Accessible Porosity Research Articles

Use of Milled Acanthocardia tuberculate Seashell as Fine Aggregate in Self-Compacting Mortars.

This study focuses on the feasibility of using ground Acanthocardia tuberculate seashells as fine aggregates for self-compacting mortar production. The obtained results show a promising future for coastal industries as their use eliminates waste products and improves the durability of these materials. The use of Acanthocardia tuberculate recycled aggregate, in terms of durability, improves the performance of all mixes made with seashells compared to those made with natural sand, although it decreases workability and slightly reduces mechanical strength. Proper mix design has beneficial effects, as it improves compressive strength, especially when the powder/sand ratio is 0.7. Three replacement ratios based on the volume (0%, 50%, and 100%) of natural limestone sand with recycled fine aggregate from Acanthocardia tuberculate seashells, and three different dosages modifying the powder/sand ratio (0.6, 0.7, and 0.8), were tested. The fresh-state properties of each self-compacting mixture were evaluated based on workability. The mineralogical phases of the hardened mixtures were characterised using X-ray diffraction, thermogravimetry, and differential analyses. Subsequently, the mechanical and durability properties were evaluated based on the compressive and flexural strengths, dry bulk density, accessible porosity for water and water absorption, drying shrinkage, mercury intrusion porosimetry, and water absorption by capillarity. Therefore, the use of Acanthocardia tuberculate seashells in cement-based systems contributes to circular economy.

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism.

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

3D in situ observation of the capillary infiltration of molten silicon in a SiC/SiC composite by X-ray tomography

The Liquid Silicon Infiltration (LSI) process is used to decrease residual porosity of SiC/SiC composite materials. However, it is not fully mastered since the mechanisms involved at 1500 °C under high vacuum are complex to analyze, especially without direct observation. Previous work had demonstrated the feasibility of using X-ray radiography to observe the front rise of silicon in a SiC/SiC composite material during the LSI process. 2D observations, as a first approach, could give a basic understanding of the mechanisms but raised several interrogations due to the superposition of these phenomena along the thickness preventing any quantification. The setup has been improved in order to make X-ray tomography using a fully integrated DC motor in place of the rotation stage commonly used. The sets of X-ray tomographs confirm two successive fillings. First, the molten silicon rapidly and non uniformly invades the accessible intergranular micro porosity of the powder. Then, the liquid slowly fills the remaining isolated powder areas. Once the SiC matrix is fully saturated, the liquid fills the bigger porosities such as cracks and intra yarn macro porosities. In addition, this 3D analysis enabled to give a better comprehension of the non uniform wetting front in the SiC matrix powder. During the 1st step, the accessibility of the powder was known to have a major effect on the speed of progression. Also, the cracks network plays a key role in the filling of the isolated areas in the powder matrix.

HTO and selenate diffusion through compacted Na-, Na–Ca-, and Ca-montmorillonite

Radionuclide transport in smectite clay barrier systems used for nuclear waste disposal is controlled by diffusion, with adsorption significantly retarding transport rates. While a relatively minor component of spent nuclear fuel, 79Se is a major driver of the safety case for spent fuel disposal due to its long half-life (3.3 × 105 yr) and its low adsorption to clay (KD < 10 L/kg), thus a thorough understanding of Se diffusion through clay is critical for understanding the long-term safety of spent fuel disposal systems. Through-diffusion experiments with tritiated water (HTO, conservative tracer) and Se(VI) were conducted with a well-characterized, purified montmorillonite source clay (SWy-2) under a constant ionic strength (0.1 M) and three different electrolyte compositions: Na+, Ca2+, and a Na + -Ca2+ mixture at pH 6.5 in order to probe the effects of electrolyte composition and interlayer cation composition on clay microstructure, Se(VI) aqueous speciation, and ultimately diffusion. The results were modeled using a reactive transport modeling approach to determine values of porosity (ε), De (effective diffusion coefficient), and KD (distribution coefficient for adsorption). HTO diffusive flux was higher in Ca-montmorillonite (De = 1.68 × 10−10 m2 s−1) compared to Na-montmorillonite (De = 7.83 × 10−11 m2 s−1). This increase in flux is likely due to a greater degree of clay layer stacking in the presence of Ca2+ compared to Na+, which leads to larger inter-particle pores. Overall, the Se(VI) flux was much lower than the HTO flux due to anion exclusion, with Se(VI) flux following the order Ca (De = 1.03 × 10−11 m2 s−1) > Na–Ca (De = 2.12 × 10−12 m2 s−1) > Na (De = 1.28 × 10−12 m2 s−1). These differences in Se(VI) flux are due to a combination of factors, including (1) larger accessible porosity in Ca-montmorillonite due to clay layer stacking and smaller electrostatic effects compared to Na-montmorillonite, (2) larger accessible porosity for neutral-charge CaSeO4 species which makes up 32% of aqueous Se(VI) in the pure Ca system, and (3) possibly higher Se(VI) adsorption for Ca-montmorillonite. Through a combination of experimental and modeling work, this study highlights the compounding effects that electrolyte and counterion compositions can have on radionuclide transport through clay. Diffusion models that neglect these effects are not transferable from laboratory experimental conditions to in situ repository conditions.

