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, [Me₂NH₂]V₃O₇, 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 [Me₂NH₂]V₃O₇ is predominantly upheld by the H-bond interaction between anionic framework [V₃O₇]_n^n- and intercalated [Me₂NH₂]⁺. The [Me₂NH₂]⁺ within [Me₂NH₂]V₃O₇ can be readily exchanged with UO₂²⁺. [Me₂NH₂]V₃O₇ exhibits high exchange capacity (q_m = 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 UO₂²⁺ ion exchange over a wide pH range (2.00-7.12). More importantly, [Me₂NH₂]V₃O₇ 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. [Me₂NH₂]V₃O₇ can also efficiently separate UO₂²⁺ from Cs⁺ or Sr²⁺ achieving the highest separation factors (SF_U/Cs of 589 and SF_U/Sr of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO₂²⁺ and [V₃O₇]_n^n-, whereas the ion exchange rate is influenced by the mobility of UO₂²⁺ and [Me₂NH₂]⁺. Our experimental findings indicate that [Me₂NH₂]V₃O₇ 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.