A general route to free-standing films of nanocrystalline molybdenum chalcogenides at a liquid/liquid interface under hydrothermal conditions

The utility of hydrothermal method applied to liquid/liquid interface for obtaining free-standing films of molybdenum chalcogenides is demonstrated. A general route for obtaining films of MoO3, MoS2 and MoSe2 at a water/toluene interface is illustrated employing a universal Mo precursor and the desired chalcogenide reactant in the two different phases. The hydrothermal conditions promote the formation of emulsions of water and toluene. A mechanism is proposed wherein the in-situ chalcogenation happens at the interfaces of tiny droplets of toluene in water and the nanosheets of the chalcogenide self-assemble at the regenerated interface during quenching to form films. The free-standing films are transferred on to various substrates for characterization. MoO3 films consist of nanobelts while MoS2 and MoSe2 films consist of a dense assembly of nanosheets. The advantage of transferring the films on arbitrary substrates is exemplified for electrochemical applications.