Effect of Grinding and the Mill Type on Magnetic Properties of Carboxylated Multiwall Carbon Nanotubes.

Agnieszka Jamrozik,Artur Małolepszy,Leszek Stobiński,Kvetoslava Burda,Janusz Przewoznik,Jozef Korecki,Sonia Krysiak,Grzegorz Trykowski

doi:10.3390/ma14144057

Abstract

The influence of the grinding process on the magnetic properties of as prepared and functionalized multiwall carbon nanotubes (MWCNTs) is presented. We have observed that 3 h mechanical grinding at 400 rpm in contrast to functionalization does not remove the iron contamination from MWCNTs. However, it changes the Fe chemical states. The magnetic properties of iron nanoparticles (Fe-NPs) embedded in the carbon matrix of MWCNTs have been analyzed in detail. We have proven that single-domain non-interacting Fe(C,O)-NPs enriched in the Fe3C phase (~10 nm) enclosed inside these nanotubes are responsible for their magnetic properties. Mechanical grinding revealed a unique impact of -COOH groups (compared to -COONH4 groups) on the magnetism of functionalized MWCNTs. In MWCNT-COOH ground in a steel mill, the contribution of the Fe2O3 and α-Fe phases increased while the content of the magnetically harder Fe3C phase decreased. This resulted in a 2-fold coercivity (Hc) decrease and saturation magnetization (MS) increase. A 2-fold remanence (Mr) decrease in MWCNT-COOH ground in an agate mill is related to the modified Fe(C,O)-NP magnetization dynamics. Comparison of the magnetostatic exchange and effective anisotropy length estimated for Fe(C,O)-NPs allows concluding that the anisotropy energy barrier is higher than the magnetostatic energy barrier. The enhanced contribution of surface anisotropy to the effective anisotropy constant and the unique effect of the -COOH groups on the magnetic properties of MWCNTs are discussed. The procedure for grinding carboxylated MWCNTs with embedded iron nanoparticles using a steel mill has a potential application for producing Fe-C nanocomposites with desired magnetic properties.

Highlights

We present studies of the magnetic properties of the iron inclusions in non-functionalized and functionalized multiwall carbon nanotubes (MWCNTs), ground in an agate or steel mill cylinder used at the end of the preparation procedure
The Mössbauer data show that functionalization and milling caused significant changes of the state of iron compounds embedded inside MWCNTs
We examined commercially available as prepared MWCNTs and their two functionalized forms containing -COOH and –COONH4 groups in terms of carbon nanotubes magnetic properties

Summary

Introduction

Chemical functionalization allows modification of the surface and core of CNTs, increasing the compatibility of nanotubes with other materials and modulation of their electronic [10,11] and mechanical properties [12]. Deagglomeration of CNTs bundles due to the presence of oxygen groups increased their hydrophilicity. Knowledge of the impact of functionalization methods on different properties of MWCTs is crucial for the further development of their potential applications [11,15]. Their electronic and magnetic properties could be exploited in modern nanotechnologies [2,16].

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Discussion

Conclusion