Microwave synthesis of carbon nanofibers – the influence of MW irradiation power, time, and the amount of catalyst

Abstract

The microwave synthesis of carbon nanofibers (CNFs) represents a fast and simple method for the preparation of carbon nanofiber coatings on different substrates utilizing commercially available equipment. With this approach the CNF growth can often be initiated within seconds of microwave irradiation leading to processing times of less than one minute and only little heating of the environment. To control and optimize these extremely fast synthesis processes, it is of great importance to understand the involved processes and to identify critical parameters. We present a systematic study regarding the influence of the microwave parameters, irradiation power and time, on the growth process as well as the morphology of carbon nanofibers utilizing a single mode microwave oven and silicon wafers as substrates. The irradiation power is varied between 100 and 400 W and structures obtained after irradiation times of 3 s to 8 min are investigated. Carbon nanofibers are obtained for all applied power levels, but the required irradiation times differ significantly as well as the morphology of the obtained structures. A high irradiation power results in CNFs with a broad diameter distribution, which can, however, be narrowed by adjusting the amount of catalyst. Finally, the synthesis process is applied to coat graphite fibers with a dense carpet of carbon nanofibers.