Li14Ln5[Si11N19O5]O2F2 with Ln = Ce, Nd--representatives of a family of potential lithium ion conductors

The isotypic layered oxonitridosilicates Li(14)Ln(5)[Si(11)N(19)O(5)]O(2)F(2) (Ln = Ce, Nd) have been synthesized using Li as fluxing agent and crystallize in the orthorhombic space group Pmmn (Z = 2, Li(14)Ce(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.178(3), b = 7.6500(15), c = 10.116(2) ?, R1 = 0.0409, wR2 = 0.0896; Li(14)Nd(5)[Si(11)N(19)O(5)]O(2)F(2): a = 17.126(2), b = 7.6155(15), c = 10.123(2) ?, R1 = 0.0419, wR2 = 0.0929). The silicate layers consist of dreier and sechser rings interconnected via common corners, yielding an unprecedented silicate substructure. A topostructural analysis indicates possible 1D ion migration pathways between five crystallographic independent Li positions. The specific Li-ionic conductivity and its temperature dependence were determined by impedance spectroscopy as well as DC polarization/depolarization measurements. The ionic conductivity is on the order of 5 × 10(-5) S/cm at 300 °C, while the activation energy is 0.69 eV. Further adjustments of the defect chemistry (e.g., through doping) can make these compounds interesting candidates for novel oxonitridosilicate based ion conductors.     

Light Regime Characterization in an Airlift Photobioreactor for Production of Microalgae with High Starch Content

The slow development of microalgal biotechnology is due to the failure in the design of large-scale photobioreactors (PBRs) where light energy is efficiently utilized. In this work, both the quality and the amount of light reaching a given point of the PBR were determined and correlated with cell density, light path length, and PBR geometry. This was made for two different geometries of the downcomer of an airlift PBR using optical fiber technology that allows to obtain information about quantitative and qualitative aspects of light patterns. This is important since the ability of microalgae to use the energy of photons is different, depending on the wavelength of the radiation. The results show that the circular geometry allows a more efficient light penetration, especially in the locations with a higher radial coordinate (r) when compared to the plane geometry; these observations were confirmed by the occurrence of a higher fraction of illuminated volume of the PBR for this geometry. An equation is proposed to correlate the relative light intensity with the penetration distance for both geometries and different microalgae cell concentrations. It was shown that the attenuation of light intensity is dependent on its wavelength, cell concentration, geometry of PBR, and the penetration distance of light.     

Tandem Transesterification–Esterification Reactions Using a Hydrophilic Sulfonated Silica Catalyst for the Synthesis of Wintergreen Oil from Acetylsalicylic Acid Promoted by Microwave Irradiation

SiO₂–SO₃H, with a surface area of 115 m²/g and pore volume of 0.38 cm³g⁻¹, and 1.32 mmol H⁺/g was used as a 20% w/w catalyst for the preparation of methyl salicylate (wintergreen oil or MS) from acetylsalicylic acid (ASA). A 94% conversion was achieved in a microwave reactor over 40 min at 120 °C in MeOH. The resulting crude product was purified by flash chromatography. The catalyst could be reused three times.