Synthesis and electrical properties of Reused-Graphite/Polyaniline composites

Polyaniline graphite composites have been synthesized using chemical oxidative polymerization method. The graphite powder has been reused which is obtained by used batteries. XRD patterns of graphite show (002) peak and no impurity peaks. Different wt. % (5, 10, 15, 20) of graphite is used for synthesis of composites and studied their electrical conductivity. XRD patterns of composites show increasing intensity with an increasing graphite content. SEM images show plate-like morphology of graphite whereas granular-morphology for PANI. Composite samples show both plate-like morphology and granular morphology indicating that graphite is embedded in the polymer matrix. Electrical characteristics of composite samples have shown a systematic increase in conductivity with an increase in the graphite concentration. Conductive fillers within the polymer matrix can increase the overall conductivity. Higher filler content provides more conductive pathways for electrons, resulting in enhanced conductivity. The detailed studies of these results are discussed and presented in this paper.


Introduction
After the introduction of polymer (a Greek term meaning, a large chemical contains the combination of various small as well as alike substances) by Jons Jacob Berzelius in the year 1833, since then, it was observed that the polymers gained wide range of applications in various fields [1][2][3].Generally, polymeric substances can be distinguished on bases of their source, structural characteristics, polymerization route, chemical bond strength, and conductivities [4,5].In the year 2000, a noble prize was awarded to scientists, MacDiarmid, Shirakawa and Heeger for their finding and development of conducting polymers [6].Consecutively, various types of conducting polymers gained importance and hence, researchers synthesized polymers and their composites like polythiophene, polypyrrole, and polyaniline composites [7,8].During the process, electrons were delocalizing on the entire polymeric chain which ultimately offers flexibility to electrons especially in conducting polymers [9][10][11].Such polymers are named as 4 th generation of polymeric ingredients [12].In current conditions, it is necessary to look for new ingredients having distinctive characteristics to improve existing technologies.For this reason, a new group of polymers (especially organic material) having the capacity of electricity conductivity was introduced and they were coined as Inherently conducting polymers (ICPs).These ICPs are extremely flexible and were being used in numerous research fields like 1300 (2024) 012014 IOP Publishing doi:10.1088/1757-899X/1300/1/012014 2 electrical, electronics, electromechanical and so on [13][14][15].Among these ICPs, polyaniline (PANI) was studied to a larger extent due to its various properties, having higher strength than other ICPs and has low cost [16][17][18].However, in certain conditions, it was observed that PANI lose its elementary configuration.To tackle this problem, researchers were looked few ingredients like graphite, metallic carbon-based bases, metallic elements, and metallic sulphonated components to improve its mechanical characteristics as well as thermal strength [19][20][21].However, not much work has been carried out on reused graphite.Hence, we have utilized graphite here to prepare PANI composite.

Preparation of Graphite
Graphite powder is prepared from a used battery cell.Briefly, graphite rod was dipped in concentrated hydrochloric acid for 2 h.Further, it was washed with double distilled water to remove acid and unwanted impurities.Later, fine powder of graphite was made using ball milling process.The powder was again washed with HCl and distilled water several times.Thus, obtained graphite powder was used in synthesis of PANI/graphite composites.

Synthesis of PANI/Graphite composite
Synthesis of PANI/Graphite was carried out as described in Ashwini et al., [22] with little modifications.Briefly, PANI/Graphite nanocomposites were prepared according to as described above.Initially, 5 g of graphite powder was dissolved in 100 ml of water for dispersion and kept in sonicator for half an hour.To this, 0.5 M aniline monomer was added with continuous stirring and was maintained in ice bath (less than 5 °C) for 15 min.Afterwards, 2 M of CH3COOH solution was added and kept it for 15 min with continuous stirring.A 0.3 M APS (Ammonium persulphate) was added to the above solution drop wise and kept for continuous stirring for 24 hours.A dark green solution of PANI/Graphite composite solution is stored in refrigerator for 24 hours.After this solution was filtered in vacuum filter and residue was washed with double distilled water and the washing process was repeated several times until the solution is purified.The obtained purified samples were dried at 50-60 °C.The dried samples were crushed in mortar to get fine powder of PANI/graphite nanocomposite.

XRD analysis
XRD patterns of pure PANI, and PANI/graphite nanocomposites are shown in Figure 1.The influence of PANI on the graphite crystal arrangement was displayed in the XRD patterns.The broad peak at 2θ = 25.5 ͦ was observed in pristine PANI.This peak corresponds to the orthorhombic structure of (200) plane.Pure graphite will be having a peak approximately at 2θ = 26.67°corresponding to (002) plane of carbon [26].All composites show similar peaks comprising ICDD (Ref.code: 00-013-0148) [27,28].Similar kind of results were observed previously [29][30][31].PANI/graphite composites show some typical peaks of both PANI as well as graphite.Further results reveal that the peak intensity increases with the increase in the content of graphite in PANI, it might be due to electronic interface at the atom.It also noticed that there is a small shift in the peak positions which indicates the existence of structural changes.PANI in composites converts from partial amorphous to crystalline.The addition of a minute quantity of graphite into the PANI configuration by is responsible for the structural changes.

SEM analysis
SEM was used to determine surface morphology of the PANI/ graphite composites (Figure 2).The SEM image of graphite shows 2-D sheets or platelike structure.PANI sample shows tubular structure because of acetic acid medium and synthesis conditions.The composite samples show the presence of both tubular structure and plate-like structure indicating the interconnection between PANI and graphite.Hence, the PANI-graphite composites synthesis under acidic condition (CH3COOH, acetic acid) was successful.Similar kind of results were also observed previously [31,32].The presence of functional groups in PANI and PANI/ Graphite composites was studied by FT-IR spectrometer and results are shown in Figure 3.The FTIR spectrum of the PANI/Graphite composites exhibit many peaks that are representative of the spectrum obtained from composite.The FTIR spectrum of pure pristine PANI gave absorption bands at 1592, 1490,1384,1187, and 1136 cm -1 corresponding to benzenoid ring, C=C vibrations, C-N stretch of aniline, C-H in-plane bending mode and quinoid units respectively.Similar kinds of results were observed previously [33][34][35][36].

I-V Characteristic and Electrical Conductivity
Figure 4a).I-V Characteristic and 4b) Electrical Conductivity of PANI/graphite composite.
I-V Characteristics and electrical conductivity of PANI/graphite composites were shown in Figure 4.The peak intensity increases with an increase in the content of graphite in PANI because of the electronic interaction at the atomic level.The symmetric behavior of I-V graph indicates that all samples have Ohmic contacts.In the Ohmic region at I-V electrical conductivity of the PANI is calculated and it found to be 9.6 ×10 -5 S/m.The increase in conductivity with an increase in Graphite concentration is observed in composites shown in electrical conductivity image.The peak intensity increases with the increase in the content of graphite in PANI because of the electronic interaction at the atomic level.A similar kind of result was observed previously [37].

Conclusions
Synthesis of PANI/Graphite composite was carried out by chemical oxidative polymerization method using ammonium persulfate as an oxidizing agent and characterized for structural and electrical properties.The diffraction peaks of the composite differ considerably, the intensity of these peaks increases with graphite concentration implies the formation of PANI-graphite composite.Furthermore, it was found that the changes in surface morphology and functional groups were observed using SEM and FT-IR.These different linkages could give rise to different diffraction peaks in the composite.Electrical conductivity increases with an increase in the concentration of graphite.Hence, PANI/graphite composite behaves more like a semiconductor than a semi-metal as a result of charge transfer between the graphite and PANI.