2D water-stable zinc-benzimidazole framework nanosheets for ultrafast and selective removal of heavy metals

A two-dimensional water-stable zinc-benzimidazole framework nanosheet adsorbent was synthesized by top-down strategy. Compared with bulk-type MOFs, two-dimensional MOF nanosheets have numerous active sites exposed to the outer surface for excellent adsorption properties. [Display omitted] •An ultrathin Zn(Bim)(OAc) nanosheet was synthesized via a facile method.•Zn(Bim)(OAc) nanosheets had high uptake capacities for both Cu(II) and Pb(II).•Zn(Bim)(OAc) nanosheets exhibited an excellent selectivity over other metal ions.•Zn(Bim)(OAc) nanosheets showed a fast adsorption saturation within 30 min.•Imino and hydroxyl groups play key roles in the removal uptake. Owning to the unique structure and dimensionality, two-dimensional (2D) layered nanosheets have received increasing research interests. In this study, for the first time, we evaluate the ability of water stable 2D zinc based metal-organic framework (MOF) nanosheets, Zn(Bim)(OAc), to capture heavy metals in the aquatic system. The obtained novel adsorbent exhibits an ultrathin structure with an average thickness of 7.05 nm. Owning to their ultrathin thickness and highly exposed active sites, the as-prepared ultrathin Zn(Bim)(OAc) nanosheets exhibit the maximum adsorption capacity of 253.8 mg/g for Pb(II) and 335.57 mg/g for Cu(II), respectively, which is far superior adsorptive uptake in contrast to their corresponding bulk-type MOF. Meanwhile, the saturation process was rapid, within 30 min for Cu(II) and 90 min for Pb(II). Intriguingly, Zn(Bim)(OAc) nanosheets own a remarkable selectivity for Pb(II) and Cu(II) over other heavy metal ions in the mixed system, which is attributed to the strong affinity of imino and hydroxyl groups for Pb(II) and Cu(II) within Zn(Bim)(OAc) nanosheets. This work highlights new prospects in designing ultrathin 2D nanoadsorbents for the use in environmental remediation.