Nanoporous Cationic Organic Cages for Trapping Heavy Metal Oxyanions

The harmful effect of poisonous oxoanions on the water environment highlights the urgent demand for effective adsorption materials. Rather than utilizing open framework materials carrying continuous pores as oxoanion traps, nanoporous molecular cages with discrete pores show promise since they are supposed to have higher adsorption efficiency. However, they are rarely reported in the field of decontamination. Herein, we utilize a nanoporous cationic organic cage, I-Cage-Cl, as a type of adsorbent that can efficaciously and selectively trap hazardous oxoanions from aqueous solutions via anion exchange. Specifically, cationic I-Cage-Cl shows a superior uptake capacity of CrO₄^2– (540 mg g^–1) that surpasses the reported nanoporous cationic frameworks along with excellent selectivity for CrO₄^2– even with a 500-fold excess of interfering ions (Br^–, NO₃^–, ClO₄^–, and BF₄^–). Furthermore, we fabricate an I-Cage-SPSf composite membrane (SPSf = sulfonated polysulfone), which can rapidly reduce trace Cr(VI) below the drinking water standard while also exhibiting extremely high water flux (80 L m^–2 h^–1 bar^–1) and admirable reproducibility. These intriguing features indicate that nanoporous organic cages are promising candidates for wastewater treatment.