Rapid industrial scale synthesis of robust carbon nanotube network electrodes for electroanalysis
Carbon nanotubes (CNT) have been extensively investigated for various electroanalytical applications. As the properties of CNTs heavily depend on the fabrication conditions, it is expected that the electrochemical performance will also vary between CNTs from different processes. However, it is still not well known how the different synthesis conditions affect the electrochemical properties of CNTs. Thus, here we investigate the effect of synthesis rate on the physicochemical properties of CNT networks. Through extensive structural and chemical analysis, we show that the widely different synthesis rates, fast and slow, produced CNT networks with surprisingly similar properties. The only distinct differences were seen in the TEM tomography 3D reconstructions, where the faster synthesis produced a less dense network with larger bundle size. Moreover, minor changes were seen in the composition of Fe catalyst particles where the faster rate network mainly exhibited metallic Fe, whereas carbide and oxidized Fe phases were observed in the slower rate network. Although no changes were seen in the electron transfer kinetics with outer-sphere probes, it was clear that even these small changes in physicochemical properties affected the surface sensitive inner-sphere analytes. With slower synthesis rate i) sensitivity towards all analgesics, especially oxycodone, was enhanced and ii) oxidation potential of all analytes shifted to cathodic direction in comparison to higher synthesis rate. In the wider context, we propose that good quality CNTs can be fabricated rapidly in industrial scale for biosensing purposes. However, in electroanalytical applications properties of CNTs should be optimized for the analyte of interest.