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.

Nickel based magnetic nanocrystals have been widely applied in magnetic and catalytic facilities. Tunable magnetic properties of nickel can be easily obtained via non-magnetic doping or phase transformation. However, phase transformation from face centered cubic (fcc) to hexagonal close packed (hcp) induced magnetism adjustment of Ni are always confused with nickel carbide (Ni₃C), due to the similar atomic structures of hcp-Ni and Ni₃C. Here, we present series of Au@Ni-carbide magnetic materials achieved from the controlled carbonation of Au@Ni core–shell structures, whose magnetism is tunable by adjusting the amount of carbon in the Ni layer. Ex-situ hard X-ray absorption spectroscopy (XAS) at the metal K edge and soft XAS at both metal L edge and carbon K edge provide solid evidence for the carbonation process from fcc-Ni to Ni_xC, rather than phase transformation to hcp-Ni. Further investigation reveals that the magnetism of the hybrids is mainly contributed from the residual fcc-Ni. The result represents an accurate and effective way to distinguish hexagonal Ni₃C from hcp-Ni, and provides the pathway to control magnetism of Ni-based materials for applications.