Self-Healing Hydrogen-Bonded Organic Frameworks for Low-Concentration Ammonia Capture

The self-healing behavior has been extensively used in intelligent sensing systems capable of molecular recognition. However, most rigid crystalline frameworks, once collapsed under external stimuli like pressure, heat, or vacuum, could hardly recover to their crystalline phases under ambient conditions. Here, we report the self-healing of a new microporous hydrogen-bonded organic framework, FDU-HOF-3 (FDU = Fudan University), for ammonia (NH₃) capture and compared it with the established mesoporous HOF-101. With the introduction of low-concentration NH₃ into the pores, the HOFs became disordered but were then simply heated under a vacuum to return to their original crystalline states after NH₃ removal. Close characterizations revealed that the repeatable self-healing behavior of these HOFs was achieved due to the COOH-NH₃ acid-base interactions accompanied by the breaking and regeneration of complementary COOH-COOH hydrogen bonds. FDU-HOF-3 showed a record-capturing capability for low-concentration NH₃ (8.13 mmol/g at 25 mbar) among all HOFs and displayed a quick photocurrent decrease after exposure to 250 ppm NH₃ for less than 10 s. These self-healing HOFs were used to capture and release NH₃ for over 10 cycles without any decrease in the adsorption capacities.