Molybdenum-Tungsten Blue Nanoparticles as a Precursor for Ultrafine Binary Carbides

Herein, we demonstrate a promising method for the synthesis of ultrafine carbide particles using dispersions of molybdenum-tungsten nanoparticles. Dispersions of molybdenum-tungsten blue nanoparticles with different initial molar ratios of molybdenum/tungsten were synthesized through the reduction of molybdate and tungstate ions by ascorbic acid in an acidic medium (pH = 1.0-2.5). Molybdenum-tungsten blue nanoparticles were characterized by ultraviolet-visual (UV-VIS), infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies; transmission electronic microscopy (TEM); and dynamic light scattering (DLS). We demonstrated that molybdenum-tungsten blue nanoparticles belong to toroidal polyoxometalate clusters (λ_max = 680-750 nm) with a predominant particle size of 4.0 nm. Molybdenum-tungsten blue dispersions were shown to be monodispersed systems with a small particle size and long-term stability (>30 days) and are suitable for further catalytic applications.