Cationic Metal–Organic\nFramework Nanoparticles\nBased on UiO-66 for Effective ReO<sub>4</sub><sup>–</sup> Capture

ReO<sub>4</sub><sup>–</sup> as a hazardous waste\nseverely\nthreatens environmental safety and human health. The high-efficiency\nadsorbent for the removal of ReO<sub>4</sub><sup>–</sup> is\nof immense interest but still faces challenges. Herein, we established\ncationic metal–organic framework nanoparticles by an amino\nprotonation strategy. Based on a facile and green method, we first\nintroduced dense amino groups (6.59 mmol/g) in UiO-66 in situ to prepare\nUiO-66-(NH<sub>2</sub>)<sub>2</sub>, during which acetic acid as a\nmodulator was applied to construct defects. Subsequently, UiO-66-(NH<sub>2</sub>)<sub>2</sub> was acidified to the cationic UiO-66-(NH<sub>3</sub><sup>+</sup>Cl<sup>–</sup>)<sub>2</sub>. Notably, this\ncationic adsorbent exhibits a high adsorption capacity of 590.2 mg\ng<sup>–1</sup> and a short adsorption equilibrium time of 240\nmin for ReO<sub>4</sub><sup>–</sup>. Besides, the excellent\nchemical stability and reusability endow UiO-66-(NH<sub>3</sub><sup>+</sup>Cl<sup>–</sup>)<sub>2</sub> with promising potential\nin practical applications. Experimental characterization and density\nfunctional theory (DFT) calculations suggest that the electrostatic\ninteraction, ion exchange, and coordination interaction jointly contribute\nto the effective removal of ReO<sub>4</sub><sup>–</sup>. Thus,\nthis work provides a highly efficient cationic metal–organic\nframework nanoparticle for ReO<sub>4</sub><sup>–</sup> removal\nand, importantly, proposes a feasible strategy for constructing cationic\nadsorbents.