Stability and Degradation of Metal–Organic-Framework Films under Ambient Air Explored by Uptake and Diffusion Experiments

The loading with guest molecules is the key feature for most applications of metal–organic frameworks (MOFs). The limited stability of MOFs against environmental factors, like humid air, is often a severe problem which hinders real-life applications. Here, the stability of four common MOFs, UiO-66, UiO-67, HKUST-1, and ZIF-8, under long-term exposure to humid air and under exposure to water vapor is explored. Transient uptake experiments with toluene and other volatile organic compounds as probe molecules are combined with structural investigations via X-ray diffraction and infrared spectroscopy. In line with previous publications showing the structural stability of ZIF-8 and UiO-66, it is found that its uptake properties are not affected by exposure to air. On the other hand, HKUST-1 shows clear structural decomposition in air and degradation of the uptake properties. Unexpectedly, while the diffraction and spectroscopy data of UiO-67 do not suggest a corrosion of the structure upon air exposure, the guest-loading data show a strong decrease of the uptake amount and a deceleration of the uptake rate. Both features strongly indicate the formation of surface barriers for the mass transfer in UiO-67, like in HKUST-1. The study underlines the importance of transient uptake experiments for characterizing the stability of MOF materials

Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Structure Analysis and 3D Reconstruction

The first example of layer‐by‐layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF‐8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two‐in‐one synthesis and TEM sample‐preparation technique and allows straightforward analysis of ZIF‐8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF‐8 by integrating a corresponding step into the layer‐by‐layer deposition process is examined. The formation of ZIF‐8 crystals on the film proceeds as under the absence of nanoparticle‐forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF‐8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques

Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Insights into the Growth Process

Metal-organic frameworks (MOFs) have received increased attention in recent years due to their exceptional properties and versatility. MOFs consist of metal nodes connected by organic linkers. Particularly interesting are surface-anchored films (SURMOFs), which are grown on bulk substrates. Transmission electron microscopy (TEM) is a key technique for the analysis of the structural and chemical properties of SURMOFs on the nanoscale. For TEM sample preparation, however, the SURMOF film must be detached from the bulk substrate and transferred to an electron-transparent support. This detachment process is a severe source of damage for the SURMOF film. The preparation of SURMOFs for TEM studies is thus an obstacle that has not yet been solved satisfactorily

Metal-Organic Framework MIL-68(In)-NH2_{2} on the Membrane Test Bench for Dye Removal and Carbon Capture

The metal-organic framework (MOF) MIL-68(In)-NH$_{2}$ was tested for dye removal from wastewater and carbon capture gas separation. MIL-68(In)-NH$_{2}$ was synthesized as a neat, supported MOF thin film membrane and as spherical particles using pyridine as a modulator to shape the morphology. The neat MIL-68(In)-NH$_{2}$ membranes were employed for dye removal in cross-flow geometry, demonstrating strong molecular sieving. MIL-68(In)-NH$_{2}$ particles were used for electrospinning of poylethersulfone mixed-matrix membranes, applied in dead-end filtration with unprecedented adsorption values. Additionally, the neat MOF membranes were used for H$_{2}$/CO$_{2}$ and CO$_{2}$/CH$_{4}$ separation

Non-standard neutrino interactions in IceCube

Non-standard neutrino interactions (NSI) may arise in various types of new physics. Their existence would change the potential that atmospheric neutrinos encounter when traversing Earth matter and hence alter their oscillation behavior. This imprint on coherent neutrino forward scattering can be probed using high-statistics neutrino experiments such as IceCube and its low-energy extension, DeepCore. Both provide extensive data samples that include all neutrino flavors, with oscillation baselines between tens of kilometers and the diameter of the Earth. DeepCore event energies reach from a few GeV up to the order of 100 GeV - which marks the lower threshold for higher energy IceCube atmospheric samples, ranging up to 10 TeV. In DeepCore data, the large sample size and energy range allow us to consider not only flavor-violating and flavor-nonuniversal NSI in the μ−τ sector, but also those involving electron flavor. The effective parameterization used in our analyses is independent of the underlying model and the new physics mass scale. In this way, competitive limits on several NSI parameters have been set in the past. The 8 years of data available now result in significantly improved sensitivities. This improvement stems not only from the increase in statistics but also from substantial improvement in the treatment of systematic uncertainties, background rejection and event reconstruction

In situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory

The IceCube Neutrino Observatory instruments about 1 km3 of deep, glacial ice at the geographic South Pole. It uses 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. An unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. We examine birefringent light propagation through the polycrystalline ice microstructure as a possible explanation for this effect. The predictions of a first-principles model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties include not only the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube light-emitting diode (LED) calibration data, the theory and parameterization of the birefringence effect, the fitting procedures of these parameterizations to experimental data, and the inferred crystal properties.Peer Reviewe

In-situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory

The IceCube Neutrino Observatory instruments about 1 km3 of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. A unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. Birefringent light propagation has been examined as a possible explanation for this effect. The predictions of a first-principles birefringence model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties do not only include the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube LED calibration data, the theory and parametrization of the birefringence effect, the fitting procedures of these parameterizations to experimental data as well as the inferred crystal properties.</p

Mechanical design of the optical modules intended for IceCube-Gen2

IceCube-Gen2 is an expansion of the IceCube neutrino observatory at the South Pole that aims to increase the sensitivity to high-energy neutrinos by an order of magnitude. To this end, about 10,000 new optical modules will be installed, instrumenting a fiducial volume of about 8 km3. Two newly developed optical module types increase IceCube’s current sensitivity per module by a factor of three by integrating 16 and 18 newly developed four-inch PMTs in specially designed 12.5-inch diameter pressure vessels. Both designs use conical silicone gel pads to optically couple the PMTs to the pressure vessel to increase photon collection efficiency. The outside portion of gel pads are pre-cast onto each PMT prior to integration, while the interiors are filled and cast after the PMT assemblies are installed in the pressure vessel via a pushing mechanism. This paper presents both the mechanical design, as well as the performance of prototype modules at high pressure (70 MPa) and low temperature (−40∘C), characteristic of the environment inside the South Pole ice

Direction reconstruction performance for IceCube-Gen2 Radio

The IceCube-Gen2 facility will extend the energy range of IceCube to ultra-high energies. The key component to detect neutrinos with energies above 10 PeV is a large array of in-ice radio detectors. In previous work, direction reconstruction algorithms using the forward-folding technique have been developed for both shallow (≲20 m) and deep in-ice detectors, and have also been successfully used to reconstruct cosmic rays with ARIANNA. Here, we focus on the reconstruction algorithm for the deep in-ice detector, which was recently introduced in the context of the Radio Neutrino Observatory in Greenland (RNO-G)

The next generation neutrino telescope: IceCube-Gen2

The IceCube Neutrino Observatory, a cubic-kilometer-scale neutrino detector at the geographic South Pole, has reached a number of milestones in the field of neutrino astrophysics: the discovery of a high-energy astrophysical neutrino flux, the temporal and directional correlation of neutrinos with a flaring blazar, and a steady emission of neutrinos from the direction of an active galaxy of a Seyfert II type and the Milky Way. The next generation neutrino telescope, IceCube-Gen2, currently under development, will consist of three essential components: an array of about 10,000 optical sensors, embedded within approximately 8 cubic kilometers of ice, for detecting neutrinos with energies of TeV and above, with a sensitivity five times greater than that of IceCube; a surface array with scintillation panels and radio antennas targeting air showers; and buried radio antennas distributed over an area of more than 400 square kilometers to significantly enhance the sensitivity of detecting neutrino sources beyond EeV. This contribution describes the design and status of IceCube-Gen2 and discusses the expected sensitivity from the simulations of the optical, surface, and radio components