The authors have declared that no competing interests exist.
The composites of Cu, Carbonyl iron (CI), carbon nanofiber (CNF), graphite nanoflake (GNF)/polypyrrole (PPy) and [(Cu-CI-CNF-GNF) 0.5-PAA]-PPy0.5 were synthesized via different methods by in-situ polymerization on the surface of nanoparticles (NPs) with core-shell structure. This paper describes a method for polyacrylic acid (PAA) coating of NPs in aqueous solution. Then PPy coating was performed by template polymerization on NPs-PAA. Morphology, magnetic and conductivity properties were observed via scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and four probe method, respectively. The microwave characterization of nanocomposite was evaluated through arch test based on a network analyzer. The PPy nanocomposites possessed the excellent microwave multi absorbers properties in 2-18 GHz. It was also found that nanocomposites with 50% w/w and light weight exhibit good microwave absorbing properties in 2-3 GHz and 5-14 GHz frequency, so can be used to cellphone, radio frequency and radar shielding.
In the last decade, various microwave (MW) absorption materials have been widely investigated for electromagnetic interference to protect human health and electronic equipment from electromagnetic pollution which is caused by the wide applications of high-power electronic devices and communication technology
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]-PPy0.5 and dried under vacuum for 24 h.
The ultrasonic experiment was carried out by an ultrasonic disperser (Hielsche, UP4005, Germany). Field emission scanning electron microscopy (FESEM) was performed by TESCAN MIRA to observe surface morphologies of samples. The magnetic measurements carried out at room temperature using a Termo company 7400 model (USA), vibrating sample magnetometer (VSM) with maximum magnetic of 10 KOe. The XRD patterns of the samples were collected on a Philips-PW 1800 with Cu Kα radiation (λ=1.54184 Å) in the 2θ= 4-900 with steps of 0.020, scanning operated at 40 kV and 30 mA (Netherland). The electrical conductivity of compressed pellet of samples and nonocomposites were calculated using a standard four-probe set-up connected to a Keithly system comprising a voltmeter and constant high-current source, made in IRAN. Microwave absorption properties of nanocomposites were measured using microwave vector network analyzer (Agilent technologies Inc.8722-USA) in the 2-18 GHz range at room temperature.
(
(
According to
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.
(
The magnetization curves versus the magnetic field of CI NPs and CI-PAA-PPy nanocomposite are shown in
Electrically conductivity of NPs and their nanocomposites were measured by four probe method and were summarized in
Sample | Conductivity (S/cm) | Sample | Conductivity (S/cm) |
Cu (chemical) | 245 | Cu-PAA-PPy | 133 |
Cu (green) | 170 | CI-PAA-PPy | 0.083 |
GNF | 20 | GNF-PAA-PPy | 0.88 |
CNF | 264 | CNF-PAA-PPy | 320 |
PPy (doped) | 0.044 | [(Cu-CI-CNF-GNF)0.5-PAA] -PPy0.5 | 280 |
PPy (undoped) | 1.4×10-6 |
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]-PPy0.5 nanocomposite are shown in
Two factors affect the absorption properties of electromagnetic waves: first, the conduction properties and second, the magnetic properties. In the selected samples, iron carbonyl has completely magnetic properties and other nanoparticles have electrical conductivity properties. In addition, the final polymer also has full electrical conductivity. Therefore, in the above project, we tried to put these compounds together with special engineering in order to achieve the maximum absorption in different areas of the microwave. So, we have synthesized green copper powder, GNF and purchased CI, CNF and describe a method for PAA coating on these. Then PPy coating was performed on template polymerization via in-situ method. Finally, we prepared their nanocomposites both separately and complex with core-shell structure. In continue, their microwave absorption properties in range of 2-18 GHz (S, H, C, X and Ku bands) were investigated. The results showed that the optimum absorption are 2-4 GHz and 5-14 GHz with RL of -12.5 and -33 dB and thickness of 1 mm, respectively. The microwave absorption of samples was increased by increasing core and PPy weight ratio and electrical conductivity. These samples can be used to microwave absorption as most multiband absorber for civil and military applications.
Conflict of interest the authors declare that they have no conflict of interest.
Shah, N., Zaman, T., Rehan, T., Khan, S., Khan, W., Khan, A., Ul-Islam, M. (2019), Preparation and Characterization of Agar Based Magnetic Nanocomposite for Potential Biomedical Applications,
Meazzini, I., Comby, S., Richards, K. D., Withers, A. M., Turquet, F. X., Houston, J. E., Owens, R. M., and Evans, R. C. (2020),Synthesis and characterisation of biocompatible organic–inorganic core–shell nanocomposite particles based on ureasils,
Binling, C., Yazdani, B., Benedetti, L., Hong, C., Yanqiu, Z., Oana, G., (2019), Fabrication of nanocomposite powders with a core-shell structure,