TY - JOUR A1 - Lange, M. A. A1 - Khan, I. A1 - Opitz, P. A1 - Hartmann, J: A1 - Ashraf, M. A1 - Qurashi, A. A1 - Prädel, L. A1 - Panthöfer, M. A1 - Cossmer, Antje A1 - Pfeifer, Jens A1 - Simon, Fabian A1 - von der Au, Marcus A1 - Meermann, Björn A1 - Mondeshki, M. A1 - Tahir, M. N. A1 - Tremel, W. T1 - A Generalized Method for High-Speed Fluorination of Metal Oxides by Spark Plasma Sintering Yields Ta3O7F and TaO2F with High Photocatalytic Activity for Oxygen Evolution from Water N2 - A general method to carry out the fluorination of metal oxides with poly(tetrafluoroethylene) (PTFE, Teflon) waste by spark plasma sintering (SPS) on a minute scale with Teflon is reported. The potential of this new approach is highlighted by the following results. i) The tantalum oxyfluorides Ta3O7F and TaO2F are obtained from plastic scrap without using toxic or caustic chemicals for fluorination. ii) Short reaction times (minutes rather than days) reduce the process time the energy costs by almost three orders of magnitude. iii) The oxyfluorides Ta3O7F and TaO2F are produced in gram amounts of nanoparticles. Their synthesis can be upscaled to the kg range with industrial sintering equipment. iv) SPS processing changes the catalytic properties: while conventionally prepared Ta3O7F and TaO2F show little catalytic activity, SPS-prepared Ta3O7F and TaO2F exhibit high activity for photocatalytic oxygen evolution, reaching photoconversion efficiencies up to 24.7% and applied bias to photoconversion values of 0.86%. This study shows that the materials properties are dictated by the processing which poses new challenges to understand and predict the underlying factors. KW - Fluorination KW - Oxygen evolution reaction KW - Photocatalysis KW - Spark plasma sintering KW - Tantalum oxyfluorides PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-524329 DO - https://doi.org/10.1002/adma.202007434 VL - 23 IS - 20 SP - 7434 PB - Wiley‐VCH GmbH AN - OPUS4-52432 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lange, M. A. A1 - Khan, I. A1 - Dören, R. A1 - Ashraf, M. A1 - Qurashi, A. A1 - Prädel, L. A1 - Panthöfer, M. A1 - von der Au, Marcus A1 - Cossmer, Antje A1 - Pfeifer, Jens A1 - Meermann, Björn A1 - Mondeshki, M. A1 - Tahir, M. N. A1 - Tremel, W. T1 - High-speed solid state fluorination of Nb2O5 yields NbO2F and Nb3O7F with photocatalytic activity for oxygen evolution from water N2 - Solid state reactions are slow because the diffusion of atoms or ions through the reactant, intermediate and crystalline product phases is the rate-limiting step. This requires days or even weeks of high temperature treatment, and consumption of large amounts of energy. We employed spark-plasma sintering, an engineering technique that is used for high-speed consolidation of powders with a pulsed Electric current passing through the sample to carry out the fluorination of niobium oxide in minute intervals. The approach saves time and large amounts of waste energy. Moreover, it allows the preparation of fluorinated niobium oxides on a gram scale using poly (tetrafluoroethylene) (®Teflon) scrap and without toxic chemicals. The synthesis can be upscaled easily to the kg range with appropriate sintering equipment. Finally, NbO2F and Nb3O7F prepared by spark plasma sintering show significant photoelectrocatalytic (PEC) oxygen evolution from water in terms of photocurrent density and incident photon-to-current Efficiency (% IPCE), whereas NbO2F and Nb3O7F prepared by conventional high temperature chemistry show little to no PEC response. Our study is a proof of concept for the quick, clean and energy saving production of valuable photocatalysts from plastic waste. KW - Fluorination KW - Nb2O5, NbO2F, Nb3O7F KW - Photocatalytic activity PY - 2021 DO - https://doi.org/10.1039/d1dt00533b VL - 50 IS - 19 SP - 6528 EP - 6538 PB - Royal Society of Chemistry AN - OPUS4-52439 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zink, N. A1 - Emmerling, Franziska A1 - Häger, T. A1 - Panthöfer, M. A1 - Tahir, M.N. A1 - Kolb, U. A1 - Tremel, W. T1 - Low temperature synthesis of monodisperse nanoscaled ZrO2 with a large specific surface area N2 - Thermal decomposition of Zr(C2O4)2·4H2O within an autoclave or in a conventional tube furnace at temperatures below 380 °C resulted in nano- and micron-sized ZrO2, respectively. Reactions under autogenic pressure yielded monodisperse monoclinic (m) and tetragonal (t) ZrO2 nanoparticles with an average diameter of ~8 nm and interconnected t-ZrO2 nanoparticles with diameters of ~4 nm, depending on the synthesis temperature. Samples were characterised by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) associated with energy dispersive X-ray spectroscopy (EDS), Raman microspectroscopy and photoluminescence spectroscopy (PL). Nanostructured zirconia materials exhibited high specific areas of 276–385 m2 g-1 which make them promising candidates as catalysts and catalyst supports. Co-existence of m- and t-ZrO2 nanoparticles with diameters of 6–9 nm, i.e. above the critical particle size of 6 nm for the formation of t-ZrO2, demonstrated that the particle size is not the only factor for stabilisation of the t-ZrO2 modification at room temperature. PY - 2013 DO - https://doi.org/10.1039/c2dt12496c SN - 1477-9226 SN - 1477-9234 SN - 1364-5447 VL - 42 SP - 432 EP - 440 PB - RSC CY - Cambridge AN - OPUS4-27733 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -