SEARCH

SEARCH BY CITATION

Keywords:

  • molybdates;
  • tungstates;
  • color pigments;
  • luminescence;
  • selective oxidation;
  • photocatalysis

Abstract

The nanometer-scale molybdates/tungstates Fe2(MoO4)3, CoMoO4, NiMoO4, CuMoO4, In2(MoO4)3, and CuWO4 are synthesized via a polyol-mediated approach. All nanomaterials are obtained as spherical particles with mean diameters between 25 and 75 nm. Detailed characterization is carried out based on DLS, SEM, XRD, EDX, UV–visible, and luminescence spectroscopy. The as-prepared, non-crystalline nanoparticles already exhibit interesting material properties. CoMoO4, CuWO4, and Fe2(MoO4)3 show brilliant blue, green, and orange-yellow colors. Moreover, a surprisingly high photocatalytic activity is observed for as-prepared, non-crystalline CuWO4 and In2(MoO4)3. Comparing the degradation of methylene blue in neutral water, CuWO4 and In2(MoO4)3 are found to be 4.2 and 7.4 times faster in daylight than standard TiO2 nanoparticles (i.e., Degussa P25). On short-timeframe sintering the nanomaterials become crystalline with an almost preserved particle size. Sintered In2(MoO4)3 (450 °C, 0.5 h) doped with europium (5 mol%) shows intense red luminescence with a quantum yield of 37%−39% upon UV excitation. Finally, sintered CuMoO4 (600 °C, 1 h) supported on commercial porous SiO2 substrates turns out to be well-suited for the oxidation of o-xylene to o-tolyl aldehyde by air, with a selectivity of 64%.