Two mesoporous anionic metal-organic frameworks for selective and efficient adsorption of cationic organic dye

Anionic metal-organic frameworks (MOFs) are beginning to have a large impact in the field of absorption and separation of ionic organic molecules due to the enhanced electrostatic interactions between their anionic frameworks and counter-ionic guests. Herein, we report the rational design and synthesis of two mesoporous anionic MOFs, [Zn3(ITTC)3](Me2 NH2)3·3DMF·H2O (1) and [Cd2(ITTC)3](Me2NH2)5·2DMF (2), where H3ITTC = 4,4',4''-(1H-imidazole-2,4,5-triyl) tribenzoic acid. Structural analysis unveils that both materials are anionic MOFs with a 2-fold interpenetrating 3D framework. The cross size of the open one-dimensional rectangular channels is 31.7 A × 15.6 A in 1, of which the architecture is indicative of an unprecedented (3,3,4,5)-connection topology. For 2, the diameter of the open one-dimensional regular hexagonal channel is about 34.1 A decorated with uncoordinated carboxyl O atoms, and the framework exhibits a (3,4)-connected fcu network. Due to their anionic frameworks and bulky pore window sizes, both MOFs can be employed for absorbing and separating cationic organic dye methylene blue (MB). The results reveal that both MOFs represent good dye adsorption selectivity of MB over MO and SDI via charge and size-matching effect, enabling them to be the potential candidates for environmental governance. By comparison, 2 presents superior selectivity and adsorptivity for cationic MB depending on the presence of basic functionalized pore surface.