Polyol-Mediated Synthesis and Properties of Nanoscale Molybdates/Tungstates: Color, Luminescence, Catalysis

The nanometer-scale molybdates/tungstates Fe-2 (MoO4)(3), CoMoO4, NiMoO4, CuMoO4, In-2(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 Fe-2(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 In-2(MoO4)(3). Comparing the degradation of methylene blue in neutral water, CuWO4 and In-2(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 In-2(MoO4)(3) (450 degrees 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 degrees 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%.