Room-temperature synthesis of defect-rich UiO-66-NH2 for effective removal of low-concentration arsenate from natural waters

The development of highly efficient and sustainable adsorbents for arsenic removal is crucial for public health. Herein, we report a room-temperature, trifluoroacetic acid (TFA)-modulated approach for synthesizing defective UiO-66-NH 2 (denoted as UiO-66-NH 2 -X, where X is the TFA dosage) to achieve deep removal of arsenate [As(V)] from water. Optimizing the TFA dosage significantly improved the crystallinity, defect density, and textural properties of UiO-66-NH 2 -X, thereby enhancing its As(V) sorption performance. Among the UiO-66-NH 2 -X variants, UiO-66-NH 2 –8 effectively reduced As(V) concentrations (50–5000 μg·L −1 ) to below the safe drinking standard of 10 μg·L −1 with minimal secondary pollution. It exhibited rapid kinetics (> 99 % removal in 60 min), a broad working pH range (2−10), resistance to coexisting ions and humic acid interference, and good reusability (> 90 % over 6 cycles). According to Langmuir model, UiO-66-NH 2 –8 exhibited a maximum adsorption capacity of 151.51 mg·g −1 , surpassing many previously reported adsorbents. However, high-concentration As(V) induced substantial release of ATA from UiO-66-NH 2 –8, with concentrations ranging from 0.26 to 73.72 mg·L −1 , mirroring the trend of As(V) uptake. Linear regression analyses indicate a strong correlation ( R 2  = 0.97) between adsorbed As(V) and released linkers at concentrations ranging from 10 to 200 mg·L −1 . Mechanistic studies reveal that As(V) is primarily adsorbed through coordination with defect sites and electrostatic interactions below 5000 μg·L −1 . As the defect sites become saturated, the sorption mechanism shifts to ligand exchange at concentrations above 10 mg·L −1 . EXAFS analysis confirmed the formation of bidentate binuclear As Zr complexes on UiO-66-NH 2 –8. Practical application was demonstrated through fixed-bed column tests, where 100 mg of UiO-66-NH 2 –8 successfully treated ∼2.58 L of As(V)-spiked Yangtze River water to safe levels. This work provides a sustainable approach for designing defect-rich MOFs and demonstrates their strong potential fro practical arsenic remediation in natural water bodies.