In this study, the adsorption enthalpy and entropy of water in the nanoconfinement of periodic mesoporous organosilicas with fine-tuned surface chemistry were investigated by integrating thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) with a continuous-flow humidity generator, providing a direct method to better understand the water adsorption process at very low surface coverage. For comparison, the commonly used indirect isosteric method was employed, yielding generally comparable results to the simultaneous DSC-TGA measurements despite differing experimental conditions. Only the calorimetric method revealed that not only more hydrophilic materials exhibit high absolute values of adsorption enthalpy of water at the first surface contact but also hydrophobic materials, as they contain surface silanol groups that can strongly interact with water until these sites are saturated. Beyond this initial humidity region of water-surface contact, both methods yield largely consistent results at higher relative humidity, clearly distinguishing between hydrophilic and hydrophobic surface behavior. More hydrophobic materials have lower absolute values of adsorption enthalpy, reflecting weaker interaction strength and less structuring before reaching the condensation enthalpy of water (-44 kJ mol-1), while hydrophilic materials exhibit higher absolute values of adsorption enthalpy before water-water interactions dominate. Additionally, results from the isosteric method indicate that, at higher surface coverage, hydrophilic materials exert a long-range structural influence extending into distant water layers. Furthermore, the influence of surface functionality and temperature on water vapor sorption isotherms was analyzed, revealing the temperature independence of both the water aggregate size prior to, and the relative pressure at, the inflection point of capillary condensation. In contrast, the desorption branch primarily governs the temperature dependence of the adsorption-desorption hysteresis. This study presents the first detailed enthalpic analysis of water adsorption in PMOs using a continuous-flow calorimetric method, providing a foundation for future research on water-surface functionality interactions either at different loadings under isothermal conditions or across varying temperatures.

Complex hydrides offer high H2 storage capacities but suffer from kinetic degradation and microstructural coarsening, requiring operations at elevated temperatures, typically above 180°C. Here, we demonstrate grain boundary complexion-mediated structural stabilization using ultra-low loading of Zr-based metal-organic frameworks (Zr-MOFs; 1 at.% Zr; UiO-66 vs. MIP-206) in the reactive hydride composite system 6Mg(NH2)2-9LiH-2LiBH4 (6.9.2-RHC). Incorporation of microporous Zr-UiO-66 significantly lowers the hydrogen absorption onset temperature from 162°C to 81°C, enables measurable hydrogen uptake at 35°C (1.07 wt.% under 80 bar H2). In addition, UiO-66 accelerates desorption by more than threefold at 140°C, increases reversible capacity from 3.2 to 4.1 wt.%, and maintains the capacity over 15 cycles compared with the pristine 6.9.2-RHC. In situ synchrotron radiation X-ray diffraction confirms that the intrinsic amide–imide reaction pathway remains unchanged, suggesting that structural stabilization plays a dominant role in the enhanced hydrogen storage performance. SAXS reveals stabilized nanoscale domains (≈2.4–3.3 nm), while SANS/USANS demonstrates suppression of hierarchical aggregation relative to pristine 6.9.2-RHC. Ball-milling of UiO-66 preserves short-range tetrahedral structural units (≈0.76 nm) that are proposed to stabilize grain-boundary complexions capable of accommodating the large (20–30 per cent) volume changes associated with hydrogen cycling. The performance hierarchy (UiO-66 > MIP-206 > pristine) demonstrates that MOF-derived short-range structural motifs suppress coarsening by promoting grain-boundary complexions, enabling practical low-temperature hydride operation through stabilized reactive interfaces.

The synthesis of palladium (Pd) nanoparticles (NPs) in the highly constrained pore network of mesoporous silicas is systematically investigated for the first time, comparing the synthesis outcomes with a reference sample of Pd NPs on the outer surface of nonporous silica. Two different families of mesoporous silica (SBA-15 and KIT-6), with different pore arrangements and connectivity, as well as two different pore sizes within both porous systems (i.e., 7 and 9 nm), are investigated as supports for Pd NPs synthesis, and the effect of mesopore confinement is explored. In particular, the mesoporous matrixes allow one to obtain smaller and homogeneously distributed Pd NPs with respect to the nonporous support, and their actual location within the mesopore-constrained environment is confirmed by electron tomography. Moreover, the application of Pd NPs on mesoporous and nonporous silicas as heterogeneous catalysts for CO oxidation is explored, and the noticeable stability of Pd NPs on the supports is assessed by probing the accessibility and dynamic response of Pd species by operando Pd K-edge X-ray absorption spectroscopy measurements. Oxidized Pd species are found to be the active phase of the catalytic reaction, and the complex interplay of several factors occurring in regulating the catalytic activity of the supported NPs is discussed.

