Search

Air pollution by SO2 and NO2 has caused significant risks on the environment and human health. Understanding the mechanism of active sites within capture materials is of fundamental importance to the development of new clean-up technologies. Here we report the crystallographic observation of reversible coordinative binding of SO2 and NO2 on open NiII sites in a metal-organic framework (NKU-100) incorporating unprecedented {Ni12 }-wheels; each wheel exhibits six open NiII sites on desolvation. Immobilised gas molecules are further stabilised by cooperative host-guest interactions comprised of hydrogen bonds, π⋅⋅⋅π interactions and dipole interactions. At 298 K and 1.0 bar, NKU-100 shows adsorption uptakes of 6.21 and 5.80 mmol g-1 for SO2 and NO2 , respectively. Dynamic breakthrough experiments have confirmed the selective retention of SO2 and NO2 at low concentrations under dry conditions. This work will inspire the future design of efficient sorbents for the capture of SO2 and NO2 .

Ammonia (NH3) is a promising energy resource owing to its high hydrogen density. However, its widespread application is restricted by the lack of efficient and corrosion-resistant storage materials. Here, we report high NH3 adsorption in a series of robust metal-organic framework (MOF) materials, MFM-300(M) (M = Fe, V, Cr, In). MFM-300(M) (M = Fe, VIII, Cr) show fully reversible capacity for >20 cycles, reaching capacities of 16.1, 15.6, and 14.0 mmol g-1, respectively, at 273 K and 1 bar. Under the same conditions, MFM-300(VIV) exhibits the highest uptake among this series of MOFs of 17.3 mmol g-1. In situ neutron powder diffraction, single-crystal X-ray diffraction, and electron paramagnetic resonance spectroscopy confirm that the redox-active V center enables host-guest charge transfer, with VIV being reduced to VIII and NH3 being oxidized to hydrazine (N2H4). A combination of in situ inelastic neutron scattering and DFT modeling has revealed the binding dynamics of adsorbed NH3 within these MOFs to afford a comprehensive insight into the application of MOF materials to the adsorption and conversion of NH3.

Structural transitions of host systems in response to guest binding dominate many chemical processes. We report an unprecedented type of structural flexibility within a meta-rigid material, MFM-520, which exhibits a reversible periodic-to-aperiodic structural transition resulting from a drastic distortion of a [ZnO4N] node controlled by the specific host-guest interactions. The aperiodic crystal structure of MFM-520 has no three-dimensional (3D) lattice periodicity but shows translational symmetry in higher-dimensional (3 + 2)D space. We have directly visualized the aperiodic state which is induced by incommensurate modulation of the periodic framework of MFM-520·H2O upon dehydration to give MFM-520. Filling MFM-520 with CO2 and SO2 reveals that, while CO2 has a minimal structural influence, SO2 can further modulate the structure incommensurately. MFM-520 shows exceptional selectivity for SO2 under flue-gas desulfurization conditions, and the facile release of captured SO2 from MFM-520 enabled the conversion to valuable sulfonamide products. MFM-520 can thus be used as a highly efficient capture and delivery system for SO2.

Emissions of SO2 from flue gas and marine transport have detrimental impacts on the environment and human health, but SO2 is also an important industrial feedstock if it can be recovered, stored and transported efficiently. Here we report the exceptional adsorption and separation of SO2 in a porous material, [Cu2(L)] (H4L = 4',4‴-(pyridine-3,5-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid)), MFM-170. MFM-170 exhibits fully reversible SO2 uptake of 17.5 mmol g-1 at 298 K and 1.0 bar, and the SO2 binding domains for trapped molecules within MFM-170 have been determined. We report the reversible coordination of SO2 to open Cu(II) sites, which contributes to excellent adsorption thermodynamics and selectivities for SO2 binding and facile regeneration of MFM-170 after desorption. MFM-170 is stable to water, acid and base and shows great promise for the dynamic separation of SO2 from simulated flue gas mixtures, as confirmed by breakthrough experiments.

Hydrogen bonds dominate many chemical and biological processes, and chemical modification enables control and modulation of host-guest systems. Here we report a targeted modification of hydrogen bonding and its effect on guest binding in redox-active materials. MFM-300(VIII) {[VIII2(OH)2(L)], LH4=biphenyl-3,3',5,5'-tetracarboxylic acid} can be oxidized to isostructural MFM-300(VIV), [VIV2O2(L)], in which deprotonation of the bridging hydroxyl groups occurs. MFM-300(VIII) shows the second highest CO2 uptake capacity in metal-organic framework materials at 298 K and 1 bar (6.0 mmol g-1) and involves hydrogen bonding between the OH group of the host and the O-donor of CO2, which binds in an end-on manner, =1.863(1) Å. In contrast, CO2-loaded MFM-300(VIV) shows CO2 bound side-on to the oxy group and sandwiched between two phenyl groups involving a unique ···c.g.phenyl interaction [3.069(2), 3.146(3) Å]. The macroscopic packing of CO2 in the pores is directly influenced by these primary binding sites.

We report the high NH3 uptake in a series of copper-carboxylate materials, namely MFM-100, MFM-101, MFM-102, MFM-126, MFM-127, MFM-190(F), MFM-170, and Cu-MOP-1a. At 273 K and 1 bar, MFM-101 shows an exceptional uptake of 21.9 mmol g−1. The presence of Cu(II)⋯NH3 interactions and changes in coordination at the [Cu2(O2CR)4] paddlewheel are analysed and discussed. [ABSTRACT FROM AUTHOR]

We report the high adsorption of NH3 in a titanium-based metal–organic framework, MFM-300(Ti), comprising extended [TiO6] ∞ chains linked by biphenyl-3,3′,5,5′ -tetracarboxylate ligands. At 273 K and 1 bar, MFM300(Ti) shows an exceptional NH3 uptake of 23.4 mmol g-1 with a record-high packing density of 0.84 g cm-3. Dynamic breakthrough experiments confirm the excellent uptake and separation of NH3 at low concentration (1000 ppm). The combination of in situ neutron powder diffraction and spectroscopic studies reveal strong, yet reversible binding interactions of NH3 to the framework oxygen sites. [ABSTRACT FROM AUTHOR]

Owing to their unique functionalities and tailorable properties that are unattainable in conventional materials, metal-organic frameworks (MOFs) have emerged as candidate materials for next-generation chemical sensors and optoelectronics. For instance, the ZnQ@OX-1 composite material, comprising a light-emitting guest encapsulated in the pores of the OX-1 framework, affords excellent sensing performance: a visible color change upon exposure to volatile acetone. In this work, a multimodal study on the exceptional vapochromism of this composite material using high-resolution spectroscopy techniques based on inelastic neutron scattering and synchrotron radiation is presented, supported by density functional theory calculations. While FTIR spectroscopy in the far-IR and mid-IR regions reveals the underlying interactions between ZnQ, OX-1, and acetone, the limit of detection at 50 ppm is determined through in situ gas dosing experiments using fluorescence spectroscopy. In addition, in situ gas dosing on the single crystal level is achieved with near-field infrared nanospectroscopy. [ABSTRACT FROM AUTHOR]