Surface modification of graphite encapsulated iron nanoparticles by plasma processing

doi:10.1016/j.diamond.2011.01.027

Diamond and Related Materials

Volume 20, Issue 3, March 2011, Pages 359-363

https://doi.org/10.1016/j.diamond.2011.01.027 Get rights and content

Abstract

The graphite encapsulated iron nanoparticles were fabricated by using arc discharge method. The synthesized nanoparticles were pre-treated by an inductively-coupled RF Ar plasma and then post-treated by NH₃ plasma under various gas pressures and treatment times. Analyses of XPS spectra have been carried out to study the effect of the plasma treatment on the surface modification of nitrogen-containing groups. The morphological changes of the particles surface by plasma treatment have also been analyzed by using HR-TEM. Present results show that the highest values of N/C atomic ratio of 5.4 % is obtained by applying 10 min of Ar plasma pre-treatment and 2 min of NH₃ plasma post-treatment conducted in RF power of 80 W and gas pressure of 50 Pa.

Research Highlights

► The graphite encapsulated iron nanoparticles were treated by an inductively coupled RF plasma. ► The nanoparticles were characterized well using HR-TEM, XPS and EDS with elemental mapping. ► The inner structures of graphene layers and the iron cores were not damaged by plasma treatment. ► The surface of the outmost graphene layer was successfully covered by nitrogen-containing groups. ► The highest N/C atomic ratio of 5.4 % was achieved by 10 min Ar plasma and 2 min NH3 plasma treatments.

Introduction

Iron nanoparticles have many great interests in potential to bio-application such as drug delivery system, hyperthermia treatments, magnetic resonance imaging contrast enhancement, etc [1], [2], [3], [4], [5], [6], [7], [8]. The carbon-encapsulated metal nanoparticles were first synthesized as LaC in 1993 by Ruoff et al. [9]. So far, these particles have been commonly produced by conventional arc discharge [10], [11], [12], [13], [14], [15], modified arc discharge [16], [17], chemical vapor deposition (CVD), combustion, laser synthesis, ion beam sputtering [18], and annealing microporous carbon or diamond with metal nanoparticles [19]. Carbon coating of the magnetic nanoparticles can leave the toxicity out without detracting their magnetic properties. Moreover, the carbon coating not only stabilize the nanoparticles but can also be used for further functionalization, such as addition of the therapeutic agent, targeting agent or fluorophore, depending on the purposes.

Among various functional groups for bio-application, the introduction of amino groups composed of primary amines to the particles surface achieves enhanced wettability and improves its adhesion. Some early work by I.H. Loh et al. reports the use of ammonia plasma, nitrogen and nitrogen/hydrogen mixtures on carbon black [20]. Recently, there are also several other papers studying about the amino functionalization for carbon nanotubes [21], [22], amorphous carbon sheet [23], nanocrystalline diamond [24], [25], carbon nanoparticles [26], etc. However, this modification has not been deeply studied on carbon-encapsulated magnetic nanoparticles. In fact very few information can be found on the topic of graphite encapsulated iron nanoparticles related to the plasma surface treatment in order to introduce nitrogen-containing group functionalities, such as amino group.

In this study, we mainly functionalize the graphite encapsulated iron nanoparticles using Ar and NH₃ plasma performed by an inductively-coupled radio frequency plasma. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution-transmission electron microscopy (HR-TEM), and energy dispersive X-ray spectroscopy (EDS) elemental mapping were used to characterize and analyze the results.

Section snippets

Experimental details

The graphite encapsulated iron particles were prepared by using arc discharge method refers to Refs. [14], [15]. The arc discharge was generated by applying a dc current of 150–200 A at about 20 V voltage between anode and cathode. Graphite electrodes molded with Fe₂O₃ powder by using graphibond-551R was used as anode. In the other side, graphite rod was used as cathode. Both of those electrodes were set with distance as near as possible in a stainless-steel vacuum chamber with 200 mm diameter.

Results and discussion

The graphite encapsulated iron nanoparticles are successfully synthesized by arc discharge method. First, it is confirmed that the synthesized powders have a magnetic property, as shown in Fig. 2a. The powders stirred in the purified water in the bottle are attracted by a permanent magnet, even when the magnet was located far from the bottle. In order to confirm their phase and structural characterization, XRD and HR-TEM analysis was carried out. The XRD profile presented in Fig. 2b shows the

Conclusion

Based on the results and discussion described above, it can be concluded that the graphite encapsulated iron nanoparticles were successfully modified by plasma processing and characterized well using HR-TEM, XPS and EDS with elemental mapping. After the plasma treatment with experimental condition applied here, the surface of the outmost graphene layer was successfully covered by nitrogen-containing groups definitively assigned by XPS spectra and the STEM-EDS elemental mapping. The

Acknowledgement

This work has been supported in part by the Grants-in-Aid for Scientific Research and performed under Research and Education Funding for Research Promotion supported by MEXT.

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^☆: Presented at NDNC 2010, the 4th International Conference on New Diamond and Nano Carbons, Suzhou, China.

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Surface modification of graphite encapsulated iron nanoparticles by plasma processing☆

Abstract

Research Highlights

Introduction

Section snippets

Experimental details

Results and discussion

Conclusion

Acknowledgement

Carbon

J. Biosci. Bioeng.

Carbon

Chem. Phys. Lett.

Carbon

Chem. Phys. Lett.

Carbon

Carbon

Diamond Relat. Mater.

Diamond Relat. Mater.

Diamond Relat. Mater.

Electrochim. Acta

Carbon

Carbon

J. Phys. D Appl. Phys.

J. Phys. D Appl. Phys.

J. Phys. D Appl. Phys.

Pharm. Res.