Zr-Porphyrin Metal–Organic Framework as nanoreactor for boosting the formation of hydrogen clathrates

We report the first experimental evidence for rapid formation of hydrogen clathrates under mild pressure and temperature conditions within the cavities of a zirconium-metalloporphyrin framework, specifically PCN-222. PCN-222 has been selected for its 1D mesoporous channels, high water-stability, and proper hydrophilic behavior. Firstly, we optimize a microwave (MW)-assisted method for the synthesis of nanosized PCN-222 particles with precise structure control (exceptional homogeneity in morphology and crystalline phase purity), taking advantage of MW in terms of rapid/homogeneous heating, time and energy savings, as well as potential scalability of the synthetic method. Second, we explore the relevance of the large mesoporous 1D open channels within the PCN-222 to promote the nucleation and growth of confined hydrogen clathrates. Experimental results show that PCN-222 drives the nucleation process at a lower pressure than the bulk system (1.35 kbar vs 2 kbar), with fast kinetics (minutes), using pure water, and with a nearly complete water-to-hydrate conversion. Unfortunately, PCN-222 cannot withstand these high pressures, which lead to a significant alteration of the mesoporous structure while the microporous network remains mainly unchanged.Authors would like to acknowledge financial support from Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21 and PID2022-141034OB-C22), Consejo Superior de Investigaciones Científicas (CSIC) for internal funds (Intramural project, 202280I170), and Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital (Project CIPROM/2021/022). A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory (project IPTS-29742.1)

Freezing/melting of water in the confined nanospace of carbon materials: Effect of an external stimulus

Freezing/melting behavior of water confined in the nanopores of activated carbon materials has been evaluated using differential scanning calorimetry (DSC) at different water loadings, and after the application of an external stimulus. Under atmospheric pressure conditions, the DSC scans show a depression in the freezing/melting point of confined water compared to the bulk system. Interestingly, water confined in narrow micropores (pores below 0.7 nm) does not exhibit any phase transition, i.e. it is non-freezable water. Inelastic neutron scattering (INS) data confirm the presence of a distorted molecular assembly in narrow micropores, whereas synchrotron X-ray powder diffraction data (SXRPD) demonstrate the non-freezable nature of the water confined in these narrow-constrictions. Similar experiments under high-pressure CH4 give rise to a completely different scenario. Under high-pressure conditions methane hydrates are formed with a water-to-hydrate yield of 100% for the under-saturated and saturated samples, i.e. in the presence of an external stimulus even water in narrow micropores is prone to experience a liquid-to-solid phase transition. These results confirm the beneficial role of carbon as a host structure to promote nucleation and growth of methane hydrates with faster kinetics and a higher yield compared to the bulk system and to other porous materials.The authors would like to acknowledge financial support from the MINECO (MAT2016-80285-p), Generalitat Valenciana (PROMETEOII/2014/004), H2020 (MSCA-RISE-2016/NanoMed Project), Spanish ALBA synchrotron (Projects 2018022707 & 2019023322) and Oak Ridge beam time availability (Project IPTS-20843.1)

Gate-opening effect in ZIF-8: the first experimental proof using inelastic neutron scattering

The gate-opening phenomenon in ZIFs is of paramount importance to understand their behavior in industrial molecular separations. Here we show for the first time using in situ inelastic neutron scattering (INS) the swinging of the –CH3 groups and the imidazolate linkers in the prototypical ZIF-8 and ZIF-8@AC hybrid materials upon exposure to mild N2 pressure.The authors acknowledge financial support from MINECO projects: MAT2013-45008-p and CONCERT Project-NASEMS (PCIN-2013-057). EVRF gratefully acknowledge support from MINECO (Spain) for his Ramón y Cajal grant (RyC-2012-11427). DFJ thanks the Royal Society (UK) for funding through a University Research Fellowship and Dr Axel Zeitler for interesting discussions. This research benefited from the use of the VISION beamline (IPTS-13608) at ONRL’s Spallation Neutron Source and the VirtuES (Virtual Experiments in Spectroscopy) project, (LDRD 7739), which are supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC

