Magnetic nanofibers for remotely triggered catalytic activity applied to the degradation of organic pollutants

This work reports on the fabrication and characterization of a novel type of electrospun magnetic nanofibers (MNFs), and their application as a magnetically-activable catalysts for degradation of organic pollutants. The magnetic stimulation capability for the catalytic action is provided by iron-manganese oxide (MnxFe2-xO4) magnetic nanoparticles (MNPs) embedded into electrospun polyacrylonitrile (PAN), which provides stability and chemical resistance. The MNPs (average size d = 40 ± 7 nm) were first obtained by a green and fast sonochemical route, and subsequently embedded into electrospun PAN nanofibers. The final MNFs showed an average diameter of 760 ± 150 nm, providing a superhydrophobic surface with contact angle (θc = 165°), as well as a considerable amount ( 50 % wt.) of embedded MNPs (Mn0.5Fe2.5O4), thermally stable up to temperatures of 330 °C. The catalytic Fe2+/3+/Mn2+/3+/4+ active centers on the MNPs of MNF’s surface could be remotely activated by alternating magnetic fields (AMF) to degrade the methyl blue (MB). Remarkable stability of the MNFs during heating under extreme pH conditions (3 80 %, after several cycles of reusing the same sample without any regeneration process. The capacity of these materials as a catalytic material with magnetic remote activation makes them appealing for those catalytic applications under conditions of darkness or restrained access, where photocatalytic reaction cannot be achieved

Supercritical solvothermal synthesis under reducing conditions to increase stability and durability of Mo/ZSM-5 catalysts in methane dehydroaromatization

Natural gas is currently envisioned as a potential energy and hydrocarbon feedstock in the forthcoming years. To overcome the detrimental flaring of this natural gas and the partial release of its major component, methane, novel and more effective strategies are required. These include the development of new, efficient and seemingly stable catalysts able to rapidly convert methane into valuable feedstocks. We show a novel synthesis method of Mo/ZSM-5 based on a solvothermal synthesis under supercritical conditions and reducing atmosphere (SC-STSE) to improve metal dispersion and enhance catalyst stability and durability during the methane dehydroaromatization (MDA) reaction. In contrast to the conventional impregnation method, SC-STS-E provides a superhigh atom-like metal dispersion at the zeolite pores resulting in the most stable Mo/ZSM-5 catalyst for MDA with the highest long-term hydrocarbon yield (xCH4=11.6% and yC2+ = 8.9%, after 15 h on stream) among the catalysts reported in literature for this reaction

The formation of very wide binaries during the star cluster dissolution phase

Over the past few decades, numerous wide (>1000 au) binaries in the Galactic field and halo have been discovered. Their existence cannot be explained by the process of star formation or by dynamical interactions in the field, and their origin has long been a mystery. We explain the origin of these wide binaries by formation during the dissolution phase of young star clusters: an initially unbound pair of stars may form a binary when their distance in phase-space is small. Using N-body simulations, we find that the resulting wide binary fraction in the semi-major axis range 1000 au - 0.1 pc for individual clusters is 1-30%, depending on the initial conditions. The existence of numerous wide binaries in the field is consistent with observational evidence that most clusters start out with a large degree of substructure. The wide binary fraction decreases strongly with increasing cluster mass, and the semi-major axis of the newly formed binaries is determined by the initial cluster size. The resulting eccentricity distribution is thermal, and the mass ratio distribution is consistent with gravitationally-focused random pairing. As a large fraction of the stars form in primordial binaries, we predict that a large number of the observed 'wide binaries' are in fact triple or quadruple systems. By integrating over the initial cluster mass distribution, we predict a binary fraction of a few per cent in the semi-major axis range 1000 au - 0.1 pc in the Galactic field, which is smaller than the observed wide binary fraction. However, this discrepancy may be solved when we consider a broad range of cluster morphologies.Comment: 14 pages, 12 figures, accepted by MNRA

Wettability and corrosion of [NTf2] anion-based ionic liquids on steel and PVD (TiN, CrN, ZrN) coatings

Thewetting and corrosion behavior of three bis(trifluoromethylsulfonyl)imide-based ionic liquids: 1-Dodecyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide [C12MIM][NTf2], tributylmethylammonium bis(trifluoromethylsulfonyl)imide [N4441][NTf2] and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide [N1888][NTf2] are tested in this research. The surface tension was measured for temperatures of 293–353 K resulting in the expected linearly decreasing behavior with temperature increase. In addition, contact angle measurements were made on AISI 52100 steel and three coatings (TiN, CrN and ZrN) obtained by PVD technique, finding the regular behavior in hydrophobic (non-polar) systems: high contact angles led to high surface tensions. Complementary parameters like spreading parameter and polarity fraction were calculated to enhance the wetting evaluation of these ionic liquids. [N1888][NTf2]/TiN resulted as the best IL-surface combination for a good wettability, due to the higher dispersion of the charge on the large size cation in this IL and the higher values of total and polar component of the surface free energy for this coating. Finally, SEM-EDS analysis determined that [N1888][NTf2]/ZrN was the best option in order to avoid corrosion problems. The evaporation of water, present as impurity in the ionic liquids, was found the main reason because of corrosion did not occur in the tests carried out at 100 °C

Development of sorptive sers platforms for identification of chemical threats in gas phase

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.Surface Enhanced Raman Spectroscopy (SERS) is one of the leading techniques for specifically acquiring a label-free, ultrasensitive, vibrational fingerprint of a variety of molecular compounds. However, trace level detection (ppbV) of gaseous compounds is hampered by the fact that only a few molecules will be in the region of substrate signal amplification (“hot-spots”). Thus, our objective is to advance in the development of SERS substrates, based on distinct plasmonic/metallic nanoparticles, for a more robust, ultrasensitive, and reliable gas detection. Here we present a SERS substrate series fabricated from core-shell nanostructures comprising Au@Ag rod nanoparticles (of tunable size and aspect ratio) as the core and mesoporous silica-based material (MCM-48) as the shell. The high surface area and specific sorption properties of MCM-48 is of interest to preconcentrate gaseous molecules at the amplification regions of the metallic cores, where the electromagnetic field is amplified due to the localized plasmon resonance effect. The resulting nanostructure is denoted as Au@Ag@MCM-48. The SERS substrates series is obtained by spin coating the colloidal suspensions on transparent glassware/holders. Its performance considers the analytical enhancement factor (AEF) as a comparative parameter and was calculated for the standard molecule 4-nitrothiophenol (4-NBT). The current substrate fabrication conditions are being improved for a more reliable gas detection of, at present, the Sarine surrogate DMMP. At the moment, our efforts in the European project SERSing (EU H2020 grant agreement nº 883390) are dedicated in evaluating the SERS performance of these substrates in the gas-phase detection of nerve substitutes and vesicants.Peer reviewe