ROOM-TEMPERATURE SYNTHESIS OF MOLYBDENUM AND TUNGSTEN CARBIDES, MO2C AND W2C, VIA CHEMICAL-REDUCTION METHODS

The preparation of nanometer-sized particles of phasepure materials is currently attracting intense interest in materials chemistry because such particles exhibit unique chemical and physical properties that are intermediate between those of molecules and extended solids.1 For example, metal chalcogenides exhibit size-dependent physical properties in the 2-100-nm size regime2 and metal particles exhibit size-dependent selectivity3 and reactivity3, 4in catalytic reactions. However, traditional solid-state synthetic methods seldom result in formation of particles smaller that 100 nm.5 New synthetic routes based on chemical methods show promise for the formation of materials with a homogeneity, morphology, composition, microstructure, and purity not otherwise obtainable. For example, the reduction of metal salts in the presence of a surfactant, often in inverse micelles, has led to formation of monodispersed nanometer-sized particles.6 However, the surfactant can lead to impurity incorporation in subsequent steps and as a result a number of groups are investigating alternative synthetic strategies. Reicke et al.7have extensively investigated the reduction of metal salts with alkali-metal naphthalenides and formed highly dispersed, reactive metal powders. Bonnemann et al.8, 9 have shown that trialkylborohydride reducing agents can be used to reduce a variety of metal complexes to form the corresponding metal colloids. The metals are reasonably pure (70-98%), the particle size was approximately 10-100 nm and generally crystalline materials were formed depending on the specific system as determined by X-ray diffraction. © 1992, American Chemical Society. All rights reserved.