Single-Layer 2D Ni-BDC MOF Obtained in Supercritical CO2-Assisted Aqueous Solution

The development of an efficient strategy for fabricating two-dimensional metal-organic framework (MOF) nanosheets with high yield and high stability is desirable. Herein, we demonstrate for the first time that large, single-layer 2D nickel-benzene dicarboxylate (Ni-BDC) MOF nanosheets can be fabricated with the assistance of supercritical (SC) CO2 in a pure aqueous system. Detailed experimental evidence reveals that the SC CO2 molecule can exchange with the lattice-coordinated H2O molecules, side-on coordinate with the metal Ni-1 sites on the Ni-BDC surface, and finally break the interlayer hydrogen bond to exfoliate the bulk Ni-BDC into a 2D MOF. More importantly, a thin SC CO2 layer building up at the water-Ni-BDC interfaces can transform the pristine hydrophilic interface into a super-hydrophobic one. This super-hydrophobic layer at the water-MOF interface can effectively prevent dissociation, thus promoting the stability of Ni-BDC in aqueous system.