Defect Control in Zr-Based Metal–Organic Framework Nanoparticles for Arsenic Removal from Water

In this study, water-stable Zr-metal–organic framework (MOF) (UiO-66) nanoparticles of various defect concentrations were successfully prepared and examined as the adsorbent for arsenate removal from water. The induced defects resulted from the addition of a monocarboxylic acid modulator [acetic acid or trifluoroacetic acid (TFA)] to the synthesis mixture. The concentrations of the defects were effectively tuned and controlled by changing the type and the amount of the modulator. As a result, different adsorption capacities for arsenate from water were obtained, in which the most modulated sample (UiO-66-36TFA) which was obtained by using TFA as the modulator showed an adsorption capacity around 200 mg g–1 at neutral pH that is the highest not only among the studied samples but also, up to our knowledge, among all other reported MOFs at neutral pH. By introducing the defects in UiO-66, the arsenate uptake percentage was enhanced by more than 100% compared to defect-free UiO-66 tested in this study. The superior arsenic uptake is attributed to the free Lewis acid sites formed in the MOF clusters as a result of missing linker defects. In addition, the nanoparticles showed outstanding arsenate selectivity against interfering anions and were efficiently recycled to maintain the same adsorption capacity after five regeneration cycles. Furthermore, a small quantity of this sample (0.5 mg) was employed to completely remove ultratrace arsenate (5 ppb), proving its high efficiency in real-life applications. Accordingly, defected nanoscale UiO-66 samples pave the way for future water purification technologies.