Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we ...incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.
A flexible, yet very stable metal–organic framework (DUT‐98, Zr6O4(OH)4(CPCDC)4(H2O)4, CPCDC=9‐(4‐carboxyphenyl)‐9H‐carbazole‐3,6‐dicarboxylate) was synthesized using a rational supermolecular ...building block approach based on molecular modelling of metal–organic chains and subsequent virtual interlinking into a 3D MOF. Structural characterization via synchrotron single‐crystal X‐ray diffraction (SCXRD) revealed the one‐dimensional pore architecture of DUT‐98, envisioned in silico. After supercritical solvent extraction, distinctive responses towards various gases stimulated reversible structural transformations, as detected using coupled synchrotron diffraction and physisorption techniques. DUT‐98 shows a surprisingly low water uptake but a high selectivity for pore opening towards specific gases and vapors (N2, CO2, n‐butane, alcohols) at characteristic pressure resulting in multiple steps in the adsorption isotherm and hysteretic behavior upon desorption.
Switchability meets stability: A flexible, yet very stable metal–organic framework (DUT‐98, Zr6O4(OH)4(CPCDC)4(H2O)4, CPCDC=9‐(4‐carboxyphenyl)‐9H‐carbazole‐3,6‐dicarboxylate) was synthesized using a rational supermolecular building block approach based on molecular modelling. DUT‐98 shows a surprisingly low water uptake but a high selectivity for pore opening towards specific gases and vapors.
Negative gas adsorption (NGA) in ordered mesoporous solids is associated with giant contractive structural transitions traversing through metastable states. Here, by systematically downsizing the ...crystal dimensions of a mesoporous MOF (DUT-49) from several micrometers to less than 200 nm, counterintuitive NGA phenomena are demonstrated to critically depend on the primary crystallite size. Adsorbing probe molecules, such as n-butane or nitrogen, gives insights into size-dependent activation barriers and thermodynamics associated with guest-induced network contraction. Below a critical crystal size, the nitrogen adsorption-induced breathing is completely suppressed as detected using parallelized synchrotron X-ray diffraction-adsorption instrumentation. In contrast, even the smallest particles show NGA in the presence of n-butane, however, associated with a significantly reduced pressure amplification. Consequently, the magnitude of NGA in terms of amount of gas expulsed and pressure amplification can be tuned, potentially paving the way towards innovative concepts for pressure amplification in micro- and macro-system engineering.
A high-flux beamline optimized for non-resonant X-ray emission spectroscopy (XES) in the tender X-ray energy range has been constructed at the BESSY II synchrotron source. The beamline utilizes a ...cryogenically cooled undulator that provides X-rays over the energy range 2.1 keV to 9.5 keV. This energy range provides access to XES and in the future X-ray absorption spectroscopy (XAS) studies of transition metals ranging from Ti to Cu (Kα, Kβ lines) and Zr to Ag (Lα, Lβ), as well as light elements including P, S, Cl, K and Ca (Kα, Kβ). The beamline can be operated in two modes. In PINK mode, a multilayer monochromator (E/ΔE ≃ 30-80) provides a high photon flux (10
photons s
at 6 keV and 300 mA ring current), allowing non-resonant XES measurements of dilute substances. This mode is currently available for general user operation. X-ray absorption near-edge structure and resonant XAS techniques will be available after the second stage of the PINK commissioning, when a high monochromatic mode (E/ΔE ≃ 10000-40000) will be facilitated by a double-crystal monochromator. At present, the beamline incorporates two von Hamos spectrometers, enabling time-resolved XES experiments with time scales down to 0.1 s and the possibility of two-color XES experiments. This paper describes the optical scheme of the PINK beamline and the endstation. The design of the two von Hamos dispersive spectrometers and sample environment are discussed here in detail. To illustrate, XES spectra of phosphorus complexes, KCl, TiO
and Co
O
measured using the PINK setup are presented.
