowski and Dékány Models [5,6], the appropriate structure that contain: epoxy (bridging oxygen atoms) and hydroxyl in the basal plane and carboxyl and carbonyl moieties lining the nanosheet edges (Figure 1) and a small number of intercalated water molecules (5-15 wt %) [7].

Preparation of materials: Preparation of GO:
Graphene oxide prepared according to Hummers' method [19].50 ml of concentrated H 2 SO 4 was cooled down below 0 o C in ice bath for 30 minutes, 1 g of graphite was then added to cool concentrated H 2 SO 4 and kept on constant stirring in an ice bath for 15 minutes.4 g of sodium nitrate was added gradually.While maintaining vigorous agitation, 6 g of potassium permanganate were added to the suspension.The rate of addition was controlled carefully to prevent the temperature of the mixture from exceeding 10°C.After 40 minutes, the color of the mixture changed from black to green due to the presence of oxidizing agent (Mn 2 O 7 ).The mixture was stirring for 12 hours in an ice bath.The ice-bath was then removed and the temperature of the mixture was kept at 35°C in water path for 20 hours.After that, the mixture became pasty(deep red-brown in color), then 50ml of DI water was then added to above mixture carefully and very slowly with vigorously stirring for 1 hour.The temperature reached 90-98 o C and avoided reaching more than that degree with the generation of the toxic gas/ (es) NO 2 , N 2 O 4 (violent effervescences).For that reason, this step was done in the hood).The above mixture was diluted by using 250 ml warm water.Following this, 30% H 2 O 2 (~ 30 ml) was added till the solution turned bright yellow(to reduce the residual permanganate and manganese dioxide to colorless soluble manganese sulfate).The graphite oxide suspension was washed with 10% HCl aqueous solution, then copiously with warm DI water until pH ~ 7, and dried at 40 o C for 24 hours in oven.(water must be warm to remove mellatic acid which may be found as a side product ) Finally, graphite oxide was dispersed in DI water with GO concentration of 1 mg per ml by ultrasonic cleaner.Preparation of TCH [20,21]: Hydrazine hydrate (20 ml) was added drop wise to 5 ml carbon disulphide (CS 2 ).This mixture was refluxed for 30 minutes, until yellowwhite precipitate was formed.The yellow-white precipitate was washed in ethanol, recrystallized in distill water yet white crystals were formed, dried it in 70 O C for 4 hours.

Preparation of GO-TCH:
Graphene oxide (0.5 g) was mixed with 1.0 g of thiocarbohydrazide (TCH) in 25 ml Pyrex beaker.The mixture was grind and put in a sand bath with a temperature of 160 ˚C.This mixture was stirred by spatula until it will be melted.The new substance was washed with hot deionized water to remove unreacted TCH and dried at 70 ˚C for 4 hours.

Preparation of PAni:
Distillated aniline (3 ml) was placed in an ice bath at 0 o C for 10 minutes.
Then, 20 ml of 1M HCl and 20 ml of (2 g Ammonium persulphate (APS) dissolved in 20 ml 1M HCl) was added correspondingly, with keeping the temperature at 0 °C.Then the above solution was stirred for 2 hours in an ice bath and the resulting solution was kept in the refrigerator overnight.The yield filtered and washed with distillated water four times and with ammonium hydroxide 1M, 20 ml with stirring for 30 minutes.Then filtered and washed with distillated water until the pH was 6-7.Finally, the precipitate was washed with 15 ml of benzene with stirring for 15 min and dried at 80 °C for 6 hours.

Preparation of GO-PAni:
Graphene oxide(1 g) was sonicated with distillated aniline for 20 minutes and filtered.The collected product was placed in a small beaker in an ice bath at 0 °C.20 ml of 1M HCl was added drop wise and 10 ml of (1 g of Ammonium persulphate (APS) dissolved in 10 ml of 1M HCl) was added drop wise with keeping the temperature at 0 °C.This solution was stirred for 2 hours in an ice bath, then the solution was kept in the refrigerator overnight.The yield filtered and washed with distillated water four times and with 20 ml ammonium hydroxide 1M with stirring for 30 minutes, then filtered and washed with distillated water until the pH was neutral.Finally, the precipitate was washed with benzene and dried at 80 °C for 6 hours.

