Enhanced phosphate removal by lanthanum functionalization using zirconium-based metal organic frameworks: Role of in situ formed La(OH)3

Developing high-efficiency adsorbents with sufficient active species to remove phosphate from wastewater is still a significant and formidable challenge. Herein, a metal-ion modification strategy was developed to construct a series of lanthanum (La 3 + )-functionalized zirconium-based metal-organic frameworks containing different functional groups through a one-step solvothermal process. The investigations for the influence of functional groups of ligands on the resulting La species and the role of La(OH) 3 in the phosphate removal are the primary focuses of this research. Unlike the simple La doping in UiO-66, UiO-66-NH 2 and many previously reported MOF systems, La(OH) 3 was in situ formed during the preparation of La-functionalized UiO-66-OH, which was confirmed by powder X-ray diffraction. At room temperature, the optimized 0.5La-UiO-66-OH, with a molar ratio of La 3+ versus the total metal precursor of 0.5, exhibits a desirable adsorption capacity of 219.6 mg g −1 , exceeding those of UiO-66 (146.8 mg g −1 ), UiO-66-OH (158.9 mg g −1 ), and many reported adsorbents. Besides, reusability tests demonstrate that 0.5La-UiO-66-OH can maintain high adsorption performance (96 %) after five cycles and the practical usability of by 0.5La-UiO-66-OH is confirmed using real lake water. In-depth investigations (X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy) on mechanism unveiled that the adsorption of phosphate by 0.5La-UiO-66-OH involved a combined process of electrostatic attraction and ligand exchange. This research presents the first regulation of generating active La species within MOFs through subtle modification and provides valuable insights for wastewater treatment.