Chemical modification of multiwalled carbon nanotubes for sorption of Zn^2+ from aqueous solution

Multiwalled carbon nanotubes (MWCNTs) were oxidized by mixed HNO3/H2SO4 (3N + 1S), HNO3, KMnO4 and NaClO and were selected as sorbents to study their characterization and isotherm of Zn^2+ sorption in an aqueous solution. The physicochemical properties of MWCNTs were improved after oxidation, which made MWCNTs possess not only a more hydrophilic surface but also a more negatively charged surface, and consequently resulted in sorption of more Zn^2+. The maximum Zn^2+ sorption capacities of MWCNTs, MWCNTs(3N + 1S), MWCNTs(HNO3), MWCNTs(KMnO4) and MWCNTs(NaClO) calculated by Langmuir model are 10.21, 18.14, 27.20, 28.01 and 32.68 mg g^−1, respectively. The MWCNTs(NaClO) have the best sorption performance of Zn^2+ and their sorption kinetics was found to follow the pseudo second-order rate law.