Potassium hydroxide as a novel catalyst for metal-free carbon nanotubes growth on powder activated carbon

In this work, powder activated carbon (PAC) treated with KOH was used to synthesize multiwall carbon nanotubes using chemical vapor deposition (CVD) where a mixture of CO2 and acetylene gas was used to conduct the reaction. Different mass ratios of PAC: KOH in the range of 1:0.25–1:3 were studied. The synthesized CNT were characterized using scanning electron microscopy (SEM), field emission transmission electron microscopy (FE-TEM) equipped with energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). TEM analysis reveals that hollow tubular structure CNT with completely closed tip were produced. It was found that increasing the concentration of KOH, increases the number and average size of CNT, and cause the distribution of CNT to appear less uniform. Finally, a mechanism was proposed to explain the route of CNT growth. The mechanism suggested that high temperature involved in the CVD reaction causes the formation and aggregation of K atoms which subsequently act as seeds on which the carbon nanotubes assemble.