Natural flake graphite with an average size of 500 µ m was used for preparing the expanded graphite nanoflakes. Concentrated sulfuric acid and concentrated nitric acid were used as chemical intercalate and oxidizers. Pyrrole monomer (analytical grade, Merck) distilled twice under reduced pressure and stored blew 0⁰C. The liquid carbonyl iron was commercially from Aldrich. Carbon nanofiber was purchased size of 10 to 20 nm industrial. Dodecylbenene sulfuric acid (DBSA, 90%) and polyacrlic acid (PAA) were purchased from the Aldrich. All the other chemical reagents were purchased from Merck without further purification.

For biological synthesis of copper nanoparticles, Nag champa (Artabotrys odoratissimus, Family: Annonaceae), leaves were collected and dried for 4 days at room temperature. The plant leaf broth solution was prepared by taking 25 g of thoroughly washed and finely cut leaves in a 1 L beaker with 500 mL of sterile distilled water and then boiling the mixture for 5 min before finally decanting it. It was stored at 4 ⁰C and used within a week. Typically, 30 mL of leaf broth was added to 170 mL of 1 mmolL⁻¹ aqueous CuSO₄.5H₂O solution for the reduction of copper ions. The effects of temperature on synthesis rate and particle size of the prepared copper nanoparticles were studied by carrying out the reaction in a water bath at 95 ^oC with reflux. The copper nanoparticle solution thus obtained was purified by repeated centrifugation at 15,000 rpm for 20 min followed by re-dispersion of the pellet in deionized water.

A mixture of concentrated sulfuric acid and nitric acid (3:1, v/v) was mixed with graphite flake at room temperature. The reaction mixture was stirred continuously for 12 h. The acid treated natural graphite was washed with water until neutralized and was then dried at 60 ^oC to remove any remaining water. The dried flakes were heat-treated at 1050 ^oC for 15s to obtain expanded graphite. Expanded graphite was immersed in a 70% of aqueous alcohol solution in an ultrasonic bath. The mixture was sonicated for 12 h, and then was filtered and dried to produce GNF.

0.5 g NPs and 50 mL PAA (5% w/v) were added into 250 mL flask and the mixture were ultrasonicated for 15 min. The mixture was stirred vigorously at 25 ^oC for 24 h. The mixture was filtered and then washed with acetic acid (2% v/v) and acetone. After vacuum drying the filtrate, NPs-PAA was achieved.

The PPy nanocomposite as core-shell nanocomposite was prepared with template polymerization by in-situ polymerization in the presence of DBSA as the surfactant and dopant and Fe(NO₃)₃.9H₂O as the oxidant. The 0.5 g DBSA dissolved in distilled water with vigorous stirring for about 20 min. The 0.287 g NPs-PAA were added to the DBSA solution under sitirring condition for approximately 1 h .Then 1 mL (0.015 mol) of freshly distilled pyrrole as monomer added to the suspension and stirred for 30 min. The NPs-PAA were dispersed well in the mixture of PPy/DBSA under ultrasonication for 2 h. 12.12 g (0.03 mol) Fe(NO₃)₃.9H₂O as intiator dissolved in 30 mL deionized water and added drop wise to stirred reaction mixture. Polymerization was allowed to proceed for 6 h. The nanocomposite was obtained by filtering was washing the suspension with deionized water and aceton, respectively. The obtained dark powder contains [(Cu-CI-CNF-GNF)_0.5-PAA]-PPy_0.5 and dried under vacuum for 24 h.

