Facile fabrication of mesoporous MgO microspheres and their enhanced adsorption performance for phosphate from aqueous solutions

Mesoporous magnesium oxide microspheres were prepared by a simple precipitation and calcination method using sodium poly (4-styrenesulfonate) (PSS) as structure-directing agent. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), nitrogen adsorption–desorption isotherms and Fourier transform infrared (FTIR) spectroscopy. Adsorption of phosphate onto the as-prepared samples from aqueous solutions was investigated and discussed. The pore structure and SEM analyses indicate that MgO microspheres are composed of at least three levels of hierarchical porous organization: small mesopores (ca. 2–5 nm), large mesopores (ca. 10–50 nm) and macropores (50–250 nm). The equilibrium adsorption data of phosphate on the as-prepared samples were analyzed by Langmuir and Freundlich models, suggesting that the Langmuir model provides the better correlation of the experimental data. The adsorption capacities for removal of phosphate were determined using the Langmuir equation and found to be 3.17 and 75.13 mg/g for MgO samples prepared in pure water and in the presence of 1.0 g/L PSS, respectively. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results indicate that pseudo-second-order kinetic equation and intra-particle diffusion model can better describe the adsorption kinetics. The as-prepared mesoporous MgO microspheres are found to be effective adsorbent for the removal of phosphate from aqueous solutions as a result of their unique porous structures and high specific surface areas.