Preparation of GO containing benzoimidazol & benzoxazol[22, 23]:
Typically, 1 g GO was dispersed in 300 ml DI water, 6g ophenylenediamine (oPD) was dispersed in 100 ml ethanol by ultrasonicator, Then, the oPD solution was added into the GO suspension, small amount of poly phosphoric acid was added to this mixture.This mixture was ultrasonicated for 1hour.
The solution was then sealed in a 500 ml Pyrex beaker and stirred for 7 days at room temperature and 5 hours at 180 o C. The mixture was naturally cooled to room temperature, filtered, washed for several times by distilled water and dried at 60 o C for 12 hours in oven.

Instruments:
The prepared materials are characterized by x-ray diffraction using (Shemadzu-XR -6000) device with Nickel -Cooper filter for the xray radiation (Cu Kα, λ = 1.5406Å).The morphology of nano materials were performed using atomic force microscope by PHYWE AFM.The Fourier transform infrared (FTIR) spectra were recorded at room temperature on 65 FT-IR Perkin Elmer Spectrophotometer orWQF-510 spectrophotometer ranging from 400 to 4000 cm -1 .Sonicator Soniprep 150 was used for dispersing of nano particles in order to make nano materials suspension.
Electronic Test Device was used measure to the Inductance (L), Capacitance (C),and Resistance (R) of a nano materials using HEWLETT.PACKARDLCR.

Results and Discussion: FTIR characterization: FTIR of GO:
The FTIR spectrum of GO (Figure 2) shows a broad peak at 3406cm -1 of -OH in the high frequency area.The absorption peaks at 2942 cm -1 and 2845 cm -1 represent the symmetric and anti-symmetric stretching vibrations of CH 2 .The peak of stretching C=O appears at 1718 cm -1 .While the peak centered at 1622 cm -1 is assigned to C=C bonds associated with skeletal vibrations of unoxidized graphite domains.1381 cm -1 represented the vibrations C-O of carboxylic acid Finally, the absorption peaks at 1200cm −1 and 1128cm −1 correspond to the stretching vibrations of C-O of epoxy and alkoxy groups [24,25].

Fig.( 2) FTIRSpectrum of graphene oxide FTIR of TCH:
Thiocarbohydrazide spectrum (Figure 3) showed peaks at 1531,755 and 1490cm -1 which are associated for N-H wagging, bending and C-N stretching vibration, respectively.The bands of the characteristic (C=S) stretching were observed in the IR spectrum at 1286 and 933 cm -1 .The band in 3305 cm -1 is due to N-H stretching vibration, and the bands at 3274 and 3204 cm -1 are due to NH 2 stretching vibrations.1639 and 1142 cm -1 bands are assigned to the NH 2 bending and wagging vibrations [26,27].

Fig. ( 4) FTIRSpectrum of GO-TCH FTIR of PAni:
As in (Figure 5) the peaks at 1586 and 1491 cm -1 corresponding to C=C quinonoid and benzenoid deformation vibrations.1293 and 1143 cm -1 are assigned to the C-N of 2aromatic amine stretching deformation and C=N stretching of (-N=quinoid=N-), respectively.While the band at 824 cm -1 is attributed to C-H of aromatic ring.The stretching vibration of N-H shows a broad peak at 3388 cm -1 [28].

Fig. ( 5) FTIR Spectrum of PAni FTIR of GO-PAni:
All character bands of PAni chains are observed in GO-PANI composite but the PAni bands are slightly shifted to lower frequency (Figure 6).This case indicates the p-p stacking and hydrogen bonding between GO nanosheets and the PAni backbone and hydrogen bonding between GO nanosheets and the PAni backbone.These peaks are 1574 and 1488 cm -1 corresponding to C=C quinonoid and benzenoid stretching vibrations.1297 and 1135 cm -1 are assigned to the C-N of 2aromatic amine stretching deformation and C=N stretching of (-N=quinoid=N-), respectively.823 cm -1 band is attributed to C-H aromatic ring.The stretching vibration of N-H shows a broad peak at 3196 cm -1 .All these bands clearly indicate the presence and formation of GO-PAni [29].The bands at 1707 and 1220 cm -1 disappear(Figure 7), moreover, the new bands at 1574,1544 cm -1 are attributed to the skeletal stretching vibration mode of quinoid and benzoid rings in phenazine.The bands at 1630,1257cm -1 can be attributed to the stretching of C=N and C-N, respectively the other one at 767 cm -1 in the fingerprint spectrum region also can be assigned to the characteristic bands of phenazine [21].

Fig. ( 10) XRD of GO-TCH XRD of PAni:
The x-ray diffraction pattern of PAni powder exhibits a narrow peak than that found in nanoparticles.XRD of pure PAni shown is in (Figure 11).The main peaks appeared at 19.8, 20.9 and 25.2 o 2θ.The peak centered may be ascribed to the repetition of benzenoid and quinoid rings in PAni chains and the peak at 2θ = ~25° may be caused by the periodicity perpendicular to the polymer chain, while the peak at 2θ = ~20° also represents the typical distance between the ring planes of benzene rings in nearby chains or the close-contact inter-chain distance [27].

