Effect of preparation method on structure and adsorption capacity of aluminum pillared montmorillonite

Aluminum pillared montmorillonites (Alpill-MMTs) were prepared by two different methods, i.e. conventional intercalation and ultrasonic assisted intercalation, in order to study the effects of preparation methods on their structures and adsorption abilities. In the conventional intercalation, a base-hydrolyzed solution of AlO₄Al₁₂(OH)₂₄(OH₂)₁₂]⁷⁺, Al₁₃⁷⁺, was firstly prepared and then mixed with a suspension of sodium montmorillonite (Na⁺-MMT) for 24 h with vigorous stirring, resulting in the cation exchange between Al₁₃⁷⁺ and Na⁺ balancing ions in the MMT interlayers. On the other hand, the high power ultrasonic was used in the second method for creating the Al₁₃⁷⁺ ions and then in situ intercalating into the MMT suspension, in which the reaction was performed for 20 min. Both Al₁₃⁷⁺ intercalated MMTs were calcined at 500 °C for 2 h in order to obtain the Alpill-MMTs. The ultrasonic could not only shortening the intercalation process, but also increasing the amount of intercalated Al₁₃⁷⁺ in the MMT. The ultrasonic synthesized Alpill-MMT (Alpill-MMT-ultra) consisted of mesoporous structure with multiple pore sizes ranging from 3 to 30 nm; therefore, it possessed higher specific surface area and pore volume than the conventionally synthesized Alpill-MMT (Alpill-MMT-str). Adsorption capacities of Alpill-MMTs were investigated using cationic adsorbate, i.e. Basic Yellow 1 (BY1). The highest adsorption capacities were respectively about 95 and 81 mg/g for the Alpill-MMT-ultra and Alpill-MMT-str, when using initial BY1 concentration of 2000 mg/L. The Alpill-MMT-ultra showed higher efficiency for BY1 removal than the Alpill-MMT-str even after thermal regeneration. The adsorption kinetics of both Alpill-MMTs for BY1 removals were found to follow a pseudo-second-order model, while their adsorption data corresponded to Langmuir isotherm. These results indicated the competency of Alpill-MMTs as the adsorbents for treatment of wastewater containing cationic dye.