The combination of multinuclear solid-state NMR and powder X-ray diffraction has been applied to characterize the octahedron-shaped crystalline nanoparticle products resulting from an inverse micelle synthesis. Rietveld refinements of the powder X-ray diffraction data from the nanoparticles reveal their general formula to be (H 3 O)Y 3 F 10 • xH 2 O. 1 H magic-angle spinning (MAS) NMR experiments provide information on sample purity, as well as serving as an excellent probe of the zeolithic incorporation of atmospheric water. 19 F MAS NMR experiments on a series of monodisperse nanoparticle samples of various sizes yield spectra featuring three unique 19 F resonances, arising from three different fluorine sites within the (H 3 O)Y 3 F 10 • xH 2 O crystal structure. Partial removal of zeolithic water from the internal cavities and tunnels of the nanoparticles leads to changes in the integrated peak intensities in the 19 F MAS NMR spectra; the origin of this behaviour is discussed in terms of 19 F longitudinal relaxation. 19 F-89 Y variable-amplitude cross-polarization (VACP) NMR experiments on both stationary samples and samples under conditions of MAS indicate that two distinct yttrium environments are present, and based on the relative peak intensities, the populations of one of the two sites is closely linked to nanoparticle size. Both 19 F MAS and 19 F-89 Y VACP/MAS experiments indicate small amounts of an impurity present in certain nanoparticles; these are postulated to be spherical amorphous YF 3 nanoparticles. We discuss the importance of probing molecular-level structure in addition to microscopic structure, and how the combination of these characterization methods is crucial for understanding nanoparticle design, synthesis, and application.

Yttrium fluoride nanoparticles of varying crystallinity, shape, and size are prepared by precipitation in reverse microemulsions of water in cyclohexane stabilized with polyoxyethylene isooctylphenyl ether. YF3 particles obtained by the classical microemulsion method are found to be monodisperse amorphous spheres, with controllable diameters between 6 and 50 nm. Particles of the same material obtained by a relatively minor variation of this method are found to be monocrystalline. Typically, mixtures of monodisperse regular hexagonal and triangular single crystals are observed. The size of the crystalline particles can be varied between about 25 and 350 nm. The formation of single crystals can be attributed to the slower incorporation of the precipitant into the micelles when introduced in this fashion.

This paper reports the use of dynamic light scattering (DLS) to study reverse micelles formed by the water/Igepal CO-520/cyclohexane system over a large range of global compositions. A novel approach for data analysis is presented, based on the realization that micelles of a given size must be in equilibrium with free surfactant of a fixed concentration. Compilation of the DLS data into sets of fixed micelle size but differing global compositions therefore allows for the determination of parameters such as free surfactant concentration, micellar molar composition, surfactant interfacial area, and aggregation numbers. Importantly, this method gives access to the variation of each of these parameters with micelle size, as is essential for the characterization of reverse micelles formed by nonionic surfactants. This approach constitutes a significant complement to other available characterization methods. The analysis also provides insight into the primary factors controlling the equilibrium distribution of surfactant within the system and the relative stability of the micelles.

Quasi-monodisperse populations of (HO)YF·xHO nanocrystals of varying size are prepared in Igepal-stabilized microemulsions. Correlations between microemulsion composition, micelle hydrodynamic radius, and final nanoparticle size are established and shed light on the mechanism of particle size control. Under the conditions considered here, size control appears to be primarily governed by the number of micelles and the quantities of precursor ions. More specifically, the number of NPs formed can be successfully correlated with the number of micelles present and final NP size is, in turn, determined by the number of nuclei and the total amount of material available for nanocrystal formation. This insight into nanoparticle formation facilitates the selection of appropriate synthetic conditions for the preparation of populations of a targeted size.

BackgroundThe coronavirus disease 2019 (COVID-19) pandemic has resulted in severe shortages of personal protective equipment (PPE) necessary to protect front-line healthcare personnel. These shortages underscore the urgent need for simple, efficient, and inexpensive methods to decontaminate SARS-CoV-2-exposed PPE enabling safe reuse of masks and respirators. Efficient decontamination must be available not only in low-resourced settings, but also in well-resourced settings affected by PPE shortages. Methylene blue (MB) photochemical treatment, hitherto with many clinical applications including those used to inactivate virus in plasma, presents a novel approach for widely applicable PPE decontamination. Dry heat (DH) treatment is another potential low-cost decontamination method.MethodsMB and light (MBL) and DH treatments were used to inactivate coronavirus on respirator and mask material. We tested three N95 filtering facepiece respirators (FFRs), two medical masks (MMs), and one cloth community mask (CM). FFR/MM/CM materials were inoculated with SARS-CoV-2 (a Betacoronavirus), murine hepatitis virus (MHV) (a Betacoronavirus), or porcine respiratory coronavirus (PRCV) (an Alphacoronavirus), and treated with 10 µM MB followed by 50,000 lux of broad-spectrum light or 12,500 lux of red light for 30 minutes, or with 75°C DH for 60 minutes. In parallel, we tested respirator and mask integrity using several standard methods and compared to the FDA-authorized vaporized hydrogen peroxide plus ozone (VHP+O3) decontamination method. Intact FFRs/MMs/CM were subjected to five cycles of decontamination (5CD) to assess integrity using International Standardization Organization (ISO), American Society for Testing and Materials (ASTM) International, National Institute for Occupational Safety and Health (NIOSH), and Occupational Safety and Health Administration (OSHA) test methods.FindingsOverall, MBL robustly and consistently inactivated all three coronaviruses with at least a 4-log reduction. DH yielded similar results, with the exception of MHV, which was only reduced by 2-log after treatment. FFR/MM integrity was maintained for 5 cycles of MBL or DH treatment, whereas one FFR failed after 5 cycles of VHP+O3. Baseline performance for the CM was variable, but reduction of integrity was minimal.InterpretationMethylene blue with light and DH treatment decontaminated masks and respirators by inactivating three tested coronaviruses without compromising integrity through 5CD. MBL decontamination of masks is effective, low-cost and does not require specialized equipment, making it applicable in all-resource settings. These attractive features support the utilization and continued development of this novel PPE decontamination method.