Application of Nitric Acid Modified Multi-Walled Carbon Nanotubes for Efficient Removal of Methylene Blue in Aqueous Solution

In this work, multi-walled carbon nanotubes (MWCNTs) was modified with nitric acid and applied as efficient adsorbents for the removal of methylene blue (MB) in aqueous solution. The morphologies of the modified MWCNTs were characterized by N-2 adsorption-desorption (BET), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Batch experiments were conducted systematically to explore the effects of various parameters including mass dosage of adsorbents, initial concentration of MB dye, pH of solution and ionic strength about the adsorption performance with modified MWCNTs. The adsorption for MB pollutants achieves the highest efficiency of 95.18 % occurring at about pH 11 when the adsorbent dosage is at 1.0 g L-1, the initial dye concentration is at 50 mg L-1 and the concentration of NaCl is 0 M. And the Langmuir, Freundlich and Temkin equilibrium isotherms were researched. The results revealed both the Freundlich and Langmuir isotherms fitted well to experimental data suggesting adsorption of MB onto MWCNTs as a result of a monolayer formation. In addition, the adsorption behavior of MB dye followed the pseudo second-order kinetics indicating there was a synergistic effect in the adsorption process based on the factors of mass transfer resistance in the particles, the external liquid membrane diffusion, surface adsorption and internal diffusion of the particles.

Automated summary

In this study, nitric acid-modified multi-walled carbon nanotubes (MWCNTs) were used as efficient adsorbents for the removal of methylene blue (MB) in aqueous solution. The experiments demonstrated that the modified MWCNTs had a high efficiency for adsorption of MB, with Freundlich and Langmuir isotherms fitting well to the experimental data. The adsorption process followed pseudo second-order kinetics.