High-Efficient removal of mercury in water by the flexible NH2-MIL-53(Al): Exploiting the gate opening effect

Flexible metal–organic frameworks (MOFs) with the gate opening feature can optimize the removal efficiency on the adsorption behavior by accommodating to the specific target molecules. In this study, a flexible MOF denoted as NH2-MIL-53(Al) was investigated to remove Hg(II) from water, in which the adsorption capacities of large-pore NH2-MIL-53(Al) (NH2-MIL-53(Al)-LP) for Hg(II) reached 433.20 mg/g, which is about 4 times higher than narrow-pore NH2-MIL-53(Al) (112.75 mg/g). Further, the kinetic experiment also revealed that nearly 90 % Hg(II) can be captured within 60 min for NH2-MIL-53(Al)-LP. Advanced characterizations and density functional theory calculations demonstrated that the strong coordination of the amino and oxygen centers on NH2-MIL-53(Al)-LP to Hg(II). Importantly, molecular dynamic simulation verified the gate opening effect of NH2-MIL-53(Al)-LP, as the faster diffusivity of Hg(II) ions in NH2-MIL-53(Al)-LP was observed. This work provides another opportunity in designing the pore geometry of porous materials for water remediation.