Synthesis of a mesoporous Mg–Al–mixed metal oxide with P123 template for effective removal of Congo red via aggregation-driven adsorption

Effective adsorption of Congo red from an aqueous solution was achieved with a mesoporous Mg-Al mixed metal oxide (MMO). Both MMO-E and MMO-W were obtained via calcination of layered double hydroxides based on a P123 template in ethanol and water, respectively, resulting in different aggregation states. The effect of P123 phases on the morphology of MMO-E and MMO-W was investigated by X-ray diffraction, N₂ adsorption-desorption isotherm, and scanning and transmission electron microscopies. MMO-E exhibited a sand-rose morphology whereas MMO-W carried small particles with relatively uniform interparticle pores. MMO-W accounted for remarkably large adsorption of Congo red up to 3470 ​mg/g, which was higher than 100% fractional occupancy. Adsorption kinetics of Congo red on MMO-E and MMO-W conformed to the pseudo-second-order kinetics, suggesting strong interactions between Congo red and both mixed metal oxides. Adsorption isotherms were described by the Langmuir model for MMO-E and Freundlich model for MMO-W, indicating effective multilayer adsorption of Congo red on MMO-W compared with monolayer adsorption on MMO-E. The uniform interparticle mesopores of MMO-W obtained by homogenous P123 micelles facilitated the adsorption of Congo red via intermolecular aggregation in the pore.