Controlled thermal functionalization for dispersion enhancement of multi-wall carbon nanotube in organic solvents

Despite extensive study on carbon nanotube (CNT), the proliferation of its real applications has been hindered by its dispersibility in various organic or inorganic media. Very often complex surface functionalization processes are required to endow CNTs with enhanced dispersibility. Hence, facile, high-yield, and scalable functionalization methods for CNT for better dispersion are highly desirable. Thermal annealing is sometimes adopted for purification of CNT; however, limited discussion has been devoted to its functionalization effect and surface chemistry, which directly determine CNT dispersibility. In this work, via controlled mild thermal annealing, enhanced dispersion of functionalized CNTs was achieved in different organic solvents, including ethanol, dimethyl formamide, chloroform and acetone. Such enhancement had been studied through qualitative (dispersion and sedimentation, TEM) and quantitative analyses (XPS, Raman) of morphological structures and chemical states of thermally functionalized CNTs. The analyses reveal that under mild thermal annealing conditions, the surface oxidative reactions of the CNT can be well controlled, with minimal damage to the graphitic structure of the CNT. A plausible functionalization mechanism involving ether and quinone functional groups is proposed. The advantages of thermal annealing toward enhanced dispersion are further demonstrated by employing the functionalized CNT in poly (vinylidene fluoride) composite and drop-cast conductive CNT pattern.