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This report deals with the modification of the physical structure and chemical properties of a bentonite clay from the Hammam Boughrara region, in the Maghnia district of western Algeria, to maximize its adsorption capacity. Purified bentonite clay (called B) was modified either by acid activation with sulfuric acid (1M) (B-Act) or by intercalation with the cationic surfactant cetyltrimethylammonium bromide (CTAB), applying a cation exchange capacity (CEC) of 100% (called B-CTAB). The modification of B was also achieved by combining these two steps consecutively, i.e. first acid activation of B followed by intercalation with CTAB (B-Act-CTAB). B-Act-CTAB was obtained by acid activation using H2SO4 (1M), followed by co-adsorption of CTAB with 100% and 300% of the CEC of B-Act as a precursor. In particular, a strong increase in specific surface area and pore volume of modified bentonites was observed for B-Act (469.83 m2/g and 0.401 cm3/g), B-Act-CTAB100( 267.72 m2/g and 0.316 cm3/g) and B-Act-CTAB 300 (111.15 m2/g and 0.171 cm3/g), compared with B (31.79 m2/g and 0.074 cm3/g) and B-CTAB ( 3.79 m2/g and 0.034 cm3/g), respectively.
Bentonite-based adsorbents were then used to evaluate the removal efficiency of an organic molecule, the azo dye Orange G (OG), as a model for persistent organic pollutants. Freundlich, Langmuir, and Sips models (Langmuir-Freundlich model) were applied to analyze equilibrium isotherms, showing a good correlation between experimental data and the Freundlich model. Good agreement was obtained between experimental adsorption kinetics data and the pseudo-second-order model, enabling rate constants to be evaluated. B-Act-CTAB300 can be used as a low-cost material for azo dye removal, as its adsorption capacity towards OG (102.80 mg/g) far exceeds that of B-CTAB (31.49 mg/g) and B-Act-CTAB100 (12.77 mg/g).
