Ethylene glycol-assisted fabrication and superb adsorption capacity of hierarchical porous flower-like magnesium oxide microspheres for phosphate

Abstract

A series of hierarchical flower-like magnesium oxide (MgO) microspheres were prepared with an ethylene glycol (EG)-assisted route at room temperature using ammonia as a precipitating agent. Effects of the ethylene glycol (EG) ratio on the structure, morphology and pore properties were carefully investigated. The hierarchical porous MgO microsphere exhibited a surface area of 75 m² g⁻¹ and total pore area of 47.37 m² g⁻¹ at the highest ratio of EG (EG/Mg²⁺ = 10) in the reaction system. The prepared MgO microspheres exhibited an outstanding removal capacity of 574.71 mg g⁻¹ for phosphate following the pseudo second order kinetic model (R² = 0.99) and Langmuir isotherm model with the endothermic nature of phosphate adsorption which resulted from the high surface area and suitable pore size. Both the isothermal parameter R_L between 0 and 1 and the negative the Gibbs free energy value suggested that phosphate adsorption on a MgO microsphere was a favorable process. Undoubtedly, this template-free mild synthesis method effectively promotes wide practical applications and mass scale production of porous MgO microsphere adsorption material.