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Highly adsorptive chitosan/saponin-bentonite composite film for removal of methyl orange and Cr(VI)

Laysandra, Livy, Ondang, Immanuel Joseph, Ju, Yi-Hsu, Ariandini, Benedikta Hervina, Mariska, Agatha, Soetaredjo, Felycia Edi, Putro, Jindrayani Nyoo, Santoso, Shella Permatasari, Darsono, Farida Lanawati, Ismadji, Suryadi
Environmental science and pollution research international 2019 v.26 no.5 pp. 5020-5037
adsorption, bentonite, chitosan, chromium, composite films, composite materials, equations, methyl orange, models, pH, saponins, sorption isotherms, temperature, thermodynamics
Robust and simple composite films for the removal of methyl orange (MO) and Cr(VI) have been prepared by combining chitosan, saponin, and bentonite at a specific ratio. There are several composite films (chitosan-saponin-bentonite (CSB)) prepared; among them, the composite films CSB₂:₃ and CSB₁:₁ have the highest removal efficiency toward MO and Cr(VI) where the maximum removal is 70.4% (pH 4.80) and 92.3% (pH 5.30), respectively. It was found that different types of adsorbate have different thermodynamic properties of the adsorption process; the adsorption of MO onto CSB₂:₃, chitosan, and acid-activated bentonite (AAB) proceeded endothermically, while the adsorption of Cr(VI) onto CSB₁:₁, chitosan, and AAB proceeded exothermically. The parameters of the adsorption were modeled by using isotherm and kinetic equations. The models of Langmuir, Freundlich, Redlich-Peterson, Sips, and Toth were used for fitting the adsorption isotherm data at a temperature of 30, 45, and 60 °C; all of the isotherm models could represent the data well. The result indicates that CSB₂:₃ has the highest adsorption capacity toward MO with qₘ of 360.90 mg g⁻¹ at 60 °C; meanwhile, CSB₁:₁ has the highest adsorption capacity toward Cr(VI) with qₘ 641.99 mg g⁻¹ at 30 °C. The pseudo-second-order model could represent the adsorption kinetics data better than the pseudo-first-order equation. The adsorption mechanism was proposed, and the thermodynamic properties of the adsorption were also studied.