Enhanced low-concentration phosphate adsorption using magnetic UiO-66@Fe₃O₄ composite with potential linker exchange

A magnetic Fe_nUiO-66 adsorbent was created to achieve high phosphate adsorption capacity. The incorporation of Fe₃O₄ facilitated the precipitation and growth of UiO-66 during crystallization, resulting in a shift towards a multilayer heterogeneous distribution of adsorption sites. The increased Fe₃O₄ content notably enhanced the magnetic properties of Fe_nUiO-66, while negligibly affecting its adsorption performance. The Fe_1.5UiO-66 demonstrated exceptional phosphate adsorption capacity (136.54 mg/g), outstanding selectivity, and sustained reusability, with an 80% removal efficiency after nine cycles of treating actual water. The mechanism of phosphate adsorption by Fe_nUiO-66 involved electrostatic attraction, ligand exchange, and linker exchange. Notably, while linker exchange significantly contributed to high adsorption capacity, it resulted in irreversible damage to the Fe_nUiO-66 crystal. These unequivocal findings will serve as a solid foundation for further research and underline the critical role of linkers in the process of phosphate adsorption.