Adsorption of Congo red from solution using chitosan modified carbon nanotubes

Chitosan (CS) modified multi-walled carbon nanotubes (MWCNTs) were used as adsorbents (CS-MWCNTs) to adsorb Congo red (CR, anionic dye) from solution in batch mode. The structure and morphology of CS-MWCNTs were characterized by TEM, FTIR, Raman and XPS. The results from analysis of FTIR and XPS showed that CS was successfully loaded onto the MWCNTs. Raman analysis showed that the basic structure of MWCNTs after CS modification did not change. Adsorption studies were performed at different pH, coexisted ions concentrations, contact time and CR concentrations in the batch mode. Results showed that the pH of CR solution at 4.0 was best for the adsorption and the adsorption capacity could reach up to 623 mg.g(-1) at 303K. The adsorption of the CR solution reached equilibrium within 8 h. Adsorption equilibrium data can be predicted by the Freundlich model while the kinetic adsorption data follow a pseudo-second-order model. Thermodynamic results showed that the adsorption process was spontaneous, and endothermic. The CR-loaded adsorbent can be regenerated using a 0.01 mol.L-1 NaOH solution, the regeneration rate can still reach 71% after three cycles. CS-MWCNTs may be available in removal of anionic dyes from solution.