RESUMEN
Natural diamonds were (and are) formed (thousands of million years ago) in the upper mantle of Earth in metallic melts at temperatures of 900-1,400 °C and at pressures of 5-6 GPa (refs. 1,2). Diamond is thermodynamically stable under high-pressure and high-temperature conditions as per the phase diagram of carbon3. Scientists at General Electric invented and used a high-pressure and high-temperature apparatus in 1955 to synthesize diamonds by using molten iron sulfide at about 7 GPa and 1,600 °C (refs. 4-6). There is an existing model that diamond can be grown using liquid metals only at both high pressure and high temperature7. Here we describe the growth of diamond crystals and polycrystalline diamond films with no seed particles using liquid metal but at 1 atm pressure and at 1,025 °C, breaking this pattern. Diamond grew in the subsurface of liquid metal composed of gallium, iron, nickel and silicon, by catalytic activation of methane and diffusion of carbon atoms into and within the subsurface regions. We found that the supersaturation of carbon in the liquid metal subsurface leads to the nucleation and growth of diamonds, with Si playing an important part in stabilizing tetravalently bonded carbon clusters that play a part in nucleation. Growth of (metastable) diamond in liquid metal at moderate temperature and 1 atm pressure opens many possibilities for further basic science studies and for the scaling of this type of growth.
RESUMEN
Two-dimensional magnetic materials are considered as promising candidates for developing next-generation spintronic devices by providing the possibility of scaling down to nanometers. However, a low Curie temperature is a crucial problem for practical applications, being intimately related to weak interlayer exchange coupling. Here, by using density functional theory calculations, we show that interlayer exchange coupling can be enhanced by intercalating 3d transition metals (Sc to Zn) into a bilayer of CrI3 and NiI2. It is found that intercalated Ni and Cr atoms exhibit strong antiferromagnetic coupling with the CrI3 and NiI2 host layers, respectively. This enhances the ferromagnetic interlayer exchange coupling between the host layers by many folds compared to pristine CrI3 and NiI2 bilayers. Moreover, both intercalated compounds show out-of-plane magnetic anisotropy with half metallic nature, which makes them ideal candidates for spintronics applications. Thereby our work provides a rational approach to raise the Curie temperature of non-metallic two-dimensional magnets by intercalation.
RESUMEN
In this research, a series of innovative and stable cross-linked gel polymer reinforced membranes (GPRMs), were successfully prepared and investigated for application in lithium-ion batteries. Herein, a gel directly within the commercial polyethylene (PE) separator is supported via electron-beam simultaneous irradiation cross-linking of commercial liquid electrolyte and poly(ethylene glycol) methacrylate (PEGMA) oligomers. The physical and electrochemical properties of the GPRMs were characterized by SEM, TEM, mechanical durability, heating shrinkage, and ion conductivity, etc. The GPRMs demonstrated excellent mechanical durability and high ion conductivity compared with traditional PE membranes. Moreover, coin-typed cells were assembled and cycle performance was also studied compared with same-typed cells with commercial PE membrane and liquid electrolyte. As a result, the coin-typed cells using GPRMs also showed a relatively good efficiency on the 50th cycles at a high 1.0 C-rate. These GPRMs with excellent properties present a very promising material for utilization in high-performance lithium-ion batteries with improved safety and reliability.
RESUMEN
Water resource pollution by nitrate-nitrogen, mainly caused by anthropogenic causes, induces eutrophication of water resources, and indicates the degree of organic pollution. Therefore, this study devised a method for coating PFSA ionomer with excellent chemical resistance without disassembling the module to improve the removal rate of nitrate-nitrogen in water by using a cyclic coating method on a commercially available nanofiltration membrane (NF membrane) module. Nafion was prepared as a supercritical fluid dispersion using a high-temperature and high-pressure reactor, and the particle size and the degree of dispersion of the dispersion were analyzed by DLS. The crystallinity was confirmed through XRD by drying the dispersion in the liquid state. After the dispersion was prepared as a membrane according to the heat treatment conditions, the characteristics according to the particle size were analyzed by tensile strength and TEM. The nitrate-nitrogen removal rate of the NF membrane module coated with the dispersion was increased by 93% compared to that before coating. Therefore, the result showed that the cycle coating method devised in this study could efficiently coat the already commercialized module and improve performance.
RESUMEN
CeOx hybrid nanoparticles were synthesized and evaluated for use as radical scavengers, in place of commercially available Ce(NO3)3 and CeO2 nanoparticles, to avoid deterioration of the initial electrochemical performance and/or spontaneous aggregation/precipitation issues encountered in polymer electrolyte membranes. When CeOx hybrid nanoparticles were used for membrane formation, the resulting membranes exhibited improved proton conductivity (improvement level = 2-15% at 30-90 °C), and thereby electrochemical single cell performance, because the -OH groups on the hybrid nanoparticles acted as proton conductors. In spite of a small amount (i.e., 1.7 mg/cm3) of introduction, their antioxidant effect was sufficient enough to alleviate the radical-induced decomposition of perfluorinated sulfonic acid ionomer under a Fenton test condition and to extend the chemical durability of the resulting reinforced membranes under fuel cell operating conditions.
RESUMEN
Saline water electrolysis (SWE) is an electrochemical process to simultaneously produce hydrogen (H2), chlorine (Cl2), and sodium hydroxide (NaOH) with high purity levels (e.g., 99.999%) by applying electric power to saline water. The state-of-the art SWE membrane, Flemion®, has excellent chemical resistance to harsh SWE conditions, but still needs to lower its energy consumption by reducing its ohmic resistance to Na+ ion transport. Meanwhile, most of cation exchange membranes (CEMs) have been suffering from chemical degradation under the alkaline conditions, owing to their single layer matrices composed of sulfonic acid moieties, though they show fast Na+ ion transport behavior. Here double-layered SWE membranes were prepared on the basis of design strategies composed of the incorporation of a chemically stable carboxylic acid layer (C layer) via UV irradiation onto one surface of perfluorinated Nafion®212 membrane chosen as one of commercially available CEMs, and the thickness control of the C layer. The resulting membranes showed excellent SWE performances and improved electrochemical service life, when compared with those of Nafion®212 and Flemion®, respectively.
RESUMEN
Silver nanoparticle-modified graphene oxide (Ag/GO) was reliably prepared by using sodium borohydride (NaBH4) in the presence of citric acid capping agent via a simple wet chemistry method. This rapidly formed Ag/GO composite exhibited good dispersity in a solution containing hydrophilic polyacrylonitrile (PAN). Subsequent electrospinning of this precursor solution resulted in the successful formation of nanofibers without any notable defects. The Ag/GO-incorporated PAN nanofibers showed thinner fiber strands (544 ± 82 nm) compared to those of GO-PAN (688 ± 177 nm) and bare-PAN (656 ± 59 nm). Subsequent thermal treatment of nanofibers resulted in the preparation of thin membranes to possess the desired pore property and outstanding wettability. The Ag/GO-PAN nanofiber membrane also showed 30% higher water flux value (390 LMH) than that of bare-PAN (300 LMH) for possible microfiltration (MF) application. In addition, the resulting Ag/GO-PAN nanofiber membrane exhibited antibacterial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Furthermore, this composite membrane exhibited outstanding anti-fouling property compared to the GO-PAN nanofiber membrane in the wastewater treatment. Therefore, the simple modification strategy allows for the effective formation of Ag/GO composite as a filler that can be reliably incorporated into polymer nanofiber membranes to possess improved overall properties for wastewater treatment applications.