Hexamethylene tetramine-assisted hydrothermal synthesis of porous magnesium oxide for high-efficiency removal of phosphate in aqueous solution

Porous magnesium oxide as the adsorbent of phosphate was prepared by hexamethylene tetramine (HMT) assisted hydrothermal method. Various techniques were used to carefully characterize crystallinity structure, morphology, pore structure, and adsorption performance of the prepared MgO samples. The results show that the HMT plays a key role during the formation of pore structure of MgO materials. The BET surface area and pore size were varied as a function of the feeding ratio of HMT and Mg2+ in the synthesis system. When the ratio is equal to 1.2, the obtained MgO sample has the appropriate BET surface area of 181.02 m2 g−1 and the averaged pore diameter of ca. 10.76 nm, which shows the highest adsorption capacity of 236 mg g−1 among the prepared samples and the outstanding adsorption performance compared with those reported in the literature. The adsorption of these porous MgO materials matches well the pseudo second order kinetic model and the Freundlich isotherms. Besides, the phosphate anions was adsorbed on MgO to produce magnesium hydrogen phosphate and magnesium phosphate.