SI methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading

Confinement of water and methane in mesopores of hydrophobized SBA-15 is demonstrated to promote methane hydrate formation. In comparison to as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics of methane storage in and delivery from the hydrate. C8 grafting density was determined at 0.5 groups nm-2 based on TGA and quantitative NMR spectroscopy. Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close spatial proximity between the grafted C8 chains and pore-intruded water species. X-ray diffraction demonstrates formation of Structure I hydrate on SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on hydrophobized SBA-15 C8 reaches 96 pct. as compared to only 71 pct. on a pristine SBA-15 sample with comparable pore size, pore volume and surface area. The clathrate loading amounted to 14.8 g g-1. 2D correlation NMR spectroscopy (1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of SBA-15 C8 as well as in interparticle volumes. Following the initial crystallization of SBA-15 C8-supported methane hydrate taking several hours, a pressure swing process at 248 K allows to desorb and re-adsorb methane from the structure within minutes and without thawing the frozen water structure. Fast loading and unloading of methane was achieved in 19 subsequent cycles without losses in kinetics. The ability to harvest the gas and regenerate the structure without the need to re-freeze the water represents a 50 pct. energy gain with respect to melting and subsequently recrystallizing the hydrate at 298 K and 248 K, respectively. After methane desorption, a small amount of residual methane hydrate in combination with an amorphous yet locally ordered ice phase is observed using 13C and 2H NMR spectroscopy

Water as a tuneable solvent: a perspective

Water is the sustainable solvent of excellence, but its high polarity limits the solubility of non-polar compounds. Confinement of water in hydrophobic pores alters its hydrogen bonding structure and related properties such as dielectric constant and solvation power. Whether this special state of confined water can be rendered useful in chemical processes is hitherto underexplored. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties, enabling the use of water as a tuneable solvent (WaTuSo). Applying pressure forces a heterogeneous mixture of poorly soluble molecules and water into hydrophobic nanopores of a host material where the lowered polarity of water enhances dissolution. Decompression after reaction causes expulsion of the solution from the pores and spontaneous demixing of reaction products because water returns to its normal polar state. Temporary dissolution enhancement during confinement is expected to be advantageous to chemical reaction and molecular storage. Nano-confined water offers a potential alternative to compression for storing CH$_4$ and H$_2$ gas, and opens new opportunities for green chemistry such as aqueous phase hydrogenation reactions which benefit from enhanced hydrogen solubility. Unprecedented control in time and space over H$_2$O solvation properties in a WaTuSo system will enable new technologies with major scientific and societal impact

Water as a tuneable solvent: a perspective.

Water is the sustainable solvent of excellence, but its high polarity limits the solubility of non-polar compounds. Confinement of water in hydrophobic pores alters its hydrogen bonding structure and related properties such as dielectric constant and solvation power. Whether this special state of confined water can be rendered useful in chemical processes is hitherto underexplored. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties, enabling the use of water as a tuneable solvent (WaTuSo). Applying pressure forces a heterogeneous mixture of poorly soluble molecules and water into hydrophobic nanopores of a host material where the lowered polarity of water enhances dissolution. Decompression after reaction causes expulsion of the solution from the pores and spontaneous demixing of reaction products because water returns to its normal polar state. Temporary dissolution enhancement during confinement is expected to be advantageous to chemical reaction and molecular storage. Nano-confined water offers a potential alternative to compression for storing CH4 and H2 gas, and opens new opportunities for green chemistry such as aqueous phase hydrogenation reactions which benefit from enhanced hydrogen solubility. Unprecedented control in time and space over H2O solvation properties in a WaTuSo system will enable new technologies with major scientific and societal impact.status: publishe

Absolute quantification of water in microporous solids with (1)H MAS NMR and standard addition

Zeolites are microporous materials driving industrial scale adsorption, ion exchange and catalytic processes. Their water content dramatically impacts their properties, but its quantification with Karl Fisher titration or thermal gravimetric analysis is problematic. Combining standard addition of water with 1H MAS NMR detection, absolute quantification of water in microporous materials becomes possible. The method was demonstrated on 5 different, commercially available zeolites.status: publishe

