Covalent functionalization of multi-walled carbon nanotubes with quaternary ammonium groups and its application in ion chromatography

An approach for fabrication of core–shell composite beads was described, with polystyrene–divinylbenzene (PS–DVB) as the core and multi-walled carbon nanotubes (MWCNTs) as the shell through electrostatic attraction-induced self-assembly. MWCNTs were easily quaternized with a defined number of bonded layers and desirable positive charge by a multi-step synthesis, using methylamine and 1,4-butanediol diglycidyl ether as monomers to build a branching polymer that has quaternary ammonium groups. PS–DVB beads were sulfonated by sulfuric acid to provide opposite charge, which had electrostatic interaction with quaternized MWCNTs. Functionalization of MWCNTs was characterized by techniques that include Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscopy. The dispersion of MWCNTs in deionized water was enhanced after the grafting of cationic polyelectrolytes on them, which was in agreement with the positive charge at any pH value. With the PS–DVB/MWCNT composite beads as anion exchange phase and potassium hydroxide solutions as eluent, the common inorganic anions were well separated with high stability.