Synthesis of hydrophilic carbon nanotubes by grafting poly(methyl methacrylate) via click reaction and its effect on poly(vinylidene fluoride)-carbon nanotube composite membrane properties

Abstract

Surface modification of azide-decorated multiwalled carbon nanotubes (MWCNTs) with well-defined alkyne-terminated poly(methyl methacrylate) (PMMA) chains was accomplished via the combination of reversible addition fragmentation chain transfer (RAFT) and “click” chemistry. Successful attachment of PMMA onto MWCNT was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), gel permeation chromatography, Raman spectroscopy, and transmission electron microscopy. The highest grafting percentage (GP) of the PMMA chains (GP=23.3%) was calculated using TGA. The effect of the PMMA-grafted-MWCNTs (MWCNTs-g-PMMA) content on the performance of the poly(vinylidene fluoride) (PVDF)-MWCNTs-g-PMMA composite membrane was studied. The MWCNTs-g-PMMA was found to be well dispersed in the PVDF composite membrane matrix because of the excellent compatibility between the PMMA and PVDF chains. The composite membranes showed improved porosity, hydrophilicity, water flux, β-PVDF content, and mechanical properties at an optimal amount of 2wt% MWCNTs-g-PMMA incorporated in the PVDF membrane matrix. In contrast, the hydroxyl functionalized MWCNTs (MWCNTs-OH) showed limited enhancement in the water flux and mechanical strength, which is mainly due to the poor dispersion of MWCNT because of the weak interaction between the MWCNT and PVDF chains. This study reveals the excellent prospect of the MWCNT-based ultrafiltration membrane with enhanced properties in water treatment applications.