In recent years, imidazole-containing porous materials have garnered significant attention due to their potential and technical advantages in various fields such as adsorption and separation, catalyst support, sensing, and energy storage. These benefits can be attributed to their high porosity, excellent chemical stability, and outstanding photoelectric properties.
Currently, the reported synthesis methods for imidazole-linked porous organic cages (POCs) mainly include: C-N bond formation via direct SN2 reaction with polyimidazole monomers; dynamic covalent cross-linking with imidazole-functionalized monomers; and metal-carbene template method. However, these synthesis methods are relatively complex.
In a study published in Angew. Chem. Int. Ed., Prof. YUAN Daqiang, Prof. SU Kongzhao, and their colleagues from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, introduced an additional NH2 group near the aromatic amino monomer, the common imine bond is cyclized in situ, thereby efficiently synthesizing ultra-stable irreversible imidazole-linked POCs (IPOCs).
Specifically, the researchers synthesized four new IPOCs in high yields under mild, catalyst-free, one-pot conditions, including three [2+4] lantern-shaped structures and one [3+6] triangular prism structure. Their structures were fully characterized using NMR, MS, and single-crystal X-ray diffraction analysis.
The researchers explored the chemical stability of IPOC-1 and IPOC-4. They found that IPOC-1 and IPOC-4 remained stable after being exposed to boiling water, concentrated HCl (12 M), HF (40%), and saturated NaOH (14 M) for 24 hours.
The researchers then studied their NH3 adsorption performance. At 298 K and 1 bar, the adsorption amounts of NH3 for IPOC-1, IPOC-2, IPOC-3, and IPOC-4 were 6.3, 11.1, 9.21, and 11.5 mmol g-1, respectively. Notably, the NH3 adsorption amounts of IPOC-2 and IPOC-4 exceeded those of many reported porous organic materials.
Additionally, the researchers investigated the ammonia sensing performance. By adding an aqueous solution of NH3 with concentrations ranging from 0 µM to 80 µM to a DMF solution containing activated IPOC-1, fluorescence sensing experiments were conducted. The detection limit was calculated to be as low as 3.35×10-6 M based on the change in emission intensity.
This study establishes an important strategy for the design and construction of stable IPOC materials for practical applications.
Schematic representation illustrating the imidazole-linked porous organic cages for ammonia capture and sensing. (Image by Prof. YUAN’s group)
Contact:
Prof. SU Kongzhao
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
Email: skz@fjirsm.ac.cn
