Towards Gas-Phase Synthesis of Carbon Nanotube Aerogels from Microwave Plasma

It is more than a decade since the floating catalyst CVD (FCCVD) process was introduced for CNT synthesis where at temperatures exceeding 1100⁰C, CNT aerogels can be directly-spun, forming macroscopic CNT fibres. The synthesis is facilitated by an aerosol of Fe nano-catalysts via the decomposition of an organometallic precursor. Seeking scale-up, global efforts have been made to map the process parameters, but despite this, the reported carbon yield has not exceeded 10%, leading to limited cost-effectiveness of the process on an industrial scale. In this publication we introduce a novel approach to produce spinnable CNT aerogels in higher efficiencies by employing an atmospheric, microwave (MW), thermal plasma. Such a method is well-known for gas-phase production of nanomaterials in a high throughput manner. Employing MW plasma in the FCCVD process naturally leads to an efficient direct-heating of the precursors and carrier gases in comparison to the conventional, indirect, furnace-based, wall heating. Using a high-power density heating method can also aid in dramatically altering the ubiquitous temperature profile associated with the conventional process. We report the employment of a stable MW plasma to produce for the first-time evidence that such a system can synthesize CNT aerogel-like materials, using SMPS techniques to characterise the catalyst particle size distributions leading to the materials. In summary, it can be concluded that it is crucial to achieve better process efficiencies to realize the immense potential of the FCCVD process and its unique product and that the employment of MW plasma may achieve such goal.

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