Adsorption characteristics of methylene blue on poplar leaf in batch mode: Equilibrium,kinetics and thermodynamics |
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Authors: | Xiuli Han Xiaona Niu Xiaojian Ma |
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Affiliation: | 1.School of Chemical Engineering and Energy,Zhengzhou University,Zhengzhou, Henan,P. R. China |
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Abstract: | Adsorption characteristics of methylene blue (MB) from aqueous solution on natural poplar leaf were investigated. Batch experiments
were carried out to study the effects of initial pH, contact time, adsorbent dosage, and initial MB concentration, salt concentration
(Ca2+ and Na+) as well as temperature on MB adsorption. The optimum condition for adsorption was found at pH 6–9 and adsorbent dosage of
2 g L−1. The equilibration time was 240 min. The salt concentration had a negative effect on MB removal. The equilibrium data were
analyzed with Langmuir, Freundlich and Koble-Corrigan isotherm models using nonlinear regression method. The adsorption process
was more effectively described by Langmuir isotherm based on the values of the correlation coefficient R2 and chi-square statistic x2. The maximum monolayer adsorption capacity of poplar leaf from the Langmuir model was 135.35 mg g−1 at 293 K. The pseudo second order equation provided a better fit to experimental data in the kinetic studies. Intraparticle
diffusion was involved in adsorption process, but it was not the only rate-controlling step. Thermodynamic quantities such
as ΔG, ΔH and ΔS were calculated, indicating that the adsorption process was spontaneous and endothermic. Dye-adsorbent interactions
were examined by FTIR and SEM analysis. The FTIR results suggested that there were hydroxyl and carboxyl groups on the surface
of poplar leaf, which would make MB adsorption possible. The SEM images showed effective adsorption of MB molecules on the
adsorbent surface. |
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