Molybdenum-based two-dimensional materials: Synthesis, dispersion, exfoliation and thin film deposition

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We report a simple and effective route to synthesize, disperse, exfoliate and process different molybdenum-based 2-dimensional (2D) materials. Starting from a reaction between ammonium molybdate and ammonium sulfide solutions, a powder consisting of a mixture between amorphous molybdenum oxide and sulfide is obtained. By tuning the atmosphere and the temperature, different compositions can be prepared by thermal treatment of this sample: heat treatments in ambient atmosphere produce MoO3 with different morphologies, controllable according to the chosen temperature. On the other hand, heat treatments in inert atmosphere produce mixtures between crystalline 2D MoS2 and MoO3. Further handling of these mixtures with acetonitrile separates the components due to the different solvent/solid affinities, with the layered MoS2 becoming homogeneously dispersed, and the MoO3 agglomerating as a solid easily removed by centrifugation. The resulting sulfide dispersions in acetonitrile present high stability, and they are constituted by exfoliated MoS2, which means that acetonitrile is a tri-functional agent, separating the sulfide/oxide mixture, exfoliating the sulfide and stabilizing the dispersion. The MoS2 dispersions were used to produce homogeneous, freestanding and transparent thin films through the liquid-liquid interfacial route, which were easily deposited over different substrates and characterized by different techniques.