Self-Healing Hydrogen-Bonded\nOrganic Frameworks for\nLow-Concentration Ammonia Capture

Abstract

The self-healing behavior has been extensively used in\nintelligent\nsensing systems capable of molecular recognition. However, most rigid\ncrystalline frameworks, once collapsed under external stimuli like\npressure, heat, or vacuum, could hardly recover to their crystalline\nphases under ambient conditions. Here, we report the self-healing\nof a new microporous hydrogen-bonded organic framework, FDU-HOF-3\n(FDU = Fudan University), for ammonia (NH₃) capture and\ncompared it with the established mesoporous HOF-101. With the introduction\nof low-concentration NH₃ into the pores, the HOFs became\ndisordered but were then simply heated under a vacuum to return to\ntheir original crystalline states after NH₃ removal. Close\ncharacterizations revealed that the repeatable self-healing behavior\nof these HOFs was achieved due to the COOH–NH₃ acid–base\ninteractions accompanied by the breaking and regeneration of complementary\nCOOH–COOH hydrogen bonds. FDU-HOF-3 showed a record-capturing\ncapability for low-concentration NH₃ (8.13 mmol/g at 25\nmbar) among all HOFs and displayed a quick photocurrent decrease after\nexposure to 250 ppm NH₃ for less than 10 s. These self-healing\nHOFs were used to capture and release NH₃ for over 10 cycles\nwithout any decrease in the adsorption capacities.