Open-Framework Vanadate as Efficient Ion Exchanger for Uranyl Removal.

The elimination of uranium from radioactive wastewater is crucial for the safe management and operation of environmental remediation. Here, we present a layered vanadate with high acid/base stability, [MeNH]VO, as an excellent ion exchanger capturing uranyl from highly complex aqueous solutions. The material possesses an indirect band gap, ferromagnetic characteristic and a flower-like morphology comprising parallel nanosheets. The layered structure of [MeNH]VO is predominantly upheld by the H-bond interaction between anionic framework [VO] and intercalated [MeNH]. The [MeNH] within [MeNH]VO can be readily exchanged with UO. [MeNH]VO exhibits high exchange capacity ( = 176.19 mg/g), fast kinetics (within 15 min), high removal efficiencies (>99%), and good selectivity against an excess of interfering ions. It also displays activity for UO ion exchange over a wide pH range (2.00-7.12). More importantly, [MeNH]VO has the capability to effectively remove low-concentration uranium, yielding a residual U concentration of 13 ppb, which falls below the EPA-defined acceptable limit of 30 ppb in typical drinking water. [MeNH]VO can also efficiently separate UO from Cs or Sr achieving the highest separation factors (SF of 589 and SF of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO and [VO], whereas the ion exchange rate is influenced by the mobility of UO and [MeNH]. Our experimental findings indicate that [MeNH]VO can be considered as a promising uranium scavenger for environmental remediation. Additionally, the simulation results provide valuable mechanistic interpretations for ion exchange and serve as a reference for designing novel ion exchangers.