Interfacial interactions significantly alter the fundamental properties of water confined in mesoporous structures with crucial implications for geological, physicochemical, and biological processes. Herein, we focused on the effect of changing the surface ionic charge of nanopores with comparable pore sizes (3.5-3.8 nm) on the dynamics of confined liquid water. The control of the pore surface ionicity was achieved by using two periodic mesoporous organosilicas (PMOs) containing either neutral or charged forms of a chemically similar bridging unit. The effect on the dynamics of water at the nanoscale was investigated in the temperature range 245-300 K, encompassing the glass transition by incoherent quasi-elastic neutron scattering (QENS). For both types of PMOs, the water dynamics revealed two distinct types of molecular motions: rapid local movements and translational jump diffusion. While the neutral PMO induces a moderate confinement effect, we show that the charged PMO drastically slows down water dynamics, reducing translational diffusion by a factor of 4 and increasing the residence time by an order of magnitude. Notably, by changing the pore filling values, we demonstrate that for charged PMOs, this effect extends beyond the interfacial layer of surface-bound water molecules to encompass the entire pore volume. Thus, our observation indicates a dramatic change in the long-range character of the interaction of water confined in nanopores with surface ionic charge compared to a simple change in hydrophilicity. This is relevant for the understanding of a broad variety of applications in (nano)technological phenomena and processes such as nanofiltration and membrane design.

A selected series of metal-organic frameworks M-MOF-74 (M = Mg, Co, Ni) and mixed metal MM-MOF-74 (Mg/Co or Mg/Ni) with different compositions of metal atoms have been prepared and further investigated by broadband dielectric spectroscopy (BDS) in a wide temperature range. The dielectric spectra show at least two relaxation processes. Process-A is observed only for the Ni-containing MOFs and is attributed to localized fluctuations of the metal oxide corners. Relaxation processes-B and -C are observed for all prepared MOFs, except that process-B is not observed for Ni-MOF-74. Large-angle fluctuations such as free rotations of the linkers can be excluded due to the structure of MOF-74, but small-angle fluctuations such as torsions are possible. According to numerical simulations carried out for MOF-74, process-B can be attributed to inward and outward fluctuations of the linkers relative to the pore center. Process-C is related to small-angle rotational fluctuations of the linker together with co-rotations of the metal nodes. The latter interpretation is supported by the dependence of the activation energy of the relaxation rate of process-C on the metal composition of the MOFs, which is discussed in terms of the bond lengths between the metal atoms and the linker which decrease in the sequence Mg, Co and Ni.

Nanoporous carbons play an important role in different electrochemical applications, such as being utilized as electrodes in supercapacitors. Application of electric potential to a porous electrode in electrolyte solution stimulates the adsorption or desorption of ions on the electrode surface. Electrosorption causes the appearance of solvation pressure in the pores and results in electrode deformation. In this work, using molecular dynamics simulations and the continuum theory based on the modified Poisson-Boltzmann equation, we studied the structure of the electrical double layer in slit graphitic micropores filled with a NaCl aqueous solution and solvation pressure in these pores. We focused on the behavior of the solvation pressure as a function of the pore width and surface charge density. Within molecular dynamics simulations, two different water models were used: an explicit model based on SPC/E water molecules and an implicit model, i.e., a structureless background with fixed dielectric permittivity. The latter allows us to relate molecular dynamics simulations to continuum theory. Simulations with explicit water show a qualitatively different behavior of the solvation pressure in the 1 and 2 nm pores as a function of the surface charge density. We demonstrated that the value of the solvation pressure is defined by a delicate balance between van der Waals and electrostatic contributions. We demonstrated that the theory predicts the dependence of the solvation pressure on the pore width, which matches the results of simulations using the implicit water model. Finally, we adapted the continuum theory developed for adsorption-induced deformation to estimate the deformation of a carbon electrode due to electrosorption. Our results can be used in the further development of nanoporous actuators working based on electrosorption-induced deformation.

