Effects of the addition of nano-MnO₂ on in situ catalytic formation of carbon nanotubes during the coking of phenolic resin

Abstract

Hollow multi-walled carbon nanotubes (MWCNTs) were formed in situ by catalytic cracking of phenolic resin with addition of nano-manganese dioxide (nano-MnO₂) as a catalyst. The effects of catalyst content, coking temperature and heating rate on in situ growth of carbon nanotubes (CNTs) were investigated. The composition and microstructure were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and laser-raman spectrum. The results showed that nano-MnO₂ could catalyze phenolic resin to partly form MWCNTs inside of the materials, which transformed pyrolytic carbon structure and improved graphitization degree of the material after carbonization. With the increase of catalyst content, the length of CNTs decreased and the optimum addition amount was at 1.0 wt %. The higher the carbonization temperature, the bigger the activity of catalyst particles. The optimum growth temperature of CNTs was at 1200°C. At a higher heating rate, hydrocarbon molecules was hard to deposite on the surface of the catalyst particles to form CNTs. CNTs obtained at a heating rate of 2 °C/min possessed the highest degree of graphitization. The growth of carbon nanotubes was accordance with the mechanism of top growth.