Synergistic and competitive adsorption of organic dyes on multiwalled carbon nanotubes

A multiwalled carbon nanotube (MWCNT) was used as an adsorbent for removal of a cationic dye (methylene blue, MB) and acid dye (acid red 183, AR183) from aqueous solution in single and binary dye systems. Characterization of the MWCNT and MWCNT-dye systems were performed using several techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TG-DTA), zeta potential and elemental analysis. Adsorption tests showed that the MWCNT presented higher adsorption of MB than AR183 in single and binary dye systems, revealing that pi-pi stacking is the main driving force responsible for the dye-MWCNT interaction. In single dye systems, the MWCNT presented the maximum adsorption capacities of MB and AR183 at 59.7 and 45.2 mg/g, respectively. In a binary dye system, a synergistic effect due to electronic attraction between MB and AR183 was found at low AR183 concentration (10 mg/L), which promotes the adsorption of both dyes on the MWCNT. However, MB adsorption could be reduced at higher AR183 concentration (>20 mg/L) due to a strong electrostatic attraction between MWCNT-AR183. (C) 2012 Elsevier B.V. All rights reserved.