In novel technologies of heating and cooling of buildings, alternative approaches to energy storage and allocation are investigated. Several of these approaches aim at energy storage that would not require the transformation of solar energy to electrical energy. Among the most promising approaches is the use of reversible chemical and physical sorption of water in the solid porous materials. Here, solar energy is used to dry (expel water from) the hydrophilic porous material. The 'excited' dried material can be stored for a very long time without thermal losses. When at a later stage water vapour is let into this porous material in a controllable manner, adsorption of water molecules into the pores releases the stored energy in the form of sensible heat. In this article we presented a stable microporous aluminophosphate with the highest sorption-based energy-storage capacity so far. The material adsorbs water in a very narrow relative-pressure range and can be regenerated (charged) at very low temperature. As such, it exhibits exceptional properties for long-term energy storage and for applications in heat pumps and cooling devices. With careful NMR and first-principles calculation studies we obtained an atomic-scale insight into the sorption mechanism. We were able to explain why microporous aluminophosphates adsorb water almost abruptly and in an extremely narrow relative-pressure interval. We also compared sorption mechanism and properties of aluminophosphates to the mechanism and properties of two promising metal-organic framework materials, MIL-160 and MOF-801.
COBISS.SI-ID: 6070810
Microporous zeolite-like aluminophosphate AlPO4-34 is a very promising material for water-adsorption-based thermal energy storage. To obtain better understanding of the dehydration of this material, we carried out a detailed variable-temperature nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and first-principles calculation study. We detected three distinct steps (phase transitions) during the dehydration. XRD and NMR were complementary to one another, not only in the sense that XRD yielded information on the average periodic long-range structure and that NMR offered an insight into the local environment of atomic nuclei and on the dynamics within the material, they also worked with very differently packed samples and because of that detected very different dynamics of dehydration. And whereas sensitivity to sample packing may had complicated the comparison of the experimental results obtained by NMR and XRD, the manifestation of this sensitivity also pointed out the very important role that packing of material will have in the potential large-scale applications of AlPO4-34 for energy conversion or heat storage.
COBISS.SI-ID: 5835546
We developed a new method for the investigation of spatial distribution of various organic linkers or functional groups within metal-organic materials. The method is based on nuclear magnetic resonance measurement of spin-diffusion rates and modeling of distributions of organic linkers within metal-organic frameworks. It can distinguish between the cases, in which different linkers form domains, and cases, in which different linkers are uniformly distributed throughout the materials. This unique tool can be employed also for studying other heterogeneous or spatially disordered materials.
COBISS.SI-ID: 5735962
In this article we carried out a detailed solid-state NMR investigation about the incorporation of model drug indomethacin into several different metal-organic porous matrices of the MIL-101 type. The investigated systems represented model drug-delivery systems. The MIL-101 matrices differed one from another in the metal centres building the vertices of their porous frameworks (Al, Fe, Cr) and in the presence or absence of functional groups on the organic linkers that connected the above mentioned metal-oxo vertices into the metal-organic frameworks. We showed that NMR spectroscopy can detect interactions between the drug molecules and the frameworks and thus provide information that is very important for the uderstanding of the drug release. We found out that the investigated metal-organic carriers are not as convenient as mesoporous silicate carriers as their system of pores are less permeable for the drug molecules. Furthermore, the MIL-101 frameworks contained also more hydrogen-bond donor sites, which attract and bond solvent molecules and make removal of these molecules from the pores more difficult.
COBISS.SI-ID: 5447706
We investigated the preferential adsorption of water from gaseous water–ethanol mixtures on porous metal-organic material MIL-100, and developed a successful new characterization approach based on coupling of infrared spectroscopy and in-situ gravimetry. Infrared spectroscopy is a powerful and recognized technique for studying the species adsorbed on materials' surfaces, which allows one to quantify the adsorbates and to characterize the active sites. In-situ gravimetry permits one to determine the mass adsorbed under different relative pressures. Coupling of the two techniques is essential for the determination of the molar absorbance coefficients for the characteristic vibration bands of adsorbates. The presented approach allows one to study the material's performance not only for water/ethanol separation, but also to study the adsorption of other vapor mixtures onto porous materials.
COBISS.SI-ID: 5760026