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 degrees C 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.