The Hydrophilic Pretreatment of CNTs and the Impact of the Pretreatment Method Upon the Loading of CuO Onto the Surface of CNTs

Carbon nanotubes (CNTs) loaded with copper oxide (CuO) as the combustion catalysts for solid propellants are able to increase the combustion rate and reduce the pressure index of propellants. The dispersibility of CNTs in water is one of the most important factors influencing the loading of CuO. In this paper, 1-dodecyl−3-methylimidazolium chloride ([C12C1Im]Cl) was prepared and used as the pretreatment agent of CNTs. The Nuclear magnetic resonance (NMR) results indicated the successful synthesis of [C12C1Im]Cl, which contains a positively charged imidazolium hydrophilic headgroup, enabling it as a cationic surfactant for the surface pretreatment of CNTs. The properties of the [C12C1Im]Cl-pretreated CNTs were compared with those pretreated with sodium dodecyl sulfate (SDS) and mixed acids (with a volume ratio of concentrated sulfuric acid to concentrated nitric acid = 3:1). X-ray diffraction (XRD) results showed that the crystalline structures of the CNTs were unchanged by using all of the three pretreatment methods. Scanning electron microscope (SEM) morphology analysis showed that the CNTs pretreated with [C12C1Im]Cl had the clearest tubular shape, the smoothest walls and the best dispersion in water without agglomeration. The impact of the pretreatment methods on the loading of CuO onto the surface of CNTs was also illustrated. It was concluded that by pretreatment with [C12C1Im]Cl, it led to the best CuO dispersion on the CNTs surface, the smallest CuO grain size and the largest CuO content. The study on the loading mechanism indicated that CuO could be successfully loaded on CNTs only when the pH > 4.6014, given the temperature is higher than 75°C.