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]nn– and intercalated [Me2NH2]+. The [Me2NH2]+ within [Me2NH2]V3O7 can be readily exchanged with UO22+. [Me2NH2]V3O7 exhibits high exchange
capacity (qm = 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
(SFU/Cs of 589 and SFU/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]nn–, 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.