If dihydrogen (H2) becomes a major part of the energy mix, massive storage in underground gas storage (UGS), such as in deep aquifers, will be needed. The development of H2 requires a growing share of H2 in natural gas (and its current infrastructure), which is expected to reach approximately 2% in Europe. The impact of H2 in aquifers is uncertain, mainly because its behavior is site dependent. The main concern is the consequences of its consumption by autochthonous microorganisms, which, in addition to energy loss, could lead to reservoir souring and alter the petrological properties of the aquifer. In this work, the coinjection of 2% H2 in a natural gas blend in a low-salinity deep aquifer was simulated in a three-phase (aquifer rock, formation water, and natural gas/H2 mix) high-pressure reactor for 3 months with autochthonous microorganisms using a protocol described in a previous study. This protocol was improved by the addition of protocol coupling experimental measures and modeling to calculate the pH and redox potential of the reactor. Modeling was performed to better analyze the experimental data. As in previous experiments, sulfate reduction was the first reaction to occur, and sulfate was quickly consumed. Then, formate production, acetogenesis, and methanogenesis occurred. Overall, H2 consumption was mainly caused by methanogenesis. Contrary to previous experiments simulating H2 injection in aquifers of higher salinity using the same protocol, microbial H2 consumption remained limited, probably because of nutrient depletion. Although calcite dissolution and iron sulfide mineral precipitation likely occurred, no notable evolution of the rock phase was observed after the experiment. Overall, our results suggested that H2 can be stable in this aquifer after an initial loss. More generally, aquifers with low salinity and especially low electron acceptor availability should be favored for H2 costorage with natural gas.

Metal-organic frameworks (MOFs) are organic-inorganic hybrid solids constructed from the coordination interaction of metal ions/clusters with organic linkers, which currently represent one of the most rapidly expanding platforms for new functional materials. Based on well-established approaches, involving tuning the pore sizes, incorporation of functional sites and post-synthetic modification, the pore structures of MOFs can be readily controlled for multifunctional applications. In this brief review, we summarize and highlight our research progresses during our journey on developing functional MOFs for various applications including gas storage, gas separations, luminescent sensing, proton conduction, and molecular recognitions.

Gases are widely used as energy resources for industry and our daily life. Developing energy cost efficient porous materials for gas storage and separation is of fundamentally and industrially important, and is one of the most important aspects of energy chemistry and materials. Metal-organic frameworks (MOFs), representing a novel class of porous materials, feature unique pore structure, such as exceptional porosity, tunable pore structures, ready functionalization, which not only enables high density energy storage of clean fuel gas in MOF adsorbents, but also facilitates distinct host-guest interactions and/or sieving effects to differentiate different molecules for energy-efficient separation economy. In this review, we summarize and highlight the recent advances in the arena of gas storage and separation using MOFs as adsorbents, including progresses in MOF-based membranes for gas separation, which could afford broader concepts to the current status and challenges in this field.

Cost-effective and facile synthetic routes to organic ligands, along with porous materials that exhibit exceptional gas-storage properties, promise significant industrial applications. Here, a two-step synthesis of novel organophosphorus ligands without metal catalysts is reported. These ligands serve as versatile linkers for the construction of metal-organic frameworks (MOFs) incorporating various metal ions, including zinc and copper. One of the zinc-based MOFs demonstrates remarkable gas-storage properties, with a hydrogen (H2) capacity exceeding 2.5 wt% at 77 K and 100 kPa as well as a carbon dioxide (CO2) capacity exceeding 20 wt% at 298 K and 100 kPa. Furthermore, this zinc-based MOF can be synthesized through a solvothermal process on the gram scale that yields high-quality single crystals.

Due to their large surface area and pore volume, three-dimensional covalent organic frameworks (3D COFs) have emerged as competitive porous materials. However, structural dynamic behavior, often observed in imine-linked 3D COFs, could potentially unlock their potential application in gas storage. Herein, we showed how a pre-locked linker strategy introduces breaking dynamic behavior in 3D COFs. A predesigned planar linker-based 3,8-diamino-6-phenylphenanthridine (DPP) was prepared to produce non-dynamic 3D JUC-595, as the benzylideneamine moiety in DPP locked the linker flexibility and restricted the molecular bond rotation of the imine linkages. Upon solvent inclusion and release, the PXRD profile of JUC-595 remained intake, while JUC-594 with a flexible benzidine linker experienced crystal transformation due to framework contraction-expansion. As a result, the activated JUC-595 achieved higher surface areas (754 m2 g-1) than that of JUC-594 (548 m2 g-1). Furthermore, improved CO2 and CH4 storages were also seen in JUC-595 compared with JUC-594. Impressively, JUC-595 recorded a high normalized H2 storage capacity that surpassed other reported high-surface area 3D COFs. This works shows important insights on manipulating the structural properties of 3D COF to tune gas storage performance.

