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 π–π 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.

► Adsorption of methylene blue and acid red 183 on a MWCNT in single and binary dye systems was investigated.
► MWCNT shows higher adsorption capacity to methylene blue in both systems.
► A synergistic effect for basic and acid dyes occurs in a binary dye system.
► π–π Stacking and electrostatic attraction are responsible for dye adsorption.