Effect of Exposure Conditions on Mortar Subjected to an External Sulfate Attack.

This study aims to investigate the influence of exposure conditions on the behavior of mortar subjected to an external sulfate attack (ESA). Three different exposure conditions (full immersion, semi-immersion, and drying/wetting cycles) were tested on mortar prisms made with Portland cement and two w/c ratios (0.45 and 0.6). To monitor degradation, it was necessary to evaluate variations in length (expansion), mass changes, compressive and tensile strengths, changes in the total porosity measured using water accessible porosity tests, and changes in the macroscopic behavior of the samples. Mercury intrusion porosimetry (MIP) was used to determine the size distribution of the pores. It was demonstrated that mixing mortar with the lower w/c ratio of 0.45 results in improved performance against an ESA. This study also demonstrates that the type of exposure to an ESA has no significant effect on the kinetics of sulfate penetration during the exposure period. However, the sample's surface becomes more cracked when subjected to repeated drying and wetting cycles. For all the considered exposure conditions, expansion occurred in three stages. In stage 1, the reaction product (ettringite) precipitated in large voids, without causing significant expansion (the expansion remained low and stable). During the second stage, the reaction products generated growing internal stress. The final stage of expansion resulted in microcracks, strength losses, and the formation of macropores, which ultimately lead to material failure. The MIP results indicate that major changes in the porosity and pore volume distribution occur at the surface layer in regard to the gel and capillary pore ranges.

ZIF-8 nanoparticles synthesis for pH-sensitive release of corrosion inhibitor

Zeolite imidazole framework-8 (ZIF-8), with porous structure and pH sensitivity, is an ideal stimulus-response nanocarrier for delivering molecules. Choosing the appropriate synthesis conditions for achieving the accessible porosity volume is the main challenge in creating ZIF-8. This study synthesized new micro-mesoporous ZIF-8 nanoparticles with a 3.11 nm pore size using an ultrasonic bath in a methanol-dimethylformamide mixed solvent. The response surface methodology was used to explore the impact of the synthesis environments. It was found that the optimized conditions were 8.38 ligand-to-metal ion ratio, 100 % power, 64 min, and 6.11 methanol/dimethylformamide. The optimized particles loaded with a corrosion inhibitor, 2-mercaptobenzothiazole, demonstrated a faster inhibitor release in acidic pHs due to the breakdown of the ZIF-8 structure. This research concluded that blending solvents with varying strengths can yield superior physicochemical properties, facilitating micro-mesoporous ZIF-8 production with high pore volume. This discovery holds promise for producing ZIF-8-based materials that benefit various applications.