Dynamic 3D covalent organic frameworks (COFs) have shown concerted structural transformation and adaptive gas adsorption due to the conformational diversity of organic linkers. However, the isolation and observation of COF rotamers constitute undergoing challenges due to their comparable free energy and subtle rotational energy barrier. Here, we report the atomic-level observation and structural evolution of COF rotamers by cryo-3D electron diffraction and synchrotron powder X-ray diffraction. Specifically, we optimize the crystallinity and morphology of COF-320 to manifest its coherent dynamic responses upon adaptive inclusion of guest molecules. We observe a significant crystal expansion of 29 vol% upon hydration and a giant swelling with volume change up to 78 vol% upon solvation. We record the structural evolution from a non-porous contracted phase to two narrow-pore intermediate phases and the fully opened expanded phase using n-butane as a stabilizing probe at ambient conditions. We uncover the rotational freedom of biphenylene giving rise to significant conformational changes on the diimine motifs from synclinal to syn-periplanar and anticlinal rotamers. We illustrate the 10-fold increment of pore volumes and 100% enhancement of methane uptake capacity of COF-320 at 100 bar and 298 K. The present findings shed light on the design of smarter organic porous materials to maximize host-guest interaction and boost gas uptake capacity through progressive structural transformation.

A series of metal-organic frameworks (MOFs) based on zinc ions and two triptycene ligands of different size have been synthesized under solvothermal conditions. Structural analyses revealed that they are isostructural 3D-network MOFs. The high porosity and thermal stability of these MOFs can be attributed to the highly rigid triptycene-based ligands. Their BET specific surface areas depend on the size of the triptycene ligands. In contrast to these surface-area data, the H2 and CO2 adsorption of these MOFs is larger for MOFs with small pores. Consequently, we introduced functional groups to the bridge-head position of the triptycene ligands and investigated their effect on the gas-sorption properties. The results unveiled the role of the functional groups in the specific CO2 binding via an induced interaction between adsorbates and the functional groups. Excellent H2 and CO2 properties in these MOFs were achieved in the absence of open metal sites.

The carbon (C) balance of permafrost peatlands in autumn and winter, which affects the annual C budget estimation, has become a hotspot of studies on peatlands C cycle. This study combined the static chamber method, in situ soil profile measurements, and incubation experiments to investigate release and storage of C during autumn and early winter in a permafrost peatland in the Da Xing\'an Mountains, Northeast China. Our results showed that the peak values of CH4 fluxes (30 August 2016) lagged behind those of CO2 fluxes (24 July 2016). At the onset of soil freezing, CH4 fluxes slightly increased, while CO2 fluxes decreased. During soil freezing in autumn, gases were found to be mainly stored in the soil as dissolved CH4 and CO2 and dissolved C concentrations (CH4, CO2, and DOC (dissolved organic carbon)) increased with depth. DOC concentrations were closely related to dissolved C gases, implying that the stored dissolved C gases might be derived from DOC decomposition. The CO2: CH4 ratio decreased sharply from the freezing of the surface layer to the total freezing of the soil, indicating larger CH4 storage in totally frozen soil. The incubation experiments also showed larger CH4 storage in the frozen soils and the stored C gases could influence the assessment of C emissions during thawing. These findings have important implications for clarifying the gas storage of permafrost peatland in autumn and early winter. The results may also clarify the key link of C emissions between the growing season and the nongrowing season.

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m2 g-1) and micropore volume (0.014 cm3 g-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I2) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I2. As a result, TAPB-QOT COP shows the highest volumetric I2 uptake (i.e., the amount of I2 uptaken per volume unit) up to 331 g cm-3 coupled with a remarkably high reversibility (>80% after five cycles).

We have developed highly porous Cu-based metal-organic frameworks (MOFs) using carbazole-type linkers. The novel topological structure of these MOFs was revealed by single-crystal X-ray diffraction analysis. Molecular adsorption/desorption experiments indicated that these MOFs are flexible and change their structure upon adsorption/desorption of organic solvents and gas molecules. These MOFs exhibit unprecedented properties that allow controlling their flexibility by adding a functional group onto the central benzene ring of the organic ligand. For example, the introduction of electron-donating substituents increases the robustness of the resulting MOFs. These MOFs also exhibit flexibility-dependent differences in gas-adsorption and -separation performance. Thus, this study represents the first example of controlling the flexibility of MOFs with the same topological structure via the substituent effect of functional groups introduced into the organic ligand.