Magnetic modification of cerium organic frame materials to improve the phosphorus adsorption performance: Modulating the valence state

Excessive phosphate levels in water bodies can lead to eutrophication, one of persistent environmental pollution problems. Metal-organic frameworks (MOFs) have garnered significant attention as a promising material for phosphorus removal due to their high capacity. However, there are challenges with solid-liquid separation necessitating magnetic modification solutions. The low adsorption capacity of magnetite (Fe 3 O 4 ) for phosphates has a potential negative impact on magnetic composites. To explore solutions that enable magnetic modification without reducing the adsorption capacity, Ce-MOFs@Fe 3 O 4 were successfully prepared. Experimental results showed an increase in adsorption capacity and removal rate post magnetic modification, with the phosphorus saturation adsorption capacity reaching 156.01 mg·g −1 . Further investigations involving the adsorbent dosing, co-existence of ions, and stability tests were conducted to explore the practical applications. The results indicated that Ce-MOFs@Fe 3 O 4 performed well across a wide pH range from 4 to 10 and exhibited excellent selectivity in the presence of SO 4 2- , Cl - , and NO 3 - . Zeta potential, FT-IR, and XPS analysis revealed electrostatic attraction and ligand exchange as the main adsorption mechanisms. Ce (III) species played a crucial role in phosphate binding by forming insoluble CePO 4 . On the contrary, Ce (IV) is not helpful for phosphate removal due to insufficient coordination number. In this study, adding Fe 3 O 4 during synthesis facilitated a substantial increase in Ce (III) content, which enhanced the phosphate adsorption capacity and imparted magnetic properties. Hence, the proposed preparation method could serve as a general magnetic strategy for Ce-based adsorbents, enhancing the phosphorus adsorption capacity.