Separation of chemically modified carbon nanotubes by surfactant free microbubble generation

Bubble separation is a widely used and effective method for separating solids from liquids. In this study, we propose a method to generate roughly ∼104 microbubbles/μl in an ethanol–water solution (surfactant-free) by subjecting the container of the solution to impact. Hydrophobic carbon nanotubes (CNTs) and hydrophilic carboxylated CNTs can be rapidly separated by the process of attachment of CNTs to rising microbubbles. More than 90% of hydrophobic CNTs can be collected on the top layer of the solution by microbubbles generated in the ethanol solution. The proposed mechanism of bubble enhancement material separation in ethanol solution is because of the effect of hydrophobic surfaces of surfactant-free microbubbles, while normal microbubbles in a surfactant solution have hydrophilic surfaces. CNTs can be separated from the solution by microbubbles with hydrophobic surfaces. The results show that the use of surfactant-free microbubbles can achieve high efficiency of recovery of CNTs in a short time, which provides a potential method for the separation of different materials based on their surface properties.