XRD of GO-PAni:
Three new broad peaks of graphene oxide functionalized with poly aniline (Figure 12) are centered at 2θ =8.3° and broad intense peak at 25.6° and around 43.1°correspond to (001), ( 002) and (100).In the GO-functionalized with poly aniline, we observed a weak and broad peak appearing nearly at 2θ = 8.3, which is lower than that of graphene oxide.This could imply that the inter planar spacing of the graphene oxide functionalized with poly aniline composite was broadened due to possible intercalation of poly aniline and that the graphene oxide was fully exfoliated by treatment with poly aniline.Therefore, the XRD patterns confirm also the formation of poly aniline grafting on the surfaces of the graphene oxide.These results provide further insight and clear evidence for the formation of functionalized graphene with poly aniline from graphene oxide during the process [30].

Fig. (12) XRD of GO-PAni
XRD of GO containing benzimidazole& benzoxazole: GO containing benzoimidazol & benzoxazol (Figure 13) shows a slightly high angle of reflection at 12.4 o with a reduced interlayer distance of 7.16 Å for GO-benzoimidazol.This decreased of interlayer distance can be explained by the formation of benzoxazole and benzoimidazol rings on the edges of GO after covalent functionalization, because the introduced aromatic molecules will weaken the electrostatic repulsion between the GO sheets and thus induce a smaller interlayer distance.Additionally, bands at 20-25 o , corresponding to the chemically converted graphene are observed in GO-benzoimidazol, indicating the partial reduction and re-stacking of GO occurring during the functionalization process [31].

Fig. (13) XRD of GO containing benzoimidazol & benzoxazol
Atomic Force Microscope (AFM):-AFM investigations of pure and functional GO all Figures [ 14-A, B, C, D] represented the GO and GO with different amine functional groups.AFM measurements showed the GO sheets and GO-TCH with thickness about 4-5 nm.

Fig. (14) AFM image of (A) GO, (B) GO-TCH and (C) GO-PAni and (D) GObenzoimadazol and benzoxazol
Electrical properties of nanomaterials: (Figures 15, 16) represented the variation of permittivity with respect to frequency of graphene oxide alone or with functional group.All charts in (Figure15) depicted the variation of the real part of dielectric permittivity (ɛ′) with frequency for all types of nanosheet materials.At low frequencies (400-1000 Hz) permittivity, attained higher values, in all cases, then diminish rapidly with increasing of frequencies (4000-100000 Hz).The charts in (Figures 17) showed the variation of results for the AC conductivity (AC) nanomaterials at different frequencies.The conductivity depends on frequency, and this was considered as a strong indication for charge migration via the whopping mechanism [32,33].Finally, it should be stated that in all studied specimens, conductivity was altered abruptly, implying that the transition from insulating to conductive behavior has been achieved by functionalization of graphene oxide with different amines.The materials that have higher value of (ɛ′) and lower value of (Ԑ″)could be enhanced electrical storage [34].In this study functional GO with poly aniline possessed a relatively highly (Ԑʹ) and (Ϭ AC ) with low (Ԑ″), as shown in (Table 1, 2 and 3).

Conclusions:
From the electrical measurements, we noticed that the electrical properties of functional GO have been developed.This promotion in the electrical properties could be attributed to the: (i) The grafting of polyaniline, benzoimidazol & benzoxazol and TCH on the surface and edge of GO leading to fully exfoliated graphene oxide in addition to the chemically reduction of GO that occurred during the functionalization process which that means that these amines behave as reducing agent and converted it to graphene which has a very high conductivity.(ii) The addition of amines promote the electrical properties of GO by increasing the pi system.Depending on all the above measurements, we can conclude the following series of the electrical properties: GO-PAni < GO-benzoimidazol & benzoxazol < GO-TCH < GO From the previous measurements (FTIR, XRD and AFM) the appropriate structure of graphene oxide functionalized with poly aniline has different bonds that; covalent and noncovalent bonds as in (Figure 18).While in the case of other material, TCH and o-PD entered ring close reaction.A reaction of only one GO alcoholic or carboxylic group with amines group makes o-PD and TCH converted into benzoimidazole and tryazole consequently, but the reaction of two neighboring alcoholic groups will convert into benzoxazol.These two compounds may be containing hydrogen bonding with GO sheet.