New insights into the breathing phenomenon in ZIF-4

Structural changes in ZIFs upon adsorption remain a paradigm due to the sensitivity of the adsorption mechanism to the nature of the organic ligands and gas probe molecules. Synchrotron X-ray diffraction under operando conditions clearly demonstrates for the first time that ZIF-4 exhibits a structural reorientation from a narrow-pore (np) to a new expanded-pore (ep) structure upon N2 adsorption, while it does not do so for CO2 adsorption. The existence of an expanded-pore structure of ZIF-4 has also been predicted by molecular simulations. In simulations the expanded structure was stabilized by entropy at high temperatures and by strong adsorption of N2 at low temperatures. These results are in perfect agreement with manometric adsorption measurements for N2 at 77 K that show the threshold pressure for breathing at ∼30 kPa. Inelastic neutron scattering (INS) measurements show that CO2 is also able to promote structural changes but, in this specific case, only at cryogenic temperatures (5 K).The authors would like to acknowledge financial support from the MINECO (MAT2016-80285-p), Generalitat Valenciana (PROMETEOII/2014/004), H2020 (MSCA-RISE-2016/NanoMed Project), Spanish ALBA synchrotron (Projects AV-2017021985 and IH-2018012591) and Oak Ridge beam time availability (Project IPTS-20843.1). JSA and JGL acknowledge financial support from UA (ACIE17-15) to cover all the expenses for INS measurements at Oak Ridge. JGL acknowledges GV (GRISOLIAP/2016/089) for the research contract

Rapid and efficient hydrogen clathrate hydrate formation in confined nanospace

Clathrate hydrates are crystalline solids characterized by their ability to accommodate large quantities of guest molecules. Although CH4 and CO2 are the traditional guests found in natural systems, incorporating smaller molecules (e.g., H2) is challenging due to the need to apply higher pressures to stabilize the hydrogen-bonded network. Another critical limitation of hydrates is the slow nucleation and growth kinetics. Here, we show that specially designed activated carbon materials can surpass these obstacles by acting as nanoreactors promoting the nucleation and growth of H2 hydrates. The confinement effects in the inner cavities promote the massive growth of hydrogen hydrates at moderate temperatures, using pure water, with extremely fast kinetics and much lower pressures than the bulk system.We would like to acknowledge financial support from Ministerio de Ciencia e Innovación (Project PID2019-108453GB-C21), MCIN/AEI/10.13039/501100011033 and EU “NextGeneration/PRTR” (Project PCI2020-111968 /3D-Photocat) – JSA. Neutron scattering experiments were performed at ORNL’s Spallation Neutron Source, IPTS-27062, supported by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC0500OR22725 with UT Battelle, LLC—J.S.A., Y.Q.C., L.D., A.J.R.C.. We gratefully acknowledge research support from the Hydrogen Materials—Advanced Research Consortium (HyMARC), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technology Office, under Contract Number DE-AC05-00OR22725—R.B.-X. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan)

Thermal expansion and decomposition of jarosite: a high-temperature neutron diffraction study

The structure of deuterated jarosite, KFe{sub 3}(SO{sub 4}){sub 2}(OD){sub 6}, was investigated using time-of-flight neutron diffraction up to its dehydroxylation temperature. Rietveld analysis reveals that with increasing temperature, its c dimension expands at a rate {approx}10 times greater than that for a. This anisotropy of thermal expansion is due to rapid increase in the thickness of the (001) sheet of [Fe(O,OH){sub 6}] octahedra and [SO{sub 4}] tetrahedra with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, a = a{sub 0} + a{sub 1} T, where a{sub 0} = 1.01 x 10{sup -4} K{sup -1} and a{sub 1} = -1.15 x 10{sup -7} K{sup -2}. On heating, the hydrogen bonds, O1{hor_ellipsis}D-O3, through which the (001) octahedral-tetrahedral sheets are held together, become weakened, as reflected by an increase in the D{hor_ellipsis}O1 distance and a concomitant decrease in the O3-D distance with increasing temperature. On further heating to 575 K, jarosite starts to decompose into nanocrystalline yavapaiite and hematite (as well as water vapor), a direct result of the breaking of the hydrogen bonds that hold the jarosite structure together

