Regenerable neodymium-doped zirconium-based MOF adsorbents for the effective removal of phosphate from water

Abstract

UiO-66-NH2 has been widely to remove phosphate from natural water, albeit having poor selectivity and low removal efficiency. Researchers are seeking to enhance the adsorption properties of this Metal-Organic Framework (MOF) and improve its practicability. In this study, the rare earth neodymium (Nd) was doped into UiO-66-NH2 to prepare NdUiO-X (X: mole ratio of Zr/Nd), which was used as an adsorbent to remove phosphate from water. The main adsorption parameters, such as pH value, equilibrium time, and initial concentration were investigated. Furthermore, the adsorption mechanism of NdUiO-0.5 was investigated via spectroscopic analysis (FTIR and XPS) and theoretical calculations (DFT and LOBA). The results showed that when the molar ratio of Nd/Zr was 0.50, the adsorption effect was at its maximum, with the calculated saturation adsorption capacity from the Langmuir model being 106.39 mg P/g. The NdUiO-0.5 adsorbent shows high stability in solutions with pH ranging from 3 to 9. This MOF was applied to the actual water sample to observe its phosphate adsorption capacity. When the dosage of NdUiO-0.5 was 0.15 g/L, the total phosphorus concentration of the actual water sample decreased from 0.57 mg P/L to 0.018 mg P/L. Mechanistic studies have shown that ligand exchange is the key mechanism of action behind phosphate removal via NdUiO-0.5. Besides, unconventional hydrogen bonds also play a very important role. Thus, the prepared NdUiO-0.5 is a high-efficient adsorbent for phosphate removal bearing potential applications in real-life scenarios.