Tailoring Multiple Sites of Metal–Organic Frameworks for Highly Efficient and Reversible Ammonia Adsorption

The structural diversity and designability of metal-organic frameworks (MOFs) make these porous materials a strong candidate for NH3 uptake. However, to achieve a high NH3 capture capacity and good recyclability of MOFs at the same time remains a great challenge. Here, a multiple-site ligand screening strategy of MOFs is proposed for highly efficient and reversible NH3 uptake for the first time. Based on the optimized DFT results for various possible ligands, pyrazole-3,5-dicarboxylate with multiple sites was screened as the best ligand to construct robust MOF-303(Al) with Al3+. It is experimentally found that the NH3 adsorption capacity of MOF-303(Al) is as high as 19.7 mmol g-1 at 25.0 °C and 1.0 bar, and the NH3 capture is fully reversible and no clear loss of capture capacity is observed after 20 cycles of adsorption-desorption. Various spectral studies verify that the superior NH3 capacity and excellent recyclability of MOF-303(Al) are mainly attributed to the hydrogen bonding interactions of NH3 with multiple sites of MOF-303(Al).