The effect of surface entropy on the heat of non-wetting liquid intrusion into nanopores

On-demand access to renewable and environmentally friendly energy sources is critical to address current and future energy needs. To achieve this, the development of new mechanisms of efficient thermal energy storage (TES) is important to improve the overall energy storage capacity. Demonstrated here is the ideal concept that the thermal effect of developing a solid−liquid interface between a non-wetting liquid and hydrophobic nanoporous material can store heat to supplement current TES technologies. The fundamental macroscopic property of a liquid’s surface entropy and its relationship to its solid surface are one of the keys to predict the magnitude of the thermal effect by the development of the liquid−solid interface in a nanoscale nvironment driven through applied pressure. Demonstrated here is this correlation of these properties with the direct measurement of the thermal effect of non-wetting liquids intruding into hydrophobic nanoporous materials. It is shown that the model can resonably predict the heat of intrusion into rigid mesoporous silica and some microporous zeolite when the temperature dependence of the contact angle is applied. Conversely, intrusion into flexible microporous metal−organic frameworks requires further improvement. The reported results with further development have the potential to lead to the development of a new supplementary method and mechanim for TES

Development of hierarchical porous materials for catalytic treatment of nitrogen compounds in water

L’objectif de cette étude, portée sur une solution catalytique hétérogène, est de rechercher les meilleures propriétés texturales de supports siliciques pour améliorer les performances catalytiques des solides Pt/SiO2. Des travaux rapportés en littérature ont étudiés les paramètres qui influencent la réduction catalytique des ions nitrites et nitrates en fonction de la nature du support catalytique utilisé, les métaux nobles, l’agent réducteur ou l’influence de pH de la solution. Dans ce travail, le paramètre de diffusion de catalyseur est étudié afin d’améliorer l’accessibilité aux sites actifs pour favoriser la conversion des ions nitrite en azote en évitant la production des ions d’ammonium. Pour atteindre cet objectif, des silices à porosité hiérarchisée sont élaborées en adaptant une méthode par double structuration permettant un contrôle indépendant des diamètres de pores. Ainsi, en ajustant simplement la taille des billes de polymères (entre 400 et 50nm), il est possible de générer des macropores ou de larges mésopores. En couplant ces objets avec un surfactant non ionique (P123) comme agent structurant, des supports siliciques à double porosité, présentant des volumes poreux bien supérieurs aux supports parents ont été obtenus. Les supports ont été imprégnés par le précurseur de Platine par voie humide et calcinés sous air, afin d’obtenir 1% en masse de catalyseur.The aim of this work focused on a heterogeneous catalytic solution to seek the best textural properties of silicic materials to improve the catalytic performance of Pt/SiO2 solids. Many works were reported in the literature have examined parameters influencing the catalytic reduction of nitrate and nitrite ions as the nature of the catalytic support used , the noble metal , the reducing agent or the influence of solution pH . In this work, the diffusion parameter of catalyst was studied in order to improve the accessibility to the active sites to promote the conversion of nitrite to nitrogen ions avoiding the production of ammonium ions. To achieve this objective, silica materials with hierarchical porosity are developed by adapting the dual templating method to give an independent control of pore diameters. Thus, by simply adjusting the size of the polymer beads (between 400 and 50 nm); it is possible to generate large mesopores and macropores. By combining these objects with a nonionic surfactant (P123) as a structuring agent, with dual porous silicic supports were obtained with pore volumes higher than the parent supports. The supports were impregnated with platinum precursor by wet route and calcined in air to obtain 1% by weight of catalyst

Facile modifications of HKUST-1 by V, Nb and Mn for low-temperature selective catalytic reduction of nitrogen oxides by NH 3

International audienceHKUST-1 catalysts were impregnated with vanadium, niobium and manganese species and tested in NH 3-SCR for NO removal. No reduction of NO by NH 3 was registered for the unmodified HKUST-1 and disappearance of NO was attributed to adsorption. After a pretreatment at 185°C, the best catalytic performance was found for HKUST-1-Mn with 100% and 80% conversion of NH 3 and NO, respectively at 185°C. For the first time, the H 2 O tolerance was examined on the modified HKUST-1 catalyst. The addition of water vapor resulted in decrease of NO and NH 3 conversions, which was immediately recovered when H 2 O feeding was stopped. The NO conversion dropped from 76% to 68% after 35 min of H 2 O addition

Pore Morphology Determines Spontaneous Liquid Extrusion from Nanopores

In this contribution we explore by means of experiments, theory, and molecular dynamics the effect of pore morphology on the spontaneous extrusion of nonwetting liquids from nanopores. Understanding and controlling this phenomenon is central for manipulating nanoconfined liquids, e.g., in nanofluidic applications, drug delivery, and oil extraction. Qualitatively different extrusion behaviors were observed in high-pressure water intrusion-extrusion experiments on porous materials with similar nominal diameter and hydrophobicity: macroscopic capillary models and molecular dynamics simulations revealed that the very presence or absence of extrusion is connected to the internal morphology of the pores and, in particular, to the presence of small-scale roughness or pore interconnections. Additional experiments with mercury confirmed that this mechanism is generic for nonwetting liquids and is rooted in the pore topology. The present results suggest a rational way to engineer heterogeneous systems for energy and nanofluidic applications in which the extrusion behavior can be controlled via the pore morphology