Optimization of the recycled aggregate processing using the full factorial design approach, chemical, physical and microstructural characterization of treated aggregates by pre-coated with cementitious paste

The present study aims to study the treatment of (RCA) faction (16/25) by their encapsulation into cement slurry with a (W/C) ratio of (0.5). A complete factorial plan 23was applied by considering three independent factors, namely the state of RCA (GR), the soaking time into slurry (DT) and the hardening time (RCA) (A). The selected responses are the compressive strength and the water accessible porosity (voids) of concrete incorporate treated (RCA), after 28 days of curing. The results were analyzed using the statistical software JMP Trial 16.The compressive strength of concretes showed an increase between 20.5 % and 21.04 % with respect to (NCA).However, the porosity of concretes showed a decline with respect to RCA. The main factor that conditions the two responses is the cure time (A), followed by the RCA state. According to the physical characteristics of RCATi, the encapsulation leads to increased water absorption, bulk, and absolute density. The XRD and TGA techniques confirmed the presence of hydrates and quartz in RCA and RCAT. The microstructural analysis of RCAT seems to be in favor of (dry RCAT) soaked in the cement slurry for 10 min where the adhesion is stronger and the (ITZ) is denser.

A Short Review of Advances in MOF Glass Membranes for Gas Adsorption and Separation.

The phenomenon of melting in metal-organic frameworks (MOFs) has recently garnered attention. Crystalline MOF materials can be transformed into an amorphous glassy state through melt-quenching treatment. The resulting MOF glass structure eliminates grain boundaries and retains short-range order while exhibiting long-range disorder. Based on these properties, it emerges as a promising candidate for high-performance separation membranes. MOF glass membranes exhibit permanent and accessible porosity, allowing for selective adsorption of different gas species. This review summarizes the melting mechanism of MOFs and explores the impact of ligands and metal ions on glassy MOFs. Additionally, it presents an analysis of the diverse classes of MOF glass composites, outlining their structures and properties, which are conducive to gas adsorption and separation. The absence of inter-crystalline defects in the structures, coupled with their distinctive mechanical properties, renders them highly promising for industrial gas separation applications. Furthermore, this review provides a summary of recent research on MOF glass composite membranes for gas adsorption and separation. It also addresses the challenges associated with membrane production and suggests future research directions.

Design of Mixed-Matrix MOF Membranes with Asymmetric Filler Density and Intrinsic MOF/Polymer Compatibility for Enhanced Molecular Sieving.

The separation of high-value-added chemicals from organic solvents is important for many industries. Membrane-based nanofiltration offers a more energy-efficient separation than the conventional thermal processes. Conceivably, mixed-matrix membranes (MMMs), encompassing metal-organic frameworks (MOFs) as fillers, are poised to promote selective separation via molecular sieving, synergistically combining polymers flexibility and fine-tuned porosity of MOFs. Nevertheless, conventional direct mixing of MOFs with polymer solutions results in underutilization of the MOF fillers owing to their uniform cross-sectional distribution. Therefore, in this work, a multizoning technique is proposed to produce MMMs with an asymmetric-filler density, in which the MOF fillers are distributed only on the surface of the membrane, and a seamless interface at the nanoscale. The design strategy demonstrates five times higher MOF surface coverage, which results in a solvent permeance five times higher than that of conventional MMMs while maintaining high selectivity. Practically, MOFs are paired with polymers of similar chemical nature to enhance their adhesion without the need for surface modification. The approach offers permanently accessible MOF porosity, which translates to effective molecular sieving, as exemplified by the polybenzimidazole and Zr-BI-fcu-MOF system. The findings pave the way for the development of composite materials with a seamless interface.

Fabrication of americium containing transmutation targets

An innovative, dust-free method for producing (U,Am)O2-x targets without the generation of Am-contaminated liquid waste has been successfully demonstrated in the Fuel Materials Laboratories at SCK CEN. The method comprises the fabrication of porous uranium oxide microspheres through internal gelation, using starch as a pore-former, and a single-step Am(NO3)3 aqueous solution infiltration process. Various samples containing targeted Am contents of 5, 10, 20, or 30 mol% were prepared. The concentration of the Am(III) stock solution was confirmed by ICP-MS and no other Am species than Am3+ were distinguished by UV–Vis spectrophotometry. The microstructural investigations revealed that the density of the porous host microspheres was approximately 65 %TD, with 30 vol% accessible porosity, suitable for an efficient infiltration. Microstructural analysis using SEM-EDS was performed on the sintered microspheres. Unexpectedly, EDS analysis was found to be incompatible due to detector interference from the 60 keV gamma-rays emitted by the sample. Therefore, examination of cross-sectioned (U,Am)O2-x microspheres was performed using wavelength dispersive spectrometry (WDS), which was unaffected by the soft gamma ray emission. A homogeneous mixing of Am and U was observed, without the formation of agglomerates with distinct doping levels. From the periphery to the center of the microspheres a radial gradient in Am content was observed, indicating a slight enrichment of Am on the surface of the microspheres. Overall, the nominal Am concentration was in very good agreement with the targeted content.

