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Experimental study of methylene
blue adsorption from aqueous solutions onto carbon nano
tubes
Zohre Shahryari, Ataallah Soltani Goharrizi* and Mehdi Azadi
Department of Chemical
Engineering, College of Engineering, Shahid Bahonar
University of Kerman, Kerman, Iran.
*Corresponding author. E-mail: a.soltani@mail.uk.ac.ir.
Accepted 28 December 2009
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In this work, batch
adsorption experiments were carried out for the removal of
methylene blue as a basic dye from aqueous solutions using
carbon nanotubes (CNTs). The effects of major variables
governing the efficiency of the process such as,
temperature, initial dye concentration, CNTs dosage, and pH
were investigated. Experimental results have shown that, the
amount of dye adsorption increased with increasing the
initial concentration of the dye, CNTs dosage, and
temperature. The dye removal using 400 mg L-1 of CNTs was
more than 90%. This dosage (400 mg L-1) was considered as
the optimum dosage of CNTs to remove methylene blue. The
adsorption kinetic data were analysed using
pseudo-first-order, pseudo-second-order and Elovich models.
It was found that the pseudo-second-order kinetic model was
the most appropriate model, describing the adsorption
kinetics. Adsorption isotherm of methylene blue onto the
CNTs was determined at 290, 300 and 310 K with 10 mg L-1 as
initial concentration of methylene blue. Adsorption
equilibrium was attained within 120 min. Equilibrium data
were fitted to the Langmuir, Freundlich, Temkin and Sips
isotherm models and isotherm constants were determined. The
equilibrium data were best represented by the Sips isotherm
model. Thermodynamic parameters such as changes in the free
energy of adsorption (ΔG◦), enthalpy (ΔH◦) and entropy (ΔS◦)
were calculated. The negative values of ΔG◦ indicate that
the methylene blue adsorption process is spontaneous in
nature and the positive value of ΔH◦ shows the endothermic
nature of the process.
Key words:
Carbon nanotubes, methylene blue, basic dye, adsorption,
equilibrium, kinetic, thermodynamics. |
