Evolution of morphology and defect states in mechanically processed ZnO+xMWCNTs nanosystems

Abstract

We used scanning electron microscopy (SEM), X-ray diffraction (XRD), laser particle size (LPS) measurements, electron paramagnetic resonance (EPR) and Raman spectroscopy to monitor the evolution of morphology and defect states in mechanically processed mixtures of ZnO and multi-walled carbon nanotubes (MWCNTs) with different content of the latter (0.1%, 0.8% and 2.5% by weight). The morphology and defect structure of initial ZnO powders have significant effect on the properties of nanoparticles formed due to MP. Initial agglomerated ZnO particles of 100–800 nm size are destroyed by MP, producing after 390 min the particle size of ∼40–50 nm. The resulting particles form aggregates with a size of the order of 10 μm. EPR measurements showed the presence of magnetic nanoinclusions Fe3О4 in ZnO component, which cause this aggregation. Increasing MP time, initiates the weak asymmetric signal at g ∼2.001. This signal was attributed to C–C bonds broken due to MP of MWCNTs, which interact with conduction electrons generated by the same process. Raman spectra exhibited characteristic features due to both ZnO and MWCNTs. After MP for 90 min, for all ZnO+xMWCNTs samples almost complete suppression of Raman peaks due to ZnO phase was evident. Nevertheless, after the longest MP for 390 min their partial regeneration was observed. The bands attributable to the carbon component were D, G, G′ and D+G modes. The changes in ID/IG and IG'/IG intensity ratios observed are indicative of a decrease in the degree of MWCNT graphitization with increasing MP duration.