Semiporous MoS2 obtained by the decomposition of thiomolybdate precursors

Abstract

The decomposition of three different ammonium thiomolybdates (NH₄)₂MoS₄xH₂O, (NH₄)₂Mo₂S₁₂xH₂O, and (NH₄)₂Mo₃S₁₃xH₂O (x=1–2) have been studied by TG–DSC under argon. While all three thiomolybdates decompose at around 673 K to yield nearly X-ray amorphous MoS₂ , the precursor (NH₄)₂Mo₃S₁₃xH₂O does so in a manner distinct from the other two precursors displaying a sharp exothermic peak in the DSC trace. We suggest that the unusual thermal behaviour of (NH₄)₂Mo₃S₁₃xH₂O might arise from a topochemical relation between the molecular cluster and 2H-MoS₂ as proposed previously. The porosity of the X-ray amorphous MoS₂ obtained from the decomposition under vacuum of (NH₄)₂Mo₃S₁₃xH₂O is unusually large and the material displays interesting sorption behaviour towards small organic molecules. This X-ray amorphous semiporous modification of MoS₂ has been characterized in detail by powder X-ray diffraction, high resolution electron microscopy and from its extended X-ray absorption fine structure. An unusual feature of this material is the presence of bent, open-ended lamellae of MoS₂ , contrasting fullerene-like MoS₂ which forms closed shells.