On the Synthesis of Carbon Nanofibers and Nanotubes by Microwave Irradiation: Parameters, Catalysts, and Substrates

Abstract

The microwave (MW)‐assisted synthesis of one dimensional carbon systems is introduced as a promising approach to improve the speed and cost‐effectiveness of the fabrication process. Improved reaction conditions are generated by direct MW heating and synthesis under advanced reaction conditions. The influence of the reaction conditions is investigated and the importance of individual process parameters on the synthesis is discussed. Temperature and pressure data recorded during the irradiation process are analyzed in detail and allow the determination of essential process parameters. This leads to improved reaction conditions, better control of the one‐dimensional carbon nanosystems by tuning the catalyst materials, and allows expanding this approach to initiate the synthesis on a variety of different substrates, such as quartz glass and mica.

Synthesis and Modification of Carbon Nanomaterials utilizing Microwave Heating

“…Microwave‐transparent substrates can be coated with a susceptor material to increase the heating efficiency and to decrease problems due to heat dissipation; for example, a metal layer, a coating of a conducting polymer, or an additional piece of silicon can be applied to enable CNT growth or the annealing of graphene on rather‐microwave‐transparent substrates; thus, without heating additives, the required elevated temperatures for the reaction could not be reached. Reaction vessels coated with silicon carbide or silicon carbide boards placed beneath a quartz vessel represent alternative approaches to increase the temperature rise of a microwave‐heated system.…”

“…Druzhinina et al utilized a commercial single‐mode microwave reactor to grow multi‐wall CNTs and CNFs on different substrates, e.g., silicon, quartz glass, and mica. A quartz‐glass support was used to vertically place the catalyst‐coated substrate above a reservoir of liquid carbon source (Figure D).…”

“…For the microwave‐transparent substrates, i.e., quartz glass and mica, it was observed that even under high‐power irradiation, no CNT growth was initiated. CNTs could only be grown on these substrates when a silicon wafer was placed behind, in order to enhance the absorption of microwaves and to compensate for the limited heating of the insulating substrates . Furthermore, micropatterned carbon‐nanofiber films with a structure width of 6 μm could be grown by utilizing a TEM grid as a stamp for the catalyst deposition (Figure G,H) .…”

Free‐Standing Carbon Nanofibrous Films Prepared by a Fast Microwave‐Assisted Synthesis Process

“…The Thicker catalyst layers result on the other hand in general in large CNF diameter distributions. With spin-coated ethanolic nickel acetate layers thinner CNFs with smaller diameter distribution can be obtained, [ 17 ] but in return those CNF layers cannot be easily disassembled to free-standing fi lms. Moreover, it was observed that if no arching occurs, CNFs can just grow on top of the catalyst layer.…”

“…[ 17 ] This method is based on the material-specifi c absorption of microwave is measured by an IR-sensor mounted outside the vial. Thus, it does not provide any information about the local temperature of the catalyst on the surface of the substrate.…”