The impact of surface hydrophilicity on the freezing, melting, and nonfreezable layer of nanoconfined water remains debated. Variability in material types, pore sizes, surface functionality organization, and experimental conditions complicate direct comparisons and conclusions. To address this, periodic mesoporous organosilicas (PMOs) with a uniform divinylbenzene bridging unit were used. By fine-tuning hydrophilicity and pore sizes, confined water's phase behavior was studied via differential scanning calorimetry (DSC). Comparing gas-phase adsorption and incipient wetness as filling methods revealed an increased t-layer density with the latter. Surface hydrophilicity has little effect on melting point depression in larger pores but becomes increasingly influential as pore size decreases. The nonfreezable layer thickness was evaluated using the Gibbs-Thomson equation and geometric enthalpy-based calculations. In hydrophobic PMOs, water exhibited larger melting point depression, lower specific enthalpies, and thicker interfacial layers than in hydrophilic ones. In contrast, charged PMOs behaved differently: despite higher hydrophilicity, confined water exhibited a larger melting temperature depression, lower specific enthalpy, larger critical pore radius, and comparatively thicker t-layers, likely due to higher disorder of the hydrogen-bonding network close to the surface. Moreover, the t-layer density did not follow a simple trend based solely on hydrophilicity. These results highlight the complex interplay between pore size, surface chemistry, and interfacial water behavior, offering valuable insights into confined water properties and phase transitions.

Titania aerogels are highly porous materials optimal for photocatalysis due to their high surface area. Further spatial structuring by 3D printing improves gas diffusion in the aerogel, leading to a higher photocatalytic activity. However, the aerogel's mechanical properties are reduced in comparison to non-3D printed aerogels. We hereby present an approach based on atomic layer deposition (ALD) of subnanometer-thin TiO2 layers to compensate for that detrimental effect. The ALD-deposited TiO2 consists of amorphous and anatase phase, with the anatase phase likely crystallizing on the aerogel's crystallites. Nanoindentation measurements confirm that the TiO2 ALD-coatings improve the aerogel's mechanical properties. Additionally, it enhances the photocatalytic properties of the TiO2 aerogel, which we attribute to the increased interface area and improved interconnection of the nanoparticle network. By further thermal postprocessing, it is possible to fully crystallize the ALD-deposited TiO2, which shows a complementary effect on photocatalytic performance, improving hydrogen evolution rate by more than 1 order of magnitude from 6.35 to 125 μmol g-1 h-1. The combination of 3D structuring of aerogels with ALD coatings demonstrated in this work could be extended in the future to a wide range of materials where the interplay between mechanical and catalytic properties is vital.

Two Co(II) mixed-ligand metal-organic frameworks (MOFs) based on 2-methylimidazole and trimesate were synthesised at room temperature. The structure and properties of the two MOFs, named material Deutsches Elektronen Synchrotron-1 and -2 (mDESY-1 and mDESY-2), were verified by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), SQUID magnetic susceptibility and N2 adsorption. The structural analysis indicates that mDESY-1 is a 3D ionic framework with 2-methyl-1H-imidazol-3-ium counterions residing in its pores, while mDESY-2 is a 2D neutral framework isostructural to ITH-1, with water as a co-crystallising solvent. PXRD data demonstrates that mDESY-1 exhibits better crystallinity than mDESY-2. Magnetic measurements indicate that both MOFs are paramagnetic with a weak ferromagnetic transition above room temperature. Although both structures suggest the presence of voids, N2 adsorption data confirms that these voids are not accessible in either MOF. Nevertheless, mDESY-1 was capable of encapsulating azobenzene during synthesis, which was observed via SCXRD. The encapsulated molecules were then slowly released in ethanol, with a release of up to 30 mg of azobenzene per g of MOF in a period of 60 days.

