A Solid-Solution Strategy for One-Step Construction of Hierarchically Porous Metal–Organic Frameworks

The construction of hierarchical porosity in metal–organic frameworks (HP-MOFs) by expanding the pore size to mesopore or even macropore region is important but still challenging. In this work, a facile solid-solution strategy is proposed here to increase the pore size, giving rise to hierarchically porous MOFs by one-step activation. It is found that for a microporous M-tpa structural platform, the cupric form collapses after activation, while the nickelous one shows the prototypical microporosity. The solid-solution Ni²⁺/Cu²⁺ form is therefore synthesized and is found to show hierarchical porosity after activation. The ratio of mesopore can be modulated by changing the relative concentration of Ni²⁺ to Cu²⁺. The effect of coordinative and noncoordinative solvents on the porosity is also investigated. Finally, it is found that the as-synthesized HP-MOFs here are able to adsorb bulky neutral and anionic dyes, while excluding cationic dyes, suggesting that the as-synthesized HP-MOFs here are probably cationic. It should be noted that the pristine microporous MOF is not able to adsorb the dye.