Facile and Nondestructive Transformation of Intrinsic Hydrophobic Behavior of a Carbon Nanotubes Sheet to Hydrophilic

It is imperative to induce hydrophilicity in intrinsically hydrophobic carbon nanotubes (CNTs) without losing their superior properties for applications that specifically deal with aqueous media. A method for transforming a CNTs sheet from hydrophobic to hydrophilic by treatment with N-methyl-2-pyrrolidone (NMP) is explored. The NMP-treated CNT sheets are assessed based on complementing characterization, and it is concluded that the binding of NMP to a CNTs surface is through noncovalent interaction without the incorporation of defects in CNTs. The induced hydrophilicity in the CNTs sheet is stable for water exposure over a longer duration while it displays a semireversible nature upon heat treatment. The mechanical and electrical properties of the NMP-treated CNTs sheet revealed enhancement in the tensile strength from 221 to 421 MPa while maintaining a good electrical conductivity of ∼1.22 × 104 S/m because of the improved interfacial properties. The hydrophilic CNTs exhibited excellent adsorption capacity for methylene blue dye. The NMP-treated CNTs sheets demonstrated their suitability in flexible hybrid supercapacitor (FHSC) devices with improved electrochemical performance with enhancement in the capacitance from 5.4 to 7.6 F/g and a decrease in the equivalent series resistance from 53 to 34 Ω compared to pristine CNTs-based devices. These solid-state FHSC devices displayed excellent cyclic charge-discharge performance along with robust behavior over thousands of bending cycles without significant performance degradation. The excellent dye removal capability and superior electrochemical performance of the NMP-treated CNTs sheet is a consequence of their improved interface with aqueous media, which is governed by the hydrophilic nature of the CNTs sheet.