Oxidized and Ethylenediamine-Functionalized Multi-Walled Carbon Nanotubes for the Separation of Low Concentration Arsenate from Water

In this work multiwalled carbon nanotubes (MWCNTs) modified by oxidation (o-MWCNTs) and by aminofunctionalization (e-MWCNTs) were examined as potential adsorbents for arsenate removal from water. Adsorption characteristics of raw and modified MWCNTs were investigated in batch adsorption experiments. The influence of solution pH (pH range 3-10), contact time, and temperature (25, 35, and 45 degrees C) were studied. Ethylenediamine-functionalized MWCNTs have the greatest affinity for arsenate ions, followed by o-MWCNTs and raw-MWCNTs. The obtained experimental data for raw- and o-MWCNTs fitted Sips isotherm model, while for the e-MWCNTs, the Freundlich model provided the best fit to the experimental points. The maximum adsorption capacity for arsenate ions was achieved using e-MWCNTs, 12.18mgg(-1). The presence of the arsenate on the adsorbent is confirmed by FTIR spectroscopy. Thermodynamic studies indicated the spontaneity and endothermic nature of the adsorption. Sodium hydroxide solution (0.1M) was found to desorb about 70% of arsenate from e-MWCNTs. The results with spiked drinking water samples demonstrated that e-MWCNTs, due to the present basic and acidic groups, were very efficient for the removal of arsenate ions, as well as of some cations, at pH 4.