AbstractMono‐ and bimetallic MOF‐74 samples with different ratios of Mg2+ and Ni2+ (9:1, 7:3, and 1:1), as well as Ni‐MOF‐74 analogs with different pore sizes and functionalities, were loaded with water through the exposure to a controlled relative humidity. To get information on the influence of the metal, pore size (1.2–3.6 nm), and functionality on the confined water, all samples were analyzed through infrared spectroscopy and the results were correlated to corresponding water sorption isotherms. Deconvolution of the O‐H stretching vibrational band made it possible to draw conclusions about differently ordered water species inside the pores. In all samples, it was visible that at lower pore loadings, the MOFs mostly comprised of less ordered water species, while higher pore loadings led to an increased formation of a more ordered, tetrahedral phase. Increasing amounts of Ni2+ within the series of bimetallic Mg/Ni‐MOF‐74 samples gave the hydrated systems a more hydrophilic behavior and favored the growth of more ordered species. Moreover, larger pores favored the less ordered water species, while hydrophilic functionalities led to the growth of water with a higher tetrahedrality and hydrophobic groups led to pores dominated by less ordered water species but can also have an ordering effect.

The potential use of carnallite (KMgCl 3 . 6H 2 O) for low temperature thermochemical heat storage has been evaluated. Carnallite is an incongruently soluble double salt and its possible decomposition and dehydration reactions have been carefully evaluated from available thermodynamic data and the phase diagram has been constructed. The dehydration and rehydration reactions have been experimentally studied and the reaction products have been characterized using thermogravimetric mass spectrometry, water vapor sorption, X-ray powder diffraction, scanning electron microscopy, Raman microscopy and calorimetry. The results of the experimental investigation of these reactions confirm the model predictions and clearly show that a thermochemical cycle including carnallite and its dihydrate (KMgCl 3 . 2H 2 O) is very promising for low temperature domestic thermochemical storage. In comparison to both pure MgCl 2 . 6H 2 O and also other salts mentioned in the literature, the double salt carnallite offers significant advantages. It has a higher deliquescence humidity and, thus, is much less sensitive to over-hydration and liquefaction. It can be easily dehydrated at only 100 degrees C and is much less prone to hydrolysis (HCl release). Carnallite has also a good reversibility between dehydration and hydration and the re -formation of carnallite by rehydration is easily achieved at low water vapor pressure and faster reaction rate than the hydration of MgCl 2 . 2H 2 O to MgCl 2 . 6H 2 O. The enthalpy of hydration is slightly higher for the hydration of KMgCl 3 . 2H 2 O than for the hydration of MgCl 2 . 2H 2 O. The only price to be paid is a slightly reduced storage density of the double salt due to its larger molar volume. However, the theoretical storage density of 1.52 kJ cm - 3 is still excellent. Also, carnallite is a low-cost material as it is available as industrial waste material or can be easily synthesized.

We investigated the structure of ice under nanoporous confinement in periodic mesoporous organosilicas (PMOs) with different organic functionalities and pore diameters between 3.4 and 4.9 nm. X-ray scattering measurements of the system were performed at temperatures between 290 and 150 K. We report the emergence of ice I with both hexagonal and cubic characteristics in different porous materials, as well as an alteration of the lattice parameters when compared to bulk ice. This effect is dependent on the pore diameter and the surface chemistry of the respective PMO. Investigations regarding the orientation of hexagonal ice crystals relative to the pore wall using x-ray cross correlation analysis reveal one or more discrete preferred orientation in most of the samples. For a pore diameter of around 3.8 nm, stronger correlation peaks are present in more hydrophilically functionalized pores and seem to be connected to stronger shifts in the lattice parameters.

