Nanocrystalline CaF2 particles obtained by high-energy ball milling

Total and Class-Specific Determination of Fluorinated Compounds in Consumer and Food Packaging Samples Using Fluorine-19 Solid-State Nuclear Magnetic Resonance Spectroscopy

Hamburger wrapping paper, coated with water-based barrier coatings, used in the food packaging industry was studied by using the total organic fluorine (TOF) method based on combustion ion chromatography and fluorine-19 solid-state nuclear magnetic resonance (19F ss-NMR) spectroscopy. Although the TOF method is a fast and affordable method used to screen for per- and polyfluoroalkyl substances (PFAS), the amount of fluorine it measures is heavily dependent on the extraction step and, therefore could lead to inaccurate results. Fluorine-19 ss-NMR spectroscopy can differentiate between organic and inorganic fluorinated sources, eliminating the need for sample clean up. To illustrate this, the 19F ss-NMR spectra of clean coated paper samples that contained naturally occurring F- ions from the talc raw material and spiked samples containing perfluorooctanoic acid were compared. A range of experimental conditions was explored to improve sensitivity for low PFAS concentrations (in the order of 10-20 mg/kg). Despite the disadvantages of ss-NMR spectroscopy, such as the low limit of detection and resolution, the results demonstrate it can be a viable tool to directly detect PFAS moieties in consumer and food packaging. Therefore, 19F solid-state NMR spectroscopy challenges and complements current methods, which only provide indirect evidence of the presence of PFAS.

Lattice distortion of CaF2 nanocrystals for shortening their 19F longitude relaxation time

As a promising ¹⁹F MRI tracer, the relatively slow lattice-spin relaxation of CaF₂ nanocrystals leads to an unacceptable scanning time in MR imaging, hampering their application. We herein controlled the size and lattice distortion of CaF₂ nanocrystals and showed that the shortened interplanar spacing pronouncedly sped up the longitude relaxation.

Mechanochemistry of fluoride solids: from mechanical activation to mechanically stimulated synthesis

Abstract

This lecture text is focused on the comparatively young field of mechanochemistry of fluoride solids, considering both their mechanical activation and their mechanochemical synthesis. Beside a literature survey, the mechanochemical synthesis of binary fluorides MF2, MF3, of complex fluorides MMgF4, of solid solutions MaxMb1−xF2 or M1−xLnxF2+x (Ln: Y, Eu) and of fluorine-containing coordination polymers is presented. Owing to their interesting potential applications in the field of fluoride ion conductivity or luminescence properties when doped, most of the given examples are alkaline earth metal compounds. A short historical survey, remarks on peculiarities and consequences of mechanical activation as well as the necessary technical equipment for mechanochemical reactions precede the section.

Graphic abstract

Combined X-ray diffraction and solid-state19F magic angle spinning NMR analysis of lattice defects in nanocrystalline CaF2

Nanocrystalline CaF2powder specimens were produced both by co-precipitation of CaCl2and NH4F and by ball milling of a coarse powder. The specimen homogeneity and a detailed picture of the lattice defects can be assessed by the simultaneous analysis of the powder diffraction pattern and of the solid-state19F magic angle spinning NMRT1relaxometry data. While diffraction line profiles provide information on domain size distribution and the content of dislocations,T1relaxometry is more sensitive to inhomogeneity of the powder (large defect-free grainsversusdefective small ones). After extensive milling it is possible to obtain fluorite domains of comparable size to the chemically synthesized CaF2(circa10–12 nm), but with a marked difference in the lattice defect types and content. It is then proved that surface defects (related to domain size), line defects (dislocations) and point (Frenkel) defects have a quite different effect on the powder pattern as well as on theT1spin-lattice relaxation time.

Degradation of phenol by mechanical activation of a rutile catalyst

In the present paper a novel mechanochemical process for the elimination of organic pollutants dissolved in water is proposed. In this regard, phenol aqueous solutions (100mgL(-1)) were ball-milled for 0, 12, 18, 24, 36, 48, and 72h with and without a well-characterized (XRD, SEM, and N(2) Adsorption), rutile powder catalyst and the reaction products analyzed with UV and GC/MS. It was found that when the catalyst was not included in the process, phenol was not affected, but when it was included, phenol was decomposed. The catalyst itself did not change and the reaction follows a pseudo-first-order kinetics. Besides, intermediates which are characteristic of the ()OH radical mechanism were found in the reaction products. Then, a mechanism similar to those accepted for other advanced oxidation processes was proposed. The value measured for the pseudo-first-order reaction constant was very low, indicating that the reported process is inefficient. Nevertheless, this problem could be solved by applying catalysts consisting of particles with smaller diameters.