Tuning wettability and surface order of MWCNTs by functionalization for water desalination
AS Kazemi and ZE Nataj and Y Abdi and MA Abdol, DESALINATION, 508, 115049 (2021).
While multiwall carbon nanotubes (MWCNTs) attract a lot of attention for their remarkable physical and mechanical properties, it is necessary to modify their surface chemistry and wettability with functionalization for successful application of these materials. Vertical and spaghetti MWCNTs were produced and functionalized with H2 and SF6 plasma treatments. Morphological and chemical characterizations were conducted. Molecular dynamics (MD) simulations demonstrated apparent unbundling of the functionalized vertical MWCNTs with the repulsive electrostatic forces between functional agents dominating the attractive van der Waals forces between the CNTs. MD simulations of hydrogenated spaghetti showed an increase in the structural order. Raman scattering provided evidence of the role played by the functional groups in increasing the graphitic character of MWCNTs. Contact angle measurements revealed the wettability tuning of the hydrogenated MWCNTs with a pronounced correlation with surface order. Hydrophobic-hydrophilic transitions of fluorinated MWCNTs with fluorination time also revealed the exchange of nonpolar and polar bonds on the side walls of the MWCNTs. Electrical conductivity measurements reflected the potential of functionalized MWCNT surfaces in holding back the salt, allowing fast transport of water, cancelling the conventional trade-off between selectivity and permeability, and presenting these materials as candidates for new generation of nanomaterials in water desalination.
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