Facile one-step strategy for synchronous oxidation and recovery of diverse phosphorus species from water using Ce/Co co-doped magnetic crab shell biochar

Background Excess phosphorus in aquatic environments causes eutrophication. Low-valence inorganic and dissolved organic phosphorus are harder to remove than orthophosphate. These species usually require oxidation before separation, whereas oxidation alone cannot reduce total phosphorus (TP), resulting in multi-stage treatment processes. Methods This study explores a waste-derived cerium-modified CoFe 2 O 4 @biochar composite (ECB) prepared from crab shells for synchronous oxidation and adsorption of phosphorus species in water. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), were conducted for material characterization. Electron spin resonance (ESR) and radical quenching tests were used to identify reactive oxygen species. Significant findings The ECB/peroxymonosulfate (PMS) system removed 95.6% of P(III) within 30 min at neutral pH, reducing residual TP below 0.5 mg/L. PMS addition accelerated phosphorus removal by oxidizing P(III) to phosphate, which was captured by surface cerium-containing sites. The adsorption followed pseudo-first-order kinetics. Mechanistic results showed CoFe 2 O 4 @biochar activated PMS to generate SO 4 •− as the main reactive species, and electrostatic interaction and ligand exchange were responsible for phosphate capture. The ECB/PMS system was effective for dissolved organic phosphonates and exhibited magnetic separability, reusability, and low metal leaching. This research presents an efficient one-step strategy for phosphorus control and recovery, supporting cleaner production and circular utilization of crab shell waste.