RESUMO
Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1-x-y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 - x - y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 - x - y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg-O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg-O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1 T) and spinning rate (20 kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.
RESUMO
LiSr2SiO4H is synthesized by solid-state reaction of LiH and α-Sr2SiO4. It crystallizes in space group P21/ m ( a = 658.63(4) pm, b = 542.36(3) pm, c = 695.01(4) pm, ß = 112.5637(9)°) as proven by X-ray and neutron diffraction, is isotypic to LiSr2SiO4F, and exhibits isolated SiO4 tetrahedra. Hydride anions are located in Li2Sr4 octahedra, which share faces to form columns, with H-H distances of 271.18(2) pm. NMR, IR, and Raman spectroscopy, density measurements, elemental analysis, and theoretical calculations confirm these results. Despite its hydridic nature, it is stable in air up to 550 K. When doped with europium, it emits bright yellow-green light with an intensity maximum at 560 nm for LiSr1.98Eu0.02SiO4H. Even after treatment in water for several hours, the solid shows luminescence. The broad emission peak is attributed to the allowed 4f65d â 4f7 transition of divalent europium. LiSr2SiO4H is the first silicate hydride, a class of compounds that might have potential as host for luminescent materials.
RESUMO
Radiation-induced graft immobilization (RIGI) is a novel method for the covalent binding of substances on polymeric materials without the use of additional chemicals. In contrast to the well-known radiation-induced graft polymerization (RIGP), RIGI can use non-vinyl compounds such as small and large functional molecules, hydrophilic polymers, or even enzymes. In a one-step electron-beam-based process, immobilization can be performed in a clean, fast, and continuous operation mode, as required for industrial applications. This study proposes a reaction mechanism using polyvinylidene fluoride (PVDF) and two small model molecules, glycine and taurine, in aqueous solution. Covalent coupling of single molecules is achieved by radical recombination and alkene addition reactions, with water radiolysis playing a crucial role in the formation of reactive solute species. Hydroxyl radicals contribute mainly to the immobilization, while solvated electrons and hydrogen radicals play a minor role. Release of fluoride is mainly induced by direct ionization of the polymer and supported by water. Hydrophobic chains attached to cations appear to enhance the covalent attachment of solutes to the polymer surface. Computational work is complemented by experimental studies, including X-ray photoelectron spectroscopy (XPS) and fluoride high-performance ion chromatography (HPIC).