Microstructure and transport properties of metakaolin-based geopolymers subjected to accelerated leaching

Towards the development of net-zero carbon concrete and the wider application of geopolymers, understanding the durability of geopolymers has become essential. However, knowledge on the evolution of microstructure and transport properties of the materials under aggressive conditions due to their interaction with external chemicals is limited. Therefore, this study investigated the leaching behaviors of metakaolin-based geopolymers with high water-to-binder (w/b) ratios under a 6 M NH4NO3 attack, focusing on their microstructure and transport properties. Microstructural insights were assessed through N2-adsorption, Mercury intrusion porosimetry, and water porosity analyses. After 28 days of leaching, total porosity slightly decreased, but pore size distribution (PSD) shifted towards larger pore sizes. The materials close to the exposed surface exhibited a relatively higher porosity and larger PSD than the deeper parts. The potential formation of Al(OH)3 and silica layers as a result of dealumination, confirmed by mass gain and SEM/EDS, contributed to the pore structural evolution. These alterations led to slight reductions in water permeability and CH4 diffusion coefficients but mostly increased the He diffusion coefficients of the geopolymers after 28-day leaching. These findings underscored the inherent microstructural characteristics of geopolymers (e.g., porosity, pore size distribution, and tortuosity) and the size of diffusing species as key factors shaping the transport properties. Notably, the permeability and diffusivity of both leached and intact geopolymers exhibited exponential correlations with the accessible porosity.

Pore structure analysis of glacial till under freeze-thaw cycles based on calibration CT data

ABSTRACT Acquiring the interior pore characteristics is essential to the utilisation of glacial till which is the material of permeability barrier to many engineering projects in cold regions. In this work, the pore space of glacial till samples with different cementation degrees and freeze-thaw cycles was investigated by CT technique. Representative elementary volume method (REV) was utilised to ensure a suitable scale of CT volume data, and a novel calibration method was proposed to detect the accuracy of CT segmentation. Subsequently, the effect of cyclic freeze-thaw action on the pore structure of glacial till samples was investigated. Quantitative pore structure analysis shows that cyclic freeze-thaw action resulted in a decrease in porosity of both well cemented and poorly cemented glacial till. The accessible porosity, fractal dimension, and coordination number of glacial till pores also decrease with the increment of freeze-thaw cycles. It can be observed that blocking of the channels of macropores is the main morphological evolution characteristic of glacial till with cyclic freezing and thawing, which can provide reference in designing permeability barrier in glacial till layers.

Soft-templating synthesis of hierarchical mordenite as high-performance catalyst for cyclic acetals production via acetylation of glycerol and benzaldehyde

Highly active hierarchical mordenite zeolite with micro/mesoporosity (TM-n) for selective synthesis of cyclic acetals via acetylation reaction is reported. The hierarchical zeolite is synthesized using soft-templating approach with variations in octadecyltrimethoxysilane (OTMS/Al2O3 ratio, n = 0.2, 0.3 and 0.4) in precursor hydrogels. The results reveal that OTMS not only creates secondary mesoporosity in zeolite framework (larger mesopore volume, external surface area, average pore diameter), but also influences the crystallization process, altering the crystal morphology, crystallinity and Si/Al ratios. Among TM-n zeolites prepared, TM-0.3 hierarchical mordenite has the optimum OTMS amount incorporated while further increasing the OTMS amount leads to the formation of ANA/GIS intergrowth. Thanks to the accessible hierarchical porosity, reduced acidity and morphological effects, the TM-0.3 hierarchical mordenite exhibits excellent catalytic performance (84.1% conversion, TOF = 0.087 s−1, 61.5% dioxolane selectivity) in acetylation of glycerol and benzaldehyde (160 °C, 20 min) better than pristine mordenite. The catalyst is reusable for five runs with minimal loss of activity (TOF = 0.087 → 0.084 s−1), making it a promising catalyst for chemical productions involving bulky molecules. In addition, comparative catalytic tests with classical homogeneous and heterogeneous catalysts, including H2SO4, HCl, CH3COOH, H–Y, H-LTL, Na-X, Na-A, were performed.

