Enhanced adsorption performance of subordinate magnesium sites in pinhole magnesium oxide nanosheets with rich oxygen vacancies

Phosphorus recovery from wastewater is important for protecting the aquatic environment and achieving sustainable development. However, as a typical phosphorus adsorbent, nanoscale magnesium oxide (MgO) exhibits aggregation and limited adsorption ability. Herein, melamine foam (MF) was selected as a self-sacrifice template to prepare an oxygen-vacancy-rich MgO/MF phosphate adsorbent with high dispersion and a multistage pore structure. Density-functional theory calculations reveal that the phosphate preferentially adsorbed on the hollow sites rather than top sites of MgO when there were oxygen vacancies, which improved the intrinsic adsorption ability of MgO/MF. The MgO/MF adsorbent exhibited excellent phosphorus removal from water within a wide pH range of 2–12; the maximum adsorption capacity of phosphate was as high as 1226 ​mg/g. The adsorption capacity of the MgO/MF adsorbent after phosphate adsorption was reactivated to ca. 100%. After six adsorption cycles, MgO/MF with a high phosphate content of 117.5 ​mg ​P/g is a potential high-quality fertilizer. This work provides a promising strategy for constructing an efficient adsorbent for wastewater treatment and resource recovery.