Adsorption Isotherm, Kinetic, and Thermodynamic Studies for Methylene Blue from Aqueous Solution by Needles of Pinus Sylvestris L.

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.