Using Hierarchically Structured, Nanoporous Particles as Building Blocks for NCM111 Cathodes.

Nanoparticles have many advantages as active materials, such as a short diffusion length, low charge transfer resistance, or a reduced probability of cracking. However, their low packing density makes them unsuitable for commercial battery applications. Hierarchically structured microparticles are synthesized from nanoscale primary particles by targeted aggregation. Due to their open accessible porosity, they retain the advantages of nanomaterials but can be packed much more densely. However, the intrinsic porosity of the secondary particles leads to limitations in processing properties and increases the overall porosity of the electrode, which must be balanced against the improved rate stability and increased lifetime. This is demonstrated for an established cathode material for lithium-ion batteries (LiNi0.33Co0.33Mn0.33O2, NCM111). For active materials with low electrical or ionic conductivity, especially post-lithium systems, hierarchically structured particles are often the only way to produce competitive electrodes.

Fracture-matrix fluid exchange in oil-bearing unconventional mudstones

The poromechanical properties of unconventional reservoir materials are in large part dictated by their mineralogy. Since these properties govern the response to stress experienced during hydraulic fracturing, fluid production, and fluid injection, they play a central role in the formation of microcracks or bedding delaminations which ultimately dominate mass transport. In this work we study access to the porosity of end member unconventional reservoir materials, where the end members are predominantly dictated by carbonate content. Access to the porosity is quantified using state of the art 3D x-ray computed tomography coupled with physics informed data analytics. Xenon gas, which attenuates x-rays, provides a spatiotemporal map of access to the porosity. The accessible porosity is quantified over a range of net confining stress relevant to the manmade disturbances listed above. These experiments demonstrate that heavily carbonated mudstones are nearly impermeable at the core (~ cm) scale, while carbonate free analogues afford better access to the microstructure. Consistent with previous qualitative 2D radiographs, access to the interior of the clastic mudstones is first observed along planar microcracks, followed by slow penetration into the surrounding matrix. Physics informed data analytics of the 3D tomography measurements presented here show that these microcracks do not permit uniform access to the adjacent rock matrix. In addition, variation of the effective pressure elucidates the mechanisms that govern fracture/matrix fluid exchange. Under conditions consistent with hydrocarbon production fluid accumulates in the immediate vicinity of the nearest microcrack. While there is clear evidence that, as intended, part of this accumulation is from the more distant matrix, fluid is also squeezed out of the microcrack. The fluid build-up at the microcrack indicates that migration out of the rock is hindered by the coupled poroelastic response of the microcrack and adjacent rock matrix. We show that these mechanisms ultimately account for the meager oil recovery factors realized in practice. These insights have implications for making reservoir scale predictions based on core scale observations, and provide a basis for devising new asset development techniques to access more porosity, and enhance fluid extraction. Finally, these findings shed light on key features and mechanisms that govern shale storage capacity, with relevance to other important industrial processes, such as geologic CO2 storage.

Diffusion of HTO, 36Cl and 22Na in the Mesozoic rocks of Northern Switzerland: III. Cross-lab comparison of diffusion measurements on argillaceous twin samples

