Synthesis of lower-valent molybdenum oxides in aqueous solutions by reducing Na2MoO4 with NaBH4

Abstract

Reduction of Na 2MoO 4 with NaBH 4 in aqueous solutions at ambient temperatures has been investigated systematically by varying the concentration and volume of NaBH 4 as well as the reaction pH. The reduction products have been characterized by X-ray diÂraction and diÂerential scanning calorimetry (DSC). The reduction yields metastable, amorphous oxides of lower-valent molybdenum, which crystallize around 350°C to give the binary oxide MoO 2 and the sodium molybdenum bronze Na 0.88 Mo 6 O 17 . The relative amounts of MoO 2 and Na 0.88 Mo 6 O 17 formed are correlated to the overall reducing power that can be achieved. The concentration and volume of NaBH 4 , the reaction pH and the changes in the degree of condensation of the molybdate ions are all found to influence the overall reducing power. Complex metal oxides are traditionally made by firing the amounts of 0.25 and 2.5  NaBH 4 . In order to understand the reactants at elevated temperatures with intermediate grindings influence of pH, reactions were also carried out with fixed in order to overcome the diÂusional limitations. Such a highamounts of Na 2 MoO 4 ( 25 ml) and NaBH 4 ( 50 ml) at diÂerent temperature approach generally gives the thermodynamically pH values. The 0.25  Na 2 MoO 4 solution was prepared by stable phases and often leads to an instability of metastable dissolving 1.3 g of Na 2MoO 4 in 25 ml of deionized water. Both phases that may have unusual valence states or structural the 0.25 and 2.5  NaBH 4 solutions were prepared by dissolvarrangements. In addition, the high-temperature approach ing required quantities of NaBH 4 in dilute NaOH solution results in samples with larger particle size and lower surface having a pH of 11-12. The initial pH of the tetrahydroborate area, which are undesirable for some applications such as solution was maintained high at 11-12 in order to suppress catalysis as well as for ceramic processing to achieve higher the hydrolysis of tetrahydroborate [reaction (1)] and prevent densities. There has been considerable interest in recent years a rapid loss of hydrogen as the hydrolysis is facilitated by to develop low-temperature methods to synthesize complex acidic conditions.12 inorganic solids.1-3 While there are several low-temperature(1) techniques such as sol-gel processing to obtain higher-valent metal oxides, methods to synthesize lower-valent transition-Experiments were carried out by keeping the molybdate solumetal oxides, particularly in aqueous solutions, are limited or tion under constant stirring on a magnetic stirrer at a predeternot known. For example, higher-valent binary oxides such as mined pH value and adding the tetrahydroborate solution Al 2 O 3 , Fe 2 O 3 , Nb 2 O 5 and WO 3 , and ternary oxides such from a burette. The pH tends to increase as the tetrahydroboas SrMoO 4, SrTiO 3 and LaNbO 4 can be made by sol-gel rate solution is added due to the formation of the basic NaBO 2 processing, control of pH, or precipitation reactions in aqueous and NaOH [see reactions (2 ) and (3), later] and so con...

Synthesis of Manganese Oxides by Reduction of KMnO4with KBH4in Aqueous Solutions

“…2), indicating that the as-prepared samples are nanocrystalline and not amorphous. This is in contrast to the as-prepared samples in the molybdate and tungstate systems, which were found to be amorphous (22)(23)(24).…”

“…Some of these binary oxides were found to be attractive as electrode materials for lithium batteries (20,21). A more systematic investigation of the molybdate (22,23) and tungstate (24), systems reveals that the volume and concentration of the borohydride, the reaction pH, and the degree of condensation of the metalate ions strongly influence the composition of the products. We report in this paper a systematic investigation of the reduction of KMnO with KBH in aqueous solutions with an aim to obtain manganese oxides.…”

Template-assisted synthesis of porous molybdenum dioxide nanofibers and nanospheres by redox etching method

“…According to more recent studies, MoO 2 nanowires were electrodeposited reductively from an alkaline MoO 4 2À solution onto highly oriented pyrolytic graphite surfaces [16,17]. MoO [20,21]. The instability of the metastable dioxides with low valence states makes their synthesis difficult in solutions [20][21][22][23].…”

Hydrothermal Synthesis of the Blue Potassium Molybdenum Bronze, K0.28MoO3

“…Manthiram et al (12,13) reported that, after a heat treatment at 623}773 K of the amorphous products formed by the reduction of K MoO in KBH solution, K MoO , K MoO , and K MoO were crystallized with MoO . We (14}17) also attained formerly by the solid state reactions a series of alkali metal bronzes containing small amounts of MoO by heating hydrated molybdenum bronzes in the neighborhood of 600 K in N atmosphere.…”