By solvothermal reactions of fluoro substituted biphenyl-3,3',5,5'-tetracarboxylic acids (H4BPTC) with the respective metal salts, four new MOFs with the MFM-300 topology were synthesized, namely [M-2(III)(OH)(2)(L)] with M-III=Ga3+, In3+ and L=4-mF-BPTC4- and 4,4'-dF-BPTC4-. Three of them were refined from X-ray single crystal diffraction data (I4(1)22, Z=4), [Ga-2(OH)(2)(4,4'-dF-BPTC)] was confirmed by Le Bail fits based on synchrotron powder diffraction data. To the best of our knowledge, these four compounds represent the very first examples of MFM-300 type MOFs with a substituted BPTC4- linker. With increasing fluorination of the linker, the thermal stability decreases, as the decarboxylation of the linker is facilitated. On the other hand, the gas uptake is enhanced significantly. E.g. the CO2 uptake (273 K, 1 bar) increases from 124 cm(3)/g for [Ga-2(OH)(2)(4-mF-BPTC)] to 136 cm(3)/g for [Ga-2(OH)(2)(4,4'-dF-BPTC)]. Surprisingly, the exact determination of specific surface areas (S-BET) turned out to be difficult. It is supposed that due to transient open metal sites, complete removal of solvent molecules (DMF, acetone) is not always possible before degradation of the framework starts.

The reduction of hazardous nitric oxide emissions remains a significant ecological challenge. Despite the variety of possibilities, sorbents able to capture low concentrations of NO from flue gas with high selectivity are still in demand. In this work a new type of mesoporous xerogel material highly loaded with ultrastable Blatter radicals (BTR, > 60% by mass) that act as selective NO sorption sites is developed. Electron Paramagnetic Resonance (EPR) spectroscopy evidences reversible NO sorption in nanometer-scale pores of BTR-based xerogels and indicates the high NO capacity of such radical-rich sorbent. Efficient NO capture from model flue gas mixture is also evidenced in experiments with a fixed bed reactor. Such advanced properties of new materials as selectivity, strong binding with NO and an ability for mild regeneration via thermodesorption promote them for future ecological applications.

Capillarity-driven transport in nanoporous solids is widespread in nature and crucial for modern liquid-infused engineering materials. During imbibition, curved menisci driven by high negative Laplace pressures exert an enormous contractile load on the porous matrix. Due to the challenge of simultaneously monitoring imbibition and deformation with high spatial resolution, the resulting coupling of solid elasticity to liquid capillarity has remained largely unexplored. Here, we study water imbibition in mesoporous silica using optical imaging, gravimetry, and high-resolution dilatometry. In contrast to an expected Laplace pressure-induced contraction, we find a square-root-of-time expansion and an additional abrupt length increase when the menisci reach the top surface. The final expansion is absent when we stop the imbibition front inside the porous medium in a dynamic imbibition-evaporation equilibrium, as is typical for transpiration-driven hydraulic transport in plants, especially in trees. These peculiar deformation behaviors are validated by single-nanopore molecular dynamics simulations and described by a continuum model that highlights the importance of expansive surface stresses at the pore walls (Bangham effect) and the buildup or release of contractile Laplace pressures as menisci collectively advance, arrest, or disappear. Our model suggests that these observations apply to any imbibition process in nanopores, regardless of the liquid/solid combination, and that the Laplace contribution upon imbibition is precisely half that of vapor sorption, due to the linear pressure drop associated with viscous flow. Thus, simple deformation measurements can be used to quantify surface stresses and Laplace pressures or transport in a wide variety of natural and artificial porous media.

A composite material of alginate and CaCl2 was tested in a laboratory reactor (1 L) for its ability to thermochemically store heat. The material was exposed to air at 25 °C and 25% RH to prevent the salt from dissolving, and the heat evolution was observed over a period of 15 cycles. To evaluate the changes in the material, samples were taken after 5, 10 and 15 cycles and the material properties and calorimetric characteristics were examined. A change of the material in favor of the heat release was determined, so that an increase of the heat storage capacity from 1.28 kJ∙cm−3 to 2.11 kJ∙cm−3 was detected, with a simultaneous steep decrease of the pore volume in the range from 0.01 to 10 μm. The temperature lift of the reactor showed a significant increase, with the first cycle showing the smallest amount.

