Why do we use sodium molybdate instead of Ammonium molybdate in synthesis of molybdenum diselenide??
Ammonium molybdate is usually the name used for the compound whose formula is (NH4)6[Mo7)24].4H2O. which is also known as ammonium heptamolybdate containing the [Mo7O24]6- is made up of MoO6 octahedra.
An aqueous solution of (NH4)6[Mo7)24].4H2O is acidic in nature. (pH is ~6) When ammonia is added there will be no reduction but a facile dissolution of the substance.
So when (NH4)6[Mo7)24].4H2O is taken in aqueous ammonia, the species present is solution will be mainly the tetrahedral [MoO4]2-. However the solid isolated from this by evaporation of the solution will be (NH4)6[Mo7)24].4H2O and not (NH4)2[MoO4].
Ammonium heptamolybdate is an odourless crystalline compound ranging in colour from white to yellow-green. It is usually tetrahydrate, whose formula is (NH4)6Mo7O24·4H2O. It is known as ammonium paramolybdate or simply as ammonium molybdate, although ammonium molybdate can also refer to ammonium orthomolybdate, (NH4)2MoO4,
Ammonium heptamolybdate is easily prepared by dissolving molybdenum trioxide in an excess of aqueous ammonia and evaporating the solution at room temperature. While the solution evaporates, the excess of ammonia escapes. This method results in the formation of six-sided transparent prisms of the tetrahydrate of ammonium heptamolybdate.
Article Molybdenum diselenide (MoSe2) for energy storage, catalysis,...
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