Efficient functionalization of carbon nanotubes: an opportunity enabled by flow chemistry
The covalent chemistry of carbon nanotubes has put forth a wide variety of interesting derivatives that widen the potential of these carbon allotropes in nanomedicine and materials science. However, the functionalization protocols often require long reaction times and frequently harsh conditions. This paper reports a flow approach to the functionalization of carbon nanotubes enabled by a Coflore ACR reactor that allows a precise reaction control through efficient heat and mass transfer. With the ACR setup we investigated the addition of an aryldiazonium salt to the mentioned carbon nanostructures and demonstrated that the solubility of the functionalized material is similar to that obtained with the flask synthesis, but can be achieved in shorter times with the potential advantage of a quick response when new solvents or the addition of new functional groups are explored.
Carbon nanotubes (CNTs) are carbon allotropes characterized by a cylindrical structure with diameters between one and 50 nm, and typical lengths in the micrometre range. Their one-dimensional structure can be seen as derived from graphite layers rolled-up with a specific geometry. Depending on the number of concentric layers it is possible to distinguish between single-, double-, and multi-wall carbon nanotubes that, depending on the chiral angle, show semiconductor or metallic behaviour (1). For their strong intertube interactions, CNTs are scarcely soluble in common solvents and require demanding chemical and physical processing to be functionalized and fully exploited for practical applications (2). However, it has been found that the use of microwave irradiation reduces reaction times for chemical modifications, yielding soluble materials with good degrees of functionalization (3). A complementary enabling technology to microwave-assisted organic synthesis, namely, the continuous-flow approach to CNTs functionalization, has been recently reported by some of us (4) opening opportunities for the effective scale-up of the functionalization ...