In the past decades, there has been a high interest in evaluations of argillaceous rock formations to host repositories for spent fuel or radioactive waste material. One of the main reasons for this interest is that argillaceous rocks are dominated by clay minerals, resulting in a fine-grained sediment matrix with micropores, low pore connectivity and thus low permeability, and good self-sealing properties. This entails that diffusion is the prime mechanism for transport of gas, fission products and radionuclides in clay-rich rocks. The determination of diffusion parameters is therefore key to evaluate the quality of the rock from long-term safety perspectives. Cross-lab comparison of diffusion data is however often challenging as various methods, concepts and models are utilised in the different laboratories across the globe. Here, a direct cross-lab comparison study of through-diffusion experiments was performed to compare and assess the effect of experimental method (through-diffusion) and modelling uncertainties of the parameters by comparing results obtained by two independent laboratories. The R&D group ‘Disposal’ at SCK CEN (Belgium) and the PSI-LES group (Switzerland) both performed through-diffusion experiments on (nearly) the same sample material using their in-house experimental and modelling methodologies for through-diffusion experiments. Adjacent (twin) samples at five depths between 870 and 940 m in the Trüllikon1-1 borehole (Switzerland) were selected and each lab subjected these five clay rock samples to diffusion in synthetic pore water with three different tracers, HTO, 36Cl− and 22Na+, representative for neutral, anionic and cationic transport behaviour. The two labs used a similar design of diffusion cell and worked with similar experimental conditions, but there were small differences in the experimental set-up/conditions and in the modelling approach. The independently determined diffusion parameters from SCK CEN and PSI-LES for all three tracers confirmed previously observed uncertainties. For all three radionuclides, the variability of the effective diffusion coefficients estimated independently by both institutes was less than a factor 2 and in general much lower (deviations ranging between 0 and 73%). Besides, the parameter estimations of the capacity factor (or accessible porosity in case of HTO and 36Cl−) agreed well. Moreover, the experimental datasets of HTO and 36Cl− were also cross-fitted. The evaluation revealed that the minor deviations can be attributed predominantly to variations in temperature (experimental conditions) and to a lesser extent to minor distinctions in the modelling approach. It is important to acknowledge that local heterogeneity might also contribute to these differences.

Chloride accessible porosity fractions across the Jurassic sedimentary rocks of northern Switzerland

The Jurassic clay-rich sedimentary sequence in northern Switzerland was investigated in the context of nuclear waste disposal. Tracer profiles across this sequence play an important role when assessing transport processes and long-term evolution of the environment. Negatively charged clay-mineral surfaces cause a depletion of anions in the porewater close to the surfaces compared to free porewater further away. The chloride accessible porosity fraction (fCl) is an important parameter to scale Cl bulk porewater concentrations from aqueous extraction to free porewater concentrations, which are required to establish anion profiles used for transport modelling of anionic tracers. A vast set of fCl data from advective displacement (AD), squeezing (SQ) and through-diffusion (DI) experiments allowed for method comparison and yielded insight into controlling factors of fCl across the sedimentary sequence. Two observations were made: (1) fCl varies strongly depending on lithology and partly on ionic strength; (2) at high ionic strength, the three methods yield consistent results, but at low ionic strength, fCl from DI are lower than those from AD and SQ. The observations are discussed in terms of influencing factors, including structural charge, ionic strength, rock texture, pore sizes and the fact that the different methods sample different parts of the pore space. The stronger variation of fCl from DI experiments with the ionic strength of the experimental porewater is in agreement with theoretical concepts. The volume fraction of small pores (r < 2 nm) inversely correlates with fCl; it accounts for ∼50% of the anion depleted pore volume. Two empirical approaches were tested to derive functions for fCl valid for the lithologically diverse sequence: the clay-content model uses a constant fCl at a clay-mineral content >30% and extrapolates to a fCl of 1 at zero clay content. The formation model applies formation- or member-specific average values of experimental fCl for each unit. Both approaches work reasonably well, with the formation model producing less apparent outliers of free porewater concentrations than the clay-content model. Still some scatter remains, particularly in heterogeneous and low-porosity formations. This work results in a comprehensive and coherent fCl dataset for all studied Jurassic formations and serves as a basis to interpret the profiles of anions with regard to transport across the entire low-permeability sequence.

