Removal of tartrazine from aqueous solution by carbon nanotubes decorated with silver nanoparticles

• Multi-walled carbon nanotubes (MCNTs) were decorated with silver nanoparticles.
• MWCNTs are promising as adsorbents of anionic tartrazine dye from aqueous solution.
• Removal of tartrazine was studied with different contact times, pH and initial dye concentrations.
• The equilibrium data were analysed by the Langmuir and Freundlich models.
• The sorption capacity of the samples, increases with increasing wt.% of Ag.

Multi-walled carbon nanotubes (CNTs) were decorated with silver nanoparticles, characterised, and used for the removal of anionic tartrazine dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact times, pH and initial dye concentrations. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of the dye from acidic solutions was better than from basic ones. The equilibrium data were analysed by the Langmuir and Freundlich models, which revealed that the Langmuir model was more suitable to describe the azo dye adsorption than the Freundlich one. Kinetics of the adsorption processes was studied using pseudo-first and second-order models and the intra-particle diffusion model. It was found that the kinetics followed a pseudo-second-order equation. The adsorption capacities of carbon nanotubes modified with silver nanoparticles decrease in the following order: 5 Ag/CNTs (84.04 mg/g) > 3 Ag/CNTs (72.33 mg/g) > 1 Ag/CNTs (62.07 mg/g) > CNTs (52.24 mg/g).

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