Synthesis of acid-base bi-functionalized multiwalled carbon nanotube using supercritical carbon dioxide

A novel approach to surface modification of carbon-based nanomaterials using supercritical fluid was used in the synthesis of an acid-base bi-functionalized multiwalled carbon nanotubes (MWCNT). The oxidized thiol and amine groups were incorporated in series using supercritical CO₂ at T=55 °C, P=9MPa, and t=1h. Successful functionalization was confirmed using Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), Field emission scanning electron microscopy–energy dispersive x-ray (FESEM-EDX), Time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray powder diffraction (XRD), and Brunauer–Emmett-Teller (BET). ScCO₂ functionalization was used to produce a bifunctional carbon-based material that maintained its structural integrity even after the addition of two incompatible functional groups on MWCNT.

Graphical abstract

The use of supercritical CO₂ results in the synthesis of an acid-base bifunctionalized MWCNT. To graft the sulfonic and amine functional groups on MWCNT, 3-mercaptopropyltrimethoxysilane oxidized with H₂O₂ and 3-aminopropyltrimethoxysilane were utilized. This green surface modification method can replace any of the time-consuming, tedious, and solvent-waste-producing steps of conventional mixing.