High-Connectivity Triazolate-Based Metal–Organic Framework for Water Harvesting

Abstract

Increasing the connectivity of structural units presents a potentially valuable approach to improve hydrolytic stability in metal–organic frameworks (MOFs). We herein leverage this strategy by synthesizing the first tritopic benzotriazolate MOF, Zn5(OAc)4(TBTT)2 (H3TBTT = 2,4,6-tris(1H-benzo[d][1,2,3]triazol-5-yl)-1,3,5-triazine), which exhibits open metal sites, high connectivity, high porosity, and significant water uptake capacity. The MOF adopts a previously unknown topology with (3,6,6)-connectivity, which is supported by single-crystal electron diffraction and elemental analysis. The framework undergoes postsynthetic metal and anion exchange with NiCl2, which increases the accessible pore volume and the net hydrophilicity of the framework. With this exchange, the apparent BET surface area increases from 1994 to 3034 m2/g, and the water uptake step shifts from 56 to 33% relative humidity (RH). The high gravimetric capacity of the Ni-rich MOF, 0.98 g/g, translates to a working capacity of 0.64 g/g during a pressure swing cycle between 20 and 40% RH at 25 °C. Combining this performance with a less than 2% loss in working capacity over 100 cycles, the new material rivals the best MOF water sorbents to date.