Thermal Expansion in 3d-Metal Prussian Blue Analogs - A Survey Study

We present a comprehensive study of the structural properties and the thermal expansion behavior of 17 different Prussian Blue Analogs (PBAs) with compositions MII3[(M')III(CN)6]2.nH2O and MII2[FeII(CN)6].nH2O, where MII = Mn, Fe, Co, Ni, Cu and Zn, (M')III = Co, Fe and n is the number of water molecules, which range from 5 to 18 for these compounds. The PBAs were synthesized via standard chemical precipitation methods, and temperature-dependent X-ray diffraction studies were performed in the temperature range between -150oC (123 K) and room-temperature. The vast majority of the studied PBAs were found to crystallize in cubic structures of space groups, and . The temperature dependence of the lattice parameters was taken to compute an average coefficient of linear thermal expansion in the studied temperature range. Of the 17 compounds, 9 display negative values for the average coefficient of linear thermal expansion, which can be as large as 39.7 x 10-6 K-1 for Co3[Co(CN)6]2.12H2O. All of the MII3[CoIII(CN)6]2.nH2O compounds show negative thermal expansion behavior, which correlates with the Irving-Williams series for metal complex stability. The thermal expansion behavior for the PBAs of the MII3[FeIII(CN)6]2.nH2O family are found to switch between positive (for M = Mn, Co, Ni) and negative (M = Cu, Zn) behavior, depending on the choice of the metal cation (M). On the other hand, all of the MII2[FeII(CN)6].nH2O compounds show positive thermal expansion behavior.Comment: Submitted, 32 pages, 3 tables, 10 figure

Alternative view of oxygen reduction on porous carbon electrocatalysts: the substance of complex oxygen-surface interactions

Electrochemical oxygen reduction reaction (ORR) is an important energy-related process requiring alternative catalysts to expensive platinum-based ones. Although recently some advancements in carbon catalysts have been reported, there is still a lack of understanding which surface features might enhance their efficiency for ORR. Through a detailed study of oxygen adsorption on carbon molecular sieves and using inelastic neutron scattering, we demonstrated here that the extent of oxygen adsorption/interactions with surface is an important parameter affecting ORR. It was found that both the strength of O2 physical adsorption in small pores and its specific interactions with surface ether functionalities in the proximity of pores positively influence the ORR efficiency. We have shown that ultramicropores and hydrophobic surface rich in ether-based groups and/or electrons enhance ORR on carbon electrocatalysts and the performance parameters are similar to those measured on Pt/C with the number of electron transfer equal to 4

Spin excitations in metallic kagome lattice FeSn and CoSn

In two-dimensional (2D) metallic kagome lattice materials, destructive interference of electronic hopping pathways around the kagome bracket can produce nearly localized electrons, and thus electronic bands that are flat in momentum space. When ferromagnetic order breaks the degeneracy of the electronic bands and splits them into the spin-up majority and spin-down minority electronic bands, quasiparticle excitations between the spin-up and spin-down flat bands should form a narrow localized spin-excitation Stoner continuum coexisting with well-defined spin waves in the long wavelengths. Here we report inelastic neutron scattering studies of spin excitations in 2D metallic Kagome lattice antiferromagnetic FeSn and paramagnetic CoSn, where angle resolved photoemission spectroscopy experiments found spin-polarized and nonpolarized flat bands, respectively, below the Fermi level. Although our initial measurements on FeSn indeed reveal well-defined spin waves extending well above 140 meV coexisting with a flat excitation at 170 meV, subsequent experiments on CoSn indicate that the flat mode actually arises mostly from hydrocarbon scattering of the CYTOP-M commonly used to glue the samples to aluminum holder. Therefore, our results established the evolution of spin excitations in FeSn and CoSn, and identified an anomalous flat mode that has been overlooked by the neutron scattering community for the past 20 years