Liquid-phase synthesis of highly aligned carbon nanotubes on preheated stainless steel substrates

A novel, low-cost, simple liquid-phase process has been developed for preparing highly aligned carbon nanotube (CNT) arrays (HACNTAs). Highly pure HACNTAs with heights of ∼10 μm were grown perpendicular to a preheated stainless steel substrate in ethanol solution by liquid-phase electrical resistance heating process without the addition of any growth catalyst for CNTs. In this paper, the effects of preheating conditions of the substrate before the synthesis on the morphology of the resulting CNTs are discussed. The optimum conditions were preheating temperature of 500 °C and preheating duration of 30-180 min in air for the substrate to form HACNTAs. The preheating brings Fe-rich oxide layer on the substrate surface and generates numerous Fe catalyst nanoparticles that promote HACNTA growth at following liquid-phase resistance heating process. In addition to ethanol, methanol and 1-butanol were also tested as carbon sources; however, the HACNTAs from those sources did not grow homogeneously on the substrate surface and contained many impurities compared with those prepared from ethanol. This unique HACNTA synthesis method is simple, since it requires neither a vacuum nor an external catalyst preparation process, and it is environmentally friendly, because it only uses ethanol and stainless steel substrates for the synthesis.