Large magnetocaloric effect in fine Gd2O3 nanoparticles embedded in porous silica matrix

The magnetocaloric properties of a composite material consisting of isolated GdO nanoparticles with a diameter of 6-8 nm embedded in the pores of a mesoporous silica matrix have been studied. The fascinating nanostructure and composition were properly characterized by small angle X-ray scattering, X-ray absorption near edge structure, and TEM. Almost ideal paramagnetic behavior of the material was observed in the temperature range of 1.8-300 K. When compared to various nanosystems, the presented composite exhibits an extraordinarily large magnetic entropy change of 40 J/kg K for a field variation of 0-5 T at cryogenic temperature (3 K). Considering only the mass of the GdO nanoparticle fraction, this corresponds to 120 J/kg K. Calculated refrigerant capacities are 100 J/kg and 400 J/kg for the composite and nanoparticles, respectively. Our findings suggest that the combination of the unique porous structure of amorphous silica with fine gadolinium oxide nanoparticles and high value of magnetic entropy change enables to extend the application of the GdO@SiO composite, to cryomagnetic refrigeration. In addition, the characteristics of the thermomagnetic behavior have been studied using the scaling analysis of the magnetic entropy change.Peer Reviewe

Large magnetocaloric effect in fine Gd2O3 nanoparticles embedded in porous silica matrix

The magnetocaloric properties of a composite material consisting of isolated GdO nanoparticles with a diameter of 6-8 nm embedded in the pores of a mesoporous silica matrix have been studied. The fascinating nanostructure and composition were properly characterized by small angle X-ray scattering, X-ray absorption near edge structure, and TEM. Almost ideal paramagnetic behavior of the material was observed in the temperature range of 1.8-300 K. When compared to various nanosystems, the presented composite exhibits an extraordinarily large magnetic entropy change of 40 J/kg K for a field variation of 0-5 T at cryogenic temperature (3 K). Considering only the mass of the GdO nanoparticle fraction, this corresponds to 120 J/kg K. Calculated refrigerant capacities are 100 J/kg and 400 J/kg for the composite and nanoparticles, respectively. Our findings suggest that the combination of the unique porous structure of amorphous silica with fine gadolinium oxide nanoparticles and high value of magnetic entropy change enables to extend the application of the GdO@SiO composite, to cryomagnetic refrigeration. In addition, the characteristics of the thermomagnetic behavior have been studied using the scaling analysis of the magnetic entropy change.Slovak Research Development Agency APVV-0073-14 APVV-520-15VEGA No. 1/0377/16 No. 1/0745/17DESY/HASYLAB No. I-20110282 ECFEDER No. MAT2013-45165-

Existence of cryogenic magnetic entropy change in Gd based nanoparticles

Magnetic nanoparticles with average diameter of 5–7 nm were prepared by nanocasting method inside of the pores of periodic silica matrix of SBA15 type. The uniform size of the pores limited the particles' growth what resulted in formation of nanocomposite consisting of monodisperse nanoparticles of Gd₂O₃ embedded in amorphous silica matrix. Magnetic properties of the material were examined in magnetic fields up to 5 T and in temperature range 2–52 K. The magnetic entropy change of 29 J/kg K was observed at 2 K for field variation 5 T in the investigated nanocomposite what suggests this material could be feasible for cryomagnetic refrigeration applications

Reservoir Management by Reducing Evaporation Using Floating Photovoltaic System: A Case Study of Lake Nasser, Egypt