(Figure 1) shows FTIR spectrum of [(Cu-CI-CNF-GNF)_0.5-PAA]-PPy_0.5 nanocomposites. We synthesized GNF by acid treatment and thermal shock. We expect see hydroxyl and carboxyl functional group on GNF. So, the band at 3439 cm^-1 can be attributed to O-H stretching (st.) vibrations of alcoholic functional group presented on the GNF, PAA and DBSA. And attributed to N-H st. vibrations of PPy, The peak at 2922 and 2845 cm^-1 are attributed to aliphatic C-H st. vibrations of PAA and DBSA. The peaks at 2359, 2332 cm^-1 and 1675, 1643 cm^-1 are related to C=O st. vibration of CI, PAA and DBSA, respectively. The different angles of Fe-C=O have been obtained for CI, so we observed to higher frequency for C=O. The specific peaks around 1537 and 1461 cm^-1 are attributed with vibrational modes of quinonic and aromatic type ring for PPy. The peaks at 1385,1461 cm^-1 are attributed to C=C st. vibration of CNF and GNF that 1461 cm^-1 cover to aromatic mode with PPy. The peaks at 1171 and 1046 cm^-1 are attributed to C-N and C-C st. vibration mode for PPy and CNF, GNF, respectively. The peaks at 779, 665 and 601, 517 cm^-1 are attributed to Cu-O and Fe-O st. vibration for Cu and CI NPs.

(Figure 2) shows XRD pattern for GNF that the peak at 2θ=26 related to carbon of GNF. The XRD patterns of molecular structures of CI-PAA-PPy, Cu-PAA-PPy and CNF-PAA-PPy in Figure 3 (a-c), were showed, respectively. The results show the diffraction peaks of NPs structures were not destroyed after the chemical polymerization of PPy as shell. We see all patterns of core NPs and shell polymers well. According to Figure 3 (a-c) characteristic peaks at 2θ=16-25, 2θ=17-25, 42, 44, 48, 50,72.38 and 2θ=16-23 with base peaks at 2θ=22.33, 72.38 and 24.83 for the CI-PAA-PPy, Cu-PAA-PPy and CNF-PAA-PPy were observed that correspond to JCPDS files no. 4073-004-98, 1646-002-98 and 2719-008-98, respectively. Figure 2 shows XRD pattern for GNF that the peak at 2θ=26 related to GNF. The XRD patterns showed molecular structures of CI-PAA-PPy, Cu-PAA-PPy and CNF-PAA-PPy in Figure 3 (a-c), respectively. The results show the diffraction peaks of NPs structures were not destroyed after the chemical polymerization of PPy as shell. We see all patterns of core NPs and shell polymers well, too.

According to Figure 3 (a-c) characteristic peaks at 2θ=16-25, 2θ=17-25, 42, 44, 48, 50,72.38 and 2θ=16-23 with base peaks at 2θ=22.33, 72.38 and 24.83 were observed for the CI-PAA-PPy, Cu-PAA-PPy and CNF-PAA-PPy that correspond to JCPDS files no. 4073-004-98, 1646-002-98 and 2719-008-98, respectively. These results and the relative width of the peaks indicate that the nanocomposite containing NPs-PAA-PPy are semi-crystalline and amorphous. According to these results and peaks observed in XRD patterns, we can ensure the existence of NPs. The average crystallite size can be calculated by the Debye-scherrer formula: D= 0.89 λ/β cosθ where λ is the wavelength of Cu K_α radiation and the value of K depends on serveral factors, including the Miller index of reflection plane and the shape of the crystal.

If the shape is unknown, K is often assigned as a value of 0.89, D is average crystallite size, θ is the Bragg’s angle, and β is the full width at half-maximum of the diffraction peaks. Therefore, from the width of the peaks observed in the XRD patterns, the average crystallite sizes of GNF, CI, Cu and CNF are calculated to 70, 21.5, 20.3 and 19.8 nm, respectively.

