Adsorption of cationic methyl violet and methylene blue dyes onto carbon nanotubes

This study examined the feasibility of removing methyl violet (MV) and methylene blue (MB) from aqueous solutions using carbon nanotubes (CNTs). The effects of dye concentration, CNTs dosage, pH and contact time on adsorption of direct dyes by CNTs were also evaluated. The amount adsorbed increased with the dose of CNTs; however, the adsorption capacity dropped as the CNTs dosage increased. Cationic dyes adsorbed increased with pH due to the electrostatic attraction between the negatively charged CNTs adsorbent surface and the positively charged cationic dyes. The correlation coefficients for the Pseudo second-order kinetics model (R²) are greater than 0.99, indicating the applicability of this kinetic equation and the second order nature of the adsorption process of MB and MV onto CNTs. Additionally, the fact that the Langmuir isotherm fits the experimental data very well may be due to the homogeneous distribution of active sites onto CNTs surface.