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

Abstract

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 (NH 3 ) capture and compared it with the established mesoporous HOF-101. With the introduction of low-concentration NH 3 into the pores, the HOFs became disordered but were then simply heated under a vacuum to return to their original crystalline states after NH 3 removal. Close characterizations revealed that the repeatable self-healing behavior of these HOFs was achieved due to the COOH−NH 3 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 NH 3 (8.13 mmol/g at 25 mbar) among all HOFs and displayed a quick photocurrent decrease after exposure to 250 ppm NH 3 for less than 10 s. These self-healing HOFs were used to capture and release NH 3 for over 10 cycles without any decrease in the adsorption capacities.

Crystalline Porous Organic Frameworks Based on Multiple Dynamic Linkages

“…Chemie observed between the two TGA curves at 220 °C, which might be attributed to the loss of NH 3 from CPOF-3@NH 3 , indicating the storage of NH 3 in the CPOFs. [20] These results collectively indicate the strong interaction between NH 3 and CPOF-3, with potential binding sites including the acidic COOH and B 3 O 3 rings.…”

Crystalline Porous Organic Frameworks Based on Multiple Dynamic Linkages

“…Additionally, a comprehensive assessment of NH 3 capture capacities has been conducted by comparing CPOFs with other known porous organic materials, including COFs, HOFs and porous organic polymers (POPs) (Table S7). Encouragingly, although exhibiting slightly lower NH 3 uptake than that of COF-10 (15.0 mmol g À 1 ), [14] CPOF-1 and À 3 surpass most metal-free porous organic materials (TpBD-(SO 3 H) 2 , [16] 11.5 mmol g À 1 ; TpPa-1, [17] 6.9 mmol g À 1 ; KUF-1a, [18] 6.67 mmol g À 1 ; PHOF-1, [19] 4.2 mmol g À 1 ; HOF-101, [20] 8.44 mmol g À 1 ; FDU-HOF-3, [20] 9.34 mmol g À 1 , etc.) and commercially available materials (Amberlyst, [21] 11.34 mmol g À 1 and 13X zeolites, [21] 9.3 mmol g À 1 ).…”

“…Notably, the diffraction peaks disappear or shift after NH 3 adsorption for all CPOFs (Figure S30), indicating the transformation from CPOFs into amorphous states or other crystalline phases, possibly associated with the disruption of hydrogen bonds after NH 3 binding. [20] The original structures can be recovered upon NH 3 removal by heating under vacuum (Figure S30). The degassing at elevated temperatures (100 °C for CPOF-1 and -2; 80 °C for CPOF-3 and -4) is necessary in this process, possibly due to the relative strong interactions between the basic NH 3 molecules and acidic binding sites (Figure S31), as also can be found for other porous framework materials (for examples, 90 °C for HOF-101, [20] 200 °C for COF-10, [14] and 130 °C for P2-CO 2 H [22] ).…”

Precise Modulation of CO2 Sorption in Ti8Ce2–Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

“…Normally regarded as geometrically rigid materials, metal oxide clusters are generally assembled by metal atoms and organic ligands that comprise bridging groups like carboxylic acids, hydroxyls, halides, and hydrides. − While their intrinsic properties with good stability and high reactivity make them useful in a range of industrial applications, their crystallographically well-defined structures with their high tunability have endowed them with great potential for being applied to fundamental studies in broad fields of chemistry, material science, and environmental science. − However, the limited porosity and surface area, − compared to the extensively studied crystalline materials [like metal–organic frameworks (MOFs) , or porous coordination polymers (PCPs), , covalent organic frameworks (COFs), , and hydrogen-bonded organic frameworks (HOFs)], , have prevented researchers from deeply investigating their sorption properties. So far, only a few papers have sought to study clusters’ sorption performance, among which the majority typically only apply N 2 sorption isotherms under liquid nitrogen temperature to confirm their robust and permanently porous nature. ,, Beyond porosity studies, Zheng’s group studied the CO 2 sorption and CO 2 /CH 4 separation performance with a series of high-nuclearity heterometallic Ni 64 Re 96 clusters, which present high selectivity of CO 2 /CH 4 .…”