(Figure 4) (a-d) shows FESEM images of Cu, CI NPs and Cu-PAA-PPy, CI-PAA-PPy nanocomposites. The diameters of samples are about 30, 59, 40 and 65 nm, respectively. Figure 5 (a-b) shows the FESEM image of the CNF and CNF-PAA-PPy. Images analysis calculation results showed that the average diameters of CNF and its nanocomposite are 18 and 55 nm, respectively. Figure 6 (a,b) shows the FESEM images of the GNF and GNF-PAA-PPy nanocomposite. We adopted ultrasonic irradiation technique to break down the expanded graphite and then obtained GNF. The average distribution of all NPs, both pure and in the composite substrate, is very good and well dispersed. This will have a direct effect on their absorption properties. Image analysis calculation results showed that the average sheet diameter is approximately 5µ _m, and average thickness of nanoflake is about 80 nm. In Figure 6 b, we can see that PPy was coated on the most of GNF. All NPs are completely coated by PPy. The thickness of PPy as shell in all nanocomposites are about 10-20 nm. The surfaces of SEM images of nanocomposites were shown uniformity with some hollow and sponge structures. This structure, which is porous and has composite cavities, helps to reduce the energy of microwaves. By observing the shapes of nanofibers and nanoflakes and their composites, it is clear that the nanofibers in the composite are completely blurred, while the nanosheets have almost retained their shape in the composite.

The magnetization curves versus the magnetic field of CI NPs and CI-PAA-PPy nanocomposite are shown in Figure 7 (a,b). The samples are ferromagnetic behavior and applied fields are 20 and 30 kO_efor CI NPs and CI-PAA-PPy respectively. The magnetic parameters such as saturation magnetization (Ms), coercivity (Hc) and remnant magnetization (Mr) are measured by the hysteretic loops. As shown in Figure 7 (a,b), the value of Ms decreased from 225.87 to 51.164 emu/g and the value of Mr increased from 1.882 to15.452 emu/g for CI to nanocomposite. On the other hands, Hc was increased from 16.558 to 151.53 Oe, too. VSM curve of nanocomposite showed semi hard magnetization behavior that can be used to magnetic memories and microwave absorber.

Electrically conductivity of NPs and their nanocomposites were measured by four probe method and were summarized in Table 1. The conductivity of PPy after polymerization by Fe(III) as initiator and DBSA as dopant is 0.044 S/cm. The conductivity of Cu that prepared by chemically method is higher than green method. This is due to completely of reduction in chemical method. On the other hands, conductivity of CNF is higher than GNF that is related to high molecular weight and crystallity of GNF. When mass content of Cu, CNF and GNF as core and PPy as shell were incorporated in composites, conductivities are increased. But incorporation of CI NPs, conductivity is decreased.

The microwave absorbing properties of nanocomposites with the coating thickness of 1 mm investingated by using vector network analyzers in the frequency range of 2-18 GHz, that this range is contained S, H, C, X and Ku bands.

The results for PPy, Cu-PAA-PPy, CI-PAA-PPy and [(Cu-CI-CNF-GNF)_0.5-PAA]_-PPy_0.5 nanocomposite are shown in Figure 8. The results for PPy, CNF-PAA-PPy , GNF-PAA-PPy, and [(Cu-CI-CNF-GNF)_0.5-PAA]-PPy_0.5 are shown in Figure 9. The best microwave absorption were obtained in 9.5 GHz for PPy, 3 and 9 GHz for Cu-PAA-PPy, 9.5 GHz for CI-PAA-PPy, 8.5 and 11 GHz for CNF-PAA-PPy, 9.14 and 16.5 GHz for GNF-PAA-PPy with minimum reflection loss in -17.5, -10, -17, -19, -31, -27, -18, -27.5 and -25 dB, respectively. The absorption bandwidth under -10 dB are 3.2, 3.5, 8.4, 12.9, 13 and 15.5 GHz ranging from 2 to 18 GHz for PPy, Cu-PAA-PPy, CI-PAA-PPy, CNF-PAA-PPy, GNF-PAA-PPy and [(Cu-CI-CNF-GNF)_0.5-PAA]-PPy_0.5 .

Conflict of interest the authors declare that they have no conflict of interest.

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