Does Water Enable Porosity in Aluminosilicate Zeolites? Porous Frameworks versus Dense Minerals

International audienc

Interfacial study of clathrates confined in reversed silica pores

Storing methane in clathrates is one of the most promising alternatives for transporting natural gas (NG) as it offers similar gas densities to liquefied and compressed NG while offering lower safety risks. However, the practical use of clathrates is limited given the extremely low temperatures and high pressures necessary to form these structures. Therefore, it has been suggested to confine clathrates in nanoporous materials, as this can facilitate clathrate's formation conditions while preserving its CH4 volumetric storage. Yet, the choice of nanoporous materials to be employed as the clathrate growing platform is still rather arbitrary. Herein, we tackle this challenge in a systematic way by computationally exploring the stability of clathrates confined in alkyl-grafted silica materials with different pore sizes, ligand densities and ligand types. Based on our findings, we are able to propose key design criteria for nanoporous materials favoring the stability of a neighbouring clathrate phase, namely large pore sizes, high ligand densities, and smooth pore walls. We hope that the atomistic insight provided in this work will guide and facilitate the development of new nanomaterials designed to promote the formation of clathrates

Atomic Force Microscopy: A tool to study zeolite growth

status: accepte

Magneto-Hydrodynamic Mixing: a New Technique for Preparing Carbomer Hydrogels

Magnetohydrodynamic mixing was evaluated as an alternative to conventional high shear mixing in the preparation of carbomer hydrogels containing 1.22 wt.% Carbopol® 980 NF. Neutralization of the carbomer dispersion (pH = 2.74) with triethanolamine (TEA) enabled to adjust the pH of the mixture and tune the viscosity of the hydrogel. Using high shear mixing, this approach was limited to 0.2 wt.% TEA (pH = 3.83) as the gel became too viscous and the recirculation flow dropped from 12 to 0.3 m3/h. Magnetohydrodynamic mixing enabled to reach TEA concentrations up to 1.0 wt.% (pH = 5.31). Apparent viscosity measurements on samples having 0.2 wt.% TEA revealed lower viscosities for carbomer hydrogels prepared with high shear mixing, i.e. 6,800 mPa·s versus 8,800 mPa for magneto-hydrodynamic mixing. Based on 1H NMR evidence, this decrease in apparent viscosity was attributed to structural damage to the carbomer backbone in combination with mechanochemical degradation of the added TEA

Engineering of hollow periodic mesoporous organosilica nanorods for augmented hydrogen clathrate formation

Abstract: Hydrogen (H2) storage, in the form of clathrate hydrates, has emerged as an attractive alternative to classical storage methods like compression or liquefaction. Nevertheless, the sluggish enclathration kinetics along with low gas storage capacities in bulk systems is currently impeding the progress of this technology. To this end, unstirred systems coupled with porous materials have been shown to tackle the aforementioned drawbacks. In line with this approach, the present study explores the use of hydrophobic periodic organosilica nanoparticles, later denoted as hollow ring-PMO (HRPMO), for H2 storage as clathrate hydrates under mild operating conditions (5.56 mol% THF, 7 MPa, and 265\u2013273 K). The surface of the HRPMO nanoparticles was carefully decorated/functionalized with THF-like moieties, which are well-known promoter agents in clathrate formation when applied in classical, homogeneous systems. The study showed that, while the non-functionalized HRPMO can facilitate the formation of binary H2-THF clathrates, the incorporation of surface-bound promotor structures enhances this process. More intriguingly, tuning the concentration of these surface-bound promotor agents on the HRPMO led to a notable effect on solid-state H2 storage capacities. An increase of 3% in H2 storage capacity, equivalent to 0.26 wt%, along with a substantial increase of up to 28% in clathrate growth kinetics, was observed when an optimal loading of 0.14 mmol g 121 of promoter agent was integrated into the HRPMO framework. Overall, the findings from this study highlight that such tuning effects in the solid-state have the potential to significantly boost hydrate formation/growth kinetics and H2 storage capacities, thereby opening new avenues for the ongoing development of H2 clathrates in industrial applications

Growth of MER-type zeolite from hydrated silicate ionic liquids

status: accepte