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Solid State Fluorination on the Minute Scale: Synthesis of WO 3− x F x with Photocatalytic Activity
Author(s) -
Lange Martin Alexander,
Krysiak Yaşar,
Hartmann Jens,
Dewald Georg,
Cerretti Giacomo,
Tahir Muhammad Nawaz,
Panthöfer Martin,
Barton Bastian,
Reich Tobias,
Zeier Wolfgang G.,
Mondeshki Mihail,
Kolb Ute,
Tremel Wolfgang
Publication year - 2020
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201909051
Subject(s) - materials science , spark plasma sintering , photocatalysis , orthorhombic crystal system , tungsten trioxide , tungsten , magic angle spinning , sintering , analytical chemistry (journal) , crystallography , catalysis , crystal structure , nuclear magnetic resonance , metallurgy , nuclear magnetic resonance spectroscopy , biochemistry , chemistry , physics , chromatography
Solid state reactions are notoriously slow, because the rate‐limiting step is diffusion of atoms or ions through reactant, intermediate, and product crystalline phases. This requires days or even weeks of high temperature treatment, consuming large amounts of energy. Metal oxides are particularly difficult to react, because they have high melting points. The study reports a high‐speed solid state fluorination of WO 3 with Teflon to the oxyfluorides WO 3– x F x on a minute (<10 min) scale by spark plasma sintering, a technique that is used typically for a high‐speed consolidation of powders. Automated electron diffraction analysis reveals an orthorhombic ReO 3 ‐type structure of WO 3– x F x with F atom disorder as demonstrated by 19 F magic angle spinning nuclear magnetic resonance spectroscopy. The potential of this new approach is demonstrated by the following results. i) Mixed‐ valent tungsten oxide fluorides WO 3– x F x with high F content (0 < x < 0.65) are obtained as metastable products in copious amounts within minutes. ii) The spark plasma sintering technique yields WO 3– x F x nanoparticles with high photocatalytic activity, whereas the corresponding bulk phases obtained by conventional solid‐state (ampoule) reactions have no photocatalytic activity. iii) The catalytic activity is caused by the microstructure originating from the processing by spark plasma sintering.