ORIGINAL RESEARCH
Adsorption Isotherm, Kinetic,
and Thermodynamic Studies for Methylene Blue
from Aqueous Solution by Needles
of Pinus Sylvestris L.
Nese Ertugay, Emine Malkoc
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Deparment of Environmental Engineering, Ataturk University, Erzurum, Turkey
Pol. J. Environ. Stud. 2014;23(6):1995-2006
KEYWORDS
ABSTRACT
The adsorption characteristics of methylene blue (MB) onto needles of Pinus sylvestris L., an unconventional
bio-adsorbent, were investigated. Maximum removal of MB was found to occur at initial pH 5.
Adsorption capacity increased from 84.46 to 99.73 mg/g with an increase in temperature from 20 to 45°C at
200 mg/L of initial MB concentration. Adsorption isotherms were modeled with the Langmuir, Freundlich,
Tempkin and Harkis-Jura adsorption isotherms. The data fit well with the Langmuir isotherm. The maximum
monolayer adsorption capacity of Pinus sylvestris L. needles was found to be 101 mg/g at 45°C. The adsorption
kinetics of pseudo first-order, pseudo second-order, and Bangham were used for the kinetic studies. The
pseudo second-order kinetic model provided the best fit to the experimental data compared with other kinetic
adsorption models. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were calculated. The adsorption
of MB increased with increasing temperature and thermodynamic parameters, suggesting that the adsorption
is spontaneous and endothermic in nature. FTIR spectrum result revealed the presence of adsorbing groups
such as carboxyl, hydroxyl, and aromatic-CN stretching in the needles of Pinus sylvestris L. The experimental
data obtained in the present study indicate that needles of Pinus sylvestris L. are suitable candidates for use
as adsorbents in the removal of MB.