Non-van-der-Waals Oriented Two-Dimensional UiO-66 Films by Rapid Aqueous Synthesis at Room Temperature

The synthesis of MOFs in a two-dimensional (2D) film morphology is attractive for several applications including molecular and ionic separation. However, 2D MOFs have only been reported from structures that crystallize in lamellar morphology, where layers are held together by van der Waals (vdW) interaction. By comparison, UiO-66, one of the most studied MOFs because of its exceptional chemical stability, has only been reported in three-dimensional (3D) morphology. 2D UiO-66 is challenging to obtain given the robust isotropic bonds in its cubic crystal structure. Herein, we report the first synthesis of non-vdW 2D UiO-66-NH2 by developing crystal growth conditions that promote in-plane growth over out-of-plane growth. Continuous, oriented UiO-66-NH2 film with thickness tunable in the range of 0.5 to 2 unit cells could be obtained by sustainable, scalable chemistry, which yielded attractive ion-ion selectivity. The preparation of non-vdW 2D MOF is highly attractive to advance the field of MOF films for diverse applications.