Abstract
During synthesis of MWCNTs using CVD, role of carbonaceous material and catalyst, besides other process parameters, has considerable influence on the structure and yield of pristine nanotubes. In present study, different flow rates (i.e. 10, 25, 40 and 55 sccm) of precursor ethanol were used for the synthesis of MWCNTs at 750 oC in a CVD reactor, where nickel particles were supported on quartz as catalyst. Further, these nanotubes were characterized using XRD, SEM, TGA and Raman spectroscopy to investigate the effect of ethanol flow rate on the catalytic activity of nickel for optimum production of MWCNTs. It was observed that at different ethanol flow rates, variations in synthesis products (i.e. CNTs, amorphous carbon and carbon nanoparticles) were associated with catalytic activity. Maximum catalytic activity of nickel particles was attained by optimizing ethanol flow rate (at 25 sccm). At the optimum flow rate a maximum purity of MWCNTs (>83%) was attained along with other relevant structures i.e. amorphous carbon <1.5% and SWCNT <10% balancing with retained catalytic particles. Any increase from the optimum limit caused not only defects within the CNTs' structure but also increased the impurities which were correlated with the reduction in activity of the nickel particles due to the saturation of active sites.
Highlights
Mendoza et al.[16] introduced a variation in Maruyama’s approach by passing hydrogen gas through an ethanol bubbler and synthesizing multi-walled carbon nanotubes (MWCNTs) at 700 °C and 900 °C on quartz supported catalyst.They increased the length of MWCNTs using a process temperature of 700 °C, by inhibiting generation of amorphous carbon caused by -OH radicals
The characterization was carried out using X-ray diffractometer (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and Raman spectroscopy
Powder samples of various CNT batches were subjected to XRD analysis using a Cu Kα radiation source and a scan rate of 0.05° s–1 from 18°-75° (2θ)
Summary
Mendoza et al.[16] introduced a variation in Maruyama’s approach by passing hydrogen gas through an ethanol bubbler and synthesizing MWCNTs at 700 °C and 900 °C on quartz supported catalyst (iron nitrate).They increased the length of MWCNTs using a process temperature of 700 °C, by inhibiting generation of amorphous carbon caused by -OH radicals. In 2009, Maruyama and his team again reported their work with an approach to reactivate the catalyst by introducing acetylene in ethanol assisted CNT growth This time they used Co/Mo mixture as catalyst at a process temperature of 800 °C and ethanol/acetylene as precursor. The previous researchers[14,15,16,17,18,19] had shown their work on alcohol assisted SWCNT growth by CVD but the effect of ethanol flow rate for the synthesis of MWCNTs associating catalytic activity of nickel particles during CVD was ignored. The characterization was carried out using X-ray diffractometer (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and Raman spectroscopy
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