Preparation and microwave absorbing properties of nickel-coated graphite nanosheet with pyrrole via in situ polymerization

doi:10.1016/j.jallcom.2011.12.136

Journal of Alloys and Compounds

Volume 520, 15 April 2012, Pages 114-121

https://doi.org/10.1016/j.jallcom.2011.12.136 Get rights and content

Abstract

Nanocomposites PPy/NanoG and PPy/Ni/NanoG were prepared via in situ polymerization of pyrrole in the presence of NanoG and nickel-coated graphite nanosheet (Ni/NanoG), respectively. The morphologies and nanostructures of NanoG, Ni/NanoG, PPy, PPy/NanoG and PPy/Ni/NanoG were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Fourier transmission infrared (FTIR) and X-ray diffraction analysis (XRD). Results show that most of PPy chains disperse on NanoG and Ni/NanoG's surfaces for the high aspect ratio (300–500) of NanoG and Ni/NanoG. From the thermogravimetric analysis (TG) it can be seen that the introduction of Ni and NanoG leads the composites PPy/NanoG and PPy/Ni/NanoG to exhibit a better thermal stability than pure PPy. According to the four-point-probe test, the conductivities of the final PPy/NanoG and PPy/Ni/NanoG composites are dramatically increased compared to pure PPy. Measurement of electromagnetic parameters shows that the reflection loss (R) of PPy/Ni/NanoG is below −19 dB at the X band (8.2–12.4 GHz) and the minimum loss value is −23.46 dB at 9.88 GHz. The reflection loss of PPy/NanoG is below −10 dB at 8.2–12.4 GHz and the minimum loss value is −13.44 dB at 10.28 GHz. The microwave absorbing properties of PPy/NanoG and PPy/Ni/NanoG are superior to those of PPy.

Graphical abstract

Highlights

► NanoG was prepared and chemically coated by nano-Ni. ► PPy/NanoG and PPy/Ni/NanoG were prepared via in situ polymerization. ► The samples were characterized by SEM, XRD, EDS and FTIR. ► PPy/NanoG and PPy/Ni/NanoG exhibit good electromagnetic properties.

Introduction

With the development of modern informationized warfare, microwave absorbing materials have absorbed much attention [1], [2]. To get the microwave absorbing materials with combination properties as thin in thickness, light in weight, broad in frequency and strong in absorbing peak, much work has been done.

According to the absorbing mechanism, microwave absorbing materials can be divided into two types: magnetic materials and electronic materials. The absorbing properties of the microwave absorbing materials can be expressed by the following parameters [3], [4]: complex permittivity (ɛ* = ɛ′ − jɛ″), complex permeability (μ* = μ′ − jμ″), dielectric loss (tan δ_e = ɛ″/ɛ′) and magnetic loss (tan δ_m = μ″/μ′). The higher the imaginary parts of the complex permittivity (ɛ″) and the complex permeability (μ″) as well as the higher tan δ_e and tan δ_m, the higher absorbing properties of the materials are.

Recently, inherently conducting polymers such as polyacetylene (PA), polypyrrole (PPy), polyaniline (PANI) and polythiophene (PTH) are deeply investigated for their good conductivity and light in weight [5], [6], [7], [8]. Up to the present, several groups have done much work on synthesizing electromagnetic PPy-based nanocomposites [9], [10], [11]. Conductive materials such as carbon black [12], carbon fiber [13], carbon nano-tube [14], magnetic materials [15], [16], [17] such as ferrite, crystal whisker and nano-metals are always added into them. Among them, conductive material graphite has absorbed much attention for its unique mechanical, chemical and electrical properties. Graphite is well known to be as a layered material with high conductivity, which can be intercalated by chemical reagents such as nitric acid (HNO₃) or sulfuric acid (H₂SO₄) and form into another kind of compound called graphite intercalation compounds (GIC). By rapid thermal treatment, GIC can expand several hundreds times the volume of its original and get expanded graphite (EG) [18], [19], [20].

In this paper, NanoG with high conductivity was prepared by ultrasonication of EG in an aqueous ethanol solution. To further improve the magnetic properties of the composites and enlarge their application, some metals are always chemically coated on NanoG's surface. Among the metals, Ni was chosen for its high magnetic properties, low price and stability. The aim of this work was to fabricate the nanocomposites via in situ polymerization of pyrrole in the presence of NanoG and Ni/NanoG. The morphologies and nanostructures of NanoG, Ni/NanoG, PPy, PPy/NanoG and PPy/Ni/NanoG were characterized by SEM, EDS, FTIR and XRD. Properties such as thermal stability, conductivity and microwave absorbing of them were measured.

Section snippets

Materials

The oxidized graphite (OG) was supplied by Shandong Qingdao Graphite Company (Qingdao, China). Pyrrole (Py, AR) was bought from Sinopharm Chemical Reagent Limited Company and was distilled in reduced pressure before being used. Ferric chloride (FeCl₃·6H₂O), palladium chloride (PdCl₂) and tin chloride dehydrate (SnCl₂·2H₂O) were bought from Chemical Company of Tianjin. Sodium hypophosphite (NaH₂PO₂), nickel sulfate (NiSO₄·6H₂O), 36% hydrochloric acid (HCl), sodium hydroxide (NaOH), ammonia (NH₃·H

SEM images of NanoG and Ni/NanoG

NanoG was prepared by treating EG with ultrasonication in an aqueous solution of 70% ethanol and 30% distilled water. Fig. 2(a and b) shows the SEM images of NanoG. It can be seen that EG has been efficiently exfoliated to ultra thin transparent graphite nanosheets with a width about 1–20 μm and a thickness about 30–90 nm, indicating a large aspect ratio (300–500) of NanoG. The higher the aspect ratio of the material, the lower the filler content as well as the higher electrical conductivity.

Conclusions

In this paper, PPy/NanoG and PPy/Ni/NanoG were fabricated via in situ polymerization of pyrrole in the presence of NanoG and Ni/NanoG. The morphologies and nanostructures of NanoG, Ni/NanoG, PPy/NanoG and PPy/Ni/NanoG were characterized by SEM, EDS, FTIR and XRD respectively. Results show that NanoG has a great aspect ratio (300–500) and can be chemically coated by Ni. By in situ polymerization, most of NanoG and Ni/NanoG nanoparticles can be encapsulated by PPy. The thermogravimetric analysis

Acknowledgements

The authors would like to thank Professor Zhou and his student Doctor Qing from Department of Materials Science and Engineering, Northwestern Polytechnical University for their help in testing the electromagnetic parameters.

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Preparation and microwave absorbing properties of nickel-coated graphite nanosheet with pyrrole via in situ polymerization

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials

SEM images of NanoG and Ni/NanoG

Conclusions

Acknowledgements

J. Alloys Compd.

J. Alloys Compd.

J. Alloys Compd.

J. Alloys Compd.

Prog. Polym. Sci.

J. Alloys Compd.

J. Alloys Compd.

Synth. Met.

J. Power Sources

Synth. Met.

Synth. Met.

J. Alloys Compd.

J. Alloys Compd.