Tunable hierarchical porous silica materials using hydrothermal sedimentation-aggregation technique

International audienceHerein, a simple and efficient synthesis based on a dual templating approach allow the preparation of tunable macroporous mesoporous silica materials. Macropores incorporation has been obtained using polymer spheres of well-defined size and their subsequent removal by thermal treatment allowed the independent control of the macropore size entrance between 200 nm and 50 nm. The addition of the block copolymer drives the formation of a second mesostructured skeleton, with a pore size centered around 4 nm, throughout the material framework. By a fine tuning of the sol–gel synthesis parameters (Polymer:TEOS ratio, aging conditions), we succeeded in guiding the SBA-15 rod-like morphology having randomly packed macropores to a derived SBA-15 with a homogeneous honeycomb macrostructure. Moreover, large mesoporous windows are generated between adjacent macropores. Hence, this simple one-pot synthesis approach, allowing scaling-up, offers fine tuning porosity at the macropore scale

Adsorption Capacities of Hygroscopic Materials Based on NaCl-TiO2 and NaCl-SiO2 Core/Shell Particles

Hygroscopic materials which possess high moisture adsorption capacity were successfully upgraded by the functionalization of sodium chloride (NaCl) using two nuances of oxides. A procedure was developed to first prepare submicron-sized NaCl crystals; thereafter, these crystals were coated by choice of either titanium dioxide (TiO2) or silica (SiO2) to enhance the hygroscopic properties of NaCl and prevent its premature deliquescence. After coating, several analytical techniques were employed to evaluate the obtained composite materials. Our findings revealed that both composites NaCl-TiO2 and NaCl-SiO2 gave excellent performances by exhibiting interesting hydrophilic properties, compared to the sole NaCl. This was demonstrated by both environmental scanning electron microscope (ESEM) and water vapor adsorption experiments. In particular, NaCl-TiO2 composite showed the highest water adsorption capacity at low relative humidity and at a faster adsorption rate, induced by the high surface energy owing to the presence of TiO2. This result was also confirmed by the kinetics of adsorption, which revealed that not only does NaCl-TiO2 adsorb more water vapor than NaCl-SiO2 or sole NaCl but also the adsorption occurred at a much higher rate. While at room temperature and high relative humidity, the NaCl-SiO2 composite showed the best adsorption properties making it ideal to be used as a hygroscopic material, showing maximum adsorption performance compared to NaCl-TiO2 or sole NaCl. Therefore, NaCl-TiO2 and NaCl-SiO2 composites could be considered as promising hygroscopic materials and potential candidates to replace the existing salt seeding agents

Perspectives in Adsorptive and Catalytic Mitigations of NOx Using Metal–Organic Frameworks

International audienceBecause of its high polluting effect, a growing research interest in NOx monitoring, removal, and control has been noticed in the last years. Motivated by the high degree of functional and structural tunability of metal–organic frameworks (MOFs), researchers explored potential MOF-based adsorbents, sensors, and catalysts for NOx mitigation/control. However, this area of research is still in its infancy. In addition, the physical–chemical properties of NOx make this task extremely challenging as some materials suffer relatively weak thermal and/or chemical stability. Nevertheless, some recent encouraging studies have demonstrated superior stability properties that enable MOFs to be considered as alternative benchmark materials for the capture and conversion of NOx. This review offers an overview on the recent progress made in this field and provides some interesting routes on the uses of MOFs for selective NOx adsorption, release, and/or catalytic conversion (via selective catalytic reduction or photocatalysis)

Investigation of Ca12Al14O33 Mayenite for hydration/dehydration thermochemical energy storage

Thermal energy storage using a reversible chemical reaction is a key parameter for increasing the storage capacity especially for medium and high temperature applications. The reversible hydration/dehydration reaction of calcium hydroxide Ca(OH)2 to calcium oxide CaO is among the most investigated system due to its reaction cyclability and interesting operating temperature above 450 ºC suitable for high temperature applications. However, the indicated reaction temperature was considered too high for some industrial applications which limit a further development of thermal energy storage technologies using this promising reaction system. In this regard, the material development is a key point to broaden the application of sustainable technologies. In this work, the investigation of Mayenite with general formula Ca12Al14O33 as a thermochemical energy storage material was conducted. Thereby, it was confirmed the possibility of the pair Ca12Al14O12(OH)42/Ca12Al14O33 to store and release the heat through chemical reaction thanks to a novel activation process of the pristine Mayenite that is presented for the first time in this work. This study might help to identify new pairs based on materials that have already been classified as inactive for the hydration/dehydration reaction. In addition, it was found that the hydration reaction temperature of Ca12Al14O12(OH)42/Ca12Al14O33 pair of 228ºC is much lower compared to that of CaO/Ca(OH)

Nano-engineered hierarchical porous silicas for enhanced catalytic efficiency in the liquid phase

International audienceBy tailoring the pore properties (size, morphology and orientation) of hierarchical catalysts, we show experimentally the importance of active phase accessibility on catalytic efficiency. This finding likely contributes to a better rationalisation of the structure sensitivity of the nitrite hydrogenation reaction, through the enhancement of mass transfer phenomena