A cellulose nanofibril-based hybrid gel material was developed by grafting the polymerized stearyl acrylate (PSA) and upconversion nanoparticles (UCNPs) onto cellulose nanofibrils (CNFs) via Cu0-mediated radical polymerization (SET-LRP) to create a highly cross-linked CNF system. A two-step strategy was exploited to surface-exchange the ligand of the UCNPs from a hydrophobic ligand (oleic acid) to a hydrophilic small-molecule ligand (2-acrylamido-2-methyl-1-propanesulfonic acid, AMPS) and therefore be suitable for SET-LRP. The characteristics and properties of the hybrid material (UCNP-PSA-CNF) were monitored by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), rheology, X-ray diffraction (XRD), and microscopic analysis. Those characterization techniques prove the efficient modification of the CNF, with the presence of 1.8% UCNPs. The luminescence measurement was carried out using a homebuilt confocal microscope with a 980 nm laser source. The nanostructure of UCNPs and their incorporated CNF species were measured by small-angle X-ray scattering (SAXS). In addition, this CNF-based hybrid gel has decisive rheological properties, such as good viscoelasticity (loss tangent was below 0.35 for the UCNP-PSA-CNF gel, while the PSA-CNF gel reached the highest value of 0.42), shear-thinning behavior, and shape retention, and was successfully applied to three-dimensional (3D) gel printing throughout various 3D print models.

Nitrogen oxides are adverse poisonous gases present in the atmosphere and having detrimental effects on the human health and environment. In this work, we propose a new type of mesoporous materials capable of capturing nitrogen monoxide (NO) from air. The designed material combines the robust Santa Barbara Amorphous-15 silica scaffold and ultrastable Blatter-type radicals acting as NO traps. Using in situ electron paramagnetic resonance spectroscopy, we demonstrate that NO capture from air is selective and reversible at practical conditions, thus making Blatter radical-decorated silica highly promising for environmental applications.

ConspectusThe ligand shells of colloidal nanoparticles (NPs) can serve different purposes. In general, they provide colloidal stability by introducing steric repulsion between NPs. In the context of biological applications, the ligand shell plays a critical role in targeting, enabling NPs to achieve specific biodistributions. However, there is also another important feature of the ligand shell of NPs, namely, the creation of a local environment differing from the bulk of the solvent in which the NPs are dispersed. It is known that charged ligand shells can attract or repel ions and change the effective charge of a NP through Debye–Hückel screening. Positively charged ions, such as H+ (or H3O+) are attracted to negatively charged surfaces, whereas negatively charged ions, such as Cl– are repelled. The distribution of the ions around charged NP surfaces is a radial function of distance from the center of the NP, which is governed by a balance of electrostatic forces and entropy of ions and ligands. As a result, the ion concentration at the NP surface is different from its bulk equilibrium concentration, i.e., the charged ligand shell around the NPs has formed a distinct local environment. This not only applies to charged ligand shells but also follows a more general principle of induced condensation and depletion. Polar/apolar ligand shells, for example, result in a locally increased concentration of polar/apolar molecules. Similar effects can be seen for biocatalysts like enzymes immobilized in nanoporous host structures, which provide a special environment due to their surface chemistry and geometrical nanoconfinement. The formation of a local environment close to the ligand shell of NPs has profound implications for NP sensing applications. As a result, analyte concentrations close to the ligand shell, which are the ones that are measured, may be very different from the analyte concentrations in bulk. Based on previous work describing this effect, it will be discussed herein how such local environments, created by the choice of used ligands, may allow for tailoring the NPs' sensing properties. In general, the ligand shell around NPs can be attractive/repulsive for molecules with distinct properties and thus forms an environment that can modulate the specific response. Such local environments can also be optimized to modulate chemical reactions close to the NP surface (for example, by size filtering within pores) or to attract specific low abundance proteins. The importance hereby is that this is based on interaction with low selectivity between the ligands and the target molecules.

The effect of pore wall chemistry and pore diameter on the structure of confined water was studied by X-ray scattering on water confined in periodic mesoporous organosilicas (PMOs). A shift in the first structure factor peak at q approximate to 1.8 & Aring;(-1) reveals a variation in the density of the confined water depending on the hydrophilicity and pore size. Smaller and more hydrophilic pores induce a lower density in the water. In contrast to bulk water, the pair distribution functions (PDFs) of confined water show a splitting of the second-neighbor peak into either two, in the case of smaller and more hydrophilic pores, or three separate peaks, in larger and more hydrophobic pores. From the running coordination number, we conclude that a smaller and more hydrophilic confinement leads to a stronger developed tetrahedral network in confined water, while confinement in larger and hydrophobic pores gives tetrahedral arrangements that are bulk-like or even less pronounced than in bulk water.