Diffusion of HTO, 36Cl and 22Na in the Mesozoic rocks of northern Switzerland: I. Effective diffusion coefficients and capacity factors across the heterogeneous sediment sequences

Argillaceous rocks are currently being examined worldwide as potential host rocks for repositories for radioactive waste and spent fuel due to their favourable characteristics such as the self-sealing ability or limited diffusive transport of fluids, solutes or gases. In this study, through-diffusion experiments focused on rock samples with different mineralogical compositions taken from deep boreholes in the Mesozoic rock sequence of northern Switzerland, to determine diffusion parameters of HTO, 36Cl− and 22Na+ perpendicular to the bedding plane. Both effective diffusion coefficients and accessible porosities were calculated from the data obtained. In the Opalinus Clay, the primary selected host rock of the repository, the effective diffusion coefficients (De) and accessible porosity values (ε) of the neutral species HTO within and across all study areas are relatively consistent (De = 8.8 ± 1.9 × 10−12 m2 s−1; ε = 0.12 ± 0.02), indicating that the material can be considered homogeneous in terms of diffusion properties. Importantly, the chemical composition of the pore water has no effect on the values of the effective diffusion coefficients of HTO. On the other hand, the rocks above and below the Opalinus Clay, up to the next aquifer, consist of tight sedimentary units (carbonates, siliciclastics including argillaceous rocks) with a wider range of diffusion coefficients, indicating a higher level of heterogeneity. The diffusion coefficients of anions, such as 36Cl−, tend to be smaller due to anion exclusion effects, while those of cations, such as 22Na+, tend to be larger due to surface enhanced diffusion. The extent of these effects is largely determined by the composition of the pore water, and – in the case of cations – by the extent of sorption which depends also on the sorption capacity – indicated by the cation exchange capacity - of the solid. As a result, variations in the effective diffusion coefficient of 36Cl− and 22Na+ can be observed firstly between different rock types (i.e. composition, fabric), and secondly between the different study areas due to differences in the chemical composition of the pore waters in contact with the solid phase.Based on the analysis of around 130 samples, it has been observed that the diffusion coefficients of the Mesozoic units in northern Switzerland exhibit a significant correlation with the total clay content of the rocks. These findings pave the way for the establishment of a diffusion database for the relevant elements under consideration in the Swiss radioactive waste programme and the Safety Case.

Hierarchical Yolk-Shell Porous Ionic Liquids with Lower Viscosity for Efficient C3H6/C3H8 Adsorption and Separation.

Yolk-shell metal-organic framework (YS-MOF) liquids are candidate materials in large-size species with high-efficiency separation, owing to their hierarchical porosity, faster mass transfer, better compatibility, and higher solution processability than MOF liquids with micropores. Nevertheless, facile synthesis strategies of yolk-shell porous ionic liquids (YSPILs) with regulations of size and morphology are an ongoing challenge. Herein, we propose a general strategy to construct YSPILs based on Z67@PDA with tunable core sizes and morphologies. Benefiting from the unique hierarchical yolk-shell structure, as-prepared YSPILs exhibit promise in C3H6/C3H8 capture and separation with the increased sizes of core in yolk-shell ZIF-67@PDA. Advanced YS-MOF liquids have improved the adsorption properties and increased our ability to tailor chemical composition and pore architecture. Impressively, the adsorption capacity of C3H6 and C3H8 of YSPILs exhibits an approximately 3-fold enhancement compared with that of the neat ILs, confirming that the accessible porosities are retained. Effective C3H6/C3H8 separation performance of YSPILs over PILs based on ZIF-67, revealing the hierarchical porosity of YS-Z67@PDA liquids, benefits larger-size gas separation. Therefore, we believe that this work can not only help us to rationally design novel hierarchically porous ionic liquids but also promote candidate applications in large-size species separation, catalysis, and nanoreactors.

Influence of recycled sand from biomass combustion on the mechanical, hydration and porous properties of mortar mixtures

The objective of this study is to valorise sands from biomass combustion from fluidised bed boilers into mortar formulations and to evaluate their effects on hydration properties, porosities and mechanical strengths. The properties of recycled sand from biomass combustion (RSBC) were compared to the boiler sand (BS) used in the combustion process in order to assess the effects of combustion. RSBC was then incorporated into mortar formulations as a volume replacement for the boiler sand (BS) from the biomass plant. Five formulations (0, 25, 50, 75 and 100% RSBC) were compared by examining their workability and strength properties (ranging from 7 to 180 days). Although a decrease in workability was observed, the substitution of sand with RSBC resulted in better mechanical properties. The accessible porosity, capillary absorption and hydration properties of three formulations (0, 50 and 100% RSBC) were also analysed. An improvement in these properties is observed when RSBC is incorporated with promising results for the valorisation of 100% RSBC.