Nanoporous Cationic Organic Cages for Trapping Heavy Metal Oxyanions

Abstract

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.

Recycling Organic Dyes within the Metal–Organic Framework for Photothermal Conversion

“…The supernatant was then measured using a UV–vis spectrophotometer to determine the concentration of the residual RhB molecule in the solution. The adsorption capacity ( q ) and removal percentage ( R ) of the RhB molecule were calculated by eqs – q t = ( C 0 − C t ) × V m q e = false( C 0 − C e false) × V m R = false( C 0 − C t false) C 0 × 100 % …”

“…The Langmuir adsorption model was used to explain the adsorption behavior and related to the adsorption capacity of RhB as a function of equilibrium concentration at room temperature. The linear form of the Langmuir isotherm equation is expressed in eq , where k b (L mg –1 ) is the Langmuir adsorption constant concerned with the binding sites C e q e = 1 q m k b + C e q m …”

Recent advances in the applications of porous organic cages

“…Zhao and co-workers synthesized a highly charged POC: I-Cage-Cl, which could efficiently select and trap CrO 4 2À ions in water owing to the strong affinity between the electropositive I-Cage-Cl and the CrO 4 2À anion. 123 Recently, some studies revealed the possible application of POCs for trapping the pollutants in sewage. Yang et al 122 used N,N-dimethylformamide (DMF) as a solvent and introduced different dihydrazide linkers onto the concave-shaped tetraformyl-functionalized C4RACHO scaffold, and the seven obtained types of calix [4]-resorcinarene-based POCs (HPOC-101, 102, 103, 104, 201, 301, and 401) all exhibited an I 3 À adsorption capability in water.…”

“…Zhao and co-workers synthesized a highly charged POC: I-Cage-Cl, which could efficiently select and trap CrO 4 2− ions in water owing to the strong affinity between the electro-positive I-Cage-Cl and the CrO 4 2− anion. 123…”