Ultrafast Removal of Phosphate from Eutrophic Waters Using a Cerium-Based Metal–Organic Framework

Phosphate removal has become a critical need to mitigate the negative effect of water eutrophication, which is responsible for the overgrowth of toxic algal blooms and the significant ecological harm generated to aquatic ecosystems. However, some of the currently available adsorbents have low removal capacity and function optimally at specific pH ranges. Here, we present an example of a cerium-based metal-organic framework (MOF) as a high-capacity sorbent for phosphate removal from eutrophic waters. Specifically, a Ce(IV)-based UiO-66 analogue, Ce 1,4-benzenedicarboxylate (Ce-BDC), was selected due to its water stability, high surface area, microporous structure, and the high binding affinity of phosphate with its open metal sites. Mechanistic studies supported by density functional theory (DFT) calculations indicate the formation of a Ce-O-P bond through ion exchange between the terminal (nonbridging) hydroxyl groups at the missing linker sites and the phosphate adducts. Experimental results demonstrate that Ce-BDC is highly selective for phosphates over other common anions (Cl-, Br-, I-, NO3-, HCO3-, SO42-) and stable in a broad pH range of (2-12), covering the relevant range for the treatment of contaminants in aquatic systems. The sorbent shows a fast removal rate, capturing significant amounts of phosphate within 4 min with a maximum adsorption capacity of 179 mg·g-1, outperforming other porous materials. These results show a remarkable adsorption capacity and fast kinetics compared with the current state-of-the-art crystalline porous materials. This study may advance the design of new microporous materials with high adsorption capabilities, good stability, and make a significant contribution to the development of future generation technology to mitigate the negative effects of water eutrophication.