Copyright: © 2021 by the authors. The shortage of water is a major obstruction to the social and economic development of many countries, including Egypt. Therefore, there is an urgent need to properly manage water resources to achieve optimum water use. One way of saving available water resources is to reduce evaporation that leads to the loss of a large amount of water from reservoirs and open lakes. This paper aims to use a floating photovoltaic system (FPVS) to cover a lake’s water surface to reduce evaporation and also for energy production. This methodology was applied to Lake Nasser as one of the largest lakes in the world where much evaporation happens due to its large area, arid environments, and the shallow depths of some parts of the lake. The estimated evaporation from the lake was 12.0 × 109 m3/year. The results show that covering 25%, 50%, 75%, and 100% of the lake can save about 2.1, 4.2, 6.3, 7.0, and 8.4 × 109 m3/year and produce energy of 2.85 × 109, 5.67 × 109, 8.54 × 109, and 11.38 × 109 MWh/year, respectively. Covering areas of shallow water depth was more efficient and economical. The results show that covering 15% of the lake’s area (depths from 0.0 to 3.0 m) can save 2.66 × 109 m3/year and produce 1.7 MWh/year. Covering 25% of the lake’s area (depths from 0.0 to 7.0) can save 3.5 × 109 m3/year and produce 2.854 MWh/year. Using an FPVS to cover parts of Lake Nasser could help manage water resources and energy production for Egypt to overcome the likely shortage of water resources due to population growth. This system could be applied in different locations of the world which could help in increasing water resources and energy production, especially in arid and semi-arid regionsThis work was supported by the projects of the Ministry of Education of the Slovak Republic, VEGA 1/0217/19: Research of Hybrid Blue and Green Infrastructure as Active Elements of a Sponge City, VEGA 1/0308/20: Mitigation of hydrological hazards—floods and droughts—by exploring extreme hydroclimatic phenomena in river basins, and the project of the Slovak Research and Development Agency APVV‐18‐0360: Active hybrid infrastructure towards a sponge city

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques - X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ~21 nm in size plus a cubic phase admixture of only 2 at. % composed of primary edge-boundary nanoparticles ~15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd...O-OH] and [Gd...O-O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5p - O 2s core-like levels in the valence band structures. The origin of [Gd...O-OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT-van der Laan model, and good agreement was established.Comment: 27 pages, 10 figures, accepted in Appl. Surf. Sc

Flow Changes after Endovascular Treatment of a Wide-Neck Anterior Communicating Artery Aneurysm by using X-configured Kissing Stents (Cross-Kissing Stents) Technique

Endovascular treatment for a wide-neck anterior communicating artery (AcomA) aneurysm remains technically challenging. Stent-assisted embolization has been proposed as an alternative of treatment of complex aneurysms. The X-configuration double-stent-assisted technique was used to achieve successful coiling of wide-neck AcomA aneurysm. Implanted stent can alter intra-arterial flow. Follow-up angiograms 4 months later showed flow changes due to used X-technique of stents implantation and filling of the anterior cerebral artery from the opposite internal carotid artery

Exchange Bias in Iron-Oxide Particles Nanocasted in Periodic Porous Silica

Iron-oxide nanoparticles were nanocasted in the periodic mesoporous silica matrix, consisting of two-dimensional hexagonally ordered channel system with the mean diameter of the channels about 7 nm. The magnetic measurements of dc magnetization confirm behavior typical of a superparamagnetic system, such as the irreversibility of the zero-field-cooled and field-cooled curves, presence of a maximum in zero-field-cooled curve related with blocking temperature $T_C$ and revealing of coercivity $H_C$ below $T_C$. The existence of negative exchange bias effect below $T_C$ was confirmed in our system represented by value of exchange bias field $H_{EB}$=-970 Oe measured at the temperature 2 K

Ordered Nanoporous Silica Modified with Nanoparticles of Lanthanide Oxides

Lanthanide oxide nanoparticles were encapsulated inside of pores of highly ordered periodic silica of SBA15 type with hexagonal symmetry. The magnetic properties of such nanoperticles were investigated. The structural characterization using the SAXS, XANES, XRD, and $N_{2}$ adsorption measurements showed the presence of lanthanide oxides of $Ln_{2}O_{3}$ type (Ln=La, Pr, Nd, Gd, Eu), with the size of about 5 nm, incorporated in nanoporous channel system. Their magnetic properties, studied by SQUID apparatus, showed the weak antiferromagnetic ordering at 2 K in the nanocomposites $Gd_{2}O_{3}$@SBA15, $Pr_{2}O_{3}$@SBA15 and $Nd_{2}O_{3}$@SBA15. This behaviour of the nanoparticles is caused by blocking process of magnetic moments, which at 300 K exhibit the superparamagnetism, evidenced from ZFC/FC magnetization