Yttrium-doped MOFs for efficient phosphate adsorption: Electrochemical properties, electro-assisted desorption, and mechanism study

Metal-organic frameworks (MOFs) are effective adsorbents for phosphate removal, but it is challenging to use them to treat the eutrophication of natural water bodies due to their harsh synthesis conditions and poor regeneration performance. In this study, the microstructure and electronic structure of UiO-66-NH2 were modulated by doping yttrium (Y) at room temperature to enhance the number of oxygen vacancies, ligand deficiency, and number of exposed metal sites. Compared with the conventional hydrothermal route, the doping process did not require a high temperature, resulting in low material preparation costs. The obtained 1Y-UiO-66-NH2 exhibited a smaller particle sizes, higher porosity, and more unsaturated coordination sites, which improved the phosphorus adsorption efficiency. The 1Y-UiO-66-NH2 achieved an optimum adsorption capacity of 104 mg P/g at 298 K. Over a wide pH range of 4–8, 1Y-UiO-66-NH2 maintained a high P adsorption capacity in the presence of interfering ions, demonstrating its excellent stability and anti-interference ability. Spectroscopy, electrochemical measurements, and density functional theory calculations revealed that binding between 1Y-UiO-66-NH2 and phosphate mainly involved coordination exchange, electrostatic adsorption, hydrogen bonding, and the occupation of defect sites. The regeneration ability of 1Y-UiO-66-NH2 was studied by electro-assisted desorption, which showed that the desorption efficiency of phosphate on 1Y-UiO-66-NH2 exceeded 90 % at a constant voltage of −3 V. After five adsorption–desorption cycles, 1Y-UiO-66-NH2 maintained adsorption capacity of 78.52 mg P/g. The proposed method has good application prospects for treating the eutrophication treatment of natural water bodies.