We present a model free analysis of the structure of a microporous carbon (Kynol fiber cloth) with neutrons (SANS) and X-rays (SAXS). SANS with contrast matching is used to analyze the accessible ...pores. It is shown that the SAXS- and the SANS-intensities agree after correction of the SANS specific background. Moreover, we analyze the scattering contribution due to the finite size and the bending of the carbon sheets. This contribution that scales with q−2 at high q-values (q: magnitude of scattering vector) is subtracted and the remaining intensity that exhibits a q−4 final slope gives the specific inner surface (1090 m2/g) and the porosity (29%) with excellent precision. The spatial distribution of the pores is analyzed in terms of the chord length distribution g(r). This distribution has its maximum below 1 nm and a finite intercept g(0) that indicates pores with sharp edges. The analysis gives furthermore the number and weight-average chord length. Finally, a parameter characterizing the degree of disorder of the carbonaceous structure introduced by Ruland was determined. Its value (25%) indicates a rather disordered structure that is visualized in terms of a detailed model. The entire analysis shows the power of small-angle scattering for a detailed analysis of microporous structures.
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An isotope-selective responsive system based on molecular recognition in porous materials has potential for the storage and purification of isotopic mixtures but is considered unachievable because of ...the almost identical physicochemical properties of the isotopes. Herein, a unique isotope-responsive breathing transition of the flexible metal–organic framework (MOF), MIL-53(Al), which can selectively recognize and respond to only D2 molecules through a secondary breathing transition, is reported. This novel phenomenon is examined using in situ neutron diffraction experiments under the same conditions for H2 and D2 sorption experiments. This work can guide the development of a novel isotope-selective recognition system and provide opportunities to fabricate flexible MOF systems for energy-efficient purification of the isotopic mixture.
Switchable metal-organic frameworks (MOFs) have been proposed for various energy-related storage and separation applications, but the mechanistic understanding of adsorption-induced switching ...transitions is still at an early stage. Here we report critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure amplifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49). These criteria are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelised to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure amplifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD
) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.
The "gate opening" mechanism in the highly flexible MOF Ni2(2,6-ndc)2dabco (DUT-8(Ni), DUT = Dresden University of Technology) with unprecedented unit cell volume change was elucidated in detail ...using combined single crystal X-ray diffraction, in situ XRD and EXAFS techniques. The analysis of the crystal structures of closed pore (cp) and large pore (lp) phases reveals a drastic and unique unit cell volume expansion of up to 254%, caused by adsorption of gases, surpassing other gas-pressure switchable MOFs significantly. To a certain extent, the structural deformation is specific for the guest molecule triggering the transformation due to subtle differences in adsorption enthalpy, shape, and kinetic diameter of the guest. Combined adsorption and powder diffraction experiments using nitrogen (77 K), carbon dioxide (195 K), and n-butane (272.5 K) as a probe molecules reveal a one-step structural transformation from cp to lp. In contrast, adsorption of ethane (185 K) or ethylene (169 K) results in a two-step transformation with the formation of intermediate phases. In situ EXAFS during nitrogen adsorption was used for the first time to monitor the local coordination geometry of the metal atoms during the structural transformation in flexible MOFs revealing a unique local deformation of the nickel-based paddle-wheel node.
•In situ instrumentation for combined XRD and adsorption experiments was developed.•Set-up assure the precise temperature control needed for adsorption experiment.•CO2 and n-butane adsorption at 273K ...up to 1bar on ELM-11 was investigated.•For the first time the crystal structures of n-butane@ELM-11 at 273K is reported.
A new instrumentation for in situ X-ray powder diffraction allows to follow structural changes in the crystal structure of flexible coordination polymers during adsorption and desorption of gases. The system is based on closed cycle He-cryostat that ensures the high temperature stability in the range of 5.5–450K. The automated gas dosing system facilitates the physisorption measurements in the pressure range of 0.01–130kPa. The system is implemented on KMC-2 and MAGS beamlines at Helmholtz Zentrum Berlin für Materialien und Energie. Using new instrumentation, the adsorption of CO2 and n-butane at 273K on a flexible two-dimensional coordination polymer ELM-11 (ELM – Elastic Layer Material) was investigated.
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