Hydrophilic surface treatment of carbon nanotube in gas-liquid interfacial plasma.

Carbon nanotubes (CNTs) are used and studied in many fields due to their inherent physical and electrical advantages. Still, it is difficult to use in practice due to aggregation by van der Waals force. In this study, we designed a specific type of low-temperature plasma, Gas-Liquid Interfacial Plasma (GLIP), to add a stable, functional hydrophilic group (including -OH and -NH₂) to improve the dispersibility of Carbon nanotubes under low concentration (0.5 M) of sulfuric acid, nitric acid, and an ammonia solution. From the optical emission spectrum, the plasma discharge in the gas phase generates N₂*, N₂⁺, O₂, and electrons, which induce various active species such as ·OH and ·H, SO₃, NO₃, and NH₂ in the liquid phase. The chemical analyses showed that -OH, S=O, and N-H groups were anchored at the Carbon nanotubes. Among all conditions, the highest dispersion was obtained with a two-step treatment of 0.5 M of nitric acid for 20 minutes, followed by 0.5 M ammonia solution. Dispersibility was greatly improved through various reactions of N-related functional groups added to Carbon nanotubes. There is no defect or change in crystallinity after all GLIP-treated Carbon nanotubes, which broadens the application of GLIP in practical applications. The plasma-treated Carbon nanotubes of 1 wt. % dispersion solution can be stored in ethanol with high stability for over one week. [ABSTRACT FROM AUTHOR]