Synthesis of magnetic graphene-Fe3O4 nanocomposites by electrochemical exfoliation method

INTRODUCTION

Graphene is a known and specific material with high electrical conductivity, high surface area and favourable biocompatibility. It has shown as a potential material to be used in technological applications such as nanoelectronics [1], sensors [2], batteries [3] and supercapacitors [4].

Large specific surface area and planar shape made graphene to be a good candidate for acting matrix role in nanocomposite. By using magnetic fillers for this matrix, the nanocomposite will be magnetized that is very useful in controlled targeted drug delivery [5], cancer drug delivery agent [6] and removal of toxic metal and dyes from aqueous solutions [7]. Therefore, production of magnetic nanocomposite without obvious toxicity is an important task for many applications. Moreover, between various types of magnetic materials, iron oxides (Fe₃O₄ and γ-Fe₂O₃) are the best choices because of their special magnetic properties, low toxicity and low cost [8].

Graphene nanosheets have often been made from expanded graphite which according to the number of layers named as few-layer graphene (FLG) and multi-layer graphene (MLG) [9].

There are several methods to produce graphene-iron oxide nanocomposite [10]. Electrochemical exfoliation method as a simple, one step and economical technique was our choice to fabricate magnetic graphene nanocomposite [11]. In this research, we used an electrochemical exfoliation method and an ammonium sulfate iron salt to produce superparamagnetic few layer graphene-iron oxide nanocomposite (FLG-IONC) representing high magnetization and superparamagnetic properties.

MATERIALS AND METHODS

Iron (II) ammonium sulfate [(NH₄)₂Fe(SO₄)₂.6H₂O] and hydrochloric acid (HCl) were prepared from Merck. Graphite foil and iron plate are used as electrodes.

The fabricated FLG-IONC was characterized by X-ray diffraction (XRD) with Cu Kα radiation between 10 and 80°. Fourier transform infrared (FTIR) spectroscopy in an optical range of 400–4000 cm^-1, scanning electron microscopy (SEM), field emission SEM (FESEM), energy dispersive spectroscopy (EDS) and vibrating sample magnetometer (VSM) techniques were applied to study the nanocomposite.

Synthesis of superparamagnetic FLG-IONC

For the production of FLG-IONC, firstly 0.1 M solution was prepared with stirring 7.8 g iron (II) ammonium sulfate in 200 ml distilled water. We used graphite foil as anode and iron plate as cathode with 3 cm distance between the electrodes. Applied voltage was 10 V DC for 3 hours, as shown schematically in Fig. 1. After the fabrication, magnetic nanocomposite products were separated by magnet and rinsed several times with distilled water and dried at 100 ° C.

RESULTS AND DISCUSSION

Fig. 2 shows XRD pattern that most of the iron oxide particles are magnetite and maghemite (Fe₃O₄ and γ-Fe₂O₃) according to the peaks in 14, 18, 26, 27, 30, 35, 43, 49, 53, 57, 63°. Characteristics and properties of iron oxide phases were reported by Ramimoghadam et al [12], and according to their review, our sample with black/ brownish black colour is Fe₃O₄ (magnetite). Also, peaks in 2θ=20, 25 and 44° are related to the presence of FLG. According to these acheivements, the name of the sample is FLG-Fe₃O₄.

The FTIR spectrum of our final production sample is given in Fig. 3. Absorption peak at 3420 cm^-1 is related to stretching vibration of N-H [13]. The peak at 3128 cm^-1 is related to stretching vibration of the coordinated –OH group [14]. The CH₂ bands at 2924 cm^-1 and 2854 cm^-1 can be observed. A strong absorption peak at 1127 cm^-1 is related to double band S=O or single band C-O.

Fig. 4 shows the hysteresis loop of FLG-Fe₃O₄ representing the fact that the sample is superparamagnetic and the specific saturation magnetization (M_S) is 57.3 emu.g^-1. As shown in the insets of Fig. 4, the magnetic FLG-Fe₃O₄ particles are suspended in the solution (left side) and after being exposed to an external magnetic field, the magnetic FLG-Fe₃O₄ nanocomposite is separated from the solution (right side).

Fig. 5a and Fig. 5b show SEM and FESEM images of FLG-Fe₃O₄. The FLG configuration can be seen clearly in Fig. 5a. Also in Fig. 5b we can see the distribution of iron oxide particles on the surface. Fig. 5c is a SEM image of sample in a 500 nm window. In this picture, iron oxide nanoparticles in the range of 44 nm, 58 nm and 98 nm can be observed. The EDS test of FLG-Fe₃O₄ is given and shown in Fig. 5d and Fig. 5e. Inset tables in this picture show the mass percent of Fe, O and C at the specified points EDS A and EDS B, determined from panel b. We compared the mass percent of each element between tables. It is found that EDS A based on high mass percentage of iron and oxygen with low carbon is related to iron oxide. The EDS B addresses the FLG that contains iron oxide particles between graphene sheets,Therefore, results of XRD, SEM, FESEM and EDS indicate the formation of FLG-Fe₃O₄. Furthermore, from the results of the VSM, it is found that the FLG-Fe₃O₄ nanocomposite show superparamagnetic like properties and because of its high saturation magnetization it is favourable for the use in different applications.

CONCLUSIONS

Superparamagnetic FLG-Fe₃O₄ nanocomposite was successfully synthesized by simple, one step and economical electrochemical exfoliation method. Our product is formed as FLG with layer number between 3 and 10 with embedded magnetic nanoparticles of Fe₃O₄. Accessible, industrial and cost-effective iron cathode makes it possible to be applied in mass production of FLG-Fe₃O₄ samples. The specific saturation magnetization of FLG-Fe₃O₄ is 57.3 emu.g^-1 which is suitable for many applications such as hyperthermia, drug delivery, supercapacitors, etc.

CONFLICT OF INTEREST

The authors declare that there is no conflict of interests regarding the publication of this manuscript.