Alginate encapsulated pillared clays: removal of a neutral/anionic biocide (pentachlorophenol) and a cationic dye (safranine) from aqueous solutions

As a result of the cross-linking process between sodium alginate, Aluminium pillared clay (Al-Mont-PILC) or surfactant-modified pillared clay (CTAB-Al-Mont-PILC) and divalent cation (Ca2+), gel-like beads were obtained under different ratios of PILCs vs. alginate. Experimental ratios (pillared clay/alginate: w/w) increased to a maximum of 3.5 to 4. The results of SEM analysis revealed that surface morphology changes by introducing Al-Mont-PILC and CTAB-Al-Mont-PILC. Structural modifications were evaluated using FTIR and thermal analysis. In agreement with previous works the pseudo-second order model equation fit well with the kinetics data. Diffusion coefficients were calculated using the Linear Adsorption Model: the D-eff obtained in this study (3-7 10(-6) cm(2)/s) are within the ranges reported in other works on inorganic pollutants or phenol diffusion in biopolymers. Adsorption isotherms of pentachlorophenol and safranine were analyzed using non-linear regression technique. Langmuir isotherms fit well with the results obtained for the sorption of safranine whereas the Freundlich isotherms was more in accordance with the pentachlorophenol sorption. A decrease of 35 to 40% in sorption capacity was observed for pentachlorophenol when the initial pH increased from 5.3 to 8. Modification of the biopolymers by introduction of pillared clays resulted in an enhancement of the adsorption capacity. (C) 2010 Elsevier B.V. All rights reserved.