ABSTRACT
A method based on infrared (IR) micro-reflectance measurements for the structural characterization of glassy nanomaterials is presented. Near-specular reflectance spectra of pressed pellets can be analyzed using a model relating the structure of silicate glasses to their dielectric response and an effective medium approximation to account for the effect of porosity. The integrated intensities of phenomenological bands attributed to Q2, Q3, and Q4 structural units allow quantifying their relative populations. These values are in good agreement with those obtained with magic-angle spinning nuclear magnetic resonance, which serves as validation of the method and proves the feasibility of extracting quantitative information about glass structure from IR micro-reflectance experiments.
ABSTRACT
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 environment-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.
ABSTRACT
Heat-storage technologies are well suited to improve the energy efficiency of power plants and the recovery of process heat. A good option for high storage capacities, especially at high temperatures, is storing thermal energy by reversible thermochemical reactions. In particular, the Co3O4/CoO and Mn2O3/Mn3O4 redox-active couples are known to be very promising systems. However, cost and toxicity issues for Co oxides and the sluggish oxidation rate (leading to poor reversibility) for Mn oxide hinder the applicability of these single oxides. Considering, instead, binary Co-Mn oxide mixtures could mitigate the above-mentioned shortcomings. To examine this in detail, here, we combine first-principles atomistic calculations and experiments to provide a structural characterization and observe the thermal behavior of novel mixed-metal oxides based on cobalt/manganese metals with the spinel structure Co3-xMnxO4. We show that novel Co3-xMnxO4 phases indeed enhance the enthalpy of the redox reactions, facilitate reversibility, and mitigate energy losses when compared to pure metal oxide systems. Our results expand therefore the limited list of currently available thermochemical heat-storage materials and pave the way toward the implementation of tunable redox temperature materials for practical applications.
ABSTRACT
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.
ABSTRACT
Cloud-seeding materials as a promising water-augmentation technology have drawn more attention recently. We designed and synthesized a type of core/shell NaCl/TiO2 (CSNT) particle with controlled particle size, which successfully adsorbed more water vapor (â¼295 times at low relative humidity, 20% RH) than that of pure NaCl, deliquesced at a lower environmental RH of 62-66% than the hygroscopic point (hg.p., 75% RH) of NaCl, and formed larger water droplets â¼6-10 times its original measured size area, whereas the pure NaCl still remained as a crystal at the same conditions. The enhanced performance was attributed to the synergistic effect of the hydrophilic TiO2 shell and hygroscopic NaCl core microstructure, which attracted a large amount of water vapor and turned it into a liquid faster. Moreover, the critical particle size of the CSNT particles (0.4-10 µm) as cloud-seeding materials was predicted via the classical Kelvin equation based on their surface hydrophilicity. Finally, the benefits of CSNT particles for cloud-seeding applications were determined visually through in situ observation under an environmental scanning electron microscope on the microscale and cloud chamber experiments on the macroscale, respectively. These excellent and consistent performances positively confirmed that CSNT particles could be promising cloud-seeding materials.
